86,535 research outputs found
BILIPROTEINS FROM THE BUTTERFLY Pieris brassicae STUDIED BY TIME-RESOLVED FLUORESCENCE AND COHERENT ANTI-STOKES RAMAN SPECTROSCOPY
The fluorescence decay time of the biliverdin IX7 chromophore present in biliproteins isolated from Pieris brassicae is determined to be 44 ± 3 ps. This value suggests a cyclic helical chromophore structure. The vibrational frequencies determined by CARS-spectroscopy are compared with those of model compounds. The data confirm that the chromophore in the protein-bound state adopts a cyclic-helical, flexible conformation
Gate voltage tuned quantum superconductor to insulator transition in an ultrathin bismuth film revisited
We explore the implications of Berezinskii-Kosterlitz-Thouless (BKT) critical
behavior and variable-range hopping on the two dimensional (2D) quantum
superconductor-insulator (QSI) transition driven by tuning the gate voltage. To
illustrate the potential and the implications of this scenario we analyze sheet
resistance data of Parendo et al. taken on a gate voltage tuned ultrathin
amorphous bismuth film. The finite size scaling analysis of the BKT-transition
uncovers a limiting length preventing the correlation length to diverge and to
enter the critical regime deeply. Nevertheless the attained BKT critical regime
reveals consistency with two parameter quantum scaling and an explicit quantum
scaling function determined by the BKT correlation length. The two parameter
scaling yields for the zero temperature critical exponents of the
QSI-transition the estimates zn = 3/2, z = 3, and n = 1/2, revealing that
hyperscaling is violated and in contrast to finite temperature disorder is
relevant at zero temperature. Furthermore, zn = 3/2 is also consistent with the
two variable quantum scaling form associated with a variable-range hopping
controlled insulating ground state
Magnetic field induced 3D to 1D crossover in Sr0:9La0:1CuO2
The effect of the magnetic field on the critical behavior of Sr0:9La0:1CuO2
is explored in terms of reversible magnetization data. As the correlation
length transverse to the magnetic field Hi,applied along the i-axis, cannot
grow beyond the limiting magnetic length LHi, related to the average distance
between vortex lines, one expects a magnetic field induced finite size effect.
Invoking the scaling theory of critical phenomena we provide clear evidence for
this effect. It implies that in type II superconductors there is a 3D to 1D
crossover line Hpi(T). Consequently, below Tc and above Hpi(T) uperconductivity
is confined to cylinders with diameter LHi(1D). Accordingly, there is no
continuous phase transition in the (H,T)-plane along the Hc2-lines as predicted
by the mean-field treatment.Comment: 4 pages, 5 figure
A systematic approach to atomicity decomposition in Event-B
Event-B is a state-based formal method that supports a refinement process in which an abstract model is elaborated towards an implementation in a step-wise manner. One weakness of Event-B is that control flow between events is typically modelled implicitly via variables and event guards. While this fits well with Event-B refinement, it can make models involving sequencing of events more difficult to specify and understand than if control flow was explicitly specified. New events may be introduced in Event-B refinement and these are often used to decompose the atomicity of an abstract event into a series of steps. A second weakness of Event-B is that there is no explicit link between such new events that represent a step in the decomposition of atomicity and the abstract event to which they contribute. To address these weaknesses, atomicity decomposition diagrams support the explicit modelling of control flow and refinement relationships for new events. In previous work,the atomicity decomposition approach has been evaluated manually in the development of two large case studies, a multi media protocol and a spacecraft sub-system. The evaluation results helped us to develop a systematic definition of the atomicity decomposition approach, and to develop a tool supporting the approach. In this paper we outline this systematic definition of the approach, the tool that supports it and evaluate the contribution that the tool makes
The NOAA/NESS program for operational snowcover mapping: Preparing for the 1980's
There are no author-identified significant results in this report
Decoherence and fidelity in ion traps with fluctuating trap parameters
We consider two different kinds of fluctuations in an ion trap potential:
external fluctuating electrical fields, which cause statistical movement
(``wobbling'') of the ion relative to the center of the trap, and fluctuations
of the spring constant, which are due to fluctuations of the ac-component of
the potential applied in the Paul trap for ions. We write down master equations
for both cases and, averaging out the noise, obtain expressions for the heating
of the ion. We compare our results to previous results for far-off resonance
optical traps and heating in ion traps. The effect of fluctuating external
electrical fields for a quantum gate operation (controlled-NOT) is determined
and the fidelity for that operation derived.Comment: 11 pages, 4 figure
IR-TF Relation In The Zone Of Avoidance With 2MASS
Using the Tully-Fisher relation, one can map the peculiar velocity field and
estimate the mass in regions such as the Great Attractor. 2MASS is surveying
the full sky in J, H and K bands and has the great advantage that it allows us
to detect galaxies more uniformly to lower Galactic latitude than optical
surveys. This study shows the feasibility of using 2MASS and the TF relation to
probe large scale structure. We found that (i) we can use axis ratio up
to 0.5; (ii) intrinsic extinction is present (up to 0.5mag at J, 0.1 mag at K);
(iii) the zero-point of the TF relation is independent of the 2MASS magnitude
measurement and is consistent with the HST Key-Project value; (iv) the 2MASS
K-band 20th mag/arcsec isophotal aperture magnitude produces the best TF
relation; and (v) there is no type dependence of the residualsComment: 8 pages, Latex using newpasp.sty. Matches version to appear in
Mapping the Hidden Universe: The Universe Behind the Milky Way - The Universe
in HI, ASP Conference Series 2000, eds R.C.Kraan-Korteweg, P.A. Henning and
H. Andernach (matched to published version; abstract bug in v2 fixed
Strain specific effects of low level lead exposure on associative learning and memory in rats.
Exposure to lead (Pb) remains a significant public health concern. Lead exposure in early life impairs the normal development of numerous cognitive and neurobehavioral processes. Previous work has shown that the effects of developmental Pb exposure on gene expression patterns in the brain are modulated by various factors including the developmental timing of the exposure, level of exposure, sex, and genetic background. Using gene microarray profiling, we previously reported a significant strain-specific effect of Pb exposure on the hippocampal transcriptome, with the greatest number of differentially expressed transcripts in Long Evans (LE) rats and the fewest in Sprague Dawley (SD) rats. The present study examined the extent to which this differential effect of Pb on hippocampal gene expression might influence behavior. Animals (males and females) were tested in a trace fear conditioning paradigm to evaluate effects of Pb exposures (perinatal (PERI; gestation to postnatal day 21) or early postnatal (EPN; postnatal day 1 to day 21)) on associative learning and memory. All animals (Pb-exposed and non-Pb-exposed controls) showed normal acquisition of the conditioned stimulus (tone)-unconditioned stimulus (footshock) association. Long Evans rats showed a significant deficit in short- and long-term recall, influenced by sex and the timing of Pb exposure (PERI or EPN). In contrast, Pb exposure had no significant effect on memory consolidation or recall in any SD rats. These results further demonstrate the important influence of genetic background to the functional outcomes from developmental Pb exposure
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