Alcatel-Lucent

About: Alcatel-Lucent is a based out in Stuttgart, Germany. It is known for research contribution in the topics: Signal & Network packet. The organization has 37003 authors who have published 53332 publications receiving 1430547 citations. The organization is also known as: Alcatel-Lucent S.A. & Alcatel.

Easily processable phenylene-thiophene-based organic field-effect transistors and solution-fabricated nonvolatile transistor memory elements.

Abstract: The synthesis of a new series of mixed phenylene−thiophene oligomers is reported; 2,5-bis(4-n-hexylphenyl)thiophene (dH-PTP, 1), 5,5‘-bis(4-n-hexylphenyl)-2,2‘-bithiophene (dH-PTTP, 2), 5,5‘ ‘-bis(4-n-hexylphenyl)-2,2‘:5‘,2‘ ‘-terthiophene (dH-PT3P, 3), 5,5‘ ‘‘-bis(4-n-hexylphenyl)-2,2‘:5‘,2‘ ‘:5‘ ‘,2‘ ‘‘-quaterthiophene (dH-PT4P, 4), 1,4-bis[5-(4-n-hexylphenyl)-2-thienyl]benzene (dH-PTPTP, 5), and 2,5-bis[4(4‘-n-hexylphenyl)phenyl]thiophene (dH-PPTPP, 6) were characterized by 1H NMR, elemental analysis, UV−visible spectroscopy, differential scanning calorimetry, and thermogravimetric analysis. Vacuum-evaporated and solution-cast films were characterized by X-ray diffraction and scanning electron microscopy. All compounds display high p-type carrier mobilities as evaporated (up to 0.09 cm2/Vs) and as solution-cast (up to 0.03 cm2/Vs) films on both Si/SiO2 and ITO/GR (glass resin) substrates. The straightforwardly synthesized dH-PTTP (2) displays an unprecedented combination of mobility, on/off ratio, stab...

Shock Geometry, Seed Populations, and the Origin of Variable Elemental Composition at High Energies in Large Gradual Solar Particle Events

Abstract: Above a few tens of MeV per nucleon, large, gradual solar energetic particle (SEP) events are highly variable in their spectral characteristics and elemental composition. The origin of this variability has been a matter of intense and ongoing debate. In this paper, we propose that this variability arises from the interplay of two factors—shock geometry and a compound seed population, typically comprising both solar-wind and flare suprathermals. Whereas quasi-parallel shocks generally draw their seeds from solar-wind suprathermals, quasi-perpendicular shocks—by requiring a higher initial speed for effective injection—preferentially accelerate seed particles from flares. Solar-wind and flare seed particles have distinctive compositional characteristics, which are then reflected in the accelerated particles. We first examine our hypothesis in the context of particles locally accelerated near 1 AU by traveling interplanetary shocks. We illustrate the implications of our hypothesis for SEPs with two very large events, 2002 April 21 and 2002 August 24. These two events arise from very similar solar progenitors but nevertheless epitomize extremes in high-energy SEP variability. We then test our hypothesis with correlation studies based on observations of 43 large SEP events in 1997-2003 by the Advanced Composition Explorer, Wind, the Interplanetary Monitoring Platform 8, and GOES. We consider correlations among high-energy Fe/O, event size, spectral characteristics, the presence of GeV protons, and event duration at high energies. The observed correlations are all qualitatively consistent with our hypothesis. Although these correlation studies cannot be construed as proof of our hypothesis, they certainly confirm its viability. We also examine the alternative hypothesis in which a direct flare component—rather than flare particles subsequently processed through a shock—dominates at high energies. This alternative would produce compositional characteristics similar to those of our hypothesis. However, the observed longitude distribution of the enhanced Fe/O events, their spectral characteristics, and recent timing studies all pose serious challenges for a direct flare component. We also comment on measurements of the mean ionic charge state of Fe at high energies. We conclude that shock geometry and seed population potentially provide a framework for understanding the overall high-energy variability in large SEP events. We suggest additional studies for testing this hypothesis.

A new path-gain/delay-spread propagation model for digital cellular channels

Abstract: We derive a statistical model for the distribution of RMS delay spread (/spl tau//sub rms/) within a cellular environment, including the effects of base-to-mobile distance, environment type (urban, suburban, rural, and mountainous areas), and the correlation between delay spread and shadow fading. We begin with intuitive arguments that /spl tau//sub rms/ should be lognormally distributed at any given distance d; that the median of this distribution should grow as some (weak) power of d and that the variation about the median should be negatively correlated with shadow fading gain. We then present empirical evidence, drawn from a wide array of published reports, which gives strong support to these conjectures. Finally, we combine our findings with the widely used model for path gain in a cellular environment. The result is a compact statistical model for the joint distribution of path gain and delay spread. The model lends itself readily to Monte Carlo simulation and is useful for performance studies of cellular systems with bandwidths up to tens of kilohertz.

Password hardening based on keystroke dynamics

Abstract: We present a novel approach to improving the security of passwords. In our approach, the legitimate user's typing patterns (e.g., durations of keystrokes, and latencies between keystrokes) are combined with the user's password to generate a hardened password that is convincingly more secure than conventional passwords against both online and offline attackers. In addition, our scheme automatically adapts to gradual changes in a user's typing patterns while maintaining the same hardened password across multiple logins, for use in file encryption or other applications requiring a longterm secret key. Using empirical data and a prototype implementation of our scheme, we give evidence that our approach is viable in practice, in terms of ease of use, improved security, and performance

Colossal magnetoresistance in Cr-based chalcogenide spinels

Abstract: Manganese oxides with a perovskite structure1 exhibit a transition between a paramagnetic insulating phase and a ferromagnetic metal phase. Associated with this transition is an effect known as colossal magnetoresistance2–5 (CMR)—in the vicinity of the transition temperature, the materials exhibit a large change in resistance in response to an applied magnetic field. Such an effect, if optimized, might find potential application in magnetic devices. But the criteria for achieving (and hence optimizing) CMR are not clear, presenting a challenge for materials scientists. The accepted description of CMR in the manganite perovskites invokes the 'double-exchange' mechanism, whereby charge transport is enhanced by the magnetic alignment of neighbouring Mn ions of different valence configuration (Mn3+ and Mn4+), and inhibited by the formation of charge-induced localized lattice distortions6,7. Here we report the existence of a large magnetoresistive effect in a class of materials—Cr-based chalcogenide spinels—that do not possess heterovalency, distortion-inducing ions, manganese, oxygen or a perovskite structure. The realization of CMR in compounds having a spinel structure should open up a vast range of materials for the further exploration and exploitation of this effect.