bluuebunny/crossref_metadata_2025 huggingface dataset:
Remote sensing of the Moon's subsurface with multifrequency microwave radiometers: A numerical study
Authors: Montopoli Mario , Di Carlofelice Alessandro , Tognolatti Piero , Marzano Frank S.
Published: February 2011

Within the renewed interest in the study of the Moon, in 2006 the European Space Agency approved a feasibility study for the European Student Moon Orbiter (ESMO) mission. In order to accomplish the ESMO mission objectives, a Microwave Radiometric Sounder (MiWaRS) was selected as a possible payload for flight on the ESMO satellite. This work summarizes the results of a numerical analysis of MiWaRS sounding capabilities. An (inhomogeneous) multilayer model of the microwave emission from the Moon's subsurface is presented, focusing the attention on the Moon's morphological, thermal, and dielectric properties. These properties have been determined and parameterized after a thorough investigation of available measurements and models. To this end, a radiative transfer numerical model, neglecting volume scattering, is coupled with a nonlinear thermal equation to simulate the microwave emission of the Moon's subsurface. Numerical simulations between L and Ka bands are performed to investigate the capability of MiWaRS to sound the characteristics of the Moon's regolith subsurface and detect the presence of rocks and ice under the near‐surface regolith layer. Under these forward model assumptions, results show that the Moon's brightness temperature response allows the detection of discontinuities within regolith media down to 2 and 5 m depth when channels at 3 and 1 GHz are used, respectively. Lunar near‐surface temperature may be also estimated within an accuracy less than a few kelvins. The discrimination of ice from rock by MiWaRS is hardly practicable and is limited to the presence of ice in the upper layers (with a depth less than 20 cm) beneath the lunar crust.
Coupled modeling of hydrogeochemical and electrical resistivity data for exploring the impact of recharge on subsurface contamination
Authors: Kowalsky M. B. , Gasperikova E. , Finsterle S. , Watson D. , Baker G. , Hubbard S. S.
Published: February 2011

The application of geophysical methods, in particular, electrical resistivity measurements, may be useful for monitoring subsurface contamination. However, interpreting geophysical data without additional data and without considering the associated hydrogeochemical processes is challenging since the geophysical response is sensitive to not only heterogeneity in rock properties but also to the saturation and chemical composition of pore fluids. We present an inverse modeling framework that incorporates the simulation of hydrogeochemical processes and time‐lapse electrical resistivity data and apply it to various borehole and cross‐borehole data sets collected in 2008 near the S‐3 Ponds at the U.S. Department of Energy's Oak Ridge Integrated Field Research Challenge site, where efforts are underway to better understand freshwater recharge and associated contaminant dilution. Our goal is to show that the coupled hydrogeochemical‐geophysical modeling framework can be used to (1) develop a model that honors all the available data sets, (2) help understand the response of the geophysical data to subsurface properties and processes at the site, and (3) allow for the estimation of petrophysical parameters needed for interpreting the geophysical data. We present a series of cases involving different data sets and increasingly complex models and find that the approach provides useful information about soil properties, recharge‐related transport processes, and the geophysical response. Spatial heterogeneity of the petrophysical model can be described sufficiently with two layers, and its parameters can be estimated concurrently with the hydrogeochemical parameters. For successful application of the approach, the parameters of interest must be sensitive to the available data, and the experimental conditions must be carefully modeled.
Groundwater residence time distributions in peatlands: Implications for peat decomposition and accumulation
Authors: Morris P. J. , Waddington J. M.
Published: February 2011

Peat soils consist of poorly decomposed plant detritus, preserved by low decay rates, and deep peat deposits are globally significant stores in the carbon cycle. High water tables and low soil temperatures are commonly held to be the primary reasons for low peat decay rates. However, recent studies suggest a thermodynamic limit to peat decay, whereby the slow turnover of peat soil pore water may lead to high concentrations of phenols and dissolved inorganic carbon. In sufficient concentrations, these chemicals may slow or even halt microbial respiration, providing a negative feedback to peat decay. We document the analysis of a simple, one‐dimensional theoretical model of peatland pore water residence time distributions (RTDs). The model suggests that broader, thicker peatlands may be more resilient to rapid decay caused by climate change because of slow pore water turnover in deep layers. Even shallow peat deposits may also be resilient to rapid decay if rainfall rates are low. However, the model suggests that even thick peatlands may be vulnerable to rapid decay under prolonged high rainfall rates, which may act to flush pore water with fresh rainwater. We also used the model to illustrate a particular limitation of the diplotelmic (i.e., acrotelm and catotelm) model of peatland structure. Model peatlands of contrasting hydraulic structure exhibited identical water tables but contrasting RTDs. These scenarios would be treated identically by diplotelmic models, although the thermodynamic limit suggests contrasting decay regimes. We therefore conclude that the diplotelmic model be discarded in favor of model schemes that consider continuous variation in peat properties and processes.
Exploiting human herpesvirus immune evasion for therapeutic gain: potential and pitfalls
Authors: Horst Daniëlle , Ressing Maaike E , Wiertz Emmanuel J H J
Published: February 2011

