1,732 research outputs found
Characteristics of AlGaAs/GaAs multiple quantum well infrared detectors
Researchers fabricated and characterized several AlGaAs/GaAs multiple quantum well infrared detectors to evaluate the ultimate performance of these devices for low infrared background applications. The detectors were designed to have a single bound state in the quantum well and the first excited state in the continuum above the AlGaAs conduction band edge. The difference in energy between the two levels, as determined by the quantum well width and aluminum mole fraction in the barrier, was chosen such that peak absorption would occur near 8 microns. The initial structures studied comprised 50 periods with 40 A well widths and 300 A Al(0.28)Ga(0.72)As barriers. The performance of these detectors are summarized. To better interpret these results and design optimized detectors, researchers modeled both the detector noise and tunneling currents. The noise model correctly predicts that multiple quantum well detectors will, indeed, exhibit noise lower than full shot noise. The tunneling current model predicts the dark current versus bias for any choice of design parameters in a multiple quantum well detector. This model predicts a substantially reduced dark current (x 10(exp 04)) for samples with 400 A barriers. To evaluate structures with thicker barriers, researchers fabricated and characterized detectors with 400 A and 500 A barriers; a comparison of detector dark currents is shown. These results are consistent with the predictions of the dark current model
Deciphering Spectral Fingerprints of Habitable Extrasolar Planets
In this paper we discuss how we can read a planets spectrum to assess its
habitability and search for the signatures of a biosphere. After a decade rich
in giant exoplanet detections, observation techniques have now reached the
ability to find planets of less than 10 MEarth (so called Super-Earths) that
may potentially be habitable. How can we characterize those planets and assess
if they are habitable? The new field of extrasolar planet search has shown an
extraordinary ability to combine research by astrophysics, chemistry, biology
and geophysics into a new and exciting interdisciplinary approach to understand
our place in the universe. The results of a first generation mission will most
likely result in an amazing scope of diverse planets that will set planet
formation, evolution as well as our planet in an overall context.Comment: 17 pages, 10 figures, Astrobiology, 10, 1, 201
An improved method for high-throughput quantification of autophagy in mammalian cells
Autophagy is a cellular homeostatic pathway with functions ranging from cytoplasmic protein turnover to immune defense. Therapeutic modulation of autophagy has been demonstrated to positively impact the outcome of autophagy-dysregulated diseases such as cancer or microbial infections. However, currently available agents lack specificity, and new candidates for drug development or potential cellular targets need to be identified. Here, we present an improved method to robustly detect changes in autophagy in a high-throughput manner on a single cell level, allowing effective screening. This method quantifies eGFP-LC3B positive vesicles to accurately monitor autophagy. We have significantly streamlined the protocol and optimized it for rapid quantification of large numbers of cells in little time, while retaining accuracy and sensitivity. Z scores up to 0.91 without a loss of sensitivity demonstrate the robustness and aptness of this approach. Three exemplary applications outline the value of our protocols and cell lines: (I) Examining autophagy modulating compounds on four different cell types. (II) Monitoring of autophagy upon infection with e.g. measles or influenza A virus. (III) CRISPR/Cas9 screening for autophagy modulating factors in T cells. In summary, we offer ready-to-use protocols to generate sensitive autophagy reporter cells and quantify autophagy in high-throughput assays
The HIPASS Catalogue - II. Completeness, Reliability, and Parameter Accuracy
The HI Parkes All Sky Survey (HIPASS) is a blind extragalactic HI 21-cm
emission line survey covering the whole southern sky from declination -90 to
+25. The HIPASS catalogue (HICAT), containing 4315 HI-selected galaxies from
the region south of declination +2, is presented in Meyer et al. (2004a, Paper
I). This paper describes in detail the completeness and reliability of HICAT,
which are calculated from the recovery rate of synthetic sources and follow-up
observations, respectively. HICAT is found to be 99 per cent complete at a peak
flux of 84 mJy and an integrated flux of 9.4 Jy km/s. The overall reliability
is 95 per cent, but rises to 99 per cent for sources with peak fluxes >58 mJy
or integrated flux > 8.2 Jy km/s. Expressions are derived for the uncertainties
on the most important HICAT parameters: peak flux, integrated flux, velocity
width, and recessional velocity. The errors on HICAT parameters are dominated
by the noise in the HIPASS data, rather than by the parametrization procedure.Comment: Accepted for publication in MNRAS. 12 pages, 11 figures. Paper with
higher resolution figures can be downloaded from http://hipass.aus-vo.or
Photon-Photon and Electron-Photon Colliders with Energies Below a TeV
We investigate the potential for detecting and studying Higgs bosons in and collisions at future linear colliders with energies below a TeV. Our study incorporates realistic spectra based on available laser technology, and NLC and CLIC acceleration techniques. Results include detector simulations. We study the cases of: a) a SM-like Higgs boson based on a devoted low energy machine with GeV; b) the heavy MSSM Higgs bosons; and c) charged Higgs bosons in collisions.We investigate the potential for detecting and studying Higgs bosons in and collisions at future linear colliders with energies below a TeV. Our study incorporates realistic spectra based on available laser technology, and NLC and CLIC acceleration techniques. Results include detector simulations. We study the cases of: a) a SM-like Higgs boson based on a devoted low energy machine with GeV; b) the heavy MSSM Higgs bosons; and c) charged Higgs bosons in collisions
Low CO Luminosities in Dwarf Galaxies
[Abridged] We present maps of CO 2-1 emission covering the entire
star-forming disks of 16 nearby dwarf galaxies observed by the IRAM HERACLES
survey. The data have 13 arcsec angular resolution, ~250 pc at our average
distance of 4 Mpc, and sample the galaxies by 10-1000 resolution elements. We
apply stacking techniques to perform the first sensitive search for CO emission
in dwarfs outside the Local Group ranging from single lines-of-sight, stacked
over IR-bright regions of embedded star formation, and stacked over the entire
galaxy. We detect 5 dwarfs in CO with total luminosities of L_CO = 3-28 1e6
Kkmspc2. The other 11 dwarfs remain undetected in CO even in the stacked data
and have L_CO < 0.4-8 1e6 Kkmspc2. We combine our sample of dwarfs with a large
literature sample of spirals to study scaling relations of L_CO with M_B and
metallicity. We find that dwarfs with metallicities of Z ~ 1/2-1/10 Z_sun have
L_CO about 1e2-1e4x smaller than spirals and that their L_CO per unit L_B is
10-100x smaller. A comparison with tracers of star formation (FUV and 24
micron) shows that L_CO per unit SFR is 10-100x smaller in dwarfs. One possible
interpretation is that dwarfs form stars much more efficiently, however we
argue that the low L_CO/SFR ratio is due to significant changes of the CO-to-H2
conversion factor, alpha_CO, in low metallicity environments. Assuming a
constant H2 depletion time of 1.8 Gyr (as found for nearby spirals) implies
alpha_CO values for dwarfs with Z ~ 1/2-1/10 Z_sun that are more than 10x
higher than those found in solar metallicity spirals. This significant increase
of alpha_CO at low metallicity is consistent with previous studies, in
particular those which model dust emission to constrain H2 masses. Even though
it is difficult to parameterize the metallicity dependence of alpha_CO, our
results suggest that CO is increasingly difficult to detect at lower
metallicities.Comment: Accepted for publication in the Astronomical Journal, 19 pages, 7
figure
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