2,999 research outputs found
Modeling the Role of the Cell Cycle in Regulating Proteus mirabilis Swarm-Colony Development
We present models and computational results which indicate that the spatial
and temporal regularity seen in Proteus mirabilis swarm-colony development is
largely an expression of a sharp age of dedifferentiation in the cell cycle
from motile swarmer cells to immotile dividing cells (also called swimmer or
vegetative cells.) This contrasts strongly with reaction-diffusion models of
Proteus behavior that ignore or average out the age structure of the cell
population and instead use only density-dependent mechanisms. We argue the
necessity of retaining the explicit age structure, and suggest experiments that
may help determine the underlying mechanisms empirically. Consequently, we
advocate Proteus as a model organism for a multiscale understanding of how and
to what extent the life cycle of individual cells affects the macroscopic
behavior of a biological system
Defending OC-SVM based IDS from poisoning attacks
Machine learning techniques are widely used to detect intrusions in the cyber security field. However, most machine learning models are vulnerable to poisoning attacks, in which malicious samples are injected into the training dataset to manipulate the classifier's performance. In this paper, we first evaluate the accuracy degradation of OC-SVM classifiers with 3 different poisoning strategies with the ADLA-FD public dataset and a real world dataset. Secondly, we propose a saniti-zation mechanism based on the DBSCAN clustering algorithm. In addition, we investigate the influences of different distance metrics and different dimensionality reduction techniques and evaluate the sensitivity of the DBSCAN parameters. The ex-perimental results show that the poisoning attacks can degrade the performance of the OC-SVM classifier to a large degree, with an accuracy equal to 0.5 in most settings. The proposed sanitization method can filter out poisoned samples effectively for both datasets. The accuracy after sanitization is very close or even higher to the original value.</p
FeH Absorption in the Near-Infrared Spectra of Late M and L Dwarfs
We present medium-resolution z-, J-, and H-band spectra of four late-type
dwarfs with spectral types ranging from M8 to L7.5. In an attempt to determine
the origin of numerous weak absorption features throughout their near-infrared
spectra, and motivated by the recent tentative identification of the E 4\Pi- A
^4\Pi system of FeH near 1.6 microns in umbral and cool star spectra, we have
compared the dwarf spectra to a laboratory FeH emission spectrum. We have
identified nearly 100 FeH absorption features in the z-, J-, and H-band spectra
of the dwarfs. In particular, we have identified 34 features which dominate the
appearance of the H-band spectra of the dwarfs and which appear in the
laboratory FeH spectrum. Finally, all of the features are either weaker or
absent in the spectrum of the L7.5 dwarf which is consistent with the weakening
of the known FeH bandheads in the spectra of the latest L dwarfs.Comment: accepted by Ap
Waste Not, Want Not: The Potential for Urban Water Conservation in California
The largest, least expensive, and most environmentally sound source of water to meet California's future needs is the water currently being wasted in every sector of our economy. This report, "Waste Not, Want Not," strongly indicates that California's urban water needs can be met into the foreseeable future by reducing water waste through cost-effective water-saving technologies, revised economic policies, appropriate state and local regulations, and public education
Characterizing mid-type M dwarfs in the Kepler field with the Discovery Channel Telescope and WIYN
Planet occurrence rates increase with decreasing stellar mass (later spectral types); therefore, M dwarf systems are our most promising targets in the search for exoplanets. The identification and characterization of stars in the original Kepler field was accomplished using photometry alone, resulting in large uncertainties for late-type stars like M dwarfs. In order to more accurately compute the planet occurrence rate around mid- type M dwarfs, we need to better constrain their stellar radii and masses, properties which strongly correlate with other stellar parameters such as temperature and metallicity. These measurements need to be performed on a statistically significant population of stars including systems with and without planets. Therefore, we have begun to spectroscopically characterize the properties of the 559 probable mid-type M dwarfs in the Kepler field using red optical spectra obtained with the DeVeny Spectrograph on the Discovery Channel Telescope (DCT) and Hydra on the WIYN telescope in order to constrain the planet occurrence rate for such stars. We will be presenting initial results from our DCT and WIYN observations, including new temperature, radius, and mass estimates which we can use in occurrence rate calculations.http://adsabs.harvard.edu/abs/2017AAS...22912608HPublished versio
Characterization of mid-type M dwarfs in the Kepler field
The planet occurrence rate has been found to increase with decreasing stellar mass (later spectral types) in the original Kepler field, and one out of four M dwarfs are expected to host Earth-sized planets within their habitable zones. M dwarf systems are, therefore, our most promising targets in the search for exoplanets. Yet the identification and characterization of M dwarfs in the Kepler field was accomplished using photometry alone and unfortunately this method provides large uncertainties for late-type stars. Notably absent from planet occurrence calculations are single planet mid-type M dwarfs (~M2-M6). In order to make an accurate calculation of the planet occurrence rate around mid-type M dwarfs, we need to constrain stellar radii and masses which depend on other stellar parameters (e.g. temperature and metallicity). We have identified 559 probable mid-type M dwarfs using photometric color selection criteria and have started to gather spectra of these objects in order to better constrain stellar properties and refine planet occurrence rates for this population. Here we outline the methods we are using for stellar classification and characterization and present some results from our initial data.http://adsabs.harvard.edu/abs/2016AAS...22743012HPublished versio
The Benchmark Ultracool Subdwarf HD 114762B: A Test of Low-Metallicity Atmospheric and Evolutionary Models
We present a near-infrared spectroscopic study of HD 114762B, the latest-type
metal-poor companion discovered to date and the only ultracool subdwarf with a
known metallicity, inferred from the primary star to be [Fe/H] = -0.7. We
obtained a medium-resolution Keck/OSIRIS J-band spectrum and a low-resolution
IRTF/SpeX 0.8-2.4 um spectrum of HD 114762B. HD 114762B exhibits spectral
features common to both late-type dwarfs and subdwarfs, and we assign it a
spectral type of d/sdM9 +/- 1. We use a Monte Carlo technique to fit
PHOENIX/GAIA synthetic spectra to the observations, accounting for the
coarsely-gridded nature of the models. Fits to the entire OSIRIS J-band and to
the metal-sensitive J-band atomic absorption features (Fe I, K I, and Al I
lines) yield model parameters that are most consistent with the metallicity of
the primary star and the high surface gravity expected of old late-type
objects. The effective temperatures and radii inferred from the model
atmosphere fitting broadly agree with those predicted by the evolutionary
models of Chabrier & Baraffe, and the model color-absolute magnitude relations
accurately predict the metallicity of HD 114762B. We conclude that current
low-mass, mildly metal-poor atmospheric and evolutionary models are mutually
consistent for spectral fits to medium-resolution J-band spectra of HD 114762B,
but are inconsistent for fits to low-resolution near-infrared spectra of mild
subdwarfs. Finally, we develop a technique for estimating distances to
ultracool subdwarfs based on a single near-infrared spectrum. We show that this
"spectroscopic parallax" method enables distance estimates accurate to < 10% of
parallactic distances for ultracool subdwarfs near the hydrogen burning minimum
mass. (abridged)Comment: Accepted by ApJ; 23 pages, 20 figure
- …