995,409 research outputs found
Comparing the effects of sun exposure and vitamin D supplementation on vitamin D insufficiency, and immune and cardio-metabolic function: the Sun Exposure and Vitamin D Supplementation (SEDS) Study
BACKGROUND Adults living in the sunny Australian climate are at high risk of skin cancer, but vitamin D deficiency (defined here as a serum 25-hydroxyvitamin D (25(OH)D) concentration of less than 50 nmol/L) is also common. Vitamin D deficiency may be a risk factor for a range of diseases. However, the optimal strategies to achieve and maintain vitamin D adequacy (sun exposure, vitamin D supplementation or both), and whether sun exposure itself has benefits over and above initiating synthesis of vitamin D, remain unclear. The Sun Exposure and Vitamin D Supplementation (SEDS) Study aims to compare the effectiveness of sun exposure and vitamin D supplementation for the management of vitamin D insufficiency, and to test whether these management strategies differentially affect markers of immune and cardio-metabolic function. METHODS/DESIGN The SEDS Study is a multi-centre, randomised controlled trial of two different daily doses of vitamin D supplementation, and placebo, in conjunction with guidance on two different patterns of sun exposure. Participants recruited from across Australia are aged 18-64 years and have a recent vitamin D test result showing a serum 25(OH)D level of 40-60 nmol/L. DISCUSSION This paper discusses the rationale behind the study design, and considers the challenges but necessity of data collection within a non-institutionalised adult population, in order to address the study aims. We also discuss the challenges of participant recruitment and retention, ongoing engagement of referring medical practitioners and address issues of compliance and participant retention. TRIAL REGISTRATION Australia New Zealand Clinical Trials Registry: ACTRN12613000290796 Registered 14 March 2013
Flip-flop phenomenon: observations and theory
In many active stars the spots concentrate on two permanent active longitudes
which are 180 degrees apart. In some of these stars the dominant part of the
spot activity changes the longitude every few years. This so-called flip-flop
phenomenon has up to now been reported in 11 stars, both single and binary
alike, and including also the Sun. To explain this phenomenon, a
non-axisymmetric dynamo mode, giving rise to two permanent active longitudes at
opposite stellar hemispheres, is needed together with an oscillating
axisymmetric magnetic field. Here we discuss the observed characteristics of
the flip-flop phenomenon and present a dynamo solution to explain them.Comment: 4 pages, 5 figures, contribution to the conference "Dynamos of the
Sun, Stars and Planets", to be published in AN Volume 32
The Sun's Journey Through the Local Interstellar Medium: The PaleoLISM and Paleoheliosphere
Over the recent past, the galactic environment of the Sun has differed
substantially from today. Sometime within the past ~130,000 years, and possibly
as recent as ~56,000 years ago, the Sun entered the tenuous tepid partially
ionized interstellar material now flowing past the Sun. Prior to that, the Sun
was in the low density interior of the Local Bubble. As the Sun entered the
local ISM flow, we passed briefly through an interface region of some type. The
low column densities of the cloud now surrounding the solar system indicate
that heliosphere boundary conditions will vary from opacity considerations
alone as the Sun moves through the cloud. These variations in the interstellar
material surrounding the Sun affected the paleoheliosphere.Comment: To be published in Astrophysics and Space Sciences Transactions
(ASTRA), for the proceedings of the workshop "Future Perspectives in
Heliospheric Research: Unsolved Problems, New Missions - New Sciences" Bad
Honnef, Germany, April 6-8, 2005, held in honor of Prof. Hans Fahr's 65th
birthda
Vainu Bappu Memorial Lecture: What is a sunspot?
Sunspots have been known in the West since Galileo Galilei and Thomas Harriot
first used telescopes to observe the Sun nearly four centuries ago; they have
been known to the Chinese for more than two thousand years. They appear as
relatively dark patches on the surface of the Sun, and are caused by
concentrations of magnetism which impede the flow of heat from deep inside the
Sun up to its othewise brilliant surface. The spots are not permanent: the
total number of spots on the Sun varies cyclically in time, with a period of
about eleven years, associated with which there appear to be variations in our
climate. When there are many spots, it is more dangerous for spacecraft to
operate. The cause of the spots is not well understood; nor is it known for
sure how they die. Their structure beneath the surface of the Sun is in some
dispute, although much is known about their properties at the surface,
including an outward material flow which was discovered by John Evershed
observing the Sun from Kodaikanal a hundred years ago. I shall give you a
glimpse of how we are striving to deepen our understanding of these fascinating
features, and of some of the phenomena that appear to be associated with them.Comment: Lecture delivered at the Indian Institute of Astrophysics, December
2008 Typing errors corrected To appear in Magnetic Coupling between the
Interior and the Atmosphere of the Sun, ed. S.S. Hasan & R.J. Rutten, Astr.
