共查询到20条相似文献,搜索用时 15 毫秒
1.
In this paper we derive estimates for the eigenvalues of the Dirac operator and their multiplicity on manifolds diffeomorphic to Sn with an isometric SO(n)-action. Especially we prove a new lower bound for the first eigenvalue and show an example, where this new bound coincides in the limit with the known upper bounds. 相似文献
2.
The lowest-energy structures and the electronic properties of Mo2nNn(n=1-5) clusters have been studied by using the density functional theory(DFT) simulating package DMol 3 in the generalized gradient approximation(GGA).The resulting equilibrium geometries show that the lowest-energy structures are dominated by central cores which correspond to the ground states of Mo n(n = 2,4,6,8,10) clusters and nitrogen atoms which surround these cores.The average binding energy,the adiabatic electron affinity(AEA),the vertical electron affinity(VEA),the adiabatic ionization potential(AIP) and the vertical ionization potential(VIP) of Mo2nNn(n=1-5) clusters have been estimated.The HOMO-LUMO gaps reveal that the clusters have strong chemical activities.An analysis of Mulliken charge distribution shows that charge-transfer moves from Mo atoms to N atoms and increases with cluster size. 相似文献
3.
采用密度泛函理论(DFT)中的B3LYP方法,在LANL2DZ基组水平上对WnNim(n+m=8)团簇的各种可能构型进行了几何参数全优化,得到了它们的基态构型;并对基态构型的偶极距、极化率、红外光谱和拉曼光谱性质进行了分析,结果表明:团簇WnNim(n+m=8)都具有极性,富W团簇非线性光学效应强,容易被外加场极化;振动频率主要分布在0-350 cm-1范围内,团簇W4Ni4因其振动方式的特殊性,红外光谱和拉曼光谱在频率421.971 cm-1处,都有明显强峰;团簇W5Ni3因其结构的高对称性在振动光谱中出现多处共振现象. 相似文献
4.
Paolo Berta Ishwar K. Puri Suresh K. Aggarwal 《Proceedings of the Combustion Institute》2005,30(1):447-453
To avoid the complexities associated with the droplet/vapor transport and nonuniform evaporation processes, a fundamental investigation of liquid fuel combustion in idealized configurations is very useful. An experimental–computational investigation of prevaporized n-heptane nonpremixed and partially premixed flames established in a counterflow burner is described. There is a general agreement between various facets of our nonpremixed flame measurements and the literature data. The partially premixed flames are characterized by a double flame structure. This becomes more distinct as the strain rate decreases and partial premixing increases, which also increases the separation distance between the two reaction zones. The peak partially premixed flame temperature increases with increasing premixing of the fuel stream. The peak CO2 and H2O concentrations are relatively insensitive to partial premixing. The CO and H2 peak concentrations on the premixed side increase as the fuel-side equivalence ratio decreases. These species are transported to the nonpremixed reaction zone where they oxidize. The C2 species have peaks in the premixed reaction zone. The concentrations of olefins are ten times larger than those of the corresponding paraffins. The oxidizer is present in partially premixed flames throughout the combustion system and there are no regions characterized by simultaneous high temperature and high fuel concentration. As a result, pyrolysis reactions leading to soot formation are greatly diminished. 相似文献
5.
The quasi-two-dimensional magnetism in the layered transition metal compound (CnH2n+1NH3)2CuCl4 (n=10, 14) was investigated by means of electron paramagnetic resonance (EPR) and superconducting quantum interference device measurements. As a result, the high temperature magnetic phase transitions were reflected in the EPR parameters in a sensitive manner. 相似文献
6.
A density-functional theory for (BAs)n clusters (n=1 14): structures, stabilities and electronic properties 下载免费PDF全文
This paper investigates the lowest-energy structures,stabilities and electronic properties of (BAs) n clusters (n=1-14) by means of the density-functional theory.The results show that the lowest-energy structures undergo a structural change from two-dimensional to three-dimensional when n=4.With the increase of the cluster size (n 6),the (BAs) n clusters tend to adopt cage-like structures,which can be considered as being built from B 2 As 2 and six-membered rings with B-As bond alternative arrangement.The binding energy per atom,second-order energy differences,vertical electron affinity and vertical ionization potential are calculated and discussed.The caculated HOMO-LUMO gaps reveal that the clusters have typical semiconductor characteristics.The analysis of partial density of states suggests that there are strong covalence and molecular characteristics in the clusters. 相似文献
7.
