bluuebunny/crossref_metadata_2025 huggingface dataset:
Importance of global aerosol modeling including secondary organic aerosol formed from monoterpene
Authors: Goto Daisuke , Takemura Toshihiko , Nakajima Teruyuki
Published: April 2008

A global three‐dimensional aerosol transport‐radiation model, coupled to an atmospheric general circulation model (AGCM), has been extended to improve the model process for organic aerosols, particularly secondary organic aerosols (SOA), and to estimate SOA contributions to direct and indirect radiative effects. Because the SOA formation process is complicated and unknown, the results in different model simulations include large differences. In this work, we simulate SOA production assuming various parameterizations of (1) primary organic aerosols (POA) mass concentrations, (2) oxidant species concentrations, and (3) volatile organic compound (VOC) concentrations in the SOA formation through gas‐to‐particle conversion governed by equilibrium partitioning of monoterpene oxidation products. Comparisons of results from observations, other models, and our simulations with/without the SOA partitioning theory lead to some findings of the influence of SOA on the radiation and cloud fields. First, the SOA number concentrations control cloud droplet effective radii near water cloud tops in the tropics and can affect the estimation of the aerosol indirect radiative effect. Second, SOA simulation results strongly depend on POA concentrations and emission data, so that disregarding this dependence may lead to a significant underestimation of the aerosol radiative effect because most of other studies assume that the SOA production level in the preindustrial era is same as in the current level. The global annual mean production of SOA formed from monoterpene is evaluated in this study as 6.74 Tg a−1, and the global annual mean radiative forcings of the direct and indirect effects by SOA from monoterpene are calculated to be –0.01 and –0.19 W m−2, respectively.
An electric force facilitator in descending vortex tornadogenesis
Authors: Patton Forest S. , Bothun Gregory D. , Sessions Sharon L.
Published: April 2008

We present a novel explanation of the physical processes behind one type of cloud and ground‐level tornadogenesis within a supercell. We point out that the charge separation naturally found in these large thunderstorms can potentially serve to contract the preexisting angular momentum through the additional process of the electric force. On the basis of this, we present a plausible geometry that explains why many tornado vortices begin at storm midlevel and build downward into ground‐level tornadoes. A simple model based on this geometry is used to demonstrate the strength of the electric force compared to the required centripetal acceleration to maintain cloud midlevel tornado vortices measurable as tornado vortex signatures (TVSs). Furthermore, a model based on this geometry is used to get a time estimate for tornado vortex formation. From this we are able to identify a plausible value for the threshold charge density that would lead to tornadogenesis and tornado maintenance on the timescale of a few minutes. We show that the proposed geometry can explain the observations that ground‐level tornadoes thrive in regions with high shear and large convective available potential energy (CAPE) and are able to make some predictions of specific measurable quantities.
Late Pleistocene earthquake‐triggered moraine dam failure and outburst of Lake Zurich, Switzerland
Authors: Strasser M. , Schindler C. , Anselmetti F. S.
Published: April 2008

Lakes impounded by moraines may be considered hazardous in glaciated areas throughout the world because dams can fail suddenly producing destructive floods with peak discharges far in excess of normal flows. Here we present a comprehensive case study in the Zurich, Switzerland, area that reveals several independent lines of evidences for the occurrence of a Late Pleistocene (∼13,760 calibrated years B.P.) moraine breach and subsequent Lake Zurich outburst (discharge volume ∼2.5 km3). We use seismic and core data in order to track and date the geological fingerprint of this event. Data from areas downstream of the lake show coarse‐grained massive (>25 m thick) reworked morainic deposits behind four breached zones. In Lake Zurich, sedimentary structures recorded in a paleowater depth of ∼36 m indicate strong outburst‐induced currents. Hydrodynamic calculations reconstructing the sediment transport capacity explaining the observed bed forms allow estimating averaged outburst discharge to exceed minimum values of ∼2400 m3s−1. The potential maximal magnitude of the outburst is inferred from calculations considering critical flow conditions through the breaches revealing estimated peak discharge of ∼20,600 m3s−1. We also discuss long‐term causes and short‐term trigger mechanisms of the dam failure that occurred several thousand years after moraine formation and show that it coincides with a reconstructed strong northern alpine earthquake (magnitude >6.5). Our data thus suggest that catastrophic drainage of Lake Zurich was initiated as a consequence of the moraine dam failure that either was triggered by primary earthquake shaking or by secondary effects, such as overtopping by landslide‐generated waves.
Oceanic loading of wildfire‐derived organic compounds from a small mountainous river
Authors: Hunsinger Glendon B. , Mitra Siddhartha , Warrick Jonathan A. , Alexander Clark R.
Published: April 2008

