Multicarrier modulated communications, involving a transmitting modem (30; 30′) and a receiving modem (40; 40′) that operate according to normal operating mode and a low-power, quiescent, mode, are disclosed. In the quiescent mode, transmitter power is saved by scaling down the amplitude of the transmitted symbols in each frame by a scaling factor (A), and transmitting multiple instances of the frames in sequence. On receipt, the repeated frames are summed, and the summed amplitudes scaled to account for the repetition factor (M) and the scaling factor (A), to recover the transmitted information. If the repetition factor (M) is greater than or equal to the square of the scaling factor (A), the signal-to-noise ratio in quiescent mode is at least as high as that in normal operation. The repeating, scaling, and summing may all be performed in the frequency domain or in the time domain, as desired.

This invention is in the field of digital communications, and is more specifically directed to power reduction techniques in communications involving multiple frequency bands.
An important and now popular modulation standard for digital subscriber line (DSL) communications is Discrete Multitone (DMT). According to DMT technology, the available spectrum is subdivided into many subchannels (e.g., 256 subchannels of 4.3125 kHz). Each subchannel is centered about a carrier frequency that is phase and amplitude modulated, typically by Quadrature Amplitude Modulation (QAM), in which each symbol value is represented by a point in the complex plane; the number of available symbol values depends, of course, on the number of bits in each symbol. During initialization of a DMT communications session, the number of bits per symbol for each subchannel (i.e., the "bit loading") is determined according to the noise currently present in the transmission channel at each subchannel frequency and according to the transmit signal attenuation at that frequency. For example, relatively noise-free subchannels may communicate data in ten-bit to fifteen-bit symbols corresponding to a relatively dense QAM constellation (with short distances between points in the constellation), while noisy channels may be limited to only two or three bits per symbol (to allow a greater distance between adjacent points in the QAM constellation). Indeed, some subchannels may not be loaded with any bits, because of the noise and attenuation in those channels. In this way, DMT maximizes the data rate for each subchannel for a given noise condition, permitting high speed access to be carried out even over relatively noisy twisted-pair lines.
FIG. 1 illustrates the data flow in conventional DSL communications, for a given direction (e.g., downstream, from a central office "CO" to customer premises equipment "CPE"). Typically, each DSL transceiver (i.e., both at the CO and also in the CPE) includes both a transmitter and a receiver, so that data is also communicated in the opposite direction over transmission channel LP according to a similar DMT process. As shown in FIG. 1, the input bitstream that is to be transmitted, typically a serial stream of binary digits in the format as produced by the data source, is applied to constellation encoder 11 in a transmitting modem 10. Constellation encoder 11 fundamentally groups the bits in the input bitstream into multiple-bit symbols that are used to modulate the DMT subchannels, with the number of bits in each symbol determined according to the bit loading assigned to its corresponding subchannel, based on the characteristics of the transmission channel as mentioned above. Encoder 11 may also include other encoding functions, such as Reed-Solomon or other forward error correction coding, trellis coding, turbo or LDPC coding, and the like. The symbols generated by constellation encoder 11 correspond to points in the appropriate modulation constellation (e.g., QAM), with each symbol associated with one of the DMT subchannels. Following constellation encoder 11, shaping function 12 derives a clip prevention signal included in the encoded signals to be modulated, to reduce the peak-to-average ratio (PAR) as transmitted as described in copending application Ser. No. 10/034,951, filed Dec. 27, 2001, published on Nov. 28, 2002 as U.S. Patent Application Publication No. 2002/0176509, incorporated herein by this reference.
The encoded symbols are applied to inverse Discrete Fourier Transform (IDFT) function 13, which associates each symbol with one subchannel in the transmission frequency band, and generates a corresponding number of time domain symbol samples according to the Fourier transform. As known in the art, cyclic insertion function 14 appends a cyclic prefix or suffix, or both, to the modulated time-domain samples from IDFT function 13, and presents the extended block of serial samples to parallel-to-serial converter 15. In ADSL2+ and VDSL, cyclic prefix and suffix insertion, and transmitter windowing, are combined into a single cyclic insertion function 14, which preferably operates on the modulated data in parallel form as shown; in ADSL, cyclic insertion function 14 preferably follows serial-to-parallel conversion, and simply prepends a selected number of sample values from the end of the block to the beginning of the block. Following conversion of the time-domain signal into a serial sequence by converter 15, and such upsampling (not shown) as appropriate, digital filter function 16 then processes the digital datastream in the conventional manner to remove image components and voice band or ISDN interference. The filtered digital datastream signal is then converted into the analog domain by digital-to-analog converter 17. After conventional analog filtering and amplification (not shown), the resulting DMT signal is transmitted over a channel LP, over some length of conventional twisted-pair wires, to a receiving DSL modem 20, which, in general, reverses the processes performed by the transmitting modem to recover the input bitstream as the transmitted communication.
At receiving DSL modem 20, analog-to-digital conversion 22 then converts the filtered analog signal into the digital domain, following which conventional digital filtering function 23 is applied to augment the function of pre-conversion receiver analog filters (not shown). A time domain equalizer (TEQ) (not shown) may apply a finite impulse response (FIR) digital filter that effectively shortens the length of the impulse response of the transmission channel LP. Serial-to-parallel converter 24 converts the datastream into a number of samples (2N) for application to Discrete Fourier Transform (DFT) function 27, after removal of the cyclic extension from each received block in function 25. At DFT function 27, the modulating symbols at each of the subchannel frequencies are recovered by reversing the IDFT performed by function 12 in transmission. The output of DFT function 27 is a frequency domain representation of the transmitted symbols multiplied by the frequency-domain response of the effective transmission channel. Frequency-domain equalization (FEQ) function 28 divides out the frequency-domain response of the effective channel, recovering the modulating symbols. Constellation decoder function 29 then resequences the symbols into a serial bitstream, decoding any encoding that was applied in the transmission of the signal and producing an output bitstream that corresponds to the input bitstream upon which the transmission was based. This output bitstream is then forwarded to the client workstation, or to the central office network, as appropriate for the location.
The DMT communications process, such as shown in FIG. 1, provides excellent transmission data rates over modest communications facilities such as twisted-pair wires. However, multicarrier methods such as IDFT modulation can result in a high peak-to-average ratio (PAR) of the signal amplitudes. The PAR is defined as the ratio of the peak sample power level to the average power level over a sequence of samples. Relatively large peaks in the modulated time-domain signal can occur because the DMT modulated signal is the sum of many independent component signals. In modern DMT modulation, for example as used in DSL communications, the number of summed subchannel signals is sufficient that the well-known central limit theorem applies, and that therefore the amplitude of the IDFT-modulated time domain signal has a Gaussian-like probability distribution function.
FIG. 2 illustrates an example of a typical Gaussian probability distribution function as resulting from modern multichannel DSL communications, in which the amplitudes are distributed around a central mean with a deviation σ. While the ideal transmitter must be capable of driving all possible amplitudes in this distribution so that no information is lost, some clipping of peak amplitudes is necessitated in practical transmitters. Conventional communications standards are quite stringent, however, specifying amplitude clipping at the transmitter is not to exceed 10−7, to minimize loss of information. This requirement requires that the maximum amplitude available in the Gaussian probability distribution is about five times the deviation σ. In practice, therefore, the conventional DMT transmitter must have a line driver power supply voltage ("rail") at voltage Vs (FIG. 1), at 5σ from the mean. The dynamic range required of conventional DMT transmitters to provide these high amplitudes while maintaining close resolution, particularly in the digital-to-analog conversion function, is very stringent.
As mentioned in Henkel, et al., "Another Application for Trellis Shaping: PAR Reduction for DMT (OFDM)", Transactions on Communications, Vol. 48, No. 5 (IEEE, Sep. 2000), pp. 1471-76, similar concerns regarding PAR arise in orthogonal frequency-division multiplexing (OFDM) communications technologies, which are beginning to be used in applications other than DSL communications, including wireless telephony and wireless networks.
The high PAR for conventional DMT signals presents significant constraints on the transmission circuitry, and can greatly complicate the analog circuitry required for high fidelity transmission. For example, a high PAR requires a large dynamic range at the inputs of digital-to-analog and analog-to-digital converters, necessitating a large number of bits of resolution, thus greatly increasing the cost and complexity of these functions. Filters and amplifiers must also become more complex and costly in order to handle both the high peak amplitudes and also the resolution required for the vast majority of the samples having lower amplitude. In addition, the high PAR results in much higher power consumption in the communications circuits, further increasing the cost of the circuits and systems used for DMT transmission and receipt, particularly those circuits often referred to as the analog front end (AFE). Various techniques for reducing the PAR of DMT signals are known in the art, particularly in the DSL context. Examples of these techniques are described in copending application Ser. No. 10/034,951, filed Dec. 27, 2001, published on Nov. 28, 2002 as U.S. Patent Application Publication No. 2002/0176509; and in Gatherer and Polley, "Controlling clipping probability in DMT transmission", Proceedings of the Asilomar Conference on Signals, Systems, and Computers, (1997), pp. 578-584, both incorporated herein by this reference.
After a DSL communications link has been established, for example between a central office (CO) and customer premises equipment (CPE), substantial periods of time may elapse in which no information traffic is being carried, but for which the active link is still to be maintained. These idle periods are referred to in the art as "quiescent" periods. Indeed, given the "always on" nature of modern broadband Internet access services, quiescent periods typically dominate active communication time for many users.
To reduce power consumption in DSL transceiver circuitry, particularly on the transmit side, it would be desirable to have a quiescent operating mode in which the average transmit power (e.g., the mean amplitude of, and all other points in, the Gaussian distribution of FIG. 1) is reduced for links that are in their idle, or quiescent, state. However, as known in the art, the initialization and "training" sequence for a new DSL communications link is based upon the signal-to-noise ratios, over frequency, of that new link, as affected by crosstalk interference from other communications links. If a given link is in its quiescent mode during the training of a new link in a neighboring facility, the training of the new link will set its transmit parameters ("bits" and "gains" for each DMT subchannel) based on the assumption that the low crosstalk from the first (idle) link will remain very low. However, once the first link exits its low power quiescent mode and again begins transmitting at full power, the interference on the newly-trained link will not have been comprehended in its training. The bit error rate of the newly-trained link will suffer, as a result.
Accordingly, it has been desirable to reduce the power supply voltage ("rail" voltage Vs of FIG. 1) of DSL transmitters in quiescent mode, thus reducing power dissipation at the transmitter, but without reducing the average power so that the training and initialization of neighboring links will be accurate. A quiescent mode that carries active signals at average power levels, but no information, would be attractive because this signal could be severely clipped to reduce the transmitter power supply rail voltage without loss of information. However, the complete absence of information in quiescent mode is too simplistic an assumption, because some higher layer protocols actually require communication of information during quiescent mode. Frequent entry into and exit from quiescent mode would therefore be necessary in this simple approach.
Various proposals for reducing the PAR in quiescent mode (referred to as "Q" mode, or "L2 mode") were considered in adoption of the ADSL2 standard. Some of these proposals are summarized in Redfern, "A comparison of transparent physical layer Q-mode proposals", submitted to Study Group 15 Question 4, ITU Telecommunications Standardization Sector, Document RN-083 (May 2001), incorporated herein by this reference. As described in that submission, however, these approaches require relatively complex operations at the transmitter, including XOR mapping and sign inversion; two of these approaches also involved phase rotation and post encoding operations that also required changes to the decoder. Because of concerns about the complexity and feasibility of these approaches, none were adopted for the standard.
Rather, conventional standard ADSL2 quiescent mode is achieved by reducing the average power from that used to transmit information-bearing DMT signals. This is accomplished by effectively re-initializing the DSL link, in which the transceivers negotiate a lower data rate in quiescent mode for downstream (CO to CPE) communications. This permits the CO transceiver to use a lower average fine gain level, thus reducing the average transmit power in this mode, and permitting implementation of a lower-power design for the CO transceiver.
However, this standard ADSL Q-mode approach has several drawbacks, as observed in practice. To effect this approach, the CO and CPE must each maintain two "bits and gains" tables for downstream communications—one for normal mode and another for Q mode; if Q mode is to be implemented also for upstream communications, then four such tables are required for each of the CO and CPE. This greatly increases the memory requirements for each transceiver, especially for ADSL2 and higher data rate DSL schemes in which as many as 4096 subchannels are used. In addition, entry into this Q mode requires the CO and CPE to calculate this second set of bits and gains for the large number of subchannels involved, and to exchange these values over the existing overhead channel, both of which consume computational and memory capacity. And since there is a separate bits and gains table for Q mode, and considering the possibility of variations in noise and environment in this mode, either the Q mode itself must support "bit swap" operations, or the transceivers must exit Q mode to effect this bit swap and then re-enter Q mode with the new bits and gains (causing unexpected interference with neighboring links). If the set of subchannels in Q mode is smaller than that in normal transmission, other maintenance operations such as updating frequency domain equalizers (FEQ) and the like cannot be done during Q mode. Framing parameters may also need to be reconfigured for this Q mode approach.

