Showing papers by "Alcatel-Lucent published in 1996"

Fluorescence intermittency in single cadmium selenide nanocrystals

Abstract: SEMICONDUCTOR nanocrystals offer the opportunity to study the evolution of bulk materials properties as the size of a system increases from the molecular scale1,2. In addition, their strongly size-dependent optical properties render them attractive candidates as tunable light absorbers and emitters in optoelectronic devices such as light-emitting diodes3,4 and quantum-dot lasers5,6, and as optical probes of biological systems7. Here we show that light emission from single fluorescing nanocrystals of cadmium selenide under continuous excitation turns on and off intermittently with a characteristic timescale of about 0.5 seconds. This intermittency is not apparent from ensemble measurements on many nanocrystals. The dependence on excitation intensity and the change in on/off times when a passivating, high-bandgap shell of zinc sulphide encapsulates the nanocrystal8,9 suggests that the abrupt turning off of luminescence is caused by photo-ionization of the nanocrystal. Thus spectroscopic measurements on single nanocrystals can reveal hitherto unknown aspects of their photophysics.

Soluble and processable regioregular poly(3‐hexylthiophene) for thin film field‐effect transistor applications with high mobility

Abstract: The electrical characteristics of field‐effect transistors using solution cast regioregular poly(3‐hexylthiophene) are discussed. We demonstrate that both high field‐effect mobilities (ca. 0.045 cm2/V s in the accumulation mode and 0.01 cm2/V s in the depletion mode), and relatively high on/off current ratios (greater than 103) can be achieved. We find that the film quality and field‐effect mobility are strongly dependent on the choice of solvents. In addition, treating a film with ammonia or heating to 100 °C under N2 can increase the on/off ratio without decreasing the mobility.

Spin-Polarized Intergrain Tunneling in La 2/3 Sr 1/3 MnO 3

Abstract: The magnetoresistance (MR) and the field dependent magnetization have been systematically examined in the low temperature ferromagnetic metallic state of single crystal and polycrystalline ${\mathrm{La}}_{2/3}{\mathrm{Sr}}_{1/3}{\mathrm{MnO}}_{3}$. We find that the intrinsic negative MR in single crystal is due to the suppression of spin fluctuations, and magnetic domain boundaries do not dominate the scattering process. In contrast, we demonstrate that the MR in the polycrystalline samples exhibits two distinct regions: large MR at low fields dominated by spin-polarized tunneling between grains and high field MR which is remarkably temperature independent from 5 to 280 K.

Optical fiber long-period grating sensors.

Abstract: We present a novel class of highly sensitive sensors based on long-period fiber gratings that can be implemented with simple and inexpensive demodulation schemes. Temperature, strain, and refractive-index resolutions of 0.65 °C, 65.75 μ∈, and 7.69 × 10−5, respectively, are demonstrated for gratings fabricated in standard telecommunication fibers.

Distributed redundant database

Abstract: A distributed redundant database architecture (10) primarily for storing a plurality of wireless service subscriber files (84, 86) is provided. The database architecture (10) include a first set of processors (44 46, 48) each having a shared memory (72, 74, 76), where the processors (44, 46, 48) are divided into processor groups (38, 40, 42). A memory storage device (80, 82) is coupled to each processor group (38, 40, 42) in a multi-initiator mode so that each memory storage device (80, 82) is accessible by the processors (44, 46, 48) in its respective processor group (38, 40, 42). The plurality of subscriber files (84, 86) are assigned to the processor groups (38, 40, 42) and further assigned to the processors (44, 46, 48) in each processor group (38, 40, 42) to achieve a substantially even distribution. The plurality of subscriber files are stored in the memory storage devices (80, 82) of respective assigned processor groups (38, 40, 42), and are mapped into the respective shared memories (72, 74, 76) of the processors. A database manager (52, 54, 66) associated with the processors and processor groups is provided for managing the distribution and redistribution of the subscriber files to the processors. A second set of similarly configured processors residing at a remote site (14) maintains a second copy of the subscriber files (84, 86) to provide database backup.

T-ray imaging

Abstract: The use of terahertz pulses for imaging has opened new possibilities for scientific and industrial applications in the terahertz frequency range. In this article, we describe the technology necessary to perform terahertz "T-ray" imaging, novel imaging techniques, and commercial applications of T-ray imaging.