Small mountainous rivers (SMRs) export substantial amounts of sediment into the world's oceans. The concomitant yield of organic carbon (OC) associated with this class of rivers has also been shown to be significant and compositionally unique. We report here excessively high loadings of polycyclic aromatic hydrocarbons (PAHs), lignin, and levoglucosan, discharged from the Santa Clara River into the Santa Barbara Channel. The abundance of PAHs, levoglucosan, and lignin in Santa Barbara Channel sediments ranged from 201.7 to 1232.3 ng gdw−1, 1.3 to 6.9 μg gdw−1, and 0.3 to 2.2 mg per 100 mg of the sedimentary OC, respectively. Assuming a constant rate of sediment accumulation, the annual fluxes of PAHs, levoglucosan, and lignin, to the Santa Barbara Channel were respectively, 885.5 ± 170.2 ng cm−2 a−1, 3.5 ± 1.9 μg cm−2 a−1 and 1.4 ± 0.3 mg per 100 mg OC cm−2 a−1, over ∼30 years. The close agreement between PAHs, levoglucosan, and lignin abundance suggests that the depositional flux of these compounds is largely biomass combustion‐derived. To that end, use of the Santa Clara River as a model for SMRs suggests this class of rivers may be one of the largest contributors of pyrolyzed carbon to coastal systems and the open ocean. Wildfire associated carbon discharged from other high yield fluvial systems, when considered collectively, may be a significant source of lignin, pyrolytic PAHs, and other pyrogenic compounds to the ocean. Extrapolating these methods over geologic time may offer useful historical information about carbon sequestration and burial in coastal sediments and affect coastal carbon budgets.
Correcting the polarization leakage phases and amplitudes throughout the primary beam of an interferometer
Authors: Reid R. I. , Gray A. D. , Landecker T. L. , Willis A. G.
Published: April 2008

Polarimetric observations are affected by leakage of unpolarized light into the polarization channels, in a way that varies with the angular position of the source relative to the optical axis. The off‐axis part of the leakage is often corrected by subtracting the product of the unpolarized map and a leakage map from each polarization image, but it is seldom realized that heterogeneities in the array shift the loci of the leaked radiation in a baseline‐dependent fashion. We present here a method to measure and remove the wide‐field polarization leakage of a heterogeneous array. The process also maps the complex voltage patterns of each antenna, which can be used to correct all Stokes parameters for imaging errors due to the primary beams.
The continental margin is a key source of iron to the HNLC North Pacific Ocean
Authors: Lam Phoebe J. , Bishop James K. B.
Published: April 2008

Here we show that labile particulate iron and manganese concentrations in the upper 500 m of the Western Subarctic Pacific, an iron‐limited High Nutrient Low Chlorophyll (HNLC) region, have prominent subsurface maxima between 100–200 m, reaching 3 nM and 600 pM, respectively. The subsurface concentration maxima in particulate Fe are characterized by a more reduced oxidation state, suggesting a source from primary volcagenic minerals such as from the Kuril/Kamchatka margin. The systematics of these profiles suggest a consistently strong lateral advection of labile Mn and Fe from redox‐mobilized labile sources at the continental shelf supplemented by a more variable source of Fe from the upper continental slope. This subsurface supply of iron from the continental margin is shallow enough to be accessible to the surface through winter upwelling and vertical mixing, and is likely a key source of bioavailable Fe to the HNLC North Pacific.
Cluster multispacecraft determination of AKR angular beaming
Authors: Mutel R. L. , Christopher I. W. , Pickett J. S.
Published: April 2008

Simultaneous observations of AKR emission using the four‐spacecraft Cluster array were used to make the first direct measurements of the angular beaming patterns of individual bursts. By comparing the spacecraft locations and AKR burst locations, the angular beaming pattern was found to be narrowly confined to a plane containing the magnetic field vector at the source and tangent to a circle of constant latitude. Most rays paths are confined within 15° of this tangent plane, consistent with numerical simulations of AKR k‐vector orientation at maximum growth rate. The emission is also strongly directed upward in the tangent plane, which we interpret as refraction of the rays as they leave the auroral cavity. The narrow beaming pattern implies that an observer located above the polar cap can detect AKR emission only from a small fraction of the auroral oval at a given location. This has important consequences for interpreting AKR visibility at a given location. It also helps re‐interpret previously published Cluster VLBI studies of AKR source locations, which are now seen to be only a subset of all possible source locations. The observations are inconsistent with either filled or hollow cone beaming models.
TM1 and TM2: two mutant alleles that are involved in the pre‐TCR/TCR signaling
Authors: Huang Fang , Naramura Mayumi , Gu Hua
Published: April 2008

It has been shown that the transgene insertional mutations TM1 and TM2 constitute a genetic trait controlling thymocyte development. Here we conducted a detailed analysis of the impact of TM1 and TM2 double mutation on thymocyte development. We found that the hemizygous TM1 and TM2 double transgenic mice possessed much smaller thymi. Flow cytometric analysis revealed a severe blockage of T‐cell development at the transition from DN3 to DN4 stage and pre‐T‐cell receptor (pre‐TCR)/TCR signaling appeared to be impaired. We could not identify any known gene that was implicated in a similar function in the chromosomal regions 7E–F1 and 11B5–C, where TM1 and TM2 mutations were mapped to respectively. Thus, TM1 and TM2 mutations represent two novel alleles that define a genetic trait controlling DN3 thymocyte development, possibly through modulating the signals downstream of the pre‐TCR.
Determination of T‐cell fate by dendritic cells: a new role for asymmetric cell division?
Authors: Russell Sarah M
Published: April 2008

