1,392 research outputs found
On the spontaneous emission of electromagnetic radiation in the CSL model
Spontaneous photon emission in the Continuous Spontaneous Localization (CSL)
model is studied one more time. In the CSL model each particle interacts with a
noise field that induces the collapse of its wave function. As a consequence of
this interaction, when the particle is electrically charged, it radiates. As
discussed in [1], the formula for the emission rate, to first perturbative
order, contains two terms: One is proportional to the Fourier component of the
noise field at the same frequency as that of the emitted photon and one is
proportional to the zero Fourier component of the noise field. As discussed in
previous works, this second term seems unphysical. In [1], it was shown that
the unphysical term disappears when the noises is confined to a bounded region
and the final particle's state is a wave packet. Here we investigate the origin
of the unphysical term and why it vanishes according to the previous
prescription. For this purpose, the electrodynamic part of the equation of
motion is solved exactly while the part due to the noise is treated
perturbatively. We show that the unphysical term is connected to exponentially
decaying function of time which dies out in the large time limit, however,
approximates to 1 in the first perturbative order in the electromagnetic field.Comment: 10 pages, 1 figure, LaTe
The Mass Shell of the Nelson Model without Cut-Offs
The massless Nelson model describes non-relativistic, spinless quantum
particles interacting with a relativistic, massless, scalar quantum field. The
interaction is linear in the field. We analyze the one particle sector. First,
we construct the renormalized mass shell of the non-relativistic particle for
an arbitrarily small infrared cut-off that turns off the interaction with the
low energy modes of the field. No ultraviolet cut-off is imposed. Second, we
implement a suitable Bogolyubov transformation of the Hamiltonian in the
infrared regime. This transformation depends on the total momentum of the
system and is non-unitary as the infrared cut-off is removed. For the
transformed Hamiltonian we construct the mass shell in the limit where both the
ultraviolet and the infrared cut-off are removed. Our approach is constructive
and leads to explicit expansion formulae which are amenable to rigorously
control the S-matrix elements.Comment: explanations added, typos correcte
Large-scale wind-tunnel tests of descent performance of an airplane model with a tilt wing and differential propeller thrust
Wind tunnel tests of wing stall, performance, and longitudinal stability & control of large model v/stol tilt wing transport aircraf
Reliable dual-redundant sensor failure detection and identification for the NASA F-8 DFBW aircraft
A technique was developed which provides reliable failure detection and identification (FDI) for a dual redundant subset of the flight control sensors onboard the NASA F-8 digital fly by wire (DFBW) aircraft. The technique was successfully applied to simulated sensor failures on the real time F-8 digital simulator and to sensor failures injected on telemetry data from a test flight of the F-8 DFBW aircraft. For failure identification the technique utilized the analytic redundancy which exists as functional and kinematic relationships among the various quantities being measured by the different control sensor types. The technique can be used not only in a dual redundant sensor system, but also in a more highly redundant system after FDI by conventional voting techniques reduced to two the number of unfailed sensors of a particular type. In addition the technique can be easily extended to the case in which only one sensor of a particular type is available
Noise gates for decoherent quantum circuits
A major problem in exploiting microscopic systems for developing a new
technology based on the principles of Quantum Information is the influence of
noise which tends to work against the quantum features of such systems. It
becomes then crucial to understand how noise affects the evolution of quantum
circuits: several techniques have been proposed among which stochastic
differential equations (SDEs) can represent a very convenient tool. We show how
SDEs naturally map any Markovian noise into a linear operator, which we will
call a noise gate, acting on the wave function describing the state of the
circuit, and we will discuss some examples. We shall see that these gates can
be manipulated like any standard quantum gate, thus simplifying in certain
circumstances the task of computing the overall effect of the noise at each
stage of the protocol. This approach yields equivalent results to those derived
from the Lindblad equation; yet, as we show, it represents a handy and fast
tool for performing computations, and moreover, it allows for fast numerical
simulations and generalizations to non Markovian noise. In detail we review the
depolarizing channel and the generalized amplitude damping channel in terms of
this noise gate formalism and show how these techniques can be applied to any
quantum circuit.Comment: 10 pages, 4 figures: journal reference added + some typos correcte
Breaking quantum linearity: constraints from human perception and cosmological implications
Resolving the tension between quantum superpositions and the uniqueness of
the classical world is a major open problem. One possibility, which is
extensively explored both theoretically and experimentally, is that quantum
linearity breaks above a given scale. Theoretically, this possibility is
