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Showing papers by "NEC published in 1993"


Journal ArticleDOI
Sumio Iijima1, Toshinari Ichihashi1
17 Jun 1993-Nature
TL;DR: In this article, the authors reported the synthesis of abundant single-shell tubes with diameters of about one nanometre, whereas the multi-shell nanotubes are formed on the carbon cathode.
Abstract: CARBON nanotubes1 are expected to have a wide variety of interesting properties. Capillarity in open tubes has already been demonstrated2–5, while predictions regarding their electronic structure6–8 and mechanical strength9 remain to be tested. To examine the properties of these structures, one needs tubes with well defined morphologies, length, thickness and a number of concentric shells; but the normal carbon-arc synthesis10,11 yields a range of tube types. In particular, most calculations have been concerned with single-shell tubes, whereas the carbon-arc synthesis produces almost entirely multi-shell tubes. Here we report the synthesis of abundant single-shell tubes with diameters of about one nanometre. Whereas the multi-shell nanotubes are formed on the carbon cathode, these single-shell tubes grow in the gas phase. Electron diffraction from a single tube allows us to confirm the helical arrangement of carbon hexagons deduced previously for multi-shell tubes1.

8,018 citations


Journal ArticleDOI
Pulickel M. Ajayan1, Sumio lijima1
28 Jan 1993-Nature
TL;DR: In this article, the authors describe experiments in which annealing of the tubules in the presence of liquid lead results in opening of the capped tube ends and subsequent filling of the tubes with molten material through capillary action.
Abstract: THE recent discovery1 and bulk synthesis2 of nanometre-scale carbon tubules has led to much speculation about possible uses of these graphitic structures3–5. Broughton and Pederson predicted on the basis of computer simulations that open nanotubes may be filled with liquid by capillary suction6. Here we describe experiments in which annealing of the tubules in the presence of liquid lead results in opening of the capped tube ends and subsequent filling of the tubes with molten material through capillary action. The nanotubes thus act as moulds for the fabrication of (possibly metallic) wires, some of which are less than two nanometres in diameter.

1,331 citations


Journal ArticleDOI
01 Apr 1993-Nature
TL;DR: In this paper, it was shown that the oxidation of carbon nanotubes in air for short durations above about 700 °C results in the etching away of the tube caps and the thinning of tubes through layer-by-layer peeling of the outer layers, starting from the cap region.
Abstract: CAPPED hollow carbon nanotubes1,2 can be modified into nanocomposite fibres by simultaneous opening of the caps (by heating in the presence of air and lead metal) and filling of the interior with an inorganic phase3. To generalize this approach, greater understanding is needed of the reaction mechanism between the tube caps and oxygen. Here we report that the oxidation of carbon nanotubes in air for short durations above about 700 °C results in the etching away of the tube caps and the thinning of tubes through layer-by-layer peeling of the outer layers, starting from the cap region. The oxidation reaction follows an Arrhenius-type relation with an activation energy barrier of about 225 kJ mol−1 in air. Heating of closed nanotubes with an oxide (Pb3O4) in an inert atmosphere lowers the activation barrier for the reaction and opening of the tubes occurs at lower temperatures. Contrary to intuition, however, open tubes are much more difficult to fill with inorganic materials than in the one-step filling of tubes reported previously3. But various other experiments might be possible in the inner nano-cavities of the open tubes such as studies of catalysis and of low-dimensional chemistry and physics.

1,026 citations


Journal ArticleDOI
TL;DR: In this article, the first and second-order Raman spectra of closed-carbon nanostructures (nanotubes and nanoparticles) have been measured and compared to those of glassy carbon and highly oriented pyrolitic graphite.

401 citations


Journal ArticleDOI
Sumio Iijima1
TL;DR: In this paper, the production, morphologies and atomic structures of carbon nanotubes are reviewed, and a mechanism for tube growth is discussed on the basis of transmission electron microscopy observations.
Abstract: The production, morphologies and atomic structures of carbon nanotubes are reviewed, and a mechanism for tube growth is discussed on the basis of transmission electron microscopy observations. Capping of carbon nanotubes is explained nicely in terms of pentagons; distributions of pentagons in a hexagon network cause various cap morphologies. Heptagons, resulting in negative curvature into a graphitic plane, also provide a variety of graphitic structures. Pentagons and heptagons seem to play a key role in tube growth. On the basis of the consistency of various tube morphologies, we propose a model for tubule growth, in which the tubules are open at their ends while growing in the carbon arc plasma. To support this open-end growth mechanism, other evidence such as layer-by-layer growth on the tube surfacces and “over-shooting growth” on tube tips is given.

