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Top 20 Most Read Articles
April 2013
The 20 articles with the most full-text downloads during the month, in descending order.
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Uncertain Acoustic Field Modeling and Robust Source Localization in Shallow Water AIP Conf. Proc. 1272, pp. 462-470; doi:http://dx.doi.org/10.1063/1.3493102 (9 pages) Online Publication Date: 28 September 2010
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Oceanic environmental uncertainty can cause significant performance degradation of the SONAR system. Understanding and modeling the uncertainty propagating from environment to acoustic field and then to steering vector is necessary for SONAR design and operation to mitigate the uncertainty effect and provide robust detection and location of targets. The statistical property of uncertainty can be described by the probability density functions or second‐order moments of environmental parameters and acoustic fields. Based on the probability description, a stochastic response surface method is used to propagate the uncertainty from environment to acoustic field by polynomial chaos expansion. Then covariance matrix and associated ellipsoidal neighboring space are used to describe the uncertainty set of acoustic field and steering vector for sonar signal processing. Finally, a robust Minimum Variance (MV) matched‐field processing method is derived by extending the constrained optimization of MV from single point to an uncertainty steering vector ellipsoid. We apply sea test data collected by a vertical array in shallow water to source localization. |
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Growth of Sn Doped ZnO Nanobelts and Their Properties AIP Conf. Proc. 1341, pp. 114-118; doi:http://dx.doi.org/10.1063/1.3586966 (5 pages) Online Publication Date: 31 May 2011
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Sn doped ZnO nanobelts (NBs) have been synthesized by using thermal evaporation method. Sn powder was mixed with the ZnO and graphite powder as the growth reactant for obtaining Sn doped ZnO NBs. It was prepared under nitrogen ambient at temperature 1000° C. The NBs formed were examined with X‐ray diffraction (XRD), Field Emission Scanning Electron Microscope (FESEM). Current‐Voltage (I–V) curve of grown NBs and p‐n junction was measured in a dark environment with forward and reverse biases. Optical property of the NBs was characterized by UV‐Visible spectrometer. |
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Preface: 20th National Symposium on Mathematical Sciences AIP Conf. Proc. 1522, pp. 1-1; doi:http://dx.doi.org/10.1063/1.4801097 (1 page)
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Silicon surface preparation for two-dimensional dopant characterization AIP Conf. Proc. 449, pp. 736-740; doi:http://dx.doi.org/10.1063/1.56918 (5 pages) Online Publication Date: 27 March 2008
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Most two-dimensional (2D) dopant characterization techniques deal with near surface carrier concentration or surface potential measurements using a device cross-section. Thus, a reproducible and well-characterized surface condition is essential for accurate measurements. We report on an X-ray photoelectron spectroscopy study of surface preparation techniques commonly used in 2D dopant characterization: (i) hydrogen termination, (ii) colloidal silica polishing, (iii) low temperature silicon oxidation. Although the presented results may be applied to any other technique, in this report we concentrate on scanning capacitance microscopy (SCM). For high quality SCM a thin, uniform, and charge-free insulating film has to be formed on top of the silicon sample. Two phenomena may have a critical impact on accuracy of SCM: (i) leakage through the insulating layer and (ii) surface charging which may cause unpredictable variations in flat-band voltage. We found that samples polished by colloidal silica have about one monolayer of oxidized silicon. If the polishing is followed by baking at 200 °C in the air then 1 to 2 monolayers of silicon are oxidized and an ultra-thin insulating layer of (4–6) Å is formed. A significant leakage through the silicon oxide layer, which may alter SCM measurements, is expected in both cases. Silicon oxidation under UV irradiation in ozone ambient improves insulating property of silicon oxide film. Interface equivalent to ca. (8–15) Å of silicon dioxide is reproducibly formed by this technique. Importantly, all tested methods of silicon surface preparation are dopant independent. No noticeable surface charging has been observed for any studied method of silicon surface preparation. For silicon oxidized by UV-generated ozone the position of the Si 2p3/2 core-level relative to the Fermi level changes systematically with dopant type and concentration. The binding energy is higher for n-type silicon and lower for p-type doping. Such behavior is expected for silicon with a relatively low density of surface electronic states and hence unpinned Fermi level. We conclude that silicon oxidation by UV-generated ozone is a promising method of silicon surface preparation for high quality SCM. © 1998 American Institute of Physics. |
