3,551 research outputs found
Efficiency at optimal work from finite reservoirs: a probabilistic perspective
We revisit the classic thermodynamic problem of maximum work extraction from
two arbitrary sized hot and cold reservoirs, modelled as perfect gases.
Assuming ignorance about the extent to which the process has advanced, which
implies an ignorance about the final temperatures, we quantify the prior
information about the process and assign a prior distribution to the unknown
temperature(s). This requires that we also take into account the temperature
values which are regarded to be unphysical in the standard theory, as they lead
to a contradiction with the physical laws. Instead in our formulation, such
values appear to be consistent with the given prior information and hence are
included in the inference. We derive estimates of the efficiency at optimal
work from the expected values of the final temperatures, and show that these
values match with the exact expressions in the limit when any one of the
reservoirs is very large compared to the other. For other relative sizes of the
reservoirs, we suggest a weighting procedure over the estimates from two valid
inference procedures, that generalizes the procedure suggested earlier in [J.
Phys. A: Math. Theor. {\bf 46}, 365002 (2013)]. Thus a mean estimate for
efficiency is obtained which agrees with the optimal performance to a high
accuracy.Comment: 14 pages, 6 figure
Retrospective Application of Human Reliability Analysis for Oil and Gas Incidents: A Case Study Using the Petro-HRA Method
Human reliability analysis (HRA) may be performed prospectively for a newly designed system or retrospectively for an as-built system, typically in response to a safety incident. The SPAR-H HRA method was originally developed for retrospective analysis in the U.S. nuclear industry. As HRA has found homes in new safety critical areas, HRA methods developed predominantly for nuclear power applications are being used in novel ways. The Petro-HRA method represents a significant adaptation of the SPAR-H method for petroleum applications. Current guidance on Petro-HRA considers only prospective applications of the method, such as for review of new systems to be installed at offshore installations. In this paper, we review retrospective applications of Petro-HRA and analyze the Macando Oil Well-Deepwater Horizon accident as a case study
A novel profiling concept leading to a significant increase in the mechanical performance of metal to composite joints
In this work, we designed metal-CFRP joints with a profiled adherend termination to improve the mechanical performance. We have applied several profiles to the edge of titanium adherends which were adhesively bonded to CFRP substrates. We conducted finite element modelling and experimental 4PB (4-Point-Bend) testing to investigate how the geometry of the adherend edge profile effects the mechanical performance of the joint. This work shows that profiling of the metal adherend can result in increases of at least 27% in the peak load, and of at least 272% in the energy dissipated up to critical failure normalised by the mechanical energy
Turbulence driven by outflow-blown cavities in the molecular cloud of NGC 1333
Outflows from young stellar objects have been identified as a possible source
of turbulence in molecular clouds. To investigate the relationship between
outflows, cloud dynamics and turbulence, we compare the kinematics of the
molecular gas associated with NGC 1333, traced in 13CO(1-0), with the
distribution of young stellar objects (YSOs) within. We find a velocity
dispersion of ~ 1-1.6 km/s in 13CO that does not significantly vary across the
cloud, and is uncorrelated with the number of nearby young stellar outflows
identified from optical and submillimeter observations. However, from velocity
channel maps we identify about 20 cavities or depressions in the 13CO intensity
of scales > 0.1-0.2 pc and velocity widths 1-3 km/s. The cavities exhibit limb
brightened rims in both individual velocity channel maps and position velocity
diagrams, suggesting that they are slowly expanding. We interpret these
cavities to be remnants of past YSO outflow activity: If these cavities are
presently empty, they would fill in on time scales of a million years. This can
exceed the lifetime of a YSO outflow phase, or the transit time of the central
star through the cavity, explaining the the absence of any clear correlation
between the cavities and YSO outflows. We find that the momentum and energy
deposition associated with the expansion of the cavities is sufficient to power
the turbulence in the cloud. In this way we conclude that the cavities are an
important intermediary step between the conversion of YSO outflow energy and
momentum into cloud turbulent motions.Comment: Accepted for publication in ApJ. Check out
http://astro.pas.rochester.edu/~aquillen/coolpics.html for channel map and
PosVel movies of N133
The XMM/BeppoSAX observation of Mkn 841
Mkn 841 has been observed simultaneously by XMM and BeppoSAX in January 2001.
