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The principal salmonella serovar associated with infections linked to eggs and egg products in the UK, most European countries and North America is Salmonella enteritidis. However, other serovars have also been implicated in a number of egg-associated outbreaks, most notably S. typhimurium exhibiting a range of phage types. The present article reviews human egg-associated salmonellosis associated with non-S. enteritidis serovars, predominantly in the European Union (EU) but also world-wide, using information from published literature and epidemiological databases. There are also brief reviews of S. enteritidis and of mechanisms leading to egg contamination by salmonella. The numbers of egg-associated infections caused by non-S. enteritidis serovars are fairly substantial (for example 22% of outbreaks and 11.5% of more than 20,000 cases in the EU in 2008), and such infections have resulted in hospitalisations and deaths. Furthermore, in parts of the world where S. enteritidis historically has not penetrated laying hen breeding flocks, egg-related salmonellosis is a problem associated specifically with non-S. enteritidis serovars. Control measures to limit the incidence of S. enteritidis and S. typhimurium in poultry flocks are vital. It is therefore important that close surveillance of salmonellosis incidence and serovars in laying flocks is used to establish suitable biosecurity and vaccination programmes throughout EU Member States and elsewhere.
We report on an experimental study of microstructure-based lasing in an optically pumped GaN/AlGaN separate confinement heterostructure (SCH). We achieved low-threshold ultra-violet lasing in optically pumped GaN/AlGaN separate confinement heterostructures over a wide temperature range. The spacing, directionality, and far-field patterns of the lasing modes are shown to be the result of microcavities that were naturally formed in the structures due to strain relaxation. The temperature sensitivity of the lasing wavelength was found to be twice as low as that of bulk-like GaN films. Based on these results, we discuss possibilities for the development of ultra-violet laser diodes with increased temperature stability of the emission wavelength.
Copper and copper alloys are frequently used in environments where short-term laboratory testing indicates that they should be resistant to corrosion. However, in long-term service, copper and its alloys show degradation mechanisms which have not been replicated in the laboratory. In this paper, corrosion mechanisms for copper alloys will be examined from the standpoint of corrosion product thermodynamics and corrosion kinetics, with particular reference to microbiologica11y influenced corrosion (MIC). Comparison will be made to the corrosion behavior of high-iron and high-nickel alloys.
Single and multi-mode room temperature laser action was observed in GaN pyramids under strong optical pumping. The 5- and 15-micron-wide hexagonal-based pyramids were laterally overgrown on a patterned GaN/AlN seeding layer grown on a (111) silicon substrate by metal-organic chemical vapor deposition. The pyramids were individually pumped, imaged, and spectrally analyzed through a high magnification optical system using a high density pulsed excitation source. We suggest that the cavity formed in a pyramid is of a ring type, formed by total internal reflections of light off the pyramids' surfaces. The mode spacing of the laser emission was found to be correlated to the size of pyramids. The effects of pyramid geometry and pulse excitation on the nature of laser oscillations inside of the pyramids is discussed.
Temperature-dependent photoluminescence (PL) studies have been performed on InGaN epilayers and InGaN/GaN multiple quantum wells (MQWs) grown by metalorganic chemical vapor deposition. We observed anomalous temperature dependent emission behavior (specifically an S-shaped decrease-increase-decrease) of the peak energy (EpL) of the InGaN-related PL emission with increasing temperature. In the case of the InGaN epilayer, EPL decreases in the temperature range of 10 - 50 K, increases for 50 - 110 K, and decreases again for 110 - 300 K with increasing temperature. For the InGaN/GaN MQWs, EPL decreases from 10 - 70 K, increases from 70 - 150 K, then decreases again for 150 - 300 K. The actual temperature dependence of the PL emission was estimated with respect to the bandgap energy determined by photoreflectance spectra. We observed that the PL peak emission shift has an excellent correlation with a change in carrier lifetime with temperature. We demonstrate that the temperature-induced S-shaped PL shift is caused by the change in carrier recombination dynamics with increasing temperature due to inhomogeneities in the InGaN structures.
