567 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
Deterministic optical rogue waves
Experimental observations of rare giant pulses or rogue waves were done in the output intensity of an optically injected semiconductor laser. The long-tailed probability distribution function of the pulse amplitude displays clear non-Gaussian features that confirm the rogue wave character of the intensity pulsations. Simulations of a simple rate equation model show good qualitative agreement with the
experiments and provide a framework for understanding the observed extreme amplitude events as the result of a deterministic nonlinear process.Peer ReviewedPostprint (published version
Analysis and preliminary characterisation of the cytochrome P450 monooxygenases from Frankia sp. EuI1c (Frankia inefficax sp.)
Frankia bacteria are nitrogen fixing species from the Actinobacterium phylum which live on the root nodules of plants. They have been hypothesised to have significant potential for natural product biosynthesis. The cytochrome P450 monooxygenase complement of Frankia sp. EuI1c (Frankia inefficax sp.), which comprises 68 members, was analysed. Several members belonged to previously uncharacterised bacterial P450 families. There was an unusually high number of CYP189 family members (21) suggesting that this family has undergone gene duplication events which are classified as "blooms". The likely electron transfer partners for the P450 enzymes were also identified and analysed. These consisted of predominantly [3Fe-4S] cluster containing ferredoxins (eight), a single [2Fe-2S] ferredoxin and a couple of ferredoxin reductases. Three of these CYP family members were produced and purified, using Escherichia coli as a host, and their substrate range was characterised. CYP1027H1 and CYP150A20 bound a broad range of norisoprenoids and terpenoids. CYP1074A2 was highly specific for certain steroids including testosterone, progesterone, stanolone and 4-androstene-3,17-dione. It is likely that steroids are the physiological substrates of CYP1074A2. These results also give an indication that terpenoids are the likely substrates of CYP1027H1 and CYP150A2. The large number of P450s belonging to distinct families as well as the associated electron transfer partners found in different Frankia strains highlights the importance of this family of enzymes has in the secondary metabolism of these bacteria.Ian C.K. Lau, René Feyereisen, David R. Nelson, Stephen G. Bel
Gene expression profiling of Spodoptera frugiperda hemocytes and fat body using cDNA microarray reveals polydnavirus-associated variations in lepidopteran host genes transcript levels
BACKGROUND: Genomic approaches provide unique opportunities to study interactions of insects with their pathogens. We developed a cDNA microarray to analyze the gene transcription profile of the lepidopteran pest Spodoptera frugiperda in response to injection of the polydnavirus HdIV associated with the ichneumonid wasp Hyposoter didymator. Polydnaviruses are associated with parasitic ichneumonoid wasps and are required for their development within the lepidopteran host, in which they act as potent immunosuppressive pathogens. In this study, we analyzed transcriptional variations in the two main effectors of the insect immune response, the hemocytes and the fat body, after injection of filter-purified HdIV. RESULTS: Results show that 24 hours post-injection, about 4% of the 1750 arrayed host genes display changes in their transcript levels with a large proportion (76%) showing a decrease. As a comparison, in S. frugiperda fat body, after injection of the pathogenic JcDNV densovirus, 8 genes display significant changes in their transcript level. They differ from the 7 affected by HdIV and, as opposed to HdIV injection, are all up-regulated. Interestingly, several of the genes that are modulated by HdIV injection have been shown to be involved in lepidopteran innate immunity. Levels of transcripts related to calreticulin, prophenoloxidase-activating enzyme, immulectin-2 and a novel lepidopteran scavenger receptor are decreased in hemocytes of HdIV-injected caterpillars. This was confirmed by quantitative RT-PCR analysis but not observed after injection of heat-inactivated HdIV. Conversely, an increased level of transcripts was found for a galactose-binding lectin and, surprisingly, for the prophenoloxidase subunits. The results obtained suggest that HdIV injection affects transcript levels of genes encoding different components of the host immune response (non-self recognition, humoral and cellular responses). CONCLUSION: This analysis of the host-polydnavirus interactions by a microarray approach indicates that the presence of HdIV induces, directly or indirectly, variations in transcript levels of specific host genes, changes that could be responsible in part for the alterations observed in the parasitized host physiology. Development of such global approaches will allow a better understanding of the strategies employed by parasites to manipulate their host physiology, and will permit the identification of potential targets of the immunosuppressive polydnaviruses
Application of time-dependent density functional theory to optical activity
As part of a general study of the time-dependent local density approximation
(TDLDA), we here report calculations of optical activity of chiral molecules.
The theory automatically satisfies sum rules and the Kramers-Kronig relation
between circular dichroism and optical rotatory power. We find that the theory
describes the measured circular dichroism of the lowest states in methyloxirane
with an accuracy of about a factor of two. In the chiral fullerene C_76 the
TDLDA provides a consistent description of the optical absorption spectrum, the
circular dichroism spectrum, and the optical rotatory power, except for an
overall shift of the theoretical spectrum.Comment: 17 pages and 13 PostScript figure
Optical response of small silver clusters
The time-dependent local density approximation is applied to the optical
response of the silver clusters, Ag_2, Ag_3, Ag_8 and Ag_9^+. The calculation
includes all the electrons beyond the closed-shell Ag^{+11} ionic core, thus
including for the first time explicitly the filled d-shell in the response. The
excitation energy of the strong surface plasmon near 4 eV agrees well with
experiment. The theoretical transition strength is quenched by a factor of 4
with respect to the pure s-electron sum rule in Ag_8 due to the d-electrons. A
comparable amount of strength lies in complex states below 6 eV excitation. The
total below 6 eV, about 50% of the s sum rule, is consistent with published
experiments.Comment: 13 pages RevTex and 9 Postscript figure
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