bluuebunny/crossref_metadata_2025 huggingface dataset:
Temperature dependence of the GaNxP1−x band gap and effect of band crossover
Authors: Rudko G. Yu. , Buyanova I. A. , Chen W. M. , Xin H. P. , Tu C. W.
Published: November 2002

The absorption edge of GaNxP1−x alloys (0.01⩽x⩽0.03) is shown to exhibit a direct-band gap-like behavior. Thermal variation of the band gap energy Eg, however, is found to be the same or even smaller than that for the indirect band gap of GaP and depends on the N content. The effect is tentatively attributed to the following counteracting contributions to the band edge formation. An interaction with N-related localized states, especially significant in the vicinity of band crossover (e.g., x=0.013), causes a substantial slow down of the Eg shift with temperature. On the contrary, an increasing contribution of Γc states, which becomes predominant for the higher compositions, leads to the larger thermal variation in Eg.
Simultaneous observation of electron and hole velocity overshoots in an Al0.3Ga0.7As-based p–i–n semiconductor nanostructure
Authors: Liang W. , Lee H. , Tsen K. T. , Sankey O. F. , Ferry D. K.
Published: November 2002

We report experimental results on simultaneous measurement of electron as well as hole transient transport in an Al0.3Ga0.7As-based p–i–n semiconductor nanostructure by using picosecond/subpicosecond Raman spectroscopy. Electron and hole velocity overshoots are directly observed. It is demonstrated that at T=300 K, E=15 kV/cm, and electron-hole pair density n≅5×1017 cm−1, electron overshoots its steady-state value by a factor of about 7; whereas hole about 2.5. These experimental results are discussed and explained.
Direct measurement and characterization of n+ superhalo implants in a 120 nm gate-length Si metal–oxide–semiconductor field-effect transistor using cross-sectional scanning capacitance microscopy
Authors: Rosenthal P. A. , Taur Y. , Yu E. T.
Published: November 2002

We have directly measured nanoscale electronic features associated with a 120 nm physical gate length p-channel silicon metal–oxide–semiconductor field-effect transistor device structure including n+ superhalo implants using cross-sectional scanning capacitance microscopy (SCM). A dc bias-dependent voltage series of SCM images representing nine bias conditions from 2 to −2 V in 0.5 V steps was obtained. The SCM contrast observed varies with the ac and dc bias applied to the sample and allows delineation of the device features, including the p+ source and drain contacts, p+ source and drain extensions, p+ polycrystalline silicon gate, electrical p–n junction, n-well, and n+ superhalo implants. It is demonstrated that the superhalo implant features are imaged only under specific SCM bias conditions. Detailed analysis of the resulting SCM contrast indicates an apparent channel length of 73±11 nm, and reveals clear asymmetry in the individual lobes of the n+ superhalo implant features.
Photoexcitation-electron-paramagnetic-resonance studies of the carbon vacancy in 4H-SiC
Authors: Son N. T. , Magnusson B. , Janzén E.
Published: November 2002

Photoexcitation-electron-paramagnetic-resonance (photo-EPR) studies were performed on p-type 4H-SiC irradiated with 2.5 MeV electrons. At W-band frequencies (∼95 GHz) different EPR spectra could be well separated, allowing a reliable determination of the ground state levels of the associated defects. The photo-EPR results obtained for the positively charged carbon vacancy (VC+) can be explained by a deep donor model with the (+/0) level located at (1.47±0.06) eV above the valence band.
Ga(As,N) layers in the dilute N limit studied by depth-resolved capacitance spectroscopy
Authors: Krispin P. , Gambin V. , Harris J. S. , Ploog K. H.
Published: November 2002

Deep carrier traps in the upper half of the band gap of Ga(As,N) layers in the dilute N limit (⩽0.1%) are examined by depth-resolved capacitance spectroscopy on n-type Ga(As,N)/GaAs heterojunctions grown by molecular-beam epitaxy. Distinct compositional fluctuations are revealed in the deep-level spectra. Native point defects are predominantly formed in regions with larger N content. High concentrations of electron traps near the surface control the properties of as-grown Ga(As,N) layers and lead to strong carrier depletion and frequency- as well as temperature-dependent capacitance (admittance dispersion). The related defects at the surface can be removed by rapid thermal annealing.
Optical anisotropy of self-assembled InGaAs quantum dots embedded in wall-shaped and air-bridge structures
Authors: Nakaoka T. , Kako S. , Ishida S. , Nishioka M. , Arakawa Y.
Published: November 2002

Strain effect on optical anisotropy of quantum dots has been investigated by changing the surrounding matrix of the dots. Optical anisotropy can be induced by lateral patterning of the matrix of the dots, although such anisotropy is absent in the as-grown dots. A reduction of the optical anisotropy is observed by changing the laterally patterned structure into a free-standing structure or an air bridge. The optical anisotropy is mainly attributed to strain asymmetry in the fabricated structures. The presence of the strain asymmetry is confirmed by the observation of a doublet fine structure in spectrally resolved photoluminescence of single quantum dots.
Ultrashort hole capture time in Mg-doped GaN thin films
Authors: Lin Kung-Hsuan , Chern Gia-Wei , Chu Shi-Wei , Sun Chi-Kuang , Xing Huili , Smorchkova Yulia , Keller Stacia , Mishra Umesh , DenBaars Steven P.
Published: November 2002

