3,178 research outputs found
Dynamic Behaviour of Floors with Cold-formed Steel Joists
Presented in this paper are the results of a recent study carried out at the University of Waterloo on the performance of residential floors supported by cold-formed steel C-section floor joists. Both static and dynamic tests were conducted on steel floors with different span lengths based on different design criteria. The purpose of the static tests was to evaluate the stiffuess and load sharing among the joists, and the purpose of the dynamic tests was to evaluate the dynamic characteristics such as frequencies of the floor systems. To identify the critical parameters that contribute to the control of floor vibration, tests were also carried out on floors without attached ceiling materials, with different bridging and blocking patterns, and with different support conditions. Test results are presented in comparison with the analytical results obtained from different design models
Incommensurate magnetic order in the alpha-Fe(Te,Se) superconductor systems
Magnetic spin fluctuations is one candidate to produce the bosonic modes that
mediate the superconductivity in the ferrous superconductors. Up until now, all
of the LaOFeAs and BaFe2As2 structure types have simple commensurate magnetic
ground states, as result of nesting Fermi surfaces. This type of
spin-density-wave (SDW) magnetic order is known to be vulnerable to shifts in
the Fermi surface when electronic densities are altered at the superconducting
compositions. Superconductivity has more recently been discovered in
alpha-Fe(Te,Se), whose electronically active antifluorite planes are
isostructural to the FeAs layers found in the previous ferrous superconductors
and share with them the same quasi-two-dimensional electronic structure. Here
we report neutron scattering studies that reveal a unique complex
incommensurate antiferromagnetic order in the parent compound alpha-FeTe. When
the long-range magnetic order is suppressed by the isovalent substitution of Te
with Se, short-range correlations survive in the superconducting phase.Comment: 27 pages, 7 figures, 1 tabl
Global Bethe lattice consideration of the spin-1 Ising model
The spin-1 Ising model with bilinear and biquadratic exchange interactions
and single-ion crystal field is solved on the Bethe lattice using exact
recursion equations. The general procedure of critical properties investigation
is discussed and full set of phase diagrams are constructed for both positive
and negative biquadratic couplings. In latter case we observe all remarkable
features of the model, uncluding doubly-reentrant behavior and ferrimagnetic
phase. A comparison with the results of other approximation schemes is done.Comment: Latex, 11 pages, 13 ps figures available upon reques
Renormalization group theory for finite-size scaling in extreme statistics
We present a renormalization group (RG) approach to explain universal
features of extreme statistics, applied here to independent, identically
distributed variables. The outlines of the theory have been described in a
previous Letter, the main result being that finite-size shape corrections to
the limit distribution can be obtained from a linearization of the RG
transformation near a fixed point, leading to the computation of stable
perturbations as eigenfunctions. Here we show details of the RG theory which
exhibit remarkable similarities to the RG known in statistical physics. Besides
the fixed points explaining universality, and the least stable eigendirections
accounting for convergence rates and shape corrections, the similarities
include marginally stable perturbations which turn out to be generic for the
Fisher-Tippett-Gumbel class. Distribution functions containing unstable
perturbations are also considered. We find that, after a transitory divergence,
they return to the universal fixed line at the same or at a different point
depending on the type of perturbation.Comment: 15 pages, 8 figures, to appear in Phys. Rev.
New results from fluctuation analysis in NA49 at the CERN SPS
The exploration of the phase diagram of strongly interacting matter,
particularly the study of the phase transition from hadronic to partonic matter
and the search for a hypothetical critical endpoint of the first order
transition line, is one of the most challenging tasks in present heavy ion
physics.