Stretched exponential relaxation in molecular and electronic glasses

Abstract: Stretched exponential relaxation, , fits many relaxation processes in disordered and quenched electronic and molecular systems, but it is widely believed that this function has no microscopic basis, especially in the case of molecular relaxation. For electronic relaxation the appearance of the stretched exponential is often described in the context of dispersive transport, where is treated as an adjustable parameter, but in almost all cases it is generally assumed that no microscopic meaning can be assigned to even at , a glass transition temperature. We show that for molecular relaxation can be understood, providing that one separates extrinsic and intrinsic effects, and that the intrinsic effects are dominated by two magic numbers, for short-range forces, and for long-range Coulomb forces, as originally observed by Kohlrausch for the decay of residual charge on a Leyden jar. Our mathematical model treats relaxation kinetics using the Lifshitz - Kac - Luttinger diffusion to traps depletion model in a configuration space of effective dimensionality, the latter being determined using axiomatic set theory and Phillips - Thorpe constraint theory. The experiments discussed include ns neutron scattering experiments, particularly those based on neutron spin echoes which measure S( Q,t) directly, and the traditional linear response measurements which span the range from to s, as collected and analysed phenomenologically by Angell, Ngai, Bohmer and others. The electronic materials discussed include a-Si:H, granular , semiconductor nanocrystallites, charge density waves in , spin glasses, and vortex glasses in high-temperature semiconductors. The molecular materials discussed include polymers, network glasses, electrolytes and alcohols, Van der Waals supercooled liquids and glasses, orientational glasses, water, fused salts, and heme proteins. In the intrinsic cases the theory of is often accurate to 2%, which is often better than the quoted experimental accuracies . The extrinsic cases are identified by explicit structural signatures which are discussed at length. The discussion also includes recent molecular dynamical simulations for metallic glasses, spin glasses, quasicrystals and polymers which have achieved the intermediate relaxed Kohlrausch state and which have obtained values of in excellent agreement with the prediction of the microscopic theory.

Organic field‐effect transistors with high mobility based on copper phthalocyanine

Abstract: Organic field‐effect transistors that employ copper phthalocyanine (Cu–Pc) as the semiconducting layer can function as p‐channel accumulation‐mode devices. The charge carrier mobility of such devices is strongly dependent on the morphology of the semiconducting thin film. When the substrate temperature for deposition of Cu–Pc is 125 °C, a mobility of 0.02 cm2/V s and on/off ratio of 4×105 can be obtained. These features along with the highly stable chemical nature of Cu–Pc make it an attractive candidate for device applications.

Signal design for transmitter diversity wireless communication systems over Rayleigh fading channels

Abstract: Transmitter diversity wireless communication systems over Rayleigh fading channels using pilot symbol assisted modulation (PSAM) are studied. Unlike conventional transmitter diversity systems with PSAM that estimate the superimposed fading process, we are able to estimate each individual fading process corresponding to the multiple transmitters by using appropriately designed pilot symbol sequences. With such sequences, special coded modulation schemes can then be designed to access the diversity provided by the multiple transmitters without having to use an interleaver or expand the signal bandwidth. The code matrix notion is introduced for the coded modulation scheme, and its design criteria are also established. In addition to the reduction in receiver complexity, simulation results are compared to, and shown to be superior to, that of an intentional frequency offset system over a wide range of system parameters.

Interpolating Subdivision for meshes with arbitrary topology

Abstract: Subdivision is a powerful paradigm for the generation of surfaces of arbitrary topology. Given an initial triangular mesh the goal is to produce a smooth and visually pleasing surface whose shape is controlled by the initial mesh. Of particular interest are interpolating schemes since they match the original data exactly, and play an important role in fast multiresolution and wavelet techniques. Dyn, Gregory, and Levin introduced the Butterfly scheme, which yields C^1 surfaces in the topologically regular setting. Unfortunately it exhibits undesirable artifacts in the case of an irregular topology. We examine these failures and derive an improved scheme, which retains the simplicity of the Butterfly scheme, is interpolating, and results in smoother surfaces.

