An apparatus for transmitting data in a base station of a wireless communication system that transmits data depending on channel status information fed back from terminals and uses a plurality of antennas. Based on the channel status information, a scheduler determines a terminal to which the base station will transmit data, determines antennas via which the base station will transmit data among the plurality of antennas, and determines a space pre-coding method. A multiplexer multiplexes transmission data into a plurality of data streams according to the number of the determined antennas. A modulation and coding unit performs modulation and coding on each of the data streams. A pre-coding controller outputs a matrix select signal for selecting one of a plurality of space pre-coding matrixes according to the space pre-coding method. A space pre-coder spatial-codes each of the coded streams with the matrix selected based on the matrix select signal. An OFDM modulator performs OFDM modulation on each of the spatial-coded streams. An RF unit transmits each of the OFDM-modulated streams via an associated antenna.

1. Field of the Invention
The present invention relates generally to an apparatus and method for transmitting/receiving data in a communication system using multiple antennas (hereinafter referred to as a "multi-antenna communication system"), and in particular, to an apparatus and method for spatial multiplexing transmission in a multi-antenna communication system.
2. Description of the Related Art
A wireless communication system has been developed to allow users to perform communication without distance limitations. A mobile communication system is the typical wireless communication system. The mobile communication system has evolved from the early voice service communication system into a high-speed, high-quality wireless packet data communication system for providing data service and multimedia service. It can be considered that the ongoing standardization on High Speed Downlink Packet Access (HSDPA) led by 3rd Generation Partnership Project (3GPP), and Evolution for Data and Voice (EV-DV) and Evolution-Data Only (EV-DO) led by 3rd Generation Partnership Project 2 (3GPP2) is a typical attempt to find a solution for the high-speed, high quality wireless packet data transmission service at 2 Mbps or higher in the 3rd generation (3G) mobile communication system.
Meanwhile, research on the 4th generation (4G) mobile communication system is being conducted with the aim of providing higher-speed, higher-quality multimedia service using Orthogonal Frequency Division Multiplexing (OFDM) and Orthogonal Frequency Division Multiple Access (OFDMA).
The current 3G wireless packet data communication systems, like the HSDPA, EV-DV and EV-DO, use an Adaptive Modulation and Coding (AMC) method and a channel sensitive scheduling resource management method to improve transmission efficiency. With the use of the AMC method, a transmitter can adjust the amount of transmission data according to channel status. That is, the transmitter decreases the amount of transmission data in a channel having bad status and increases the amount of transmission data in a channel having good status, thereby efficiently transmitting the large amount of data while maintaining a desired reception error probability.
With the channel sensitive scheduling resource management method, a transmitter selects a good-channel status user, thereby increasing the data throughput. In the AMC method and the channel sensitive scheduling resource management method, the transmitter receives partial channel status information fed back from a receiver, and applies an appropriate modulation and coding technique determined at the time to be most efficient.
In order for the AMC method and the channel sensitive scheduling resource management method to help improve the system capacity substantially, the channel status information fed back by the receiver should be matched to the channel status at the transmission time. Generally, however, in the mobile communication environment, because the transmitter or the receiver moves from place to place, the channel status changes continuously. The continuous change in the channel status is related to moving velocity of the transmitter or the receiver, and this is called Doppler spread. High moving velocity deepens the Doppler spread. In this case, the channel status information fed back by the receiver may be invalid.
In this situation, therefore, even the use of the AMC method and the channel sensitive scheduling resource management method cannot accomplish system capacity improvement. To make up for the defects, the 3G wireless packet data communication system adopts Hybrid Automatic ReQuest (HARQ). In the HARQ technology, when a receiver fails to normally receive the data transmitted by a transmitter, the receiver immediately informs the transmitter of the failure so that the transmitter rapidly performs retransmission in a physical layer.
Meanwhile, an OFDM scheme, recently spotlighted in the wireless communication system, sends modulation signals on orthogonal frequency signals, that is, sub-carriers. Therefore, an OFDMA scheme is a method for sending different user signals on different sub-carriers based on the OFDM scheme. In the OFDMA scheme, channel sensitive scheduling which could be performed only in the time axis can be performed even in the frequency axis. That is, for data transmission, the OFDMA system schedules a sub-carrier preferred by each user in the frequency selective fading environment through frequency scheduling, thereby improving the system capacity as compared with the case where scheduling is performed only in the time axis. Therefore, in order to efficiently perform frequency scheduling, it is preferable to use a bundle of adjacent sub-carriers having a similar channel response for data transmission taking into account of overhead of the channel status feedback.
Further, a Multiple-Input Multiple-Output (MIMO) system using multiple antennas for a transmitter and a receiver is now under active discussion as a core technology for providing high-speed, high-quality data service in wireless communication. Theoretically, it is known in the MIMO system that as the number of transmission/reception antennas increases without an additional increase in frequency bandwidth, the serviceable data capacity linearly increases in proportion to the number of transmission/reception antennas. Therefore, the MIMO-based technology can be roughly divided into a Spatial Diversity technique and a Spatial Domain Multiplexing (SDM) technique according to its purpose. A description will now be made of the Spatial Diversity technique and the SDM technique.
The Spatial Diversity technique is developed to prevent a reduction in link performance due to fading occurring in a mobile communication channel by using multiple transmission/reception antennas. The Spatial Diversity technique can efficiently reduce a reception error probability, when a transmitter has channel status information and cannot adaptively adjust the amount of transmission information. The SDM technique is developed to transmit the larger amount of data using the MIMO scheme, as compared with the single-transmission/reception antenna technique. The SDM technique can efficiently increase data throughput in an environment where the spatial correlation is very low due to the scattering objects having a sufficient number of channel environments.
The SDM technique extended based on multiple access is a Spatial Domain Multiple Access (SDMA) technique. The SDM technique increases the number of transmission channels over which data is transmitted, using multiple transmission/reception antennas. In an environment where the spatial correlation is low, it is possible to increase the data throughput using the SDM technique. However, in an environment where the spatial correlation is high, even though the data throughput is increased, it is not possible to prevent an increase in the reception error probability. However, in an environment where the spatial correlation is high, if transmission channels over which the data (the amount of which is increased with the use of the MIMO scheme) is transmitted are allocated to different users, it helps increase the system capacity. This is because if the spatial correlation is high, interference between user signals having different spatial characteristics may decrease. That is, the SDMA technique is a spatial processing technique capable of increasing the system capacity in the high-spatial correlation environment.
Each of such spatial processing techniques as Spatial Diversity technique, SDM technique and SDMA technique differs in available scope according to traffic type and channel environment showing capacity improvement. For example, for a voice call, because similar amounts of data are always generated, it is difficult to apply the AMC method and the channel sensitive scheduling resource management method, both of which vary the data throughput. In addition, if the channel status becomes bad due to fading, a reception error is unavoidable. In this situation, the use of the Spatial Diversity technique can prevent the channel status from deteriorating. In the channel environment where the spatial correlation is low, the use of the SDM technique can increase the data throughput, together with the AMC method and the channel sensitive scheduling resource management method. In the channel environment where the spatial correlation is high, the SDMA technique can improve the system capacity. Therefore, there is a need to appropriately select the spatial processing technique according to the channel environment and traffic type.
A description will now be made of a transmitter for each of the systems described above.
FIG. 1 is a diagram illustrating a structure of a transmitter in a wireless communication system employing Space-Time Coding (STC). With reference to FIG. 1, a description will now be made of an apparatus and method for transmitting data using STC coding.
If data (such as an information bit stream) 10 that an upper layer desires to transmit is received, the data 10 is input to an AMC unit 100. The AMC unit 100 includes therein a channel coding/modulation unit 110 and an AMC controller 101. The channel coding/modulation unit 110 includes therein a channel encoder 111, a channel interleaver 112, and a modulator 113. Therefore, the data 10 is input to the channel encoder 111. The data coded by the channel encoder 111 is dispersed (or permutated) by the channel interleaver 112. The reason for dispersing the data by the channel interleaver 112 is to prevent deterioration of coding performance due to fading during data transmission. The data dispersed by the channel interleaver 112 is converted into a modulation signal by the modulator 113. A series of processes where the data undergoes coding 111, interleaving 112, and modulation 113 is called a "channel coding and modulation" process. Therefore, this process is performed in the channel coding/modulation unit 110.
The channel coding/modulation unit 110 can apply a different scheme depending on Channel Status Information (CSI) feedback 105 that a receiver has delivered according to the system. For example, if the channel status is good, the channel coding/modulation unit 110 increases a channel coding rate and a modulation order so that the increased amount of data is transmitted. However, if the channel status is bad, the channel coding/modulation unit 110 decreases the coding rate and the modulation order so that the decreased amount of data is transmitted more reliably. In this way, the transmitter applies AMC based on the CSI feedback 105, and the AMC controller 101 determines which coding and modulation schemes it will use. The AMC controller may be omitted, according to the particular design. That is, it is meant in FIG. 1 that the signals shown by a dotted line are optional. For example, in the case where several users receive the same information such as a broadcast, because it is not possible to adaptively change the coding and modulation schemes according to a channel status of a particular user, the transmitter need not support AMC. A process in which the AMC controller 101 adaptively changes the channel coding and modulation schemes based on the CSI feedback 105 is called an AMC process. Therefore, an apparatus provided for performing the AMC process is shown as an AMC unit 100 in FIG. 1.
The signal modulated by the AMC unit 100 is STC-coded by an STC encoder 121. The STC encoder 121 typically adopts an Alamouti coding method, which is applied to two transmission antennas. The Alamouti coding method, which corresponds to Orthogonal Space Time Coding (OSTC), can obtain the maximum diversity gain. In the Alamouti coding method, there should be no change in the channel between Alamouti-coded adjacent time signals in order to maintain orthogonality. If the channel between the adjacent time signals undergoes an abrupt change, the Alamouti coding method cannot guarantee orthogonality, causing self-interference and performance deterioration due thereto.
However, it is known that the OSTC coding method guaranteeing orthogonality provides the maximum diversity gain. The general STC coding method is performed without depending on the CSI that the receiver feeds back. Therefore, the STC coding method is designed to maximize the diversity gain, rather than being modified to be adaptive to the channel. The signal obtained by STC-coding the modulation signal is converted into a transmission band signal by a Radio Frequency (RF) unit 122, generating a plurality of symbols to be transmitted via multiple transmission antennas 131 through 132. For example, the STC coding method applied to a 2-transmission antenna system receives one data stream and outputs two symbol streams. The generated symbol streams are transmitted via different transmission antennas 131 and 132.
The symbol stream to which the STC coding method is applied is converted by the RF unit 122 into an RF signal to be transmitted via a transmission antenna. The RF unit 122 performs filtering for satisfying a spectrum characteristic, adjusts transmission power, and converts a baseband signal into an RF signal. After this process, the output signals are transmitted via their associated antennas 131 and 132.
