6,385 research outputs found
Globular Clusters in the dE,N galaxy NGC 3115 DW1: New Insights from Spectroscopy and HST Photometry
The properties of globular clusters in dwarf galaxies are key to
understanding the formation of globular cluster systems, and in particular in
verifying scenarios in which globular cluster systems of larger galaxies formed
(at least partly) from the accretion of dwarf galaxies. Here, we revisit the
globular cluster system of the dE,N galaxy NGC 3115 DW1 - a companion of the
nearby S0 galaxy NGC 3115 - adding Keck/LRIS spectroscopy and HST/WFPC2 imaging
to previous ground-based photometry. Spectra for seven globular clusters reveal
normal abundance ratios with respect to the Milky Way and M31 clusters, as well
as a relatively high mean metallicity ([Fe/H] = -1.0+/-0.1 dex). Crude
kinematics indicate a high velocity dispersion within 10 kpc which could either
be caused by dark matter dominated outer regions, or by the stripping of outer
globular clusters by the nearby giant galaxy NGC 3115. The total galaxy mass
out to 3 and 10 kpc lies between 10^10 and 10^11 solar masses and 2*10^10 and
4*10^11 solar masses, respectively, depending on the mass estimator used and
the assumptions on cluster orbits and systemic velocity. The HST imaging allows
measurement of sizes for two clusters, returning core radii around 2.0 pc,
similar to the sizes observed in other galaxies. Spectroscopy allows an
estimate of the degree of contamination by foreground stars or background
galaxies for the previous ground-based photometry, but does not require a
revision of previous results: NGC 3115 DW1 hosts around 60+/-20 clusters which
corresponds to a specific frequency of 4.9+/-1.9, on the high end for massive
dEs. Given its absolute magnitude (M_V=-17.7 mag) and the properties of its
cluster system, NGC 3115 DW1 appears to be a transition between a luminous dE
and low-luminosity E galaxy.Comment: 25 pages, 8 figures, accepted for publication in The Astronomical
Journal, August 2000 issu
Learning and generation of long-range correlated sequences
We study the capability to learn and to generate long-range, power-law
correlated sequences by a fully connected asymmetric network. The focus is set
on the ability of neural networks to extract statistical features from a
sequence. We demonstrate that the average power-law behavior is learnable,
namely, the sequence generated by the trained network obeys the same
statistical behavior. The interplay between a correlated weight matrix and the
sequence generated by such a network is explored. A weight matrix with a
power-law correlation function along the vertical direction, gives rise to a
sequence with a similar statistical behavior.Comment: 5 pages, 3 figures, accepted for publication in Physical Review
Speciation of cadmium mixed ligand complexes in salt water lakes
Amalgam voltammetry has been used to study heavy metal interaction in model lake water in KNO3 at 23 oC at concentration levels of genuine lake water. The hanging drop amalgam electrode was prepared in situ before exchanging the medium for the sample solution. Half-wave potentials at two metal ion concentrations were measured, one at the actual concentration in the lake while the other at a much lower one. The experimentally determined shifts in half-wave potentials are used to compute several formation constants. At the natural [CO32-] of 0.5 M in the lake, the main contributor to the speciation of cadmium is [Cd(CO3Cl2)]2-. At high [Cd2+], the DPASV detects the presence of free Cd2+ ions, hence, potential polluting effect, while the amalgam reports [Cd(CO3)2Cl)]3- to be dominant above [CO32-] = 0.8 M. There is a variation in the number of complexes detected, their stabilities and percentage distribution in the two methods. Cd2+ ion concentration also affects the number of complexes formed and their stabilities. KEY WORDS: Heavy metals, Hanging drop electrode, Amalgam voltammetry, Speciation, Cadmium mixed ligand complexes  Bull. Chem. Soc. Ethiop. 2003, 17(1), 85-94
Generalized four-point characterization method for resistive and capacitive contacts
In this paper, a four-point characterization method is developed for
resistive samples connected to either resistive or capacitive contacts.
Provided the circuit equivalent of the complete measurement system is known
including coaxial cable and connector capacitances as well as source output and
amplifier input impedances, a frequency range and capacitive scaling factor can
be determined, whereby four-point characterization can be performed. The
technique is demonstrated with a discrete element test sample over a wide
frequency range using lock-in measurement techniques from 1 Hz - 100 kHz. The
data fit well with a circuit simulation of the entire measurement system. A
high impedance preamplifier input stage gives best results, since lock-in input
impedances may differ from manufacturer specifications. The analysis presented
here establishes the utility of capacitive contacts for four-point
characterizations at low frequency.Comment: 21 pages, 10 figure
Charge delocalization and hyperpolarizability in ionic liquids
In this work the role that charge delocalization plays in the non-linear
optical response of ionic liquids is evaluated. The first hyperpolarizability
for the non-linear process of second harmonic generation (SHG) and second
hyperpolarizability for the non-linear process of electro-optical Kerr-Effect
(EOKE) of a large number of ionic liquid forming ions were estimated by means
of density functional theory calculations. The results point to that both
charge delocalization and molecular geometry are the key features that govern
their hyperpolarizabilities. Our findings show that some of the most commonly
used anions in ionic liquids are expected to present strong non-linear
responses while common cations present a much more limited performance.
