11,219 research outputs found
A Geometric Model of Arbitrary Spin Massive Particle
A new model of relativistic massive particle with arbitrary spin
(()-particle) is suggested. Configuration space of the model is a product
of Minkowski space and two-dimensional sphere, . The system describes Zitterbewegung at the classical level.
Together with explicitly realized Poincar\'e symmetry, the action functional
turns out to be invariant under two types of gauge transformations having their
origin in the presence of two Abelian first-class constraints in the Hamilton
formalism. These constraints correspond to strong conservation for the
phase-space counterparts of the Casimir operators of the Poincar\'e group.
Canonical quantization of the model leads to equations on the wave functions
which prove to be equivalent to the relativistic wave equations for the massive
spin- field.Comment: 25 pages; v2: eq. (45.b) correcte
Massive spinning particle on anti-de Sitter space
To describe a massive particle with fixed, but arbitrary, spin on
anti-de Sitter space , we propose the point-particle model with
configuration space , where the sphere
corresponds to the spin degrees of freedom. The model possesses two gauge
symmetries expressing strong conservation of the phase-space counterparts of
the second- and fourth-order Casimir operators for . We prove that the
requirement of energy to have a global positive minimum over the
configuration space is equivalent to the relation , being the
particle's spin, what presents the classical counterpart of the quantum massive
condition. States with the minimal energy are studied in detail. The model is
shown to be exactly solvable. It can be straightforwardly generalized to
describe a spinning particle on -dimensional anti-de Sitter space ,
with the corresponding configuration
space.Comment: 23 pages, LaTe
The body in the library: adventures in realism
This essay looks at two aspects of the virtual ‘material world’ of realist fiction: objects encountered by the protagonist and the latter’s body. Taking from Sartre two angles on the realist pact by which readers agree to lend
their bodies, feelings, and experiences to the otherwise ‘languishing signs’ of the text, it goes on to examine two sets of first-person fictions published between 1902 and 1956 — first, four modernist texts in which banal objects defy and then gratify the protagonist, who ends up ready and almost able to write; and, second, three novels in which the body of the protagonist is indeterminate in its sex, gender, or sexuality. In each of these cases, how do we as readers make texts work for us as ‘an adventure of the body’
Looking into DNA breathing dynamics via quantum physics
We study generic aspects of bubble dynamics in DNA under time dependent
perturbations, for example temperature change, by mapping the associated
Fokker-Planck equation to a quantum time-dependent Schroedinger equation with
imaginary time. In the static case we show that the eigenequation is exactly
the same as that of the -deformed nuclear liquid drop model, without the
issue of non-integer angular momentum. A universal breathing dynamics is
demonstrated by using an approximate method in quantum mechanics. The
calculated bubble autocorrelation function qualitatively agrees with
experimental data. Under time dependent modulations, utilizing the adiabatic
approximation, bubble properties reveal memory effects.Comment: 5 pages, 1 figur
Testing the Hubble Law with the IRAS 1.2 Jy Redshift Survey
We test and reject the claim of Segal et al. (1993) that the correlation of
redshifts and flux densities in a complete sample of IRAS galaxies favors a
quadratic redshift-distance relation over the linear Hubble law. This is done,
in effect, by treating the entire galaxy luminosity function as derived from
the 60 micron 1.2 Jy IRAS redshift survey of Fisher et al. (1995) as a distance
indicator; equivalently, we compare the flux density distribution of galaxies
as a function of redshift with predictions under different redshift-distance
cosmologies, under the assumption of a universal luminosity function. This
method does not assume a uniform distribution of galaxies in space. We find
that this test has rather weak discriminatory power, as argued by Petrosian
(1993), and the differences between models are not as stark as one might expect
a priori. Even so, we find that the Hubble law is indeed more strongly
supported by the analysis than is the quadratic redshift-distance relation. We
identify a bias in the the Segal et al. determination of the luminosity
function, which could lead one to mistakenly favor the quadratic
redshift-distance law. We also present several complementary analyses of the
density field of the sample; the galaxy density field is found to be close to
homogeneous on large scales if the Hubble law is assumed, while this is not the
case with the quadratic redshift-distance relation.Comment: 27 pages Latex (w/figures), ApJ, in press. Uses AAS macros,
postscript also available at
http://www.astro.princeton.edu/~library/preprints/pop682.ps.g
Large-scale structure and the redshift-distance relation
In efforts to demonstrate the linear Hubble law v = Hr from galaxy
observations, the underlying simplicity is often obscured by complexities
arising from magnitude-limited data. In this paper we point out a simple but
previously unremarked fact: that the shapes and orientations of structures in
redshift space contain in themselves independent information about the
cosmological redshift-distance relation.
The orientations of voids in the CfA slice support the Hubble law, giving a
redshift-distance power index p = 0.83 +/- 0.36 (void data from Slezak, de
Lapparent, & Bijoui 1993) or p = 0.99 +/- 0.38 (void data from Malik &
Subramanian 1997).Comment: 11 pages (AASTeX), 4 figures, to appear in the Astrophysical Journal
Letter
Confinement effects in a guided-wave interferometer with millimeter-scale arm separation
Guided-wave atom interferometers measure interference effects using atoms
held in a confining potential. In one common implementation, the confinement is
primarily two-dimensional, and the atoms move along the nearly free dimension
under the influence of an off-resonant standing wave laser beam. In this
configuration, residual confinement along the nominally free axis can introduce
a phase gradient to the atoms that limits the arm separation of the
interferometer. We experimentally investigate this effect in detail, and show
that it can be alleviated by having the atoms undergo a more symmetric motion
in the guide. This can be achieved by either using additional laser pulses or
by allowing the atoms to freely oscillate in the potential. Using these
techniques, we demonstrate interferometer measurement times up to 72 ms and arm
separations up to 0.42 mm with a well controlled phase, or times of 0.91 s and
separations of 1.7 mm with an uncontrolled phase.Comment: 14 pages, 6 figure
Role of Double Balloon Enteroscopy in the Diagnosis of Obscure Gastrointestinal Bleeding
Obscure gastrointestinal bleeding (OGIB) is bleeding in the digestive tract which persist or recur and with unclear aetiology. OGIB is one of the important problems in the gastrointestinal field due to difficulty in diagnosing the aetiology and determining the source of digestive tract bleeding in patients. In diagnosing the cause of OGIB, clinical approach through history taking and physical examination still have important roles. Most of the sources of bleeding in OGIB is from the small intestine, which cannot be reached by esophagogastroduodenoscopy (EGD) or colonoscopy. Therefore, role of diagnostic tool which is able to perform total enteroscopy becomes important in diagnosing the cause of OGIB.Double balloon enteroscopy (DBE) technique is a safe endoscopy procedure which may use oral or even rectal approach. In finding the cause of OGIB, where most of the lesions is found in the proximal region of the small intestine, oral approach is more beneficial. When bleeding is not found after conventional endoscopy is performed, it needs to be suspected that the source might come from the small intestine. Currently, the two main modalities which can be used in the evaluation are video capsule endoscopy (VCE) and DBE. However, based on cost effectiveness DBE without prior VCE has benefit because it can also administer therapy in the abnormalities being found
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