FIG. 2 is a diagram illustrating a structure of a transmitter employing OFDM-STC coding. With reference to FIG. 2, a description will now be made of a structure and operation of a transmitter employing OFDM-STC coding.
An AMC unit 100 is equal to that of FIG. 1 in operation, so a description thereof is omitted here. The signal modulated by the AMC unit 100 is input to an OFDM modulator 210. The OFDM modulator 210 includes therein an Inverse Fast Fourier Transform (IFFT) unit 211 and a Cyclic Prefix (CP) symbol adder 212. Therefore, the signal modulated by the AMC unit 100 is input to the IFFT unit 211. The IFFT unit 211 performs IFFT on the modulation signal such that the modulated signals should be carried on orthogonal frequency signals, that is, sub-carriers. Thereafter, a CP symbol is added to the IFFT-processed signal by the CP symbol adder 212. The CP is achieved by copying a part of the last part of a generated sub-carrier and adding the copied part to the head of the symbol, to maintain the orthogonality between sub-carriers even though delay spread occurs due to multi-path fading, thereby preventing interference. If OFDM symbols are generated by the OFDM modulator 210, an STC encoder 121 performs STC coding on consecutive OFDM symbols. Thereafter, an RF unit 122 converts the STC-coded OFDM symbols into transmission band RF signals, and then transmits the RF signals via multiple transmission antennas 131 and 132. In the transmitter employing OFDM-STC coding, if a change in the channel between consecutive OFDM symbols is considerable, the orthogonality may be affected, causing interference.
FIG. 3 is a block diagram illustrating a structure of a transmitter employing OFDM-SFC coding. A description will now be made of a structure and operation of a transmitter employing OFDM-SFC (Space Frequency Coding) coding.
In the OFDM scheme, modulation signals can be carried on different frequencies at different times. Therefore, an SFC coding method can be implemented by applying the STC coding method to consecutive frequency signals, that is, sub-carriers, instead of applying the STC coding method to consecutive time signals. An AMC unit 100 outputs a modulated signal using an input information bit stream 10 and SCI feedback information 105. The output modulation signal is input to an SFC encoder 300. The SFC encoder 300 performs the same process as the STC coding process, but finally applies STC coding to the consecutive frequency signals, so this coding method is called an SFC coding method. The signal stream modulated by the SFC encoder 300 is obtained by applying STC coding to consecutive time signals. One stream is coded into a plurality of streams by the SFC encoder 300, and the streams are separately modulated by ODFM modulators 210a to 210n. The STC-coded signals are converted into OFDM signals by the OFDM modulators 210a to 210n. It can be considered herein that the STC coding applied to the consecutive time signals by the OFDM modulators 210a to 210n are applied to consecutive frequency signals. Thereafter, the OFDM signals are converted into transmission signals by an RF unit 122, and then transmitted via associated transmission antennas 131 and 132. In the transmitter employing OFDM-SFC coding, if a change in the channel between consecutive sub-carriers is considerable, the orthogonality may be affected, causing interference.
FIGS. 2 and 3 respectively show a transmission scheme employing STC coding, and a transmission scheme employing SFC coding that implements STC coding in the frequency axis. Such conventional techniques were designed to obtain the maximum spatial diversity gain, as described above. Therefore, such techniques show excellent link performance in the low-spatial correlation environment, but cannot provide a multi-antenna gain if the spatial correlation increases. The reason for showing the excellent link performance in the low-spatial correlation environment is because the use of the diversity technique, like other kinds of diversity techniques, can reduce the change in channel with the passage of time. However, the diversity technique helps reduce the probability of channel deterioration by reducing the change in the channel, but reduces a large number of channels capable of transmitting data. For this reason, it is known that in the system supporting AMC and channel sensitive scheduling, the diversity technique reduces the system capacity undesirably.
FIG. 4 is a block diagram illustrating a structure of a transmitter employing OFDM-based spatial multiplexing. With reference to FIG. 4, a description will now be made of a structure and operation of a transmitter employing OFDM-based spatial multiplexing.
Before a description of FIG. 4 is given, the foregoing techniques and a spatial multiplexing technique will be described in brief. With the use of multiple transmission antennas, the STC coding technique and the SFC coding technique transmit one data stream, whereas the spatial multiplexing technique transmits a plurality of data streams. In the channel environment where the low-spatial correlation MIMO scheme is used because of a large number of scattering objects, a predetermined number of data streams can be transmitted, wherein the predetermined number corresponds to a smaller one from among the number of transmission antennas and the number of reception antennas. For example, in the above channel environment, if the number of transmission antennas is 2 and the number of reception antennas is 4, the transmitter can transmit 2 data streams. Therefore, in order for the system of FIG. 4 to stably operate, the receiver also needs more than M antennas. For reference, because the STC coding technique and the SFC coding scheme transmit only one data stream, they do not need a plurality of reception antennas.
In the MIMO system, it is known that in order to increase the capacity, it is preferable to increase the number of transmission data streams rather than improving a Signal-to-Noise Ratio (SNR) with the number of transmission data streams being fixed to one. Therefore, the spatial multiplexing technique uses such characteristics of the MIMO system.
Referring to FIG. 4, transmission data streams are individually input to AMC units 100a to 100n where they undergo an AMC process independently. Thereafter, the resulting streams are OFDM-modulated by OFDM modulators 210a to 210n. The OFDM-modulated symbols are converted into RF transmission signals by an RF unit 122, and then transmitted to a receiver via multiple transmission antennas 131 and 132. That is, different data streams are transmitted via different transmission antennas. The AMC units 100a to loon shown in FIG. 4 can be used when the system performs CSI feedback. If the CSI is not fed back, the fixed coding and modulation schemes are performed. In this case, the AMC units 100a to 100n perform the fixed coding and modulation schemes.
In the spatial multiplexing technique, there are two methods of performing AMC using CSI feedback. A first method applies the same AMC method for all transmission antennas. In order to support this method, a receiver is allowed to feed back only one representative CSI. A second method applies different AMC methods for all transmission antennas. In order to support this method, the receiver should feed back a CSI corresponding to each of the transmission antennas. That is, the former method is less than the latter method in terms of the CSI feedback overhead. However, in the former method, because only one AMC is applied to different transmission antennas experiencing different channel statuses, the capacity improvement effect of the system supporting AMC and channel sensitive scheduling is reduced. FIG. 4 shows the latter method that allows the receiver to feed back a CSI for each of the transmission antennas, and shows the transmitter employing an AMC method according thereto. Such a spatial multiplexing method is known as Per Antenna Rate Control (PARC).
FIG. 5 is a block diagram illustrating a structure of a transmitter employing PARC in a system supporting AMC and channel sensitive scheduling. With reference to FIG. 5, a description will now be made of a structure and operation of a transmitter employing PARC in a system supporting AMC and channel sensitive scheduling.
A scheduler 501 receives transmission data 10a to 10n of K multiple users from an upper layer. Herein, the scheduler 501 is a channel sensitive scheduler (hereinafter referred to as "scheduler" for simplicity). The scheduler 501 selects the most preferred user terminal to which it will transmit data at the present time, based on the CSI fed back from each user terminal. In order to deliver the necessary control information in the following process of transmitting data of the selected user, the scheduler 501 provides scheduling information 510 to an AMC controller 505. Then the AMC controller 505 analyzes the scheduled user and issues an AMC command according to a channel status of the user. That is, the scheduler 501 generates the information indicating via which antenna and with which coding and modulation methods it will transmit transmission data, and provides the generated information to the AMC controller 505. Therefore, the AMC controller 505 can determine the number of transmission data streams and a size of the transmission data for each individual antenna, based on the information on the transmission antennas.
A multiplexer 503 multiplexes user information bit stream scheduled by the scheduler 501 according to the number of transmission antennas and a data rate for each individual antenna based on the information provided from the AMC controller 505. For example, the multiplexer 503 multiplexes the scheduled user's information bit stream such that the larger amount of data stream should be transmitted via the transmission antenna having a good channel status. In the next process, PARC is applied to the multiplexed data stream. That is, the multiplexed data streams are individually input to channel coding/modulation units 110a to 110m where they are coded and modulated. The coded/modulated data streams are individually input to OFDM modulators 210a to 210m where they are OFDM-modulated. Thereafter, the OFDM-modulated data streams are converted into RF signals, and transmitted via associated antennas 131 to 132.
The system shown in FIG. 5 selects only one user at the transmission time and transmits data streams over the full band. That is, the system is not an OFDMA system. However, it is possible to simply extend the system to an OFDMA system supporting AMC and channel sensitive scheduling by dividing the full system band into sub-channels each composed of adjacent sub-carriers and independently applying PARC to each of the sub-channels. However, because only one user signal is transmitted via a plurality of antennas, SDMA is not implemented.
The two different spatial processing techniques have been described as the conventional MIMO technology.
The first technique, a spatial diversity technique, fixes the number of transmission data streams to one to reduce the change in the channel with the passage of time. The second technique, a spatial multiplexing technique, transmits a plurality of data streams.
The STC coding and SFC coding techniques described in FIGS. 2 and 3 can be classified as the spatial diversity technique. As described above, the diversity technique helps reduce the probability of channel deterioration by reducing the change in the channel, but reduces a large number of channels capable of transmitting data. For this reason, it is known that the spatial diversity technique reduces the system capacity undesirably. However, the spatial diversity helps broaden the coverage for the traffic that the transmitter can hardly change the transmission method according to the channel status, like the broadcast.
Although the STC coding technique and the SFC coding technique were designed to maintain orthogonality in order to obtain the maximum spatial diversity gain, if the adjacent channels change, the techniques cause self-interference undesirably. For example, the STC coding technique helps complement the AMC and channel sensitive scheduling in the fast-moving environment, but decreases in link performance undesirably because the orthogonality is damaged. In the case of the SFC coding technique, because adjacent sub-carriers experience different channel responses in the environment where the time delay spread is considerable, the link performance deteriorates even in this case due to the affect on orthogonality.
The PARC technique described in FIGS. 4 and 5 can be classified as a spatial multiplexing technique. The PARC technique has disadvantages in that reception performance deteriorates in the high-spatial correlation environment. Because the PARC technique performs AMC by feeding back only the channel status of each individual transmission channel, it undesirably transmits the data whose amount exceeds the capacity supportable by the channel in the high-spatial correlation environment. The high spatial correlation means that there is a high probability that when one transmission antenna experiences a good channel status, other transmission antennas will also experience the good channel status. However, because the channels experienced by different antennas are similar to each other, the receiver cannot separate the signals transmitted from the different antennas. Therefore, interference occurs between the simultaneously transmitted streams, deteriorating the reception link performance. The PARC technique cannot avoid the deterioration of the reception link performance due to spatial correlation because it was designed on the assumption that the channels have no spatial correlation.
As another problem, the PARC technique does not support SDMA. The system supporting AMC and channel sensitive scheduling improves the system capacity by obtaining a multi-user diversity gain. The multi-user diversity selects a proper user through scheduling in the channel-varying mobile communication environment and transmits data to the selected user. The system capacity decreases undesirably as compared with the environment where the channels do not vary. Accordingly, there is a need for an improved apparatus and method for transmitting/receiving data in a multi-antenna communication system.

