2,287 research outputs found
A comparative analysis of the value of information in a continuous time market model with partial information: the cases of log-utility and CRRA
We study the question what value an agent in a generalized Black-Scholes model with partial information attributes to the complementary information. To do this, we study the utility maximization problems from terminal wealth for the two cases partial information and full information. We assume that the drift term of the risky asset is a dynamic process of general linear type and that the two levels of observation correspond to whether this drift term is observable or not. Applying methods from stochastic filtering theory we derive an analytical tractable formula for the value of information in the case of logarithmic utility. For the case of constant relative risk aversion (CRRA) we derive a semianalytical formula, which uses as an input the numerical solution of a system of ODEs. For both cases we present a comparative analysis
Ledoux-Convection in Protoneutron Stars --- a Clue to Supernova Nucleosynthesis?
Two-dimensional hydrodynamical simulations of the deleptonization of a newly
formed neutron star were performed. Driven by negative lepton fraction and
entropy gradients, convection starts near the neutrinosphere about 20-30 ms
after core bounce, but moves deeper into the protoneutron star, and after about
one second the whole protoneutron star is convective. The deleptonization of
the star proceeds much faster than in the corresponding spherically symmetrical
model because the lepton flux and the neutrino luminosities increase by up to a
factor of two. The convection below the neutrinosphere raises the
neutrinospheric temperatures and mean energies of the emitted neutrinos by
10-20%. This can have important implications for the supernova explosion
mechanism and changes the detectable neutrino signal from the Kelvin-Helmholtz
cooling of the protoneutron star. In particular, the enhanced electron neutrino
flux relative to the electron antineutrino flux during the early post-bounce
evolution might solve the overproduction problem of certain elements in the
neutrino-heated ejecta in models of type-II supernova explosions.Comment: 17 pages, LaTeX, 8 postscript figures, uses epsf.sty. To appear in
ApJ 473 (Letters), 1996 December 1
Parent-only interventions in the treatment of childhood obesity: a systematic review of randomized controlled trials
Background An effective and cost-effective treatment is required for the treatment of childhood obesity. Comparing parent-only interventions with interventions including the child may help determine this. Methods A systematic review of published and ongoing studies until 2013, using electronic database and manual searches. Inclusion criteria: randomized controlled trials, overweight/obese children aged 5-12 years, parent-only intervention compared with an intervention that included the child, 6 months or more follow-up. Outcomes included measures of overweight. Results Ten papers from 6 completed studies, and 2 protocols for ongoing studies, were identified. Parent-only groups are either more effective than or similarly effective as child-only or parent-child interventions, in the change in degree of overweight. Most studies were at unclear risk of bias for randomization, allocation concealment and blinding of outcome assessors. Two trials were at high risk of bias for incomplete outcome data. Four studies showed higher dropout from parent-only interventions. One study examined programme costs and found parent-only interventions to be cheaper. Conclusions Parent-only interventions appear to be as effective as parent-child interventions in the treatment of childhood overweight/obesity, and may be less expensive. Reasons for higher attrition rates in parent-only interventions need further investigatio
Gravitational waves from relativistic rotational core collapse
We present results from simulations of axisymmetric relativistic rotational
core collapse. The general relativistic hydrodynamic equations are formulated
in flux-conservative form and solved using a high-resolution shock-capturing
scheme. The Einstein equations are approximated with a conformally flat
3-metric. We use the quadrupole formula to extract waveforms of the
gravitational radiation emitted during the collapse. A comparison of our
results with those of Newtonian simulations shows that the wave amplitudes
agree within 30%. Surprisingly, in some cases, relativistic effects actually
diminish the amplitude of the gravitational wave signal. We further find that
the parameter range of models suffering multiple coherent bounces due to
centrifugal forces is considerably smaller than in Newtonian simulations.Comment: 4 pages, 3 figure
Field-induced structure transformation in electrorheological solids
We have computed the local electric field in a body-centered tetragonal (BCT)
lattice of point dipoles via the Ewald-Kornfeld formulation, in an attempt to
examine the effects of a structure transformation on the local field strength.
