To send content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about sending content to .
To send content items to your Kindle, first ensure firstname.lastname@example.org
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about sending to your Kindle.
Note you can select to send to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be sent to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
High resolution Bragg-case X-ray double and triple axis diffractometry and Laue-case white beam synchrotron X-ray topography experiments have been performed on undoped  oriented float-zone GaAs crystals have been grown under microgravity conditions in space on the D2 mission. Near the seed, excellent anomalous transmission was achieved and a clear cellular structure of dislocations observed. The double and triple axis rocking curves were comparable with those from semi-insulating terrestrial material. Following a heater failure, the molten zone height dropped and reciprocal space maps revealed a long ridge of scatter transverse to the diffraction vector direction. This corresponds to the presence of a distribution of sub-grains containing little internal strain. Continued growth resulted in twin formation.
Multi-sire mating of a mob of ewes is commonly used in commercial sheep production systems. However, ram mating success (defined as the number of lambs sired by an individual) can vary between rams in the mating group. If this trait was repeatable and heritable, selection of rams capable of siring larger numbers of lambs could reduce the number of rams required for mating and ultimately lead to increased genetic gain. However, genetic correlations with other productive traits, such as growth and female fertility, could influence the potential for ram mating success to be used as a selection trait. In order to investigate this trait, parentage records (including accuracy of sire assignment) from 15 commercial ram breeding flocks of various breeds were utilised to examine the repeatability and heritability of ram mating success in multi-sire mating groups. In addition, genetic and phenotypic correlations with growth and female fertility traits were estimated using ASReml. The final model used for the ram mating success traits included age of the ram and mating group as fixed effects. Older rams (3+years old) had 15% to 20% greater mating success than younger rams (1 or 2 years of age). Increasing the stringency of the criteria for inclusion of both an individual lamb, based on accuracy of sire assignment, or a whole mating group, based on how many lambs had an assigned sire, increased repeatability and heritability estimates of the ram mating success traits examined. With the most stringent criteria employed, where assignment of sire accuracy was >0.95 and the total number of lambs in the progeny group that failed to have a sire assigned was<0.05, repeatability and heritability for loge(number of lambs) was 0.40±0.09 and 0.26±0.12, respectively. For proportion of lambs sired, repeatability and heritability were both 0.30±0.09. The two ram mating traits (loge(nlamb) and proportion) were highly correlated, both phenotypically and genetically (0.88±0.01 and 0.94±0.06, respectively). Both phenotypic and genetic correlations between ram mating success and growth and other female fertility traits were low and non-significant. In conclusion, there is scope to select rams capable of producing high numbers of progeny and thus increase selection pressure on rams to increase genetic gain.
Chronic suppurative otitis media is a massive public health problem in numerous low- and middle-income countries. Unfortunately, few low- and middle-income countries can offer surgical therapy.
A six-month long programme in Cambodia focused on training local surgeons in type I tympanoplasty was instigated. Qualitative educational and quantitative surgical outcomes were evaluated in the 12 months following programme completion. A four-month long training programme in mastoidectomy and homograft ossiculoplasty was subsequently implemented, and the preliminary surgical and educational outcomes were reported.
A total of 124 patients underwent tympanoplasty by the locally trained surgeons. Tympanic membrane closure at six weeks post-operation was 88.5 per cent. Pure tone audiometry at three months showed that 80.9 per cent of patients had improved hearing, with a mean gain of 17.1 dB. The trained surgeons reported high confidence in performing tympanoplasty. Early outcomes suggest the local surgeons can perform mastoidectomy and ossiculoplasty as safely as overseas-trained surgeons, with reported surgeon confidence reflecting these positive outcomes.
The training programme has demonstrated success, as measured by surgeon confidence and operative outcomes. This approach can be emulated in other settings to help combat the global burden of chronic suppurative otitis media.
Schizophrenia is a highly heritable disorder, linked to several structural abnormalities of the brain. More specifically, previous findings have suggested that increased gyrification in frontal and temporal regions are implicated in the pathogenesis of schizophrenia.
The current study included participants at high familial risk of schizophrenia who remained well (n = 31), who developed sub-diagnostic symptoms (n = 28) and who developed schizophrenia (n = 9) as well as healthy controls (HC) (n = 16). We first tested whether individuals at high familial risk of schizophrenia carried an increased burden of trait-associated alleles using polygenic risk score analysis. We then assessed the extent to which polygenic risk was associated with gyral folding in the frontal and temporal lobes.
