10,498 research outputs found
A New Approach to Black Hole Microstates
If one encodes the gravitational degrees of freedom in an orthonormal frame
field there is a very natural first order action one can write down (which in
four dimensions is known as the Goldberg action). In this essay we will show
that this action contains a boundary action for certain microscopic degrees of
freedom living at the horizon of a black hole, and argue that these degrees of
freedom hold great promise for explaining the microstates responsible for black
hole entropy, in any number of spacetime dimensions. This approach faces many
interesting challenges, both technical and conceptual.Comment: 6 pages, 0 figures, LaTeX; submitted to Mod. Phys. Lett. A.; this
essay received "honorable mention" from the Gravity Research Foundation, 199
Characterization of the Active Site and Insight into the Binding Mode of the Anti-angiogenesis Agent Fumagillin to the Manganese(II)-Loaded Methionyl Aminopeptidase from \u3cem\u3eEscherichia coli\u3c/em\u3e
EPR spectra were recorded for methionine aminopeptidase from Escherichia coli (EcMetAP-I) samples (~2.5 mM) to which one and two equivalents of Mn(II) were added (the latter is referred to as [MnMn(EcMetAP-I)]). The spectra for each sample were indistinguishable except that the spectrum of [MnMn(EcMetAP-I)] was twice as intense. The EPR spectrum of [MnMn(EcMetAP-I)] exhibited the characteristic six-line g≈2 EPR signal of mononuclear Mn(II) with A av(55Mn)=9.3 mT (93 G) and exhibited Curie-law temperature dependence. This signal is typical of Mn(II) in a ligand sphere comprising oxygen and/or nitrogen atoms. Other features in the spectrum were observed only as the temperature was raised from that of liquid helium. The temperature dependences of these features are consistent with their assignment to excited state transitions in the S=1, 2 ... 5 non-Kramer’s doublets, due to two antiferromagnetically coupled Mn(II) ions with an S=0 ground state. This assignment is supported by the observation of a characteristic 4.5 mT hyperfine pattern, and by the presence of signals in the parallel mode consistent with a non-Kramers’ spin ladder. Upon the addition of the anti-angiogenesis agent fumagillin to [MnMn(EcMetAP-I)], very small changes were observed in the EPR spectrum. MALDI-TOF mass spectrometry indicated that fumagillin was, however, covalently coordinated to EcMetAP-I. Therefore, the inhibitory action of this anti-angiogenesis agent on EcMetAP-I appears to involve covalent binding to a polypeptide component at or near the active site rather than direct binding to the metal ions
A Study of the Critical Uncertainty Contributions in the Analysis of PCBs in Ambient Air
The measurement of polychlorinated biphenyls (PCBs) in ambient air requires
a complex, multistep sample preparation procedure prior to analysis by gas
chromatography—mass spectrometry (GC-MS). Although routine analytical
laboratories regularly carry out these measurements, they are often undertaken
with little regard to the accurate calculation of measurement uncertainty, or
appreciation of the sensitivity of the accuracy of the measurement to each step of the
analysis. A measurement equation is developed for this analysis, and the contributory
sources to the overall uncertainty when preparing calibration standards and other
solutions by gravimetric and volumetric approaches are discussed and compared. For
the example analysis presented, it is found that the uncertainty of the measurement is
dominated by the repeatability of the GC-MS analysis and suggested that volumetric
(as opposed to gravimetric) preparation of solutions does not adversely affect the
overall uncertainty. The methodology presented in this work can also be applied to
analogous methods for similar analytes, for example, those used to measure polycyclic
aromatic hydrocarbons (PAHs), pesticides, dioxins, or furans in ambient air
The State of Health Insurance in California: Findings From the 2003 California Health Interview Survey
Provides an overview of the shift from job-based health insurance to enrollment in public insurance programs, and discusses the advantages and disadvantages of key public policy options to extend coverage to California's uninsured residents
On the Optimum Sampling Time for the Measurement of Pollutants in Ambient Air
No measurement
result of any kind is complete without an associated statement of
uncertainty. In general, the aim is to minimise this measurement
uncertainty to the extent that the measurement made is fit for
purpose, or the uncertainty meets an acceptable level such as a
“data quality objective”. This paper
demonstrates how the sampling time used to measure a pollutant in
ambient air over a given time period, particularly with automatic
instruments, can affect the uncertainty of the measurement result.
It is shown that the uncertainty of the overall result depends
critically on how the precision characteristics of the measuring
instrumentation vary with analyte abundance. An example of the
determination of these characteristics for mercury vapour
measurement and the conclusions that may be drawn about optimum
sampling times to minimise uncertainty are presented. For
situations where uncertainty is minimised by the use of long
sampling periods, the implications of this strategy on the
“information richness” of the data
and on the detection of short-term episodes, as well as peak
concentrations, are discussed
Improvements to parallel plate flow chambers to reduce reagent and cellular requirements
BACKGROUND: The parallel plate flow chamber has become a mainstay for examination of leukocytes under physiologic flow conditions. Several design modifications have occurred over the years, yet a comparison of these different designs has not been performed. In addition, the reagent requirements of many designs prohibit the study of rare leukocyte populations and require large amounts of reagents. RESULTS: In this study, we evaluate modifications to a newer parallel plate flow chamber design in comparison to the original parallel plate flow chamber described by Lawrence et al. We show that modifications in the chamber size, internal tubing diameters, injection valves, and a recirculation design may dramatically reduce the cellular and reagent requirements without altering measurements. CONCLUSIONS: These modifications are simple and easily implemented so that study of rare leukocyte subsets using scarce or expensive reagents can occur
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