7,018 research outputs found
Detection of an unknown rank-one component in white noise
We consider the detection of an unknown and arbitrary rank-one signal in a spatial sector scanned by a small number of beams. We address the problem of finding the maximal invariant for the problem at hand and show that it consists of the ratio of the eigenvalues of a Wishart matrix to its trace. Next, we derive the generalized-likelihood ratio test (GLRT) along with expressions for its probability density function (pdf) under both hypotheses. Special attention is paid to the case m= 2, where the GLRT is shown to be a uniformly most powerful invariant (UMPI). Numerical simulations attest to the validity of the theoretical analysis and illustrate the detection performance of the GLRT
Relativistic Magnetic Monopole Flux Constraints from RICE
We report an upper limit on the flux of relativistic monopoles based on the
non-observation of in-ice showers by the Radio Ice Cherenkov Experiment (RICE)
at the South Pole. We obtain a 95% C.L. limit of order 10^{-18}/(cm^2-s-sr) for
intermediate mass monopoles of 10^7<gamma<10^{12} at the anticipated energy
E=10^{16} GeV. This bound is over an order of magnitude stronger than all
previously published experimental limits for this range of boost parameters
gamma, and exceeds two orders of magnitude improvement over most of the range.
We review the physics of radio detection, describe a Monte Carlo simulation
including continuous and stochastic energy losses, and compare to previous
experimental limits.Comment: 16 pages, 6 figures. Accepted for publication in Phys. Rev. D. Minor
revisions, including expanded discussion of monopole energy uncertaint
Molecular relaxation effects in hydrogen chloride photoacoustic detection
A photoacoustic (PA) sensor has been developed to monitor hydrogen chloride at sub-ppm level in the 1740-nm region. The system was designed to control the process in the novel low-water-peak optical fiber manufacturing process. Relaxation effects in hydrogen chloride PA detection in oxygen-helium and nitrogen-helium gas mixtures are presented, showing that the generation of the PA signal is strongly affected by the ratio of these substances. In addition, the role of water vapor in the PA signal is investigate
Near-infrared laser photoacoustic detection of methane: the impact of molecular relaxation
A photoacoustic sensor has been developed for trace-gas monitoring using a near-infrared semiconductor laser emitting in the 2Μ3 band of methane at 1.65Όm. The apparatus was designed for on-line process control in the manufacturing of the novel low-water-peak fibres developed for optical telecommunications. The importance of collisional relaxation processes in the generation of the photoacoustic signal is reported in the particular case of CH4 detection in dry O2 and O2-N2 mixtures. The negative influence of these effects results in a strongly reduced and phase-shifted photoacoustic signal, induced by a fast resonant coupling between the vibrational states of methane and oxygen, associated with the slow relaxation of the excited oxygen molecules. An unusual parabolic response of the sensor with respect to the methane concentration has been observed and is discussed. Finally, the beneficial effect of several species, including water vapour and helium, acting as a catalyst to hasten the relaxation of the CH4-O2 system, is demonstrate
Ammonia trace measurements at ppb level based on near-IR photoacoustic spectroscopy
A photoacoustic sensor using a laser diode emitting near 1532nm in combination with an erbium-doped fibre amplifier has been developed for ammonia trace gas analysis at atmospheric pressure. NH3 concentration measurements down to 6ppb and a noise-equivalent detection limit below 3ppb in dry air are demonstrated. Two wavelength-modulation schemes with 1f and 2f detection using a lock-in amplifier were investigated and compared to maximise the signal-to-noise ratio. A quantitative analysis of CO2 and H2O interference with NH3 is presented. Typical concentrations present in ambient air of 400ppm CO2 and 1.15% H2O (50% relative humidity at 20°C) result in a NH3 equivalent concentration of 36ppb and 100ppb, respectivel
Development of a pilot data management infrastructure for biomedical researchers at University of Manchester â approach, findings, challenges and outlook of the MaDAM Project
Management and curation of digital data has been becoming ever more important in a higher education and research environment characterised by large and complex data, demand for more interdisciplinary and collaborative work, extended funder requirements and use of e-infrastructures to facilitate new research methods and paradigms. This paper presents the approach, technical infrastructure, findings, challenges and outlook (including future development within the successor project, MiSS) of the âMaDAM: Pilot data management infrastructure for biomedical researchers at University of Manchesterâ project funded under the infrastructure strand of the JISC Managing Research Data (JISCMRD) programme. MaDAM developed a pilot research data management solution at the University of Manchester based on biomedical researchersâ requirements, which includes technical and governance components with the flexibility to meet future needs across multiple research groups and disciplines
Inférence de source de traces d'essence retrouvées dans des débris d'incendie: Evaluation de la contribution de la chromatographie en phase gazeuse couplée à la spectrométrie de masse à rapport isotopique
Lorsque de l'essence est employĂ©e pour allumer et/ou propager un incendie, l'infĂ©rence de la source de l'essence peut permettre d'Ă©tablir un lien entre le sinistre et une source potentielle. Cette infĂ©rence de la source constitue une alternative intĂ©ressante pour fournir des Ă©lĂ©ments de preuve dans ce type d'Ă©vĂ©nements oĂč les preuves matĂ©rielles laissĂ©es par l'auteur sont rares.
