Standard Cosmic Ray Energetics and Light Element Production

The recent observations of Be and B in metal poor stars has led to a reassessment of the origin of the light elements in the early Galaxy. At low it is metallicity ([O/H] < -1.75), it is necessary to introduce a production mechanism which is independent of the interstellar metallicity (primary). At higher metallicities, existing data might indicate that secondary production is dominant. In this paper, we focus on the secondary process, related to the standard Galactic cosmic rays, and we examine the cosmic ray energy requirements for both present and past epochs. We find the power input to maintain the present-day Galactic cosmic ray flux is about 1.5e41 erg/s = 5e50 erg/century. This implies that, if supernovae are the sites of cosmic ray acceleration, the fraction of explosion energy going to accelerated particles is about 30%, a value which we obtain consistently both from considering the present cosmic ray flux and confinement and from the present 9Be and 6Li abundances. Using the abundances of 9Be (and 6Li) in metal-poor halo stars, we extend the analysis to show the effect of the interstellar gas mass on the standard galactic cosmic ray energetic constraints on models of Li, Be, and B evolution. The efficiency of the beryllium production per erg may be enhanced in the past by a factor of about 10; thus the energetic requirement by itself cannot be used to rule out a secondary origin of light elements. Only a clear and undisputable observational determination of the O-Fe relation in the halo will discriminate between the two processes. (abridged)Comment: 24 pages, LaTeX, uses aastex macro

The Spiral Structure of the Milky Way, Cosmic Rays, and Ice Age Epochs on Earth

The short term variability of the Galactic cosmic ray flux (CRF) reaching Earth has been previously associated with variations in the global low altitude cloud cover. This CRF variability arises from changes in the solar wind strength. However, cosmic ray variability also arises intrinsically from variable activity of and motion through the Milky Way. Thus, if indeed the CRF climate connection is real, the increased CRF witnessed while crossing the spiral arms could be responsible for a larger global cloud cover and a reduced temperature, thereby facilitating the occurrences of ice ages. This picture has been recently shown to be supported by various data (Shaviv, 2001). In particular, the variable CRF recorded in Iron meteorites appears to vary synchronously with the appearance ice ages. Here we expand upon the original treatment with a more thorough analysis and more supporting evidence. In particular, we discuss the cosmic ray diffusion model which considers the motion of the Galactic spiral arms. We also elaborate on the structure and dynamics of the Milky Way's spiral arms. In particular, we bring forth new argumentation using HI observations which imply that the galactic spiral arm pattern speed appears to be that which fits the glaciation period and the cosmic-ray flux record extracted from Iron meteorites. In addition, we show that apparent peaks in the star formation rate history, as deduced by several authors, coincides with particularly icy epochs, while the long period of 1 to 2 Gyr before present, during which no glaciations are known to have occurred, coincides with a significant paucity in the past star formation rate.Comment: 33 pages, 11 figures. To Appear in New Astronom

Mass extinctions and supernova explosions

A nearby supernova (SN) explosion could have negatively influenced life on Earth, maybe even been responsible for mass extinctions. Mass extinction poses a significant extinction of numerous species on Earth, as recorded in the paleontologic, paleoclimatic, and geological record of our planet. Depending on the distance between the Sun and the SN, different types of threats have to be considered, such as ozone depletion on Earth, causing increased exposure to the Sun's ultraviolet radiation, or the direct exposure of lethal x-rays. Another indirect effect is cloud formation, induced by cosmic rays in the atmosphere which result in a drop in the Earth's temperature, causing major glaciations of the Earth. The discovery of highly intensive gamma ray bursts (GRBs), which could be connected to SNe, initiated further discussions on possible life-threatening events in Earth's history. The probability that GRBs hit the Earth is very low. Nevertheless, a past interaction of Earth with GRBs and/or SNe cannot be excluded and might even have been responsible for past extinction events.Comment: Chapter for forthcoming book: Handbook of Supernovae, P. Murdin and A. Alsabeti (eds.), Springer International Publishing (in press

Differential diagnosis of pre-swallow pooling : a diagnostic dilemma.