In this talk new results on chemical (particle ratio), transverse momentum,
multiplicity and azimuthal angle fluctuations will be presented. We also
discuss their connection to the onset of deconfinement and to the critical
endpoint.Comment: The Proceedings of the International Conference "Critical Point and
Onset of Deconfinement - CPOD 2011", Wuhan, November 7-11, 201
Optical Study of LaO_0.9F_0.1FeAs: Evidence for a Weakly Coupled Superconducting State
We have studied the reflectance of the recently discovered superconductor
LaO_0.9F0.FeAs in a wide energy range from the far infrared to the visible
regime. We report on the observation of infrared active phonons, the plasma
edge (PE) and possible interband transitions. On the basis of this data and the
reported in-plane penetration depth lambda_L(0) about 254 nm [H. Luetkens et
al., Phys. Rev. Lett. v. 101, 0970009 (2008)] a disorder sensitive relatively
small value of the total electron electron-boson coupling constant
lambda_tot=lambda_e-ph+lambda_e-sp ~ 0.6 +- 0.35 can be estimated adopting an
effective single-band picture.Comment: Changed title, updated references, final published versio
Cryogenic Ion Trapping Systems with Surface-Electrode Traps
We present two simple cryogenic RF ion trap systems in which cryogenic
temperatures and ultra high vacuum pressures can be reached in as little as 12
hours. The ion traps are operated either in a liquid helium bath cryostat or in
a low vibration closed cycle cryostat. The fast turn around time and
availability of buffer gas cooling made the systems ideal for testing
surface-electrode ion traps. The vibration amplitude of the closed cycled
cryostat was found to be below 106 nm. We evaluated the systems by loading
surface-electrode ion traps with Sr ions using laser ablation, which
is compatible with the cryogenic environment. Using Doppler cooling we observed
small ion crystals in which optically resolved ions have a trapped lifetime
over 2500 minutes.Comment: 10 pages, 13 EPS figure
Supertwistor space for 6D maximal super Yang-Mills
6D maximal super Yang-Mills on-shell amplitudes are formulated in superspace
using 6 dimensional twistors. The 3,4,5-point tree amplitudes are obtained by
supersymmetrizing their bosonic counterparts and confirmed through the BCFW
construction. In contrast to 4D this superspace is non-chiral, reflecting the
fact that one cannot differentiate MHV from in 6D. Combined
with unitarity methods, this superspace should be useful for the study of
multi-loop D dimensional maximal super Yang-Mills and gravity amplitudes.
Furthermore, the non-chiral nature gives a natural framework for an off-shell
construction. We show this by matching our result with off-shell D=4 N=4 super
Yang-Mills amplitudes, expressed in projective superspace.Comment: 6 figures 28 pages. with better sign
Complex networks theory for analyzing metabolic networks
One of the main tasks of post-genomic informatics is to systematically
investigate all molecules and their interactions within a living cell so as to
understand how these molecules and the interactions between them relate to the
function of the organism, while networks are appropriate abstract description
of all kinds of interactions. In the past few years, great achievement has been
made in developing theory of complex networks for revealing the organizing
principles that govern the formation and evolution of various complex
biological, technological and social networks. This paper reviews the
accomplishments in constructing genome-based metabolic networks and describes
how the theory of complex networks is applied to analyze metabolic networks.Comment: 13 pages, 2 figure
Chaotic Phenomenon in Nonlinear Gyrotropic Medium
Nonlinear gyrotropic medium is a medium, whose natural optical activity
depends on the intensity of the incident light wave. The Kuhn's model is used
to study nonlinear gyrotropic medium with great success. The Kuhn's model
presents itself a model of nonlinear coupled oscillators. This article is
devoted to the study of the Kuhn's nonlinear model. In the first paragraph of
the paper we study classical dynamics in case of weak as well as strong
nonlinearity. In case of week nonlinearity we have obtained the analytical
solutions, which are in good agreement with the numerical solutions. In case of
strong nonlinearity we have determined the values of those parameters for which
chaos is formed in the system under study. The second paragraph of the paper
refers to the question of the Kuhn's model integrability. It is shown, that at
the certain values of the interaction potential this model is exactly
integrable and under certain conditions it is reduced to so-called universal
Hamiltonian. The third paragraph of the paper is devoted to quantum-mechanical
consideration. It shows the possibility of stochastic absorption of external
field energy by nonlinear gyrotropic medium. The last forth paragraph of the
paper is devoted to generalization of the Kuhn's model for infinite chain of
interacting oscillators
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