1,352 research outputs found
A Relativistic Version of the Two-Level Atom in the Rest-Frame Instant Form of Dynamics
We define a relativistic version of the two-level atom, in which an extended
atom is replaced by a point particle carrying suitable Grassmann variables for
the description of the two-level structure and of the electric dipole. After
studying the isolated system "atom plus the electro-magnetic field" in the
electric-dipole representation as a parametrized Minkowski theory, we give its
restriction to the inertial rest frame and the explicit form of the Poincar\'e
generators. After quantization we get a two-level atom with a spin 1/2 electric
dipole and the relativistic generalization of the Hamiltonians of the Rabi and
Jaynes-Cummings models.Comment: 23 page
Crisis Preparedness: Do School Administrators and First Responders Feel Ready to Act?
This study explored the perceptions of school principals in regards to school crisis preparedness planning and training using survey data. ANOVAs indicated that elementary schools reported greater external security measures than high schools (F = 3.17, p = .049); high schools reported greater internal security measures (F = 11.06, p = .001) and drills with first responders than elementary and middle schools (F = 6.09, p = .004). Implications for educators regarding a relationship between the perceptions of preparedness to respond to a school crisis that requires a coordinated, multi-agency effort, and the collaborative training between school districts and their first responders were discussed
Bioconjugated Plasmonic Nanoparticles for Enhanced Skin Penetration
Plasmonic nanoparticles (NPs) are one of the most promising and studied inorganic nanomaterials for different biomedical applications. Plasmonic NPs have excellent biocompatibility, long-term stability against physical and chemical degradation, relevant optical properties, well-known synthesis methods and tuneable surface functionalities. Herein, we review recently reported bioconjugated plasmonic NPs using different chemical approaches and loading cargoes (such as drugs, genes, and proteins) for enhancement of transdermal delivery across biological tissues. The main aim is to understand the interaction of the complex skin structure with biomimetic plasmonic NPs. This knowledge is not only important in enhancing transdermal delivery of pharmaceutical formulations but also for controlling undesired skin penetration of industrial products, such as cosmetics, sunscreen formulations and any other mass-usage consumable that contains plasmonic NPs
Single degree-of-freedom exoskeleton mechanism design for finger rehabilitation
This paper presents the kinematic design of a single
degree-of-freedom exoskeleton mechanism: a planar eight-bar
mechanism for finger curling. The mechanism is part of a fingerthumb
robotic device for hand therapy that will allow users to
practice key pinch grip and finger-thumb opposition, allowing
discrete control inputs for playing notes on a musical gaming
interface. This approach uses the mechanism to generate the
desired grasping trajectory rather than actuating the joints of
the fingers and thumb independently. In addition, the mechanism
is confined to the back of the hand, so as to allow sensory input
into the palm of the hand, minimal size and apparent inertia,
and the possibility of placing multiple mechanisms side-by-side
to allow control of individual fingersPeer ReviewedPostprint (author’s final draft
Charged Particles and the Electro-Magnetic Field in Non-Inertial Frames of Minkowski Spacetime: II. Applications: Rotating Frames, Sagnac Effect, Faraday Rotation, Wrap-up Effect
We apply the theory of non-inertial frames in Minkowski space-time, developed
in the previous paper, to various relevant physical systems. We give the 3+1
description without coordinate-singularities of the rotating disk and the
Sagnac effect, with added comments on pulsar magnetosphere and on a
relativistic extension of the Earth-fixed coordinate system. Then we study
properties of Maxwell equations in non-inertial frames like the wrap-up effect
and the Faraday rotation in astrophysics.Comment: This paper and the second one are an adaptation of arXiv 0812.3057
for publication on Int.J.Geom. Methods in Modern Phys. 36
Centers of Mass and Rotational Kinematics for the Relativistic N-Body Problem in the Rest-Frame Instant Form
In the Wigner-covariant rest-frame instant form of dynamics it is possible to
develop a relativistic kinematics for the N-body problem. The Wigner
hyperplanes define the intrinsic rest frame and realize the separation of the
center-of-mass. Three notions of {\it external} relativistic center of mass can
be defined only in terms of the {\it external} Poincar\'e group realization.
Inside the Wigner hyperplane, an {\it internal} unfaithful realization of the
Poincar\'e group is defined. The three concepts of {\it internal} center of
mass weakly {\it coincide} and are eliminated by the rest-frame conditions. An
adapted canonical basis of relative variables is found. The invariant mass is
the Hamiltonian for the relative motions. In this framework we can introduce
the same {\it dynamical body frames}, {\it orientation-shape} variables, {\it
spin frame} and {\it canonical spin bases} for the rotational kinematics
developed for the non-relativistic N-body problem.Comment: 78 pages, revtex fil
Justifying and Explaining Disproportionality 1968—2008: A Critique of Underlying Views of Culture
This is the publisher's version, also found here: http://cec.metapress.com/content/e7835w1374x7g141/?p=0ee3fcac0688484aacb1d3c83c9c469c&pi=2Special education has made considerable advances in research, policy, and practice in its short history. However, students from historically underserved groups continue to be disproportionately identified as requiring special education. Support for color-blind practices and policies can justify racial disproportionality in special education and signal a retrenchment to deficit views about students from historically underserved groups. We respond to these emerging concerns through an analysis of arguments that justify disproportionality. We also identify explanations of the problem and critique the views of culture that underlie these explanations. We conclude with a brief discussion of implications and future directions
The York map as a Shanmugadhasan canonical transformation in tetrad gravity and the role of non-inertial frames in the geometrical view of the gravitational field
A new parametrization of the 3-metric allows to find explicitly a York map in
canonical ADM tetrad gravity, the two pairs of physical tidal degrees of
freedom and 14 gauge variables. These gauge quantities (generalized inertial
effects) are all configurational except the trace of
the extrinsic curvature of the instantaneous 3-spaces (clock
synchronization convention) of a non-inertial frame. The Dirac hamiltonian is
the sum of the weak ADM energy (whose density is coordinate-dependent due to the inertial
potentials) and of the first-class constraints. Then: i) The explicit form of
the Hamilton equations for the two tidal degrees of freedom in an arbitrary
gauge: a deterministic evolution can be defined only in a completely fixed
gauge, i.e. in a non-inertial frame with its pattern of inertial forces. ii) A
general solution of the super-momentum constraints, which shows the existence
of a generalized Gribov ambiguity associated to the 3-diffeomorphism gauge
group. It influences: a) the explicit form of the weak ADM energy and of the
super-momentum constraint; b) the determination of the shift functions and then
of the lapse one. iii) The dependence of the Hamilton equations for the two
pairs of dynamical gravitational degrees of freedom (the generalized tidal
effects) and for the matter, written in a completely fixed 3-orthogonal
Schwinger time gauge, upon the gauge variable ,
determining the convention of clock synchronization. Therefore it should be
possible (for instance in the weak field limit but with relativistic motion) to
try to check whether in Einstein's theory the {\it dark matter} is a gauge
relativistic inertial effect induced by .Comment: 90 page
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