Efficient low-power mode for multicarrier communications


The present invention provides a catalyst which exhibits a high catalytic activity and allows asymmetric reaction in a high asymmetric yield to obtain a reaction product having a high optical purity. The present invention also provides a process for the preparation of an optically active 4-methyl-2-oxetanone having a high optical purity useful as starting material of polymer in a high yield in a short period in the presence of the foregoing catalyst. A novel ruthenium-iodo-optically active phosphine complex is provided, represented by the following general formula (1): EQU Ru--I.sub.2 -(R.sup.1 -BINAP) (1). wherein R.sup.1 -BINAP represents an optically active tertiary phosphine represented by the following general formula (2): ##STR1## wherein R.sup.1 represents an aryl group which may have a substituent selected from the group consisting of a C.sub.1-4 lower alkyl group, a C.sub.1-4 lower alkoxy group, a C.sub.1-4 lower alkylamino group, and a halogen atom or a C.sub.3-8 cycloalkyl group.

Many transition metal complexes have been heretofore used as catalysts for organic synthesis reaction. In particular, metal complexes made of ruthenium metal and optically active tertiary phosphine have been well known as asymmetric hydrogenation reaction catalysts. Examples of ruthenium-optically-active phosphine complexes containing as a ligand an optically active tertiary phosphine such as 2,2-bis(diphenylphosphino)-1,1-binaphthyl include the following compounds: EQU Ru.sub.x H.sub.y Cl.sub.z (tertiary phosphine).sub.2 (A).sub.p
wherein A represents a tertiary amine, with the proviso that if y is 0, x, z and p represent 2, 4 and 1, respectively, and if y is 1, x, z and p represent 1, 1 and 0, respectively (JP-A-61-63690 (The term "JP-A" as used herein means an "unexamined published Japanese patent application"), JP-A-63-135397); EQU [RuH.sub.r (tertiary phosphine).sub.m ]T.sub.n
wherein T represents ClO.sub.4, BF.sub.4 or PF.sub.6, with the proviso that if r is 0, m and n represent 1 and 2, respectively, and if r is 1, m and n represent 2 and 1, respectively (JP-A-63-41487, JP-A-63-145492); EQU [RuX.sub.a (Q).sub.b (tertiary phosphine)]Y.sub.c
wherein X represents a halogen atom; Q represents benzene which may have a substituent or acetonitrile; and Y represents a halogen atom, ClO.sub.4, PF.sub.6, BPh.sub.4 (Ph hereinafter represents a phenyl group) or BF.sub.4, if Q is benzene which may have a substituent, a, b and c each represent 1, if Q is acetonitrile, when a is 0, b and c represent 4 and 2, respectively, or when a is 1, b and c represent 2 and 1, respectively, and if the benzene having a substituent represented by Q is p-cymene and X and Y each are iodine atom, a, b and c each are 1 or a, b and c are 1, 1 and 3, respectively (JP-A-2-191289, JP-A-5-111639); EQU (Tertiary phosphine).sub.w Ru(OCOR') (OCOR")
wherein R' and R" each represent a lower alkyl group, a halogenated lower alkyl group, a phenyl group which may have a lower alkyl substituent, an .alpha.-aminoalkyl group or an .alpha.-aminophenylalkyl group or R' and R" together form an alkylene group; and w represents 1 or 2 (JP-A-62-265293, JP-A-63-145291); EQU RuJ.sub.2 (tertiary phosphine)
wherein J represents a chlorine atom, a bromine atom or an iodine atom (R. Noyori et al., J. Am. Chem. Soc., Vol. 109, No. 19, pp. 5856-5859 (1987));
RuG.sub.2 (tertiary phosphine) PA1 (a) Process which comprises subjecting 3-bromobutyric acid obtained by adding hydrobromic acid to crotonic acid to optical resolution with an optically active naphthyl ethylamine, and then cyclizing the product (J. Reid Shelton et al., Polymer Letters, Vol. 9, pp. 173-178, 1971; T. Sato et al., Tetrahedron Lett., Vol. 21, pp. 3377-3380, 1980); PA1 (b) Process which comprises reacting an optically active 3-hydroxybutyric acid with triethylorthoacetic acid to obtain an optically active 2-ethoxy-2,6-dimethyl-1,3-dioxane-4-one which is then thermally decomposed (A. Griesbeck et al., Helv. Chim. Acta, Vol. 70, pp. 1320-1325, 1987; R. Breitschuh et al., Chimia, Vol. 44, pp. 216-218, 1990); and PA1 (c) Process which comprises reacting an optically active 3-hydroxybutyric acid ester with methanesulfonylchloride for mesylation of the hydroxy group, hydrolyzing the resulting ester, and then reacting with sodium carbonate for condensation cyclization (Y. Zhang et al., Macromolecules, Vol. 23, pp. 3206-3212, 1990). PA1 (d) Process which comprises the asymmetric hydrogenation of 4-methylene-2-oxetanone (also referred to as "diketene") in an aprotic solvent such as methylene chloride and tetrahydrofuran in the presence of [RuCl[(S)- or (R)-BINAP (benzene)]Cl or Ru.sub.2 Cl.sub.4 [(S)- or (R)-BINAP].sub.2 (NEt.sub.3) [in which BINAP represents 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl, and Et represents an ethyl group] as a catalyst (T. Ohta et al., J. Chem. Soc., Chem. Cmmun., 1725, 1992) PA1 (a) 2,2'-Bis(diphenylphosphino)-1,1'-binaphthyl (hereinafter abbreviated as "BINAP") PA1 (b) 2,2'-Bis(di-p-tolylphosphino)-1,1'-binaphthyl (hereinafter abbreviated as "T-BINAP") PA1 (c) 2,2'-Bis[di-(p-tert-butylphenyl)phosphino]-1,1'-binaphthyl (hereinafter abbreviated as "tBu-BINAP") PA1 (d) 2,2'-Bis(di-m-tolylphosphino)-1,1'-binaphthyl (hereinafter abbreviated as "m-T-BINAP") PA1 (e) 2,2'-Bis[di-(3,5-dimethylphenyl)phosphino]-1,1'-binaphthyl (hereinafter abbreviated as "DM-BINAP") PA1 (f) 2,2'-Bis[di-(3,5-di-tert-butylphenyl)phosphino]-1,1'-binaphthyl (hereinafter abbreviated as "DtBu-BINAP") PA1 (g) 2,2'-Bis [di-(p-methoxyphenyl)phosphino]-1,1'-binaphthyl (hereinafter abbreviated as "MeO-BINAP") PA1 (h) 2,2'-Bis[di-(p-chlorophenyl)phosphino]-1,1'-binaphthyl (hereinafter abbreviated as "p-Cl-BINAP") PA1 (i) 2,2'-Bis(di-2-naphthylphosphino)-1,1'-binaphthyl (hereinafter abbreviated as "Naph-BINAP") PA1 (j) 2,2'-Bis(dicyclopentylphosphino)-1,1'-binaphthyl (hereinafter abbreviated as "CpBINAP") PA1 (k) 2,2'-Bis(dicyclohexylphosphino)-1,1'-binaphthyl (hereinafter abbreviated as "CyBINAP") PA1 [RuI(benzene)(BINAP)] I PA1 [RuI(benzene)(T-BINAP)] I PA1 [RuI(benzene)(tBu-BINAP)] I PA1 [RuI(benzene)(m-T-BINAP)] I PA1 [RuI(benzene)(DM-BINAP)] I PA1 [RuI(benzene)(DtBu-BINAP)] I PA1 [RuI(benzene)(MeO-BINAP)] I PA1 [RuI(benzene)(p-Cl-BINAP)] I PA1 [RuI(benzene)(Naph-BINAP)] I PA1 [RuI(benzene) (CpBINAP)] I PA1 [RuI(benzene)(CyBINAP)] I PA1 [RuI(p-cymene)(BINAP)] I PA1 [RuI(p-cymene)(T-BINAP)] I PA1 [RuI(p-cymene) (tBu-BINAP)] I PA1 [RuI(p-cymene)(m-T-BINAP))] I PA1 [RuI(p-cymene)(DM-BINAP)] I PA1 [RuI(p-cymene)(DtBu-BINAP)] I PA1 [RuI(p-cymene)(MeO-BINAP)] I PA1 [RuI(p-cymene)(p-Cl-BINAP)] I PA1 [RuI(p-cymene)(Naph-BINAP)] I PA1 [RuI(p-cymene)(CpBINAP)] I PA1 [RuI(p-cymene) (CyBINAP)] I PA1 [RuI.sub.2 (benzene)].sub.2 PA1 [RuI.sub.2 (p-cymene)].sub.2 PA1 Ru(CH.sub.3 COO).sub.2 (BINAP) PA1 Ru(CF.sub.3 COO).sub.2 (BINAP) PA1 Ru(CH.sub.3 COO).sub.2 (T-BINAP) PA1 Ru(CH.sub.3 COO).sub.2 (tBu-BINAP) PA1 Ru(CH.sub.3 COO).sub.2 (m-T-BINAP) PA1 Ru(CH.sub.3 COO).sub.2 (DM-BINAP) PA1 Ru(CH.sub.3 COO).sub.2 (DtBu-BINAP) PA1 Ru(CH.sub.3 COO).sub.2 (MeO-BINAP) PA1 Ru(CH.sub.3 COO).sub.2 (p-Cl-BINAP) PA1 Ru(CH.sub.3 COO).sub.2 (Naph-BINAP) PA1 Ru(CH.sub.3 COO).sub.2 (CpBINAP) PA1 Ru(CH.sub.3 COO).sub.2 (CyBINAP) PA1 Ru--I.sub.2 -(BINAP) PA1 Ru--I.sub.2 -(T-BINAP) PA1 Ru--I.sub.2 -(tBu-BINAP) PA1 Ru--I.sub.2 -(m-T-BINAP) PA1 Ru--I.sub.2 -(DM-BINAP) PA1 Ru--I.sub.2 -(DtBu-BINAP) PA1 Ru--I.sub.2 -(MeO-BINAP) PA1 Ru--I.sub.2 -(p-Cl-BINAP) PA1 Ru--I.sub.2 -(Naph-BINAP) PA1 Ru--I.sub.2 -(CpBINAP) PA1 Ru--I.sub.2 -(CyBINAP) PA1 Ru--I.sub.2 -(R.sup.1 -BINAP) of the present invention thus obtained is a compound which exhibits an extremely high catalytic activity and thus can find wide application as an asymmetric synthesis catalyst. The use of this compound as a catalyst particularly for the asymmetric hydrogenation reaction of 4-methylene-2-oxetanone makes it possible to prepare an optically active 4-methyl-2-oxetanone having a high optical purity in a high yield in a short period of time. PA1 Gas chromatograph: HEWLETT PACKARD 5890 SERIES II
wherein G represents an allyl group or a methallyl group (J. P. Genet et al., Tetrahedron: Asymmetry, Vol. 2, No. 7, pp. 555-567 (1991))
However, even the use of these ruthenium-optically active phosphine complexes has found difficulties in practical use on an industrial basis. For example, these ruthenium-optically active phosphine complexes exhibit an insufficient catalytic activity or asymmetric yield. On the other hand, 4-methyl-2-oxetanone (also referred to as ".beta.-butyrolactone" or ".beta.-methyl-.beta.-propiolactone") has heretofore been used as a raw material of polymers. In recent years, 4-methyl-2-oxetanone has been noted particularly because its optically active form is useful according to JP-A-6-256482, JP-A-6-329768, JP-A-7-53694, JP-A-8-53540 and JP-A-8-127645.
As processes for the preparation of optically active 4-methyl-2-oxetanone there have been reported the following processes:
As a process for the preparation of an optically active 4-methyl-2-oxetanone in the presence of the previously mentioned ruthenium-optically active phosphine complex there has been reported the following process:
However, these processes have the following disadvantages. In other words, the process (a) requires the use of a special optically active amine as an optically resolving agent in an amount equimolecular with the starting compound. Further, the process (a) subsidiarily produces an undesirable enantiomer in an amount equimolecular with the desired product. Thus, the process (a) is wasteful and economically disadvantageous.
The processes (b) and (c) are disadvantageous in that the optically active 3-hydroxybutyric acid or ester thereof as starting compound can be hardly synthesized. In other words, it is necessary that an optically active poly-3-hydroxybutyric acid ester in which microorganisms propagate themselves be thermally decomposed or 4-methylene-2-oxetanone be converted to acetoacetic acid ester by alcoholysis reaction before asymmetric reduction. This requires many steps and thus complicates the operation.
The process (d) gives solutions to most of the foregoing problems of the processes (a) to (c) but still leave something to be desired. In other words, the process (d) is disadvantageous in that the catalyst used exhibits a low activity, prolonging the reaction time. Further, the resulting product has an optical purity as low as 70 to 92% e.e. As reported in JP-A-6-128245, JP-A-7-188201 and JP-A-7-206885, this process has been improved. However, because of its low catalytic activity, this process leaves something to be desired on an industrial basis.

