Methods are described for the isolation of nucleic acid ligands to integrins using the SELEX process. SELEX is an acronym for Systematic Evolution of Ligands by EXponential enrichment. The nucleic acid ligands of the present invention are useful as therapeutic and diagnostic agents.

The integrins are a class of heterodimeric integral membrane proteins, one or more of which are expressed by most cell types (Hynes (1992) Cell 69:11–25). Some 16 homologous alpha subunits and 8 homologous beta subunits associate in various combinations to yield an extensive family of receptors. Each integrin heterodimer has a large extracellular domain that mediates binding to specific ligands. These ligands may include plasma proteins, proteins expressed on the surface of adjacent cells, or components of the extracellular matrix. Several of the integrins show affinity for more than one ligand and many have overlapping specificities (Hynes (1992) Cell 69:11–25). Both the α and β subunits contribute to a small intracellular domain that contacts components of the actin cytoskeleton, thus forming a physical link between proteins outside and inside the cell. Integrins play an important role in cellular adhesion and migration, and these properties are controlled by the cell, in part, by modulation of integrin affinity for its ligands (so-called "inside-out" signaling). Conversely, the presence or absence of integrin ligation provides specific information about the cellular microenvironment, and in many instances integrins serve as a conduit for signal transduction. Ligand binding by an integrin may promote its incorporation into focal adhesions, the assembly of cytoskeletal and intracellular signaling molecules into supra-molecular complexes, and the initiation of a cascade of downstream signaling events including protein phosphorylation, calcium release, and an increase in intracellular pH (reviewed by Schwartz et al. (1995) Ann. Rev. Cell Dev. Biol. 11:549–99). Such "outside-in" signaling ties into pathways controlling cell proliferation, migration and apoptosis (Stromblad et al. (1996) J. Clin. Invest. 98:426–33; Eliceiri et al. (1998) J. Cell. Biol. 140:1255–63). Integrins have been shown to play a role in such diverse physiological settings as embryonic development, wound healing, angiogenesis, clot formation, leukocyte extravasation, bone resorption and tumor metastasis.
The β3-containing integrins are among the best studied of the receptor superfamily. The β3 subunit forms heterodimers with either αv (αvβ3) or αIIb (αIIbβ3). While these integrins show substantial overlap in ligand specificity, they play very different roles in normal physiology and in disease.
αvβ3 is expressed by activated endothelial cells, smooth muscle cells, osteoclasts, and, at a very low level, by platelets. It is also expressed by a variety of tumor cell types. The integrin binds to a number of plasma proteins or proteins of the extracellular matrix, many of which are associated with sites of inflammation or wound healing (Albelda (1991) Am. J. Resp. Cell Mol. Biol. 4:195–203). These include vitronectin, fibronectin, osteopontin, von Willebrand factor, thrombospondin, fibrinogen, and denatured collagen Type I (Hynes (1992) Cell 69:11–25). Each of these proteins share a common sequence motif, arginine-glycine-aspartic acid (RGD), that forms the core of the integrin binding site.
αvβ3 has been most intensely studied in the context of new blood vessel formation (angiogenesis) where it mediates the adhesion and migration of endothelial cells through the extracellular matrix. Angiogenesis in adults is normally associated with the cyclical development of the corpus luteum and endometrium and with the formation of granulation tissue during wound repair. In the latter case, microvascular endothelial cells form vascular sprouts that penetrate into the temporary matrix within a wound. These cells transiently express αvβ3 and inhibition of the ligand binding function of the integrin temporarily inhibits the formation of granulation tissue (Clark et al. (1996) Am. J. Pathol. 148:1407–21). In cytokine-stimulated or unstimulated angiogenesis on the chick chorioallantoic membrane, blockade of αvβ3 with a heterodimer-specific antibody prevents new vessel formation without affecting the pre-existing vasculature (Brooks et al. (1994) Science 264:569–71). Furthermore, the loss of adhesive contacts by endothelial cells activated for angiogenesis induces a phenotype characteristic of apoptotic cells (Brooks et al. (1994) Cell 79:1157–64); that is, ligand binding by αvβ3 appears to transmit a survival signal to the cell. Thus, adhesion and/or signaling mediated by αvβ3 is essential for the formation of new blood vessels.
Solid tumors are unable to grow to significant size without an independent blood supply. It is currently hypothesized that the acquisition of an angiogenic phenotype is one of the limiting steps in the growth of primary tumors and of tumors at secondary sites (Folkman (1995) Nat. Med. 1:27–31). In addition, while the vasculature that penetrates a tumor mass provides a source of oxygen and nutrients, it also serves as a conduit for metastatic cells to leave the primary tumor and migrate throughout the body. Thus, inhibition of angiogenesis may limit both the growth and metastasis of cancerous lesions. In experimental settings of tumor-induced angiogenesis, inhibition of ligand-binding by endothelial αvβ3 prevented the formation of new blood vessels (Brooks et al. (1994) Cell 79:1157–64; Brooks et al. (1995) J. Clin. Invest. 96:1815–22), and inhibitors of αvβ3 were shown to reduce the growth of experimental tumors in vivo (Brooks et al. (1995) J. Clin. Invest. 96:1815–22; Carron et al. (1998) Canc. Res. 58:1930–5).
αvβ3 is not only expressed by the microvasculature within tumors, but in some cases, is also found on the surface of tumor cells themselves. In particular, expression of αvβ3 integrin has been detected in tissue sections from tumors of melanocytic and astroglial origin (Albelda et al. (1990) Canc. Res. 50:6757–64; Gladson and Cheresh (1991) J. Clin. Invest. 88:1924–32), and the level of integrin expression has been correlated with the stage or metastatic potential of the tumor (Albelda et al. (1990) Canc. Res. 50:6757–64; Gladson et al. (1996) Am. J. Pathol. 148:1423–34; Hieken et al. (1996) J. Surg. Res. 63:169–73). Furthermore, melanoma cells grown in vitro in a three-dimensional matrix of denatured collagen undergo apoptosis upon αvβ3 blockade.
Data such as these have driven an interest in inhibitors of αvβ3 for the treatment of cancer. At present, two such inhibitors are in or near clinical trial: Vitaxin is a chimeric Fab fragment derived from the αvβ3-specific monoclonal antibody, LM609 (Wu et al. (1998) Proc. Nat. Acad. Sci. 95:6037–42). A phase I trial in late-stage cancer patients has been completed and no significant treatment-associated toxicities were observed (Gutheil et al. (1998) Am. Soc. Clin. Onc.). EMD121974 is a cyclic pentapeptide inhibitor of αvβ3. A Phase I study of this compound in Kaposi's sarcoma, brain tumors and solid tumors is scheduled to begin in 1999.
Angiogenesis (and αvβ3) are implicated in the pathology of several other diseases, including psoriasis (Creamer et al. (1995) Am. J. Pathol. 147:1661–7), rheumatoid arthritis (Walsh et al. (1998) Am. J. Pathol. 152:691–702; Storgard et al. (1999) J. Clin. Invest. 103:47–54), endometriosis (Healy et al. (1998) Hum. Reprod. Update 4:736–40), and several proliferative diseases of the eye (Casaroli Marano et al. (1995) Exp. Eye Res. 60:5–17; Friedlander et al. (1996) Proc. Nat. Acad. Sci. 93:9764–9; Hammes et al. (1996) Nat. Med. 2:529–33). Inhibition of integrin ligand binding in each of these contexts may provide significant therapeutic benefit.
Atheromatous plaque and restenosis following angioplasty are pathologies characterized by thickening of the intima, the innermost layer of the arterial wall. The proliferation and/or migration of smooth muscle cells into the neointima with concomitant deposition of fibrous extracellular proteins contributes to vessel wall thickening and subsequent vessel occlusion. Platelets may also contribute to the development of restenotic lesions through adhesion to endothelial cells and the release of growth factors and cytokines that stimulate the underlying smooth muscle cell layer (Le Breton et al. (1996) J. Am. Coll. Cardiol. 28:1643–51). αvβ3 integrin is expressed on arterial smooth muscle cells (Hoshiga et al. (1995) Circ. Res. 77:1129–35) and mediates their migration on vitronectin and osteopontin (Brown et al. (1994) Cardiovasc. Res. 28:1815–20; Jones et al. (1996) Proc. Nat. Acad. Sci. 93:2482–7; Liaw et al. (1995) J. Clin. Invest. 95:713–24; Panda et al. (1997) Proc. Nat. Acad. Sci. 94:9308–13), both matrix proteins that are associated with atheroschlerotic tissues in vivo (Brown et al. (1994) Cardiovasc. Res. 28:1815–20; Giachelli et al. (1995) Ann. N. Y. Acad. Sci. 760:109–26; Panda et al. (1997) Proc. Nat. Acad. Sci. 94:9308–13). In addition, αvβ3 expression on endothelial cells, and to a much lesser extent on platelets, is responsible for at least part of the adhesive interaction between these cell types (Le Breton et al. (1996) J. Am. Coll. Cardiol. 28:1643–51; Gawaz et al. (1997) Circulation 96:1809–18). αvβ3 blockade with RGD-containing peptides or a monoclonal antibody was found to limit neointimal hyperplasia in several animal models of restenosis following arterial injury (Choi et al. (1994) J. Vasc. Surg. 19:125–34; Srivatsa et al. (1997) Cardiovasc. Res. 36:408–28; Slepian et al. (1998) Circulation 97:1818–27; Coleman et al. (1999) Circ. Res. 84:1268–76). Furthermore, treatment of patients undergoing percutaneous coronary intervention with an anti-β3 antibody (Reopro/abciximab/c7E3), which blocks both the platelet fibrinogen receptor, αIIbβ3, and αvβ3, provided long term reduction in the rates of death or myocardial infarction and in the rate of reocclusion of the artery (Lefkovits et al. (1996) Am. J. Cardiol. 77:1045–51), an effect that may be mediated through inhibition of αvβ3 ligation. The observation that αvβ3 is expressed by microvascular smooth muscle cells after experimentally-induced focal cerebral ischemia (Okada et al. (1996) Am. J. Pathol. 149:37–44) suggests that this integrin may also play some role in the development of ischemia/reperfusion injury in stroke.
Finally, αvβ3 mediates the attachment of osteoclasts to matrix proteins, particularly osteopontin, on the surface of bone. Osteoclasts are responsible for the resorption of bone in normal physiology as well as in pathological conditions such as osteoporosis. A monoclonal antibody specific for αvβ3 inhibited the binding and resorption of bone particles by osteoclasts in vitro (Ross et al. (1993) J. Biol. Chem. 268:9901–7). Furthermore, an RGD-containing protein, echistatin, was shown to block parathyroid-stimulated bone resorption in an animal model, as monitored by serum calcium levels (Fisher et al. (1993) Endocrin. 132:1411–3). Inhibitors of αvβ3 integrin are thus considered of potential utility in treating debilitating bone loss such as occurs in osteoporosis.