Herpesviruses stand out for their capacity to establish lifelong infections of immunocompetent hosts, generally without causing overt symptoms. Herpesviruses are equipped with sophisticated immune evasion strategies, allowing these viruses to persist for life despite the presence of a strong antiviral immune response. Although viral evasion tactics appear to target virtually any stage of the innate and adaptive host immune response, detailed knowledge is now available on the molecular mechanisms underlying herpesvirus obstruction of MHC class I‐restricted antigen presentation to T cells. This opens the way for clinical application. Here, we review and discuss recent efforts to exploit human herpesvirus MHC class I evasion strategies for the rational design of novel strategies for vaccine development, cancer treatment, transplant protection and gene therapy.
Human FoxP3+CD4+ regulatory T cells: their knowns and unknowns
Authors: Miyara Makoto , Sakaguchi Shimon
Published: February 2011

Human regulatory T cells (Tregs) expressing the transcription factor FoxP3 play indispensable roles for the maintenance of immunological self‐tolerance and immune homeostasis. In this review, we discuss immunological characteristics of human FoxP3+ Tregs and to what extent they are similar to or different from the murine counterparts. We also discuss important issues that remain to be addressed in the field to better understand the pathophysiology of autoimmune disease and to build solid basis for immunotherapies targeting FoxP3+ Tregs.
Insights into human CD8+ T‐cell memory using the yellow fever and smallpox vaccines
Authors: Ahmed Rafi , Akondy Rama S
Published: February 2011

Live virus vaccines provide a unique opportunity to study human CD8+ T‐cell memory in the context of a controlled, primary acute viral infection. Yellow fever virus‐17D and Dryvax are two such live‐virus vaccines that are highly efficacious, used worldwide and provide long‐term immunity against yellow fever and smallpox respectively. In this review, we describe the properties of virus‐specific memory CD8+ T cells generated in smallpox and yellow fever vaccinees. We address fundamental questions regarding magnitude, functional quality and longevity of the CD8+ T‐cell response, which are otherwise challenging to address in humans. These findings provide insights into the attributes of the human immune system as well as provide a benchmark for the optimal quality of a CD8+ T‐cell response that can be used to evaluate novel candidate vaccines.
Phonon confinement in Ge nanocrystals in silicon oxide matrix
Authors: Jie Yiaxiong , Wee A. T. S. , Huan C. H. A. , Shen Z. X. , Choi W. K.
Published: February 2011

Spherical Ge nanocrystals well-dispersed in amorphous silicon oxide matrix have been synthesized with different sizes, and significant size-dependent Raman shift and broadening have been observed. The lattice constant of Ge nanocrystals well-bonded to silicon oxide matrix has been characterized nearly size-independent. With our proposed stress generation and relaxation mechanisms, stress effects in our samples have been analyzed to be insignificant with respect to phonon confinement effects. The phenomenological model introduced by [Richter, Wang, and Ley, Solid State Commun. 39, 625 (1981] with Gaussian weighting function and TO2 phonon dispersion function has been found to give a quite good description of the measured size-dependence of Raman shift and broadening. A 3-peak fitting method has been proposed to determine Ge nanocrystal size and film crystallinity. After physically quantizing quantum-confined one-dimensional elastic waves, we have deduced that each quantum-confined phonon possesses an instantaneous momentum of a given magnitude ℏk with an equal chance of being either positive or negative and momentum conservation is retained in an electron-phonon scattering process. Therefore, on the basis of the first-principle microscopic model and our experimental results, we deduced that Raman scattering in spherical nanocrystals is a concurrent two-phonon process, one phonon generation and one phonon transition.
Surface acoustic wave devices as passive buried sensors
Authors: Friedt J.-M. , Rétornaz T. , Alzuaga S. , Baron T. , Martin G. , Laroche T. , Ballandras S. , Griselin M. , Simonnet J.-P.
Published: February 2011

Surface acoustic wave (SAW) devices are currently used as passive remote-controlled sensors for measuring various physical quantities through a wireless link. Among the two main classes of designs—resonator and delay line—the former has the advantage of providing narrow-band spectrum informations and hence appears compatible with an interrogation strategy complying with Industry-Scientific-Medical regulations in radio-frequency (rf) bands centered around 434, 866, or 915 MHz. Delay-line based sensors require larger bandwidths as they consists of a few interdigitated electrodes excited by short rf pulses with large instantaneous energy and short response delays but is compatible with existing equipment such as ground penetrating radar (GPR). We here demonstrate the measurement of temperature using the two configurations, particularly for long term monitoring using sensors buried in soil. Although we have demonstrated long term stability and robustness of packaged resonators and signal to noise ratio compatible with the expected application, the interrogation range (maximum 80 cm) is insufficient for most geology or geophysical purposes. We then focus on the use of delay lines, as the corresponding interrogation method is similar to the one used by GPR which allows for rf penetration distances ranging from a few meters to tens of meters and which operates in the lower rf range, depending on soil water content, permittivity, and conductivity. Assuming propagation losses in a pure dielectric medium with negligible conductivity (snow or ice), an interrogation distance of about 40 m is predicted, which overcomes the observed limits met when using interrogation methods specifically developed for wireless SAW sensors, and could partly comply with the above-mentioned applications. Although quite optimistic, this estimate is consistent with the signal to noise ratio observed during an experimental demonstration of the interrogation of a delay line buried at a depth of 5 m in snow.
Effects of synthesized method on glassy behavior and freezing process of 0.75PFW–0.25PT ceramics
Authors: Hong Cheng-Shong , Chu Sheng-Yuan , Tsai Cheng-Che , Su Wen-Chang , Hsu Chi-Cheng
Published: February 2011

