4,608 research outputs found
Earthshine observation of vegetation and implication for life detection on other planets - A review of 2001 - 2006 works
The detection of exolife is one of the goals of very ambitious future space
missions that aim to take direct images of Earth-like planets. While
associations of simple molecules present in the planet's atmosphere (,
, etc.) have been identified as possible global biomarkers, we
review here the detectability of a signature of life from the planet's surface,
i.e. the green vegetation. The vegetation reflectance has indeed a specific
spectrum, with a sharp edge around 700 nm, known as the "Vegetation Red Edge"
(VRE). Moreover vegetation covers a large surface of emerged lands, from
tropical evergreen forest to shrub tundra. Thus considering it as a potential
global biomarker is relevant. Earthshine allows to observe the Earth as a
distant planet, i.e. without spatial resolution. Since 2001, Earthshine
observations have been used by several authors to test and quantify the
detectability of the VRE in the Earth spectrum. The egetation spectral
signature is detected as a small 'positive shift' of a few percents above the
continuum, starting at 700 nm. This signature appears in most spectra, and its
strength is correlated with the Earth's phase (visible land versus visible
ocean). The observations show that detecting the VRE on Earth requires a
photometric relative accuracy of 1% or better. Detecting something equivalent
on an Earth-like planet will therefore remain challenging, moreover considering
the possibility of mineral artifacts and the question of 'red edge'
universality in the Universe.Comment: Invited talk in "Strategies for Life Detection" (ISSI Bern, 24-28
April 2006) to appear in a hardcopy volume of the ISSI Space Science Series,
Eds, J. Bada et al., and also in an issue of Space Science Reviews. 13 pages,
8 figures, 1 tabl
Jet-Tagged Back-Scattering Photons For Quark Gluon Plasma Tomography
Several sources of direct photons are known to contribute to the total photon
yield in high energy nuclear collisions. All of these photons carry
characteristic and important information on the initial nuclei or the hot and
dense fireball created in the collision. We investigate the possibility to
separate photons from back-scattering of high momentum quarks off quark gluon
plasma from other sources. Their unique kinematics can be utilized through high
energy jet triggers on the away-side. We discuss the basic idea and estimate
the feasibility of such a measurement at RHIC and LHC.Comment: Contribution to Hard Probes 2012; 4 pages, 4 figure
CReSIS airborne radars and platforms for ice and snow sounding
This work is licensed under a Creative Commons Attribution 4.0 International License.This paper provides an update and overview of the Center for Remote Sensing of Ice Sheets (CReSIS) radars and platforms, including representative results from these systems. CReSIS radar systems operate over a frequency range of 14–38 GHz. Each radar system's specific frequency band is driven by the required depth of signal penetration, measurement resolution, allocated frequency spectra, and antenna operating frequencies (often influenced by aircraft integration). We also highlight recent system advancements and future work, including (1) increasing system bandwidth; (2) miniaturizing radar hardware; and (3) increasing sensitivity. For platform development, we are developing smaller, easier to operate and less expensive unmanned aerial systems. Next-generation platforms will further expand accessibility to scientists with vertical takeoff and landing capabilities
Factors in the development of secondary hyperparathyroidism during graded renal failure in the rat
Factors in the development of secondary hyperparathyroidism during graded renal failure in the rat. Secondary hyperparathyroidism (2° HPT) develops as a result of renal failure. Hypocalcemia, phosphorus retention, calcitriol deficiency and skeletal resistance to the calcemic action of parathyroid hormone (PTH) are closely interrelated pathogenic factors important for the development of 2° HPT in renal failure. Since previous studies have mainly focused on advanced renal failure, only limited data are available in early renal failure. The goal of the present study was to evaluate how alterations in the dietary calcium and phosphorus composition affect the factors known to contribute to the genesis of 2° HPT in early and more advanced renal failure. To achieve this goal, graded differences in renal function were surgically induced in 453 rats while the dietary content of calcium and phosphorus was varied. Three different diets were used: (1) a high phosphorus