17,492 research outputs found
The Physiological Basis for Altered Na\u3csup\u3e+\u3c/sup\u3e and Cl\u3csup\u3e-\u3c/sup\u3e Movement Across the Gills of Rainbow Trout (\u3cem\u3eOncorhynchus mykiss\u3c/em\u3e) in Alkaline (pH=9.5) Water
To test the hypothesis that internal ion imbalances at high pH are caused by altered branchial ion transporting capacity and permeability, radiotracers (24Na+ and 36Cl-) were used to measure ion movements across the gills of intact rainbow trout (Oncorhynchus mykiss) during 3 d exposure to pH 9.5. At control pH (pH 8.0), the trout were in net ion balance, but by 8 h at high pH, 60%â70% reductions in Cl- influx (Cl) and Na+ influx (JNa/in) led to net Cl- and Na+ losses of -200 ”mol kg-1 h-1. Outflux (diffusive efflux plus renal ion losses) was not initially altered. By 72 h, net Cl- balance was reestablished because of a restoration of JCl/in. Although JNa/in remained 50% lower at this time, counterbalancing reductions in Na+ outflux restored net Na+ balance. One-substrate ion-uptake kinetics analyses indicated that reduced ion influx after 8 h at pH 9.5 was caused by 50% decreases in Cl- and Na+ maximal transport rates (JCl/max, JNa/max), likely reflecting decreased numbers of functional transport sites. Two-substrate kinetic analyses indicated that reduced internal HCO3- and H+ supply for respective branchial Cl-/base and Na+/acid transport systems also contributed to lower JCl/in and, to a lesser extent, lower JNa/in at pH 9.5. Recovery in in of JCl/in after 3 d accounted for restoration of Cl- balance and max likely reflected increased numbers of transport sites. In contrast, JNa/in remained 33% lower after 3 d, but a lower affinity of the max gills for Na+ (fourfold greater KNa/m) accounted for the chronic m reduction in Na+ influx at pH 9.5. Thus, reestablishment of Cl- uptake capacity and counterbalancing reductions in Na+ outflux allows rainbow trout to reestablish net ion balance in alkaline waters
Holomorphic Poisson Manifolds and Holomorphic Lie Algebroids
We study holomorphic Poisson manifolds and holomorphic Lie algebroids from
the viewpoint of real Poisson geometry. We give a characterization of
holomorphic Poisson structures in terms of the Poisson Nijenhuis structures of
Magri-Morosi and describe a double complex which computes the holomorphic
Poisson cohomology. A holomorphic Lie algebroid structure on a vector bundle
is shown to be equivalent to a matched pair of complex Lie algebroids
, in the sense of Lu. The holomorphic Lie algebroid
cohomology of is isomorphic to the cohomology of the elliptic Lie algebroid
. In the case when is a holomorphic Poisson
manifold and , such an elliptic Lie algebroid coincides with the
Dirac structure corresponding to the associated generalized complex structure
of the holomorphic Poisson manifold.Comment: 29 pages, v2: paper split into two, part 1 of 2, v3: two references
added, v4: final version to appear in International Mathematics Research
Notice
Trace anomaly of the conformal gauge field
The proposed by Bastianelli and van Nieuwenhuizen new method of calculations
of trace anomalies is applied in the conformal gauge field case. The result is
then reproduced by the heat equation method. An error in previous calculation
is corrected. It is pointed out that the introducing gauge symmetries into a
given system by a field-enlarging transformation can result in unexpected
quantum effects even for trivial configurations.Comment: 9 pages, LaTeX file, BI-TP 93/3
Progress in Atomic Fountains at LNE-SYRTE
We give an overview of the work done with the Laboratoire National de
M\'etrologie et d'Essais-Syst\`emes de R\'ef\'erence Temps-Espace (LNE-SYRTE)
fountain ensemble during the last five years. After a description of the clock
ensemble, comprising three fountains, FO1, FO2, and FOM, and the newest
developments, we review recent studies of several systematic frequency shifts.
This includes the distributed cavity phase shift, which we evaluate for the FO1
and FOM fountains, applying the techniques of our recent work on FO2. We also
report calculations of the microwave lensing frequency shift for the three
fountains, review the status of the blackbody radiation shift, and summarize
recent experimental work to control microwave leakage and spurious phase
perturbations. We give current accuracy budgets. We also describe several
applications in time and frequency metrology: fountain comparisons,
calibrations of the international atomic time, secondary representation of the
SI second based on the 87Rb hyperfine frequency, absolute measurements of
optical frequencies, tests of the T2L2 satellite laser link, and review
fundamental physics applications of the LNE-SYRTE fountain ensemble. Finally,
we give a summary of the tests of the PHARAO cold atom space clock performed
using the FOM transportable fountain.Comment: 19 pages, 12 figures, 5 tables, 126 reference
Improved tests of Local Position Invariance using 87Rb and 133Cs fountains
We report tests of local position invariance based on measurements of the
ratio of the ground state hyperfine frequencies of 133Cs and 87Rb in
laser-cooled atomic fountain clocks. Measurements extending over 14 years set a
stringent limit to a possible variation with time of this ratio: d
ln(nu_Rb/nu_Cs)/dt=(-1.39 +/- 0.91)x 10-16 yr-1. This improves by a factor of
7.7 over our previous report (H. Marion et al., Phys. Rev. Lett. 90, 150801
(2003)). Our measurements also set the first limit to a fractional variation of
the Rb/Cs ratio with gravitational potential at the level of c^2 d
ln(nu_Rb/nu_Cs)/dU=(0.11 +/- 1.04)x 10^-6, providing a new stringent
differential redshift test. The above limits equivalently apply to the
fractional variation of the quantity alpha^{-0.49}x(g_Rb/g_Cs), which involves
the fine structure constant alpha and the ratio of the nuclear g-factors of the
two alkalis. The link with variations of the light quark mass is also presented
together with a global analysis combining with other available highly accurate
clock comparisons.Comment: 5 pages, 3 figures, 3 tables, 34 reference
Polarized Gamma-ray Emission from the Galactic Black Hole Cygnus X-1
Because of their inherently high flux allowing the detection of clear
signals, black hole X-ray binaries are interesting candidates for polarization
studies, even if no polarization signals have been observed from them before.
Such measurements would provide further detailed insight into these sources'
emission mechanisms. We measured the polarization of the gamma-ray emission
from the black hole binary system Cygnus X-1 with the INTEGRAL/IBIS telescope.
Spectral modeling of the data reveals two emission mechanisms: The 250-400 keV
data are consistent with emission dominated by Compton scattering on thermal
electrons and are weakly polarized. The second spectral component seen in the
400keV-2MeV band is by contrast strongly polarized, revealing that the MeV
emission is probably related to the jet first detected in the radio band.Comment: 11 pages, 3 figures, to be published in Science in April 22nd 2011,
available on Science Express Web site (March 24th edition
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