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1.
A simple M-shaped model has been proposed for the density of states of the π bands of the graphene. The model has been used to derive
the expression for the local density of states on the adsorbed atom and to calculate the corresponding occupation numbers
for different model parameters. Additional simplifications have made it possible to represent the band contribution n
b
to the total occupation number of the adatom n
a
in the analytical form. The contributions of local states n
l
to n
a
= n
b
+ n
l
have been calculated for different parameters. The charge has been numerically evaluated for the case of adsorption of alkali
metal atoms on the graphene. The results obtained have been verified using the model of a surface diatomic molecule calculated
by the Harrison bond-orbital method. The verification has demonstrated that the charges calculated in terms of radically different
models are in good agreement. 相似文献
2.
Popova A. A. Shikin A. M. Rybkin A. G. Marchenko D. E. Vilkov O. Yu. Makarova A. A. Varykhalov A. Yu. Rader O. 《Physics of the Solid State》2011,53(12):2539-2544
A study is reported of the role played by covalent interaction in the coupling of graphene formed on Ni(111) to the Ni substrate
and after intercalation of Au and Cu monolayers underneath the graphene. Covalent interaction of the graphene π states with
d states of the underlying metal (Ni, Au, Cu) has been shown to bring about noticeable distortion of the dispersion relations
of the graphene electronic π states in the region of crossing with d states, which can be described in terms of avoided-crossing effects and formation of bonding and antibonding d-π states. The overall graphene coupling to a substrate is mediated by the energy and occupation of the hybridized states
involved. Because graphene formed directly on the Ni(111) surface has only bonding-type occupied states, the coupling to the
substrate is very strong. Interaction with intercalated Au and Cu layers makes occupation of states of the antibonding and
bonding types comparable, which translates into a weak resultant overall coupling of graphene to the substrate. As a result,
after intercalation of Au atoms, the electronic structure becomes similar to that of quasi-free-standing graphene, with linear
dispersion of π states at the K point of the Brillouin zone and the Dirac point localized close to the Fermi level. Intercalation of Cu atoms under the graphene
monolayer results, besides generation of covalent interaction, in a slight charge transport, with a partial occupation of
the previously unoccupied π* states and the Dirac point shifted by 0.35 eV toward increasing binding energy. 相似文献
3.
A. F. Rozenfeld K. Laneri E. V. Albano 《The European physical journal. Special topics》2007,143(1):3-8
A dynamic scaling Ansatz for the approach to stationary states in complex systems
is proposed and tested by means of extensive simulations applied to both
the Bak-Sneppen (BS) model, which exhibits robust Self-Organised
Critical (SOC) behaviour, and the Game of Life (GOL) of J. Conway,
whose critical behaviour is under debate. Considering the dynamic scaling behaviour of the density of
sites (ρ(t)), it is shown that i) by starting the dynamic measurements with configurations
such that ρ(t=0) →0, one observes an initial increase of the
density with exponents θ= 0.12(2) and θ= 0.11(2) for the BS and GOL models, respectively;
ii) by using initial configurations with ρ(t=0) →1, the density decays with exponents δ= 0.47(2) and δ= 0.28(2) for the BS
and GOL models, respectively.
It is also shown that the temporal autocorrelation decays with exponents
Ca = 0.35(2) (Ca = 0.35(5)) for the BS (GOL) model.
By using these dynamically determined critical exponents
and suitable scaling relationships, we also obtain the dynamic
exponents z = 2.10(5) (z = 2.10(5)) for the
BS (GOL) model.
Based on this evidence we conclude that the dynamic
approach to stationary states of the investigated models
can be described by suitable power-law functions
of time with well-defined exponents. 相似文献
4.
Self-pressure-induced, as well as argon- and nitrogen-induced, broadening γ and shifting δ coefficients of vibrational-rotational
lines of the water molecule have been calculated. The asymptotic behavior of the coefficients γ and δ at J → 42 and K
a
→ J has been studied. For the calculation of the parameters γ and δ, we used the wave functions obtained from the analysis of
highly excited rotational states of the H2O molecule with the maximal ever observed values of rotational quantum numbers J
max = 42, K
amax = 32. Rotational states were analyzed in the method of effective Hamiltonians using generating functions for the first eight
vibrational states of the molecule. 相似文献
5.
On the basis of the total cross sections for neutron-proton scattering in the region of laboratory energies below 150 keV,
the value of σ0 = 20.4288(146) b was obtained for the total cross sections for neutron-proton scattering at zero energy. This value is in
very good agreement with the experimental cross sections obtained by Houke and Hurst, but it is at odds with Dilg’s experimental
cross section. By using the value that we found for σ0 and the experimental values of the neutron-proton coherent scattering length f, the deuteron binding energy ɛ
t
, the deuteron effective radius ρ
t
(−ɛ
t
, −ɛ
t
), and the total cross section in the region of energies below 5 MeV, the following values were found in the shape-parameter
approximation for the low-energy parameters of neutron-proton scattering in the spin-triplet and spin-singlet states: a
t
= 5.4114(27) fm, r
0t
= 1.7606(35) fm, v
2t
= 0.157 fm3, a
s
= −23.7154(80) fm, r
0s
= 2.706(67) fm, and v
2s
= 0.491 fm3. 相似文献
6.
