Region of the anomalous compression under Bondi-Hoyle accretion

We investigate the properties of an axisymmetric non-magnetized gas flow without angular momentum on a small compact object, in particular, on a Schwarzschild black hole in the supersonic region near the object; the velocity of the object itself is assumed to be low compared to the speed of sound at infinity. First of all, we see that the streamlines intersect (i.e., a caustic forms) on the symmetry axis at a certain distance $r_x$ from the center on the front side if the pressure gradient is neglected. The characteristic radial size of the region, in which the streamlines emerging from the sonic surface at an angle no larger than $\theta_0$ to the axis intersect, is $\Delta r= r_x\theta^2_0/3.$ To refine the flow structure in this region, we numerically compute the system in the adiabatic approximation without ignoring the pressure. We estimate the parameters of the inferred region with anomalously high matter temperature and density accompanied by anomalously high energy release.Comment: 10 pages, 2 figure

Implications of nonlinearity for spherically symmetric accretion

We subject the steady solutions of a spherically symmetric accretion flow to a time-dependent radial perturbation. The equation of the perturbation includes nonlinearity up to any arbitrary order, and bears a form that is very similar to the metric equation of an analogue acoustic black hole. Casting the perturbation as a standing wave on subsonic solutions, and maintaining nonlinearity in it up to the second order, we get the time-dependence of the perturbation in the form of a Li\'enard system. A dynamical systems analysis of the Li\'enard system reveals a saddle point in real time, with the implication that instabilities will develop in the accreting system when the perturbation is extended into the nonlinear regime. The instability of initial subsonic states also adversely affects the temporal evolution of the flow towards a final and stable transonic state.Comment: 14 pages, ReVTeX. Substantially revised with respect to the previous version. Three figures and a new section (Sec. VI) adde

The Life Science Exchange: a case study of a sectoral and sub-sectoral knowledge exchange programme

Background: Local and national governments have implemented sector-specific policies to support economic development through innovation, entrepreneurship and knowledge exchange. Supported by the Welsh Government through the European Regional Development Fund, The Life Science Exchange® project was created with the aim to increase interaction between stakeholders, to develop more effective knowledge exchange mechanisms, and to stimulate the formation and maintenance of long-term collaborative relationships within the Welsh life sciences ecosystem. The Life Science Exchange allowed participants to interact with other stakeholder communities (clinical, academic, business, governmental), exchange perspectives and discover new opportunities.Methods: Six sub-sector focus groups comprising over 200 senior stakeholders from academia, industry, the Welsh Government and National Health Service were established. Over 18 months, each focus group provided input to inform healthcare innovation policy and knowledge mapping exercises of their respective sub-sectors. Collaborative projects identified during the focus groups and stakeholder engagement were further developed through sandpit events and bespoke support.Results: Each sub-sector focus group produced a report outlining the significant strengths and opportunities in their respective areas of focus, made recommendations to overcome any ‘system failures’, and identified the stakeholder groups which needed to take action. A second outcome was a stakeholder-driven knowledge mapping exercise for each area of focus. Finally, the sandpit events and bespoke support resulted in participants generating more than £1.66 million in grant funding and inward investment. This article outlines four separate outcomes from the Life Science Exchange programme.Conclusions: The Life Science Exchange process has resulted in a multitude of collaborations, projects, inward investment opportunities and special interest group formations, in addition to securing over ten times its own costs in funding for Wales. The Life Science Exchange model is a simple and straightforward mechanism for a regional or national government to adapt and implement in order to improve innovation, skills, networks and knowledge exchange

Perturbations on steady spherical accretion in Schwarzschild geometry

The stationary background flow in the spherically symmetric infall of a compressible fluid, coupled to the space-time defined by the static Schwarzschild metric, has been subjected to linearized perturbations. The perturbative procedure is based on the continuity condition and it shows that the coupling of the flow with the geometry of space-time brings about greater stability for the flow, to the extent that the amplitude of the perturbation, treated as a standing wave, decays in time, as opposed to the amplitude remaining constant in the Newtonian limit. In qualitative terms this situation simulates the effect of a dissipative mechanism in the classical Bondi accretion flow, defined in the Newtonian construct of space and time. As a result of this approach it becomes impossible to define an acoustic metric for a conserved spherically symmetric flow, described within the framework of Schwarzschild geometry. In keeping with this view, the perturbation, considered separately as a high-frequency travelling wave, also has its amplitude reduced.Comment: 8 pages, no figur

