bluuebunny/crossref_metadata_2025 huggingface dataset:
Bioenergetic trajectories underlying partial migration in Patuxent River (Chesapeake Bay) white perch (Morone americana)
Authors: Kerr Lisa A. , Secor David H.
Published: April 2009

Partial migration, the coexistence of resident and migratory individuals within the same population, may be common in fish populations. A proposed mechanism underlying partial migration is differing dispersive responses to early growth conditions, but few studies have explicitly tested this. During their first year of life, white perch ( Morone americana ) in the Patuxent River (Maryland, USA) exhibit either residency in freshwater natal habitats (resident contingent) or disperse down-estuary into brackish habitats (dispersive contingent). We tested whether white perch juveniles exhibited differing growth and metabolic trajectories based on contingent membership or in response to salinity. A randomized factorial experiment with two contingent types and two salinity treatments (1 and 8) was conducted over a 30-day period. The experiments supported a contingent effect, with the dispersive contingent exhibiting higher consumption rates and a higher scope for growth. In addition, we identified a weak salinity effect with evidence of increased consumption and routine metabolism in mesohaline conditions. Juvenile growth rates calculated from individuals in the field supported laboratory results, with dispersive contingent members exhibiting higher growth rates. We conclude that contingent membership and the related phenomenon of partial migration in this population is associated with varying energetic tactics that significantly influence the scope for growth.
Factors influencing coastal cutthroat trout (Oncorhynchus clarkii clarkii) seasonal survival rates: a spatially continuous approach within stream networks
Authors: Berger Aaron M. , Gresswell Robert E.
Published: April 2009

Mark–recapture methods were used to examine watershed-scale survival of coastal cutthroat trout ( Oncorhynchus clarkii clarkii ) from two headwater stream networks. A total of 1725 individuals (≥100 mm, fork length) were individually marked and monitored seasonally over a 3-year period. Differences in survival were compared among spatial (stream segment, subwatershed, and watershed) and temporal (season and year) analytical scales, and the effects of abiotic (discharge, temperature, and cover) and biotic (length, growth, condition, density, movement, and relative fish abundance) factors were evaluated. Seasonal survival was consistently lowest and least variable (years combined) during autumn (16 September – 15 December), and evidence suggested that survival was negatively associated with periods of low stream discharge. In addition, relatively low (–) and high (+) water temperatures, fish length (–), and boulder cover (+) were weakly associated with survival. Seasonal abiotic conditions affected the adult cutthroat trout population in these watersheds, and low-discharge periods (e.g., autumn) were annual survival bottlenecks. Results emphasize the importance of watershed-scale processes to the understanding of population-level survival.
Communication and cohesion in aquatic science literature
Authors: Neff Margaret R. , Jackson Donald A.
Published: April 2009

In 1982, Frank Rigler challenged limnologists and fisheries biologists to address gaps in theory, experimental research, and management practices that have limited the advancement of both fields. We followed up on Rigler’s concerns using a literature study to determine the objectives and methodologies of studies across a range of subdisciplines within aquatic science. We surveyed both recent and historical literature from five leading journals that range in emphasis to include a broad array of subjects in aquatic science. Literature from 1982 was compared with recent publications to determine how communication and integration within aquatic science has changed. We found limited changes in the breadth of coverage provided by any journal. We further analyzed contemporary literature according to subject matter, methods of analysis, location of the research, and scale of study. We used correspondence analysis to identify the differences and associations across these fields and to uncover those particular research areas that have more clearly bridged some of these gaps previously identified. Our findings indicate that there are still clear divisions within modern aquatic science literature and that the journals considered typically show specific emphasis in the types of questions posed, methods of analysis, and the geographic representation of authors.
Angular momentum of the physical electron
Authors: Stewart A. M.
Published: April 2009

The angular momentum of the physical electron, modeled as a Dirac fermion coupled to the electromagnetic field, is found to be ħ/2, the same as that of a bare Dirac fermion and independent of the sign and magnitude of the electric charge. The contribution of the electromagnetic field to the angular momentum is zero.
Numerical simulation of facet dendritic growth in a forced flow
Authors: Chen Zhi , Le Chen Chang , Hao Li Mei
Published: April 2009

A numerical simulation based on a new regularized phase-field model is developed to describe the silicon solidification in a forced flow. The effect of forced flow, anisotropy, and mesh grid on dendritic growth shape is investigated. These results indicate that crystals grow into an equiaxial facet dendritic without flow and into an asymmetrical facet dendritic with flow, that is, upstream arm growth is promoted, and downstream inhibited, however, there is no such effect on perpendicular arms. It is also found that the asymmetrical growth feature becomes noticeable with increase in the flow velocity. With the increase in the anisotropy value, the tip velocities of upstream and downstream decrease gradually.
Thermophoresis particle deposition — thermal radiation interaction on mixed convection from vertical surfaces embedded in porous medium
Authors: Duwairi H. M. , Damseh Rebhi A.
Published: April 2009

