Effective mass theory of monolayer \delta-doping in the high-density limit

Monolayer \delta-doped structures in silicon have attracted renewed interest with their recent incorporation into atomic-scale device fabrication strategies as source and drain electrodes and in-plane gates. Modeling the physics of \delta-doping at this scale proves challenging, however, due to the large computational overhead associated with ab initio and atomistic methods. Here, we develop an analytical theory based on an effective mass approximation. We specifically consider the Si:P materials system, and the limit of high donor density, which has been the subject of recent experiments. In this case, metallic behavior including screening tends to smooth out the local disorder potential associated with random dopant placement. While smooth potentials may be difficult to incorporate into microscopic, single-electron analyses, the problem is easily treated in the effective mass theory by means of a jellium approximation for the ionic charge. We then go beyond the analytic model, incorporating exchange and correlation effects within a simple numerical model. We argue that such an approach is appropriate for describing realistic, high-density, highly disordered devices, providing results comparable to density functional theory, but with greater intuitive appeal, and lower computational effort. We investigate valley coupling in these structures, finding that valley splitting in the low-lying \Gamma band grows much more quickly than the \Gamma-\Delta band splitting at high densities. We also find that many-body exchange and correlation corrections affect the valley splitting more strongly than they affect the band splitting

Studies on times of lambing in ewes grazing subterranean clover based pastures in relation to stocking rates in south-western Australia

The investigation is reported in six parts: effect on ewe liveweight and fertility, lamb losses, effect on lamb growth and subsequent growth after weaning, wool production, pasture production and composition, and conclusions and practical implications. The results show that in the absence of supplementary feeding the physiological requirements of ewes in late pregnancy are better met by spring rather than autumn lambing

Physical limits of inference

I show that physical devices that perform observation, prediction, or recollection share an underlying mathematical structure. I call devices with that structure "inference devices". I present a set of existence and impossibility results concerning inference devices. These results hold independent of the precise physical laws governing our universe. In a limited sense, the impossibility results establish that Laplace was wrong to claim that even in a classical, non-chaotic universe the future can be unerringly predicted, given sufficient knowledge of the present. Alternatively, these impossibility results can be viewed as a non-quantum mechanical "uncertainty principle". Next I explore the close connections between the mathematics of inference devices and of Turing Machines. In particular, the impossibility results for inference devices are similar to the Halting theorem for TM's. Furthermore, one can define an analog of Universal TM's (UTM's) for inference devices. I call those analogs "strong inference devices". I use strong inference devices to define the "inference complexity" of an inference task, which is the analog of the Kolmogorov complexity of computing a string. However no universe can contain more than one strong inference device. So whereas the Kolmogorov complexity of a string is arbitrary up to specification of the UTM, there is no such arbitrariness in the inference complexity of an inference task. I end by discussing the philosophical implications of these results, e.g., for whether the universe "is" a computer.Comment: 43 pages, updated version of Physica D version, which originally appeared in 2007 CNLS conference on unconventional computatio

Symptom burden in patients with chronic kidney disease not requiring renal replacement therapy

Background: Although evidence shows that patients with end stage renal disease (ESRD) experience a high symptom burden which impacts on quality of life (QoL), less is known about patients with earlier stages of chronic kidney disease (CKD). This study aimed to explore symptom burden and potential contributing factors in patients with CKD Stage 1-5 not requiring renal replacement therapy (RRT). Methods: Patients with CKD Stage 1-5 and not on RRT were asked to report their symptoms using the Leicester Uraemic Symptom Score (LUSS), a questionnaire which assesses the frequency and intrusiveness of 11 symptoms commonly reported by kidney patients. Results: Symptoms were assessed in 283 CKD Stage 1-5 patients: 54% male, mean age 60.5 standard error± 1.0, mean eGFR 38ml/min/1.73m2. Some 96% (95% confidence interval 93.2-98.0) of participants reported experiencing at least one symptom, the median reported being six. Excessive tiredness (81%;76.0-85.6), sleep disturbance (70%;64.3-75.3) and pain in bones/joints (69%;63.4-74.6) were reported most commonly. Overall, few significant associations were found between biochemical markers of disease severity and symptom burden. Men tended to report fewer symptoms than women and South Asian patients often described experiencing symptoms with a greater severity. Older patients found musculoskeletal symptoms more intrusive whereas younger patients found reduced concentration more intrusive. Conclusions: Our findings suggest that patients with CKD stages 1-5 experience a multitude of symptoms that could potentially impact QoL. Using multidimensional tools like the LUSS, more exploration and focus could provide a greater opportunity for patient focussed symptom control from the earliest stages of CKD.Peer-reviewedPublisher Versio

Opportunities for topical antimicrobial therapy: permeation of canine skin by fusidic acid

BACKGROUND: Staphylococcal infection of the canine epidermis and hair follicle is amongst the commonest reasons for antimicrobial prescribing in small animal veterinary practice. Topical therapy with fusidic acid (FA) is an attractive alternative to systemic therapy based on low minimum inhibitory concentrations (MICs, commonly <0.03 mg/l) documented in canine pathogenic staphylococci, including strains of MRSA and MRSP (methicillin-resistant Staphylococcus aureus and S. pseudintermedius). However, permeation of canine skin by FA has not been evaluated in detail. This study aimed to define the degree and extent of FA permeation in canine skin in vitro from two sites with different hair follicle density following application of a licensed ophthalmic formulation that shares the same vehicle as an FA-betamethasone combination product approved for dermal application in dogs. Topical FA application was modelled using skin held in Franz-type diffusion cells. Concentrations of FA in surface swabs, receptor fluid, and transverse skin sections of defined anatomical depth were determined using high-performance liquid chromatography and ultraviolet (HPLC-UV) analysis. RESULTS: The majority of FA was recovered by surface swabs after 24 h, as expected (mean ± SEM: 76.0 ± 17.0%). FA was detected within 424/470 (90%) groups of serial sections of transversely cryotomed skin containing follicular infundibula, but never in 48/48 (100%) groups of sections containing only deeper follicular structures, nor in receptor fluid, suggesting that FA does not permeate beyond the infundibulum. The FA concentration (mean ± SEM) in the most superficial 240 μm of skin was 2000 ± 815 μg/g. CONCLUSIONS: Topically applied FA can greatly exceed MICs for canine pathogenic staphylococci at the most common sites of infection. Topical FA therapy should now be evaluated using available formulations in vivo as an alternative to systemic therapy for canine superficial bacterial folliculitis.Peer reviewedFinal Published versio