Apparatus and method for transmitting/receiving data in a multi-antenna communication system


The objective lens driving device of the present invention for an optical pickup device is provided. The device includes first and second objective lenses, and a lens holder for supporting the first and second objective lenses. The lens holder has a first through-hole for passage of first laser beam and a second through-hole for passage of second laser beam. Where a plane defined by a central axis of the first objective lens and a central axis of the second objective lens is a central plane, a plane perpendicular to the central plane and including the central axis of the first objective lens is a first plane, and a plane perpendicular to the central plane and including the central axis of the second objective lens is a second plane; the first through-hole is asymmetrical with respect to the first plane and/or the second through-hole is asymmetrical with respect to the second plane.

1. Field of the Invention
The present invention relates to an optical disk drive for writing data to, and reading data from, a plurality of types of optical disks having different recording densities, an optical pickup device usable for such an optical disk drive, and an objective lens driving device usable for such an optical pickup device; and more particularly relates to an objective lens driving device, usable for an optical pickup device, having a plurality of objective lens mounted thereon.
2. Description of the Related Art
As disk-type recording mediums (optical disks) usable for data write and/or data read utilizing light, CDs (Compact Discs) and DVDs (Digital Versatile Discs) are currently in wide use. In addition to these disks, BDs (Blu-ray Discs) and other optical disks having a high recording density have been recently proposed and developed. The wavelength of used for such optical disks is 780 nm or the vicinity thereof for CDs, 660 nm or the vicinity thereof for DVDs, and 405 nm or the vicinity thereof for BDs or the like.
It is desired that one optical pickup device should be usable to perform data recording to, and data reproduction from, a plurality of types of optical disks used with different wavelengths of laser beam. In one example of an optical pickup device proposed to realize this, different objective lenses respectively prepared for CDs/DVDS and BDs are mounted on one objective lens driving device.
FIG. 10A shows an exemplary objective lens driving device, in a conventional optical pickup device, having two types of objective lenses mounted thereon. Such an objective lens driving device is described in, for example, Japanese Laid-Open Patent Publication No. 2003-281758.
A lens holder 300 includes a first objective lens setting opening 301 and a second objective lens setting opening 302, which are respectively formed to allow a first objective lens and a second objective lens (not shown) to be mounted therein.
FIG. 10B shows a first through-hole 303 and a second through-hole 304 which pass through the lens holder 300. The first objective lens setting opening 301 and the second objective lens setting opening 302 are respectively open ends of the first through-hole 303 and the second through-hole 304. It is not necessary that the first objective lens setting opening 301 and the second objective lens setting opening 302 have the same diameter or that the first through-hole 303 and the second through-hole 304 have the same diameter.
The first through-hole 303 and the second through-hole 304 are optical paths for laser beam incident from a light source (not shown) provided below the first through-hole 303 and the second through-hole 304 in a focusing direction. The laser beam which has passed through the first or second objective lens is focused at an optical disk (not shown) provided above the first through-hole 303 or the second through-hole 304 in the focusing direction, and the light reflected by the optical disk returns in the corresponding path in the opposite direction back to a detector (not shown) provided on the light source side.
The lens holder 300 also includes a magnetic circuit elastically supported by a spring (not shown) for driving the first or second objective lens independently in the focusing direction perpendicular to a recording surface of the optical disk and in a tracking direction matching a radial direction of the optical disk.
The recent demand for a higher recoding/reproduction speed requires an increased driving force, which in turn requires a movable section including the lens holder 300 to be more lightweight, and accordingly, to have a higher sensitivity. The movable section is also required to have a higher rigidity and thus to have a higher resonance frequency in a high frequency range, so that the movable section is compatible with a control system having an increased gain. Namely, the objective lens driving device is desired to have opposing characteristics of a less weight and a higher rigidity.
In an optical pickup device having two types of objective lenses mounted thereon, the two lenses often have different weights. The material for the lenses is preferably a plastic material for reducing the cost and weight, but glass is occasionally chosen as the material of the objective lens used for laser beam having a wavelength of 405 nm from the viewpoint of the resistance against light. Assuming, for example, the objective lens used for DVDs is formed of a plastic material, the glass objective lens may be three time or more heavier than the plastic objective lens due to the difference in the specific gravity between glass and plastics.
When such lenses having different weights are mounted on the lens holder 300, the weight balance is destroyed and the gravity center is shifted from the center of the movable section. If the entire lens holder 300 is sufficiently large to optimize the positions of the individual lenses, it is possible to set the gravity center at the center of the lens holder 300, which matches the center of the driving force generated by the magnetic circuit.
However, it is preferred that the lens holder 300 is as small as possible in order to fulfill the recent demands for a less weight and a higher rigidity required for an operation in more highly multiplied speed modes. It is also desired that the two lenses are located as close as possible to each other, which significantly restricts the designing freedom. Therefore, it is difficult to optimize the weight balance by lens arrangement.
Where the weight balance is destroyed and thus the gravity center is shifted from the center of the movable section (driving force center), the following problems occur. When a driving force generated by the magnetic circuit is acted on the movable section, a rotation moment is generated due to the center of the driving force being shifted from the gravity center. This causes unnecessary resonance and thus destabilizes the control on the objective lens driving device.
For example, in the example shown in FIG. 10A, the objective lenses are located side by side in the tracking direction. Therefore, the weight balance in the tracking direction is destroyed. As a result, when the movable section is entirely driven in the focusing direction, rolling resonance is generated by which the movable section is rotated with a tangential direction being used as the rotation axis. In a different example where the objective lenses are located side by side in the tangential direction, when the movable section is entirely driven in the focusing direction, pitching resonance is generated by which the movable section is rotated with the tracking direction being used as the rotation axis.

