1,177 research outputs found
Oxygen isotope equilibrium between muscovite and water
Oxygen isotopes have been equilibrated between muscovite and aqueous alkali chloride solution and between paragonite and alkali chloride solution in the temperature range of 400°–650°C at 1 and 1.5 kb fluid pressure. Isotopic equilibrium was inferred from the fact that compatible fractionation factors were obtained using 3 different chemical reactions to produce the mica: (1) muscovite or paragonite was prepared by reacting natural kaolinite with 2–3 molal KCl or NaCl solutions; (2) muscovite was crystallized in pure water from a gel; and (3) synthetic paragonite was reacted with 2–3 molal KCl solution, producing muscovite by an alkali ion exchange reaction. The 1 M modification of the mica was made in every experiment. In several cases the extent of oxygen exchange was traced by running companion equilibrations in solutions of unusually low O^(18)/O^(16) ratio. No isotopic fractionation was discernible between muscovite and paragonite in the temperature range studied. Per mille fractionations between muscovite and water are given by the expression 10^3 In α = 2.38(10^6T^(−2)) − 3.89. These data can be combined with the results of other laboratory equilibration studies to establish a set of calibrated oxygen isotope geothermometers. Analogous to the alkali feldspar systems previously reported, the direct relationship between cation and oxygen isotope exchange suggests that some type of solution-redeposition mechanism operated during muscovite-paragonite transformations in aqueous solutions. Also, the extensive oxygen isotope exchange (with the solution) that accompanies the formation of muscovite from kaolinite implies a breakdown of the kaolinite structure. This notion does not concur with hypotheses based on rate studies and X-ray measurements that the unaltered kaolinite structure is partially inherited by the mica
Hubble Space Telescope Planetary Camera Images of NGC 1316
We present HST Planetary Camera V and I~band images of the central region of
the peculiar giant elliptical galaxy NGC 1316. The inner profile is well fit by
a nonisothermal core model with a core radius of 0.41" +/- 0.02" (34 pc). At an
assumed distance of 16.9 Mpc, the deprojected luminosity density reaches \sim
2.0 \times 10^3 L_{\sun} pc.
Outside the inner two or three arcseconds, a constant mass-to-light ratio of
is found to fit the observed line width measurements. The
line width measurements of the center indicate the existence of either a
central dark object of mass 2 \times 10^9 M_{\sun}, an increase in the
stellar mass-to-light ratio by at least a factor of two for the inner few
arcseconds, or perhaps increasing radial orbit anisotropy towards the center.
The mass-to-light ratio run in the center of NGC 1316 resembles that of many
other giant ellipticals, some of which are known from other evidence to harbor
central massive dark objects (MDO's).
We also examine twenty globular clusters associated with NGC 1316 and report
their brightnesses, colors, and limits on tidal radii. The brightest cluster
has a luminosity of 9.9 \times 10^6 L_{\sun} (), and the
faintest detectable cluster has a luminosity of 2.4 \times 10^5 L_{\sun}
(). The globular clusters are just barely resolved, but their core
radii are too small to be measured. The tidal radii in this region appear to be
35 pc. Although this galaxy seems to have undergone a substantial merger
in the recent past, young globular clusters are not detected.Comment: 21 pages, latex, postscript figures available at
ftp://delphi.umd.edu/pub/outgoing/eshaya/fornax
Hubble Space Telescope Observations of M32: The Color-Magnitude Diagram
We present a V-I color-magnitude diagram for a region 1'-2' from the center
of M32 based on Hubble Space Telescope WFPC2 images. The broad color-luminosity
distribution of red giants shows that the stellar population comprises stars
with a wide range in metallicity. This distribution cannot be explained by a
spread in age. The blue side of the giant branch rises to M_I ~ -4.0 and can be
fitted with isochrones having [Fe/H] ~ -1.5. The red side consists of a heavily
populated and dominant sequence that tops out at M_I ~ -3.2, and extends beyond
V-I=4. This sequence can be fitted with isochrones with -0.2 < [Fe/H] < +0.1,
for ages running from 15 Gyr to 5 Gyr respectively. We do not find the
optically bright asymptotic giant branch stars seen in previous ground-based
