bluuebunny/crossref_metadata_2025 huggingface dataset:
Microstructure study of amorphous vanadium oxide thin films using raman spectroscopy
Authors: Lee Se-Hee , Cheong Hyeonsik M. , Je Seong Maeng , Liu Ping , Tracy C. Edwin , Mascarenhas Angelo , Pitts J. Roland , Deb Satyen K.
Published: September 2002

Microstructural changes of amorphous V2O5 films with lithium intercalation are studied using Raman-scattering measurements. The Raman spectra of as-deposited films show two broad peaks around at 520 and 650 cm−1, due to the stretching modes of the V3–O and V2–O bonds, respectively, and a relatively sharp peak at 1027 cm−1 due to the V5+=O stretching mode of terminal oxygen atoms. In addition, there is a peak at 932 cm−1 that we attribute to the V4+=O bonds. Comparison of the Raman spectra of V2O5 films with different oxygen deficiencies confirms this assignment. This Raman peak due to the stretching mode of the V4+=O bonds develops and shifts toward lower frequencies with increasing lithium concentration. Comparison to results from gasochromic hydrogen insertion indicates that the 932 cm−1 Raman peak is not a result of vibrations which involve Li or H atoms. We propose that the V4+=O bonds are created by two different mechanisms: a direct conversion from V5+=O bonds and the breaking of the single oxygen bonds involving V4+ ions.
Internal photoemission of electrons and holes from (100)Si into HfO2
Authors: Afanas’ev V. V. , Stesmans A. , Chen F. , Shi X. , Campbell S. A.
Published: September 2002

The electron energy band alignment at the Si/HfO2 interfaces with different interlayers (Si3N4, SiON, and SiO2) is directly determined using internal photoemission of electrons and holes from Si into the Hf oxide. Irrespective of the interlayer type, the energy barrier for the Si valence electrons was found to be equal 3.1±0.1 eV, yielding the conduction band offset of 2.0±0.1 eV. Photoemission of holes is effectively suppressed by SiON and SiO2 interlayers, yet it is observed to occur across the Si3N4 interlayer with a barrier of 3.6±0.1 eV, which corresponds to a Si/HfO2 valence band offset of 2.5±0.1 eV. The HfO2 band gap width of 5.6 eV, thus derived from the band offsets, coincides with the bulk value obtained from the oxide photoconductivity spectra.
Patterning Sub-50 nm features with near-field embedded-amplitude masks
Authors: Goodberlet James G. , Kavak Hamide
Published: September 2002

Sub-50 nm lines, holes, and posts have been patterned photolithographically using near-field embedded-amplitude masks and an exposing wavelength of 220 nm generated by an arc-lamp source. Interference in the optical near field is utilized to produce the fine patterns. In some cases, the feature sizes on the mask are more than six times larger than the size of the smallest features patterned on the substrate. Numerical simulations support the experimental results.
Current-controlled bi-stable domain configurations in Ni81Fe19 elements: An approach to magnetic memory devices
Authors: Koo H. , Krafft C. , Gomez R. D.
Published: September 2002

The discovery of current-switchable bi-stable remanent domain configurations on small ferromagnetic islands is reported. Rectangular NiFe islands with a thickness of 50 to 100 nm and lateral dimensions on the order of several microns were imaged using magnetic force microscopy after application of 10 ns current pulses through the material. The closure configuration can be set into either the 4 or 7 domain configuration by applying positive or negative current polarity at density on the order 107 A/cm2. The chirality of the closure patterns is fixed, implying that only two rather than four states are stable in these patterns. The possibility of using these configurations as a means of storing a logic state for memory applications is discussed.
R
K
/100
and RK/200 quantum Hall array resistance standards
Authors: Poirier W. , Bounouh A. , Hayashi K. , Fhima H. , Piquemal F. , Genevès G. , André J. P.
Published: September 2002

It is theoretically possible to combine several Hall bars in arrays to define quantum standards with perfectly quantized resistance values. We have thus developed and fabricated quantum Hall array resistance standards (QHARS) made of a large number N (N=100, 50) of Hall bars placed in parallel using a triple connections technique. The Hall resistance of these quantum standards is found to be very well quantized. On the i=2 Hall plateau, the resistance of specific good arrays stays equal to RK/2N within 5 parts in 109 for supplying currents up to 2 mA at a temperature of 1.3 K. The mean longitudinal resistance of the Hall bars which constitute the arrays has been determined through the analysis of the array equivalent electrical circuit. This measurement shows that the carrier transport in the Hall bars is dissipationless. This work, therefore, demonstrates the efficiency of the multiple connections technique and consequently that QHARS are likely to extend the quantum Hall effect metrological applications.
Reflective liquid-crystal display using an in-plane-switching super-twisted nematic cell
Authors: Sun Yubao , Ma Hongmei , Zhang Zhidong , Wu Shin-Tson
Published: September 2002

Two in-plane-switching (IPS) super-twisted nematic (STN) cells are proposed for reflective liquid-crystal displays. The IPS 180°-STN cell exhibits a normally black display with a relatively low-operating voltage, fast response time, and wide viewing angle. Potential applications for large screen reflective displays are foreseeable.
Field emission from individual B–C–N nanotube rope
Authors: Dorozhkin P. , Golberg D. , Bando Y. , Dong Z.-C.
Published: September 2002