αIIbβ3 (also referred to as GPIIbIIIa) is the major integrin on the surface of platelets where it mediates the adhesion of activated platelets to the plasma protein fibrinogen (Nachman and Leung (1982) J. Clin. Invest. 69:263–9; Shattil et al. (1985) J. Biol. Chem. 260:11107–14). During clot formation, fibrinogen dimers cross-link platelets to one another through the integrin receptor. αIIbβ3 also binds to several other plasma and cell matrix proteins, including von Willebrand factor, vitronectin, and fibronectin (Faull and Ginsberg (1996) J. Am. Soc. Nephrol. 7:1091–7).
Clot formation is a tightly regulated process that balances the need for rapid response to vascular injury with the risk of aberrant occlusion of critical vessels. The αIIbβ3 heterodimer is constitutively expressed on the surface of resting platelets at approximately 80,000 copies per cell (Wagner et al. (1996) Blood 88:907–14); however, the affinity of the integrin for fibrinogen is very low on these cells. Activation of platelets by ADP, epinephrine, collagen or thrombin leads to a dramatic enhancement in integrin ligand binding activity (Bennett and Vilaire (1979) J. Clin. Invest. 64:1393–401; Marguerie et al. (1979) J. Biol. Chem. 254:5357–63), probably accomplished through a conformational change in the receptor (Shattil et al. (1985) J. Biol. Chem. 260:11107–14; O'Toole et al. (1990) Cell Reg. 1:883–93; Du et al. (1993) J. Biol. Chem. 268:23087–92). In this prototypic example of "inside-out" control of integrin function, cross-linking of platelets through the αIIbβ3-fibrinogen interaction is confined to local sites of platelet activation.
Inhibitors of αIIbβ3 ligand binding have been primarily explored in the context of cardiovascular disease (Chong (1998) Am. J. Health Syst. Pharm. 55:2363–86; Topol et al. (1999) Lancet 353:227–31), but may have application in any of a number of indications where thrombus formation is suspected or is likely. Three αIIbβ3 inhibitors have been approved for use in patients experiencing acute coronary syndrome and/or in patients who are undergoing percutaneous coronary intervention. Reopro (Centocor/Eli Lilly) is a humanized murine monoclonal antibody Fab fragment with specificity for the β3 chain of αIIbβ3. Integrilin (COR Therapeutics) is a cyclic heptapeptide based on the integrin binding site of barbourin, an αIIbβ3 inhibitory protein derived from snake venom. Aggrastat (Merck & Co.) is a non-peptide small molecule antagonist of the integrin. Unlike the small molecule inhibitors, Reopro cross-reacts with αvβ3, a fact which may account for the greater reduction in long-term rates of death and non-fatal myocardial infarction associated with its use (see above). A significant effort is underway to identify new inhibitors of the platelet integrin with characteristics not found in the cohort of approved drugs. Specifically, compounds with specificity for the active, ligand-binding conformation of αIIbβ3 may reduce the risk of bleeding complications associated with the existing anti-clotting therapies. Orally available compounds would be particularly useful for longer term therapy of patients at risk for recurrent myocardial infarction or unstable angina.
Given the role of integrins in the various disease states described above, it would be desirable to have high specificity inhibitors of particular integrins. The present invention provides such agents.
The dogma for many years was that nucleic acids had primarily an informational role. Through a method known as Systematic Evolution of Ligands by EXponential enrichment, termed the SELEX process, it has become clear that nucleic acids have three dimensional structural diversity not unlike proteins. The SELEX process is a method for the in vitro evolution of nucleic acid molecules with highly specific binding to target molecules and is described in U.S. patent application Ser. No. 07/536,428, filed Jun. 11, 1990, entitled "Systematic Evolution of Ligands by EXponential Enrichment," now abandoned, U.S. Pat. No. 5,475,096, entitled "Nucleic Acid Ligands" and U.S. Pat. No. 5,270,163 (see also WO 91/19813), entitled "Methods for Identifying Nucleic Acid Ligands," each of which is specifically incorporated by reference herein in its entirety. Each of these applications, collectively referred to herein as the SELEX Patent Applications, describes a fundamentally novel method for making a nucleic acid ligand to any desired target molecule. The SELEX process provides a class of products which are referred to as nucleic acid ligands or aptamers, each having a unique sequence, and which has the property of binding specifically to a desired target compound or molecule. Each SELEX-identified nucleic acid ligand is a specific ligand of a given target compound or molecule. The SELEX process is based on the unique insight that nucleic acids have sufficient capacity for forming a variety of two- and three-dimensional structures and sufficient chemical versatility available within their monomers to act as ligands (form specific binding pairs) with virtually any chemical compound, whether monomeric or polymeric. Molecules of any size or composition can serve as targets. The SELEX method applied to the application of high affinity binding involves selection from a mixture of candidate oligonucleotides and step-wise iterations of binding, partitioning and amplification, using the same general selection scheme, to achieve virtually any desired criterion of binding affinity and selectivity. Starting from a mixture of nucleic acids, preferably comprising a segment of randomized sequence, the SELEX method includes steps of contacting the mixture with the target under conditions favorable for binding, partitioning unbound nucleic acids from those nucleic acids which have bound specifically to target molecules, dissociating the nucleic acid-target complexes, amplifying the nucleic acids dissociated from the nucleic acid-target complexes to yield a ligand-enriched mixture of nucleic acids, then reiterating the steps of binding, partitioning, dissociating and amplifying through as many cycles as desired to yield highly specific high affinity nucleic acid ligands to the target molecule.
It has been recognized by the present inventors that the SELEX method demonstrates that nucleic acids as chemical compounds can form a wide array of shapes, sizes and configurations, and are capable of a far broader repertoire of binding and other functions than those displayed by nucleic acids in biological systems.
The basic SELEX method has been modified to achieve a number of specific objectives. For example, U.S. patent application Ser. No. 07/960,093, filed Oct. 14, 1992, now abandoned, and U.S. Pat. No. 5,707,796, both entitled "Method for Selecting Nucleic Acids on the Basis of Structure," describe the use of the SELEX process in conjunction with gel electrophoresis to select nucleic acid molecules with specific structural characteristics, such as bent DNA. U.S. patent application Ser. No. 08/123,935, filed Sep. 17, 1993, entitled "Photoselection of Nucleic Acid Ligands,", now abandoned, U.S. Pat. No. 5,763,177, entitled "Systematic Evolution of Ligands by Exponential Enrichment: Photoselection of Nucleic Acid Ligands and Solution SELEX" and U.S. patent application Ser. No. 09/093,293, filed Jun. 8, 1998, entitled "Systematic Evolution of Ligands by Exponential Enrichment: Photoselection of Nucleic Acid Ligands and Solution SELEX," describe a SELEX based method for selecting nucleic acid ligands containing photoreactive groups capable of binding and/or photocrosslinking to and/or photoinactivating a target molecule. U.S. Pat. No. 5,580,737, entitled "High-Affinity Nucleic Acid Ligands That Discriminate Between Theophylline and Caffeine," describes a method for identifying highly specific nucleic acid ligands able to discriminate between closely related molecules, which can be non-peptidic, termed Counter-SELEX. U.S. Pat. No. 5,567,588, entitled "Systematic Evolution of Ligands by EXponential Enrichment: Solution SELEX," describes a SELEX-based method which achieves highly efficient partitioning between oligonucleotides having high and low affinity for a target molecule.
The SELEX method encompasses the identification of high-affinity nucleic acid ligands containing modified nucleotides conferring improved characteristics on the ligand, such as improved in vivo stability or improved delivery characteristics. Examples of such modifications include chemical substitutions at the ribose and/or phosphate and/or base positions. SELEX process-identified nucleic acid ligands containing modified nucleotides are described in U.S. Pat. No. 5,660,985, entitled "High Affinity Nucleic Acid Ligands Containing Modified Nucleotides," that describes oligonucleotides containing nucleotide derivatives chemically modified at the 5- and 2′-positions of pyrimidines. U.S. Pat. No. 5,580,737, supra, describes highly specific nucleic acid ligands containing one or more nucleotides modified with 2′-amino (2′-NH2), 2′-fluoro (2′-F), and/or 2′-O-methyl (2′-OMe). U.S. patent application Ser. No. 08/264,029, filed Jun. 22, 1994, entitled "Novel Method of Preparation of Known and Novel 2′ Modified Nucleosides by Intramolecular Nucleophilic Displacement," now abandoned, describes oligonucleotides containing various 2′-modified pyrimidines.
The SELEX method encompasses combining selected oligonucleotides with other selected oligonucleotides and non-oligonucleotide functional units as described in U.S. Pat. No. 5,637,459, entitled "Systematic Evolution of Ligands by EXponential Enrichment: Chimeric SELEX," and U.S. Pat. No. 5,683,867, entitled "Systematic Evolution of Ligands by EXponential Enrichment: Blended SELEX," respectively. These applications allow the combination of the broad array of shapes and other properties, and the efficient amplification and replication properties, of oligonucleotides with the desirable properties of other molecules.
The SELEX method further encompasses combining selected nucleic acid ligands with lipophilic compounds or non-immunogenic, high molecular weight compounds in a diagnostic or therapeutic complex as described in U.S. patent application Ser. No. 08/434,465, filed May 4, 1995, entitled "Nucleic Acid Ligand Complexes". Each of the above described patent applications which describe modifications of the basic SELEX procedure are specifically incorporated by reference herein in their entirety.
It is an object of the present invention to provide methods that can be used to identify nucleic acid ligands that bind with high specificity and affinity to particular integrins.
It is a further object of the present invention to obtain nucleic acid ligands to particular integrins that inhibit the ability of that integrin to bind its cognate ligand.
It is a further object of the present invention to obtain integrin inhibiting pharmaceutical compositions for controlling thrombosis, tumor angiogenesis, tumor cell migration, proliferative ocular diseases, rheumatoid arthritis, psoriasis, osteoporosis, and restenosis.
It is yet a further object of the invention to obtain imaging agents for the non-invasive detection of deep vein or arterial thrombi.


