1,595 research outputs found
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
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
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
Assay, Purification, and Partial Characterization of Choline Monooxygenase from Spinach
Astrocladistics: a phylogenetic analysis of galaxy evolution I. Character evolutions and galaxy histories
This series of papers is intended to present astrocladistics in some detail
and evaluate this methodology in reconstructing phylogenies of galaxies. Being
based on the evolution of all the characters describing galaxies, it is an
objective way of understanding galaxy diversity through evolutionary
relationships. In this first paper, we present the basic steps of a cladistic
analysis and show both theoretically and practically that it can be applied to
galaxies. For illustration, we use a sample of 50 simulated galaxies taken from
the GALICS database, which are described by 91 observables (dynamics, masses
and luminosities). These 50 simulated galaxies are indeed 10 different galaxies
taken at 5 cosmological epochs, and they are free of merger events. The
astrocladistic analysis easily reconstructs the true chronology of evolution
relationships within this sample. It also demonstrates that burst characters
are not relevant for galaxy evolution as a whole. A companion paper is devoted
to the formalization of the concepts of formation and diversification in galaxy
evolution.Comment: 16 pages, 6 figure
Astrocladistics: a phylogenetic analysis of galaxy evolution II. Formation and diversification of galaxies
This series of papers is intended to evaluate astrocladistics in
reconstructing phylogenies of galaxies. The objective of this second paper is
to formalize the concept of galaxy formation and to identify the processes of
diversification. We show that galaxy diversity can be expected to organize
itself in a hierarchy. In order to better understand the role of mergers, we
have selected a sample of 43 galaxies from the GALICS database built from
simulations with a hybrid model for galaxy formation studies. These simulated
galaxies, described by 119 characters and considered as representing still
undefined classes, have experienced different numbers of merger events during
evolution. Our cladistic analysis yields a robust tree that proves the
existence of a hierarchy. Mergers, like interactions (not taken into account in
the GALICS simulations), are probably a strong driver for galaxy
diversification. Our result shows that mergers participate in a branching type
of evolution, but do not seem to play the role of an evolutionary clock.Comment: 14 pages, 4 figure
Novel Topology for Four-Quadrant Converter
Particle accelerators, like the LHC (Large Hadron Collider), make use of true bipolar power converters to feed superconducting magnets. Moreover, the LHC imposes that most converters must be installed underground. This constraint leads to the necessity of a high efficiency and a reduced volume for all the power converters. In this paper, the authors present a novel four-quadrant topology composed by an association of a ZVS-inverter and a ZCS-rectifier. This DC-AC-DC converter is fully reversible and a soft-switching operation mode is achieved for all switches over the full operating range. After a thorough analysis of the prototype design [±600A, ±10V], simulation and experimental results confirm the general performance of this power structure
A statistical mechanics approach to autopoietic immune networks
The aim of this work is to try to bridge over theoretical immunology and
disordered statistical mechanics. Our long term hope is to contribute to the
development of a quantitative theoretical immunology from which practical
applications may stem. In order to make theoretical immunology appealing to the
statistical physicist audience we are going to work out a research article
which, from one side, may hopefully act as a benchmark for future improvements
and developments, from the other side, it is written in a very pedagogical way
both from a theoretical physics viewpoint as well as from the theoretical
immunology one.
Furthermore, we have chosen to test our model describing a wide range of
features of the adaptive immune response in only a paper: this has been
necessary in order to emphasize the benefit available when using disordered
statistical mechanics as a tool for the investigation. However, as a
consequence, each section is not at all exhaustive and would deserve deep
investigation: for the sake of completeness, we restricted details in the
analysis of each feature with the aim of introducing a self-consistent model.Comment: 22 pages, 14 figur
Prophylactic radiotherapy against heterotopic ossification following internal fixation of acetabular fractures: a comparative estimate of risk.
OBJECTIVE: Radiotherapy (RT) is effective in preventing heterotopic ossification (HO) around acetabular fractures requiring surgical reconstruction. We audited outcomes and estimated risks from RT prophylaxis, and alternatives of indometacin or no prophylaxis. METHODS: 34 patients underwent reconstruction of acetabular fractures through a posterior approach, followed by a 8-Gy single fraction. The mean age was 44 years. The mean time from surgery to RT was 1.1 days. The major RT risk is radiation-induced fatal cancer. The International Commission on Radiological Protection (ICRP) method was used to estimate risk, and compared with a method (Trott and Kemprad) specifically for estimating RT risk for benign disease. These were compared with risks associated with indometacin and no prophylaxis. RESULTS: 28 patients (82%) developed no HO; 6 developed Brooker Class I; and none developed Class II-IV HO. The ICRP method suggests a risk of fatal cancer in the range of 1 in 1000 to 1 in 10,000; the Trott and Kemprad method suggests 1 in 3000. For younger patients, this may rise to 1 in 2000; and for elderly patients, it may fall to 1 in 6000. The risk of death from gastric bleeding or perforation from indometacin is 1 in 180 to 1 in 900 in older patients. Without prophylaxis risk of death from reoperation to remove HO is 1 in 4000 to 1 in 30,000. CONCLUSION: These results are encouraging, consistent with much larger series and endorse our multidisciplinary management. Risk estimates can be used in discussion with patients. ADVANCES IN KNOWLEDGE: The risk from RT prophylaxis is small, it is safer than indometacin and substantially overlaps with the range for no prophylaxis.NGB is supported by the National Institute for Health Research (NIHR) Cambridge Biomedical Research Centre. JES is supported by Cancer Research UK through the Cambridge Cancer Centre.This is the accepted manuscript version. The final version is available from the BIR at http://www.birpublications.org/doi/abs/10.1259/bjr.20140398?url_ver=Z39.88-2003&rfr_id=ori:rid:crossref.org&rfr_dat=cr_pub%3dpubmed&
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