Hole capture time in p-type GaN was measured by using a femtosecond pump-probe technique. The capture time constant that holes are trapped by Mg-related states was found to be shorter than 10 ps. The hole capture time increases with decreased hole excess energy. By comparing two samples with different doping concentrations, it was found that the hole capture time also decreases with increased doping concentrations.
Bipolaron dynamics in pure and doped SrTiO3 and KTaO3 perovskite systems
Authors: Levstik A. , Filipič C. , Bobnar V. , Pirc R.
Published: November 2002

The dielectric relaxation in SrTiO3, Sr0.942Ca0.058TiO3, and K0.989Li0.011TaO3 was analyzed. While at higher temperatures the characteristic relaxation frequency follows the Arrhenius behavior, its value is temperature independent at low temperatures. It is shown that such a behavior is a consequence of the dynamic properties of bipolarons, which undergo a transition from thermally activated hopping to a tunneling regime.
Recursive asymptotic stiffness matrix method for analysis of surface acoustic wave devices on layered piezoelectric media
Authors: Wang L. , Rokhlin S. I.
Published: November 2002

Based on a simple second-order thin layer asymptotic expansion for the transfer matrix, an asymptotic solution for the stiffness matrix for a general anisotropic piezoelectric thin layer is obtained. The total stiffness matrix for thick layers or multilayers is calculated with arbitrary precision by subdividing them into thin sublayers and combining recursively the thin layer stiffness matrices. It is shown that this method converges to the exact solution and is computationally stable, efficient and easy to implement. A semispace substrate is substituted for by a finite thickness layer loaded by a perfectly matched attenuating layer. The effective permittivity and general Green’s functions for a layered system on a substrate are formulated in terms of stiffness and compliance matrices. The advantage of the method is that one does not need to compute the exact wave propagation solution for an anisotropic piezoelectric layer or semispace.
Linear and nonlinear optical properties of Ag nanocluster/BaTiO3 composite films
Authors: Yang Guang , Wang Weitian , Zhou Yueliang , Lu Huibin , Yang Guozhen , Chen Zhenghao
Published: November 2002

To investigate the optical properties of metallic nanocluster/oxide composite films, Ag nanocluster/BaTiO3 composite films were synthesized on MgO (100) substrates by co-depositing the Ag and BaTiO3 targets using pulsed laser deposition. The x-ray diffraction results demonstrated that the Ag and BaTiO3 were well crystallized. The x-ray photoelectron spectroscopy analysis indicated that the samples were composed of nano-metal Ag embedded in the BaTiO3 matrices. The optical absorption properties were measured from 300 to 800 nm, and the absorption peaks due to the surface plasmon resonance of Ag particles were observed. With increasing the Ag concentration, the peak absorption increased and shifted to longer wavelength (redshift). Furthermore, the z-scan results showed that the films exhibited large optical nonlinearities and the signs of the nonlinear absorption (β) and nonlinear refractive index (n2) changed with increasing the Ag concentration.
High-efficiency top-emitting organic light-emitting devices
Authors: Lu M.-H. , Weaver M. S. , Zhou T. X. , Rothman M. , Kwong R. C. , Hack M. , Brown J. J.
Published: November 2002

Based on theoretical arguments that top-emitting organic light-emitting devices (TOLEDs) can be more efficient than equivalent bottom-emitting devices, we fabricated TOLEDs comprising reflective anodes and transparent compound cathodes that emit 20.8% more photons in the forward 120° cone than equivalent bottom-emitting OLEDs. Device optimization by tuning the thickness of the top indium–tin–oxide layer according to a microcavity model is also reported.
Origin and consequences of a high stacking fault density in epitaxial ZnO layers
Authors: Gerthsen D. , Litvinov D. , Gruber Th. , Kirchner C. , Waag A.
Published: November 2002

Transmission electron microscopy was applied to study ZnO grown by metalorganic vapor phase epitaxy on Al2O3(0001) substrates. The defect structure of the material is dominated by an extraordinary high density of small stacking faults with extensions between 5 and 25 nm which induce a bright small-scale speckle contrast under weak-beam imaging conditions. The stacking faults are terminated by Frank partial dislocations with Burgers vectors of the type 1/6 〈22̄03〉. The precipitation of interstitial atoms is the most likely process for the generation of the stacking faults, which are characterized by an additional (0002) plane. The high stacking fault density can be considered as an indicator for high point defect concentrations, which are expected to aggravate the control of the electrical conductivity.
Fast Q-tensor method for modeling liquid crystal director configurations with defects
Authors: Lee Gi-Dong , Anderson James , Bos Philip J.
Published: November 2002

A fast Q-tensor method, which can model the configuration of the liquid crystal director fields containing defects, is proposed. Conceptually based on the Oseen–Frank approach, we have added temperature energy density terms in addition to the strain energy term. We have also derived an improved normalization method for fast calculations. The method is used to model the conversion of a reverse tilt wall to a pair of disclination lines.
Mechanism for cathode spot grouping in vacuum arcs
Authors: Beilis I. I.
Published: November 2002

