110 research outputs found
Transmission Lines in CMOS: An Explorative Study
On-chip transmission line modelling and design become increasingly important as frequencies are continuously going up. This paper explores possibilities to implement transmission lines on CMOS ICs via coupled coplanar strips. EM-field simulations with SONNET are used to estimate important transmission line properties like characteristic impedance, propagation velocity and loss in a 0.18 micron CMOS Technology. Both metal losses and substrate losses are modeled. Special attention is paid to the effect of the Silicon substrate, in particular to the so called “slow-wave mode” that can occur in the Si-SiO2 system
Wilsonian effective action for SU(2) Yang-Mills theory with Cho-Faddeev-Niemi-Shabanov decomposition
The Cho-Faddeev-Niemi-Shabanov decomposition of the SU(2) Yang-Mills field is
employed for the calculation of the corresponding Wilsonian effective action to
one-loop order with covariant gauge fixing. The generation of a mass scale is
observed, and the flow of the marginal couplings is studied. Our results
indicate that higher-derivative terms of the color-unit-vector
field are necessary for the description of topologically stable knotlike
solitons which have been conjectured to be the large-distance degrees of
freedom.Comment: 15 pages, no figures, v2: minor improvements, one reference added,
version to appear in PR
Fermi's golden rule and exponential decay as a RG fixed point
We discuss the decay of unstable states into a quasicontinuum using models of
the effective Hamiltonian type. The goal is to show that exponential decay and
the golden rule are exact in a suitable scaling limit, and that there is an
associated renormalization group (RG) with these properties as a fixed point.
The method is inspired by a limit theorem for infinitely divisible
distributions in probability theory, where there is a RG with a Cauchy
distribution, i.e. a Lorentz line shape, as a fixed point. Our method of
solving for the spectrum is well known; it does not involve a perturbation
expansion in the interaction, and needs no assumption of a weak interaction. We
use random matrices for the interaction, and show that the ensemble
fluctuations vanish in the scaling limit. Thus the limit is the same for every
model in the ensemble with probability one.Comment: 20 pages, 1 figur
Surface states and their possible role in the superconductivity of MgB2
We report layer-Korringa-Kohn-Rostocker calculations for bulk and surface
states as well as the corresponding angle resolved photoemission (ARPES)
intensities of MgB2. Our theoretical results reproduce very well the recent
ARPES data by Uchiyama et al., cond-mat/0111152. At least two surface states
are assigned. Consequences of SFS on the anisotropy of the upper critical
fields and other properties in the superconducting state of small grains in
micropowder samples are briefly discussed.Comment: 4pages, 6figures, corrected typos, references adde
Gauged Yukawa Matrix Models and 2-Dimensional Lattice Theories
We argue that chiral symmetry breaking in three dimensional QCD can be
identified with N\'eel order in 2-dimensional quantum antiferromagnets. When
operators which drive the chiral transition are added to these theories, we
postulate that the resulting quantum critical behavior is in the universality
class of gauged Yukawa matrix models. As a consequence, the chiral transition
is typically of first order, although for a limited class of parameters it can
be second order with computable critical exponents.Comment: LaTeX, 11 page
Upper critical field in dirty two-band superconductors: breakdown of the anisotropic Ginzburg-Landau theory
We investigate the upper critical field in a dirty two-band superconductor
within quasiclassical Usadel equations. The regime of very high anisotropy in
the quasi-2D band, relevant for MgB, is considered. We show that strong
disparities in pairing interactions and diffusion constant anisotropies for two
bands influence the in-plane in a different way at high and low
temperatures. This causes temperature-dependent anisotropy, in
accordance with recent experimental data in MgB. The three-dimensional
band most strongly influences the in-plane near , in the
Ginzburg-Landau (GL) region. However, due to a very large difference between
the c-axis coherence lengths in the two bands, the GL theory is applicable only
in an extremely narrow temperature range near . The angular dependence of
deviates from a simple effective-mass law even near .Comment: 12 pages, 5 figures, submitted to Phys.Rev.
