513 research outputs found
Competition between charge and spin order in the extended Hubbard model on the triangular lattice
Several new classes of compounds can be modeled in first approximation by
electrons on the triangular lattice that interact through on-site repulsion
as well as nearest-neighbor repulsion . This extended Hubbard model on a
triangular lattice has been studied mostly in the strong coupling limit for
only a few types of instabilities. Using the extended two-particle self
consistent approach (ETPSC), that is valid at weak to intermediate coupling, we
present an unbiased study of the density and interaction dependent crossover
diagram for spin and charge density wave instabilities of the normal state at
arbitrary wave vector. When dominates over and electron filling is
large, instabilities are chiefly in the spin sector and are controlled mostly
by Fermi surface properties. Increasing eventually leads to charge
instabilities. In the latter case, it is mostly the wave vector dependence of
the vertex that determines the wave vector of the instability rather than Fermi
surface properties. At small filling, non-trivial instabilities appear only
beyond the weak coupling limit. There again, charge density wave instabilities
are favored over a wide range of dopings by large at wave vectors
corresponding to superlattice in real space.
Commensurate fillings do not play a special role for this instability.
Increasing leads to competition with ferromagnetism. At negative values of
or , neglecting superconducting fluctuations, one finds that charge
instabilities are favored. In general, the crossover diagram presents a rich
variety of instabilities. We also show that thermal charge-density wave
fluctuations in the renormalized classical regime can open a pseudogap in the
single-particle spectral weight, just as spin or superconducting fluctuations
Single-particle and collective excitations in a charged Bose gas at finite temperature
The main focus of this work is on the predictions made by the dielectric
formalism in regard to the relationship between single-particle and collective
excitation spectra in a gas of point-like charged bosons at finite temperature
below the critical region of Bose-Einstein condensation. Illustrative
numerical results at weak coupling () are presented within the Random
Phase Approximation. We show that within this approach the single-particle
spectrum forms a continuum extending from the transverse to the longitudinal
plasma mode frequency and leading to a double-peak structure as increases,
whereas the density fluctuation spectrum consists of a single broadening peak.
We also discuss the momentum distribution and the superfluidity of the gas.Comment: 15 pages, 5 figure
Conditions for magnetically induced singlet d-wave superconductivity on the square lattice
It is expected that at weak to intermediate coupling, d-wave
superconductivity can be induced by antiferromagnetic fluctuations. However,
one needs to clarify the role of Fermi surface topology, density of states,
pseudogap, and wave vector of the magnetic fluctuations on the nature and
strength of the induced d-wave state. To this end, we study the generalized
phase diagram of the two-dimensional half-filled Hubbard model as a function of
interaction strength , frustration induced by second-order hopping
, and temperature . In experiment, and
can be controlled by pressure. We use the two-particle self-consistent approach
(TPSC), valid from weak to intermediate coupling. We first calculate as a
function of and the temperature and wave vector at which
the spin response function begins to grow exponentially.D-wave
superconductivity in a half-filled band can be induced by such magnetic
fluctuations at weak to intermediate coupling, but only if they are near
commensurate wave vectors and not too close to perfect nesting conditions where
the pseudogap becomes detrimental to superconductivity. For given there
is thus an optimal value of frustration where the
superconducting is maximum. The non-interacting density of states plays
little role. The symmetry d vs d of the superconducting
order parameter depends on the wave vector of the underlying magnetic
fluctuations in a way that can be understood qualitatively from simple
arguments
A novel composite web service selection based on quality of service
Using the internet, as a dynamic environment thanks to its distributed characteristic, for web service deployment has become a crucial issue in QoS-driven service composition. An accurate adaption should be undertaken to provide a reliable service composition which enables the composited services are being executed appropriately. That is, the critical aspect of service composition is the proper execution of combination of web services while the appropriate service adaption performed with respect to predetermined functional and non-functional characteristics. In this paper, we attempts to deliberate the optimization approaches to devise the appropriate scheme for QoS-based composite web service selection
Analytic theory of ground-state properties of a three-dimensional electron gas at varying spin polarization
We present an analytic theory of the spin-resolved pair distribution
functions and the ground-state energy of an electron gas
with an arbitrary degree of spin polarization. We first use the Hohenberg-Kohn
variational principle and the von Weizs\"{a}cker-Herring ideal kinetic energy
functional to derive a zero-energy scattering Schr\"{o}dinger equation for
. The solution of this equation is implemented
within a Fermi-hypernetted-chain approximation which embodies the Hartree-Fock
limit and is shown to satisfy an important set of sum rules. We present
numerical results for the ground-state energy at selected values of the spin
polarization and for in both a paramagnetic and a fully
spin-polarized electron gas, in comparison with the available data from Quantum
Monte Carlo studies over a wide range of electron density.Comment: 13 pages, 8 figures, submitted to Phys. Rev.
