2,585 research outputs found
The Effect of Air on Granular Size Separation in a Vibrated Granular Bed
Using high-speed video and magnetic resonance imaging (MRI) we study the
motion of a large sphere in a vertically vibrated bed of smaller grains. As
previously reported we find a non-monotonic density dependence of the rise and
sink time of the large sphere. We find that this density dependence is solely
due to air drag. We investigate in detail how the motion of the intruder sphere
is influenced by size of the background particles, initial vertical position in
the bed, ambient pressure and convection. We explain our results in the
framework of a simple model and find quantitative agreement in key aspects with
numerical simulations to the model equations.Comment: 14 pages, 16 figures, submitted to PRE, corrected typos, slight
change
Intergenerational Education: The significance of 'reciprocity' and 'place'
In this article, the case is made for greater clarity in the definition of intergenerational practice and intergenerational education. Theoretically, the effects of all-age reciprocity and the significance of attending to 'place' are explored. Taken together, they help point to what is distinctive about the scope and purpose of intergenerational education. The author argues that any intergenerational practice must always involve an educative element that is focused, at least in part, on the on-going reciprocal production of new relations between generations through the way challenges are purposefully responded to in some specific place
Curriculum Making as the Enactment of Dwelling in Places
This article uses an account of dwelling to interrogate the concept of curriculum making. Tim Ingold's use of dwelling to understand culture is productive here because of his implicit and explicit interest in intergenerational learning. His account of dwelling rests on a foundational ontological claim-that mental construction and representation are not the basis upon which we live in the world-which is very challenging for the kinds of curriculum making with which many educators are now familiar. It undermines assumptions of propositional knowledge and of the use of mental schemas to communicate and share. At the level of critique, then, dwelling destabilizes contemporary ideas of curriculum as textual, pre-specified content for transmission or pre-defined objectives or standardized activity. The positive claims of dwelling are equally challenging, for these are that the world is a domain of relational entanglement in which an organism can be no more than a point of growth for an emergent ‘environment', and meaning only inheres in these relations. The paper articulates how differentiation (of learner, salient meanings, knowledge, skill and place) are possible in such an ontology, and how curriculum making can be understood from this perspective as being the remaking of relationships between these
Crustal Emission and the Quiescent Spectrum of the Neutron Star in KS 1731-260
(Abridged). The type-I X-ray bursting low mass X-ray binary KS 1731-260 was
recently detected for the first time in quiescence by Wijnands et al.,
following an approximately 13 yr outburst which ended in Feb 2001. Unlike all
other known transient neutron stars, the duration of this recent outburst is as
long as the thermal diffusion time of the crust. The large amount of heat
deposited by reactions in the crust will have heated the crust to temperatures
much higher than the equilibrium core temperature. As a result, the thermal
luminosity currently observed from the neutron star is dominated not by the
core, but by the crust. Moreover, the level and the time evolution of quiescent
luminosity is determined mostly by the amount of heat deposited in the crust
during the most recent outburst. Using estimates of the outburst mass accretion
rate, our calculations of the quiescent flux immediately following the end of
the outburst agree with the observed quiescent flux to within a factor of a
few. We present simulations of the evolution of the quiescent lightcurve for
different scenarios of the crust microphysics, and demonstrate that monitoring
observations (with currently flying instruments) spanning from 1--30 yr can
measure the crust cooling timescale and the total amount of heat stored in the
crust. These quantities have not been directly measured for any neutron star.Comment: Submitted to ApJ; 7 text pages, 3 figures, uses emulateapj.sty and
apjfonts.st
An Update of Sounding of the Atmosphere Using Broadband Emission Radiometry (SABER) Calibration
The sounding of the atmosphere using broadband emission radiometry (SABER) instrument is a 10-channel infrared (1.27–16.9μm) radiometer launched on the TIMED (Thermosphere, Ionosphere, Mesosphere Energetics, and Dynamics) satellite in December 2001 from Vandenburg Air Force Base. SABER measures earthlimb emissions and characterizes infrared radiation, allowing calculation of atmospheric temperature and composition (ozone, water vapor, and carbon dioxide), as well as solar and chemical heating rates and infrared cooling rates. Although SABER focuses on the unexplored 60-180km region, it makes measurements covering the 10-350km altitude region. Ground calibration testing was completed in September 1999. Subsequent data analyses and report generation were completed in June, 2000. This paper provides a brief overview of instrument design, calibration planning, ground calibration testing, and results. Also included is an assessment of nearly five years of post launch validation and calibration maintenance. Using SABER as an example, conclusions are given regarding the benefit of a detailed calibration approach and how it enhances the quality of science data and mission success
The intracellular chloride ion channel protein CLIC1 undergoes a redox-controlled structural transition.
Most proteins adopt a well defined three-dimensional structure; however, it is increasingly recognized that some proteins can exist with at least two stable conformations. Recently, a class of intracellular chloride ion channel proteins (CLICs) has been shown to exist in both soluble and integral membrane forms. The structure of the soluble form of CLIC1 is typical of a soluble glutathione S-transferase superfamily protein but contains a glutaredoxin-like active site. In this study we show that on oxidation CLIC1 undergoes a reversible transition from a monomeric to a non-covalent dimeric state due to the formation of an intramolecular disulfide bond (Cys-24-Cys-59). We have determined the crystal structure of this oxidized state and show that a major structural transition has occurred, exposing a large hydrophobic surface, which forms the dimer interface. The oxidized CLIC1 dimer maintains its ability to form chloride ion channels in artificial bilayers and vesicles, whereas a reducing environment prevents the formation of ion channels by CLIC1. Mutational studies show that both Cys-24 and Cys-59 are required for channel activity
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