980 research outputs found
Vacuum polarization induced by a cylindrical boundary in the cosmic string spacetime
In this paper we investigate the Wightman function, the renormalized vacuum
expectation values of the field square, and the energy-momentum tensor for a
massive scalar field with general curvature coupling inside and outside of a
cylindrical shell in the generalized spacetime of straight cosmic string. For
the general case of Robin boundary condition, by using the generalized
Abel-Plana formula, the vacuum expectation values are presented in the form of
the sum of boundary-free and boundary-induced parts. The asymptotic behavior of
the vacuum expectation values of the field square, energy density and stresses
are investigated in various limiting cases. The generalization of the results
to the exterior region is given for a general cylindrically symmetric static
model of the string core with finite support.Comment: 21 pages, 5 figure
Protective Effect of Liposome-Encapsulated Glutathione in a Human Epidermal Model Exposed to a Mustard Gas Analog
Sulfur mustard or mustard gas (HD) and its monofunctional analog, 2-chloroethyl ethyl sulfide (CEES), or “half-mustard gas,” are alkylating agents that induce DNA damage, oxidative stress, and inflammation. HD/CEES are rapidly absorbed in the skin causing extensive injury. We hypothesize that antioxidant liposomes that deliver both water-soluble and lipid-soluble antioxidants protect skin cells from immediate CEES-induced damage via attenuating oxidative stress. Liposomes containing water-soluble antioxidants and/or lipid-soluble antioxidants were evaluated using in vitro model systems. Initially, we found that liposomes containing encapsulated glutathione (GSH-liposomes) increased cell viability and attenuated production of reactive oxygen species (ROS) in HaCaT cells exposed to CEES. Next, GSH-liposomes were tested in a human epidermal model, EpiDerm. In the EpiDerm, GSH-liposomes administered simultaneously or 1 hour after CEES exposure (2.5 mM) increased cell viability, inhibited CEES-induced loss of ATP and attenuated changes in cellular morphology, but did not reduce caspase-3 activity. These findings paralleled the previously described in vivo protective effect of antioxidant liposomes in the rat lung and established the effectiveness of GSH-liposomes in a human epidermal model. This study provides a rationale for use of antioxidant liposomes against HD toxicity in the skin considering further verification in animal models exposed to HD
Protective Effect of Liposome-Encapsulated Glutathione in a Human Epidermal Model Exposed to a Mustard Gas Analog
Sulfur mustard or mustard gas (HD) and its monofunctional analog, 2-chloroethyl ethyl sulfide (CEES), or half-mustard gas , are alkylating agents that induce DNA damage, oxidative stress, and inflammation. HD/CEES are rapidly absorbed in the skin causing extensive injury. We hypothesize that antioxidant liposomes that deliver both water-soluble and lipid-soluble antioxidants protect skin cells from immediate CEES-induced damage via attenuating oxidative stress. Liposomes containing water-soluble antioxidants and/or lipid-soluble antioxidants were evaluated using in vitro model systems. Initially, we found that liposomes containing encapsulated glutathione (GSH-liposomes) increased cell viability and attenuated production of reactive oxygen species (ROS) in HaCaT cells exposed to CEES. Next, GSH-liposomes were tested in a human epidermal model, EpiDerm. In the EpiDerm, GSH-liposomes administered simultaneously or 1 hour after CEES exposure (2.5mM) increased cell viability, inhibited CEES-induced loss of ATP and attenuated changes in cellular morphology, but did not reduce caspase-3 activity. These findings paralleled the previously described in vivo protective effect of antioxidant liposomes in the rat lung and established the effectiveness of GSH-liposomes in a human epidermal model. This study provides a rationale for use of antioxidant liposomes against HD toxicity in the skin considering further verification in animal models exposed to HD
Fermionic current densities induced by magnetic flux in a conical space with a circular boundary
We investigate the vacuum expectation value of the fermionic current induced
by a magnetic flux in a (2+1)-dimensional conical spacetime in the presence of
a circular boundary. On the boundary the fermionic field obeys MIT bag boundary
condition. For irregular modes, a special case of boundary conditions at the
cone apex is considered, when the MIT bag boundary condition is imposed at a
finite radius, which is then taken to zero. We observe that the vacuum
expectation values for both charge density and azimuthal current are periodic
functions of the magnetic flux with the period equal to the flux quantum
whereas the expectation value of the radial component vanishes. For both
exterior and interior regions, the expectation values of the current are
decomposed into boundary-free and boundary-induced parts. For a massless field
the boundary-free part in the vacuum expectation value of the charge density
vanishes, whereas the presence of the boundary induces nonzero charge density.
