1,766 research outputs found
How the Weak Variance of Momentum Can Turn Out to be Negative
Weak values are average quantities,therefore investigating their associated
variance is crucial in understanding their place in quantum mechanics. We
develop the concept of a position-postselected weak variance of momentum as
cohesively as possible, building primarily on material from Moyal (Mathematical
Proceedings of the Cambridge Philosophical Society, Cambridge University Press,
Cambridge, 1949) and Sonego (Found Phys 21(10):1135, 1991) . The weak variance
is defined in terms of the Wigner function, using a standard construction from
probability theory. We show this corresponds to a measurable quantity, which is
not itself a weak value. It also leads naturally to a connection between the
imaginary part of the weak value of momentum and the quantum potential. We
study how the negativity of the Wigner function causes negative weak variances,
and the implications this has on a class of `subquantum' theories. We also
discuss the role of weak variances in studying determinism, deriving the
classical limit from a variational principle.Comment: 22 page
One-point fluctuation analysis of IceCube neutrino events outlines a significant unassociated isotropic component and constrains the Galactic contribution
The origins of the extraterrestrial neutrinos observed in IceCube have yet to
be determined. In this study we perform a one-point fluctuation analysis of the
six-year high-energy starting event (HESE) shower data, with fixed
non-Poissonian contributions from atmospheric, Galactic and some extragalactic
components, as well as an isotropic (and weakly non-Poissonian) template. In
addition to the star-forming galaxies and blazars, our analysis suggests the
presence of an additional isotropic component, not associated with any known
class of sources, with best-fit intensity of . For the first time, we
also consider high-energy extrapolations of several phenomenological models for
the diffuse Galactic emission (tuned to both local cosmic-ray data and diffuse
gamma-ray emission in the GeV-TeV domain). We demonstrate the potential of our
framework in discriminating between different scenarios, with possible
implications on the physics of cosmic ray transport in the TeV-PeV range.Comment: 10 pages, 3 figures, accepted for publication in PR
How bright can the brightest neutrino source be?
After the discovery of extraterrestrial high-energy neutrinos, the next major
goal of neutrino telescopes will be identifying astrophysical objects that
produce them. The flux of the brightest source , however, cannot
be probed by studying the diffuse neutrino intensity. We aim at constraining
by adopting a broken power-law flux distribution, a hypothesis
supported by observed properties of any generic astrophysical sources. The
first estimate of comes from the fact that we can only observe
one universe, and hence, the expected number of sources above
cannot be too small compared with one. For abundant source classes such as
starburst galaxies, this one-source constraint yields a value of
that is an order of magnitude lower than the current upper limits from
point-source searches. Then we derive upper limits on assuming
that the angular power spectrum is consistent with neutrino shot noise yet. We
find that the limits obtained with upgoing muon neutrinos in IceCube can
already be quite competitive, especially for rare but bright source populations
such as blazars. The limits will improve nearly quadratically with exposure,
and therefore be even more powerful for the next generation of neutrino
telescopes.Comment: 13 pages, 10 figures, accepted by Phys.Rev.
