Effect of biotin antagonists and related substances upon the growth of the coagulase-negative staphylococci

The biotin activity, or anti-biotin properties of a number of substances, wastested on a group of biotin-requiring, coagulase-negative Staphylococcus strains. Of the 18 cultures tested desthiobiotin served as a source of biotin for 17 strains. This substance appeared to be 40 per cent as active as biotin in supporting growth for two of the cultures tested. This substance possessed antibiotin properties for one strain (S19). Homobiotin, one of the chemical homologs of biotin, served as a biotin source for 17 of the 18 strains. Its activity appeared to be less than 0.1 percent of that of biotin among the 8 strains tested. Although it replaced biotin in high concentrations, small quantities appeared to possess anti-biotin properties for one of the Staphylococcus strains. Homobiotin acted as an ariti-biotin substance for strain S36 in all concentrations tested. In contrast 'to studies reported on other biotin-requiring microorganisms, there appeared to be no stoichiometric relationship between biotin and avidin in the nutrition of Staphylococcus, strain H17C. Upon adding increasing increments of egg white to a medium containing a limited amount of biotion, growth was unaffected until a critical concentration of avidin was reached. At this level little or no growth of the microorganism occurred. At higher levels growth again occurred, the amount depending directly upon the level of egg white added. All Staphylococcus cultures tested (18 strains) were able to utilize biocytin in place of biotin. On a molar basis this substance appeared to have an activity equal to that of biotin. Strain S36 failed to grow in a biotin deficient medium to which 0.1 percent Tween 80 was added. All other strains tested were able to grow under these conditions. In comparison with other strains culture H10A appeared to require approximately 100 times as much biotin for growth. This high requirement could be demonstrated in spite of the fact that the culture was able to grow to a limited degree in the absence of added biotin. This culture also demonstrated similar high requirements for biocytin, homobiotion, and desthiobiotin in a biotin free medium.O artigo não apresenta resumo

Respiratory symptoms and cross-shift lung function in relation to cotton dust and endotoxin exposure in textile workers in Nepal: a cross-sectional study

Objectives: Inhalation of a cotton-based particulates has previously been associated with respiratory symptoms and impaired lung function. This study investigates the respiratory health of Nepalese textile workers in relation to dust and endotoxin exposure. Methods: A total of 938 individuals from four sectors (garment, carpet, weaving and recycling) of the textile industry in Kathmandu, Nepal completed a health questionnaire and performed spirometry. A subset (n=384) performed cross-shift spirometry. Personal exposure to inhalable dust and airborne endotoxin was measured during a full shift for 114 workers. Results: The overall prevalence of persistent cough, persistent phlegm, wheeze ever, breathlessness ever and chest tightness ever was 8.5%, 12.5%, 3.2%, 6.5% and 12.3%, respectively. Symptoms were most common among recyclers and least common among garment workers. Exposure to inhalable dust significantly predicted persistent cough and chest tightness. Exposure to endotoxin did not have any independent predictive effect. Significant cross-shift reduction in forced expiratory volume in 1 s (FEV1) and forced vital capacity (FVC) were found (p<0.001 for both) being largest for FEV1 in the recyclers (−143 mL), and least in the garment workers (−38 mL; p=0.012). Exposure to inhalable dust predicted a cross-shift reduction in FEV1. Conclusions: This study is the first to investigate the respiratory health of Nepalese cotton workers. The measured association between inhalable dust exposure and reporting of respiratory symptoms and across-shift decrement in FEV1 and FVC indicates that improved dust control measures should be instituted, particularly in the recycling and carpet sectors. The possible role of other biologically active agents of cotton dust beyond endotoxin should be further explored