work and argue that the majority of them were artifacts of crowding. Our
results are consistent with the presence of the infrared-luminous giants found
in ground-based studies, though their existence cannot be directly confirmed by
our data. There is little evidence for an extended or even a red horizontal
branch, but we find a strong clump on the giant branch itself. If the age
spread is not extreme, the distribution of metallicities in M32 is considerably
narrower than that of the closed-box model of chemical evolution, and also
appears somewhat narrower than that of the solar neighborhood. Overall, the M32
HST color-magnitude diagram is consistent with the average luminosity-weighted
age of 8.5 Gyr and [Fe/H] = -0.25 inferred from integrated spectral indices.Comment: 22 pages, AASTeX, aaspp4 and flushrt style files included, 11
postscript figures, figures 1,2,5,7, and 8 available at
ftp://bb3.jpl.nasa.gov/pub/m32 . Submitted to the Astronomical Journa
Star Cluster Formation and Evolution in Nearby Starburst Galaxies: II. Initial Conditions
We use the ages, masses and metallicities of the rich young star cluster
systems in the nearby starburst galaxies NGC 3310 and NGC 6745 to derive their
cluster formation histories and subsequent evolution. We further expand our
analysis of the systematic uncertainties involved in the use of broad-band
observations to derive these parameters by examining the effects of a priori
assumptions on the individual cluster metallicities. The age (and metallicity)
distributions of both the clusters in the circumnuclear ring in NGC 3310 and of
those outside the ring are statistically indistinguishable, but there is a
clear and significant excess of higher-mass clusters IN the ring compared to
the non-ring cluster sample; it is likely that the physical conditions in the
starburst ring may be conducive for the formation of higher-mass star clusters,
on average, than in the relatively more quiescent environment of the main
galactic disc. For the NGC 6745 cluster system we derive a median age of ~10
Myr. NGC 6745 contains a significant population of high-mass "super star
clusters", with masses in the range 6.5 <= log(M_cl/M_sun) <= 8.0. This
detection supports the scenario that such objects form preferentially in the
extreme environments of interacting galaxies. The age of the cluster
populations in both NGC 3310 and NGC 6745 is significantly lower than their
respective characteristic cluster disruption time-scales. This allows us to
obtain an independent estimate of the INITIAL cluster mass function slope,
alpha = 2.04(+- 0.23)(+0.13)(-0.43) for NGC 3310, and 1.96(+- 0.15)(+- 0.19)
for NGC 6745, respectively, for masses M_cl >= 10^5 M_sun and M_cl >= 4 x 10^5
M_sun. These mass function slopes are consistent with those of other young star
cluster systems in interacting and starburst galaxies.Comment: 17 pages LaTeX, incl. 11 postscript figures, accepted for publication
in MNRA
Stellar Populations in the Central 0.5 pc of Our Galaxy III: The Dynamical Sub-structures
We measure the 3D kinematic structures of the young stars within the central
0.5 parsec of our Galactic Center using the 10 m telescopes of the W.~M.~Keck
Observatory over a time span of 25 years. Using high-precision measurements of
positions on the sky, and proper motions and radial velocities from new
observations and the literature, we constrain the orbital parameters for each
young star. Our results show two statistically significant sub-structures: a
clockwise stellar disk with 18 candidate stars, as has been proposed before,
but with an improved disk membership; a second, almost edge-on plane of 10
candidate stars oriented East-West on the sky that includes at least one IRS 13
star. We estimate the eccentricity distribution of each sub-structure and find
that the clockwise disk has = 0.39 and the edge-on plane has =
0.68. We also perform simulations of each disk/plane with incompleteness and
spatially-variable extinction to search for asymmetry. Our results show that
the clockwise stellar disk is consistent with a uniform azimuthal distribution
within the disk. The edge-on plane has an asymmetry that cannot be explained by
variable extinction or incompleteness in the field. The orientation, asymmetric
stellar distribution, and high eccentricity of the edge-on plane members
suggest that this structure may be a stream associated with the IRS 13 group.