In continuous magnetic fields H up to 28 T, we have studied the out-of-plane transport properties and tunneling characteristics of high-quality nondoped single crystals of the Bi-cuprate family: Bi2Sr2CuO6+δ (Bi2201), Bi2Sr2CaCu2O8+δ (Bi2212) and Bi2Sr2Ca2Cu3O10+δ (Bi2223) grown by an identical method. For all compounds the out-of-plane magnetotransport ρc(H) is negative in the temperature region where ρc(T) shows in the normal state a semiconducting-like temperature dependence. The negative magnetoresistance of ρc corresponds to the suppression of the semiconducting temperature dependence of ρc(T) which is found to be isotropic. For the Bi2201 compound, where the normal state can be reached in the available magnetic fields (28 T), a nearly complete suppression of the low-temperature upturn in ρc(T) is observed in the highest magnetic fields with a tendency towards a metallic behavior down to the lowest temperatures (0.4 K). Using the break-junction technique, especially for the Bi2212 and Bi2232 compounds, a clear superconducting gap structure can be observed. Both for temperatures above the critical temperature and for magnetic fields above the upper critical field, a pseudogap structure remains present in the tunneling spectra. The applied magnetic fields yield a stronger suppression of the superconducting state compared to that of the normal-state gap structures as manifested in ρc(T) transport and tunneling. 相似文献
8.
The geometries of MgnNi2 (n=1-6) clusters are studied by using the hybrid density functional theory (B3LYP) with LANL2DZ basis sets. For the ground-state structures of MgnNi2 clusters, the stabilities and the electronic properties are investigated. The results show that the groundstate structures and symmetries of Mg clusters change greatly due to the Ni atoms. The average binding energies have a growing tendency while the energy gaps have a declining tendency. In addition, the ionization energies exhibit an odd-even oscillation feature. We also conclude that n=3, 5 are the magic numbers of the MgnNi2 clusters. The Mg3 Ni2 and Mg5Ni2 clusters are more stable than neighbouring clusters, and the Mg4Ni2 cluster exhibits a higher chemical activity. 相似文献
9.
Monte Carlo study of the universal area distribution of clusters in honeycomb O(n) loop model 下载免费PDF全文
We investigate the area distribution of clusters (loops) for the honeycomb O(n) loop model by means of worm algorithm with n=0.5, 1, 1.5, and 2. At the critical point, the number of clusters, whose enclosed area is greater than A, is proportional to A-1 with a proportionality constant C. We confirm numerically that C is universal, and its value agrees well with the predictions based on the Coulomb gas method. 相似文献
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12.
D. G. Chukhchin 《Journal of Applied Spectroscopy》1997,64(3):414-418
A new algorithm for resolving individual bands in absorption spectra is developed. It is assumed that the spectrum consists
of absorption bands with halfwidths determined by different kinds of interactions—specific and nonspecific. The method has
good accuracy in the case of the strong overlap of bands (the ratio of the distance between maxima of the peaks to the halfwidth
is less than 0.2) and a high computational efficiency.
Arkhangelsk State Technical University, 17, Naberezhnaya Severnoi Dviny, Arkhangelsk, 163007, Russia. Translated from Zhurnal
Prikladnoi Spektroskopii, Vol. 64, No. 3, pp. 400–404, May–June, 1997. 相似文献
13.
Niina Jalarvo Camilla Haavik Camilla Kongshaug Poul Norby Truls Norby 《Solid State Ionics》2009,180(20-22):1151-1156
The hydrated oxygen deficient complex perovskite-related materials Sr4(Sr2Nb2)O11·nH2O and Sr4(Sr2Ta2)O11·nH2O were studied at high water vapour pressures over a large temperature range by electrical conductivity measurements, thermogravimetry (TG), and X-ray powder diffraction (XRPD). In humid atmospheres both materials are known to exhibit protonic conductivity below dehydration temperatures, with peak-shaped maxima at about 500 °C. In this work we show that the peaks expand to plateaus of high conductivity from 500 to 700 °C at a water vapour pressure of 1 atm. However, in situ synchrotron XRPD of Sr4(Sr2Nb2)O11·nH2O as a function of temperature shows that these observations are in fact coincident with melting and dehydration of a secondary phase Sr(OH)2. The stability of Sr4(Sr2Nb2)O11·nH2O and Sr4(Sr2Ta2)O11·nH2O in humid atmospheres is thus insufficient, causing decomposition into perovskites with lower Sr content and SrO/Sr(OH)2 secondary phases. This, in turn, rationalizes the observation of peaks and plateaus in the conductivity of these materials. 相似文献
14.
