485 research outputs found
Dielectric and Mechanical Behavior of Thermally Aged EPR/CPE Cable Materials
Power and instrumentation cables play a crucial role in the safe operation of Nuclear Power Plants (NPPs). Thermal and other stressors present in the reactor environment cause the cable materials to degrade. In this work, dielectric and mechanical properties of cable insulation and jacket materials are studied as they are thermally aged, supporting development of non-destructive evaluation sensors for monitoring cable aging. Materials selected for this study are found in certain types of single-core unshielded power cables. These utilize ethylene propylene rubber (EPR)-based insulation material and chlorinated polyethylene (CPE)-based jacket material. Flat mats of these materials were obtained from the cable manufacturer and thermally aged at 140 °C in an air-circulating oven. Elongation-at-break was measured on tensile specimens stamped from the aged mats, and dielectric properties were measured from 100 Hz to 100 kHz using a parallel plate capacitor and precision LCR meter. In the case of aged EPR-based materials, rapid decrease in elongation at break indicating end of useful life was accompanied by a significant increase in dissipation factor, D, measured at 100 kHz. Capacitive measurement of D shows promise, therefore, as a non-destructive indicator of corresponding mechanical property changes in thermally-aged EPR-based insulation materials
Inflation, quantum fields, and CMB anisotropies
Inflationary cosmology has proved to be the most successful at predicting the
properties of the anisotropies observed in the cosmic microwave background
(CMB). In this essay we show that quantum field renormalization significantly
influences the generation of primordial perturbations and hence the expected
measurable imprint of cosmological inflation on the CMB. However, the new
predictions remain in agreement with observation, and in fact favor the
simplest forms of inflation. In the near future, observations of the influence
of gravitational waves from the early universe on the CMB will test our new
predictions.Comment: 11 pages, 1 figure, Awarded with the fourth prize in the Gravity
Research Foundation 2009 Essay Competitio
Observational Consequences of a Landscape
In this paper we consider the implications of the "landscape" paradigm for
the large scale properties of the universe. The most direct implication of a
rich landscape is that our local universe was born in a tunnelling event from a
neighboring vacuum. This would imply that we live in an open FRW universe with
negative spatial curvature. We argue that the "overshoot" problem, which in
other settings would make it difficult to achieve slow roll inflation, actually
favors such a cosmology.
We consider anthropic bounds on the value of the curvature and on the
parameters of inflation. When supplemented by statistical arguments these
bounds suggest that the number of inflationary efolds is not very much larger
than the observed lower bound. Although not statistically favored, the
likelihood that the number of efolds is close to the bound set by observations
is not negligible. The possible signatures of such a low number of efolds are
briefly described.Comment: 21 pages, 4 figures v2: references adde
Acceleration of the universe, vacuum metamorphosis, and the large-time asymptotic form of the heat kernel
We investigate the possibility that the late acceleration observed in the
rate of expansion of the universe is due to vacuum quantum effects arising in
curved spacetime. The theoretical basis of the vacuum cold dark matter (VCDM),
or vacuum metamorphosis, cosmological model of Parker and Raval is revisited
and improved. We show, by means of a manifestly nonperturbative approach, how
the infrared behavior of the propagator (related to the large-time asymptotic
form of the heat kernel) of a free scalar field in curved spacetime causes the
vacuum expectation value of its energy-momentum tensor to exhibit a resonance
effect when the scalar curvature R of the spacetime reaches a particular value
related to the mass of the field. we show that the back reaction caused by this
resonance drives the universe through a transition to an accelerating expansion
phase, very much in the same way as originally proposed by Parker and Raval.
Our analysis includes higher derivatives that were neglected in the earlier
analysis, and takes into account the possible runaway solutions that can follow
from these higher-derivative terms. We find that the runaway solutions do not
occur if the universe was described by the usual classical FRW solution prior
to the growth of vacuum energy-density and negative pressure (i.e., vacuum
metamorphosis) that causes the transition to an accelerating expansion of the
universe in this theory.Comment: 33 pages, 3 figures. Submitted to Physical Review D15 (Dec 23, 2003).
