2,195 research outputs found
Moduli-Space Dynamics of Noncommutative Abelian Sigma-Model Solitons
In the noncommutative (Moyal) plane, we relate exact U(1) sigma-model
solitons to generic scalar-field solitons for an infinitely stiff potential.
The static k-lump moduli space C^k/S_k features a natural K"ahler metric
induced from an embedding Grassmannian. The moduli-space dynamics is blind
against adding a WZW-like term to the sigma-model action and thus also applies
to the integrable U(1) Ward model. For the latter's two-soliton motion we
compare the exact field configurations with their supposed moduli-space
approximations. Surprisingly, the two do not match, which questions the
adiabatic method for noncommutative solitons.Comment: 1+15 pages, 2 figures; v2: reference added, to appear in JHE
Salmonella Isolated from Animals and Feed Production in Sweden Between 1993 and 1997
This paper presents Salmonella data from animals, feedstuffs and feed mills in Sweden between 1993 and 1997. During that period, 555 isolates were recorded from animals, representing 87 serotypes. Of those, 30 serotypes were found in animals in Sweden for the first time. The majority of all isolates from animals were S. Typhimurium (n = 91), followed by S. Dublin (n = 82). There were 115 isolates from cattle, 21 from broilers, 56 from layers and 18 from swine. The majority of these isolates were from outbreaks, although some were isolated at the surveillance at slaughterhouses. The number of isolates from the feed industry was similar to that of the previous 5-year period. Most of those findings were from dust and scrapings from feed mills, in accordance with the HACCP programme in the feed control programme. It can be concluded that the occurrence of Salmonella in animals and in the feed production in Sweden remained favourable during 1993–97
A Quantum Hall Fluid of Vortices
In this note we demonstrate that vortices in a non-relativistic Chern-Simons
theory form a quantum Hall fluid. We show that the vortex dynamics is
controlled by the matrix mechanics previously proposed by Polychronakos as a
description of the quantum Hall droplet. As the number of vortices becomes
large, they fill the plane and a hydrodynamic treatment becomes possible,
resulting in the non-commutative theory of Susskind. Key to the story is the
recent D-brane realisation of vortices and their moduli spaces.Comment: 10 pages. v2(3): (More) References adde
Autocatalytic amplification of Alzheimer-associated Aβ42 peptide aggregation in human cerebrospinal fluid
Alzheimer’s disease is linked to amyloid β (Aβ) peptide aggregation in the brain, and a
detailed understanding of the molecular mechanism of Aβ aggregation may lead to improved
diagnostics and therapeutics. While previous studies have been performed in pure buffer, we
approach the mechanism in vivo using cerebrospinal fluid (CSF). We investigated the
aggregation mechanism of Aβ42 in human CSF through kinetic experiments at several Aβ42
monomer concentrations (0.8–10 µM). The data were subjected to global kinetic analysis and
found consistent with an aggregation mechanism involving secondary nucleation of monomers on the fibril surface. A mechanism only including primary nucleation was ruled out. We
find that the aggregation process is composed of the same microscopic steps in CSF as in
pure buffer, but the rate constant of secondary nucleation is decreased. Most importantly, the
autocatalytic amplification of aggregate number through catalysis on the fibril surface is
prevalent also in CSF
Cold Strangelets Formation with Finite Size Effects in High Energy Heavy-Ion Collisions
We have studied the phase diagram and evolution of a strangelet in
equilibrium with a finite hadronic gas. Significant finite size modifications
of the phase diagram are found and their parameter dependences are studied.
With the inclusion of finite size effects we have also been able to obtain the
detailed properties of the cold strangelet emerging in the final stage of the
isentropic expansion of a finite strange fireball in high energy heavy-ion
collisions.Comment: 19 pages(RevTex), 11 Postscript figures; To appear in Phys. Rev.
The pigmented life of a redhead.