Objective lens driving device, optical pickup device, and optical disk drive


A process for the polymerization of olefin's, including: introducing an olefin and a polymerization catalyst into a polymerization reactor to form a polyolefin, the polymerization reactor including: a fluidized bed region having a top and a bottom; and a motive bed region; wherein a first end of the motive bed region is fluidly connected to the top of the fluidized bed region; and wherein a second end of the motive bed region is fluidly connected to the bottom of the fluidized bed region; and wherein a diameter of the fluidized bed region is greater than a diameter of the motive bed region; circulating at least a portion of the olefin, the catalyst, and the polyolefin through the fluidized bed region and the motive bed region; maintaining a dense-phase fluidized bed within the fluidized bed region; recovering polyolefin from the fluidized bed region, is provided. A reactor system directed to the process is also provided.

It is known that many polymers can be produced as powders in fluid bed reactors where the fluidization is provided by a circulating mixture of gases including one or more monomers. For example, vapor phase polymerization is a common process, widely used for the production of polyolefins, such as ethylene, and polyolefin copolymers. One particularly arrangement of a fluid bed polyolefin process is disclosed in U.S. Pat. No. 4,882,400. Other examples of fluid bed polyolefin technology are described in, for example, U.S. Pat. Nos. 3,709,853; 4,003,712; 4,011,382; 4,302,566; 4,543,399; 4,882,400; 5,352,749; 5,541,270; 7,122,607, and 7,300,987. These patents disclose gas phase polymerization processes wherein the polymerization medium is either mechanically agitated or fluidized by the continuous flow of gaseous monomer and diluent.
One example of a prior art vapor phase polymerization method is illustrated in FIG. 1. A catalyst is fed through supply line 2 into a fluidized bed reactor 4 and, simultaneously, a gaseous olefin is caused to pass through supply line 6 and blown into the bottom of the fluidized bed reactor 4 through a gas distributor plate 8. The gas distributor plate 8 may include, for example, a perforate plate having a plurality of through holes, and is arranged in the vicinity of the bottom of the fluidized bed reactor 4. In this way, a fluidized bed 10 is formed and held in the fluidized state in the fluidized bed reactor 4. Polymerization of the monomer is carried out in the fluidized bed 10, and polymer particles produced by the polymerization reaction are continuously discharged through line 12. Unreacted gaseous olefin having passed through fluidized bed 10 has its flow rate reduced in a velocity reduction zone 14 provided in an upper part of the fluidized bed reactor 4, where the vapor velocity is reduced so as to avoid or reduce entrainment of polymer particles from fluidized bed 10. The unreacted monomer is discharged outside the fluidized bed reactor 4 through gas outlet 16 disposed at a top of velocity reduction zone 14. The unreacted gaseous olefin is then recycled via line 18 to the bottom of fluidized bed reactor 4 via compressor 20. Monomer added via line 6 accounts for monomer reacted to form the polymer removed via flow line 12, thus maintaining a constant supply of monomer to reactor 4. The heat of polymerization generated in fluid bed 10 may be removed from the system by cooling the recycle gas in heat exchanger 22.
The active, growing powder in a fluidized bed polyolefin reactor, such as that described in FIG. 1 and the aforementioned patents, contains a wide range of particle sizes. Thus, the powder is referred to as having a broad particle size distribution. Some of the reasons for the broad size distribution are the size range of the initial catalyst particles (or prepolymer particles) charged to the reactor, the difference in catalytic activity of each catalyst particle, the difference in residence time for each growing polymer particle, the agglomeration of polymer particles, and the spalling of polymer particles.
The size distribution of particles can be characterized by various physical measurements relating to the particle mass, physical dimensions, or specific surface area. Two commonly used methods of measurement, owing to ease and reproducibility, are mechanical sieve analysis and the light scattering behavior of a cloud of particles. The very small polymer particles are called fines. As used in the art, the term "fines" refers to some defined fraction of the polymer powder particles that are smaller than the average of the entire population of powder particles present in the fluid bed. Particularly small polymer particles, for example, smaller than 125 microns, are considered fines.
In the fluid bed processes for the production of polyethylene and ethylene copolymers, high levels of polymer powder fines in the reactor pose significant and well known operating difficulties. Within the reactor, a higher level of fines often leads to increased agglomeration of the polymer powder. Outside the reactor, the fines may deposit in the recycle system and grow, fouling the piping, heat exchangers, compressors, and the reactor inlet gas distribution grid.
Inside the reactor, fines are a leading contributor to the formation of powder agglomerates. For various reasons, fines tend to segregate into certain poorly circulated and poorly cooled regions of the reactor. Exacerbating the segregation problem is the tendency of fines to have higher than average catalytic activity, causing the fines to be hotter than the average particle. This higher catalytic activity in fines is due to higher concentrations of active catalyst components in the fines and due to short diffusion paths for monomers and co-catalyst molecules.
One undesirable place at which fines accumulate is along the reactor vessel wall in the zone occupied by the main fluid bed. This accumulation is believed to occur because fines are more greatly affected by static forces due to their larger ratio of surface area (static charge) to mass (inertia). Thus, fines can cling by static electric forces to the electrically grounded metal wall of the reactor. Polymerization in the stagnant layer of reactor wall fines releases heat which can lead to melting and fusing of polymer into sheets along the vessel wall. These sheets of fused polymer may grow quite large before coming loose and falling into the fluid bed. Once fallen into the main fluid bed, such sheets can obstruct powder fluidization, circulation, and withdrawal. In some cases, the sheets may be so large as to significantly disrupt the normal fluidization and circulation of gas and solids of the entire fluid bed, leading to extensive fusing of the main bed. When powder withdrawal slows or the bed fuses, the reactor production must be stopped and the reactor vessel opened for cleaning. This is a very costly production outage.
Another undesirable place where fines accumulate is in the velocity reduction section of the reaction vessel. The velocity reduction section (disengaging zone) of the reactor is a region of expanded cross-sectional area that is above the zone in which bed level normally resides. The purpose of the expanded area is to reduce the velocity of the fluidizing gas in order to minimize the entrainment of fine particles in the gas leaving the reactor. In the disengaging section, fines tend to concentrate in the regions of lower gas velocity nearer the downward sloping vessel wall. In fact, it is intended that most of the fines fall onto the sloped wall of the disengaging section and slide downwards and back into the main fluidized bed. However, when the concentration of fines increases in the disengaging section, the polymerization heat load on the sloped wall becomes larger. This can be observed by increasing temperatures seen from indicators placed in the sloped wall in the disengaging section. The concentration of fines and resulting heat can become great enough to lead to melting and fusing of the powder into sheets along the sloped wall. These sheets will tend to grow until their own weight and hydrodynamic forces cause them to fall into the main fluid bed, there, as discussed above, obstructing powder withdrawals and possibly causing more extensive bed fusing. As with the above, when either of these occurs, the reactor production must be stopped and the reactor vessel opened for cleaning.
In addition to problems caused inside the reactor, problems are also caused by fines outside the fluid bed reactor vessel. Some fines will leave the reactor vessel in the overhead piping that carries the recycle gas away for cooling and compression. The exiting fines may attach to surfaces of piping, heat exchangers, and other process equipment in the recycle loop. Recycled fines may also settle in regions of lower gas velocity, such as the bottom of the reactor underneath the distribution grid for the fluidizing gas.
Because fines exiting the reactor retain their catalytic activity, they continue to react outside the reactor. Thus, fines depositing in the recycle system equipment grow and fuse to create skins, sheets, and lumps of polymer. These skins, sheets, and lumps reduce heat transfer efficiency and modify mass flow in the recycle gas piping and equipment. Also, some fines will return to the reactor via the recycle system. Because the temperature and gas composition are very different at some locations in the recycle system, the polymer produced outside the reactor may have very undesirable properties. Although a minute fraction of the total polymer production, the fines returning to the reactor can nonetheless seriously impact the suitability of the overall product. The presence of non-homogeneous polymer fines in the final product can significantly affect the quality of the product and resulting articles produced therefrom, such as the formation of gels in polyethylene films.
Several methods for addressing the operating problems associated with fines discussed above are presented in U.S. Pat. Nos. 4,956,427, 4,882,400, 4,803,251, 4,532,311, 5,126,414, 4,933,149, 5,352,749, 5,428,118, 5,461,123, 6,905,654, European Patent Application Publication EP 453,116 A1 and U.S. Patent Application Publication No. 2008/0027185.
In light of the above, there exists a need in the art for gas-phase reactors that may be operated in a manner to avoid the formation of at least one of polymer sheets, skins, lumps, and agglomerates.

