Showing papers by "University of St Andrews published in 2002"

Histone-deacetylase inhibitors: novel drugs for the treatment of cancer

Abstract: The opposing actions of histone acetyltransferases (HATs) and histone deacetylases (HDACs) allow gene expression to be exquisitely regulated through chromatin remodelling. Aberrant transcription due to altered expression or mutation of genes that encode HATs, HDACs or their binding partners, is a key event in the onset and progression of cancer. HDAC inhibitors can reactivate gene expression and inhibit the growth and survival of tumour cells. The remarkable tumour specificity of these compounds, and their potency in vitro and in vivo, underscore the potential of HDAC inhibitors as exciting new agents for the treatment of cancer.

Simultaneous micromanipulation in multiple planes using a self-reconstructing light beam

Abstract: Optical tweezers1 are commonly used for manipulating microscopic particles, with applications in cell manipulation2, colloid research3,4,5, manipulation of micromachines6 and studies of the properties of light beams7. Such tweezers work by the transfer of momentum from a tightly focused laser to the particle, which refracts and scatters the light and distorts the profile of the beam. The forces produced by this process cause the particle to be trapped near the beam focus. Conventional tweezers use gaussian light beams, which cannot trap particles in multiple locations more than a few micrometres apart in the axial direction, because of beam distortion by the particle and subsequent strong divergence from the focal plane. Bessel beams8,9, however, do not diverge and, furthermore, if part of the beam is obstructed or distorted the beam reconstructs itself after a characteristic propagation distance10. Here we show how this reconstructive property may be utilized within optical tweezers to trap particles in multiple, spatially separated sample cells with a single beam. Owing to the diffractionless nature of the Bessel beam, secondary trapped particles can reside in a second sample cell far removed (∼3 mm) from the first cell. Such tweezers could be used for the simultaneous study of identically prepared ensembles of colloids and biological matter, and potentially offer enhanced control of ‘lab-on-a-chip’ and optically driven microstructures.

The magnetic nature of solar flares

Abstract: The main challenge for the theory of solar eruptions has been to understand two basic aspects of large flares. These are the cause of the flare itself and the nature of the morphological features which form during its evolution. Such features include separating ribbons of H $\alpha$ emission joined by a rising arcade of soft x-ray loops, with hard x-ray emission at their summits and at their feet. Two major advances in our understanding of the theory of solar flares have recently occurred. The first is the realisation that a magnetohydrodynamic (MHD) catastrophe is probably responsible for the basic eruption and the second is that the eruption is likely to drive a reconnection process in the field lines stretched out by the eruption. The reconnection is responsible for the ribbons and the set of rising soft x-ray loops, and such a process is well supported by numerical experiments and detailed observations from the Japanese satellite Yohkoh. Magnetic energy conversion by reconnection in two dimensions is relatively well understood, but in three dimensions we are only starting to understand the complexity of the magnetic topology and the MHD dynamics which are involved. How the dynamics lead to particle acceleration is even less well understood. Particle acceleration in flares may in principle occur in a variety of ways, such as stochastic acceleration by MHD turbulence, acceleration by direct electric fields at the reconnection site, or diffusive shock acceleration at the different kinds of MHD shock waves that are produced during the flare. However, which of these processes is most important for producing the energetic particles that strike the solar surface remains a mystery.

Application of the Theory of Planned Behaviour in Behaviour Change Interventions: A Systematic Review

Abstract: This paper reviews studies explicitly applying the Theory of Planned Behaviour (TPB) to behaviour change interventions. A systematic and multiple search strategy identified 30 papers, describing 24 distinct interventions. Studies were rarely explicit about use of the TPB. The TPB was mainly used to measure process and outcome variables and to predict intention and behaviour, and less commonly to develop the intervention. Behaviour change methods were mostly persuasion and information, with increasing skills, goal setting, and rehearsal of skills used less often. When reported, half of the interventions were effective in changing intention, and two-thirds in changing behaviour, with generally small effect sizes, where calculable. Effectiveness was unrelated to use of the theory to develop interventions. Evidence about mediation of effects by TPB components was sparse. The TPB may have potential for developing behaviour change interventions, but more comprehensive studies are needed that compare the utility...

