4,116 research outputs found
The Principal Axis of the Virgo Cluster
Using accurate distances to individual Virgo cluster galaxies obtained by the
method of Surface Brightness Fluctuations, we show that Virgo's brightest
ellipticals have a remarkably collinear arrangement in three dimensions. This
axis, which is inclined by 10 to 15 degrees from the line of sight, can be
traced to even larger scales where it appears to join a filamentary bridge of
galaxies connecting Virgo to the rich cluster Abell 1367. The orientations of
individual Virgo ellipticals also show some tendency to be aligned with the
cluster axis, as does the jet of the supergiant elliptical M87. These results
suggest that the formation of the Virgo cluster, and its brightest member
galaxies, have been driven by infall of material along the Virgo-A1367
filament.Comment: 8 pages, 4 figures, accepted for publication in ApJ Letter
A method of evaluating efficiency during space-suited work in a neutral buoyancy environment
The purpose was to investigate efficiency as related to the work transmission and the metabolic cost of various extravehicular activity (EVA) tasks during simulated microgravity (whole body water immersion) using three space suits. Two new prototype space station suits, AX-5 and MKIII, are pressurized at 57.2 kPa and were tested concurrently with the operationally used 29.6 kPa shuttle suit. Four male astronauts were asked to perform a fatigue trial on four upper extremity exercises during which metabolic rate and work output were measured and efficiency was calculated in each suit. The activities were selected to simulate actual EVA tasks. The test article was an underwater dynamometry system to which the astronauts were secured by foot restraints. All metabolic data was acquired, calculated, and stored using a computerized indirect calorimetry system connected to the suit ventilation/gas supply control console. During the efficiency testing, steady state metabolic rate could be evaluated as well as work transmitted to the dynamometer. Mechanical efficiency could then be calculated for each astronaut in each suit performing each movement
Intergalactic Globular Clusters
We confirm and extend our previous detection of a population of intergalactic
globular clusters in Abell 1185, and report the first discovery of an
intergalactic globular cluster in the nearby Virgo cluster of galaxies. The
numbers, colors and luminosities of these objects can place constraints on
their origin, which in turn may yield new insights to the evolution of galaxies
in dense environments.Comment: 2 pages, no figures. Talk presented at JD6, IAU General Assembly XXV,
Sydney, Australia, July 2003, to appear in Highlights of Astronomy, Vol. 1
Globular Cluster Population of Hickson Compact Group 22a and 90c
We present the first measurement of the globular cluster populations of
galaxies in Hickson compact groups, in order to investigate the effect of these
high density environments on the formation and evolution of globular cluster
systems. Based on V and R band images that we obtained of HCG 22a and HCG 90c
with the ESO New Technology Telescope (NTT), we find a total globular cluster
population of for HCG 22a and for 90c. The specific
frequency for HCG 22a was found to be and for HCG 90c. A power-law fit to the globular cluster radial profile of HCG
22a yields and for HCG 90c we found . A comparison of the globular cluster radial profiles with
the surface brightness of the parent galaxy shows that the globular cluster
systems are at least as extended as the halo light. The measured values for the
specific frequency are consistent with a scenario in which the host galaxies
were in a low density ``field-like'' environment when they formed their
globular cluster systems.Comment: 28 pages, 13 figures, 3 tables, accepted for publication in the
Astrophysical Journa
Tentacle probes: eliminating false positives without sacrificing sensitivity
The majority of efforts to increase specificity or sensitivity in biosensors result in trade-offs with little to no gain in overall accuracy. This is because a biosensor cannot be more accurate than the affinity interaction it is based on. Accordingly, we have developed a new class of reagents based on mathematical principles of cooperativity to enhance the accuracy of the affinity interaction. Tentacle probes (TPs) have a hairpin structure similar to molecular beacons (MBs) for enhanced specificity, but are modified by the addition of a capture probe for increased kinetics and affinity. They produce kinetic rate constants up to 200-fold faster than MB with corresponding stem strengths. Concentration-independent specificity was observed with no false positives at up to 1 mM concentrations of variant analyte. In contrast, MBs were concentration dependent and experienced false positives above 3.88 μM of variant analyte. The fast kinetics of this label-free reagent may prove important for extraction efficiency, hence sensitivity and detection time, in microfluidic assays. The concentration-independent specificity of TPs may prove extremely useful in assays where starting concentrations and purities are unknown as would be the case in bioterror or clinical point of care diagnostics