Accurate assessment and diagnosis of swallowing disorders is key to providing appropriate intervention. Selection of treatment relies on our diagnostic methodology. If incorrect treatment is selected, then swallowing disorders may not improve. Pre-swallow pooling is a feature of dysphagia that can cause aspiration before or during swallowing. It is presumed to be caused by two different pathophysiological impairments. One is presumed to be a motor impairment, which causes poor bolus containment as a result of oral weakness. This leads to some or all of the bolus entering the pharynx prior to purposeful propulsion of the bolus in the mouth. The other is presumed to be a sensory impairment whereby reduced sensation in the mouth causes a delay or absence of the pharyngeal swallowing response, after the bolus is propelled into the pharynx. However, assessment and diagnosis of pre-swallow pooling is poorly defined in the literature. In clinical practice, observations on videofluoroscopic swallowing studies are used to distinguish between poor bolus containment and delayed pharyngeal swallowing. However, videofluoroscopic swallowing studies allow for observation of biomechanics and cannot provide information regarding a sensory or motor impairment. Therefore, this PhD program investigated the phenomenon of pre-swallow pooling in stroke, to understand how it is differentiated into either poor bolus containment or delayed pharyngeal swallowing and whether a sensory and motor cause of pre-swallow pooling can be established. This PhD program of research involved four studies and a scoping review. The scoping review findings were included within the literature review for continuity. This identified a large variation of the terms used to describe pre-swallow pooling, the measurement methods, and the methods by which to differentiate poor bolus containment from delayed pharyngeal swallowing. Study one was a normative study on 60 healthy participants. This study evaluated normative and reliability data of a novel oral sensory threshold measurement, and posterior lingual-palatal pressure measurement and the relationship between them. Electrical stimulation was used to establish sensory thresholds in the mouth including the lips, tongue and faucial palate. Whilst lingual-palatal pressure norms have previously been reported, there is scant data on the posterior position that includes both isometric lingual-palatal pressure and lingual-palatal pressure during swallowing. The relationship between both physiological measures has not previously been investigated. Results suggest that there is some preliminary evidence that these tools can be used to determine a motor or sensory cause of pre-swallow pooling. Study two was the first study to evaluate the agreement of speech pathologists’ current methods for distinguishing poor bolus containment from delayed pharyngeal swallowing. This study evaluated inter- and intra-rater reliability of speech pathologist’s current practice in the diagnosis of poor bolus containment and delayed pharyngeal swallowing using videofluoroscopic swallowing studies. Thirty videofluoroscopic thin fluid swallows with five of those appearing twice, were presented via an online survey to examine agreement both between and within raters. Definitions of poor bolus containment and delayed pharyngeal swallowing were provided to one of two groups to evaluate whether this information increased reliability. Reliability was poor for inter and intra-rater reliability for both the group with, and the group without, definitions. This indicated that our current methodology for determining poor bolus containment from delayed pharyngeal swallowing is unreliable. Further, the addition of definitions to guide speech pathologists in determining one from the other did not increase agreement, suggesting that the application or interpretation of measures is too subjective. Study three was an exploratory study to determine whether distinct groups could be formed based on the physiological data obtained by the oral sensory threshold and posterior lingual-palatal pressure measurements. As there is no “gold-standard” for determining the difference between poor bolus containment and delayed pharyngeal swallowing, cluster analysis methodology was used to identify clusters that could be differentiated into one of potentially 3 groups. The groups were proposed to include a sensory group, a motor group, and a sensory-motor group. The aim was then to evaluate these groups against speech pathologists’ diagnosis of poor bolus containment and delayed pharyngeal swallowing in an attempt to determine whether a sensory and motor cause of pre-swallow pooling could be differentiated by clinicians. However, due to inconsistencies in speech pathologists’ diagnosis of poor bolus containment and delayed pharyngeal swallowing, this could not be completed. Since distinct groups could be established via cluster analysis, it is likely that evidence for a sensory and motor cause of pre-swallow pooling exists, however, our current methods for determining this is flawed. The final study evaluated the groups identified by the cluster analysis against common swallowing measures including oral transit time (OTT), stage transition duration (STD) and the Penetration-Aspiration Scale (PAS). Due to small numbers, most of the statistical methodology could not be applied, and results were presented descriptively. This research addressed the need for more consistent terminology to describe the two causes of pre-swallow pooling and improved methods for distinguishing between poor bolus containment and delayed pharyngeal swallowing. There is evidence that subjects who have pre-swallow pooling following a stroke can be separated into those who have both a sensory and motor impairment and those who have a motor impairment alone. However, there remains no evidence for linking poor bolus containment with a motor impairment and delayed pharyngeal swallowing with a sensory impairment. New methodologies for determining the cause of pre-swallow pooling are required to ensure correct selection of dysphagia intervention and optimise rehabilitation outcomes