213 citations


Journal ArticleDOI
TL;DR: The simulation results show that the injection of autocorrelation into interarrival times, and to a lesser extent into service demands, can have a dramatic impact on performance measures.
Abstract: The performance of single-server queues with independent interarrival intervals and service demands is well understood, and often analytically tractable. In particular, the M/M/1 queue has been thoroughly studied, due to its analytical tractability. Little is known, though, when autocorrelation is introduced into interarrival times or service demands, resulting in loss of analytical tractability. Even the simple case of an M/M/1 queue with autocorrelations does not appear to be well understood. Such autocorrelations do, in fact, abound in real-life systems, and worse, simplifying independence assumptions can lead to very poor estimates of performance measures. This paper reports the results of a simulation study of the impact of autocorrelation on performance in an FIFO queue. The study used two computer methods for generating autocorrelated random sequences, with different autocorrelation characteristics. The simulation results show that the injection of autocorrelation into interarrival times, and to a lesser extent into service demands, can have a dramatic impact on performance measures. From a performance viewpoint, these effects are generally deleterious, and their magnitude depends on the method used to generate the autocorrelated process. The paper discusses these empirical results and makes some recommendations to practitioners of performance analysis of queuing systems.

187 citations


Patent
Tetsuya Homma1, Mieko Suzuki1
14 Apr 1993
TL;DR: In this article, a method of manufacturing a semiconductor device, incorporating the steps of: performing reactive ion etching using a fluorine compound gas to surface-treat the lower level wirings which permits selective deposition of the second silicon oxide film, selectively depositing a second silicone oxide film between said lower level Wirings by a CVD method using an organic silicon compound gas and an oxidizable gas as source gases, depositing an entire surface and forming through holes connected to the lower Wiring; and forming upper level WIRings connected with the lower-level
Abstract: A method of manufacturing a semiconductor device, incorporates the steps of: performing reactive ion etching using a fluorine compound gas to surface-treat the lower level wirings which permits selective deposition of the second silicon oxide film; selectively depositing a second silicon oxide film between said lower level wirings by a CVD method using an organic silicon compound gas and an oxidizable gas as source gases; depositing a third silicon oxide film on an entire surface and forming through holes connected to the lower wirings; and forming upper level wirings connected to the lower level wirings. Further, an additional silicon oxide film can be deposited on the major surface so as to form a side wall thereof on the lower level wirings. The reactive ion etching is then performed.

182 citations


Patent
Narushi Ito1
27 Aug 1993
TL;DR: In this paper, a memory for storing data including a data and a time of fabricating the biosensor, a lot number of the sensors, an effective period of the sensor, the biosensors characteristics, and administrative data of the bios sensors.
Abstract: A biosensor is provided with a memory for storing data including a data and a time of fabricating the biosensor, a lot number of the biosensor, an effective period of the biosensor, the biosensor characteristics, and administrative data of the biosensor. The memory may store additional data such as the measured date, the consecutive (total) measuring time, the measured results, etc.

176 citations


Patent
Akio Tamagawa1
02 Sep 1993
TL;DR: A voltage converting circuit of the charge pump step-up type includes a first circuit means for charging each of first and second capacitors with the voltage of a voltage source at a first timing as mentioned in this paper.
Abstract: A voltage converting circuit of the charge pump step-up type includes a first circuit means for charging each of first and second capacitors with the voltage of a voltage source at a first timing. A second circuit operates to serially connect the charged first capacitor between a positive electrode of the voltage source and a positive voltage output terminal at a second timing so that a positive voltage which is a double of the voltage source voltage, is supplied from positive voltage output terminal. A third circuit operates to the charged first and second capacitors in series between a ground terminal and a negative voltage output terminal at a third timing so that a negative voltage which is a double of the voltage source voltage, is supplied from the negative voltage output terminal. Since the positive voltage and the negative voltage are generated independently of each other, a voltage variation on one of the positive and negative voltage output terminals caused by an external load causes no voltage variation on the other of the positive and negative voltage output terminals.

