21,996 research outputs found
vbyCaHbeta CCD Photometry of Clusters. VI. The Metal-Deficient Open Cluster NGC 2420
CCD photometry on the intermediate-band vbyCaHbeta system is presented for
the metal-deficient open cluster, NGC 2420. Restricting the data to probable
single members of the cluster using the CMD and the photometric indices alone
generates a sample of 106 stars at the cluster turnoff. The average E(b-y) =
0.03 +/- 0.003 (s.e.m.) or E(B-V) = 0.050 +/- 0.004 (s.e.m.), where the errors
refer to internal errors alone. With this reddening, [Fe/H] is derived from
both m1 and hk, using b-y and Hbeta as the temperature index. The agreement
among the four approaches is reasonable, leading to a final weighted average of
[Fe/H] = -0.37 +/- 0.05 (s.e.m.) for the cluster, on a scale where the Hyades
has [Fe/H] = +0.12. When combined with the abundances from DDO photometry and
from recalibrated low-resolution spectroscopy, the mean metallicity becomes
[Fe/H] = -0.32 +/- 0.03. It is also demonstrated that the average cluster
abundances based upon either DDO data or low-resolution spectroscopy are
consistently reliable to 0.05 dex or better, contrary to published attempts to
establish an open cluster metallicity scale using simplistic offset corrections
among different surveys.Comment: scheduled for Jan. 2006 AJ; 33 pages, latex, includes 7 figures and 2
table
Heat and extension at mid- and lower crustal levels of the Rio Grande rift
The process by which large amounts (50 to 200 percent) of crustal extension are produced was concisely described by W. Hamilton in 1982 and 1983. More recently, England, Sawyer, P. Morgan and others have moved toward quantifying models of lithospheric thinning by incorporating laboratory and theoretical data on rock rheology as a function of composition, temperature, and strain rate. Hamilton's description identifies three main crustal layers, each with a distinctive mechanical behavior; brittle fracturing and rotation in the upper crust, discontinuous ductile flow in the middle crust and laminar ductile flow in the lower crust. The temperature and composition dependent brittle-ductile transition essentially defines the diffuse boundary between upper and middle crust. It was concluded that the heat responsible for the highly ductile nature of the lower crust and the lensoidal and magma body structures at mid-crustal depths in the rift was infused into the crust by relatively modest ( 10 percent by mass) magmatic upwelling (feeder dikes) from Moho levels. Seismic velocity-versus-depth data, supported by gravity modeling and the fact that volumes of rift related volcanics are relatively modest ( 6000 cubic km) for the Rio Grande system, all imply velocities and densities too small to be consistent with a massive, composite, mafic intrusion in the lower crust
Coupled atomic-molecular condensates in a double-well potential: decaying molecular oscillations
We present a four-mode model that describes coherent photo-association (PA)
in a double-well Bose-Einstein condensate, focusing on the molecular
populations in certain parameters. Our numerical results predict an interesting
strong-damping effect of molecular oscillations by controlling the particle
tunnellings and PA light strength, which may provide a promising way for
creating a stable molecular condensate via coherent PA in a magnetic
double-well potential.Comment: 6 pages, 4 figures, submitte
Frequency Dependent Specific Heat from Thermal Effusion in Spherical Geometry
We present a novel method of measuring the frequency dependent specific heat
at the glass transition applied to 5-polyphenyl-4-ether. The method employs
thermal waves effusing radially out from the surface of a spherical thermistor
that acts as both a heat generator and thermometer. It is a merit of the method
compared to planar effusion methods that the influence of the mechanical
boundary conditions are analytically known. This implies that it is the
longitudinal rather than the isobaric specific heat that is measured. As
another merit the thermal conductivity and specific heat can be found
independently. The method has highest sensitivity at a frequency where the
thermal diffusion length is comparable to the radius of the heat generator.
This limits in practise the frequency range to 2-3 decades. An account of the
3omega-technique used including higher order terms in the temperature
dependency of the thermistor and in the power generated is furthermore given.Comment: 17 pages, 15 figures, Substantially revised versio
Molecular Approaches to Sarcoma Therapy
Soft tissue sarcomas comprise a heterogeneous group of aggressive tumors that have a relatively poor prognosis. Although
conventional therapeutic regimens can effectively cytoreduce the overall tumor mass, they fail to consistently achieve a
curative outcome. Alternative gene-based approaches that counteract the underlying neoplastic process by eliminating
the clonal aberrations that potentiate malignant behavior have been proposed. As compared to the accumulation of gene
alterations associated with epithelial carcinomas, sarcomas are frequently characterized by the unique presence of a single
chromosomal translocation in each histological subtype. Similar to the Philadelphia chromosome associated with CML,
these clonal abnormalities result in the fusion of two independent unrelated genes to generate a unique chimeric protein
that displays aberrant activity believed to initiate cellular transformation. Secondary gene mutations may provide an additional
growth advantage that further contributes to malignant progression. The recent clinical success of the tyrosine kinase
inhibitor, STI571, suggests that therapeutic approaches specifically directed against essential survival factors in sarcoma cells
may be effective. This review summarizes published approaches targeting a specific molecular mechanism associated with
sarcomagenesis. The strategy and significance of published translational studies in six distinct areas are presented. These
include: (1) the disruption of chimeric transcription factor activity; (2) inhibition of growth stimulatory post-translational
modifications; (3) restoration of tumor suppressor function; (4) interference with angiogenesis; (5) induction of apoptotic
pathways; and (6) introduction of toxic gene products. The potential for improving outcomes in sarcoma patients and the
conceptual obstacles to be overcome are discussed
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