442 research outputs found
A study of consecutive competitive reaction systems
Experimental kinetic data are most conveniently correlated by the integrated form of the differential rate equations which the reactions are presumed to obey. A new method of obtaining an approximate integral solution of the differential equations is described and applied to a set of three consecutive competitive reactions. The approximate integral solution is used to correlate experimental data on systems whose stoichiometry would indicate a consecutivecompetitive mechanism. The compositions of the reaction mixes are predicted with a standard error of estimate of less than 4% of the original concentration of the initiating reactant, in most cases less than 2%. The estimates of the rate constants, found by fitting the approximate solution to the data, are within experimental error of the values obtained by differentiation of the published results.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/37325/1/690080503_ftp.pd
Discussion: âComparison of Statistical Methods for Assessing Spatial Correlations Between Maps of Different Arterial Propertiesâ (Rowland, E. M., Mohamied, Y., Chooi, K. Y., Bailey, E. L., and Weinberg, P. D., 2015, ASME J. Biomech. Eng., 137(10), p. 101003): An Alternative Approach Using Segmentation Based on Local Hemodynamics
The biological response of living arteries to mechanical forces is an important component of the atherosclerotic process and is responsible, at least in part, for the well-recognized spatial variation in atherosusceptibility in man. Experiments to elucidate this response often generate maps of force and response variables over the arterial surface, from which the forceâresponse relationship is sought. Rowland et al. discussed several statistical approaches to the spatial autocorrelation that confounds the analysis of such maps and applied them to maps of hemodynamic stress and vascular response obtained by averaging these variables in multiple animals. Here, we point out an alternative approach, in which discrete surface regions are defined by the hemodynamic stress levels they experience, and the stress and response in each animal are treated separately. This approach, applied properly, is insensitive to autocorrelation and less sensitive to the effect of confounding hemodynamic variables. The analysis suggests an inverse relation between permeability and shear that differs from that in Rowland et al. Possible sources of this difference are suggested
Relationship between hemodynamics and atherosclerosis in aortic arches of apolipoprotein E-null mice on 129S6/SvEvTac and C57BL/6J genetic backgrounds
We investigated the relationships between hemodynamics and differential plaque development at the aortic arch of apolipoprotein E (apoE)-null mice on 129S6/SvEvTac (129) and C57BL/6J (B6) genetic backgrounds
A Study of the Reionization History of Intergalactic Helium with FUSE and VLT
We obtained high-resolution VLT and FUSE spectra of the quasar HE2347-4342 to
study the properties of the intergalactic medium between redshifts z=2.0-2.9.
The high-quality optical spectrum allows us to identify approximately 850 HeII
absorption components with column densities between N~5X10^11 and $ 10^18
cm^-2. The reprocessed FUSE spectrum extends the wavelength coverage of the
HeII absorption down to an observed wavelength of 920 A. Approximately 1400
HeII absorption components are identified, including 917 HeII Ly-alpha systems
and some of their HeII Ly-beta, Ly-gamma, and Ly-delta counterparts. The
ionization structure of HeII is complex, with approximately 90 components that
are not detected in the hydrogen spectrum. These components may represent the
effect of soft ionizing sources. The ratio Eta=N(HeII)/N(HI) varies
approximately from unity to more than a thousand, with a median value of 62 and
a distribution consistent with the intrinsic spectral indices of quasars. This
suggests that the dominant ionizing field is from the accumulated quasar
radiation, with contributions from other soft sources such as star-forming
regions and obscured AGN, which do not ionize helium. We find an evolution in
Eta toward smaller values at lower redshift, with the gradual disappearance of
soft components. At redshifts z>2.7, the large but finite increase in the HeII
opacity, Tau=5+/-1, suggests that we are viewing the end stages of a
reionization process that began at an earlier epoch. Fits of the absorption
profiles of unblended lines indicate comparable velocities between hydrogen and
He^+ ions. At hydrogen column densities N<3X10^12 cm^-2 the number of forest
lines shows a significant deficit relative to a power law, and becomes
negligible below N=10^11 cm^-2.Comment: 40 pages, 10 Postscript figures, uses Aastex.sty The Astrophysical
Journal, in pres
FUSE Observations of Molecular Hydrogen in Translucent Interstellar Clouds: The Line of Sight Toward HD 73882
We report the results of initial FUSE observations of molecular hydrogen (H2)
in translucent clouds. These clouds have greater optical depth than any of the
diffuse clouds previously observed for far-UV H2 absorption, and provide new
insights into the physics and chemistry of such regions. Our initial results
involve observations of HD 73882, a well-studied southern hemisphere star lying
behind substantial interstellar material (E(B-V) = 0.72; A_V = 2.44). We find a
total H2 column density, N(H2) = 1.2 x 10^{21} cm^{-2}, about three times
larger than the values for diffuse clouds previously measured in the far-UV.