The production, from a single naive T cell, of the many different activated T cell types required for an effective immune response has fascinated immunologists for decades. This process underpins the development of vaccines, immunosuppressive regimes in transplant patients, and immunotherapy in cancer among other things. Despite the enormous advances in detailing the mechanisms and influencing factors in the differentiation of each T‐cell subtype, it is still not clear how the different T‐cell progeny are produced in proportions that are appropriate for each situation. This review discusses the notion that asymmetric cell division might allow for the regulated generation of different cell populations.
Synergistic antitumor effects of CpG oligodeoxynucleotide and STAT3 inhibitory agent JSI‐124 in a mouse melanoma tumor model
Authors: Molavi Ommoleila , Ma Zengshuan , Hamdy Samar , Lai Raymond , Lavasanifar Afsaneh , Samuel John
Published: April 2008

One of the major limitations for cancer immunotherapy is related to the frequent existence of an intra‐tumoral immunosuppressive environment, to which STAT3 (Signal transducer and activator of transcription‐3) activation in tumor and dendritic cells (DCs) are believed to contribute. In this study, we tested the hypothesis that the combination of CpG (a DC activator) and JSI‐124 (a STAT3 inhibitor) may generate synergistic antitumor effects compared to CpG or JSI‐124 alone. B16‐F10, a mouse melanoma cell line that has constitutively active STAT3, was grafted in C57BL/6 mice and then tumor‐bearing mice treated intra‐tumorally with (a) phosphate buffered saline, (b) 10 μg CpG, (c) 1 mg kg−1 JSI‐124 or (d) 10 μg CpG+1 mg kg−1 JSI‐124. The effects of treatments on tumor growth, survival and antitumor immune responses were evaluated. Although significant antitumor effects were detected with the single‐agent treatments, the CpG+JSI‐124 treatment resulted in synergistic antitumor effects compared to CpG or JSI‐124 alone. Correlating with these findings, the combination therapy resulted in significantly higher intra‐tumoral levels of several proinflammatory, TH1‐related cytokines (including IL‐12, IFN‐γ, TNF‐α and IL‐2), increases in intra‐tumoral CD8+ and CD4+ T cells expressing activation/memory markers and NK cells and increases in activated DCs in the tumors and regional lymph nodes (LNs). Concomitantly, the combination therapy led to a significantly decreased level of immunosuppression, as evidenced by lower intra‐tumoral level of VEGF and TGF‐β, and decreased number of CD4+CD25+Foxp3+ regulatory T cells in the regional LNs. This study has provided the proof‐of‐principle for combining CpG and JSI‐124 to enhance antitumor immune responses.
1st INCF Workshop on Global Portal Services for Neuroscience
Authors: van Pelt Jaap , Shepherd Gordon
Published: April 2008

The goal of this meeting was to map out existing portal services for neuroscience, identify their features and future plans, and outline opportunities for synergistic developments. The workshop discussed alternative formats of future global and integrated portal services.
Iran's Pieta: Motherhood, Sacrifice and Film in the Aftermath of the Iran–Iraq War
Authors: Varzi Roxanne
Published: April 2008

The Iran–Iraq war, which took place from 1980 to 1988, was one of the longest and bloodiest conventional wars in the history of the last century. The war was also the largest mobilization of the Iranian population and was achieved primarily by producing and promoting a culture of martyrdom based on religious themes found in Shi'i Islam. It was the war that created and consolidated what we know today as the Islamic republic of Iran. For years there have been two popular public discourses in post-war Iran: the secular discourse, which is to evade, to ignore, to escape to the Caspian; and then the state's discourse, of the strong, mourning women and the heroic martyrs. It is the group of women who exist betwixt the dominant discourses of the secular versus the religious and the idea of womanhood versus motherhood that I am interested in exploring here by looking at the most recent work of a secular female filmmaker, Rakhshan Bani-Etemad.
Gendered Embodiments: Mapping the Body-Politic of the Raped Woman and the Nation in Bangladesh
Authors: Mookherjee Nayanika
Published: April 2008

There has been much academic work outlining the complex links between women and the nation. Women provide legitimacy to the political projects of the nation in particular social and historical contexts. This article focuses on the gendered symbolization of the nation through the rhetoric of the ‘motherland’ and the manipulation of this rhetoric in the context of national struggle in Bangladesh. I show the ways in which the visual representation of this ‘motherland’ as fertile countryside, and its idealization primarily through rural landscapes has enabled a crystallization of essentialist gender roles for women. This article is particularly interested in how these images had to be reconciled with the subjectivities of women raped during the Bangladesh Liberation War ( Muktijuddho) and the role of the aestheticizing sensibilities of Bangladesh's middle class in that process.
Modeling nuclear fusion in dense plasmas using a cryogenic non-neutral plasma
Authors: Dubin Daniel H. E.
Published: April 2008

An analogy between the nuclear reaction rate in a dense neutral plasma and the energy equipartition rate in a strongly magnetized non-neutral plasma is discussed. This analogy allows the first detailed measurements of plasma screening enhancements in the strong screening and pycnonuclear regimes. In strong magnetic fields and at low temperatures, cyclotron energy, like nuclear energy, is released only through rare close collisions between charges. The probability of such collisions is enhanced by plasma screening, just as for nuclear reactions. Rate enhancements of up to 1010 are measured in simulations of equipartition, and are compared to theories of screened nuclear reactions.
Product state resolved excitation spectroscopy of He–, Ne–, and Ar–Br2 linear isomers: Experiment and theory
Authors: Pio Jordan M. , van der Veer Wytze E. , Bieler Craig R. , Janda Kenneth C.
Published: April 2008