A search for TeV gamma-ray emission from SNRs, pulsars and unidentified GeV sources in the Galactic plane in the longitude range between -2 deg and 85 deg

Using the HEGRA system of imaging atmospheric Cherenkov telescopes, one quarter of the Galactic plane (-2 deg < l < 85 deg) was surveyed for TeV gamma-ray emission from point sources and moderately extended sources (diameter <= 0.8 deg). The region covered includes 86 known pulsars (PSR), 63 known supernova remnants (SNR) and nine GeV sources, representing a significant fraction of the known populations. No evidence for emission of TeV gamma radiation was detected, and upper limits range from 0.15 Crab units up to several Crab units, depending on the observation time and zenith angles covered. The ensemble sums over selected SNR and pulsar subsamples and over the GeV-sources yield no indication for emission from these potential sources. The upper limit for the SNR population is at the level of 6.7% of the Crab flux and for the pulsar ensemble at the level of 3.6% of the Crab flux.Comment: 10 pages, 5 figures, 4 tables, accepted for publication in A&

A simple model for the evolution of disc galaxies: The Milky Way

A simple model for the evolution of disc galaxies is presented. We adopt three numbers from observations of the Milky Way disc, the local surface mass density, the stellar scale length (of the assumedly exponential disc) and the amplitude of the (assumedly flat) rotation curve, and physically, the (local) dynamical Kennicutt star formation prescription, standard chemical evolution equations assuming and a model for spectral evolution of stellar populations. We can determine the detailed evolution of the model with only the addition of standard cosmological scalings with time of the dimensional parameters. A surprising wealth of detailed specifications follows from this prescription including the gaseous infall rate as a function of radius and time, the distribution of stellar ages and metallicities with time and radius, surface brightness profiles at different wavelengths, colours etc. At the solar neighbourhood stars start to form $\approx 10 Gyrs$ ago at an increasing rate peaking 4 billion years ago and then slowly declining in good agreement with observations. The mean age of long lived stars at the solar neighbourhood is about $4 Gyrs$. The local surface density of the stars and gas are 35 and $15 M_{\odot}pc^{-2}$, respectively. The metallicity distribution of the stars at the solar radius is narrow with a peak at $[Z/Z_{\odot}] = -0.1$.Both a Salpeter IMF and a Chabrier IMF are consistent with observations. Comparisons with the current and local fossil evidence provides support for the model which can then be used to assess other local disc galaxies, the evolution of disc galaxies in deep optical surveys and also for theoretical investigations such as simulations of merging disc galaxies (abbreviated).Comment: acceppted for publication in MNRA

