158 research outputs found
PERINATAL COMPLIANCE: A MULTIDISCIPLINARY APPROACH TO PROTECT THE MENTAL HEALTH OF WOMEN DURING PREGNANCY
PERINATAL COMPLIANCE: A MULTIDISCIPLINARY APPROACH TO PROTECT THE MENTAL HEALTH OF WOMEN DURING PREGNANCY
Femtosecond pump/supercontinuum-probe spectroscopy: Optimized setup and signal analysis for single-shot spectral referencing
A setup for pump/supercontinuum-probe spectroscopy is described which (i) is optimized to cancel fluctuations of the probe light by single-shot referencing, and (ii) extends the probe range into the near-uv (1000–270 nm). Reflective optics allow 50 μm spot size in the sample and upon entry into two separate spectrographs. The correlation γsame between sample and reference readings of probe light level at every pixel exceeds 0.99, compared to γconsec<0.92 reported for consecutive referencing. Statistical analysis provides the confidence interval of the induced optical density, ΔOD. For demonstration we first examine a dye (Hoechst 33258) bound in the minor groove of double-stranded DNA. A weak 1.1 ps spectral oscillation in the fluorescence region, assigned to DNA breathing, is shown to be significant. A second example concerns the weak vibrational structure around t=0 which reflects stimulated Raman processes. With 1% fluctuations of probe power, baseline noise for a transient absorption spectrum becomes 25 μOD rms in 1 s at 1 kHz, allowing to record resonance Raman spectra of flavine adenine dinucleotide in the S0 and S1 stateWe are grateful to the Deutsche Forschungsgemeinschaft for support (SFB 450 and Cluster of Excellence “Unifying Concepts in Catalysis”)S
New model for system of mesoscopic Josephson contacts
Quantum fluctuations of the phases of the order parameter in 2D arrays of
mesoscopic Josephson junctions and their effect on the destruction of
superconductivity in the system are investigated by means of a quantum-cosine
model that is free of the incorrect application of the phase operator. The
proposed model employs trigonometric phase operators and makes it possible to
study arrays of small superconducting granules, pores filled with superfluid
helium, or Josephson junctions in which the average number of particles
(effective bosons, He atoms, and so on) is small, and the standard approach
employing the phase operator and the particle number operator as conjugate ones
is inapplicable. There is a large difference in the phase diagrams between
arrays of macroscopic and mesoscopic objects for and ( is
the characteristic interaction energy of the particle per granule and is
the Josephson coupling constant). Reentrant superconductivity phenomena are
discussed.Comment: 4 pages, 3 Postscript figure
Electron Correlations in an Electron Bilayer at Finite Temperature: Landau Damping of the Acoustic Plasmon
We report angle-resolved Raman scattering observations of the temperature
dependent Landau damping of the acoustic plasmon in an electron bilayer system
realised in a GaAs double quantum well structure. Corresponding calculations of
the charge-density excitation spectrum of the electron bilayer using forms of
the random phase approximation (RPA), and the static local field formalism of
Singwi, Tosi, Land and Sj\"{o}lander (STLS) extended to incorporate non-zero
electron temperature and phenomenological damping, are also
presented. The STLS calculations include details of the temperature dependence
of the intra- and inter-layer local field factors and pair-correlation
functions. Good agreement between experiment and the various theories is
obtained for the acoustic plasmon energy and damping for , the Fermi temperature. However, contrary to current expectations,
all of the calculations show significant departures from our experimental data
for . From this, we go on to demonstrate
unambiguously that real local field factors fail to provide a physically
accurate description of exchange correlation behaviour in low dimensional
electron gases. Our results suggest instead that one must resort to a
{\em{dynamical}} local field theory, characterised by a {\em{complex}} field
factor to provide a more accurate description.Comment: 53 pages, 16 figure
HIGH-RESOLUTION LAMB DIP SPECTROSCOPY ON OD AND SiCl IN A MOLECULAR BEAM
Contains fulltext :
99073.pdf (publisher's version ) (Open Access
Statistical Mechanics of Structural Fluctuations
The theory of mesoscopic fluctuations is applied to inhomogeneous solids
consisting of chaotically distributed regions with different crystalline
structure. This approach makes it possible to describe statistical properties
of such mixture by constructing a renormalized Hamiltonian. The relative
volumes occupied by each of the coexisting structures define the corresponding
geometric probabilities. In the case of a frozen heterophase system these
probabilities should be given a priori. And in the case of a thermal
heterophase mixture the structural probabilities are to be defined
self-consistently by minimizing a thermodynamical potential. This permits to
find the temperature behavior of the probabilities which is especially
important near the points of structural phase transitions. The presense of
these structural fluctuations yields a softening of a crystal and a decrease of
the effective Debye temperature. These effects can be directly seen by nuclear
gamma resonance since the occurrence of structural fluctuations is accompanied
by a noticeable sagging of the M\"ossbauer factor at the point of structural
phase transition. The structural fluctuations also lead to the attenuation of
sound and increase of isothermic compressibility.Comment: 1 file, 18 pages, RevTex, no figure
Temperature dependence of the EPR linewidth of Yb3+ - ions in Y0.99Yb0.01Ba2Cu3OX compounds: Evidence for an anomaly near TC
Electron paramagnetic resonance experiments on doped Yb3+ ions in YBaCuO
compounds with different oxygen contents have been made. We have observed the
strong temperature dependence of the EPR linewidth in the all investigated
samples caused by the Raman processes of spin-lattice relaxation. The
spin-lattice relaxation rate anomaly revealed near TC in the superconducting
species can be assigned to the phonon density spectrum changesComment: 10 pages, 4 figures Renewed versio
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