This work deals with thermophoresis particle deposition and thermal radiation interaction on mixed convection heat and mass transfer by steady laminar boundary-layer flow over a nonisothermal vertical flat plate embedded in a fluid-saturated porous medium. The governing partial-differential equations are transformed into nonsimilar form by using a special transformation and then solved numerically by using an implicit finite-difference method. Different results are obtained and displayed graphically to explain the effect of various physical parameters on the wall thermophoretic deposition velocity, Nusselt numbers, and temperature and concentration profiles. It was found that the increasing of radiation parameter or dimensionless temperature ratio heated the fluid and decreased the temperature gradients near the impermeable wall, which increased the local Nusselt numbers and decreased the wall thermophoresis velocities. It was also found that the effect of power indexes of either temperatures or concentration enhances both local Nusselt numbers and wall thermophoresis velocities. Comparison with previously published work in the limits of absent thermophoresis and thermal radiation effects shows excellent agreement.
First-principle calculations of the structure and elastic properties of GaAs under pressure
Authors: Cui Hong-Ling , Luo Fen , Chen Xiang-Rong , Ji Guang-Fu
Published: April 2009

A first-principles plane-wave method with the ultrasoft pseudopotential scheme in the framework of density functional theory is performed to calculate the lattice parameters, the bulk modulus B0 and its pressure derivative B0' of the zinc-blende GaAs (ZB–GaAs), rocksalt GaAs (RS–GaAs), CsCl–GaAs, NiAs–GaAs, and wurtzite GaAs (WZ–GaAs). We also calculate the phase transition pressures between different phases, Debye temperatures, and the anisotropies. Our results are consistent with other theoretical results.
Electric field emission of electrons from spherical metallic dust particles
Authors: Sodha Mahendra Singh , Dixit Amrit , Agarwal Sujeet Kumar
Published: April 2009

In this paper, an almost exact expression for the tunneling probability of an electron through the potential barrier on account of a negative charge on a spherical metallic particle has been derived and used to obtain the field emission current density from the surface of the particle. Based on these results a parametric analysis of the phenomenon and comparison with the results of the Jeffreys–Wentzel–Kramers–Brillouin (JWKB) approximation (similar to the Fowler–Nordheim theory) has been presented. It is seen that the JWKB theory underestimates the tunneling probability. The investigation is of relevance to dusty plasmas in space and in the laboratory.
Experimental investigation of single value variables of three-dimensional density current
Authors: Firoozabadi B. , Afshin H. , Sheikhi J.
Published: April 2009

The height of a dense layer underflow is defined as the interface between a dyed saline solution fluid and colorless ambient fluid. In this paper, the density current height or vision height of three-dimensional saline water under pure water is measured empirically, and the relation of this parameter with the location of maximum velocity is investigated. Because of the absence of a clear interface between the dense underflow and pure water, researchers were unable to define a unique parameter for the evaluation of density current height. The parameters used by some researchers include the height corresponding to the location of maximum, half-maximum, and quarter-maximum velocity in the velocity profiles. In this work, the velocity components were measured by an acoustic Doppler velocimeter (ADV), and corresponding parameters were computed based on these velocities. In this laboratory, channel walls were made of glass, so in all experiments the vision height of the dense layer could be measured. Therefore, a relation between the velocity profiles and the dense layer height was established. Results show that dense layer height has a close correlation with height corresponding to the location of the quarter-maximum velocity. Finally, the effects of concentration, bed slope, and discharge on the dense layer height were studied. Experimental data also show that an increase in the inlet flow rate leads to an increase in the dense layer height, and this parameter decreases with an increase in the bed slope or concentration.
Physics of particle collisions at high energies: limits to phenomenology, Part 3
Authors: Sau Goutam , Biswas S. K. , De Bhaskar , Guptaroy P. , Bhattacharya A. , Bhattacharyya S.
Published: April 2009

In continuation of our series of works on the phenomenological studies on production of particles in various high-energy collisions, we attempt here to deal exclusively with some very crucial aspects of Au–Au collisions at RHIC-BNL. With emphasis on understanding the qualitative and quantitative properties of several important observables related to Au–Au interactions at RHIC, we have also endeavored to analyze and assess, if possible, the limits to the successes and failures of such absolutely phenomenological approaches. As all the models in the domain of high-energy physics are invariably and essentially phenomenological in nature, we have also tried to pinpoint the main and major constrictions of and constraints on these approaches-cum-models. By this yardstick, even the so-called Standard Model (SM), which is too greatly lauded and taken for granted, cannot escape our critical remarks that are cast on the general framework of what is termed “phenomenology”, in the realm of physics in particular and of science in general.
High-pressure phase transition and thermodynamic properties of MgSe: Ab initio study
Authors: Fu Hongzhi , Liu WenFang , Gao Tao
Published: April 2009

The transition phase of MgSe from a rock salt structure (B1) to a cesium chloride structure(B2) is investigated by ab initio calculations. The thermodynamic properties of the B1 and B2 structures are obtained through the quasi-harmonic Debye model. Moreover, the dependences of the relative volume V/V0 on the pressure P, the Debye temperature Θ, and heat capacity CV on the pressure P, as well as the heat capacity CV on the temperature T are estimated.
NITROGEN INCORPORATED HYDROGENATED AMORPHOUS CARBON THIN FILMS DEPOSITED BY MICROWAVE SURFACE-WAVE PLASMA CHEMICAL VAPOR DEPOSITION
Authors: ADHIKARI SUDIP , UMENO MASAYOSHI
Published: April 2009