The field-emission characteristics of individual ropes made of B–C–N nanotubes were measured in situ in a low-energy electron point source microscope. The tungsten field emission tip of the microscope was used as a movable electrode, approaching the rope, and acting as an anode during field-emission measurements. The atomic structure and chemical composition of the ropes were analyzed by high-resolution transmission electron microscopy and electron energy-loss spectroscopy. The tubes assembled within the ropes typically revealed open-tip ends, a small number of layers and zigzag chirality. We found that the field-emission properties of the B–C–N nanotube ropes are competitive with conventional C nanotubes, with the expected additional benefit that the B–C–N ropes exhibit higher environmental stability.
Stress-induced electron emission from nanocomposite amorphous carbon thin films
Authors: Poa C. H. , Lacerda R. G. , Cox D. C. , Silva S. R. P. , Marques F. C.
Published: September 2002

Traditionally, the emission of electrons from materials have been explained using either the Fowler–Nordheim emission mechanism where high electric fields are used to extract electrons from surfaces or using conventional thermal emission where high currents are used to “boil” off electrons to vacuum. In this letter, we propose an alternative mechanism for electron emission from highly compressive thin films based on stress-induced “band structure” modification of nano-ordered sp2 regions in the thin films. Experimental results are recorded which show that the localized compressive stress governs electron emission in the amorphous carbon thin films studied here rather than the surface nanostructures/features or the diamond-like sp3 hybridized bond component. This analysis is in agreement with the concept of an internal or nongeometric field enhancement from sp2 nanostructures giving rise to high dielectric inhomogeneity within the carbon thin film. The results presented could be extended to explain the anomalous field emission behavior of carbon nanotubes.
A conformational study of the S1(n,π*) excited state of formic acid
Authors: Beaty-Travis Leanne M. , Moule David C. , Lim Edward C. , Judge Richard H.
Published: September 2002

Recent high resolution data from the vibronic bands in the S1←S0 electronic transition in HCOOH were combined with UMP2 ab initio calculations to establish the torsion-wagging potential energy surface over θ=±90° for the torsional coordinate and α=±60° for the wagging angle for the S1 electronic state. The separations between the c- and a/b-type band origins were used to establish a global maximum of 5275 cm−1 for the torsion-wagging potential function. The stability of the structural conformers in the S1 state was obtained from the vibrational intervals in the OH torsional progression that were fitted to the levels calculated from a two dimensional torsion-wagging vibrational model. The fitted potential surface revealed a pair of stable conformers with minima at θ=+68.08, α=+57.51 and θ=−68.08, α=−57.51 deg. A second pair of conformers with minima at θ=−48.50, α=+44.77 or θ=+48.50, α=−44.77 deg was found to be 1207 cm−1 less stable and to be separated by a torsional saddle point of 1270 cm−1 from the more stable conformers.
Acoustic spectroscopy of lithium niobate: Elastic and piezoelectric coefficients
Authors: Ogi Hirotsugu , Kawasaki Yasunori , Hirao Masahiko , Ledbetter Hassel
Published: September 2002

We report simultaneous measurement of the complete set of elastic and piezoelectric coefficients of lithium niobate (LiNbO3), which has trigonal crystal symmetry (3m point group) and thus six independent elastic-stiffness coefficients Cij, four piezoelectric coefficients eij, and two dielectric coefficients κij. We used a single specimen: an oriented rectangular parallelepiped about 5 mm in size. Our measurement method, acoustic spectroscopy, focuses on the crystal’s macroscopic resonance frequencies and is sensitive to any property that affects those frequencies. We overcame the principal obstacle to precise measurements—mode misidentification—by using laser-Doppler interferometry to detect the displacement distribution on a vibrating surface. This approach yields unambiguous mode identification. We used 56 resonances ranging in frequency from 0.3 to 1.2 MHz and determined the Cij and eij with known κij. The ten unknowns always converged to the same values even with unreasonable initial guesses. The Cij uncertainty averages 0.09% for the diagonal Cij. The eij uncertainty averages 5%. All our coefficients fall within the (surprisingly wide) error limits of previous (conventional) measurements.
Very high trapped fields in neutron irradiated and reinforced YBa2Cu3O7−δ melt-textured superconductors
Authors: Gonzalez-Arrabal R. , Eisterer M. , Weber H. W. , Fuchs G. , Verges P. , Krabbes G.
Published: September 2002

We report on very high trapped fields (13.3 T at 33 K) achieved in bulk YBa2Cu3O7−δ melt-textured monoliths, which were reinforced by steel tubes to compensate the tensile stress generated during activation. The flux pinning properties were improved by neutron irradiation. The resulting increase of the critical current density shifts the maximum attainable trapped fields to higher temperatures (by about 10 K).
Ultrafast optical switching properties of single-wall carbon nanotube polymer composites at 1.55 μm
Authors: Chen Y.-C. , Raravikar N. R. , Schadler L. S. , Ajayan P. M. , Zhao Y.-P. , Lu T.-M. , Wang G.-C. , Zhang X.-C.
Published: September 2002

Using a pump–probe method with a 150 fs laser at the wavelength of 1.55 μm, we have experimentally demonstrated that single-walled carbon nanotubes (SWNT) have an exciton decay time of less than 1 ps and a high third-order polarizability, which is reasonably interpreted as due to their azimuthal symmetry. These experimental results reveal that a SWNT polymer composite may be a candidate material for high-quality subpicosecond all-optical switches.
Ferroelectric BaTiO3 thin-film optical waveguide modulators
Authors: Petraru A. , Schubert J. , Schmid M. , Buchal Ch.
Published: September 2002

