620 research outputs found
Direct and indirect transmission of four Salmonella enterica serotypes in pigs
<p>Abstract</p> <p>Background</p> <p>Feed-borne spread of <it>Salmonella </it>spp. to pigs has been documented several times in recent years in Sweden. Experiences from the field suggest that feed-associated serotypes might be less transmittable and subsequently easier to eradicate from pig herds than other serotypes more commonly associated to pigs. Four <it>Salmonella </it>serotypes were selected for experimental studies in pigs in order to study transmissibility and compare possible differences between feed-assoociated (<it>S </it>Cubana and <it>S </it>Yoruba) and pig-associated serotypes (<it>S </it>Derby and <it>S </it>Typhimurium).</p> <p>Methods</p> <p>Direct contact transmission was studied in four groups of pigs formed by six 10-week-old salmonella negative pigs commingled with two fatteners excreting one of the four salmonella serotypes. Indirect transmission was studied by putting six 10-week-old salmonella negative pigs in each of four salmonella contaminated rooms. Each room had previously housed a group of pigs, excreting one of the four selected serotypes.</p> <p>All pigs were monitored for two weeks with respect to the faecal excretion of salmonella and the presence of serum antibodies. At the end of the trial, eight samples from inner tissues and organs were collected from each pig at necropsy.</p> <p>Results</p> <p>In the four direct transmission groups, one pig shed <it>Salmonella </it>(Cubana) at one occasion. At necropsy, <it>S </it>Typhimurium was isolated from one pig.</p> <p>In the indirect transmission groups, two pigs in the Yoruba room and one pig in each of the other rooms were excreting detectable levels of <it>Salmonella </it>once during the study period of two weeks. At necropsy, <it>S </it>Derby was isolated from one of six pigs in the Derby room and <it>S </it>Typhimurium was isolated from four of the six pigs in the Typhimurium room.</p> <p>No significant serological response could be detected in any of the 48 pigs.</p> <p>Conclusions</p> <p>These results show that all four selected serotypes were able to be transmitted in at least one of these field-like trials, but the transmission rate was low in all groups and no obvious differences between feed-associated and pig-associated serotypes in the transmission to naïve pigs and their subsequent faecal shedding were revealed. However, the post mortem results indicated a higher detection of <it>S </it>Typhimurium in the ileocecal lymph nodes of pigs introduced into a contaminated environment in comparison with the other three serotypes.</p
High Resolution Hybrid Pixel Sensors for the e+e- TESLA Linear Collider Vertex Tracker
In order to fully exploit the physics potential of a future high energy e+e-
linear collider, a Vertex Tracker, providing high resolution track
reconstruction, is required. Hybrid Silicon pixel sensors are an attractive
option, for the sensor technology, due to their read-out speed and radiation
hardness, favoured in the high rate environment of the TESLA e+e- linear
collider design but have been so far limited by the achievable single point
space resolution. In this paper, a conceptual design of the TESLA Vertex
Tracker, based on a novel layout of hybrid pixel sensors with interleaved cells
to improve their spatial resolution, is presented.Comment: 12 pages, 5 figures, to appear in the Proceedings of the Vertex99
Workshop, Texel (The Netherlands), June 199
Evidence for non-exponential elastic proton proton differential cross-section at low vertical bar t vertical bar and √ s = 8 TeV by TOTEM
The TOTEM experiment has made a precise measurement of the elastic proton proton differential cross-section at the centre-of-mass energy root s = 8 TeV based on a high-statistics data sample obtained with the beta* = 90 m optics. Both the statistical and systematic uncertainties remain below 1%, except for the t-independent contribution from the overall normalisation. This unprecedented precision allows to exclude a purely exponential differential cross-section in the range of four-momentum transfer squared 0.027 <vertical bar t vertical bar <0.2 GeV2 with a significance greater than 7 sigma. Two extended parametrisations, with quadratic and cubic polynomials in the exponent, are shown to be well compatible with the data. Using them for the differential cross-section extrapolation to t = 0, and further applying the optical theorem, yields total cross-section estimates of (101.5 +/- 2.1) mb and (101.9 +/- 2.1) mb, respectively, in agreement with previous TOTEM measurements. (C) 2015 The Authors. Published by Elsevier B.V.Peer reviewe
Diffraction and Total Cross-Section at the Tevatron and the LHC