One-point fluctuation analysis of the high-energy neutrino sky
We perform the first one-point fluctuation analysis of the high-energy
neutrino sky. This method reveals itself to be especially suited to
contemporary neutrino data, as it allows to study the properties of the
astrophysical components of the high-energy flux detected by the IceCube
telescope, even with low statistics and in the absence of point source
detection. Besides the veto-passing atmospheric foregrounds, we adopt a simple
model of the high-energy neutrino background by assuming two main
extra-galactic components: star-forming galaxies and blazars. By leveraging
multi-wavelength data from Herschel and Fermi, we predict the spectral and
anisotropic probability distributions for their expected neutrino counts in
IceCube. We find that star-forming galaxies are likely to remain a diffuse
background due to the poor angular resolution of IceCube, and we determine an
upper limit on the number of shower events that can reasonably be associated to
blazars. We also find that upper limits on the contribution of blazars to the
measured flux are unfavourably affected by the skewness of the blazar flux
distribution. One-point event clustering and likelihood analyses of the IceCube
HESE data suggest that this method has the potential to dramatically improve
over more conventional model-based analyses, especially for the next generation
of neutrino telescopes.Comment: 41 pages, 6 figures, 2 tables; different blazar model than v1 but
same result
Social and Engineering Aspects of an Aquacultural Development Project in the Nakasongola District of Uganda
Rosana G. Moreira, Editor-in-Chief; Texas A&M UniversityThis is an Invited Paper from International Commission of Agricultural Engineering (CIGR, Commission Internationale du Genie Rural) E-Journal Volume 4 (2002): G. Feyereisen. Social and Engineering Aspects of an Aquacultural Development Project in the Nakasongola District of Uganda. Vol. IV. September 2002
Cytochromes P450: a success story
Cytochrome P450 proteins, named for the absorption band at 450 nm of their carbon-monoxide-bound form, are one of the largest superfamilies of enzyme proteins. The P450 genes (also called CYP) are found in the genomes of virtually all organisms, but their number has exploded in plants. Their amino-acid sequences are extremely diverse, with levels of identity as low as 16% in some cases, but their structural fold has remained the same throughout evolution. P450s are heme-thiolate proteins; their most conserved structural features are related to heme binding and common catalytic properties, the major feature being a completely conserved cysteine serving as fifth (axial) ligand to the heme iron. Canonical P450s use electrons from NAD(P)H to catalyze activation of molecular oxygen, leading to regiospecific and stereospecific oxidative attack of a plethora of substrates. The reactions carried out by P450s, though often hydroxylation, can be extremely diverse and sometimes surprising. They contribute to vital processes such as carbon source assimilation, biosynthesis of hormones and of structural components of living organisms, and also carcinogenesis and degradation of xenobiotics. In plants, chemical defense seems to be a major reason for P450 diversification. In prokaryotes, P450s are soluble proteins. In eukaryotes, they are usually bound to the endoplasmic reticulum or inner mitochondrial membranes. The electron carrier proteins used for conveying reducing equivalents from NAD(P)H differ with subcellular localization. P450 enzymes catalyze many reactions that are important in drug metabolism or that have practical applications in industry; their economic impact is therefore considerable
Diversity and evolution of the P450 family in arthropods
The P450 family (CYP genes) of arthropods encodes diverse enzymes involved in the metabolism of foreign compounds and in essential endocrine or ecophysiological functions. The P450 sequences (CYPome) from 40 arthropod species were manually curated, including 31 complete CYPomes, and a maximum likelihood phylogeny of nearly 3000 sequences is presented. Arthropod CYPomes are assembled from members of six CYP clans of variable size, the CYP2, CYP3, CYP4 and mitochondrial clans, as well as the CYP20 and CYP16 clans that are not found in Neoptera. CYPome sizes vary from two dozen genes in some parasitic species to over 200 in species as diverse as collembolans or ticks. CYPomes are comprised of few CYP families with many genes and many CYP families with few genes, and this distribution is the result of dynamic birth and death processes. Lineage-specific expansions or blooms are found throughout the phylogeny and often result in genomic clusters that appear to form a reservoir of catalytic diversity maintained as heritable units. Among the many P450s with physiological functions, six CYP families are involved in ecdysteroid metabolism. However, five so-called Halloween genes are not universally represented and do not constitute the unique pathway of ecdysteroid biosynthesis. The diversity of arthropod CYPomes has only partially been uncovered to date and many P450s with physiological functions regulating the synthesis and degradation of endogenous signal molecules (including ecdysteroids) and semiochemicals (including pheromones and defense chemicals) remain to be discovered. Sequence diversity of arthropod P450s is extreme, and P450 sequences lacking the universally conserved Cys ligand to the heme have evolved several times. A better understanding of P450 evolution is needed to discern the relative contributions of stochastic processes and adaptive processes in shaping the size and diversity of CYPomes
Laboratoire de transition territoriale LorrAgri. Rapport de l'atelier "produits locaux dans les cantines"
Ce rapport vise à faire le point sur la méthodologie et les apprentissages de l’atelier « Produits locaux dans les cantines » qui a eu lieu le mercredi 22 mars 2017. Par ce travail, ce rapport propose des perspectives en termes d’action sur le territoire de la province de Luxembourg pour développer les produits locaux dans les cantines
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