High-quality BaTiO3 epitaxial thin films on MgO substrates have been grown by pulsed-laser deposition. Both, c-axis and a-axis BaTiO3 orientations were studied. Mach–Zehnder optical waveguide modulators with a fork angle of 1.7° have been fabricated by ion-beam etching. The waveguides are of the ridge type, the BaTiO3 thickness is 1 μm, the ridge step 50 nm, and the width 2 μm. Light was coupled into the waveguides from optical fibers. The BaTiO3 waveguide propagation losses are 2–3 dB/cm. Electrodes of 3 mm length were deposited besides the waveguides. Electro-optic modulation has been demonstrated with Vπ=6.3 V at 632 nm wavelength and Vπ=9.5 V at 1550 nm wavelength for the a-axis samples, and with Vπ=8 V at 632 nm wavelength and Vπ=15 V at 1550 nm for the c-axis samples. Theoretical modelling of the Mach–Zehnder modulators for both crystalline orientations of the BaTiO3 films gave the Pockels coefficients r51=80 pm/V for the c-axis film and an effective Pockels coefficient reff=734 pm/V for the a-axis films at 632 nm wavelength.
Equilibrium structure and lateral stress distribution of amphiphilic bilayers from dissipative particle dynamics simulations
Authors: Shillcock Julian C. , Lipowsky Reinhard
Published: September 2002

The equilibrium structure and lateral stress profile of fluid bilayer membrane patches are investigated using the Dissipative Particle Dynamics simulation technique. Although there are no attractive forces between the model amphiphiles, they spontaneously aggregate into planar bilayers under suitable conditions of concentration and amphiphile architecture. Pure bilayers of single-chain and double-chain amphiphiles are simulated, and the amphiphile architecture and interaction parameters varied. We find that a strong chain stiffness potential is essential to create the lamellar order typical in natural lipid membranes. Single-chain amphiphiles form bilayers whose lamellar phase is destabilized by reductions in the tail stiffness. Double-chain amphiphiles form bilayers whose rigidity is sensitive to their architecture, and that remain well-ordered for smaller values of their tail stiffness than bilayers of single-chain linear amphiphiles with the same hydrophobic tail length. The lateral stress profile across the bilayers contains a detailed structure reflecting contributions from all the interaction potentials, as well as the amphiphile architecture. We measure the surface tension of the bilayers, and extract estimates of the membrane area stretch modulus and bending rigidity that are comparable to experimental values for typical lipid bilayers. The stress profile is similar to that found in coarse-grained Molecular Dynamics simulations, but requires a fraction of the computational cost. Dissipative Particle Dynamics therefore allows the study of the equilibrium behavior of fluid amphiphilic membranes hundreds of times larger than can be achieved using Molecular Dynamics simulations, and opens the way to the investigation of complex mesoscopic cellular phenomena.
Indirect evidence for strong nonadiabatic coupling in N2 associative desorption from and dissociative adsorption on Ru(0001)
Authors: Diekhöner L. , Hornekær L. , Mortensen H. , Jensen E. , Baurichter A. , Petrunin V. V. , Luntz A. C.
Published: September 2002

This paper reports the simultaneous internal state and translational energy resolved associative desorption flux of N2 from Ru(0001) using two different experimental approaches. Both experiments show that the nascent N2 is formed with little vibrational excitation and that the total excitation in all N2 degrees of freedom accounts for only 13 of the barrier energy. Roughly 23 of the energy necessary to surmount the barrier is lost to the surface in desorption. This behavior, as well as the unusual behavior noted previously in direct measurements of dissociative adsorption, both imply strong vibrational quenching in reactive trajectories passing over the high exit channel (vibrational) barrier. Adiabatic quasiclassical dynamical calculations based on the ab initio potential energy surface and various models of coupling to the lattice are not qualitatively consistent with N2 vibrational damping to phonons. However, including a strong nonadiabatic coupling of the vibrational coordinate to electron–hole pairs in the dynamics does yield qualitative agreement between experiments and calculated dynamics, and we suggest this as indirect evidence for strong nonadiabatic coupling. We argue that the nonadiabatic coupling is strong in this case because of the high vibrational excitation necessary to pass over the high exit channel barrier in the reactive processes and the large charge transfer inherent in making or breaking π bonds. We believe that the same factors will be important in most activated dissociations of π bonded molecules on transition metal surfaces, e.g., for O2, NO, N2, and CO, and if this scenario is correct then nonadiabaticity should be important in the activated dissociation dynamics of these systems as well.
Counterexample to an additivity conjecture for output purity of quantum channels
Authors: Werner R. F. , Holevo A. S.
Published: September 2002

A conjecture arising naturally in the investigation of additivity of classical information capacity of quantum channels states that the maximal purity of outputs from a quantum channel, as measured by the p-norm, should be multiplicative with respect to the tensor product of channels. We disprove this conjecture for p>4.79. The same example (with p=∞) also disproves a conjecture for the multiplicativity of the injective norm of Hilbert space tensor products.
Low-threshold terahertz quantum-cascade lasers
Authors: Rochat Michel , Ajili Lassaad , Willenberg Harald , Faist Jérôme , Beere Harvey , Davies Giles , Linfield Edmund , Ritchie David
Published: September 2002