We perform rigorously the charge renormalization of the so-called reduced Bogoliubov-Dirac-Fock (rBDF) model. This nonlinear
theory, based on the Dirac operator, describes atoms and molecules while taking into account vacuum polarization effects.
We consider the total physical density ρ
ph including both the external density of a nucleus and the self-consistent polarization of the Dirac sea, but no ‘real’ electron.
We show that ρ
ph admits an asymptotic expansion to any order in powers of the physical coupling constant α
ph, provided that the ultraviolet cut-off behaves as L ~ e3p(1-Z3)/2aph >> 1{\Lambda\sim e^{3\pi(1-Z_3)/2\alpha_{\rm ph}} \gg 1}. The renormalization parameter 0 < Z
3 < 1 is defined by Z
3 = α
ph/α, where α is the bare coupling constant. The coefficients of the expansion of ρ
ph are independent of Z
3, as expected. The first order term gives rise to the well-known Uehling potential, whereas the higher order terms satisfy
an explicit recursion relation. 相似文献
7.
The effect of gamma irradiation on the dielectric properties and ac conductivity of a TlInS2 single crystal with a layered structure has been investigated in the frequency range from 5 × 104 to 3.5 × 107Hz. It has been shown that gamma irradiation of the TlInS2 single crystal with a dose of 104–2.25 × 106 rad leads to a considerable increase in the dielectric loss tangent tanδ, the real part ɛ′ and imaginary part ɛ″ of the complex
permittivity, and the ac conductivity σ
ac
across the layers. It has been established that, for all gamma irradiation doses, the TlInS2 single crystal is characterized by the dielectric loss due to electrical conduction up to a frequency of 107 Hz and by the relaxation loss at a higher frequency. Irradiation of the TlInS2 single crystal results in an increase in the dispersion of tan δ, ɛ′, and ɛ″. It has been demonstrated that, as the gamma
irradiation dose is accumulated in the TlInS2 single crystal, the density of localized states near the Fermi level N
F increases (from 5.2 × 1018 to 1.9 × 1019 eV−1 cm−3). 相似文献
8.
The correlation of the local density of states 〈ρɛ(r
1)ρɛ + ω(r
2)〉 in quasi-one-dimensional disordered wires in a magnetic field is calculated under the assumption that |r
1 − r
2| is much smaller than the localization length. This amounts to finding the zero mode of the transfer-matrix Hamiltonian for
the supersymmetric σ model, which is done exactly by mapping to the three-dimensional Coulomb problem. Both the regimes of
level repulsion and level attraction are obtained, depending on |r
1 − r
2|. We demonstrate that the correlations of different eigenfunctions in the quasi-one-dimensional and strictly one-dimensional
cases are dissimilar.
The text was submitted by the authors in English. 相似文献
9.
Benjamin Fain 《Foundations of Physics Letters》1997,10(3):221-233
The prerequisite of quantum measurement is a transformation of an initially off-diagonal density matrix
ρmα;nβ
describing an interacting measured object and measuring device into a diagonal density matrix
ρmα;mαδmnδαβ
. The latter density matrix describes a proper mixture of states having definitem-values. On the other hand, the irreversible relaxation (towards the thermodynamic equilibrium) is also characterized by transformation
of an initially off-diagonal matrix into a diagonal one. It has been shown that the process of irreversible relaxation can
be used to perform quantum measurement, provided the duration Δt of the measurement is much larger thanT
2, the phase relaxation time, and much smaller thanT
1, the population relaxation time:T
2 ≪ Δt ≪T
1. Agedanken experiment describing this kind of measurement is provided. Aπ/2-pulse transforms an initials
z
= −1/2 state into superposition ofs
z
= ±1/2 states. The irreversible relaxation leads to the proper mixture ofs
z
= 1/2 ands
z
= −1/2 state. Results of the measurements are verified by the second electromagnetic pulse. 相似文献
10.
We investigate the effect of the isotropic velocity-dependent potentials on the bound state energy eigenvalues of the Morse potential for any quantum states. When the velocity-dependent term is used as a constant parameter, ρ(r) = ρ 0, the energy eigenvalues can be obtained analytically by using the Pekeris approximation. When the velocity-dependent term is considered as an harmonic oscillator type, ρ(r) = ρ 0 r 2, we show how to obtain the energy eigenvalues of the Morse potential without any approximation for any n and ℓ quantum states by using numerical calculations. The calculations have been performed for different energy eigenvalues and different numerical values of ρ 0, in order to show the contribution of the velocity-dependent potential on the energy eigenvalues of the Morse potential. 相似文献
11.