Valence excitation spectra for the linear isomers of He–, Ne–, and Ar–Br2 are reported and compared to a two-dimensional simulation using the currently available potential energy surfaces. Excitation spectra from the ground electronic state to the region of the inner turning point of the Rg–Br2 (B,ν′) stretching coordinate are recorded while probing the asymptotic Br2 (B,ν′) state. Each spectrum is a broad continuum extending over hundreds of wavenumbers, becoming broader and more blueshifted as the rare gas atom is changed from He to Ne to Ar. In the case of Ne–Br2, the threshold for producing the asymptotic product state reveals the X-state linear isomer bond energy to be 71±3cm−1. The qualitative agreement between experiment and theory shows that the spectra can be correctly regarded as revealing the one-atom solvent shifts and also provides new insight into the one-atom cage effect on the halogen vibrational relaxation. The measured spectra provide data to test future ab initio potential energy surfaces in the interaction of rare gas atoms with the halogen valence excited state.
Single switch surface hopping for molecular dynamics with transitions
Authors: Fermanian Kammerer Clotilde , Lasser Caroline
Published: April 2008

A trajectory surface hopping algorithm is proposed, which stems from a mathematically rigorous analysis of propagation through conical intersections of potential energy surfaces. Since nonadiabatic transitions are only performed when a classical trajectory attains one of its local minimal surface gaps, the algorithm is called single switch surface hopping. Numerical experiments for a two mode Jahn–Teller system are presented, which illustrate the asymptotic justification of the method as well as its good performance in the physically relevant parameter range.
Observation of the 5p Rydberg states of sulfur difluoride radical by resonance-enhanced multiphoton ionization spectroscopy
Authors: Zhang Qun , Zhou Xiaoguo , Li Quanxin , Yu Shuqin , Ma Xingxiao
Published: April 2008

Sulfur difluoride radicals in their ground state have been produced by a “laser-free” pulsed dc discharge of the SF6∕Ar gas mixtures in a supersonic molecular beam and detected by mass-selective resonance-enhanced multilphoton ionization (REMPI) spectroscopy in the wavelength range of 408–420nm. Analyses of the (3+1) REMPI excitation spectrum have enabled identification of three hitherto unknown Rydberg states of this radical. Following the Rydberg state labeling in our previous work [see J. Phys. Chem. A 102, 7233 (1998)], these we label the K̃(5p1) [ν0-0=71837cm−1, ω1′(a1symstr)=915cm−1], L̃(5p2) [ν0-0=72134cm−1, ω1′(a1symstr)=912cm−1], and M̃(5p3) [ν0-0=72336cm−1, ω1′(a1symstr)=926cm−1] Rydberg states, respectively. [Origins, relative to the lowest vibrational level of the X̃A11 ground state, and vibrational frequencies of the symmetric S–F stretching mode are suggested by the numbers in brackets.] Photofragmentation process of SF2+→SF++F that relates to the REMPI spectrum was discussed.
Environment induced bipartite entanglement
Authors: Benatti Fabio , Liguori-Schremp Alexandar M. , Nagy Adam
Published: April 2008

Recently, a sufficient condition on the structure of the Kossakowski–Lindblad master has been given such that the generated reduced dynamics of two results entangling for at least one among their initial separable pure states. In this paper we study to which extent this condition is also necessary. Further, we find sufficient conditions for bath-mediated generation in higher dimensional bipartite
Thermoacoustic instability in a Rijke tube: Non-normality and nonlinearity
Authors: Balasubramanian Koushik , Sujith R. I.
Published: April 2008

The role of non-normality and nonlinearity in thermoacoustic interaction in a Rijke tube is investigated in this paper. The heat release rate of the heating element is modeled by a modified form of King’s law. This fluctuating heat release from the heating element is treated as a compact source in the one-dimensional linear model of the acoustic field. The temporal evolution of the acoustic perturbations is studied using the Galerkin technique. It is shown that any thermoacoustic system is non-normal. Non-normality can cause algebraic growth of oscillations for a short time even though the eigenvectors of the system could be decaying exponentially with time. This feature of non-normality combined with the effect of nonlinearity causes the occurrence of triggering, i.e., the thermoacoustic oscillations decay for some initial conditions whereas they grow for some other initial conditions. If a system is non-normal, then there can be large amplification of oscillations even if the excited frequency is far from the natural frequency of the system. The dependence of transient growth on time lag and heater positions is studied. Such amplifications (pseudoresonance) can be studied using pseudospectra, as eigenvalues alone are not sufficient to predict the behavior of the system. The geometry of pseudospectra can be used to obtain upper and lower bounds on the growth factor, which provide both necessary and sufficient conditions for the stability of a thermoacoustic system.
Cumulative effect of the Weibel-type instabilities in symmetric counterstreaming plasmas with kappa anisotropies
Authors: Lazar M. , Schlickeiser R. , Shukla P. K.
Published: April 2008

