704 research outputs found
Scattering Experiments with Microwave Billiards at an Exceptional Point under Broken Time Reversal Invariance
Scattering experiments with microwave cavities were performed and the effects
of broken time-reversal invariance (TRI), induced by means of a magnetized
ferrite placed inside the cavity, on an isolated doublet of nearly degenerate
resonances were investigated. All elements of the effective Hamiltonian of this
two-level system were extracted. As a function of two experimental parameters,
the doublet and also the associated eigenvectors could be tuned to coalesce at
a so-called exceptional point (EP). The behavior of the eigenvalues and
eigenvectors when encircling the EP in parameter space was studied, including
the geometric amplitude that builds up in the case of broken TRI. A
one-dimensional subspace of parameters was found where the differences of the
eigenvalues are either real or purely imaginary. There, the Hamiltonians were
found PT-invariant under the combined operation of parity (P) and time reversal
(T) in a generalized sense. The EP is the point of transition between both
regions. There a spontaneous breaking of PT occurs
Council with the Sioux Indians at Fort Pierre : Message from the President of the United States, Communicating Minutes of a Council Held at Fort Pierre with the Sioux Indians, by General Harney, &c.
https://openprairie.sdstate.edu/archives_rare-books/1023/thumbnail.jp
Quantum estimation of a damping constant
We discuss an interferometric approach to the estimation of quantum
mechanical damping. We study specific classes of entangled and separable probe
states consisting of superpositions of coherent states. Based on the assumption
of limited quantum resources we show that entanglement improves the estimation
of an unknown damping constant.Comment: 7 pages, 5 figure
Significance in gamma-ray astronomy - the Li & Ma problem in Bayesian statistics
The significance of having detected an astrophysical gamma ray source is
usually calculated by means of a formula derived by Li & Ma in 1983. We solve
the same problem in terms of Bayesian statistics, which provides a logically
more satisfactory framework. We do not use any subjective elements in the
present version of Bayesian statistics. We show that for large count numbers
and a weak source the Li & Ma formula agrees with the Bayesian result. For
other cases the two results differ, both due to the mathematically different
treatment and the fact that only Bayesian inference can take into account prior
knowldege.Comment: 12 pages, 3 figures, accepted for publication in A&
Culture industries: Critical interventions
Irresistibly enchanted by a seeming grassroots cornucopiaâstruck by the digital sublimeâ many cybertarian technophiles attribute magical properties to today's communications and cultural technologies..
A unidirectional transition from migratory to perivascular macrophage is required for tumor cell intravasation
Summary: Tumor-associated macrophages (TAMs) are critical for tumor metastasis. Two TAM subsets support cancer cell intravasation: migratory macrophages guide cancer cells toward blood vessels, where sessile perivascular macrophages assist their entry into the blood. However, little is known about the inter-relationship between these functionally distinct TAMs or their possible inter-conversion. We show that motile, streaming TAMs are newly arrived monocytes, recruited via CCR2 signaling, that then differentiate into the sessile perivascular macrophages. This unidirectional process is regulated by CXCL12 and CXCR4. Cancer cells induce TGF-ÎČ-dependent upregulation of CXCR4 in monocytes, while CXCL12 expressed by perivascular fibroblasts attracts these motile TAMs toward the blood vessels, bringing motile cancer cells with them. Once on the blood vessel, the migratory TAMs differentiate into perivascular macrophages, promoting vascular leakiness and intravasation. : Tumor-associated macrophages (TAMs) are essential for metastasis. Arwert et al. show that, following extravasation, monocytes initially become motile TAMs. Tumor-derived TGF-ÎČ then induces CXCR4 on TAMs, stimulating them to migrate toward CXCL12-expressing perivascular fibroblasts. Once adjacent to blood vessels, TAMs differentiate into metastasis-assisting perivascular TAMs. Keywords: tumor associated macrophages, TAMs, TGF beta, breast cancer, metastasis, CXCR4, CCR2, TMEM, Men
Signatures of the correlation hole in total and partial cross sections
In a complex scattering system with few open channels, say a quantum dot with
leads, the correlation properties of the poles of the scattering matrix are
most directly related to the internal dynamics of the system. We may ask how to
extract these properties from an analysis of cross sections. In general this is
very difficult, if we leave the domain of isolated resonances. We propose to
consider the cross correlation function of two different elastic or total cross
sections. For these we can show numerically and to some extent also
analytically a significant dependence on the correlations between the
scattering poles. The difference between uncorrelated and strongly correlated
poles is clearly visible, even for strongly overlapping resonances.Comment: 25 pages, 13 Postscript figures, typos corrected and references adde
PT symmetry and spontaneous symmetry breaking in a microwave billiard
We demonstrate the presence of parity-time (PT) symmetry for the
non-Hermitian two-state Hamiltonian of a dissipative microwave billiard in the
vicinity of an exceptional point (EP). The shape of the billiard depends on two
parameters. The Hamiltonian is determined from the measured resonance spectrum
on a fine grid in the parameter plane. After applying a purely imaginary
diagonal shift to the Hamiltonian, its eigenvalues are either real or complex
conjugate on a curve, which passes through the EP. An appropriate basis choice
reveals its PT symmetry. Spontaneous symmetry breaking occurs at the EP
Analyzing symmetry breaking within a chaotic quantum system via Bayesian inference
Bayesian inference is applied to the level fluctuations of two coupled
microwave billiards in order to extract the coupling strength. The coupled
resonators provide a model of a chaotic quantum system containing two coupled
symmetry classes of levels. The number variance is used to quantify the level
fluctuations as a function of the coupling and to construct the conditional
probability distribution of the data. The prior distribution of the coupling
parameter is obtained from an invariance argument on the entropy of the
posterior distribution.Comment: Example from chaotic dynamics. 8 pages, 7 figures. Submitted to PR
Underwater microscope for measuring spatial and temporal changes in bed-sediment grain size
This paper is not subject to U.S. copyright. The definitive version was published in Sedimentary Geology 202 (2007): 402-408, doi:10.1016/j.sedgeo.2007.03.020.For more than a century, studies of sedimentology and sediment transport have measured bed-sediment grain size by collecting samples and transporting them back to the laboratory for grain-size analysis. This process is slow and expensive. Moreover, most sampling systems are not selective enough to sample only the surficial grains that interact with the flow; samples typically include sediment from at least a few centimeters beneath the bed surface. New hardware and software are available for in situ measurement of grain size. The new technology permits rapid measurement of surficial bed sediment. Here we describe several systems we have deployed by boat, by hand, and by tripod in rivers, oceans, and on beaches
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