Ruthenium-optically active phosphine complex, process for the preparation thereof and process for the preparation of optically active 4-methyl-2-oxetanone using same


A system and method for online reorganization of an existing database that occurs while read and update activity of the existing database continues. The system and method comprise unloading the existing database, reloading the existing database directly to a shadow database, building shadow database indexes, creating a first intermediary image copy of the existing database, analyzing the existing database, capturing updates for the existing database, applying the captured updates to the shadow database, taking the existing database offline, finalizing the shadow database with any remaining updates, creating a final image copy, comparing the existing database and the finalized shadow database, and placing the finalized shadow database online.

1. Field
The present disclosure relates to databases. More specifically, the present disclosure relates to a method and system for online reorganization of database systems.
2. Description of the Related Art
Hierarchical database systems such as the IBM Information Management System (IMS) are well-known and widely used systems. A hierarchical database consists of records connected with each other via links in a tree-like logical structure. A record is a collection of field values that provide information relating to an entity or a relationship instance. Records of the same type can be grouped into record types which can be given a name and its structure can be defined by a collection of named fields or data items. A parent-child relationship exists between two record types in a 1:N relationship. For example, FIG. 16 shows an example of a hierarchical database 10 with three record types and two parent-child relationship types. The record types 12 are Department, Employee and Project. The parent-child relationship types 14 are (Department, Employee) and (Department, Project). Although not shown, the field names, further specifying the data in each record type, can be displayed under each record type in the diagram. FIG. 15 shows an IMS database (DB) structure. Components of database 20 include Multiple Virtual Storage (MVS) data sets 22, database description (DBD) 24, and Job Control Language (JCL) 26. JCL is a means of communicating with the IBM MVS Operating System. JCL statements provide information that the operating system desires to execute a job (unit of work). MVS data sets DS1 and DS2 (22) hold byte strings B1 and B2, respectively. Mapping of byte strings B1 and B2 is defined by DBD. JCL may be correctly set up to tie the MVS data sets 22, holding the DB byte strings, to the DBD. Failure to do so may lead to non-recoverable DB errors. Each byte string has a unique relative base address (RBA). Other MVS copies of byte strings B1 and B2 may be made. Copies on tape or Direct Access Storage Device (DASD) data sets that are not named via any DBD and JCL are Image Copies (IC).
When a transaction is performed such that data is added, updated and/or deleted from the database, the data may become disorganized or fragmented. When this occurs, response time to database queries can be compromised. Accordingly, many systems provide a method of reorganizing the data so that the related data can be physically grouped together. This makes access to the data faster and more efficient. Accordingly, performance of the database can be improved by reorganization. Reorganization may also reclaim previously unusable space in the database. However, conventional systems take the database offline for reorganization.
In today's eBusiness world, critical IMS data may be available as close to 100% of the time (i.e., 24 hours per day, seven days per week) as possible. The opportunity to take IMS databases offline for maintenance activities such as reorganization is thus fast disappearing. However, unless the databases are periodically reorganized, the efficiency and effectiveness of the database system decreases as access times increase and databases run out of space.
Therefore, there is a problem in that when reorganizing an IMS database, there is a significant amount of outage or downtime which the customer incurs. There is an increasing desire to reduce this outage or downtime. Conventional systems may make extra copies of the database in order to reorganize it and accomplish reorganization in multiple job steps, which may add significantly to the downtime.

Method and system for online reorganization of databases


A servo motor controlling method includes: directly or indirectly detecting a position of a moving body which performs a circular-arc interpolation feeding motion by a servo motor; performing a feedback control for enabling the position of the moving body to comply with a position command; and at a quadrant changing time when a moving direction of the moving body is changed, performing torque correction on a torque command value according to a distance from a position where the moving direction is changed. By this method, a quadrant protrusion and a torque change with respect to a friction caused from a free zone at a time of reversion of a ball screw can be appropriately corrected. Especially, by performing a first torque correction for a static friction at the position where the moving direction is changed, and by performing a second torque correction for a moving friction after movement by the distance corresponding to the free zone, more appropriate correction can be obtained.

