共查询到20条相似文献,搜索用时 31 毫秒
1.
X. G. Kong Y. Yu T. Gao 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,76(3):365-371
The ab initio pseudopotential method within the
generalized gradient approximation (GGA) and quasiparticle approximation has
been used to investigate the electronic properties of titanium dioxide in
the rutile, anatase, and fluorite structures, respectively. Here we present
the GW approximation for the electronic self-energy, which allows to
calculate excited-state properties, especially electronic band structures.
For this calculation, good agreement with the experimental results for the
minimum band gaps in rutile and anatase phase is obtained. In the fluorite
phase we predict that titanium dioxide will be an indirect (Γ to X)
wide band-gap semiconductor (2.367 or 2.369 eV) and the properties remain to
be confirmed by experiment. 相似文献
2.
The morphology of pentacene organic thin films deposited on SiO2 and Au(111) surfaces using organic molecular beam deposition (OMBD) has been characterized by a multi-technique approach.
Among the techniques applied were X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), scanning electron
microscopy (SEM) and thermal desorption spectroscopy (TDS). Our rather detailed studies reveal that on both substrates the
growth is strongly influenced by dewetting and islanding phenomena, yielding very rough surfaces. Surprisingly, substantial
changes in the morphology were observed also after deposition on room-temperature samples on a time scale of several hours.
The rather extensive set of in situ XPS data was analyzed in the framework of a simple model, which allows us to derive rather
detailed information on the roughness parameters. 相似文献
3.
B. I. Ermolaev M. Greco S. I. Troyan 《The European Physical Journal C - Particles and Fields》2008,58(1):29-35
We examine the recent COMPASS data on the spin structure function g
1 singlet. We show that it is rather difficult to use the data in the present form in order to draw conclusions on the initial
parton densities. However, our tentative estimate is that the data better agree with positive than with negative initial gluon
densities. 相似文献
4.
The estimates of the background for the associate W Higgs production, which stems from the two parton shower production, leads to a background which is of the order of the signal
for the non-perturbative contribution. In the perturbative approach the background turns out to be small. This background
does not depend on the rapidity difference between the W and the
pair, while the signal peaks when the rapidity difference is zero. Detailed calculations for the enhanced diagrams’ contribution
to this process are presented, and it is shown that the overlapping singularities, being important theoretically, lead to
a small contribution for the LHC range of energies. 相似文献
5.
L. Fan Y. X. Fan Y. H. Duan Q. Wang H. T. Wang G. H. Jia C. Y. Tu 《Applied physics. B, Lasers and optics》2009,94(4):553-557
We report a continuous-wave intracavity Raman laser at 1179.5 nm with a SrWO4 Raman crystal in a diode-end-pumped Nd:YVO4 laser. The highest output power of 2.23 W is obtained at the laser diode power of 21.2 W corresponding to the slope efficiency
of 17.3% and a diode-to-stokes optical conversion efficiency of 10.5%. The dependence of the Raman laser performance on the
pump polarization is also studied. The measured Raman thresholds are about 9.3 and 8.3 W in the diode pump laser power for
the a- and b-polarized configurations, respectively. The Raman gain coefficients of the c-cut SrWO4 crystal for a- and b-polarized pumps are estimated to be about 4.9 and 4.7 cm/GW, respectively. 相似文献
6.
S.?Firmino?Mendes C.?M.?Costa V.?Sencadas J.?Serrado?Nunes P.?Costa R.?GregorioJr. S.?Lanceros-Méndez 《Applied Physics A: Materials Science & Processing》2009,94(4):899-904
Laser-induced backside wet and dry etching (LIBWE and LIBDE) methods were developed for micromachining of transparent materials.
