Benchmarking the performance of Density Functional Theory and Point Charge Force Fields in their Description of sI Methane Hydrate against Diffusion Monte Carlo

High quality reference data from diffusion Monte Carlo calculations are presented for bulk sI methane hydrate, a complex crystal exhibiting both hydrogen-bond and dispersion dominated interactions. The performance of some commonly used exchange-correlation functionals and all-atom point charge force fields is evaluated. Our results show that none of the exchange-correlation functionals tested are sufficient to describe both the energetics and the structure of methane hydrate accurately, whilst the point charge force fields perform badly in their description of the cohesive energy but fair well for the dissociation energetics. By comparing to ice Ih, we show that a good prediction of the volume and cohesive energies for the hydrate relies primarily on an accurate description of the hydrogen bonded water framework, but that to correctly predict stability of the hydrate with respect to dissociation to ice Ih and methane gas, accuracy in the water-methane interaction is also required. Our results highlight the difficulty that density functional theory faces in describing both the hydrogen bonded water framework and the dispersion bound methane.Comment: 8 pages, 4 figures, 1 table. Minor typos corrected and clarification added in Method

The new towns of Israel: Origins, development and implementation

Israel is not generally perceived as a highly urbanized country yet 86% of its population now live in urban areas. The dominance of the anti-city Zionist ideology of the pre-1948 pioneers stressing the value of rural society and agricultural labout overshadowed the reality of urban development and growth. Shortly after independence, demographic and defense pressures necessitated a policy for population dispersal and immigrant absorption. The dispersal of population policy utilized two approaches namely the creation of new towns and to a lesser degree the establishment of rural settlements. The new towns have been described as 'planted* or 'administered' communities because of the highly centralized, externally imposed and paternalistic style of planning and administration. They were conceived of as regional, urban service centres in their respective rural areas. Primary emphasis was upon settlement, with economic goals and social planning as secondary considerations. The policy of rapid urbanization led to a very rapid filling-up of the country especially in the first 10 years. Thirty new towns were created. The growth of the Tel Aviv area has been limited and its share of the national population reduced. The urban hierarchy was modified by the creation of intermediate sized settlements and in general, the policy of population dispersal has been a significant accomplishment. But there are problems and failures. Many of the planned new towns are neither economically nor socially viable. Many are too small and too few have acquired urban characteristics or become regional centres as intended. Economic benefits have lagged despite tax benefits, loans, grants, and other fiscal incentives. Too great an emphasis on spatial and physical development, on the rapid settlement of people without providing for economic and social infrastructure has generated an exodus of the younger, more upwardly mobile, able and energetic residents. Those left behind in the towns are the least able to cope with the difficulties. The vast majority of the outmigrants have left the new towns which had been assigned to them, despite their ineligibility for housing and employment assistance in their next community. The volume of the exodus is testimony to the perception by many of the unsuitability of the new towns. In spite of the apparent shortcomings, little remedial action has been taken to rectify the situation. Since the mid-1960's no new towns have been founded and apart from one notable though unfinished study there has been no significant large scale research initiated by the Israeli Government into the present state of the towns. This study suggests that by recognising the deficiencies and by adopting measures to overcome the problems, the new towns programme could be resuscitated. The programme may at present be a political failure which the Government is loath to admit. Further avoidance of the issues can only compound the failure. Detailed research and action are needed immediately

Continuum variational and diffusion quantum Monte Carlo calculations

This topical review describes the methodology of continuum variational and diffusion quantum Monte Carlo calculations. These stochastic methods are based on many-body wave functions and are capable of achieving very high accuracy. The algorithms are intrinsically parallel and well-suited to petascale computers, and the computational cost scales as a polynomial of the number of particles. A guide to the systems and topics which have been investigated using these methods is given. The bulk of the article is devoted to an overview of the basic quantum Monte Carlo methods, the forms and optimisation of wave functions, performing calculations within periodic boundary conditions, using pseudopotentials, excited-state calculations, sources of calculational inaccuracy, and calculating energy differences and forces

Phase Transformations of Calcium Phosphates Formed in Wet Field Environments

The crystal phase and morphology of calcium phosphate salts precipitated in a wet field environment at temperatures between 30 and 70 °C and pHs between 3 and 8 were examined. Dicalcium Phosphate Dihydrate (DCPD) was the most prevalent phase precipitated. Using accelerated ageing study techniques, precipitates studied were aged, under dry conditions at 50 °C for 8 and 16 days, before being re-examined using XRD, FTIR and SEM techniques. DCPD was found to be most stable when precipitated at 40 °C and 5 pH. Considerably more phase transformation to Octacalcium Phosphate (OCP), Amorphous Calcium Phosphate (ACP) and Hydroxyapatite (HA) was seen at high temperatures and high pHs, and a greater tendency to form anhydrous salts was seen at high temperatures and low pHs. Using techniques such as XRD, FTIR and SEM the transformation of the DCPD precipitate to OCP was analysed and appeared to occur without the presence of an intermediate amorphous phase. However, transformation from OCP to HA did result in the formation of an intermediate amorphous phase. © 2007 Springer Science+Business Media, LLC

Investigation into the Ultrasonic Setting of Glass Ionomer Cements : Part II Setting Times and Compressive Strengths

The ultrasonic setting of glass ionomer cements (GIC) was discussed. It was observed that the ultrasonic setting resulted in improvements of compressive strength. An increase in the PAA molecular weight from PAA50 to PAA200 resulted in an increase in the strength, but with a further increase in the PAA molecular weight to PAA450, there was a reduction in the strength. Results show that the strength of the ultrasonically set materials after 1 day were close to the values for the 7 days chemically set samples

Clinical Risk Factors for Osteoporosis in Ireland and the UK: A Comparison of FRAX and QFractureScores

