2,183 research outputs found
The FIR-absorption of short period quantum wires and the transition from one to two dimensions
We investigate the FIR-absorption of short period parallel quantum wires in a
perpendicular quantizing magnetic field. The external time-dependent electric
field is linearly polarized along the wire modulation. The mutual Coulomb
interaction of the electrons is treated self-consistently in the ground state
and in the absorption calculation within the Hartree approximation. We consider
the effects of a metal gate grating coupler, with the same or with a different
period as the wire modulation, on the absorption. The evolution of the
magnetoplasmon in the nonlocal region where it is split into several Bernstein
modes is discussed in the transition from: narrow to broad wires, and isolated
to overlapping wires. We show that in the case of narrow and not strongly
modulated wires the absorption can be directly correlated with the underlying
electronic bandstructure.Comment: 15 pages, 9 figures, Revtex, to appear in Phys. Rev.
Thomas-Fermi-Dirac-von Weizsacker hydrodynamics in laterally modulated electronic systems
We have studied the collective plasma excitations of a two-dimensional
electron gas with an arbitrary lateral charge-density modulation. The dynamics
is formulated using a previously developed hydrodynamic theory based on the
Thomas-Fermi-Dirac-von Weizsacker approximation. In this approach, both the
equilibrium and dynamical properties of the periodically modulated electron gas
are treated in a consistent fashion. We pay particular attention to the
evolution of the collective excitations as the system undergoes the transition
from the ideal two-dimensional limit to the highly-localized one-dimensional
limit. We also calculate the power absorption in the long-wavelength limit to
illustrate the effect of the modulation on the modes probed by far-infrared
(FIR) transmission spectroscopy.Comment: 27 page Revtex file, 15 Postscript figure
A study to examine the relationship between uterine pathology and depletion of oxytetracycline in plasma and milk after intrauterine infusion
Citation: Gorden, P. J., Ydstie, J., Kleinhenz, M. D., Wulf, L. W., Gehring, R., Wang, C., & Coetzee, J. F. (2016). A study to examine the relationship between uterine pathology and depletion of oxytetracycline in plasma and milk after intrauterine infusion. Journal of Animal Science, 94, 30-30. doi:10.2527/msasas2016-065Metritis is a frequent problem in postpartum dairy cows. Intrauterine therapy with oxytetracycline (OTC) is often used to improve therapeutic outcomes, although efficacy data supporting this therapy are ambiguous. Several manuscripts describe the depletion of OTC from milk following intrauterine therapy. However, none of these studies have correlated uterine severity scores with milk OTC concentrations using highly sensitive detection systems. Our objective was to do this to test the hypothesis that cows with more severe uterine severity would have higher OTC residues in milk following intrauterine therapy. Thirty-two cows received a single treatment of 4 g of OTC via intrauterine infusion. Blood and milk samples were collected before intrauterine therapy and throughout the trial period of 96 h after infusion. Uterine severity scores were assigned at initiation of therapy and every 24 h throughout the remainder of the trial. Plasma and milk samples were analyzed for OTC concentrations using liquid chromatography coupled with mass spectrometry. Following treatment, OTC rapidly diffused from the uterus to plasma and from plasma to milk. Maximum concentration in plasma and milk occurred within 24 h following intrauterine infusion and 18 of the cows still had detectable levels of OTC in milk 4 d after intrauterine infusion. Greater uterine severity score at the initiation of treatment showed a significant positively correlation with higher milk OTC concentration at the second milking following treatment (R2 = 0.46, P = 0.01) but there was no correlation between initial uterine severity score and OTC concentration at the conclusion of the study (R2 = ?0.06, P = 0.75). In the United States, intrauterine administration of OTC is considered to be an extra-label therapy. The use of uterine severity score can be used to predict OTC concentration in the first day following therapy but should not be used as a predictor of OTC concentrations 96 h after treatment. Dairy producers should consult with their veterinarian to develop strategies that will prevent the presence of violative residues of OTC in bulk tank milk following intrauterine therapy
A small-molecule antagonist of the β-catenin/TCF4 interaction blocks the self-renewal of cancer stem cells and suppresses tumorigenesis
Wnt/beta-catenin signaling is a highly conserved pathway essential for embryogenesis and tissue homeostasis. However, deregulation of this pathway can initiate and promote human malignancies, especially of the colon and head and neck. Therefore, Wnt/beta-catenin signaling represents an attractive target for cancer therapy. We performed high-throughput screening (HTS) using AlphaScreen and ELISA techniques to identify small molecules that disrupt the critical interaction between beta-catenin and the transcription factor TCF4 required for signal transduction. We found that compound LF3, a 4-thioureido-benzenesulfonamide derivative, robustly inhibited this interaction. Biochemical assays revealed clues that the core structure of LF3 was essential for inhibition. LF3 inhibited Wnt/beta-catenin signals in cells with exogenous reporters and in colon cancer cells with endogenously high Wnt activity. LF3 also suppressed features of cancer cells related to Wnt signaling, including high cell motility, cell cycle progression, and the overexpression of Wnt target genes. However, LF3 did not cause cell death or interfere with cadherin-mediated cell-cell adhesion. Remarkably, the self-renewal capacity of cancer stem cells was blocked by LF3 in concentration-dependent manners, as examined by sphere formation of colon and head and neck cancer stem cells under non-adherent conditions. Finally, LF3 reduced tumor growth and induced differentiation in a mouse xenograft model of colon cancer. Collectively, our results strongly suggest that LF3 is a specific inhibitor of canonical Wnt signaling with anticancer activity that warrants further development for preclinical and clinical studies as a novel cancer therapy