We report the results of an experimental study on near-threshold gain mechanisms in optically pumped GaN epilayers and InGaN/GaN heterostructures at temperatures as high as 700 K. We show that the dominant near-threshold gain mechanism in GaN epilayers is inelastic excitonexciton scattering for temperatures below ∼ 150 K, characterized by band-filling phenomena and a relatively low stimulated emission (SE) threshold. An analysis of both the temperature dependence of the SE threshold and the relative shift between stimulated and band-edge related emission indicates electron-hole plasma is the dominant gain mechanism for temperatures exceeding 150 K. The dominant mechanism for SE in InGaN epilayers and InGaN/GaN multiple quantum wells was found to be the recombination of carriers localized at potential fluctuations resulting from nonuniform indium incorporation. The SE spectra from InGaN epilayers and multiple quantum wells were comprised of extremely narrow emission lines and no spectral broadening of the lines was observed as the temperature was raised from 10 K to over 550 K. Based on the presented results, we suggest a method for significantly reducing the carrier densities needed to achieve population inversion in GaN, allowing for the development of GaNactive-medium laser diodes.
The optical properties of (In, Al) GaN thin films and heterostructures have been compared under the conditions of strong nanosecond excitation. The stimulated emission (SE) threshold from AIGaN epilayers was found to increase with increasing Al content compared to GaN, in contrast to InGaN epilayers, where an order of magnitude decrease is observed. Optically pumped SE has been observed from AIGaN films with aluminum concentrations as high as 26%. Room temperature SE at wavelengths as low as 327 nm has been achieved. In contrast to the increase of SE threshold seen for AlGaN films, we found that AlGaN/GaN heterostructures which utilize carrier confinement and optical waveguiding drastically enhance the lasing characteristics. We demonstrate that AIGaN/GaN heterostructures are suitable for the development of deep ultraviolet laser diodes.
In situ, real time spectroscopic ellipsometry (RTSE) has been used to study the growth processes and optical properties of Cu2-xSe - an important binary compound in the fabrication of high efficiency copper indium gallium diselenide (CIGS) photovoltaic devices. It was found that the high surface roughness of the Cu2-xSe layers necessitated a “graded” optical model in order to extract meaningful dielectric functions at both 550 °C and room temperature. The optical model was verified at room temperature against SEM micrographs and reflectance measurements carried out ex situ. The growth temperature dielectric functions presented in this study are expected to allow for a greater level of control and understanding of the so-called 2- and 3-stage processes for CIGS fabrication in which a Cu2-xSe phase, present at the CIGS grain boundaries, acts as a fluxing agent for the growth of photovoltaic quality CIGS. Real time optical feedback via RTSE combined with the growth temperature dielectric functions presented here could play an important role in improving material fabrication on both the laboratory and industrial scales.
We investigated an international outbreak of Salmonella Agona with a distinct PFGE pattern associated with an Irish Food company (company X) producing pre-cooked meat products sold in various food outlet chains in Europe. The outbreak was first detected in Ireland. We undertook national and international case-finding, food traceback and microbiological investigation of human, food and environmental samples. We undertook a matched case-control study on Irish cases. In total, 163 cases in seven European countries were laboratory-confirmed. Consumption of food from food outlet chains supplied by company X was significantly associated with being a confirmed case (mOR 18·3, 95% CI 2·2–149·2) in the case-control study. The outbreak strain was isolated from the company's pre-cooked meat products and production premises. Sufficient evidence was gathered to infer the vehicles of infection and sources of the outbreak and to justify the control measures taken, which were plant closure and food recall.
A major outbreak of tuberculosis occurred in cattle on a farm in Dorset between 1970 and 1976. Six hundred and twenty-six cattle were slaughtered either because they reacted to the tuberculin test or had been exposed to infection. No source of infection was found until 1974 when badgers infected with Mycobacterium bovis were first discovered.
An analysis of the tuberculin test records of this herd and the six surrounding herds indicated that tuberculosis had been a sporadic problem since the early 1960's. Two peaks of infection occurred in the most severely affected herd in 1970 and 1974 when 29·8% and 27·3% of animals, respectively, reacted to the tuberculin test. These figures are exceptionally high. During the last 20 years there have been two periods when all the herds in the area had synchronous outbreaks consistent with a common source.
Analysis indicated that cattle were at greatest risk in April and May and suggest that there was re-exposure to infection at this time each year. In addition the cattle were apparently exposed to M. bovis, at sufficiently high levels for transmission to occur, for only a relatively short period of time.
