527 research outputs found
Lineage-specific Gene Expression in the Sea Urchin Embryo
Within a few days of fertilization, the sea urchin embryo develops into a small differentiated organism consisting of about 1800 cells and capable of feeding, swimming, and the further ontogenic transformations required in the succeeding weeks of larval growth. A number of distinct cell lineages that are clearly specialized at the morphological and functional levels can be discerned in the advanced embryo, and many of these can be traced back to particular sets of early blastomeres. Classical cell lineage and experimental studies (Hörstadius 1939; for review, see Angerer and Davidson 1984) have shown that certain of these lineages appear to be specified, at least in part, in consequence of the maternal components inherited in those regions of egg cytoplasm occupied by their progenitor cells. Specification of others among the early cell lineages clearly depends on inductive interactions that occur between blastomeres during cleavage. For the molecular biologist, as for his predecessors, this rapidly developing and simply constructed embryo offers the advantages of experimental accessibility. Thus, in respect to direct molecular-level analyses of gene activity in the embryo, for both specific genes and overall transcript populations and their protein products, the sea urchin is at present the best known embryonic system (e.g., reviews of Hentschel and Birnstiel 1981; Davidson et al. 1982; Angerer and Davidson 1984)
Dust in Spiral Galaxies: Comparing Emission and Absorption to Constrain Small-Scale and Very Cold Structures
The detailed distribution of dust in the disks of spiral galaxies is
important to understanding the radiative transfer within disks, and to
measuring overall dust masses if significant quantities of dust are either very
opaque or very cold. We address this issue by comparing measures of dust
absorption, using the galaxy-overlap technique in the optical, with measures of
the dust grains' thermal emission from 50-2000 micron using ISOPHOT on board
ISO and SCUBA at the JCMT. We examine three spiral galaxies projected partially
in front of E/S0 galaxies --- AM1316-241, NGC 5545, and NGC 5091 (for NGC 5091
we have only optical and ISO data). Adopting an empirical exponential model for
the dust distribution, we compare column densities and dust masses derived from
the absorption and emission techniques. This comparison is sensitive to the
amount of dust mass in small, opaque structures, which would not contribute
strongly to area-weighted absorption measures, and to very cold dust, which
would contribute to optical absorption but provide only a small fraction of the
sub-mm emission. In AM1316-241, we find global dust masses of 2-5 x 10^7
M_solar, both techniques agreeing at the 50% level. NGC 5545 has about half
this dust mass. The concordance of dust masses is well within the errors
expected from our knowledge of the radial distribution of dust, and argues
against any dominant part of the dust mass being so cold or opaque. The 50-2000
micron data are well fitted by modified Planck functions with an emissivity law
beta=-2, at 21 +/- 2 K. We also present 12 micron ISOCAM observations of these
pairs.Comparison of H-alpha and 12 micron images of NGC 5545 indicate that
ISOCAM images are reliable tracers of star formation.Comment: 16 pages, 4 tables, 8 figures, in press for October Astronomical
Journa
Advanced Space Transportation Concepts and Propulsion Technologies for a New Delivery Paradigm
This paper describes Advanced Space Transportation Concepts and Propulsion Technologies for a New Delivery Paradigm. It builds on the work of the previous paper "Approach to an Affordable and Productive Space Transportation System". The scope includes both flight and ground system elements, and focuses on their compatibility and capability to achieve a technical solution that is operationally productive and also affordable. A clear and revolutionary approach, including advanced propulsion systems (advanced LOX rich booster engine concept having independent LOX and fuel cooling systems, thrust augmentation with LOX rich boost and fuel rich operation at altitude), improved vehicle concepts (autogeneous pressurization, turbo alternator for electric power during ascent, hot gases to purge system and keep moisture out), and ground delivery systems, was examined. Previous papers by the authors and other members of the Space Propulsion Synergy Team (SPST) focused on space flight system engineering methods, along with operationally efficient propulsion system concepts and technologies. This paper continues the previous work by exploring the propulsion technology aspects in more depth and how they may enable the vehicle designs from the previous paper. Subsequent papers will explore the vehicle design, the ground support system, and the operations aspects of the new delivery paradigm in greater detail