A model of cathode spot grouping observed when the vacuum arc runs in a transverse magnetic field is proposed. The current per group spot is calculated considering the relation between the plasma kinetic pressure and magnetic pressure in the acceleration region of current carried cathode plasma jet. The calculated currents per group spot increase linearly with the magnetic field and this dependence agrees well with previous measurements.
Oxygen-assisted room-temperature deposition of CoPt3 films with perpendicular magnetic anisotropy
Authors: Maranville B. B. , Hellman F.
Published: November 2002

Trace amounts of oxygen in the deposition environment are shown to induce perpendicular magnetic anisotropy and remanence in nominally cubic CoPt3 grown by vapor deposition at or slightly above room temperature. Oxygen is known to act as a surfactant during epitaxial growth of Pt, and here is shown to affect the surface roughness of CoPt3 films. The dependence on oxygen partial pressure and on growth temperature suggest that the oxygen may act to increase the surface mobility of the growing films, thereby enhancing the clustering which leads to anisotropy. A strong orientation dependence in the anisotropy is found, which was not seen in the absence of oxygen. CO by contrast uniformly reduces anisotropy.
Efficient characterization of stationary points on potential energy surfaces
Authors: Deglmann Peter , Furche Filipp
Published: November 2002

Traditional methods for characterizing an optimized molecular structure as a minimum or as a saddle point on the nuclear potential energy surface require the full Hessian. However, if f denotes the number of nuclear degrees of freedom, a full Hessian calculation is more expensive than a single point geometry optimization step by the order of magnitude of f. Here we present a method which allows to determine the lowest vibrational frequencies of a molecule at significantly lower cost. Our approach takes advantage of the fact that only a few perturbed first-order wave functions need to be computed in an iterative diagonalization scheme instead of f ones in a full Hessian calculation. We outline an implementation for Hartree–Fock and density functional methods. Applications indicate a scaling similar to that of a single point energy or gradient calculation, but with a larger prefactor. Depending on the number of soft vibrational modes, the iterative method becomes effective for systems with more than 30–50 atoms.
Electrical characterization of acceptor levels in Be-implanted GaN
Authors: Nakano Yoshitaka , Jimbo Takashi
Published: November 2002

We have investigated electrically the acceptor levels that are present in Be-implanted GaN. Slight p-type conductivity was attained in undoped GaN films by Be implantation and subsequent annealing at 1050 °C with a SiO2 encapsulation layer. Capacitance-frequency measurements showed a typical dispersion effect characteristic of deep acceptors in fabricated Schottky diodes. Thermal admittance spectroscopy measurements revealed a discrete deep level located at ∼231 meV above the valence band. This energy level is in reasonable agreement with the frequency dependence of the capacitance in view of the impurity transition frequency. Therefore, this energy level can most probably be assigned to a Be-related deep acceptor.
Shifted hysteresis loops from magnetic nanowires
Authors: Allwood D. A. , Vernier N. , Xiong Gang , Cooke M. D. , Atkinson D. , Faulkner C. C. , Cowburn R. P.
Published: November 2002

We demonstrate that positively and negatively field-shifted magnetic hysteresis loops can be obtained from a single continuous L-shaped magnetic nanostructure. This is achieved by controlling the coercivity of one arm of the L-shape structure with the magnetization direction of the orthogonal arm. Furthermore, a memory effect is demonstrated by reversing the magnetization direction of one arm while leaving the other unchanged. Good discrimination between the different switching field magnitudes and the ease of fabrication make these continuous magnetic structures more suitable than chains of discrete magnetic dots for performing logical operations.
Effect of deuterium postmetal annealing on the reliability characteristics of an atomic-layer-deposited HfO2/SiO2 stack gate dielectrics
Authors: Sim Hyunjun , Hwang Hyunsang
Published: November 2002

The characteristics of atomic-layer-deposited (ALD) HfO2(30 Å)/SiO2(10 Å) stacks gate dielectrics were investigated after annealing in a deuterium (D2) ambient. Compared with oxides annealed in a forming gas containing hydrogen (H2), the stack dielectrics annealed in D2 ambient exhibited various advantages such as less charge trapping, less generation of interface state density (Dit), a larger charge-to-breakdown (Qbd), and longer time-dependent dielectric breakdown characteristics under conditions of electrical stress. The improved reliability can be attributed to the strength of the deuterium bond. This deuterium postmetal annealing of a high-k gate dielectric has considerable potential for future use in ultralarge-scale integration device applications.
Creating large bandwidth line defects by embedding dielectric waveguides into photonic crystal slabs
Authors: Lau Wah Tung , Fan Shanhui
Published: November 2002

We introduce a general designing procedure that allows us, for any given photonic crystal slab, to create an appropriate line defect structure that possesses single-mode bands with large bandwidth and low dispersion within the photonic band-gap region below the light line. This procedure involves designing a high index dielectric waveguide that is phase matched with the gap of the photonic crystal slab, and embedding the dielectric waveguide as a line defect into a crystal in a specific configuration that is free of edge states within the guiding bandwidth. As an example, we show a single mode line defect waveguide with a bandwidth approaching 13% of the center-band frequency, and with a linear dispersion relation throughout most of the bandwidth.
Growth mode and strain evolution during InN growth on GaN(0001) by molecular-beam epitaxy
Authors: Ng Y. F. , Cao Y. G. , Xie M. H. , Wang X. L. , Tong S. Y.
Published: November 2002