Nitrogen incorporated hydrogenated amorphous carbon (a-C:N:H) thin films have been deposited by microwave surface-wave plasma chemical vapor deposition on silicon and quartz substrates, using helium, methane and nitrogen ( N 2) as plasma source. The deposited a-C:N:H films were characterized by their optical, structural and electrical properties through UV/VIS/NIR spectroscopy, Raman spectroscopy, atomic force microscope and current-voltage characteristics. The optical band gap decreased gently from 3.0 eV to 2.5 eV with increasing N 2 concentration in the films. The a-C:N:H film shows significantly higher electrical conductivity compared to that of N 2-free a-C:H film.
CHARACTERIZATION OF AlN THIN FILMS FABRICATED BY REACTIVE DC SPUTTERING: EXPERIMENTAL MEASUREMENTS AND HÜCKEL CALCULATIONS
Authors: GARCÍA-MÉNDEZ MANUEL , MORALES-RODRÍGUEZ SANTOS , GALVÁN DONALD H. , MACHORRO ROBERTO
Published: April 2009

A set of AlN thin films was prepared by reactive magnetron sputtering at room temperature. The effect of oxygen impurities on the structural and optical properties of AlN films is discussed. The structural and optical properties were characterized using X-ray diffraction (XRD) and spectroscopic ellipsometry, respectively. Depending on the deposition conditions, films can grow hexagonal (würzite, P 63 m 3) or cubic (zinc-blende, Fm3m) in microstructure. From the optical measurements, the ellipsometric parameters (ψ, Δ) and the real refractive index as a function of energy were obtained. From the ellipsometric measurements, a model of Lorentz single-oscillator was employed to estimate the optical band gap, Eg. In the theoretical part, a calculation of density of states (DOS) and band structure was performed to be compared with the experimental results.
RECOVERING THE STATIONARY PHASE CONDITION FOR ACCURATELY OBTAINING SCATTERING AND TUNNELING TIMES
Authors: BERNARDINI A. E.
Published: April 2009

The stationary phase method is often employed for computing tunneling phase times of analytically-continuous gaussian or infinite-bandwidth step pulses which collide with a potential barrier. The indiscriminate utilization of this method without considering the barrier boundary effects leads to some misconceptions in the interpretation of the phase times. After re-examining the above barrier diffusion problem where we notice the wave packet collision necessarily leads to the possibility of multiple reflected and transmitted wave packets, we study the phase times for tunneling/reflecting particles in a framework where an idea of multiple wave packet decomposition is recovered. To partially overcome the analytical incongruities which rise up when tunneling phase time expressions are obtained, we present a theoretical exercise involving a symmetrical collision between two identical wave packets and a one-dimensional squared potential barrier, where the scattered wave packets can be recomposed by summing the amplitudes of simultaneously reflected and transmitted waves.
SPECTRA OF THE JAYNES-CUMMINGS MODEL IN PRESENCE OF A SECOND HARMONIC GENERATION
Authors: BATARFI H. A. , Al-KHAYAT ISA A. , SEBAWE ABDALLA M. , HASSAN S. S.
Published: April 2009

Dipole and cavity field transient spectra are investigated for a modified Jaynes-Cummings (JC) model due to the presence of a second harmonic generation (SHG) cavity field. For initially de-excited atom and field in a coherent state, detuning effects due to SHG affects the symmetry and splitting structure of both spectra.
NEW TYPES OF MULTIPLE SOLITARY WAVE SOLUTIONS FOR THE HIGH-ORDER BROER–KAUP EQUATIONS
Authors: BAI CHENG-JIE , ZHAO HONG , ZHANG XIA , XU HENG-YING
Published: April 2009

Using the extended homogeneous balance method, we obtain a new type of multiple solitary wave solutions for the (1+1)-dimensional high-order Broer–Kaup equations and a new type of multiple solitary wave-like solutions for the (2+1)-dimensional high-order BK equations. The method used here is very concise and primary, and can be generalized to deal with other class of nonlinear equation.
EXISTENCE OF ASYMMETRIC BURGERS VORTICES AND THEIR ASYMPTOTIC BEHAVIOR AT LARGE CIRCULATIONS
Authors: MAEKAWA YASUNORI
Published: April 2009

The asymmetric Burgers vortices are vortex solutions to the three-dimensional stationary Navier–Stokes equations for viscous incompressible fluids in the presence of an asymmetric background straining flow. The asymmetry of the straining flow is expressed by a non-negative parameter less than 1. The Burgers vortices have been used as a model which expresses tube-like structures of concentrated vorticity fields in turbulence, and they are numerically well investigated especially in the case of large circulation numbers. However, their existence was proved mathematically only when either the asymmetry of the straining flow is not so strong or the circulation number is sufficiently small. In this paper, we prove the existence of asymmetric Burgers vortices for all circulation numbers and each asymmetry parameter less than 1. We also obtain their asymptotic expansion at large circulation numbers, which gives an explanation for a symmetrizing effect by a fast rotation.
CONVERGENCE OF ADAPTIVE FINITE ELEMENT METHODS FOR EIGENVALUE PROBLEMS
Authors: GARAU EDUARDO M. , MORIN PEDRO , ZUPPA CARLOS
Published: April 2009

In this paper we prove convergence of adaptive finite element methods for second-order elliptic eigenvalue problems. We consider Lagrange finite elements of any degree and prove convergence for simple as well as multiple eigenvalues under a minimal refinement of marked elements, for all reasonable marking strategies, and starting from any initial triangulation.
MINIMAL DEGREE SEQUENCE FOR TORUS KNOTS OF TYPE (p, q)
Authors: MADETI PRABHAKAR , MISHRA RAMA
Published: April 2009

