1,231 research outputs found
Reconstructing the conformal mode in simplicial gravity
We verify that summing 2D DT geometries correctly reproduces the Polyakov
action for the conformal mode, including all ghost contributions, at large
volumes. The Gaussian action is reproduced even for central charges greater
than one lending strong support to the hypothesis that the space of all
possible dyamical triangulations approximates well the space of physically
distinct metrics independent of the precise nature of the matter coupling.Comment: 3 pages, 4 figures, contribution to Lattice 9
The Inattentive Participant: Portfolio Trading Behavior in 401(k) Plans
Most workers in defined contribution retirement plans are inattentive portfolio managers: only a few engage in any trading at all, and only a tiny minority trades actively. Using a rich new dataset on 1.2 million workers in over 1,500 plans, we find that most 401(k) plan participants are characterized by profound inertia. Almost all participants (80%) initiate no trades, and an additional 11% makes only a single trade, in a two-year period. Even among traders, portfolio turnover rates are one-third the rate of professional money managers. Those who trade in their 401(k) plans are more affluent older men, with higher incomes and longer job tenure. They tend to use the internet for 401(k) account access, hold a larger number of investment options, and are more likely to hold active equity funds rather than index or lifecycle funds. Some plan features, including offering own-employer stock, also raise trading levels.
The Efficiency of Pension Menus and Individual Portfolio Choice in 401(k) Pensions
Though millions of US workers have 401(k) plans, few studies evaluate participant investment performance. Using data on over 1,000 401(k) plans and their participants, we identify key portfolio investment inefficiencies and attribute them to offered investment menus versus individual portfolio choices. We show that the vast majority of 401(k) plans offers reasonable investment menus. Nevertheless, participants âundoâ the efficient menu and make substantial mistakes: in a 20-year career it will reduce retirement wealth by one-fifth, in fact, more than what a naive allocation strategy would yield. We outline implications for plan sponsors and participants seeking to enhance portfolio efficiency: donât just offer or choose more funds, but help people invest smarter.
Physical activity throughout pregnancy is key to preventing chronic disease
According to The Developmental Origins of Health and Disease theory, the intrauterine environment of the developing fetus may impact later life physiology, including susceptibility to chronic disease conditions. Maternal exposures during pregnancy can affect the intrauterine environment and result in fetal programming for chronic diseases through changes in the structure or function of specific organs. Negative maternal exposures, such as poor nutrition intake, have been shown to increase the risk for later life chronic diseases. On the contrary, healthful behaviors, such as physical activity, may have a positive and protective effect against chronic disease risk. This narrative review summarizes literature to discuss the potential preventative role prenatal physical activity may have on prevalent chronic diseases: obesity, type 2 diabetes, and cardiovascular disease. We describe the natural physiological response to pregnancy that may increase the risk for complications and consequently later life disease for both mother and baby. We then present evidence highlighting the role prenatal exercise may have in preventing pregnancy complications and downstream chronic disease development, as well as proposing potential mechanisms that may explain the protective maternal and fetal physiological response to exercise. As the prevalence of these non-communicable diseases increase globally, intervening during pregnancy with an effective exercise intervention may be the key to preventing chronic disease risk in more than one generation
Stress Tensor from the Trace Anomaly in Reissner-Nordstrom Spacetimes
The effective action associated with the trace anomaly provides a general
algorithm for approximating the expectation value of the stress tensor of
conformal matter fields in arbitrary curved spacetimes. In static, spherically
symmetric spacetimes, the algorithm involves solving a fourth order linear
differential equation in the radial coordinate r for the two scalar auxiliary
fields appearing in the anomaly action, and its corresponding stress tensor. By
appropriate choice of the homogeneous solutions of the auxiliary field
equations, we show that it is possible to obtain finite stress tensors on all
Reissner-Nordstrom event horizons, including the extreme Q=M case. We compare
these finite results to previous analytic approximation methods, which yield
invariably an infinite stress-energy on charged black hole horizons, as well as
with detailed numerical calculations that indicate the contrary. The
approximation scheme based on the auxiliary field effective action reproduces
all physically allowed behaviors of the quantum stress tensor, in a variety of
