995 research outputs found
Precise time and time interval users, requirements and specifications
The functional areas of application of Precise Time and Time Interval (PTTI) were considered and expanded. A comprehensive overview of the PTTI requirements and applications would provide an opportunity for individuals working in a specific functional area. Mutual problems, requirements, applications or successes shared by those in other functional areas were studied. Based upon the results of a two year study a compendium of PTTI requirements, applications and the means of meeting the requirements among Department of Defense components, other government agencies and major commercial users was compiled and is presented. It was found that the planning process for PTTI support for new acquisitions or new programs was less than a well defined, coordinated process. The processes are described in general terms and a generic model for requirements determination and subsequent coordination which may enhance the planning process and introduce cost benefits to the program is also presented
Department of Defense Precise Time and Time Interval program improvement plan
The United States Naval Observatory is responsible for ensuring uniformity in precise time and time interval operations including measurements, the establishment of overall DOD requirements for time and time interval, and the accomplishment of objectives requiring precise time and time interval with minimum cost. An overview of the objectives, the approach to the problem, the schedule, and a status report, including significant findings relative to organizational relationships, current directives, principal PTTI users, and future requirements as currently identified by the users are presented
Concept of Formation Length in Radiation Theory
The features of electromagnetic processes are considered which connected with
finite size of space region in which final particles (photon, electron-positron
pair) are formed. The longitudinal dimension of the region is known as the
formation length. If some external agent is acting on an electron while
traveling this distance the emission process can be disrupted. There are
different agents: multiple scattering of projectile, polarization of a medium,
action of external fields, etc. The theory of radiation under influence of the
multiple scattering, the Landau-Pomeranchuk-Migdal (LPM) effect, is presented.
The probability of radiation is calculated with an accuracy up to "next to
leading logarithm" and with the Coulomb corrections taken into account. The
integral characteristics of bremsstrahlung are given, it is shown that the
effective radiation length increases due to the LPM effect at high energy. The
LPM effect for pair creation is also presented. The multiple scattering
influences also on radiative corrections in a medium (and an external field
too) including the anomalous magnetic moment of an electron and the
polarization tensor as well as coherent scattering of a photon in a Coulomb
field. The polarization of a medium alters the radiation probability in soft
part of spectrum. Specific features of radiation from a target of finite
thickness include: the boundary photon emission, interference effects for thin
target, multi-photon radiation. The experimental study of LPM effect is
described. For electron-positron colliding beams following items are discussed:
the separation of coherent and incoherent mechanisms of radiation, the
beam-size effect in bremsstrahlung, coherent radiation and mechanisms of
electron-positron creation.Comment: Revised review paper, 96 pages, 28 figures. Description of SLAC E-146
experiment removed, discussion of CERN SPS experiment adde
HVEM of Gromia (Protista) from the Abyss
Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 - August 5, 201
Peer-reviewed public health journals from Arabic-speaking countries: An updated snapshot.
There is a positive association between availability of regional peer-reviewed public health information systems and progressive change in community and population health. The objective of this brief report was to identify public health journals in Arabic-speaking countries actively publishing as of 2016. We conducted an electronic search in several electronic database records for public health journals using a combination of search terms. We excluded journals that focused on human medicine, veterinary medicine, nursing, and other discipline-specific or clinical health professions. We identified twenty-five public health journals for review. Five journals were interrupted or discontinued. Only three journals had a consistent, uninterrupted active publication history of greater than 20Â years. Most journals were not in the regional native language. Introduction of regional public health-dedicated journals with in-print and electronic availability and also to be published in region-native languages may require interdisciplinary partnerships. Region-wide public health journals such as the Eastern Mediterranean Health Journal could serve as an ideal model for the establishment of additional local and regional public health journals in Arabic-speaking countries
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