A hydraulic damper (100) comprises a cylinder (10) with a bottom wall (11), a head wall (12) and side walls (13) that define a damping chamber (15) containing a damping fluid (17); in the damping chamber (15) a piston (20) slides with a first face (20a) and a second face (20b) opposite to each other. In particular, the piston (20) defines a first chamber (21) and a second chamber (22) separate from each other and is integral to a shaft (25) with an external connection end (36). The piston (20) is suitable for carrying out a forward stroke (A), between a first dead point (BDP), towards a second dead point (TDP) and a back stroke (B) between the second dead point (TDP) and the first dead point (BDP). In particular, the piston (20) comprises a plurality of permanent holes (33) suitable for permanently connecting the first chamber (21) and second chamber (22) and a plurality of apertures (26) associated each to a plurality of plug elements (37) pivotally connected by connection means (40), on a face of the piston (20) at the apertures (26). The plug elements (37) are suitable to pass spontaneously from a closed configuration (C), in which they close the apertures (26) and allow the leakage of the damping fluid (17) through the plurality of permanent holes (33), in order to damp the movement of the piston (20), to an open configuration (D), in which they open the apertures (26) and allow the free passage of the damping fluid (17) between the first (21) and second chamber (22) allowing a substantial passage of the damping fluid (17) between the first (21) and second chamber (22), in order to reduce the time that takes the piston (20) in the return stroke to return to the starting position BDP.

Different types of hydraulic dissipators or dampers are known, also commonly called viscous dissipators.
In particular, a type of viscous dissipator is a cylinder-piston mechanism capable of damping the movement transferred to it by means of viscous friction. The viscous force with which the dissipator reacts to the action is proportional to the speed and has an opposite direction to the input force. Such device is often used in combination with an elastic element, in particular a spring.
More in particular, the piston that slides in the cylinder defines a first and a second chamber separate from each other, in such a way that during the stroke of the piston there is a leakage of the viscous fluid between the first and the second chamber.
In order to obtain the leakage that determines the rate of dissipation of the damper, dedicated fixed passages are provided, or valves, on the piston. These are represented, for example, by holes with minimum diameter that damp the leakage of the fluid from a chamber to the other and then determine the dissipation.
A further example provides instead the presence of valve elements suitable to pass from a more open configuration to a more closed configuration changing the damping force.
However the above described hydraulic dampers are not effective if they have to dissipate or damp a plurality of actions temporally close to each other. It emerged, in fact, that the leakage of the viscous fluid through the valve means affects both the forward stroke both the back stroke of the piston. Therefore, the piston takes substantially the same time to go back to a starting position as the forward stroke.
In addition, such types of dissipators are not capable to have a horizontal position, or inclined, since in this case the valve element cannot return spontaneously to the starting position.
It is desirable, for example in the nautical field, to have dampers suitable for damping the actions caused by waves on a watercraft. To this end, spring damping devices are known, as described in WO9006453A1, or with resilient rubber elements, as described in WO03106251A1, arranged between two portions of a mooring, suitable for damping movements of the watercraft, caused by waves, when the watercraft is moored, for example, in a harbour.
On the other hand, the use of other damping systems different from those above cited would not be suitable to this object, since the viscous dampers of known type are not capable of dissipating actions that are temporally close to each other, like a movement caused by waves. In fact, according to the principle of operation of the above described shock absorbers, a movement of the watercraft away from the point of mooring, causes mooring ropes to be pulled abruptly and damped by the shock absorber, in order not to cause back stroke to the watercraft and negatively affecting the comfort of the passengers. However, the cylinder-piston mechanism if subject to pulling forces close to each other, owing for example to a succession of waves that displace the watercraft, once done a forward stroke and arrived to the second dead point of the damper, after damping a first wave, requires a time substantially equal for carrying out the back stroke and returning to the first dead point of the damper.
Therefore, in case of waves temporally close to each other the shock absorber loses progressively its function damping correctly the waves only if they are regularly paced. More in particular, the piston that slides in the cylinder, after having damped the first wave, starts to carry out the back stroke, and if a second wave arrives close to the first, the piston will be located in an intermediate position between the second dead point and the first dead point of the damper, thus reducing remarkably its damping effectiveness. In particular, for a succession of waves very close the shock absorber it can lose almost completely its damping effectiveness.
DE102008042822A1 describes an hydraulic damper of viscous type, with adjustable viscous resistance. The shock absorber also comprises plugs on the head of the piston in the form of leaf springs, which are foldably connected to a fastening point. Such plugs, if they were subject to high deformation elevate, would have the drawback of a quick wear and then break. In any case, such an hydraulic damper would not solve the problem of a quick back stroke, as it would be desirable in case of shock absorbers for watercrafts.
In case of shock absorbers for damping the effect of the waves on watercrafts moored in a harbour, as well as for other applications, it would be also desirable to exploit the energy accumulated by the shock absorbers for generating electric energy, for example for recharging batteries on wharfs or on watercrafts, or for any other use.

Hydraulic damper including hingedly connected plug elements for quick return to starting position


Internal power supply voltage Vint is generated from internal high voltage Vpp used for word line driving or the like, using an n channel MOS transistor which operates in a source follower mode. During operation of internal circuitry, gate potential of this source follower transistor is boosted by charge pumping operation of a capacitor. Thus, conductance of the source follower mode transistor can be increased during operation of the internal circuitry without using an internal high voltage generating circuit dedicated to generation of internal power supply voltage.