Dielectric relaxation measurements of formamide (FMD)-N,N-dimethylaminoethanol (DMAE) solvent mixtures have been carried out over the entire concentration range using time domain
reflectometry technique at 25, 35 and 45°C in the frequency range of 10 MHz to 20 GHz. The mixtures exhibit a principle dispersion
of the Davidson-Cole relaxation type at microwave frequencies. Bilinear calibration method is used to obtain complex permittivity
ɛ*(ω) from complex reflection coefficient ρ*(ω) over the frequency range of 10 MHz to 10 GHz. The excess permittivity (ɛ
E), excess inverse relaxation time (1/τ)E, Kirkwood correlation factor (g
eff), activation energy and Bruggeman factor (f
B) are also calculated to study the solute-solvent interaction.
相似文献
12.
Shi-Lin Zhu 《The European Physical Journal A - Hadrons and Nuclei》1999,4(3):277-281
The light cone QCD sum rules are derived for the K
*
Kπ coupling g
K
*
Kπ and the ρππ coupling g
ρππ. The contribution from the excited states and the continuum is subtracted cleanly through the double Borel transform with
respect to the two external momenta, p
1
2, p
2
2= (p−q)2. Our result g
K
*
Kπ= (8.7 ± 0.5) and g
ρππ= (11.5 ± 0.8) is in good agreement with the experimental value.
Received: 31 July 1998 / Revised version: 20 November 1998 相似文献
13.
S. Santhosh Kumar 《Pramana》2008,71(1):175-180
In the present calculation we have used the Monte Carlo method of generating collective spin and total energy of the nucleus
for various configurations of the system with N
0 single particle states available for n number of particles. The different configurations (arrangements of occupied single particle states) leading to a particular
energy E and spin J are then collected to get the density of states for the given energy E and spin J. We find that if we use the cranked Nilsson model single particle states for the rotational frequency Ω = 0.0ħω, 0.05ħω and 0.1ħω there is a shift in the maximum density of states W
max with a tendency for the system to become more oblate or prolate depending on the shift in the maximum density of states as
the angular momentum decreases or increases. The change in nuclear level density with collectivity, i.e. with the use of cranked
Nilsson model single particle levels has been noticed.
相似文献
14.
Marek Szydłowski Włodzimierz Godłowski Radosław Wojtak 《General Relativity and Gravitation》2006,38(5):795-821
In this paper we proposed to use the group of analysis of symmetries of the dynamical system to describe the evolution of the Universe. This method is used in searching for the unknown equation of state. It is shown that group of symmetries enforce the form of the equation of state for noninteracting scaling multifluids. We showed that symmetries give rise to the equation of state in the form p =-Λ + w
1ρ(a) + w
2
a
β + 0 and energy density ρ = Λ+ρ01
a
-3(1+w) +ρ02
a
α +ρ03
a
-3, which is commonly used in cosmology. The FRW model filled with scaling fluid (called homological) is confronted with the observations of distant type Ia supernovae. We found the class of model parameters admissible by the statistical analysis of SNIa data.We showed that the model with scaling fluid fits well to supernovae data. We found that Ωm,0 ≃ 0.4 and n ≃ -1 (β = -3n), which can correspond to (hyper) phantom fluid, and to a high density universe. However if we assume prior that Ωm,0 = 0.3 then the favoured model is close to concordance ΛCDM model. Our results predict that in the considered model with scaling fluids distant type Ia supernovae should be brighter than in the ΛCDM model, while intermediate distant SNIa should be fainter than in the ΛCDM model. We also investigate whether the model with scaling fluid is actually preferred by data over ΛCDM model. As a result we find from the Akaike model selection criterion: it prefers the model with noninteracting scaling fluid. 相似文献
15.
Michel Planat 《International Journal of Theoretical Physics》2010,49(5):1044-1054
In quantum information context, the groups generated by Pauli spin matrices, and Dirac gamma matrices, are known as the single
qubit Pauli group ℘, and two-qubit Pauli group ℘2, respectively. It has been found (Socolovsky, Int. J. Theor. Phys. 43: 1941, 2004) that the CPT group of the Dirac equation is isomorphic to ℘. One introduces a two-qubit entangling orthogonal matrix S basically related to the CPT symmetry. With the aid of the two-qubit swap gate, the S matrix allows the generation of the three-qubit real Clifford group and, with the aid of the Toffoli gate, the Weyl group
W(E
8) is generated (Planat, Preprint , 2009). In this paper, one derives three-qubit entangling groups [(P)\tilde]\tilde{\mathcal{P}} and [(P)\tilde]2\tilde{\mathcal{P}}_{2}, isomorphic to the CPT group ℘ and to the Dirac group ℘2, that are embedded into W(E
8). One discovers a new class of pure three-qubit quantum states with no-vanishing concurrence and three-tangle that we name
CPT states. States of the GHZ and CPT families, and also chain-type states, encode the new representation of the Dirac group and its CPT subgroup. 相似文献
16.
