712 research outputs found
Isolation of a photosystem 2 preparation from higher plants with highly enriched oxygen evolution activity
AbstractDetergent-treatment of higher plant thylakoids with Triton X-100 at pH 6.3 has been used to purify a PS2 fraction with very high rates of oxygen evolution (1000 ÎŒmol.mg chlâ1.hâ1). A photosynthetic unit size of about 300 chlorophyll (chl) molecules has been determined by optical methods, suggesting an average turnover time for PS2 of about 2 ms. The donor system for P680+ is particularly well preserved in the preparation, as judged by P680+ reduction kinetics, the detection by EPR of Signal IILT and the presence of the high potential form of cytochrome b-559 (at a ratio of 1:1 with the reaction centre)
Is group psychotherapy feasible for oncology outpatients attenders selected on the basis of psychological morbidity?
Of 120 consecutive attenders at an oncology outpatients department, 108 were screened for psychological symptoms using the Hospital Anxiety and Depression Scale (Zigmond & Snaith, 1983). Thirty-nine patients had significant scores indicating moderate anxiety and/or depression. We felt that this warranted an offer of group psychotherapy in the belief that sharing issues and exploring personal concerns may alleviate some of the experienced psychological distress. Only 10 patients consented to and were able to attend this group, with which five patients persisted. Thus in this group of patients with advanced cancer group psychotherapy was applicable only to a limited number of selected patients. The nature of this study and the size of the population markedly limited our ability to comment on the usefulness of group psychotherapy. Many patients, particularly the most severely psychologically distressed, continued to require other forms of support, particularly domiciliary individual therapy
Rapid electron transfer reactions associated with oxygen evolution in photosystem II preparations from spinach and Phormidium laminosum
AbstractWe have measured the nanosecond kinetics of Chl-a+II reduction in oxygen-evolving detergent preparations of PS II from the cyanobacterium Phormidium laminosum and from higher plants (spinach) at 824 and 680 nm. Compared to earlier studies at 680 nm with higher plant material, we obtained an improved signal: noise ratio for measurements on a ns to ms time scale. The kinetics of Chl-a+II reduction in the ns range are consistent in the two preparations and are comparable to other studies of higher plant and cyanobacterial material. The ns kinetics are tightly connected to the ability for O2 evolution. Analysis of the ÎŒs kinetics indicates three phases: (a) the slow phase (t12 ~ 150 ÎŒs in spinach and ~ 500 ÎŒs in Phormidium) reflects the back reaction between Chl-a+II and Qâ; (b) the phase with t125â10 ÎŒs is probably due to a donor which is not connected to an intact water oxidation system; (c) the intermediate ÎŒs component (t12 30â40 ÎŒs) may be related to water oxidation
Breakdown of the Landauer bound for information erasure in the quantum regime
A known aspect of the Clausius inequality is that an equilibrium system
subjected to a squeezing \d S of its entropy must release at least an amount
|\dbarrm Q|=T|\d S| of heat. This serves as a basis for the Landauer
principle, which puts a lower bound for the heat generated by erasure
of one bit of information. Here we show that in the world of quantum
entanglement this law is broken. A quantum Brownian particle interacting with
its thermal bath can either generate less heat or even {\it adsorb} heat during
an analogous squeezing process, due to entanglement with the bath. The effect
exists even for weak but fixed coupling with the bath, provided that
temperature is low enough. This invalidates the Landauer bound in the quantum
regime, and suggests that quantum carriers of information can be much more
efficient than assumed so far.Comment: 13 pages, revtex, 2 eps figure
Naked Singularity Explosion
It is known that the gravitational collapse of a dust ball results in naked
singularity formation from an initial density profile which is physically
reasonable. In this paper, we show that explosive radiation is emitted during
the formation process of the naked singularity.Comment: 6 pages, 3 figures, Accepted for Publication in Phys. Rev. D as a
Rapid Communicatio
Resonant transmission through an open quantum dot
We have measured the low-temperature transport properties of a quantum dot
formed in a one-dimensional channel. In zero magnetic field this device shows
quantized ballistic conductance plateaus with resonant tunneling peaks in each
transition region between plateaus. Studies of this structure as a function of
applied perpendicular magnetic field and source-drain bias indicate that
resonant structure deriving from tightly bound states is split by Coulomb
charging at zero magnetic field.Comment: To be published in Phys. Rev. B (1997). 8 LaTex pages with 5 figure
The distribution of transit durations for Kepler planet candidates and implications for their orbital eccentricities
