1,877 research outputs found
Float zone experiments in space
The molten zone/freezing crystal interface system and all the mechanisms were examined. If Marangoni convection produces oscillatory flows in the float zone of semiconductor materials, such as silicon, then it is unlikely that superior quality crystals can be grown in space using this process. The major goals were: (1) to determine the conditions for the onset of Marangoni flows in molten tin, a model system for low Prandtl number molten semiconductor materials; (2) to determine whether the flows can be suppressed by a thin oxide layer; and (3) based on experimental and mathematical analysis, to predict whether oscillatory flows will occur in the float zone silicon geometry in space, and if so, could it be suppressed by thin oxide or nitride films. Techniques were developed to analyze molten tin surfaces in a UHV system in a disk float zone geometry to minimize buoyancy flows. The critical Marangoni number for onset of oscillatory flows was determined to be greater than 4300 on atomically clean molten tin surfaces
Timing as a sexually selected trait: the right mate at the right moment
Sexual selection favours the expression of traits in one sex that attract members of the opposite sex for mating. The nature of sexually selected traits such as vocalization, colour and ornamentation, their fitness benefits as well as their costs have received ample attention in field and laboratory studies. However, sexually selected traits may not always be expressed: coloration and ornaments often follow a seasonal pattern and behaviours may be displayed only at specific times of the day. Despite the widely recognized differences in the daily and seasonal timing of traits and their consequences for reproductive success, the actions of sexual selection on the temporal organization of traits has received only scant attention. Drawing on selected examples from bird and mammal studies, here we summarize the current evidence for the daily and seasonal timing of traits. We highlight that molecular advances in chronobiology have opened exciting new opportunities for identifying the genetic targets that sexual selection may act on to shape the timing of trait expression. Furthermore, known genetic links between daily and seasonal timing mechanisms lead to the hypothesis that selection on one timescale may simultaneously also affect the other. We emphasize that studies on the timing of sexual displays of both males and females from wild populations will be invaluable for understanding the nature of sexual selection and its potential to act on differences within and between the sexes in timing. Molecular approaches will be important for pinpointing genetic components of biological rhythms that are targeted by sexual selection, and to clarify whether these represent core or peripheral components of endogenous clocks. Finally, we call for a renewed integration of the fields of evolution, behavioural ecology and chronobiology to tackle the exciting question of how sexual selection contributes to the evolution of biological clocks.This article is part of the themed issue 'Wild clocks: integrating chronobiology and ecology to understand timekeeping in free-living animals'
SPEDEN: Reconstructing single particles from their diffraction patterns
Speden is a computer program that reconstructs the electron density of single
particles from their x-ray diffraction patterns, using a single-particle
adaptation of the Holographic Method in crystallography. (Szoke, A., Szoke, H.,
and Somoza, J.R., 1997. Acta Cryst. A53, 291-313.) The method, like its parent,
is unique that it does not rely on ``back'' transformation from the diffraction
pattern into real space and on interpolation within measured data. It is
designed to deal successfully with sparse, irregular, incomplete and noisy
data. It is also designed to use prior information for ensuring sensible
results and for reliable convergence. This article describes the theoretical
basis for the reconstruction algorithm, its implementation and quantitative
results of tests on synthetic and experimentally obtained data. The program
could be used for determining the structure of radiation tolerant samples and,
eventually, of large biological molecular structures without the need for
crystallization.Comment: 12 pages, 10 figure
Tillage system effect on the epidemic of soybean brown spot.
