Lattice Boltzmann method for the fractional advection-diffusion equation

Mass transport, such as movement of phosphorus in soils and solutes in rivers, is a natural phenomenon and its study plays an important role in science and engineering. It is found that there are numerous practical diffusion phenomena that do not obey the classical advection-diffusion equation (ADE). Such diffusion is called abnormal or superdiffusion, and it is well described using a fractional advection-diffusion equation (FADE). The FADE finds a wide range of applications in various areas with great potential for studying complex mass transport in real hydrological systems. However, solution to the FADE is difficult, and the existing numerical methods are complicated and inefficient. In this study, a fresh lattice Boltzmann method is developed for solving the fractional advection-diffusion equation (LabFADE). The FADE is transformed into an equation similar to an advection-diffusion equation and solved using the lattice Boltzmann method. The LabFADE has all the advantages of the conventional lattice Boltzmann method and avoids a complex solution procedure, unlike other existing numerical methods. The method has been validated through simulations of several benchmark tests: a point-source diffusion, a boundary-value problem of steady diffusion, and an initial-boundary-value problem of unsteady diffusion with the coexistence of source and sink terms. In addition, by including the effects of the skewness β, the fractional order α, and the single relaxation time τ, the accuracy and convergence of the method have been assessed. The numerical predictions are compared with the analytical solutions, and they indicate that the method is second-order accurate. The method presented will allow the FADE to be more widely applied to complex mass transport problems in science and engineering.

Deficiencies in education and experience in the management of acute kidney injury among Malawian healthcare workers

BACKGROUND

Acute kidney injury (AKI) is a common but under-recognised disease process, which carries a high risk of mortality or chronic complications, such as chronic kidney disease and other organ dysfunction. Management of AKI, however, is suboptimal, both in developed settings and in Malawi. This is partly because of deficiencies in AKI education and training.

AIM

To establish current levels of AKI education in a range of healthcare workers in Malawi.

METHODS

An AKI symposium was held in Blantyre in March 2015. Delegates were asked to complete a survey at the start of the symposium to assess their clinical experience and education in the management of AKI.

RESULTS

From 100 delegates, 89 nurses, clinical officers, and physicians, originating from 11 different districts, responded to the survey. Twenty-two percent of healthcare workers (including 28% of district workers of the various cadres and 31% of nurses) had never received teaching on any aspect of renal disease, and 50% (including 63% of district workers and 61% of nurses) had never received teaching specifically on AKI. Forty-four percent did not feel confident managing AKI, and 98% wanted more support managing patients with renal disease. Thirty-four percent (including 55% of district workers) were unaware that haemodialysis was available at Queen Elizabeth Central Hospital (QECH) for the treatment of AKI and 53% (74% of district workers) were unaware that peritoneal dialysis was available for the treatment of AKI in children. Only 33% had ever referred a patient with AKI to QECH.

CONCLUSIONS

There are deficiencies in education about, and clinical experience in, the management of AKI among Malawian healthcare workers, in addition to limited awareness of the renal service available at QECH. Urgent action is required to address these issues in order to prevent morbidity and mortality from AKI in Malawi.

Optimal serum cholesterol concentrations are associated with accelerated bone loss in African ancestry men

We tested if serum lipid and lipoprotein cholesterol levels are associated with longitudinal measures of bone mineral density (BMD) in 1289 African ancestry men. After 6 years of mean follow-up, men with clinically optimal levels of low-density lipoprotein (LDL), high-density lipoprotein (HDL), or triglycerides at baseline experienced the greatest BMD loss, independent of potential confounding factors (all p < 0.05).

INTRODUCTION

Studies of lipid and lipoprotein cholesterol associations with bone mineral density (BMD) and bone loss have been inconclusive, and longitudinal data are sparse. Therefore, the aim of this study was to test if fasting serum lipid and lipoprotein cholesterol levels are associated with areal and volumetric BMD and BMD change.

METHODS

We determined the association of serum triglycerides, high-density lipoprotein (HDL), and low-density lipoprotein (LDL) cholesterol concentrations with cross-sectional and longitudinal (mean follow-up, 6.1 years) measures of BMD in a cohort of 1289 in African ancestry men (mean age, 56.4 years). Fasting serum triglycerides, HDL, and LDL were measured at baseline concurrent with BMD assessments. Dual-energy X-ray absorptiometry was used to quantify integral hip BMD, and peripheral quantitative computed tomography at the radius and tibia was used to quantify volumetric BMD. Men were categorized as optimal, borderline, or high risk for triglyceride, HDL, and LDL concentrations based on Adult Treatment Panel III guidelines.

