1,482,620 research outputs found
Weak ferromagnetism and spiral spin structures in honeycomb Hubbard planes
Within the Hartree Fock- RPA analysis, we derive the spin wave spectrum for
the weak ferromagnetic phase of the Hubbard model on the honeycomb lattice.
Assuming a uniform magnetization, the polar (optical) and acoustic branches of
the spin wave excitations are determined. The bipartite lattice geometry
produces a q-dependent phase difference between the spin wave amplitudes on the
two sub-lattices. We also find an instability of the uniform weakly magnetized
configuration to a weak antiferromagnetic spiraling spin structure, in the
lattice plane, with wave vector Q along the Gamma-K direction, for electron
densities n>0.6. We discuss the effect of diagonal disorder on both the
creation of electron bound states, enhancement of the density of states, and
the possible relevance of these effects to disorder induced ferromagnetism, as
observed in proton irradiated graphite.Comment: 13 pages, 7 figure
Automatic balancing device Patent
Automatic balancing device for use on frictionless supported attitude-controlled test platform
Cross Recurrence Plot Based Synchronization of Time Series
The method of recurrence plots is extended to the cross recurrence plots
(CRP), which among others enables the study of synchronization or time
differences in two time series. This is emphasized in a distorted main diagonal
in the cross recurrence plot, the line of synchronization (LOS). A
non-parametrical fit of this LOS can be used to rescale the time axis of the
two data series (whereby one of it is e.g. compressed or stretched) so that
they are synchronized. An application of this method to geophysical sediment
core data illustrates its suitability for real data. The rock magnetic data of
two different sediment cores from the Makarov Basin can be adjusted to each
other by using this method, so that they are comparable.Comment: Nonlinear Processes in Geophysics, 9, 2002, in pres
Experimental Design at the Intersection of Mathematics, Science, and Technology in Grades K-6
Interdisciplinary courses, highlighting as they do the area(s) the disciplines have in common, often give the misperception of a single body of knowledge and/or way of knowing. However, discipline based courses often leave the equally mistaken notion that the disciplines have nothing in common. The task of the methods courses described in this paper is to reach an appropriate balance so that our pre-service elementary (K-6) teachers have a realistic perception of the independence and interdependence of mathematics and science. At the College of William and Mary each cohort of pre-service elementary teachers enrolls in mathematics and science methods courses taught in consecutive hours. Both instructors emphasize the importance of the content pedagogy unique to their disciplines such as strategies for teaching problem solving, computation, algebraic thinking, and proportional reasoning in mathematics and strategies for teaching students how to investigate and understand the concepts of science. The instructors model interdisciplinary instruction by collaboratively teaching common content pedagogy such as the use of technology, data analysis, and interpretation. Students also identify real-life application of the mathematical principles they are learning that can be applied to science. The concept of simultaneously teaching appropriately selected math and science skills are stressed. Given this approach students are not left with the notion that mathematics is the handmaid of science nor the notion that it is the queen of the sciences. Rather, they view mathematics as a co-equal partner
Using Technology as a Vehicle to Appropriately Integrate Mathematics and Science Instruction for the Middle School
At the College of William and Mary, pre-service middle school science and mathematics teachers enroll in their respective methods courses taught in the same time period. Both instructors emphasize the importance of the content pedagogy unique to their disciplines in their individual courses such as strategies for teaching problem solving, computation, proportional reasoning, algebraic and geometric thinking in mathematics, and strategies for teaching students how to investigate or design and conduct experiments in science. However, the two classes come together for sessions in which they examine the relationship of the two disciplines and the proper role of technology, both graphing calculator and computer, in their instruction Starting with resources such as Science in Seconds for Kids by Jean Potter [1], the science students collaborate with the math students to design and conduct brief experiments. The data generated is analyzed using spreadsheets and later graphing calculators. Various classes of mathematical curves are examined using data generated by sensors/probes and CBLs. Through this experience the pre-service teachers learn to work collaboratively with their colleagues on meaningful tasks, strengthening the effectiveness of all participants
Integrated Green Cloud Computing Architecture
Arbitrary usage of cloud computing, either private or public, can lead to
uneconomical energy consumption in data processing, storage and communication.
Hence, green cloud computing solutions aim not only to save energy but also
reduce operational costs and carbon footprints on the environment. In this
paper, an Integrated Green Cloud Architecture (IGCA) is proposed that comprises
of a client-oriented Green Cloud Middleware to assist managers in better
overseeing and configuring their overall access to cloud services in the
greenest or most energy-efficient way. Decision making, whether to use local
machine processing, private or public clouds, is smartly handled by the
middleware using predefined system specifications such as service level
agreement (SLA), Quality of service (QoS), equipment specifications and job
description provided by IT department. Analytical model is used to show the
feasibility to achieve efficient energy consumption while choosing between
local, private and public Cloud service provider (CSP).Comment: 6 pages, International Conference on Advanced Computer Science
Applications and Technologies, ACSAT 201
Magnetic and superconducting instabilities in the periodic Anderson model: an RPA stud
We study the magnetic and superconducting instabilities of the periodic
Anderson model with infinite Coulomb repulsion U in the random phase
approximation. The Neel temperature and the superconducting critical
temperature are obtained as functions of electronic density (chemical pressure)
and hybridization V (pressure). It is found that close to the region where the
system exhibits magnetic order the critical temperature T_c is much smaller
than the Neel temperature, in qualitative agreement with some T_N/T_c ratios
found for some heavy-fermion materials. In our study, all the magnetic and
superconducting physical behaviour of the system has its origin in the
fluctuating boson fields implementing the infinite on-site Coulomb repulsion
among the f-electrons.Comment: 9 pages, 2 figure
Affine Toda field theory as a 3-dimensional integrable system
The affine Toda field theory is studied as a 2+1-dimensional system. The
third dimension appears as the discrete space dimension, corresponding to the
simple roots in the affine root system, enumerated according to the
cyclic order on the affine Dynkin diagram. We show that there exists a
natural discretization of the affine Toda theory, where the equations of motion
are invariant with respect to permutations of all discrete coordinates. The
discrete evolution operator is constructed explicitly. The thermodynamic Bethe
ansatz of the affine Toda system is studied in the limit . Some
conjectures about the structure of the spectrum of the corresponding discrete
models are stated.Comment: 17 pages, LaTe
The Semiclassical and Quantum Regimes of Superradiant Light Scattering from a Bose-Einstein Condensate
We show that many features of the recent experiments of Schneble et al. [D.
Schneble, Y. Torii, M. Boyd, E.W. Streed, D.E. Pritchard and W. Ketterle,
Science vol. 300, p. 475 (2003)], which demonstrate two different regimes of
light scattering by a Bose-Einstein condensate, can be described using a
one-dimensional mean-field quantum CARL model, where optical amplification
occurs simultaneously with the production of a periodic density modulation in
the atomic medium. The two regimes of light scattering observed in these
experiments, originally described as ``Kapiza-Dirac scattering'' and
``Superradiant Rayleigh scattering'', can be interpreted as the semiclassical
and quantum limits respectively of CARL lasing.Comment: 10 pages, 5 figures - to appear in Journal of Optics
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