1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly, to a structure of a semiconductor memory device intended to reduce access time and power consumption thereof.
2. Description of the Background Art
In order to reduce power consumption of a semiconductor device such as a semiconductor memory device, it is effective to reduce power supply voltage Vcc supplied to the semiconductor device. This is because internal resistance is constant and power consumption is proportional to the square of the power supply voltage Vcc. However, compatibility of the semiconductor device with a semiconductor memory device which operates with power supply voltage which has not been reduced as operating power supply voltage must be maintained. Therefore, an internal voltage down-converter for down-converting externally supplied power supply voltage (hereinafter simply referred to as power supply voltage) Vcc to produce internal power supply voltage (hereinafter simply referred to as internal power supply) Vint which is lower than the power supply voltage Vcc is generally provided inside the semiconductor memory device. The semiconductor memory device is made to operate by the internal power supply Vint produced by the internal voltage down-converter.
FIG. 15 is a schematic diagram showing a structure of a conventional internal voltage generating circuit. FIG. 15 shows, together with the circuit for generating internal power supply Vint, a structure of a portion for generating internal high voltage Vpp which is higher than the internal power supply Vint. The circuit portion for generating internal power supply Vint and internal high voltage Vpp is hereinafter referred to as an internal voltage generating circuit.
The internal voltage generating circuit in FIG. 15 includes a constant current source 202 for supplying constant current; a reference potential generating circuit 203 for receiving constant current Ir from constant current source 202, and generating a reference potential Vref at a fixed voltage level which does not depend on power supply voltage Vcc when the power supply voltage Vcc is in a prescribed range; an internal power supply generating circuit 204 for generating internal power supply Vint on an internal power supply node 204x according to the reference potential Vref; and an internal high voltage generating circuit 205 for receiving the reference potential Vref and generating internal high voltage Vpp by charge pumping operation. The voltage level of internal high voltage Vpp is determined by the voltage level of reference potential Vref.
Internal power supply generating circuit 204 includes a differential amplifier 204a for differentially amplifying internal power supply Vint on internal power supply node 204x and reference potential Vref; a drive transistor 204b constituted by a p channel MOS transistor (an insulated gate type field effect transistor) coupled between an external power supply node EV and internal power supply node 204x and having its gate receiving an output signal from the differential amplifier 204a; a differential amplifier 204c activated upon activation of a row address strobe signal RAS, for differentially amplifying internal power supply Vint on internal power supply node 204x and reference potential Vref; a drive transistor 204d constituted by a p channel MOS transistor coupled between external power supply node EV and internal power supply node 204x and having its gate receiving an output signal from the differential amplifier 204c; and a p channel MOS transistor 204e coupled between external power supply node EV and the gate of drive transistor 204d and having its gate receiving row address strobe signal RAS. Differential amplifier 204a always operates, and increases conductance of drive transistor 204b by outputting a signal at a low level and supplies current from external power supply node EV to internal power supply node 204x when internal power supply Vint is lower than reference potential Vref. Since differential amplifier 204a operates at all times, it is made to have a small current driving capability in order to reduce current consumption thereof.
Differential amplifier 204c operates when row address strobe signal RAS is active. When the row address strobe signal RAS is inactive, that is, the semiconductor memory device is on standby, differential amplifier 204c is in a non-operative state. Differential amplifier 204c is made to have a large current driving capability. When the row address strobe signal RAS is active and internal circuitry operates consuming internal power supply Vint, differential amplifier 204c quickly responds to drive the drive transistor 204d to supply relatively large current from external power supply node EV to internal power supply node 204x through drive transistor 204d. Thus, reduction in internal power supply Vint during operation of the internal circuitry is suppressed. MOS transistor 204e is rendered conductive when the row address strobe signal RAS is inactive (at an L level), and supplies power supply voltage Vcc applied to external power supply node EV to the gate of drive transistor 204d, whereby it is ensured that drive transistor 204d is kept off. Thus, a current flowing path through drive transistor 204d is cut off during standby.
FIG. 16 is a diagram showing a structure of differential amplifiers 204a and 204c shown in FIG. 15. In FIG. 16, differential amplifier 204a includes a p channel MOS transistor 204aa connected between external power supply node EV and an internal node 204ax; a p channel MOS transistor 204ab connected between external power supply node EV and an internal node 204ay; an n channel MOS transistor 204ac connected between internal node 204ax and an internal node 204az and having its gate receiving reference potential Vref; an n channel MOS transistor 204ad connected between internal node 204ay and internal node 204az and having its gate receiving internal power supply Vint; and an n channel MOS transistor 204ae connected between internal node 204az and a ground node and having its gate receiving constant voltage Vcs. The constant potential Vcs is applied from constant current source 202 shown in FIG. 15, and MOS transistor 204ae functions as a current source.
Voltage to be applied to the gate of drive transistor 204b is output from internal node 204ax. MOS transistors 204aa and 204ab constitute a current mirror circuit, and MOS transistors 204ac and 204ad constitute a comparison stage. In this differential amplifier 204a, the gate of transistor 204a receives constant potential Vcs, and the supplying current thereof is reduced. Therefore, driving current (current flowing from external power supply node EV to the ground node) of differential amplifier 204a is reduced.
Differential amplifier 204c includes a p channel MOS transistor 204ba connected between external power supply node EV and an internal node 204bx and having its gate connected to an internal node 204by; a p channel MOS transistor 204bb connected between external power supply node EV and internal node 204by and having its gate connected to internal node 204by; an n channel MOS transistor 204bc connected between internal node 204bx and an internal node 204bz and having its gate receiving reference potential Vref; an n channel MOS transistor 204bd connected between internal node 204by and internal node 204bz and having its gate receiving internal power supply Vint; and an n channel MOS transistor 204be connected between internal node 204bz and the ground node and having its gate receiving the row address strobe signal RAS. MOS transistors 204ba and 204bb constitute a current mirror circuit, and MOS transistors 204bc and 204bd constitute a comparison stage.
Row address strobe signal RAS applied to the gate of current source transistor 204be varies between internal power supply Vint and ground potential. Therefore, current source transistor 204be is turned on completely when being conductive, and conductance thereof is made sufficiently larger than that of current source transistor 204ae. Furthermore, current supplying capability (channel width) of transistors included in differential amplifier 204c is also made relatively superior to (larger than) that of transistors in differential amplifier 204a. When row address strobe signal RAS attains an H level, internal circuitry of the semiconductor memory device operates and internal power supply Vint is reduced, differential amplifier 204b operates at a high speed, reducing the voltage level applied to internal node 204bx. Thus, conductance of drive transistor 204d rapidly increases, compensating for the reduction in internal power supply Vint, so that internal power supply Vint is returned to the reference potential Vref level.
In the case of the structure of the internal voltage generating circuit shown in FIGS. 15 and 16, differential amplifier 204c having large driving capability operates when row address strobe signal RAS is active. Accordingly, power consumption of differential amplifier 204c is large, and reduction in current consumption and power consumption of the entire semiconductor memory device cannot be achieved.
FIG. 17 is a diagram showing another structure of a conventional internal voltage generating circuit. The internal voltage generating circuit shown in FIG. 17 operates with power supply voltage Vcc on an external power supply node EV as operating power supply voltage, and includes a charge pumping circuit 210 for generating an internal voltage on a node N1 by charge pumping operation, a drive transistor 226 constituted by an n channel MOS transistor connected between external power supply node EV and an internal power supply node IV and having its gate connected to node N1, and a p channel MOS transistor 227 connected between node N1 and a ground node and having its gate receiving reference potential Vref from a reference potential generating circuit 203.
Charge pumping circuit 210 includes three stages of inverters 219, 220 and 221 constituting a ring oscillator; an inverter 222 for inverting an output signal of inverter 221; a charge pumping capacitor C1 responsive to an output signal of inverter 222 for performing charge pumping operation to change potential of a node 210a; an n channel MOS transistor 224 connected between external power supply node EV and a node 210a; a charge pumping capacitor C2 responsive to an output signal of inverter 221 for performing charge pumping operation to change a gate potential of MOS transistor 224; a diode-connected n channel MOS transistor 223 connected between external power supply node EV and the gate of MOS transistor 224; and an n channel MOS transistor 225 connected between node 210a and internal node N1 and having its gate connected to internal node 210a. This MOS transistor 225 functions as a diode.
MOS transistor 223 functions as a diode, and clamps the gate potential of MOS transistor 224 to the voltage level of Vcc-Vth. Vth is threshold voltage of MOS transistor 224. Charge pumping capacitor C2 causes the gate potential of MOS transistor 224 to change between 2.cndot.Vcc-Vth and Vcc-Vth according to the charge pumping operation thereof. MOS transistor 224 transmits power supply voltage Vcc to node 210a when the gate potential thereof is 2.cndot.Vcc-Vth. Charge pumping capacitor C1 causes potential of internal node 210 to change between 2.cndot.Vcc and Vcc according to an output signal of inverter 222. Therefore, voltage of 2.cndot.Vcc-Vth is transmitted to node N1 through MOS transistor 225. MOS transistor 227 has threshold voltage Vthp, has its gate receiving reference potential Vref, and operates in a source follower mode. Accordingly, potential of node N1 is clamped to the voltage level of Vref+.vertline.Vthp.vertline..
Drive transistor 226 operates in a source follower mode, and keeps the potential difference between the gate (node N1) thereof and internal power supply node IV at the level of threshold voltage Vthn. Therefore, internal power supply Vint is Vref+.vertline.Vthp.vertline.-Vthn.
The circuit structure shown in FIG. 17 is not provided with a differential amplifier. However, charge pumping circuit 210 operates at all times, resulting in large power consumption thereof. In particular, if the difference between voltage of 2.cndot.Vcc-Vthn output from charge pumping circuit 210 and reference potential Vref is large, MOS transistor 227 conducts at all times and supplies current from node N1 to the ground node, and therefore, current is consumed unnecessarily.
In addition, drive transistor 226 operates in a source follower mode, and supplies current from external power supply node EV to internal power supply node IV according to the potential difference between the gate and the source thereof, that is, the potential difference between node N1 and internal power supply node IV. When internal circuitry operates and internal power supply Vint rapidly reduces, large current flows through drive transistor 226. Drive transistor 226 is constituted by an MOS transistor, and has a specific channel resistance determined by its gate potential. Therefore, if relatively large current flows therethrough, the potential level of internal power supply Vint is reduced by the channel resistance of drive transistor 226, and the operating power supply voltage level of the internal circuitry is accordingly decreased, resulting in reduction in operation speed of the internal circuits. Consequently, in this case, the internal circuitry cannot operate stably at a high speed, and high speed access cannot be realized.
FIG. 18 is a diagram showing a structure of a data input/output (I/O) circuit of a semiconductor memory device. FIG. 18 shows a structure of a data I/O portion for 1 bit. In FIG. 18, a data output portion of the data I/O circuit includes an inverter 234 for inverting internal read data R; 2-input NAND circuits 237 and 238 activated in response to a data read instruction signal .phi.O, for inverting internal read data R and output data of inverter 234 to transmit those inverted data to internal nodes Na1 and Na2, respectively; an inverter 235 for inverting a data signal on a node Na1; a capacitor 247 responsive to an output signal of inverter 235 for carrying out charge pumping operation to transmit charges to a node Na3; a diode-connected n channel MOS transistor 240 connected between an internal power supply node IV and node Na3; an n channel MOS transistor 243 connected between external power supply node EV and a data I/O terminal Na4; an n channel MOS transistor 241 connected between the gate of MOS transistor 243 and a ground node and having its gate connected to node Na1; and a p channel MOS transistor 246 connected between node Na3 and the gate of MOS transistor 243 and having its gate connected to node Na1. MOS transistor 243 transmits power supply voltage Vcc on external power supply node EV to data I/O node Na4 when it is rendered conductive.
The data output portion further includes an n channel MOS transistor 244 connected between data I/O node Na4 and the ground node; a p channel MOS transistor 245 connected between internal power supply node IV and the gate of MOS transistor 244 and having its gate connected to node Na2; and an n channel MOS transistor 242 connected between the gate of MOS transistor 244 and the ground node and having its gate connected to node Na2.
A data write portion of the data I/O circuit includes an NAND circuit 239 for receiving a data write instruction signal .phi.I and write data on data I/O node Na4, an inverter circuit 236 for inverting an output signal of NAND circuit 239 to produce internal write data W. Operation will now be described briefly.
First, description of data read operation will be given. When a data read instruction signal .phi.O is inactive at an L level, a potential level on nodes Na1 and Na2 is an H level (an internal power supply Vint level). In this condition, node Na3 is held, by MOS transistor 240, at a voltage level lower than internal power supply Vint by threshold voltage thereof. Therefore, MOS transistor 246 is made turned off, while MOS transistor 241 is made turned on. In addition, MOS transistor 245 is off, while MOS transistor 242 is on. Thus, MOS transistors 243 and 244 of the output portion have respective gate potentials at the ground potential level and are made turn off, and data output node Na4 is forced to be in an output high impedance state.
If the data read instruction signal .phi.O attains an H level, NAND circuits 237 and 238 are enabled. Assuming that internal read data R is now at an H level, potential of node Na1 falls to an L level and an output of inverter 235 rises to an H level. In response to the rise of the output signal of inverter 235, potential on node Na3 rises to the level of 2.cndot.Vcc-Vth by the function of charge pumping capacitor 247. Thus, the potential on node Na3 is transmitted to the gate of MOS transistor 243 through MOS transistor 246. At this time, since MOS transistor 241 is off, gate potential of MOS transistor 243 is made at the level of 2.cndot.Vcc-Vthn, and the MOS transistor transmits voltage at the Vcc level to data I/O node Na4. At this time, internal node Na2 is at an H level and MOS transistor 244 is off.
When internal read data R is at an L level, potential level on node Na1 is an H level and potential level on internal node Na2 is an L level. In this condition, MOS transistors 246 and 243 are made turned off, while MOS transistor 241 is made turned on (this is the same condition as that in the case where the signal .phi.O is at an L level). On the other hand, MOS transistor 245 is turned on, while MOS transistor 242 is turned off, and gate potential of MOS transistor 244 is set at the internal power supply Vint level. Thus, MOS transistor 244 is turned on, and potential on data I/O node Na4 is discharged to the ground potential level.
In data write operation, write instruction signal .phi.I is activated at an H level. Thus, NAND circuit 239 and inverter 236 as a whole function as a buffer, and buffer write data applied to data I/O node Na4 to produce internal write data W.
In the structure of the data I/O circuit shown in FIG. 18, only the last data output stage is connected to the external power supply node, and other components operate with internal power supply Vint as operating power supply voltage. Interface between a memory and an external device can be achieved by outputting a signal, which swings between the external power supply voltage Vcc level and the ground voltage level, to data I/O node Na4.
However, internal power supply Vint is applied to the gate of MOS transistor 244. The gate potential of MOS transistor 244 is a potential level lower than an H level of data I/O node Na4, and conductance of MOS transistor 244 is reduced, so that data I/O node Na4 cannot be discharged at a high speed. If a channel width of MOS transistor 244 is increased in order to achieve large current driving capability thereof, data I/O node Na4 is accompanied with junction capacitance (substrate-drain capacitance and drain-gate capacitance) of MOS transistor 244 as parasitic capacitance. Therefore, parasitic capacitance of data I/O node Na4 increases, and thus cannot satisfy the capacitance value of, for example, 7pF at data I/O node Na4 determined by the specification value, so that quick charge/discharge of data I/O node Na4 cannot be achieved. In particular, data I/O node Na4 is also used for writing of data, and an external device cannot charge/discharge data I/O node Na4 quickly if this parasitic capacitance increases, so that the data writing speed is accordingly reduced. Consequently, if internal power supply Vint is reduced, data cannot be input/output at a high speed, resulting in difficulty in implementation of a semiconductor memory device which operates at a high speed.