A quantum-cascade laser operating at λ=66 μm is demonstrated. It consists of a three-quantum-well chirped-superlattice active region embedded in a waveguide based on a single interface plasmon and a buried contact. A threshold current density of 210 A/cm2 at T=12 K, a maximum peak optical power of 4 mW, and operation up to T=44 K are achieved in a 2.7 mm long device with a high reflectivity backfacet coating.
Properties of carbon onions produced by an arc discharge in water
Authors: Sano N. , Wang H. , Alexandrou I. , Chhowalla M. , Teo K. B. K. , Amaratunga G. A. J. , Iimura K.
Published: September 2002

A simple method to fabricate high-quality nanoparticles including spherical carbon onions and elongated fullerene-like nanoparticles similar to nanotubes in large quantities without the use of vacuum equipment is reported. The nanoparticles are obtained in the form of floating powder on the water surface following an arc discharge between two graphite electrodes submerged in water. High-resolution transmission electron microscopy (HRTEM) and scanning electron microscopy images confirm the presence of spherical carbon onions with diameters ranging from 4 to 36 nm. The specific surface area of the floating powder was found to be very large, 984.3 m2/g, indicating that the material is promising for gas storage. From the surface area measurements, the mean particle diameter was calculated to be 3.7 nm. This value is close to the lower limit of the carbon onions observed in HRTEM. However, closer HRTEM observations also reveal that some carbon onions are not well crystallized. The large specific surface area can be attributed to the “surface roughness” induced by the defective nature of the carbon onion shells. To explain the formation mechanism of the carbon onions, a model of arc discharge in water with two quenching zones is proposed: (1) the presence of ion current conducive for elongated nanoparticles growth and (2) the absence of ion current for isotropic growth of carbon onions. Based on this model, we propose that the physical characteristics of the product can be controlled.
Preparation of sintered degenerate n-type PbTe with a small grain size and its thermoelectric properties
Authors: Kishimoto Kengo , Koyanagi Tsuyoshi
Published: September 2002

Sintered degenerate n-type PbTe samples with small grain sizes ranging from 0.7 to 4 μm were prepared and the effects of grain size on their thermoelectric properties were then investigated. The Seebeck coefficient of the sintered samples increased almost double when the grain size decreased from 4 to 0.7 μm. On the other hand, their electrical and thermal conductivity decreased with decreasing grain size. Accordingly, decreasing their grain size increased their thermoelectric figure-of-merit. A maximum value of the figure-of-merit of the obtained small grain-size samples was significantly higher than that of large grain-size samples with the same carrier concentration reported. This favorable result was caused mainly by the increase in the Seebeck coefficient. The influences of grain boundaries on the increase in the Seebeck coefficient were discussed. It is concluded that the Seebeck coefficient was increased by potential barrier scattering, which occurred at the grain boundaries in the sintered samples.
Polaron model in self-assembled InAs/GaAs quantum dots— A perturbative approach
Authors: Lelong Ph. , Lin S. H.
Published: September 2002

We propose an analytic study of the polaron spectrum in self-assembled InAs/GaAs quantum dots. The approach is based on the first-order degenerate perturbation theory and, therefore, it allows us to describe the one-phonon processes. In such framework, we are able to interpret recent experimental findings obtained by magneto-far-infrared and Raman spectroscopy.
Investigation of the correlation between structural relaxation time and configurational entropy under high pressure in a chlorinated biphenyl
Authors: Casalini R. , Paluch M. , Fontanella J. J. , Roland C. M.
Published: September 2002

Dielectric relaxation measurements on a chlorinated biphenyl (PCB62) were carried out over a broad frequency range, with variation of both temperature and pressure. In combination with calorimetric determinations of the configurational entropy, these data could be described using the Adam–Gibbs model. Specifically, the experimental results were interpreted using a recently introduced equation for both the temperature and pressure dependencies of the structural relaxation time. The τ(T,P) data for PCB62 yielded values of the fitting parameters consistent with known physical properties of the material. A change of the dynamics was evident in isobaric measurements at atmospheric pressure, corresponding to a value of the relaxation time τB∼5×10−5 s. A related change of dynamics was observed in isothermal experiments at varying pressures. It is noteworthy that the latter transpired at a very similar τ∼τB. Moreover, the shape of the relaxation function depended only on the value of τ. We believe this is the first reported evidence of such a change of dynamics in experiments using pressure as a variable. These results suggest that this change is governed by the time scale of the relaxation, independently of any particular combination of T and P.
Magnon modes for thin circular vortex-state magnetic dots
Authors: Ivanov B. A. , Zaspel C. E.
Published: September 2002

The magnetization in a magnetic microdot made from soft magnetic materials can have a vortex-like ground-state structure resulting from competition between the exchange and dipolar interactions. Normal mode magnon frequencies for such dots are calculated taking into account both exchange and magnetostatic effects. The presence of a low-lying mode as well as doublet structure with small splitting is demonstrated. Estimates of the mode frequencies for permalloy dots are obtained, and the possibility of experimental detection of such modes is discussed.
Deposition kinetics on particles in a dusty plasma reactor
Authors: Cao Jin , Matsoukas Themis
Published: September 2002

