138 research outputs found
Probing active forces via a fluctuation-dissipation relation: Application to living cells
We derive a new fluctuation-dissipation relation for non-equilibrium systems
with long-term memory. We show how this relation allows one to access new
experimental information regarding active forces in living cells that cannot
otherwise be accessed. For a silica bead attached to the wall of a living cell,
we identify a crossover time between thermally controlled fluctuations and
those produced by the active forces. We show that the probe position is
eventually slaved to the underlying random drive produced by the so-called
active forces.Comment: 5 page
Comparison of simulated longitudinal profiles of hadronic air showers with MASS2 balloon data
The KASKADE and CORSIKA air shower generators are compared to the data
collected by MASS2 balloon experiment in 1991. The test of longitudinal profile
for proton, helium and muon flux production provide good constraints on these
air shower generators. KASKADE and CORSIKA especially with the new simulator
UrQMD for low energies are found to fit these data well. This study is limited
to a comparison of longitudinal profiles and therefore does not provide
constraints on the overall shower development.Comment: to be published in Astroparticle Physic
Optical Intensity Interferometry with Atmospheric Cherenkov Telescope Arrays
In the 1970s, the Narrabri intensity interferometer was used to measure 32
stellar diameters; some as small as 0.4 milli-arc-seconds (mas). The
interferometer consisted of a pair of 6.5m telescopes with relatively crude
optics, similar to those currently in use as Atmospheric Cherenkov Telescopes
(ACT). We explore the possibility of implementing a modern intensity
interferometer on an ACT array. Developments in fast digital signal processing
technology now make such a system relatively easy to implement, and provide
improved sensitivity. Allowing measurements at short wavelength (<400nm), with
long baselines (> 100m), which are still challenging for Michelson
interferometers, present ACT arrays could be used to probe angular structures
as small as ~0.2mas, and smaller with large array projects already being
discussed. This would provide measurements of stellar diameters, binary
systems, circumstellar environments and, possibly, stellar surface features.
ACT arrays could be used as intensity interferometers during bright moon
periods, providing valuable scientific output for little expense and no impact
on the gamma-ray observing schedule.Comment: Accepted for publicaion in Ap
Juvenile emperor penguin range calls for extended conservation measures in the Southern Ocean
To protect the unique and rich biodiversity of the Southern Ocean, conservation measures such as marine protected areas (MPAs) have been implemented. Currently, the establishment of several additional protection zones is being considered based on the known habitat distributions of key species of the ecosystems including emperor penguins and other marine top predators. However, the distribution of such species at sea is often insufficiently sampled. Specifically, current distribution models focus on the habitat range of adult animals and neglect that immatures and juveniles can inhabit different areas. By tracking eight juvenile emperor penguins in the Weddell Sea over 1 year and performing a meta-analysis including previously known data from other colonies, we show that conservation efforts in the Southern Ocean are insufficient for protecting this highly mobile species, and particularly its juveniles. We find that juveniles spend approximately 90% of their time outside the boundaries of proposed and existing MPAs, and that their distribution extends beyond (greater than 1500 km) the species' extent of occurrence as defined by the International Union for Conservation of Nature. Our data exemplify that strategic conservation plans for the emperor penguin and other long-lived ecologically important species should consider the dynamic habitat range of all age classes
No evidence of microplastic ingestion in emperor penguin chicks (Aptenodytes forsteri) from the Atka Bay colony (Dronning Maud Land, Antarctica)
Microplastic (500 ÎĽm using Attenuated Total Reflection Fourier-transform Infrared (ATR-FTIR) spectroscopy. A total of 85 putative particles, mostly in the shape of fibers (65.9 %), were sorted. However, none of the particles were identified as MP applying state-of-the-art methodology. Sorted fibers were further evidenced to originate from contamination during sample processing and analyses. We find that MP concentrations in the local food web of the Weddell Sea and Dronning Maud Land coastal and marginal sea-ice regions; the feeding grounds to chick-rearing emperor penguin adults, are currently at such low levels that no detectable biomagnification is occurring via trophic transfer. Being in contrast to MP studies on other Antarctic and sub-Antarctic penguin species, our comparative discussion including these studies, highlights the importance for standardized procedures for sampling, sample processing and analyses to obtain comparable results. We further discuss other stomach contents and their potential role for MP detection, as well as providing a baseline for the long-term monitoring of MP in apex predator species from this region
New Astrophysical Opportunities Exploiting Spatio-Temporal Optical Correlations
The space-time correlations of streams of photons can provide fundamentally
new channels of information about the Universe. Today's astronomical
observations essentially measure certain amplitude coherence functions produced
by a source. The spatial correlations of wave fields has traditionally been
exploited in Michelson-style amplitude interferometry. However the technology
of the past was largely incapable of fine timing resolution and recording
multiple beams. When time and space correlations are combined it is possible to
achieve spectacular measurements that are impossible by any other means.
