Defect segregation facilitates oxygen transport at fluorite UO2 grain boundaries.

An important challenge for modelling transport in materials for energy applications is that in most applications they are polycrystalline, and hence it is critical to understand the properties in the presence of grain boundaries. Moreover, most grain boundaries are not pristine stoichiometric interfaces and hence dopants are likely to play a significant role. In this paper, we describe our recent work on using atomistic molecular dynamics simulations to model the effect of doped grain boundaries on oxygen transport of fluorite structured UO2. UO2, much like other fluorite grain boundaries, are found to be sinks for oxygen vacancy segregation relative to the grain interior, thus facilitating oxygen transport. Fission products further enhance diffusivity via strong interactions between the impurities and oxygen defects. Doping produces a striking structural alteration in the Σ5 class of grain boundaries that enhances oxygen diffusivity even further. This article is part of a discussion meeting issue 'Energy materials for a low carbon future'.

A rapidly-reversible absorptive and emissive vapochromic Pt(II) pincer-based chemical sensor.

Selective, robust and cost-effective chemical sensors for detecting small volatile-organic compounds (VOCs) have widespread applications in industry, healthcare and environmental monitoring. Here we design a Pt(II) pincer-type material with selective absorptive and emissive responses to methanol and water. The yellow anhydrous form converts reversibly on a subsecond timescale to a red hydrate in the presence of parts-per-thousand levels of atmospheric water vapour. Exposure to methanol induces a similarly-rapid and reversible colour change to a blue methanol solvate. Stable smart coatings on glass demonstrate robust switching over 104 cycles, and flexible microporous polymer membranes incorporating microcrystals of the complex show identical vapochromic behaviour. The rapid vapochromic response can be rationalised from the crystal structure, and in combination with quantum-chemical modelling, we provide a complete microscopic picture of the switching mechanism. We discuss how this multiscale design approach can be used to obtain new compounds with tailored VOC selectivity and spectral responses.

Atomistic simulation studies of magnetite surface structures and adsorption behavior in the presence of molecular and dissociated water and formic acid.

Static energy minimization techniques have been used to elucidate the surface structures of magnetite crystals in pure and hydroxylated forms. Adsorption energy values in the presence of molecular water, dissociate water and simple carboxylic group molecule (formic acid) are calculated and we found that the carboxylic group do not adsorb strongly in most of the pure and hydroxylated surfaces in comparison to water. Since the associated calcium minerals are floated from magnetite using fatty acid collector, our calculations corroborate the flotation practice of removing these impurity minerals from magnetite.

Competitive adsorption on wollastonite: an atomistic simulation approach.

Atomistic simulation techniques are used to simulate surface structure and adsorption behavior of scarcely floatable wollastonite mineral in the presence of molecular and dissociated water, methanoic acid, and methylamine. The latter two additives represent the two widely used collector head-group molecules. The static energy minimization code METADISE was used to perform the simulation to obtain pure surface energy and adsorption energy in the presence of added molecule. The hydroxylation was performed on those surfaces where low-coordinated silicon was made to saturate by bonding with hydroxyl group, and the subsequent charge neutralization was maintained by adding proton on single-coordinated surface oxygen. A comparison of surface energies revealed that all the surfaces become stabilized in the presence of added molecules; however, the presence of methylamine decreased the surface energy to lower values. Adsorption of dissociated water is preferred by the {100} and {102} surfaces, whereas the {001} surface preferred methylamine adsorption, because these show highly negative adsorption energies. In terms of molecular adsorption, the preferred adsorption sequence for all the surfaces is methylamine > methanoic acid > water without considering coadsorption. For the {100} and {102} surfaces, the adsorption energy values of carboxylic acid and amine are more negative than that of water and therefore we conclude that both carboxyl and amine head-group molecules adsorb preferably on wollastonite. Our simulation verify usability of carboxylic acid head group as widely used collectors for wollastonite flotation and, at the same time, it predicts the use of amine head-group collectors as possible modifiers, which corresponds well with our experimental findings.

Hydride ion formation in stoichiometric UO2.

We investigated atomic hydrogen solubility in UO2 using DFT. We predict that hydrogen energetically prefers to exist as a hydride ion rather than form a hydroxyl group by 0.27 eV, and that on diffusion hydrogen's charge state will change. The activation energy for conversion of hydride to hydroxyl is 0.94 eV.

A Giant Reconstruction of α-quartz (0001) Interpreted as Three Domains of Nano Dauphine Twins.