We report on the use of dusty plasma chemical vapor deposition for the coating of micron and submicron sized particles. Particles are introduced into a capacitively coupled low-pressure plasma where they become charged and remain electrostatically confined over extended periods of time. Introduction of a hydrocarbon in the plasma results in the formation of a cross-linked solid (plasma polymer) which deposits on the particle surface in the form of a film. The thickness of the coating varies from 3 nm to more than several hundred nanometers and is found to be a linear function of time. The size distribution and the uniformity of deposition are studied as a function of the deposition time and particle size and the results are interpreted qualitatively via a surface deposition model.
Growth of aligned carbon nanotubes on self-similar macroscopic templates
Authors: Cao Anyuan , Wei Bingqing , Jung Y. , Vajtai Robert , Ajayan P. M. , Ramanath G.
Published: September 2002

We demonstrate a two-step chemical vapor deposition process to obtain carbon nanotube (CNT) networks using aligned nanotube films themselves as growth templates. Track patterns of exposed silica created in CNT films grown in the first step serve as macroscopic templates for growing CNT stripes in the second step. The nanotubes in both the template and the stripes are vertically aligned. The CNT templates can be selectively removed while retaining the network of CNT stripes grown among them in the predefined patterns. Two-step processes such as described here will be of interest for creating multilayered CNT architectures through pattern transfer and growth sequences.
High-speed multiplication-type photodetecting device using organic codeposited films
Authors: Matsunobu Goh , Oishi Yuko , Yokoyama Masaaki , Hiramoto Masahiro
Published: September 2002

High-speed photocurrent multiplication devices using codeposited films of copper phthalocyanine and fullerene were fabricated. The photoresponse time for the light-on and -off reached 3 and 15 ms, respectively, which were in striking contrast to those for single fullerene films requiring several seconds. Performance of the present device is promising for the application to multiplication-type photodetector.
Photoinduced ferroelectric hysteresis curve in organic CuPc photoconductor/inorganic BaTiO3 ferroelectric heterojunction photomemory
Authors: Park Young-Geun , Lee Hea-Yeon , Tanaka Hidekazu , Tabata Hitoshi , Kawai Tomoji
Published: September 2002

Photoinduced switching of the ferroelectric P–E hysteresis curve has been achieved in organic photoconductor (PC) copper phthalocyanine (CuPc)/inorganic ferroelectric (FE) BaTiO3 (BTO) heterojunction photomemory in the visible ray region. Light irradiation could switch the remanent polarization of ferroelectric BTO in this heterojunction up to 3 μC/cm2, almost full remanent polarization of BTO single layer, whereas remanent polarization of that without light irradiation was almost zero. We have also investigated the effect of CuPc thickness on the photoinduced change of ferroelectric P–E hysteresis curve, and found that the insulating dark resistance of the organic photoconductor CuPc film layer plays an important role for high efficiency of PC/FE heterojunction photomemory. The efficiency of this heterojunction photomemory reached up to 500%.
Parametric and cascaded parametric interactions in a quasiperiodic optical superlattice
Authors: Du Y. , Zhu S. N. , Zhu Y. Y. , Xu P. , Zhang C. , Chen Y. B. , Liu Z. W. , Ming N. B. , Zhang X. R. , Zhang F. F. , Zhang S. Y.
Published: September 2002

Quasi-phase-matching optical parametric and cascaded parametric processes in a two-component quasiperiodic superlattice were studied in theory and experiment. This letter demonstrates how to obtain red at 666 nm and blue at 443 nm simultaneously from the superlattice using a 532 nm laser as a pump through these two processes mentioned above. The result confirms that some nonlinear frequency conversion processes occurring in a high-dimension χ(2) nonlinear photonic crystal may be efficiently achieved in such a one-dimension quasiperiodic optical superlattice.
Thin-film transistor circuits on large-area spherical surfaces
Authors: Hsu P. I. , Bhattacharya R. , Gleskova H. , Huang M. , Xi Z. , Suo Z. , Wagner S. , Sturm J. C.
Published: September 2002

We report amorphous silicon (a-Si:H) thin-film transistors (TFTs) fabricated on a planar foil substrate, which is then permanently deformed to a spherical dome, where they are interconnected to inverter circuits. This dome subtends as much as 66° (∼1 sr) with the tensile strain reaching a maximum value of ∼6% on its top. Functional TFTs are obtained if design rules are followed to make stiff TFT islands of limited size on compliant substrates. Photoresist patterns for island interconnects are made on the flat structure, are plastically deformed during the shaping of the dome, and then serve to delineate interconnects deposited after deformation by lift-off. We describe the effect of deformation on the TFTs before and after deformation and the performance of TFT inverter circuits. Our results demonstrate that the concept of stiff circuit islands fabricated on deformable foil substrates is a promising approach to electronics on surfaces with arbitrary shapes.
Fuzzy-junction organic light-emitting devices
Authors: Chen C.-W. , Cho T.-Y. , Wu C.-C. , Yu H.-L. , Luh T.-Y.
Published: September 2002