173 citations


Patent
Kanai Toshihito1
23 Dec 1993
TL;DR: In this article, an average bit error rate y is measured on a receiving side in connection with a communication channel being in use and the transmission power is increased by a predetermined amount on the transmitting side.
Abstract: In order to provide for a mobile communication network of a cellular type a transmission power control system capable of keeping a signal quality constant, an average bit error rate y is measured on a receiving side in connection with a communication channel being in use (step 100). If the average bit error rate y is not greater than a first rate threshold value LV1, transmission power is decreased by a predetermined amount on a transmitting side (step 102). If the average bit error rate y is not less than a second rate threshold value LV2 which is greater than the first rate threshold value LV1 (step 103), the transmission power is increased by the predetermined amount on the transmitting side (step 104). Preferably, an average reception level is additionally measured to adjust the transmission power when the bit error rate is less or greater than the first or the second rate threshold value. The first and/or the second rate threshold value is adaptively adjusted by counting the number of times by which the bit error rate exceeds a predetermined maximum allowable rate. It is possible to use an average carrier to interference ratio with threshold ratio values substituted for the threshold rate values and with a predetermined minimum allowable ratio used.

167 citations


Patent
30 Mar 1993
TL;DR: A teleconferencing video system uses two cameras at each station symmetrically positioned on opposite sides of the optical axis between the speaker and the monitor used to produce an image of the listener.
Abstract: A teleconferencing video system uses two cameras at each station symmetrically positioned on opposite sides of the optical axis between the speaker and the monitor used to produce an image of the listener. The two cameras are used to provide from the two images observed by the cameras a virtual image corresponding to the image that would be viewed by a camera located on the first-mentioned optical axis. This system permits eye contact to be maintained between a speaker and a listener at different stations whereby the feeling of intimacy is enhanced.

Patent
Tetsuya Homma1
26 May 1993
TL;DR: In this paper, a spin-on glass film is used as a flattening material to flatten a multilevel interconnection structure and then an insulator film is formed thereon.
Abstract: Disclosed is a process for producing semiconductor devices of multilevel interconnection structure which are absolutely free from cracking in the insulator films and voids or disconnections in the aluminum wirings. After a fluorine-containing silicon oxide film 4 is formed at a temperature of 50° C. or less using an alkoxyfluorosilane vapor and a water vapor, a spin-on glass film 5 is formed thereon by baking at a temperature of 200° C. or less, which is exposed to the alkoxyfluorosilane vapor to effect condensation of the spin-on glass film at room temperature, and then an insulator film is formed thereon, using the thus treated spin-on glass film as a flattening material.

Patent
Katsumi Sekiguchi1
22 Feb 1993
TL;DR: In this paper, a common channel signaling network comprises a first and a second subnetwork each being composed of interconnected signaling nodes having a service entity, and a common signaling node is provided for protocol conversion.
Abstract: A common channel signaling network comprises a first and a second subnetwork each being composed of interconnected signaling nodes having a service entity. The first and second subnetworks employ different versions of protocol for message transmission. A common signaling node is provided for protocol conversion. As the common signaling node receives a message from a service entity of each subnetwork, it converts the message format to the protocol of the other subnetwork, and transmits it to a service entity of the other subnetwork.

Patent
Shibata Kazuo1
04 May 1993

Journal ArticleDOI
T. Sasaki1, Mitsuhiro Kitamura1, Ikuo Mito1
TL;DR: In this article, a mask-patterned planar planar InP substrate is used to grow InGaAsP/InP layers on typically 2 μm wide open stripe regions between pairs of SiO 2 mask stripes.

Patent
12 Feb 1993
TL;DR: In this paper, a semiconductor device having an IC (Integrated Circuit) chip packaged on a circuit board, and a cap for hermetically sealing the chip is described, where the cap is bonded to the circuit board at the edges of an open end of the chip and the chip at the underside or bottom thereof.
Abstract: A semiconductor device having an IC (Integrated Circuit) chip packaged on a circuit board, and a cap for hermetically sealing the chip. The cap is bonded to the circuit board at the edges of an open end thereof and bonded to the chip at the underside or bottom thereof. To accurately position the chip on the circuit board, the circuit board is provided with a groove or a shoulder in a position where it faces the edges of the open end of the cap. After the chip has been positioned on the circuit board, the cap is bonded to the circuit board via the groove or the shoulder.