Reactor systems and processes for using the same


A method according to the invention ensures optimal memory configuration in a computer: A determination is made whether performance can be improved by rearranging the DIMMs that are installed in the computer. If so, then a user of the computer is notified that the DIMMs can be rearranged to improve performance.

In most computer systems, a memory controller provides an interface between main memory and many of the other components of the system including the CPU. Such a memory controller typically is responsible for handling data flow to and from main memory and governs support for different types, sizes and speeds of memory devices. For many years, most memory controllers were of the single-channel variety. Recently, however, dual-channel memory controllers have risen in popularity. Dual-channel memory controllers typically support similar types, sizes and speeds of memory devices as did single-channel controllers, but dual-channel controllers increase bandwidth by adding a second data path to and from the devices.
While dual-channel controllers provide a performance benefit relative to single-channel controllers, they also impose certain limitations on memory configuration: Usually, dual-channel memory controllers require that the slots of channel A be populated identically with the slots in channel B. In other words, if a slot in channel A is populated with a dual inline memory module ("DIMM") having certain size and speed characteristics, then the corresponding slot in channel B must be populated with a DIMM having the same size and speed characteristics as that in channel A. If not, then either the system will hang or the memory controller will default to single-channel operation. Either result deteriorates system performance.

Method for ensuring optimal memory configuration in a computer

Hewlett-Packard Development Company, L.P.


A method for bit recovery in a data channel includes the steps of: inputting a read channel signal, providing a main signal processor for adaptive bit recovery from the read channel signal, providing an auxiliary signal processor for bit recovery from the read channel signal, using an output of the auxiliary signal processor for adaptation of the main signal processor, and outputting a recovered binary bit stream.

In many of today's applications large amounts of data need to be stored. In the area of Personal Computers and in addition in the area of consumer electronics harddisks as fixed storage media and optical disks as removable storage media are commonly used for this purpose. Due to emerging incremental data bandwidth needs (HDTV, fast copy) the data throughput of the applications is increasing continuously. Consequently, the corresponding disk devices have to provide the appropriate data and data bandwidth, too. Therefore, a plurality of high density optical recording media have been developed, e.g. the Digital Versatile Disk (DVD) or the Blu-Ray Disk (BD) using blue laser light for reading and recording.
The readout signal from such high density optical disks is deteriorated mainly by two factors. The first factor is the small ratio between the amplitudes of the shortest run-length symbols and the longest run-length symbols (e.g. the I2/I8 ratio in the case of Blu-Ray disks), which is caused by the high information density, i.e. the ratio between the diameter of the laser spot and the physical length of a channel bit. This ratio is time-variant due to effects like disk tilt or de-focusing. The second factor is the waveform asymmetry, which is caused by an unequal length of the pits and lands due to recording and/or mastering imperfections. This asymmetry is also known as domain bloom.
In "Combined Adaptive Controlled Partial Response and Maximum Likelihood Signal Processing for High-Density Optical Disks", Jpn. J. Appl. Phys. Vol. 42 (2003), pp. 924-930, Takehara et al. propose to use both an adaptive equalizer and a Viterbi detector with adaptive reference levels in order to allow a highly reliable recovery of the stored user data. However, both adaptation schemes rely on the recovered bit stream and are in fact gain control loops. Therefore, the adaptation is difficult to control and tends to instability. Furthermore, this detector arrangement has problems at start-up, i.e. it needs a proper pre-setting of all coefficients and a complicated range checking during the adaptation process. Finally, an additional automatic gain control loop, which is also necessarily present, forms a third loop which modifies the gain.
It is an object of the invention to propose an improved method for adaptive bit recovery.


An apparatus comprising a fiber placement head assembly and an infrared heating assembly is provided. The fiber placement head assembly includes a compaction roller assembly and a feeder assembly. An infrared heating assembly, a cooling mechanism, temperature sensors, and a controller are operably coupled to the fiber placement head assembly. The infrared heating assembly includes an infrared heater that generates a heating profile. The heating profile defines a heating zone on either a tool or previously laid tows. If the burn point of either the tool or previously laid tows within the heating zone is approached, the controller, which receives temperature readings from the temperature sensors, simultaneously disables the infrared heater and activates the cooling mechanism. As such, the tool and the previously laid tows are protected from being ruined due to an over temperature condition.

Automated fiber placement machines are widely used to manufacture parts, components and structures from composite material. The materials used in automated fiber placement are typically composed of longitudinal fibers and resin consolidated into tapes, or thin strips, commonly known as "tows." Anywhere from a single tow to several of the tows arranged side-by-side are fed out of the fiber placement machine as the fiber placement machine lays and compacts a "ply" or "course" over and onto a tool. The number of tows released by the fiber placement machine and placed over and onto the tool depends on several factors, including, for example, the size, dimensions, shape, and contour of the tool. As each ply or course is laid upon a previously laid and compacted ply or course, a composite part is built up and formed, in layer-by-layer fashion, upon the tool.
The automated fiber placement process generally described above enables the construction of complex composite structures having steered or curvilinear fiber paths. This method of producing composite structures is more cost effective than manual methods. It also provides an improved structural efficiency due to its ability to orient the fibers along local internal loads paths, which potentially results in lighter and stronger structures and a lower cost of making the part when compared to structures made by other production methods.
During the automated fiber placement process, the tows are typically heated as they are being laid over and onto the tool or over a previous layer of tows. The heat supplied to the tows causes them to become tacky (a.k.a., sticky). When tacky, the individual tows bond and join together with adjacent or proximate tows to form a cohesive ply or composite part.
Unfortunately, the fiber placement machinery today is limited in its use partially due to the inability to quickly heat the tool or the carbon fiber tows proximate the point of application and compaction. Previous methods of heating require complex, expensive assemblies and use the heat transfer method of convection. Blowing hot air in the direction of the tool or the previously laid tows is a somewhat effective heating method, but it is slow reacting and is much more difficult to control.
The invention provides a system and method of heating the tool or the previously laid tows proximate the point of application and compaction without the associated problems and drawbacks existing with the current methods and apparatuses. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.

System and method for heating carbon fiber using infrared radiation in a fiber placement machine


The present application relates to a safety valve, in particular a safety valve which can be released by manual operation and automatic operation. The safety valve comprising: valve body having an inlet, an outlet and a releasing port; and valve core being movable within the valve body between a close position in which the inlet communicates with the outlet and an open position in which the inlet communicates with the releasing port, the valve core comprises a resilient member which biases the valve core to the close position; wherein the position of the valve core can be manually or automatically controlled such that the valve core is able to switch between the close position and the open position, fluid flows from the inlet to the outlet in the close position and flows from the inlet to the releasing port in the open position.

Safety valves are generally needed for a pressure loop in the gaseous pressure device and the hydraulic pressure device in the prior art to guarantee that the pressure will be released when the pressure is beyond a predetermined level, or the pressure can be released as desired. The safety valve can be divided into manual safety valve and automatic safety valve according to the trigger methods. The automatic safety valve will automatically open to release the pressure without manual input when the pressure is beyond the pressure threshold. The manual safety valve will manually open to release the pressure by manual operation or outside input. In order to prevent the risk of the failure of the automatic safety valve, it is preferred that a manual safety valve is provided together so that over pressure can be manually released if needed.
As it is required to provide two safety valves in the pressure loop, the configuration of the pressure loop would be more complicated. Moreover, the space would be a prominent issue in some applications. Two safety valves would possess more space, which is not desired.


According to embodiments of the present invention, a phase-locked loop (PLL) may include circuitry to select a wide pulse width for the phase-frequency detector control signal when the PLL is in a frequency acquisition stage, a narrow pulse width for the phase-frequency detector control signal when the PLL is in a phase capture stage, and a wide pulse width of the phase-frequency detector control signal when the PLL is in a lock stage.

1. Field
Embodiments of the present invention relate to integrated circuit devices and, in particular, to phase-locked loops.
2. Discussion of Related Art
Integrated circuits, such as communication chips, microprocessors, micro-controllers, and/or other devices, often operate at relatively high frequency. The frequency may be in the gigahertz (GHz) range, and future generations of devices may operate even faster.
The devices' operation may be stabilized by a clock source. The clock source may have a phase-locked loop. A phase-locked loop is a circuit or device that compares the phase of two signals, such as for example, a reference signal and a voltage-controlled signal. A phase difference between the two signals produces an error voltage that locks the frequency of the voltage-controlled signal to that of the reference signal. Traditional phase-locked loops have limitations, however.

Phase-locked loop having dynamically adjustable up/down pulse widths


A vinyl chloride resin composition comprising 100 parts by mass of a vinyl chloride resin and a co-ground mixture of (a) 0.001 to 10 parts by mass of at least one member selected from the group consisting of an organic phosphoric ester compound and a metal salt thereof and (b) 0.001 to 10 parts by mass of a grinding aid. The composition is excellent in transparency, heat stability, and heat discoloration resistance.