Silica (SiO2) is one of the most common materials on Earth. The crystalline form α-quartz is the stable silica polymorph at ambient conditions although metastable forms exist. α-quartz is a piezoelectric material, it can be produced artificially and is widely used for example in electronics and the biosciences. Despite the many application areas, the atomic surface structures of silica polymorphs are neither well understood nor well characterized. Here we present measurements of α-quartz (0001). Helium Atom Scattering combined with Atomic Force Microscopy reveals a giant reconstruction consisting of 5.55 ± 0.07 nm wide ribbons, oriented 10.4° ± 0.8° relative to the bulk unit cell. The ribbons, with the aid of atomistic modelling, can be explained as a self-organised pattern of nano Dauphine twins (nano electrical twins).

Crystal structure and thermoelectric properties of Sr-Mo substituted CaMnO3: a combined experimental and computational study.

A combination of experimental and computational techniques has been employed to study doping effects in perovskite CaMnO3. High quality Sr-Mo co-substituted CaMnO3 ceramics were prepared by the conventional mixed oxide route. Crystallographic data from X-ray and electron diffraction showed an orthorhombic to tetragonal symmetry change on increasing the Sr content, suggesting that Sr widens the transition temperature in CaMnO3 preventing phase transformation-cracking on cooling after sintering, enabling the fabrication of high density ceramics. Atomically resolved imaging and analysis showed a random distribution of Sr in the A-site of the perovskite structure and revealed a boundary structure of 90° rotational twin boundaries across {101}orthorhombic; the latter are predominant phonon scattering sources to lower the thermal conductivity as suggested by molecular dynamics calculations. The effect of doping on the thermoelectric properties was evaluated. Increasing Sr substitution reduces the Seebeck coefficient but the power factor remains high due to improved densification by Sr substitution. Mo doping generates additional charge carriers due to the presence of Mn3+ in the Mn4+ matrix, reducing electrical resistivity. The major impact of Sr on thermoelectric behaviour is the reduction of the thermal conductivity as shown experimentally and by modelling. Strontium containing ceramics showed thermoelectric figure of merit (ZT) values higher than 0.1 at temperatures above 850 K. Ca0.7Sr0.3Mn0.96Mo0.04O3 ceramics exhibit enhanced properties with S1000K = -180 µV K-1, ρ1000K = 5 × 10-5 Ωm, k1000K = 1.8 W m-1 K-1 and ZT ≈ 0.11 at 1000 K.

Tetrahydroaminoacridine facilitates passive avoidance learning in rats with nucleus basalis magnocellularis lesions.

The effect of bilateral ibotenic acid lesions of the nucleus basalis magnocellularis (NBM) on performance in a step-through passive avoidance task and the ability of tetrahydroaminoacridine (THA) to enhance learning were evaluated. Fischer 344 rats were used in a passive avoidance task in which footshock was replaced by ultrasound (30-62 K Hz, 125 dB) as the aversive training stimulus. THA was given immediately after each single daily training trial and retention was tested 24 hr later for 10 consecutive days. Although NBM lesions alone did not impair passive avoidance learning, THA at 5 mg/kg (i.p.), but not 1 mg/kg, significantly facilitated latency performance in NBM-lesioned rats.

PUVA-induced blisters, complement deposition, and damage to the dermoepidermal junction.

We followed the course of 56 patients receiving psoralen plus long-wave ultraviolet light (PUVA) therapy. Nonhemorrhagic blisters developed on clinically normal skin on the limbs of seven patients. Seeming to be related to friction and trauma, the blisters form as a result of damage to the basal and suprabasal layers. Perilesional skin specimens from all blistered patients contained granular deposits of C3 at the dermoepidermal junction, around the upper dermal blood vessels, or at both sites. The average time for initiation and complete formation of suction blisters was measured in 51 patients at different stages during the course of PUVA treatment. Blister separation was in the lamina lucida, with the pemphigoid antigen in the roof while the blister floor contained the lamina densa, laminin, and type IV collagen. This impaired dermoepidermal adhesion was a general phenomenon that occurred in all PUVA-treated patients. The mechanism remains to be determined.

Habituation and retention of the head-shake response: lack of impairment by nucleus basalis magnocellularis lesions.

Bilateral ibotenic acid lesions of the nucleus basalis magnocellularis (NBM) were examined on the habituation and retention of the head-shake response (HSR). HSR, a rapid, stereotyped rotation of the head about a front-to-rear axis, was elicited by a stream of mildly pressurized air directed at the ear in Fischer 344 rats. HSR training consisted of 40 stimulated trials followed by a 30-min retention test of 20 stimulated trials. Stimulus duration was 15 sec per trial with a 15-sec intertrial interval. Frontal cortex choline acetyltransferase was reduced by 22% in the NBM-lesioned group compared to the controls. The NBM-lesioned rats and the controls were not significantly different on either frequency or latency measures of HSR habituation or retention. The results do not support a role for cortical cholinergic mediation of the HSR.

eScience for molecular-scale simulations and the eMinerals project.

