Fluid transport at low Reynolds number with magnetically actuated artificial cilia

By numerical modeling we investigate fluid transport in low-Reynolds-number flow achieved with a special elastic filament or artifical cilium attached to a planar surface. The filament is made of superparamagnetic particles linked together by DNA double strands. An external magnetic field induces dipolar interactions between the beads of the filament which provides a convenient way of actuating the cilium in a well-controlled manner. The filament has recently been used to successfully construct the first artificial micro-swimmer [R. Dreyfus at al., Nature 437, 862 (2005)]. In our numerical study we introduce a measure, which we call pumping performance, to quantify the fluid transport induced by the magnetically actuated cilium and identify an optimum stroke pattern of the filament. It consists of a slow transport stroke and a fast recovery stroke. Our detailed parameter study also reveals that for sufficiently large magnetic fields the artificial cilium is mainly governed by the Mason number that compares frictional to magnetic forces. Initial studies on multi-cilia systems show that the pumping performance is very sensitive to the imposed phase lag between neighboring cilia, i.e., to the details of the initiated metachronal wave.Comment: 12 pages, 10 figures. To appear in EPJE, available online at http://dx.doi.org/10.1140/epje/i2008-10388-

Factors Associated with Revision Surgery after Internal Fixation of Hip Fractures

Background: Femoral neck fractures are associated with high rates of revision surgery after management with internal fixation. Using data from the Fixation using Alternative Implants for the Treatment of Hip fractures (FAITH) trial evaluating methods of internal fixation in patients with femoral neck fractures, we investigated associations between baseline and surgical factors and the need for revision surgery to promote healing, relieve pain, treat infection or improve function over 24 months postsurgery. Additionally, we investigated factors associated with (1) hardware removal and (2) implant exchange from cancellous screws (CS) or sliding hip screw (SHS) to total hip arthroplasty, hemiarthroplasty, or another internal fixation device. Methods: We identified 15 potential factors a priori that may be associated with revision surgery, 7 with hardware removal, and 14 with implant exchange. We used multivariable Cox proportional hazards analyses in our investigation. Results: Factors associated with increased risk of revision surgery included: female sex, [hazard ratio (HR) 1.79, 95% confidence interval (CI) 1.25-2.50; P = 0.001], higher body mass index (fo

Green and brown manures in dryland wheat production systems in Mediterranean-Type environments

In this review, we draw together research on the use of green and brown manures in wheat cropping systems in Mediterranean-type environments in the light of contemporary pressures on cropping systems including changing climates, increasing costs and declining profit margins.Green and brown manuring have been demonstrated to have benefits in terms of weed control, delaying the development of resistance to herbicides, reducing populations of disease organisms, altering soil water, soil quality and biology, erosion control, and contributing to the nutrition of subsequent crops. However, few researchers have attempted to measure more than one of these variables, which presents difficulties in both interpreting the causes behind results of field trials and in estimating the total benefit of manuring, and hence its consequences for profitability.Well-designed experiments have been reported on component mechanisms (such as weed numbers or N 2 fixation). However, these experiments are often not taken through to maturity of the crop following the manuring treatment. As a result, there is limited yield and grain quality data on which to base sound analyses of profitability. A few reports are available which present the impact of manuring on wheat yield and profitability in specific areas and systems but the results vary widely. For such reports to be of value, further research is needed into the factors inducing the changes in response (climate, soil type, or the specifics of the farming system at the time the treatments are imposed) and the mechanisms by which these act. Thus, research is needed into both the mechanisms and yield benefits that flow from the individual responses to manuring.Two further limitations to determining the economic benefit of manuring emerge. Firstly, impacts are primarily reported for a single year after a single manuring treatment. However, if measurements are made over a number of years, effects can often still be detected. More studies aimed to assess the longer-term impacts of manuring on soil health, disease prevalence, and weed populations are required. Secondly, there has been very little effort to explore the whole-farm impact of using manures. These impacts could include effects on other farm enterprises as well as business-level impacts such as potential changes in labor requirements, cash flow, and risk.The incorporation of manuring into wheat production systems may have multiple on-farm and off-farm benefits. However, there is a substantial research requirement before these approaches could be recommended. The highest priority is a sound demonstration of short- to medium-term economic benefits to growers. Without this, adoption can be expected to be poor

Spatial organization, group living and ecological correlates in low-density populations of Eurasian badgers, Meles meles