Epitaxial growth of InN on GaN(0001) by plasma-assisted molecular-beam epitaxy is investigated over a range of growth parameters including source flux and substrate temperature. Combining reflection high-energy electron diffraction (RHEED) and scanning tunneling microscopy (STM), we establish a relationship between film growth mode and the deposition condition. Both two-dimensional (2D) and three-dimensional (3D) growth modes of the film are observed. For 2D growth, sustained RHEED intensity oscillations are recorded while STM reveals 2D nucleation islands. For 3D growth, less than three oscillation periods are observed indicating the Stranski–Krastanov (SK) growth mode of the film. Simultaneous measurements of (reciprocal) lattice constant by RHEED suggest a gradual relaxation of the strain in film, which commences during the first bilayer (BL) deposition and almost completes after 2–4 BLs. For SK growth, 3D islanding initiates after the strain has mostly been relieved, presumably by dislocations, so the islands are likely strain free.
Reflectance difference spectroscopy of an ultrathin indium arsenide layer on indium phosphide (001)
Authors: Li C. H. , Sun Y. , Visbeck S. B. , Law D. C. , Hicks R. F.
Published: November 2002

A model system has been created which allows the surface and bulk contributions to the reflectance difference spectrum to be distinguished. In particular, an indium arsenide film, less than 10 Å thick, has been grown on indium phosphide (001). Reflectance difference spectra of the InAs/InP surfaces were collected and compared to those of InP and InAs. It was found that the InAs/InP heterostructures exhibited electronic transitions between surface states characteristic of InAs (001), while retaining the surface-perturbed bulk transitions characteristic of InP (001). Furthermore, the optical anisotropy arising from the arsenic dimer bonds was shifted 0.2 eV higher for InAs/InP compared to that for InAs. This shift is proportional to 1/a2, where a is the bulk lattice constant.
Effect of substitutionally dissolved Ce in Si on the magnetic and electric properties of magnetic semiconductor Si1−xCex films
Authors: Yokota T. , Fujimura N. , Ito T.
Published: November 2002

A magnetic semiconductor Si:Ce thin film was prepared using a vacuum evaporation system with electron-beam guns. The as-deposited thin film was amorphous and exhibited n-type conduction. It showed temperature dependence of resistivity (ρ–T), as in a normal semiconductor, and a diamagnetic property. By annealing at 973 K, however, the film epitaxially crystallizes and the conduction changes to the p-type. The resistivity of the film abruptly decreases by three orders of magnitude below 30 K, unlike that of the as-deposited film. The magnetic susceptibility measured at a low magnetic field (750 Oe) also decreases around the same temperature in ρ–T curves. These magnetic and carrier transport phenomena are responsible for the substitutionally dissolved Ce in Si.
Formation of epitaxial Au/Ni/Au ohmic contacts to p-GaN
Authors: Narayan J. , Wang H. , Oh T.-H. , Choi H. K. , Fan J. C. C.
Published: November 2002

We have designed a promising contact scheme to p-GaN, where Au/Ni/Au layers are deposited on p-GaN and annealed in air for 30 min at 470 °C to produce low-resistivity ohmic contacts. The Au layer in contact with p-GaN grows epitaxially via domain matching epitaxy, which acts as a template for NiO growth via lattice matching epitaxy. The 〈111〉 oriented gold rotates 30° in the basal (0001) plane of GaN by 30° with the following orientation relationship: [111]Au//[0001]GaN; [112̄]Au//[21̄1̄0]GaN. As a result, we can create epitaxial NiO–Au composite, where Au as well as NiO are in contact with p-GaN. This epitaxial composite structure is envisaged to be important in achieving low-resistivity ohmic contacts in p-GaN. We present the details of atomic structure, epitaxial relationship, chemistry, and electrical properties of ohmic contacts.
Thermal stability of ion-implanted hydrogen in ZnO
Authors: Ip K. , Overberg M. E. , Heo Y. W. , Norton D. P. , Pearton S. J. , Kucheyev S. O. , Jagadish C. , Williams J. S. , Wilson R. G. , Zavada J. M.
Published: November 2002

The evolution of implanted 2H profiles in single-crystal ZnO was examined as a function of annealing temperature (500–700 °C) by secondary ion mass spectrometry. The as-implanted profiles show a peak concentration of ∼2.7×1019 cm−3 at a depth of ∼0.96 μm for a dose of 1015 cm−2. Subsequent annealing causes outdiffusion of 2H from the ZnO, with the remaining hydrogen decorating the residual implant damage. Only 0.2% of the original dose is retained after annealing at 600 °C. Rutherford backscattering/channeling of samples implanted with 1H at a dose of 1016 cm−2 showed no change in backscattering yield near the ZnO surface, but did result in an increase near the end-of-range from 6.5% of the random level before 1H implantation to ∼7.8% after implantation. Results of both cathodoluminescence and photoluminescence studies show that even for a 1H dose of 1015 cm−2, the intensity of the near gap emission from ZnO is reduced more than 2 orders of magnitude from the values in unimplanted samples. This is due to the formation of effective nonradiative recombination centers associated with ion-beam-induced defects.
Nanothermodynamic analysis of surface effect on expansion characteristics of Ga in carbon nanotubes
Authors: Gao Yihua , Bando Yoshio
Published: November 2002

