1,565 research outputs found
Lagrange-Fedosov Nonholonomic Manifolds
We outline an unified approach to geometrization of Lagrange mechanics,
Finsler geometry and geometric methods of constructing exact solutions with
generic off-diagonal terms and nonholonomic variables in gravity theories. Such
geometries with induced almost symplectic structure are modelled on
nonholonomic manifolds provided with nonintegrable distributions defining
nonlinear connections. We introduce the concept of Lagrange-Fedosov spaces and
Fedosov nonholonomic manifolds provided with almost symplectic connection
adapted to the nonlinear connection structure.
We investigate the main properties of generalized Fedosov nonholonomic
manifolds and analyze exact solutions defining almost symplectic Einstein
spaces.Comment: latex2e, v3, published variant, with new S.V. affiliatio
Lagrangian dynamical geography of the Gulf of Mexico
We construct a Markov-chain representation of the surface-ocean Lagrangian
dynamics in a region occupied by the Gulf of Mexico (GoM) and adjacent portions
of the Caribbean Sea and North Atlantic using satellite-tracked drifter
trajectory data, the largest collection so far considered. From the analysis of
the eigenvectors of the transition matrix associated with the chain, we
identify almost-invariant attracting sets and their basins of attraction. With
this information we decompose the GoM's geography into weakly dynamically
interacting provinces, which constrain the connectivity between distant
locations within the GoM. Offshore oil exploration, oil spill contingency
planning, and fish larval connectivity assessment are among the many activities
that can benefit from the dynamical information carried in the geography
constructed here.Comment: Submitted to Scientific Report
Extended Absolute Parallelism Geometry
In this paper, we study Absolute Parallelism (AP-) geometry on the tangent
bundle of a manifold . Accordingly, all geometric objects defined in
this geometry are not only functions of the positional argument , but also
depend on the directional argument . Moreover, many new geometric objects,
which have no counterpart in the classical AP-geometry, emerge in this
different framework. We refer to such a geometry as an Extended Absolute
Parallelism (EAP-) geometry. The building blocks of the EAP-geometry are a
nonlinear connection assumed given a priori and linearly independent
vector fields (of special form) defined globally on defining the
parallelization. Four different -connections are used to explore the
properties of this geometry. Simple and compact formulae for the curvature
tensors and the W-tensors of the four defined -connections are obtained,
expressed in terms of the torsion and the contortion tensors of the EAP-space.
Further conditions are imposed on the canonical -connection assuming that it
is of Cartan type (resp. Berwald type). Important consequences of these
assumptions are investigated. Finally, a special form of the canonical
-connection is studied under which the classical AP-geometry is recovered
naturally from the EAP-geometry. Physical aspects of some of the geometric
objects investigated are pointed out and possible physical implications of the
EAP-space are discussed, including an outline of a generalized field theory on
the tangent bundle of Comment: 27 pages, LaTeX-file, The last version of this paper was replaced by
mistake (by arXiv: 0905.0209[gr-qc]
From service provision to function based performance - perspectives on public health systems from the USA and Israel
If public health agencies are to fulfill their overall mission, they need to have defined measurable targets and should structure services to reach these targets, rather than offer a combination of ill-targeted programs. In order to do this, it is essential that there be a clear definition of what public health should do- a definition that does not ebb and flow based upon the prevailing political winds, but rather is based upon professional standards and measurements.