Effect of dynamic stall on the aerodynamics of vertical-axis wind turbines

Accurate simulations of the aerodynamic performance of vertical-axis wind turbines pose a significant challenge for computational fluid dynamics methods. The aerodynamic interaction between the blades of the rotor and the wake that is produced by the blades requires a high-fidelity representation of the convection of vorticity within the wake. In addition, the cyclic motion of the blades induces large variations in the angle of attack on the blades that can manifest as dynamic stall. The present paper describes the application of a numerical model that is based on the vorticity transport formulation of the Navier–Stokes equations, to the prediction of the aerodynamics of a verticalaxis wind turbine that consists of three curved rotor blades that are twisted helically around the rotational axis of the rotor. The predicted variation of the power coefficient with tip speed ratio compares very favorably with experimental measurements. It is demonstrated that helical blade twist reduces the oscillation of the power coefficient that is an inherent feature of turbines with non-twisted blade configurations

Approach to a rational rotation number in a piecewise isometric system

We study a parametric family of piecewise rotations of the torus, in the limit in which the rotation number approaches the rational value 1/4. There is a region of positive measure where the discontinuity set becomes dense in the limit; we prove that in this region the area occupied by stable periodic orbits remains positive. The main device is the construction of an induced map on a domain with vanishing measure; this map is the product of two involutions, and each involution preserves all its atoms. Dynamically, the composition of these involutions represents linking together two sector maps; this dynamical system features an orderly array of stable periodic orbits having a smooth parameter dependence, plus irregular contributions which become negligible in the limit.Comment: LaTeX, 57 pages with 13 figure

Regular Moebius transformations of the space of quaternions

Let H be the real algebra of quaternions. The notion of regular function of a quaternionic variable recently presented by G. Gentili and D. C. Struppa developed into a quite rich theory. Several properties of regular quaternionic functions are analogous to those of holomorphic functions of one complex variable, although the diversity of the quaternionic setting introduces new phenomena. This paper studies regular quaternionic transformations. We first find a quaternionic analog to the Casorati-Weierstrass theorem and prove that all regular injective functions from H to itself are affine. In particular, the group Aut(H) of biregular functions on H coincides with the group of regular affine transformations. Inspired by the classical quaternionic linear fractional transformations, we define the regular fractional transformations. We then show that each regular injective function from the Alexandroff compactification of H to itself is a regular fractional transformation. Finally, we study regular Moebius transformations, which map the unit ball B onto itself. All regular bijections from B to itself prove to be regular Moebius transformations.Comment: 12 page

Comparison of Langevin and Markov channel noise models for neuronal signal generation

The stochastic opening and closing of voltage-gated ion channels produces noise in neurons. The effect of this noise on the neuronal performance has been modelled using either approximate or Langevin model, based on stochastic differential equations or an exact model, based on a Markov process model of channel gating. Yet whether the Langevin model accurately reproduces the channel noise produced by the Markov model remains unclear. Here we present a comparison between Langevin and Markov models of channel noise in neurons using single compartment Hodgkin-Huxley models containing either $Na^{+}$ and $K^{+}$, or only $K^{+}$ voltage-gated ion channels. The performance of the Langevin and Markov models was quantified over a range of stimulus statistics, membrane areas and channel numbers. We find that in comparison to the Markov model, the Langevin model underestimates the noise contributed by voltage-gated ion channels, overestimating information rates for both spiking and non-spiking membranes. Even with increasing numbers of channels the difference between the two models persists. This suggests that the Langevin model may not be suitable for accurately simulating channel noise in neurons, even in simulations with large numbers of ion channels

Quenching across quantum critical points in periodic systems: dependence of scaling laws on periodicity