How the brain keeps the eyes still

Abstract: The brain can hold the eyes still because it stores a memory of eye position. The brain’s memory of horizontal eye position appears to be represented by persistent neural activity in a network known as the neural integrator, which is localized in the brainstem and cerebellum. Existing experimental data are reinterpreted as evidence for an “attractor hypothesis” that the persistent patterns of activity observed in this network form an attractive line of fixed points in its state space. Line attractor dynamics can be produced in linear or nonlinear neural networks by learning mechanisms that precisely tune positive feedback.

Direct Measurement of Coupling Between Dendritic Spines and Shafts

Abstract: Characterization of the diffusional and electrotonic coupling of spines to the dendritic shaft is crucial to understanding neuronal integration and synaptic plasticity. Two-photon photobleaching and photorelease of fluorescein dextran were used to generate concentration gradients between spines and shafts in rat CA1 pyramidal neurons. Diffusional reequilibration was monitored with two-photon fluorescence imaging. The time course of reequilibration was exponential, with time constants in the range of 20 to 100 milliseconds, demonstrating chemical compartmentalization on such time scales. These values imply that electrical spine neck resistances are unlikely to exceed 150 megohms and more likely range from 4 to 50 megohms.

Subdiffusion and Anomalous Local Viscoelasticity in Actin Networks.

Abstract: We use magnetic tweezers to study local viscoelastic response in filamentous actin networks. Thechoice of magnetic, colloidal particles of varying size allows us to explore properties on the relevantmicron and submicron scales. At these scales the mechanical response is determined by the bendingproperties of individual filaments and described by an anomalous power-law behavior. In the absenceof external forces the particles exhibit a subdiffusive motion. [S0031-9007(96)01627-4]

Improving the Accuracy and Speed of Support Vector Machines

Abstract: Support Vector Learning Machines (SVM) are finding application in pattern recognition, regression estimation, and operator inversion for ill-posed problems. Against this very general backdrop, any methods for improving the generalization performance, or for improving the speed in test phase, of SVMs are of increasing interest. In this paper we combine two such techniques on a pattern recognition problem. The method for improving generalization performance (the "virtual support vector" method) does so by incorporating known invariances of the problem. This method achieves a drop in the error rate on 10,000 NIST test digit images of 1.4% to 1.0%. The method for improving the speed (the "reduced set" method) does so by approximating the support vector decision surface. We apply this method to achieve a factor of fifty speedup in test phase over the virtual support vector machine. The combined approach yields a machine which is both 22 times faster than the original machine, and which has better generalization performance, achieving 1.1 % error. The virtual support vector method is applicable to any SVM problem with known invariances. The reduced set method is applicable to any support vector machine.

Commensurate to incommensurate charge ordering and its real space images in La0.5Ca0.5MnO3.

Abstract: The antiferromagnetic to ferromagnetic transition in L${\mathrm{a}}_{0.5}$C${\mathrm{a}}_{0.5}$Mn${\mathrm{O}}_{3}$ is accompanied by a commensurate to incommensurate charge-ordering transition. The presence of incommensurate charge correlation in the ferromagnetic phase is a remarkable interplay between charge and spin in double-exchange ferromagnets. Furthermore, a dark-field imaging technique has provided real-space images of charge-ordered domains revealing discommensurations inside the nearly commensurate domains. Local density fluctuations of discommensurations are responsible for the similar variations of the charge-ordering wave vector.

Status of and prospects for organic electroluminescence

Abstract: We review the device and materials science behind organic electroluminescent diodes made both using discrete evaporable molecules and spin-cast organic polymers. A great deal of progress has been made in improving the efficiencies and spectral properties of organic light-emitting diodes, and these are now adequate for many applications. More work is necessary to understand the stability and degradation of emissive and charge-transporting organics, but some systems have been shown to be stable for 104 hours at display brightness. Major challenges still face the community in terms of developing satisfactory systems design and processing techniques if organic electroluminescence is to realize either performance or economic advantages over technologies and significantly penetrate the display market. We present an analysis of the suitability of organic light-emitting diodes for various applications, and consider the materials and manufacturing obstacles that must be overcome.

