9,657 research outputs found
Conformally Invariant Gauge Theory of 3-Branes in 6D and the Cosmological Constant
It is shown that the gauge theory of relativistic 3-Branes can be formulated
in a conformally invariant way if the embedding space is six-dimensional. The
implementation of conformal invariance requires the use of a modified measure,
independent of the metric in the action. Brane-world scenarios without the need
of a cosmological constant in 6D are constructed. Thus, no ``old'' cosmological
constant problem appears at this level.Comment: 12 pages, Latex, no figures; final version accepted for publication
in Phys.Rev. D; Sect.II expande
The investigation of heavy metal ion content in rock and coal production
Приведено олгляд методів визначення вмісту важких металів у вугіллі та продуктах вуглевидобутку. Виявлена доцільність використання НВЧ-поля та зниження температури озолення проб для підвищення точності визначення та зниження витрат часу на проведення аналізу.Приведен обзор методов определения тяжелых металлов в угле и продуктах угледобычи. Выявлена целесообразность использования СВЧ-поля и снижения температуры озоления проб для повышения точности определения и уменьшения затрат времени на проведения анализа.A review over the methods of heavy metals determination in coal and products of coal mining is present. Expediency of the use of microwave and declines of temperature for ash tests is educed for the exactness increase of determination and diminishing time for analysis
Dynamical measure and field theory models free of the cosmological constant problem
Summary of abstract Field theory models including gauge theories with SSB are
presented where the energy density of the true vacuum state (TVS) is zero
without fine tuning. The above models are constructed in the gravitational
theory where a measure of integration \Phi in the action is not necessarily
\sqrt{-g} but it is determined dynamically through additional degrees of
freedom. The ratio \Phi/\sqrt{-g} is a scalar field which can be solved in
terms of the matter degrees of freedom due to the existence of a constraint. We
study a few explicit field theory models where it is possible to combine the
solution of the cosmological constant problem with: 1) possibility for
inflationary scenario for the early universe; 2) spontaneously broken gauge
unified theories (including fermions). The models are free from the well known
problem of the usual scalar-tensor theories in what is concerned with the
classical GR tests. The only difference of the field equations in the Einstein
frame from the canonical equations of the selfconsistent system of Einstein's
gravity and matter fields, is the appearance of the effective scalar field
potential which vanishes in TVS without fine tuning.Comment: Extended version of the contribution to the fourth Alexander
Friedmann International Seminar on Gravitation and Cosmology; accepted for
publication in Phys. Rev. D; 31 page
Transverse tripolar stimulation for selective FNS
Various anode-cathode configurations in a nerve cuff were modeled in order to optimize its spatial selectivity characteristics for FNS. Apart from the usual configurations (monopole, bipole, longitudinal tripole, ¿steering¿ anode), a transverse tripolar configuration (central cathode) was examined. The model predictions were verified by acute animal experiments. It is concluded that a transverse tripole activates superficial nerve fibers in a more selective way than other configurations d
Determining whether estimated spore release rates for Aspergillus fumigatus are compatible with their measured growth rates in composting systems
The composting process like other waste management activities has the potential to generate large concentrations of bioaerosols which can be widely dispersed into the surrounding environment. There has been considerable interest in the literature of the effect of bioaerosols and in particular Aspergillus fumigatus on the health of plant operators and those living in close proximity to composting plants (Olver, 1994; Fischer et al., 1999; Fischer et al., 2000; Bunger et al., 200). Although bioaerosols can be generated through a range of operational procedures it has also been suggested
that large numbers of Aspergillus fumigatus spores can be emitted from static compost piles through the action of
natural air movements across the surface of the biodegrading material. Through the use of a portable wind tunnel apparatus researchers have determined the rate of emission of Aspergillus fumigatus spores as a result of air movement across the surface of the material (Taha et al., 2004; 2005; 2006 & 2007). The aim of this work was to use controlled laboratory experiments using compost samples and Aspergillus fumigatus spores to determine the sporulation rate of Aspergillus fumigatus. Using this data it would then be possible to verify whether bioaerosol emission rates from static compost windrows calculated and quoted in the literature can in fact be maintained over longer time periods. A series of experiments were carried out using Aspergillus fumigatus spores on agar plates and small samples of green waste compost to determine the number of spores that could be generated by each existing spore over a seven day period. From the experiments the sporulation rate determined from the agar plates varied with averages of either 4.48x104 or 2.83 spores/day depending upon the date set used and from the compost experiments it was 1.33 spores/day. Using this data and making a number of assumptions for moisture content (50%), bulk density (650 kg/m3) and the wind penetration depth (10-25mm) the potential release rates were calculated. The data from the agar experiments yielded a potential release rate at 10mm up to 5 orders of magnitude in excess of that quoted by Taha et al. (2004 & 2005. Using the trimmed data set the agar release figures are between 6.17 x 103 and 1.23 x 104 cfu/m2/s depending upon the wind penetration depth used and are comparable to those quoted in the literature. The release rate calculated using the compost experiments was slightly lower than the agar 2 data and consequently the release rates even at a wind penetration depth of 25mm are just outside the range quoted by Taha et al. (2004 & 2005).
Although the data presented in this paper were determined from controlled laboratory experiments they show that it is
possible for Aspergillus fumigatus to generate spores at a sufficient rate to allow the release of significant numbers of spores. The calculated sporulation rates would allow spores to be released at the rates quoted in the literature and suggest that the fugitive release rates quoted in the literature would be able to be maintained over long periods of time. However it is recognised that the data is affected greatly by the assumptions one makes, in particular the existing concentration of Aspergillus fumigatus. Despite the limitations the original intention of the work was to attempt to establish the long term applicability of the fugitive release rates for Aspergillus fumigatus from green waste compost
quoted in the literature and it has achieved this objective
Searching with Tags: Do Tags Help Users Find Things?