Two different methods, the conventional direct oxide synthesized method and the two-step indirect synthesized (IS) method, were employed to synthesize the 0.75Pb(Fe2/3W1/3)O3–0.25PbTiO3 ceramics. The low-field dielectric responses were investigated using the empirical law and the Curie–Weiss law. The temperature-dependent local ordering parameters were derived from the experimental results using the spin-glass model and the modified-Landau theory separately. According to the experimental data and the fitting results, it is concluded that the temperature-dependent local order parameters are changed from a short-range-ordered relaxor to a long-range-ordered ferroelectric state using the IS method. On the basis of the physical concepts of the spin-glass model, the modified-Landau theory and the ordering models, it is suggested that local polarizations are affected not only by degree of ordering but also by space charge polarization. In contrast, the glassy behavior of local polarization is affected only by degree of ordering but has nothing to do with space charge polarization. It is because local fields induced by space charge polarization have the same effect on local polarizations and are neutralized when calculating the correlation between neighboring polar microregions. On the other hand, the freezing process of local polarizations is affected by both degree of ordering and space charge polarization because local polarization affected by local fields cannot be neutralized when calculating the individual behavior of local polarization.
A numerical algorithm for the explicit calculation of SU(N) and $\mbox{SL}(N,\mathbb {C})$SL(N,C) Clebsch–Gordan coefficients
Authors: Alex Arne , Kalus Matthias , Huckleberry Alan , von Delft Jan
Published: February 2011

We present an algorithm for the explicit numerical calculation of SU(N) and \documentclass[12pt]{minimal}\begin{document}$\mbox{SL}(N,\mathbb {C})$\end{document}SL(N,C) Clebsch–Gordan coefficients, based on the Gelfand–Tsetlin pattern calculus. Our algorithm is well suited for numerical implementation; we include a computer code in an appendix. Our exposition presumes only familiarity with the representation theory of SU(2).
Vibronic line shapes of PTCDA oligomers in helium nanodroplets
Authors: Roden Jan , Eisfeld Alexander , Dvořák Matthieu , Bünermann Oliver , Stienkemeier Frank
Published: February 2011

Oligomers of the organic semiconductor 3,4,9,10-perylene-tetracarboxylic-dianhydride, C24H8O6 (PTCDA) are studied by means of helium nanodroplet isolation spectroscopy. In contrast to the monomer absorption spectrum, which exhibits clearly separated, very sharp absorption lines, it is found that the oligomer spectrum consists of three main peaks having an apparent width orders of magnitude larger than the width of the monomer lines. Using a simple theoretical model for the oligomer, in which a Frenkel exciton couples to internal vibrational modes of the monomers, these experimental findings are nicely reproduced. The three peaks present in the oligomer spectrum can already be obtained taking only one effective vibrational mode of the PTCDA molecule into account. The inclusion of more vibrational modes leads to quasicontinuous spectra, resembling the broad oligomer spectra.
Study of the Wigner function at the device boundaries in one-dimensional single- and double-barrier structures
Authors: Savio Andrea , Poncet Alain
Published: February 2011

In this work, we compute the Wigner distribution function on one-dimensional devices from wave functions generated by solving the Schrödinger equation. Our goal is to investigate certain issues that we encountered in implementing Wigner transport equation solvers, such as the large discrepancies observed between the boundary conditions and the solution in the neighborhood of the boundaries. By evaluating the Wigner function without solving the Wigner transport equation, we intend to ensure that the actual boundary conditions are consistent with those commonly applied in literature. We study both single- and double-barrier unbiased structures. We use simple potential profiles, so that we can compute the wave functions analytically for better accuracy. We vary a number of structure geometry, material, meshing, and numerical parameters, among which are the contact length, the barrier height, the number of incident wave functions, and the numerical precision used for the computations, and we observe how the Wigner function at the device boundaries is affected. For the double-barrier structures, we look at the density matrix function and we study a model for the device transmission spectrum which helps explain the lobelike artifacts that we observe on the Wigner function.
Unraveling the spectroscopy of coupled intramolecular tunneling modes: A study of double proton transfer in the formic-acetic acid complex
Authors: Tayler Michael C. D. , Ouyang Bin , Howard Brian J.
Published: February 2011

The rotational spectrum of the hetero dimer comprising doubly hydrogen-bonded formic acid and acetic acid has been recorded between 4 and 18 GHz using a pulsed-nozzle Fourier transform microwave spectrometer. Each rigid-molecule rotational transition is split into four as a result of two concurrently ongoing tunneling motions, one being proton transfer between the two acid molecules, and the other the torsion/rotation of the methyl group within the acetyl part. We present a full assignment of the spectrum J = 1 to J = 6 for the ground vibronic states. The transitions are fitted to within a few kilohertz of the observed frequencies using a molecule-fixed effective rotational Hamiltonian for the separate A and E vibrational species of the G12 permutation-inversion symmetry group. Interpretation of the motion problem uses an internal-vibration and overall-rotation angular momentum coupling scheme and full sets of rotational and centrifugal distortion constants are determined. The tunneling frequencies of the proton-transfer motion are measured for the ground A and E methyl rotation states as 250.4442(12) and −136.1673(30) MHz, respectively. The slight deviation of the latter tunneling frequency from being one half of the former, as simple theory otherwise predicts, is due to different degrees of mixing in wavefunctions between the ground and excited states.
Human aquaporin 4 gating dynamics in dc and ac electric fields: A molecular dynamics study
Authors: Garate J.-A. , English Niall J. , MacElroy J. M. D.
Published: February 2011

