1,945 research outputs found
Contamination cannot explain the lack of large-scale power in the cosmic microwave background radiation
Several anomalies appear to be present in the large-angle cosmic microwave
background (CMB) anisotropy maps of WMAP. One of these is a lack of large-scale
power. Because the data otherwise match standard models extremely well, it is
natural to consider perturbations of the standard model as possible
explanations. We show that, as long as the source of the perturbation is
statistically independent of the source of the primary CMB anisotropy, no such
model can explain this large-scale power deficit. On the contrary, any such
perturbation always reduces the probability of obtaining any given low value of
large-scale power. We rigorously prove this result when the lack of large-scale
power is quantified with a quadratic statistic, such as the quadrupole moment.
When a statistic based on the integrated square of the correlation function is
used instead, we present strong numerical evidence in support of the result.
The result applies to models in which the geometry of spacetime is perturbed
(e.g., an ellipsoidal Universe) as well as explanations involving local
contaminants, undiagnosed foregrounds, or systematic errors. Because the
large-scale power deficit is arguably the most significant of the observed
anomalies, explanations that worsen this discrepancy should be regarded with
great skepticism, even if they help in explaining other anomalies such as
multipole alignments.Comment: 9 pages. Submitted to Phys. Rev.
Overcoming a limitation of deterministic dense coding with a non-maximally entangled initial state
Under two-party deterministic dense-coding, Alice communicates (perfectly
distinguishable) messages to Bob via a qudit from a pair of entangled qudits in
pure state |Psi>. If |Psi> represents a maximally entangled state (i.e., each
of its Schmidt coefficients is sqrt(1/d)), then Alice can convey to Bob one of
d^2 distinct messages. If |Psi> is not maximally entangled, then Ji et al.
[Phys. Rev. A 73, 034307 (2006)] have shown that under the original
deterministic dense-coding protocol, in which messages are encoded by unitary
operations performed on Alice's qudit, it is impossible to encode d^2-1
messages. Encoding d^2-2 is possible; see, e.g., the numerical studies by Mozes
et al. [Phys. Rev. A 71, 012311 (2005)]. Answering a question raised by Wu et
al. [Phys. Rev. A 73, 042311 (2006)], we show that when |Psi> is not maximally
entangled, the communications limit of d^2-2 messages persists even when the
requirement that Alice encode by unitary operations on her qudit is weakened to
allow encoding by more general quantum operators. We then describe a
dense-coding protocol that can overcome this limitation with high probability,
assuming the largest Schmidt coefficient of |Psi> is sufficiently close to
sqrt(1/d). In this protocol, d^2-2 of the messages are encoded via unitary
operations on Alice's qudit, and the final (d^2-1)-th message is encoded via a
(non-trace-preserving) quantum operation.Comment: 18 pages, published versio
Marine Debris Survey and Plastic Ingestion of Pacific Albatross on Sand Island, Midway Atoll 1997
proposalUH
The use of motion pictures and filmstrips in teaching industrial arts in the seventh and eighth grades
Thesis (Ed.M.)--Boston University, 1948. This item was digitized by the Internet Archive
Three-body recombination rate of atomic nitrogen inlow pressure plasma flows
International audienc
Subspace hypercyclicity
A bounded linear operator T on Hilbert space is subspace-hypercyclic for a
subspace M if there exists a vector whose orbit under T intersects the subspace
in a relatively dense set. We construct examples to show that
subspace-hypercyclicity is interesting, including a nontrivial
subspace-hypercyclic operator that is not hypercyclic. There is a Kitai-like
criterion that implies subspace-hypercyclicity and although the spectrum of a
subspace-hypercyclic operator must intersect the unit circle, not every
component of the spectrum will do so. We show that, like hypercyclicity,
subspace-hypercyclicity is a strictly infinite-dimensional phenomenon.
Additionally, compact or hyponormal operators can never be
subspace-hypercyclic.Comment: 15 page
Influence of the angular scattering of electrons on the runaway threshold in air
International audienceThe runaway electron mechanism is of great importance for the understanding of the generation of x- and gamma rays in atmospheric discharges. In 1991, terrestrial gamma-ray flashes (TGFs) were discovered by the Compton Gamma-Ray Observatory. Those emissions are bremsstrahlung from high energy electrons that run away in electric fields associated with thunderstorms. In this paper, we discuss the runaway threshold definition with a particular interest in the influence of the angular scattering for electron energy close to the threshold. In order to understand the mechanism of runaway, we compare the outcome of different FokkerPlanck and Monte Carlo models with increasing complexity in the description of the scattering. The results show that the inclusion of the stochastic nature of collisions smooths the probability to run away around the threshold. Furthermore, we observe that a significant number of electrons diffuse out of the runaway regime when we take into account the diffusion in angle due to the scattering. Those results suggest using a runaway threshold energy based on the FokkerPlanck model assuming the angular equilibrium that is 1.6 to 1.8 times higher than the one proposed by [1, 2], depending on the magnitude of the ambient electric field. The threshold also is found to be 5 to 26 times higher than the one assuming forward scattering. We give a fitted formula for the threshold field valid over a large range of electric fields. Furthermore, we have shown that the assumption of forward scattering is not valid below 1 MeV where the runaway threshold usually is defined. These results are important for the thermal runaway and the runaway electron avalanche discharge mechanisms suggested to participate in the TGF generation
A hypercyclic finite rank perturbation of a unitary operator
A unitary operator and a rank operator acting on a Hilbert space
\H are constructed such that is hypercyclic. This answers affirmatively
a question of Salas whether a finite rank perturbation of a hyponormal operator
can be supercyclic.Comment: published in Mathematische Annale
ACCURACY AND PRECISION OF THE KINETIC ANALYSIS OF COUNTER MOVEMENT JUMP PERFORMANCE
The purpose of this study was to quantify the accuracy and precision of measuring counter movement jump (CMJ) performance kinetically (i.e. measuring impulse using a force plate). A 14-camera 3D motion analysis system and a force plate were used simultaneously to obtain vertical trajectories of centre of mass (CM) for comparison. Fifty-eight CMJs were analyzed from eleven physically active males. Jump height differences were trivial, and small bias was obtained thereby showing good accuracy as well as small typical errors for performance. Our study indicates that force plates can be used confidently for CMJ analysis
Study of the Stability of a Selective Solar Absorber Coating under Air and High Temperature Conditions
Abstract Selective solar absorber material is one of the major components in the Concentrated Solar Power (CSP) technologies. Its optical properties determine the efficiency of the energy conversion from the concentrated sun irradiation to the heat recovered by the heat transfer fluid. Development of the CSP requires costs reduction for this technology. To achieve this goal, one way is the increase of the work temperature up to 400 – 500 °C or more. For economic reasons, the bankable of CSP technology requires a lifetime over 25 years for components and so for solar absorbers. The development of solar receiver, able to operate under air, instead of vacuum conditions, is a challenge to reduce the costs. Along the 25 years of a CSP plant lifetime, solar absorber material is daily exposed to high levels of stresses: high solar flux, high thermal gradient. As the oxidation is one of the main factors involved in degradation processes air stability of the absorber coating under high temperatures should be studied as it could be a critical point in the solar field maintainability in case of accidental vacuum loss. In this article we present a durability study of selective solar absorber from Archimede Solar Energy (ASE) exposed in air at high temperature (up to 500 °C). The results show a good stability of this materials up to 450 °C during 3000h without change of solar absorptance and emittance. An analysis of the degradation process at higher temperature is presented
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