Application of Proteomics in Lab Diagnosis
Proteomics is defined as a large-scale study of proteins, in particular their functions and structures. This review was aimed to introduce the application of proteomics in lab diagnosis. Beforehand, we introduce the methods, which were used in proteomics also the advantages and disadvantages of proteomics are challenged. In the end, the necessity of proteomics for understanding the structure, function, and interaction of proteins in different fields of sciences including biomarkers, drug discovery, etc. will be discussed
Analytical expressions for the charge-charge local-field factor and the exchange-correlation kernel of a two-dimensional electron gas
We present an analytical expression for the static many-body local field
factor of a homogeneous two-dimensional electron gas, which
reproduces Diffusion Monte Carlo data and embodies the exact asymptotic
behaviors at both small and large wave number . This allows us to also
provide a closed-form expression for the exchange and correlation kernel
, which represents a key input for density functional studies of
inhomogeneous systems.Comment: 5 pages, 3 figure
Correlation energy of a two-dimensional electron gas from static and dynamic exchange-correlation kernels
We calculate the correlation energy of a two-dimensional homogeneous electron
gas using several available approximations for the exchange-correlation kernel
entering the linear dielectric response of the system.
As in the previous work of Lein {\it et al.} [Phys. Rev. B {\bf 67}, 13431
(2000)] on the three-dimensional electron gas, we give attention to the
relative roles of the wave number and frequency dependence of the kernel and
analyze the correlation energy in terms of contributions from the plane. We find that consistency of the kernel with the electron-pair
distribution function is important and in this case the nonlocality of the
kernel in time is of minor importance, as far as the correlation energy is
concerned. We also show that, and explain why, the popular Adiabatic Local
Density Approximation performs much better in the two-dimensional case than in
the three-dimensional one.Comment: 9 Pages, 4 Figure
Improved battery life for context awareness application in smart-phones
The new smart-phones with new operating system and portable sensors support the basis for context awareness systems and applications for handling user activity and user privacy. Nowadays, individuals need new services and real time information anywhere and anytime. Context awareness is an emerging service, which could be able to improve the user experiences in current situation. Context awareness can be considered as location, calendar, user activity and etc. The review of the literature proves that context awareness in mobile phone can be useful and studied as unavoidable service in next generation of smart-phone applications. In this paper, a short review about context awareness in mobile phone is studied, furthermore, we critically analyzed related works of context awareness in smart-phones. The review shows that the most important context in mobile phone is location, which is mostly obtained by using Global Positioning System (GPS) sensor in mobile phones but GPS can significantly increases battery consumption in mobile phones. In this regard, a framework as Improved Battery life in Context Awareness System (IBCS) is proposed to improve battery life and reduce cost of using GPS in context awareness applications based on smart-phones. The review argues the weakness and strength of these studies, and aims to (a) indicate the most important context in mobile phone, (b) reduce the battery consumption of GPS sensor in mobile phone
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