Random matrix theory and symmetric spaces
In this review we discuss the relationship between random matrix theories and
symmetric spaces. We show that the integration manifolds of random matrix
theories, the eigenvalue distribution, and the Dyson and boundary indices
characterizing the ensembles are in strict correspondence with symmetric spaces
and the intrinsic characteristics of their restricted root lattices. Several
important results can be obtained from this identification. In particular the
Cartan classification of triplets of symmetric spaces with positive, zero and
negative curvature gives rise to a new classification of random matrix
ensembles. The review is organized into two main parts. In Part I the theory of
symmetric spaces is reviewed with particular emphasis on the ideas relevant for
appreciating the correspondence with random matrix theories. In Part II we
discuss various applications of symmetric spaces to random matrix theories and
in particular the new classification of disordered systems derived from the
classification of symmetric spaces. We also review how the mapping from
integrable Calogero--Sutherland models to symmetric spaces can be used in the
theory of random matrices, with particular consequences for quantum transport
problems. We conclude indicating some interesting new directions of research
based on these identifications.Comment: 161 pages, LaTeX, no figures. Revised version with major additions in
the second part of the review. Version accepted for publication on Physics
Report
Pairing and Density Correlations of Stripe Electrons in a Two-Dimensional Antiferromagnet
We study a one-dimensional electron liquid embedded in a 2D antiferromagnetic
insulator, and coupled to it via a weak antiferromagnetic spin exchange
interaction. We argue that this model may qualitatively capture the physics of
a single charge stripe in the cuprates on length- and time scales shorter than
those set by its fluctuation dynamics. Using a local mean-field approach we
identify the low-energy effective theory that describes the electronic spin
sector of the stripe as that of a sine-Gordon model. We determine its phases
via a perturbative renormalization group analysis. For realistic values of the
model parameters we obtain a phase characterized by enhanced spin density and
composite charge density wave correlations, coexisting with subleading triplet
and composite singlet pairing correlations. This result is shown to be
independent of the spatial orientation of the stripe on the square lattice.
Slow transverse fluctuations of the stripes tend to suppress the density
correlations, thus promoting the pairing instabilities. The largest amplitudes
for the composite instabilities appear when the stripe forms an antiphase
domain wall in the antiferromagnet. For twisted spin alignments the amplitudes
decrease and leave room for a new type of composite pairing correlation,
breaking parity but preserving time reversal symmetry.Comment: Revtex, 28 pages incl. 5 figure
Combined Boyden-Flow Cytometry Assay Improves Quantification and Provides Phenotypification of Leukocyte Chemotaxis
Chemotaxis has been studied by classical methods that measure chemotactic and random motility responses in vitro, but these methods do not evaluate the total number and phenotype of migrating leukocytes simultaneously. Our objective was to develop and validate a novel assay, combined Boyden-flow cytometry chemotaxis assay (CBFCA), for simultaneous quantification and phenotypification of migrating leukocytes. CBFCA exhibited several important advantages in comparison to the classic Boyden chemotaxis assay (CBCA): 1) improved precision (intra-assay coefficients of variation (CVs): CBFCA-4.7 and 4.8% vs. CBCA-30.1 and 17.3%; inter-observer CVs: CBFCA-3.6% vs. CBCA 30.1%); 2) increased recovery of cells, which increased assay to provide increased sensitivity; 3) high specificity for determining the phenotype of migrating/attracted leukocytes; and 4) reduced performance time (CBFCA 120 min vs. CBCA 265 min). Other advantages of CBFCA are: 5) robustness, 6) linearity, 7) eliminated requirement for albumin and, importantly, 8) enabled recovery of migrating leukocytes for subsequent studies. This latter feature is of great benefit in the study of migrating leukocyte subsets. We conclude that the CBFCA is a novel and improved technique for experiments focused on understanding leukocyte trafficking during the inflammatory response
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