5,924 research outputs found
Self-tuning experience weighted attraction learning in games
Self-tuning experience weighted attraction (EWA) is a one-parameter theory of learning in
games. It addresses a criticism that an earlier model (EWA) has too many parameters, by
fixing some parameters at plausible values and replacing others with functions of experience
so that they no longer need to be estimated. Consequently, it is econometrically simpler
than the popular weighted fictitious play and reinforcement learning models.
The functions of experience which replace free parameters “self-tune” over time, adjusting
in a way that selects a sensible learning rule to capture subjects’ choice dynamics. For
instance, the self-tuning EWA model can turn from a weighted fictitious play into an averaging
reinforcement learning as subjects equilibrate and learn to ignore inferior foregone
payoffs. The theory was tested on seven different games, and compared to the earlier parametric
EWA model and a one-parameter stochastic equilibrium theory (QRE). Self-tuning
EWA does as well as EWA in predicting behavior in new games, even though it has fewer
parameters, and fits reliably better than the QRE equilibrium benchmark
Polarization Evolution in A Strongly Magnetized Vacuum: QED Effect and Polarized X-ray Emission from Magnetized Neutron Stars
X-ray photons emitted from the surface or atmosphere of a magnetized neutron
star is highly polarized. However, the observed polarization may be modified
due to photon propagation through the star's magnetosphere. For photon
frequencies much larger than the typical radio frequency, vacuum birefringence
due to strong-field quantum electrodynamics dominates over the plasma effect.
We study the evolution of photon polarization in the magnetized QED vacuum of a
neutron star magnetosphere, paying particular attention to the propagation
effect across the quasi-tangential (QT) point, where the photon momentum is
nearly aligned with the magnetic field. In agreement with previous studies, we
find that in most regions of the magnetosphere, the photon polarization modes
are decoupled due to vacuum birefringence, and therefore a large net linear
polarization can be expected when the radiation escapes the magnetosphere.
However, we show that X-ray polarization may change significantly when the
photon passes through the QT region. When averaging over a finite emission
area, the net effect of QT propagation is to reduce the degree of linear
polarization; the reduction factor depends on the photon energy, magnetic field
strength, geometry, rotation phase and the emission area, and can be more than
a factor of two. We derive the general conditions under which the QT
propagation effect is important, and provide an easy-to-use prescription to
account for the QT effect for most practical calculations of X-ray polarization
signals from magnetic neutron stars. For a neutron star with a dipole magnetic
field, the QT effect can be important for emission from the polar cap for
certain magnetic field and energy ranges, and is negligible for emission from
the entire stellar surface.Comment: 29 pages, 17 figures, accepted by MNRA
Stability and fluctuation modes of giant gravitons with NSNS B field
We study the stability of the giant gravitons in the string theory background
with NSNS B field. We consider the perturbation of giant gravitons formed by a
probe D brane in the background generated by D-D branes for
. We use the quadratic approximation to the brane action to find
the equations of motion. For , giant graviton configurations are stable
independent of the size of the brane. For , we calculated the range of
the size of the brane where they are stable. We also present the mode
frequencies explicitly for some special cases.Comment: 16 pages, spectrum of fluctuation modes included, title chang
Soft X-ray Polarization in Thermal Magnetar Emission
Emission spectra from magnetars in the soft X-ray band likely contain a
thermal component emerging directly from the neutron star surface. However, the
lack of observed absorption-like features in quiescent spectra makes it
difficult to directly constrain physical properties of the atmosphere. We argue
that future X-ray polarization measurements represent a promising technique for
directly constraining the magnetar magnetic field strength and geometry. We
construct models of the observed polarization signal from a finite surface
hotspot, using the latest NS atmosphere models for magnetic fields B = 4 x
10^13--5 x 10^14 G. Our calculations are strongly dependent on the NS magnetic
field strength and geometry, and are more weakly dependent on the NS equation
of state and atmosphere composition. We discuss how the complementary
dependencies of phase-resolved spectroscopy and polarimetry might resolve
degeneracies that currently hamper the determination of magnetar physical
parameters using thermal models.Comment: 23 pages, 7 figures; MNRAS accepte
Hepatic protein kinase C is not activated despite high intracellular 1,2-sn-diacylglycerol in obese Zucker rats
AbstractHigh intracellular 1,2,-sn-diacylglycerol (DAG) usually activates protein kinase C (PKC). In choline-deficient Fischer 344 rats, we previously showed that fatty liver was associated with elevated hepatic DAG and sustained activation of PKC. Steatosis is a sequelae of many liver toxins, and we wanted to determine whether fatty liver is always associated with accumulation of DAG with activation of PKC. Obese Zucker rats had 11-fold more triacylglycerol in their livers and 2-fold more DAG in their hepatic plasma membrane than did lean control Zucker rats. However, this increased diacylglycerol was not associated with translocation or activation of PKC in hepatic plasma membrane (activity in obese rats was 897 pmol/mg protein×min−1 vs. 780 pmol/mg protein×min−1 in lean rats). No differences in PKC isoform expression were detected between obese and lean rats. In additional studies, we found that choline deficiency in the Zucker rat did not result in activation of PKC in liver, unlike our earlier observations in the choline deficient Fischer rat. This dissociation between fatty liver, DAG accumulation and PKC activation in Zucker rats supports previous reports of abnormalities in PKC signaling in this strain of rats
Generalized Fractal Kinetics in Complex Systems (Application to Biophysics and Biothechnology)
We derive a universal function for the kinetics of complex systems. This
kinetic function unifies and generalizes previous theoretical attempts to
describe what has been called "fractal kinetic".The concentration evolutionary
equation is formally similar to the relaxation function obtained in the
stochastic theory of relaxation, with two exponents a and n. The first one is
due to memory effects and short-range correlations and the second one finds its
origin in the long-range correlations and geometrical frustrations which give
rise to ageing behavior. These effects can be formally handled by introducing
adequate probability distributions for the rate coefficient. We show that the
distribution of rate coefficients is the consequence of local variations of the
free energy (energy landscape) appearing in the exponent of the Arrhenius
formula. We discuss briefly the relation of the (n,a) kinetic formalism with
the Tsallis theory of nonextensive systems.Comment: 15 pages, 3 figures, submitted to Physica
Achieving High Breast Cancer Survival for Women in Rural and Remote Areas
Background: Significant improvements in breast cancer survival have been made in the past few decades in many developed countries including Australia with a five-year relative survival of 90%. The aim of the present study is to obtain a brief estimate of the relative importance of demographic factors such as rurality, socio-economic standard and ethnicity versus traditional risk factors for women diagnosed with breast cancer in Far North Queensland, Australia.