Patent
Takao Bakuya1, Masato Matsui1
20 May 1993
TL;DR: In this paper, a trigger definition means which defines activation condition an contents of a triggered operation activated upon execution of updating for a table further defines an operation where an exception is generated for an update request against the constraint given to the table.
Abstract: In a database management system of the present invention, a trigger definition means which defines activation condition an contents of a triggered operation activated upon execution of updating for a table further defines an operation where an exception is generated for an update request against the constraint given to the table, or a triggered operation based on the reference constraint given among a plurality of tables, or a triggered operation based on the relations among the system tables contained in the system directory. The trigger definition means also specifies an operation mode as a condition for execution of the triggered operation. The trigger execution means executes the triggered operation when the trigger operation mode designated by the update request and the operation mode specified in the trigger definition are the same and does not execute any trigger execution when they are not the same.

Journal ArticleDOI
TL;DR: In this article, the growth of nanotubes in carbon arc plasma is described in detail, and the structure and organization of the nanotube deposits observed by SEM and AFM reveal a fractal-like pattern of growth.

Proceedings ArticleDOI
14 Jun 1993
TL;DR: This paper focuses on the problem of mapping a technology independent circuit to a technology specific one, using gates from a given library, with power as the optimization metric, and observes that a significant variation in the power consumption is possible just by varying the choice of gates.
Abstract: The last couple of years have seen the addition of a new dimension in the evaluation of circuit quality - its power requirements. Low power circuits are emerging as an important application domain, and synthesis for low power is demanding attention. The research presented in this paper addresses one aspect of low power synthesis. It focuses on the problem of mapping a technology independent circuit to a technology specific one, using gates from a given library, with power as the optimization metric. Several issues in modeling and measuring circuit power, as well as algorithms for technology mapping for low power are presented here. Empirically, it is observed that a significant variation in the power consumption is possible just by varying the choice of gates. Technology mapping for low power provides circuits with up to 24% lower power requirements than those obtained by technology mapping for area.

Patent
29 Jan 1993
TL;DR: In a vertical power field effect transistor, a side surface of a gate electrode is covered with a side oxide film, and a groove is formed in self-alignment with the side oxide films to extend from a surface area of a silicon substrate between a pair of adjacent gate electrodes, to reach a base region as mentioned in this paper.
Abstract: In a vertical power field effect transistor, a side surface of a gate electrode is covered with a side oxide film, and a groove is formed in self-alignment with the side oxide film to extend from a surface area of a silicon substrate between a pair of adjacent gate electrodes, to reach a base region. A tungsten film is filled into the groove thus formed, and a source electrode-is formed in contact with the tungsten film within the groove.

Patent
21 Oct 1993
TL;DR: In this article, an interface housing which has a fiber spool to store slack in the fiber trunks and a card cage to interface the trunk mounted on the door of the housing is described.
Abstract: An interface housing which has a fiber spool to store slack in the fiber trunks and a card cage to interface the trunk mounted on the door of the housing. The door is hinged on one side of the housing so that, when the door swings open, the entire card cage and fiber spool are clear of the housing and readily accessible and releases the PCB lock. A ribbon connector connects the back plane of the card cage to an interface terminal board on the wall of the housing to which external wire-wrap and/or RJ48X connections may be made. Backup batteries in a tray are disposed along the bottom of the housing and secured in place with a cover. When the housing door swings shut, the fiber optic spool fits in front of back-up batteries in the tray and the card cage fits over the batteries.

Journal ArticleDOI
Yoshinori Ando, Sumio Iijima1
TL;DR: In this article, extremely thin graphite filaments with a tubular structure were grown in carbon deposits formed on the negative electrode during generation of fullerenes by dc carbon-arc discharge evaporation.
Abstract: Extremely thin graphite filaments with a tubular structure were grown in carbon deposits formed on the negative electrode during generation of fullerenes by dc carbon-arc-discharge evaporation. The filaments and small graphite particles coexist in the central portion of the deposits. Three kinds of morphologies of carbon, namely nanotubes, polyhedra and sheets were observed in transmission electron micrographs. The filaments were formed in He, Ar or CH4 gas environment at a pressure between 20-200 Torr.

Patent
Toshihiro Hara1
01 Feb 1993
TL;DR: In this paper, a mobile radio station transmits a response signal to a base radio station where the field intensity is the highest, and the response signal is reported to a radio channel control unit where the contents of the zone register is revised in accordance with the reported response.
Abstract: In a service area of a mobile telephone system, there are plural base radio stations. A mobile radio station in the service area broadcasts a request signal of zone registration. All the base stations in the service area receive this request signal, measure the field intensity of the signal, and transmit the value of the measured intensity to the mobile radio station. The mobile radio station transmits a response signal to a base radio station where the field intensity is the highest. This response signal is reported to a radio channel control unit where the contents of the zone register is revised in accordance with the reported response.