Stellar intensity interferometry is ripe for development and is one of the few
unexploited mechanisms to obtain potentially revolutionary new information in
astronomy. As we discuss below, the modern use of stellar intensity
interferometry can yield unprecedented measures of stellar diameters, binary
stars, distance measures including Cepheids, rapidly rotating stars, pulsating
stars, and short-time scale fluctuations that have never been measured before.Comment: Science white paper prepared for the Astro2010 Decadal Revie
Spectrum and Variability of Mrk501 as observed by the CAT Imaging Telescope
The CAT Imaging Telescope has observed the BL Lac object Markarian 501
between March and August 1997. We report here on the variability over this time
including several large flares. We present also preliminary spectra for all
these data, for the low emission state, and for the largest flare.Comment: 4 pages, 4 figures, Late
Detection of Vhe Gamma-Rays from MRK 501 with the Cat Imaging Telescope
The CAT imaging telescope on the site on the former solar plant Themis has
been observing gamma-rays from Mrk501 above 220 GeV in March and April 1997.
This source is shown to be highly variable and the light curve is presented.
The detected gamma-ray rate for the most intense flare is in excess of 10 per
minute.Comment: 5 pages, 4 figures, Tex, contribution to 25th ICRC Durba
Observation of the Crab Nebula Gamma-Ray Emission Above 220 Gev by the Cat Cherenkov Imaging Telescope
The CAT imaging telescope, recently built on the site of the former solar
plant Themis (French Pyrenees), observed gamma-rays from the Crab nebula from
October 1996 to March 1997. This steady source, often considered as the
standard candle of very-high-energy gamma-ray astronomy, is used as a test-beam
to probe the performances of the new telescope, particularly its energy
threshold (220 GeV at 20 degrees zenith angle) and the stability of its
response. Due to the fine-grain camera, an accurate analysis of the
longitudinal profiles of shower images is performed, yielding the source
position in two dimensions for each individual shower.Comment: 5 pages, 3 figures, Tex, contribution to 25th ICRC Durba
Very High Energy Gamma-ray spectral properties of Mrk 501 from CAT Cerenkov telescope observations in 1997
The BL Lac object Mrk 501 went into a very high state of activity during
1997, both in VHE gamma-rays and X-rays. We present here results from
observations at energies above 250 GeV carried out between March and October
1997 with the CAT Cerenkov imaging Telescope. The average differential spectrum
between 30 GeV and 13 TeV shows significant curvature and is well represented
by phi_0 * E_TeV^{-(alpha + beta*log10(E_TeV))}, with: phi_0 = 5.19 +/- 0.13
{stat} +/- 0.12 {sys-MC} +1.66/-1.04 {sys-atm} * 10^-11 /cm^2/s/TeV alpha =
2.24 +/- 0.04 {stat} +/- 0.05 {sys} beta = 0.50 +/- 0.07 {stat} (negligible
systematics). The TeV spectral energy distribution of Mrk 501 clearly peaks in
the range 500 GeV-1 TeV. Investigation of spectral variations shows a
significant hardness-intensity correlation with no measurable effect on the
curvature. This can be described as an increase of the peak TeV emission energy
with intensity. Simultaneous and quasi-simultaneous CAT VHE gamma-ray and
BeppoSAX hard X-ray detections for the highest recorded flare on 16th April and
for lower-activity states of the same period show correlated variability with a
higher luminosity in X-rays than in gamma-rays. The observed spectral energy
distribution and the correlated variability between X-rays and gamma-rays, both
in amplitude and in hardening of spectra, favour a two-component emission
scheme where the low and high energy components are attributed to synchrotron
and inverse Compton (IC) radiation, respectively.Comment: Submitted to Astronomy and Astrophysics, 8 pages including 6 figures.
Published with minor change
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