25,116 research outputs found
The suppression of hidden order and onset of ferromagnetism in URu2Si2 via Re substitution
Substitution of Re for Ru in the heavy fermion compound URu2Si2 suppresses
the hidden order transition and gives rise to ferromagnetism at higher
concentrations. The hidden order transition of URu(2-x)Re(x)Si2, tracked via
specific heat and electrical resistivity measurements, decreases in temperature
and broadens, and is no longer observed for x>0.1. A critical scaling analysis
of the bulk magnetization indicates that the ferromagnetic ordering temperature
and ordered moment are suppressed continuously towards zero at a critical
concentration of x = 0.15, accompanied by the additional suppression of the
critical exponents gamma and (delta-1) towards zero. This unusual trend appears
to reflect the underlying interplay between Kondo and ferromagnetic
interactions, and perhaps the proximity of the hidden order phase.Comment: 8 pgs, 5 figs, ICM 2009; please refer to Phys. Rev. Lett. 103, 076404
(2009), arXiv:0908.1809 for details on magnetic scaling and phase diagram
(reference added to this version
Half-duplex energy harvesting relay network over different fading environment: System performance with effect of hardware impairment
In this paper, we introduce a half-duplex (HD) energy harvesting (EH) relay network over the different fading environment with the effect of hardware impairment (HI). The model system was investigated with the amplify-and-forward (AF) and the power splitting (PS) protocols. The system performance analysis in term of the outage probability (OP), achievable throughput (AT), and bit error rate (BER) were demonstrated with the closed-form expressions. In addition, the power splitting (PS) factor was investigated. We verified the analytical analysis by Monte Carlo simulation with all primary parameters. From the results, we can state that the analytical and simulation results match well with each other.Web of Science911art. no. Unsp 228
A maximum power point tracking of a photovoltaic system connected to a three-phase grid using a variable step size perturb and observe algorithm
Purpose. The production of electricity from solar energy is necessary because of the global consumption of this energy. This article’s study is based on increased energy extraction by improving maximum power point tracking (MPPT). From different MPPT techniques proposed, the perturb and observe (P&O) technique is developed because of its low implementation cost and ease of implementation. Methods. A modified variable step-size P&O MPPT algorithm is investigated which uses fuzzy logic to automatically adjust step-size to better track maximum power point, compared with the conventional fixed step-size method. The variable step P&O improves the speed and the tracking accuracy. This controller is implemented on a boost DC-DC power converter to track the maximum power point. The suggested controlled solar energy system includes a boost converter, a voltage-source inverter, and a grid filter. The control scheme of a three-phase current-controlled pulse-width modulation inverter in rotating synchronous coordinate d-q with the proposed MPPT algorithm and feed-forward compensation is studied. Results. The photovoltaic grid-connected system controller employs multi-loop control with the filter inductor current of the inverter in the inner loop to achieve a fast dynamic response and the outer loop to control bus voltage for MPPT, the modeling, and control of three phase grid connected to photovoltaic generator is implemented in the MATLAB/Simulink environment and validated by simulation results.Мета. Виробництво електроенергії із сонячної енергії необхідне через глобальне споживання цієї енергії. Дослідження цієї статті ґрунтується на збільшенні вилучення енергії за рахунок покращення відстеження точки максимальної потужності (MPPT). З різних запропонованих методів MPPT був розроблений метод збурення та спостереження (P&O) через його низьку вартість реалізації та простоту реалізації. Методи. Досліджується модифікований алгоритм P&O MPPT зі змінним розміром кроку, який використовує нечітку логіку для автоматичного налаштування розміру кроку для кращого відстеження точки максимальної потужності порівняно із звичайним методом фіксованого розміру кроку. Змінний крок P&O підвищує швидкість та точність відстеження. Цей контролер реалізований на перетворювачі, що підвищує потужності постійного струму для відстеження точки максимальної потужності. Пропонована керована сонячна енергетична система включає підвищуючий перетворювач, інвертор джерела напруги і мережевий фільтр. Досліджується схема управління трифазним струмокерованим інвертором з широтно-імпульсною модуляцією в синхронній координаті, що обертається, d-q із запропонованим алгоритмом MPPT і попереджувальною компенсацією. Результати. Контролер фотоелектричної системи, підключеної до мережі, використовує багатоконтурне керування зі струмом індуктора фільтра інвертора у внутрішньому контурі для досягнення швидкого динамічного відгуку та зовнішнім контуром для керування напругою шини для MPPT, моделювання та керування трифазною мережею. підключений до фотогальванічного генератора, реалізований у середовищі MATLAB/Simulink та підтверджений результатами моделювання
Birth/birth-death processes and their computable transition probabilities with biological applications
Birth-death processes track the size of a univariate population, but many
biological systems involve interaction between populations, necessitating
models for two or more populations simultaneously. A lack of efficient methods
for evaluating finite-time transition probabilities of bivariate processes,
however, has restricted statistical inference in these models. Researchers rely
on computationally expensive methods such as matrix exponentiation or Monte
Carlo approximation, restricting likelihood-based inference to small systems,
or indirect methods such as approximate Bayesian computation. In this paper, we
introduce the birth(death)/birth-death process, a tractable bivariate extension
of the birth-death process. We develop an efficient and robust algorithm to
calculate the transition probabilities of birth(death)/birth-death processes
using a continued fraction representation of their Laplace transforms. Next, we
identify several exemplary models arising in molecular epidemiology,
macro-parasite evolution, and infectious disease modeling that fall within this
class, and demonstrate advantages of our proposed method over existing
approaches to inference in these models. Notably, the ubiquitous stochastic
susceptible-infectious-removed (SIR) model falls within this class, and we
emphasize that computable transition probabilities newly enable direct
inference of parameters in the SIR model. We also propose a very fast method
for approximating the transition probabilities under the SIR model via a novel
branching process simplification, and compare it to the continued fraction
representation method with application to the 17th century plague in Eyam.