Single mode intracavity absorption is investigated from an analytical point of view in order to explain the periodical modulation of the power observed in intracavity absorption of CO2 laser lines by CFC gases. Intracavity absorption is incorporated into the laser rate equations in form of an additional broadband loss. Detuning due to changes in the refractive index with increase in absorber pressure is accounted for by considering the impact of the frequency shift of the oscillating mode on the effective pump rate and the population densities of the laser upper and lower levels. The steady state solution of the rate equations leads to an analytical formula, which fits the measured intracavity absorption curves with only two fit parameters being adjusted to the actual values of the absorption cross section and the mean linear polarizability of the absorber molecule. The formula is applied to analyze the intracavity absorption of the CO2 10R lines by CFC-11. The obtained results are in reasonable agreement with the values available in the literature. 相似文献
15.
A. D. Gazazyan E. A. Gazazyan A. G. Margaryan 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,53(2):243-251
The possibility of storage of quantum information with photons is studied in the case of resonant transitions via many close
lying exciton levels in a solid with impurity -atoms. The upper levels of the impurity atom form resonant Fano states, similar to the autoionization atomic states, due
to the configuration interaction with the continuum of the exciton band. In this case slowing of light pulses is shown to
be realistic, in the presence of the control field, down to the group velocity much lower than that in vacuum. The possibility
of storage and reconstruction of a quantum pulse is studied in the case of the instantaneous switching on/off of the control
field. It is shown that the signal quantum pulse cannot be stored undistorted for differing values of Fano parameters and
for non-zero two-photon detuning and decay rate between the lower levels (decoherence). However, for small difference of the
Fano parameters and for small values of the two-photon detuning and the decoherence there is no distortion in the case where
the length of the pulse is much longer than the linear absorption (amplification) length, so the shape and quantum state of
the light pulse can be restored. 相似文献
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17.
Operators’s-parameterized ordering and its classical correspondence in quantum optics theory 下载免费PDF全文
In reference to the Weyl ordering xmpn→(1/2)mΣι=0m(ιm)Xm-ιPnXι , where X and P are coordinate and momentum operator, respectively, this paper examines operators’s-parameterized ordering and its classical correspondence, finds the fundamental function-operator correspondence ((1-s)/2)(n+m)/2Hm,n((2/(1-s))~(1/2)α,(2/(1-s))~(1/2)α)→a+man,and its complementary relation αnα*m→(-i)n+m((1-s)/2)(m+n)/2:Hm,n(i(2/(1-s))~(1/2)a+,i((2/(1-s))~(1/2)a):,where H m,n is the two-variable Hermite polynomial, a, a+ are bosonic annihilation and creation operators respectively, s is a complex parameter. The s’-ordered operator power-series expansion of s-ordered operator sa+mans in terms of the two-variable Hermite polynomial is also derived. Application of operators’s-ordering formula in studying displaced-squeezed chaotic field is discussed. 相似文献
18.
Xinshun Wang Jianrong Qiu Juan Song Jian Xu Yang Liao Haiyi Sun Zhizhan Xu 《Optics Communications》2008,281(2):299-302
Near-infrared to ultraviolet upconversion luminescence was observed in the Pr3+:Y2SiO5 crystal with 120 fs, 800 nm infrared laser irradiation. The observed emissions at around 270 nm and 305 nm could be assigned to 5d → 4f transitions of Pr3+ ions. The relationship between the upconversion luminescence intensity and the pump power of the femtosecond laser reveals that the UV emission belongs to simultaneous three-photon absorption induced upconversion luminescence. 相似文献
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20.
Generation of Wn state with three atoms trapped in two remote cavities coupled by an optical fibre 下载免费PDF全文
We propose two schemes for the generation of the Wn state with three atoms separately trapped in two distant cavities coupled by an optical fibre.One is implemented by controlling the interaction time,the other is implemented via the adiabatic passage.The influence of various decoherence processes,such as spontaneous emission of the atoms and photon leakages of the cavities and the optical fibre,on the fidelity is also investigated.It is found that the Wn state can be generated with high fidelity even when these decoherence processes are present. 相似文献