v2: 1 reference added. No other change
Stimulated creation of quanta during inflation and the observable universe
Inflation provides a natural mechanism to account for the origin of cosmic
structures. The generation of primordial inhomogeneities during inflation can
be understood via the spontaneous creation of quanta from the vacuum. We show
that when the corresponding {\it stimulated} creation of quanta is considered,
the characteristics of the state of the universe at the onset of inflation are
not diluted by the inflationary expansion and can be imprinted in the spectrum
of primordial inhomogeneities. The non-gaussianities (particularly in the
so-called squeezed configuration) in the cosmic microwave background and galaxy
distribution can then tell us about the state of the universe that existed at
the time when quantum field theory in curved spacetime first emerged as a
plausible effective theory.Comment: Awarded with the First Prize in the Gravity Research Foundation Essay
Competition 201
Disturbing Implications of a Cosmological Constant
In this paper we consider the implications of a cosmological constant for the
evolution of the universe, under a set of assumptions motivated by the
holographic and horizon complementarity principles. We discuss the ``causal
patch" description of spacetime required by this framework, and present some
simple examples of cosmologies described this way. We argue that these
assumptions inevitably lead to very deep paradoxes, which seem to require major
revisions of our usual assumptions.Comment: 26 pages, 7 figures v2: references added v3: reference adde
Field Measurements of Terrestrial and Martian Dust Devils
Surface-based measurements of terrestrial and martian dust devils/convective vortices provided from mobile and stationary platforms are discussed. Imaging of terrestrial dust devils has quantified their rotational and vertical wind speeds, translation speeds, dimensions, dust load, and frequency of occurrence. Imaging of martian dust devils has provided translation speeds and constraints on dimensions, but only limited constraints on vertical motion within a vortex. The longer mission durations on Mars afforded by long operating robotic landers and rovers have provided statistical quantification of vortex occurrence (time-of-sol, and recently seasonal) that has until recently not been a primary outcome of more temporally limited terrestrial dust devil measurement campaigns. Terrestrial measurement campaigns have included a more extensive range of measured vortex parameters (pressure, wind, morphology, etc.) than have martian opportunities, with electric field and direct measure of dust abundance not yet obtained on Mars. No martian robotic mission has yet provided contemporaneous high frequency wind and pressure measurements. Comparison of measured terrestrial and martian dust devil characteristics suggests that martian dust devils are larger and possess faster maximum rotational wind speeds, that the absolute magnitude of the pressure deficit within a terrestrial dust devil is an order of magnitude greater than a martian dust devil, and that the time-of-day variation in vortex frequency is similar. Recent terrestrial investigations have demonstrated the presence of diagnostic dust devil signals within seismic and infrasound measurements; an upcoming Mars robotic mission will obtain similar measurement types
Parkinson's disease age at onset genome-wide association study : Defining heritability, genetic loci, and α-synuclein mechanisms
Background Increasing evidence supports an extensive and complex genetic contribution to PD. Previous genome-wide association studies (GWAS) have shed light on the genetic basis of risk for this disease. However, the genetic determinants of PD age at onset are largely unknown. Objectives To identify the genetic determinants of PD age at onset. Methods Using genetic data of 28,568 PD cases, we performed a genome-wide association study based on PD age at onset. Results We estimated that the heritability of PD age at onset attributed to common genetic variation was similar to 0.11, lower than the overall heritability of risk for PD (similar to 0.27), likely, in part, because of the subjective nature of this measure. We found two genome-wide significant association signals, one at SNCA and the other a protein-coding variant in TMEM175, both of which are known PD risk loci and a Bonferroni-corrected significant effect at other known PD risk loci, GBA, INPP5F/BAG3, FAM47E/SCARB2, and MCCC1. Notably, SNCA, TMEM175, SCARB2, BAG3, and GBA have all been shown to be implicated in alpha-synuclein aggregation pathways. Remarkably, other well-established PD risk loci, such as GCH1 and MAPT, did not show a significant effect on age at onset of PD. Conclusions Overall, we have performed the largest age at onset of PD genome-wide association studies to date, and our results show that not all PD risk loci influence age at onset with significant differences between risk alleles for age at onset. This provides a compelling picture, both within the context of functional characterization of disease-linked genetic variability and in defining differences between risk alleles for age at onset, or frank risk for disease. (c) 2019 International Parkinson and Movement Disorder SocietyPeer reviewe
Search for a W' boson decaying to a bottom quark and a top quark in pp collisions at sqrt(s) = 7 TeV
Results are presented from a search for a W' boson using a dataset
corresponding to 5.0 inverse femtobarns of integrated luminosity collected
during 2011 by the CMS experiment at the LHC in pp collisions at sqrt(s)=7 TeV.
The W' boson is modeled as a heavy W boson, but different scenarios for the
couplings to fermions are considered, involving both left-handed and
right-handed chiral projections of the fermions, as well as an arbitrary
mixture of the two. The search is performed in the decay channel W' to t b,
leading to a final state signature with a single lepton (e, mu), missing
transverse energy, and jets, at least one of which is tagged as a b-jet. A W'
boson that couples to fermions with the same coupling constant as the W, but to
the right-handed rather than left-handed chiral projections, is excluded for
masses below 1.85 TeV at the 95% confidence level. For the first time using LHC
data, constraints on the W' gauge coupling for a set of left- and right-handed
coupling combinations have been placed. These results represent a significant
improvement over previously published limits.Comment: Submitted to Physics Letters B. Replaced with version publishe
Search for the standard model Higgs boson decaying into two photons in pp collisions at sqrt(s)=7 TeV
A search for a Higgs boson decaying into two photons is described. The
analysis is performed using a dataset recorded by the CMS experiment at the LHC
from pp collisions at a centre-of-mass energy of 7 TeV, which corresponds to an
integrated luminosity of 4.8 inverse femtobarns. Limits are set on the cross
section of the standard model Higgs boson decaying to two photons. The expected
exclusion limit at 95% confidence level is between 1.4 and 2.4 times the
standard model cross section in the mass range between 110 and 150 GeV. The
analysis of the data excludes, at 95% confidence level, the standard model
Higgs boson decaying into two photons in the mass range 128 to 132 GeV. The
largest excess of events above the expected standard model background is
observed for a Higgs boson mass hypothesis of 124 GeV with a local significance
of 3.1 sigma. The global significance of observing an excess with a local
significance greater than 3.1 sigma anywhere in the search range 110-150 GeV is
estimated to be 1.8 sigma. More data are required to ascertain the origin of
this excess.Comment: Submitted to Physics Letters
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