1,650 research outputs found
On birational involutions of
Let be a rationally connected three-dimensional algebraic variety and let
be an element of order two in the group of its birational selfmaps.
Suppose that there exists a non-uniruled divisorial component of the
-fixed point locus. Using the equivariant minimal model program we give a
rough classification of such elements.Comment: 24 pages, late
On the Hamiltonian form of the Einstein equations for gravitational field
It is shown that Einstein gravitational equations and canonical equations
following from the Dirac-Schwinger Hamiltonian in the Faddeev variables
coincide. For proving of this at first, the Einstein equations has been
rewritten in canonical variables, and after this, the time derivative of the
generalized momenta of the gravitational field in Faddeev form has been
calculated using canonical Poisson brackets. The results coincide.Comment: 7 page
Impact of the strong electromagnetic field on the QCD effective potential for homogeneous Abelian gluon field configurations
The one-loop quark contribution to the QCD effective potential for the
homogeneous Abelian gluon field in the presence of external strong
electromagnetic field is evaluated. The structure of extrema of the potential
as a function of the angles between chromoelectric, chromomagnetic and
electromagnetic fields is analyzed. In this setup, the electromagnetic field is
considered as an external one while the gluon field represents domain
structured nonperturbative gluon configurations related to the QCD vacuum in
the confinement phase. Two particularly interesting gluon configurations,
(anti-)self-dual and crossed orthogonal chromomagnetic and chromoelectric
fields, are discussed specifically. Within this simplified framework it is
shown that the strong electromagnetic fields can play a catalysing role for a
deconfinement transition. At the qualitative level, the present consideration
can be seen as a highly simplified study of an impact of the electromagnetic
fields generated in relativistic heavy ion collisions on the strongly
interacting hadronic matter.Comment: 9 pages, 4 figure
Metastable phases and "metastable" phase diagrams
The work discusses specifics of phase transitions for metastable states of
substances. The objects of condensed media physics are primarily equilibrium
states of substances with metastable phases viewed as an exception, while the
overwhelming majority of organic substances investigated in chemistry are
metastable. It turns out that at normal pressure many of simple molecular
compounds based on light elements (these include: most hydrocarbons; nitrogen
oxides, hydrates, and carbides; carbon oxide (CO); alcohols, glycerin etc) are
metastable substances too, i.e. they do not match the Gibbs' free energy
minimum for a given chemical composition. At moderate temperatures and
pressures, the phase transitions for given metastable phases throughout the
entire experimentally accessible time range are reversible with the equilibrium
thermodynamics laws obeyed. At sufficiently high pressures (1-10 GPa), most of
molecular phases irreversibly transform to more energy efficient polymerized
phases, both stable and metastable. These transformations are not consistent
with the equality of the Gibbs' free energies between the phases before and
after the transition, i.e. they are not phase transitions in "classical"
meaning. The resulting polymeric phases at normal pressure can exist at
temperatures above the melting one for the initial metastable molecular phase.
Striking examples of such polymers are polyethylene and a polymerized
modification of CO. Many of energy-intermediate polymeric phases can apparently
be synthesized by the "classical" chemistry techniques at normal pressure.Comment: 5 pages, 4 figure
Experimenting with Cigarettes and Physical Activity Among Mexican Origin Youth: A Cross Sectional Analysis of the Interdependent Associations Among Sensation Seeking, Acculturation, and Gender
Sensation seeking tendencies tend to manifest during adolescence and are associated with both health-compromising behaviors and health-enhancing behaviors. The purpose of this study is to evaluate the relationship between sensation seeking and physical activity, a health-enhancing behavior, and between sensation seeking and experimenting with cigarettes, a health compromising-behavior, among a cohort of Mexican origin adolescents residing in the United States with different levels of acculturation. Methods: In 2009, 1,154 Mexican origin youth (50.5% girls, mean age 14.3 years (SD = 1.04)) provided data on smoking behavior, physical activity, linguistic acculturation, and sensation seeking. We conducted Pearson's chi(2) tests to examine the associations between categorical demographic characteristics (i.e. gender, age, country of birth and parental educational attainment) and both cigarette experimentation and physical activity and Student's t-tests to examine mean differences on the continuous variables (i.e. sensation seeking subscale) by the behaviors. We examined mean differences in the demographic characteristics, acculturation, and both behaviors for each of the sensation seeking subscales using analysis of variance (ANOVA). To examine relationships between the sensation seeking subscales, gender, and both behaviors, at different levels of acculturation we completed unconditional logistic regression analyses stratified by level of acculturation. Results: Overall, 23.3% had experimented with cigarettes and 29.0% reported being physically active for at least 60 minutes/day on at least 5 days/week. Experimenting with cigarettes and being physically active were more prevalent among boys than girls. Among girls, higher levels of sensation seeking tendencies were associated with higher levels of acculturation and experimentation with cigarettes, but not with physical activity. Among boys, higher levels of sensation seeking tendencies were associated with higher levels of acculturation, experimenting with cigarettes and being physically active. Conclusions: Our results suggest that interventions designed to prevent smoking among Mexican origin youth may need to address social aspects associated with acculturation, paying close attention to gendered manifestations of sensation seeking.National Cancer Institute CA105203, CA126988Caroline W. Law Fund for Cancer PreventionDan Duncan Family Institute for Cancer Prevention and Risk AssessmentCenter for Health Promotion and Disease Prevention Research in Underserved Population
Uncertainty relations in curved spaces
Uncertainty relations for particle motion in curved spaces are discussed. The
relations are shown to be topologically invariant. New coordinate system on a
sphere appropriate to the problem is proposed. The case of a sphere is
considered in details. The investigation can be of interest for string and
brane theory, solid state physics (quantum wires) and quantum optics.Comment: published version; phase space structure discussion adde
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