52 research outputs found
Rotation and Spin in Physics
We delineate the role of rotation and spin in physics, discussing in order
Newtonian classical physics, special relativity, quantum mechanics, quantum
electrodynamics and general relativity. In the latter case, we discuss the
generalization of the Kepler formula to post-Newtonian order )
including spin effects and two-body effects. Experiments which verify the
theoretical results for general relativistic spin-orbit effects are discussed
as well as efforts being made to verify the spin-spin effects
Bianchi Type-II String Cosmological Models in Normal Gauge for Lyra's Manifold with Constant Deceleration Parameter
The present study deals with a spatially homogeneous and anisotropic
Bianchi-II cosmological models representing massive strings in normal gauge for
Lyra's manifold by applying the variation law for generalized Hubble's
parameter that yields a constant value of deceleration parameter. The variation
law for Hubble's parameter generates two types of solutions for the average
scale factor, one is of power-law type and other is of the exponential form.
Using these two forms, Einstein's modified field equations are solved
separately that correspond to expanding singular and non-singular models of the
universe respectively. The energy-momentum tensor for such string as formulated
by Letelier (1983) is used to construct massive string cosmological models for
which we assume that the expansion () in the model is proportional to
the component of the shear tensor . This
condition leads to , where A, B and C are the metric coefficients
and m is proportionality constant. Our models are in accelerating phase which
is consistent to the recent observations. It has been found that the
displacement vector behaves like cosmological term in the
normal gauge treatment and the solutions are consistent with recent
observations of SNe Ia. It has been found that massive strings dominate in the
decelerating universe whereas strings dominate in the accelerating universe.
Some physical and geometric behaviour of these models are also discussed.Comment: 24 pages, 10 figure
ISSN exercise & sport nutrition review: research & recommendations
Sports nutrition is a constantly evolving field with hundreds of research papers published annually. For this reason, keeping up to date with the literature is often difficult. This paper is a five year update of the sports nutrition review article published as the lead paper to launch the JISSN in 2004 and presents a well-referenced overview of the current state of the science related to how to optimize training and athletic performance through nutrition. More specifically, this paper provides an overview of: 1.) The definitional category of ergogenic aids and dietary supplements; 2.) How dietary supplements are legally regulated; 3.) How to evaluate the scientific merit of nutritional supplements; 4.) General nutritional strategies to optimize performance and enhance recovery; and, 5.) An overview of our current understanding of the ergogenic value of nutrition and dietary supplementation in regards to weight gain, weight loss, and performance enhancement. Our hope is that ISSN members and individuals interested in sports nutrition find this review useful in their daily practice and consultation with their clients
Conservation of energy-momentum of matter as the basis for the gauge theory of gravitation
According to Yang \& Mills (1954), a {\it conserved} current and a related
rigid (`global') symmetry lie at the foundations of gauge theory. When the
rigid symmetry is extended to a {\it local} one, a so-called gauge symmetry, a
new interaction emerges as gauge potential ; its field strength is . In gravity, the conservation of the energy-momentum current of
matter and the rigid translation symmetry in the Minkowski space of special
relativity lie at the foundations of a gravitational gauge theory. If the
translation invariance is made local, a gravitational potential
arises together with its field strength . Thereby
the Minkowski space deforms into a Weitzenb\"ock space with nonvanishing
torsion but vanishing curvature. The corresponding theory is reviewed and
its equivalence to general relativity pointed out. Since translations form a
subgroup of the Poincar\'e group, the group of motion of special relativity,
one ought to straightforwardly extend the gauging of the translations to the
gauging of full Poincar\'e group thereby also including the conservation law of
the {\it angular momentum} current. The emerging Poincar\'e gauge (theory of)
gravity, starting from the viable Einstein-Cartan theory of 1961, will be
shortly reviewed and its prospects for further developments assessed.Comment: 46 pages, 4 figures, minor corrections, references added,
contribution to "One Hundred Years of Gauge Theory" edited by S. De Bianchi
and C. Kiefe
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