A “fuzzy-junction” organic light-emitting device (OLED) containing a graded organic–organic interface is reported. Such graded junction is effectively produced utilizing interdiffusion through an ultrathin interfacial fusing layer sandwiched between two functional layers. With a glass transition temperature (Tg) lower than remaining layers, this fusing layer permits smooth interdiffusion and mixing of neighboring layers by annealing above its Tg. With appropriate material combinations, fuzzy-junction OLEDs thus prepared exhibit both reduced voltage and enhanced emission efficiency in comparison with conventional abrupt-junction devices. As an instance, a green fluorescent OLED with such fuzzy junction shows a high peak power efficiency of ∼20 lm/W, substantially higher than ∼14 lm/W of a corresponding abrupt-junction device.
Growth mode and matrix effects on the magneto-optical activity of ultrathin films
Authors: Menéndez J. L. , Armelles G. , Cebollada A. , Quintana C. , Ravelosona D. , Chappert C. , Peiró F. , Cornet A.
Published: September 2002

The magneto-optical activity of Fe nanoparticulate systems is studied in this work as a function of the matrix that surrounds the particles and the Fe concentration in the effective layer. It is shown that the magneto-optical activity is not linear or proportional to the amount of Fe even at low coverages when the matrix surrounding the particles is an insulator. As a conclusion, it is also demonstrated that the magneto-optical response of a magnetic ultrathin film system strongly depends on its growth mode, with modifications of up to 100% in its magneto-optical activity.
Enhanced field emission from carbon nanotubes by hydrogen plasma treatment
Authors: Zhi C. Y. , Bai X. D. , Wang E. G.
Published: September 2002

The field emission capability of the carbon nanotubes (CNTs) has been improved by hydrogen plasma treatment, and the enhanced emission mechanism has been studied systematically using Fourier-transform infrared spectroscopy, Raman, and transmission electron microscopy. The hydrogen concentration in the samples increases with increasing plasma treatment duration. A Cδ−–Hδ+ dipole layer may form on CNTs’ surface and a high density of defects results from the plasma treatment, which is likely to make the external surface of CNTs more active to emit electrons after treatment. In addition, the sharp edge of CNTs’ top, after removal of the catalyst particles, may increase the local electronic field more effectively. The present study suggests that hydrogen plasma treatment is a useful method for improving the field electron emission property of CNTs.
Magnetocrystalline anisotropy in single-crystal Co–Ni–Al ferromagnetic shape-memory alloy
Authors: Morito H. , Fujita A. , Fukamichi K. , Kainuma R. , Ishida K. , Oikawa K.
Published: September 2002

The magnetocrystalline anisotropy in a single-crystal Co37Ni34Al29 ferromagnetic shape-memory alloy has been investigated. The prestrain was applied to the parent phase in order to nucleate the specific variant in the sample cooled down through the martensitic transformation temperature. The applied magnetic field facilitates the growth of variants parallel to the applied magnetic field in analogy with the prestrain. From these results of selective nucleation of variants, the magnetocrystalline anisotropy energy in the single crystal Co37Ni34Al29 β′ martensite phase is estimated to be 3.9×106 erg/cm3. In the single crystal, the observed magnitude of the reversible magnetic-field-induced strains is 0.06%.
Observation of coupled plasmon-polariton modes in Au nanoparticle chain waveguides of different lengths: Estimation of waveguide loss
Authors: Maier Stefan A. , Kik Pieter G. , Atwater Harry A.
Published: September 2002

Near-field interactions between closely spaced Au nanoparticles were characterized by studying the spectral position of the extinction bands corresponding to longitudinal (L) and transverse (T) plasmon-polariton modes of Au nanoparticle chains. Far-field spectroscopy and finite-difference time-domain simulations on arrays of 50 nm diameter Au spheres with an interparticle spacing of 75 nm both show a splitting ΔE between the L and T modes that increases with chain length and saturates at a length of seven particles at ΔE=65 meV. We show that the measured splitting will result in a propagation loss of 3 dB/15 nm for energy transport. Calculations indicate that this loss can be reduced by at least one order of magnitude by modifying the shape of the constituent particles.
Nonlinear optical transmission in VOx nanotubes and VOx nanotube composites
Authors: Xu J.-F. , Czerw R. , Webster S. , Carroll D. L. , Ballato J. , Nesper R.
Published: September 2002

Optical-limiting behavior of vanadium oxide nanotubes is characterized for the visible and infrared spectral ranges using 8 ns pulses from a Nd:YAG laser with an f/40 optical system. Vanadium oxide nanotube dispersions were investigated in both water suspensions and embedded in solid polymethyl methacrylate films. In each case, these nanotubes exhibit strong optical-limiting at 532 nm (in comparison to carbon nanotubes); however, no nonlinear behavior is observed for 1064 nm. This suggests that a two photon or excited state absorption mechanism is responsible for the observed nonlinearity.
Configural Features in the Context of Upright and Inverted Faces
Authors: Leder Helmut , Candrian Gian , Huber Oswald , Bruce Vicki
Published: September 2002

When faces are turned upside down, recognition is known to be severely disrupted. This effect is thought to be due to disruption of configurai processing. Recently, Leder and Bruce (2000, Quarterly Journal of Experimental Psychology A53 513–536) argued that configural information in face processing consists at least partly of locally processed relations between facial elements. In three experiments we investigated whether a local relational feature (the interocular distance) is processed differently in upside-down versus upright faces. In experiment 1 participants decided in which of two sequentially presented photographic faces the interocular distance was larger. The decision was more difficult in upside-down presentation. Three different conditions were used in experiment 2 to investigate whether this deficit depends upon parts of the face beyond the eyes themselves; displays showed the eye region alone, the eyes and nose, or the eyes and nose and mouth. The availability of additional features did not interact with the inversion effect which was observed strongly even when the eyes were shown in isolation. In experiment 3 all eyes were turned upside down in the inverted face condition as in the Thatcher illusion (Thompson, 1980 Perception9 483–484). In this case no inversion effect was found. These results are in accordance with an explanation of the face-inversion effect in which the disruption of configural facial information plays the critical role in memory for faces, and in which configural information corresponds to spatial information that is processed in a way which is sensitive to local properties of the facial features involved.
Characterization of the mangrove plant community and associated sediment of Todos os Santos Bay, Bahia, Brazil
Authors: Freitas H. , Guedes M. L. S. , Smith D. H. , Oliveira S. S. , Santos E. S. , da Silva E. M.
Published: September 2002

