15,769 research outputs found
The Low Column Density Lyman-alpha Forest
We develop an analytical method based on the lognormal approximation to
compute the column density distribution of the Lyman-alpha forest in the low
column density limit. We compute the column density distributions for six
different cosmological models and found that the standard, COBE-normalized CDM
model cannot fit the observations of the Lyman-alpha forest at z=3. The
amplitude of the fluctuations in that model has to be lowered by a factor of
almost 3 to match observations. However, the currently viable cosmological
models like the lightly tilted COBE-normalized CDM+Lambda model, the CHDM model
with 20% neutrinos, and the low-amplitude Standard CDM model are all in
agreement with observations, to within the accuracy of our approximation, for
the value of the cosmological baryon density at or higher than the old Standard
Bing Bang Nucleosynthesis value of 0.0125 for the currently favored value of
the ionizing radiation intensity. With the low value for the baryon density
inferred by Hogan & Rugers (1996), the models can only marginally match
observations.Comment: three postscript figures included, submitted to ApJ
The effect of legislation on the contractor's attitudes on solid waste reduction
It has been a difficult task to reduce and handle solid wastes generated from construction and demolition (C&D) activities in a number of countries. In Hong Kong, the C&D soHd wastes of which many of them are suitable for recycling land reclamation were typically disposed to landfills. Regarding this, in December 2005, a main piece of legislation regarding the C&D solid waste minimization namely the Construction Waste Disposal Charging Scheme (CWDCS) was enacted in Hong Kong. Since then disposal of C&D solid waste to public landfill sites has no longer been a 'free meal' for the contractors. While the government statistics indicate that the average quantity of C&D solid waste disposed to the public landfill has been tremendously decreased, disgraceful news about the illegal disposal of C&D waste by contractors have begun to mount. Some criticized that the illegal disposal was indeed driven by the legislation. It is because the legislation itself basically cannot solve the problems encountered by the contractors i.e. an effective solid waste reduction and management. As such, a behavioral change of solid waste disposal by the contractors has yet been noted. This study uses the enactment of the CWCS as a benchmark, and seeks to investigate [I] whether the Scheme has prompted the construction contractors to adopt C&D solid wastes reduction strategies in the construction projects; and [2] the effect of the strategy applied by the contractors on C&D solid waste reduction in their projects. A questionnaire survey was conducted. The analysed results based on the Pearson correlation analysis show that the enactment of the CWCS merely led the main contractors reorient their operational practices. Collaboration among project team members in C&D solid waste reduction remains inadequate. Recommendation in response to the research findings was suggested
An experimental investigation of criteria for continuous variable entanglement
We generate a pair of entangled beams from the interference of two amplitude
squeezed beams. The entanglement is quantified in terms of EPR-paradox [Reid88]
and inseparability [Duan00] criteria, with observed results of and , respectively. Both results clearly beat the standard quantum
limit of unity. We experimentally analyze the effect of decoherence on each
criterion and demonstrate qualitative differences. We also characterize the
number of required and excess photons present in the entangled beams and
provide contour plots of the efficacy of quantum information protocols in terms
of these variables.Comment: 4 pages, 5 figure
Energy flux of electromagnetic field in stochastic model of radiative heat transfer in dielectric solid medium
The stochastic model that describes radiative heat tran sfe r in dielectric medium is analyzed. The model is based on the representation that heat tran sfer is realized both by its heat conductivity and by electromagnetic radiation th a t is generated by thermal fluctuations in the medium. Such physical suppositions, using fluctuation-dissipative theorem, are realized in the form of the infinite dimensional Ornstein-Uhlenbeck process that describes medium fluctuation
String Organization of Field Theories: Duality and Gauge Invariance
String theories should reduce to ordinary four-dimensional field theories at
low energies. Yet the formulation of the two are so different that such a
connection, if it exists, is not immediately obvious. With the Schwinger
proper-time representation, and the spinor helicity technique, it has been
shown that field theories can indeed be written in a string-like manner, thus
resulting in simplifications in practical calculations, and providing novel
insights into gauge and gravitational theories. This paper continues the study
of string organization of field theories by focusing on the question of local
duality. It is shown that a single expression for the sum of many diagrams can
indeed be written for QED, thereby simulating the duality property in strings.
The relation between a single diagram and the dual sum is somewhat analogous to
the relation between a old- fashioned perturbation diagram and a Feynman
diagram. Dual expressions are particularly significant for gauge theories
because they are gauge invariant while expressions for single diagrams are not.Comment: 20 pages in Latex, including seven figures in postscrip
Gauge Consistent Wilson Renormalization Group II: Non-Abelian Case
We give a wilsonian formulation of non-abelian gauge theories explicitly
consistent with axial gauge Ward identitities. The issues of unitarity and
dependence on the quantization direction are carefully investigated. A
wilsonian computation of the one-loop QCD beta function is performed.Comment: 34 pages, 1 eps figure, latex2e. Minor changes, version to appear in
Int. J. Mod. Phy
Quasi-dark Mode in a Metamaterial for Analogous Electromagnetically-induced Transparency
We study a planar metamaterial supporting electromagnetically-induced
transparency (EIT)-like effect by exploiting the coupling between bright and
quasi-dark eigenmodes. The specific design of such a metamaterial consists of a
cut-wire (CW) and a single-gap split-ring resonator (SRR). From the numerical
and the analytical results we demonstrate that the response of SRR, which is
weakly excited by external electric field, is mitigated to be a quasi-dark
eigenmode in the presence of strongly radiative CW. This result suggests more
relaxed conditions for the realization of devices utilizing the EIT-like
effects in metamaterial, and thereby widens the possibilities for many
different structural implementations.Comment: 11 pages, 4 figure
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