Methods: This was a retrospective longitudinal study of all women diagnosed with their first episode of breast cancer in 1999-2013 in Far North Queensland, Australia. Cox proportional hazards regression analysis was used to identify factors independently associated with mortality for women with any type of breast cancer (in situ or invasive) and for women with invasive cancer. Life tables were used to assess five and ten-year absolute survival. Standard linear regression and binary logistic regression were used to identify any association between demographic factors and late presentation.
Results: Five and ten-year absolute survival was 0.90 and 0.86 respectively. Aboriginal and Torres Strait Islander status, remoteness of area of residence, and socioeconomic status were not associated with more advanced disease at presentation or increased risk of breast cancer death. Only traditional risk factors such as increased tumour size, absence of progesterone receptor, high tumour grade and presence of metastasis in axillary lymph nodes were associated with increased risk of breast cancer death.
Conclusion: The effect of the classical risk factors on breast cancer mortality outweighs the effects of demographic factors. The fact that ethnicity, remoteness and socioeconomic status is not associated with late presentation or breast cancer death suggests that given appropriate resources it may be possible to close the gap of inequalities in breast cancer
Dengue Virus-Infected Dendritic Cells, but Not Monocytes, Activate Natural Killer Cells through a Contact-Dependent Mechanism Involving Adhesion Molecules
Natural killer (NK) cells play a protective role against dengue virus (DENV) infection, but the cellular and molecular mechanisms are not fully understood. Using an optimized humanized mouse model, we show that human NK cells, through the secretion of gamma interferon (IFN-γ), are critical in the early defense against DENV infection. Depletion of NK cells or neutralization of IFN-γ leads to increased viremia and more severe thrombocytopenia and liver damage in humanized mice. In vitro studies using autologous human NK cells show that DENV-infected monocyte-derived dendritic cells (MDDCs), but not monocytes, activate NK cells in a contact-dependent manner, resulting in upregulation of CD69 and CD25 and secretion of IFN-γ. Blocking adhesion molecules (LFA-1, DNAM-1, CD2, and 2β4) on NK cells abolishes NK cell activation, IFN-γ secretion, and the control of DENV replication. NK cells activated by infected MDDCs also inhibit DENV infection in monocytes. These findings show the essential role of human NK cells in protection against acute DENV infection in vivo, identify adhesion molecules and dendritic cells required for NK cell activation, and delineate the sequence of events for NK cell activation and protection against DENV infection.IMPORTANCE Dengue is a mosquito-transmitted viral disease with a range of symptoms, from mild fever to life-threatening dengue hemorrhagic fever. The diverse disease manifestation is thought to result from a complex interplay between viral and host factors. Using mice engrafted with a human immune system, we show that human NK cells inhibit virus infection through secretion of the cytokine gamma interferon and reduce disease pathogenesis, including depletion of platelets and liver damage. During a natural infection, DENV initially infects dendritic cells in the skin. We find that NK cells interact with infected dendritic cells through physical contact mediated by adhesion molecules and become activated before they can control virus infection. These results show a critical role of human NK cells in controlling DENV infection in vivo and reveal the sequence of molecular and cellular events that activate NK cells to control dengue virus infection
Twisted Bundles on Noncommutative and D-brane Bound States
We construct twisted quantum bundles and adjoint sections on noncommutative
, and investigate relevant D-brane bound states with non-Abelian
backgrounds. We also show that the noncommutative with non-Abelian
backgrounds exhibits SO duality and via this duality we get a Morita
equivalent on which only D0-branes exist. For a reducible non-Abelian
background, the moduli space of D-brane bound states in Type II string theory
takes the form .Comment: 19 pages, Latex. v2: Title is changed. Minor corrections. A reference
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