11,413 research outputs found
Experimental study of laser detected magnetic resonance based on atomic alignment
We present an experimental study of the spectra produced by
optical/radio-frequency double resonance in which resonant linearly polarized
laser light is used in the optical pumping and detection processes. We show
that the experimental spectra obtained for cesium are in excellent agreement
with a very general theoretical model developed in our group and we investigate
the limitations of this model. Finally, the results are discussed in view of
their use in the study of relaxation processes in aligned alkali vapors.Comment: 8 pages, 9 figures. Submitted to Phys. Rev. A. Related to
physics/060523
Superconductivity in the Sn-Ba-Sr-Y-Cu-O system
Since Bednorz and Muller discovered high-T(sub c) superconductivity in the La-Ba-Cu-O compound, several families of superconducting oxides have been synthesized. Here, researchers report the results of search for superconductivity in the compounds based on tin, which has a lone electron pair like Bi, Tl, Pb. The following compounds were synthesized: Sn1Ba1Sr1Cu3Ox, Sn1Ba1Ca1Cu3Ox, Sn1Ba1Mg1Cu3Ox, Sn1Sr1Ca1Cu3Ox, Sn1Sr1Mg1Cu3Ox, Sn1Ca1Mg1Cu3Ox. The initial components were oxides and carbonates of the appropriate elements. Standard firing-grinding procedure was used. Final heating was carried out at 960 C during 12 hours. Then the samples were cooled inside the furnace. All the synthesis cycles were carried out in air atmosphere. Among the synthesized compounds only Sn1Ba1Sr1Cu3Ox showed remarkable conductivity. Other compounds were practically dielectrics. Presence of a possible superconductivity in Sn1Ba1Sr1Cu3Ox was defined by using the Meissner effect. At low temperature a deviation from paramagnetic behavior is observed. The hysteresis loops obtained at lower temperatures undoubtly testify to the presence of a superconductive phase in the sample. However, the part of the superconductive phase in the Sn1Ba1Sr1Cu3Ox ceramic turned out to be small, less than 2 percent, which agrees with the estimation from magnetic data. In order to increase the content of the superconductive phase two-valent cations Ba, Sr were partially substituted by univalent (K) and three-valent ones (Y)
Optical measurements of spin noise as a high resolution spectroscopic tool
The intrinsic fluctuations of electron spins in semiconductors and atomic
vapors generate a small, randomly-varying "spin noise" that can be detected by
sensitive optical methods such as Faraday rotation. Recent studies have
demonstrated that the frequency, linewidth, and lineshape of this spin noise
directly reveals dynamical spin properties such as dephasing times, relaxation
mechanisms and g-factors without perturbing the spins away from equilibrium.
Here we demonstrate that spin noise measurements using wavelength-tunable probe
light forms the basis of a powerful and novel spectroscopic tool to provide
unique information that is fundamentally inaccessible via conventional linear
optics. In particular, the wavelength dependence of the detected spin noise
power can reveal homogeneous linewidths buried within inhomogeneously-broadened
optical spectra, and can resolve overlapping optical transitions belonging to
different spin systems. These new possibilities are explored both theoretically
and via experiments on spin systems in opposite limits of inhomogeneous
broadening (alkali atom vapors and semiconductor quantum dots).Comment: 4 pages, 4 figure
Theory of double resonance magnetometers based on atomic alignment
We present a theoretical study of the spectra produced by
optical-radio-frequency double resonance devices, in which resonant linearly
polarized light is used in the optical pumping and detection processes. We
extend previous work by presenting algebraic results which are valid for atomic
states with arbitrary angular momenta, arbitrary rf intensities, and arbitrary
geometries. The only restriction made is the assumption of low light intensity.
The results are discussed in view of their use in optical magnetometers
Characterizing normal crossing hypersurfaces
The objective of this article is to give an effective algebraic
characterization of normal crossing hypersurfaces in complex manifolds. It is
shown that a hypersurface has normal crossings if and only if it is a free
divisor, has a radical Jacobian ideal and a smooth normalization. Using K.
Saito's theory of free divisors, also a characterization in terms of
logarithmic differential forms and vector fields is found and and finally
another one in terms of the logarithmic residue using recent results of M.
Granger and M. Schulze.Comment: v2: typos fixed, final version to appear in Math. Ann.; 24 pages, 2
figure
A Low-Noise High-Density Alkali Metal Scalar Magnetometer
We present an experimental and theoretical study of a scalar atomic
magnetometer using an oscillating field-driven Zeeman resonance in a
high-density optically-pumped potassium vapor. We describe an experimental
implementation of an atomic gradiometer with a noise level below 10
fT/Hz^{1/2}, fractional field sensitivity below 10^{-9}/Hz^{1/2}, and an active
measurement volume of about 1.5 cm^3. We show that the fundamental field
sensitivity of a scalar magnetometer is determined by the rate of alkali-metal
spin-exchange collisions even though the resonance linewidth can be made much
smaller than the spin-exchange rate by pumping most atoms into a stretched spin
state.Comment: 10 pages, 7 figures. Version 2 is longer, with more complete
description of theoretical analysis and comparison between analytical and
experimental result
Shell closure effects studied via cluster decay in heavy nuclei
The effects of shell closure in nuclei via the cluster decay is studied. In
this context, we have made use of the Preformed Cluster Model () of Gupta
and collaborators based on the Quantum Mechanical Fragmentation Theory. The key
point in the cluster radioactivity is that it involves the interplay of close
shell effects of parent and daughter. Small half life for a parent indicates
shell stabilized daughter and long half life indicates the stability of the
parent against the decay. In the cluster decay of trans lead nuclei observed so
far, the end product is doubly magic lead or its neighbors. With this in our
mind we have extended the idea of cluster radioactivity. We investigated decay
of different nuclei where Zirconium is always taken as a daughter nucleus,
which is very well known deformed nucleus. The branching ratio of cluster decay
and -decay is also studied for various nuclei, leading to magic or
almost doubly magic daughter nuclei. The calculated cluster decay half-life are
in well agreement with the observed data. First time a possibility of cluster
decay in nucleus is predicted
The Role of Vascular Endothelial Growth Factor and Antithrombin III In The Pathogenesis of the Ovarian Hyperstimulation Syndrome
Ovarian hyperstimulation syndrome (OHSS) is an iatrogenic complication of controlled ovarian hyperstimulation (COH). Its pathogenesis is not clarified yet. In the recent years a number of studies focused on the vascular endothelial growth factor (VEGF) and antihtrombin III (AT III) indicators. VEGF is homodimeric, heparin-binding glycoprotein, stimulating vascular permeability. Antithrombin III is protease inhibitor of activated clotting factors. This study aimed at examining the VEGF-A165 and AT III indicators with two OHSS patients. Two methods were used for the determination of the indicators of VEGF-A165 and AT III: ELISA for VEGF and chromogenic assay for ATT III. Kits of R/D Systems and American Diagnostica Inc. were used to estimate VEGF and AT III indicators in serum and plasma. There were higher indicators of VEGF-A165 (180pg/ml) and reduction of AT III indicators (48%) in the patient with a severe form of OHSS than in the control group while these indicators were normal in the patient with a moderate form of OHSS. Our results confirmed some published data concerning the importance of VEGF and AT III in the genesis of OHSS. This study should include a larger group of patients in order tofollow-up statistically and authentically the variations of the indicators of both factors and their importance for OHSS
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