Trapped radiation experiment

Trapped radiation detector on Mariner IV space probe measurement of outer Van Allen belt - feasibility of detecting trapped radiation at Mar

Absence of martian radiation belts and implications thereof

Absence of electrons in Mars atmosphere and implications thereo

Relativistic cross sections of mass stripping and tidal disruption of a star by a super-massive rotating black hole

[abbreviated] We consider the problem of tidal disruption of a star by a super-massive Kerr black hole. Using a numerically fast Lagrangian model of the tidally disrupted star we survey the parameter space of the problem and find the regions in the parameter space where the total disruption of the star or a partial mass loss take place as a result of fly-by around the black hole. Our treatment is based on General Relativity, and we consider the range of the black hole masses where the tidal disruption competes with the relativistic effect of direct capture of the star by the black hole. We find that our results can be represented on the plane of specific orbital angular momenta of the star $(j_{\theta}, j_{\phi})$. We calculate the contours of a given mass loss of the star on this plane, referred to as the tidal cross sections, for a given black hole mass $M$, rotational parameter $a$ and inclination of the trajectory of the star with respect to the black hole equatorial plane. It is shown that the tidal cross sections can be approximated as circles symmetric above the axis $j_{\phi}=0$, and shifted with respect to the origin of the coordinates in direction of negative $j_{\theta}$. The radii and shifts of these circles are obtained numerically for the black hole masses in the range $5\cdot 10^{5}M_{\odot}-10^{9}M_{\odot}$ and different values of $a$. It is shown that when $a=0$ the tidal disruption takes place for $M < 5\cdot 10^{7}M_{\odot}$ and when $a\approx 1$ the tidal disruption is possible for $M < 10^{9}M_{\odot}$.Comment: 11 pages, 16 figures, A&A in press, the text is clarified, the title and the abstract shown in text are change

Detection of the tau protein in human serum by a sensitive four-electrode electrochemical biosensor

This study presents a novel approach based on a four-electrode electrochemical biosensor for the detection of tau protein – one of the possible markers for the prediction of Alzheimer's disease (AD). The biosensor is based on the formation of stable antibody–antigen complexes on gold microband electrodes covered with a layer of a self-assembled monolayer and protein G. Antibodies were immobilized on the gold electrode surface in an optimal orientation by protein G interaction. Electrochemical impedance spectroscopy was used to analyze impedance change, which revealed a linear response with increasing tau concentrations. The assay is fast (<1 h for incubation and measurement) and very sensitive. The limit of quantification for the full-length 2N4R tau protein is 0.03 pM, a value unaltered when the assay was processed in bovine serum albumin or human serum. This technology could be adapted for the detection of other biomarkers to provide a multiple assay to identify AD progression in a point of care setting

Shock waves in tidally compressed stars by massive black holes

We interest in the case of a main-sequence star deeply penetrating within the tidal radius of a massive black hole. We focus on the compression phase leading to a so-called pancake configuration of the star at the instant of maximal compression. The aim is to study the tidal compression process paying particular attention to the development of shock waves;to deduce reliable estimates of the thermodynamical quantities involved in the pancake star; and to solve a controversy about whether or not thermonuclear reactions can be triggered in the core of a tidally compressed star. We have set up a one-dimensional hydrodynamical model well-adapted to the geometry of the problem. Based on the high-resolution shock-capturing Godunov-type approach, it allows to study the compression phase undergone by the star in the direction orthogonal to its orbital plane. We show the existence of two regimes depending on whether shock waves develop before or after the instant of maximal core compression. In both cases we confirm high compression and heating factors in the stellar core able to trigger a thermonuclear explosion. Moreover, we show that the shock waves carry outwards a brief but very high peak of temperature from the centre to the surface of the star. We tentatively conclude that the phenomenon could give rise to hard electromagnetic radiation, to be compared to some X-ray flares already observed in some galactic nuclei harbouring massive black holes. Finally, we estimate that the rate of pancake stars should be about $10^{-5}$ per galaxy per year. If generated in hard X- or $\gamma$-ray band, several events of this kind per year should be detectable within the full observable universe.Comment: 19 pages, 38 figures, 7 tables; v2 : corrected to match version accepted in Astron. Astrophys. Tables and references added, new simulations also performed for adiabatic index 4/

A mixed methods approach to advance the understanding of physical activity behaviour during pregnancy

An active pregnancy encompasses benefits that apply to both mother and baby. However, before investing resources in interventions aimed at changing or supporting expectant mothers’ physical activity behaviours, it is necessary to have a greater fundamental understanding of the modifiable factors influencing women’s decisions during this time. Therefore, the main purpose of this study was to investigate the socio-cognitive determinants of physical activity during pregnancy. A mixed methods research approach using a multiphase design framed by the Theory of Planned Behaviour (TPB; Ajzen, 1991, Organizational Behavior and Human Decision Processes, 50, 179-211) guided the investigation. Following ethical approval and permission to carry out the study, participants were recruited from randomly selected antenatal clinics in the East Kent region of England. Application of the TPB required both qualitative and quantitative cross-sectional data to be collected. Study One (n = 18) involved the elicitation of pregnant women’s beliefs towards being physically active. The modal salient behavioural, normative and control beliefs were used to inform the development of a TPB questionnaire which was implemented during the next phase of the investigation. Study Two (n = 78) examined the predictive utility of the TPB in explaining pregnant women’s physical activity intentions and behaviour and scrutinised the role of past behaviour within this context. Finally, Study Three (n = 10) comprised semi-structured interviews involving community midwives. Meta-inferences maintained the function of improving the validity of the study and advancing the overall aim of the research project. Specifically, triangulation was used to ascertain convergence, corroboration, and correspondence of findings between studies. Whilst results of the individual studies hold merit, meta-inferences point towards the development of three main themes: (1) pregnant women lack access to the necessary information that would allow them to make informed decisions regarding their engagement in physical activities; (2) a co-ordinated effort involving interprofessional collaboration is required to support pregnant women in overcoming barriers associated with regular physical activity participation; and (3) profiling pregnant women according to motivation and behaviour status could serve as a useful and manageable starting point for intervening to produce positive changes in pregnant women’s physical activity behaviour. In normalising physical activity during pregnancy and achieving better health outcomes for mothers and babies, it is necessary to consider the modifiable factors involved in behaviour change, identify opportune moments to intervene, and involve a network of professionals in facilitating and supporting pregnant women’s engagement with physical activities

A new model of a tidally disrupted star

A new semi-analytical model of a star evolving in a tidal field is proposed. The model is a generalization of the so-called 'affine' stellar model. In our model the star is composed of elliptical shells with different parameters and different orientations, depending on time and on the radial Lagrangian coordinate of the shell. The evolution equations of this model are derived from the virial relations under certain assumptions, and the integrals of motion are identified. It is shown that the evolution equations can be deduced from a variational principle. The evolution equations are solved numerically and compared quantitatively with the results of 3D numerical computations of the tidal interaction of a star with a supermassive black hole. The comparison shows very good agreement between the main ``integral'' characteristics describing the tidal interaction event in our model and in the 3D computations. Our model is effectively a one-dimensional Lagrangian model from the point of view of numerical computations, and therefore it can be evolved numerically $10^{2}-10^{3}$ times faster than the 3D approach allows. This makes our model well suited for intensive calculations covering the whole parameter space of the problem.Comment: This version is accepted for publication in ApJ. Stylistic and grammatical changes, new Appendix adde