3,177 research outputs found
Spectroscopy of Candidate Members of the Eta Cha and MBM12 Young Associations
We present an analysis of candidate members of the Eta Cha and MBM 12A young
associations. For an area of 0.7 deg^2 toward Eta Cha, we have performed a
search for members of the association by combining JHK_s photometry from 2MASS
and i photometry from DENIS with followup optical spectroscopy at Magellan
Observatory. We report the discovery of three new members with spectral types
of M5.25-M5.75, corresponding to masses of 0.13-0.08 M_sun by theoretical
evolutionary models. Two and three of these members were found independently by
Lyo and coworkers and Song and coworkers, respectively. Meanwhile, no brown
dwarfs were detected in Eta Cha down to the completeness limit of 0.015 M_sun.
For MBM 12A, we have obtained spectra of three of the remaining candidate
members that lacked spectroscopy at the end of the survey by Luhman, all of
which are found to be field M dwarfs. Ogura and coworkers have recently
presented four "probable" members of MBM 12A. However, two of these objects
were previously classified as field dwarfs by the spectroscopy of Luhman. In
this work, we find that the other two objects are field dwarfs as well.Comment: to be published in The Astrophysical Journal, 19 pages, 7 figure
The Effect of Substratum Roughness on Osteoclast-like Cells In Vitro
Calcium phosphate powders were used to produce three groups of experimental substrata for the culture of primary rat bone marrow cells in conditions which permitted the survival and function of osteoclasts. Each of the three experimental groups were subdivided by differences in substratum surface roughness and following a culture period of 7 to 11 days, the culture units were stained for tartrate-resistant acid phosphatase activity. In all samples both small, sometimes mononuclear, and large multinucleate cells stained positive for tartrate-resistant acid phosphatase activity and the numbers and types of cells were quantified and statistically analyzed. Following histochemical staining the samples were dehydrated and gold coated for examination by scanning electron microscopy. Cells were found to create distinct resorption lacunae in most substrata, but not on the dense, high temperature sintered hydroxyapatite, and cells responsible for this activity were confirmed as exhibiting positive tartrate resistant acid phosphatase activity. Statistical analyses showed that both the total number of tartrate-resistant acid phosphatase positive cells and the number of multinucleate tartrate-resistant acid phosphatase positive cells was greater on the rougher than the smoother surfaces
Triggered Star Formation by Massive Stars
We present our diagnosis of the role that massive stars play in the formation
of low- and intermediate-mass stars in OB associations (the Lambda Ori region,
Ori OB1, and Lac OB1 associations). We find that the classical T Tauri stars
and Herbig Ae/Be stars tend to line up between luminous O stars and
bright-rimmed or comet-shaped clouds; the closer to a cloud the progressively
younger they are. Our positional and chronological study lends support to the
validity of the radiation-driven implosion mechanism, where the Lyman continuum
photons from a luminous O star create expanding ionization fronts to evaporate
and compress nearby clouds into bright-rimmed or comet-shaped clouds. Implosive
pressure then causes dense clumps to collapse, prompting the formation of
low-mass stars on the cloud surface (i.e., the bright rim) and
intermediate-mass stars somewhat deeper in the cloud. These stars are a
signpost of current star formation; no young stars are seen leading the
ionization fronts further into the cloud. Young stars in bright-rimmed or
comet-shaped clouds are likely to have been formed by triggering, which would
result in an age spread of several megayears between the member stars or star
groups formed in the sequence.Comment: 2007, ApJ, 657, 88
Three-Dimensional X-ray Observation of Atmospheric Biological Samples by Linear-Array Scanning-Electron Generation X-ray Microscope System
Recently, we developed a soft X-ray microscope called the scanning-electron generation X-ray microscope (SGXM), which consists of a simple X-ray detection system that detects X-rays emitted from the interaction between a scanning electron beam (EB) and the thin film of the sample mount. We present herein a three-dimensional (3D) X-ray detection system that is based on the SGXM technology and designed for studying atmospheric biological samples. This 3D X-ray detection system contains a linear X-ray photodiode (PD) array. The specimens are placed under a CuZn-coated Si3N4 thin film, which is attached to an atmospheric sample holder. Multiple tilt X-ray images of the samples are detected simultaneously by the linear array of X-ray PDs, and the 3D structure is calculated by a new 3D reconstruction method that uses a simulated-annealing algorithm. The resulting 3D models clearly reveal the inner structure of the bacterium. In addition, the proposed method can easily be used for diverse samples in a broad range of scientific fields
The Statistical Mechanics of the Three-Dimensional Euclidean Black Hole
In its formulation as a Chern-Simons theory, three-dimensional general
relativity induces a Wess-Zumino-Witten action on spatial boundaries. Treating
the horizon of the three-dimensional Euclidean black hole as a boundary, I
count the states of the resulting WZW model, and show that when analytically
continued back to Lorentzian signature, they yield the correct
Bekenstein-Hawking entropy. The relevant states can be understood as ``would-be
gauge'' degrees of freedom that become dynamical at the horizon.Comment: 9 pages, LaTeX. Significant sign error corrected, continuation to
Lorentzian signature clarified, several other clarifications (although
conclusion is unaffected). To appear in Phys. Rev.