S. I. Krasnosvobodtsev N. P. Shabanova V. S. Nozdrin A. I. Golovashkin 《Physics of the Solid State》1999,41(8):1256-1259
The high-temperature superconductors YBa2Cu3O7−δ
, HoBa2Cu3O7−δ
, and Nd1.85Ce0.15CuO4−δ
are found to possess a common anomaly in the variation of the upper critical magnetic field owing to irradiation by helium
ions. While the resistivity ρ increases by many times, the increase in H
c2 from scattering by radiation defects typical of ordinary superconductors does not occur. In terms of the ordinary mechanism,
the anomaly may be explained by a significant reduction in the conduction electron density resulting from a loss of oxygen,
which causes a significant rise in ρ with a small change in the scattering.
Fiz. Tverd. Tela (St. Petersburg) 41, 1372–1376 (August 1999) 相似文献
17.
Scott Funkhouser 《International Journal of Theoretical Physics》2012,51(4):1089-1099
By manipulating the integral expression for the proper radius R
e
of the cosmological event horizon (CEH) in a Friedmann-Robertson-Walker (FRW) universe we obtain an analytical expression
for the change δR
e
in response to a uniform fluctuation δρ in the average cosmic background density ρ. We stipulate that the fluctuation arises within a vanishing interval of proper time, during which the CEH is approximately
stationary, and evolves subsequently such that δρ/ρ is constant. The respective variations 2πR
e
δR
e
and δE
e
in the horizon entropy S
e
and enclosed energy E
e
should be therefore related through the cosmological Clausius relation. In that manner we find that the temperature T
e
of the CEH at an arbitrary time in a flat FRW universe is E
e
/S
e
, which recovers asymptotically the usual static de Sitter temperature. Furthermore it is proven that during radiation-dominance
and in late times the CEH conforms to the fully dynamical First Law T
e
dS
e
=PdV
e
−dE
e
, where V
e
is the enclosed volume and P is the average cosmic pressure. 相似文献
18.
Extensive ab initio calculations have been performed to study the energetics of a sodium (Na) atom and its dimer adsorbed on graphene using the SIESTA package Soler et al. (2002) [1] which works within a DFT(density functional theory)–GGA (generalized gradient approximation) pseudopotential framework. The adsorption energy, geometry, charge transfer, ionization potential and density of states (DOS), partial density states (PDOS) of adatom/dimer-graphene system have been calculated. After considering various sites for adsorption of Na on graphene, the center of a hexagonal ring of carbon atoms is found to be the preferred site of adsorption while the Na2 dimer prefers to rest parallel to the graphene sheet. We find insignificant energy differences among adsorption configurations involving different possible sites in parallel orientation, which implies high mobility of the dimer on the graphene sheet. We also notice only a slight distortion of the graphene sheet perpendicular to its plane upon adatom adsorption. However, some lateral displacements seen are more perceptible. 相似文献
19.
The effects of the elastic deformation on the mechanical and physical properties of graphene are a subject of intensive current
studies. Nevertheless, the stability range for a flat graphene sheet subjected to in-plane deformation is still unknown. Here,
this problem is solved by atomistic simulations. In the three-dimensional space corresponding to the ɛ
xx
, ɛ
yy
, and ɛ
xy
components of the planar strain tensor, the surface bounding the stability range for a flat graphene sheet has been constructed
disregarding the thermal vibrations and the effects of boundary conditions. For the points of this surface, force components
T
x
, T
y
, and T
xy
have been calculated. It is shown that graphene is structurally stable up to strains on the order of 0.3–0.4, but it is unstable
with respect to the shear in the absence of stretching forces. In addition, graphene cannot preserve its flat shape under
the effect of a compressive force since it has zero flexural stiffness. 相似文献
20.
We discuss the high density behavior of a system of hard spheres of diameter d on the hypercubic lattice of dimension n, in the limit n→∞, d→∞, d/n = δ. The problem is relevant for coding theory, and the best available bounds state that the maximum density of the system falls in the interval 1 ≤ ρ V
d
≤ exp (n κ(δ)), being κ(δ) > 0 and V
d
the volume of a sphere of radius d. We find a solution of the equations describing the liquid up to an exponentially large value of ρ = ρ V
d
, but we show that this solution gives a negative entropy for the liquid phase for ρ >rsimn. We then conjecture that a phase transition towards a different phase might take place, and we discuss possible scenarios for this transition.
PACS: 05.20.Jj, 64.70.Pf, 61.20.Gy 相似文献