1. Field of the Invention
The present invention relates to a servo motor controlling method and, more particularly to a servo motor controlling method or driving a feeding shaft of a machine tool or an arm of an industrial robot.
2. Related Art
In order to improve a movement accuracy of a numerical control (NC) machine tool or an industrial robot, an accuracy of shape of each component needs to be improved, and assembling of mechanisms and adjusting of a control system need to be accurately performed so as to optimally control operations.
For example in a general servo motor control system for a servo motor in a machine tool which performs two-axis arc interpolation feeding movement, a position loop for allowing a deviation between an NC position command and a feedback signal output, from a position detector disposed a servo motor or a moving body such as a table saddle driven by the servo motor to be zero is provided, and a velocity loop for a velocity feedback signal obtained by differentiating a position feedback signal is provided to use an output of a velocity loop gain as a torque control value.
However, in such a servo motor control system, wherein a rotating direction of the servo motor is reversed, the moving direction of the moving body cannot be directly reversed. This is caused from a lost motion or friction in a feed driving mechanism. When such a circular-arc cutting is performed, a quadrant of a circular arc is changed, and an actual moving path deviates out from a commanded path, so that a bulge of path may occur. The phenomenon is referred to as a stick motion or a quadrant protrusion and becomes one of factors of deterioration in accuracy of contour machining which is one of important operations of the machine tool.
The phenomenon is regarded to cause temporary stoppage of a feeding shaft. More specifically, when the moving direction is reversed, a torque command corresponding to a frictional torque needed to be reversed. However, in a guide, a ball bearing, a ball screw or the like, a three-point contact becomes a two-point contact when the moving direction of the servo motor is reversed. Therefore, a delay occurs in the velocity loop, so that the feeding shaft may be temporarily stopped.
In order to correct the error, techniques for correction of torque at the time of reversion are disclosed. Particularly, Japanese Patent Application Laid-Open Publication (JP-A) No. 10-63325 (Patent document) previously filed by the applicant of the present invention describes that the torque is assisted only at the time of moving direction reversion.
In addition to the phenomenon, recent researches show that a friction after reversion is changed in a free zone, that is, a low-friction region of a ball screw (referred to as a ball contact number changing region). If the changing friction is not corrected, the protrusion-shaped machining error remains, or a depressed portion may occur.
For example, since the technique disclosed in JP-A-10-63325 cannot cope with the change in friction caused from the aforementioned free zone, the protrusion-shaped machining error cannot become zero.
As a prior art for coping with a change in friction caused from the free zone, JP-A-7-13631 describes a technique for performing control by determining starting and ending positions of correction based on a moving amount from reversion of the servo motor and providing a velocity command.
However, in the technique disclosed in JP-A-7-13631 (Patent document 2), since the velocity command is corrected, the correction amount is changed according to a passing velocity in the same tool. Therefore, command amounts corresponding to various passing velocities need to be prepared, so that the control becomes complicated.


A peristaltic pump includes a removable carrier against which a flexible tube is pressed by rollers. The carrier includes an intermediate deformable section having an internal cylindrical surface whose axis coincides with the main axis of rotation of the rollers and lateral rigid arms arranged on both sides of the intermediate section. The free ends of the lateral arms include guides. The pump case is provided with paths on which the guides are slidable. The path directions are predefined in order to constrain the displacement of the free ends of the lateral arms and to deform the intermediate section in such a way that the radius of the internal face is modified keeping the axis thereof coinciding with the main axis, thereby making it possible to use a tube having variable characteristics.

1. Field of the Invention
The present invention relates to peristaltic pumps with deformable tubing.
2. Description of the Related Art
In general, peristaltic pumps are composed of a frame to which is fastened a motor whose shaft rotates a cage comprising a plurality of rollers. The rollers are in contact with a deformable tubing that they compress until it is sealed. The angular displacement of the point of sealing causes, behind the compressed zone, a vacuum in the tubing that immediately fills with fluid. The amount of fluid trapped in the deformable tubing between two rollers is then propelled to the outlet of the pump. A liquid, pumped at an open end of the deformable tubing, called the intake or upstream end, is thus conveyed to the other end of the deformable tubing, called the delivery or downstream end. Most peristaltic pumps comprise a casing having a cylindrical inner surface, called the bearing surface, against which the tubing is compressed by the rollers to seal it. The envelope swept by the paths of the outer surfaces of the rollers is called the runway or rolling path.
The main component of a peristaltic pump is its pump body tubing, which is generally made of elastomer. The pump body tubing is made by extrusion. The physical and dimensional properties of the tubing given by the manufacturer are only average values. The measured values of a particular property fluctuate statistically, for example according to Gauss' Law, about the corresponding average value. The deformable tubing manufacturer defines a tolerance interval around the average value in which there is an increased probability of finding the measured value of the property. The measured thickness of a deformable tubing at the point where it is deformed fluctuates about the average value. It is therefore probable that the portion of deformable tubing compressed by the rollers has walls whose combined thickness is less than or greater than the nominal sealing dimension provided for by the pump manufacturer. Incidentally, the sealing of the pump body tubing, characterized by the sealing dimension, consists in first placing the two walls of the tubing in contact and then applying an appropriate clamping action depending on the thickness of the tubing, its hardness, the temperature, etc.
Similarly, during the use of the deformable tubing, the wall suffers from wear, swelling, loss of thickness, modification of the physical nature of the material of which the tubing is made, etc. This wear in the broad sense may be due to the repeated mechanical action of the rollers on the outer surface of the tubing, to the chemical action of the liquids conveyed within the tubing on the inner surface of the tubing, or to the conditions under which the peristaltic pump is used, for example temperature. Consequently, the combined thickness of the walls of the deformable tubing tends to vary over time. The time comes when the cumulative thickness of the walls becomes less than or greater than the nominal sealing dimension.
When the nominal sealing dimension is not complied with, either the peristaltic pump becomes less efficient because the seal is not achieved, or the excessive thickness leads to excessive clamping, increasing the resistive torque of the peristaltic pump.
For a given type of tubing, there is therefore a need for a peristaltic pump that can compensate for variations in the properties of the tubing.
Moreover, it must be possible for a user to be able to replace a first tubing by a second pump body tubing rapidly. The adjustments required in order for the peristaltic pump to be able to operate with a second tubing must be easy to carry out, and preferably automatic, minimizing risks of error.
Moreover, in the medical field in particular, the deformable tubing must be completely changed for each new application, in particular for reasons of hygiene. There is a permanent need to simplify the consumable so as to increase the number of parts that can be reused from one application to the next, to reduce the operating cost of the pump and the number of components, often made of plastic, that are thrown away on each new application.
To solve these various problems, the manufacturers of peristaltic pumps have to find mechanical solutions that will guarantee sealing. The best known solutions consist in mechanically varying the radial distance between the inner surface of the bearing surface and the rolling paths of the rollers on the pump body tubing.
Patent SU 1 262 106 of 7 Oct. 1986 discloses an improved peristaltic pump for limiting fluctuations in flow rate during use. The flexible tubing is in this case compressed between a plurality of rollers and a flexible U-shaped strip. The curve of the flexible strip is set by tangential adjustment pins connected to the ends of the flexible strip and radial adjustment pins connected to a central portion of the flexible strip. By turning the adjustment pins to a greater or lesser extent, the user gives the flexible strip an optimum shape.
The deformable tubing is compressed until it is sealed only against the central portion of the flexible strip whose profile is an arc of a circle with an opening of 360°/κ and a radius r1=r0+2e (where κ is the number of rollers and r0 is the radius of the rolling path run by the rollers). The profile of the input and output sections is curved and follows the equation r2=r1+D 2r (where r is the internal radius of the tubing and D a parameter corresponding to the degree of compression of the tubing varying between 0 and 1).
That document does not describe how the deformable tubing is inserted between the flexible strip and the rollers. Although in the above equations the thickness and the radius of the deformable tubing are in the form of parameters, the use of deformable tubing having variable properties is not discussed. No particular information about the variation of the parameter D along the input and output sections is given in order to define the optimum profile. Lastly, the curve of the flexible strip is adjusted manually by the user during operation of the pump.
Patent SU 794 243 of 7 Jan. 1981 describes a peristaltic pump whose tubing support is wound to form a helical turn around a roller mounted on a shaft that is off-centre with respect to the axis of the helix. The deformable tubing is placed between the roller and the tubing support. The tubing support consists of a metal strip having a degree of elasticity whose tubing ends are joined by an adjustment screw. When the user turns the screw, the two ends of the strip move towards or away from one another. As a result, the radius of the helix is modified to change the distance between the tubing support and the roller to modify the occlusion of the deformable tubing making it possible to compensate for the thickness of the tubing.
Moreover, the tubing support is connected to the frame by a series of bolts that are distributed regularly in an annular arrangement, each engaged in a guide groove. The guide grooves, whose shape is not described, make it possible indirectly to limit the displacement of the tubing support so that it has a constant radius of curvature all along its length. Once the user has made the adjustment, the bolts are tightened, which prevents any modification of the radius during operation of the pump.
Lastly, U.S. Pat. No. 5,549,461, granted on 27 Aug. 1996, discloses a peristaltic pump comprising an occluder ring linked to a hinged support by means of a series of threaded bolts. While the rollers are turning, the hinged support is lowered so that the deformable tubing is compressed against the occluder ring, thus functioning as a clutch for the pump. In the lowered position, the hinged support is kept against the frame by a closure system that prevents excessive pressure if necessary. The radius of the occluder ring, which is concentric with the axis of rotation of the rollers, can be adjusted by the user by means of a series of screws to allow the pump to be used with deformable tubing of different thicknesses.
The peristaltic pump described is not made for delicate laboratory or medical applications. The curvature of the ring and the means of obtaining it by screwing the bolts are not described.

Peristaltic pump with a removable and deformable carrier


A polymer composition of cellulose esters, plasticizer, a cellulose linked anhydride as a compatibilizer and organically modified clay. The composites have superior tensile and flexural strengths, modulus, dimensional stability and heat deflection temperature (HDT).