This work presents the phytosociological characteristics of Todos os Santos Bay mangrove communities in Brazil as well as the chemical composition of the leaves of the three mangrove species and their associated sediment. For the qualitative, phytosociological investigation, the contiguous parcel method was used at five sites associated with petroleum extraction (Site 4, Fontes Island), transportation (Site 2, Madre de Deus and 3, Pati Island), and refining (Site 1, Mataripe). Each site was divided into seven 10 x 10 m parcels. Results indicated that the Todos os Santos mangrove ecosystem has a fringe physiognomy with low bearing, containing the obligate species, Laguncularia racemosa, Rhizophora mangle, and Avicennia schaueriana, the former being the dominant species. The sediment presented a predominantly sandy texture and the average levels of the elements P, Ca, K, Mg, Na, Cu, Zn, Mn, and Fe were within the normal range of variation for this kind of environment. The chemical analysis of leaves revealed significant differences among the species, although Rhizophora mangle and Laguncularia racemosa demonstrated a great similarity in their average concentrations of the minerals N, P, K. Ca, Mg, S, Cu, Fe, Mn, and Zn. For the three species, the individuals collected at Mataripe (Site 1) site, presented significantly higher (p<0.05) concentration of the elements N, P,and Cu, when compared to the others sites, thus suggesting the influence of the oil refinery on mangrove plants.
Notch1 control of oligodendrocyte differentiation in the spinal cord
Authors: Genoud Stéphane , Lappe-Siefke Corinna , Goebbels Sandra , Radtke Freddy , Aguet Michel , Scherer Steven S. , Suter Ueli , Nave Klaus-Armin , Mantei Ned
Published: September 2002

We have selectively inhibited Notch1 signaling in oligodendrocyte precursors (OPCs) using the Cre/loxP system in transgenic mice to investigate the role of Notch1 in oligodendrocyte (OL) development and differentiation. Early development of OPCs appeared normal in the spinal cord. However, at embryonic day 17.5, premature OL differentiation was observed and ectopic immature OLs were present in the gray matter. At birth, OL apoptosis was strongly increased in Notch1 mutant animals. Premature OL differentiation was also observed in the cerebrum, indicating that Notch1 is required for the correct spatial and temporal regulation of OL differentiation in various regions of the central nervous system. These findings establish a widespread function of Notch1 in the late steps of mammalian OPC development in vivo.
Rab32 is an A-kinase anchoring protein and participates in mitochondrial dynamics
Authors: Alto Neal M. , Soderling Jacquelyn , Scott John D.
Published: September 2002

A-kinase anchoring proteins (AKAPs) tether the cAMP-dependent protein kinase (PKA) and other signaling enzymes to distinct subcellular organelles. Using the yeast two-hybrid approach, we demonstrate that Rab32, a member of the Ras superfamily of small molecular weight G-proteins, interacts directly with the type II regulatory subunit of PKA. Cellular and biochemical studies confirm that Rab32 functions as an AKAP inside cells. Anchoring determinants for PKA have been mapped to sites within the conserved α5 helix that is common to all Rab family members. Subcellular fractionation and immunofluorescent approaches indicate that Rab32 and a proportion of the cellular PKA pool are associated with mitochondria. Transient transfection of a GTP binding–deficient mutant of Rab32 promotes aberrant accumulation of mitochondria at the microtubule organizing center. Further analysis of this mutant indicates that disruption of the microtubule cytoskeleton results in aberrantly elongated mitochondria. This implicates Rab32 as a participant in synchronization of mitochondrial fission. Thus, Rab32 is a dual function protein that participates in both mitochondrial anchoring of PKA and mitochondrial dynamics.
Evidence for a role of platelet endothelial cell adhesion molecule-1 in endothelial cell mechanosignal transduction
Authors: Osawa Masaki , Masuda Michitaka , Kusano Ken-ichi , Fujiwara Keigi
Published: September 2002

Fluid shear stress (FSS) induces many forms of responses, including phosphorylation of extracellular signal–regulated kinase (ERK) in endothelial cells (ECs). We have earlier reported rapid tyrosine phosphorylation of platelet endothelial cell adhesion molecule-1 (PECAM-1) in ECs exposed to FSS. Osmotic changes also induced similar PECAM-1 and ERK phosphorylation with nearly identical kinetics. Because both FSS and osmotic changes should mechanically perturb the cell membrane, they might activate the same mechanosignaling cascade. When PECAM-1 is tyrosine phosphorylated by FSS or osmotic changes, SHP-2 binds to it. Here we show that ERK phosphorylation by FSS or osmotic changes depends on PECAM-1 tyrosine phosphorylation, SHP-2 binding to phospho-PECAM-1, and SHP-2 phosphatase activity. In ECs under flow, detectable amounts of SHP-2 and Gab1 translocated from the cytoplasm to the EC junction. When magnetic beads coated with antibodies against the extracellular domain of PECAM-1 were attached to ECs and tugged by magnetic force for 10 min, PECAM-1 associated with the beads was tyrosine phosphorylated. ERK was also phosphorylated in these cells. Binding of the beads by itself or pulling on the cell surface using poly-l–coated beads did not induce phosphorylation of PECAM-1 and ERK. These results suggest that PECAM-1 is a mechanotransduction molecule.
Sweet solution
Authors: Freeze Hudson H.
Published: September 2002