The 2dF Galaxy Redshift Survey: The environmental dependence of galaxy star formation rates near clusters

Abstract: We have measured the equivalent width of the Hα emission line for 11 006 galaxies brighter than M_b-=-−19 (Ω_Λ = 0.7, Ω_m = 0.3, H_0 = 70 km s^(−1) Mpc^(−1)) at 0.05 < z < 0.1 in the 2dF Galaxy Redshift Survey (2dFGRS), in the fields of 17 known galaxy clusters. The limited redshift range ensures that our results are insensitive to aperture bias, and to residuals from night sky emission lines. We use these measurements to trace μ*, the star formation rate normalized to L*, as a function of distance from the cluster centre, and local projected galaxy density. We find that the distribution of μ* steadily skews toward larger values with increasing distance from the cluster centre, converging to the field distribution at distances greater than ∼3 times the virial radius. A correlation between star formation rate and local projected density is also found, which is independent of cluster velocity dispersion and disappears at projected densities below ∼1 galaxy Mpc^(−2) (brighter than M_b = −19). This characteristic scale corresponds approximately to the mean density at the cluster virial radius. The same correlation holds for galaxies more than two virial radii from the cluster centre. We conclude that environmental influences on galaxy properties are not restricted to cluster cores, but are effective in all groups where the density exceeds this critical value. The present-day abundance of such systems, and the strong evolution of this abundance, makes it likely that hierarchical growth of structure plays a significant role in decreasing the global average star formation rate. Finally, the low star formation rates well beyond the virialized cluster rule out severe physical processes, such as ram pressure stripping of disc gas, as being completely responsible for the variations in galaxy properties with environment.

The 2dF Galaxy Redshift Survey: The bias of galaxies and the density of the Universe

Abstract: We compute the bispectrum of the 2dF Galaxy Redshift Survey (2dFGRS) and use it to measure the bias parameter of the galaxies. This parameter quantifies the strength of clustering of the galaxies relative to the mass in the Universe. By analysing 80 x 10 6 triangle configurations in the wavenumber range 0.1 < k < 0.5 h Mpc - 1 (i.e. on scales roughly between 5 and 30 h - 1 Mpc) we find that the linear bias parameter is consistent with unity: b 1 = 1.04 ′ 0.11, and the quadratic (non-linear) bias is consistent with zero: b 2 = -0.054 ′ 0.08. Thus, at least on large scales, optically selected galaxies do indeed trace the underlying mass distribution. The bias parameter can be combined with the 2dFGRS measurement of the redshift distortion parameter β ≃ Ω 0 . 6 m /b 1 , to yield Ωm = 0.27 ′0.06 for the matter density of the Universe, a result that is determined entirely from this survey, independent of other data sets. Our measurement of the matter density of the Universe should be interpreted as Ω m at the effective redshift of the survey (z = 0.17).

