340 research outputs found
Random sequential adsorption of shrinking or spreading particles
We present a model of one-dimensional irreversible adsorption in which
particles once adsorbed immediately shrink to a smaller size or expand to a
larger size. Exact solutions for the fill factor and the particle number
variance as a function of the size change are obtained. Results are compared
with approximate analytical solutions.Comment: 9 pages, 8 figure
The Effects of 2-Br-Alpha-Ergocryptine on Sodium Levels in Gulf Killifish (Fundulus grandis) and Other Vertebrates
Readout electronics for the SiPM tracking plane in the NEXT-1 prototype
NEXT is a new experiment to search for neutrinoless double beta decay using a 100 kg radio-pure high-pressure gaseous xenon TPC with electroluminescence readout. A large-scale prototype with a SiPM tracking plane has been built. The primary electron paths can be reconstructed from time-resolved measurements of the light that arrives to the SiPM plane. Our approach is to measure how many photons have reached each SiPM sensor each microsecond with a gated integrator. We have designed and tested a 16-channel front-end board that includes the analog paths and a digital section. Each analog path consists of three different stages: a transimpedance amplifier, a gated integrator and an offset and gain control stage. Measurements show good linearity and the ability to detect single photoelectrons. © 2011 Elsevier B.V.The authors would like to acknowledge the support of the NEXT Collaboration, the DATE team at CERN PH-AID and the CONSOLIDER-INGENIO2010 grant CSD2008-0037 (Canfranc Underground Physics) from the Spanish Ministry of Science and Innovation.Herrero Bosch, V.; Toledo Alarcón, JF.; Català Pérez, JM.; Esteve Bosch, R.; Gil Ortiz, A.; Lorca, D.; Monzó Ferrer, JM.... (2012). Readout electronics for the SiPM tracking plane in the NEXT-1 prototype. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. 695:229-232. https://doi.org/10.1016/j.nima.2011.12.057S22923269
Atomically resolved phase transition of fullerene cations solvated in helium droplets
Helium has a unique phase diagram and below 25 bar it does not form a solid
even at the lowest temperatures. Electrostriction leads to the formation of a
solid layer of helium around charged impurities at much lower pressures in
liquid and superfluid helium. These so-called ‘Atkins snowballs’ have been
investigated for several simple ions. Here we form HenC60+ complexes with n
exceeding 100 via electron ionization of helium nanodroplets doped with C60.
Photofragmentation of these complexes is measured by merging a tunable narrow-
bandwidth laser beam with the ions. A switch from red- to blueshift of the
absorption frequency of HenC60+ on addition of He atoms at n=32 is associated
with a phase transition in the attached helium layer from solid to partly
liquid (melting of the Atkins snowball). Elaborate molecular dynamics
simulations using a realistic force field and including quantum effects
support this interpretation
Searching for interstellar C60+ using a new method for high signal-to-noise HST/STIS spectroscopy
Due to recent advances in laboratory spectroscopy, the first optical detection of a very large molecule has been claimed in the diffuse interstellar medium (ISM): (ionized Buckminsterfullerene). Confirming the presence of this molecule would have significant implications regarding the carbon budget and chemical complexity of the ISM. Here we present results from a new method for ultra-high signal-to-noise ratio (S/N) spectroscopy of background stars in the near-infrared (at wavelengths of 0.9–1 μm), using the Hubble Space Telescope (HST) Imaging Spectrograph (STIS) in a previously untested "STIS scan" mode. The use of HST provides the crucial benefit of eliminating the need for error-prone telluric-correction methods in the part of the spectrum where the bands lie and where the terrestrial water vapor contamination is severe. Our STIS spectrum of the heavily reddened B0 supergiant star BD+63 1964 reaches an unprecedented S/N for this instrument (~600–800), allowing the detection of the diffuse interstellar band (DIB) at 9577 Å attributed to , as well as new DIBs in the near-IR. Unfortunately, the presence of overlapping stellar lines, and the unexpected weakness of the bands in this sightline, prevents conclusive detection of the weaker bands. A probable correlation between the 9577 Å DIB strength and interstellar radiation field is identified, which suggests that more strongly irradiated interstellar sightlines will provide the optimal targets for future searches
Ultra High Energy Cosmology with POLARBEAR
Observations of the temperature anisotropy of the Cosmic Microwave Background
(CMB) lend support to an inflationary origin of the universe, yet no direct
evidence verifying inflation exists. Many current experiments are focussing on
the CMB's polarization anisotropy, specifically its curl component (called
"B-mode" polarization), which remains undetected. The inflationary paradigm
