40,722 research outputs found
Constitutive Equations for Use in Design Analyses of Long-life Elevated Temperature Components
Design analysis needs and procedures relative to elevated temperature components in liquid metal fast breeder reactor (LMFBR) system were examined. The effects of the thermal transients on the pressure boundary components are enhanced by the excellent heat transfer properties of the liquid sodium coolant. Design criteria for high temperature nuclear reactor components recognize the potential occurrence of inelastic structural response. Specifically, criteria and limits were developed which reflect a recognition of this potential and employ design by analysis concepts that requires that inelastic (elastic-plastic and creep) analyses be performed. Constitutive equations to represent multiaxial time-dependent responses of LMFBR alloys are established. The development of equations applicable under cyclic loading conditions are outlined
The expected background spectrum in NaI dark matter detectors and the DAMA result
Detailed Monte Carlo simulations of the expected radioactive background rates
and spectra in NaI crystals are presented. The obtained spectra are then
compared to those measured in the DAMA/NaI and DAMA/LIBRA experiments. The
simulations can be made consistent with the measured DAMA spectrum only by
assuming higher than reported concentrations of some isotopes and even so leave
very little room for the dark matter signal. We conclude that any
interpretation of the annual modulation of the event rate observed by DAMA as a
dark matter signal, should include full consideration of the background
spectrum. This would significantly restrict the range of dark matter models
capable of explaining the modulation effect.Comment: 17 pages, 6 figure
Comparing verbal media for alarm handling: Speech versus textual displays
The rise of computers in command and control domains has meant that control operations can be performed via desk-based visual display terminals. This trend has also produced the potential to display information to operators in a variety of formats. Of particular interest has been the use of text-based displays for alarm presentation. There are possible limitations to the use of text for alarm presentation, not least of which is the need for a dedicated alarms display screen (or, at least, a display page). Given the capability of computers to synthesize speech, it is possible that speech-based alarms could generate the same information as text-based displays without the need for dedicated screen space. In this paper an experimental comparison of speech-based and text-based displays for presentation of alarms is reported. The findings show that speech leads to longer response times than text displays, but that it has minimal effect on the efficacy of fault handling. The results are discussed within the alarm initiated activities framework and implications for alarm system design are outlined
Emission lines and optical continuum in low-luminosity radio galaxies
We present spectroscopic observations of a complete sub-sample of 13
low-luminosity radio galaxies selected from the 2Jy sample. The underlying
continuum in these sources is carefully modelled in order to make a much-needed
comparison between the emission line and continuum properties of FRIs with
those of other classes of radio sources. We find that 5 galaxies in the sample
show a measurable UV excess: 2 of the these sources are BL Lacs and in the
remaining 3 galaxies we argue that the most likely contributor to the UV excess
is a young stellar component. Excluding the BL Lacs, we therefore find that
\~30% of the sample show evidence for young stars, which is similar to the
results obtained for higher luminosity samples. We compare our results with
far-infrared measurements in order to investigate the far-infrared-starburst
link. The nature of the optical-radio correlations is investigated in light of
this new available data and, in contrast to previous studies, we find that the
FRI sources follow the correlations with a similar slope to that found for the
FRIIs. Finally, we compare the luminosity of the emission lines in the FRI and
BL Lac sources and find a significant difference in the [OIII] line
luminosities of the two groups. Our results are discussed in the context of the
unified schemes.Comment: 18 pages, 31 figures, MNRAS in press, (all enquiries to Clive
Tadhunter ([email protected])
The heating mechanism for the warm/cool dust in powerful, radio-loud AGN
The uncertainty surrounding the nature of the heating mechanism for the dust
that emits at mid- to far-IR (MFIR) wavelengths in active galaxies limits our
understanding of the links between active galactic nuclei (AGN) and galaxy
evolution, as well as our ability to interpret the prodigious infrared and
sub-mm emission of some of the most distant galaxies in the Universe. Here we
report deep Spitzer observations of a complete sample of powerful, intermediate
redshift (0.05 < z < 0.7) radio galaxies and quasars. We show that AGN power,
as traced by [OIII]5007 emission, is strongly correlated with both the mid-IR
(24 micron) and the far-IR (70 micron) luminosities, however, with increased
scatter in the 70 micron correlation. A major cause of this increased scatter
is a group of objects that falls above the main correlation and displays
evidence for prodigious recent star formation activity at optical wavelengths,
along with relatively cool MFIR colours. These results provide evidence that
illumination by the AGN is the primary heating mechanism for the dust emitting
at both 24 and 70 microns, with starbursts dominating the heating of the cool
dust in only 20 -- 30% of objects. This implies that powerful AGN are not
always accompanied by the type of luminous starbursts that are characteristic
of the peak of activity in major gas-rich mergers.Comment: 13 pages, 3 figures. Accepted for publication in astrophysical
journal letter
Achieving spatially precise diagnosis and therapy in the mammalian gut using synthetic microbial gene circuits
The mammalian gut and its microbiome form a temporally dynamic and spatially heterogeneous environment. The inaccessibility of the gut and the spatially restricted nature of many gut diseases translate into difficulties in diagnosis and therapy for which novel tools are needed. Engineered bacterial whole-cell biosensors and therapeutics have shown early promise at addressing these challenges. Natural and engineered sensing systems can be repurposed in synthetic genetic circuits to detect spatially specific biomarkers during health and disease. Heat, light, and magnetic signals can also activate gene circuit function with externally directed spatial precision. The resulting engineered bacteria can report on conditions in situ within the complex gut environment or produce biotherapeutics that specifically target host or microbiome activity. Here, we review the current approaches to engineering spatial precision for in vivo bacterial diagnostics and therapeutics using synthetic circuits, and the challenges and opportunities this technology presents
Lower semicontinuity of attractors for non-autonomous dynamical systems
This paper is concerned with the lower semicontinuity of attractors for semilinear
non-autonomous differential equations in Banach spaces. We require the unperturbed
attractor to be given as the union of unstable manifolds of time-dependent hyperbolic
solutions, generalizing previous results valid only for gradient-like systems in which
the hyperbolic solutions are equilibria. The tools employed are a study of the continuity
of the local unstable manifolds of the hyperbolic solutions and results on the continuity of
the exponential dichotomy of the linearization around each of these solutions
- …