This study examines the question of whether tags can be useful in the process of information retrieval. Participants searched a social bookmarking tool specialising in academic articles (CiteULike) and an online journal database (Pubmed). Participant actions were captured using screen capture software and they were asked to describe their search process. Users did make use of tags in their search process, as a guide to searching and as hyperlinks to potentially useful articles. However, users also made use of controlled vocabularies in the journal database to locate useful search terms and of links to related articles supplied by the database
Determining whether estimated spore release rates for Aspergillus fumigatus are compatible with their measured growth rates in composting systems
The composting process like other waste management activities has the potential to generate large concentrations of bioaerosols which can be widely dispersed into the surrounding environment. There has been considerable interest in the literature of the effect of bioaerosols and in particular Aspergillus fumigatus on the health of plant operators and those living in close proximity to composting plants (Olver, 1994; Fischer et al., 1999; Fischer et al., 2000; Bunger et al., 200). Although bioaerosols can be generated through a range of operational procedures it has also been suggested
that large numbers of Aspergillus fumigatus spores can be emitted from static compost piles through the action of
natural air movements across the surface of the biodegrading material. Through the use of a portable wind tunnel apparatus researchers have determined the rate of emission of Aspergillus fumigatus spores as a result of air movement across the surface of the material (Taha et al., 2004; 2005; 2006 & 2007). The aim of this work was to use controlled laboratory experiments using compost samples and Aspergillus fumigatus spores to determine the sporulation rate of Aspergillus fumigatus. Using this data it would then be possible to verify whether bioaerosol emission rates from static compost windrows calculated and quoted in the literature can in fact be maintained over longer time periods. A series of experiments were carried out using Aspergillus fumigatus spores on agar plates and small samples of green waste compost to determine the number of spores that could be generated by each existing spore over a seven day period. From the experiments the sporulation rate determined from the agar plates varied with averages of either 4.48x104 or 2.83 spores/day depending upon the date set used and from the compost experiments it was 1.33 spores/day. Using this data and making a number of assumptions for moisture content (50%), bulk density (650 kg/m3) and the wind penetration depth (10-25mm) the potential release rates were calculated. The data from the agar experiments yielded a potential release rate at 10mm up to 5 orders of magnitude in excess of that quoted by Taha et al. (2004 & 2005. Using the trimmed data set the agar release figures are between 6.17 x 103 and 1.23 x 104 cfu/m2/s depending upon the wind penetration depth used and are comparable to those quoted in the literature. The release rate calculated using the compost experiments was slightly lower than the agar 2 data and consequently the release rates even at a wind penetration depth of 25mm are just outside the range quoted by Taha et al. (2004 & 2005).
Although the data presented in this paper were determined from controlled laboratory experiments they show that it is
possible for Aspergillus fumigatus to generate spores at a sufficient rate to allow the release of significant numbers of spores. The calculated sporulation rates would allow spores to be released at the rates quoted in the literature and suggest that the fugitive release rates quoted in the literature would be able to be maintained over long periods of time. However it is recognised that the data is affected greatly by the assumptions one makes, in particular the existing concentration of Aspergillus fumigatus. Despite the limitations the original intention of the work was to attempt to establish the long term applicability of the fugitive release rates for Aspergillus fumigatus from green waste compost
quoted in the literature and it has achieved this objective
Superextendons with a modified measure
For superstrings, the consequences of replacing the measure of integration
in the Polyakov's action by where is
a density built out of degrees of freedom independent of the metric
defined in the string are studied. As in Siegel reformulation of
the Green Schwarz formalism the Wess-Zumino term is the square of
supersymmetric currents. As opposed to the Siegel case, the compensating fields
needed for this do not enter into the action just as in a total derivative.
They instead play a crucial role to make up a consistent dynamics. The string
tension appears as an integration constant of the equations of motion. The
generalization to higher dimensional extended objects is also studied using in
this case the Bergshoeff and Sezgin formalism with the associated additional
fields, which again are dynamically relevant unlike the standard formulation.
Also unlike the standard formulation, there is no need of a cosmological term
on the world brane.Comment: typos corrected, references adde
Intertwining Laplace Transformations of Linear Partial Differential Equations
We propose a generalization of Laplace transformations to the case of linear
partial differential operators (LPDOs) of arbitrary order in R^n. Practically
all previously proposed differential transformations of LPDOs are particular
cases of this transformation (intertwining Laplace transformation, ILT). We
give a complete algorithm of construction of ILT and describe the classes of
operators in R^n suitable for this transformation.
Keywords: Integration of linear partial differential equations, Laplace
transformation, differential transformationComment: LaTeX, 25 pages v2: minor misprints correcte
On a pair of difference equations for the type orthogonal polynomials and related exactly-solvable quantum systems
We introduce a pair of novel difference equations, whose solutions are
expressed in terms of Racah or Wilson polynomials depending on the nature of
the finite-difference step. A number of special cases and limit relations are
also examined, which allow to introduce similar difference equations for the
orthogonal polynomials of the and types. It is shown that
the introduced equations allow to construct new models of exactly-solvable
quantum dynamical systems, such as spin chains with a nearest-neighbour
interaction and fermionic quantum oscillator models.Comment: 8 pages, to be published in Springer Proceedings in Mathematics &
Statistic
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