Semiconductor memory device achieving reduction in access time without increase in power consumption


A data receiving part receives data transmitted from a plurality of measuring devices. A time determining part distinguishes management time from date and time of the data. The record generating part stores data of the same management time which are received during a predetermined acceptance time, in the same record. When un-arrived data belonging to the same management time exists at the end of the acceptance time, arrival of the un-arrived data is waited for during a predetermined wait time. Even if the data is arrived with some delay, arrival-delayed data can be stored in the same record. Thus, the missing data occurrence frequency can be suppressed.

Generally, a measuring device such as an electric power sensor or temperature sensor performs measurement periodically and outputs data indicating the measurement result.
The data structure of the data outputted from the measuring device is constituted by "date and time" at which the measurement was conducted, a "device ID" which can identify the corresponding measuring device uniquely, and a "measurement value" obtained by the measurement.
A method which prevails conventionally most widely for managing the data in the table of the database is the one that stores the data in the table without changing the original data format described above.
If all data of the same time are to be extracted for the use of, for example, monitoring, at once from the database which has been accumulated in the above format, since the time added to the data itself differs depending on the measuring device, it is difficult to compare the data which are measured at the same time.
According to the conventional management scheme, the data of the respective devices are stored all in the direction of column for each time. When, for example, the correlation between the temperature and electric power is to be obtained, a complicated process is required.
As opposed to the above scheme, for the object of comparing sensor data which are measured periodically, in a time series manner, Patent Literature 1 discloses a technique for generating a record segmented on the time base, and storing data in a record whose time is close to the time of the data, so that a plurality of pieces of data having the same time or times close to each other are stored in one record.

Data processing apparatus, data processing method, and program


The present invention relates to soil redeposition inhibiting agents, soil redeposition inhibiting articles comprising such soil redeposition inhibiting agents, method for using such soil redeposition inhibiting articles for removing soils from dry or essentially dry fabrics, and systems employing said soil redeposition inhibiting agents such that soil is removed from dry or essentially dry fabrics exposed to the soil redeposition inhibiting agents.

Soil redeposition from one garment to another garment in traditional laundry processes is a well-known phenomenon, whether it be aqueous based home laundry processes or solvent based dry cleaning processes. Models explaining this redeposition of soils from one garment to another theorize that this problem is associated with the cleaning process itself. In essence, after the water or solvent plus detergent system removes the soil from one garment, the soil can redeposit onto another garment before wash liquor is rinsed from the treated garments. To prevent this, the cleaning solution must contain ingredients capable of suspending or trapping the soil in the wash liquor, thereby preventing it from redepositing on garments. Given this model, extensive effort has gone into developing detergent systems capable of better soil suspension or trapping within the wash liquor. It is well-known to current practitioners of the art that as the suspension or trapping of soils in the wash liquor improves, the amount of soil redeposition decreases. The problem with this knowledge is that it also limits association of the problem of soil redeposition to cleaning processes involving water or solvents and detergent systems.
Conventionally soils and soil components, especially colorless soils and soil components have thought to have been effectively removed from dry or essentially dry fabrics via the drying process, oftentimes within an automatic clothes dryer. Formulators were of the mindset that the soils were volatilized and/or vaporized and removed from the dryer.
It has been surprisingly found that such soils are not effectively removed from dry or essentially dry fabrics because of the problem of redeposition of such soils onto the fabric after initially removing the soils from the fabrics, especially during the period when the fabric is cooling in temperature, for example when the fabrics are no longer being subjected to additional heat.
Accordingly, there is a need to develop compositions, articles, methods and/or systems to effectively remove soils and soil components from fabrics while inhibiting the redeposition of those soils and soil components onto the fabrics being treated.

Soil redeposition inhibition agents and systems


An improvement for an apparatus conveying sheets of paper seriatim along a deck between a plurality of roller pairs, including lower driven rollers and corresponding upper biased idler rollers. The improvement comprises a roller and guide plate assembly pivotably mounted on the deck. The roller and guide plate assembly includes a guide plate operatively coupled to rigid support shafts and upper roller assemblies of the roller pairs, and means for supporting the guide plate a fixed distance above the deck. The guide plate is mounted to at least two shaft support blocks, the rigid support shafts for the upper roller assemblies being mounted to the support blocks above the guide plate, the guide plate including slots through which the biased upper rollers of the upper roller assemblies extend therethrough to cooperate with the corresponding lower driven rollers to convey sheets across the deck. One of the shaft support blocks is pivotably mounted to the deck whereby the roller and guide plate assembly is pivotable between a raised position and a lowered operating position. There is a locking mechanism, including a support bracket and means for locking the roller and guide plate assembly to the support bracket in the lowered operating position, the roller and guide plate assembly being supported by a lower leg of the support bracket when the roller and guide plate assembly is in a lowered operating position.

Multi-station document inserting machines generally include a plurality of various stations which are configured for specific applications. Typically, such inserting machines, also known as console inserting machines, are manufactured to perform operations customized for a particular customer. Such machines are known in the art and are generally used by organizations which make up large volume mailings where the content of each mail piece may vary.
An example of a document inserting machine is disclosed in U.S. Pat. No. 4,547,856 issued to Piotroski, et al. on Oct. 15, 1985 and assigned to the assignee of the present invention. This inserting machine includes a plurality of serially arranged stations including an envelope feeder and insert station, a plurality of insert feeder stations and a burster-folder station. There is a computer generated forms or web feeder that feeds continuous form control documents having control coded marks printed thereon to the burster-folder station for separating and folding. The control marks on the control documents are sensed by a control scanner located in the burster-folder station. Thereafter, the serially arranged insert feeder stations sequentially feed the necessary documents onto a transport deck at each station as the control document arrives at the respective station to form a precisely collated stack of documents which is transported to the envelope feeder-insert station where the stack is inserted into the envelope.
Generally, control documents are fed in a predetermined orientation, i.e., landscape or portrait, that facilitates a fixed beam scanner reading control marks on the moving documents. In certain applications, after the control marks are read, it is necessary to convey the documents in the other orientation for further processing, such as insertion into an envelope. One conventional way for achieving landscape to portrait, or portrait to landscape change in orientation of sheets as they are conveyed through an inserting machine includes a first paper path conveying to a distinct second paper path. The first paper path, conveying in a first direction, ends at a second paper path which is typically orthogonal to the first paper path and conveying in a second direction. Generally, the conveying means of the second paper path does not begin to convey until the sheet has been transferred from the first paper path to the second paper path. Such an arrangement ensures the proper orientation of the sheet being conveyed in the second direction but reduces the throughput of the inserting machine.
In U.S. Pat. No. 5,180,154, issued Jan. 19, 1993 and assigned to the assignee of the present invention, a right angle transfer device is disclosed. The transfer device changes the direction of travel of a flat article being conveyed at a high speed, e.g. 100 inches/second, without turning the article. The device includes a take away unit which receives the article being conveyed in a first direction, and conveys the article in a second direction, preferably 45.degree. from the first direction, to a registration wall extending in a third direction which is orthogonal to the first direction. A third direction conveying means conveys the article for further processing. Although the right angle transfer device is suitable for changing the direction of travel of flat articles having a certain thickness or rigidity, the device has not suitable for changing the direction of single sheets being conveyed at a high speed. Specifically, the single sheets tend to crash into the registration wall at high speed resulting in a crumpling of the sheet and a subsequent paper jam.
U.S. Pat. No. 5,188,355, issued Feb. 23, 1993 and assigned to the assignee of the present invention, provides an apparatus for changing the direction of travel of sheets of paper being conveyed seriatim along a paper path without changing the orientation of the sheets with respect to a first direction of travel. The apparatus comprises a deck having an upstream end for receiving a sheet being conveyed along a paper path in a first direction. There are a plurality of first roller pairs operatively coupled to the deck and disposed in a second direction for seizing a first leading edge of the sheet and conveying the sheet in the second direction along the deck. The second direction forms an acute angle of at most 45.degree. with the first direction. It is noted in U.S. Pat. No. 5,188,355 that conveying individual sheets at a high speed, for example, 105 inches per second, through the transfer unit to an alignment unit causes portions of a sheet to lift off of the deck unless such sheet portions are restrained. A plurality of guide fingers are operatively coupled to the first roller pairs to prevent a portion of each sheet from raising off the deck when the portion is not controlled by the first roller pairs. The alignment unit includes a plurality of second roller pairs which are operatively coupled to the deck and disposed in a third direction for seizing a second leading edge of the sheet and conveying the sheet in the third direction along the deck. The third direction forms a right angle with the first direction. The first and second roller pairs include lower driven rollers and upper biased rollers. The guide fingers include a plurality of spring structure for preventing a portion of the sheet from lifting off the deck when being conveyed at high speed. The apparatus is suitable for conveying sheets landscape to portrait or portrait to landscape.
The apparatus in U.S. Pat. No. 5,188,355, eliminated the problem associated with a registration wall in U.S. Pat. No. 5,180,154. However, another problem has been experienced relating to the spring guide fingers. The guide fingers improved the performance of the apparatus without fingers, but jams were still experienced because, notwithstanding the guide fingers, the sheets have a propensity to lift off the deck as they are conveyed at high speed through the apparatus. In particular, jams were experienced between the transfer unit and the alignment unit of the apparatus as the sheets are engaged by the second roller pairs. Thus, the number and placement of the guide fingers are directly related to the reliability of sheets being successfully fed through the apparatus. Furthermore, it was determined that the number of fingers needed and the placement thereof may differ for different sized sheets, thus requiring adjustments whenever the type of sheets being fed changed. Alternate methods, such as a brush or guide wires, are disclosed in application 816,442 for restraining the sheets from lifting off the deck.