Lineage-specific Gene Expression in the Sea Urchin Embryo
Within a few days of fertilization, the sea urchin embryo develops into a small differentiated organism consisting of about 1800 cells and capable of feeding, swimming, and the further ontogenic transformations required in the succeeding weeks of larval growth. A number of distinct cell lineages that are clearly specialized at the morphological and functional levels can be discerned in the advanced embryo, and many of these can be traced back to particular sets of early blastomeres. Classical cell lineage and experimental studies (Hörstadius 1939; for review, see Angerer and Davidson 1984) have shown that certain of these lineages appear to be specified, at least in part, in consequence of the maternal components inherited in those regions of egg cytoplasm occupied by their progenitor cells. Specification of others among the early cell lineages clearly depends on inductive interactions that occur between blastomeres during cleavage. For the molecular biologist, as for his predecessors, this rapidly developing and simply constructed embryo offers the advantages of experimental accessibility. Thus, in respect to direct molecular-level analyses of gene activity in the embryo, for both specific genes and overall transcript populations and their protein products, the sea urchin is at present the best known embryonic system (e.g., reviews of Hentschel and Birnstiel 1981; Davidson et al. 1982; Angerer and Davidson 1984)
Stringy Robinson-Trautman Solutions
A class of solutions of the low energy string theory in four dimensions is
studied. This class admits a geodesic, shear-free null congruence which is
non-twisting but in general diverging and the corresponding solutions in
Einstein's theory form the Robinson-Trautman family together with a subset of
the Kundt's class. The Robinson-Trautman conditions are found to be frame
invariant in string theory. The Lorentz Chern-Simons three form of the stringy
Robinson-Trautman solutions is shown to be always closed. The stringy
generalizations of the vacuum Robinson-Trautman equation are obtained and three
subclasses of solutions are identified. One of these subclasses exists, among
all the dilatonic theories, only in Einstein's theory and in string theory.
Several known solutions including the dilatonic black holes, the pp- waves, the
stringy C-metric and certain solutions which correspond to exact conformal
field theories are shown to be particular members of the stringy
Robinson-Trautman family. Some new solutions which are static or asymptotically
flat and radiating are also presented. The radiating solutions have a positive
Bondi mass. One of these radiating solutions has the property that it settles
down smoothly to a black hole state at late retarded times.Comment: Latex, 30 Pages, 1 Figure; to appear in Phys. Rev.
Quantum Optics and Photonics
Contains reports on nine research projects.U.S. Air Force - Office of Scientific Research (Contract F49620-82-C-0091)U.S. Air Force - Rome Air Development CenterJoint Services Electronics Program (Contract DAAG29-83-K-0003)National Science Foundation Grant (Grant PHY 82-710369
Re-HEDP : pharmacokinetic characterization, clinical and dosimetric evaluation in osseous metastatic patients with two levels of radiopharmaceutical dose
BACKGROUND: A study for pain relief therapy with (188)Re-HEDP was done in patients with bone metastases secondary to breast and prostate cancer. MATERIALS AND METHODS: Patients received 1.3 or 2.2 GBq, in single or multiple doses. Platelets, white and red cells were evaluated during 11 weeks. Pharmacokinetic characterization was done from blood and urine samples for 5 patients along 24 hours. Urinary excretion was evaluated in other 16 patients during 6 hours. Bone uptake was estimated as remaining activity in whole body. Scintigraphic images were acquired at 2 and 24 hs post-administration. Absorbed dose in bone marrow was estimated with Mirdose3. Analgesics intake and pain score were daily recorded. Tumour markers (PSA, and Tn-structure) were monitored in 9 patients during 4 to 6 months. Single doses of low activity (1.3 GBq) were given to twelve patients. Nine patients received multiple doses. RESULTS: All except one patient had normal levels of platelets, white and red cells. Remaining dose in blood at 2 hours was 9%. Urinary elimination was 58%. Bone uptake at 24 hours was 43% (mean value; n = 5). No changes of the haematological parameters were detected along follow-up period. Pain relief was evidenced by decrease or supression of opioid analgesic and by subjective index. PSA showed a decrease in prostate cancer patients (n = 4). Tn-structure showed a significant increase after 4 to 8 months. CONCLUSION: Single or multiple dose scheme could be safely used, with administered activity of (188)Re-HEDP up to 60 mCi, with low bone marrow absorbed doses