Counterstreaming plasma structures are ubiquitous in laboratory experiments and astrophysical systems, and they are investigated either to prevent unstable modes arising in beam-plasma experiments or to prove the existence of large scale magnetic fields in astrophysical objects. Filamentation instability arises in a counterstreaming plasma and is responsible for the magnetization of the plasma. A filamentationally unstable mode is described by assuming two symmetric counterstreaming plasmas, each with an isotropic Lorentzian (kappa) distribution. In this case, the filamentation instability growth rate can reach a maximum value markedly larger than that for a plasma with a Maxwellian distribution function. This behavior is opposite to what was observed for the Weibel instability growth rate in a bi-kappa plasma, which is always smaller than that obtained for a bi-Maxwellian plasma. The approach is further generalized for a counterstreaming plasma with a bi-kappa temperature anisotropy. In this case, the filamentation instability growth rate is enhanced by the Weibel effect when the plasma is hotter in the streaming direction, and the growth rate becomes even larger. These effects significantly improve the efficiency of the magnetic field generation, and provide further support for the potential role of the Weibel-type instabilities in the fast magnetization scenarios.
Localized dynamic kinetic-energy-based models for stochastic coherent adaptive large eddy simulation
Authors: De Stefano Giuliano , Vasilyev Oleg V. , Goldstein Daniel E.
Published: April 2008

Stochastic coherent adaptive large eddy simulation (SCALES) is an extension of the large eddy simulation approach in which a wavelet filter-based dynamic grid adaptation strategy is employed to solve for the most “energetic” coherent structures in a turbulent field while modeling the effect of the less energetic background flow. In order to take full advantage of the ability of the method in simulating complex flows, the use of localized subgrid-scale models is required. In this paper, new local dynamic one-equation subgrid-scale models based on both eddy-viscosity and non-eddy-viscosity assumptions are proposed for SCALES. The models involve the definition of an additional field variable that represents the kinetic energy associated with the unresolved motions. This way, the energy transfer between resolved and residual flow structures is explicitly taken into account by the modeling procedure without an equilibrium assumption, as in the classical Smagorinsky approach. The wavelet-filtered incompressible Navier–Stokes equations for the velocity field, along with the additional evolution equation for the subgrid-scale kinetic energy variable, are numerically solved by means of the dynamically adaptive wavelet collocation solver. The proposed models are tested for freely decaying homogeneous turbulence at Reλ=72. It is shown that the SCALES results, obtained with less than 0.5% of the total nonadaptive computational nodes, closely match reference data from direct numerical simulation. In contrast to classical large eddy simulation, where the energetic small scales are poorly simulated, the agreement holds not only in terms of global statistical quantities but also in terms of spectral distribution of energy and, more importantly, enstrophy all the way down to the dissipative scales.
Analytical reconsideration of the von Neumann paradox in the reflection of a shock wave over a wedge
Authors: Vasilev Eugene I. , Elperin Tov , Ben-Dor Gabi
Published: April 2008

The reflection of weak shock waves has been reconsidered analytically using shock polars. Based on the boundary condition across the slipstream, the solutions of the three-shock theory (3ST) were classified as “standard-3ST solutions” and “nonstandard-3ST solutions.” It was shown that there are two situations in the nonstandard case: A situation whereby the 3ST provides solutions of which at least one is physical and a situation when the 3ST provides a solution which is not physical, and hence a reflection having a three-shock confluence is not possible. In addition, it is shown that there are initial conditions for which the 3ST does not provide any solution. In these situations, a four-wave theory, which is also presented in this study, replaces the 3ST. It is shown that four different wave configurations can exist in the weak shock wave reflection domain, a Mach reflection, a von Neumann reflection, a ?R (this reflection is not named yet!), and a modified Guderley reflection (GR). Recall that the wave configuration that was hypothesized by Guderley [“Considerations of the structure of mixed subsonic-supersonic flow patterns,” Air Materiel Command Technical Report No. F-TR-2168-ND, ATI No. 22780, GS-AAF-Wright Field No. 39, U.S. Wright–Patterson Air Force Base, Dayton, OH (October 1947); Theorie Schallnaher Strömungen (Springer-Verlag, Berlin, 1957)] and later termed Guderley reflection did not include a slipstream (see Fig. 7). Our numerical study revealed that the wave structure proposed by Guderley must be complemented by a slipstream (see Fig. 4) in order to be relevant for explaining the von Neumann paradox. Hereafter, for simplicity, this modified GR wave configuration will be also termed Guderley reflection. The domains and transition boundaries between these four types of reflection are elucidated.
Monitoring the thermal power of nuclear reactors with a prototype cubic meter antineutrino detector
Authors: Bernstein A. , Bowden N. S. , Misner A. , Palmer T.
Published: April 2008

In this paper, we estimate how quickly and how precisely a reactor’s operational status and thermal power can be monitored over hour to month time scales, using the antineutrino rate as measured by a cubic meter scale detector. Our results are obtained from a detector we have deployed and operated at 25m standoff from a reactor core. This prototype can detect a prompt reactor shutdown within 5h and monitor relative thermal power to within 7days. Monitoring of short-term power changes in this way may be useful in the context of International Atomic Energy Agency’s reactor safeguards regime or other cooperative monitoring regimes.
Combining density functional theory and cluster expansion methods to predict H2 permeance through Pd-based binary alloy membranes
Authors: Semidey-Flecha Lymarie , Sholl David S.
Published: April 2008