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Characterization of ultra-thin oxides using electrical C-V and I-V measurements AIP Conf. Proc. 449, pp. 235-239; doi:http://dx.doi.org/10.1063/1.56801 (5 pages) Online Publication Date: 27 March 2008
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The measurement of electrical parameters from capacitance-voltage (C-V) and current-voltage (I-V) curves provides a fast means of characterizing oxides in MOS capacitors or transistor structures. For ultra-thin oxides (<2 nm), conventional, well-established techniques must be reconsidered and modified due to several increasingly important physical effects including polysilicon depletion and surface quantum mechanical effects. In this work these effects have been incorporated into a rapid analysis program for extracting ultra-thin oxide parameters from measured C-V and I-V data. The technique uses a physically based model of structure charge and potential combined with a non-linear least squares fitting technique to extract device parameters. © 1998 American Institute of Physics. |
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A coupled damage and reaction model for simulating energetic material response to impact hazards AIP Conf. Proc. 505, pp. 651-654; doi:http://dx.doi.org/10.1063/1.1303557 (4 pages)
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The Baer-Nunziato multiphase reactive theory for a granulated bed of energetic material is extended to allow for dynamic damage processes, which generate new surfaces as well as porosity. The Second Law of Thermodynamics is employed to constrain the constitutive forms of the mass, momentum, and energy exchange functions as well as those for the mechanical damage model ensuring that the models will be dissipative. The focus here is on the constitutive forms of the exchange functions. The mechanical constitutive modeling is discussed in a companion paper. The mechanical damage model provides dynamic surface area and porosity information needed by the exchange functions to compute combustion rates and interphase momentum and energy exchange rates. The models are implemented in the CTH shock physics code and used to simulate delayed detonations due to impacts in a bed of granulated energetic material and an undamaged cylindrical sample. © 2000 American Institute of Physics. |
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Numerical Analysis of Parametric Downconversion AIP Conf. Proc. 1110, pp. 220-223; doi:http://dx.doi.org/10.1063/1.3131312 (4 pages) Online Publication Date: 27 April 2009
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Parametric downconversion (PDC) is a popular technique to produce twin beams of photons that are entangled in multiple degrees of freedom. The generated states form the basis for numerous applications that require entanglement. An exact quantification of this resource is therefore essential, for instance for quantum cryptography that relies on a complete knowledge of the correlation contained in the state. While the determination of an entanglement monotone for the PDC process is only possible analytically in special cases, an exact calculation must usually be performed numerically. Recent work by Mikhailova et al. [2] analyses a certain class of PDC states for which the concurrence entanglement measure can be obtained by an analytical approximation. In this contribution, we analyse the validity of the approximation by comparison with exact numerical methods. |
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Unidirectional Amplification as a Mechanism for Low‐Frequency Hearing in Mammals AIP Conf. Proc. 1403, pp. 507-512; doi:http://dx.doi.org/10.1063/1.3658139 (6 pages) Online Publication Date: 7 November 2011
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Sound detection is achieved in the inner ear, or cochlea, which spatially separates frequencies. The highest frequencies are detected at the organ's base and successively lower frequencies at progressively more apical positions. Although a mechanism termed critical‐layer absorption accounts for the spatial separation of frequencies above 1 kHz, hearing at lower frequencies appears to operate by a distinct mechanism that is poorly understood. We discuss a recently proposed ratchet mechanism for spatial separation of these low frequencies. This mechanism involves the synergistic interplay of two known active processes in the mechanoreceptive hair cells—active hair‐bundle motility and membrane‐based electromotility—to implement unidirectional amplification. It thus represents a mechanical analogue of the operational amplifier in electrical engineering. The mechanism provides a general design principle for unidirectional mechanical amplification that we have also employed to construct an active microphone. |
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AIP Conf. Proc. 1110, pp. 351-354; doi:http://dx.doi.org/10.1063/1.3131346 (4 pages) Online Publication Date: 27 April 2009