Water self-diffusion within human aquaporin 4 has been studied using molecular dynamics (MD) simulations in the absence and presence of external ac and dc electric fields. The computed diffusive (pd) and osmotic (pf) permeabilities under zero-field conditions are (0.718 ± 0.24) × 10−14 cm3 s−1 and (2.94 ± 0.47) × 10−14 cm3 s−1, respectively; our pf agrees with the experimental value of (1.50 ± 0.6) × 10−14 cm3 s−1. A gating mechanism has been proposed in which side-chain dynamics of residue H201, located in the selectivity filter, play an essential role. In addition, for nonequilibrium MD in external fields, it was found that water dipole orientation within the constriction region of the channel is affected by electric fields (e-fields) and that this governs the permeability. It was also found that the rate of side-chain flipping motion of residue H201 is increased in the presence of e-fields, which influences water conductivity further.
Experiments on long-wavelength instability and reconnection of a vortex pair
Authors: Leweke Thomas , Williamson Charles H. K.
Published: February 2011

We present results from an experimental study of the long-wavelength “Crow” instability of a counter-rotating vortex pair. Employing a vortex generator in a water tank, comprising rotating horizontal computer-controlled flaps, we follow the vortices, marked by laser-induced fluorescence, using dual simultaneous light-sheets to determine the growth rate of the Crow instability as a function of the perturbation wavelength. In order to make a meaningful comparison to theory [S. C. Crow, AIAA J. 8, 2172 (1970); S. E. Widnall, Annu. Rev. Fluid Mech. 4, 141 (1975)], one requires, as input to the theory, the distribution of circumferential velocity and thereby the “equivalent” core size of the vortices. These distributions are measured using particle image velocimetry. The resulting agreement of the growth rates, between theory and experiment, appears to be very good. Of relevance to this study, we compute a stability diagram using the exact expression for the self-induced rotation speed of perturbation waves on the vortices. Measurement of the nondimensional reconnection time, when the vortex pair evolves into a series of rings at later times, is compared to existing numerical simulations, and we find evidence to suggest it varies with the inverse curvature of the vortices where they approach each other. The major axes of the resulting elliptical vortex rings switch with their minor axes, as the rings descend in the fluid, leading to a surprising phenomenon where the rings reconnect for the second time. By considering the conservation of impulse, and a linear relationship between the major axis length and the vortex spacing, we find that the relative descent speed of the rings increases with Reynolds number. It is coincidentally only at our chosen value that the descent speed of the subsequent rings appears to be close to the initial speed of the vortex pairs. Finally, the paper presents clear visualizations of the Crow instability phenomenon.
Measuring the relative concentration of H2 and D2 in HD gas with gas chromatography
Authors: Whisnant C. Steven , Hansen Patrick A. , Kelley Travis D.
Published: February 2011

Frozen-spin polarized hydrogen deuteride (HD) targets are being prepared for photonuclear experiments at Jefferson Lab. The targets are frozen HD gas. To polarize and achieve the required spin–lattice relaxation times, the targets are made from high purity HD gas in which the residual H2 and D2 concentrations are known. To determine these residual concentrations, a gas chromatograph is used. The separation of the gas components is done in a column cooled to ≈120 K by immersing it in a mixture of liquid nitrogen and isopentane and using neon as the carrier gas. The different hydrogen isotopes have different transit times through the column and their arrival is registered by a thermal conductivity detector. The peaks in the chromatograms are fit using an exponentially modified Gaussian line shape to extract the areas of these peaks. The ratios of areas are corrected for differences in thermal conductivity to give the relative concentrations. Here, H2 and D2 concentrations on the order of a few percent have been measured with uncertainties of less than ± 5%. The linear response of the system is confirmed to within about ± 6.3%.
Mechanics of viscous vortex reconnection
Authors: Hussain Fazle , Duraisamy Karthik
Published: February 2011

This work is motivated by our long-standing claim that reconnection of coherent structures is the dominant mechanism of jet noise generation and plays a key role in both energy cascade and fine-scale mixing in fluid turbulence [F. Hussain, Phys. Fluids 26, 2816 (1983); J. Fluid Mech. 173, 303 (1986)]. To shed further light on the mechanism involved and quantify its features, the reconnection of two antiparallel vortex tubes is studied by direct numerical simulation of the incompressible Navier–Stokes equations over a wide range (250–9000) of the vortex Reynolds number, Re (=circulation/viscosity) at much higher resolutions than have been attempted. Unlike magnetic or superfluid reconnections, viscous reconnection is never complete, leaving behind a part of the initial tubes as threads, which then undergo successive reconnections (our cascade and mixing scenarios) as the newly formed bridges recoil from each other by self-advection. We find that the time tR for orthogonal transfer of circulation scales as tR≈Re−3/4. The shortest distance d between the tube centroids scales as d≈a[Re(t0−t)]3/4 before reconnection (collision) and as d≈b[Re(t−t0)]2 after reconnection (repulsion), where t0 is the instant of smallest separation between vortex centroids. We find that b is a constant, thus suggesting self-similarity, but a is dependent on Re. Bridge repulsion is faster than collision and is more autonomous as local induction predominates, and, given the associated acceleration of vorticity, is potentially a source of intense sound generation. At the higher Re studied, the tails of the colliding threads are compressed into a planar jet with multiple vortex pairs. For Re>6000, there is an avalanche of smaller scales during the reconnection, the rate of small scale generation and the spectral content (in vorticity, transfer function and dissipation spectra) being quite consistent with the structures visualized by the λ2 criterion. The maximum rate of vortex circulation transfer, enstrophy production, and dissipation scale as Re1, Re7/4, and Re−1/2, respectively. A more detailed study of subsequent reconnection of threads requires much higher-resolution simulations that are currently not feasible.
A regionally contracted multireference configuration interaction method: General theory and results of an incremental version
Authors: Hoyau Sophie , Maynau Daniel , Malrieu Jean-Paul
Published: February 2011