Two integral representations are given for the boundary-free part in the case
of a massive fermionic field for arbitrary values of the opening angle of the
cone and magnetic flux. The behavior of the induced fermionic current is
investigated in various asymptotic regions of the parameters. At distances from
the boundary larger than the Compton wavelength of the fermion particle, the
vacuum expectation values decay exponentially with the decay rate depending on
the opening angle of the cone. We make a comparison with the results already
known from the literature for some particular cases.Comment: 34 pages, 6 figure
Is There a Role for Benefit-Cost Analysis in Environmental, Health, and Safety Regulation?
Benefit-cost analysis has a potentially important role to play in helping inform regulatory decision-making, although it should not be the sole basis for such decision-making. This paper offers eight principles on the appropriate use of benefit-cost analysis.Environment, Health and Safety, Regulatory Reform
Benefit-Cost Analysis in Environmental, Health, and Safety Regulation: A Statement of Principles
Benefit-cost analysis can play a very important role in legislative and regulatory policy debates on improving the environment, health, and safety. It can help illustrate the tradeoffs that are inherent in public policymaking as well as make those tradeoffs more transparent. It can also help agencies set regulatory priorities. Benefit-cost analysis should be used to help decisionmakers reach a decision. Contrary to the views of some, benefit-cost analysis is neither necessary nor sufficient for designing sensible public policy. If properly done, it can be very helpful to agencies in the decisionmaking process. Decisionmakers should not be precluded from considering the economic benefits and costs of different policies in the development of regulations. Laws that prohibit costs or other factors from being considered in administrative decisionmaking are inimical to good public policy. Currently, several of the most important regulatory statutes have been interpreted to imply such prohibitions. Benefit-cost analysis should be required for all major regulatory decisions, but agency heads should not be bound by a strict benefit-cost test. Instead, they should be required to consider available benefit-cost analyses and to justify the reasons for their decision in the event that the expected costs of a regulation far exceed the expected benefits. Agencies should be encouraged to use economic analysis to help set regulatory priorities. Economic analyses prepared in support of particularly important decisions should be subjected to peer review both inside and outside government. Benefits and costs of proposed major regulations should be quantified wherever possible. Best estimates should be presented along with a description of the uncertainties. Not all benefits or costs can be easily quantified, much less translated into dollar terms. Nevertheless, even qualitative descriptions of the pros and cons associated with a contemplated action can be helpful. Care should be taken to ensure that quantitative factors do not dominate important qualitative factors in decisionmaking. The Office of Management and Budget, or some other coordinating agency, should establish guidelines that agencies should follow in conducting benefit-cost analyses. Those guidelines should specify default values for the discount rate and certain types of benefits and costs, such as the value of a small reduction in mortality risk. In addition, agencies should present their results using a standard format, which summarizes the key results and highlights major uncertainties.
Exact Solutions of the Klein-Gordon Equation in the Presence of a Dyon, Magnetic Flux and Scalar Potential in the Specetime of Gravitational Defects
In this paper we analyse the relativistic quantum motion of a charged spin-0
particle in the presence of a dyon, Aharonov-Bohm magnetic field and scalar
potential, in the spacetimes produced by an idealized cosmic string and global
monopole. In order to develop this analysis, we assume that the dyon and the
Aharonov-Bohm magnetic field are superposed to both gravitational defects. Two
distinct configurations for the scalar potential, , are considered:
the potential proportional to the inverse of the radial distance, i.e.,
, and the potential proportional to this distance, i.e.,
. For both cases the center of the potentials coincide with the
dyon's position. In the case of the cosmic string the Aharonov-Bohm magnetic
field is considered along the defect, and for the global monopole this magnetic
field pierces the defect. The energy spectra are computed for both cases and
explicitly shown their dependence on the electrostatic and scalar coupling
constants. Also we analyse scattering states of the Klein-Gordon equations, and
show how the phase shifts depend on the geometry of the spacetime and on the
coupling constants parameter.Comment: To be published in CQG. Minor comments adde
Casimir Effect as a Test for Thermal Corrections and Hypothetical Long-Range Interactions
We have performed a precise experimental determination of the Casimir
pressure between two gold-coated parallel plates by means of a micromachined
oscillator. In contrast to all previous experiments on the Casimir effect,
where a small relative error (varying from 1% to 15%) was achieved only at the
shortest separation, our smallest experimental error (%) is achieved
over a wide separation range from 170 nm to 300 nm at 95% confidence. We have
formulated a rigorous metrological procedure for the comparison of experiment
and theory without resorting to the previously used root-mean-square deviation,
which has been criticized in the literature. This enables us to discriminate
among different competing theories of the thermal Casimir force, and to resolve
a thermodynamic puzzle arising from the application of Lifshitz theory to real
metals. Our results lead to a more rigorous approach for obtaining constraints
on hypothetical long-range interactions predicted by extra-dimensional physics
and other extensions of the Standard Model. In particular, the constraints on
non-Newtonian gravity are strengthened by up to a factor of 20 in a wide
interaction range at 95% confidence.Comment: 17 pages, 7 figures, Sixth Alexander Friedmann International Seminar
on Gravitation and Cosmolog
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