3,697 research outputs found
Monte Carlo Simulation of the Heisenberg Antiferromagnet on a Triangular Lattice: Topological Excitations
We have simulated the classical Heisenberg antiferromagnet on a triangular
lattice using a local Monte Carlo algorithm. The behavior of the correlation
length , the susceptibility at the ordering wavevector , and
the spin stiffness clearly reflects the existence of two temperature
regimes -- a high temperature regime , in which the disordering
effect of vortices is dominant, and a low temperature regime ,
where correlations are controlled by small amplitude spin fluctuations. As has
previously been shown, in the last regime, the behavior of the above quantities
agrees well with the predictions of a renormalization group treatment of the
appropriate nonlinear sigma model. For , a satisfactory fit of the
data is achieved, if the temperature dependence of and is
assumed to be of the form predicted by the Kosterlitz--Thouless theory.
Surprisingly, the crossover between the two regimes appears to happen in a very
narrow temperature interval around .Comment: 13 pages, 8 Postscript figure
Microleakage of composite resin restorations in cervical cavities prepared by Er,Cr: YSGG laser radiation
Background: Evaluation of microleakage is important for assessing the success of new methods for surface preparation and new adhesive restorative materials. The aim of this laboratory study was to assess microleakage at the margins of composite restorations in Er,Cr:YSGG laser prepared cavities on the cervical aspects of teeth by means of dye penetration, and compare this with conventionally prepared and conditioned cavities. Methods: Class V cavities were produced on sound extracted human teeth, which had been assigned randomly to one of three groups (N = 10 each), as follows: Group 1 â prepared using a diamond cylindrical bur and then treated with 37% phosphoric acid; Group 2 â irradiated with an Er,Cr:YSGG laser (Biolase Waterlase) and then treated with 37% phosphoric acid; Group 3 â irradiated only with the laser. After application of bonding agent (Excite, Ivoclar Vivadent), all cavities were restored with composite resin (Heliomolar). After polishing the restorations, the teeth were thermocycled from 5â50°C for 500 cycles. Dye leakage was assessed after immersion in methylene blue, by examining longitudinal sections in a stereomicroscope at Ă30 magnification. Results: The extent of dye penetration was lowest in the laser only group (Group 3). Penetration of dye to dentine and axial walls occurred in 80 per cent of conventionally prepared (bur + acid) specimens, but in the laser group, dye penetration to the axial wall occurred in only 30 per cent of cases. There was a strong statistical association between treatment group and the distribution of microleakage scores (Chi-square, P = 0.0023). Conclusions: For Class V cavities, with the adhesive materials employed, higher microleakage occurs with phosphoric acid etching of bur- or laser-cut surfaces, than with the surface created by use of the laser alone without additional conditioning
A Factorization Algorithm for G-Algebras and Applications
It has been recently discovered by Bell, Heinle and Levandovskyy that a large
class of algebras, including the ubiquitous -algebras, are finite
factorization domains (FFD for short).
Utilizing this result, we contribute an algorithm to find all distinct
factorizations of a given element , where is
any -algebra, with minor assumptions on the underlying field.
Moreover, the property of being an FFD, in combination with the factorization
algorithm, enables us to propose an analogous description of the factorized
Gr\"obner basis algorithm for -algebras. This algorithm is useful for
various applications, e.g. in analysis of solution spaces of systems of linear
partial functional equations with polynomial coefficients, coming from
. Additionally, it is possible to include inequality constraints
for ideals in the input
The effectiveness of polder systems on peak discharge capping of floods along the middle reaches of the Elbe River in Germany
International audienceIn flood modelling, many one-dimensional (1-D) hydrodynamic models are too restricted in capturing the spatial differentiation of processes within a polder or system of polders and two-dimensional (2-D) models are very demanding in data requirements and computational resources. The latter is an important consideration when uncertainty analyses using the Monte Carlo techniques are to complement the modelling exercises. This paper describes the development of a quasi-2-D modeling approach, which still calculates the dynamic wave in 1-D but the discretisation of the computational units are in 2-D, allowing a better spatial representation of the flow in polders and avoiding large additional expenditure on data pre-processing and computational time. The model DYNHYD (1-D hydrodynamics) from the WASP5 modeling package was used as a basis for the simulations and extended to incorporate the quasi-2-D approach. A local sensitivity analysis shows the sensitivity of parameters and boundary conditions on the filling volume of polders and capping of the peak discharge in the main river system. Two flood events on the Elbe River, Germany were used to calibrate and test the model. The results show a good capping effect on the flood peak by the proposed systems. The effect of capping reduces as the flood wave propagates down stream from the polders (up to 0.5 cm of capping is decreased for each additional kilometer from the polder)
The spectrum of high-energy cosmic rays measured with KASCADE-Grande
The energy spectrum of cosmic rays between 10**16 eV and 10**18 eV, derived
from measurements of the shower size (total number of charged particles) and
the total muon number of extensive air showers by the KASCADE-Grande
experiment, is described. The resulting all-particle energy spectrum exhibits
strong hints for a hardening of the spectrum at approximately 2x10**16 eV and a
significant steepening at c. 8x10**16 eV. These observations challenge the view
that the spectrum is a single power law between knee and ankle. Possible
scenarios generating such features are discussed in terms of astrophysical
processes that may explain the transition region from galactic to extragalactic
origin of cosmic rays.Comment: accepted by Astroparticle Physics June 201
The LOPES experiment - recent results, status and perspectives
The LOPES experiment at the Karlsruhe Institute of Technology has been taking
radio data in the frequency range from 40 to 80 MHz in coincidence with the
KASCADE-Grande air shower detector since 2003. Various experimental
configurations have been employed to study aspects such as the energy scaling,
geomagnetic dependence, lateral distribution, and polarization of the radio
emission from cosmic rays. The high quality per-event air shower information
provided by KASCADE-Grande has been the key to many of these studies and has
even allowed us to perform detailed per-event comparisons with simulations of
the radio emission. In this article, we give an overview of results obtained by
LOPES, and present the status and perspectives of the ever-evolving experiment.Comment: Proceedings of the ARENA2010 conference, Nantes, Franc
Absolute calibration of the LOPES antenna system
Radio emission in extensive air showers arises from an interaction with the
geomagnetic field and is subject of theoretical studies. This radio emission
has advantages for the detection of high energy cosmic rays compared to
secondary particle or fluorescence measurement methods. Radio antennas like the
LOPES30 antenna system are suited to investigate this emission process by
detecting the radio pulses. The characteristic observable parameters like
electric field strength and pulse length require a calibration which was done
with a reference radio source resulting in an amplification factor representing
the system behavior in the environment of the KASCADE-Grande experiment.
Knowing the amplification factor and the gain of the LOPES antennas LOPES30 is
calibrated absolutely for systematic analyses of the radio emission.Comment: 5 pages, Proceedings of International Workshop on Acoustic and Radio
EeV Neutrino detection Activities: ARENA, May 17-19, 2005, DESY Zeuthe
Investigation of the Properties of Galactic Cosmic Rays with the KASCADE-Grande Experiment
The properties of galactic cosmic rays are investigated with the
KASCADE-Grande experiment in the energy range between and
eV. Recent results are discussed. They concern mainly the all-particle energy
spectrum and the elemental composition of cosmic rays.Comment: Proc. RICAP 09, Nucl. Instr. and Meth. in pres
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