(1) Field of the Invention
The invention deals with fabrication of biodegradable green cellulose ester nanocomposites from a plasticized cellulose ester bioplastic and various organically modified clays in presence of a novel compatibilizer, such as maleated cellulose ester.
(2) Description of Related Art
Green nanocomposites are the wave of the future and are considered as the next generation of new materials. The lofty goals set by U.S. governments for the creation of bio-based economy present significant challenges to Industry, Academia and Agriculture/Forestry. Cellulose from trees is attracting interest as a substitute for petroleum feedstock in making plastic in the commercial market. Different raw materials such as cotton, recycled paper, wood cellulose, and sugarcane are being used in making cellulose ester biopolymers. Cellulose esters (such as Cellulose acetate or CA, Cellulose acetate propionate or CAP, and cellulose acetate butyrate or CAB) are considered as potentially useful biodegradable polymers of the future.
U.S. Pat. No. 3,922,239 describes a mixture of cellulose esters or ethers which are mixed with polymeric cyclic esters, such as oligomer of .epsilon.-caprolactone. This substance is said to be thermoplastic. It was found that the components of the mixture do not posses satisfactory compatibility. This is shown by the fact that during the thermoplastic processing no homogeneous melt is obtained. To some extent even a de-mixing can be observed during the processing.
GR-A-2 152 944 describes plasticized cellulose acetates which were obtained from the reaction of cellulose acetate having a free hydroxyl group with a cyclic ester, in particular ε-caprolactone, in the presence of a catalyst. The weight ratio of the cellulose acetate to the cyclic ester is said to be between 1/99 and 95/5 and the polymerization temperatures are said to be between 120° and 230° C. The quantity of cyclic ester which is to be reacted with the hydroxyl group-containing cellulose acetate, is preferably between 0.5 and 4.0 mol units per anhydroglucose unit of the cellulose acetate. The melting temperature of the plasticized cellulose acetate is reduced through an "inner" plasticization. The decomposition temperature is simultaneously raised.
U.S. Pat. No. 4,529,788 deals with a process for the production of graft polymerization in which a cyclic ester is subjected to a catalyzed ring-splitting polymerization in the presence of a cellulose derivative.
Polymer-nanocomposites research is primarily concerned with commercial nonbiodegradable thermoplastics like nylon, polypropylene (PP), thermoplastic polyolefin (TPO) and thermosets like epoxies, polyesters, and the like. Biodegradable nanocomposites from starch plastic and clay are known in the literature and such efforts are targeted for packaging applications.
It is also well known in the prior art to heat fillers of the nanocomposite type to provide the polymer matrix to improve the interfacial adhesion of the mineral to the matrix. For example, in Papalos, U.S. Pat. No. 3,227,675, kaolin clays are described, the surfaces of which are modified with organofunctional silanes. Additional references of this type include Iannicelli, U.S. Pat. Nos. 3,290,165 and 3,567,680. Similarly, in U.S. Pat. No. 4,789,403 to Rice and U.S. Pat. No. 6,828,367 to Campbell, a method is disclosed for producing a layered lattice silicate which is surface modified with an organic material. The layered lattice silicate is contacted with an organic monomer, comonomers, or a pre-polymer, and surface polymerization or reaction in situ is affected in the presence of a gaseous hydrogen atmosphere. Among the organic monomers that can be used in the process are various precursors of nylon.
Recently, disclosures in producing composite materials composed of a polymer and a smectite-type clay mineral, with the mineral being connected to the polymer through ionic bonding. For example, in Kawasumi et al., U.S. Pat. No. 4,810,734 a process is disclosed wherein a smectite-type clay mineral is contacted with a swelling agent in the presence of a dispersion medium thereby forming a complex. The patent states that the swelling agent acts to expand the interlayer distance of the clay mineral, thereby permitting the clay mineral to take monomers into the interlayer space. The swelling agent is a compound having an onium ion and a functional ion capable of reacting and bonding with a polymer compound. Examples of polymers used in this system are polyamide resins, vinyl polymers, thermosetting resins, polyester resins, polyamide resins and the like. Related disclosures are found in U.S. Pat. No. 4,739,007 to Okada et al and U.S. Pat. No. 4,889,885 to Usuki et al.
U.S. Pat. No. 5,480,922 to Mulhaupt et al; U.S. Pat. No. 3,922,239 to Koleske et al., U.S. Pat. No. 4,529,788 to Asami et al, U.S. Pat. No. 5,554,670 to Giaannelis et al.
There are three common processes for fabricating polymer-clay nanocomposites. They are melt compounding; solution processing; and in-situ intercalation polymerization. In the usual melt compounding technique the polymer pellets and clay are extruded to derive the polymer-clay nanocomposites. For uniform mixing of clay and polymer granules; both the clay and the polymer are sometimes extruded twice. The extruded samples are further injection molded or compression molded to provide the test specimens.
Phthalate plasticizers, used in commercial cellulose acetate plastic, pose an environmental and perhaps a health threat and thus it is a serious concern about their long-term use. Plasticized CA is a potentially useful biodegradable polymer of the future with considerable toughness, excellent optical clarity. It has, however, low dimensional stability under high humidity and elevated temperature, and high melt processing temperature. Therefore, the flow properties are low for automotive and packaging applications. Improvement of flow properties of CA or CAB can be done through plasticization using plasticizer like phthalates or glycerol. Unfortunately, the existence plasticizer migration greatly decreased mechanical properties.

Compositions of cellulose esters and layered silicates and process for the preparation thereof

Board of Trustees of Michigan State University


The very thin, high carbon wire is 0.05 to 0.50 mm in diameter and comprises, in mass %, 0.90-1.20% of C, 0.05-1.2% of Si, 0.2-1.0% of Mn, and 0.0050% or less of N, with the balance being iron and impurities. In a differential scanning thermal analysis curve A of the steel wire, the steel wire has an exothermic peak X in the temperature range of 60° to 130° C., and a maximum height h of the exothermic peak X relative to a reference line Y joining the point of 60° C. and the point of 130° C. in the differential scanning thermal analysis curve is set at 5 μW/mg or more. The very thin, high carbon steel wire is free of delamination in high-speed stranding and superior in both strength and ductility.

1. Field of the Invention
The present invention relates to a very thin, high carbon steel wire having a high strength and superior in high-speed strandable ductility, as well as a method of producing the same.
2. Description of the Related Art
A very thin, high carbon steel wire having a diameter of 0.05 to 0.50 and a strength as high as 4200 MPa or more has come to be used as steel cord or as saw wire for cutting a semiconductor. Generally, the very thin, high carbon steel wire is produced by subjecting a steel wire rod of 4.0 to 5.5 mm in diameter which has been subjected, as necessary, to hot rolling and subsequent conditioned cooling to primary wire drawing, subsequent final patenting treatment and further wire drawing.
More particularly, the above patenting treatment involves heating the steel wire rod to a temperature range (750-1100° C.) of A3 point or higher for treatment to γ phase, subsequent quenching and allowing an isothermal transformation to proceed in the temperature range of 550-680° C., to afford a steel wire of a pearlite structure. This steel wire then goes through brass plating as a surface-layer lubricant coating treatment and is made into a very thin, high carbon steel wire by a continuous, final wet lubrication wire drawing with use of dies arranged in multiple stages.
Many of high strength, very thin, high carbon steel wires thus produced are used as stranded two- or five-ply steel cords or saw wires for cutting a semiconductor.
The very thin, high carbon steel wires applied to the aforesaid uses are required to possess such characteristics as 1) being higher in strength, 2) superior in high-speed wire drawability, 3) superior in fatigue characteristic, and 4) superior in torsional deformability (ductility) in the aforesaid stranding work.
Particularly, as the strength becomes higher than 4200 MPa, the ductility of each very thin, high carbon steel wire is deteriorated. Consequently, delamination (longitudinal cracking) becomes easier to occur during torsional deformation of the very thin, high carbon steel wire.
Anti-delamination property of the very thin, high carbon steel wire can be grasped and evaluated in advance by a phenomenon that, upon occurrence of delamination in a twisting test of the very thin, high carbon steel wire, there occurs a sudden drop of torque in a rotational angle-torque chart in the twisting test.
For enhancing the anti-delamination property of the high strength, very thin, high carbon steel wire, various techniques have heretofore been proposed with respect to the steel wire. For example, it has been proposed to control the hardness of the surface layer of the steel wire in accordance with the wire diameter and thereby prevent the occurrence of delamination (see Japanese Unexamined Patent Publication No. 2000-336459).
It has also been proposed to control the difference in tensile strength between the very thin, high carbon steel wire just after wire drawing and the very thin, high carbon steel wire after wire drawing and after subsequent age hardening to a predetermined certain range and thereby preventing the occurrence of delamination (see Japanese Unexamined Patent Publication No. 2002-302736).
Various techniques have been proposed also with respect to wire drawing. For example, there has been proposed a technique in which two separated drawing dies having different bore diameters are used and wire drawing is performed once without giving any drawing force between both drawing dies (see Japanese Unexamined Patent Publication No. Hei 7(1995)-1028).
Further, it has been proposed to effect wire drawing by raw drawing without intermediate heat treatment and setting a die approach angle at a low angle during wire drawing to optimize the reduction of area in each stage (see Japanese Unexamined Patent Publication No. 2001-192772).
However, even by the above conventional proposed techniques, delamination cannot be prevented effectively in the case of very thin, high carbon steel wires having a diameter of 0.05 to 0.50 mm and having a strength as high as 4200 MPa or more. This is presumed to be because a new delamination generating mechanism so far not found out is added in the region of those high strength, very thin, high carbon steel wires in comparison with the conventional lower strength region.

Very thin, high carbon steel wire and method of producing same


A wireless communication module includes a plurality of monolithic millimeter-wave integrated circuits (MMICs) for signal processing attached to the top surface of a multi-layer low temperature co-fired ceramic substrate; a planar transmission line formed on the top surface of the multi-layer substrate for communications between the MMICs; a metal base attached to the bottom surface of the multi-layer substrate and having an opening to which an antenna is attached; a plurality of vias for connecting the metal base and the planar transmission line within the multi-layer substrate to establish a uniform potential on a ground plane of the multi-layer substrate; an embedded waveguide formed in the opening surrounded with the vias within the multi-layer substrate; and a planar transmission line-to-waveguide transition apparatus for the transition of waves between the planar transmission line and the embedded waveguide.