First-principles calculations offer a useful complement to experimental approaches for characterizing hydrogen permeance through dense metal membranes. A challenge in applying these methods to disordered alloys is to make quantitative predictions for the net solubility and diffusivity of interstitial H based on the spatially local information that can be obtained from first-principles calculations. In this study, we used a combination of density functional theory calculations and a cluster expansion method to describe interstitial H in alloys of composition Pd96M4, where M=Ag, Cu, and Rh. The cluster expansion approach highlights the shortcomings of simple lattice models that have been used in the past to study similar systems. We use Sieverts’ law to calculate H solubility and a kinetic Monte Carlo scheme to find the diffusivity of H in PdAg, PdCu, and PdRh alloys at a temperature range of 400⩽T⩽1200K. From these results, we are able to predict the permeability of hydrogen through membranes made from these Pd-based binary alloys.
Effects of grain modification on the dielectric properties of A0.03Ti0.10Ni0.87O (A:K+,Mg2+,Y3+) ceramics
Authors: Cheng Bo , Lin Yuan-Hua , Mei Ao , Cai Jing-Nan , Nan Ce-Wen , He Jinliang
Published: April 2008

We prepared K+-, Mg2+-, and Y3+-doped Ni–Ti–O polycrystalline ceramics by chemical synthesis combined with a traditional ceramic processing. Analysis of the microstructure and phase composition reveals that a core/shell structure can be observed and NiTiO3 phase exists as the grain boundary. Our results indicate that K+, Mg2+, and Y3+ doping have remarkable influence on the dielectric properties of these NiO-based ceramics, which should be mainly attributed to the large variation of the activation energies of the conductivity in the grain interiors. The special core/shell structure and related interfacial polarization are responsible for the observed high dielectric behavior.
Intramolecular basis set superposition error effects on the planarity of benzene and other aromatic molecules: A solution to the problem
Authors: Asturiol David , Duran Miquel , Salvador Pedro
Published: April 2008

Recently, the surprising result that ab initio calculations on benzene and other planar arenes at correlated MP2, MP3, configuration interaction with singles and doubles (CISD), and coupled cluster with singles and doubles levels of theory using standard Pople’s basis sets yield nonplanar minima has been reported. The planar optimized structures turn out to be transition states presenting one or more large imaginary frequencies, whereas single-determinant-based methods lead to the expected planar minima and no imaginary frequencies. It has been suggested that such anomalous behavior can be originated by two-electron basis set incompleteness error. In this work, we show that the reported pitfalls can be interpreted in terms of intramolecular basis set superposition error (BSSE) effects, mostly between the C–H moieties constituting the arenes. We have carried out counterpoise-corrected optimizations and frequency calculations at the Hartree–Fock, B3LYP, MP2, and CISD levels of theory with several basis sets for a number of arenes. In all cases, correcting for intramolecular BSSE fixes the anomalous behavior of the correlated methods, whereas no significant differences are observed in the single-determinant case. Consequently, all systems studied are planar at all levels of theory. The effect of different intramolecular fragment definitions and the particular case of charged species, namely, cyclopentadienyl and indenyl anions, respectively, are also discussed.
Effects of nanosized contact spots on thermal contact resistance
Authors: Lee Sangyoung , Jang Yong Hoon , Kim Woochul
Published: April 2008

We investigate the effects of nanosized contact spots on the thermal contact resistance (TCR) in multiscale contacts. As the contact size decreases below the phonon mean free path, the thermal conductivity varies with the size of the contact and is not the same as its bulk counterpart. We take this into account in our model and we calculate the TCR of silicon contacted with other silicon. The TCR increases as the number of nanosized contact spots increases. However, if we do not consider the thermal conductivity reduction as the contact size decreases below the size of the phonon mean free path, there is a finite limit of the TCR. A parametric study on the effects of distance and size of the contact spots is also presented.
Excitation levels and magic numbers of small parahydrogen clusters (N⩽40)
Authors: Guardiola Rafael , Navarro Jesús
Published: April 2008

The excitation energies of parahydrogen clusters have been systematically calculated by the diffusion Monte Carlo technique in steps of 1molecule from 3to40molecules. These clusters possess a very rich spectra, with angular momentum excitations arriving up to L=13 for the heavier ones. No regular pattern can be guessed in terms of the angular momenta and the size of the cluster. Clusters with N=13 and 36 are characterized by a peak in the chemical potential and a large energy gap of the first excited level, which indicate the magical character of these clusters. From the calculated excitation energies, the partition function has been obtained, thus allowing for an estimate of thermal effects. An enhanced production is predicted for cluster sizes of N=13, 31, and 36, which is in agreement with the experiment.
Non-Borel summable Φ4 theory in zero dimension: A toy model for testing numerical and analytical methods
Authors: Marucho M.
Published: April 2008

The exact analytical solution for the generating functional of the zero-dimensional Φ4 theory with degenerate minima is obtained in the whole complex coupling parameter plane for testing purposes. The efficiency and precision of different computing tools, proposed in non-Borel summable field theories to obtain approximate solutions in both perturbative and nonperturbative regimes, are analyzed. Furthermore, a new resummation approach is proposed in order to successfully deal with factorially divergent series. It provides a representation of the generating function in terms of an unambiguously defined Laplace–Borel integral. On the other hand, a recent approach called the generalized Borel transform is shown to be an accurate and robust technique to capture non perturbative contributions in the coupling parameter. An extension of this approach to path integrals is proposed.
Membrane-enhanced surface acoustic wave analysis of grafted polymer brushes
Authors: Brass David A. , Shull Kenneth R.
Published: April 2008