Habitable Zones in the Universe

Habitability varies dramatically with location and time in the universe. This was recognized centuries ago, but it was only in the last few decades that astronomers began to systematize the study of habitability. The introduction of the concept of the habitable zone was key to progress in this area. The habitable zone concept was first applied to the space around a star, now called the Circumstellar Habitable Zone. Recently, other, vastly broader, habitable zones have been proposed. We review the historical development of the concept of habitable zones and the present state of the research. We also suggest ways to make progress on each of the habitable zones and to unify them into a single concept encompassing the entire universe.Comment: 71 pages, 3 figures, 1 table; to be published in Origins of Life and Evolution of Biospheres; table slightly revise

Differences in [18F]FDG uptake in BAT of UCP1 −/− and UCP1 +/+ during adrenergic stimulation of non-shivering thermogenesis

Background: Brown adipose tissue (BAT) is a fat tissue found in most mammals that helps regulate energy balance and core body temperature through a sympathetic process known as non-shivering thermogenesis. BAT activity is commonly detected and quantified in [18F]FDG positron emission tomography/computed tomography (PET/CT) scans, and radiotracer uptake in BAT during adrenergic stimulation is often used as a surrogate measure for identifying thermogenic activity in the tissue. BAT thermogenesis is believed to be contingent upon the expression of the protein UCP1, but conflicting results have been reported in the literature concerning [18F]FDG uptake within BAT of mice with and without UCP1. Differences in animal handling techniques such as feeding status, type of anesthetic, type of BAT stimulation, and estrogen levels were identified as possible confounding variables for [18F]FDG uptake. In this study, we aimed to assess differences in BAT [18F]FDG uptake between wild-type and UCP1-knockout mice using a protocol that minimizes possible variations in BAT stimulation caused by different stress responses to mouse handling. Results: [18F]FDG PET/CT scans were run on mice that were anesthetized with pentobarbital after stimulation of non-shivering thermogenesis by norepinephrine. While in wild-type mice [18F]FDG uptake in BAT increased significantly with norepinephrine stimulation of BAT, there was no consistent change in [18F]FDG uptake in BAT of mice lacking UCP1. Conclusions: [18F]FDG uptake within adrenergically stimulated BAT of wild-type and UCP1-knockout mice can significantly vary such that an [18F]FDG uptake threshold cannot be used to differentiate wild-type from UCP1-knockout mice. However, while an increase in BAT [18F]FDG uptake during adrenergic stimulation is consistently observed in wild-type mice, in UCP1-knockout mice [18F]FDG uptake in BAT seems to be independent of β3-adrenergic stimulation of non-shivering thermogenesis

Gas flows, star formation and galaxy evolution

In the first part of this article we show how observations of the chemical evolution of the Galaxy: G- and K-dwarf numbers as functions of metallicity, and abundances of the light elements, D, Li, Be and B, in both stars and the interstellar medium (ISM), lead to the conclusion that metal poor HI gas has been accreting to the Galactic disc during the whole of its lifetime, and is accreting today at a measurable rate, ~2 Msun per year across the full disc. Estimates of the local star formation rate (SFR) using methods based on stellar activity, support this picture. The best fits to all these data are for models where the accretion rate is constant, or slowly rising with epoch. We explain here how this conclusion, for a galaxy in a small bound group, is not in conflict with graphs such as the Madau plot, which show that the universal SFR has declined steadily from z=1 to the present day. We also show that a model in which disc galaxies in general evolve by accreting major clouds of low metallicity gas from their surroundings can explain many observations, notably that the SFR for whole galaxies tends to show obvious variability, and fractionally more for early than for late types, and yields lower dark to baryonic matter ratios for large disc galaxies than for dwarfs. In the second part of the article we use NGC 1530 as a template object, showing from Fabry-Perot observations of its Halpha emission how strong shear in this strongly barred galaxy acts to inhibit star formation, while compression acts to stimulate it.Comment: 20 pages, 10 figures, to be presented at the "Penetrating Bars through Masks of Cosmic Dust" conference in South Africa, proceedings published by Kluwer, Eds. D.L. Block, K.C. Freeman, I. Puerari, & R. Groes