The auxiliary region method: A hybrid method for coupling PDE- and Brownian-based dynamics for reaction-diffusion systems

Reaction-diffusion systems are used to represent many biological and physical phenomena. They model the random motion of particles (diffusion) and interactions between them (reactions). Such systems can be modelled at multiple scales with varying degrees of accuracy and computational efficiency. When representing genuinely multiscale phenomena, fine-scale models can be prohibitively expensive, whereas coarser models, although cheaper, often lack sufficient detail to accurately represent the phenomenon at hand. Spatial hybrid methods couple two or more of these representations in order to improve efficiency without compromising accuracy. In this paper, we present a novel spatial hybrid method, which we call the auxiliary region method (ARM), which couples PDE and Brownian-based representations of reaction-diffusion systems. Numerical PDE solutions on one side of an interface are coupled to Brownian-based dynamics on the other side using compartment-based "auxiliary regions". We demonstrate that the hybrid method is able to simulate reaction-diffusion dynamics for a number of different test problems with high accuracy. Further, we undertake error analysis on the ARM which demonstrates that it is robust to changes in the free parameters in the model, where previous coupling algorithms are not. In particular, we envisage that the method will be applicable for a wide range of spatial multi-scales problems including, filopodial dynamics, intracellular signalling, embryogenesis and travelling wave phenomena.Comment: 29 pages, 14 figures, 2 table

What Will it Take to Make Solar Panels Cool?

With the predicted results of climate change looming, humanity must do all it can to limit greenhouse gas emissions. Maintaining a habitable environment along with the high quality of living associated with developed nations requires investment in renewable energy. Because national governments often fail to make responsible decisions for their country\u27s future, this burden falls to institutions like UMass Amherst. Although costly investments like solar panels substantially improve the sustainability of campus, some innovative improvements of existing solar energy infrastructure can go a long way. For example, when solar panels heat up they lose photovoltaic efficiency. We propose that UMass institute cooling systems on current and future solar panel structures. This may sound extravagant, but in this paper we outline a plan for a simple and affordable cooling system that can be constructed from supplies bought at a local hardware store. The University spent approximately $1.5 million dollars on the new solar canopy atop the Robsham’s Visitor Center. This structure generates an estimated$40,000 worth of electricity each year, with a 38 year return on investment. We expect a cooling system for each canopy to cost around $500 and to improve power output by more than 10 percent. This means that by the most conservative estimate, a$500 investment will generate an additional $4,000 worth of electricity, reducing the return on investment time by 4 years. Compared with the initial solar canopy investment, this magnitude of electricity generation would have cost$150,000. By comparison, $500 is peanuts. Read on to see how a little ingenuity can go a long way to save money and the environment

The effects of inclination, gravity darkening and differential rotation on absorption profiles of fast rotators

Mechanisms influencing absorption line profiles of fast rotating stars can be sorted into two groups; (i) intrinsic variations sensitive to temperature and pressure, and (ii) global effects common to all spectral lines. I present a detailed study on the latter effects focusing on gravity darkening and inclination for various rotational velocities and spectral types. It is shown that the line shapes of rapidly and rigidly rotating stars mainly depend on the equatorial velocity $v_{\rm e}$, not on the projected rotational velocity $v \sin{i}$ which determines the lines width. The influence of gravity darkening and spectral type on the line profiles is shown. The results demonstrate the possibility of determining the inclination angle $i$ of single fast rotators, and they show that constraints on gravity darkening can be drawn for stellar samples. While significant line profile deformation occurs in stars rotating as fast as v_{\rm e} \ga 200 km s$^{-1}$, for slower rotators profile distortion are marginal. In these cases spectral signatures induced by, e.g., differential rotation are not affected by gravity darkening and the methods applicable to slow rotators can be applied to these faster rotators, too.Comment: 7 pages, accepted by A&

The COOH-terminal domain of agrin signals via a synaptic receptor in central nervous system neurons

Agrin is a motor neuron–derived factor that directs formation of the postsynaptic apparatus of the neuromuscular junction. Agrin is also expressed in the brain, raising the possibility that it might serve a related function at neuron–neuron synapses. Previously, we identified an agrin signaling pathway in central nervous system (CNS) neurons, establishing the existence of a neural receptor that mediates responses to agrin. As a step toward identifying this agrin receptor, we have characterized the minimal domains in agrin that bind and activate it. Structures required for agrin signaling in CNS neurons are contained within a 20-kD COOH-terminal fragment of the protein. Agrin signaling is independent of alternative splicing at the z site, but requires sequences that flank it because their deletion results in a 15-kD fragment that acts as an agrin antagonist. Thus, distinct regions within agrin are responsible for receptor binding and activation. Using the minimal agrin fragments as affinity probes, we also studied the expression of the agrin receptor on CNS neurons. Our results show that both agrin and its receptor are concentrated at neuron–neuron synapses. These data support the hypothesis that agrin plays a role in formation and/or function of CNS synapses