An analysis is developed for the frequency response of a quartz crystal resonator (often referred to as a quartz crystal microbalance) that is modified with a grafted solvent-swollen polymer brush and placed in contact with a membrane capping layer. The shear wave generated at the resonator surface couples into the membrane layer with an efficiency that is strongly dependent on the thickness of the swollen brush layer. As a result, the resonant frequency changes by a maximum amount that is closely approximated by the Sauerbrey shift for the capping layer. The calculated shift substantially decreases for increases in the brush thickness of approximately 10nm, which gives a net frequency response that is extremely sensitive to the degree of swelling of the polymer brush. An optimum capping layer thickness is determined by balancing the Sauerbrey shift against dissipative effects that weaken the crystal resonance. This optimum membrane thickness depends only weakly on the properties of the membrane material and is in the micron range. Detailed multilayer calculations are presented for the specific case of a poly(ethylene glycol) brush swollen with water and brought into contact with an elastomeric water-permeable membrane. These calculations confirm that the method is sensitive to the properties of the brush layer in the experimentally relevant thickness regime. Connections are also made to conceptually simpler two and three layer models of the acoustic impedance of the material systems that are brought into contact with the resonator.
Increasing the noise margin in organic circuits using dual gate field-effect transistors
Authors: Spijkman M. , Smits E. C. P. , Blom P. W. M. , de Leeuw D. M. , Bon Saint Côme Y. , Setayesh S. , Cantatore E.
Published: April 2008

Complex digital circuits reliably work when the noise margin of the logic gates is sufficiently high. For p-type only inverters, the noise margin is typically about 1V. To increase the noise margin, we fabricated inverters with dual gate transistors. The top gate is advantageously used to independently tune the threshold voltage. The shift can be quantitatively described by ΔVth=(Ct∕Cb)Vtopgate, where Ct and Cb are the top and bottom gate capacitances. We show that by adjusting the top gate biases, the noise margin of dual gate inverters can be significantly improved up to about 5V.
Wavelength tuning limitations in optically pumped type-II antimonide lasers
Authors: Ongstad A. P. , Kaspi R. , Dente G. C. , Tilton M. L. , Barresi R. , Chavez J. R.
Published: April 2008

In this paper, we examine the wavelength tuning limitations of type-II antimonide lasers containing InAs∕InGaSb∕InAs quantum wells. Wavelength tuning is accomplished by varying the thickness of the InAs electron wells while keeping all else fixed. In principle, these wells can be tuned from λ≈2.5μm out to far IR wavelengths by increasing the thickness of the InAs layers. However, a practical upper limit of λ≈9.5μm is set due to the high waveguide losses awg and the diminishing modal overlap with the gain at longer wavelengths. The waveguide losses grow as awg∝λ3.44 and are attributable to free carrier absorbance. In order for the long-IR laser devices to achieve threshold, they must continually band fill, spectrally tuning to shorter wavelengths, until the laser gain exceeds the losses, which occurs near 9.5μm.
Symmetry breaking in binary mixtures in closed nanoslits
Authors: Berim Gersh O. , Ruckenstein Eli
Published: April 2008

The symmetry breaking (SB) of the fluid density distribution (FDD) in closed nanoslits between two identical parallel solid walls described by Berim and Ruckenstein [J. Chem. Phys. 128, 024704 (2008)] for a single component fluid is examined for binary mixtures on the basis of a nonlocal canonical ensemble density functional theory. As in Monte Carlo simulations, the periodicity of the FDD in one of the lateral (parallel to the wall surfaces) directions, denoted as the x direction, was assumed. In the other lateral direction, y direction, the FDD was considered to be uniform. The molecules of the two components have different diameters and their Lennard–Jones interaction potentials have different energy parameters. It was found that depending on the average fluid density in the slit and mixture composition, SB can occur for both or none of the components but never for only one of them. In the direction perpendicular to the walls (h direction), the FDDs of both components can be asymmetrical about the middle plane between walls. In the x direction, the SB occurs as bumps and bridges enriched in one of the components, whereas the composition of the mixture between them is enriched in the other component. The dependence of the SB states on the length Lx of the FDD period at fixed average densities of the two components was examined for Lx in the range from 10 to 120 molecular diameters of the smaller size component. It was shown that for large Lx, the stable state of the system corresponds to a bridge. Because the free energy of that state decreases monotonically with increasing Lx, one can conclude that the real period is very large (infinite) and that a single bridge exists in the slit.
Characterization of the crystallographic microstructure of the stress-induced void in Cu interconnects
Authors: Lee Hyo-Jong , Han Heung Nam , Kim Jae-Hun , Kang Suk Hoon , Cho Yi-Gil , Sun Jeong-Yun , Kim Do Hyun , Oh Kyu Hwan
Published: April 2008

Stepwise cross-sectional crystallographic measurement was performed on the stress-induced void (SIV) of copper interconnect and it was possible to investigate the three-dimensional crystallographic structures near the submicron scale void. The void mainly happened at a triple junction of grain boundaries and there were at least two grains with high biaxial elastic modulus near the triple junction. The preferred site for the SIV could well be understood by considering the elastic anisotropy of each grain and the grain boundary type.
Impact of template variations on shape and arrangement of Si∕Ge quantum dot arrays
Authors: Dais C. , Solak H. H. , Müller E. , Grützmacher D.
Published: April 2008