Evolution of transonicity in an accretion disc

For inviscid, rotational accretion flows driven by a general pseudo-Newtonian potential on to a Schwarzschild black hole, the only possible fixed points are saddle points and centre-type points. For the specific choice of the Newtonian potential, the flow has only two critical points, of which the outer one is a saddle point while the inner one is a centre-type point. A restrictive upper bound is imposed on the admissible range of values of the angular momentum of sub-Keplerian flows through a saddle point. These flows are very unstable to any deviation from a necessarily precise boundary condition. The difficulties against the physical realisability of a solution passing through the saddle point have been addressed through a temporal evolution of the flow, which gives a non-perturbative mechanism for selecting a transonic solution passing through the saddle point. An equation of motion for a real-time perturbation about the stationary flows reveals a very close correspondence with the metric of an acoustic black hole, which is also an indication of the primacy of transonicity.Comment: 18 page

Exploring hypotheses of the actions of TGF-beta 1 in epidermal wound healing using a 3D computational multiscale model of the human epidermis

In vivo and in vitro studies give a paradoxical picture of the actions of the key regulatory factor TGF-beta 1 in epidermal wound healing with it stimulating migration of keratinocytes but also inhibiting their proliferation. To try to reconcile these into an easily visualized 3D model of wound healing amenable for experimentation by cell biologists, a multiscale model of the formation of a 3D skin epithelium was established with TGF-beta 1 literature-derived rule sets and equations embedded within it. At the cellular level, an agent-based bottom-up model that focuses on individual interacting units ( keratinocytes) was used. This was based on literature-derived rules governing keratinocyte behavior and keratinocyte/ECM interactions. The selection of these rule sets is described in detail in this paper. The agent-based model was then linked with a subcellular model of TGF-beta 1 production and its action on keratinocytes simulated with a complex pathway simulator. This multiscale model can be run at a cellular level only or at a combined cellular/subcellular level. It was then initially challenged ( by wounding) to investigate the behavior of keratinocytes in wound healing at the cellular level. To investigate the possible actions of TGF-beta 1, several hypotheses were then explored by deliberately manipulating some of these rule sets at subcellular levels. This exercise readily eliminated some hypotheses and identified a sequence of spatial-temporal actions of TGF-beta 1 for normal successful wound healing in an easy-to-follow 3D model. We suggest this multiscale model offers a valuable, easy-to-visualize aid to our understanding of the actions of this key regulator in wound healing, and provides a model that can now be used to explore pathologies of wound healing

The spatio-relational nature of urban innovation systems: Universities, knowledge intensive business service firms, and collaborative networks

The need to better identify the spatio-relational nature of urban innovation systems and spaces is increasingly acknowledged. The aim of this paper, therefore, is to provide an enhanced understanding of the knowledge networks existing between urban Knowledge Intensive Business Services firms (KIBS) and universities, which are often key components of such systems and spaces. Drawing on an analysis of urban KIBS firms and universities in the UK, it is found that the nature of firms, the location in which they are based, and the research intensity of their university partners are important determinants of the spatiality and localisation of the networks they form. The results show that the smallest urban KIBS firms have the highest propensity to engage in local links with universities, suggesting that they rely most significantly on their own urban innovation system for collaborative network ties. Keywords : innovation systems; urban innovation spaces; knowledge-based development; proximity; networks; KIBS; universities

Knowledge networks and universities : locational and organisational aspects of knowledge transfer interactions