Thermodynamic analysis was performed with respect to the effect of surface tension on the expansion characteristics of a one-dimensional nanoscale liquid Ga column inside a carbon nanotube. The analysis showed that the surface tension affects the column inner pressure, and that the smaller the column diameter, the greater the surface effect. Based on the analysis, it is quantitatively explained why a liquid Ga column with 75 nm diameter has virtually the same expansion coefficient as that of Ga in a macroscopic state in the range of 50 to 500 °C, and suggested that the volumetric expansion coefficient can be directly used for the calibration of a given nanothermometer with a diameter larger than 10 nm.
Vibrational spectroscopy on single C60 molecules: The role of molecular orientation
Authors: Pascual J. I. , Gómez-Herrero J. , Sánchez-Portal D. , Rust H.-P.
Published: November 2002

The excitation of a fullerene-cage vibrational mode by inelastic tunneling electrons has been observed on single C60 molecules adsorbed on Ag(110). The vibration is assigned to the Hg(ω2) mode. A critical enhancement of the inelastic signal was found on fullerenes oriented along one of their symmetry axis upon adsorption. In strong coincidence, those fullerenes maintain a resonance structure at the Fermi level that resembles the first unoccupied molecular orbital distribution of a free molecule, as determined by comparison with ab initio calculations. The degree of symmetry of the adsorbed fullerene is found to be crucial for resonant mechanism of vibrational excitation. We also propose that mode degeneracy splitting may reduce mode detection.
A seven-dimensional quantum study of the H+CH4 reaction
Authors: Yang Minghui , Zhang Dong H. , Lee Soo-Y.
Published: November 2002

The initial state selected time-dependent wave packet method has been developed to study the H+CH4 reaction in seven dimensions by employing the model developed by Palma and Clary [J. Chem. Phys. 112, 1859 (2000)]. The latter eight-dimensional model only assumes that the nonreacting CH3 group keeps a C3V symmetry in reaction. The CH bond lengths in the nonreacting CH3 group were fixed in the study to reduce the number of degrees of freedom to seven. Our calculations reveal that it is very important to accurately deal with the umbrella motion of the CH3 group while studying this reaction. We investigated the effects of the fundamental vibrational excitations of CH4 on the reaction. Finally, we compare our rate constant for the ground rovibrational initial state with available experimental and other theoretical results.
Dispersive coherence-enhanced radiology: Experimental test and modeling
Authors: Groso A. , Margaritondo G. , Hwu Y. , Tsai Wen-Li , Je J. H. , Lai B.
Published: November 2002

Can the photon energy dependence of coherence-enhanced radiographs lead to elemental identification? Our tests pave the way to a positive response by showing that image details do change as the photon energy crosses an absorption threshold. The observed changes are explained by a simple model of the interplay between the real and imaginary parts of the refractive index.
Power laws for turbulent boundary layer flow
Authors: Keller Joseph B.
Published: November 2002

A differential equation for the mean velocity u(y) at distance y from the wall in a turbulent boundary layer flow is proposed and solved. It leads to a power law for u(y), followed by a rapid transition to a different power law, in agreement with the results of Barenblatt, Chorin and Prostokishin [Phys. Fluids 12, 2159 (2000)].
Composition and temperature dependence of the magnetocrystalline anisotropy in Ni2+xMn1+yGa1+z (x+y+z=0) Heusler alloys
Authors: Albertini F. , Pareti L. , Paoluzi A. , Morellon L. , Algarabel P. A. , Ibarra M. R. , Righi L.
Published: November 2002

The composition dependence of magnetic and structural transformations, as well as the temperature and composition dependence of the magnetocrystalline anisotropy, were studied in the martensitic Ni2+xMn1+yGa1+z (x+y+z=0) Heusler alloys. Moving away from the stoichiometric composition, a slight variation, a large reduction, and a marked enhancement, were, respectively, observed for the Curie temperature, the magnetic anisotropy, and the structural (martensitic–austenitic) transformation temperatures.
Fault Detection and Fault Diagnosis Techniques for Lookup Table FPGAs
Authors: Lu Shyue-Kung , Yeh Fu-Min , Shih Jen-Sheng
Published: November 2002

In this paper, we present a novel fault detection and fault diagnosis technique for Field Programmable Gate Arrays (FPGAs). The cell is configured to implement a bijective function to simplify the testing of the whole cell array. The whole chip is partitioned into disjoint one‐dimensional arrays of cells. For the lookup table (LUT), a fault may occur at the memory matrix, decoder, input or output lines. The input patterns can be easily generated with a k‐bit binary counter, where k denotes the number of input lines of a configurable logic block (CLB). Theoretical proofs show that the resulting fault coverage is 100%. According to the characteristics of the bijective cell function, a novel built‐in self‐test structure is also proposed. Our BIST approaches have the advantages of requiring less hardware resources for test pattern generation and output response analysis. To locate a faulty CLB, two diagnosis sessions are required. However, the maximum number of configurations is k + 4 for diagnosing a faulty CLB. The diagnosis complexity of our approach is also analyzed. Our results show that the time complexity is independent of the array size of the FPGA. In other words, we can make the FPGA array C‐diagnosable.
Efficient Implementation of a Demultiplexer Based on a Multirate Filter Bank for the Skyplex Satellites DVB System
Authors: Re Marco , Re Andrea Del , Cardarilli Gian Carlo
Published: November 2002