Surface acoustic wave attenuation by a two-dimensional electron gas in a strong magnetic field
The propagation of a surface acoustic wave (SAW) on GaAs/AlGaAs
heterostructures is studied in the case where the two-dimensional electron gas
(2DEG) is subject to a strong magnetic field and a smooth random potential with
correlation length Lambda and amplitude Delta. The electron wave functions are
described in a quasiclassical picture using results of percolation theory for
two-dimensional systems. In accordance with the experimental situation, Lambda
is assumed to be much smaller than the sound wavelength 2*pi/q. This restricts
the absorption of surface phonons at a filling factor \bar{\nu} approx 1/2 to
electrons occupying extended trajectories of fractal structure. Both
piezoelectric and deformation potential interactions of surface acoustic
phonons with electrons are considered and the corresponding interaction
vertices are derived. These vertices are found to differ from those valid for
three-dimensional bulk phonon systems with respect to the phonon wave vector
dependence. We derive the appropriate dielectric function varepsilon(omega,q)
to describe the effect of screening on the electron-phonon coupling. In the low
temperature, high frequency regime T << Delta (omega_q*Lambda
/v_D)^{alpha/2/nu}, where omega_q is the SAW frequency and v_D is the electron
drift velocity, both the attenuation coefficient Gamma and varepsilon(omega,q)
are independent of temperature. The classical percolation indices give
alpha/2/nu=3/7. The width of the region where a strong absorption of the SAW
occurs is found to be given by the scaling law |Delta \bar{\nu}| approx
(omega_q*Lambda/v_D)^{alpha/2/nu}. The dependence of the electron-phonon
coupling and the screening due to the 2DEG on the filling factor leads to a
double-peak structure for Gamma(\bar{\nu}).Comment: 17 pages, 3 Postscript figures, minor changes mad
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Structural and Functional Dissection of Mif2p, a Conserved DNA-binding Kinetochore Protein
Mif2p is the budding-yeast orthologue of the mammalian centromere-binding protein CENP-C. We have mapped domains of Saccharomyces cerevisiae Mif2p and studied the phenotyptic consequences of their deletion. Using chromatin immunoprecipitation (ChIP) and electrophoretic mobility shift assays, we have further shown that Mif2p binds in the CDEIII region of the budding-yeast centromere, probably in close spatial association with Ndc10p. Moreover, ChIP experiments show that Mif2p recruits to yeast kinetochores a substantial subset of inner and outer kinetochore proteins, but not the Ndc80 or Spc105 complexes. We have determined the crystal structure of the C-terminal, dimerization domain of Mif2p. It has a "cupin" fold, extremely similar both in polypeptide chain conformation and in dimer geometry to the dimerization domain of a bacterial transcription factor. The Mif2p dimer seems to be part of an enhanceosome-like structure that nucleates kinetochore assembly in budding yeast.Molecular and Cellular Biolog
Technological Devices in the Archives: A Policy Analysis
Doing research in the archive is the cornerstone of humanities scholarship.
Various archives institute policies regarding the use of technological
devices, such as mobile phones, laptops, and cameras in their reading rooms.
Such policies directly affect the scholars as the devices mediate the nature of
their interaction with the source materials in terms of capturing, organizing,
note taking, and record keeping for future use of found materials. In this paper,
we present our analysis of the policies of thirty archives regarding the use of
technology in their reading rooms. This policy analysis, along with data from
interviews of scholars and archivists, is intended to serve as a basis for developing
mobile applications for assisting scholars in their research activities. In this
paper we introduce an early prototype of such a mobile application—
AMTracker.Informatio
The developmental dynamics of terrorist organizations
We identify robust statistical patterns in the frequency and severity of
violent attacks by terrorist organizations as they grow and age. Using
group-level static and dynamic analyses of terrorist events worldwide from
1968-2008 and a simulation model of organizational dynamics, we show that the
production of violent events tends to accelerate with increasing size and
experience. This coupling of frequency, experience and size arises from a
fundamental positive feedback loop in which attacks lead to growth which leads
to increased production of new attacks. In contrast, event severity is
independent of both size and experience. Thus larger, more experienced
organizations are more deadly because they attack more frequently, not because
their attacks are more deadly, and large events are equally likely to come from
large and small organizations. These results hold across political ideologies
and time, suggesting that the frequency and severity of terrorism may be
constrained by fundamental processes.Comment: 28 pages, 8 figures, 4 tables, supplementary materia
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