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

Brain natriuretic peptide and NT-proBNP levels reflect pulmonary artery systolic pressure in trekkers at high altitude.

Our objective was to evaluate the utility of the natriuretic peptides BNP (brain natriuretic peptide) and NT-proBNP as markers of pulmonary artery systolic pressure (PASP) in trekkers ascending to high altitude (HA). 20 participants had BNP and NT-proBNP assayed and simultaneous echocardiographic assessment of PASP performed during a trek to 5150 m. PASP increased significantly (p=0.006) with ascent from 24+/-4 to 39+/-11 mm Hg at 5150 m. At 5150 m those with a PASP>/=40 mm Hg (n=8) (versus those with PASP/=400 pg/ml) rise in NT-proBNP at 5150 m (n=4) PASP was significantly higher: 45.9+/-7.5 vs. 32.2+/-6.2 mm Hg (p=0.015). BNP and NT-proBNP may reflect elevated PASP, a central feature of high altitude pulmonary oedema, at HA

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 $T^{0.5}$, 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

Estimates of genetic parameters of distal limb fracture and superficial digital flexor tendon injury in UK Thoroughbred racehorses

A retrospective cohort study of distal limb fracture and superficial digital flexor tendon (SDFT) injury in Thoroughbred racehorses was conducted using health records generated by the British Horseracing Authority (BHA) between 2000 and 2010. After excluding records of horses that had both flat and jump racing starts, repeated records were reduced to a single binary record per horse (<i>n</i> = 66,507, 2982 sires), and the heritability of each condition was estimated using residual maximum likelihood (REML) with animal logistic regression models. Similarly, the heritability of each condition was estimated for the flat racing and jump racing populations separately. Bivariate mixed models were used to generate estimates of genetic correlations between SDFT injury and distal limb fracture. The heritability of distal limb fracture ranged from 0.21 to 0.37. The heritability of SDFT injury ranged from 0.31 to 0.34. SDFT injury and distal limb fracture were positively genetically correlated. These findings suggest that reductions in the risk of the conditions studied could be attempted using targeted breeding strategies

Neutrophil gelatinase-associated lipocalin: its response to hypoxia and association with acute mountain sickness.

Acute Mountain Sickness (AMS) is a common clinical challenge at high altitude (HA). A point-of-care biochemical marker for AMS could have widespread utility. Neutrophil gelatinase-associated lipocalin (NGAL) rises in response to renal injury, inflammation and oxidative stress. We investigated whether NGAL rises with HA and if this rise was related to AMS, hypoxia or exercise. NGAL was assayed in a cohort (n = 22) undertaking 6 hours exercise at near sea-level (SL); a cohort (n = 14) during 3 hours of normobaric hypoxia (FiO2 11.6%) and on two trekking expeditions (n = 52) to over 5000 m. NGAL did not change with exercise at SL or following normobaric hypoxia. During the trekking expeditions NGAL levels (ng/ml, mean ± sd, range) rose significantly (P < 0.001) from 68 ± 14 (60-102) at 1300 m to 183 ± 107 (65-519); 143 ± 66 (60-315) and 150 ± 71 (60-357) at 3400 m, 4270 m and 5150 m respectively. At 5150 m there was a significant difference in NGAL between those with severe AMS (n = 7), mild AMS (n = 16) or no AMS (n = 23): 201 ± 34 versus 171 ± 19 versus 124 ± 12 respectively (P = 0.009 for severe versus no AMS; P = 0.026 for mild versus no AMS). In summary, NGAL rises in response to prolonged hypobaric hypoxia and demonstrates a relationship to the presence and severity of AMS

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

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

Low-temperature and high magnetic field dynamic scanning capacitance microscope

We demonstrate a dynamic scanning capacitance microscope (DSCM) that operates at large bandwidths, cryogenic temperatures and high magnetic fields. The setup is based on a non-contact atomic force microscope (AFM) with a quartz tuning fork sensor with non-optical excitation and read-out for topography, force and dissipation measurements. The metallic AFM tip forms part of an rf resonator with a transmission characteristics modulated by the sample properties and the tip-sample capacitance. The tip motion gives rise to a modulation of the capacitance at the frequency of the AFM sensor and its harmonics, which can be recorded simultaneously with the AFM data. We use an intuitive model to describe and analyze the resonator transmission and show that for most experimental conditions it is proportional to the complex tip-sample conductance, which depends on both the tip-sample capacitance and the sample resistivity. We demonstrate the performance of the DSCM on metal disks buried under a polymer layer and we discuss images recorded on a two-dimensional electron gas in the quantum Hall effect regime, i.e. at cryogenic temperatures and high magnetic fields, where we directly image the formation of compressible stripes at the physical edge of the sample

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 $S_R/R^2$ 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, $S_R/R^2 \sim R^{2.4}$, 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

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