In this paper, an extensive comparison among alternative algorithms for the implementation of a digital demultiplexer has been carried out. The computational complexity, the performances and the accuracy with respect to the quantization effects (quantization noise and coefficient quantization) have been evaluated for the different algorithms. The selected digital architecture has been designed to be compliant with the Eutelsat specifications for the Skyplex Digital Video Broadcast (DVB) television system (Re, M., Cardarilli, G.C., Del Re, A. and Lojacono R. (2000) “FPGA Implementation of a Demux based on a multirate filter bank”. International Symposium on Circuits and Systems 2000, 5 (May), 353–356). At present, a more expensive and complex analog structure, based on six Surface Acoustic Wave (SAW) filters, is used. The new digital architecture has been mapped on six Altera Flex 10K‐100 devices. The final test bed, that includes a complete interface to the demodulator, has been implemented on a four‐layers PCB.
Low‐power Implementation of an Encryption/Decryption System with Asynchronous Techniques
Authors: Sklavos Nikos , Papakonstantinou Alexandros , Theoharis Spyros , Koufopavlou Odysseas
Published: November 2002

An asynchronous VLSI implementation of the International Data Encryption Algorithm (IDEA) is presented in this paper. In order to evaluate the asynchronous design a synchronous version of the algorithm was also designed. VHDL hardware description language was used in order to describe the algorithm. By using Synopsys commercial available tools the VHDL code was synthesized. After placing and routing both designs were fabricated with 0.6 μm CMOS technology. With a system clock of up to 8 MHz and a power supply of 5 V the two chips were tested and evaluated comparing with the software implementation of the IDEA algorithm. This new approach proves efficiently the lowest power consumption of the asynchronous implementation compared to the existing synchronous. Therefore, the asynchronous chip performs efficiently in Wireless Encryption Protocols and high speed networks.
Charge Pump Circuits for Low‐voltage Applications
Authors: Moisiadis Y. , Bouras I. , Arapoyanni A.
Published: November 2002

In this paper, a low‐voltage, high performance charge pump circuit, suitable for implementation in standard CMOS technologies is proposed. Its pumping operation is based on cascading several cross‐connected NMOS voltage doubler stages. For very low‐voltage applications (1.2 V, 0.9 V), where the performance of the NMOS transistors is limited due to body effect, two improved versions of the charge pump with cascaded voltage doublers (charge pump with CVD) are also proposed. The first utilises PMOS transistors (charge pump with CVD‐PMOS) in parallel to the cross‐connected NMOS transistors, while the second improves the pumping gain by boosting the clock amplitude (charge pump with CVD‐BCLK). Simulations at 50 MHz have shown that a five‐stages charge pump with CVD can achieve a 1.5–8.4 V voltage conversion. For the same stage number and frequency, an output voltage of 4 and 7.3 V can be generated from 0.9 V, by using the charge pump with CVD‐PMOS and the charge pump with CVD‐BCLK, respectively.
Basic Algorithms for the Asynchronous Reconfigurable Mesh
Authors: Ben-Asher Yosi , Stein Esti
Published: November 2002

Many constant time algorithms for various problems have been developed for the reconfigurable mesh (RM) in the past decade. All these algorithms are designed to work with synchronous execution, with no regard for the fact that large size RMs will probably be asynchronous. A similar observation about the PRAM model motivated many researchers to develop algorithms and complexity measures for the asynchronous PRAM (APRAM). In this work, we show how to define the asynchronous reconfigurable mesh (ARM) and how to measure the complexity of asynchronous algorithms executed on it. We show that connecting all processors in a row of an n × n ARM (the analog of barrier synchronization in the APRAM model) can be solved with complexity Θ(nlog⁡n). Intuitively, this is average work time for solving such a problem. Next, we describe general a technique for simulating T -step synchronous RM algorithms on the ARM with complexity of Θ(T · n2log⁡n). Finally, we consider the simulation of the classical synchronous algorithm for counting the number of non‐zero bits in an n bits vector using (k < n) × n RM. By carefully optimizing the synchronization to the specific synchronous algorithm being simulated, one can (at least in the case of counting) improve upon the general simulation.
High‐performance Multiplexer‐based Logic Synthesis Using Pass‐transistor Logic
Authors: Hsiao Shen-Fu , Yeh Jia-Siang , Chen Da-Yen
Published: November 2002

