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991.
Vijay R. D'Costa José Menéndez John Tolle Stefan Zollner 《Solid State Communications》2006,138(6):309-313
We present a detailed analysis of the compositional dependence of the average of the E1 and E1+Δ1 transition energies in Ge1−x−ySixSny alloys. We show that this dependence can be explained in terms of three bowing parameters—bSiGe, bGeSn, and bSiSn—which scale with the product ΔχΔR of the Phillips electronegativity and size mismatches between Si, Ge, and Sn. 相似文献
992.
Deschamps M Campbell ID 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2006,178(2):206-211
In experiments performed on protonated proteins at high fields, 80% of the NMR spectrometer time is spent waiting for the 1H atoms to recover their polarization after recording the free induction decay. Selective excitation of a fraction of the protons in a large molecule has previously been shown to lead to faster longitudinal relaxation for the selected protons [K. Pervushin, B. Vögeli, A. Eletsky, Longitudinal 1H relaxation optimization in TROSY NMR spectroscopy, J. Am. Chem. Soc. 124 (2002) 12898–12902; P. Schanda, B. Brutscher, Very fast two-dimensional NMR spectroscopy for real-time investigation of dynamic events in proteins on the time scale of seconds, J. Am. Chem. Soc. 127 (2005) 8014–8015; H.S. Attreya, T. Szyperski, G-matrix Fourier transform NMR spectroscopy for complete protein resonance assignment, Proc. Natl. Acad. Sci. USA 101 (2004) 9642–9647]. The pool of non-selected protons acts as a “thermal bath” and spin-diffusion processes (“flip-flop” transitions) channel the excess energy from the excited pool to the non-selected protons in regions of the molecule where other relaxation processes can dissipate the excess energy. We present here a sensitivity enhanced HSQC sequence (COST-HSQC), based on one selective E-BURP pulse, which can be used on protonated 15N enriched proteins (with or without 13C isotopic enrichment). This experiment is compared to a gradient sensitivity enhanced HSQC with a water flip-back pulse (the water flip-back pulse quenches the spin diffusion between 1HN and 1Hα spins). This experiment is shown to have significant advantages in some circumstances. Some observed limitations, namely sample overheating with short recovery delays and complex longitudinal relaxation behaviour are discussed and analysed. 相似文献
993.
Class IV Flextensional Transducers (FTs), which are the most popular among the various FTs used for underwater sound projection, are inherently omni-directional and therefore their possible application areas are limited. In this work, we investigate the possibility of getting directional performance from a 3 kHz Class IV FT, using a reflector. Finite element modeling (FEM), with the help of a commercially available package ATILA, has been made use of. Results indicate that a parabolic reflector with a air–water interface as the reflecting surface, would give an excellent directivity of 60° (3 dB) with a front-to-back ratio better than 30 dB. Experimental results, making use of a sound-reflecting coating as the reflector has shown a directivity of 82°, with a front-to-back ratio of 21 dB. It is also observed that the reflector causes the FTs to vibrate in asymmetrical modes, the long-term implications of which needs to be studied to ensure the reliability of the device. 相似文献
994.
Babur Z. Chowdhry Trevor J. Dines Stephen A. Leharne John P. Ryall Iqbal T. Shadi Robert Withnall 《Journal of Raman spectroscopy : JRS》2011,42(2):230-238
Infrared (IR) and Raman spectra were obtained for N,N′‐dicyclohexylcarbodiimide (DCC) in the solid state and in CHCl3 solution. Structures and vibrational spectra of isolated, gas‐phase DCC molecules with C2 and Ci symmetries, computed at the B3‐LYP/cc‐pVTZ level, show that the IR and Raman spectra provide convincing evidence for a C2 structure in both the solid state and in CHCl3 solution. Using a scaled quantum‐chemical force field, these density functional theory calculations have provided detailed assignments of the observed IR and Raman bands in terms of potential energy distributions. Comparison of solid‐state and solution spectra, together with a Raman study of the melting behaviour of DCC, revealed that no solid‐state effects were evident in the spectra. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
995.
W. G. Kong Alian Wang John J. Freeman Pablo Sobron 《Journal of Raman spectroscopy : JRS》2011,42(5):1120-1129
The identification of iron sulfates on Mars by the Mars Exploration Rovers (MERs) and the Mars Reconnaissance Orbiter emphasized the importance of studying iron sulfates in laboratory simulation experiments. The copiapite group of minerals was suggested as one of the potential iron sulfates occurring on the surface and subsurface on Mars, so it is meaningful to study their spectroscopic features, especially the spectral changes caused by cation substitutions. Four copiapite samples with cation substitutions (Fe3+, Al3+, Fe2+, Mg2+) were synthesized in our laboratory. Their identities were confirmed by powder X‐ray diffraction (XRD). Spectroscopic characterizations by Raman, mid‐IR, vis‐NIR and laser‐induced‐breakdown spectroscopy (LIBS) were conducted on those synthetic copiapite samples, as these technologies are being (and will be) used in current (and future) missions to Mars. We have found a systematic ν1peak shift in the Raman spectra of the copiapite samples with cation substitutions, a consistent atomic ratio detection by LIBS, a set of systematic XRD line shifts representing structural change caused by the cation substitutions and a weakening of selection rules in mid‐IR spectra caused by the low site symmetry of (SO4)2− in the copiapite structures. The near‐infrared (NIR) spectra of the trivalent copiapite species show two strong diagnostic water features near 1.4 and 1.9 µm, with two additional bands near 2.0 µm. In the vis‐NIR spectra, the position of an electronic band shifts from 0.85 µm for ferricopiapite to 0.866 µm for copiapite, and this shift suggests the appearance of a Fe2+ electronic transition band near 0.9 µm. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
996.
