Requirements for Power Converters

This paper introduces the requirements for power converters needed for particle accelerators. It describes the role of power converters and the challenges and constraints when powering magnets. The different circuit layouts are presented as well as the operating cycles. The power converter control and high precision definition are also introduced. This paper lists the key circuit parameters to be taken into consideration to properly specify a power converter that can be compiled in a functional specification.Comment: 14 pages, contribution to the 2014 CAS - CERN Accelerator School: Power Converters, Baden, Switzerland, 7-14 May 201

The Magnetic Fraction of Coal Fly Ash: Its Separation, Properties, and Utilization

A laboratory-size electromagnetic device has been built to separate the high-iron magnetic fraction from coal fly ash. Fly ash, the fine particulate matter produced when pulverized coal is burned, contains an average of 18 wt. percent iron expressed as Fe2O3 found in a distinctive fraction of finely divided, dense, largely spheroidal particles of high magnetic susceptibility. Seventy to eighty percent of the iron in bituminous coal fly ash is found in this fraction which represents about 20 weight percent or 10 volume percent of the fly ash. In this work the iron-rich fraction has been characterized as to particle size, composition, and density. It appears to have a market potential as a material for preparation of high-density media used in coal washing and other mineral dressing processes. Dense-media material, which costs about $100 per metric ton, is being utilized in increasingly large quantities as the demand for washed coal expands. The magnetic fraction also appears to have potential as a source of iron. If further processing can reduce the silica level found in the fraction as it is separated from the ash, pellets with a composition similar to taconite can be prepared for use as blast furnace feed. Separation and use of this fraction of the coal ash could be profitable for utility companies and could be the beginning of the utilization of the large amount of ash which now constitutes a waste disposal problem

Recovery of Alumina From Coal Fly Ash By High Temperature Chlorination

The recovery of metals from low value sources will help reduce our national demand for foreign resources. The ash from bituminous type coals contains about 20 percent aluminum oxide and 20 percent iron oxides by weight. Recovery of these metals would provide an alternate source to the ores now used. The iron and aluminum materials in fly ash are recoverable by high temperature chlorination. Passing dry chlorine gas through a bed of nonmagnetic fly ash maintained at 850 to 900 degrees C. chlorinates the iron and aluminum constituents forming volatile compounds which are carried from the bed by the exit gas stream. In exploratory runs, 55 percent of the aluminum has been recovered as aluminum chloride in a nearly silica-free state

Cloud optical thickness and liquid water path – does the <i>k</i> coefficient vary with droplet concentration?

Cloud radiative transfer calculations in general circulation models involve a link between cloud microphysical and optical properties. Indeed, the liquid water content expresses as a function of the mean volume droplet radius, while the light extinction is a function of their mean surface radius. There is a small difference between these two parameters because of the droplet spectrum width. This issue has been addressed by introducing an empirical multiplying correction factor to the droplet concentration. Analysis of in situ sampled data, however, revealed that the correction factor decreases when the concentration increases, hence partially mitigating the aerosol indirect effect. <br><br> Five field experiments are reanalyzed here, in which standard and upgraded versions of the droplet spectrometer were used to document shallow cumulus and stratocumulus topped boundary layers. They suggest that the standard probe noticeably underestimates the correction factor compared to the upgraded versions. The analysis is further refined to demonstrate that the value of the correction factor derived by averaging values calculated locally along the flight path overestimates the value derived from liquid water path and optical thickness of a cloudy column, and that there is no detectable relationship between the correction factor and the droplet concentration. It is also shown that the droplet concentration dilution by entrainment-mixing after CCN activation is significantly stronger in shallow cumuli than in stratocumulus layers. These various effects are finally combined to produce the today best estimate of the correction factor to use in general circulation models

