9,873 research outputs found
Quasi-Particles, Conformal Field Theory, and -Series
We review recent results concerning the representation of conformal field theory characters in terms of fermionic quasi-particle excitations, and describe in detail their construction in the case of the integrable three-state Potts chain. These fermionic representations are q-series which are generalizations of the sums occurring in the Rogers-Ramanujan identities
Existence and Vanishing of the Breathing Mode in Strongly Correlated Finite Systems
One of the fundamental eigenmodes of finite interacting systems is the mode
of {\em uniform radial expansion and contraction} -- the ``breathing'' mode
(BM). Here we show in a general way that this mode exists only under special
conditions: i) for harmonically trapped systems with interaction potentials of
the form or , or ii) for
some systems with special symmetry such as single shell systems forming
platonic bodies. Deviations from the BM are demonstrated for two examples:
clusters interacting with a Lennard-Jones potential and parabolically trapped
systems with Yukawa repulsion. We also show that vanishing of the BM leads to
the occurence of multiple monopole oscillations which is of importance for
experiments
Terahertz wave transmission in flexible polystyrene-lined hollow metallic waveguides for the 2.5-5 THz band.
A low-loss and low-dispersive optical-fiber-like hybrid HE11 mode is developed within a wide band in metallic hollow waveguides if their inner walls are coated with a thin dielectric layer. We investigate terahertz (THz) transmission losses from 0.5 to 5.5 THz and bending losses at 2.85 THz in a polystyrene-lined silver waveguides with core diameters small enough (1 mm) to minimize the number of undesired modes and to make the waveguide flexible, while keeping the transmission loss of the HE11 mode low. The experimentally measured loss is below 10 dB/m for 2 < ? < 2.85 THz (âŒ4-4.5 dB/m at 2.85 THz) and it is estimated to be below 3 dB/m for 3 < ? < 5 THz according to the numerical calculations. At âŒ1.25 THz, the waveguide shows an absorption peak of âŒ75 dB/m related to the transition between the TM11-like mode and the HE11 mode. Numerical modeling reproduces the measured absorption spectrum but underestimates the losses at the absorption peak, suggesting imperfections in the waveguide walls and that the losses can be reduced further. © 2013 Optical Society of America
Self consistent theory of unipolar charge-carrier injection in metal/insulator/metal systems
A consistent device model to describe current-voltage characteristics of
metal/insulator/metal systems is developed. In this model the insulator and the
metal electrodes are described within the same theoretical framework by using
density of states distributions. This approach leads to differential equations
for the electric field which have to be solved in a self consistent manner by
considering the continuity of the electric displacement and the electrochemical
potential in the complete system. The model is capable of describing the
current-voltage characteristics of the metal/insulator/metal system in forward
and reverse bias for arbitrary values of the metal/ insulator injection
barriers. In the case of high injection barriers, approximations are provided
offering a tool for comparison with experiments. Numerical calculations are
performed exemplary using a simplified model of an organic semiconductor.Comment: 21 pages, 8 figure
Interaction between dust grains near a conducting wall
The effect of the conducting electrode on the interaction of dust grains in a
an ion flow is discussed. It is shown that two grains levitating above the
electrode at the same height may attract one another. This results in the
instability of a dust layer in a plasma sheath.Comment: 9 pages. 3 figures. Submitted to Plasma Physics Report
Magnetization reversal and local switching fields of ferromagnetic Co/Pd microtubes with radial magnetization
Three-dimensional nanomagnetism is a rapidly growing field of research covering both noncollinear spin textures and curved magnetic geometries including microtubular structures. We spatially resolve the field-induced magnetization reversal of free-standing ferromagnetic microtubes utilizing multifrequency magnetic force microscopy (MFM). The microtubes are composed of Co/Pd multilayer films with perpendicular magnetic anisotropy that translates to an anisotropy with radial easy axis upon rolling-up. Simultaneously mapping the topography and the perpendicular magnetostatic force derivative, the relation between surface angle and local magnetization configuration is evaluated for a large number of locations with slopes exceeding 45 degrees. The angle-dependence of the switching field is concurrent with the Kondorsky model, i.e., the rolled-up nanomembrane behaves like a planar magnetic film with perpendicular anisotropy and a pinning dominated magnetization reversal. Additionally, we discuss methodological challenges when detecting magnetostatic force derivatives near steep surfaces
Self-consistent model of unipolar transport in organic semiconductor diodes: accounting for a realistic density-of-states distribution
A self-consistent, mean-field model of charge-carrier injection and unipolar
transport in an organic semiconductor diode is developed utilizing the
effective transport energy concept and taking into account a realistic
density-of-states distribution as well as the presence of trap states in an
organic material. The consequences resulting from the model are discussed
exemplarily on the basis of an indium tin oxide/organic semiconductor/metallic
conductor structure. A comparison of the theory to experimental data of a
unipolar indium tin oxide/poly-3-hexyl-thiophene/Al device is presented.Comment: 6 pages, 2 figures; to be published in Journal of Applied Physic
Multiculturalism and American Democracy
Multiculturalism: is it the face of twenty-first century America or merely a passing intellectual fad? With its celebration of ethnic diversity and strong advocacy of tolerance, this contemporary movement provides philosophical justification for many who seek to correct social inequities. But while its proponents see it as a means of promoting self-esteem among marginalized groups, its critics see it as a dangerous form of relativism that culminates, paradoxically, in a new form of intolerance. The fourteen essays in this volume address the pros and cons of multiculturalism and explore its relationship with liberal democracy. A team of stellar contributorsâC. Vann Woodward, Linda Chavez, Stanley Fish, and othersâoffers viewpoints on multiculturalism from the perspectives of political theory, history, philosophy, and fiction. The editors first help explain multiculturalism by contrasting it with the Sixties counterculture. How is it, they ask, that yesterday\u27s radicals, so concerned with economic justice, have given way to the multiculturalist preoccupation with identity politics? The contributors then explore different facets of the multiculturalism issue: they present disparate views of the stakes involved as older notions of pluralism and assimilation give way to multiculturalism; examine it in its relation to the principles of liberal democracy; and assess its place in public education. In a final section, the role of the arts in the multiculturalism debate is addressed by celebrated novelists J. M. Coetzee and Mario Vargas Llosa. Because multiculturalism is a movement without a leader or guiding document, its tenets remain difficult to define. This book not only tells what the controversy is about but also clarifies the concerns it should raise for thoughtful citizens. The points of view expressed here will prove helpful to those who are trying to frame their own opinions about multiculturalismâand they are guaranteed to spark new debate among those who have already chosen sides. Description Arthur Melzer is professor of political science at Michigan State University. He is the author, editor, or coeditor of eleven books, including The Supreme Court and the Idea of Constitutionalism. Jerry Weinberger is University Distinguished Professor Emeritus of political science at Michigan State University. He has written, edited, and coedited several books on political thought, including Benjamin Franklin Unmasked: On the Unity of His Moral, Religious, and Political Thought. M. Richard Zinman is University Distinguished Professor Emeritus of political theory in James Madison College at Michigan State University. With Melzer and Weinberger, he has co-edited several books on democracy and modern politics. This Kansas Open Books title is funded by a grant from the National Endowment for the Humanities and the Andrew W. Mellon Foundation Humanities Open Book Program.https://digitalcommons.pittstate.edu/kansas_open_books/1045/thumbnail.jp
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