Templated self-assembly allows the fabrication of quantum dot (QD) arrays for use in nanoelectronic devices. Here, we show the strong dependence of the shape and arrangement of QDs on the template structures. Arrays of etched pits are patterned on Si (100) substrates by extreme ultraviolet interference lithography on which Si∕Ge layers are grown in a molecular beam epitaxy system. Single Ge dome clusters or quantum molecules consisting of four Ge hut clusters are obtained by a change of the pit diameter. Both arrays exhibit a narrow size distribution and exact alignment of the dots. In addition, multiple stacking of these arrays is demonstrated.
Biofunctionalized magnetic nanoparticles for in vitro labeling and in vivo locating specific biomolecules
Authors: Wu C. C. , Lin L. Y. , Lin L. C. , Huang H. C. , Yang Y. F. , Liu Y. B. , Tsai M. C. , Gao Y. L. , Wang W. C. , Hung S. W. , Yang S. Y. , Horng H. E. , Yang H. C. , Tseng W. Y. I. , Yeh H. I. , Hsuan C. F. , Lee T. L. , Tseng W. K.
Published: April 2008

In this work, we developed processes to biofunctionalize magnetic nanoparticles dispersed in phosphate buffer saline solution. For future clinical utility, magnetic nanoparticles were biofunctionalized with anti-vascular cell adhesion molecule-1 (VCAM-1) to label the VCAM-1 molecule, which served as an indicator for the lesions prone to vulnerable atherosclerotic plaque formation. The biofunctionalized magnetic nanoparticles were used to magnetically label, in vitro, cells expressing VCAM-1, as well as to locate the vulnerable aortic lesions of hypercholesterolemic rabbits with the aid of magnetic resonance imaging. In addition to demonstrating the feasibility of using biofunctionalized magnetic nanoparticles for biomolecule assays, the relevant physical mechanisms are discussed.
Band-gap luminescence of GaP:S shock compressed to 5GPa
Authors: Grivickas P. , McCluskey M. D. , Gupta Y. M.
Published: April 2008

Changes in the indirect band gap of GaP due to uniaxial strain compression were observed using photoluminescence (PL) spectroscopy in shock wave experiments. Longitudinal stresses up to 5GPa were generated in [111], [110], and [100] orientated samples. PL lines from sulfur bound excitons exhibited redshifts upon shock compression. At larger uniaxial strains, the measured shifts were smaller than predicted from published optical deformation potentials for GaP. It is shown that overestimation of spin-dependent interactions is most likely responsible for the observed discrepancies. An accurate set of deformation potentials for GaP is derived.
In situ electron holographic analysis of biased Si n+-p junctions
Authors: Han Myung-Geun , Smith David J. , McCartney Martha R.
Published: April 2008

The two-dimensional electrostatic potential distribution across Si n+-p junctions over a range of positive and negative biasing conditions has been studied in situ using off-axis electron holography. A sample holder with a movable probe as the electrode was used to bias focused-ion-beam-milled membranes during hologram acquisition. Reverse biasing of the junction resulted in an increase in potential across the junction, whereas the junction potential decreased with forward bias and eventually completely disappeared. The trends of the experimental results matched reasonably well with computer simulations.
Thulium-based bulk metallic glass
Authors: Yu H. B. , Yu P. , Wang W. H. , Bai H. Y.
Published: April 2008

We report the formation and properties of a thulium-based bulk metallic glass (BMG). Compared with other known rare-earth (RE) based BMGs, Tm-based BMGs show features of excellent glass formation ability, considerable higher elastic modulus, smaller Poisson’s ratio, high mechanical strength, and intrinsic brittleness. The reasons for the different properties between the Tm-based and other RE-based BMGs are discussed. It is expected that the Tm-based glasses with the unique properties are appropriate candidates for studying some important issues in BMGs.
X-ray absorption study of the electronic structure of Mn-doped amorphous Si
Authors: Zeng Li , Huegel A. , Helgren E. , Hellman F. , Piamonteze C. , Arenholz E.
Published: April 2008

The electronic structure of Mn in amorphous Si (a-MnxSi1−x) is studied by x-ray absorption spectroscopy at the Mn L3,2 edges for x=0.005−0.18. Except for the x=0.005 sample, which shows a slight signature of Mn2+ atomic multiplets associated with a local Mn moment, all samples have broad and featureless L3,2 absorption peaks, corresponding to an itinerant state for all 3d electrons. The broad x-ray absorption spectra exclude the possibility of a localized 3d moment and explain the unexpectedly quenched Mn moment in this magnetically doped amorphous semiconductor. Such a fully delocalized d state of Mn dopant in Si has not been previously suggested.
Thermally stable polymer memory devices based on a π-conjugated triad
Authors: Ling Qi-Dan , Kang En-Tang , Neoh Koon-Gee , Chen Yu , Zhuang Xiao-Dong , Zhu Chunxiang , Chan Daniel Siu Hung
Published: April 2008

Polymer memory devices based on a π-conjugated poly [9,9-bis(4-diphenylaminophenyl)-2,7-fluorene] covalently bridged, Disperse Red 1 (a dye) triad were fabricated. The devices exhibit electrical bistability in the I-V characteristics and can be used to perform read-write-erase memory functions. The memory devices exhibit good performance with an on/off current ratio up to 103 and stable on and off states under a constant voltage stress and read pulses. Furthermore, memory retention tests show that it is possible to preserve both states at 150°C under ambient atmosphere for about 1h when using Cu as the top electrode.