We review the work carried out within the eMinerals project to develop eScience solutions that facilitate a new generation of molecular-scale simulation work. Technological developments include integration of compute and data systems, developing of collaborative frameworks and new researcher-friendly tools for grid job submission, XML data representation, information delivery, metadata harvesting and metadata management. A number of diverse science applications will illustrate how these tools are being used for large parameter-sweep studies, an emerging type of study for which the integration of computing, data and collaboration is essential.

Management of diverticular fistulae to the female genital tract.

OBJECTIVE: Fistulae to the female genital tract are an infrequent but severe complication of diverticular disease. The purpose of this study was to evaluate treatment and outcome in patients with diverticular colo-genital fistulae. METHOD: Sixty women treated for diverticular fistulae (DF) to the female genital tract during 1992-2004 were identified. Clinic and operative charts were reviewed. Mean age was 70 years and mean follow-up time after surgery was 1 year. RESULTS: Most common presenting symptoms were vaginal discharge of faeces or gas (95% of patients) and abdominal pain (43%). About 75% of patients had undergone a hysterectomy. Forty-six patients underwent at least one radiological contrast study and the fistula was demonstrated in 35 (76%) patients. Fifty-seven patients had surgery, and findings included colo-vaginal fistulae (n = 47), colo-uterine fistulae (n = 2) and multiple fistulae involving vagina and other organs (n = 8). A sigmoid resection and primary anastomosis was performed in 51 and a Hartmann procedure with colostomy in six patients. Sixteen (28%) patients experienced morbidity after surgery, including anastomotic dehiscence (n = 4) and ureteric injury (n = 3). There was no mortality. CONCLUSION: Diverticular fistulae to the female genital tract usually occur in elderly patients with a prior hysterectomy. Radiological contrast studies demonstrate the fistulous tract in most cases. Sigmoid resection and primary anastomosis results in a satisfactory outcome in the majority of patients.

Practical problems of conducting patient-satisfaction surveys.

OBJECTIVE: Patient-satisfaction surveys have been used frequently to assess the humanistic behaviors and skills of internal medicine housestaff. In conducting their first such survey, the authors found that many practical problems affected the progress and outcome of the project. This discussion of the authors' experiences is intended to be helpful to others considering patient-satisfaction surveys as part of their housestaff-evaluation process. DESIGN: A description of the practical aspects of conducting a patient-satisfaction survey as well as the problems that the authors encountered. SETTING: Both inpatient and outpatient settings at a major university internal medicine residency program. PATIENTS/PARTICIPANTS: Ambulatory and hospitalized patients under the care of categorical internal medicine interns were eligible for participation in the study. INTERVENTIONS: An established, validated patient-satisfaction questionnaire with high reported reliability was given to patients. MEASUREMENTS AND MAIN RESULTS: Although well over 90% of patients were willing to participate, 10% of participating outpatients and 16% of participating hospital patients could not provide a usable patient-satisfaction questionnaire even with assistance. Certain patient characteristics were responsible for these decreased completion rates. Among the hospitalized patients, 42% of all eligible patients were either too ill or too cognitively impaired to even be approached for participation in the study. CONCLUSIONS: Patient-satisfaction surveys are labor-intensive, require significant resources, and are temporally demanding. Results from them must be viewed with certain caveats.

Didactic value of the clinical evaluation exercise. Missed opportunities.

The clinical evaluation exercise (CEX), a direct observation of trainees' clinical skills, is a common method of house officer evaluation. During our studies of its reliability, the extent of the CEX's didactic value surfaced. This brief report describes the amount of information passed from the evaluator to the house officer in 73 CEXs. On average, evaluators made eight teaching points in postexamination sessions. However, there were as many points recorded on the CEX forms that evaluators never mentioned. In a subset of CEXs carried out with two observers present, agreement in the teaching points presented to the house officer within the pairs witnessing the same examination was 18%. Positive feedback constituted 9% to 12% of the points presented. Our observations suggest that the more systematic feedback mechanisms may enhance the didactic value of the CEX.

Scleredema.

We report a classical case of scleredema which pursued a chronic progressive course and was associated with poorly controlled diabetes mellitus.

Renal artery stenosis: a disease worth pursuing.

Consider renovascular hypertension (HT) when: Newly diagnosed hypertension presents with features that are atypical of essential hypertension; Resistant hypertension is associated with risk factors for atheroma; or Angiotensin-converting enzyme (ACE) inhibitor or angiotensin-II-receptor antagonist therapy is associated with increasing plasma creatinine levels. Atheromatous renovascular HT can often be managed medically, which includes intensive correction of cardiovascular risk factors. ACE inhibitors are probably second-line antihypertensives for patients with unilateral renal artery stenosis and two kidneys. First-line antihypertensives are diuretics, beta-blockers and calcium-channel blockers. Bilateral renal artery stenosis, or a unilateral stenosis in a patient with only one kidney, is an absolute contraindication to ACE inhibition.