Comparison of these techniques is helpful in understanding the etching mechanism but was not realized due to complications
in setting up comparable experimental conditions. In our comparative investigations we used a solid tin film for dry and molten
tin droplets for wet etching of fused-silica plates. A tin–fused-silica interface was irradiated through the sample by a KrF
excimer laser beam (λ=248 nm, FWHM=25 ns); the fluence was varied between 400 and 2100 mJ/cm2. A significant difference between the etch depths of the two investigated methods was not found. The slopes of the lines
fitted to the measured data (slLIBDE=0.111 nm/mJ cm−2, slLIBDE=0.127 nm/mJ cm−2) were almost similar. Etching thresholds for LIBDE and LIBWE were approximately 650 and 520 mJ/cm2, respectively. To compare the dependence of etch rates on the pulse number, target areas were irradiated at different laser
fluences and pulse numbers. With increasing pulse number a linear rise of depth was found for wet etching while for dry etching
the etch depth increase was nonlinear. Secondary ion mass spectroscopic investigations proved that this can be due to the
reconstruction of a new thinner tin-containing surface layer after the first pulse. 相似文献
7.
K. Urbanowski 《The European Physical Journal C - Particles and Fields》2008,58(1):151-157
By analyzing the survival probability amplitude of an unstable state we show that the energy corrections to this state in
the long (t→∞) and relatively short (lifetime of the state) time regions are different. It is shown that in the considered model the
above corrections decrease to zero as t→∞. It is hypothesized that this property could be detected by analyzing the spectra of distant astrophysical objects. The
above property of unstable states may influence the measured values of possible deviations of the fine structure constant
α as well as other astrophysical and cosmological parameters. 相似文献
8.
T. I. Milenov V. I. Dimov P. M. Rafailov M. M. Gospodinov 《Applied Physics A: Materials Science & Processing》2008,92(3):643-649
Lattice defects in a scintillation detector made of Bi4Ge3O12 (BGO) could severely impact detector efficiency via non-radiative transfer of electron excitation, thus making thorough investigations
of these defects highly important. Here we present a combined experimental and theoretical study of two- and three-dimensional
defects in a Czochralski-grown BGO crystal. Upon examination by transmission electron microscopy the selected-area electron
diffraction (SAED) patterns in two neighboring parts of the specimen reveal different kinds of two- and three-dimensional
defects. Three sub-grains misoriented at 2.47° with reference to each other and probable presence of stacking faults lying
in {011} planes were observed in the first examined local area. The SAED image taken from an area in the close neighborhood
is much more complicated and is explained in terms of the superposition of reflections from: (i) a partially textured GeO2 second-phase inclusion; (ii) the basic lattice of BGO and (iii) a superlattice-like structure based on the BGO lattice. The
atomic structure of such a superlattice-like structure was theoretically modeled and the corresponding simulated SAED patterns
were found to be in good agreement with the experimentally observed one. 相似文献
9.
Lavinia P. Curecheriu Liliana Mitoseriu Adelina Ianculescu Ana Braileanu 《Applied Physics A: Materials Science & Processing》2009,97(3):587-594
In the present paper, Pb(Mg1/3Nb2/3)O3 (PMN) ceramics prepared by the columbite method were investigated. The dielectric study indicates typical relaxor properties,
with a frequency dispersion in the range of 200–350 K. The relaxor-to-paraelectric phase transition was evidenced by the continuous
decrease of the local order parameter derived from the permittivity-temperature data. As a result of the critical behavior,
the main Raman modes show anomalies at: (i) ∼150 K; (ii) ∼220 K (i.e. close to the critical temperature reported for the field-induced
ferroelectric state in PMN single crystal); (iii) ∼260 K (i.e. the temperature of the permittivity maximum); (iv) ∼350 K (the
temperature for initiation of the cluster freezing process T
*); (v) ∼620 K (Burns temperature). The frequency split of the doublet at ∼605 and ∼500 cm−1 presents a critical behavior related to the local symmetry lowering and to the structure ordering due to a phase transformation
which takes place below T
*. The tunability in the paraelectric state was interpreted in terms of reorientation of the non-interacting nanopolar clusters
in a double-well potential. The temperature dependence of the nanopolar domain size also shows anomalies in the range of T
*. The size and dynamics of the polar nanodomains is essential in determining the functional properties of the Pb(Mg1/3Nb2/3)O3 relaxor. 相似文献
10.