Six field experiments were carried out during the summers of 1997 to 2003 to evaluate disease progress of soybean brown spot caused by Septoria glycines considering two tillage systems, conventional and no-tillage (wheat was cultivated during winter in all plots). Two logistic models were fitted to the disease progress data: (i) a logistic model with constant disease progress rate r [y=1/(1+(1/y0-1)exp(-rt)), where y0 is the initial disease level at time t=0] and (ii) a logistic model with an exponentially increasing progress rate r(t)=r0 ebt [y=1/(1+(1/y0-1) exp(r0/b(1-ebt))), where r0 is the initial progress rate at time t=0, b the rate increasing parameter, and y0 again the initial disease level]. The logistic model with constant rate underestimated disease incidence on the first disease assessment in nine out of twelve epidemics. The logistic model with an increasing rate gave a better fit to all disease progress curves (R2 between 0.90 and 0.99; no pattern in the residuals). According to this model, y0 was in most cases (four out of six) significantly smaller in the plots with no-tillage compared with conventional tillage, but no differences were detected in the initial rate parameter r0 and the rate increasing parameter b (with one exception). It is proposed that these results are due to higher susceptibility of old leaflets compared with young leaflets, as demonstrated by artificial inoculation: In four laboratory experiments the mean brown spot severity was 16.7 % on old leaflets but only 3.9 % on young leaflets
Measurement of the ground-state distributions in bistable mechanically interlocked molecules using slow scan rate cyclic voltammetry
In donorâacceptor mechanically interlocked molecules that exhibit bistability, the relative populations of the translational isomersâpresent, for example, in a bistable [2]rotaxane, as well as in a couple of bistable [2]catenanes of the donorâacceptor vintageâcan be elucidated by slow scan rate cyclic voltammetry. The practice of transitioning from a fast scan rate regime to a slow one permits the measurement of an intermediate redox couple that is a function of the equilibrium that exists between the two translational isomers in the case of all three mechanically interlocked molecules investigated. These intermediate redox potentials can be used to calculate the ground-state distribution constants, K. Whereas, (i) in the case of the bistable [2]rotaxane, composed of a dumbbell component containing Ï-electron-rich tetrathiafulvalene and dioxynaphthalene recognition sites for the ring component (namely, a tetracationic cyclophane, containing two Ï-electron-deficient bipyridinium units), a value for K of 10 ± 2 is calculated, (ii) in the case of the two bistable [2]catenanesâone containing a crown ether with tetrathiafulvalene and dioxynaphthalene recognition sites for the tetracationic cyclophane, and the other, tetrathiafulvalene and butadiyne recognition sitesâthe values for K are orders (one and three, respectively) of magnitude greater. This observation, which has also been probed by theoretical calculations, supports the hypothesis that the extra stability of one translational isomer over the other is because of the influence of the enforced side-on donorâacceptor interactions brought about by both Ï-electron-rich recognition sites being part of a macrocyclic polyether
Progress in Three-Dimensional Coherent X-Ray Diffraction Imaging
The Fourier inversion of phased coherent diffraction patterns offers images
without the resolution and depth-of-focus limitations of lens-based tomographic
systems. We report on our recent experimental images inverted using recent
developments in phase retrieval algorithms, and summarize efforts that led to
these accomplishments. These include ab-initio reconstruction of a
two-dimensional test pattern, infinite depth of focus image of a thick object,
and its high-resolution (~10 nm resolution) three-dimensional image.
Developments on the structural imaging of low density aerogel samples are
discussed.Comment: 5 pages, X-Ray Microscopy 2005, Himeji, Japa
Making SPIFFI SPIFFIER: Upgrade of the SPIFFI instrument for use in ERIS and performance analysis from re-commissioning
SPIFFI is an AO-fed integral field spectrograph operating as part of SINFONI
on the VLT, which will be upgraded and reused as SPIFFIER in the new VLT
instrument ERIS. In January 2016, we used new technology developments to
perform an early upgrade to optical subsystems in the SPIFFI instrument so
ongoing scientific programs can make use of enhanced performance before ERIS
arrives in 2020. We report on the upgraded components and the performance of
SPIFFI after the upgrade, including gains in throughput and spatial and
spectral resolution. We show results from re-commissioning, highlighting the
potential for scientific programs to use the capabilities of the upgraded
SPIFFI. Finally, we discuss the additional upgrades for SPIFFIER which will be