With exponential demand for wireless communications having high speed and large capacity, high-speed broadband wireless communication techniques have been required to meet such a demand and to process data at a high Gbps transfer rate. In recent developments, millimeter-wave band wireless communication modules having a wide bandwidth have drawn a lot of attention. One of the biggest issues regarding the high-speed broadband wireless communication techniques is to develop small size, low cost wireless communication modules operating at millimeter-wave bands, and this may be achieved in general through the use of a system-in-package (SiP) technique. In the SiP technique, an antenna is an absolute factor that determines the total size of a wireless communication module. However, when the antenna is installed at the same plane as a signal processing circuit, for example, a monolithic millimeter-wave integrated circuit (MMIC), the overall size of the wireless communication module increases and incomplete isolation between the antenna and the signal processing circuit is also likely to degrade the performance of the wireless communication module. As an attempt to resolve these problems, the antenna was attached to the rear side of the wireless communication module, so the wireless communication module was significantly reduced in size, thereby getting the benefits of low cost and small size.
Meanwhile, to reduce a loss between the antenna and the signal processing circuit, the wireless communication module includes a planar transmission line-to-waveguide transition apparatus that connects the antenna and MMIC, through a planar transmission line such as a microstrip line or a coplanar waveguide (CPW), to the waveguide.
For example, a conventional transition apparatus is described in the article by Yusuke Deguchi, Kunio Sakakibara, Nobuyoshi Kikuma and Hiroshi Hirayama, entitled "Millimeter-Wave Microstrip-to-Waveguide Transition Operating over Broad Frequency Bandwidth", which is disclosed in IEEE MTT-S Int. Microwave Symp., pp. 2107-2110, June 2005.
The transition apparatus disclosed in the article by Yusuke Deguchi et al. exhibits low loss wide-band characteristics but has shortcomings in that an upper waveguide has to be manufactured additionally through a mechanical process and that the process of obtaining a certain shape of the upper waveguide is very difficult. This results in an increase in the overall size of the wireless communication module.
Another conventional transition apparatus is found in the article by Florian Poprawa, Andreas Ziroff, and Frank Ellinger, entitled "A Novel Approach for a Periodic Structure Shielded Microstrip Line to Rectangular Waveguide Transition", which is disclosed in IEEE MTT-S Int. Microwave Symp., pp. 1599-1562, June 2007.
The transition apparatus disclosed in the article by Florian Poprawa et al. includes a periodic shield structure for shielding a microstrip line-waveguide transition. However, it requires an additional manufacturing process to attach the periodic shield structure to the microstrip line-waveguide transition part, which renders it difficult to make the wireless communication module small in size.
As described above, the conventional techniques require an additional waveguide structures i.e., an upper waveguide or a periodically structured shield, in addition to the existing waveguide, so as to transmit signals from the antenna that is attached to the rear side of the transition apparatus through the waveguide. Therefore, an additional process is needed for joining those structures with the wireless communication module. As a result, this makes the overall size of the wireless communication module bulky, and also makes the layout of the wireless communication module very complicated which incurs high manufacturing cost as well as brings about a difficulty for making the wireless communication module in small size.
Moreover, problems may occur by processing error during the manufacture of those structures, and the complexity of the matching circuit gets worse.
Therefore, there is a need for a transition apparatus which has a low insertion loss and a wide frequency band, but does not require an additional process in the wireless communication module operating at millimeter-wave bands, thereby realizing a low price transition apparatus of super-small size.

Planar transmission line-to-waveguide transition apparatus having an embedded bent stub

Korea Advanced Institute of Science and Technology (KAIST)


A raising lever for a pedal steel guitar has a pin means for pivotal connection to a control bridge, a pivot means for pivotally attaching a lowering lever to the raising lever, and a raise attachment means for selectable attachment of a pull rod for actuation of the raising lever from a neutral position to an actuated position. A cabinet slot engaging portion remains in contact with a cabinet slot portion of the steel guitar when the raising lever is in the neutral position. The raise attachment has a raising flange integral to the raising lever and a plurality of holes for selectable connection of pull rods. A pitch-changing device to be used in a pedal steel guitar having the raising finger is also shown, as well as a pedal steel guitar employing the pitch changing device having the raised finger assembly.

1. Field of the Invention
This invention relates generally to pedal steel guitars, and more particularly to an improved pitch-changing device.
2. Description of the Prior Art
The pedal steel guitar is a stringed instrument often having one or two necks, each normally utilizing from eight to fourteen strings. A pitch-changing mechanism or "changer" is actuated by a pedal or lever and used to raise and/or lower the pitch of the selected strings to achieve new chords and sounds. Each string is adjusted to a set pitch or open tuning, and changers can increase or decrease the tension on the selected strings, resulting in an alteration of pitch.
FIGS. 1, 2 and 3 depict a typical pitch-changing device employed in pedal steel guitars. FIG. 1 depicts a wrap around design in an all-pull pedal steel guitar showing the placement of the string, tension control lever, pitch raising and lowering levers, pull rods, return spring, and return stop. During operation as shown in FIG. 2, in raising the pitch of the string, a foot or knee activated pedal pulls a pull rod connected to a tuning nut which engages the pitch raising lever creating more tension on the string and thus raising the pitch of the selected string. After the pedal is released, the string tension brings the raising lever to return to the resting, neutral position by resting against a fixed return plate as depicted in FIG. 1. FIG. 3 shows a pull rod activating a lowering lever activated so that the raising lever behind may be shown in the resting, neutral position. A typical pedal steel guitar is shown and described in U.S. Pat. No. 5,092,214, herein incorporated by reference.
After the pedal is released, the return spring causes the lowering lever to return to the resting, neutral position against the fixed return plate as depicted in FIG. 1.
Existing pitch-changers tend to require excessive and unnecessary movement to change string tension and also tend to return to the open, or "at rest" pitch imperfectly. Existing pitch changers have also suffered from excessive friction between the levers when changing tension on the strings.
To a large degree, the tonal quality of guitars is determined by the transmission of the string energy through the guitar. This includes transmission of energy through the various components of the guitar including the endplates, pitch changer, levers, keyheads, return stops, cabinet, etc.

Pitch-changing device for a pedal steel guitar


A pedestrian bridge is configured to be portable and expandable. The pedestrian bridge comprises a bridge mechanically coupled to feet and configured to be elevated above a hazard. A front ramp is rotatably coupled to the bridge and configured to be folded upon the bridge making the pedestrian bridge portable. A rear ramp rotatably coupled to the bridge and configured to be folded upon the bridge further making the pedestrian bridge portable.

The embodiments herein relate generally to bridges primary traversed by foot.
Prior to embodiments of the disclosed invention, standing water impeded the safe ingress, egress and movement of pedestrians. In addition to water, many other obstacles can also cause inconvenient or dangerous hazards, trips and falls and potential injury. Embodiments of the disclosed invention solve these problems.


A method of fabricating a gate quality oxide-compound semiconductor structure includes forming an insulating Ga.sub.2 O.sub.3 layer on the surface of a compound semiconductor wafer structure by a supersonic gas jet containing gallium oxide molecules and oxygen. In a preferred embodiment, a III-V compound semiconductor wafer structure with an atomically ordered and chemically clean semiconductor surface is transferred from a semiconductor growth chamber into an insulator deposition chamber via an ultra high vacuum preparation chamber. Ga.sub.2 O.sub.3 deposition onto the surface of the wafer structure is initiated by a supersonic gas jet pulse and proceeds via optimization of pulse duration, speed of gas jet, mole fraction of gallium oxide molecules and oxygen atoms, and plasma energy.