Zhi-Gang Wang 《The European Physical Journal C - Particles and Fields》2009,62(2):375-382
In this article, we assume that there exists a scalar hidden charm tetraquark state in the π
+
χ
c1 invariant mass distribution, and we study its mass using the QCD sum rules. The numerical result M
Z
=(4.36±0.18) GeV is consistent with the mass of the Z(4250). The Z(4250) may be a tetraquark state, but other possibilities, such as a hadro-charmonium resonance and a
molecular state, are not excluded. 相似文献
11.
Koji?Nagata 《International Journal of Theoretical Physics》2009,48(12):3358
We show that any N-qubit state which is diagonal in the Greenberger-Horne-Zeilinger basis is full N-qubit entangled state if and only if no partial transpose of the multiqubit state is positive with respect to any partition. 相似文献
12.
SmAlO3 nanocrystalline powders were successfully synthesized by the polymeric precursor method using ethylenediaminetetraacetic
acid as a chelating agent. The precursor and the derived powders were characterized by thermogravimetry analysis (TG) and
differential scanning calorimetry analysis (DSC), infrared spectroscopy (IR), X-ray diffractometry (XRD) and transmission
electron microscopy (TEM). The results showed that pure SmAlO3 powder with orthorhombic perovskite structure could be synthesized at 800°C for 2 h without formation of any intermediate
phase. The average particle size of the powder synthesized at 900°C was as low as 28 nm. Subsequently, the bulk SmAlO3 ceramics were prepared at various sintering temperatures using the synthesized powders calcined at 900°C for 2 h as starting
materials. The sintering experiments indicated that the sample sintered at 1550°C for 2 h exhibited the highest relative density
of 97.2% and possessed the best microwave dielectric properties of ε
r=20.94, Q×f=78600 GHz and τ
f=−71.8 ppm/°C. 相似文献
13.
The local reggeon field theory is studied perturbatively taking advantage of the PT symmetry in the Hamiltonian formulation. In the lowest non-trivial order we show that the pomeron interactions renormalize
the slope. In the same order we find a non-local pair potential acting between pomerons, which has a singular structure. However,
the analysis of the scattering operator shows that at small coupling constant bound states do not appear so that the two-particle
spectrum is not changed. 相似文献
14.
Yu. E. Titarenko V. F. Batyaev M. A. Butko K. V. Pavlov A. Yu. Titarenko S. G. Mashnik A. V. Ignatyuk V. S. Barashenkov 《Physics of Atomic Nuclei》2007,70(7):1149-1153
The results of the experimental measurement and numerical simulation of the cross sections for residual radioactive nuclei production in thin 209Bi, natPb, 206Pb, 207Pb, and 208Pb targets bombarded with protons in the energy range from 0.04 to 2.6 GeV are reported. The nuclide production cross sections were measured using γ spectrometry with a high-resolution Ge detector. The experimental data include a total of 5972 reaction cross sections at 11 proton energy values. The results are compared to the data from other laboratories reported in 80 papers. The model calculations were carried out using eight simulation code packages: LAHET, INCL4 + ABLA, CEM03, LAQGSM + GEM2, CASCADE, CASCADE-2004, CASCADO, and LAHETO. A detailed analysis of discrepancies between the measured and calculated data is presented. 相似文献
15.
C. Pahl S. Bethke O. Biebel S. Kluth J. Schieck 《The European Physical Journal C - Particles and Fields》2009,64(4):533-547
Predictions of analytical models for hadronisation, namely the dispersive model, the shape function and the single dressed
gluon approximation, are compared with moments of hadronic event shape distributions measured in e+e− annihilation at centre-of-mass energies between 14 and 209 GeV. In contrast to Monte Carlo models for hadronisation, analytical
models require to adjust only two universal parameters, the strong coupling and a second quantity parametrising non-perturbative
corrections. The extracted values of α
S are consistent with the world average and competitive with previous measurements. The variance of event shape distributions
is compared with predictions given by some of these models. Limitations of the models, probably due to unknown higher order
corrections, are demonstrated and discussed. 相似文献
16.