Recently two algorithms have become available to estimate the 10-year probability of fracture in patients suspected to have osteoporosis on the basis of clinical risk factors: the FRAX algorithm and QFractureScores algorithm (QFracture). The aim of this study was to compare the performance of these algorithms in a study of fracture patients and controls recruited from six centers in the United Kingdom and Ireland. A total of 246 postmenopausal women aged 50-85 years who had recently suffered a low-trauma fracture were enrolled and their characteristics were compared with 338 female controls who had never suffered a fracture. Femoral bone mineral density was measured by dual-energy X-ray absorptiometry, and fracture risk was calculated using the FRAX and QFracture algorithms. The FRAX algorithm yielded higher scores for fracture risk than the QFracture algorithm. Accordingly, the risk of major fracture in the overall study group was 9.5% for QFracture compared with 15.2% for FRAX. For hip fracture risk the values were 2.9% and 4.7%, respectively. The correlation between FRAX and QFracture was R = 0.803 for major fracture and R = 0.857 for hip fracture (P ≤ 0.0001). Both algorithms yielded high specificity but poor sensitivity for prediction of osteoporosis. We conclude that the FRAX and QFracture algorithms yield similar results in the estimation of fracture risk. Both of these tools could be of value in primary care to identify patients in the community at risk of osteoporosis and fragility fractures for further investigation and therapeutic intervention. © 2011 Springer Science+Business Media, LLC

Characterizing the potential for drought action from combined hydrological and societal perspectives

Drought is a function of both natural and human influences, but fully characterizing the interactions between human and natural influences on drought remains challenging. To better characterize parts of the drought feedback loop, this study combines hydrological and societal perspectives to characterize and quantify the potential for drought action. For the hydrological perspective, we examine historical groundwater data, from which we determine the decadal likelihoods of exceeding hydrologic thresholds relevant to different water uses. Stakeholder interviews yield data about how people rate the importance of water for different water uses. We combine these to quantify the Potential Drought Action Indicator (PDAI). The PDAI is demonstrated for a study site in south-central Oklahoma, where water availability is highly influenced by drought and management of water resources is contested by local stakeholders. For the hydrological perspective, we find that the historical decadal likelihood of exceedance for a moderate threshold associated with municipal supply has ranged widely: from 23&thinsp;% to 75&thinsp;%, which corresponds well with natural drought variability in the region. For the societal perspective, stakeholder interviews reveal that people value water differently for various uses. Combining this information into the PDAI illustrates that potential drought action increases as the hydrologic threshold is exceeded more often; this occurs as conditions get drier and when water use thresholds are more moderate. The PDAI also shows that for water uses where stakeholders have diverse views of importance, the PDAI will be diverse as well, and this is exacerbated under drier conditions. The variability in stakeholder views of importance is partially explained by stakeholders' cultural worldviews, pointing to some implications for managing water when drought risks threaten. We discuss how the results can be used to reduce potential disagreement among stakeholders and promote sustainable water management, which is particularly important for planning under increasing drought.</p

Personal protective equipment solution for UK military medical personnel working in an Ebola virus disease treatment unit in Sierra Leone.

The combination of personal protective equipment (PPE) together with donning and doffing protocols was designed to protect British and Canadian military medical personnel in the Kerry Town Ebola Treatment Unit (ETU) in Sierra Leone. The PPE solution was selected to protect medical staff from infectious risks, notably Ebola virus, and chemical (hypochlorite) exposure. PPE maximized dexterity, enabled personnel to work in hot temperatures for periods of up to 2h, protected mucosal membranes when doffing outer layers, and minimized potential contamination of the doffing area with infectious material by reducing the requirement to spray PPE with hypochlorite. The ETU was equipped to allow medical personnel to provide a higher level of care than witnessed in many existing ETUs. This assured personnel working as part of the international response that they would receive as close to Western treatment standards as possible if they were to contract Ebola virus disease (EVD). PPE also enabled clinical interventions that are not seen routinely in West African EVD treatment regimens, whilst providing a robust protective barrier. Competency in using PPE was developed during a nine-day pre-deployment training programme. This allowed over 60 clinical personnel per deployment to practice skills in PPE in a simulated ETU and in classrooms. Overall, the training provided: (i) an evidence base underpinning the PPE solution chosen; (ii) skills in donning and doffing of PPE; (iii) personnel confidence in the selected PPE; and (iv) quantifiable testing of each individual's capability to don PPE, perform tasks and doff PPE safely

Fabrication of CaO-NaO-SiO2/TiO2 Scaffolds for Surgical Applications

A series of titanium (Ti) based glasses were formulated (0.62 SiO2-0.14 Na2O-0.24 CaO, with 0.05 mol% TiO2 substitutions for SiO2) to develop glass/ceramic scaffolds for bone augmentation. Glasses were initially characterised using X-ray diffraction (XRD) and particle size analysis, where the starting materials were amorphous with 4.5 μm particles. Hot stage microscopy and high temperature XRD were used to determine the sintering temperature (̃700 °C) and any crystalline phases present in this region (Na2Ca3Si6O16, combeite and quartz). Hardness testing revealed that the Ti-free control (ScC- 2.4 GPa) had a significantly lower hardness than the Ti-containing materials (Sc1 and Sc2 ̃6.6 GPa). Optical microscopy determined pore sizes ranging from 544 to 955 lm. X-ray microtomography calculated porosity from 87 to 93 % and surface area measurements ranging from 2.5 to 3.3 SA/mm3. Cytotoxicity testing (using mesenchymal stem cells) revealed that all materials encouraged cell proliferation, particularly the higher Ti-containing scaffolds over 24-72 h. © Springer Science+Business Media, LLC 2012