2,162 research outputs found
Novel Symmetry of Non-Einsteinian Gravity in Two Dimensions
The integrability of -gravity with torsion in two dimensions is traced
to an ultralocal dynamical symmetry of constraints and momenta in Hamiltonian
phase space. It may be interpreted as a quadratically deformed
-algebra with the deformation consisting of the Casimir operators of
the undeformed algebra. The locally conserved quantity encountered in the
explicit solution is identified as an element of the centre of this algebra.
Specific contractions of the algebra are related to specific limits of the
explicit solutions of this model.Comment: 17 pages, TUW-92-04 (LaTeX
Comment on: ``Trace anomaly of dilaton coupled scalars in two dimensions''
The trace anomaly for nonminimally coupled scalars in spherically reduced
gravity obtained by Bousso and Hawking (hep-th/9705236) is incorrect. We
explain the reasons for the deviations from our correct (published) result
which is supported by several other recent papers.Comment: 2 page
Universal conservation law and modified Noether symmetry in 2d models of gravity with matter
It is well-known that all 2d models of gravity---including theories with
nonvanishing torsion and dilaton theories---can be solved exactly, if matter
interactions are absent. An absolutely (in space and time) conserved quantity
determines the global classification of all (classical) solutions. For the
special case of spherically reduced Einstein gravity it coincides with the mass
in the Schwarzschild solution. The corresponding Noether symmetry has been
derived previously by P. Widerin and one of the authors (W.K.) for a specific
2d model with nonvanishing torsion. In the present paper this is generalized to
all covariant 2d theories, including interactions with matter. The related
Noether-like symmetry differs from the usual one. The parameters for the
symmetry transformation of the geometric part and those of the matterfields are
distinct. The total conservation law (a zero-form current) results from a two
stage argument which also involves a consistency condition expressed by the
conservation of a one-form matter ``current''. The black hole is treated as a
special case.Comment: 3
Study of diode-iris controlled waveguide slot radiators
Diode-iris controlled waveguide slot radiator
Computed tomography-osteoabsorptiometry for assessing the density distribution of subchondral bone as a measure of long-term mechanical adaptation in individual joints
To estimate subchondral mineralisation patterns which represent the long-term loading history of individual joints, a method has been developed employing computed tomography (CT) which permits repeated examination of living joints. The method was tested on 5 knee, 3 sacroiliac, 3 ankle and 5 shoulder joints and then investigated with X-ray densitometry. A CT absorptiometric presentation and maps of the area distribution of the subchondral bone density areas were derived using an image analyser. Comparison of the results from both X-ray densitometry and CT-absorptiometry revealed almost identical pictures of distribution of the subchondral bone density. The method may be used to examine subchondral mineralisation as a measure of the mechanical adaptability of joints in the living subject
The Complete Solution of 2D Superfield Supergravity from graded Poisson-Sigma Models and the Super Pointparticle
Recently an alternative description of 2d supergravities in terms of graded
Poisson-Sigma models (gPSM) has been given. As pointed out previously by the
present authors a certain subset of gPSMs can be interpreted as "genuine"
supergravity, fulfilling the well-known limits of supergravity, albeit deformed
by the dilaton field. In our present paper we show that precisely that class of
gPSMs corresponds one-to-one to the known dilaton supergravity superfield
theories presented a long time ago by Park and Strominger. Therefore, the
unique advantages of the gPSM approach can be exploited for the latter: We are
able to provide the first complete classical solution for any such theory. On
the other hand, the straightforward superfield formulation of the point
particle in a supergravity background can be translated back into the gPSM
frame, where "supergeodesics" can be discussed in terms of a minimal set of
supergravity field degrees of freedom. Further possible applications like the
(almost) trivial quantization are mentioned.Comment: 48 pages, 1 figure. v3: after final version, typos correcte
Study of advanced antenna techniques for rendezvous radar
Advanced antenna techniques for rendezvous and lunar landing radar system
modCHIMERA: A novel murine closed-head model of moderate traumatic brain injury
AbstractTraumatic brain injury is a major source of global disability and mortality. Preclinical TBI models are a crucial component of therapeutic investigation. We report a tunable, monitored model of murine non-surgical, diffuse closed-head injury—modCHIMERA—characterized by impact as well as linear and rotational acceleration. modCHIMERA is based on the Closed-Head Impact Model of Engineered Rotational Acceleration (CHIMERA) platform. We tested this model at 2 energy levels: 1.7 and 2.1 Joules—substantially higher than previously reported for this system. Kinematic analysis demonstrated linear acceleration exceeding injury thresholds in humans, although outcome metrics tracked impact energy more closely than kinematic parameters. Acute severity metrics were consistent with a complicated-mild or moderate TBI, a clinical population characterized by high morbidity but potentially reversible pathology. Axonal injury was multifocal and bilateral, neuronal death was detected in the hippocampus, and microglial neuroinflammation was prominent. Acute functional analysis revealed prolonged post-injury unconsciousness, and decreased spontaneous behavior and stimulated neurological scores. Neurobehavioral deficits were demonstrated in spatial learning/memory and socialization at 1-month. The overall injury profile of modCHIMERA corresponds with the range responsible for a substantial portion of TBI-related disability in humans. modCHIMERA should provide a reliable platform for efficient analysis of TBI pathophysiology and testing of treatment modalities.</jats:p
Global surfaces of section in the planar restricted 3-body problem
The restricted planar three-body problem has a rich history, yet many
unanswered questions still remain. In the present paper we prove the existence
of a global surface of section near the smaller body in a new range of energies
and mass ratios for which the Hill's region still has three connected
components. The approach relies on recent global methods in symplectic geometry
and contrasts sharply with the perturbative methods used until now.Comment: 11 pages, 1 figur
Sierpinski signal generates spectra
We investigate the row sum of the binary pattern generated by the Sierpinski
automaton: Interpreted as a time series we calculate the power spectrum of this
Sierpinski signal analytically and obtain a unique rugged fine structure with
underlying power law decay with an exponent of approximately 1.15. Despite the
simplicity of the model, it can serve as a model for spectra in a
certain class of experimental and natural systems like catalytic reactions and
mollusc patterns.Comment: 4 pages (4 figs included). Accepted for publication in Physical
Review
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