The complex dynamical structure of the young nuclear cluster indicates that the
star formation process involved complex gas structures and dynamics and is
inconsistent with a single massive gaseous disk.Comment: 41 pages, 26 figures, 13 tables, 2 appendices. Accepted for
publication in Ap
Developing Secure Power Systems Professional Competence: Alignment and Gaps in Workforce Development Programs?Summary Report
This document is a summarization of the report, Developing Secure Power Systems Professional Competence: Alignment and Gaps in Workforce Development Programs, the final report for phase 2 of the SPSP (DOE workforce study) project
Dirac's Observables for the Rest-Frame Instant Form of Tetrad Gravity in a Completely Fixed 3-Orthogonal Gauge
We define the {\it rest-frame instant form} of tetrad gravity restricted to
Christodoulou-Klainermann spacetimes. After a study of the Hamiltonian group of
gauge transformations generated by the 14 first class constraints of the
theory, we define and solve the multitemporal equations associated with the
rotation and space diffeomorphism constraints, finding how the cotriads and
their momenta depend on the corresponding gauge variables. This allows to find
quasi-Shanmugadhasan canonical transformation to the class of 3-orthogonal
gauges and to find the Dirac observables for superspace in these gauges.
The construction of the explicit form of the transformation and of the
solution of the rotation and supermomentum constraints is reduced to solve a
system of elliptic linear and quasi-linear partial differential equations. We
then show that the superhamiltonian constraint becomes the Lichnerowicz
equation for the conformal factor of the 3-metric and that the last gauge
variable is the momentum conjugated to the conformal factor. The gauge
transformations generated by the superhamiltonian constraint perform the
transitions among the allowed foliations of spacetime, so that the theory is
independent from its 3+1 splittings. In the special 3-orthogonal gauge defined
by the vanishing of the conformal factor momentum we determine the final Dirac
observables for the gravitational field even if we are not able to solve the
Lichnerowicz equation. The final Hamiltonian is the weak ADM energy restricted
to this completely fixed gauge.Comment: RevTeX file, 141 page
Plasma Dynamics
Contains reports on ten research projects split into two sections.National Science Foundation (Grant ENG77-00340)U.S. Department of Energy (Contract EY-76-S-02-2766)U.S. Air Force - Office of Scientific Research (Grant AFOSR-77-3143)U.S. Department of Energy (Contract ET-78-C-01-3019)U.S. Department of Energy (Contract ET-78-S-02-4681)U.S. Department of Energy (Contract ET-78-S-02-4682)U.S. Department of Energy (Grant EG-77-G-01-4107)U.S. Department of Energy (Contract ET-78-S-02-4714)U.S. Department of Energy (Contract ET-78-S-02-4886)U.S. Department of Energy (Contract ET-78-S-02-4690
Expression of human beta-defensins 1 and 2 in kidneys with chronic bacterial infection
BACKGROUND: Constitutive expression and localization of antimicrobial human β-defensin-1 (HBD-1) in human kidneys as a potential mechanism of antimicrobial defense has been previously reported. Inducible expression of human β-defensin-2 (HBD-2) has been described in various epithelial organs but not for the urogenital tract. METHODS: We investigated the gene- and protein expression of HBD-1 and HBD-2 by reverse transcriptase-polymerase chain reaction, and immunohistochemistry in 15 normal human kidney samples and 15 renal tissues with chronic bacterial infection. Additionally, cell culture experiments were performed to study HBD gene expression by real-time RT-PCR in response to inflammatory cytokines TNFα and IL-1β as well as lipopolysaccharide from Gram-negative bacteria. RESULTS: Constitutive HBD-1 gene- and protein expression was detected in normal renal tissue and kidneys with chronic infection. As a novel finding, inducible HBD-2 gene- and protein expression was demonstrated in tubulus epithelia with chronic infection but not in normal renal tissue. In pyelonephritic kidneys HBD-1 and HBD-2 expression showed a similar pattern of localizaton in distal tubules, loops of Henle and in collecting ducts of the kidney. Furthermore, real-time RT-PCR of kidney derived cell lines stimulated with inflammatory agents TNF-α, IL-1β and LPS revealed a strong increase in relative HBD-2 transcription level and also a slight increase in relative HBD-1 transcription level. CONCLUSIONS: Upregulated HBD-2 expression in renal tubulus epithelium indicates a role of a wider range of human defensins for antimicrobial host defense in the urogenital tract than previously recognized
- …