However, this limitation can be overcome by a proper tailoring of cations to
present charge delocalization over large molecular regions. The hypothesis of
additivity of hyperpolarizabilities in ionic liquids is tested and exploited to
obtain a map of second and third order non-linear susceptibilities of 1496 ion
combinations. This map is intended to be a guide for future works on the
hyperpolarizability of ILsComment: 12 pages, 6 figures, 4 tables, supplementary data associated with
this article can be found, in the online version, at
https://doi.org/10.1016/j.molliq.2021.11815
Neonatal exposure to xenobiotic estrogen alters the adult immune response and exacerbates endometriosis in mice [abstract]
Faculty Mentor: Dr. Susan C. Nagel, Obstetrics/Gynecology, and Women's HealthAbstract only availableEndometriosis is a common medical condition affecting 5-10% of women worldwide, and results in severe cramps, pelvic pain, and infertility. The cause of the disease is still unknown. Endometriosis occurs when endometrial tissue, which escapes into the peritoneal cavity via retrograde menstruation, adheres to other tissues in the cavity and causes irritated, inflamed lesions. Studies have suggested that the risk of developing endometriosis increases in women who have been exposed to xenobiotic (foreign to the body) estrogens during developmental stages of life. Thus, it is our hypothesis that programming of the immune system by xenoestrogens during development could potentially exacerbate endometriosis. This could occur by altering the peritoneal environment and/or the invading endometrial tissue. Therefore, it is our goal to study the effects of neonatal xenoestrogen exposure on the immune system; and ultimately, on the establishment of endometriosis in adulthood. In order to study this response, we dosed two strains of mice (CD1 and C57) with xenobiotic estrogens on postnatal days 2-14. In experiment A, CD1 mice were dosed with vehicle control (corn oil), 20 µg/kg/day, or 200 µg/kg/day bisphenol A. In experiment B, C57 mice were dosed with a vehicle control (corn oil) or 0.1 µg/kg/day diethylstilbestrol. At 8 weeks of age, endometriosis was induced in each strain via both a surgical induction and an injection technique. At 12 weeks, the endometriotic implants were counted and weighed to determine which mice had a greater susceptibility to the condition. Our next objective will be to analyze peritoneal fluid from the treated mice to identify key immune functions (for example, the release of certain cytokines) that may have been programmed by developmental xenoestrogen exposure.Endometriosis is a common medical condition affecting 5-10% of women worldwide, and results in severe cramps, pelvic pain, and infertility. The cause of the disease is still unknown. Endometriosis occurs when endometrial tissue, which escapes into the peritoneal cavity via retrograde menstruation, adheres to other tissues in the cavity and causes irritated, inflamed lesions. Studies have suggested that the risk of developing endometriosis increases in women who have been exposed to xenobiotic (foreign to the body) estrogens during developmental stages of life. Thus, it is our hypothesis that programming of the immune system by xenoestrogens during development could potentially exacerbate endometriosis. This could occur by altering the peritoneal environment and/or the invading endometrial tissue. Therefore, it is our goal to study the effects of neonatal xenoestrogen exposure on the immune system; and ultimately, on the establishment of endometriosis in adulthood. In order to study this response, we dosed two strains of mice (CD1 and C57) with xenobiotic estrogens on postnatal days 2-14. In experiment A, CD1 mice were dosed with vehicle control (corn oil), 20 µg/kg/day, or 200 µg/kg/day bisphenol A. In experiment B, C57 mice were dosed with a vehicle control (corn oil) or 0.1 µg/kg/day diethylstilbestrol. At 8 weeks of age, endometriosis was induced in each strain via both a surgical induction and an injection technique. At 12 weeks, the endometriotic implants were counted and weighed to determine which mice had a greater susceptibility to the condition. Our next objective will be to analyze peritoneal fluid from the treated mice to identify key immune functions (for example, the release of certain cytokines) that may have been programmed by developmental xenoestrogen exposure
Magnetic Flares on Asymptotic Giant Branch Stars
We investigate the consequences of magnetic flares on the surface of
asymptotic giant branch (AGB) and similar stars. In contrast to the solar wind,
in the winds of AGB stars the gas cooling time is much shorter than the outflow
time. As a result, we predict that energetic flaring will not inhibit, and may
even enhance, dust formation around AGB stars. If magnetic flares do occur
around such stars, we expect some AGB stars to exhibit X-ray emission; indeed
certain systems including AGB stars, such as Mira, have been detected in
X-rays. However, in these cases, it is difficult to distinguish between
potential AGB star X-ray emission and, e.g., X-ray emission from the vicinity
of a binary companion. Analysis of an archival ROSAT X-ray spectrum of the Mira
system suggests an intrinsic X-ray luminosity 2x10^{29} erg/sec and temperature
10^7 K. These modeling results suggest that magnetic activity, either on the
AGB star (Mira A) or on its nearby companion (Mira B), is the source of the
X-rays, but do not rule out the possibility that the X-rays are generated by an
accretion disk around Mira B.Comment: ApJ, Accepted; revised version of astro-ph/020923
Spectroscopy of Globular Clusters in M81
We present moderate-resolution spectroscopy of globular clusters (GCs) around
the Sa/Sb spiral galaxy M81 (NGC 3031). Sixteen candidate clusters were
observed with the Low Resolution Imaging Spectrograph on the Keck I telescope.