John Ellis Jason L. Evans Feng Luo Keith A. Olive Jiaming Zheng 《The European Physical Journal C - Particles and Fields》2018,78(5):425
Stop coannihilation may bring the relic density of heavy supersymmetric dark matter particles into the range allowed by cosmology. The efficiency of this process is enhanced by stop-antistop annihilations into the longitudinal (Goldstone) modes of the W and Z bosons, as well as by Sommerfeld enhancement of stop annihilations and the effects of bound states. Since the couplings of the stops to the Goldstone modes are proportional to the trilinear soft supersymmetry-breaking A-terms, these annihilations are enhanced when the A-terms are large. However, the Higgs mass may be reduced below the measured value if the A-terms are too large. Unfortunately, the interpretation of this constraint on the stop coannihilation strip is clouded by differences between the available Higgs mass calculators. For our study, we use as our default calculator FeynHiggs 2.13.0, the most recent publicly available version of this code. Exploring the CMSSM parameter space, we find that along the stop coannihilation strip the masses of the stops are severely split by the large A-terms. This suppresses the Higgs mass drastically for \(\mu \) and \(A_0 > 0\), whilst the extent of the stop coannihilation strip is limited for \(A_0 < 0\) and either sign of \(\mu \). However, in sub-GUT models, reduced renormalization-group running mitigates the effect of the large A-terms, allowing larger LSP masses to be consistent with the Higgs mass calculation. We give examples where the dark matter particle mass may reach \(\gtrsim 8\) TeV. 相似文献
997.
998.
Acosta D Affolder T Albrow MG Ambrose D Amidei D Anikeev K Antos J Apollinari G Arisawa T Artikov A Ashmanskas W Azfar F Azzi-Bacchetta P Bacchetta N Bachacou H Badgett W Barbaro-Galtieri A Barnes VE Barnett BA Baroiant S Barone M Bauer G Bedeschi F Behari S Belforte S Bell WH Bellettini G Bellinger J Benjamin D Beretvas A Bhatti A Binkley M Bisello D Bishai M Blair RE Blocker C Bloom K Blumenfeld B Bocci A Bodek A Bolla G Bolshov A Bortoletto D Boudreau J Bromberg C Brubaker E Budagov J 《Physical review letters》2005,94(17):171802
We report the first largely model independent measurement of charged particle multiplicities in quark and gluon jets, Nq and Ng, produced at the Fermilab Tevatron in pp collisions with a center-of-mass energy of 1.8 TeV and recorded by the Collider Detector at Fermilab. The measurements are made for jets with average energies of 41 and 53 GeV by counting charged particle tracks in cones with opening angles of theta(c) = 0.28, 0.36, and 0.47 rad around the jet axis. The corresponding jet hardness Q = Ejet theta c varies in the range from 12 to 25 GeV. At Q = 19.2 GeV, the ratio of multiplicities r = Ng/Nq is found to be 1.64+/-0.17, where statistical and systematic uncertainties are added in quadrature. The results are in agreement with resummed perturbative QCD calculations. 相似文献
999.
We investigate the spin-orbit (SO) interaction in two-dimensional electron gases in quantum wells with two subbands. From the 8x8 Kane model, we derive a new intersubband-induced SO term which resembles the functional form of the Rashba SO but is nonzero even in symmetric structures. This follows from the distinct parity of the confined states (even or odd) which obliterates the need for asymmetric potentials. We self-consistently calculate the new SO coupling strength for realistic wells and find it comparable to the usual Rashba constant. Our new SO term gives rise to a nonzero ballistic spin-Hall conductivity, which changes sign as a function of the Fermi energy (epsilonF) and can induce an unusual Zitterbewegung with cycloidal trajectories without magnetic fields. 相似文献
1000.
A computationally efficient finite element model with perfectly matched layers applied to scattering from axially symmetric objects 总被引:1,自引:0,他引:1
Zampolli M Tesei A Jensen FB Malm N Blottman JB 《The Journal of the Acoustical Society of America》2007,122(3):1472
A frequency-domain finite-element (FE) technique for computing the radiation and scattering from axially symmetric fluid-loaded structures subject to a nonsymmetric forcing field is presented. The Berenger perfectly matched layer (PML), applied directly at the fluid-structure interface, makes it possible to emulate the Sommerfeld radiation condition using FE meshes of minimal size. For those cases where the acoustic field is computed over a band of frequencies, the meshing process is simplified by the use of a wavelength-dependent rescaling of the PML coordinates. Quantitative geometry discretization guidelines are obtained from a priori estimates of small-scale structural wavelengths, which dominate the acoustic field at low to mid frequencies. One particularly useful feature of the PML is that it can be applied across the interface between different fluids. This makes it possible to use the present tool to solve problems where the radiating or scattering objects are located inside a layered fluid medium. The proposed technique is verified by comparison with analytical solutions and with validated numerical models. The solutions presented show close agreement for a set of test problems ranging from scattering to underwater propagation. 相似文献