Sp. Sci. Pro
Is sunlight good for our heart?
Humans evolved being exposed for about half of the day to the light of the sun. Nowadays, exposure to sunlight is actively discouraged for fear of skin cancer, and contemporary lifestyles are associated with long hours spent under artificial light indoors. Besides an increasing appreciation for the adverse effects of these life-style-related behavioural changes on our chronobiology, the balance between the beneficial and harmful effects of sunlight on human health is the subject of considerable debate, in both the scientific and popular press, and the latter is of major public health significance. While there is incontrovertible evidence that ultraviolet radiation (UVR) in the form of sunlight is a significant predisposing factor for non-melanoma and melanoma skin cancers in pale skinned people,1 a growing body of data suggest general health benefits brought about by sunlight.2 These are believed to be mediated either by melatonin or vitamin D. Melatonin is produced from serotonin by the pineal gland located in the centre of the brain during periods of darkness, and its release is suppressed as a function of the visible light intensity sensed through ocular photoreceptors. Vitamin D is formed by ultraviolet B (UVB)-mediated photolysis of 7-dehydrocholesterol in the skin. Both melatonin and vitamin D are pleiotropic hormones that exert a multitude of cellular effects by interacting with membrane and nuclear receptors, and receptor-independent actions. People with more heavily pigmented skin require higher doses of UVB to produce adequate amounts of vitamin D, and this may have been an evolutionary driver to the variation of human skin colour with latitude and intensity of solar irradiation. Our degree of exposure to sunlight is easily modified by behavioural factors such as the use of clothing, sunglasses, and sun-blocking creams, and time spent outdoors. Balancing the carcinogenic risks with the requirement for vitamin D has led to advice on moderating sun exposure, while supplementing food with vitamin D. Guidance on such behaviour is part of the public health campaigns in most countries with Caucasian populations. Following these suggestions, we may, however, be missing out on other health benefits provided by natural sunlight that are less obvious and unrelated to the above classical mediators
Outstanding Issues in Solar Dynamo Theory
The magnetic activity of the Sun, as manifested in the sunspot cycle,
originates deep within its convection zone through a dynamo mechanism which
involves non-trivial interactions between the plasma and magnetic field in the
solar interior. Recent advances in magnetohydrodynamic dynamo theory have led
us closer towards a better understanding of the physics of the solar magnetic
cycle. In conjunction, helioseismic observations of large-scale flows in the
solar interior has now made it possible to constrain some of the parameters
used in models of the solar cycle. In the first part of this review, I briefly
describe this current state of understanding of the solar cycle. In the second
part, I highlight some of the outstanding issues in solar dynamo theory related
to the the nature of the dynamo -effect, magnetic buoyancy and the
origin of Maunder-like minima in activity. I also discuss how poor constraints
on key physical processes such as turbulent diffusion, meridional circulation
and turbulent flux pumping confuse the relative roles of these vis-a-vis
magnetic flux transport. I argue that unless some of these issues are
addressed, no model of the solar cycle can claim to be ``the standard model'',
nor can any predictions from such models be trusted; in other words, we are
still not there yet.Comment: To appear in "Magnetic Coupling between the Interior and the
Atmosphere of the Sun", eds. S.S. Hasan and R.J. Rutten, Astrophysics and
Space Science Proceedings, Springer-Verlag, Heidelberg, Berlin, 200
Initial test bed concentrator characterization
The operational characteristics and the mirror alignment technique of the test bed concentrator control system are highlighted. The final design of the TBC control system provided one axis of fast slew capability so that either the Sun acquisition or emergency off-Sun mode could be obtained in a minimum time. The procedure for getting on and off Sun is to run the elevation axis up to the approximate elevation of the Sun for the particular time of acquisition and then slew the concentrator on Sun in azimuth. The automatic Sun-acquisition system is controlled by two Sun sensors, one for each axis; each has a 2deg acquisition cone angle within which the concentrators are programmed to point. The mirror alignment technique chosen utilized a semi-distant incandescent light source which produced a reflected image on the focal point target. The concentrator was boresighted to the light by moving the concentrator while sighting along the cross hairs and through the apertures in the disks to the light source resulting in a maximum point error of 0.11 deg. Test plans to install a solar flux mapper to characterize the solar spot and to measure the size, shape, and intensity of the Sun's image are outlined
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