This paper explores the nature of the significant knowledge networks universities form with external organisations through knowledge transfer activities. Focussing on the UK higher education system, the analysis focuses on examining the extent to which organisational and locational characteristics are associated with the nature of these networks, finding that the nature of the networks universities form through knowledge transfer are related to both characteristics. In particular, we find that the institution’s status is important with more established universities are likely to have a more diverse range of organisations with which they interact, as well as a higher number of non-local interactions. In terms of geographic location, we find that universities within lagging regions tend to have more locally focused networks than universities in more leading regions. Overall, the knowledge transfer networking capacity of universities is found to be associated with the regional business environment within which they are situated, with the results going someway to confirming the importance of the role of universities in regional innovation systems, However, it also the case that more established, research focussed, universities are more likely to form part of wider , and possibly even more globalised, knowledge networks. Therefore, both the flow and stock of knowledge within regions is likely to be influenced by the networks formed by its universities, which has implications for both regional innovation capability and regional competitiveness

Importance of amino acid composition to improve skin collagen protein synthesis rates in UV-irradiated mice

Skin collagen metabolism abnormalities induced by ultraviolet (UV) radiation are the major causes of skin photoaging. It has been shown that the one-time exposure of UV irradiation decreases procollagen mRNA expression in dermis and that chronic UV irradiation decreases collagen amounts and induces wrinkle formation. Amino acids are generally known to regulate protein metabolism. Therefore, we investigated the effects of UV irradiation and various orally administered amino acids on skin collagen synthesis rates. Groups of 4–5 male, 8-week-old HR-1 hairless mice were irradiated with UVB (66 mJ/cm2) twice every other day, then fasted for 16 h. The fractional synthesis rate (FSR; %/h) of skin tropocollagen was evaluated by incorporating l-[ring-2H5]-phenylalanine. We confirmed that the FSR of dermal tropocollagen decreased after UVB irradiation. The FSR of dermal tropocollagen was measured 30 min after a single oral administration of amino acids (1 g/kg) to groups of 5–16 UVB-irradiated mice. Branched-chain amino acids (BCAA, 1.34 ± 0.32), arginine (Arg, 1.66 ± 0.39), glutamine (Gln, 1.75 ± 0.60), and proline (Pro, 1.48 ± 0.26) did not increase the FSR of skin tropocollagen compared with distilled water, which was used as a control (1.56 ± 0.30). However, essential amino acids mixtures (BCAA + Arg + Gln, BCAA + Gln, and BCAA + Pro) significantly increased the FSR (2.07 ± 0.58, 2.04 ± 0.54, 2.01 ± 0.50 and 2.07 ± 0.59, respectively). This result suggests that combinations of BCAA and glutamine or proline are important for restoring dermal collagen protein synthesis impaired by UV irradiation

Maize ABP9 enhances tolerance to multiple stresses in transgenic Arabidopsis by modulating ABA signaling and cellular levels of reactive oxygen species

The phytohormone abscisic acid (ABA) and reactive oxygen species (ROS) play critical roles in mediating abiotic stress responses in plants. It is well known that ABA is involved in the modulation of ROS levels by regulating ROS-producing and ROS-scavenging genes, but the molecular mechanisms underlying this regulation are poorly understood. Here we show that the expression of maize ABP9 gene, which encodes a bZIP transcription factor capable of binding to the ABRE2 motif in the maize Cat1 promoter, is induced by ABA, H2O2, drought and salt. Constitutive expression of ABP9 in transgenic Arabidopsis leads to remarkably enhanced tolerance to multiple stresses including drought, high salt, freezing temperature and oxidative stresses. ABP9 expressing Arabidopsis plants also exhibit increased sensitivity to exogenously applied ABA during seed germination, root growth and stomatal closure and improved water-conserving capacity. Moreover, constitutive expression of ABP9 causes reduced cellular levels of ROS, alleviated oxidative damage and reduced cell death, accompanied by elevated expression of many stress/ABA responsive genes including those for scavenging and regulating ROS. Taken together, these results suggest that ABP9 may play a pivotal role in plant tolerance to abiotic stresses by fine tuning ABA signaling and control of ROS accumulation