Le but principal de cette recherche était le développement d'une méthode d'analyse de spécimens d'essence par GC-IRMS, méthode pas routiniÚre et peu étudiée en science forensique, puis l'évaluation de son potentiel à inférer la source de traces d'essence en comparaison aux performances de la GC-MS.
Un appareillage permettant d'analyser simultanément les échantillons par MS et par IRMS a été utilisé dans cette recherche. Une méthode d'analyse a été développée, optimisée et validée pour cet appareillage. Par la suite, des prélÚvements d'essence provenant d'un échantillonnage conséquent et représentatif du marché de la région lausannoise ont été analysés. Finalement, les données obtenues ont été traitées et interprétées à l'aide de méthodes chimiométriques.
Les analyses effectuĂ©es ont permis de montrer que la mĂ©thodologie mise en place, aussi bien pour la composante MS que pour l'IRMS, permet de diffĂ©rencier des Ă©chantillons d'essence non altĂ©rĂ©e provenant de diffĂ©rentes stations-service. Il a Ă©galement pu ĂȘtre dĂ©montrĂ© qu'Ă chaque nouveau remplissage des cuves d'une station-service, la composition de l'essence distribuĂ©e par cette station est quasi unique. La GC-MS permet une meilleure diffĂ©renciation d'Ă©chantillons prĂ©levĂ©s dans diffĂ©rentes stations, alors que la GC-IRMS est plus performante lorsqu'il s'agit de comparer des Ă©chantillons collectĂ©s aprĂšs chacun des remplissages d'une cuve. Ainsi, ces rĂ©sultats indiquent que les deux composantes de la mĂ©thode peuvent ĂȘtre complĂ©mentaires pour l'analyse d'Ă©chantillons d'essence non altĂ©rĂ©e.
Les rĂ©sultats obtenus ont Ă©galement permis de montrer que l'Ă©vaporation des Ă©chantillons d'essence ne compromet pas la possibilitĂ© de grouper des Ă©chantillons de mĂȘme source par GC-MS. Il est toutefois nĂ©cessaire d'effectuer une sĂ©lection des variables afin d'Ă©liminer celles qui sont influencĂ©es par le phĂ©nomĂšne d'Ă©vaporation.
Par contre, les analyses effectuĂ©es ont montrĂ© que l'Ă©vaporation des Ă©chantillons d'essence a une forte influence sur la composition isotopique des Ă©chantillons. Cette influence est telle qu'il n'est pas possible, mĂȘme en effectuant une sĂ©lection des variables, de grouper correctement des Ă©chantillons Ă©vaporĂ©s par GC-IRMS.
Par conséquent, seule la composante MS de la méthodologie mise en place permet d'inférer la source d'échantillons d'essence évaporée.
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When gasoline is used to start and / or propagate an arson, source inference of gasoline can allow to establish a link between the fire and a potential source. This source inference is an interesting alternative to provide evidence in this type of events where physical evidence left by the author are rare.