Roller/guide plate assembly for ninety degree document transfer unit


Apparatus for determining the optimum position of an object with respect to a focal point of a focused beam of radiation. The apparatus has a resolution limit and includes a radiation source, a lens for focusing the beam of radiation on the object, and a reticle interposed between the radiation source and the lens. A focusing pattern, formed on the reticle, when projected onto the object by the focusing means, produces a projected focusing pattern which is not resolvable, the resolution of the projected focusing pattern being not greater than the resolution limit of the apparatus.

1. Field of the Invention
This invention relates to a pattern for determining the optimum position of an object with respect to the focal point of a beam of radiation focused on the object. In particular, it relates to a reticle pattern formed on a reticle for determining the optimum position of a wafer with respect to the focal point of a beam of light which projects an image on the surface of the wafer as part of a semiconductor manufacturing process. Moreover, it relates to a method for estimating the optimum position of a wafer or other object with respect to the focal point of a beam of light by the use of a reticle pattern formed on a reticle.
2. Description of the Related Art
A conventional reduction projection exposure method for forming high resolution image patterns on a wafer by the use of a mask is described in "VLSI Technology Guide Nyumon!" (Heibonshia), p. 143-144. An advantage of this method is that the mask is not damaged during the exposure process because the mask and wafer do not come into contact with each other thereby ensuring that the mask remains free of defects that might result from such contact. Another advantage of the process is that it results in a relatively high yield of the semiconductor product being manufactured. Apparatuses used for the reduction projection exposure method are referred to as steppers, an example of a conventional stepper being shown in FIG. 17.
In FIG. 17, a mercury vapor lamp 171 provides a source of light that is passed through a condenser lens 172 and a filter (not shown) along a vertical Z-axis to provide a beam of substantially single frequency light. The filtered light beam impinges on a reticle 173 having deposited thereon an original of an image pattern consisting of opaque and transparent areas, the letter "A" being shown in FIG. 17 as an example. The light passes through the transparent portions of the image pattern and is focused, after passing through a reduction lens 174, onto the surface of a wafer 175 covered with a photoresist material. The light is automatically focused on the wafer, which is mounted on a stage 176 movable along X, Y and Z axes, under predetermined exposure conditions by means of a sensor (not shown) located near the light source. The sensor detects the relative position of the photoresist covered surface of the wafer with respect to the focal point of the focused light. Means (not shown) are provided for changing the relative positions of the wafer and the focal point of the focused light along the Z-axis.
A disadvantage of this system in that the relative position of the wafer along the Z-axis, as set by the sensor, and the focal point at which the optical system brings the light into focus are not always matched. Consequently, any deviation in the position of the wafer surface from the optimum position must be measured and corrected.

Method for estimating optimum position of a wafer for forming image patterns thereon


The invention is a method for producing flitches prepared from roundwood logs, a method for the manufacture of wood slices or slats from the flitches, and methods of combining the strips into composite lumber products. The methods are based in part on the concept of preparing flitches that retain the sweep or natural longitudinal curvature of the log and slicing or sawing around the sweep to prepare the slats for further conversion into composite lumber products. An opening cut is made in the log essentially following or parallel to the curve of any sweep to divide it into two approximately equal volume pieces. An opposing surfaces is machined parallel to the surface generated by the opening cut to produce a flitch. The flitches are then flattened so that the sweep curvature is made planar. They are then sliced or sawn parallel to the now planar surface to produce slats. The natural surface of the log is preferably retained on the sides of the flitches. Slats may then be edged and adhesively combined in various ways to produce composite lumber products. The method achieves an especially high yield from raw logs of products that simulate solid sawn lumber in appearance, properties, and ease of use.

Sawn lumber in standard dimensions is the major construction material used in framing homes and many commercial structures. The available old growth forests that once provided most of this lumber have now largely been cut. Most of the lumber produced today is from much smaller trees obtained from second growth forests and, increasingly, from tree plantations. Intensively managed plantation forests stocked with genetically improved trees are now being harvested on cycles that vary from about 25 to 40 years in the pine region of the southeastern and south central United States and about 40 to 60 years in the Douglas-fir region of the Pacific Northwest. Similar short harvesting cycles are also being used in many other parts of the world where managed forests are important to the economy. Plantation thinnings, trees from 15 to 25 years old, are also a source of small saw logs.
Whereas old growth trees were typically between 0.6 m to 1.8 m in diameter at the base (two to six feet), plantation trees are much smaller. Rarely are they more than two feet (0.6 m) at the base and usually they are considerably less than that. One might consider as an example a typical 35 year old North Carolina loblolly pine plantation tree on a good growing site. The site would have been initially planted to about 900 trees per hectare (400 per acre) and thinned to half that number by 15 years. A plot would often have been fertilized one or more times during its growth cycle. The typical 35 year old tree at harvest would be about 40 cm (16 in) diameter at the base and 15 cm (6 in) at a height of 20 m (66 ft). Trees from the Douglas-fir region would normally be allowed to grow somewhat larger before harvest.
American construction lumber, so-called "dimension lumber", is nominally 2 inches (actually 38 mm (11/2 inches)) in thickness and varies in nominal 2 inch (51 mm) width increments from 31/2 inches to 111/4 inches (89 mm to 286 mm), measured at about 12% moisture content. Lengths typically begin at 8 feet (2.43 m) and increase in 2 foot (0.61 m) intervals up to 20 ft (6.10 m). Unfortunately, when using logs from plantation trees it is now more difficult to produce the larger and/or longer sizes and grades in the same quantities as in the past.
The smaller trees of today's forests pose additional challenges for the sawmill. Because of their smaller diameter there is inherently a higher percentage of waste in converting them to rectangular lumber. While this waste is often converted into pulp chips, these are of inherently much lower value than the lumber. Also, the physical geometry of the logs is a cause for additional waste. The logs tend to have considerable taper and often have sweep as well. Sweep is longitudinal curvature along the tree. Defined otherwise, it is the deviation from a straight line of the concave edge when the log is allowed to assume its natural position on a flat surface. While occasional occurrences of extreme sweep will occur, most often it will not exceed about 100 mm in a log about 5 m long (about 4 inches in 16 feet). If logs are squared in a conventional manner prior to lumber manufacture, there is significant additional waste from sweep removal. Sawmilling machinery has recently been developed to saw logs parallel to the sweep curvature. Typically the logs are first oriented with the greatest curvature up or down ("horns up" or "horns down") and parallel faces produced on the sides by saws or chipper heads. They are then turned on one of these flat sides and sawn "around the curve". Surprisingly, the resulting boards, though originally containing the curve of the sweep, will flatten during drying. Average lumber recovery using around the curve sawing may approach 12% greater than by using conventional methods. Exemplary equipment for around the curve sawing is shown in U.S. Pat. Nos. 4,633,924 to Hasenwinkle et al. and 4,653,560 to Wislocker et al. Sawmill equipment for around the curve sawing is commercially available from McGehee Equipment Company, Ukiah, Calif. and other vendors.
Veneers have been "sliced" from prepared cants or flitches for many years. In the past, slicing has been limited to thin products, rarely more than about 3 mm in thickness. Since no sawdust is produced in slicing, conversion from flitch to useable product is high. The typical slicer cuts veneers transversely from flitches; i.e., across the width rather than along the length. Often these veneers are from fine hardwoods and are used for furniture, cabinetry, paneling, or in other applications where appearance is important. In many cases these hardwoods may be extremely rare and expensive. Rosewood or walnut would be examples. Sliced veneers enable a product to appear as if it was made from solid wood but at a small fraction of the cost of a solid wood product. Many decorative treatments are possible with sliced veneers that would not be practical or possible with solid sawn woods; e.g., book matched panels.
Rotary cut veneers peeled in a continuous ribbon from logs are primarily used in the production of plywood. This method is less often used for production of thin decorative veneers. Rotary veneer if used as a surface layer is normally used for products of lower ultimate value than those made with sliced veneers. The undistinguished flat grain is esthetically less pleasing than the appearance of sliced veneers. Due the lathe checks produced when the log is peeled, and other restraints, rotary cut veneers are not available in thicknesses much in excess of about 6 mm (1/4 inch).
In order to increase conversion percentage of sawlogs to lumber, researchers have over the years looked at methods of kerfless cutting; i.e., cutting by some method that does not use saws and produce wasteful sawdust. An early example would be U.S. Pat. No. 3,327,747 to Collins. High energy lasers have also been suggested for kerfless cutting, as in U.S. Pat. No. 4,402,574 to McConnel. Unfortunately, until recently no practical method has been found other than the manufacture of rotary cut or sliced veneer and the available veneer thickness has limited its usefulness in lumber products. An exception might be found in products such as those described in U.S. Pat. No. 3,813,842 to Troutner where plies of rotary veneer cut to the maximum practical thickness of about 6 mm are laid up with the grain direction parallel to produce lumber-like products.
The picture has changed in recent years as slicers capable of cutting slats up to about 20 mm (3/4 inch) in thickness have become commercially available. In contrast to slicers for producing decorative veneers, these generally feed the flitches longitudinally against a fixed knife rather than transversely. The resulting slats have minimal structural damage, such as checks or tears, but may come out cupped or twisted by internal stresses so that they require a subsequent flattening treatment. This may be accomplished by mechanical deformation or by the use of restraint applied during drying. After drying and flattening, the slices may be laid up into panels and the panels subsequently ripped longitudinally to produce lumber-like products in a known manner. Exemplary machines of this type are described in U.S. Pat. Nos. 4,825,917, 5,052,452, 5,318,083, 5,390,716, 5,400,843, and 5,427,163 to Gonner or Goinner et al; 3,783,917 and 5,010,934 to Mochizuki and Mochizuki et al. respectively; and Pat. No. 5,088,533 to Binder. In U.S. Pat. No. 4,977,940, Gonner et al. shows a device for straightening boards or slats produced on slicers of the above type. Gonner describes a composite wood member produced from sliced slats in U.S. Pat. No. 5,069,977 as do Traben and Gonner in U.S. Pat. No. 5,352,317.
It is normal in using the above slicers to use cants or flitches that have been squared; i.e. formed into rectangular parallelepipeds in which each face is at 90.degree. to its adjacent faces. Because of this, considerable wood is lost from the outside of the log in forming a rectangle of the largest possible cross sectional area from the particular cut being formed into a flitch. This waste includes that due to sweep and taper which must be cut out and used for fuel or other lower value products.
The present method is directed to a process for producing composite lumber products using methods that eliminate much of the waste caused by the sweep and taper naturally present in sawlogs.