diet (HPD), to induce phosphorus retention and stimulate 2° HPT; (2) a high calcium diet (HCaD), to inhibit calcitriol synthesis; and (3) a moderate calcium-moderate phosphorus diet (MCaPD), to separate the effects of high dietary phosphorus and calcium. Based on the serum creatinine (SCr) concentration rats were assigned to one of four different groups: (1) normal renal function (SCr ≤ 0.3 mg/dl); (2) mild renal failure (SCr 0.4 to 0.6 mg/dl); (3) moderate renal failure (SCr 0.7 to 0.8 mg/dl); or (4) advanced renal failure (SCr ≥ 0.9 mg/dl). As the severity of renal failure increased, progressive 2° HPT developed in each of the dietary groups. In the HPD group, the increase in PTH in normals from 47 ± 2 to 135 ± 14 pg/ml in mild renal failure (P < 0.001) was associated with hyperphosphatemia, a decrease in calcitriol and a decreased calcemic response to PTH. In the HCaD group, the increase in PTH in normals from 42 ± 2 to 74 ± 4 pg/ml in mild renal failure (P < 0.001) was associated with a decrease in calcitriol. In the MCaPD group, 2° HPT developed (40 ± 2 vs. 70 ± 4 pg/ml, normals vs. mild renal failure, P < 0.001) despite normal serum calcium, phosphorus and calcitriol levels; however, a decreased calcemic response to PTH was observed. In advanced renal failure, progressive increases of PTH were observed in all groups, but PTH levels were approximately three-fold greater in the HPD than the HCaD and MCaPD groups (410 ± 24, 114 ± 14 and 138 ± 17 pg/ml, respectively; P < 0.001). While serum calcitriol levels were markedly decreased in the HPD and HCaD groups in advanced renal failure, normal calcitriol levels were present in the MCaPD group. In summary, the development and magnitude of 2° HPT in the HPD group could be best explained by the contribution of several additive factors which included: hypocalcemia, phosphorus retention, a calcitriol deficiency and a decreased calcemic response to PTH. In the HCaD group, a calcitriol deficiency appeared to be the most important factor for the development of 2° HPT. In the MCaPD group, a decreased calcemic response to PTH, which may have been due to uremia, was the only factor to which 2° HPT could be attributed
Biomarkers in disk-averaged near-UV to near-IR Earth spectra using Earthshine observations
We analyse the detectability of vegetation on a global scale on Earth's
surface. Considering its specific reflectance spectrum showing a sharp edge
around 700 nm, vegetation can be considered as a potential global biomarker.
This work, based on observational data, aims to characterise and to quantify
this signature in the disk-averaged Earth's spectrum. Earthshine spectra have
been used to test the detectability of the "Vegetation Red Edge" (VRE) in the
Earth spectrum. We obtained reflectance spectra from near UV (320 nm) to near
IR (1020 nm) for different Earth phases (continents or oceans seen from the
Moon) with EMMI on the NTT at ESO/La Silla, Chile. We accurately correct the
sky background and take into account the phase-dependent colour of the Moon.
VRE measurements require a correction of the ozone Chappuis absorption band and
Rayleigh plus aerosol scattering. Results : The near-UV spectrum shows a dark
Earth below 350 nm due to the ozone absorption. The Vegetation Red Edge is
observed when forests are present (4.0% for Africa and Europe), and is lower
when clouds and oceans are mainly visible (1.3% for the Pacific Ocean). Errors
are typically , and in the worst case. We discuss the
different sources of errors and bias and suggest possible improvements. We
showed that measuring the VRE or an analog on an Earth-like planet remains very
difficult (photometric relative accuracy of 1% or better). It remains a small
feature compared to atmospheric absorption lines. A direct monitoring from
space of the global (disk-averaged) Earth's spectrum would provide the best VRE
follow-up.Comment: Accepted for publication in A&A. 9 pages, 8 figure
Tools for populating cultural heritage environments with interactive virtual humans, open digital cultural heritage systems
Spectral modeling of scintillator for the NEMO-3 and SuperNEMO detectors
We have constructed a GEANT4-based detailed software model of photon
transport in plastic scintillator blocks and have used it to study the NEMO-3
and SuperNEMO calorimeters employed in experiments designed to search for
neutrinoless double beta decay. We compare our simulations to measurements
using conversion electrons from a calibration source of and show
that the agreement is improved if wavelength-dependent properties of the
calorimeter are taken into account. In this article, we briefly describe our
modeling approach and results of our studies.Comment: 16 pages, 10 figure