Patent
Fukuzo Yukio1
23 Mar 1993
TL;DR: In this paper, a dynamic random access memory device is used to provide a data path from a data input/output port and a memory cell selected from the memory cell array, and latch circuits are provided in addressing section and the data transferring path for temporarily storing address decoded signal and write-in and read-out data bits in response to latch control signals higher in frequency than the system clock signal, thereby controlling the data stream in a pipeline fashion.
Abstract: A dynamic random access memory device is responsive to a row address signal and a column address signal supplied in synchronism with a system clock signal for providing a data path from a data input/output port and a memory cell selected from the memory cell array, and latch circuits are provided in the addressing section and the data transferring path for temporarily storing address decoded signal and write-in and read-out data bits in response to latch control signals higher in frequency than the system clock signal, thereby controlling the data stream in a pipeline fashion.

Journal ArticleDOI
TL;DR: This paper proposes an architecture of neural networks that have interval weights and interval biases, and develops a learning algorithm derived from the cost function in a similar manner as the BP (Back-Propagation) algorithm.

Patent
Takeshi Hirayama1, M. Fukuma1
16 Apr 1993
TL;DR: In this article, an internal circuit including a plurality of transistors formed on a P-type or an N-type substrate (or a well) which carries out a prescribed signal processing operation during the time of operation mode, a standby detection circuit, a bias potential generating circuit, and a switching circuit which supplies to the substrate (well) the potential of the source electrode and the bias potential in response to the active level and the inactive level, respectively, of the standby detection signal.
Abstract: The semiconductor IC according to this invention comprises an internal circuit including a plurality of transistors formed on a P-type or an N-type substrate (or a well) which carries out a prescribed signal processing operation during the time of operation mode, a standby detection circuit which generates a standby detection signal of active level by detecting standby mode, a bias potential generating circuit which generates a forward bias potential from the substrate (well) of the transistor to the source electrode, and a switching circuit which supplies to the substrate (well) the potential of the source electrode and the bias potential in response to the active level and the inactive level, respectively, of the standby detection signal. At the time of the operation mode, a high speed operation is secured by bringing the transistors to a low threshold voltage by receiving the supply of the bias potential, while at the time of the standby mode, the generation of malfunctions and defective data holding are prevented and the power consumption is saved by raising the threshold voltage of the transistors through a halt of supply of the bias voltage to the substrate (well).

Journal ArticleDOI
01 Oct 1993-Neuron
TL;DR: Findings suggest that UNC-18 participates in the axonal transport system and influences the acetylcholine flow in motor neurons.

Patent
01 Oct 1993
TL;DR: In this article, the authors present an apparatus and method of enabling efficient exchange of packet data routing information for information protocol and information protocol exchange routers by providing different routing table information maintenance modes which a user can select, such as a default mode, a forced mode, and a periodic mode.
Abstract: In a wide-area computer network system providing bandwidth based on network demand, throughput, and delay requirements, distribution of network load over multiple, parallel connections from the originating node to a distinction node, an apparatus and method of enabling efficient exchange of packet data routing information for information protocol and information protocol exchange routers by providing different routing table information maintenance modes which a user can select, such as a default mode, a forced mode, and a periodic mode. In addition, the system provides, a virtual interface as a logical network interface for providing circuit switched connectivity, such as a connection between a host/application and a remote network where a particular path between a host and a remote network is dynamically assigned based on the network traffic demand at that time.

Journal ArticleDOI
TL;DR: In this article, high-resolution electron microscopy images of carbon nano-tubes and nano-partcles are presented, and the symmetric and asymmetric distribution of pentagons at their end surfaces is analyzed.

Patent
N. Tanabe1
22 Oct 1993
TL;DR: In this article, the memory elements are disposed in a matrix such that they are spaced across and along the word lines and paired memory elements whose switching transistors have drains connected to the same bit line are positioned symmetrically with respect to the reference word line.
Abstract: A plurality of word lines extend linearly and parallel to each other. A reference word line is positioned to divide the word lines into two groups of word lines. A plurality of bit lines are folded on the reference word line symmetrically with respect to the reference word line and spaced at intervals from each other. Each of memory elements comprises a capacitive element and a switching transistor having a source connected to the capacitive element, a drain connected to one of the bit lines, and a gate connected to one of the word lines. The memory elements are disposed in a matrix such that they are spaced across and along the word lines and paired memory elements whose switching transistors have drains connected to the same bit line are positioned symmetrically with respect to the reference word line.