quantum states, for fields of any spin, in the vicinity of the entire family (0
le Q le M) of RN horizons.Comment: 43 pages, 12 figure
VaporâLiquid Equilibria of Quaternary Systems of Interest for the Supercritical Antisolvent Process
In the Supercritical Antisolvent process (SAS), the thermodynamic behavior of complex multicomponent systems can influence the particlesâ morphology. However, due to the limited thermodynamic data for multicomponent systems, the effect of solutes is often neglected, and the system is considered as pseudo-binary. It has been demonstrated that the presence of a solute can significantly influence the thermodynamic behavior of the system. In particular, when the SAS process is adopted for the production of drug/polymer coprecipitated microparticles, the effect of both the drug and the polymer in the solvent/CO2 mixture should be considered. In this work, the effect of polyvinylpyrrolidone (PVP), used as the carrier, and of the liposoluble vitamins menadione (MEN) and α-tocopherol (TOC), as model drugs, was investigated as a deviation from the fundamental thermodynamic behavior of the DMSO/CO2 binary system. Vaporâliquid equilibria (VLE) were evaluated at 313 K, with a PVP concentration in the organic solution equal to 20 mg/mL. The effect of the presence of PVP, MEN, and TOC on DMSO/CO2 VLE at 313 K was studied; furthermore, the effect of PVP/MEN and PVP/TOC, at a polymer/drug ratio of 5/1 and 3/1, was determined. Moreover, SAS precipitation experiments were performed at the same polymer/drug ratios using a pressure of 90 bar. Thermodynamic studies revealed significant changes in phase behavior for DMSO/CO2/PVP/TOC and DMSO/CO2/PVP/MEN systems compared to the binary DMSO/CO2 system. From the analysis of the effect of the presence of a single compound on the binary system VLE, it was noted that PVP slightly affected the thermodynamic behavior of the system. In contrast, these effects were more evident for the DMSO/CO2/TOC and DMSO/CO2/MEN systems. SAS precipitation experiments produced PVP/MEN and PVP/TOC microparticles, and the obtained morphology was justified considering the quaternary systems VLE
Periodic Instantons in SU(2) Yang-Mills-Higgs Theory
The properties of periodic instanton solutions of the classical SU(2) gauge
theory with a Higgs doublet field are described analytically at low energies,
and found numerically for all energies up to and beyond the sphaleron energy.
Interesting new classes of bifurcating complex periodic instanton solutions to
the Yang-Mills-Higgs equations are described.Comment: 11 pages, 3 figures (in 5 included eps files), ReVTeX (minor typos
corrected and reference added
Cosmological Dark Energy: Prospects for a Dynamical Theory
We present an approach to the problem of vacuum energy in cosmology, based on
dynamical screening of Lambda on the horizon scale. We review first the
physical basis of vacuum energy as a phenomenon connected with macroscopic
boundary conditions, and the origin of the idea of its screening by particle
creation and vacuum polarization effects. We discuss next the relevance of the
quantum trace anomaly to this issue. The trace anomaly implies additional terms
in the low energy effective theory of gravity, which amounts to a non-trivial
modification of the classical Einstein theory, fully consistent with the
Equivalence Principle. We show that the new dynamical degrees of freedom the
anomaly contains provide a natural mechanism for relaxing Lambda to zero on
cosmological scales. We consider possible signatures of the restoration of
conformal invariance predicted by the fluctuations of these new scalar degrees
of freedom on the spectrum and statistics of the CMB, in light of the latest
bounds from WMAP. Finally we assess the prospects for a new cosmological model
in which the dark energy adjusts itself dynamically to the cosmological horizon
boundary, and therefore remains naturally of order H^2 at all times without
fine tuning.Comment: 50 pages, Invited Contribution to New Journal of Physics Focus Issue
on Dark Energ
The Refractory-to-Ice Mass Ratio in Comets
We review the complex relationship between the dust-to-gas mass ratio usually estimated in the material lost by comets, and the Refractory-to-Ice mass ratio inside the nucleus, which constrains the origin of comets. Such a relationship is dominated by the mass transfer from the perihelion erosion to fallout over most of the nucleus surface. This makes the Refractory-to-Ice mass ratio inside the nucleus up to ten times larger than the dust-to-gas mass ratio in the lost material, because the lost material is missing most of the refractories which were inside the pristine nucleus before the erosion. We review the Refractory-to-Ice mass ratios available for the comet nuclei visited by space missions, and for the Kuiper Belt Objects with well defined bulk density, finding the 1-Ï lower limit of 3. Therefore, comets and KBOs may have less water than CI-chondrites, as predicted by models of comet formation by the gravitational collapse of cm-sized pebbles driven by streaming instabilities in the protoplanetary disc
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