Ten Million Degree Gas in M 17 and the Rosette Nebula: X-ray Flows in Galactic H II Regions
We present the first high-spatial-resolution X-ray images of two high-mass
star forming regions, the Omega Nebula (M 17) and the Rosette Nebula (NGC
2237--2246), obtained with the Chandra X-ray Observatory Advanced CCD Imaging
Spectrometer (ACIS) instrument. The massive clusters powering these H II
regions are resolved at the arcsecond level into >900 (M 17) and >300 (Rosette)
stellar sources similar to those seen in closer young stellar clusters.
However, we also detect soft diffuse X-ray emission on parsec scales that is
spatially and spectrally distinct from the point source population. The diffuse
emission has luminosity L_x ~ 3.4e33 ergs/s in M~17 with plasma energy
components at kT ~0.13 and ~0.6 keV (1.5 and 7 MK), while in Rosette it has L_x
\~6e32 ergs/s with plasma energy components at kT ~0.06 and ~0.8 keV (0.7 and 9
MK). This extended emission most likely arises from the fast O-star winds
thermalized either by wind-wind collisions or by a termination shock against
the surrounding media. We establish that only a small portion of the wind
energy and mass appears in the observed diffuse X-ray plasma; in these blister
H II regions, we suspect that most of it flows without cooling into the
low-density interstellar medium. These data provide compelling observational
evidence that strong wind shocks are present in H II regions.Comment: 35 pages, including 11 figures; to appear in ApJ, August 20, 2003. A
version with high-resolution figures is available at
ftp://ftp.astro.psu.edu/pub/townsley/diffuse.ps.g
SCUBA Mapping of Spitzer c2d Small Clouds and Cores
We present submillimeter observations of dark clouds that are part of the
Spitzer Legacy Program, From Molecular Cores to Planet-Forming Disks (c2d). We
used the Submillimetre Common User's Bolometer Array to map the regions
observed by Spitzer by the c2d program to create a census of dense molecular
cores including data from the infrared to the submillimeter. In this paper, we
present the basic data from these observations: maps, fluxes, and source
attributes. We also show data for an object just outside the Perseus cloud that
was serendipitously observed in our program. We propose that this object is a
newly discovered, evolved protostar.Comment: 37 pages, accepted to The Astronomical Journa
Finite size corrections in massive Thirring model
We calculate for the first time the finite size corrections in the massive
Thirring model. This is done by numerically solving the equations of periodic
boundary conditions of the Bethe ansatz solution. It is found that the
corresponding central charge extracted from the term is around 0.4 for
the coupling constant of and decreases down to zero when
. This is quite different from the predicted central
charge of the sine-Gordon model.Comment: 8 pages, Latex, 2 figure
Insulator-to-metal transition in Kondo insulators under strong magnetic field
Magnetization curve and changes of the single-particle excitation spectra by
magnetic field are calculated for the periodic Anderson model at half-filling
in infinite spatial dimension by using the exact diagonalization method. It is
found that the field-induced insulator-to-metal transition occurs at a critical
field , which is of the order of the single ion Kondo temperature. The
transition is of first order, but could be of second order in the infinite
system size limit. These results are compared with the experiments on the Kondo
insulator YbB.Comment: 11 pages, REVTEX, no figures; 7 figures available on request; To
appear in Phys. Rev. B, Mar.15, 199
Massless Thirring model in canonical quantization scheme
It is shown that the exact solvability of the massless Thirring model in the
canonical quantization scheme originates from the intrinsic linearizability of
its Heisenberg equations in the method of dynamical mappings. The corresponding
role of inequivalent representations of free massless Dirac field is
elucidated.Comment: 10 page
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