In this paper we prove the following result: for coprime positive integers p and q with p < q, if r is the least positive integer such that 2p-1 and q + r are coprime, then the minimal degree sequence for a torus knot of type (p, q) is the triple (2p - 1, q + r, d) or (q + r, 2p - 1, d) where q + r + 1 ≤ d ≤ 2q - 1.
TIME DOMAIN IDENTIFICATION OF STRUCTURAL PARAMETERS AND INPUT TIME HISTORY USING A SUBSTRUCTURAL APPROACH
Authors: SANDESH S. , SHANKAR K.
Published: April 2009

This paper presents a substructural approach to parameter identification of structures, with the simultaneous identification of structural parameters and input time history of the applied excitation. The substructural approach reduces the computational effort when dealing with large structures. The substructural parameters, including the unknown interface forces at the ends of the substructure, are identified iteratively. The locations of input forces must be known; however, their magnitudes can be unknown. The method requires the measurement of accelerations at the interior DOFs but not interface DOFs of the substructure. Numerical simulations are performed for three examples, viz. global models of a 15 DOF shear building model, a planar truss of 55 members and a cantilever beam of 20 elements. The examples are excited with harmonic, random and impulse excitations. The effect of noisy data is studied. Even with noise, the proposed substructural method is found to identify the structural parameters with appreciable accuracy and with a considerable saving of CPU time. However, the identification of damping parameters is found to be prone to more errors than for the stiffness parameters.
NUMERICAL SOLUTIONS TO THE FREE VIBRATION PROBLEM OF MINDLIN SECTOR PLATES USING THE DISCRETE SINGULAR CONVOLUTION METHOD
Authors: CIVALEK ÖMER
Published: April 2009

This paper presents the free vibration analysis of annular sector plates based on Mindlin's first-order shear deformation theory using the discrete singular convolution (DSC) method. In the solution process, the governing equations of the motions and boundary conditions of the plate are discretized by the method. The effect of some geometric parameters on frequencies is investigated. Comparisons are made with existing numerical and analytical solutions in the literature. It is found that the DSC method yields accurate results for the plate problems under investigation.
PARAMETER STUDY OF NONLINEAR AERO-THERMOELASTIC BEHAVIOR OF FUNCTIONALLY GRADED PLATES
Authors: NAVAZI H. M. , HADDADPOUR H.
Published: April 2009

In this paper, the effects of different parameters on the nonlinear aeroelastic behavior of functionally graded flat plates are investigated. Considering the through-the-thickness continuous variation of the material properties, a combination of the simple rule of mixtures and the Mori–Tanaka scheme is used for estimating the effective properties at each point. The von-Karman large strains and the piston theory are used to model the structural nonlinearity and aerodynamic loading, respectively. By Hamilton's principle the governing nonlinear partial differential equations of motion are derived and then converted to a set of nonlinear ordinary differential equations using the Galerkin method. The system of nonlinear ordinary differential equations is solved in the time domain using the time integration schemes to determine the aeroelastic response. It is shown that for in-plane-loaded functionally graded plates with temperature-independent material properties, less stability capacity is predicted by the Mori–Tanaka scheme than by the simple rule of mixtures.
THE MAXIMUM FAILURE TIME DISTRIBUTION
Authors: NADARAJAH SARALEES , KOTZ SAMUEL
Published: April 2009

For systems with parallel components, the variable of primary importance is the maximum of the failure times of the different components. In this paper, we study the exact probability distribution of the maximum failure time. Explicit expressions are derived for the cumulative distribution function, probability density function, hazard rate function, moment-generating function, nth moment, variance, skewness, kurtosis, mean deviation, Shannon entropy, and the order statistics. Estimation procedures are derived by the methods of moments and maximum likelihood. We expect that these results could be useful for performance assessment of parallel systems.
OPTIMAL SHAPE OF A HEAVY ELASTIC ROD LOADED WITH A TIP-CONCENTRATED FORCE AGAINST LATERAL BUCKLING
Authors: NOVAKOVIC BRANISLAVA N. , ATANACKOVIC TEODOR M.
Published: April 2009

By using Pontryagin's maximum principle, we determine the optimal shape of an elastic rod free at one and clamped at the other. The rod is loaded with a concentrated force at the free end and its own weight. The optimality criterion is the volume of the rod guaranteeing lateral stability.
AN EFFICIENT DETERMINISTIC SECURE QUANTUM COMMUNICATION SCHEME WITH CLUSTER STATE
Authors: YUAN HAO , SONG JUN , HU XIAOYUAN , HOU KUI
Published: April 2009

A novel efficient scheme for deterministic secure quantum communication with cluster state is proposed. By utilizing Bell-basis- and [Formula: see text]-basis-measurements, the two legitimate users can directly transmit secret message after exchanging some additional classical information. It has a high capacity as each cluster state can carry two bits of information, and has a high intrinsic efficiency because almost all the instances are useful. Since the present scheme is based on the cluster state which is robust against decoherence, it is easily processed by a one-way quantum computer. Furthermore, this scheme is feasible with present-day technique.
SCHEME FOR IMPLEMENTING ASSISTED CLONING OF AN UNKNOWN THREE-PARTICLE THREE-DIMENSION EQUATORIAL ENTANGLED STATE
Authors: MA PENG-CHENG , ZHAN YOU-BANG
Published: April 2009