At the Tevatron, the total p_bar-p cross-section has been measured by CDF at 546 GeV and 1.8 TeV, and by E710/E811 at 1.8 TeV. The two results at 1.8 TeV disagree by 2.6 standard deviations, introducing big uncertainties into extrapolations to higher energies. At the LHC, the TOTEM collaboration is preparing to resolve the ambiguity by measuring the total p-p cross-section with a precision of about 1 %. Like at the Tevatron experiments, the luminosity-independent method based on the Optical Theorem will be used. The Tevatron experiments have also performed a vast range of studies about soft and hard diffractive events, partly with antiproton tagging by Roman Pots, partly with rapidity gap tagging. At the LHC, the combined CMS/TOTEM experiments will carry out their diffractive programme with an unprecedented rapidity coverage and Roman Pot spectrometers on both sides of the interaction point. The physics menu comprises detailed studies of soft diffractive differential cross-sections, diffractive structure functions, rapidity gap survival and exclusive central production by Double Pomeron Exchange.Peer reviewe
First measurement of elastic, inelastic and total cross-section at √s = 13TeV by TOTEM and overview of cross-section data at LHC energies : TOTEM Collaboration
The TOTEM collaboration has measured the proton- proton total cross section at v s = 13 TeV with a luminosity- independent method. Using dedicated ss * = 90m beam optics, the Roman Pots were inserted very close to the beam. The inelastic scattering rate has been measured by the T1 and T2 telescopes during the same LHC fill. After applying the optical theorem the total proton- proton cross section is stot = (110.6 +/- 3.4) mb, well in agreement with the extrapolation from lower energies. This method also allows one to derive the luminosity- independent elastic and inelastic cross sections: sel = (31.0 +/- 1.7) mband sinel = (79.5 +/- 1.8) mb.Peer reviewe
Pressure Induced Hydration Dynamics of Membranes
Pressure-jump initiated time-resolved x-ray diffraction studies of dynamics
of the hydration of the hexagonal phase in biological membranes show that (i)
the relaxation of the unit cell spacing is non-exponential in time; (ii) the
Bragg peaks shift smoothly to their final positions without significant
broadening or loss in crystalline order. This suggests that the hydration is
not diffusion limited but occurs via a rather homogeneous swelling of the whole
lattice, described by power law kinetics with an exponent .Comment: REVTEX 3, 10 pages,3 figures(available on request),#
TOTEM Physics
This article discusses the physics programme of the TOTEM experiment at the LHC. A new special beam optics with beta* = 90 m, enabling the measurements of the total cross-section, elastic pp scattering and diffractive phenomena already at early LHC runs, is explained. For this and the various other TOTEM running scenarios, the acceptances of the leading proton detectors and of the forward tracking stations for some physics processes are described.Peer reviewe
Photo-induced second-order nonlinearity in stoichiometric silicon nitride waveguides
We report the observation of second-harmonic generation in stoichiometric
silicon nitride waveguides grown via low-pressure chemical vapour deposition.
Quasi-rectangular waveguides with a large cross section were used, with a
height of 1 {\mu}m and various different widths, from 0.6 to 1.2 {\mu}m, and
with various lengths from 22 to 74 mm. Using a mode-locked laser delivering
6-ps pulses at 1064 nm wavelength with a repetition rate of 20 MHz, 15% of the
incoming power was coupled through the waveguide, making maximum average powers
of up to 15 mW available in the waveguide. Second-harmonic output was observed
with a delay of minutes to several hours after the initial turn-on of pump
radiation, showing a fast growth rate between 10 to 10 s,
with the shortest delay and highest growth rate at the highest input power.
After this first, initial build-up, the second-harmonic became generated
instantly with each new turn-on of the pump laser power. Phase matching was
found to be present independent of the used waveguide width, although the
latter changes the fundamental and second-harmonic phase velocities. We address
the presence of a second-order nonlinearity and phase matching, involving an
initial, power-dependent build-up, to the coherent photogalvanic effect. The
effect, via the third-order nonlinearity and multiphoton absorption leads to a
spatially patterned charge separation, which generates a spatially periodic,
semi-permanent, DC-field-induced second-order susceptibility with a period that
is appropriate for quasi-phase matching. The maximum measured second-harmonic
conversion efficiency amounts to 0.4% in a waveguide with 0.9 x 1 {\mu}m
cross section and 36 mm length, corresponding to 53 {\mu}W at 532 nm with 13 mW
of IR input coupled into the waveguide. The according amounts to
3.7 pm/V, as retrieved from the measured conversion efficiency.Comment: 20 pages, 10 figure
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