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In this paper we present limitations imposed by sequential attacks on the maximal distance achievable by a differential‐phase‐shift (DPS) quantum key distribution (QKD) protocol with weak coherent pulses. Specifically, we compare the performance of two possible sequential attacks against DPS QKD where Eve realizes, respectively, optimal unambiguous state discrimination of Alice’s signal states, and optimal unambiguous discrimination of the relative phases between consecutive signal states. We show that the second eavesdropping strategy provides tighter upper bounds for the security of a DPS QKD scheme than the former one. |
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AIP Conf. Proc. 1520, pp. 1-2; doi:http://dx.doi.org/10.1063/1.4795943 (2 pages)
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Size Selective Precipitation of CdSe Colloidal Quantum Dots AIP Conf. Proc. 1199, pp. 309-310; doi:http://dx.doi.org/10.1063/1.3295425 (2 pages) Online Publication Date: 15 January 2010
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Cadmium Selenide (CdSe) nanoparticles were synthesized through the colloidal chemistry approach. Dynamic light scattering experiments (DLS) have been performed in CdSe aqueous dispersions in order to determine the nanoparticle hydrodynamic radii. The DLS data together with photoluminescence (PL) measurements allowed for size analyses throughout the synthetic and post‐preparative procedures. We report here a study of size‐selective precipitation (SSP). DLS technique provided fast results, yielding values for the hydrodynamic radii in several size separation steps. Efficiency of the SSP procedure could thus be estimated. |
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RF sputter deposition of Y‐Ba‐Cu‐O superconducting thin films from an oxide powder target AIP Conf. Proc. 165, pp. 58-65; doi:http://dx.doi.org/10.1063/1.37081 (8 pages) Online Publication Date: 4 June 2008
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Thin films of Y‐Ba‐Cu‐O have been fabricated using rf diode sputtering from a single mixed‐oxide powder target. The target consisted of about 200 grams of mixed reacted CuO, BaCO3, and Y2O3 powders spread over an 8‐inch Cu plate, and mounted horizontally in a standard‐model sputtering system. Such a target was used for repeated rf‐diode depositions in a ‘‘sputter‐up’’ mode to a substrate hanging face‐down, with deposition rate of order 50–100 Å/minute. Substrates investigated include sapphire and yttria‐ stabilized zirconia. Well‐cooled substrates yielded films close to the composition of an YBa2Cu3O7 target. In contrast, uncooled or heated substrates yielded films dramatically deficient in Cu relative to the target. Sputtering for several hours in Ar plasma with 10% O2 yielded shiny, black films ≊1 μm thick. Subsequent processing of films on zirconia substrates up to 850 °C in pure O2 yielded an onset of superconductivity at ≊87 K, with a broad transition to zero resistance at ≊50 K. Improvements in this transition are expected as process parameters are refined. Effects of varying substrate temperature, rf power, target composition, and post‐deposition annealing treatment will be discussed. |
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AIP Conf. Proc. 1521, pp. 184-190; doi:http://dx.doi.org/10.1063/1.4796074 (7 pages)
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A non-perturbative probe laser induced fluorescence (LIF) system has been developed to observe a laser-cooled one-component plasma. Since the undistorted spectra can be obtained using this measurement system, a quantitative evaluation of the spectrum shape of the laser-cooled plasma was achieved. The spectra are decomposed into the Doppler and Lorentzian components using a Voigt function. The ion temperature is calculated as 4.5 K from the Doppler component, and the Coulomb coupling parameter Γ is calculated as 0.5 using the ion temperature. On the other side, the Lorentz width is unexpectedly larger than the natural linewidth by 70 MHz or more, and much larger than the ion-ion collisional broadening derived from the Debye screening assumption. The results show that the Debye screening assumption is already incorrect at Γ = 0.5. |
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New Efficient Design for XOR Function on the Transistor Level AIP Conf. Proc. 1324, pp. 346-348; doi:http://dx.doi.org/10.1063/1.3526229 (3 pages) Online Publication Date: 3 December 2010
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This paper proposes a new design of 3T XOR gate. The proposed design of XOR gate is superior in terms of the speed, power consumption and power‐delay product in comparison to other 3T XOR gate designs available in the literature. The simulation has been carried out on Tanner EDA tool on BSIM3v3 90 nm technology. |
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AIP Conf. Proc. 1523, pp. 1-1; doi:http://dx.doi.org/10.1063/1.4802102 (1 page)
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Energy and Environment Chronology AIP Conf. Proc. 1401, pp. 447-454; doi:http://dx.doi.org/10.1063/1.3653869 (8 pages) Online Publication Date: 1 November 2011