In this paper, we proposed a protocol which can produce a perfect copy of an unknown three-particle three-dimension equatorial entangled state with assistance from a state preparer. Two stages were included in this protocol. The first stage requires usual teleportation, after Alice's (the state sender) generalized Bell-state measurement. Bob (the state receiver) can get the original state with a certain probability. In the second stage, after having received Victor's (the state preparer) classical message, and using the rest resource of the teleportation process, the perfect copy of an original unknown state can be produced in Alice's place. Furthermore, we have also investigated that the quantum channel is a non-maximally entangled state case. Alice also can re-establish the original unknown state in the certain probability.
TIME IN RELATIVISTIC AND NONRELATIVISTIC QUANTUM MECHANICS
Authors: NIKOLIĆ HRVOJE
Published: April 2009

The kinematic time operator can be naturally defined in relativistic and nonrelativistic quantum mechanics (QM) by treating time on an equal footing with space. The space–time position operator acts in the Hilbert space of functions of space and time. Dynamics, however, makes eigenstates of the time operator unphysical. This poses a problem for the standard interpretation of QM and reinforces the role of alternative interpretations such as the Bohmian one. The Bohmian interpretation, despite of being nonlocal in accordance with the Bell theorem, is shown to be relativistic covariant.
SCHEME FOR IMPLEMENTATION OF THE OPTIMAL 1 → 2 UNIVERSAL QUANTUM CLONING WITH SQUID QUBITS IN A CAVITY VIA A RAMAN TRANSITION
Authors: YANG ZHEN , FANG BAO-LONG , ZHANG WEN-HAI , YE LIU
Published: April 2009

We propose a scheme to realize the optimal 1 → 2 universal quantum cloning (UQC) in 2-dimension with superconducting quantum-interference device (SQUID) qubits in a microwave cavity. In our scheme, three-SQUIDs are fixed in a microwave cavity via a Raman transition for their manipulation. Using this method, no transfer of quantum information between the SQUIDs and the cavity is required, the cavity field is only virtually excited and thus the cavity decay is suppressed during the cloning process. Furthermore, our scheme only requires using the two lower flux states of the SQUID system and the excited state is not excited. So the effect of decoherence based on the levels of the SQUID system is possible to minimize.
A NOTE ON QUANTUM ENTANGLEMENT AND PPT
Authors: FEI SHAO-MING , LI-JOST XIANQING
Published: April 2009

We study quantum states for which the PPT criterion is both sufficient and necessary for separability. We present a class of 3 × 3 bipartite mixed states and show that these states are separable if and only if they are PPT.
BOOK REVIEW: "AN INTRODUCTION TO THE MATHEMATICAL STRUCTURE OF QUANTUM MECHANICS, A SHORT COURSE FOR MATHEMATICIANS", BY F. STROCCHI
Authors: LAWTON WAYNE
Published: April 2009

This book provides a concise introduction to quantum mechanics for students versed in mathematics and mechanics. Dr Strocchi imparts a holistic perspective of the quantum landscape by focussing on three concepts: the algebra of observables, basic quantum systems, and stochastic processes. After mastering these concepts, readers are prepared to study specific quantum theories of information, statistical mechanics, and fields.
IMPROVED CAPACITIVE BEHAVIOR OF MnO2 THIN FILMS PREPARED BY ELECTRODEPOSITION ON THE PT SUBSTRATE WITH A MnOx BUFFER LAYER
Authors: XIA H. , XIAO W. , LAI M. O. , LU L.
Published: April 2009

Nanostructured MnO 2 thin films were prepared on two types of substrates, Pt / Ti / SiO 2/ Si (PT) and MnO x/ Pt / Ti / SiO 2/ Si ( MnO x/ PT ), by the technique of cyclic-voltammetric electrodeposition. The MnO x buffer layer was deposited on the PT substrate by pulsed laser deposition (PLD). The as-deposited MnO 2 thin films were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and X-ray photoelectron spectroscopy (XPS). The electrochemical properties of the thin film MnO 2 electrodes were investigated using cyclic voltammetry (CV) in 1 M Na 2 SO 4 electrolyte. It was found that the adhesion between the MnO 2 film and the Pt substrate was poor, resulting in cracks and peeling of the MnO 2 film after deposition. However, the adhesion of the MnO 2 film with the MnO x buffer layer was greatly improved, resulting in superior pseudocapacitive performance of the thin film electrodes. A specific capacitance of about 364 F/g of MnO 2 thin films deposited on the MnO x buffer layer can be obtained at a scan rate of 10 mV/s in the voltage window between 0 and 0.9 V versus the Ag / AgCl reference electrode. The MnO 2 thin film deposited on the MnO x/ PT substrate exhibits good rate capability and excellent cycle performance, which makes it promising for supercapacitor application.
ZnO NANOPOROUS DISK–TiO2 NANOPARTICLE HYBRID FILM ELECTRODE FOR DYE-SENSITIZED SOLAR CELLS
Authors: GAO XIANG-DONG , GAO WEI , YAN XIAO-DONG , ZHUGE FU-WEI , BIAN JI-MING , LI XIAO-MIN
Published: April 2009