A. K. Chaudhuri 《The European Physical Journal C - Particles and Fields》2009,61(2):331-338
In a hydrodynamic model, we have studied J/ψ production in Au+Au/Cu+Cu collisions at RHIC energy,
GeV. At the initial time, J/ψ’s are randomly distributed in the fluid. As the fluid evolves in time, the free streaming J/ψ’s are dissolved if the local fluid temperature exceeds a threshold temperature T
J/ψ
. Sequential melting of charmonium states (χ
c
, ψ
′ and J/ψ), with melting temperatures
, T
J/ψ
≈2T
c
and feed-down fraction F≈0.3, explains the PHENIX data on the centrality dependence of J/ψ suppression in Au+Au collisions. J/ψ
p
T
spectra and the nuclear modification factor in Au+Au collisions are also well explained in the model. The model however overpredicts
the centrality dependence of J/ψ suppression in Cu+Cu collisions by 20–30%. The J/ψ
p
T
spectra are underpredicted by 20–30%. The model predicts that in central Pb+Pb collisions at LHC energy,
GeV, J/ψ’s are suppressed by a factor of ∼10. The model predicted a J/ψ
p
T
distribution in Pb+Pb collisions at LHC is similar to that in Au+Au collisions at RHIC. 相似文献
17.
A. W. K. Mok K. J. Sebastian 《The European Physical Journal C - Particles and Fields》2009,63(1):101-114
Using the helicity formalism, we calculate the combined angular distribution function of the two gamma photons and the electron in the cascade process \({\bar{p}p}\to{}^{3}{D}_{2}\to\chi_{J}+\gamma_{1}\to(\psi +\gamma_{2})+\gamma_{1}\to({e}^{+}+{e}^{-})+\gamma_{1}+\gamma_{2}\) (J=0,1,2), when \({\bar{p}}\) and p are arbitrarily polarized. We also present the partially integrated angular distribution functions in six different cases. Our results show that by measuring the two-particle angular distribution of γ 1 and γ 2 and that of γ 1 and e ?, one can determine the relative magnitudes as well as the relative phases of all the helicity amplitudes in the two radiative decay processes 3 D 2→χ J +γ 1 and χ J →ψ+γ 2. 相似文献
18.
J.?G.?Due?as N.?Gutierrez R.?Martínez F.?Ochoa 《The European Physical Journal C - Particles and Fields》2009,60(4):653-659
We analyse the possibilities to detect a new Z
′ boson in di-electron events at Tevatron and LHC in the framework of the 331 model with right-handed neutrinos. We also study
other fermions and Higgs events as final state at LHC. Using
collision data collected by the CDF II detector at Fermilab Tevatron, we find that the 331 Z
′ boson is excluded with masses below 920 GeV. For an integrated luminosity of 100 fb−1 at LHC, and considering a central value
GeV, we obtain the invariant-mass distribution in the process pp→Z
′→e
+
e
−, where a huge peak, corresponding to 800 signal events/(20 GeV), is found above the SM background. The number of di-electron
events vary from 50000 to 2400 in the mass range of
–2000 GeV. We also obtain branching ratios and cross sections in other fermion and Higgs channels at LHC, where a heavy top
quark T exhibits the biggest ratio with m
T
=300 GeV. 相似文献
19.
A. V. Derbin A. I. Egorov I. A. Mitropol’sky V. N. Muratova D. A. Semenov E. V. Unzhakov 《The European Physical Journal C - Particles and Fields》2009,62(4):755-760
A search for resonant absorption of 14.4 keV solar axions by a 57Fe target was performed. The Si(Li) detector placed inside the low-background setup was used to detect the γ-quanta appearing in the deexcitation of the 14.4 keV nuclear level: A+57Fe→57Fe*→57Fe+γ. The new upper limit for the hadronic axion mass has been obtained of m
A
≤159 eV (95% c.l.) (S=0.5, z=0.56). 相似文献
20.
The NA50 experiment at CERN SPS studies charmonia and Drell-Yan production in the μ+ μ? decay channel at 158A GeV. The data collected in Pb?Pb collisions during 1995, 1996 and 1998 run periods show that the J/ψ is anomalously suppressed in central collisions. This observed suppression pattern can be considered as a strong indication of the production of Quark-Gluon Plasma. 相似文献