2,874 research outputs found
Increased surface flashover voltage in microfabricated devices
With the demand for improved performance in microfabricated devices, the
necessity to apply greater electric fields and voltages becomes evident. When
operating in vacuum, the voltage is typically limited by surface flashover
forming along the surface of a dielectric. By modifying the fabrication process
we have discovered it is possible to more than double the flashover voltage.
Our finding has significant impact on the realization of next-generation micro-
and nano-fabricated devices and for the fabrication of on-chip ion trap arrays
for the realization of scalable ion quantum technology
Concepts of animal well-being and predicting the impact of procedures on experimental animals
1. We argue that:
• in their application to non-human animals, \u27welfare\u27 and \u27well-being\u27 are interchangeable words; and that
• good welfare/well-being is the state of being manifest in an animal when its nutritional, environmental, health, behavioural and mental needs are met.
2. These latter are essentially the \u27five freedoms\u27 formulated by the Farm Animal Welfare Council of the United Kingdom.
3. Using the five freedoms as a basis, we have developed a system for assessing the impact of a proposed animal experiment or usage. The freedoms are now transformed into \u27domains of potential compromise\u27 and are redefined better to emphasise the extent of welfare compromise rather than the ideal of absence of compromise. Domain 1 is Thirst/hunger/malnutrition, 2 is Environmental challenge, 3 is Disease/injury/functional impairment, 4 is Behavioural/interactive restriction, and domain 5 is Anxiety/fear/pain/distress. A proposal would be examined systematically in all domains, and the degree of compromise in each rated on a 5-step non-numerical scale - O, A, B, C, X. Anxiety/fear/pain/distress arising from compromise in domains 1-4 would be cumulated into domain 5. The overall rating would commonly be that given to domain 5, but if this were low or unknown, it would be given to the highest rating in the other domains.
4. The proposer would be required to present to the institutional Animal Ethics Committee his/her assessment of the impact of a proposed experiment on the animals involved, together with an appropriate justification for the work and a cost-benefit analysis.
5. The extent of the justification required for a proposal would be directly related to the severity of compromise expected, being low for grade O and very high for grade X.
6. The cost-benefit decision would be based on the balance between the expected severity of welfare compromise and the expected benefits set out in the justification.
7. The major advantage of this system for assessing the impact on welfare is that it encourages systematic consideration of all sources of possible compromise. Such wider consideration would allow more accurate assessment of the severity of impact and thereby would improve the validity and efficiency of cost-benefit analyses.
8. The philosophical background to our approach is outlined, graded examples of welfare compromise are given and ethical and practical implications of using the system are discussed.
9. We also set out what we consider to be the ethical and practical responsibilities of the researcher to the animals, and to his/her assistants. The conscientiousness and comprehensiveness of the assessments of welfare compromise and the actions taken to minimise it are measures of the researcher\u27s acceptance of ethical responsibility for all features of each experiment which affect the animals adversely
Dissipation due to tunneling two-level systems in gold nanomechanical resonators
We present measurements of the dissipation and frequency shift in
nanomechanical gold resonators at temperatures down to 10 mK. The resonators
were fabricated as doubly-clamped beams above a GaAs substrate and actuated
magnetomotively. Measurements on beams with frequencies 7.95 MHz and 3.87 MHz
revealed that from 30 mK to 500 mK the dissipation increases with temperature
as , with saturation occurring at higher temperatures. The relative
frequency shift of the resonators increases logarithmically with temperature up
to at least 400 mK. Similarities with the behavior of bulk amorphous solids
suggest that the dissipation in our resonators is dominated by two-level
systems
Resistance Noise Scaling in a Dilute Two-Dimensional Hole System in GaAs
We have measured the resistance noise of a two-dimensional (2D)hole system in
a high mobility GaAs quantum well, around the 2D metal-insulator transition
(MIT) at zero magnetic field. The normalized noise power increases
strongly when the hole density p_s is decreased, increases slightly with
temperature (T) at the largest densities, and decreases strongly with T at low
p_s. The noise scales with the resistance, , as for a
second order phase transition such as a percolation transition. The p_s
dependence of the conductivity is consistent with a critical behavior for such
a transition, near a density p* which is lower than the observed MIT critical
density p_c.Comment: 4 pages, 4 figures, to be published in Phys. Rev. Let
Herd-level risk factors associated with the presence of Phage type 21/28 E. coli O157 on Scottish cattle farms
<p>Background: E. coli O157 is a bacterial pathogen that is shed by cattle and can cause severe disease in humans. Phage type (PT) 21/28 is a subtype of E. coli O157 that is found across Scotland and is associated with particularly severe human morbidity.</p>
<p>Methods: A cross-sectional survey of Scottish cattle farms was conducted in the period Feb 2002-Feb 2004 to determine the prevalence of E. coli O157 in cattle herds. Data from 88 farms on which E. coli O157 was present were analysed using generalised linear mixed models to identify risk factors for the presence of PT 21/28 specifically.</p>
<p>Results: The analysis identified private water supply, and northerly farm location as risk factors for PT 21/28 presence. There was a significant association between the presence of PT 21/28 and an increased number of E. coli O157 positive pat samples from a farm, and PT 21/28 was significantly associated with larger E. coli O157 counts than non-PT 21/28 E. coli O157.</p>