We study the quenching dynamics of a many-body system in one dimension described by a Hamiltonian that has spatial periodicity. Specifically, we consider a spin-1/2 chain with equal xx and yy couplings and subject to a periodically varying magnetic field in the z direction or, equivalently, a tight-binding model of spinless fermions with a periodic local chemical potential, having period 2q, where q is a natural number. For a linear quench of the magnetic field strength (or potential strength) at rate 1/\tau across a quantum critical point, we find that the density of defects thereby produced scales as 1/\tau^{q/(q+1)}, deviating from the 1/\sqrt{\tau} scaling that is ubiquitous to a range of systems. We analyze this behavior by mapping the low-energy physics of the system to a set of fermionic two-level systems labeled by the lattice momentum k undergoing a non-linear quench as well as by performing numerical simulations. We also find that if the magnetic field is a superposition of different periods, the power law depends only on the smallest period for very large values of \tau although it may exhibit a cross-over at intermediate values of \tau. Finally, for the case where a zz coupling is also present in the spin chain, or equivalently, where interactions are present in the fermionic system, we argue that the power associated with the scaling law depends on a combination of q and interaction strength.Comment: 13 pages including 11 figure

Consequences of converting graded to action potentials upon neural information coding and energy efficiency

Information is encoded in neural circuits using both graded and action potentials, converting between them within single neurons and successive processing layers. This conversion is accompanied by information loss and a drop in energy efficiency. We investigate the biophysical causes of this loss of information and efficiency by comparing spiking neuron models, containing stochastic voltage-gated Na+ and K+ channels, with generator potential and graded potential models lacking voltage-gated Na+ channels. We identify three causes of information loss in the generator potential that are the by-product of action potential generation: (1) the voltage-gated Na+ channels necessary for action potential generation increase intrinsic noise and (2) introduce non-linearities, and (3) the finite duration of the action potential creates a ‘footprint’ in the generator potential that obscures incoming signals. These three processes reduce information rates by ~50% in generator potentials, to ~3 times that of spike trains. Both generator potentials and graded potentials consume almost an order of magnitude less energy per second than spike trains. Because of the lower information rates of generator potentials they are substantially less energy efficient than graded potentials. However, both are an order of magnitude more efficient than spike trains due to the higher energy costs and low information content of spikes, emphasizing that there is a two-fold cost of converting analogue to digital; information loss and cost inflation

Social physique anxiety and physical activity in early adolescent girls : the influence of maturation and physical activity motives

This study considered the influence of maturation on social physique anxiety (SPA), the relationship between SPA and current and future physical activity (PA) levels and the influence of motives for physical activity on this relationship in early adolescent girls (n=162; mean age=11.80±0.33 years). Participants completed the Pubertal Development Scale, the modified Social Physique Anxiety Scale and the Motives for Physical Activity Scale at baseline and the Physical Activity Questionnaire for Older Children at baseline and 6 months later. The girls became less active across the 6 months and girls in the early stages of maturation had significantly lower SPA than the girls in the middle and late stages of maturation. SPA was not related to current or future physical activity in the sample as a whole. Cluster analysis identified four groups with different motive profiles and the High Appearance and Fitness group demonstrated a moderate negative relationship between SPA and PA at phase 1, whereas the other groups did not. These findings indicate that SPA may increase with maturation and the relationship between SPA and PA is dependent on reasons for being active. For girls who are motivated to be active primarily by body-related reasons SPA is likely to lead to lower levels of PA

Healthier prisons: The role of a prison visitors' centre

Since the inception of the prison as a ‘setting’ for health promotion, there has been a focus on how the health of those men and women who spend ‘time inside’ can at least be maintained and if possible, enhanced, during their prison sentence. This paper presents findings from a mainly qualitative evaluation of a prison visitors' centre in the UK. It reports experiences of prisoners' families, prisoners, prison staff, the local community and the ways in which the visitors' centre has contributed positively to their health and well-being. In addition, key stakeholders were interviewed to ascertain the role this visitors' centre has in policy frameworks related to re-offending. The findings from this evaluation underscore how the visitors' centre improved the quality of visits, and contributed towards the maintenance of family ties through the help and support it provides for families and prisoners. The paper concludes by suggesting that visitors' centres are an essential part of a modern prison service helping to address the government's health inequalities agenda