Method of producing wood strips for conversion into composite lumber products


An optical detection system capable of detecting even small particles or defects on a specimen such as a mask with high sensitivity and being unaffected by diffracted light from the edges of the pattern even when inspecting a thick specimen. The optical detection system includes a light emission means for illuminating a pattern surface on the specimen with light, a first light reception optical system placed on the pattern surface side of the specimen for receiving scattered light emanating from the pattern surface, a second light reception optical system placed on the glass side of the specimen in symmetry with the first light reception optical system relative to the pattern surface for receiving scattered light emanating from the pattern surface through the specimen and a corrective optical element for correcting for differences in the aberration states of the first and second light reception optical systems.

Semiconductor device fabrication includes, for example, a process in which a pattern formed on a mask is transferred to a photosensitive substrate. During this process, if there is any defects and/or particles, e.g. dust, etc., adhering to the surface of the mask on which the pattern is formed, the image of the defects and/or particles will also be transferred to the substrate and cause circuit pattern defects. Therefore, before performing the pattern-transfer exposure, the pattern surface of the mask must be inspected for defects and/or particles, using a defects and/or particles optical detection system.
An example of an optical inspection system for detecting the presence of defects and/or particles on a pattern surface of a mask (reticle) is disclosed in Japanese Laid-Open patent H 5-87549. This optical system has a scanning optical system placed over the pattern side of the mask, and a light reception optical system placed over the same side.
A defect inspecting system using conventional technology is also disclosed in U.S. Pat. No. 4,468,120. This system employs a reception optical system arranged at a position in which diffracted light beams through the mask material will not enter.
The optical detection system of present invention employs a first light reception optical system placed on the pattern surface side of the mask, a second light reception optical system placed on the side of the mask opposite the pattern side and a corrective optical element for correcting differences in aberration states of the first and second optical systems. The light reception optical system of the present invention is arranged at a position at which it can receive both scattered light from defects on the mask and diffracted light from patterns on the mask. An alternative apparatus for detecting defects on a mask using both a reflection detection system and a transmission detection system is taught and described in Applicants corresponding copending U.S. Pat. application Ser. No. 08/636,511, entitled "Apparatus For Detecting Defects on A Mask", the disclosure of which is herein incorporated by reference.
The object of the present invention is to provide an optical detection system that is capable of detecting even small defects and/or particles on the surface of a mask with high sensitivity, unaffected by diffracted light from the edges of the patterns even when inspecting surface patterns on thick masks.

Optical detection system for detecting defects and/or particles on a substrate


There is provided a display device including a display panel and a background panel which are arranged opposite to each other, and a light source which is disposed on a side surface of the background panel. The background panel is in a transmissive state where no voltage is applied thereto, is in a light-scattering state where a direct-current (DC) voltage is applied thereto, and is in a transflective state where a high-frequency alternating-current (AC) voltage is applied thereto.

Liquid crystal displays (LCDs) have dominated the current flat-panel display market due to the characteristics of small size, low power consumption, non-radiation and the like. In an LCD, as liquid crystal does not emit light by itself and only adjusts and controls transmissive light, images can only be displayed when an LCD panel (also referred to as LCD screen) is equipped with light sources (e.g., backlights, front lights or external light sources).
With the rapid development of the LCD technologies, a transparent LCD is proposed. A transparent LCD utilizes ambient light (including natural light and light emitted by external light sources) and light emitted by a transparent backlight to display images on an LCD panel. The LCD generally employs side-lit backlights and comprises light sources, a light guide plate and an optical film assemble. When the ambient light is strong, the transparent LCD mainly employs the ambient light as the light source; and when the ambient light is weak, the transparent LCD mainly employs the transparent backlight as the light source.
Currently, the transparent LCD has been applied in a kind of refrigerator and used as a "window" of the refrigerator, namely a refrigerator window, through which users can see food stored therein without opening the refrigerator. Moreover, a series of user-friendly features can be also developed for different user groups, for example, the display of shelf life and nutrient content of stored foods, weather forecast, and notes left to family members, and even playing of movie. However, as the power of the light sources in the traditional transparent LCD is great, relatively great heat can be irradiate, and hence the storage of refrigerated/frozen foods therein can be affected when the transparent LCD is applied to the refrigerator.


A loudspeaker device comprising a power amplifier (13) to which an input signal is delivered via a subtracter (6), a speaker unit (1) for reproducing output signals delivered from the power amplifier (13), an acoustic pipe (2) coupled in front of the speaker unit for guiding the sound waves, a microphone (4) for detecting an acoustic outputs radiated from the speaker unit, a microphone amplifier (5) for amplifying an acoustic output signals detected by the microphone, and a negative feedback circuit. Output signals of the microphone amplifier are delivered to the subtracter, at the same time the same output signal is connected to a high-pass filter (7) to be delivered to the subtracter. Thus the negative feedback circuit is formed to suppress peaks and dips for providing a flattened sound pressure frequency characteristic.

A conventional speaker device of the same type is described with reference to FIG. 7, FIG. 8 (A) and FIG. 8 (B). FIG. 7 is a block diagram, FIG. 8 (A) shows microphone output signals, FIG. 8 (B) shows sound output characteristics of the conventional speaker device, where, curve "a" shows a sound pressure characteristic, and curve "b" shows a phase characteristic.
Referring to FIG. 7, a speaker unit 1 generates sound waves, and the speaker unit 1 is coupled with an acoustic pipe 2. At both sides of the acoustic pipe 2 are sound absorbing material (not shown) provided for suppressing resonance. Inside the acoustic pipe 2, a microphone 4 is provided close to the speaker unit 1 for detecting sound output signals.
When a signal is delivered to the speaker unit 1 via a subtracter 6 and a power amplifier 3, the speaker unit 1 radiates acoustic output, which is radiated from the opening through the acoustic pipe 2. The standing wave due to the length of the acoustic pipe 2 and the one generated within the acoustic pipe 2 causes a speaker device to reproduce sounds having steep peaks and dips in the sound pressure frequency characteristic. In order to prevent this, a sound absorbing material is employed to suppress the standing waves. However, the sound absorbing material is not effective enough to suppress the standing waves completely. So, a microphone 4 detects the remaining standing wave and feeds it back to the subtracter 6 via a microphone amplifier 5. Thus, the standing wave in acoustic pipe 2 is suppressed, and the reproduced sounds with a flat sound pressure frequency characteristic are obtained.
An acoustic pipe coupled in the front of a speaker unit is known to produce a resonance in the pipe; the resonance frequency f generated is represented by the formula below:f=(n+1)C/4L
where; f: pipe resonance frequency, n: the n-th resonance, C: sound velocity, L: length of the pipe.
In the above configured speaker device, when a primary resonance (n=1) due to the pipe length is corrected by means of the phase difference between the electrical input signal delivered to the speaker unit 1 and the sound output signal radiated from the speaker unit 1, the resonance component shifts and appears as a peak in the sound output characteristic after the correction. So, it has been difficult to flatten the sound output characteristic. Furthermore, since the feedback is performed for an entire frequency range from a low frequency component to a high frequency component, it is impossible to control a certain desired frequency component.
The relationship between the input and the output is shown below:V out/V in=A/(1+A·T(S))
where; V out: output voltage, V in: input voltage, A: total amplification by amplifiers, T (S) transfer function.
Assuming that the microphone 4 has an approximately flat characteristic and the T (S) is substantially equal to the transfer function of the speaker unit 1, the T (S) becomes minus 1 as a result of phase shift caused by the speaker unit 1 and the second, or the third, pipe resonance of acoustic pipe 2.
Namely, in some cases the denominator becomes 0 to be ready for making oscillation. This makes it difficult to apply too many feedbacks taking an oscillation margin into consideration, and to effectively control a low frequency region and a pipe resonance.
The present invention addresses the above problems and aims to provide a speaker device that has stable characteristics.

