100 research outputs found
Review of ground-based measurements
Early measurements of the solar constant are described and discussed with particular emphasis on the Smithsonian program. A brief description is given of the monitoring program currently operating at San Diego State
Possible relationships between solar activity and atmospheric constituents
The large body of data on solar variations and atmospheric constituents collected between 1902 and 1953 by the Astrophysical Observatory of the Smithsonian Institution (APO) was examined. Short-term variations in amounts of atmospheric aerosols and water vapor due to seasonal changes, volcanic activity, air pollution, and frontal activity are discussed. Preliminary evidence indicates that increased solar activity is at times associated with a decrease in attenuation due to airborne particulates
Bioinformatics challenges and potentialities in studying extreme environments
Cold environments are populated by organisms able to contravene deleterious effects of low temperature by diverse adaptive strategies, including the production of ice binding proteins (IBPs) that inhibit the growth of ice crystals inside and outside cells. We describe the properties of such a protein (EfcIBP) identified in the metagenome of an Antarctic biological consortium composed of the ciliate Euplotes focardii and psychrophilic non-cultured bacteria. Recombinant EfcIBP can resist freezing without any conformational damage and is moderately heat stable, with a midpoint temperature of 66.4 degrees C. Tested for its effects on ice, EfcIBP shows an unusual combination of properties not reported in other bacterial IBPs. First, it is one of the best-performing IBPs described to date in the inhibition of ice recrystallization, with effective concentrations in the nanomolar range. Moreover, EfcIBP has thermal hysteresis activity (0.53 degrees C at 50 mu M) and it can stop a crystal from growing when held at a constant temperature within the thermal hysteresis gap. EfcIBP protects purified proteins and bacterial cells from freezing damage when exposed to challenging temperatures. EfcIBP also possesses a potential N-terminal signal sequence for protein transport and a DUF3494 domain that is common to secreted IBPs. These features lead us to hypothesize that the protein is either anchored at the outer cell surface or concentrated around cells to provide survival advantage to the whole cell consortium
Integrated multiāomics analysis of ovarian cancer using variational autoencoders
Cancer is a complex disease that deregulates cellular functions at various molecular levels (e.g., DNA, RNA, and proteins). Integrated multiāomics analysis of data from these levels is necessary to understand the aberrant cellular functions accountable for cancer and its development. In recent years, Deep Learning (DL) approaches have become a useful tool in integrated multiāomics analysis of cancer data. However, high dimensional multiāomics data are generally imbalanced with too many molecular features and relatively few patient samples. This imbalance makes a DL based integrated multiāomics analysis difficult. DLābased dimensionality reduction technique, including variational autoencoder (VAE), is a potential solution to balance high dimensional multiāomics data. However, there are few VAEābased integrated multiāomics analyses, and they are limited to pancancer. In this work, we did an integrated multiāomics analysis of ovarian cancer using the compressed features learned through VAE and an improved version of VAE, namely Maximum Mean Discrepancy VAE (MMDāVAE). First, we designed and developed a DL architecture for VAE and MMDāVAE. Then we used the architecture for monoāomics, integrated diāomics and triāomics data analysis of ovarian cancer through cancer samples identification, molecular subtypes clustering and classification, and survival analysis. The results show that MMDāVAE and VAEābased compressed features can respectively classify the transcriptional subtypes of the TCGA datasets with an accuracy in the range of 93.2ā95.5% and 87.1ā95.7%. Also, survival analysis results show that VAE and MMDāVAE based compressed representation of omics data can be used in cancer prognosis. Based on the results, we can conclude that (i) VAE and MMDāVAE outperform existing dimensionality reduction techniques, (ii) integrated multiāomics analyses perform better or similar compared to their monoāomics counterparts, and (iii) MMDāVAE performs better than VAE in most omics dataset
A Close Companion Search Around L Dwarfs Using Aperture Masking Interferometry and Palomar Laser Guide Star Adaptive Optics
We present a close companion search around 16 known early L dwarfs using aperture masking interferometry with Palomar laser guide star adaptive optics (LGS AO). The use of aperture masking allows the detection of close binaries, corresponding to projected physical separations of 0.6-10.0 AU for the targets of our survey. This survey achieved median contrast limits of ĪK ~ 2.3 for separations between 1.2Ī»/D-4Ī»/D and ĪK ~ 1.4 at 2/3Ī»/D. We present four candidate binaries detected with moderate-to-high confidence (90%-98%). Two have projected physical separations less than 1.5 AU. This may indicate that tight-separation binaries contribute more significantly to the binary fraction than currently assumed, consistent with spectroscopic and photometric overluminosity studies. Ten targets of this survey have previously been observed with the Hubble Space Telescope as part of companion searches. We use the increased resolution of aperture masking to search for close or dim companions that would be obscured by full aperture imaging, finding two candidate binaries. This survey is the first application of aperture masking with LGS AO at Palomar. Several new techniques for the analysis of aperture masking data in the low signal-to-noise regime are explored
YSOVAR: Six pre-main-sequence eclipsing binaries in the Orion Nebula Cluster
Eclipsing binaries (EBs) provide critical laboratories for empirically
testing predictions of theoretical models of stellar structure and evolution.