This work proposes to take benefit of the localizability of both occupied and virtual inactive molecular orbitals (MOs) in the context of complete active space singles and doubles configuration interaction (CAS-SDCI). The doubly occupied MOs are partitioned into blocks, or regions, corresponding to a subset of adjacent bonds and lone pairs. The localized virtual MOs are attributed to these regions from a spatial criterion. Then a series of limited post-CAS-CI calculations is performed, using the same reference space, one for each block, and then one per pair of blocks. From these independent CI calculations contracted external functions are defined for each block or for each pair of blocks, and for each state. A general multistate formalism is proposed, the CI matrix being expressed in the space defined by the CAS and the contracted functions. Preliminary numerical studies, resting on the evaluation of single-block and two-block contributions to the dynamical correlation energy of each state, are presented. Provided that size-consistency corrections are taken into account the results of the procedure are shown to be in excellent agreement with those of the nonpartitioned post-CAS-CI. The computational benefits of this evidently parallelizable procedure are underlined.
The chemistry of acetone at extreme conditions by density functional molecular dynamics simulations
Authors: Ferrante Francesco , Celso Fabrizio Lo , Triolo Roberto , Taleyarkhan Rusi P.
Published: February 2011

Density functional molecular dynamics simulations have been performed in the NVT ensemble (moles (N), volume (V) and temperature (T)) on a system formed by ten acetone molecules at a temperature of 2000 K and density ρ = 1.322 g cm−3. These conditions resemble closely those realized at the interface of an acetone vapor bubble in the early stages of supercompression experiments and result in an average pressure of 5 GPa. Two relevant reactive events occur during the simulation: the condensation of two acetone molecules to give hexane-2,5-dione and dihydrogen and the isomerization to the enolic propen-2-ol form. The mechanisms of these events are discussed in detail.
Long-term dynamics for well productivity index for nonlinear flows in porous media
Authors: Aulisa Eugenio , Bloshanskaya Lidia , Ibragimov Akif
Published: February 2011

Motivated by the reservoir engineering concept of the well productivity index (PI) we study a time dependent functional for general nonlinear Forchheimer equation. The PI of the well characterizes the well capacity with respect to drainage area of the well. Unlike the linear case for which this concept is well developed, there are only a few recent publications dedicated to the PI for nonlinear case. In this paper the PI is comprehensively studied both theoretically and numerically. The impact of the nonlinearity of the flow filtration on the value of the PI is analyzed. Exact formula for the so called “skin factor” in radial case is derived depending on the rate of the flow, the order of nonlinearity and the geometric parameters. Dynamics of the PI for the class of boundary conditions is studied and its convergence to the specific value of steady state PI was justified. Developed framework is applied to obtain nonlinear analog of Peaceman formula for the well-block pressure in unstructured grid. Numerical simulations sustain theoretical results.
Quantum chemical assessment of the binding energy of CuO+
Authors: Rezabal Elixabete , Gauss Jürgen , Matxain Jon M. , Berger Robert , Diefenbach Martin , Holthausen Max C.
Published: February 2011

We present a detailed theoretical investigation on the dissociation energy of CuO+, carried out by means of coupled cluster theory, the multireference averaged coupled pair functional (MR-ACPF) approach, diffusion quantum Monte Carlo (DMC), and density functional theory (DFT). At the respective extrapolated basis set limits, most post-Hartree–Fock approaches agree within a narrow error margin on a De value of 26.0 kcal mol−1 [coupled-cluster singles and doubles level augmented by perturbative triples corrections, CCSD(T)], 25.8 kcal mol−1 (CCSDTQ via the high accuracy extrapolated ab initio thermochemistry protocol), and 25.6 kcal mol−1 (DMC), which is encouraging in view of the disaccording data published thus far. The configuration-interaction based MR-ACPF expansion, which includes single and double excitations only, gives a slightly lower value of 24.1 kcal mol−1, indicating that large basis sets and triple excitation patterns are necessary ingredients for a quantitative assessment. Our best estimate for D0 at the CCSD(T) level is 25.3 kcal mol−1, which is somewhat lower than the latest experimental value (D0 = 31.1 ± 2.8 kcal mol−1; reported by the Armentrout group) [Int. J. Mass Spectrom. 182/183, 99 (1999)]. These highly correlated methods are, however, computationally very demanding, and the results are therefore supplemented with those of more affordable DFT calculations. If used in combination with moderately-sized basis sets, the M05 and M06 hybrid functionals turn out to be promising candidates for studies on much larger systems containing a [CuO]+ core.
Mesophase formation in two-component cylindrical bottlebrush polymers
Authors: Erukhimovich Igor , Theodorakis Panagiotis E. , Paul Wolfgang , Binder Kurt
Published: February 2011

