14,287 research outputs found
Minkowski Spacetime and QED from Ontology of Time
Classical mechanics, relativity, electrodynamics and quantum mechanics are
often depicted as separate realms of physics, each with its own formalism and
notion. This remains unsatisfactory with respect to the unity of nature and to
the necessary number of postulates. We uncover the intrinsic connection of
these areas of physics and describe them using a common symplectic Hamiltonian
formalism. Our approach is based on a proper distinction between variables and
constants, i.e. on a basic but rigorous ontology of time. We link these concept
with the obvious conditions for the possibility of measurements. The derived
consequences put the measurement problem of quantum mechanics and the
Copenhagen interpretation of the quantum mechanical wavefunction into
perspective. According to our (onto-) logic we find that spacetime can not be
fundamental. We argue that a geometric interpretation of symplectic dynamics
emerges from the isomorphism between the corresponding Lie algebra and the
representation of a Clifford algebra. Within this conceptional framework we
derive the dimensionality of spacetime, the form of Lorentz transformations and
of the Lorentz force and fundamental laws of physics as the Planck-Einstein
relation, the Maxwell equations and finally the Dirac equation.Comment: 36 pages, 3 figures, several typos corrected, references with title
Cyclotrons with Fast Variable and/or Multiple Energy Extraction
We discuss the principle possibility of stripping extraction in combination
with reverse bends in isochronous separate sector cyclotrons (and/or FFAGs). If
one uses reverse bends between the sectors (instead of drifts) and places
stripper foils at the sector exit edges, the stripped beam has a reduced
bending radius and it should be able to leave the cyclotron within the range of
the reverse bend - even if the beam is stripped at less than full energy.
We are especially interested in -cyclotrons, which allow to double the
charge to mass ratio by stripping. However the principle could be applied to
other ions or ionized molecules as well. For the production of proton beams by
stripping extraction of an -beam, we discuss possible designs for three
types of machines: First a low-energy cyclotron for the simultaneous production
of several beams at multiple energies - for instance 15 MeV, 30 MeV and 70 MeV
- thus allowing to have beam on several isotope production targets. In this
case it is desired to have a strong energy dependence of the direction of the
extracted beam thus allowing to run multiple target stations simultaneously.
Second we consider a fast variable energy proton machine for cancer therapy
that should allow extraction (of the complete beam) at all energies in the
range of about 70 MeV to about 250 MeV into the same beam line. And third, we
consider a high intensity high energy machine, where the main design goals are
extraction with low losses, low activation of components and high reliability.
The price that has to be paid for these advantages is an increase in size
and/or in field strength compared to proton machines with standard extraction
at the final energy.Comment: 10 pages, 9 figure
California Health Care Market Report 2005
Examines relationships among providers, physicians, hospitals, and patients, differences in the way physicians and hospitals organize, and factors that have prompted hospitals, medical groups, and health plans to redefine their relationships
Israel\u27s Transboundary Water Disputes
As water is necessary to the function of life, it is imperative to understand the role of water in the politically turbulent Middle East. This paper will focus on Israel’s water disputes with her neighbors and how such disputes have either led to military confrontation, have been partially resolved, and otherwise continue to exist. As populations in the region are expected to increase, the need for water, already in short supply, will be magnified. Thus negotiations to settle water disputes and provide for equitable distribution of the water resources will become more contentious. This legal analysis of Israel’s water disputes will hopefully provide some guidance to the settlement of such issues in Israel’s future peace negotiations with the Syrians and Palestinians
International Trade and Worker Turnover – Empirical Evidence for Germany
Using a linked employer-employee data set for Germany, this paper studies how worker turnover is related to establishments‘ international trade involvement. The descriptive analysis shows that trading establishments have lower worker turnover rates than non-traders, suggesting a higher degree of employment stability. Conditional on an extensive set of control variables, exporting is further associated with a higher net job flow rate, which is almost entirely due to a lower separation rate (particularly for highskilled workers and transitions into non-employment). In contrast, an increase in import intensity is associated with a lower accession rate (particularly for low-skilled workers and their accessions out of non-employment). These results are more pronounced for smaller establishments, and they partly lose statistical significance once unobservable establishment characteristics are taken into account.International trade; worker turnover; job turnover; linked employer-employee data
A general constitutive model for dense, fine particle suspensions validated in many geometries
Fine particle suspensions (such as cornstarch mixed with water) exhibit
dramatic changes in viscosity when sheared, producing fascinating behaviors
that captivate children and rheologists alike. Recent examination of these
mixtures in simple flow geometries suggests inter-granular repulsion is central
to this effect --- for mixtures at rest or shearing slowly, repulsion prevents
frictional contacts from forming between particles, whereas, when sheared more
forcefully, granular stresses overcome the repulsion allowing particles to
interact frictionally and form microscopic structures that resist flow.
Previous constitutive studies of these mixtures have focused on particular
cases, typically limited to two-dimensional, steady, simple shearing flows. In
this work, we introduce a predictive and general, three-dimensional continuum
model for this material, using mixture theory to couple the fluid and particle
phases. Playing a central role in the model, we introduce a micro-structural
state variable, whose evolution is deduced from small-scale physical arguments
and checked with existing data. Our space- and time-dependent model is
implemented numerically in a variety of unsteady, non-uniform flow
configurations where it is shown to accurately capture a variety of key
behaviors: (i) the continuous shear thickening (CST) and discontinuous shear
thickening (DST) behavior observed in steady flows, (ii) the time-dependent
propagation of `shear jamming fronts', (iii) the time-dependent propagation of
`impact activated jamming fronts', and (iv) the non-Newtonian, `running on
oobleck' effect wherein fast locomotors stay afloat while slow ones sink
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