Pre-main-sequence (PMS) EBs are particularly valuable, both due to their rarity
and the highly dynamic nature of PMS evolution, such that a dense grid of PMS
EBs is required to properly calibrate theoretical PMS models. Analyzing
multi-epoch, multi-color light curves for 2400 candidateOrion Nebula Cluster
(ONC) members from our Warm Spitzer Exploration Science Program YSOVAR, we have
identified 12 stars whose light curves show eclipse features. Four of these 12
EBs are previously known. Supplementing our light curves with follow-up optical
and near-infrared spectroscopy, we establish two of the candidates as likely
field EBs lying behind the ONC. We confirm the remaining six candidate systems,
however, as newly identified ONC PMS EBs. These systems increase the number of
known PMS EBs by over 50% and include the highest mass (Theta1 Ori E, for which
we provide a complete set of well-determined parameters including component
masses of 2.807 and 2.797 solar masses) and longest period (ISOY
J053505.71-052354.1, P \sim 20 days) PMS EBs currently known. In two cases
(Theta1 Ori E and ISOY J053526.88-044730.7), enough photometric and
spectroscopic data exist to attempt an orbit solution and derive the system
parameters. For the remaining systems, we combine our data with literature
information to provide a preliminary characterization sufficient to guide
follow-up investigations of these rare, benchmark systems.Comment: Accepted by Ap
A Hybrid of Metabolic Flux Analysis and Bayesian Factor Modeling for Multiomic Temporal Pathway Activation.
The
growing availability of multiomic data provides a highly comprehensive
view of cellular processes at the levels of mRNA, proteins, metabolites,
and reaction fluxes. However, due to probabilistic interactions between
components depending on the environment and on the time course, casual,
sometimes rare interactions may cause important effects in the cellular
physiology. To date, interactions at the pathway level cannot be measured
directly, and methodologies to predict pathway cross-correlations
from reaction fluxes are still missing. Here, we develop a multiomic
approach of flux-balance analysis combined with Bayesian factor modeling
with the aim of detecting pathway cross-correlations and predicting
metabolic pathway activation profiles. Starting from gene expression
profiles measured in various environmental conditions, we associate
a flux rate profile with each condition. We then infer pathway cross-correlations
and identify the degrees of pathway activation with respect to the
conditions and time course using Bayesian factor modeling. We test
our framework on the most recent metabolic reconstruction of Escherichia coli in both static and dynamic environments,
thus predicting the functionality of particular groups of reactions
and how it varies over time. In a dynamic environment, our method
can be readily used to characterize the temporal progression of pathway
activation in response to given stimuli
Know The Star, Know the Planet. IV. A Stellar Companion to the Host star of the Eccentric Exoplanet HD 8673b
HD 8673 hosts a massive exoplanet in a highly eccentric orbit (e=0.723).
Based on two epochs of speckle interferometry a previous publication identified
a candidate stellar companion. We observed HD 8673 multiple times with the 10 m
Keck II telescope, the 5 m Hale telescope, the 3.63 m AEOS telescope and the
1.5m Palomar telescope in a variety of filters with the aim of confirming and
characterizing the stellar companion. We did not detect the candidate
companion, which we now conclude was a false detection, but we did detect a
fainter companion. We collected astrometry and photometry of the companion on
six epochs in a variety of filters. The measured differential photometry
enabled us to determine that the companion is an early M dwarf with a mass
estimate of 0.33-0.45 M?. The companion has a projected separation of 10 AU,
which is one of the smallest projected separations of an exoplanet host binary
system. Based on the limited astrometry collected, we are able to constrain the
orbit of the stellar companion to a semi-major axis of 35{60 AU, an
eccentricity ? 0.5 and an inclination of 75{85?. The stellar companion has
likely strongly in uenced the orbit of the exoplanet and quite possibly
explains its high eccentricity.Comment: Accepted to the Astronomical Journal, 6 Pages, 5 Figure
The quasar fraction in low-frequency selected complete samples and implications for unified schemes
Low-frequency radio surveys are ideal for selecting orientation-independent
samples of extragalactic sources because the sample members are selected by
virtue of their isotropic steep-spectrum extended emission. We use the new 7C
Redshift Survey along with the brighter 3CRR and 6C samples to investigate the
fraction of objects with observed broad emission lines - the `quasar fraction'
- as a function of redshift and of radio and narrow emission line luminosity.
We find that the quasar fraction is more strongly dependent upon luminosity
(both narrow line and radio) than it is on redshift. Above a narrow [OII]
emission line luminosity of log L_[OII] > 35 W (or radio luminosity log L_151 >
26.5 W/Hz/sr), the quasar fraction is virtually independent of redshift and
luminosity; this is consistent with a simple unified scheme with an obscuring
torus with a half-opening angle theta_trans approx 53 degrees. For objects with
less luminous narrow lines, the quasar fraction is lower. We show that this is
not due to the difficulty of detecting lower-luminosity broad emission lines in
a less luminous, but otherwise similar, quasar population. We discuss evidence
which supports at least two probable physical causes for the drop in quasar
fraction at low luminosity: (i) a gradual decrease in theta_trans and/or a
gradual increase in the fraction of lightly-reddened (0 < A(V) < 5)
lines-of-sight with decreasing quasar luminosity; and (ii) the emergence of a
distinct second population of low luminosity radio sources which, like M87,
lack a well-fed quasar nucleus and may well lack a thick obscuring torus.Comment: 10 pages, 4 figures, accepted for publication in MNRA
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