16,845 research outputs found
Post-buckling behavior of a beam-column on a nonlinear elastic foundation with a gap
The structural behavior of an elastic beam-column placed with a gap between two nonlinearity elastic layers each resting on a rigid foundation was examined. The beam-column was laterally supported at both ends and subjected to a uniform transverse load and axial compression. Its slenderness was such that the axial compressive force exceeds the amount that would be necessary to buckle it as a simple supported column. The elastic layers were represented by an elastic foundation with a strongly nonlinear specific reaction taken as a rapidly increasing function of the layer compression. The analytical model developed simulated the entire pattern of the deflection and stress state including layer and end support reactions, under gradually increasing axial force
Possible detection of a magnetic field in T Tauri
Medium-resolution circular spectropolarimetry of T Tauri is
presented. The star was observed twice: on November 11, 1996 and January 22,
2002. Weak circular polarization has been found in photospheric absorption
lines, indicating a mean surface longitudinal magnetic field of
G and G at the epoch of the first and second
observations respectively. While these values are near the detection limit of
our apparatus, we belive that they are real. In any case one can conclude from
our data that of T Tau does not significantly exceed 200 G, which is
much less than surface magnetic field strength of the star ( kG) found by
Guenther et al. (1999) and Johns-Krull et al. (2000). We discuss possible
reasons of this difference.Comment: 5 pages, 3 figure
Conceptual design and analysis of orbital cryogenic liquid storage and supply systems
A wide variety of orbital cryogenic liquid storage and supply systems are defined in NASA and DOD long-range plans. These systems include small cooling applications, large chemical and electrical orbit transfer vehicles and supply tankers. All have the common requirements of low-g fluid management to accomplish gas-free liquid expulsion and efficient thermal control to manage heat leak and tank pressure. A preliminary design study was performed to evaluate tanks ranging from 0.6 to 37.4 cu m (22 to 1320 cu ft). Liquids of interest were hydrogen, oxygen, methane, argon and helium. Conceptual designs were generated for each tank system and fluid dynamic, thermal and structural analyses were performed for Shuttle compatible operations. Design trades considered the paradox of conservative support structure and minimum thermal input. Orbital performance and weight data were developed, and a technology evaluation was completed
Magnetic fields of intermediate mass T Tauri stars
Aims. In this paper, we aim to measure the strength of the surface magnetic
fields for a sample of five intermediate mass T Tauri stars and one low mass T
Tauri star from late-F to mid-K spectral types. While magnetic fields of T
Tauri stars at the low mass range have been extensively characterized, our work
complements previous studies towards the intermediate mass range; this
complementary study is key to evaluate how magnetic fields evolve during the
transition from a convective to a radiative core.
Methods. We studied the Zeeman broadening of magnetically sensitive spectral
lines in the H-band spectra obtained with the CRIRES high-resolution
near-infrared spectrometer. These data are modelled using magnetic spectral
synthesis and model atmospheres. Additional constraints on non-magnetic line
broadening mechanisms are obtained from modelling molecular lines in the K band
or atomic lines in the optical wavelength region.
Results. We detect and measure mean surface magnetic fields for five of the
six stars in our sample: CHXR 28, COUP 107, V2062 Oph, V1149 Sco, and Par 2441.
Magnetic field strengths inferred from the most magnetically sensitive
diagnostic line range from 0.8 to 1.8 kG. We also estimate a magnetic field
strength of 1.9 kG for COUP 107 from an alternative diagnostic. The magnetic
field on YLW 19 is the weakest in our sample and is marginally detected, with a
strength of 0.8 kG.