First radial velocity results from the MINiature Exoplanet Radial Velocity Array (MINERVA)
The MINiature Exoplanet Radial Velocity Array (MINERVA) is a dedicated
observatory of four 0.7m robotic telescopes fiber-fed to a KiwiSpec
spectrograph. The MINERVA mission is to discover super-Earths in the habitable
zones of nearby stars. This can be accomplished with MINERVA's unique
combination of high precision and high cadence over long time periods. In this
work, we detail changes to the MINERVA facility that have occurred since our
previous paper. We then describe MINERVA's robotic control software, the
process by which we perform 1D spectral extraction, and our forward modeling
Doppler pipeline. In the process of improving our forward modeling procedure,
we found that our spectrograph's intrinsic instrumental profile is stable for
at least nine months. Because of that, we characterized our instrumental
profile with a time-independent, cubic spline function based on the profile in
the cross dispersion direction, with which we achieved a radial velocity
precision similar to using a conventional "sum-of-Gaussians" instrumental
profile: 1.8 m s over 1.5 months on the RV standard star HD 122064.
Therefore, we conclude that the instrumental profile need not be perfectly
accurate as long as it is stable. In addition, we observed 51 Peg and our
results are consistent with the literature, confirming our spectrograph and
Doppler pipeline are producing accurate and precise radial velocities.Comment: 22 pages, 9 figures, submitted to PASP, Peer-Reviewed and Accepte
A regional Bayesian POT model for flood frequency analysis
Flood frequency analysis is usually based on the fitting of an extreme value
distribution to the local streamflow series. However, when the local data
series is short, frequency analysis results become unreliable. Regional
frequency analysis is a convenient way to reduce the estimation uncertainty. In
this work, we propose a regional Bayesian model for short record length sites.
This model is less restrictive than the index flood model while preserving the
formalism of "homogeneous regions". The performance of the proposed model is
assessed on a set of gauging stations in France. The accuracy of quantile
estimates as a function of the degree of homogeneity of the pooling group is
also analysed. The results indicate that the regional Bayesian model
outperforms the index flood model and local estimators. Furthermore, it seems
that working with relatively large and homogeneous regions may lead to more
accurate results than working with smaller and highly homogeneous regions
The composition of the protosolar disk and the formation conditions for comets
Conditions in the protosolar nebula have left their mark in the composition
of cometary volatiles, thought to be some of the most pristine material in the
solar system. Cometary compositions represent the end point of processing that
began in the parent molecular cloud core and continued through the collapse of
that core to form the protosun and the solar nebula, and finally during the
evolution of the solar nebula itself as the cometary bodies were accreting.
Disentangling the effects of the various epochs on the final composition of a
comet is complicated. But comets are not the only source of information about
the solar nebula. Protostellar disks around young stars similar to the protosun
provide a way of investigating the evolution of disks similar to the solar
nebula while they are in the process of evolving to form their own solar
systems. In this way we can learn about the physical and chemical conditions
under which comets formed, and about the types of dynamical processing that
shaped the solar system we see today.
This paper summarizes some recent contributions to our understanding of both
cometary volatiles and the composition, structure and evolution of protostellar
disks.Comment: To appear in Space Science Reviews. The final publication is
available at Springer via http://dx.doi.org/10.1007/s11214-015-0167-
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