Although the two methods produce similar maximum a posteriori estimates, the
branching process approximation fails to capture the correlation structure in
the joint posterior distribution
On Steering Swarms
The main contribution of this paper is a novel method allowing an external
observer/controller to steer and guide swarms of identical and
indistinguishable agents, in spite of the agents' lack of information on
absolute location and orientation. Importantly, this is done via simple global
broadcast signals, based on the observed average swarm location, with no need
to send control signals to any specific agent in the swarm
The ideal energy of classical lattice dynamics
We define, as local quantities, the least energy and momentum allowed by
quantum mechanics and special relativity for physical realizations of some
classical lattice dynamics. These definitions depend on local rates of
finite-state change. In two example dynamics, we see that these rates evolve
like classical mechanical energy and momentum.Comment: 12 pages, 4 figures, includes revised portion of arXiv:0805.335
Spin Dynamics of a J1-J2-K Model for the Paramagnetic Phase of Iron Pnictides
We study the finite-temperature spin dynamics of the paramagnetic phase of
iron pnictides within an antiferromagnetic J_1-J_2 Heisenberg model on a square
lattice with a biquadratic coupling between the
nearest-neighbor spins. Our focus is on the paramagnetic phase in the parameter
regime of this J_1-J_2-K model where the ground state is a (\pi,0) collinear
antiferromagnet. We treat the biquadratic interaction via a
Hubbard-Stratonovich decomposition, and study the resulting effective
quadratic-coupling model using both modified spin wave and Schwinger boson
mean-field theories; the results for the spin dynamics derived from the two
methods are very similar. We show that the spectral weight of dynamical
structure factor S(q,\omega) is peaked at ellipses in the momentum space at low
excitation energies. With increasing energy, the elliptic features expand
towards the zone boundary, and gradually split into two parts, forming a
pattern around (\pi,\pi). Finally, the spectral weight is anisotropic, being
larger along the major axis of the ellipse than along its minor axis. These
characteristics of the dynamical structure factor are consistent with the
recent measurements of the inelastic neutron scattering spectra on BaFe_2As_2
and SrFe_2As_2.Comment: 13 pages, 11 figures, to be published in Phys. Rev.
Kondo physics in a dissipative environment
We report nonperturbative results for the interacting quantum-critical
behavior in a Bose-Fermi Kondo model describing a spin-1/2 coupled both to a
fermionic band with a pseudogap density of states and to a dissipative bosonic
bath. The model serves as a paradigm for studying the interplay between Kondo
physics and low-energy dissipative modes in strongly correlated systems.Comment: 2 pages, 2 figures. Proceedings of The International Conference on
Strongly Correlated Electron Systems (SCES'07), accepted for publication in
Physica
Orientation and strain modulated electronic structures in puckered arsenene nanoribbons
Orthorhombic arsenene was recently predicted as an indirect bandgap
semiconductor. Here, we demonstrate that nanostructuring arsenene into
nanoribbons can successfully transform the bandgap to be direct. It is found
that direct bandgaps hold for narrow armchair but wide zigzag nanoribbons,
which is dominated by the competition between the in-plane and out-of-plane
bondings. Moreover, straining the nanoribbons also induces a direct bandgap and
simultaneously modulates effectively the transport property. The gap energy is
largely enhanced by applying tensile strains to the armchair structures. In the
zigzag ones, a tensile strain makes the effective mass of holes much higher
while a compressive strain cause it much lower than that of electrons. Our
results are crutial to understand and engineer the electronic properties of two
dimensional materials beyond the planar ones like graphene
Tyrosine kinase inhibitors for the therapy of anaplastic thyroid cancer
Anaplastic thyroid cancer (ATC) is often incurable so new therapeutic approaches are needed. Tyrosine kinases inhibitors (such as imanitib, sunitinib or sorafenib) are under evaluation for the treatment of ATC. Other vascular disrupting agents, such as combretastatin A4 phosphate, and antiangiogenic agents, such as aplidin, PTK787/ZK222584 and human VEGF monoclonal antibodies (bevacizumab, cetuximab), have been evaluated. Small-molecule adenosine triphosphate competitive inhibitors directed intracellularly at EGFRs tyrosine kinase, such as erlotinib or gefitinib, are also studied. Furthermore, new molecules have been shown to be active against ATC, such as CLM94 and CLM3. However, more research is needed to finally identify therapies able to control and to cure this disease
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