Oxide-semiconductor structures are the major workhorse of the Si semiconductor industry. The requirements for gate quality insulator-semiconductor structures are manifold: (i) low interface state density, e.g. D.sub.it <10.sup.11 cm.sup.-2 ev.sup.-1 ; (ii) low trap density, e.g. N.sub.t .ltoreq.low 10.sup.11 cm.sup.-2, in the insulating film; (iii) thermodynamic interface and insulator stability; and (iv) interface and insulator reliability in particular related to insulator damage caused by injection of (hot) carriers. So far, the only systems which satisfy all of the above outlined specifications is thermal SiO.sub.2 --Si, jet vapor deposited (JVD) Si.sub.3 N.sub.4 --Si, and JVD Si.sub.3 N.sub.4 --SiO.sub.2 --Si.
For Si technology, prior art, for instance A. Malik et al., J. Appl. Phys., 79, 8507 (1996), describes the use of supersonic gas jets for the fabrication of insulating, gate quality silicon nitride films with low N.sub.t on Si. Jet vapor deposition (JVD) uses a supersonic free jet of inert carrier gas to transport vapor species generated from evaporation sources to the surface of a substrate. The quality of silicon nitride films produced by JVD was mainly attributed to a high dissociation efficiency of N.sub.2 (up to 60%) in the supersonic beam using an RF discharge source, see for instance, J. E. Pollard, Rev. Sci.Instrum., vol. 63, 1771 (1992), the small fraction of generated ions, and the absence of H in the silicon nitride films. Some effects of high speed gas dynamics and chemical reactions involved are still under discussion. The technique has been particularly applied for rapidly growing metal and semiconducting films on substrates, see for instance, U.S. Pat. No. 4,788,082, entitled "Method and Apparatus for the deposition of Solid Films of a Material from a Jet Stream Entraining the gaseous phase of Said Material", issued Nov. 29, 1988; U.S. Pat. No. 5,164,040, entitled "Method and Apparatus for Rapidly Growing Films on Substrates Using Pulsed Supersonic Jets", issued Nov. 17, 1992, and U.S. Pat. No. 5,356,673, entitled "Evaporation System and Method for Gas Jet Deposition of Thin Film Materials", issued Oct. 18, 1994. Prior art also includes plasma assisted supersonic gas jets, see for instance, U.S. Pat. No. 5,256,205, entitled "Microwave Plasma Assisted Gas Jet Deposition of Thin Film Materials", issued Oct. 26, 1993, U.S. Pat. No. 5,356,672 entitled "Method for Microwave Plasma Assisted Supersonic Gas Jet Deposition of Thin Films, issued Oct. 18, 1994; and pulsed supersonic gas jets, see for instance, U.S. Pat. No. 5,164,040, entitled "Method and Apparatus for Rapidly Growing Films on Substrates Using Pulsed Supersonic Jets", issued Nov. 17, 1992, U.S. Pat. No. 5,330,610, entitled "Method of Digital Epitaxy by Externally Controlled Closed Loop Feedback, issued Jul. 19, 1994, and U.S. Pat. No. 5,540,783, entitled "Apparatus for Externally Controlled Closed Loop Feedback Digital Epitaxy", issued Jul. 30, 1996.
For compound semiconductors, a low interface state density Dit of 2.5.times.10.sup.10 cm.sup.-2 ev.sup.-1 and full accessibility of the GaAs band gap were demonstrated. Pivotal fabrication aspects include (i) an extremely low GaAs surface exposure to impurities (<10-100 Langmuirs) prior to deposition of the insulating film, and (ii) the preservation of GaAs bulk and surface stoichiometry and the complete exclusion of GaAs surface oxidation. Satisfying the latter requirements and using in-situ deposition of specific molecules (Ga.sub.2 O.sub.3) on GaAs based semiconductor epitaxial layers while maintaining ultra-high vacuum (UHV), resulted in low, D.sub.it interfaces. The GaAs surface exposure (predominantly oxygen) prior to completion of the first Ga.sub.2 O.sub.3 monolayer was typically less than 10 Langmuirs, GaAs surface oxidation was excluded, and GaAs surface stoichiometry preserved. Also, thermodynamic interface stability was demonstrated. See for instance, U.S. Pat. No. 5,451,548 entitled "Electron beam deposition of gallium oxide thin films using a single purity crystal source", issued Sep. 19, 1995, M. Passlack et al., Appl. Phys. Lett., vol. 68, 1099 (1996), Appl. Phys. Lett., vol. 68, 3605 (1996), and Appl. Phys. Lett., vol. 69, 302 (1996).
For compound semiconductors, the remaining problems are associated with stability and reliability issues including charge trapping, carrier injection, and eventually, oxide degradation and breakdown. Trap densities as high as 2.times.10.sup.12 cm.sup.-2 have been found in e-beam deposited Ga.sub.2 O.sub.3 films causing long term drift of device parameters in accumulation and inversion. Consequently, the performance of unipolar and bipolar devices is affected and the fabrication of stable and reliable MOSFETs based on compound semiconductors has been impossible.
Accordingly, it would be highly desirable to provide new methods of manufacturing which overcome these problems.
It is a purpose of the present invention to provide a new and improved method of manufacturing a gate quality oxide-compound semiconductor structure.
It is another purpose of the present invention to provide a new and improved method of manufacturing a gate quality Ga.sub.2 O.sub.3 -compound semiconductor structure.
It is still another purpose of the present invention to provide a new and improved method of manufacturing a gate quality Ga.sub.2 O.sub.3 -compound semiconductor structure with oxide trap density.ltoreq.10.sup.11 cm.sup.-2.
It is a further purpose of the present invention to provide a new and improved method of manufacturing a gate quality Ga.sub.2 O.sub.3 -compound semiconductor structure with oxide trap density.ltoreq.10 .sup.11 cm.sup.-2 and interface state density.ltoreq.10.sup.11 eV.sup.-1 cm.sup.-2.
It is still a further purpose of the present invention to provide a new and improved method of manufacturing a gate quality oxide-compound semiconductor structure with improved stability and reliability.
It is yet a further purpose of the present invention to provide a new and improved method of manufacturing a gate quality oxide-compound semiconductor structure which allows the implementation of stable, reliable, and manufacturable accumulation and/or inversion mode devices using compound semiconductors.
It is still a further purpose of the present invention to provide a new and improved method of manufacturing a gate quality Ga.sub.2 O.sub.3 -compound semiconductor structure which is relatively easy to fabricate and use.

Fabrication method for a gate quality oxide-compound semiconductor structure


An adjustable corner tool is provided having outwardly biased blades. The back surfaces of the blades are connected to an angle control assembly that includes fixed-length arms pivotally connected between each of the blades and a central mounting block. Springs rotationally bias the arms away from each other such that the arms push against the back surfaces of the blades to urge the blades apart. In use, resistive force applied against the front surfaces of the blades moves the blades together. Thus, the adjustable corner tool dynamically adjusts to variations in wall corner angles. The adjustable corner tool can be used with corners in the range of about 160 degrees to 40 degrees and the angle of the tool can also optionally be fixed or maximally limited. In addition, the adjustable corner tool may be adapted to also function as an injection head for delivering spreadable material to a corner.

Drywall corner tools are commonly used to finish wall corners provided by adjacent intersecting walls. Many conventional drywall corner finishing tools in the marketplace are limited to applications against typical 90 degree angular inside corner wall joints. In recent years, the use of other angular measurements have been incorporated in building construction, resulting in larger and smaller angles than 90 degrees, such as vaulted ceilings or corner bay window coves.
Angles other than 90 degrees can be finished by hand using a joint knife or variable angle hand trowel. This method is very time consuming since each side of the angle must be finished separately and allowed to dry. To assist in this finishing process, a product called "corner bead" was made available in a variety of popular angles, which is placed into the corner to fill the joint gap and provide a straight vertical corner line before drywall compound (mastic or mud) is applied and finished by hand. Such corner bead strips, however, increase the cost of drywalling.
To alleviate problems associated with variable wall corner angles, drywall corner tools have been developed having adjustable corner angles. For example, such tools have been disclosed in U.S. Pat. No. 5,442,832, issued on Aug. 22, 1995; U.S. Pat. No. 5,467,497, issued on Nov. 21, 1995; U.S. Pat. No. 5,544,384 issued on Aug. 13, 1996; and U.S. Pat. No. 5,774,924, issued on Jul. 7, 1998. Each of these patents disclose corner tools having hinged blades for pivotal movement of the blades about the hinge axis to form a variety of corner angles. Slideably or pivotally connected arms extend between the blades to support the blades and adjust the blades to a desired corner angle. Typically, the angle is fixed by a locking member that prevents sliding or rotation of the arms about the handle prior to use. Alternatively, the '497 patent discloses a locking pin bolt extending through the hinge for fixing the blades at a desired angle.
In some cases, a particular wall corner angle is variable, either by design or because the corner is not true, such that fixedly variable angle corner tools may not adequately finish such a corner. Although it is possible to not fix the angle of the prior art corner tools to allow the blades to move together for adjusting to decreasing wall corner angles during use, the blades will not automatically return to their original position or adjust to increasing wall angles.
There is, therefore, a need for an improved adjustable corner tool.


Disclosed herein is a lithium secondary cell including 20 to 100 wt. % of lithium transition metal oxide represented by a formula of Li1+zNibMncMe1−(b+c)O2, relative to a total amount of a cathode active material, as well as an electrolyte consisting of a lithium salt and a non-aqueous solvent, wherein a first additive to form a protective film (that is, a solid electrolyte interface film: SEI film) over a surface of an anode active material and a second additive to form another SEI film over the surface of the anode active material while inactivating impurities contained in the cathode active material are included in the electrolyte.

