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991.
We present theoretical analysis of bromine adsorption on the Ge(001)-p(1×2) surface. Bromine adsorbs dissociatively at the
Ge(001) surface and the adlayer of bromine develops ordered structures of adatoms bound to substrate dimers. We analyse atomic
configurations of the Ge(001) surface covered by 0.25, 0.5, 0.75 and 1 monolayer of bromine. Various stable surface structures,
found in calculations, are presented and their energies are compared. Simulated STM images are also discussed for the considered
configurations.
相似文献
992.
Alver B Back BB Baker MD Ballintijn M Barton DS Betts RR Bindel R Busza W Chai Z Chetluru V García E Gburek T Gulbrandsen K Hamblen J Harnarine I Henderson C Hofman DJ Hollis RS Hołyński R Holzman B Iordanova A Kane JL Kulinich P Kuo CM Li W Lin WT Loizides C Manly S Mignerey AC Nouicer R Olszewski A Pak R Reed C Richardson E Roland C Roland G Sagerer J Sedykh I Smith CE Stankiewicz MA Steinberg P Stephans GS Sukhanov A Szostak A Tonjes MB Trzupek A van Nieuwenhuizen GJ Vaurynovich SS Verdier R 《Physical review letters》2006,96(21):212301
We present transverse momentum distributions of charged hadrons produced in Cu + Cu collisions at square root of SNN = 62.4 and 200 GeV. The spectra are measured for transverse momenta of 0.25 < pT < 5.0 GeV/c at square root of SNN = 62.4 GeV and 0.25 < pT < 7.0 GeV/c at square root of SNN = 200 GeV, in a pseudorapidity range of 0.2 < eta < 1.4. The nuclear modification factor R(AA) is calculated relative to p + p data at both collision energies as a function of collision centrality. At a given collision energy and fractional cross section, R(AA) is observed to be systematically larger in Cu + Cu collisions compared to Au + Au. However, for the same number of participating nucleons, R(AA) is essentially the same in both systems over the measured range of pT, in spite of the significantly different geometries of the Cu + Cu and Au + Au systems. 相似文献
993.
Synthesis, Structure, and Properties of Three Tetrasodium Tetrametaphosphimate Hydrates Single crystals of three tetrasodium tetrametaphosphimate hydrates Na4(PO2NH)4 · x H2O with x = 2 and 3, respectively, have been obtained and characterized by single crystal X-ray diffraction. Dimorphous Na4(PO2NH)4 · 3 H2O is formed at RT. It crystallizes monoclinic ( 1 ) or triclinic ( 2 ) (α-Na4(PO2NH)4 · 3 H2O ( 1 ): P21, a = 1002.7(2), b = 1189.7(2), c=1193.1(2)pm, β=104.93(1)°, Z=4; β-Na4(PO2NH)4 · 3 H2O ( 2 ): P 1¯, a = 843.64(9), b = 848.54(10), c = 994.7(2) pm, α = 83.07(1), β = 76.31(1), γ = 87.46(1)°, Z = 2). Compound 2 is formed in the presence of NaCl during the crystallization from aqueous solution. Tetrasodium tetrametaphosphimate dihydrate ( 3 ) is formed at 60 °C (Na4(PO2NH)4 · 2 H2O ( 3 ): C2/c, a = 2225.6(3), b = 513.0(1), c = 1566.7(2) pm, β = 134.21(1)°, Z = 4). In 1 and 2 the P4N4 ring of the tetrametaphosphimate ions attains a saddle and in 3 a twistboat conformation. The conformations of the anions have been analysed using torsion angles, displacement asymmetry parameters, and puckering parameters. The (PO2NH)44– rings of the compounds 1 , 2 , and 3 are linked by N–H · · &mid 相似文献
994.
High-refractive-index polymers for intraocular lenses are presented whose refractive index can be tuned post-operatively in a non-invasive manner to enable focal length and aspheric corrections in vivo. The polymer materials contain covalently attached photochemically crosslinkable coumarin side groups, to cause a change in refractive index of Deltan > 0.02, which enables one to tune the focal length of a standard IOL by two diopters. This is enough to ensure that more than 80% of all cataract patients can be adjusted non-invasively to optimal vision after cataract surgery, thus providing a remedy to a major shortcoming of today's cataract surgery. 相似文献
995.