Matsushita Electric Industrial Co., Ltd.


A magnetic induction flowmeter has a time-varying magnetic field imposed across the flow passage, and a first and second pairs of electrodes disposed respectively on a first plane dividing the cross section of the flow passage into two equal opposite halves and a second plane offset from the first plane wherein the two electrodes belonging to each pair of electrodes are respectively affixed to the two diametrically opposite sides of the wall of the flow passage, wherein the flow rate of electrically conductive media moving through the flow passage is determined as a function of a differential combination of the electromotive force between the first pair of electrodes and the electromotive force between the second pair of electrodes.

The nonintrusive structure of the magnetic induction flowmeters makes them an ideal apparatus for measuring the flow rates of electrically conductive fluids which are corrosive or abrasive. One major short-coming of the magnetic induction flowmeters available at the present time is the high cost arising from the design feature that accurately and precisely controls the imposed magnetic field, whereby the electromotive force induced as a result of electromagnetic interaction between the imposed magnetic field and the motion of the electrically conductive media is directly proportional to the flow rate of the media. As the micro-chip based computer technology has become very widely used and quite inexpensive, an economically priced magnetic induction flowmeter can be constructed by employing the imposed magnetic field generated by a simple and inexpensive method and using a micro-chip based data analysis that isolates the net value of the induced electromotive force generated solely by the moving media.


Technologies are generally described for a gas filtration device including an array of parallel carbon nanotubes. The carbon nanotubes may extend between first and second substrates, and the ends of the carbon nanotubes may be embedded in the substrates and cut to expose openings at each end of the carbon nanotubes. The carbon nanotubes may be composed from a graphene membrane which may be perforated with a plurality of discrete pores of a selected size for enabling one or more molecules to pass through the pores. A fluid mixture including two or more molecules for filtering may be directed through the first openings of the array of nanotubes, and the fluid mixture may be filtered by enabling smaller molecules to pass through the discrete pores of the graphene membrane walls of the carbon nanotubes to produce in a filtrate fraction including the smaller molecules and a retentate fraction including larger molecules.

Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
Porous graphene is considered to be a desirable membrane for gas separation. Theoretical and experimental studies indicate that atom-scale holes in the graphene lattice may provide significant selectivity for separating gases based on molecular size. Further, monolayer graphene, at one atom thick, is a desirable candidate because the gas permeation rate through a membrane increases with decreasing membrane thickness.
Consequently, porous graphene membranes are being pursued for their potential to significantly outperform conventional polymeric membranes, e.g., in separating gases that are synthesized at high temperatures. For example, the "shift reaction" used to create hydrogen gas from water and carbon dioxide may run at temperatures over 400° C. Since there is currently no membrane that effectively purifies hydrogen in a single step, much less at such high temperatures, current hydrogen purification may include capital and energy intensive steps such as cooling, as well as removal of water, carbon dioxide, and other impurities.
A graphene membrane with uniformly sized pores may effectively purify hydrogen from the "shift reaction" in a single step. However, current graphene membranes having uniformly sized pores have a low membrane throughput and may be inefficient for separation when used in a two-dimensional or flat configuration. Some factors affecting the membrane throughput and efficiency of the flat graphene membranes include low probability of successful trajectory for enabling the molecule to align with and pass through a pore, a low pore area percentage, e.g. a low pore to membrane ratio, and a low gas adsorption to graphene. Some known nanofiltration methods have used porous graphene in cylindrical form for increasing the membrane throughput.

Graphene nanotube array for gas filtration


An analog-to-digital conversion arrangement for converting an analog input signal into a digital output signal with a most significant part and a least significant part comprises sample means for sampling the analog input signal, a plurality of coarse resolution analog-to-digital converters for converting the sampled analog input signal into a coarse digital signal representing the most significant part of the digital output signal, whereby the coarse resolution analog-to-digital converters are operated in an interleaved way. The analog-to-digital conversion arrangement further comprises a fine resolution analog-to-digital converter for converting the sampled analog input signal into a fine digital signal representing the least significant part of the digital output signal, based upon the coarse digital signal generated by any of said coarse resolution analog-to-digital converters.

The invention relates to an analog-to-digital conversion arrangement for converting an analog input signal into a digital output signal with a most significant part and a least significant part, comprising sample means for sampling the analog input signal, a plurality of coarse resolution analog-to-digital converters for converting the sampled analog input signal into a coarse digital signal representing the most significant part of the digital output signal, whereby the coarse resolution analog-to-digital converters are operated in an interleaved way.
Such an analog-to-digital conversion arrangement is known from U.S. Pat. No. 5,262,779. In this document's a conversion arrangement is described with coarse and fine resolution analog-to-digital converters, arranged in parallel configurations of subsequently a coarse and a fine resolution analog-to-digital converter operating in an interleaved way to increase the sample rate. To match differences, caused by offset and gain differences, between the parallel configurations, autocalibration is applied.
A disadvantage of this known conversion arrangement is that the coarse and fine analog-to-digital converters in each of the parallel conversion channels must have the accuracy needed to obtain the desired resolution of the digital output signal, while further specific autocalibration means are required and a relatively high energy consumption is obtained.

Analog-to-digital converter having interleaved coarse sections coupled to a single fine section


An oxygen amount (an oxygen storage amount OSA) stored by metal cerium during a storage cycle is obtained based on an output value of an A/F sensor in a time period immediately before an exhaust air-fuel ratio (a downstream side A/F) detected by the A/F sensor shifts to a lean region, and degradation relating to OSC of the three-way catalyst is detected. In the storage cycle, a target air-fuel ratio is set so that an air-fuel ratio of exhaust emission flowing into an S/C changes from rich to lean. Therefore, the downstream side A/F shifts from stoichiometry to the lean region at a time after reaching stoichiometry. When the three-way catalyst degrades, the downstream side A/F shifts to the lean region from stoichiometry at a time. Therefore, the calculated oxygen storage amount OSA becomes extremely smaller as compared with that at a normal time.

There has been conventionally known a device that executes control of forcefully and periodically switching an exhaust air-fuel ratio at an upstream side from a three-way catalyst to a rich side and a lean side from stoichiometry (hereinafter, called "air-fuel ratio active control"), and detects degradation of the three-way catalyst. For example, Patent Literature 1 discloses the catalyst-degradation detection device that detects degradation of a three-way catalyst by using a stoichiometry holding time period of an exhaust air-fuel ratio that is detected by an air-fuel ratio sensor at a downstream side from the three-way catalyst during execution of air-fuel ratio active control.
The three-way catalyst has an ability to adsorb and store oxygen in exhaust emission when the exhaust air-fuel ration is lean, and to emit the oxygen that is adsorbed and stored when the exhaust air-fuel ratio is rich. Therefore, during execution of air-fuel ratio active control, the stoichiometry holding time period in which the exhaust air-fuel ratio at the downstream side from the three-way catalyst temporarily remains stoichiometric can be detected by the above described air-fuel ratio sensor. The stoichiometry holding time period has correlation with the amount of oxygen stored in or emitted from the three-way catalyst during this time period, and becomes short due to reduction in oxygen storage capacity (OSC) of the three-way catalyst. Accordingly, if the stoichiometry holding time period is used, degradation relating to the OSC of the three-way catalyst can be detected.


A rectifier system, in particular a rectifier bridge for a three-phase generator, includes a plurality of rectifier elements, specifiable rectifier elements being different from the other rectifier elements in at least one property. The rectifier elements are, for example, diodes which differ from one another with regard to the following properties: switching time or the reverse recovery switching time and/or current density and/or chip area and/or chip thickness and/or the breakdown voltage and/or internal resistance and/or path resistance and/or with regard to another property which is suited for reducing ripple.

Rectifiers for motor vehicle three-phase generators are normally equipped with 6 silicon diodes which are connected to form a bridge. It is a characteristic of all of these rectifier configurations that they generally are either equipped only with high-blocking diodes, i.e., diodes without a voltage limiting function, or Zener diodes, i.e., diodes having a voltage limiting function. In doing so, only semiconductor diodes of the same type are used. An exception is rectifiers in which an additional pair of diodes is connected to the star point of the generator stator winding. For reasons of cost, the star point diodes in this case are sometimes designed as high-blocking diodes while, however, the phase diodes are designed as Zener diodes.
Rectifiers having 7, 8, 12, 14 or more diodes are also in use. In doing so, the number of diodes is then doubled from 6 to 12, when high temperature or current demands in particular must be met. The diodes are then connected in such a way that two diodes are connected in parallel.
The level of the rectified signal, i.e., the generator current or the generator voltage, shows a characteristic variation which is a function of different influence factors. This variation is known as generator ripple. The reverse recovery time trr of the diodes makes a significant contribution to generator ripple. Reverse recovery time trr is a form of switching time.
When conventional generators are operated at high speeds and large currents, the voltage ripple or current ripple increases strongly because the current sloped IF/dt to be switched increases.

Rectifier system having different rectifier elements