The Damping of Coronal Loop Oscillations

Abstract: Motivated by recent Transition Region and Coronal Explorer (TRACE) observations of damped oscilla- tions in coronal loops, we consider analytically the motion of an inhomogeneous coronal magnetic tube of radius a in a zero-� plasma. An initially perturbed tube may vibrate in its kink mode of oscillation, but those vibrations are damped. The damping is due to resonant absorption, acting in the inhomogeneous regions of the tube, which leads to a transfer of energy from the kink mode to Alfven (azimuthal) oscillations within the inhomogeneous layer. We determine explicitly the decrement � (decay time � � 1 ) for a coronal flux tube whose plasma density varies only in a thin layer of thickness  on the tube boundary. The effect of viscosity is also considered. We show that, in general, the problem involves two distinct timescales, � � 1 and ! � 1 k R 1=3 , where R is the Reynolds number and !k is the frequency of the kink mode. Under coronal conditions (when � � 1 5 ! � 1 k R 1=3 ), the characteristic damping time of global oscillations is � � 1 . During this time, most of the energy in the initial perturbation is transferred into a resonant absorption layer of thickness of order  2 =a, with motions in this layer having an amplitude of order a= times the initial amplitude. We apply our results to the observations, suggesting that loop oscillations decay principally because of inhomogeneities in the loop. Our theory suggests that only those loops with density inhomogeneities on a small scale (confined to within a thin layer of order a�=! k in thickness) are able to support coherent oscillations for any length of time and so be observable. Loops with a more gradual density variation, on the scale of the tube radius a, do not exhibit pronounced oscillations. Subject headings: MHD — plasmas — Sun: corona — waves

The 2dF Galaxy Redshift Survey: the dependence of galaxy clustering on luminosity and spectral type

Abstract: We investigate the dependence of galaxy clustering on luminosity and spectral type using the 2dF Galaxy Redshift Survey (2dFGRS). Spectral types are assigned using the principal-component analysis of Madgwick et al. We divide the sample into two broad spectral classes: galaxies with strong emission lines ('late types') and more quiescent galaxies ('early types'). We measure the clustering in real space, free from any distortion of the clustering pattern owing to peculiar velocities, for a series of volume-limited samples. The projected correlation functions of both spectral types are well described by a power law for transverse separations in the range 2<(σ/h-1 Mpc)<15, with a marginally steeper slope for early types than late types. Both early and late types have approximately the same dependence of clustering strength on luminosity, with the clustering amplitude increasing by a factor of 2.5 between L* and 4L*. At all luminosities, however, the correlation function amplitude for the early types is 50 per cent higher than that of the late types. These results support the view that luminosity, and not type, is the dominant factor in determining how the clustering strength of the whole galaxy population varies with luminosity.

Informal insurance arrangements with limited commitment: Theory and evidence from village economies

Abstract: Recent work on consumption allocations in village economies finds that idiosyncratic variation in consumption is systematically related to idiosyncratic variation in income, thus rejecting the hypothesis of full risk-pooling. We attempt to explain these observations by adding limited commitment as an impediment to risk-pooling. We provide a general dynamic model and completely characterise efficient informal insurance arrangements constrained by limited commitment, and test the model using data from three Indian villages. We find that the model can fully explain the dynamic response of consumption to income, but that it fails to explain the distribution of consumption across households.

The regulation of nitrate and ammonium transport systems in plants

Abstract: Inorganic nitrogen concentrations in soil solutions vary across several orders of magnitude among different soils and as a result of seasonal changes In order to respond to this heterogeneity, plants have evolved mechanisms to regulate and influx In addition, efflux analysis using (13)N has revealed that there is a co-ordinated regulation of all component fluxes within the root, including biochemical fluxes Physiological studies have demonstrated the presence of two high-affinity transporter systems (HATS) for and one HATS for in roots of higher plants By contrast, in Arabidopsis thaliana there exist seven members of the NRT2 family encoding putative HATS for and five members of the AMT1 family encoding putative HATS for The induction of high-affinity transport and Nrt21 and Nrt22 expression occur in response to the provision of, while down-regulation of these genes appear to be due to the effects of glutamine High-affinity transport and AMT11 expression also appear to be subject to down-regulation by glutamine In addition, there is evidence that accumulated and may act post-transcriptionally on transporter function The present challenge is to resolve the functions of all of these genes In Aspergillus nidulans and Chlamydomonas reinhardtii there are but two high-affinity transporters and these appear to have undergone kinetic differentiation that permits a greater efficiency of absorption over the wide range of concentration normally found in nature Such kinetic differentiation may also have occurred among higher plant transporters The characterization of transporter function in higher plants is currently being inferred from patterns of gene expression in roots and shoots, as well as through studies of heterologous expression systems and knockout mutants