Sugar pills are usually placebos, but Smith et al. (2002, this issue) use one to rescue designer mice unable to make GDP-Fucose. Dietary fucose enters a salvage pathway and spares the mice. Sound simple? Not so. Unknown genetic factors determine life or death.
Roles of knowledge management in online procurement systems
Authors: Hsieh Chang‐tseh , Yang Huiqing , Lin Binshan
Published: September 2002

The implementation of an online procurement system has never been easy due to the barriers created by the different hardware/software, diverse corporate culture and varying users’ skills of interacting with IS/IT. Recent development in knowledge management technology may help alleviate the problems associated with the implementation of an online procurement system. This paper explores how knowledge management technology may be incorporated into the framework of an online procurement system to enhance its effectiveness and efficiency.
Private key generation from on‐line handwritten signatures
Authors: Feng Hao , Choong Wah Chan
Published: September 2002

n recent years, public key infrastructure (PKI) has emerged as co‐existent with the increasing demand for digital security. A digital signature is created using existing public key cryptography technology. This technology will permit commercial transactions to be carried out across insecure networks without fear of tampering or forgery. The relative strength of digital signatures relies on the access control over the individual’s private key. The private key storage, which is usually password‐protected, has long been a weak link in the security chain. In this paper, we describe a novel and feasible system – BioPKI cryptosystem – that dynamically generates private keys from users’ on‐line handwritten signatures. The BioPKI cryptosystem eliminates the need of private key storage. The system is secure, reliable, convenient and non‐invasive. In addition, it ensures non‐repudiation to be addressed on the maker of the transaction instead of the computer where the transaction occurs.
The kinetics of G‐CSF folding
Authors: Brems David N.
Published: September 2002

The folding kinetics of G‐CSF were determined by trp‐fluorescence and far‐UV circular dichroism. Folding and unfolding was achieved by rapid dilution and mixing of the denaturant, GdnHCl. G‐CSF is a four‐helical bundle protein with two long loops between the first and second helices and between the third and fourth helices. The entire conformational change expected by fluorescence was observed by stopped‐flow technology, but due to rapid refolding kinetics only a portion was observed by circular dichroism. G‐CSF contains two trp residues, and their contribution to the fluorescent‐detected kinetics were deciphered through the use of single‐site trp mutants. The trp moieties are probes of the local conformation surrounding their environment. One trp at residue 118 is located within the third helix while the other trp at residue 58 is part of the long loop between the first and second helices. The refolding results were most consistent with the following mechanism: U ↔ I1 ↔ I2 ↔ N; where U represents the unfolded protein, I1 represents intermediate state 1, I2 represents intermediate state 2, and N represents the native state. I1 is characterized as having approximately one‐half of the native‐like helical structure and none of the native‐like fluorescence. I2 has 100% of the native helical structure and most of the trp‐118 and little of the trp‐58 native‐like fluorescence. Thus refolding occurs in distinct stages with half of the helix forming first followed by the remaining half of the helix including the third helix and finally the loop between the first and second helices folds.
Topological investigation of amyloid fibrils obtained from β2‐microglobulin
Authors: Monti Maria , Principe Serena , Giorgetti Sofia , Mangione Palma , Merlini Gianpaolo , Clark Anne , Bellotti Vittorio , Amoresano Angela , Pucci Piero
Published: September 2002

Amyloid fibrils of patients treated with regular hemodialysis essentially consists of β2‐microglobulin (β2‐m) and its truncated species ΔN6β2‐m lacking six residues at the amino terminus. The truncated fragment has a more flexible three‐dimensional structure and constitutes an excellent candidate for the analysis of a protein in the amyloidogenic conformation. The surface topology of synthetic fibrils obtained from intact β2‐m and truncated ΔN6β2‐m was investigated by the limited proteolysis/mass spectrometry approach that appeared particularly suited to gain insights into the structure of β2‐m within the fibrillar polymer. The distribution of prefential proteolytic sites observed in both fibrils revealed that the central region of the protein, which had been easily cleaved in the full‐length globular β2‐m, was fully protected in the fibrillar form. In addition, the amino‐ and carboxy‐terminal regions of β2‐m became exposed to the solvent in the fibrils, whereas they were masked completely in the native protein. These data indicate that β2‐m molecules in the fibrils consist of an unaccessible core comprising residues 20–87 with the strands I and VIII being not constrained in the fibrillar polymer and exposed to the proteases. Moreover, proteolytic cleavages observed in vitro at Lys 6 and Lys 19 reproduce specific cleavages that have to occur in vivo to generate the truncated forms of β2‐m occuring in natural fibrils. On the basis of these data, a possible mechanism for fibril formation from native β2‐m is discussed and an explanation for the occurrence of truncated protein species in natural fibrils is given.