RESULTS

Lower serum triglyceride or LDL and higher HDL concentrations were associated with lower trabecular BMD at baseline (all p < 0.05). Similarly, men classified as having optimal levels of LDL, HDL, or triglycerides at baseline experienced the greatest integral BMD loss at the hip and trabecular BMD loss at the tibia (all p < 0.05), independent of potential confounding factors.

CONCLUSIONS

We found that clinically optimal serum lipid and lipoprotein cholesterol concentrations were associated with accelerated bone loss among Afro-Caribbean men. Further studies are needed to better understand the mechanisms involved and potential clinical significance of these findings.

Changing climate and nutrient transfers: Evidence from high temporal resolution concentration-flow dynamics in headwater catchments

We hypothesise that climate change, together with intensive agricultural systems, will increase the transfer of pollutants from land to water and impact on stream health. This study builds, for the first time, an integrated assessment of nutrient transfers, bringing together a) high-frequency data from the outlets of two surface water-dominated, headwater (~10km(2)) agricultural catchments, b) event-by-event analysis of nutrient transfers, c) concentration duration curves for comparison with EU Water Framework Directive water quality targets, d) event analysis of location-specific, sub-daily rainfall projections (UKCP, 2009), and e) a linear model relating storm rainfall to phosphorus load. These components, in combination, bring innovation and new insight into the estimation of future phosphorus transfers, which was not available from individual components. The data demonstrated two features of particular concern for climate change impacts. Firstly, the bulk of the suspended sediment and total phosphorus (TP) load (greater than 90% and 80% respectively) was transferred during the highest discharge events. The linear model of rainfall-driven TP transfers estimated that, with the projected increase in winter rainfall (+8% to +17% in the catchments by 2050s), annual event loads might increase by around 9% on average, if agricultural practices remain unchanged. Secondly, events following dry periods of several weeks, particularly in summer, were responsible for high concentrations of phosphorus, but relatively low loads. The high concentrations, associated with low flow, could become more frequent or last longer in the future, with a corresponding increase in the length of time that threshold concentrations (e.g. for water quality status) are exceeded. The results suggest that in order to build resilience in stream health and help mitigate potential increases in diffuse agricultural water pollution due to climate change, land management practices should target controllable risk factors, such as soil nutrient status, soil condition and crop cover.

Financial returns on R&D: looking back at history, looking forward to adaptive licensing

Investment in R&D for drugs launched in the late 1970s to early 1990s generated good returns for investors. R&D was inexpensive. Clinical trial success rates were high. Consumption was increasing. Drug prices were outstripping inflation, which raised profit margins. Tax rates were falling. However, returns on R&D have been falling since the early 1990s given rising clinical trial costs, rising trial failure rates, and lower consumption growth in developed markets. Many investors believe that average financial returns on today's R&D will be below the cost of capital, particularly if US drug price inflation moderates. Thus R&D investment by major drug companies is flat or perhaps falling in real terms. Various regulatory initiatives have tried to streamline clinical development and approval. The latest is Adaptive Licensing (AL). The near-term effect of AL on industry-level financial returns will be modest. AL will, however, be salient for decisions to invest in specific trials and may make it easier for smaller companies to fund development. AL could become more important in the long run if it helps shift industry, regulators, and payers from what has been an increasingly linear model of innovation; predicated on the ideas that basic science predicts, trials test predictions, and trial results form a complete description of a drug's attributes. History shows that many drugs become important because doctors and patients discover utility that was not initially apparent to regulators, payers, or investors. One hope for AL, therefore, is that it will bring more acceptably safe chemical diversity into real world use at lower R&D cost.

The local compressibility of liquids near non-adsorbing substrates: a useful measure of solvophobicity and hydrophobicity?