Conclusions. We populate an uncharted area of the pre-main-sequence HR
diagram with mean magnetic field measurements from high-resolution
near-infrared spectra. Our sample of intermediate mass T Tauri stars in general
exhibits weaker magnetic fields than their lower mass counterparts. Our
measurements will be used in combination with other spectropolarimetric studies
of intermediate mass and lower mass T Tauri stars to provide input into
pre-main-sequence stellar evolutionary models.Comment: 8 pages, 8 figures, accepted for publication in Astronomy and
Astrophysic
University undergraduate students and library-related privacy issues
New technologies increase the ability to capture and retrieve data about library usage patterns and users. Collecting, analyzing, and using patron data, however, may raise concerns among library users about their online privacy and how the data collected might be used to their advantage or disadvantage. This article examines undergraduate students\u27 knowledge and perceptions of online privacy issues, their opinions regarding who should collect and retain information about them, for what purposes, and under what circumstances
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The Town Lake Report, Volumes I and II
This report makes brief references to sediment and other trends seen in Waller Creek.EXECUTIVE SUMMARY: Town Lake’s importance as a natural resource is growing in tandem with Austin’s rapid population. The lake is a source of drinking water for the City, and its greenbelt and open waters are widely used for recreation and as a focal-point for public events. In 1992, under the Clean Lakes program, a comprehensive report entitled the “Town Lake Study” (COA 1992a; COA 1992b; COA 1992c) was prepared. It examined the condition of the lake (Volume I), water quality control alternatives (Volume II) and a feasibility study (Volume III). This report updates the diagnostic study, Volume I (COA 1992a), including the current status of water quality with data analyzed through the year 2000. It also includes a summary of measures taken to reduce pollution from urban runoff since 1990.Waller Creek Working Grou
Convective Dynamos and the Minimum X-ray Flux in Main Sequence Stars
The objective of this paper is to investigate whether a convective dynamo can
account quantitatively for the observed lower limit of X-ray surface flux in
solar-type main sequence stars. Our approach is to use 3D numerical simulations
of a turbulent dynamo driven by convection to characterize the dynamic
behavior, magnetic field strengths, and filling factors in a non-rotating
stratified medium, and to predict these magnetic properties at the surface of
cool stars. We use simple applications of stellar structure theory for the
convective envelopes of main-sequence stars to scale our simulations to the
outer layers of stars in the F0--M0 spectral range, which allows us to estimate
the unsigned magnetic flux on the surface of non-rotating reference stars. With
these estimates we use the recent results of \citet{Pevtsov03} to predict the
level of X-ray emission from such a turbulent dynamo, and find that our results
compare well with observed lower limits of surface X-ray flux. If we scale our
predicted X-ray fluxes to \ion{Mg}{2} fluxes we also find good agreement with
the observed lower limit of chromospheric emission in K dwarfs. This suggests
that dynamo action from a convecting, non-rotating plasma is a viable
alternative to acoustic heating models as an explanation for the basal emission
level seen in chromospheric, transition region, and coronal diagnostics from
late-type stars.Comment: ApJ, accepted, 30 pages with 7 figure
Delineating the role of βIV-Tubulins in pancreatic cancer: βIVb-tubulin inhibition sensitizes pancreatic cancer cells to vinca alkaloids
Pancreatic cancer (PC) is a lethal disease which is characterized by chemoresistance. Components of the cell cytoskeleton are therapeutic targets in cancer. βIV-tubulin is one such component that has two isotypes—βIVa and βIVb. βIVa and βIVb isotypes only differ in two amino acids at their C-terminus. Studies have implicated βIVa-tubulin or βIVb-tubulin expression with chemoresistance in prostate, breast, ovarian and lung cancer. However, no studies have examined the role of βIV-tubulin in PC or attempted to identify isotype specific roles in regulating cancer cell growth and chemosensitivity. We aimed to determine the role of βIVa- or βIVb-tubulin on PC growth and chemosensitivity. PC cells (MiaPaCa-2, HPAF-II, AsPC1) were treated with siRNA (control, βIVa-tubulin or βIVb-tubulin). The ability of PC cells to form colonies in the presence or absence of chemotherapy was measured by clonogenic assays. Inhibition of βIVa-tubulin in PC cells had no effect chemosensitivity. In contrast, inhibition of βIVb-tubulin in PC cells sensitized to vinca alkaloids (Vincristine, Vinorelbine and Vinblastine), which was accompanied by increased apoptosis and enhanced cell cycle arrest. We show for the first time that βIVb-tubulin, but not βIVa-tubulin, plays a role in regulating vinca alkaloid chemosensitivity in PC cells. The results from this study suggest βIVb-tubulin may be a novel therapeutic target and predictor of vinca alkaloid sensitivity for PC and warrants further investigation
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