All are confirmed as bona fide GCs, although one of the clusters appears to
have been undergoing a transient event during our observations. In general, the
M81 globular cluster system (GCS) is found to be very similar to the Milky Way
(MW) and M31 systems, both chemically and kinematically. A kinematic analysis
of the velocities of 44 M81 GCS, (the 16 presented here and 28 from previous
work) strongly suggests that the red, metal-rich clusters are rotating in the
same sense as the gas in the disk of M81. The blue, metal-poor clusters have
halo-like kinematics, showing no evidence for rotation. The kinematics of
clusters whose projected galactocentric radii lie between 4 and 8 kpc suggest
that they are rotating much more than those which lie outside these bounds. We
suggest that these rotating, intermediate-distance clusters are analogous to
the kinematic sub-population in the metal-rich, disk GCs observed in the MW and
we present evidence for the existence of a similar sub-population in the
metal-rich clusters of M31. With one exception, all of the M81 clusters in our
sample have ages that are consistent with MW and M31 GCs. One cluster may be as
young as a few Gyrs. The correlations between absorption-line indices
established for MW and M31 GCs also hold in the M81 cluster system, at least at
the upper end of the metallicity distribution (which our sample probes). On the
whole, the mean metallicity of the M81 GCS is similar to the metallicity of the
MW and M31 GCSs. The projected mass of M81 is similar to the masses of the MW
and M31. Its mass profile indicates the presence of a dark matter halo.Comment: 35 pages, including 11 figures and 9 tables. Accepted for publication
in the Astronomical Journa
A measurement of the differential cross section for the two-body photodisintegration of 3He at theta_LAB = 90deg using tagged photons in the energy range 14 -- 31 MeV
The two-body photodisintegration of 3He has been investigated using tagged
photons with energies from 14 -- 31 MeV at MAX-lab in Lund, Sweden. The
two-body breakup channel was unambiguously identified by the (nonsimultaneous)
detection of both protons and deuterons. This approach was made feasible by the
over-determined kinematic situation afforded by the tagged-photon technique.
Proton- and deuteron-energy spectra were measured using four silicon
surface-barrier detector telescopes located at a laboratory angle of 90deg with
respect to the incident photon-beam direction. Average statistical and
systematic uncertainties of 5.7% and 6.6% in the differential cross section
were obtained for 11 photon-energy bins with an average width of 1.2 MeV. The
results are compared to previous experimental data measured at comparable
photon energies as well as to the results of two recent Faddeev calculations
which employ realistic potential models and take into account three-nucleon
forces and final-state interactions. Both the accuracy and precision of the
present data are improved over the previous measurements. The data are in good
agreement with most of the previous results, and favor the inclusion of
three-nucleon forces in the calculations.Comment: 12 pages, 13 figures; further Referee comments addresse
Neonatal exposure to xenobiotic estrogen may alter the adult immune response and exacerbate endometriosis in mice [abstract]
Abstract only availableEndometriosis is a common medical condition affecting 5-10% of women worldwide and often results in severe cramps, pelvic pain, and infertility. The condition occurs when endometrial tissue, which escapes into the peritoneal cavity via retrograde menstruation, adheres to peritoneal cavity tissues and causes irritated, inflamed lesions. Studies have suggested that the risk of developing endometriosis increases in women who have been exposed to xenobiotic (foreign to the body) estrogens during development. This could be due to developmental programming of the peritoneal environment, and specifically, an altered immune function within this environment. Therefore, it is our hypothesis that developmental programming by xenoestrogens alters the immune response to shed endometrial tissue and exacerbates endometriosis. To better understand the role of xenoestrogens in immune programming, we are conducting our studies using a mouse model of surgically induced endometriosis. In particular, we are concentrating on two major aspects of immunity: 1) the presence of immune cells and 2) the function of those cells. Our study of the former is being largely performed using methods of immunohistochemistry (IHC). IHC allows us to quantify the macrophages present in the peritoneal fluid of experimental mice (exposed to diethylstilbestrol) versus control mice (no xenoestrogen exposure). In order to study our second focus, immune cell function, we are using a cytokine antibody array to determine the relative cytokine concentrations in the peritoneal fluid samples. By identifying the degree to which certain cytokine concentrations differ, we hope to better understand the effect of xenoestrogen exposure on immune cell function.Life Sciences Undergraduate Research Opportunity Progra
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