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From The Lab to The Fab: Transistors to Integrated Circuits AIP Conf. Proc. 683, pp. 3-39; doi:http://dx.doi.org/10.1063/1.1622451 (37 pages) Online Publication Date: 1 October 2003
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Transistor action was experimentally observed by John Bardeen and Walter Brattain in n‐type polycrystalline germanium on December 16, 1947 (and subsequently polycrystalline silicon) as a result of the judicious placement of gold‐plated probe tips in nearby single crystal grains of the polycrystalline material (i.e., the point‐contact semiconductor amplifier, often referred to as the point‐contact transistor).The device configuration exploited the inversion layer as the channel through which most of the emitted (minority) carriers were transported from the emitter to the collector. The point‐contact transistor was manufactured for ten years starting in 1951 by the Western Electric Division of AT&T. The a priori tuning of the point‐contact transistor parameters, however, was not simple inasmuch as the device was dependent on the detailed surface structure and, therefore, very sensitive to humidity and temperature as well as exhibiting high noise levels. Accordingly, the devices differed significantly in their characteristics and electrical instabilities leading to “burnout” were not uncommon. With the implementation of crystalline semiconductor materials in the early 1950s, however, p‐n junction (bulk) transistors began replacing the point‐contact transistor, silicon began replacing germanium and the transfer of transistor technology from the lab to the lab accelerated. We shall review the historical route by which single crystalline materials were developed and the accompanying methodologies of transistor fabrication, leading to the onset of the Integrated Circuit (IC) era. Finally, highlights of the early years of the IC era will be reviewed from the 256 bit through the 4M DRAM. Elements of IC scaling and the role of Moore’s Law in setting the parameters by which the IC industry’s growth was monitored will be discussed. © 2003 American Institute of Physics |
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An entropy method for floodplain monitoring network design AIP Conf. Proc. 1479, pp. 1780-1783; doi:http://dx.doi.org/10.1063/1.4756522 (4 pages)
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In recent years an increasing number of flood-related fatalities has highlighted the necessity of improving flood risk management to reduce human and economic losses. In this framework, monitoring of flood-prone areas is a key factor for building a resilient environment. In this paper a method for designing a floodplain monitoring network is presented. A redundant network of cheap wireless sensors (GridStix) measuring water depth is considered over a reach of the River Dee (UK), with sensors placed both in the channel and in the floodplain. Through a Three Objective Optimization Problem (TOOP) the best layouts of sensors are evaluated, minimizing their redundancy, maximizing their joint information content and maximizing the accuracy of the observations. A simple raster-based inundation model (LISFLOOD-FP) is used to generate a synthetic GridStix data set of water stages. The Digital Elevation Model (DEM) that is used for hydraulic model building is the globally and freely available SRTM DEM. |
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An improved computational constitutive model for brittle materials AIP Conf. Proc. 309, pp. 981-984; doi:http://dx.doi.org/10.1063/1.46199 (4 pages) Online Publication Date: 12 May 2008
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An improved computational constitutive model for brittle materials is presented. It is applicable for brittle materials subjected to large strains, high strain rates and high pressures, and is well‐suited for computations in both Lagrangian and Eulerian codes. The equivalent strength is dependent on the intact strength, fractured strength, strain rate, pressure, and damage. The pressure includes the effect of bulking, which is introduced through the transfer of internal energy from decreased shear and deviator stresses to potential internal energy associated with increased hydrostatic pressure. Examples are presented to illustrate the model. © American Institute of Physics |
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High-efficiency multijunction solar cells employing dilute nitrides AIP Conf. Proc. 1477, pp. 14-19; doi:http://dx.doi.org/10.1063/1.4753823 (6 pages)
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Solar Junction has developed a set of dilute nitride compound semiconductors with antimony that offer tunable absorption between the GaAs and Ge bandedges, while retaining lattice matching to GaAs or Ge substrates. By replacing the Ge junction in a conventional triple junction solar cell with a GaInNAsSb junction, world record cell efficiencies of 43.5% have been achieved, and CPV module efficiencies (DC) exceeding 35% may now be possible in the near future. |
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Sandia National Laboratories
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