âIn these times, during the rise in the popularity of institutional repositories, the Society does not forbid authors from depositing their work in such repositories. However, the AAS regards the deposit of scholarly work in such repositories to be a decision of the individual scholar, as long as the individual's actions respect the diligence of the journals and their reviewers.â Original article can be found at : http://iopscience.iop.org/ Copyright American Astronomical SocietyDoppler planet searches have discovered that giant planets follow orbits with a wide range of orbital eccentricities, revolutionizing theories of planet formation. The discovery of hundreds of exoplanet candidates by NASA's Kepler mission enables astronomers to characterize the eccentricity distribution of small exoplanets. Measuring the eccentricity of individual planets is only practical in favorable cases that are amenable to complementary techniques (e.g., radial velocities, transit timing variations, occultation photometry). Yet even in the absence of individual eccentricities, it is possible to study the distribution of eccentricities based on the distribution of transit durations (relative to the maximum transit duration for a circular orbit). We analyze the transit duration distribution of Kepler planet candidates. We find that for host stars with T > 5100 K we cannot invert this to infer the eccentricity distribution at this time due to uncertainties and possible systematics in the host star densities. With this limitation in mind, we compare the observed transit duration distribution with models to rule out extreme distributions. If we assume a Rayleigh eccentricity distribution for Kepler planet candidates, then we find best fits with a mean eccentricity of 0.1-0.25 for host stars with T †5100 K. We compare the transit duration distribution for different subsets of Kepler planet candidates and discuss tentative trends with planetary radius and multiplicity. High-precision spectroscopic follow-up observations for a large sample of host stars will be required to confirm which trends are real and which are the results of systematic errors in stellar radii. Finally, we identify planet candidates that must be eccentric or have a significantly underestimated stellar radius.Peer reviewedFinal Accepted Versio
Monopole characteristics in various Abelian gauges
Renormalization group (RG) smoothing is employed on the lattice to
investigate and to compare the monopole structure of the SU(2) vacuum as seen
in different gauges (maximally Abelian (MAG), Polyakov loop (PG) and Laplacian
gauge (LG)). Physically relevant types of monopoles (LG and MAG) are
distinguished by their behavior near the deconfining phase transition. For the
LG, Abelian projection reproduces well the gauge independent monopole structure
encoded in an auxiliary Higgs field. Density and localization properties of
monopoles, their non-Abelian action and topological charge are studied. Results
are presented confirming the Abelian dominance with respect to the
non-perturbative static potential for all gauges considered.Comment: 36 pages, 12 figure
Semiclassical Instability of the Cauchy Horizon in Self-Similar Collapse
Generic spherically symmetric self-similar collapse results in strong
naked-singularity formation. In this paper we are concerned with particle
creation during a naked-singularity formation in spherically symmetric
self-similar collapse without specifying the collapsing matter. In the generic
case, the power of particle emission is found to be proportional to the inverse
square of the remaining time to the Cauchy horizon (CH). The constant of
proportion can be arbitrarily large in the limit to marginally naked
singularity. Therefore, the unbounded power is especially striking in the case
that an event horizon is very close to the CH because the emitted energy can be
arbitrarily large in spite of a cutoff expected from quantum gravity. Above
results suggest the instability of the CH in spherically symmetric self-similar
spacetime from quantum field theory and seem to support the existence of a
semiclassical cosmic censor. The divergence of redshifts and blueshifts of
emitted particles is found to cause the divergence of power to positive or
negative infinity, depending on the coupling manner of scalar fields to
gravity. On the other hand, it is found that there is a special class of
self-similar spacetimes in which the semiclassical instability of the CH is not
efficient. The analyses in this paper are based on the geometric optics
approximation, which is justified in two dimensions but needs justification in
four dimensions.Comment: 14 pages, 4 figures, minor errors corrected and some sentences added
in the introduction, accepted for publication in Physical Review
Electromagnetic field correlations near a surface with a nonlocal optical response
The coherence length of the thermal electromagnetic field near a planar
surface has a minimum value related to the nonlocal dielectric response of the
material. We perform two model calculations of the electric energy density and
the field's degree of spatial coherence. Above a polar crystal, the lattice
constant gives the minimum coherence length. It also gives the upper limit to
the near field energy density, cutting off its divergence. Near an
electron plasma described by the semiclassical Lindhard dielectric function,
the corresponding length scale is fixed by plasma screening to the Thomas-Fermi
length. The electron mean free path, however, sets a larger scale where
significant deviations from the local description are visible.Comment: 15 pages, 7 figure files (.eps), \documentclass[global]{svjour},
accepted in special issue "Optics on the Nanoscale" (Applied Physics B, eds.
V. Shalaev and F. Tr\"ager
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