The main purpose of this research was to develop a GC-IRMS method for the analysis of gasoline samples, a non-routine method and little investigated in forensic science, and to evaluate its potential to infer the source of gasoline traces compared to the GC-MS performances.
An instrument allowing to analyze simultaneously samples by MS and IRMS was used in this research. An analytical method was developed, optimized and validated for this instrument. Thereafter, gasoline samples from a large sampling and representative of the Lausanne area market were analyzed. Finally, the obtained data were processed and interpreted using chemometric methods.
The analyses have shown that the methodology, both for MS and for IRMS, allow to differentiate unweathered gasoline samples from different service stations. It has also been demonstrated that each new filling of the tanks of a station generates an almost unique composition of gasoline. GC-MS achieves a better differentiation of samples coming from different stations, while GC-IRMS is more efficient to distinguish samples collected after each filling of a tank. Thus, these results indicate that the two components of the method can be complementary to the analysis of unweathered gasoline samples.
The results have also shown that the evaporation of gasoline samples does not compromise the possibility to group samples coming from the same source by GC-MS. It is however necessary to make a selection of variables in order to eliminate those which are influenced by the evaporation.
On the other hand, the carried out analyses have shown that the evaporation of gasoline samples has such a strong influence on the isotopic composition of the samples that it is not possible, even by performing a selection of variables, to properly group evaporated samples by GC-IRMS.
Therefore, only the MS allows to infer the source of evaporated gasoline samples
Local monotonicity of Riemannian and Finsler volume with respect to boundary distances
We show that the volume of a simple Riemannian metric on is locally
monotone with respect to its boundary distance function. Namely if is a
simple metric on and is sufficiently close to and induces
boundary distances greater or equal to those of , then . Furthermore, the same holds for Finsler metrics and the
Holmes--Thompson definition of volume. As an application, we give a new proof
of the injectivity of the geodesic ray transform for a simple Finsler metric.Comment: 13 pages, v3: minor corrections and clarifications, to appear in
Geometriae Dedicat
Predictions for the Cosmogenic Neutrino Flux in Light of New Data from the Pierre Auger Observatory
The Pierre Auger Observatory (PAO) has measured the spectrum and composition
of the ultrahigh energy cosmic rays with unprecedented precision. We use these
measurements to constrain their spectrum and composition as injected from their
sources and, in turn, use these results to estimate the spectrum of cosmogenic
neutrinos generated in their propagation through intergalactic space. We find
that the PAO measurements can be well fit if the injected cosmic rays consist
entirely of nuclei with masses in the intermediate (C, N, O) to heavy (Fe, Si)
range. A mixture of protons and heavier species is also acceptable but (on the
basis of existing hadronic interaction models) injection of pure light nuclei
(p, He) results in unacceptable fits to the new elongation rate data. The
expected spectrum of cosmogenic neutrinos can vary considerably, depending on
the precise spectrum and chemical composition injected from the cosmic ray
sources. In the models where heavy nuclei dominate the cosmic ray spectrum and
few dissociated protons exceed GZK energies, the cosmogenic neutrino flux can
be suppressed by up to two orders of magnitude relative to the all-proton
prediction, making its detection beyond the reach of current and planned
neutrino telescopes. Other models consistent with the data, however, are
proton-dominated with only a small (1-10%) admixture of heavy nuclei and
predict an associated cosmogenic flux within the reach of upcoming experiments.
Thus a detection or non-detection of cosmogenic neutrinos can assist in
discriminating between these possibilities.Comment: 10 pages, 7 figure
New limits for neutrinoless tau decays
Neutrinoless 3-prong tau lepton decays into a charged lepton and either two charged particles or one neutral meson have been searched for using 4.79fb^(-1) of data collected with the CLEO II detector at Cornell Electron Storage Ring. This analysis represents an update of a previous study and the addition of six decay channels. In all channels the numbers of events found are compatible with background estimates and branching fraction upper limits are set for 28 different decay modes. These limits are either more stringent than those set previously or represent the first attempt to find these decays
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