The 2dF Galaxy Redshift Survey: The bJ-band galaxy luminosity function and survey selection function

Abstract: We use more than 110 500 galaxies from the 2dF Galaxy Redshift Survey (2dFGRS) to estimate the bJ-band galaxy luminosity function at redshift z = 0, taking account of evolution, the distri- bution of magnitude measurement errors and small corrections for incompleteness in the galaxy catalogue. Throughout the interval −16.5 > MbJ − 5 log10 h > −22, the luminosity function is accurately described by a Schechter function with MJ − 5 log10 h =− 19.66 ± 0.07, α = −1.21 ± 0.03 and � � = (1.61 ± 0.08) × 10 −2 h 3 Mpc −3 , giving an integrated luminosity den- sity of ρL = (1.82 ± 0.17) × 10 8 h LMpc −3 (assuming an � 0 = 0.3, 0 = 0.7 cosmology). The quoted errors have contributions from the accuracy of the photometric zero-point, from large-scale structure in the galaxy distribution and, importantly, from the uncertainty in the ap- propriate evolutionary corrections. Our luminosity function is in excellent agreement with, but has much smaller statistical errors than, an estimate from the Sloan Digital Sky Survey (SDSS) data when the SDSS data are accurately translated to the bJ band and the luminosity functions are normalized in the same way. We use the luminosity function, along with maps describing the redshift completeness of the current 2dFGRS catalogue, and its weak dependence on ap- parent magnitude, to define a complete description of the 2dFGRS selection function. Details and tests of the calibration of the 2dFGRS photometric parent catalogue are also presented.

Abundance of harbour porpoise and other cetaceans in the North Sea and adjacent waters

Abstract: 1. The status of small cetaceans in the North Sea and adjacent waters has been of concern for many years. Shipboard and aerial line transect surveys were conducted to provide accurate and precise estimates of abundance as a basis for conservation strategy in European waters. 2. The survey, known as SCANS (Small Cetacean Abundance in the North Sea), was conducted in summer 1994 and designed to generate precise and unbiased abundance estimates. Thus the intensity of survey was high, and data collection and analysis methods allowed for the probability of detection of animals on the transect line being less than unity and, for shipboard surveys, also allowed for animal movement in response to the survey platform. 3. Shipboard transects covered 20 000 km in an area of 890 000 km2. Aerial transects covered 7000 km in an area of 150 000 km2. 4. Three species dominated the data. Harbour porpoise Phocoena phocoena were encountered throughout the survey area except in the Channel and the southern North Sea. Whitebeaked dolphin Lagenorhynchus albirostris and minke whale Balaenoptera acutorostrata were found mainly in the north-western North Sea. 5. Phocoena phocoena abundance for the entire survey area was estimated as 341 366 [coefficient of variation (CV) = 0.14; 95% confidence interval (CI) = 260 000-449 000]. The estimated number of B. acutorostrata was 8445 (CV = 0.24; 95% CI 5000-13 500). The estimate for L. albirostris based on confirmed sightings of this species was 7856 (CV = 0.30; 95% CI = 4000-13 000). When Atlantic whitesided dolphin Lagenorhynchus acutus and Lagenorhynchus spp. sightings were included, this estimate increased to 11 760 (CV = 0.26; 95% CI 5900-18 500). 6. Shortbeaked common dolphin Delphinus delphis were found almost exclusively in the Celtic Sea. Abundance was estimated as 75 450 (CV = 0.67; 95% CI = 23 000-149 000). 7. Current assessments and recommendations by international fora concerning the impact on P. phocoena of bycatch in gillnet fisheries in the North Sea and adjacent waters are based on these estimates.