1. Territoriality and group living are described in a low-density population of Eurasian badgers, Meles meles L., by studying the patterns of spatial grouping and territory marking, as well as the differences between individuals in some of their characteristics (body condition and dispersal) and in their space use (seasonally, periods of activity and interaction between pairs of individuals) under strong seasonal fluctuations in the availability of the key resource ( young rabbits, Oryctolagus cuniculus L.). Finally, the role of the spatial distribution of the main prey ( young rabbits) in the development of sociality was also studied in order to test some of the assumptions and predictions of the resource dispersion hypothesis (RDH). 2. Badgers were territorial, showing a flexible system of territory marking, which includes the marking of the most used areas (sett-latrines at the centres of activity) and additionally, at the smaller territories, a system of border-latrines in the areas of contact between territories. The maximum use of border-latrines was associated with the reproductive season, and that of sett-latrines with the season of food scarcity. 3. In the study area where badgers had rabbits as main prey, territories were occupied by small groups of animals, formed by one adult female who reproduced, one adult male who also showed signs of reproductive activity, the cubs of the year (if there was reproduction) and some animals born during previous years, which remained in their natal territory until their dispersal (normally during the mating season of their third or fourth year of life). This system was not strictly fixed as males, given the opportunity, expanded their territories to encompass additional females. Territories in another study site were occupied by one adult female (marked), plus the cubs of the year and another adult individual (unmarked). 4. In winter and spring dominant females and subordinates used only a small fraction of their territories, moved short distances, at a low speed and covering small areas per night. These seasons corresponded with the reproduction of rabbits (highest food availability). Dominant females were the only individuals using all the territory available in the summer (lowest food availability), when badgers had the worst body condition. Food availability increased again in autumn, as did body condition, while range sizes were again reduced. Dominant males used the same proportion of their territories over all seasons. However, in winter (reproductive season) they moved faster, over longer distances, and covered larger areas per period of activity. These results indicate that use of space by dominant males was affected by different factors from that of dominant females and subordinates. 5. RDH does not seem to explain group living in our populations because: (a) territori- ality in each pair of primary animals was driven by different factors (trophic resources for females and females for males); (b) dominant males acted as expansionists; and (c) territory size was related to its richness and not to patch dispersion.6. We propose an integrative hypothesis to explain not only group formation but also interpopulation variability in the social organization of badgers within ecological, demographic and behavioural constraints and in the light of current theory on delayed dispersalPeer reviewe

Global and local genetic diversity at two microsatellite loci in Plasmodium vivax parasites from Asia, Africa and South America

Background: Even though Plasmodium vivax has the widest worldwide distribution of the human malaria species and imposes a serious impact on global public health, the investigation of genetic diversity in this species has been limited in comparison to Plasmodium falciparum. Markers of genetic diversity are vital to the evaluation of drug and vaccine efficacy, tracking of P. vivax outbreaks, and assessing geographical differentiation between parasite populations._x000D_ Methods: The genetic diversity of eight P. vivax populations (n = 543) was investigated by using two microsatellites (MS), m1501 and m3502, chosen because of their seven and eight base-pair (bp) repeat lengths, respectively. These were compared with published data of the same loci from six other P. vivax populations._x000D_ Results: In total, 1,440 P. vivax samples from 14 countries on three continents were compared. There was highest heterozygosity within Asian populations, where expected heterozygosity (He) was 0.92-0.98, and alleles with a high repeat number were more common. Pairwise FST revealed significant differentiation between most P. vivax populations, with the highest divergence found between Asian and South American populations, yet the majority of the diversity (~89%) was found to exist within rather than between populations._x000D_ Conclusions: The MS markers used were informative in both global and local P. vivax population comparisons and their seven and eight bp repeat length facilitated population comparison using data from independent studies. A complex spatial pattern of MS polymorphisms among global P. vivax populations was observed which has potential utility in future epidemiological studies of the P. vivax parasite

Multiple origins of mutations in the mdr1 gene—a putative marker of chloroquine resistance in P. vivax

Background Chloroquine combined with primaquine has been the ecommended antimalarial treatment of Plasmodium vivax malaria infections for six decades but the efficacy of this treatment regimen is threatened by chloroquine resistance (CQR). Single nucleotide polymorphisms (SNPs) in the multidrug resistance gene, Pvmdr1 are putative determinants of CQR but the extent of their emergence at population level remains to be explored. Objective In this study we describe the prevalence of SNPs in the Pvmdr1 among samples collected in seven P. vivax endemic countries and we looked for molecular evidence of drug selection by characterising polymorphism at microsatellite (MS) loci flanking the Pvmdr1 gene. Methods We examined the prevalence of SNPs in the Pvmdr1 gene among 267 samples collected from Pakistan, Afghanistan, Sri Lanka, Nepal, Sudan, Sao Tome and Ecuador. We measured and diversity in four microsatellite (MS) markers flanking the Pvmdr1 gene to look evidence of selection on mutant alleles. Results SNP polymorphism in the Pvmdr1 gene was largely confined to codons T958M, Y976F and F1076L. Only 2.4% of samples were wildtype at all three codons (TYF, n = 5), 13.3% (n =28) of the samples were single mutant MYF, 63.0% of samples (n = 133) were double mutant MYL, and 21.3%(n = 45) were triple mutant MFL. Clear geographic differences in the prevalence of these Pvmdr mutation combinations were observed. Significant linkage disequilibrium (LD) between Pvmdr1 and MS alleles was found in populations sampled in Ecuador, Nepal and Sri Lanka, while significant LD between Pvmdr1 and the combined 4 MS locus haplotype was only seen in Ecuador and Sri Lanka. When combining the 5 loci, high level diversity, measured as expected heterozygosity (He), was seen in the complete sample set (He = 0.99), while He estimates for individual loci ranged from 0.00–0.93. Although Pvmdr1 haplotypes were not consistently associated with specific flanking MS alleles, there was significant differentiation between geographic sites which could indicate directional selection through local drug pressure. Conclusions Our observations suggest that Pvmdr1 mutations emerged independently on multiple occasions even within the same population. In Sri Lanka population analysis at multiple sites showed evidence of local selection and geographical dispersal of Pvmdr1 mutations between sites

Global genetic diversity of var2csa in Plasmodium falciparum with implications for malaria in pregnancy and vaccine development

10.1038/s41598-018-33767-3Scientific Reports811542