As a redhead I have had a personal interest in red hair, freckles and sunburns since childhood. An observation of a formaldehyde-induced fluorescence in human epidermal melanocytes initiated my scientific interest in these cells. Prota and Nicolaus demonstrated that oxidation products of cysteinyldopas are the main components of pheomelanin. Our identification of 5-S-cysteinyldopa as the source of formaldehyde-induced fluorescence of normal and pathological melanocytes started a series of investigations into this amino acid, enzymatic and non-enzymatic oxidation of catecholic compounds and the metabolism of thiols. All melanocytes with functioning tyrosinase produce cysteinyldopas and the levels of 5-S-cysteinyldopa in serum and urine are related to the size and pigment forming activity of the melanocyte population. The determination of 5-S-cysteinyldopa in serum or urine is a sensitive diagnostic method in the detection of melanoma metastasis. Some non-specific formation of cysteinyldopa is present in the body, as demonstrated by 5-S-cysteinyldopa in individuals with tyrosinase-negative albinism
Cirrus cloud occurrence as function of ambient relative humidity: A comparison of observations from the Southern and Northern Hemisphere midlatitudes obtained during the INCA experiment
International audienceThe occurrence frequency of cirrus clouds as function of ambient relative humidity over ice, based on in-situ observations performed during the INCA experiment, show a clear difference between the campaign carried out at Southern Hemisphere (SH) midlatitudes and the campaign carried out at Northern Hemisphere (NH) midlatitudes. At a given relative humidity above ice saturation, clouds are more frequent in the NH. At relative humidities near ice saturation, clouds defined as containing particles with sizes larger than 0.55 µm diameter and an integral number density above 0.2 cm-3 were present 70% of the time during the SH campaign, whereas clouds where present 95% of the time during the NH campaign. Using a size threshold of 1 µm diameter to define the presence of clouds result in a less frequent occurrence of 60% of the time in the SH campaign and 75% of the time in the NH campaign. The data show that the presence of particles is a common characteristic of cirrus clouds. Clouds at ice saturation defined as having crystal sizes of at least 5 µm diameter and a number density exceeding 0.001 cm-3 were present in about 80% of the time during the SH campaign, and almost 90% of the time during the NH campaign. The observations reveal a significant cloud presence fraction at humidities well below ice saturation. Local minima in the cloud presence fraction as a function of relative humidity are interpreted as systematic underestimation of cloud presence because cloud particles may become invisible to cloud probes. Based on this interpretation the data suggests that clouds in the SH form preferentially at relative humidities between 140 and 155%, whereas clouds in the NH formed at relative humidities less than 130%. A simple assumption about the probability to reach successively higher humidities in an ice supersaturated air parcel provides a model that explains the main trend of the cloud presence fraction as function of relative humidity. If adiabatic processes are assumed a cloud water content distribution can be derived from this probability model. The resulting distribution agrees well in shape compared to observations, but the observed mean cloud water content is less than expected from simply adiabatic processes
Competition-based model of pheromone component ratio detection in the moth
For some moth species, especially those closely interrelated and sympatric, recognizing a specific pheromone component concentration ratio is essential for males to successfully locate conspecific females. We propose and determine the properties of a minimalist competition-based feed-forward neuronal model capable of detecting a certain ratio of pheromone components independently of overall concentration. This model represents an elementary recognition unit for the ratio of binary mixtures which we propose is entirely contained in the macroglomerular complex (MGC) of the male moth. A set of such units, along with projection neurons (PNs), can provide the input to higher brain centres. We found that (1) accuracy is mainly achieved by maintaining a certain ratio of connection strengths between olfactory receptor neurons (ORN) and local neurons (LN), much less by properties of the interconnections between the competing LNs proper. An exception to this rule is that it is beneficial if connections between generalist LNs (i.e. excited by either pheromone component) and specialist LNs (i.e. excited by one component only) have the same strength as the reciprocal specialist to generalist connections. (2) successful ratio recognition is achieved using latency-to-first-spike in the LN populations which, in contrast to expectations with a population rate code, leads to a broadening of responses for higher overall concentrations consistent with experimental observations. (3) when longer durations of the competition between LNs were observed it did not lead to higher recognition accuracy
A Cognitive Model of an Epistemic Community: Mapping the Dynamics of Shallow Lake Ecosystems
We used fuzzy cognitive mapping (FCM) to develop a generic shallow lake
ecosystem model by augmenting the individual cognitive maps drawn by 8
scientists working in the area of shallow lake ecology. We calculated graph
theoretical indices of the individual cognitive maps and the collective
cognitive map produced by augmentation. The graph theoretical indices revealed
internal cycles showing non-linear dynamics in the shallow lake ecosystem. The
ecological processes were organized democratically without a top-down
hierarchical structure. The steady state condition of the generic model was a
characteristic turbid shallow lake ecosystem since there were no dynamic
environmental changes that could cause shifts between a turbid and a clearwater
state, and the generic model indicated that only a dynamic disturbance regime
could maintain the clearwater state. The model developed herein captured the
empirical behavior of shallow lakes, and contained the basic model of the
Alternative Stable States Theory. In addition, our model expanded the basic
model by quantifying the relative effects of connections and by extending it.
In our expanded model we ran 4 simulations: harvesting submerged plants,
nutrient reduction, fish removal without nutrient reduction, and
biomanipulation. Only biomanipulation, which included fish removal and nutrient
reduction, had the potential to shift the turbid state into clearwater state.
The structure and relationships in the generic model as well as the outcomes of
the management simulations were supported by actual field studies in shallow
lake ecosystems. Thus, fuzzy cognitive mapping methodology enabled us to
understand the complex structure of shallow lake ecosystems as a whole and
obtain a valid generic model based on tacit knowledge of experts in the field.Comment: 24 pages, 5 Figure
- …