1. Field of the Invention
This invention relates to a vinyl chloride resin composition characterized by containing a co-ground mixture of at least one member selected from the group consisting of an organic phosphoric ester compound and its metal salt and a grinding aid.
2. Description of the Related Art
Vinyl chloride resins are used in a wide range of applications; for they are inexpensive and can have their hardness adjusted easily by using a plasticizer.
However, vinyl chloride resins have a light/heat stability problem. It is noted that a vinyl chloride resin is liable to decompose primarily due to dehydrohalogenation during heat molding processing or in use. Hence there have been attempts to improve stability of vinyl chloride resins by addition of a metal compound as a main stabilizer in combination with various co-stabilizers.
A problem is that some of the co-stabilizers have poor compatibility with a vinyl chloride resin only to yield moldings with deteriorated physical properties such as transparency. Another problem is that a poorly dispersible co-stabilizer can cause sudden blackening in spots on the resulting moldings, which is called zinc burning.
Patent Document: 1 discloses an antimicrobial composition for polymeric materials that contains a phosphoric ester compound or a metal salt thereof. The publication gives no mention nor suggestion that the phosphoric ester compound or its metal salt is effective in improving transparency of polymers.
Patent Document: 2 teaches that a phosphoric ester metal salt is usable as a nucleating agent for crystalline resins. A nucleating agent is to become crystalline nuclei of a crystalline resin and produces its effect as being retained inside resin crystals. There is no suggestion of using a phosphoric ester metal salt for noncrystalline polymers.
Patent Document: 1JP-A-2001-220464Patent Document: 2JP-A-58-1736


A method of a coating by additive manufacturing on a turbomachine casing includes depositing on an internal surface of the turbomachine casing a filament of an abradable material to create a three-dimensional scaffold of filaments. A filamentary material deposition system is positioned from the internal surface of the casing; a first layer of the coating is deposited over 360′; a rotation of the filamentary material deposition system is carried out by a first predetermined angle and the filamentary material deposition system is positioned from the deposited layer; a second layer of coating is deposited on the first coating layer, on a sector of the casing; a displacement is carried out corresponding to the first sector already covered, then for the following sectors until 360° is covered; and after having carried out a rotation of the filamentary material deposition system.

The present invention relates to the general field of manufacturing of parts of polymer, particularly thermosetting materials, of metallic, metal alloy or ceramic parts by additive manufacturing and it relates more particularly, but not exclusively, to the manufacture of abradable coatings having acoustic functionalities, particularly for fan casings.
The control of noise nuisances due to airplanes in the vicinity of airports has become a public health challenge. Ever more severe standards and regulations are imposed on airplane manufacturers and on airport managers. Consequently, constructing a silent airplane has become a powerful selling point over the years. At present, the noise generated by airplane motors is attenuated by localized reaction acoustic coatings which allow reducing the sound intensity of the engine over one or two octaves, based on the principle of Helmholtz resonators. These coatings appear conventionally in the form of composite panels consisting of a rigid plate associated with a honeycomb core covered with a perforated skin located at the nacelle or the upstream and downstream propagation conducts. However, in new engine generations (for example in turbofan engines), the zones available for acoustic coatings are caused to be substantially reduced, as in the UHBR (ultra-high bypass ratio) technology. Moreover, these casing zones of composite material are likely to have forming defects which it is appropriate to compensate with an additional machining operation prior to the installation of the coating.
It is therefore important to propose new methods and/or new materials (particularly porous materials) allowing eliminating or significantly reducing the noise level generated by airplane engines, particularly during the takeoff and landing phases, and over a larger frequency range than currently, including the low frequencies, while retaining the performance of the engine. That is the reason for which new noise reduction technologies are currently sought to reduce this nuisance, as well as new acoustic treatment surfaces, this with minimum impact on the other functionalities of the engine such as specific fuel consumption, which constitutes an important economic advantage.
Yet within airplane engines, the noise originating in the fan is one of the primary contributors to noise nuisances, favored by the increase in the bypass ratio which these new airplane generations seek.
Moreover, it is currently customary and advantageous to have recourse to additive manufacturing methods instead of traditional foundry, forging and mass machining methods, to easily and rapidly produce at reduced cost three-dimensional complex parts. The aeronautical field lends itself particularly well to the use of these methods. Among these can be cited for example the wire beam deposition method.

Method for in situ additive manufacturing of a coating on a turbomachine casing


A stabilized aqueous slurry of magnesium hydroxide and a method for preparing the same are provided. The method involves an aqueous magnesium hydroxide slurry prepared with a combination of (a) one or more polymeric dispersants and (b) one or more water-soluble alkali metal salts. Slurries prepared according to the invention are less susceptible to increases in viscosity upon standing and remain flowable after several days.

Magnesium hydroxide is used in large quantities in various applications including toothpaste additives and as an acid neutralizer. Magnesium hydroxide Mg(OH).sub.2 ! is also the precursor in the manufacture of magnesium oxide (MgO) which is used in antacid formulations and as a pigment in the paper industry. It is desirable to be able to ship and store magnesium hydroxide as a high solids aqueous slurry. However, these slurries are fairly unstable and form either gels or hard-pack sediment upon standing, thereby rendering the slurries difficult to use and potentially damaging to piping, pumps, and other slurry handling mechanical equipment.
Magnesium hydroxide and magnesium oxide slurry stability has been the subject of extensive research and has been a long standing problem for the magnesium hydroxide industry. The art has addressed the problem by focusing on methods of reducing the viscosity of high solids magnesium hydroxide slurries. U.S. Pat. No. 4,230,610 teaches a method of reducing the viscosity of magnesium oxide slurries by using 0.1 to 5.0 percent by weight of poly(acrylic acid) neutralized to a pH of from about 8.0 to about 12.0. U.S. Pat. No. 4,375,526 teaches a method of reducing the viscosity and enhancing the stability of magnesium hydroxide slurries by using anionic polymers and copolymers. U.S. Pat. No. 4,430,248 teaches a method of reducing the viscosity of magnesium hydroxide slurries by using cationic polymers and copolymers.
Those approaches are somewhat effective in reducing the viscosity of magnesium oxide and magnesium hydroxide slurries but I have found that these approaches are not satisfactory for maintaining the stability of the slurries over an extended period of time.
It is an object of this invention to provide a method of preparing stable aqueous slurries of magnesium hydroxide.


Disclosed are an ultrasound diagnostic apparatus and an ultrasound image producing method capable of producing a spatial compound image with reduced artifacts. Reception data of frame images is repeatedly acquired in a data acquisition cycle of four frames such that, of three frame images for use in producing a spatial compound image, the angle difference in steering angle between two frames for which the acquisition of reception data is most temporally separated is smaller than a maximum value among the angle differences in steering angle between two frame images among three frame images having different steering angles, and each time reception data of two frame images or reception data of another two frame images is acquired, three frame images sequentially produced based on reception data for three frames sequentially acquired hitherto are synthesized to produce a spatial compound image.

1. Field of the Invention
The present invention relates to an ultrasound diagnostic apparatus and an ultrasound image producing method, and in particular, to an ultrasound diagnostic apparatus and an ultrasound image producing method which synthesize a plurality of frame images having different steering angles of an ultrasonic beam to produce an update image (spatial compound image).
2. Description of the Related Art
An ultrasound diagnostic apparatus using an ultrasound image has hitherto been put into practical use in the field of medicine. In general, in this type of ultrasound diagnostic apparatus, an ultrasound image is produced by transmitting an ultrasonic beam from a transducer array having a plurality of transducers arranged therein toward a subject, receiving an ultrasonic echo from the subject by the transducer array, and electrically processing the reception signal.
In the ultrasound diagnostic apparatus, while a two-dimensional tomographic image in the subject can be acquired in real time by scanning the ultrasonic beam, a plurality of reflected waves from a fine structure in the subject interfere with one another to cause speckle noise, and speckle noise is one of the factors for causing deterioration in image quality of the ultrasound image.
As a method of reducing speckle noise, for example, a spatial compounding method disclosed in JP 2013-141519 A is known. In the spatial compounding method, a plurality of frame images are produced by transmitting an ultrasonic beam from different directions toward the same region in the subject, and a plurality of frame images are synthesized to produce one spatial compound image. Since the pattern of speckle noise fluctuates according to the transmission direction of the ultrasonic beam, a plurality of frame images produced by transmitting the ultrasonic beam from different directions are synthesized, whereby it is possible to reduce speckle noise.
For example, as shown in FIG. 12, a frame image A based on reception data acquired by transmitting and receiving an ultrasonic beam in a direction perpendicular to a transducer array, that is, in a direction of a steering angle of 0 degrees, a frame image B based on reception data acquired by transmitting and receiving an ultrasonic beam in a direction of a steering angle −a, and a frame image C based on reception data acquired by transmitting and receiving an ultrasonic beam in a direction of a steering angle +a are repeatedly produced in a three-frame cycle in the same order, and each time reception data of one frame is acquired, the frame images for three frames including previous two frame images are synthesized to produce a spatial compound image. With this, the spatial compound image made from the frame images A, B, and C corresponding to the three kinds of steering angles is constantly updated.
However, in the ultrasound image, in addition to speckle noise, patterns, such as acoustic shadow, different from an actual structure are produced, and these patterns are generated to have different shapes at different angles according to the steering angle of the ultrasonic beam to be transmitted and received. For this reason, if the inside of the subject is about to be observed by the spatial compound image to be sequentially updated while moving the transducer array along the body surface of the subject, the pattern shapes and angles of speckle noise and acoustic shadow fluctuate for each frame, and as a result, there is a problem in that artifacts in which an image vibrates like a wave occur.