predicted by collapse models. They provide quantitative information on where
violations of the superposition principle become manifest. Here we show that
the lower bound on the collapse parameter lambda, coming from the analysis of
the human visual process, is ~ 7 +/- 2 orders of magnitude stronger than the
original bound, in agreement with more recent analysis. This implies that the
collapse becomes effective with systems containing ~ 10^4 - 10^5 nucleons, and
thus falls within the range of testability with present-day technology. We also
compare the spectrum of the collapsing field with those of known cosmological
fields, showing that a typical cosmological random field can yield an efficient
wave function collapse.Comment: 13 pages, LaTeX, 3 figure
Antimicrobial use and resistance and the relationship with health and biosecurity status in CIPARS data from Canadian grower-finisher swine herds
Antimicrobial resistance (AMR) is a global threat to public and animal health. The Canadian Integrated Program for Antimicrobial Resistance Surveillance (CIPARS), created in 2002, is a national program dedicated to the collection, integration, analysis, and communication of trends in antimicrobial use (AMU) and resistance (AMR) in selected bacteria from humans, animals, and animal-derived food sources across Canada. This information supports (i) the creation of evidence‐based policies for AMU in hospitals, communities, and food‐animal production with the aim of prolonging the effectiveness of these drugs and (ii) the identification of appropriate measures to contain the emergence and spread of resistant bacteria among animals, food, and people
Antimicrobial resistance in fecal generic Escherichia coli in 90 Alberta swine finishing farms: prevalence and risk factors for resistance
The objective of this retrospective study was to determine the prevalence of antimicrobial resistance (AMR) in generic Escherichia coli isolates obtained from 90 Alberta finisher swine farms, and to evaluate the potential associations between on-farm antimicrobial use (AMU) practices and observed AMR. The farms were visited three times, approximately one month apart (n=269 farm visits). In total, 5 pen fecal samples were collected per each visit and mixed into one pool per visit. Conventional culture and susceptibility testing were employed. Reported AMU practices through feed, water and injection in different phases of pig production, were collected using a questionnaire
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Plasmon response evaluation based on image-derived arbitrary nanostructures
The optical response of realistic 3D plasmonic substrates composed of randomly shaped particles of different size and interparticle distance distributions in addition to nanometer scale surface roughness is intrinsically challenging to simulate due to computational limitations. Here, we present a Finite Element Method (FEM)-based methodology that bridges in-depth theoretical investigations and experimental optical response of plasmonic substrates composed of such silver nanoparticles. Parametrized scanning electron microscopy (SEM) images of surface enhanced Raman spectroscopy (SERS) active substrate and tip-enhanced Raman spectroscopy (TERS) probes are used to simulate the far-and near-field optical response. Far-field calculations are consistent with experimental dark field spectra and charge distribution images reveal for the first time in arbitrary structures the contributions of interparticle hybridized modes such as sub-radiant and super-radiant modes that also locally organize as basic units for Fano resonances. Near-field simulations expose the spatial position-dependent impact of hybridization on field enhancement. Simulations of representative sections of TERS tips are shown to exhibit the same unexpected coupling modes. Near-field simulations suggest that these modes can contribute up to 50% of the amplitude of the plasmon resonance at the tip apex but, interestingly, have a small effect on its frequency in the visible range. The band position is shown to be extremely sensitive to particle nanoscale roughness, highlighting the necessity to preserve detailed information at both the largest and the smallest scales. To the best of our knowledge, no currently available method enables reaching such a detailed description of large scale realistic 3D plasmonic systems
The 35S U5 snRNP is generated from the activated spliceosome during In vitro splicing
Primary gene transcripts of eukaryotes contain introns, which are removed during processing by splicing machinery. Biochemical studies In vitro have identified a specific pathway in which introns are recognised and spliced out. This occurs by progressive formation of spliceosomal complexes designated as E, A, B, and C. The composition and structure of these spliceosomal conformations have been characterised in many detail. In contrast, transitions between the complexes and the intermediates of these reactions are currently less clear. We have previously isolated a novel 35S U5 snRNP from HeLa nuclear extracts. The protein composition of this particle differed from the canonical 20S U5 snRNPs but was remarkably similar to the activated B* spliceosomes. Based on this observation we have proposed a hypothesis that 35S U5 snRNPs represent a dissociation product of the spliceosome after both transesterification reactions are completed. Here we provide experimental evidence that 35S U5 snRNPs are generated from the activated B* spliceosomes during In vitro splicing
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