Due to operational contingency, the 30ks XMM observation was split into two
parts, separated by about 15 hours. We first report the presence of a narrow
iron line which appears to be rapidly variable between the two pointings,
requiring a non-standard interpretation. We then focus on the analysis of the
broad band (0.3-200 keV) continuum using the XMM/EPIC, RGS and SAX/PDS data.
The Mkn 841 spectrum is well fitted by a comptonization model in a geometry
more photon-fed than a simple slab geometry above a passive disk. It presents a
relatively large reflection (R>2) which does not agree with an apparently weak
iron line. It also show the presence of a strong soft excess wellfitted by a
comptonized spectrum in a cool plasma, suggesting the presence of a
multi-temperature corona.Comment: 4 pages, 5 figures. Proc. of the meeting: "The Restless High-Energy
Universe" (Amsterdam, The Netherlands), E.P.J. van den Heuvel, J.J.M. in 't
Zand, and R.A.M.J. Wijers Ed
Recommended from our members
The Origins of the SPAR-H Method's Performance Shaping Factor Multipliers
The Standardized Plant Analysis Risk-Human Reliability Analysis (SPAR-H) method has proved to be a reliable, easy-to-use method for human reliability analysis. Calculation of human error probability (HEP) rates is especially straightforward, starting with pre-defined nominal error rates for cognitive vs. action oriented tasks, and incorporating performance shaping factor (PSF) multipliers upon those nominal error rates. SPAR-H uses eight PSFs with multipliers typically corresponding to nominal, degraded, and severely degraded human performance for individual PSFs. Additionally, some PSFs feature multipliers to reflect enhanced performance. Although SPAR-H enjoys widespread use among industry and regulators, current source documents on SPAR-H such as NUREG/CR-6883 do not provide a clear account of the origin of these multipliers. The present paper redresses this shortcoming and documents the historic development of the SPAR-H PSF multipliers, from the initial use of nominal error rates, to the selection of the eight PSFs, to the mapping of multipliers to available data sources such as a Technique for Human Error Rate Prediction (THERP). Where error rates were not readily derived from THERP and other sources, expert judgment was used to extrapolate appropriate values. In documenting key background information on the multipliers, this paper provides a much needed cross-reference for human reliability practitioners and researchers of SPAR-H to validate analyses and research findings
Radio continuum properties of young planetary nebulae
We have selected a small sample of post-AGB stars in transition towards the
planetary nebula and present new Very Large Array multi-frequency high-angular
resolution radio observations of them. The multi-frequency data are used to
create and model the targets' radio continuum spectra, proving that these stars
started their evolution as very young planetary nebulae. In the optically thin
range, the slopes are compatible with the expected spectral index (-0.1). Two
targets (IRAS 18062+2410 and 17423-1755) seem to be optically thick even at
high frequency, as observed in a handful of other post-AGB stars in the
literature, while a third one (IRAS 20462+3416) shows a possible contribution
from cold dust. In IRAS 18062+2410, where we have three observations spanning a
period of four years, we detect an increase in its flux density, similar to
that observed in CRL 618.
High-angular resolution imaging shows bipolar structures that may be due to
circumstellar tori, although a different hypothesis (i.e., jets) could also
explain the observations. Further observations and monitoring of these sources
will enable us to test the current evolutionary models of planetary nebulae.Comment: 8 pages, 3 figures, accepted for publication in MNRA
Finite-Size Scaling in the Energy-Entropy Plane for the 2D +- J Ising Spin Glass
For square lattices with the 2D Ising spin glass with
+1 and -1 bonds is found to have a strong correlation between the energy and
the entropy of its ground states. A fit to the data gives the result that each
additional broken bond in the ground state of a particular sample of random
bonds increases the ground state degeneracy by approximately a factor of 10/3.
For (where is the fraction of negative bonds), over this range of
, the characteristic entropy defined by the energy-entropy correlation
scales with size as . Anomalous scaling is not found for the
characteristic energy, which essentially scales as . When , a
crossover to scaling of the entropy is seen near . The results
found here suggest a natural mechanism for the unusual behavior of the low
temperature specific heat of this model, and illustrate the dangers of
extrapolating from small .Comment: 9 pages, two-column format; to appear in J. Statistical Physic
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