Ultrasound diagnostic apparatus and ultrasound image producing method


A system, an apparatus and a method for simulating and assessing a damaged corrosion film in a pipe segment for pitting corrosion potential under field conditions, including variations in cathode to anode ratios. The apparatus has an anode case that holds a working electrode, a first body portion attachable to one end of the pipe segment, and a second body portion attachable to another end of the pipe segment, the first and second body portions defining a corrosion simulation cell. The anode case can be contained within the corrosion simulation cell, and the working electrode can include a test matrix.

Corrosion of metal is a serious problem in many industries, including, among others, construction, manufacturing, petroleum and transportation. In the petroleum industry, for instance, corrosion tends to be particularly pervasive and problematic since the industry depends heavily on carbon steel alloys for its metal structures such as pipelines, supplies, equipment, and machinery. The problem of corrosion in such industries can be extremely challenging and costly to assess and remediate due to the harsh and corrosive environments within which the metal structures must exist and operate. Age and the presence of corrosive materials, such as, for example, oxygen (O2), water (H2O), hydrogen sulfide (H2S), carbon-dioxide (CO2), sulfates, carbonates, sodium chloride, potassium chloride, and microbes in oil and gas production can exacerbate the problem.
There exists an urgent unmet need for a technological solution that can simulate and assess corrosion initiation under field conditions.

Method and system for corrosion simulation and assessment


A hot fluid generating apparatus includes a combustion chamber, a regenerative combustion burner, a fluid passage formed along a wall structure of the combustion chamber, and a device for causing fluid to flow in the fluid passage. The combustion chamber has a flame radiation heat transfer only as a heat transfer portion. A portion of the wall structure opposite to the burner is utilized as a radiation heat transfer portion. A portion of exhaust gas from the burner is recirculated to the supply air to suppress generation of NOx. A portion of the wall structure close to the burner is formed to be a cone.

1. Field of the Invention
The present invention relates to a hot fluid generating or producing device. The fluid may be gas, such as air, or liquid, such as water.
2. Description of Related Art
A typical conventional hot fluid generating apparatus in the form of a hot air generating furnace used for heating or drying is illustrated in FIG. 11. The furnace includes a combustion chamber 73 defined within combustion chamber walls, fire tubes 75, a smoke box 74, a casing 72 and a burner 76. The burner 76 sends a flame 77 into the combustion chamber 73 and exhaust gas is exhausted to the atmosphere through an interior of each fire tube 75, the smoke box 74 and an exhaust duct connected to the smoke box 74. Combustion air is supplied by a fan 71 to an exterior of each fire tube 75 where heat of the exhaust gas is transferred to the supply air by convection and then is further heated by radiation from the flame when the supply air passes through a passage 78 between the wall of the combustion chamber 73 and the casing 72. The heated air is supplied via a duct to a thermal equipment (not shown) requiring the heated air.
However, the conventional furnace has the following problems:
1 In combustion conducted using the conventional gun-type burner, a hot spot is generated in a wall of the combustion chamber and a concentrated thermal stress is caused at the hot spot. To endure the concentrated stress, grading-up of the wall material is necessary, accompanied by an increase in cost. The reason for causing the hot spot is that a flame of the conventional gun-type burner has a non-flat temperature distribution having a peak as illustrated in FIG. 12.
2 In the furnace having the conventional gun-type burner, not only the combustion chamber (i.e., a radiation heat transfer portion) but also the fire tube portion (convective heat transfer portion) needs to be provided for obtaining a high efficiency. More particularly, in the combustion chamber of the conventional furnace, heat transfer by convection is weak because substantially no circulation of combustion gas occurs in the combustion chamber and heat transfer by radiation is also weak because a flat and high temperature distribution is not generated in the combustion chamber. Since heat of the combustion gas is not sufficiently transferred to the air flowing in the fluid passage by means of the combustion chamber only, the fire tube portion has to be provided to obtain a high rate of heat transfer. As a result, the furnace is complicated in structure and large in size, resulting in an increase in cost.


A wafer polishing in which a polishing liquid is supplied to a polishing pad for polishing a wafer carried on a carrier head; and the polishing liquid is supplied from one or more polishing liquid supplying devices onto the polishing pad, by a polishing liquid supplying member of the polishing liquid supplying device being positioned close to or in contact with the polishing pad, and is relatively moved against the polishing pad, so that the polishing liquid supplied to the upper portion of the polishing liquid supplying member flows down along the polishing liquid supplying member to be painted on a surface of the polishing pad.

1. Field of the Invention
The present invention relates to a wafer polishing apparatus for chemical mechanical polishing, and a wafer polishing method.
2. Description of the Related Art
Wafers for semiconductor equipments and electronic components are manufactured through processings including cutting, polishing, and the like. Recently, development of semiconductor technology has promoted miniaturization and multi-layer wiring in a design rule for semiconductor integrated circuit, and larger diameter wafers have been used from the view of reducing costs. In such a context, when a pattern layer is formed on a previous pattern layer in a conventional way, due to the concavo-convex profile of the previous pattern layer, it is difficult to form an accurate pattern thereon, which often leads to defects.
So, a planarization process has been used to planarize a surface of a pattern formed layer before another pattern layer is formed thereon. In the planarization process, frequently chemical mechanical polishing (CMP) is used. When a wafer is polished in chemical mechanical polishing, a wafer carrier head carries the wafer and holds the wafer against a rotating polishing pad at a predetermined pressure, and then a polishing liquid such as slurry or chemical is supplied between the polishing pad and the wafer.
In the polishing by chemical mechanical polishing, a polishing liquid supplied onto the polishing pad is a significant factor which influences the result of polishing, and a consistent supply of a polishing liquid to a polishing pad is required to uniformly polish wafers.
Because an oversupply of a polishing liquid increases the cost for polishing, a consistent supply of a polishing liquid needs to be effectively performed by a small amount of a polishing liquid to a polishing pad.
Conventionally, to address the above problem, grooves are formed in a polishing pad to effectively distribute a polishing liquid over an entire surface of the polishing pad, and the grooves are in shapes having various designs (see a document: G. P. Muldowney, Optimization of CMP Pad Groove Arrays for Improved Slurry Transport, Wafer Profile Correction, and Defectivity Reduction, Proceeding of CMP-MIC (2005). pp 156-167).
However, a polishing liquid needs to be transported to a surface of a polishing pad, not into the grooves, for polishing. Therefore, there has been a need for a method to effectively supply a polishing liquid to a surface of a polishing pad, not into grooves formed in the polishing pad.
In order to address the problem, apparatuses such as a wafer polishing apparatus in which a position to supply a polishing liquid can be changed by using a movable arm, and a polishing apparatus in which a polishing liquid is sprayed in a form of mist and a squeegee is provided to spread the polishing liquid on a surface to be polished have been suggested (for example, see Japanese Patent Application Laid-Open No. 2004-63888, Japanese Patent Application Laid-Open No. 11-70464, and Japanese Patent Application Laid-Open No. 10-296618).

Wafer polishing apparatus and wafer polishing method


A control method and device for uplink access transmission power are provided that can control inter-cell interference in a radio communications system. In a radio communications system including a plurality of radio communication devices which control a plurality of cells respectively, each radio communication device detects an uplink access delay in its own cell, compares the uplink access delay with a target delay, and, based on the result of this comparison, controls a value related to uplink access transmission power.