Globular Cluster Systems and the Missing Satellite Problem: Implications for Cold Dark Matter Models
We analyze the metallicity distributions of globular clusters belonging to 28
early-type galaxies in the survey of Kundu & Whitmore (2001). A Monte Carlo
algorithm which simulates the chemical evolution of galaxies that grow
hierarchically via dissipationless mergers is used to determine the most
probable protogalactic mass function for each galaxy. Contrary to the claims of
Kundu & Whitmore, we find that the observed metallicity distributions are in
close agreement with the predictions of such hierarchical formation models. The
mass spectrum of protogalactic fragments for the galaxies in our sample has a
power-law behavior, with an exponent of roughly -2. This spectrum is
indistinguishable from the mass spectrum of dark matter halos predicted by cold
dark matter models for structure formation. We argue that these protogalactic
fragments, the likely sites of globular cluster formation in the early
universe, are the disrupted remains of the "missing" satellite galaxies
predicted by cold dark matter models. Our findings suggest that the solution to
the missing satellite problem is through the suppression of gas accretion in
low-mass halos after reionization, or via self-interacting dark matter, and
argue against models with suppressed small-scale power or warm dark matter.Comment: 28 pages, 19 postscript figures. Accepted for publication in the
Astrophysical Journa
Quantum spectrum as a time series : Fluctuation measures
The fluctuations in the quantum spectrum could be treated like a time series.
In this framework, we explore the statistical self-similarity in the quantum
spectrum using the detrended fluctuation analysis (DFA) and random matrix
theory (RMT). We calculate the Hausdorff measure for the spectra of atoms and
Gaussian ensembles and study their self-affine properties. We show that DFA is
equivalent to statistics of RMT, unifying two different
approaches.We exploit this connection to obtain theoretical estimates for the
Hausdorff measure.Comment: 4+ pages. 2 figure
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Galvanostatic Intermittent Titration Study of the Positive Electrode of a Na|Ni(Fe)-Chloride Cell
The response to open-circuit interrupts of porous mixed iron-nickel cathodes operating in NaCl-buffered, molten NaAlCl4 electrolyte has been characterized as a function of state of charge (SOC) for different iron loadings and different charge and discharge rates. After discharge, the open-circuit potential (OCP) can evolve in time from the iron plateau to the nickel plateau, and this behavior can be explained by galvanic interactions between iron metal and Ni2+. Characteristic times of the OCP transients depend on SOC and can be large. When the OCP has converged on a steady state during discharge, its value may provide an estimate of the mole fraction of NiCl2 at the interface of the triclinic (Ni,Fe)Cl2 film that resulted from metal oxidation. Detailed analyses of the experiment require modeling of the galvanic conversion rates, which depend on both charge-transfer and mass-transfer phenomena
Recommended from our members
Galvanostatic Intermittent Titration Study of the Positive Electrode of a Na|Ni(Fe)-Chloride Cell
The response to open-circuit interrupts of porous mixed iron-nickel cathodes operating in NaCl-buffered, molten NaAlCl4 electrolyte has been characterized as a function of state of charge (SOC) for different iron loadings and different charge and discharge rates. After discharge, the open-circuit potential (OCP) can evolve in time from the iron plateau to the nickel plateau, and this behavior can be explained by galvanic interactions between iron metal and Ni2+. Characteristic times of the OCP transients depend on SOC and can be large. When the OCP has converged on a steady state during discharge, its value may provide an estimate of the mole fraction of NiCl2 at the interface of the triclinic (Ni,Fe)Cl2 film that resulted from metal oxidation. Detailed analyses of the experiment require modeling of the galvanic conversion rates, which depend on both charge-transfer and mass-transfer phenomena
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