Partnership status and the temporal context of relationships influence human female preferences for sexual dimorphism in male face shape

Abstract: Secondary sexual characteristics may indicate quality of the immune system and therefore a preference for masculinity may confer genetic benefits to offspring; however, high masculinity may be associated with costs of decreased paternal investment. The current study examined women's preferences for masculinity in male faces by using computer graphics to allow transformation between feminine and masculine versions of individual male faces. We found that preferences for masculinity are increased when women either have a partner or are considering a short-term relationship. Such preferences are potentially adaptive, serving to: (i) maximize parental investment and cooperation in long-term relationships by biasing choices towards feminine faced males, and (ii) maximize possible good-gene benefits of short-term or extra-pair partners by biasing choices towards masculine faced males. We also found that individuals using oral contraception do not show the above effects, indicating that such hormonal intervention potentially disrupts women's choices for evolutionarily relevant benefits from males.

The formation mechanism of brown dwarfs

Abstract: We present results from the first hydrodynamical star formation calculation to demonstrate that brown dwarfs are a natural and frequent product of the collapse and fragmentation of a turbulent molecular cloud. The brown dwarfs form via the fragmentation of dense molecular gas in unstable multiple systems and are ejected from the dense gas before they have been able to accrete to stellar masses. Thus, they can be viewed as 'failed stars'. Approximately three-quarters of the brown dwarfs form in gravitationally unstable circumstellar discs while the remainder form in collapsing filaments of molecular gas. These formation mechanisms are very efficient, producing roughly the same number of brown dwarfs as stars, in agreement with recent observations. However, because close dynamical interactions are involved in their formation, we find a very low frequency of binary brown dwarf systems (≤5 per cent) and that those binary brown dwarf systems that do exist must be close, ≤ 10 au. Similarly, we find that young brown dwarfs with large circumstellar discs (radii ≥ 10 au) are rare ( 5 per cent).

Accretion during the Merger of Supermassive Black Holes

Abstract: We study the evolution of disk accretion during the merger of supermassive black hole binaries in galactic nuclei. In hierarchical galaxy formation models, the most common binaries are likely to arise from minor galactic mergers and have unequal-mass black holes. Once such a binary becomes embedded in an accretion disk at a separation of a ~ 0.1 pc, the merger proceeds in two distinct phases. During the first phase, the loss of orbital angular momentum to the gaseous disk shrinks the binary on a timescale of ~107 yr. The accretion rate onto the primary black hole is not increased, and can be substantially reduced, during this disk-driven migration. At smaller separations, gravitational radiation becomes the dominant angular momentum loss process, and any gas trapped inside the orbit of the secondary is driven inward by the inspiralling black hole. The implied accretion rate just prior to coalescence exceeds the Eddington limit, so the final merger is likely to occur within a common envelope formed from the disrupted inner disk and to be accompanied by high-velocity (~104 km s-1) outflows.

Orbital angular momentum of a high-order Bessel light beam

Abstract: The orbital angular momentum density of Bessel beams is calculated explicitly within a rigorous vectorial treatment. This allows us to investigate some aspects that have not been analysed previously, such as the angular momentum content of azimuthally and radially polarized beams. Furthermore, we demonstrate experimentally the mechanical transfer of orbital angular momentum to trapped particles in optical tweezers using a high-order Bessel beam. We set transparent particles of known dimensions into rotation, where the sense of rotation can be reversed by changing the sign of the singularity. Quantitative results are obtained for rotation rates. This paper's animations are available from the Multimedia Enhancements page.

Biochemistry: biosynthesis of an organofluorine molecule.

Abstract: Although fluorine in the form of fluoride minerals is the most abundant halogen in the Earth's crust, only 12 naturally occurring organofluorine compounds have so far been found, and how these are biosynthesized remains a mystery. Here we describe an enzymatic reaction that occurs in the bacterium Streptomyces cattleya and which catalyses the conversion of fluoride ion and S-adenosylmethionine (SAM) to 5'-fluoro-5'-deoxyfluoroadenosine (5'-FDA). To our knowledge, this is the first fluorinase enzyme to be identified, a discovery that opens up a new biotechnological opportunity for the preparation of organofluorine compounds.