We investigate the suitability of the local compressibility χ(z) as a measure of the solvophobicity or hydrophobicity of a substrate. Defining the local compressibility as the derivative of the local one-body density ρ(z) w.r.t. the chemical potential μ at fixed temperature T, we use density functional theory (DFT) to calculate χ(z) for a model fluid, close to bulk liquid-gas coexistence, at various planar substrates. These range from a 'neutral' substrate with a contact angle of θ≈90°, which favours neither the liquid nor the gas phase, to a very solvophobic, purely repulsive substrate which exhibits complete drying, i.e. θ = 180°. We find that the maximum in the local compressibility χ(z), which occurs within one-two molecular diameters of the substrate, and the integrated quantity χ(ex) (the surface excess compressibility, defined below) both increase rapidly as θ increases and the substrate becomes more solvophobic. χ(z) provides a more pronounced indicator of solvophobicity than the density depletion in the vicinity of the surface which increases only weakly with increasing θ. For the limiting case of drying, θ = 180°, we find lnχ(l) ∼ l, where l is the thickness of the intruding film of gas which diverges in the approach to bulk coexistence μ → μ(co). When the fluid is confined in a parallel slit with two identical solvophobic walls, or with competing solvophobic and solvophilic walls, χ(z) close to the solvophobic wall is altered little from that at the single substrate. We connect our results with simulation studies of water near to hydrophobic surfaces exploring the relationship between χ(z) and fluctuations in the local density and between χ(ex) and the mean-square fluctuation in the number of adsorbed molecules.

Quantitative and qualitative differences in DNA complementary to avian myeloblastosis virus between normal and leukemic chicken cells

Hybridization of avian myeloblastosis virus (AMV) RNA with DNA immobilized on filters or in liquid with a vast DNA excess was used to measure the viral specific DNA sequences in chicken cells. Newly synthesized viral DNA (v-DNA) appears within an hour after infection of chicken embryo fibroblasts (CEF) with avian oncornaviruses. A fraction of newly synthesized v-DNA becomes integrated into the cellular genome and the remainder gradually disappears. A covalent linkage between v-DNA and cellular DNA was demonstrated to exist in CEF and in leukemic myeloblasts by alkaline sucrose velocity sedimentation. Hybridization of AMV RNA in DNA excess has revealed that there are 2 clases of viral specific sequences within normal as well as in leukemic cells. The 2 types of sequences differ in their rate of hybridization. The amount of both types of DNA sequences is about 2 times higher in leukemic cells than in normal cells. Both the fast- and slowly reacting sequences in leukemic cells exhibit a higher Tm (2 degrees C) than the respective DNA sequences in normal cells. Furthermore, when nucleotide sequences in AMV RNA complementary to normal DNA are removed first by exhaustive hybridization with normal DNA, the residual RNA only hybridizes with leukemic DNA but not with normal DNA. These results suggest that leukemic cells contain viral specific DNA sequences which are absent in normal cells. Endogenous v-DNA has been shown to be integrated in cellular DNA region(s) with a reiteration frequency of approximately 1,200 copies per cell and each integration unit appears to have a size approximately equivalent to the 35S RNA subunit of the viral genome. Viral sequences acquired after infection appear to be integrated in the unique region of cell DNA, or in tandem with the endogenous viral sequences.

Upper extremity deep vein thrombosis in a TV cameraman

We report the case of a 40-year-old right-handed man who developed a right subclavian vein thrombosis due to work as a TV cameraman. He presented with a sudden onset of marked swelling and blue discolouration of his right arm 3 weeks after the most strenuous and prolonged episode of TV camera work that he had ever undertaken. This involved carrying a 9kg camera on his shoulder, with his right arm flexed and abducted, for a 60min period with provocation of severe pain and marked discomfort persisting during the subsequent 3 weeks before presentation. A clinical diagnosis of upper extremity deep vein thrombosis (UEDVT) was made, with the diagnosis confirmed by ultrasound. He was treated with catheter-induced thrombolysis and a 3 month course of anticoagulation. He was advised that his UEDVT was caused by his occupation and that he should no longer work as a cameraman. This case shows the importance of identifying any occupational cause of UEDVT.

Liquid-gas asymmetry and the wave-vector-dependent surface tension

Attempts to extend the capillary-wave theory of fluid interfacial fluctuations to microscopic wavelengths, by introducing an effective wave-vector (q)-dependent surface tension σeff(q), have encountered difficulties. There is no consensus as to even the shape of σeff(q). By analyzing a simple density functional model of the liquid-gas interface, we identify different schemes for separating microscopic observables into background and interfacial contributions. In order for the backgrounds of the density-density correlation function and local structure factor to have a consistent and physically meaningful interpretation in terms of weighted bulk gas and liquid contributions, the background of the total structure factor must be characterized by a microscopic q-dependent length ζ(q) not identified previously. The necessity of including the q dependence of ζ(q) is illustrated explicitly in our model and has wider implications; i.e., in typical experimental and simulation studies, an indeterminacy in ζ(q) will always be present, reminiscent of the cutoff used in capillary-wave theory. This leads inevitably to a large uncertainty in the q dependence of σeff(q).