46,571 research outputs found
Monotone Volume Formulas for Geometric Flows
We consider a closed manifold M with a Riemannian metric g(t) evolving in
direction -2S(t) where S(t) is a symmetric two-tensor on (M,g(t)). We prove
that if S satisfies a certain tensor inequality, then one can construct a
forwards and a backwards reduced volume quantity, the former being
non-increasing, the latter being non-decreasing along the flow. In the case
where S=Ric is the Ricci curvature of M, the result corresponds to Perelman's
well-known reduced volume monotonicity for the Ricci flow. Some other examples
are given in the second section of this article, the main examples and
motivation for this work being List's extended Ricci flow system, the Ricci
flow coupled with harmonic map heat flow and the mean curvature flow in
Lorentzian manifolds with nonnegative sectional curvatures. With our approach,
we find new monotonicity formulas for these flows.Comment: v2: final version (as published
Quantification of Cell Subpopulations, Fractions of Dead Cells and Debris in Cell Suspensions by Laser Diffractometry
Laser diffractometry was employed for size analysis in liver cell and blood cell suspensions to assess its suitability for characterizing cell populations. The method proved sensitive to detect subpopulations in liver cells (bimodal or trimodal distributions) and to quantify their volume fractions. Cell debris and aggregates of cells could also be quantified, dead cell populations recognized by their shift in the mean cell diameter. Laser diffractometry is therefore suitable for determining the quality of cell isolations (e.g. by liver perfusion) or for following alterations in cell populations during culture of cells in suspension. Analysis of human blood allowed differenciations to be made between thrombocytes and other blood cells. No peak separation was obtained for the populations of erythrocytes and granulocytes due to their similarity in size. Monocytes could not be detected due to their extremely low number in the blood indicating the limit of the metho
Fundamental Plane Distances to Early-type Field Galaxies in the South Equatorial Strip. I. The Spectroscopic Data
Radial velocities and central velocity dispersions are derived for 238 E/S0
galaxies from medium-resolution spectroscopy. New spectroscopic data have been
obtained as part of a study of the Fundamental Plane distances and peculiar
motions of early-type galaxies in three selected directions of the South
Equatorial Strip, undertaken in order to investigate the reality of large-scale
streaming motion; results of this study have been reported in M\"uller
(1998). The new APM South Equatorial Strip Catalog () was used to select the sample of field galaxies in
three directions: (1) 15h10 - 16h10; (2) 20h30 - 21h50; (3) 00h10 - 01h30. The
spectra obtained have a median S/N per of 23, an instrumental
resolution (FWHM) of 4 , and the spectrograph resolution
(dispersion) is 100 km~s. The Fourier cross-correlation method
was used to derive the radial velocities and velocity dispersions. The velocity
dispersions have been corrected for the size of the aperture and for the galaxy
effective radius. Comparisons of the derived radial velocities with data from
the literature show that our values are accurate to 40 km~s. A
comparison with results from J\orgensen et al. (1995) shows that the derived
central velocity dispersion have an rms scatter of 0.036 in .
There is no offset relative to the velocity dispersions of Davies et al.
(1987).Comment: accepted for publication in Astronomy & Astrophysics Supplement
Serie
Zoo-FISH in the European mole (Talpa europaea) detects all ancestral Boreo-Eutherian human homologous chromosome associations
Zoo-FISH with human whole-chromosome paint probes delineated syntenic association of human homologous chromosome segments 3-21, 14-15, 16-19, 4-8, 7-16 and 12-22 (twice) in the European mole (Talpa europaea, Talpidae, Eulipotyphla, Mammalia). These segment associations represent shared ancestral Boreo-Eutherian traits, half of which were previously not described for Eulipotyphla. The karyotype of the European mole acquired a minimum of 19 translocations and six inversions compared to the presumed Boreo-Eutherian ancestor. Copyright (c) 2006 S. Karger AG, Basel
Interpretation of increased energetic particle flux measurements by SEPT aboard the STEREO spacecraft and contamination
Context. Interplanetary (IP) shocks are known to be accelerators of energetic
charged particles observed in-situ in the heliosphere. However, the
acceleration of near-relativistic electrons by shocks in the interplanetary
medium is often questioned. On 9 August 2011 a Corotating Interaction Region
(CIR) passed STEREO B (STB) that resulted in a flux increase in the electron
and ion channels of the Solar Electron and Proton Telescope (SEPT). Because
electron measurements in the few keV to several 100 keV range rely on the
so-called magnet foil technique, which is utilized by SEPT, ions can contribute
to the electron channels. Aims. We aim to investigate whether the flux increase
in the electron channels of SEPT during the CIR event on 9 August 2011 is
caused by ion contamination only. Methods. We compute the SEPT response
functions for protons and helium utilizing an updated GEANT4 model of SEPT. The
CIR energetic particle ion spectra for protons and helium are assumed to follow
a Band function in energy per nucleon with a constant helium to proton ratio.