With technological advancement and demand for mobile instruments, demand for secondary cells as an energy source is rapidly increasing. Among such secondary cells, a lithium secondary cell having high energy density and working potential, a long life cycle, and reduced self-discharge is widely used in the related art.
For a lithium secondary cell, lithium ions move from lithium metal oxide used as a cathode to graphite used as an anode at an initial charge stage, in turn, being interposed between interlayers of the graphite anode. In this regard, lithium is highly active and an electrolyte reacts with a lithium salt on a surface of the graphite anode having lithium interposed between the interlayers thereof, so as to generate a particular compound such as Li2CO3, Li2O, LiOH, etc. This compound forms, in general, a passivation layer on the surface of the graphite anode and such a passivation layer is referred to as a solid electrolyte interface "SEI" layer.
The formed SEI layer serves as an ion tunnel to selectively pass lithium ions therethrough which, in turn, prevents side reaction of the lithium ions with the graphite anode or other materials. A charge quantity consumed for forming the SEI layer is substantially an irreversible charge capacity which is not reversibly used for a discharge process. Therefore, the electrolyte is not further decomposed and an amount of lithium ions in the electrolyte is reversibly retained, thereby attaining stable charge-discharge performance (J. Powder Sources (1994) 51:79-104). As a result, when the SEI layer is formed, the amount of lithium ions may be reversibly retained and a lithium cell may have enhanced lifespan properties.
The SEI layer described above is relatively rigid under general conditions for maintaining stability of an electrolyte, that is, at a temperature of −20 to 60° C. and a voltage of not more than 4V, thus sufficiently preventing side reaction between an anode and the electrolyte. However, if a cell is stored in a full-charge state at a high temperature (for example, when the cell is left at 90° C. for 4 hours after completely charging the same at 4.2V), a significant problem such as slow deterioration in durability of SEI film is entailed.
More particularly, when a lithium cell is stored in a full-charge state, an SEI film gradually collapses over time and exposes an anode of the cell, and a surface of the exposed anode reacts with an electrolyte to occur a side reaction and generate gases such as CO, CO2, CH4, C3H6, etc., thus causing increase in internal pressure of the cell.
The SEI layer shows varied characteristics depending on types of a solvent contained in the electrolyte and/or chemical properties of additives and such characteristics are known as a major parameter that influences transfer of ions and charge, in turn, varying cell performance (see Shoichiro Mori, "Chemical properties of various organic electrolytes for lithium rechargeable batteries," J. Power Source (1997) Vol. 68).
Accordingly, there is a requirement for development of novel techniques to prevent variation in cell performance by adding a desired amount of additive to a cell in order to inhibit adverse effects on transfer of ions and charge while embodying inherent efficiency of the additive.
A major cathode active material for the lithium secondary cell comprises lithium-containing cobalt oxide (LiCoO2). Other substances including, for example, lithium-containing manganese oxide such as LiMnO2 with a layered crystalline structure or LiMn2O4 with a spinel crystalline structure, lithium-containing nickel oxide LiNiO2, and the like may also be considered.
Especially, although LiCoO2 with favorable features such as excellent cycle characteristics is widely used, the above material has some disadvantages such as high price due to inclusion of cobalt as a limited mineral resource and, in turn, restriction in mass application as a power source for electric vehicles, and so forth.
Lithium manganese oxides such as LiMnO2, LiMn2O4, etc. have economic merits of using manganese as a raw material, which is an eco-friendly and abundant natural resource, thus drawing considerable attention as a new cathode active material for replacement of LiCoO2. However, they have some drawbacks such as low capacity, poor cycle characteristics, and the like.
In addition, lithium nickel based oxide such as LiNiO2 is relatively cheap and shows high discharge capacity when being charged to 4.3V and, in particular, a reversible capacity of doped LiNiO2 is near 200 mAh/g exceeding a capacity of LiCoO2 (about 165 mAh/g). Therefore, in spite of its low average discharge voltage and volumetric density, a commercially available battery utilizing an LiNiO2 cathode active material exhibits enhanced energy density. Studies into such nickel based cathode active materials are recently increasing number in order to develop improved high capacity cells.
However, the foregoing LiNiO2 based cathode active material encounters some problems including, for example, a rapid phase transformation in crystalline structure caused by variation in volume during a charge-discharge cycle, drastically reduced chemical resistance when exposed to air and moisture, generation of a large quantity of gas during storage or charge-discharge cycle, etc., thus restricting practical utilization thereof.
In order to solve such problems, a lithium transition oxide wherein nickel in the oxide was partially substituted with any other transition metal such as manganese, cobalt, and the like has been proposed. Such metal substituted nickel-lithium transition oxide has excellent cycle characteristics and capacity properties, however, if a cell is used for a long time, the cycle characteristics are drastically deteriorated and some problems of the cell such as cell swelling due to gas generation, impurities generated due to reduced chemical stability, etc. are not sufficiently overcome. Especially, a lithium nickel transition metal oxide with high Ni content entails problems such as significant cell swelling and poor stability at a high temperature.
Accordingly, there is still a strong requirement for development of improved techniques to solve high temperature stability problems caused by impurities while utilizing a lithium nickel based cathode active material suitable for high capacity cells.
In this regard, as electrolyte additives useful for enhancing cycle characteristics and high temperature stability of a cell, vinylene carbonate, vinylethylene carbonate, and the like have been disclosed. These materials are known to react with an electrolyte to form an SEI film over a surface of an anode.
However, such formed SEI film has relatively low thermal stability and, when being used at room temperature or more for a long period of time or being stored at a high temperature, is decomposed to expose a surface of the anode, in turn deteriorating performance of the cell. Further, if the foregoing material is used in a cell containing nickel-lithium transition metal oxide as a cathode active material, cell swelling and high temperature stability are more seriously deteriorated. Therefore, it is substantially impossible to apply the foregoing additive to the cell.
In this regard, Korean Laid-Open Patent Application No. 2004-0065152 describes a cell having LiCoO2 as a cathode active material, wherein a non-aqueous electrolyte of the cell includes a polyether modified silicon oil with a structure having a polyether chain bonded to a terminal of a linear polysiloxane chain, and ethylene carbonate (EC) mixed with the silicon oil.
Japanese Laid-Open Patent Application No. 2006-086101 describes a cell having LiCoO2 as a cathode active material wherein a polymer electrolyte contained in the cell comprises: (1) a polymer having a main chain consisting of polyolefin, polysiloxane or polyphosphazene and a branched chain with an oxide structure; (2) an additive based on a low molecular weight compound with a molecular weight of 103 to 108; (3) a lithium salt compound; and (4) a cyclic carbonate having an un-saturated group.
According to disclosures by the present inventors, however, even when the foregoing technologies are applied, a cell containing nickel-lithium transition metal oxide as a cathode active material does not have enhanced cycle characteristics and, in addition, high temperature stability and/or cell swelling is substantially not improved.
Accordingly, for application of lithium transition metal oxide with high Ni content as a cathode active material, a novel technique to prevent deterioration of cycle characteristics, capacity properties and/or high temperature stability caused by impurities is required.

Lithium secondary battery with improved cell characteristics


A process for direct compression of hydrogen separated from a hydrocarbon source is described herein. The process comprises a first zone wherein a hydrocarbon reaction that produce hydrogen occurs, a ceramic proton conductor which under an applied electric field transport hydrogen from said first zone to said second zone, and a second zone where compressed hydrogen is produced. The heat energy generated by ohmic resistance in the membrane is partially recuperated as chemical energy in the hydrocarbon reforming process to generate hydrogen.

Hydrogen can be produced from steam methane reforming (SMR), following the equation:CH4+H2O↔3H2+CO.
The reaction is endothermic (ΔH298=206 kJ mol−1), and is commercially operated at high temperatures, >900° C. Downstream the hydrogen concentration is further increased by the shift reaction:CO+H2O↔H2+CO2(ΔH298=−41 kJ mol−1),
before the hydrogen is separated using e.g. pressure swing absorption (PSA). Finally, the hydrogen is compressed using available compressor technologies such as piston or diaphragm mechanical compressors or using electrochemical/chemical compressors.
Alternatively, hydrogen separation can be included in the steam reforming reaction using hydrogen selective membranes. The vast majority of membrane reactors for SMR utilize the metallic hydrogen permselective Pd or Pd in combination with Ag, Cu (Pd-SMR). This enables operation at lower temperatures while still maintaining a high conversion as the hydrogen permeation shifts the steam reforming reaction. The lower temperature and hydrogen extraction facilitates also the shift reaction and allows for further permeation of H2 and a high selectivity of the feed exhaust to CO2.
The drawback for the Pd-SMR is the significant partial pressure difference of H2 needed across the membrane, pH2(retanate)>pH2(permeate). The driving force for hydrogen transport is the chemical potential gradient of hydrogen across the membrane. When the hydrogen partial pressure in the retanate is low, high hydrogen recovery will be challenging.
It follows that the final pressure of hydrogen in the permeate will always be low and further pressurization of hydrogen requires large compressors on a volumetric basis. This is demanding and adds complexity to the overall process and inhibits high energy efficiencies.
Two further challenges are present for the Pd-SMR.
1) Pd-SMR is restricted by temperature. If operated above 500-600° C. failures have been seen due to embrittlement and coke poisoning;
2) External heat management is needed for the endothermic reforming reaction.
Analogous to the Pd-based membranes are mixed ceramic conductors. Example of such a membrane is the LaWO12—LaCrO3 based composite described in PCT/EP2014/060708. Although this composite has lower permeability it can be operated at higher temperatures compared to the Pd-SMR; the mechanical and chemical stability is also higher.
For production of synthesis gas, this membrane can produce the heat in-situ if operated with an oxygen containing sweep gas; the permeated hydrogen will react with oxygen and produce steam and heat. By tuning the oxygen content in the sweep gas the SMR process can be operated autothermally. The oxygen containing sweep will also provide the necessary driving force for the permeation. However, by using an oxygen containing sweep, a portion of the permeated hydrogen will be consumed in the reaction with oxygen and thereby decrease the hydrogen recovery. Further, although a counter flow reactor configuration can be used, the hydrogen recovery will be limited by the partial pressure of hydrogen content in the sweep gas.
Two drawbacks using this type of membrane are therefore:
1) Additional separation step of hydrogen from steam is needed and
2) partial pressure of hydrogen cannot exceed that of partial pressure on feed side.
Several chemical processes are thermodynamically limited and/or endothermic and can only be operated at low conversion at low/medium temperatures. Examples of such reactions are:CH4+H2O↔3H2+CO  (1)6CH4═C6H6+9H2  (2)
This restricts the system efficiencies, both on a carbon and energy basis. Herein, with hydrogen being a part of the reaction product, the yield of the desired product is thermodynamically limited by the partial pressure of hydrogen in the product mixture.
Similarly, several chemical processes require external heat due to their endothermic nature. Examples of such reactions are:CO+H2O ↔H2+CO2  (3)CH3OH+H2O ↔CO2+3H2  (4)
This also restricts the system efficiencies, on energy basis. The endothermic nature of the reactions necessitates the need of external heat being supplied to the system. The production of external heat lowers the total energy efficiency of the system.
It is generally accepted that the hydrogen compressor technology will not be able to meet future infrastructure demands in a cost-effective manner Currently, the hydrogen compressors used today face considerable wear due to the usage of technology with moving parts. Research has shown that for piston pumps the piston sealing ring fails due to non-uniform pressure distribution, and failure of pistons is due to severe impact.
Diaphragm compressors are prone to shorter lifetimes due to contaminations/debris in the H2 gas and improper priming procedures when restarting a compressor after stopping. The operating pressures is high enough to cause local plastic deformation around trapped hard particles leaving residual stresses that reduce the fatigue life of the diaphragm.
The present inventors have appreciated that electrochemical hydrogen compressors will increase the reliability/availability over mechanical compressors as they operate without any moving parts. There remain challenges in designing these electrochemical compressors, such as their energy efficiencies.
This invention solves three separate challenges simultaneously which have hampered the commercial deployment of a range of chemical processes by introducing a galvanic driven protonic membrane compressor. In particular, the protonic membranes of the invention:                1. will remove hydrogen from the reaction chamber and shift a thermodynamically limited process towards higher conversion towards the desired product;        2. will provide heat to an endothermic reaction process; and        3. will simultaneously compress the hydrogen to a desired pressure at the permeate side of the membrane.
Moreover, the high selectivity of the membrane allows only for hydrogen to pass through. The hydrogen produced is therefore of high purity; a final purification stage is therefore not needed.
The combination of these four effects in a single stage results in high energy efficiency. More specifically this yields distinct advantages. The conversion and yield of a chemical process can be increased to a commercial attractive level and the by-product, hydrogen, has an attractive partial pressure and purity for further usage. Finally, the joule heat produced enables operation of the overall process in an autothermal state.

Process for producing compressed hydrogen in a membrane reactor and reactor therefor