When two types of side chains (A,B) are densely grafted to a (stiff) backbone and the resulting bottlebrush polymer is in a solution under poor solvent conditions, an incompatibility between A and B leads to microphase separation in the resulting cylindrical brush. The possible types of ordering are reminiscent of the ordering of block copolymers in cylindrical confinement. Starting from this analogy, Leibler's theory of microphase separation in block copolymer melts is generalized to derive a description of the system in the weak segregation limit. Also molecular dynamics simulation results of a corresponding coarse-grained bead-spring model are presented. Using side chain lengths up to N = 50 effective monomers, the ratio of the Lennard-Jones energy parameter between unlike monomers (εAB) and monomers of the same kind (εAA = εBB) is varied. Various correlation functions are analyzed to study the conditions when (local) Janus-cylinder-type ordering and when (local) microphase separation in the direction along the cylinder axis occurs. Both the analytical theory and the simulations give evidence for short-range order due to a tendency toward microphase separation in the axial direction, with a wavelength proportional to the side chain gyration radius, irrespective of temperature and grafting density, for a wide range of these parameters.
Fabrication of submicron La2−xSrxCuO4 intrinsic Josephson junction stacks
Authors: Kubo Yuimaru , Takahide Yamaguchi , Tanaka Takayoshi , Ueda Shinya , Ishii Satoshi , Tsuda Shunsuke , Islam ATM Nazmul , Tanaka Isao , Takano Yoshihiko
Published: February 2011

Intrinsic Josephson junction (IJJ) stacks of cuprate superconductors have potential to be implemented as intrinsic phase qubits working at relatively high temperatures. We report success in fabricating submicron La2−xSrxCuO4 (LSCO) IJJ stacks carved out of single crystals. We also show a new fabrication method in which argon ion etching is performed after focused ion beam etching. As a result, we obtained an LSCO IJJ stack in which resistive multibranches appeared. It may be possible to control the number of stacked IJJs with an accuracy of a single IJJ by developing this method.
Terahertz enhancement from terahertz-radiation-assisted large aperture photoconductive antenna
Authors: Gao Yaohui , Chen Meng-ku , Yin Stuart , Ruffin Paul , Brantley Christina , Edwards Eugene
Published: February 2011

The observation of enhanced terahertz (THz) wave generation from the large aperture photoconductive (PC) antenna excited by both a femtosecond pump beam and a collinearly propagating ZnTe-pregenerated THz wave is reported within this paper. An analysis based on both the calculated and experimental results demonstrated that the superposition acts as the main physical mechanism of this THz enhancement effect due to the dominant contribution from the rapid change in photoexcited carrier density. A prerequisite for the THz enhancement requires that the polarization of the applied bias and the ZnTe-pregenerated THz should be identical in order to have a constructive superposition. Therefore, this observation introduces the possibility of recycling the unused portion of the pump beam to further improve the THz radiation. The enhancement effect could be optimized by changing the thickness of ZnTe, which could affect the photoexcited-free-carrier absorption of THz in the PC antenna and the bandwidth of final enhanced THz radiation.
All-optical technique to measure the pyroelectric coefficient in electro-optic crystals
Authors: Parravicini Jacopo , Safioui Jassem , Degiorgio Vittorio , Minzioni Paolo , Chauvet Mathieu
Published: February 2011

We report an all-optical method to measure the pyroelectric coefficient p of electro-optic crystals. Through this technique, we first acquire the birefringence variation δΔn of the crystal as a function of its temperature T, both in closed and open-circuit conditions, using a Sénarmont phase-compensation configuration. Then the pyroelectric field is deduced from the difference between these two measurements, so it leads to the material spontaneous polarization change, whose derivative with respect to the temperature finally gives p. This technique is applied on congruent and stoichiometric lithium niobate.
Localized surface plasmon resonance of single silver nanoparticles studied by dark-field optical microscopy and spectroscopy
Authors: Cao Wei , Huang Tao , Xu Xiao-Hong Nancy , Elsayed-Ali Hani E.
Published: February 2011

Localized surface plasmon resonance (LSPR) of Ag nanoparticles (NPs) with different shapes and disk-shaped Ag NP pairs with varying interparticle distance is studied using dark-field optical microscopy and spectroscopy (DFOMS). Disk-, square-, and triangular-shaped Ag NPs were fabricated on indium tin oxide-coated glass substrates by electron beam lithography. The LSPR spectra collected from single Ag NPs within 5×5 arrays using DFOMS exhibited pronounced redshifts as the NP shape changed from disk to square and to triangular. The shape-dependent experimental LSPR spectra are in good agreement with simulations using the discrete dipole approximation model, although there are small deviations in the peak wavelengths for square- and triangular-shaped NPs. The LSPR spectra of disk-shaped Ag NP pairs with varying interparticle distances were acquired from five different locations across the pair axis. It was clearly observed that the LSPR wavelength redshifts as the interparticle distance decreases, indicating a strong interaction when two Ag NPs are close to each other.
Statistical approaches to forcefield calibration and prediction uncertainty in molecular simulation
Authors: Cailliez Fabien , Pernot Pascal
Published: February 2011