The Self Model and the Conception of Biological Identity in Immunology

The self/non-self model, first proposed by F.M. Burnet, has dominated immunology for sixty years now. According to this model, any foreign element will trigger an immune reaction in an organism, whereas endogenous elements will not, in normal circumstances, induce an immune reaction. In this paper we show that the self/non-self model is no longer an appropriate explanation of experimental data in immunology, and that this inadequacy may be rooted in an excessively strong metaphysical conception of biological identity. We suggest that another hypothesis, one based on the notion of continuity, gives a better account of immune phenomena. Finally, we underscore the mapping between this metaphysical deflation from self to continuity in immunology and the philosophical debate between substantialism and empiricism about identity

Towards a Phylogenetic Analysis of Galaxy Evolution : a Case Study with the Dwarf Galaxies of the Local Group

Context: The Hubble tuning fork diagram has always been the preferred scheme for classification of galaxies. It is based on morphology only. At the opposite, biologists have long taken into account the genealogical relatedness of living entities for classification purposes. Aims: Assuming branching evolution of galaxies as a 'descent with modification', we show here that the concepts and tools of phylogenetic systematics widely used in biology can be heuristically transposed to the case of galaxies. Methods: This approach that we call "astrocladistics" is applied to Dwarf Galaxies of the Local Group and provides the first evolutionary tree for real galaxies. Results: The trees that we present here are sufficiently solid to support the existence of a hierarchical organization in the diversity of dwarf galaxies of the Local Group. This also shows that these galaxies all derive from a common ancestral kind of objects. We find that some kinds of dIrrs are progenitors of both dSphs and other kinds of dIrrs.We also identify three evolutionary groups, each one having its own characteristics and own evolution. Conclusions: The present work opens a new way to analyze galaxy evolution and a path towards a new systematics of galaxies. Work on other galaxies in the Universe is in progress.Comment: 13 pages 5 figures with 3 online onl

Optical and Radio Polarimetry of the M87 Jet at 0.2" Resolution

We discuss optical (HST/WFPC2 F555W) and radio (15 GHz VLA) polarimetry observations of the M87 jet taken during 1994-1995. Many knot regions are very highly polarized ($\sim 40-50$, approaching the theoretical maximum for optically thin synchrotron radiation), suggesting highly ordered magnetic fields. High degrees of polarization are also observed in interknot regions. While the optical and radio polarization maps share many similarities, we observe significant differences between the radio and optical polarized structures, particularly for bright knots in the inner jet, giving us important insight into the jet's radial structure. Unlike in the radio, the optical magnetic field position angle becomes perpendicular to the jet at the upstream ends of knots HST-1, D, E and F. Moreover, the optical polarization decreases markedly at the position of the flux maxima in these knots. In contrast, the magnetic field position angle observed in the radio remains parallel to the jet in most of these regions, and the decreases in radio polarization are smaller. More minor differences are seen in other jet regions. Many of the differences between optical and radio polarimetry results can be explained in terms of a model whereby shocks occur in the jet interior, where higher-energy electrons are concentrated and dominate both polarized and unpolarized emissions in the optical, while the radio maps show strong contributions from lower-energy electrons in regions with {\bf B} parallel, near the jet surface.Comment: 28 pages, 7 figures; accepted for publication in AJ (May 1999

ON or OFF?: Modulating the N-Methyl-D-Aspartate Receptor in Major Depression

Since the discovery that a single dose of ketamine, an N-methyl-D-aspartate receptor (NMDAR) antagonist, had rapid and long-lasting antidepressant effects, there has been increased interest in using NMDAR modulators in the pharmacotherapy of depression. Ketamine's efficacy seems to imply that depression is a disorder of NMDAR hyperfunctionality. However, studies showing that not all NMDAR antagonists are able to act as antidepressants challenge this notion. Furthermore, NMDAR co-agonists have also been gaining attention as possible treatments. Co-agonists such as D-serine and sarcosine have shown efficacy in both pre-clinical models and human trials. This raises the question of how both NMDAR antagonists and agonists are able to have converging behavioral effects. Here we critically review the evidence and proposed therapeutic mechanisms for both NMDAR antagonists and agonists, and collate several theories on how both activation and inhibition of NMDARs appear to have antidepressant effects