2,602,617 research outputs found
Duality, Time-asymmetry and the Condensation of Vacuum
A variant of the divergence theory for vacuum-condensation developed in a
previous communication is analyzed from the viewpoint of a 'time' asymmetric
law in vacuum. This law is found to establish a substantial distinction between
dynamically allowed vacuum-configurations related by signature changing duality
transformations.Comment: 6 pages, latex fil
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The pupillary response of cephalopods
This paper provides the first detailed description of the time courses of light-evoked pupillary constriction for two species of cephalopods, Sepia officinalis (a cuttlefish) and Eledone cirrhosa (an octopus). The responses are much faster than hitherto reported, full contraction in Sepia taking less than 1 s, indicating it is among the most rapid pupillary responses in the animal kingdom. We also describe the dependence of the degree of pupil constriction on the level of ambient illumination and show considerable variability between animals. Furthermore, both Sepia and Eledone lack a consensual light-evoked pupil response. Pupil dilation following darkness in Sepia is shown to be very variable, often occurring within a second but at other times taking considerably longer. This may be the result of extensive light-independent variations in pupil diameter in low levels of illumination
Gifford-McMahon refrigerator with split cold head
Leybold-Heraeus Co. have developed, built and successfully tested a Gifford-McMahon cryocooler with splitted cold head for cooling a cryopump. The refrigerating part of the cold head and the gas flow control device have been separated (splitted cold head) and the distance between them is bridged by only two thin lines for carrying the working gas. Due to this separation the size of the refrigerating part is virtually defined only by the size of the displacers whilst the gas flow control device can be of any desired design. It has been shown that dimensioning of the connecting lines and the corresponding losses became less critical with increasing size of the expander, but additional cooling in proportion to the refrigerating capacity is required
Hydrogenated grain boundaries in graphene
We have investigated by means of first principles calculations the structural
and electronic properties of hydrogenated graphene structures with distinct
grain boundary defects. Our total energy results reveal that the adsorption of
a single H is more stable at grain boundary defect. The electronic structure of
the grains boundaries upon hydrogen adsorption have been examined. Further
total energy calculations indicate that the adsorption of two H on two neighbor
carbons, forming a basic unit of graphane, is more stable at the defect region.
Therefore, we expect that these extended defects would work as a nucleation
region for the formation of a narrow graphane strip embedded in graphene
region
Study of a colliding laser-produced plasma by analysis of time and space-resolved image spectra
The interaction of two counter-propagating laser-produced plasmas was studied using simultaneous
imaging and spectroscopic techniques. Spectrally-filtered time-gated ICCD imaging was used
to obtain information about the spatial dynamics and temporal evolution of the collision process.
While, time-resolved imaging spectroscopy was used to determine the spatial and temporal distributions
of electron temperature and density within the interaction region. We examine specifically
the interaction of plasmas whose parameters match those typically used in pulsed laser deposition
of thin films. These low temperature plasmas are highly collisional leading to the creation of a
pronounced stagnation layer in the interaction region
X-rays from the Eclipsing Millisecond Pulsar PSR J1740-5340 in the Globular Cluster NGC 6397
The millisecond pulsar PSR J1740-5340 in the globular cluster NGC 6397 shows
radio eclipses over ~40% of its binary orbit. A first Chandra observation
revealed indications for the X-ray flux being orbit dependent as well. In this
work we analysed five data sets of archival Chandra data taken between 2000 and
2007 in order to investigate the emission across the pulsar's binary orbit.
Utilizing archival Chandra observations of PSR J1740-5340, we have performed a
systematic timing and spectral analysis of this binary system. Using a
chi-square-test the significance for intra-binary orbital modulation is found
to be between 88.5% and 99.6%, depending on the number of phase bins used to
construct the light curve. Applying the unbiased statistical Kolmogorov-Smirnov
(KS) test did not indicate any significant intra-binary orbital modulation,
though. However, comparing the counting rates observed at different epochs a
flux variability on times scales of days to years is indicated. The possible
origin of the X-ray emission is discussed in a number of different scenarios.Comment: 5 pages, 4 figures. Accepted for publication in Astronomy and
Astrophysic
High-temperature gas/liquid stress relaxometers
Two relaxometers allow testing of elastomers in various fluids. First relaxometer uses fork-like loading spacer interposed between loading lever and support ring, so that sample is stretched predetermined amount. In second relaxometer, degree of initial elongation is set by means of adjustable collar, which, when locked in place on piston rod, enables sample to be stretched predetermined length
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Helium isotopic ratios in carbonaceous chondrites: Significant for the early solar nebula and circumstellar diamonds?
Stepwise etching of acid-resistant residues from carbonaceous chondrites yields a new, extraordinarily low He isotopic ratio for phase Q that might represent early solar nebula composition. A much lower ratio possibly characterizes He-P3 from circumstellar diamonds
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