3,067 research outputs found
Analysis of a solar collector field water flow network
A number of methods are presented for minimizing the water flow variation in the solar collector field for the Solar Building Test Facility at the Langley Research Center. The solar collector field investigated consisted of collector panels connected in parallel between inlet and exit collector manifolds to form 12 rows. The rows were in turn connected in parallel between the main inlet and exit field manifolds to complete the field. The various solutions considered included various size manifolds, manifold area change, different locations for the inlets and exits to the manifolds, and orifices or flow control valves. Calculations showed that flow variations of less than 5 percent were obtainable both inside a row between solar collector panels and between various rows
Approximate treatment of electron Coulomb distortion in quasielastic (e,e') reactions
In this paper we address the adequacy of various approximate methods of
including Coulomb distortion effects in (e,e') reactions by comparing to an
exact treatment using Dirac-Coulomb distorted waves. In particular, we examine
approximate methods and analyses of (e,e') reactions developed by Traini et al.
using a high energy approximation of the distorted waves and phase shifts due
to Lenz and Rosenfelder. This approximation has been used in the separation of
longitudinal and transverse structure functions in a number of (e,e')
experiments including the newly published 208Pb(e,e') data from Saclay. We find
that the assumptions used by Traini and others are not valid for typical (e,e')
experiments on medium and heavy nuclei, and hence the extracted structure
functions based on this formalism are not reliable. We describe an improved
approximation which is also based on the high energy approximation of Lenz and
Rosenfelder and the analyses of Knoll and compare our results to the Saclay
data. At each step of our analyses we compare our approximate results to the
exact distorted wave results and can therefore quantify the errors made by our
approximations. We find that for light nuclei, we can get an excellent
treatment of Coulomb distortion effects on (e,e') reactions just by using a
good approximation to the distorted waves, but for medium and heavy nuclei
simple additional ad hoc factors need to be included. We describe an explicit
procedure for using our approximate analyses to extract so-called longitudinal
and transverse structure functions from (e,e') reactions in the quasielastic
region.Comment: 30 pages, 8 figures, 16 reference
Renormalization in Self-Consistent Approximation schemes at Finite Temperature III: Global Symmetries
We investigate the symmetry properties for Baym's -derivable schemes.
We show that in general the solutions of the dynamical equations of motion,
derived from approximations of the -functional, do not fulfill the
Ward-Takahashi identities of the symmetry of the underlying classical action,
although the conservation laws for the expectation values of the corresponding
Noether currents are fulfilled exactly for the approximation. Further we prove
that one can define an effective action functional in terms of the
self-consistent propagators which is invariant under the operation of the same
symmetry group representation as the classical action. The requirements for
this theorem to hold true are the same as for perturbative approximations: The
symmetry has to be realized linearly on the fields and it must be free of
anomalies, i.e., there should exist a symmetry conserving regularization
scheme. In addition, if the theory is renormalizable in Dyson's narrow sense,
it can be renormalized with counter terms which do not violate the symmetry.Comment: 32 papges, 3 figures, uses ReVTeX 4, V2: Added one more reference,
V3: Corrected some typos, added two more sections about the large-N expansio
Human error analysis: Review of past accidents and implications for improving robustness of system design
Since the establishment of the high-technology industry and industrial systems, developments of new materials and fabrication techniques, associated with cutting-edge structural and engineering assessments, are contributing to more reliable and consistent systems, thus reducing the likelihood of losses. However, recent accidents are acknowledged to be linked to human factors which led to catastrophic consequences. Therefore, the understanding of human behavioural characteristics interlaced with the actual technology aspects and organisational context is of paramount importance for the safety & reliability field. This study first approaches this multidisciplinary problem by classifying and reviewing 200 major accident data from insurance companies and regulatory authorities under the Cognitive Reliability and Error Analysis framework. Then, specific attention is dedicated to discuss the implications for improving robustness of system design and tackling the surrounding factors and tendencies that could lead to the manifestation of human errors
Learning from accidents: Investigating the genesis of human errors in multi-attribute settings to improve the organisation of design