Induction of tumor-specific T cell memory by NK cell-mediated tumor rejection.

Abstract: Natural killer (NK) cells may modulate the development of adaptive immune responses, but until now there has been little evidence to support this hypothesis. We investigated the primary and secondary immunity elicited by various tumor cell lines that express CD70 and interact with CD70 ligand (CD27), which is constitutively expressed on NK cells. CD70 expression enhanced primary tumor rejection in vivo as well as T cell immunity against secondary tumor challenge. Primary rejection of major histocompatibility complex (MHC) class I-deficient RMA-S.CD70 tumor cells was mediated by NK cells and perforin- and interferon-gamma-dependent mechanisms. This NK cell-mediated process also efficiently evoked the subsequent development of tumor-specific cytotoxic and T helper type 1 responses to the parental, MHC class I-sufficient, RMA tumor cells. Thus CD27-CD70 interactions provide a key link between innate NK cell responses and adaptive T cell immunity.

The 2dF Galaxy Redshift Survey: galaxy luminosity functions per spectral type

Abstract: We calculate the optical bJ luminosity function of the 2dF Galaxy Redshift Survey (2dFGRS) for different subsets defined by their spectral properties. These spectrally selected subsets are defined using a new parameter, �, which is a linear combination of the first two projections derived from a Principal Component Analysis. This parameter � identifies the average emission and absorption line strength in the galaxy rest-frame spectrum and hence is a useful indicator of the present star formation. We use a total of 75,000 galaxies in our calculations, chosen from a sample of high signal-tonoise ratio, low redshift galaxies observed before January 2001. We find that there is a systematic steepening of the faint end slope (�) as one moves from passive (� = 0.54) to active (� = 1.50) star-forming galaxies, and that there is also a corresponding faintening of the rest-frame characteristic magnitude M � 5log10(h) (from 19.6 to 19.2). We also show that the Schechter function provides a poor fit to the quiescent (Type 1) LF for very faint galaxies (MbJ 5log10(h) fainter than 16.0), perhaps suggesting the presence of a significant dwarf population. The luminosity functions presented here give a precise confirmation of the trends seen previously in a much smaller preliminary 2dFGRS sample, and in other surveys. We also present a new procedure for determining self-consistent K-corrections and investigate possible fibreaperture biases.

Parameter constraints for flat cosmologies from cosmic microwave background and 2dFGRS power spectra

Abstract: We constrain flat cosmological models with a joint likelihood analysis of a new compilation of data from the cosmic microwave background (CMB) and from the 2dF Galaxy Redshift Survey (2dFGRS). Fitting the CMB alone yields a known degeneracy between the Hubble constant h and the matter density Omega(m), which arises mainly from preserving the location of the peaks in the angular power spectrum. This 'horizon-angle degeneracy' is considered in some detail and is shown to follow the simple relation Omega(m) h(3.4) = constant. Adding the 2dFGRS power spectrum constrains Omega(m) h and breaks the degeneracy. If tensor anisotropies are assumed to be negligible, we obtain values for the Hubble constant of h = 0.665 +/- 0.047, the matter density Omega(m) = 0.313 +/- 0.055, and the physical cold dark matter and baryon densities Omega(c)h(2) = 0.115 +/- 0.009, Omega(b)h(2) = 0.022 +/- 0.002 (standard rms errors). Including a possible tensor component causes very little change to these figures; we set an upper limit to the tensor-to-scalar ratio of r < 0.7 at a 95 per cent confidence level. We then show how these data can be used to constrain the equation of state of the vacuum, and find w < -0.52 at 95 per cent confidence. The preferred cosmological model is thus very well specified, and we discuss the precision with which future CMB data can be predicted, given the model assumptions. The 2dFGRS power-spectrum data and covariance matrix, and the CMB data compilation used here, are available from http://www.roe.ac.uk/similar towjp/.