implemented before it is integrated into ERIS.Comment: 20 pages, 12 figures. Proceedings from SPIE Astronomical Telescopes
and Instrumentation 201
GASP II. A MUSE view of extreme ram-pressure stripping along the line of sight: kinematics of the jellyfish galaxy JO201
This paper presents a spatially-resolved kinematic study of the jellyfish
galaxy JO201, one of the most spectacular cases of ram-pressure stripping (RPS)
in the GASP (GAs Stripping Phenomena in Galaxies with MUSE) survey. By studying
the environment of JO201, we find that it is moving through the dense
intra-cluster medium of Abell 85 at supersonic speeds along our line of sight,
and that it is likely accompanied by a small group of galaxies. Given the
density of the intra-cluster medium and the galaxy's mass, projected position
and velocity within the cluster, we estimate that JO201 must so far have lost
~50% of its gas during infall via RPS. The MUSE data indeed reveal a smooth
stellar disk, accompanied by large projected tails of ionised (Halpha) gas,
composed of kinematically cold (velocity dispersion <40km/s) star-forming knots
and very warm (>100km/s) diffuse emission which extend out to at least ~50 kpc
from the galaxy centre. The ionised Halpha-emitting gas in the disk rotates
with the stars out to ~6 kpc but in the disk outskirts becomes increasingly
redshifted with respect to the (undisturbed) stellar disk. The observed
disturbances are consistent with the presence of gas trailing behind the
stellar component, resulting from intense face-on RPS happening along the line
of sight. Our kinematic analysis is consistent with the estimated fraction of
lost gas, and reveals that stripping of the disk happens outside-in, causing
shock heating and gas compression in the stripped tails.Comment: ApJ, revised version after referee comments, 15 pages, 16 figures.
The interactive version of Figure 9 can be viewed at
web.oapd.inaf.it/gasp/publications.htm
Enhancing capacity of coherent optical information storage and transfer in a Bose-Einstein condensate
Coherent optical information storage capacity of an atomic Bose-Einstein
condensate is examined. Theory of slow light propagation in atomic clouds is
generalized to short pulse regime by taking into account group velocity
dispersion. It is shown that the number of stored pulses in the condensate can
be optimized for a particular coupling laser power, temperature and interatomic
interaction strength. Analytical results are derived for semi-ideal model of
the condensate using effective uniform density zone approximation. Detailed
numerical simulations are also performed. It is found that axial density
profile of the condensate protects the pulse against the group velocity
dispersion. Furthermore, taking into account finite radial size of the
condensate, multi-mode light propagation in atomic Bose-Einstein condensate is
investigated. The number of modes that can be supported by a condensate is
found. Single mode condition is determined as a function of experimentally
accessible parameters including trap size, temperature, condensate number
density and scattering length. Quantum coherent atom-light interaction schemes
are proposed for enhancing multi-mode light propagation effects.Comment: 12pages. Laser Physics, in pres
GMOS Integral Field Spectroscopy of a Merging System with Enhanced Balmer Absorption
In this paper we present the three dimensional dynamics of the galaxy SDSS
J101345.39+011613.66, selected for its unusually strong Balmer absorption lines
(Wo(H-delta)=7.5A). Using the GMOS-South IFU in Nod & Shuffle mode we have
mapped the continuum and optical absorption lines of this z=0.1055 field
galaxy. This galaxy has a disturbed morphology, with a halo of diffuse material
distributed asymmetrically toward the north. Using the [OII] emission line
(Wo([OII])=4.1A) we find that the gas and hot OB stars are offset from the
older stars in the system. The gas also has a spatially extended and elongated
morphology with a velocity gradient of 100+/-20km/s across 6kpc in projection.
Using the strong H-gamma and H-delta absorption lines we find that the A- stars
are widely distributed across the system and are not centrally concentrated
arguing that the A-star population has formed in molecular clouds outside the
nucleus. By cross correlating the spectra from the datacube with an A-star
template we find evidence that the A-star population has a 40km/s shear in the
same direction as the gas. The disturbed morphology, strong colour gradients
and strong H-delta and H-gamma absorption lines in SDSS J101345.39 argue that
this is a recent tidal interaction/merger between a passive elliptical and
star-forming galaxy. Although based on a single object, these results show that
we can spatially resolve and constrain the dynamics of this short lived (yet
important) phase of galaxy formation in which the evolutionary process take
galaxies from star-forming to their quiescent end products.Comment: 7 pages, 7 figures. Accepted for publication in Ap
- âŠ