4,024 research outputs found
Up-down symmetry of the turbulent transport of toroidal angular momentum in tokamaks
Two symmetries of the local nonlinear delta-f gyrokinetic system of equations
in tokamaks in the high flow regime are presented. The turbulent transport of
toroidal angular momentum changes sign under an up-down reflection of the
tokamak and a sign change of both the rotation and the rotation shear. Thus,
the turbulent transport of toroidal angular momentum must vanish for up-down
symmetric tokamaks in the absence of both rotation and rotation shear. This has
important implications for the modeling of spontaneous rotation.Comment: 15 pages, 2 figure
Why the Poor Get Fat: Weight Gain and Economic Insecurity
Something about being poor makes people fat. Though there are many possible explanations for the income-body weight gradient, we investigate a promising butlittle-studied hypothesis: that economic insecurity acts as an independent cause of weight gain. We use data on working age men from the 1979 National Longitudinal Survey of Youth (NLSY79) to identify the effect of various measures of economic insecurity on weight gain. We find in particular that over the 12-year period between 1988 and 2000, a one point (0.01) increase in the probability of becoming unemployed causes weight gain over this period to increase by about one pound, and each realized drop in annual income results in an increase of about 5.5 pounds. The mechanism also appears to work in reverse, with health insurance and government "social safety net" payments leading to smaller weight gains.obesity, unemployment, moral hazard, NLSY79
Stellar rotation, binarity, and lithium in the open cluster IC4756
An important aspect in the evolutionary scenario of cool stars is their
rotation and the rotationally induced magnetic activity and interior mixing.
Stars in open clusters are particularly useful tracers for these aspects
because of their known ages. We aim to characterize the open cluster IC4756 and
measure stellar rotation periods and surface differential rotation for a sample
of its member stars. Thirty-seven cluster stars were observed continuously with
the CoRoT satellite for 78 days in 2010. Follow-up high-resolution spectroscopy
of the CoRoT targets and deep Str\"omgren and H photometry
of the entire cluster were obtained with our robotic STELLA facility and its
echelle spectrograph and wide-field imager, respectively. We determined
high-precision photometric periods for 27 of the 37 CoRoT targets and found
values between 0.155 and 11.4 days. Twenty of these are rotation periods.
Twelve targets are spectroscopic binaries of which 11 were previously unknown;
orbits are given for six of them. Six targets were found that show evidence of
differential rotation with in the range 0.04-0.15. Five
stars are non-radially pulsating stars with fundamental periods of below 1d,
two stars are semi-contact binaries, and one target is a micro-flaring star
that also shows rotational modulation. Nine stars in total were not considered
members because of much redder color(s) and deviant radial velocities with
respect to the cluster mean. H photometry indicates that the cluster
ensemble does not contain magnetically over-active stars. The cluster average
metallicity is -0.080.06 (rms) and its logarithmic lithium abundance for
12 G-dwarf stars is 2.390.17 (rms). [...]Comment: A&A, in pres
Lost Gems: Identifying Rare and Unusual Monographs in a University\u27s Circulating Collection
Identifying and evaluating the oldest published content held by the library using a set of transfer criteria provided a means to systematically evaluate and, if necessary, move rare or unusual content into a more secure location. The process enabled us to correct cataloging errors, identify and address items with condition issues, be familiar with the library\u27s unique holdings and finally, to identify and add content distinctly associated with EMU\u27s history to the University Archives and Special Collections
BB Intermeson Potentials in the Quark Model
In this paper we derive quark model results for scattering amplitudes and
equivalent low energy potentials for heavy meson pairs, in which each meson
contains a heavy quark. This "BB" system is an attractive theoretical
laboratory for the study of the nuclear force between color singlets; the
hadronic system is relatively simple, and there are lattice gauge theory (LGT)
results for V_BB(r) which may be compared to phenomenological models. We find
that the quark model potential (after lattice smearing) has qualitative
similarities to the LGT potential in the two B*B* channels in which direct
comparison is possible, although there is evidence of a difference in length
scales. The quark model prediction of equal magnitude but opposite sign for I=0
and I=1 potentials also appears similar to LGT results at intermediate r. There
may however be a discrepancy between the LGT and quark model I=1 BB potentials.
A numerical study of the two-meson Schrodinger equations in the (bqbar)(bqbar)
and (cqbar)(cqbar) sectors with the quark model potentials finds a single
"molecule", in the I=0 BB* sector. Binding in other channels might occur if the
quark model forces are augmented by pion exchange.Comment: 30 pages, 5 figures, revtex and epsfig. Submitted to Phys. Rev.
Globular Cluster Population of Hickson Compact Group 22a and 90c
We present the first measurement of the globular cluster populations of
galaxies in Hickson compact groups, in order to investigate the effect of these
high density environments on the formation and evolution of globular cluster
systems. Based on V and R band images that we obtained of HCG 22a and HCG 90c
with the ESO New Technology Telescope (NTT), we find a total globular cluster
population of for HCG 22a and for 90c. The specific
frequency for HCG 22a was found to be and for HCG 90c. A power-law fit to the globular cluster radial profile of HCG
22a yields and for HCG 90c we found . A comparison of the globular cluster radial profiles with
the surface brightness of the parent galaxy shows that the globular cluster
systems are at least as extended as the halo light. The measured values for the
specific frequency are consistent with a scenario in which the host galaxies
were in a low density ``field-like'' environment when they formed their
globular cluster systems.Comment: 28 pages, 13 figures, 3 tables, accepted for publication in the
Astrophysical Journa
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Short and long-term carbon balance of bioenergy electricity production fueled by forest treatments
Background:
Forests store large amounts of carbon in forest biomass, and this carbon can be released to the atmosphere following forest disturbance or management. In the western US, forest fuel reduction treatments designed to reduce the risk of high severity wildfire can change forest carbon balance by removing carbon in the form of biomass, and by altering future potential wildfire behavior in the treated stand. Forest treatment carbon balance is further affected by the fate of this biomass removed from the forest, and the occurrence and intensity of a future wildfire in this stand. In this study we investigate the carbon balance of a forest treatment with varying fates of harvested biomass, including use for bioenergy electricity production, and under varying scenarios of future disturbance and regeneration.
Results:
Bioenergy is a carbon intensive energy source; in our study we find that carbon emissions from bioenergy electricity production are nearly twice that of coal for the same amount of electricity. However, some emissions from bioenergy electricity production are offset by avoided fossil fuel electricity emissions. The carbon benefit achieved by using harvested biomass for bioenergy electricity production may be increased through avoided pyrogenic emissions if the forest treatment can effectively reduce severity.
Conclusion:
Forest treatments with the use of harvested biomass for electricity generation can reduce carbon emissions to the atmosphere by offsetting fossil fuel electricity generation emissions, and potentially by avoided pyrogenic emissions due to reduced intensity and severity of a future wildfire in the treated stand. However, changes in future wildfire and regeneration regimes may affect forest carbon balance and these climate-induced changes may influence forest carbon balance as much, or more, than bioenergy production
Autonomous three dimensional Newtonian systems which admit Lie and Noether point symmetries
We determine the autonomous three dimensional Newtonian systems which admit
Lie point symmetries and the three dimensional autonomous Newtonian Hamiltonian
systems, which admit Noether point symmetries. We apply the results in order to
determine the two dimensional Hamiltonian dynamical systems which move in a
space of constant non-vanishing curvature and are integrable via Noether point
symmetries. The derivation of the results is geometric and can be extended
naturally to higher dimensions.Comment: Accepted for publication in Journal of Physics A: Math. and Theor.,13
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