Micron-sized ZnO disks with nanosized pores were synthesized by decomposing the solution-grown layered zinc compound ZnCl 2 · [ Zn ( OH )2]4 · H 2 O ( ZCOH ) at 500°C. ZnO – TiO 2 hybrid film electrodes were prepared by the doctor-blade method, adding ZnO disk powder to the TiO 2 slurry. The crystallinity, microstructure and optical properties of the ZCOH , ZnO nanoporous disk, and the resulting hybrid films, were investigated. Electrochemical impedance spectroscopy and the photocurrent density–voltage curve were employed to characterize the interfacial electron-transporting properties and photoelectrochemical performance of dye-sensitized solar cells (DSCs) using the ZnO – TiO 2 hybrid electrode. Results indicated that the incorporation of a small amount of ZnO disks into the TiO 2 film (less than 1%) can roughen the surface structure, reduce the film thickness, enhance the light scattering in the visible and infrared bands, and increase the interfacial charge transport rate. Hybrid cells showed efficiency improvements of 145% and 109% with the concentrations of ZnO of 0.5% and 1% in the hybrid film respectively, compared with the traditional TiO 2 cell, with a significant increase in the short-currency density and the fill factor. Although the 2.7% efficiency (J sc = 4.0 mA ° cm -2; Voc = 0.74 was not high with the 0.5% ZnO disk incorporated, this work highlighted the potential improvement that novel ZnO nanostructures in hybrid DSCs can achieve.
STRUCTURAL ANALYSIS AND IONIC CONDUCTIVITY AT ROOM TEMPERATURE OF A Ce-DOPED La0.9MnO3-δ PEROVSKITE PREPARED BY THE PECHINI ROUTE
Authors: BOUREMMAD FARIDA , BENABBAS ABDERRAHIM , BOUNAR NEDJMEDDINE , RIDA KAMEL , ROPA PATRICK , CARRU JEAN-CLAUDE
Published: April 2009

A Ce -doped La 0.9 MnO 3-δ sample was prepared by the Pechini route, consisting of a polymerization of citric acid and ethylene glycol, in order to prepare a phase with oxygen deficiency that can be used in fuel cell applications. To substitute a part of lanthanum by cerium, we added CeO 2 in excess to force it to react and diffuse in the perovskite. The Fourier Transformed infrared (FTIR) spectrum of the resin at 200°C has shown the formation of complex metals form and polymerized form of ethylene glycol. The X-ray diffraction (XRD) spectrum of the sample, calcined at 900°C, has revealed that the sample is mainly constituted by a deficient rhombohedra perovskite phase. The measurement of the ionic conductivity by complex impedance at room temperature has given a relatively high value, which opens up an opportunity for solid oxide fuel cell applications.
ELECTROCHEMICALLY ACTIVE LITHIATED NICKEL OXIDE FILMS FABRICATED BY NOVEL THERMAL SYNTHESIS USING Ni/Li/Ni FILMS
Authors: CHO GYUBONG , KIM KIWON , NAM TAEHYUN
Published: April 2009

Lithiated nickel oxide films were thermally synthesized using Ni / Li / Ni films at various temperatures between 873 K and 1123 K. Structural and electrochemical properties of the synthesized films were investigated by means of X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and galvanostatic charge–discharge half-cell tests between 4.5 V and 2.5 V. Lithiated nickel oxide films with the composition near stoichiometric LiNiO 2 could be obtained under annealing conditions (973–1073 K, 1 h). Surfaces of synthesized films consisted of some particles and became smoother with an increase in annealing temperature. Particles with the sharpest edge were formed at 1023 K. Cells with synthesized electrodes showed reversible Li ion transfer and clear voltage plateaus in charge–discharge curves that can confirm the phase transformation of LiNiO 2.
AMLOUK–BOUBAKER EXPANSIVITY: A BPES-RELATED PARAMETER FOR OPTIMIZING PV–T HYBRID SOLAR CELL FUNCTIONAL MATERIALS
Authors: FRIDJINE SANA , BOUBAKER KAREM , AMLOUK MOSBAH
Published: April 2009

In this study, we define a synthetic parameter, optothermal expansivity, as a quantitative guide to evaluating and optimizing PV–T functional materials in both thermal and optical performance. This parameter, ψ AB (or Amlouk–Boubaker expansivity), is calculated using both the thermal diffusivity and the optical effective absorptivity of the material. The values of this parameter, which seems to be a characteristic one, correspond to the total volume that contains a fixed amount of heat per unit time (m3s-1) and can be considered, for future use, as a 3D velocity of the transmitted heat inside the material.
FUNCTIONAL CATHODE MATERIALS FOR Li-ION BATTERIES — PART III: POTENTIAL CATHODE MATERIALS LixNi1-y-zCoyMnzO2 AND LiMn2O4
Authors: MOLENDA JANINA , MARZEC JACEK
Published: April 2009

This paper briefly reviews physicochemical properties of intercalated transition metal compounds with layered and spinel type structure to correlate their microscopic electronic properties, i.e. the nature of electronic states with the efficiency of the lithium intercalation process that is controlled by the chemical diffusion coefficient of lithium. The data concerning cell voltages and characteristics of discharge for various materials are correlated with the nature of chemical bonding and electronic structures.
Historical reflectionsThe rise, fall, and resurrection of software as a service
Authors: Campbell-Kelly Martin
Published: April 2009