The gas kinetic temperature indicated by the ratio N(J=1)/N(J=0) is 58 +/- 10
K. With the aid of ground-based data to calculate an appropriate
multi-component curve of growth, we have determined column densities for all
rotational levels up to J = 7. The J >= 2 states can be reasonably fitted with
a rotational excitation temperature of 307 +/- 23 K. Both the kinetic and
rotational temperatures are similar to those found in previous investigations
of diffuse clouds. The ratios of carbonaceous molecules to hydrogen molecules
are also similar to ratios in diffuse clouds, suggesting a similar chemistry
for this line of sight.Comment: 7 pages, 3 figures, to appear in ApJ Letters (FUSE first-results
issue
Detections of Diffuse Interstellar Bands in the SDSS Low-resolution Spectra
Diffuse interstellar bands (DIBs) have been discovered for almost a century,
but their nature remains one of the most challenging problems in astronomical
spectroscopy. Most recent work to identify and investigate the properties and
carriers of DIBs concentrates on high-resolution spectroscopy of selected
sight-lines. In this paper, we report detections of DIBs in the Sloan Digital
Sky Survey (SDSS) low-resolution spectra of a large sample of Galactic stars.
Using a template subtraction method, we have successfully identified the DIBs
5780, 6283 in the SDSS spectra of a sample of about 2,000
stars and measured their strengths and radial velocities. The sample is by far
the largest ever assembled. The targets span a large range of reddening, E(B-V)
~ 0.2 -- 1.0, and are distributed over a large sky area and involve a wide
range of stellar parameters (effective temperature, surface gravity and
metallicity), confirming that the carriers of DIBs are ubiquitous in the
diffuse interstellar medium (ISM). The sample is used to investigate relations
between strengths of DIBs and magnitudes of line-of-sight extinction, yielding
results (i.e., EW(5780)= 0.61 x E(B-V) and EW(6283) = 1.26 x E(B-V)) consistent
with previous studies. DIB features have also been detected in the
commissioning spectra of the Guoshoujing Telescope (LAMOST) of resolving power
similar to that of SDSS. Detections of DIBs towards hundreds of thousands of
stars are expected from the on-going and up-coming large scale spectroscopic
surveys such as RAVE, SDSS III and LAMOST, particularly from the LAMOST Digital
Sky Survey of the Galactic Anti-center (DSS-GAC). Such a huge database will
provide an unprecedented opportunity to study the demographical distribution
and nature of DIBs as well as using DIBs to probe the distribution and
properties of the ISM and the dust extinction.Comment: 10 pages, 5 figures, accepted for publication in MNRA
Leptin Receptor Signaling and Action in the Central Nervous System
The increasing incidence of obesity in developed nations represents an everâgrowing challenge to health care by promoting diabetes and other diseases. The discovery of the hormone, leptin, a decade ago has facilitated the acquisition of new knowledge regarding the regulation of energy balance. A great deal remains to be discovered regarding the molecular and anatomic actions of leptin, however. Here, we discuss the mechanisms by which leptin activates intracellular signals, the roles that these signals play in leptin action in vivo, and sites of leptin action in vivo. Using âreporterâ mice, in which LRbâexpressing (long form of the leptin receptor) neurons express the histological marker, ÎČâgalactosidase, coupled with the detection of LRbâmediated signal transducer and activator of transcription 3 signaling events, we identified LRb expression in neuronal populations both within and outside the hypothalamus. Understanding the regulation and physiological function of these myriad sites of central leptin action will be a crucial next step in the quest to understand mechanisms of leptin action and energy balance.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/93692/1/oby.2006.310.pd
Resolving the Structure of Ionized Helium in the Intergalactic Medium with the Far Ultraviolet Spectroscopic Explorer
The neutral hydrogen and the ionized helium absorption in the spectra of
quasars are unique probes of structure in the early universe. We present
Far-Ultraviolet Spectroscopic Explorer observations of the line of sight to the
quasar HE2347-4342 in the 1000-1187 A band at a resolving power of 15,000. We
resolve the He II Ly alpha absorption as a discrete forest of absorption lines
in the redshift range 2.3 to 2.7. About 50 percent of these features have H I
counterparts with column densities log N(HI) > 12.3 that account for most of
the observed opacity in He II Ly alpha. The He II to H I column density ratio
ranges from 1 to >1000 with an average of ~80. Ratios of <100 are consistent
with photoionization of the absorbing gas by a hard ionizing spectrum resulting
from the integrated light of quasars, but ratios of >100 in many locations
indicate additional contributions from starburst galaxies or heavily filtered
quasar radiation. The presence of He II Ly alpha absorbers with no H I
counterparts indicates that structure is present even in low-density regions,
consistent with theoretical predictions of structure formation through
gravitational instability.Comment: 8 pages, 4 PostScript figures, uses aaspp4.sty. Appearing in Science,
Vol. 293, Issue 5532, August 10, 200
Inhibition of 11ÎČHSD1 with the S-phenylethylaminothiazolone BVT116429 increases adiponectin concentrations and improves glucose homeostasis in diabetic KKAy mice
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