An Improved Method for Estimating the Masses of Stars with Transiting Planets

To determine the physical parameters of a transiting planet and its host star from photometric and spectroscopic analysis, it is essential to independently measure the stellar mass. This is often achieved by the use of evolutionary tracks and isochrones, but the mass result is only as reliable as the models used. The recent paper by Torres et al (2009) showed that accurate values for stellar masses and radii could be obtained from a calibration using T_eff, log g and [Fe/H]. We investigate whether a similarly good calibration can be obtained by substituting log rho - the fundamental parameter measured for the host star of a transiting planet - for log g, and apply this to star-exoplanet systems. We perform a polynomial fit to stellar binary data provided in Torres et al (2009) to obtain the stellar mass and radius as functions of T_eff, log rho and [Fe/H], with uncertainties on the fit produced from a Monte Carlo analysis. We apply the resulting equations to measurements for seventeen SuperWASP host stars, and also demonstrate the application of the calibration in a Markov Chain Monte Carlo analysis to obtain accurate system parameters where spectroscopic estimates of effective stellar temperature and metallicity are available. We show that the calibration using log rho produces accurate values for the stellar masses and radii; we obtain masses and radii of the SuperWASP stars in good agreement with isochrone analysis results. We ascertain that the mass calibration is robust against uncertainties resulting from poor photometry, although a good estimate of stellar radius requires good-quality transit light curve to determine the duration of ingress and egress.Comment: 5 pages, 2 figures, accepted for publication in A&

JAK/STAT signaling and human in vitro myogenesis

<p>Abstract</p> <p>Background</p> <p>A population of satellite cells exists in skeletal muscle. These cells are thought to be primarily responsible for postnatal muscle growth and injury-induced muscle regeneration. The Janus kinase/signal transducers and activators of transcription (JAK/STAT) signaling cascade has a crucial role in regulating myogenesis. In rodent skeletal muscle, STAT3 is essential for satellite cell migration and myogenic differentiation, regulating the expression of myogenic factors. The aim of the present study was to investigate and compare the expression profile of JAK/STAT family members, using cultured primary human skeletal muscle cells.</p> <p>Results</p> <p>Near confluent proliferating myoblasts were induced to differentiate for 1, 5 or 10 days. During these developmental stages, members of the JAK/STAT family were examined, along with factors known to regulate myogenesis. We demonstrate the phosphorylation of JAK1 and STAT1 only during myoblast proliferation, while JAK2 and STAT3 phosphorylation increases during differentiation. These increases were correlated with the upregulation of genes associated with muscle maturation and hypertrophy.</p> <p>Conclusions</p> <p>Taken together, these results provide insight into JAK/STAT signaling in human skeletal muscle development, and confirm recent observations in rodents.</p

“There isn't anybody else like me around here”: the insider-outsider status of LGBT residents in housing with care schemes for older people

The intersections between aging, social minority status and housing needs in later life is a neglected area of sociological exploration, even more so for older people who identify as lesbian, gay, bisexual and trans (LGBT). Recent sociological findings indicate that older LGBT people in housing schemes stress the importance of bonding social capital and look to other people in their social networks who reflect their identities and experiences as sources of support. In this paper, we examine the insider-outsider status occupied by older LGBT residents living in housing schemes that provide some form of care and support, for example extra care and independent living schemes. We present qualitative findings generated from a mixed-methods study of social inclusion practices in housing with care in England and Wales (UK) (2019-22). In this study 15 LGBT residents participated in semi-structured interviews (55–79 years of age) across a total of 31 interviews. Through a queer gerontological lens we examine how older LGBT people are socially situated within mainstream housing schemes in which they experience partial visibility while also encountering exclusionary pressures that locate them as “the other.” This insider-outsider status undermines the premise of housing with care schemes to provide safe, secure spaces to grow old. We discuss three core themes: (1) how LGBT residents navigate their outsider status in scheme life and how the intersection of disability and minority status amplifies this social location; (2) the exclusionary practices exercised by other residents that reinforce boundaries of sexual and gender normalcy; and, (3) the heightened importance of maintaining external social connections among LGBT residents. We conclude by introducing an alternative notion of marginal aging and expanding on the implications for housing providers, reflecting on their responsibilities for promoting and maintaining queer-friendly environments

Vasa Nervorum in rat major pelvic ganglion are innervated by nitrergic nerve fibers

INTRODUCTION The vasa nervorum comprises a network of small diameter blood vessels that provide blood supply to nerves and ganglia. The cell bodies of autonomic nerves innervating the urogenital organs are housed in the major pelvic ganglia (MPG) in rats. The vasa nervorum of rat MPG have not been characterized previously, and it is not known whether these blood vessels are innervated by neuronal nitric oxide synthase (nNOS) containing nitrergic nerves. AIM To characterize the blood vessels in and around the rat MPG and to assess their nitrergic innervation. MAIN OUTCOME MEASURES Characterization of small blood vessels in and around the rat MPG and expression of nNOS in nerve fibers around those blood vessels. METHODS MPG were obtained from healthy Sprague Dawley rats, fixed in paraformaldehyde, frozen and sectioned using a cryostat. The blood vessels and their nitrergic innervation were assessed with immunohistochemistry using antibodies against alpha-smooth muscle actin (smooth muscle marker), CD31 (endothelial marker), collagen IV (basal membrane marker) and nNOS. The immunofluorescence was imaged using a laser scanning confocal microscope. RESULTS The neuronal cell bodies were contained within a capsule in the MPG. Blood vessels were observed within the capsule of the MPG as well as outside the capsule. The blood vessels inside the capsule were CD31-positive capillaries with no smooth muscle staining. Outside the capsule capillaries, arterioles and venules were observed. The extra-capsular arterioles and venules, but not the capillaries were innervated by nNOS-positive nerve fibers. CONCLUSIONS This study, to our knowledge, is the first to demonstrate the blood vessel distribution pattern and their nitrergic innervation in the rat MPG. While similar studies in human pelvic plexus are warranted, these results suggest that the blood flow in the MPG may be regulated by nitrergic nerve fibers and reveal a reciprocal relationship between nerves and blood vessels. Beetson KA, Smith SF, Muneer A, Cameron NE, Cotter MA, and Cellek S. Vasa nervorum in rat major pelvic ganglion are innervated by nitrergic nerve fibers. J Sex Med **;**:**-**