A look at the volatile history of remote computing and online software services.
EducationTeaching computing to everyone
Authors: Guzdial Mark
Published: April 2009

Studying the lessons learned from creating high-demand computer science courses for non-computing majors.
API design matters
Authors: Henning Michi
Published: April 2009

Bad application programming interfaces plague software engineering. How do we get things right?
Lest we remember
Authors: Halderman J. Alex , Schoen Seth D. , Heninger Nadia , Clarkson William , Paul William , Calandrino Joseph A. , Feldman Ariel J. , Appelbaum Jacob , Felten Edward W.
Published: April 2009

Contrary to widespread assumption, dynamic RAM (DRAM), the main memory in most modern computers, retains its contents for several seconds after power is lost, even at room temperature and even if removed from a motherboard. Although DRAM becomes less reliable when it is not refreshed, it is not immediately erased, and its contents persist sufficiently for malicious (or forensic) acquisition of usable full-system memory images. We show that this phenomenon limits the ability of an operating system to protect cryptographic key material from an attacker with physical access to a machine. It poses a particular threat to laptop users who rely on disk encryption: we demonstrate that it could be used to compromise several popular disk encryption products without the need for any special devices or materials. We experimentally characterize the extent and predictability of memory retention and report that remanence times can be increased dramatically with simple cooling techniques. We offer new algorithms for finding cryptographic keys in memory images and for correcting errors caused by bit decay. Though we discuss several strategies for mitigating these risks, we know of no simple remedy that would eliminate them.
PuzzledUnderstanding relationships among numbers
Authors: Winkler Peter
Published: April 2009

Welcome to three new challenging mathematical puzzles. Solutions to the first two will be published next month; the third is as yet (famously) unsolved. In each puzzle, the issue is how numbers interact with one another.
Recommendation algorithms, online privacy, and more
Authors: CACM Staff
Published: April 2009

Greg Linden, Jason Hong, Michael Stonebraker, and Mark Guzdial discuss recommendation algorithms, online privacy, scientific databases, and programming in introductory computer science classes.
Classifying search queries using the Web as a source of knowledge
Authors: Gabrilovich Evgeniy , Broder Andrei , Fontoura Marcus , Joshi Amruta , Josifovski Vanja , Riedel Lance , Zhang Tong
Published: April 2009

We propose a methodology for building a robust query classification system that can identify thousands of query classes, while dealing in real time with the query volume of a commercial Web search engine. We use a pseudo relevance feedback technique: given a query, we determine its topic by classifying the Web search results retrieved by the query. Motivated by the needs of search advertising, we primarily focus on rare queries, which are the hardest from the point of view of machine learning, yet in aggregate account for a considerable fraction of search engine traffic. Empirical evaluation confirms that our methodology yields a considerably higher classification accuracy than previously reported. We believe that the proposed methodology will lead to better matching of online ads to rare queries and overall to a better user experience.
A large-scale empirical study of P3P privacy policies
Authors: Reay Ian , Dick Scott , Miller James
Published: April 2009

Numerous studies over the past ten years have shown that concern for personal privacy is a major impediment to the growth of e-commerce. These concerns are so serious that most if not all consumer watchdog groups have called for some form of privacy protection for Internet users. In response, many nations around the world, including all European Union nations, Canada, Japan, and Australia, have enacted national legislation establishing mandatory safeguards for personal privacy. However, recent evidence indicates that Web sites might not be adhering to the requirements of this legislation. The goal of this study is to examine the posted privacy policies of Web sites, and compare these statements to the legal mandates under which the Web sites operate. We harvested all available P3P (Platform for Privacy Preferences Protocol) documents from the 100,000 most popular Web sites (over 3,000 full policies, and another 3,000 compact policies). This allows us to undertake an automated analysis of adherence to legal mandates on Web sites that most impact the average Internet user. Our findings show that Web sites generally do not even claim to follow all the privacy-protection mandates in their legal jurisdiction (we do not examine actual practice, only posted policies). Furthermore, this general statement appears to be true for every jurisdiction with privacy laws and any significant number of P3P policies, including European Union nations, Canada, Australia, and Web sites in the USA Safe Harbor program.
Extraction and classification of dense implicit communities in the Web graph
Authors: Dourisboure Yon , Geraci Filippo , Pellegrini Marco
Published: April 2009

The World Wide Web (WWW) is rapidly becoming important for society as a medium for sharing data, information, and services, and there is a growing interest in tools for understanding collective behavior and emerging phenomena in the WWW. In this article we focus on the problem of searching and classifying
communities
in the Web. Loosely speaking a community is a group of pages related to a common interest. More formally, communities have been associated in the computer science literature with the existence of a locally dense subgraph of the Web graph (where Web pages are nodes and hyperlinks are arcs of the Web graph). The core of our contribution is a new scalable algorithm for finding relatively dense subgraphs in massive graphs. We apply our algorithm on Web graphs built on three publicly available large crawls of the Web (with raw sizes up to 120M nodes and 1G arcs). The effectiveness of our algorithm in finding dense subgraphs is demonstrated experimentally by embedding artificial communities in the Web graph and counting how many of these are blindly found. Effectiveness increases with the size and density of the communities: it is close to 100% for communities of thirty nodes or more (even at low density). It is still about 80% even for communities of twenty nodes with density over 50% of the arcs present. At the lower extremes the algorithm catches 35% of dense communities made of ten nodes. We also develop some sufficient conditions for the detection of a community under some local graph models and not-too-restrictive hypotheses. We complete our
Community Watch
system by clustering the communities found in the Web graph into homogeneous groups by topic and labeling each group by representative keywords.
Fast switching of threads between cores
Authors: Strong Richard , Mudigonda Jayaram , Mogul Jeffrey C. , Binkert Nathan , Tullsen Dean
Published: April 2009