An automatic logic/circuit synthesizer is developed which takes several Boolean functions as input and generates netlist output with basic composing cells from the pass‐transistor cell library containing only two types of cells: 2‐to‐1 multiplexers and inverters. The synthesis procedure first constructs efficient binary decision diagrams (BDDs) for these Boolean functions considering both multi‐function sharing and minimum width. Each node in the BDD trees is realized by using a 2‐to‐1 multiplexer (MUX) of proper driving capability designed pass‐transistor logic. The inverters are then inserted all along the MUX paths in order to improve the speed performance and to alleviate the voltage‐drop problem. Several methods are proposed to reduce the critical path delay in the multiplexer‐chains for generation of faster circuits. Compared to the recently proposed pass‐transistor‐based top‐down design, our synthesizer has better speed and area performance due to the reduced number of cascaded inverters.
Managing uncertainty: information and insurance under the risk of starvation
Authors: Dall Sasha R. X. , Johnstone Rufus A.
Published: November 2002

In an uncertain world, animals face both unexpected opportunities and danger. Such outcomes can select for two potential strategies: collecting information to reduce uncertainty, or insuring against it. We investigate the relative value of information and insurance (energy reserves) under starvation risk by offering model foragers a choice between constant and varying food sources over finite foraging bouts. We show that sampling the variable option (choosing it when it is not expected to be good) should decline both with lower reserves and late in foraging bouts; in order to be able to reap the reduction in uncertainty associated with exploiting a variable resource effectively, foragers must be able to afford and compensate for an initial increase in the risk of an energetic shortfall associated with choosing the option when it is bad. Consequently, expected exploitation of the varying option increases as it becomes less variable, and when the overall risk of energetic shortfall is reduced. In addition, little activity on the variable alternative is expected until reserves are built up early in a foraging bout. This indicates that gathering information is a luxury while insurance is a necessity, at least when foraging on stochastic and variable food under the risk of starvation.
Behavioural and ecological consequences of limited attention
Authors: Dukas Reuven
Published: November 2002

Ecological research in the past few decades has shown that most animals acquire and respond adaptively to information that affects survival and reproduction. At the same time, neurobiological studies have established that the rate of information processing by the brain is much lower than the rate at which information is encountered in the environment, and that attentional mechanisms enable the brain to focus only on the most essential information at any given time. Recent integration of the ecological and neurobiological approaches helps us to understand key behaviours with broad ecological and evolutionary implications. Specifically, current data indicate that limited attention affects diet choice and constrains animals‘ ability simultaneously to feed and attend to predators. Recent experiments also suggest that limited attention influences social interactions, courtship and mating behaviour.
Potential disadvantages of using socially acquired information
Authors: Giraldeau Luc–Alain , Valone Thomas J. , Templeton Jennifer J.
Published: November 2002

The acquisition and use of socially acquired information is commonly assumed to be profitable. We challenge this assumption by exploring hypothetical scenarios where the use of such information either provides no benefit or can actually be costly. First, we show that the level of incompatibility between the acquisition of personal and socially acquired information will directly affect the extent to which the use of socially acquired information can be profitable. When these two sources of information cannot be acquired simultaneously, there may be no benefit to socially acquired information. Second, we assume that a solitary individual's behavioural decisions will be based on cues revealed by its own interactions with the environment. However, in many cases, for social animals the only socially acquired information available to individuals is the behavioural actions of others that expose their decisions, rather than the cues on which these decisions were based. We argue that in such a situation the use of socially acquired information can lead to informational cascades that sometimes result in sub–optimal behaviour. From this theory of informational cascades, we predict that when erroneous cascades are costly, individuals should pay attention only to socially generated cues and not behavioural decisions. We suggest three scenarios that might be examples of informational cascades in nature.
Credible threats and promises
Authors: McNamara John M. , Houston Alasdair I.
Published: November 2002

We consider various implications of information about the other player in two–player evolutionary games. A simple model of desertion shows that information about the partner's behaviour can be disadvantageous, and highlights the idea of credible threats. We then discuss the general issue of whether the partner can convince the focal player that it will behave in a specific way, i.e. whether the focal player can make credible threats or promises. We show that when desertion decisions depend on reserves, a player can manipulate its reserves so as to create a credible threat of desertion. We then extend previous work on the evolution of trust and commitment, discussing conditions under which it is advantageous to assume that a partner will behave in a certain way even though it is not in its best interest.
No accident: genetic codes freeze in error–correcting patterns of the standard genetic code
Authors: Ardell David H. , Sella Guy
Published: November 2002

The standard genetic code poses a challenge in understanding the evolution of information processing at a fundamental level of biological organization. Genetic codes are generally coadapted with, or ‘frozen‘ by, the protein–coding genes that they translate, and so cannot easily change by natural selection. Yet the standard code has a significantly non–random pattern that corrects common errors in the transmission of information in protein–coding genes. Because of the freezing effect and for other reasons, this pattern has been proposed not to be due to selection but rather to be incidental to other evolutionary forces or even entirely accidental.

