3,199 research outputs found
Is simultaneous and --scaling in the quasi-elastic region accidental?
We study the and --scaling of the nuclear response at large momentum
transfer in order to understand how scaling based on very different
descriptions of the elementary interaction can occur simultaneously. We find
that the approximate validity of -scaling at low energy loss arises from
the coincidental behavior of the quasielastic and deep inelastic cross
sections.Comment: 4 pages, 3 Postscript figure
Direct mapping of the finite temperature phase diagram of strongly correlated quantum models
Optical lattice experiments, with the unique potential of tuning interactions
and density, have emerged as emulators of nontrivial theoretical models that
are directly relevant for strongly correlated materials. However, so far the
finite temperature phase diagram has not been mapped out for any strongly
correlated quantum model. We propose a remarkable method for obtaining such a
phase diagram for the first time directly from experiments using only the
density profile in the trap as the input. We illustrate the procedure
explicitly for the Bose Hubbard model, a textbook example of a quantum phase
transition from a superfluid to a Mott insulator. Using "exact" quantum Monte
Carlo simulations in a trap with up to bosons, we show that kinks in the
local compressibility, arising from critical fluctuations, demarcate the
boundaries between superfluid and normal phases in the trap. The temperature of
the bosons in the optical lattice is determined from the density profile at the
edge. Our method can be applied to other phase transitions even when reliable
numerical results are not available.Comment: 12 pages, 5 figure
Present state of power electronics circuitry and perspectives of its development
This paper is devoted mainly to the circuitry, because element base is a big independent issue. Let us say a few words about terminology. A modern converter can be rarely represented as a simple device like “rectifier”, “inverter” etc. It usually consists of the combination of several units, performing elementary functions. For such multistage units it makes sense to use a definition of converter “technology”, keeping in mind some actions with electric current for a certain purpose. It is similar to the step activities in chemistry: to take a substance, to heat it etc. After the formulation of a goal and a number of necessary actions it is possible to present a corresponding structure circuit. According to described above we tried to mention basic technologies used in modern power electronics. The perspectives of the electronics in the nearest future are connected with the further improvement of basic technologies, because their combination allows for developing new technologies. In our opinion, there are four such technologies.Стаття присвячена проблемам схемотехніки у сучасній енергетиці. Розглянуто декілька напрямків розробок електроприводів, відмічено їхні переваги та недоліки. Описано сучасні схемотехнічні можливості та перспективні напрямки їхнього подальшого розвитку в Україні
Microwave Antennas and Circuits Modeling Using Electromagnetic Field Simulator
Electromagnetic field simulators have become a widely used tool in a design process of microwave circuits and systems. A proper usage of electromagnetic (EM) field simulators allows substantial reduction of the design time providing reliable results. In such case the required parameters of the designed circuit can be reached even at the first manufactured prototype in spite of high complexity of the structure. However, EM simulation as a numerical process suffers from systematic and random errors similar to measurement using real equipment. Thus the setting of the EM-field simulator such as a frequency range, mesh properties, usage of PEC and PMC walls etc. has to be done with the highest attention and the simulation results have to be always verified using well-established techniques. The aim of the paper is to demonstrate the selected capability of EM-field simulators with a few examples of antenna and circuit modeling. Also an issue of reliability and simulation errors will be discussed
Когнітивні викликані потенціали у спортсменів різної спеціалізації
Викликані потенціали кори головного мозку є проявом активаційних процесів, пов’язаних із сприйняттям та обробкою стимульної інформації. Згідно з існуючими уявленнями особливу роль у дослідженні мозкових механізмів когнітивних функцій спортсменів відіграють методи електричної активності, зокрема метод викликаних потенціалів
Connections of Trapezoidal Sheets under Fire
This paper describes two different experiments on connections of trapezoidal sheets under elevated temperatures. The first experiments were tensile tests carried out on four sets of tests with screwed connections under ambient and elevated temperatures. One diameter of self-drilling screws and three different thicknesses of trapezoidal sheets were used. The applied screws were without washers, or with sealed or steel washers. The second experiment was performed in a laboratory furnace to check the catenary action of a thin-walled trapezoidal sheet. The basic theory tested in this experiment was that in the first phase of the fire the sheet behaves as a simply supported beam, while in the second phase the load bearing is transferred by a tension membrane. These experiments will be used to develop a design model of connections at high temperatures. High fire resistance of the trapezoidal sheet, dependent on suitable design of the screwed connection to the bearing structure, was confirmed. The experiment with the simple beam also confirmed catenary action.
Anomalous Spin Dynamics in Doped Quantum Antiferromagnets
Finite-temperature spin dynamics in planar t-J model is studied using the
method based on the Lanczos diagonalization of small systems. Dynamical spin
structure factor at moderate dopings shows the coexistence of free-fermion-like
and spin-fluctuation timescales. At T<J, the low-frequency and static
susceptibility show pronounced T dependence, supporting a scenario, related to
the marginal Fermi-liquid one, for the explanation of neutron-scattering and
NMR-relaxation experiments in cuprates. Calculated NMR relaxation rates
reasonably reproduce experimental ones.Comment: 10 pages + 4 figures, Postscript in uuencoded compressed tar file,
IJS-TP-94/2
Quantum Critical Scaling in a Moderately Doped Antiferromagnet
Using high temperature expansions for the equal time correlator and
static susceptibility for the t-J model, we present evidence for
quantum critical (QC), , behavior at intermediate temperatures in a
broad range of ratio, doping, and temperatures. We find that the
dynamical susceptibility is very close to the universal scaling function
computable for the asymptotic QC regime, and that the dominant energy scale is
temperature. Our results are in excellent agreement with measurements of the
spin-echo decay rate, , in LaCuO, and provide qualitative
understanding of both and nuclear relaxation rates in
doped cuprates.Comment: 11 pages, REVTeX v3.0, PostScript file for 3 figures is attached,
UIUC-P-93-07-068. In this revised version, we calculate the scaling functions
and thus present new and more direct evidence in favor of our original
conclusion
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