The establishment of the Essential Public Health Services framework in the U.S.A. was a major move in that direction, and the model, or revisions of the model, have been adopted beyond the borders of the U.S. This article reviews the U.S. public health system, the needs and processes which brought about the development of the 10 Essential Public Health Services (EPHS), and historical and contemporary applications of the model. It highlights the value of establishing a common delineation of public health activities such as those contained in the EPHS, and explores the validity of using the same process in other countries through a discussion of the development in Israel of a similar model, the 10 Public Health Essential Functions (PHEF), that describes the activities of Israel’s public health system. The use of the same process and framework to develop similar yet distinct frameworks suggests that the process has wide applicability, and may be beneficial to any public health system. Once a model is developed, it can be used to measure public health performance and improve the quality of services delivered through the development of standards and measures based upon the model, which could, ultimately, improve the health of the communities that depend upon public health agencies to protect their well-being
From service provision to function based performance - perspectives on public health systems from the USA and Israel
If public health agencies are to fulfill their overall mission, they need to have defined measurable targets and should structure services to reach these targets, rather than offer a combination of ill-targeted programs. In order to do this, it is essential that there be a clear definition of what public health should do- a definition that does not ebb and flow based upon the prevailing political winds, but rather is based upon professional standards and measurements. The establishment of the Essential Public Health Services framework in the U.S.A. was a major move in that direction, and the model, or revisions of the model, have been adopted beyond the borders of the U.S. This article reviews the U.S. public health system, the needs and processes which brought about the development of the 10 Essential Public Health Services (EPHS), and historical and contemporary applications of the model. It highlights the value of establishing a common delineation of public health activities such as those contained in the EPHS, and explores the validity of using the same process in other countries through a discussion of the development in Israel of a similar model, the 10 Public Health Essential Functions (PHEF), that describes the activities of Israel’s public health system. The use of the same process and framework to develop similar yet distinct frameworks suggests that the process has wide applicability, and may be beneficial to any public health system. Once a model is developed, it can be used to measure public health performance and improve the quality of services delivered through the development of standards and measures based upon the model, which could, ultimately, improve the health of the communities that depend upon public health agencies to protect their well-being
Building a Maxey--Riley framework for surface ocean inertial particle dynamics
A framework for the study of surface ocean inertial particle motion is built
from the Maxey--Riley set. A new set is obtained by vertically averaging each
term of the original set, adapted to account for Earth's rotation effects,
across the extent of a sufficiently small spherical particle that floats at an
assumed unperturbed air--sea interface with unsteady nonuniform winds and ocean
currents above and below, respectively. The inertial particle velocity is shown
to exponentially decay in time to a velocity that lies close to an average of
seawater and air velocities, weighted by a function of the seawater-to-particle
density ratio. Such a weighted average velocity turns out to fortuitously be of
the type commonly discussed in the search-and-rescue literature, which alone
cannot explain the observed role of anticyclonic mesoscale eddies as traps for
marine debris or the formation of great garbage patches in the subtropical
gyres, phenomena dominated by finite-size effects. A heuristic extension of the
theory is proposed to describe the motion of nonspherical particles by means of
a simple shape factor correction, and recommendations are made for
incorporating wave-induced Stokes drift, and allowing for inhomogeneities of
the carrying fluid density. The new Maxey--Riley set outperforms an ocean
adaptation that ignored wind drag effects and the first reported adaption that
attempted to incorporate them.Comment: To appear in Phys. Fluid
Transition paths of marine debris and the stability of the garbage patches
We used transition path theory (TPT) to infer "reactive" pathways of floating
marine debris trajectories. The TPT analysis was applied on a pollution-aware
time-homogeneous Markov chain model constructed from trajectories produced by
satellite-tracked undrogued buoys from the NOAA Global Drifter Program. The
latter involved coping with the openness of the system in physical space, which
further required an adaptation of the standard TPT setting. Directly connecting
pollution sources along coastlines with garbage patches of varied strengths,
the unveiled reactive pollution routes represent alternative targets for ocean
cleanup efforts. Among our specific findings we highlight: constraining a
highly probable pollution source for the Great Pacific Garbage Patch;
characterizing the weakness of the Indian Ocean gyre as a trap for plastic
waste; and unveiling a tendency of the subtropical gyres to export garbage
toward the coastlines rather than to other gyres in the event of anomalously
intense winds.Comment: Submitted to Chao
Potts-Percolation-Gauss Model of a Solid
We study a statistical mechanics model of a solid. Neighboring atoms are
connected by Hookian springs. If the energy is larger than a threshold the
"spring" is more likely to fail, while if the energy is lower than the
threshold the spring is more likely to be alive. The phase diagram and
thermodynamic quantities, such as free energy, numbers of bonds and clusters,
and their fluctuations, are determined using renormalization-group and
Monte-Carlo techniques.Comment: 10 pages, 12 figure
- …