Remarkable advances in engineering and system controls in recent times and the consequent development of state-of-the-art technologies are clearly resulting in economic, environmental and safety benefits to the society. Latest disasters, however, put human error in the glare of the media spotlight. The February 2016 train collision in southern Bavaria, Germany, which took 11 lives and left more than 90 people injured, is one of several examples where human errors appear to have played a significant role in a major accident. In this emblematic case, the railway system had multiple safety barriers in place, such as an automatic braking system if a train crosses a stop signal, but the track controller had reportedly disabled it. When he realised the error and tried to warn the drivers, it was too late (BBC, 2016)
Learning from major accidents to improve system design
© 2015 Elsevier Ltd.Despite the massive developments in new technologies, materials and industrial systems, notably supported by advanced structural and risk control assessments, recent major accidents are challenging the practicality and effectiveness of risk control measures designed to improve reliability and reduce the likelihood of losses. Contemporary investigations of accidents occurred in high-technology systems highlighted the connection between human-related issues and major events, which led to catastrophic consequences. Consequently, the understanding of human behavioural characteristics interlaced with current technology aspects and organisational context seems to be of paramount importance for the safety & reliability field. First, significant drawbacks related to the human performance data collection will be minimised by the development of a novel industrial accidents dataset, the Multi-attribute Technological Accidents Dataset (MATA-D), which groups 238 major accidents from different industrial backgrounds and classifies them under a common framework (the Contextual Control Model used as basis for the Cognitive Reliability and Error Analysis Method). The accidents collection and the detailed interpretation will provide a rich data source, enabling the usage of integrated information to generate input to design improvement schemes. Then, implications to improve robustness of system design and tackle the surrounding factors and tendencies that could lead to the manifestation of human errors will be effectively addressed
Self-consistent Approach to Off-Shell Transport
The properties of two forms of the gradient expanded Kadanoff--Baym
equations, i.e. the Kadanoff--Baym and Botermans-Malfliet forms, suitable to
describe the transport dynamics of particles and resonances with broad spectral
widths, are discussed in context of conservation laws, the definition of a
kinetic entropy and the possibility of numerical realization. Recent results on
exact conservations of charge and energy-momentum within Kadanoff-Baym form of
quantum kinetics based on local coupling schemes are extended to two cases
relevant in many applications. These concern the interaction via a finite range
potential, and, relevant in nuclear and hadron physics, e.g. for the
pion--nucleon interaction, the case of derivative coupling.Comment: 35 pages, submitted to issue of Phys. Atom. Nucl. dedicated to S.T.
Belyaev on the occasion of his 80th birthday. Few references are adde
Gator: a low-background counting facility at the Gran Sasso Underground Laboratory
A low-background germanium spectrometer has been installed and is being
operated in an ultra-low background shield (the Gator facility) at the Gran
Sasso underground laboratory in Italy (LNGS). With an integrated rate of ~0.16
events/min in the energy range between 100-2700 keV, the background is
comparable to those of the world's most sensitive germanium detectors. After a
detailed description of the facility, its background sources as well as the
calibration and efficiency measurements are introduced. Two independent
analysis methods are described and compared using examples from selected sample
measurements. The Gator facility is used to screen materials for XENON, GERDA,
and in the context of next-generation astroparticle physics facilities such as
DARWIN.Comment: 14 pages, 6 figures, published versio
Global literature review of Haemophilus influenzae type b and Streptococcus pneumoniae invasive disease among children less than five years of age 1980-2005
Soft Photons from Off-shell Particles in a Hot Plasma
Considering the propagation of off-shell particles in the framework of
thermal field theory, we present the general formalism for the calculation of
the production rate of soft photons and dileptons from a hot plasma. This
approach is illustrated with an electrodynamic plasma. The photon production
rate from strongly interacting quarks in the quark-gluon plasma, which might be
formed in ultrarelativistic heavy ion collisions, is calculated in the
previously unaccessible regime of photon energies of the order of the plasma
temperature within an effective field theory incorporating dynamical chiral
symmetry breaking.Comment: 8 pages in RevTeX format, 3 figures uuencoded postscript added. Also
available by anonymous ftp at ftp://tpri6c.gsi.de/pub/phenning/qh95ga
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