We present results from a deterministic population genetic model of code–message coevolution. We explicitly represent the freezing effect of genes on genetic codes and the perturbative effect of changes in genetic codes on genes. We incorporate characteristic patterns of mutation and translational error, namely, transition bias and positional asymmetry, respectively. Repeated selection over small successive changes produces genetic codes that are substantially, but not optimally, error correcting. In particular, our model reproduces the error–correcting patterns of the standard genetic code. Aspects of our model and results may be applicable to the general problem of adaptation to error in other natural information–processing systems.
Towards a healthy high street: developing mentoring schemes for smaller retailers
Authors: Hudson‐Davies Richard , Parker Cathy , Byrom John
Published: November 2002

The small‐ to medium‐sized enterprise (SME) retailing sector in the UK is facing challenging times. In order to help the sector meet these challenges a number of initiatives have been set up primarily with the intention to train, develop and support SME retailers through these times of change. Nevertheless, although a number of schemes exist at the European, national, regional and local levels, their ability to engage with the sector and facilitate change is questionable. Many of the training schemes and advice services are just not perceived by SME retailers to be relevant to their needs. In this paper, we suggest that a practical alternative to many of the structured and formal approaches currently on offer is that of mentoring. By reviewing the literature pertaining to the method and by presenting SME applications of mentoring we develop a framework for mentoring in the SME retail sector.
Organisational determinants of e‐learning
Authors: Nisar Tahir M.
Published: November 2002

Managers now view e‐learning as an important instrument for obtaining skill‐based organisational outcomes. Not all organisations are likely to implement this training strategy, however, because there are significant trade‐offs involved in terms of both costs and benefits. This article examines the organisational determinants of e‐learning: larger establishments, organisations which employ educated workforce and well established internal labour markets are more likely to adopt an e‐learning strategy. The influence of many such factors requires that a value‐based analysis is undertaken to help organisations make optimal decisions about the choice of e‐learning.
A blended e‐learning approach to intercultural training
Authors: Stewart Joan M.
Published: November 2002

As employees become more globally and technically savvy, it is inevitable that e‐learning finds its way into the practice of intercultural training. After a decade of providing customized face‐to‐face intercultural training, Cendant Mobility’s intercultural experts are responding to the changing profile of the global workforce. Together with their e‐learning partner, Mentergy, they embarked upon a journey toward developing a blended learning solution that is designed to unlock the potential of e‐learning, while maintaining their commitment to genuinely impactful skill‐based intercultural training. The focus of this article is on challenges and lessons learned which include: maintaining cultural appropriateness; technological accessibility; training trainers for this new modality; and attaining user acceptance for a global rollout of a blended e‐learning intercultural training program.
Analyzing student satisfaction with instructional technology techniques
Authors: Roy Matthew H. , Elfner Eliot
Published: November 2002

Corporate universities, higher educational institutions, and training professionals have been using instructional technology (IT) tools and techniques for years. Institutions spend heavily to constantly update their instructional resources, computer labs, and library holdings. Unfortunately, most institutions have not studied the effectiveness of these investments in terms of student satisfaction or learning outcomes. This empirical analysis of 215 student responses provides some insights into the effectiveness of various IT tools and techniques. The findings show that some tools are more effective than others in achieving student satisfaction and positive behavioral outcomes. This study may be useful as a pedagogical tool for instructors planning learning ventures or to justify technological expenditures at the administrative level.
Forgiveness in the workplace
Authors: Stone Michael
Published: November 2002

Most of us have some appreciation for the healing nature of forgiveness in our personal lives, even if we do not always practice it! But, in the world of work it is an act even more rare than the expression of authentic gratitude and appreciation. It is the intention of this paper to show that, in this new economy, which is characterized by escalating speed of change, increasing alienation and a growing search for meaning, it makes good business sense to practice the art of forgiveness. True forgiveness supports the retention of valued employees, allows for greater creativity and innovation, leads to increased profitability, and generates greater flexibility in adapting to changing market conditions.
Problems and projects in action learning
Authors: Edmonstone John
Published: November 2002

Action learning is about individual and organizational learning, but also about the problem‐solving process, which involves both hard and soft inputs. Problems should be distinguished from “puzzles” and criteria for identifying real problems are described. Mapping problems in terms of task and setting is a useful means of clarification.
Questionnaire surveys to discover academic staff and library staff perceptions of a National Union catalogue
Authors: Stubley Peter , Kidd Tony
Published: November 2002

During the feasibility study into a National Union catalogue for the UK (UKNUC), a questionnaire survey was undertaken of the needs of both academic staff in higher education and library staff. A response rate of 40‐50 per cent was achieved, 846 questionnaires being returned for academics and 724 for librarians. The analysis suggests that a UKNUC would be highly valued and heavily used by all categories. Academics felt it would have a positive effect on their information searching, and wished to include the holdings of the British Library, and libraries of both the major research universities and the “traditional” universities. They wanted it to be comprehensive and easy to use, to include locations of both books and journals, and to facilitate subject collection searching. Library staff have similar priorities to academics, although there are more variations by sector and a recognition of a UKNUC’s value as a potential source of bibliographic records.
A Web‐based survey on adolescents’ perceptions of food
Authors: Subratty A.H. , Imrit S. , Jowaheer V.
Published: November 2002

This article focuses on the assessment of adolescents’ perceptions of the importance of food using the World Wide Web. Adolescents were found to be much aware of health‐related issues but in practice their eating habits were more likely to be influenced by the way they feel generally. Adolescent girls perceived their diets in the light of appearance and body shape, while boys were more concerned by fitness and general wellbeing. With age and maturity, adolescents give less importance to fitness and become more conscious about health issues.