<p>Conclusion: PT 21/28 has significant risk factors that distinguish it from other phage types of E. coli O157. This finding has implications for the control of E. coli O157 as a whole and suggests that control could be tailored to target the locally dominant PT.</p>
Nonlinear modal coupling in a high-stress doubly-clamped nanomechanical resonator
We present results from a study of the nonlinear intermodal coupling between
different flexural vibrational modes of a single high-stress, doubly-clamped
silicon nitride nanomechanical beam. The measurements were carried out at 100
mK and the beam was actuated using the magnetomotive technique. We observed the
nonlinear behavior of the modes individually and also measured the coupling
between them by driving the beam at multiple frequencies. We demonstrate that
the different modes of the resonator are coupled to each other by the
displacement induced tension in the beam, which also leads to the well known
Duffing nonlinearity in doubly-clamped beams.Comment: 15 pages, 7 figure
The adrenocortical response to synthetic ACTH following a trek to high altitude
Background: Gradual ascent to high altitude is typically associated with reduced resting aldosterone and unchanged cortisol, features that may facilitate acclimatization but are poorly understood. Aims: To investigate the cortisol and aldosterone response to adrenocorticotrophic hormone at altitude. Methods: Eleven subjects underwent a 250 µg short synacthen test at sea-level and again after trekking to 3600 m in Nepal. Cortisol and aldosterone were measured by conventional assay from blood samples taken immediately prior to the administration of synacthen (T0) and then 30 (T30) and 60 (T60) minutes later. Results: At 3600 m resting basal cortisol and aldosterone levels were both significantly lower than they were at sea-level (p=0.004, p=0.003 respectively). Cortisol values at T30 and T60 were no different between sea-level and 3600 m but the increment after synacthen was significantly (p=0.041) greater at 3600 m due to a lower basal value. Aldosterone at T30 and T60 was significantly lower (p=0.003 for both) at 3600 m than at sea-level and the increment following synacthen was also significantly (p=0.003) less at 3600 m. Conclusions: At 3600 m there appears to be a divergent adrenal response to synthetic adrenocorticotrophic hormone with an intact cortisol response but a reduced aldosterone response, relative to sea-level. This may reflect a specific effect of hypoxia on aldosterone synthesis and may be beneficial to acclimatization
Birthweight, HIV exposure and infant feeding as predictors of malnutrition in Botswanan infants
Background: A better understanding of the nutritional status of infants who are HIV-Exposed-Uninfected (HEU) and HIV-Unexposed-Uninfected (HUU) during their first 1000 days is key to improving population health, particularly in sub-Saharan Africa. Methods: A cross-sectional study compared the nutritional status, feeding practices and determinants of nutritional status of HEU and HUU infants residing in representative selected districts in Botswana during their first 1000 days of life. Four hundred and thirteen infants (37.3% HIV-exposed), aged 6–24 months, attending routine child health clinics, were recruited. Anthropometric, 24-h dietary intake and socio-demographic data was collected. Anthropometric Z-scores were calculated using 2006 World Health Organization growth standards. Modelling of the determinants of malnutrition was undertaken using logistic regression. Results: Overall, the prevalences of stunting, wasting and being underweight were 10.4%, 11.9% and 10.2%, respectively. HEU infants were more likely to be underweight (15.6% versus 6.9%), (P < 0.01) and stunted (15.6% versus 7.3%), (P < 0.05) but not wasted (P = 0.14) than HUU infants. HEU infants tended to be formula fed (82.5%), whereas HUU infants tended to breastfeed (94%) for the first 6 months (P < 0.001). Significant predictors of nutritional status were HIV exposure, birthweight, birth length, APGAR (appearance, pulse, grimace, activity and respiration) score and mother/caregiver's education with little influence of socio-economic status. Conclusions: HEU infants aged 6–24 months had worse nutritional status compared to HUU infants. Low birthweight was the main predictor of undernutrition in this population. Optimisation of infant nutritional status should focus on improving birthweight. In addition, specific interventions should target HEU infants aiming to eliminate growth disparity between HEU and HUU infants.</p
Particle Production and Positive Energy Theorems for Charged Black Holes in deSitter
We study quantum mechanical and classical stability properties of
Reissner-Nordstrom deSitter spacetimes, which describe black holes with mass
and charge in a background with cosmological constant .
There are two sources of particle production in these spacetimes; the black
hole horizon and the cosmological horizon. A scattering calculation is done to
compute the Hawking radiation in these spacetimes. We find that the flux from
the black hole horizon equals the flux from the cosmological horizon, if and
only if , indicating that this is a state of thermodynamic equilibrium.
The spectrum, however, is not thermal. We also show that spacetimes containing
a number of charge equal to mass black holes with , have
supercovariantly constant spinors, suggesting that they may be minimum energy
states in a positive energy construction. As a first step in this direction, we
present a positive energy construction for asymptotically deSitter spacetimes
with vanishing charge. Because the construction depends only on a spatial
slice, our result also holds for spacetimes which are asymptotically
Robertson-Walker.Comment: 11 pages (1 figure not included), UMHEP-39
Scoping review of approaches for improving antimicrobial stewardship in livestock farmers and veterinarians
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