4,794 research outputs found
The Quest for Understanding in Relativistic Quantum Physics
We discuss the status and some perspectives of relativistic quantum physics.Comment: Invited contribution to the Special Issue 2000 of the Journal of
Mathematical Physics, 38 pages, typos corrected and references added, as to
appear in JM
De problematiek van de kasgrondteelten: Mogelijke oplossingen aangedragen door ondernemers met substraatbedden in het bijzonder
De kasgrond glastuinbouw ziet zich geconfronteerd met stijgende kosten en een afname van de hoeveelheid toegelaten gewasbeschermingsmiddelen. Het middelenpakket tegen schadelijke bodemschimmels en aaltjes wordt mogelijk verkleind (Spruit e.a. 2008). Op dit moment is grondstomen nog een optie, maar door de sterk toenemende energie- en arbeidskosten wordt grondstomen steeds duurder. In voorgaande gesprekken met ondernemers en betrokkenen blijkt dat een teeltsysteem dat relatief goedkoop, en gemakkelijk in de praktijk is in te passen, de voorkeur heeft. Doelstelling van dit project is daarom het in kaart brengen van problemen met mogelijke oplossingen ten aanzien van bodemproblematiek in kasgrondteelten
Thermodynamics of a d-wave Superconductor Near a Surface
We study the properties of an anisotropically paired superconductor in the
presence of a specularly reflecting surface. The bulk stable phase of the
superconducting order parameter is taken to have symmetry.
Contributions by order parameter components of different symmetries vanish in
the bulk, but may enter in the vicinity of a wall. We calculate the
self-consistent order parameter and surface free energy within the
quasiclassical formulation of superconductivity. We discuss, in particular, the
dependence of these quantities on the degree of order parameter mixing and the
surface to lattice orientation. Knowledge of the thermodynamically stable order
parameter near a surface is a necessary precondition for calculating measurable
surface properties which we present in a companion paper.Comment: 12 pages of revtex text with 12 compressed and encoded figures. To
appear in J. Low Temp. Phys., December, 199
RSV-encoded NS2 promotes epithelial cell shedding and distal airway obstruction
Respiratory syncytial virus (RSV) infection is the major cause of bronchiolitis in young children. The factors that contribute to the increased propensity of RSV-induced distal airway disease compared with other commonly encountered respiratory viruses remain unclear. Here, we identified the RSV-encoded nonstructural 2 (NS2) protein as a viral genetic determinant for initiating RSV-induced distal airway obstruction. Infection of human cartilaginous airway epithelium (HAE) and a hamster model of disease with recombinant respiratory viruses revealed that NS2 promotes shedding of infected epithelial cells, resulting in two consequences of virus infection. First, epithelial cell shedding accelerated the reduction of virus titers, presumably by clearing virus-infected cells from airway mucosa. Second, epithelial cells shedding into the narrow-diameter bronchiolar airway lumens resulted in rapid accumulation of detached, pleomorphic epithelial cells, leading to acute distal airway obstruction. Together, these data indicate that RSV infection of the airway epithelium, via the action of NS2, promotes epithelial cell shedding, which not only accelerates viral clearance but also contributes to acute obstruction of the distal airways. Our results identify RSV NS2 as a contributing factor for the enhanced propensity of RSV to cause severe airway disease in young children and suggest NS2 as a potential therapeutic target for reducing the severity of distal airway disease
The split property for locally covariant quantum field theories in curved spacetime
The split property expresses the way in which local regions of spacetime define subsystems of a quantum field theory. It is known to hold for general theories in Minkowski space under the hypothesis of nuclearity. Here, the split property is discussed for general locally covariant quantum field theories in arbitrary globally hyperbolic curved spacetimes, using a spacetime deformation argument to transport the split property from one spacetime to another. It is also shown how states obeying both the split and (partial) Reeh–Schlieder properties can be constructed, providing standard split inclusions of certain local von Neumann algebras. Sufficient conditions are given for the theory to admit such states in ultrastatic spacetimes, from which the general case follows. A number of consequences are described, including the existence of local generators for global gauge transformations, and the classification of certain local von Neumann algebras. Similar arguments are applied to the distal split property and circumstances are exhibited under which distal splitting implies the full split property
From coinductive proofs to exact real arithmetic: theory and applications
Based on a new coinductive characterization of continuous functions we
extract certified programs for exact real number computation from constructive
proofs. The extracted programs construct and combine exact real number
algorithms with respect to the binary signed digit representation of real
numbers. The data type corresponding to the coinductive definition of
continuous functions consists of finitely branching non-wellfounded trees
describing when the algorithm writes and reads digits. We discuss several
examples including the extraction of programs for polynomials up to degree two
and the definite integral of continuous maps
Simulations of Weighted Tree Automata
Simulations of weighted tree automata (wta) are considered. It is shown how
such simulations can be decomposed into simpler functional and dual functional
simulations also called forward and backward simulations. In addition, it is
shown in several cases (fields, commutative rings, Noetherian semirings,
semiring of natural numbers) that all equivalent wta M and N can be joined by a
finite chain of simulations. More precisely, in all mentioned cases there
exists a single wta that simulates both M and N. Those results immediately
yield decidability of equivalence provided that the semiring is finitely (and
effectively) presented.Comment: 17 pages, 2 figure
Lamb Shift of 3P and 4P states and the determination of
The fine structure interval of P states in hydrogenlike systems can be
determined theoretically with high precision, because the energy levels of P
states are only slightly influenced by the structure of the nucleus. Therefore
a measurement of the fine structure may serve as an excellent test of QED in
bound systems or alternatively as a means of determining the fine structure
constant with very high precision. In this paper an improved analytic
calculation of higher-order binding corrections to the one-loop self energy of
3P and 4P states in hydrogen-like systems with low nuclear charge number is
presented. A comparison of the analytic results to the extrapolated numerical
data for high ions serves as an independent test of the analytic
evaluation. New theoretical values for the Lamb shift of the P states and for
the fine structure splittings are given.Comment: 33 pages, LaTeX, 4 tables, 4 figure
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