We address the software costs of switching threads between cores in a multicore processor. Fast core switching enables a variety of potential improvements, such as thread migration for thermal management, fine-grained load balancing, and exploiting asymmetric multicores, where performance asymmetry creates opportunities for more efficient resource utilization. Successful exploitation of these opportunities demands low core-switching costs. We describe our implementation of core switching in the Linux kernel, as well as software changes that can decrease switching costs. We use detailed simulations to evaluate several alternative implementations. We also explore how some simple architectural variations can reduce switching costs. We evaluate system efficiency using both real (but symmetric) hardware, and simulated asymmetric hardware, using both microbenchmarks and realistic applications.
Enhancing operating system support for multicore processors by using hardware performance monitoring
Authors: Azimi Reza , Tam David K. , Soares Livio , Stumm Michael
Published: April 2009

Multicore processors contain new hardware characteristics that are different from previous generation single-core systems or traditional SMP (symmetric multiprocessing) multiprocessor systems. These new characteristics provide new performance opportunities and challenges. In this paper, we show how hardware performance monitors can be used to provide a fine-grained, closely-coupled feedback loop to dynamic optimizations done by a multicore-aware operating system. These multicore optimizations are possible due to the advanced capabilities of hardware performance monitoring units currently found in commodity processors, such as execution pipeline stall breakdown and data address sampling. We demonstrate three case studies on how a multicore-aware operating system can use these online capabilities for (1) determining cache partition sizes, which helps reduce contention in the shared cache among applications, (2) detecting memory regions with bad cache usage, which helps in isolating these regions to reduce cache pollution, and (3) detecting sharing among threads, which helps in clustering threads to improve locality. Using realistic applications from standard benchmark suites, the following performance improvements were achieved: (1) up to 27% improvement in IPC (instructions-per-cycle) due to cache partition sizing; (2) up to 10% reduction in cache miss rates due to reduced cache pollution, resulting in up to 7% improvement in IPC; and (3) up to 70% reduction in remote cache accesses due to thread clustering, resulting in up to 7% application-level improvement.
Factored operating systems (fos)
Authors: Wentzlaff David , Agarwal Anant
Published: April 2009

The next decade will afford us computer chips with 100's to 1,000's of cores on a single piece of silicon. Contemporary operating systems have been designed to operate on a single core or small number of cores and hence are not well suited to manage and provide operating system services at such large scale. If multicore trends continue, the number of cores that an operating system will be managing will continue to double every 18 months. The traditional evolutionary approach of redesigning OS subsystems when there is insufficient parallelism will cease to work because the rate of increasing parallelism will far outpace the rate at which OS designers will be capable of redesigning subsystems. The fundamental design of operating systems and operating system data structures must be rethought to put scalability as the prime design constraint. This work begins by documenting the scalability problems of contemporary operating systems. These studies are used to motivate the design of a factored operating system (fos). fos is a new operating system targeting manycore systems with scalability as the primary design constraint, where space sharing replaces time sharing to increase scalability.We describe fos, which is built in a message passing manner, out of a collection of Internet inspired services. Each operating system service is factored into a set of communicating servers which in aggregate implement a system service. These servers are designed much in the way that distributed Internet services are designed, but instead of providing high level Internet services, these servers provide traditional kernel services and replace traditional kernel data structures in a factored, spatially distributed manner. fos replaces time sharing with space sharing. In other words, fos's servers are bound to distinct processing cores and by doing so do not fight with end user applications for implicit resources such as TLBs and caches. We describe how fos's design is well suited to attack the scalability challenge of future multicores and discuss how traditional application-operating systems interfaces can be redesigned to improve scalability.
OS execution on multi-cores
Authors: Nellans David , Balasubramonian Rajeev , Brunvand Erik
Published: April 2009

Large-scale multi-core chips open up the possibility of implementing heterogeneous cores on a single chip, where some cores can be customized to execute common code patterns. The operating system is an example of a common code pattern that is constantly executing on every processor. It is therefore a prime candidate for core customization. Recent work has begun to explore this possibility, where some fraction of system calls and other OS functionality is off-loaded to a separate special-purpose core. Studies have shown that this can improve overall system performance and power consumption. However, our explorations in this arena reveal that the primary benefits of off-loading can be captured with alternative mechanisms that eliminate the negative effects of off-loading. This position paper articulates this alternative mechanism with initial results that demonstrate promise.
Paper rating vs. paper ranking
Authors: Douceur John R.
Published: April 2009

Within the computer-science community, submitted conference papers are typically evaluated by means of rating, in two respects: First, individual reviewers are asked to provide their evaluations of papers by assigning a rating to each paper's overall quality. Second, program committees collectively rate each paper as being either worthy or unworthy of acceptance, according to the aggregate judgment of the committee members. This paper proposes an alternative approach to these two processes, based on rankings rather than ratings. It also presents experiences from employing rankings in PC discussions of a major CS conference.