Following a major outbreak of tuberculosis in cattle on a farm in Dorset, badgers were discovered to be infected with Mycobacterium bovis. Two hundred and forty sets were found in the 1200 hectares of the study area. The sets were found predominantly in areas of Portland Sand. A high prevalence of tuberculosis was found in the badger population which was removed and repopulation prevented for 3 years. The removal of the infected badgers led to the resolution of the problem in cattle. Re-colonization of the area has progressed slowly and the cattle have remained free from infection for a period of 5 years.
A large sample of the wild mammals found on a farm in South Dorset were trapped and examined for the presence of Mycobacterium bovis following the discovery of widespread infection in cattle and badgers. M. bovis was isolated from the lymph nodes of two out of 90 rats (Rattus norvegicus) and one out of seven foxes (Vulpes vulpes) but no lesions of tuberculosis were observed. It was concluded that the badger was the only species of wild mammal which was a reservoir of M. bovis in this area.
A detailed investigation of the possible role of wild mammals, other than badgers, in the maintenance of Mycobacterium bovis in an area on the South Downs of East Sussex was carried out over 3 years. Estimates of population sizes were made where possible and minimum sample sizes were selected to be 95 % certain of including at least one infected animal if the prevalence was at least 5 %. Samples of wild mammals were taken from populations which had the highest potential direct or indirect contact rate with known infected badgers. M. bovis was not isolated from any of the 15 species of wild mammals.
It was concluded that badgers are able to maintain M. bovis in an area independently of other species, and that in the area studied other species were not a source of infection for the cattle herds.
Understanding genetic relationships amongst the life-history traits of parasites is crucial for testing hypotheses on the evolution of virulence. This study therefore examined variation between parasite isolates (the bacterium Pasteuria ramosa) from the crustacean Daphnia magna. From a single wild-caught infected host we obtained 2 P. ramosa isolates that differed substantially in the mortality they caused. Surprisingly, the isolate causing higher early mortality was, on average, less successful at establishing infections and had a slower growth rate within hosts. The observation that within-host replication rate was negatively correlated with mortality could violate a central assumption of the trade-off hypothesis for the evolution of virulence, but we discuss a number of caveats which caution against premature rejection of the trade-off hypothesis. We sought to test if the characteristics of these parasite isolates were constant across host genotypes in a second experiment that included 2 Daphnia host clones. The relative growth rates of the two parasite isolates did indeed depend on the host genotype (although the rank order did not change). We suggest that testing evolutionary hypotheses for virulence may require substantial sampling of both host and parasite genetic variation, and discuss how selection for virulence may change with the epidemiological state of natural populations and how this can promote genetic variation for virulence.
Previous studies of rod photoreceptors in vivo have employed
a paired-flash electroretinographic (ERG) technique to determine rod
response properties. To test whether absence versus presence of
the ERG b-wave affects the photoreceptor response derived by the
paired-flash method, we examined paired-flash-derived responses obtained
from nob mice, a mutant strain with a defect in signal
transduction between photoreceptors and ON bipolar cells that causes a
lack of the b-wave. Normal littermates of the nob mice
served as controls. The normalized amplitude-intensity relation of the
derived response determined in nob mice at the near-peak time of
86 ms was similar to that determined for the controls. The full time
course of the derived rod response was obtained for test flash strengths
ranging from 0.11 to 17.38 scotopic cd s m−2 (sc cd s
m−2). Time-course data obtained from nob and
control mice exhibited significant but generally modest differences. With
saturating test flash strengths, half-recovery times for the derived
response of nobversus control mice differed by ∼60
ms or less about the combined (nob and control) average
respective values. Time course data also were obtained before
versus after intravitreal injection of
l-2-amino-4-phosphonobutyrate (APB) (which blocks transmission
from photoreceptors to depolarizing bipolar cells) and of cis
2,3-piperidine dicarboxylic acid (PDA) (which blocks transmission to OFF
bipolar cells, and to horizontal, amacrine and ganglion cells). Neither
APB nor PDA substantially affected derived responses obtained from
nob or control mice. The results provide quantitative information
on the effect of b-wave removal on the paired-flash-derived
response in mouse. They argue against a substantial skewing effect of the
b-wave on the paired-flash-derived response obtained in normal
mice and are consistent with the notion that, to good approximation, this
derived response represents the isolated flash response of the
photoreceptors in both nob and normal mice.