Insulator-to-Metal Crossover in the Normal State of La 2 − x Sr x CuO 4 Near Optimum Doping

Abstract: A 61-T pulsed magnetic field suppresses superconductivity in ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{CuO}}_{4}$ single crystals and reveals an insulator-to-metal (IM) crossover for both in-plane resistivity ${\ensuremath{\rho}}_{\mathrm{ab}}$ and $c$-axis resistivity ${\ensuremath{\rho}}_{c}$ at a Sr concentration near optimum doping ( $x\ensuremath{\simeq}0.16$). The IM transition is unusual in that all underdoped samples ( $xl0.16$) show low-temperature insulating behavior, even in samples with linear- $T$ ${\ensuremath{\rho}}_{\mathrm{ab}}$ above ${T}_{c}$ and apparently large ${k}_{F}l$.

File system for a data storage device having a power fail recovery mechanism for write/replace operations

Abstract: The present invention provides a method and apparatus in a data storage device of a data storage system under the control of a microprocessor for preventing a microprocessor stall upon the occurrence of a power failure during read/write operations. During normal operations, files are written to a first storage area of the data storage device where a first flag associated with each file is set when the writing of the respective file has successfully completed. Upon the occurrence of a power failure, a data storage device initialization routine is commenced upon reboot of the microprocessor. During initialization, an analysis phase is begun to generate sequences of events for at least those files not having the first flag set. The events comprise memory operations and associated data and are each re-executable upon interruption of its execution and before execution of another event without modifying results of a previous execution of the respective event. The events generated are then written to an event storage area in the data storage device. During an execution phase of the data storage device initialization, the events are retrieved and executed by the microprocessor to cause the files having at least the first flag set to be written in a compacted manner to storage locations in a second storage area of the memory device to maintain the integrity of those files. Subsequently, the first storage area of the memory device is erased to provide additional storage space for the writing of new files to the memory device. If a power failure or system failure occurs during the two-phase initialization process, the process is re-started generally at the point where it was interrupted so as not to leave the data storage device in a partially compacted, and hence, a potentially inconsistent state.

Apparatus and method for combining high bandwidth and low bandwidth data transfer

Abstract: Data communications apparatus and methods employing a bidirectional low bandwidth channel and a unidirectional high bandwidth channel. A PC is coupled to an information source by a communications system which provides both a bidirectional low bandwidth channel between the PC and the information source and a high bandwidth channel in which the information source is the source and the PC is the sink. A component of the communications system termed the director responds to a message received in the low bandwidth channel by switching the information being sent from the information source to the PC to the high or low bandwidth channel as specified in the message. The message may come either from the PC or the information source. A graphical user interface at the PC provides the user with "buttons" to specify the bandwidth. The apparatus and methods may be advantageously employed to provide telecommuting services.

Thermodynamic and electron diffraction signatures of charge and spin ordering in La1-xCaxMnO3

Abstract: The large-magnetoresistance compounds ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{MnO}}_{3}$ have been studied using specific heat, sound velocity $(v)$, and electron diffraction. For $0.63\ensuremath{\le}x\ensuremath{\le}0.67$ charge ordering is observed at 260 K and accompanied by a dramatic $(g10%)$ increase in $v$. This simultaneous occurrence of electron and lattice ordering features implies extremely strong electron-phonon coupling, known to exist for the octahederally coordinated ${d}^{4}$ ion and originating in the Jahn-Teller effect. A dynamic manifestation of this Jahn-Teller coupling has been suggested by Millis et al. as the origin for colossal magnetoresistance.

Nonuniversal conductance quantization in quantum wires

Abstract: We have measured the transport properties of high-quality quantum wires fabricated in GaAs-AlGaAs by using cleaved edge overgrowth. The low temperature conductance is quantized as the electron density in the wire is varied. While the values of the conductance plateaus are reproducible, they deviate from multiples of the universal value of ${2e}^{2}/h$ by as much as 25%. As the temperature or dc bias increases the conductance steps approach the universal value. Several aspects of the data can be explained qualitatively using Luttinger liquid theory although there remain major inconsistencies with such an interpretation.