Calibration of forcefields for molecular simulation should account for the measurement uncertainty of the reference dataset and for the model inadequacy, i.e., the inability of the force-field/simulation pair to reproduce experimental data within their uncertainty range. In all rigour, the resulting uncertainty of calibrated force-field parameters is a source of uncertainty for simulation predictions. Various calibration strategies and calibration models within the Bayesian calibration/prediction framework are explored in the present article. In the case of Lennard-Jones potential for Argon, we show that prediction uncertainty for thermodynamical and transport properties, albeit very small, is larger than statistical simulation uncertainty.
Existence of a ground state for the Nelson model with a singular perturbation
Authors: Hidaka Takeru
Published: February 2011

The existence of a ground state of the Nelson Hamiltonian with perturbations of the form \documentclass[12pt]{minimal}\begin{document}$\sum _{j=1}^{4}c_{j}\phi ^{j}$\end{document}∑j=14cjφj with c4 > 0 is considered. The self-adjointness of the Hamiltonian and the existence of a ground state are proven for arbitrary values of coupling constants.
Excitation threshold for the discrete coupled Schrödinger lattice system
Authors: Cheng Ming
Published: February 2011

This paper is concerned with the excitation threshold for the ground state in the coupled discrete nonlinear Schrödinger lattice system. Excitation threshold is characterized by the variational methods. We establish the existence of the excitation threshold connected with the dimensionality d of the lattice. We prove that if d ⩾ 2, then the excitation threshold exists and the ground state exists if and only if the total power is greater than the excitation threshold. The compactness of the minimizing sequence follows by the concentration compactness principle. We also prove the upper estimates on the excitation threshold and the frequency of the ground state.
Convergent perturbative power series solution of the stationary Maxwell–Born–Infeld field equations with regular sources
Authors: Kiessling M. K.-H.
Published: February 2011

The stationary Maxwell–Born–Infeld field equations of electromagnetism with regular sources \documentclass[12pt]{minimal}\begin{document}$\rho \in (C^\alpha _0\cap L^1)({\mathbb R}^3)$\end{document}ρ∈(C0α∩L1)(R3) and \documentclass[12pt]{minimal}\begin{document}$j\in (C^\alpha _0\cap L^1)({\mathbb R}^3)$\end{document}j∈(C0α∩L1)(R3) (componentwise) are solved using a perturbation series expansion in powers of Born's electromagnetic constant. The convergence in \documentclass[12pt]{minimal}\begin{document}$C^{1,\alpha }_0$\end{document}C01,α of the power series for the fields is proved with the help of Banach algebra arguments and complex analysis. The finite radius of convergence depends on the “\documentclass[12pt]{minimal}\begin{document}$C^{1,\alpha }_0$\end{document}C01,α size” of both, the Coulomb field generated by ρ and the Ampère field generated by j. No symmetry is assumed.
The C–H bond dissociation energy of furan: Photoelectron spectroscopy of the furanide anion
Authors: Vogelhuber Kristen M. , Wren Scott W. , Sheps Leonid , Lineberger W. Carl
Published: February 2011

Using photoelectron spectroscopy, we interrogate the cyclic furanide anion (C4H3O−) to determine the electron affinity and vibrational structure of the neutral furanyl radical and the term energy of its first excited electronic state. We present the 364-nm photoelectron spectrum of the furanide anion and measure the electron affinity of the $\tilde X^2 {\rm A' }$X̃2A′ ground state of the α-furanyl radical to be 1.853(4) eV. A Franck–Condon analysis of the well-resolved spectrum allows determination of the harmonic frequencies of three of the most active vibrational modes upon $\tilde X^2 {\rm A' }$X̃2A′ ← $\tilde X^1 {\rm A' }$X̃1A′ photodetachment: 855(25), 1064(25), and 1307(40) cm−1. These modes are ring deformation vibrations, consistent with the intuitive picture of furanide anion photodetachment, where the excess electron is strongly localized on the α-carbon atom. In addition, the $\tilde A^2 {\rm A^{\prime \prime}}$Ã2A′′ excited state of the α-furanyl radical is observed 0.68(7) eV higher in energy than the $\tilde X^2 {\rm A' }$X̃2A′ ground state. Through a thermochemical cycle involving the known gas-phase acidity of furan, the electron affinity of the furanyl radical yields the first experimental determination of the C–Hα bond dissociation energy of furan (DH298(C4H3O–Hα)): 119.8(2) kcal mol−1.
On the relation between the activation energy for electron attachment reactions and the size of their thermal rate coefficients
Authors: Hotop H. , Ruf M.-W. , Kopyra J. , Miller T. M. , Fabrikant I. I.
Published: February 2011