Green Phosphorescent Dendrimer for Light‐Emitting Diodes

Abstract: Highly efficient organic LEDs made by solution processing are reported. It is shown that the dendritic architecture (see Figure) can be used to solubilize luminescent chromophores and form uniform films of blends. The simple device structures containing a light-emitting chromophore are amongst the most efficient solution-processed devices reported. Thanks to this technique, the inkjet printing of phosphorescent materials becomes feasible.

Universities and Fundamental Research: Reflections on the Growth of University–Industry Partnerships

Abstract: The recent rise in university-industry partnerships has stimulated an important public policy debate regarding how these relationships affect fundamental research. In this paper, we examine the antecedents and consequences of policies to promote university-industry alliances. Although the preliminary evidence appears to suggest that these partnerships have not had a deleterious effect on the quantity and quality of basic research, some legitimate concerns have been raised about these activities that require additional analysis. We conclude that additional research is needed to provide a more accurate assessment of the optimal level of commercialisation.

Assessment of argos location accuracy from satellite tags deployed on captive gray seals

Abstract: The Argos satellite system is commonly used to track and relay behavioral data from marine mammals, but their underwater habit results in a high proportion of locations of non-guaranteed accuracy (location classes (LC) O, A, and B). The accuracy of these locations is poorly documented in marine mammals. We assessed the accuracy of all LCs on four juvenile gray seals fitted with Argos satellite relay data loggers and held in captivity in an outdoor tank for a total of 61 seal-days. Four hundred and twenty-six locations were obtained from seals in captivity, and their latitude and longitude error was assessed before and after filtering, following MConnell et al. (1992). There was significantly more error in longitude than latitude in all LCs except I. C A. The ratio of the standard deviations of longitude : latitude ranged from 1.77 (LC 3) to 2.58 (LC 1). Filtering had very little effect on errors in LCs 3-1, but in the remaining LCs filtering resulted in error reductions ranging from 8% to 63%. In LCs O, A, and B, error reduction was greater in the 95th percentile errors, especially in longitude. The averages of the latitude and longitude 68th percentile errors and those predicted by Argos (in brackets) were 226 (150), 372 (350), and 757 (1000) m for LCs 3, 2, and 1 respectively. Both latitude and longitude errors of LCs > O were normally distributed. Both filtered and unfiltered LC A locations were of a similar accuracy to LC 1 locations, and considerably better than LC O locations.

The formation of close binary systems by dynamical interactions and orbital decay

Abstract: We present results from the first hydrodynamical star formation calculation to demonstrate that close binary stellar systems (separations 10 au) need not be formed directly by fragmentation. Instead, a high frequency of close binaries can be produced through a combination of dynamical interactions in unstable multiple systems and the orbital decay of initially wider binaries. Orbital decay may occur as a result of gas accretion and/or the interaction of a binary with its circumbinary disc. These three mechanisms avoid the problems associated with the fragmentation of optically thick gas to form close systems directly. They also result in a preference for close binaries to have roughly equal-mass components because dynamical exchange interactions and the accretion of gas with high specific angular momentum drive mass ratios towards unity. Furthermore, because of the importance of dynamical interactions, we find that stars with greater masses ought to have a higher frequency of close companions, and that many close binaries ought to have wide companions. These properties are in good agreement with the results of observational surveys.

Self-employment Wealth and Job Creation: The Roles of Gender, Non-pecuniary Motivation and Entrepreneurial Ability

Abstract: This paper uses National Child Development Study data for a large cohort of British individuals, to explore the influence of education, inheritance and other background characteristics on the propensity to become self-employed; and also on subsequent success, as measured by job and wealth creation. For the first time, we study the effects of our regressor variables on our success measures via disaggregation of our sample by gender – and, in this way, reveal striking differences between the determinants of male and female entrepreneurial performance.