Long-period High-amplitude Red Variables in the KELT Survey
We present a sample of 4132 Mira-like variables (red variables with long periods and high amplitudes) in the Kilodegree Extremely Little Telescope (KELT) survey. Of these, 376 are new Mira-like detections. We used Two Micron All Sky Survey (2MASS) colors to identify candidate asymptotic giant branch stars. We searched for photometric variability among the candidate asymptotic giant branch stars and identified stars that show periodic variability. We selected variables with high amplitudes and strong periodic behavior using a Random Forest classifier. Of the sample of 4132 Mira-like variables, we estimate that 70% are Miras and 30% are semiregular (SR) variables. We also adopt the method of using (W_(RP) - W_(K)) versus (J - K_s) colors in distinguishing between O-rich and C-rich Miras and find it to be an improvement over 2MASS colors
Comparison of Figulla Flex® and Amplatzer™ devices for atrial septal defect closure: A meta-analysis
Background: Atrial septal defect (ASD) is one of the most common congenital heart diseases. Percutaneousclosure is the preferred treatment, but certain complications remain a concern. The most common devices are AMPLATZER™ (ASO) (St. Jude Medical, St. Paul, MN, USA) and Figulla Flex® septal occluders (FSO) (Occlutech GmbH, Jena, Germany). The present study aimed to assess main differences in outcomes.Methods: A systematic search in Pubmed and Google scholarship was performed by two independent reviewers for any study comparing ASO and FSO. Searched terms were “Figulla”, “Amplatzer”, and “atrial septal defect”. A random-effects model was used.Results: A total of 11 studies including 1770 patients (897 ASO; 873 FSO) were gathered. Baseline clinical and echocardiographic characteristics were comparable although septal aneurysm was more often reported in patients treated with ASO (32% vs. 25%; p = 0.061). Success rate (94% vs. 95%; OR: 0.81; 95% CI: 0.38–1.71; p = 0.58) and peri-procedural complications were comparable. Procedures were shorter, requiring less fluoroscopy time with an FSO device (OR: 0.59; 95% CI: 0.20–0.97; p = 0.003). Although the global rate of complications in long-term was similar, the ASO device was associated with a higher rate of supraventricular arrhythmias (14.7% vs. 7.8%, p = 0.009).Conclusions: Percutaneous closure of ASD is a safe and effective, irrespective of the type of device. No differences exist regarding procedural success between the ASO and FSO devices but the last was associated to shorter procedure time, less radiation, and lower rate of supraventricular arrhythmias in follow-up. Late cardiac perforation did not occur and death in the follow-up was exceptional
The Genomic Signature of Crop-Wild Introgression in Maize
The evolutionary significance of hybridization and subsequent introgression
has long been appreciated, but evaluation of the genome-wide effects of these
phenomena has only recently become possible. Crop-wild study systems represent
ideal opportunities to examine evolution through hybridization. For example,
maize and the conspecific wild teosinte Zea mays ssp. mexicana, (hereafter,
mexicana) are known to hybridize in the fields of highland Mexico. Despite
widespread evidence of gene flow, maize and mexicana maintain distinct
morphologies and have done so in sympatry for thousands of years. Neither the
genomic extent nor the evolutionary importance of introgression between these
taxa is understood. In this study we assessed patterns of genome-wide
introgression based on 39,029 single nucleotide polymorphisms genotyped in 189
individuals from nine sympatric maize-mexicana populations and reference
allopatric populations. While portions of the maize and mexicana genomes were
particularly resistant to introgression (notably near known
cross-incompatibility and domestication loci), we detected widespread evidence
for introgression in both directions of gene flow. Through further
characterization of these regions and preliminary growth chamber experiments,
we found evidence suggestive of the incorporation of adaptive mexicana alleles
into maize during its expansion to the highlands of central Mexico. In
contrast, very little evidence was found for adaptive introgression from maize
to mexicana. The methods we have applied here can be replicated widely, and
such analyses have the potential to greatly informing our understanding of
evolution through introgressive hybridization. Crop species, due to their
exceptional genomic resources and frequent histories of spread into sympatry
with relatives, should be particularly influential in these studies
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