1. Field of the Invention
This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2007-120298, filed on Apr. 27, 2007, the disclosure of which is incorporated herein in its entirety by reference.
The present invention relates to a radio communications system having a plurality of radio zones (hereinafter, referred to as cells) and, more particularly, to a method and a device for controlling the transmission power of an uplink access control signal.
2. Description of the Related Art
In a mobile communications system, for a base station and a mobile station to perform data communication, they need to establish synchronization between them in advance. Since initial access from the mobile station in particular is not always in synchronization, the base station requires some procedure for uplink synchronization with the mobile station.
According to Long Term Evolution (LTE), which is being standardized by the 3rd generation partnership project (3GPP), a random access channel (RACH) and an uplink shared channel (UL-SCH) are provided for uplink synchronization and uplink data transmission. The RACH is a channel to transmit a control signal for the establishment of uplink synchronization and further to request a resource for the transmission of uplink data. To establish uplink synchronization without a long delay, it is preferable that the probability of RACH transmission collision be reduced as low as possible (see 3GPP TS 36.300 V.1.0.0, Mar. 19, 2007). On the other hand, the UL-SCH is a channel to transmit data and Layer-2/Layer-3 control packets.
FIG. 1A is a diagram schematically showing a generic structure of a mobile communications system according to LTE, and FIG. 1B is a resource structure diagram schematically showing radio resources based on both frequency-division and time-division techniques.
In wideband code division multiple access (WCDMA), a RACH and an enhanced dedicated channel (EDCH) share the same frequency resource, multiplexed by using different spreading and scrambling codes. On the other hand, in LTE, a plurality of frequency-divided and time-divided resources are shared by a RACH and an UL-SCH exclusively of each other. Specifically, the LTE uplink has a resource structure in which a system bandwidth of 10 MHz is time-divided into time intervals of 1 msec, each of which is further frequency-divided into widths of 1.25 MHz. Referring to FIG. 1B, each of t1, t2, . . . on the horizontal axis corresponds to a 1-msec-long time resource, and each of FB#1, FB#2, . . . on the vertical axis corresponds to a 1.25-MHz-wide frequency resource. Hereinafter, one rectangular block defined by one time resource and one frequency resource as shown in FIG. 1B will be simply referred to as "resource."
It is each base station eNB that determines how to allocate such system resources to the RACH and UL-SCH. In general, a RACH resource is periodically allocated as shown in FIG. 1B so that a mobile station UE can gain access to the base station without a long delay. It is also possible to allocate a plurality of RACH resources at a time and thereby secure a sufficient RACH access capacity. Each base station eNB generally broadcasts information indicative of which resources) is allocated to the RACH Therefore, every mobile station UE (User Equipment) in a cell can gain access to the RACH resource(s) whenever the mobile station UE needs, in accordance with the broadcast information.
In LTE, some were of the opinion that there was no need to control RACH transmission power, because it had been decided at the beginning that the same frequency band was not shared between the RACH and UL-SCH. In the case where the RACH and UL-SCH are frequency-divided, even if a mobile station UE performs RACH transmission at maximum transmission power, no interference occurs with the UL-SCH transmission of another mobile station UE. Accordingly, there is no significant reason to control RACH transmission power at least within a single cell, from the viewpoint of the occurrence of interference.
However, in the case where a plurality of resources are shared by the RACH and UL-SCH exclusively of each other as shown in FIG. 1B, and where resource allocation is determined in each cell, there is a possibility that the same resource that is allocated for RACH transmission in one of neighboring cells may be allocated for UL-SCH transmission or RACH transmission in the other cell. Accordingly, when a mobile station UE is performing RACH transmission to its serving cell at maximum transmission power, the possibility cannot be ignored that this RACH transmission will interfere with UL-SCH transmission or RACH transmission performed in a neighboring cell. To prevent such inter-cell interference, it is preferable to control RACH transmission power by using some method.
For one of the methods for reducing inter-cell interference as much as possible, power ramping control has been proposed (see 3GPP TS 36.300 V.1.0.0, Mar. 19, 2007). Hereinafter, RACH transmission power control through power ramping will be described briefly.
FIG. 2A is a sequence diagram showing a procedure of uplink access through a RACH, and FIG. 2B is a schematic time chart showing an example of the power ramping performed before synchronization is established through a RACH. For example, when a mobile station UE desires to transmit data, the mobile station UE first receives a broadcast channel (BCH) broadcast by a base station eNB, thereby acquiring an initial coefficient K and RACH resource information. The mobile station UE then calculates initial RACH transmission power Pinit by using a path loss PLOSS, which is measured from a pilot signal (reference signal), and the initial coefficient K (for example, Pinit=K×PLOSS). Thus, the initial RACH transmission power Pinit is set so that the reception quality of a RACH signal received by the base station eNB will be kept at a desired level. The mobile station UE performs RACH transmission using a RACH resource at this initial transmission power Pinit. Upon arrival of this RACH transmission at the base station eNB, the base station eNB sends a RACH response including a value for timing adjustment back to the mobile station UE, whereby the mobile station UE can establish physical-layer synchronization. After the establishment of synchronization, the mobile station UE sends a scheduling request to the base station eNB. The base station eNB allocates UL-SCH resources in response to this request and sends back a transmission grant. Thus, the mobile station UE transmits data packets by using the allocated UL-SCH resources.
However, when a RACH signal does not arrive at the base station eNB due to an increase in the level of interference or due to the occurrence of fading, the mobile station UE receives no RACH response even after a predetermined period of time has passed. Therefore, the mobile station UE increases its RACH transmission power by a predetermined step Pdel at each time as shown in FIG. 2B until the mobile station UE receives a RACH response. Such increasing in RACH transmission power step by step is called "power ramping". A period during which the RACH transmission power is increased step by step, starting from the first RACH transmission, is called "power ramping period," and this power ramping period plus an elapsed time before physical-layer synchronization is established upon receipt of the RACH response is called "RACH access delay." Accordingly, when a RACH transmission collision occurs, the RACH access delay increases.
Moreover, the sum of the RACH access delay and an elapsed time between the establishment of physical-layer synchronization and the establishment of connection upon receipt of the transmission grant is called "LTE call setup delay." The LTE call setup delay also serves as a key performance indicator (KPI), an object of evaluation, of system performance.
By RACH transmission power control through the power ramping, the RACH transmission power of the mobile station UE can be set at such a level that sufficient RACH reception quality is secured at the base station eNB while interference to a neighboring cell is suppressed. For example, in the case of a mobile station UE having a low path loss, since power ramping can be started from a lower power level than the initial RACH transmission power Pinit, the mobile station UE can establish synchronization by RACH transmission at lower transmission power than a mobile station UE having a high path loss. Accordingly, uplink interference to a neighboring cell can be effectively prevented.
However, according to the above-described power ramping control, once RACH interference occurs between neighboring cells, a phenomenon called "party effect," which will be described below, may be caused, in which the initial RACH transmission power increases in all cells one after another.
FIG. 3A is a diagram schematically showing how neighboring cells interfere with each other, FIG. 3B is a graph showing the RACH access delay varying with the level of RACH interference, and FIG. 3C is a graph showing the RACH access delay varying with the load of RACH access. Moreover, FIG. 4 is a time chart showing variation in the average RACH access delay and variation in the RACH transmission power offsets to describe the party effect between neighboring cells.
Generally, a base station tries to make the RACH access delay as short as possible because failing in gaining RACH access causes a delay in a call setup or handover procedure. The RACH access delay can be reduced by increasing the initial RACH transmission power as described above. Here, referring to FIG. 3A, it is assumed that the initial RACH transmission power Pinit has been increased in a cell A. This increase in initial RACH transmission power in the cell A causes an increase in RACH interference with a neighboring cell B. When the RACH interference is increased, a base station eNB2 controlling the cell B allows the initial RACH transmission power Pinit to be increased in the cell B in order to shorten the RACH access delay. This increase in initial RACH transmission power in the cell B causes an increase in interference with the neighboring cell A and another neighboring cell C. In each of the cells A and C, since the RACH interference is increased, the initial RACH transmission power is further increased. In this manner, a phenomenon called "party effect" is caused, in which the cause and effect repeat between neighboring cells, whereby the initial RACH transmission power is increased more and more. Accordingly, once interference occurs, the initial RACH transmission power is reciprocally increased between neighboring cells, which causes a chain reaction, resulting in the initial RACH transmission power Pinit being ultimately set at a maximum value in every cell.
Referring to FIGS. 3B and 3C, in general, as the level of RACH interference becomes higher, or as the frequency of RACH access becomes higher (the load becomes larger), the RACH access delay becomes longer. The level of RACH interference can be measured, for example, as the number of failed RACH transmissions (that is, the number of RACH transmissions made before a RACH response shown in FIG. 2B is received), which is reported to a base station from a mobile station present in the cell of the base station. Therefore, the RACH access delay is measured by using this number, and statistical processing is further performed, whereby the average RACH access delay can be obtained. Moreover, the frequency of RACH access (the load of RACH access) can be measured as the number of times a base station receives RACH access from mobile stations present in the cell of the base station. Therefore, this number is similarly subjected to statistical processing, whereby the average RACH access delay can be obtained.
When the thus-measured RACH access delay increases, each base station eNB raises a RACH transmission power offset as shown in FIG. 4 so that the initial RACH transmission power will be increased step by step. This operation causes the above-described "party effect," resulting in the initial RACH transmission power being set at a maximum value in every cell in the end. This is a cause for degradation of the uplink capacity in the entire network.
Such a problem concerns not only the LTE, but may exist in cell-based general radio communications systems using an access scheme (FTDMA) based on a frequency-divided and time-divided resource structure. Particularly in a system in which resource allocation control is individually performed by base stations or radio communication devices controlling respective cells, there is no provision of a mechanism of automatically controlling RACH transmission power in the entire network. Therefore, inter-cell interference cannot be controlled, leading to the easy occurrence of the above-described "party effect."

Control method and device of uplink access transmission power in radio communications system