FPGA-based processor

Abstract: A multiprocessor having an input/output controller, a process controller, and a multidimensional arrays of field programmable gate arrays (FPGAs), each FPGA having its own local memory. The multiprocessor may be programmed to function as a single-instruction, multiple-data (SIMD) parallel processor having a matrix of processing elements (PEs), where each FPGA may be programmed to operate as a submatrix array of PEs. The multiprocessor is especially useful for image processing, pattern recognition, and neural network applications.

Physics and applications of organic microcavity light emitting diodes

Abstract: The important changes produced on the electroluminescence characteristics of organic materials due to planar microcavity effects are examined in detail. The photon density of states is redistributed such that only certain wavelengths, which correspond to allowed cavity modes, are emitted in a given direction. This enables us to realize color selectivity over a large wavelength (and color coordinate) range with broadband emitters such as 8‐hydroxyquinoline aluminum (Alq), and intensity enhancement in narrow band emitters. The intensity enhancement in Alq‐based cavity light emitting diodes (LEDs) is extensively evaluated both experimentally and theoretically. The design considerations for and device characteristics of a novel multiple emissive layer LED are also described.

Iterated register coalescing

Abstract: An important function of any register allocator is to target registers so as to eliminate copy instructions. Graph-coloring register allocation is an elegant approach to this problem. If the source and destination of a move instruction do not interfere, then their nodes can be coalesced in the interference graph. Chaitin's coalescing heuristic could make a graph uncolorable (i.e., introduce spills); Briggs et al. demonstrated a conservative coalescing heuristic that preserves colorability. But Briggs's algorithm is too conservative and leaves too many move instructions in our programs. We show how to interleave coloring reductions with Briggs's coalescing heuristic, leading to an algorithm that is safe but much more aggressive.

Full duplex modulated backscatter system

Abstract: A duplex radio communication system includes an Interrogator which generates a first modulated signal by modulating a first information signal onto a radio carrier signal. The Interrogator transmits the first modulated signal to at least one remote Tag of the system. The remote Tag receives and processes the first modulated signal received at its Antenna. A Backscatter Modulator uses a second information signal to modulate the reflection of the first modulated signal from the Antenna, the reflected signal being a second modulated signal. The Interrogator receives and demodulates the second modulated signal to obtain the second information signal.

The Visual Design and Control of Trellis Display

Abstract: Trellis display is a framework for the visualization of data. Its most prominent aspect is an overall visual design, reminiscent of a garden trelliswork, in which panels are laid out into rows, columns, and pages. On each panel of the trellis, a subset of the data is graphed by a display method such as a scatterplot, curve plot, boxplot, 3-D wireframe, normal quantile plot, or dot plot. Each panel shows the relationship of certain variables conditional on the values of other variables. A number of display methods employed in the visual design of Trellis display enable it to succeed in uncovering the structure of data even when the structure is quite complicated. For example, Trellis display provides a powerful mechanism for understanding interactions in studies of how a response depends on explanatory variables. Three examples demonstrate this; in each case, we make important discoveries not appreciated in the original analyses. Several control methods are also essential to Trellis display. A con...

Code division multiple access system providing load and interference based demand assignment service to users

Abstract: A code division multiple access system provides a way of allocating an increased data rate to a requesting mobile station A mobile station requesting a data rate in excess of the basic data rate sends received pilot strength data for its base station and base stations in adjacent cells The received pilot strength data is used to determine an increased data rate to be assigned to the requesting mobile station One feature assigns an increased data rate when the received pilot strength data has a predetermined relationship to an established threshold Another feature utilizes a series of threshold levels, each pair of levels associated with a different permitted data rate Using the received pilot strength data, a data rate is determined which satisfies all adjacent cell interference concerns Another feature uses average adjacent cell capacity loads rather than threshold levels, together with the received pilot strength data, to determine the appropriate increased data rate to be assigned to a user requesting an increased data rate

System and method to automatically provide an electronic consumer rebate

Abstract: A system to automatically provide to a consumer an electronic rebate by an existing telephone network and system. The consumer dials a dedicated preassigned telephone number and is prompted to enter the product code and a serial number for purchase verification purposes. A rebate is provided instantaneously in the form of a credit to the consumer's telephone account. The rebates so provided to consumers are collated on a per manufacturer basis, and the telephone service provider issues statements to the rebating manufacturers to cover the rebates issued as well as its service charge.