Quantum Computation with Quantum Dots

We propose a new implementation of a universal set of one- and two-qubit gates for quantum computation using the spin states of coupled single-electron quantum dots. Desired operations are effected by the gating of the tunneling barrier between neighboring dots. Several measures of the gate quality are computed within a newly derived spin master equation incorporating decoherence caused by a prototypical magnetic environment. Dot-array experiments which would provide an initial demonstration of the desired non-equilibrium spin dynamics are proposed.Comment: 12 pages, Latex, 2 ps figures. v2: 20 pages (very minor corrections, substantial expansion), submitted to Phys. Rev.

Stocking rate and wool production at Kojonup

RESEARCH workers in several parts of the world have recognised the overriding importance of stocking rate in raising animal production per acre. This article describes some of the initial work on the effect of stocking rate on wool production and liveweight change in medium-Peppin Merino sheep. The work was carried out at the C.S.I.R.O. Glen Lossie Field Station at Kojonup, Western Australia

XMM−NewtonXMM-Newton Ω\Omega project: III. Gas mass fraction shape in high redshift clusters

We study the gas mass fraction, $f\_{\rm gas},$ behavior in $XMM-Newton$ $\Omega$ project. The typical $f\_{\rm gas}$ shape of high redshift galaxy clusters follows the global shape inferred at low redshift quite well. This result is consistent with the gravitational instability picture leading to self similar structures for both the dark and baryonic matter. However, the mean $f\_{\rm gas} in distant clusters shows some differences to local ones, indicating a departure from strict scaling. This result is consistent with the observed evolution in the luminosity-temperature relation. We quantitatively investigate this departure from scaling laws. Within the local sample we used, a moderate but clear variation of the amplitude of the gas mass fraction with temperature is found, a trend that weakens in the outer regions. These variations do not explain departure from scaling laws of our distant clusters. An important implication of our results is that the gas fraction evolution, a test of the cosmological parameters, can lead to biased values when applied at radii smaller than the virial radius. From our$XMM$ clusters, the apparent gas fraction at the virial radius is consistent with a non-evolving universal value in a high matter density model and not with a concordance.Comment: Accepted, A&A, in pres

An XMM-Newton observation of the massive, relaxed galaxy cluster ClJ1226.9+3332 at z=0.89

A detailed X-ray analysis of an XMM-Newton observation of the high-redshift (z=0.89) galaxy cluster ClJ1226.9+3332 is presented. The X-ray temperature is found to be 11.5{+1.1}{-0.9}keV, the highest X-ray temperature of any cluster at z>0.6. In contrast to MS1054-0321, the only other very hot cluster currently known at z>0.8, ClJ1226.9+3332 features a relaxed X-ray morphology, and its high overall gas temperature is not caused by one or several hot spots. The system thus constitutes a unique example of a high redshift, high temperature, relaxed cluster, for which the usual hydrostatic equilibrium assumption, and the X-ray mass is most reliable. A temperature profile is constructed (for the first time at this redshift) and is consistent with the cluster being isothermal out to 45% of the virial radius. Within the virial radius (corresponding to a measured overdensity of a factor of 200), a total mass of (1.4+/-0.5)*10^15 M_solar is derived, with a gas mass fraction of 12+/-5%. The bolometric X-ray luminosity is (5.3+/-0.2)*10^45 erg/s. The probabilities of finding a cluster of this mass within the volume of the discovery X-ray survey are 8*10^{-5} for Omega_M=1 and 0.64 for Omega_M=0.3, making Omega_M=1 highly unlikely. The entropy profile suggests that entropy evolution is being observed. The metal abundance (of Z=0.33{+0.14}{-0.10} Z_solar), gas mass fraction, and gas distribution are consistent with those of local clusters; thus the bulk of the metals were in place by z=0.89.Comment: 13 pages, 8 figures. Accepted for publication in MNRA

Process evaluation for complex interventions in primary care: understanding trials using the normalization process model

Background: the Normalization Process Model is a conceptual tool intended to assist in understanding the factors that affect implementation processes in clinical trials and other evaluations of complex interventions. It focuses on the ways that the implementation of complex interventions is shaped by problems of workability and integration.Method: in this paper the model is applied to two different complex trials: (i) the delivery of problem solving therapies for psychosocial distress, and (ii) the delivery of nurse-led clinics for heart failure treatment in primary care.Results: application of the model shows how process evaluations need to focus on more than the immediate contexts in which trial outcomes are generated. Problems relating to intervention workability and integration also need to be understood. The model may be used effectively to explain the implementation process in trials of complex interventions.Conclusion: the model invites evaluators to attend equally to considering how a complex intervention interacts with existing patterns of service organization, professional practice, and professional-patient interaction. The justification for this may be found in the abundance of reports of clinical effectiveness for interventions that have little hope of being implemented in real healthcare setting