We found that individuals at high familial risk of schizophrenia who developed schizophrenia carried a significantly greater burden of risk-conferring variants for the disorder compared to those at high risk (HR) who developed sub-diagnostic symptoms or remained well and HC. Furthermore, within the HR cohort, there was a significant and positive association between schizophrenia polygenic risk score and bilateral frontal gyrification.
These results suggest that polygenic risk for schizophrenia impacts upon early neurodevelopment to confer greater gyral folding in adulthood and an increased risk of developing the disorder.
Radio echo soundings on Rusty Glacier, a small surge-type glacier in Yukon Territory reveal that the ice is considerably thicker than previously believed. A reinterpretation of deep ice-temperature measurements made in 1969 and 1970 suggests that a large zone of temperate basal ice exists. This result supports thermal instability as the surge mechanism for Rusty Glacier.
As part of a program to study surge-type glaciers, a radar-depth survey, using a frequency of 620 MHz, has been made of Trapridge Glacier, Yukon Territory. Soundings were taken at 26 locations on the glacier surface and a maximum ice thickness of 143 m was measured. A rapid change in surface slope in the lower ablation region marks the boundary between active and stagnant ice and is suggestive of an “ice dam” or the water “collection zone” postulated by Robin and Weertman for surging glaciers.
Measurement of basal sliding is an important component in studying the mechanical and hydrological coupling between a glacier and its bed. During the 1992 summer field season we used a “drag spool” to measure sliding at the ice/bed interface of Trapridge Glacier, a small surge-type glacier in the St Elias Mountains, Yukon Territory, Canada. Measured diurnal variations in sliding appear to be correlated to subglacial water pressure fluctuations. In contrast to other observations where peak subglacial water pressure and glacier motion appear to coincide, our data imply that maximum sliding rates coincide with rises in water pressure. If the growth of water-filled cavities at the glacier bed is associated with these pressure increases, then our observations may correspond to numerical results by Iken (1981) which indicate that the largest sliding velocity occurs during cavity growth and not when the steady-state size of cavitation is attained. However, our data suggest the idea that a localized stick–slip relaxation process is at work. As the water pressure rises, a local strain build-up in the ice is released, resulting in a momentary increase in sliding rate; once the finite relaxation has occurred, further rises in water pressure do not produce additional enhancement of basal sliding, and the stick–slip cycle begins again by accumulation of elastic strain. We have developed a theoretical model for the sliding motion of ice over a surface having a basal drag that varies temporally in response to changes in subglacial water pressure. Our model results support the proposed stick–slip sliding process at the glacier base, whereby accumulated elastic strain in the ice is released as the rising water pressure decouples the ice from the bed.
A high-resolution radio echo-sounder operating at a frequency of 840 MHz has been developed for airborne sounding of small and medium-sized polar glaciers and ice caps. The sounder uses a compact,, high-gain antenna which suppresses valley-wall echoes and simplifies operation from light aircraft, Successful field trials were carried out on Rusty, Trapridge, and Hazard Glaciers, Yukon Territory, Canada. Results compare well with ice depths obtained from earlier ground-based soundings on Rusty and Trapridge Glaciers. The maximum ice thickness encountered was 200 m on Hazard Glacier.
Owing to the high operating frequency, random scattering from inhomogeneities within the ice is a major cause of signal degradation. For this reason the sounder cannot penetrate great thicknesses of temperate or debris-rich ice. Spatial averaging, an immediate result of operating from a moving platform, reduces the effects of back-scattered “clutter”.
Response tests are widely used in ground-water studies to assess the hydraulic properties of sub-surface water-flow systems. The simplicity of such tests also makes them attractive for investigation of subglacial hydraulic conditions. This paper describes a systematic, quantitative approach to the analysis of borehole-response test data. The approach uses the theoretical model of Stone and Clarke (1993), which describes water motion in a coupled borehole—subglacial flow system; this framework provides the basis for an inversion scheme that is focused on quantifying physical properties of the basal-flow system, as it is characterized in the theoretical model. The inversion procedure was applied to response-test data from Trapridge Glacier, Yukon Territory, Canada. Results of the inversions suggest that the subglacial drainage network can be described as a confined layer comprising coarse-sand-to fine-gravel-sized sediments, having a thickness of 0.1 – 0.3 m, and a hydraulic conductivity of about 5 × 10−4ms−1. Based on the water-drainage rates from boreholes, as they connect with the subglacial water-flow system, specific storage of the sediment layer was estimated to be approximately 1 × 10−4m−1. Further consideration of subglacial water-flow conditions suggests that connection drainage test results may tend to underestimate specific storage of the overall glacier substrate.