For the ground state of an electrorheological solid of hard spheres, we
identified a novel structure transformation from the BCT to the face-centered
cubic (FCC) lattices by changing the uniaxial lattice constant c under the hard
sphere constraint. In contrast to the previous results, the local field
exhibits a non-monotonic transition from BCT to FCC. As c increases from the
BCT ground state, the local field initially decreases rapidly towards the
isotropic value at the body-centered cubic lattice, decreases further, reaching
a minimum value and increases, passing through the isotropic value again at an
intermediate lattice, reaches a maximum value and finally decreases to the FCC
value. An experimental realization of the structure transformation is
suggested. Moreover, the change in the local field can lead to a generalized
Clausius-Mossotti equation for the BCT lattices.Comment: Submitted to Phys. Rev.
Effects of geometric anisotropy on local field distribution: Ewald-Kornfeld formulation
We have applied the Ewald-Kornfeld formulation to a tetragonal lattice of
point dipoles, in an attempt to examine the effects of geometric anisotropy on
the local field distribution. The various problems encountered in the
computation of the conditionally convergent summation of the near field are
addressed and the methods of overcoming them are discussed. The results show
that the geometric anisotropy has a significant impact on the local field
distribution. The change in the local field can lead to a generalized
Clausius-Mossotti equation for the anisotropic case.Comment: Accepted for publications, Journal of Physics: Condensed Matte
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Evolutionary bi-stability in pathogen transmission mode
Many pathogens transmit to new hosts by both infection (horizontal transmission) and transfer to the
infected host's offspring (vertical transmission). These two transmission modes require speci®c adap-
tations of the pathogen that can be mutually exclusive, resulting in a trade-off between horizontal and
vertical transmission. We show that in mathematical models such trade-offs can lead to the simultaneous
existence of two evolutionary stable states (evolutionary bi-stability) of allocation of resources to the two
modes of transmission. We also show that jumping between evolutionary stable states can be induced by
gradual environmental changes. Using quantitative PCR-based estimates of abundance in seed and vege-
tative parts, we show that the pathogen of wheat, Phaeosphaeria nodorum, has jumped between two
distinct states of transmission mode twice in the past 160 years, which, based on published evidence,
we interpret as adaptation to environmental change. The ®nding of evolutionary bi-stability has impli-
cations for human, animal and other plant diseases. An ill-judged change in a disease control
programme could cause the pathogen to evolve a new, and possibly more damaging, combination of
transmission modes. Similarly, environmental changes can shift the balance between transmission
modes, with adverse effects on human, animal and plant health
Putative ligand binding sites of two functionally characterized bark beetle odorant receptors
Background: Bark beetles are major pests of conifer forests, and their behavior is primarily mediated via olfaction. Targeting the odorant receptors (ORs) may thus provide avenues towards improved pest control. Such an approach requires information on the function of ORs and their interactions with ligands, which is also essential for understanding the functional evolution of these receptors. Hence, we aimed to identify a high-quality complement of ORs from the destructive spruce bark beetle Ips typographus (Coleoptera, Curculionidae, Scolytinae) and analyze their antennal expression and phylogenetic relationships with ORs from other beetles. Using 68 biologically relevant test compounds, we next aimed to functionally characterize ecologically important ORs, using two systems for heterologous expression. Our final aim was to gain insight into the ligand-OR interaction of the functionally characterized ORs, using a combination of computational and experimental methods. Results: We annotated 73 ORs from an antennal transcriptome of I. typographus and report the functional characterization of two ORs (ItypOR46 and ItypOR49), which are responsive to single enantiomers of the common bark beetle pheromone compounds ipsenol and ipsdienol, respectively. Their responses and antennal expression correlate with the specificities, localizations, and/or abundances of olfactory sensory neurons detecting these enantiomers. We use homology modeling and molecular docking to predict their binding sites. Our models reveal a likely binding cleft lined with residues that previously have been shown to affect the responses of insect ORs. Within this cleft, the active ligands are predicted to specifically interact with residues Tyr84 and Thr205 in ItypOR46. The suggested importance of these residues in the activation by ipsenol is experimentally supported through site-directed mutagenesis and functional testing, and hydrogen bonding appears key in pheromone binding. Conclusions: The emerging insight into ligand binding in the two characterized ItypORs has a general importance for our understanding of the molecular and functional evolution of the insect OR gene family. Due to the ecological importance of the characterized receptors and widespread use of ipsenol and ipsdienol in bark beetle chemical communication, these ORs should be evaluated for their potential use in pest control and biosensors to detect bark beetle infestations
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