Rate coefficients k(T) for dissociative electron attachment (DEA) to molecules in many cases exhibit a more or less strong rise with increasing temperature T (the electron temperature Te and the molecular temperature TG are assumed to be in thermal equilibrium, i.e., T = Te = TG). This rise is frequently modeled by the Arrhenius equation k(T) = kA exp[−Ea/(kBT)], and an activation energy Ea is deduced from fits to the experimental data k(T). This behavior reflects the presence of an energy barrier for the anion on its path to the dissociated products. In a recent paper [J. Kopyra, J. Wnorowska, M. Foryś, and I. Szamrej, Int. J. Mass Spectrom. 268, 60 (2007)] it was suggested that the size of the rate coefficients for DEA reactions at room temperature exhibits an exponential dependence on the activation energy, i.e., k(Ea; T ≈ 300 K) = k1 exp[−Ea/E0]. More recent experimental data for molecules with high barriers [T. M. Miller, J. F. Friedman, L. C. Schaffer, and A. A. Viggiano, J. Chem. Phys. 131, 084302 (2009)] are compatible with such a correlation. We investigate the validity and the possible origin of this dependence by analyzing the results of R-matrix calculations for temperature-dependent rate coefficients of exothermic DEA processes with intermediate barrier toward dissociation. These include results for model systems with systematically varied barrier height as well as results of molecule-specific calculations for CH3Cl, CH3Br, CF3Cl, and CH2Cl2 (activation energies above 0.2 eV) involving appropriate molecular parameters. A comparison of the experimental and theoretical results for the considered class of molecules (halogenated alkanes) supports the idea that the exponential dependence of k(T = 300 K) on the activation energy reflects a general phenomenon associated with Franck–Condon factors for getting from the initial neutral vibrational levels to the dissociating final anion state in a direct DEA process. Cases are discussed for which the proposed relation does not apply.
The p-type ZnO film realized by a hydrothermal treatment method
Authors: Ding Meng , Zhao Dongxu , Yao Bin , Li Binghui , Zhang Zhenzhong , Shen Dezhen
Published: February 2011

Reproducible and high quality N-doped ZnO (ZnO:N) films were achieved by a hydrothermal treatment method. The ZnO:N films exhibited p-type characteristics by means of the Hall-effect and the photoluminescence measurements. At room temperature, the electrical properties of ZnO:N film showed a hole concentration of 1×1016 cm−3 and hole mobility of 8.6 cm2 V−1 s−1. At 83 K two acceptor related emission peaks could be observed located at 3.353 and 3.237 eV, which were assigned to the acceptor-bound exciton and the donor-acceptor pair emissions. This result gave a direct evidence for the generation of the acceptor energy level after the hydrothermal treatment process. Also, a ZnO homojunction diode was fabricated by this method, which displayed a good rectification characteristic at room temperature. This study revealed that the hydrothermal treatment method was effective and practicable in producing p-type ZnO.
Diameter-dependent analytical model for light spot movement in carbon nanotube array transistors
Authors: Abdolkader Tarek M. , Alam Muhammad A.
Published: February 2011

We present a rigorous analytical model for the movement of light spot emitted in single-wall nanotube transistors (SWNTs) including the dependence of this movement on tube diameter. Since the rate of change of light spot movement with gate bias is a sensitive function of the tube diameter, the model can be used as an in situ nondestructive tool to probe the electrically relevant diameter distribution in SWNT arrays and thereby could complement traditional indirect techniques like Raman spectroscopy and atomic force microscopy. Establishing such a diameter distribution has broad implications regarding the performance/integration of SWNT for potential applications in emerging carbon electronics.
Using nonproduct quadrature grids to solve the vibrational Schrödinger equation in 12D
Authors: Avila Gustavo , Carrington Tucker
Published: February 2011

In this paper we propose a new quadrature scheme for computing vibrational spectra and apply it, using a Lanczos algorithm, to CH3CN. All 12 coordinates are treated explicitly. We need only 157'419'523 quadrature points. It would not be possible to use a product Gauss grid because 33 853 318 889 472 product Gauss points would be required. The nonproduct quadrature we use is based on ideas of Smolyak, but they are extended so that they can be applied when one retains basis functions \documentclass[12pt]{minimal}\begin{document}$\theta _{n_{1}}(r_{1}) \cdots \theta _{n_{D}}(r_{D})$\end{document}θn1(r1)⋯θnD(rD) that satisfy the condition α1n1 + ⋅⋅⋅ + αDnD ⩽ b, where the αk are integers. We demonstrate that it is possible to exploit the structure of the grid to efficiently evaluate the matrix–vector products required to use the Lanczos algorithm.
The accuracy of dipole moments from spin-component scaled CC2 in ground and electronically excited states
Authors: Hellweg Arnim
Published: February 2011

The accuracy of dipole moments calculated from wave function methods based on second-order perturbation theory is investigated in the ground and electronically excited states. Results from the approximate coupled-cluster singles-and-doubles model, CC2, Møller–Plesset perturbation theory, MP2, and the algebraic diagrammatic construction through second-order, ADC(2), are discussed together with the spin-component scaled and the scaled opposite-spin variants of these methods. The computed dipole moments show a very good correlation with data from high-resolution spectroscopy. Compared to the unscaled methods, the spin-component scaling increases the accuracy of the results and improves the robustness of the calculations. An accuracy about 0.2 to 0.1 D in the ground state and about 0.3 to 0.2 D in the electronically excited states can be achieved with these approaches.
Influence of gas rarefaction on the lateral resolution achievable by thermocapillary patterning
Authors: Liu Nan , Troian Sandra M.
Published: February 2011

Molten polymer nanofilms subject to a large transverse thermal gradient can undergo a thermocapillary instability leading to the growth of nanopillar arrays on the cooler side. The array pitch can be estimated from the fastest growing wavelength from linear stability analysis. Here we quantify the influence of gas rarefaction on thermal conduction for cases in which the gas layer thickness above the film approaches dimensions of the molecular mean free path. For experimentally relevant parameters, rarefaction increases the pitch by as much as 65%, an important consideration for noncontact three-dimensional structure formation by thermocapillary lithography.