The fragmented ecosystems along the Niagara Escarpment World Biosphere Reserve provide important habitats for biota including lichens. Nonetheless, the Reserve is disturbed by dense human populations and associated air pollution. Here we investigated patterns of lichen diversity within urban and rural sites at three different locations (Niagara, Hamilton, and Owen Sound) along the Niagara Escarpment in Ontario, Canada. Our results indicate that both lichen species richness and community composition are negatively correlated with increasing human population density and air pollution. However, our quantitative analysis of community composition using canonical correspondence analysis (CCA) indicates that human population density and air pollution is more independent than might be assumed. The CCA analysis suggests that the strongest environmental gradient (CCA1) associated with lichen community composition includes regional pollution load and climatic variables; the second gradient (CCA2) is associated with local pollution load and human population density factors. These results increase the knowledge of lichen biodiversity for the Niagara Escarpment and urban and rural fragmented ecosystems as well as along gradients of human population density and air pollution; they suggest a differential influence of regional and local pollution loads and population density factors. This study provides baseline knowledge for further research and conservation initiatives along the Niagara Escarpment World Biosphere Reserve.
The Murchison Widefield Array is a Square Kilometre Array Precursor. The telescope is located at the Murchison Radio–astronomy Observatory in Western Australia. The MWA consists of 4 096 dipoles arranged into 128 dual polarisation aperture arrays forming a connected element interferometer that cross-correlates signals from all 256 inputs. A hybrid approach to the correlation task is employed, with some processing stages being performed by bespoke hardware, based on Field Programmable Gate Arrays, and others by Graphics Processing Units housed in general purpose rack mounted servers. The correlation capability required is approximately 8 tera floating point operations per second. The MWA has commenced operations and the correlator is generating 8.3 TB day−1 of correlation products, that are subsequently transferred 700 km from the MRO to Perth (WA) in real-time for storage and offline processing. In this paper, we outline the correlator design, signal path, and processing elements and present the data format for the internal and external interfaces.
The Australian dairy herd size has doubled over the last 20 years substantially increasing the time that farmers require for individual animal attention to monitor and intervene with events such as calving. Technology will help focus this limited labour resource on individual cows that require assistance. The objective of this experiment was to first determine the profiles of rumination duration and level of activity as determined by sensors between, and within, days around calving and second to use these data to predict the day of calving for pasture-based dairy cows. After 2 weeks from the expected calving date, 27 cows were fitted with SCR HR LD Tags, located in 40×90 m2 paddock and offered ad libitum oaten hay and 2 kg grain-based concentrate/cow per day until calving. Hourly activity and rumination data for each cow, as determined by the SCR tags, were fitted with linear mixed models and all parameters were estimated using restricted maximum likelihood. Rumination duration decreased by 33% over the day prior and the day of calving, with the decline in rumination duration starting the day prepartum. Activity levels were maintained prepartum but increased in the days postpartum. The day of calving was recorded and used to determine the gold standard positive (the day before calving) and negative (all other) dates. A threshold rumination level of 0.9 (decline in rumination duration of 10%) gave the optimal combination of 70% sensitivity and 70% specificity. This experiment shows the potential to use rumination duration to predict the day of calving and the opportunity to use sensor data to monitor animal health.
Altered corticostriatothalamic encoding of reinforcement is a core feature of depression. Here we examine reinforcement learning in late-life depression in the theoretical framework of the vascular depression hypothesis. This hypothesis attributes the co-occurrence of late-life depression and poor executive control to prefrontal/cingulate disconnection by vascular lesions.
Our fMRI study compared 31 patients aged ⩾60 years with major depression to 16 controls. Using a computational model, we estimated neural and behavioral responses to reinforcement in an uncertain, changing environment (probabilistic reversal learning).
Poor executive control and depression each explained distinct variance in corticostriatothalamic response to unexpected rewards. Depression, but not poor executive control, predicted disrupted functional connectivity between the striatum and prefrontal cortex. White-matter hyperintensities predicted diminished corticostriatothalamic responses to reinforcement, but did not mediate effects of depression or executive control. In two independent samples, poor executive control predicted a failure to persist with rewarded actions, an effect distinct from depressive oversensitivity to punishment. The findings were unchanged in a subsample of participants with vascular disease. Results were robust to effects of confounders including psychiatric comorbidities, physical illness, depressive severity, and psychotropic exposure.
Contrary to the predictions of the vascular depression hypothesis, altered encoding of rewards in late-life depression is dissociable from impaired contingency learning associated with poor executive control. Functional connectivity and behavioral analyses point to a disruption of ascending mesostriatocortical reward signals in late-life depression and a failure of cortical contingency encoding in elderly with poor executive control.