14 research outputs found
Direct Instantons in QCD Nucleon Sum Rules
We study the role of direct (i.e. small-scale) instantons in QCD correlation
functions for the nucleon. They generate sizeable, nonperturbative corrections
to the conventional operator product expansion, which improve the quality of
both QCD nucleon sum rules and cure the long-standing stability problem, in
particular, of the chirally odd sum-rule.Comment: 10 pages, UMD PP#93-17
Current-induced cooling phenomenon in a two-dimensional electron gas under a magnetic field
We investigate the spatial distribution of temperature induced by a dc
current in a two-dimensional electron gas (2DEG) subjected to a perpendicular
magnetic field. We numerically calculate the distributions of the electrostatic
potential phi and the temperature T in a 2DEG enclosed in a square area
surrounded by insulated-adiabatic (top and bottom) and isopotential-isothermal
(left and right) boundaries (with phi_{left} < phi_{right} and T_{left}
=T_{right}), using a pair of nonlinear Poisson equations (for phi and T) that
fully take into account thermoelectric and thermomagnetic phenomena, including
the Hall, Nernst, Ettingshausen, and Righi-Leduc effects. We find that, in the
vicinity of the left-bottom corner, the temperature becomes lower than the
fixed boundary temperature, contrary to the naive expectation that the
temperature is raised by the prevalent Joule heating effect. The cooling is
attributed to the Ettingshausen effect at the bottom adiabatic boundary, which
pumps up the heat away from the bottom boundary. In order to keep the adiabatic
condition, downward temperature gradient, hence the cooled area, is developed
near the boundary, with the resulting thermal diffusion compensating the upward
heat current due to the Ettingshausen effect.Comment: 25 pages, 7 figure
Fluctuations, dissipation and the dynamical Casimir effect
Vacuum fluctuations provide a fundamental source of dissipation for systems
coupled to quantum fields by radiation pressure. In the dynamical Casimir
effect, accelerating neutral bodies in free space give rise to the emission of
real photons while experiencing a damping force which plays the role of a
radiation reaction force. Analog models where non-stationary conditions for the
electromagnetic field simulate the presence of moving plates are currently
under experimental investigation. A dissipative force might also appear in the
case of uniform relative motion between two bodies, thus leading to a new kind
of friction mechanism without mechanical contact. In this paper, we review
recent advances on the dynamical Casimir and non-contact friction effects,
highlighting their common physical origin.Comment: 39 pages, 4 figures. Review paper to appear in Lecture Notes in
Physics, Volume on Casimir Physics, edited by Diego Dalvit, Peter Milonni,
David Roberts, and Felipe da Rosa. Minor changes, a reference adde
Views of Community-Dwelling, Old-Old People on Barriers and Aids to Nutritional Health
Purpose: To examine barriers and aids to maintaining the nutritional health of community-dwelling old-old residents from their perspectives.
Design: Cross-sectional exploratory study completed in March 2002 of old-old people living independently in one county in the Midwestern United States (US).
Methods: Sixty-eight in-home interviews were conducted with community-dwelling people aged 80 or older. Content analysis was done to examine answers to two open-ended questions about barriers and helps to nutritional health.
Findings: These old-old people believed they were doing well nutritionally despite reduced independence and physical limitations. They were positive about their lives and creative in problem solving to remain independent. Social connectedness was the major factor for maintaining independence into old age. The leading barrier to maintaining nutritional health was health problems. Those with more barriers were more likely to be depressed.
Conclusions: Knowledge of aids and barriers to nutritional health, from a personal perspective, gives an understanding of the issues and concerns of old-old people
Views of CommunityâDwelling, OldâOld People on Barriers and Aids to Nutritional Health
Deconstructing compassionate conservation
Compassionate conservation focuses on 4 tenets: first, do no harm; individuals matter; inclusivity of individual animals; and peaceful coexistence between humans and animals. Recently, compassionate conservation has been promoted as an alternative to conventional conservation philosophy. We believe examples presented by compassionate conservationists are deliberately or arbitrarily chosen to focus on mammals; inherently not compassionate; and offer ineffective conservation solutions. Compassionate conservation arbitrarily focuses on charismatic species, notably large predators and megaherbivores. The philosophy is not compassionate when it leaves invasive predators in the environment to cause harm to vastly more individuals of native species or uses the fear of harm by apex predators to terrorize mesopredators. Hindering the control of exotic species (megafauna, predators) in situ will not improve the conservation condition of the majority of biodiversity. The positions taken by so-called compassionate conservationists on particular species and on conservation actions could be extended to hinder other forms of conservation, including translocations, conservation fencing, and fertility control. Animal welfare is incredibly important to conservation, but ironically compassionate conservation does not offer the best welfare outcomes to animals and is often ineffective in achieving conservation goals. Consequently, compassionate conservation may threaten public and governmental support for conservation because of the limited understanding of conservation problems by the general public