Results. Our analysis leads to a helium to proton ratio of 16.9% and a proton
flux following a Band function with the parameters /
(cm2 s sr MeV/nuc.), keV/nuc. and spectral indices of and which are in good agreement with measurements by
the Suprathermal Ion Telescope (SIT) aboard STB. Conclusions. Since our results
explain the SEPT measurements, we conclude that no significant amount of
electrons were accelerated between keV and keV by the CIR
Voltage-flux-characteristics of asymmetric dc SQUIDs
We present a detailed analysis of voltage-flux V(Phi)-characteristics for
asymmetric dc SQUIDs with various kinds of asymmetries. For finite asymmetry
alpha_I in the critical currents of the two Josephson junctions, the minima in
the V(Phi)-characteristics for bias currents of opposite polarity are shifted
along the flux axis by Delta_Phi = (alpha_I)*(beta_L) relative to each other;
beta_L is the screening parameter. This simple relation allows the
determination of alpha_I in our experiments on YBa_2Cu_3O_(7-x} dc SQUIDs and
comparison with theory. Extensive numerical simulations within a wide range of
beta_L and noise parameter Gamma reveal a systematic dependence of the transfer
function V_Phi on alpha_I and alpha_R (junction resistance asymmetry). As for
the symmetric dc SQUID, V_Phi factorizes into
g(Gamma*beta_L)*f(alpha_I,beta_L), where now f also depends on alpha_I. For
\beta_L below five we find mostly a decrease of V_Phi with increasing alpha_I,
which however can only partially account for the frequently observed
discrepancy in V_Phi between theory and experiment for high-T_c dc SQUIDs.Comment: 4 pages, 7 figures, Applied Superconductivity Conference 2000, to be
published in IEEE Trans. Appl. Supercon
Calculation of geometric phases in electric dipole searches with trapped spin-1/2 particles based on direct solution of the Schr\"odinger equation
Pendlebury [Phys. Rev. A , 032102 (2004)] were
the first to investigate the role of geometric phases in searches for an
electric dipole moment (EDM) of elementary particles based on Ramsey-separated
oscillatory field magnetic resonance with trapped ultracold neutrons and
comagnetometer atoms. Their work was based on the Bloch equation and later work
using the density matrix corroborated the results and extended the scope to
describe the dynamics of spins in general fields and in bounded geometries. We
solve the Schr\"odinger equation directly for cylindrical trap geometry and
obtain a full description of EDM-relevant spin behavior in general fields,
including the short-time transients and vertical spin oscillation in the entire
range of particle velocities. We apply this method to general macroscopic
fields and to the field of a microscopic magnetic dipole.Comment: 11 pages, 4 figure
Universal observation of multiple order parameters in cuprate superconductors
The temperature dependence of the London penetration depth \lambda was
measured for an untwined single crystal of YBa_2Cu_3O_{7-\delta} along the
three principal crystallographic directions (a, b, and c). Both in-plane
components (\lambda_a and \lambda_b) show an inflection point in their
temperature dependence which is absent in the component along the c-direction
(\lambda_c). The data provide convincing evidence that the in-plane
superconducting order parameter is a mixture of s+d-wave symmetry whereas it is
exclusively s-wave along the c-direction. In conjunction with previous results
it is concluded that coupled s+d-order parameters are universal and intrinsic
to cuprate superconductors.Comment: 5 pages, 3 figure
Opportunities for farming in alpine countries – pathways to truly grassland-based beef and milk production in Austria and Switzerland
Farming in the alpine countries of Austria and Switzerland fulfils important economic, socio-cultural and ecological functions for society. However, even though both Austria and Switzerland have increasingly focused their agricultural policy towards ecology, in both countries negative environmental impacts of agriculture still have to be reduced massively
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