2,190 research outputs found
The changing tide: Federal support of civilian-sector R and D
The involvement of the Federal government in civilian sector research and development is discussed. Relevant policies are put in an historical perspective. The roles played by industrial research and public funding are reveiwed. Government support of basic an generic research, clientele-oriented applied research, and research with commercial ends is studied. Procurement, anti-trust, and patent policies, all of which affect the climate for private research and development, are examined
Of Hackers and Hairdressers: Modularity and the Organizational Economics of Open-source Collaboration
By employing modularity theory, we study the general phenomenon of open-source collaboration, which includes, e.g., collective invention and open science besides open-source software production. We focus on how open-source collaboration coordinates the division of labor. We find that open-source collaboration is an organizational form based on the exchange of effort rather than of products where suppliers of effort self-identify like suppliers of products in a market rather than accepting assignments like employees in a firm. Our finding suggests that actual open-source software (and other) projects are neither bazaars nor cathedrals, but hybrids manifesting both voluntary production and conscious planning
Massive scalar states localized on a de Sitter brane
We consider a brane scenario with a massive scalar field in the
five-dimensional bulk. We study the scalar states that are localized on the
brane, which is assumed to be de Sitter. These localized scalar modes are
massive in general, their effective four-dimensional mass depending on the mass
of the five-dimensional scalar field, on the Hubble parameter in the brane and
on the coupling between the brane tension and the bulk scalar field. We then
introduce a purely four-dimensional approach based on an effective potential
for the projection of the scalar field in the brane, and discuss its regime of
validity. Finally, we explore the quasi-localized scalar states, which have a
non-zero width that quantifies their probability of tunneling from the brane
into the bulk.Comment: 14 pages; 5 figure
Cockpit Weather Information System Requirements for Flight Operations in Icing Conditions
In order to support the development of remote sensing technologies, the requirements of cockpit
information systems for flight operations in icing conditions were investigated. Pilot information
needs were investigated in a web-based survey. Results identified important information
elements, frequently used information paths for obtaining icing-related information, and data on
significant icing encounters and key icing-related information and decision criteria. In addition,
the influence of potential ice detection system features on pilot decision-making was investigated
in a web-based experiment. Results showed that the use of graphical displays improved pilot
decision-making over existing text-based icing information. The use of vertical view was found
to support better decision-making. Range enhancement was not found to have strong positive
influence; however the minimum range tested was 25 nautical miles, which may be in excess of
current technical capabilities. The depiction of multiple icing severity levels was not found to be
as important as accurate information on the location of icing conditions. This may have
significant impact for remote sensing and forecasting efforts currently under way, as the
technical challenges for accurate detection of icing presence may be significantly inferior to
those of accurate detection of multiple icing severity levels
Scalar potential from de Sitter brane in 5D and effective cosmological constant
We derive the scalar potential in zero mode effective action arising from a
de Sitter brane embedded in five dimensions with bulk cosmological constant
. The scalar potential for a scalar field canonically normalized is
given by the sum of exponential potentials. In the case of and
, we point out that the scalar potential has an unstable local
maximum at the origin and exponentially vanishes for large positive scalar
field. In the case of , the scalar potential has an unstable local
maximum at the origin and a stable local minimum, it is shown that the positive
cosmological constant in brane is reduced by negative potential energy of
scalar at minimum.Comment: 14 pages, 5 figures, add the section of cosmological implication
The initial changes of fat deposits during the decomposition of human and pig remains
The early stages of adipocere formation in both pig and human adipose tissue in aqueous environments have been investigated. The aims were to determine the short-term changes occurring to fat deposits during decomposition and to ascertain the suitability of pigs as models for human decomposition. Subcutaneous adipose tissue from both species after immersion in distilled water for up to six months was compared using Fourier transform infrared spectroscopy, gas chromatography-mass spectrometry and inductively coupled plasma-mass spectrometry. Changes associated with decomposition were observed, but no adipocere was formed during the initial month of decomposition for either tissue type. Early-stage adipocere formation in pig samples during later months was detected. The variable time courses for adipose tissue decomposition were attributed to differences in the distribution of total fatty acids between species. Variations in the amount of sodium, potassium, calcium, and magnesium were also detected between species. The study shows that differences in total fatty acid composition between species need to be considered when interpreting results from experimental decomposition studies using pigs as human body analogs. © 2008 American Academy of Forensic Sciences
Strong gravitational lensing by braneworld black holes
In this paper, we use the strong field limit approach to investigate the
gravitational lensing properties of braneworld black holes. Applying this
method to the supermassive black hole at the centre of our galaxy, the lensing
observables for some candidate braneworld black hole metrics are compared with
those for the standard Schwarzschild case. It is found that braneworld black
holes could have significantly different observational signatures to the
Schwarzschild black hole.Comment: 8 pages, 4 figures, RevTeX4; v2 reference added; v3 minor technical
correctio
Gauss-Bonnet brane gravity with a confining potential
A brane scenario is envisaged in which the -dimensional bulk is endowed
with a Gauss-Bonnet term and localization of matter on the brane is achieved by
means of a confining potential. The resulting Friedmann equations on the brane
are modified by various extra terms that may be interpreted as the X-matter,
providing a possible phenomenological explanation for the accelerated expansion
of the universe. The age of the universe in this scenario is studied and shown
to be consistent with the present observational data.Comment: 14 pages, 4 figures, to appear in PR
The inflationary prediction for primordial non-gaussianity
We extend the \delta N formalism so that it gives all of the stochastic
properties of the primordial curvature perturbation \zeta if the initial field
perturbations are gaussian. The calculation requires only the knowledge of some
family of unperturbed universes. A formula is given for the normalisation \fnl
of the bispectrum of \zeta, which is the main signal of non-gaussianity.
Examples of the use of the formula are given, and its relation to cosmological
perturbation theory is explained.Comment: Revtex Latex file. 4 pages, no figures. v4: minor changes, typos
corrected, references added and updated. Version published in Physical Review
Letter
Primordial gravitational waves in inflationary braneworld
We study primordial gravitational waves from inflation in Randall-Sundrum
braneworld model. The effect of small change of the Hubble parameter during
inflation is investigated using a toy model given by connecting two de Sitter
branes. We analyze the power spectrum of final zero-mode gravitons, which is
generated from the vacuum fluctuations of both initial Kaluza-Klein modes and
zero-mode. The amplitude of fluctuations is confirmed to agree with the
four-dimensional one at low energies, whereas it is enhanced due to the
normalization factor of zero-mode at high energies. We show that the
five-dimensional spectrum can be well approximated by applying a simple mapping
to the four-dimensional fluctuation amplitude.Comment: 16 pages, 4 figures, typos correcte
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