Blends of PBT with PET or PC were studied by X-ray diffraction and DSC for different conditions of crystallization. PBT and PET crystallize very similarly, though they are recognized as partially compatible in the melt. In the PBT/PC blends X-ray diffraction examinations show crystallization of PC after 4 h of annealing. In the melt, both components are compatible. Tg-calculations indicate a plasticizing effect. In both kinds of blends, PBT crystallizes faster than PC or PET. Fast crystallization processes were examined by X-ray diffraction measurements with synchrotron radiation. 相似文献
996.
The information storage is developing toward high speed access and massive stor-age capacity. Optical holographic storage has not only high speed parallel data access and high addressing speed without mechanical motion but also high storage density with multiplexed volume holographic storage[1]. In recent years, optical holographic storage is studied intensely in the field of information storage. It has been shown that the polari-zation of light could also be recorded with polarization hologra… 相似文献
997.
J. A. Dayton V. O. Heinen N. Stankiewicz T. M. Wallett 《International Journal of Infrared and Millimeter Waves》1987,8(10):1257-1268
NASA Lewis Research Center is engaged in a program to develop a series of backward wave oscillators (BWO's) for the frequency range 500 to 2000 GHz. Generically BWO's are electron beam traveling wave tubes operating in a dispersive regime in which the group velocity and the phase velocity of the induced electromagnetic wave are in opposite directions. The oscillation frequency of a BWO is controlled by the electron beam velocity (anode voltage).Such tubes because of their frequency tunability, phase locking capability, and large bandwidth are ideal local oscillators for heterdyne receiver/spectrometers.The design of the BWO's will be discussed with emphasis on the etched slow wave structure, zero compression electron beam, long life cathode, and moderate operating voltages. 相似文献
998.
Zsolt?Ajtony Norbert?Szoboszlai Zsuzsanna?Bella Szilvia?Bolla Pál?Szakál László?BencsEmail author 《Mikrochimica acta》2005,150(1):1-8
A flow injection hydride generation graphite furnace atomic absorption spectrometric (FI-HG-GFAAS) method was applied to the determination of Se in Se-doped and undoped cereals and bakery products. For the purpose of doping, the soils used for the cultivation of the cereals were dosed with Se-doped foliar fertilizers. The samples were dissolved in a mixture of HNO3 and H2O2 solutions using microwave-assisted digestion. The decomposition of H2Se generated from the sample solutions and the trapping of elemental Se were performed at a temperature of 300°C on an Ir-pretreated integrated graphite platform of a transversally heated graphite atomizer (THGA). For release of the trapped Se within a fairly short atomization time (5s), an atomization temperature of 2200°C was observed to be optimal. The overall efficiency of hydride generation, transport and trapping was 86%.The upper limit of the linear dynamic range of calibration was 10µgL–1, which corresponds to 0.5µgg–1 for solid samples. Recovery of the samples spiked with SeVI solutions was found to be 93±6% on average. The relative standard deviation of the determinations was less than 8%. The limit of detection was found to be 0.06µgL–1, corresponding to 3ngg–1 for solid samples. The accuracy of the method was verified with the use of IAEA-155 (whey powder) certified reference material. End-capped THGA tubes resulted in an extension of the linear calibration range compared to that of standard THGAs.The Se content in bakery products made of undoped cereals ranged from 7.7 to 68ngg–1 (wet weight) in 18 samples, whereas the Se content of the corresponding cereals was found to be below 100ngg–1 (wet weight). The Se level of cereals grown on soils treated with Se-doped fertilizers ranged from 128 to 1046ngg–1 (wet weight), and it depended linearly on the Se concentration of the corresponding foliar fertilizer. 相似文献
999.
1000.
Zernike phase contrast microscopy is extended and combined with a phase-shifting mechanism to perform quantitative phase measurements of microscopic objects. Dozens of discrete point light sources on a ring are constructed for illumination. For each point light source, three different levels of point-like phase steps are designed, which are alternatively located along a ring on a silica plate to perform phase retardation on the undiffracted (dc) component of the object waves. These three levels of the phase steps are respectively selected by rotating the silica plate. Thus, quantitative evaluation of phase specimens can be performed via phase-shifting mechanism. The proposed method has low "halo" and "shade-off" effects, low coherent noise level, and high lateral resolution due to the improved illumination scheme. 相似文献