predicts the existence of a primordial gravitational wave background that
imprints a unique B-mode signature on the CMB's polarization at large angular
scales. The CMB B-mode signal also encodes gravitational lensing information at
smaller angular scales, bearing the imprint of cosmological large scale
structures (LSS) which in turn may elucidate the properties of cosmological
neutrinos. The quest for detection of these signals; each of which is orders of
magnitude smaller than the CMB temperature anisotropy signal, has motivated the
development of background-limited detectors with precise control of systematic
effects. The POLARBEAR experiment is designed to perform a deep search for the
signature of gravitational waves from inflation and to characterize lensing of
the CMB by LSS. POLARBEAR is a 3.5 meter ground-based telescope with 3.8
arcminute angular resolution at 150 GHz. At the heart of the POLARBEAR receiver
is an array featuring 1274 antenna-coupled superconducting transition edge
sensor (TES) bolometers cooled to 0.25 Kelvin. POLARBEAR is designed to reach a
tensor-to-scalar ratio of 0.025 after two years of observation -- more than an
order of magnitude improvement over the current best results, which would test
physics at energies near the GUT scale. POLARBEAR had an engineering run in the
Inyo Mountains of Eastern California in 2010 and will begin observations in the
Atacama Desert in Chile in 2011.Comment: 8 pages, 6 figures, DPF 2011 conference proceeding
Radiation hardness studies of a 130 nm Silicon Germanium BiCMOS technology with a dedicated ASIC
We present the radiation hardness studies on the bipolar devices of the 130 nm 8WL Silicon Germanium (SiGe) BiCMOS technology from IBM. This technology has been proposed as one of the candidates for the Front-End (FE) readout chip of the upgraded Inner Detector (ID) and the Liquid Argon Calorimeter (LAr) of the ATLAS Upgrade experiment. After neutron irradiations, devices remain at acceptable performances at the maximum radiation levels expected in the Si tracker and LAr calorimeter
The new generation CMB B-mode polarization experiment: POLARBEAR
We describe the Cosmic Microwave Background (CMB) polarization experiment
called Polarbear. This experiment will use the dedicated Huan Tran Telescope
equipped with a powerful 1,200-bolometer array receiver to map the CMB
polarization with unprecedented accuracy. We summarize the experiment, its
goals, and current status
South Pole Telescope Detections of the Previously Unconfirmed Planck Early SZ Clusters in the Southern Hemisphere
We present South Pole Telescope (SPT) observations of the five galaxy cluster
candidates in the southern hemisphere which were reported as unconfirmed in the
Planck Early Sunyaev-Zel'dovich (ESZ) sample. One cluster candidate, PLCKESZ
G255.62-46.16, is located in the 2500-square-degree SPT SZ survey region and
was reported previously as SPT-CL J0411-4819. For the remaining four
candidates, which are located outside of the SPT SZ survey region, we performed
short, dedicated SPT observations. Each of these four candidates was strongly
detected in maps made from these observations, with signal-to-noise ratios
ranging from 6.3 to 13.8. We have observed these four candidates on the
Magellan-Baade telescope and used these data to estimate cluster redshifts from
the red sequence. Resulting redshifts range from 0.24 to 0.46. We report
measurements of Y_0.75', the integrated Comptonization within a 0.75' radius,
for all five candidates. We also report X-ray luminosities calculated from
ROSAT All-Sky Survey catalog counts, as well as optical and improved SZ
coordinates for each candidate. The combination of SPT SZ measurements, optical
red-sequence measurements, and X-ray luminosity estimates demonstrates that
these five Planck ESZ cluster candidates do indeed correspond to real galaxy
clusters with redshifts and observable properties consistent with the rest of
the ESZ sample.Comment: 7 emulateapj pages, 4 figures, 1 table. Revised to match published
versio
A Measurement of the Correlation of Galaxy Surveys with CMB Lensing Convergence Maps from the South Pole Telescope
We compare cosmic microwave background lensing convergence maps derived from South Pole Telescope (SPT) data with galaxy survey data from the Blanco Cosmology Survey, WISE, and a new large Spitzer/IRAC field designed to overlap with the SPT survey. Using optical and infrared catalogs covering between 17 and 68 deg^2 of sky, we detect a correlation between the SPT convergence maps and each of the galaxy density maps at >4σ, with zero correlation robustly ruled out in all cases. The amplitude and shape of the cross-power spectra are in good agreement with theoretical expectations and the measured galaxy bias is consistent with previous work. The detections reported here utilize a small fraction of the full 2500 deg^2 SPT survey data and serve as both a proof of principle of the technique and an illustration of the potential of this emerging cosmological probe
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