3,161 research outputs found
Comparison of application methods to prolong the survival of potential biocontrol bacteria on stored sugar-beet seed
A condition for any realistic theory of quantum systems
In quantum physics, the density operator completely describes the state.
Instead, in classical physics the mean value of every physical quantity is
evaluated by means of a probability distribution. We study the possibility to
describe pure quantum states and events with classical probability
distributions and conditional probabilities and prove that the distributions
can not be quadratic functions of the quantum state. Some examples are
considered. Finally, we deal with the exponential complexity problem of quantum
physics and introduce the concept of classical dimension for a quantum system
Concentration‐dependent optical‐absorption coefficient in n‐type GaAs
The doping-dependent, near-band-edge optical-absorption coefficient CY(h v) was deduced from optical transmission measurements in n-type GaAs thin films. The selenium-doped films were grown by metalorganic chemical-vapor deposition and do ed to produce room-temperature electron concentrations from 1.3 x 10” to 3.8X 1018 cm- P . The transmission measurements covered photon energies between 1.35 and 1.7 eV and were performed on double heterostructures with the substrate removed by selective etching. The results show good qualitative agreement with previous studies and good quantitative agreement, except for the heavily doped samples. For na=3.8 X 10” cme3, a( 1.42 eV\u3e is approximately four times that reported by previous workers. Secondary-ion-mass spectrometry measurements on flms grown under differing conditions demonstrate that a(hv) is sensitive to electrically inactive dopants and supports the hypothesis that precipitates or compensation influenced previous measurements. These comprehensive results on high-quality, uncompensated material should prove useful for fundamental studies of optical transitions in n-type GaAs as well as for modeling optoelectronic devices
A holistic approach to dissecting SPARC family protein complexity reveals FSTL-1 as an inhibitor of pancreatic cancer cell growth.
SPARC is a matricellular protein that is involved in both pancreatic cancer and diabetes. It belongs to a wider family of proteins that share structural and functional similarities. Relatively little is known about this extended family, but evidence of regulatory interactions suggests the importance of a holistic approach to their study. We show that Hevin, SPOCKs, and SMOCs are strongly expressed within islets, ducts, and blood vessels, suggesting important roles for these proteins in the normal pancreas, while FSTL-1 expression is localised to the stromal compartment reminiscent of SPARC. In direct contrast to SPARC, however, FSTL-1 expression is reduced in pancreatic cancer. Consistent with this, FSTL-1 inhibited pancreatic cancer cell proliferation. The complexity of SPARC family proteins is further revealed by the detection of multiple cell-type specific isoforms that arise due to a combination of post-translational modification and alternative splicing. Identification of splice variants lacking a signal peptide suggests the existence of novel intracellular isoforms. This study underlines the importance of addressing the complexity of the SPARC family and provides a new framework to explain their controversial and contradictory effects. We also demonstrate for the first time that FSTL-1 suppresses pancreatic cancer cell growth
Generalized "Quasi-classical" Ground State for an Interacting Two Level System
We treat a system (a molecule or a solid) in which electrons are coupled
linearly to any number and type of harmonic oscillators and which is further
subject to external forces of arbitrary symmetry. With the treatment restricted
to the lowest pair of electronic states, approximate "vibronic"
(vibration-electronic) ground state wave functions are constructed having the
form of simple, closed expressions. The basis of the method is to regard
electronic density operators as classical variables. It extends an earlier
"guessed solution", devised for the dynamical Jahn-Teller effect in cubic
symmetry, to situations having lower (e.g., dihedral) symmetry or without any
symmetry at all. While the proposed solution is expected to be quite close to
the exact one, its formal simplicity allows straightforward calculations of
several interesting quantities, like energies and vibronic reduction (or Ham)
factors. We calculate for dihedral symmetry two different -factors (""
and "") and a -factor. In simplified situations we obtain . The formalism enables quantitative estimates to be made for the dynamical
narrowing of hyperfine lines in the observed ESR spectrum of the dihedral
cyclobutane radical cation.Comment: 28 pages, 4 figure
Apollo asteroids (1566) Icarus and 2007 MK6: Icarus family members?
Although it is more complicated to search for near-Earth object (NEO)
families than main belt asteroid (MBA) families, since differential orbital
evolution within a NEO family can cause current orbital elements to drastically
differ from each other, we have found that Apollo asteroids (1566) Icarus and
the newly discovered 2007 MK6 are almost certainly related. Specifically, their
orbital evolutions show a similar profile, time shifted by only ~1000 yr, based
on our time-lag theory. The dynamical relationship between Icarus and 2007 MK6
along with a possible dust band, the Taurid-Perseid meteor swarm, implies the
first detection of an asteroidal NEO family, namely the "Icarus asteroid
family".Comment: 11 pages, 1 figure, to appear on Astrophysical Journal Letters
(journal info added
Retired A Stars and Their Companions: Exoplanets Orbiting Three Intermediate-Mass Subgiants
We report precision Doppler measurements of three intermediate-mass subgiants
from Lick and Keck Observatories. All three stars show variability in their
radial velocities consistent with planet-mass companions in Keplerian orbits.
We find a planet with a minimum mass of 2.5 Mjup in a 351.5 day orbit around HD
192699, a planet with a minimum mass of 2.0 Mjup in a 341.1 day orbit around HD
210702, and a planet with a minimum mass of 0.61 Mjup in a 297.3 day orbit
around HD 175541. Stellar mass estimates from evolutionary models indicate that
all of these stars were formerly A-type dwarfs with masses ranging from 1.65 to
1.85 Msun. These three long-period planets would not have been detectable
during their stars' main-sequence phases due to the large rotational velocities
and stellar jitter exhibited by early-type dwarfs. There are now 9 "retired"
(evolved) A-type stars (Mstar > 1.6 Msun) with known planets. All 9 planets
orbit at distances a \geq 0.78 AU, which is significantly different than the
semimajor axis distribution of planets around lower-mass stars. We examine the
possibility that the observed lack of close-in planets is due to engulfment by
their expanding host stars, but we find that this explanation is inadequate
given the relatively small stellar radii of K giants (Rstar < 32 Rsun = 0.15
AU) and subgiants (Rstar < 7 Rsun = 0.03 AU). Instead, we conclude that planets
around intermediate-mass stars reside preferentially beyond ~0.8 AU, which may
be a reflection of different formation and migration histories of planets
around A-type stars.Comment: 31 pages, 9 figures, 6 tables, ApJ accepted, corrected minor typo
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