666 research outputs found
Universal properties of knotted polymer rings
By performing Monte Carlo sampling of -steps self-avoiding polygons
embedded on different Bravais lattices we explore the robustness of
universality in the entropic, metric and geometrical properties of knotted
polymer rings. In particular, by simulating polygons with up to we
furnish a sharp estimate of the asymptotic values of the knot probability
ratios and show their independence on the lattice type. This universal feature
was previously suggested although with different estimates of the asymptotic
values. In addition we show that the scaling behavior of the mean squared
radius of gyration of polygons depends on their knot type only through its
correction to scaling. Finally, as a measure of the geometrical
self-entanglement of the SAPs we consider the standard deviation of the writhe
distribution and estimate its power-law behavior in the large limit. The
estimates of the power exponent do depend neither on the lattice nor on the
knot type, strongly supporting an extension of the universality property to
some features of the geometrical entanglement.Comment: submitted to Phys.Rev.
Phase transitions in a gas of anyons
We continue our numerical Monte Carlo simulation of a gas of closed loops on
a 3 dimensional lattice, however now in the presence of a topological term
added to the action corresponding to the total linking number between the
loops. We compute the linking number using certain notions from knot theory.
Adding the topological term converts the particles into anyons. Using the
correspondence that the model is an effective theory that describes the
2+1-dimensional Abelian Higgs model in the asymptotic strong coupling regime,
the topological linking number simply corresponds to the addition to the action
of the Chern-Simons term. We find the following new results. The system
continues to exhibit a phase transition as a function of the anyon mass as it
becomes small \cite{mnp}, although the phases do not change the manifestation
of the symmetry. The Chern-Simons term has no effect on the Wilson loop, but it
does affect the {\rm '}t Hooft loop. For a given configuration it adds the
linking number of the 't Hooft loop with all of the dynamical vortex loops to
the action. We find that both the Wilson loop and the 't Hooft loop exhibit a
perimeter law even though there are no massless particles in the theory, which
is unexpected.Comment: 6 pages, 5 figure
Disconnect within Agriculture and Ecosystem Climate Effects, Adaptations and Policy
Frequently, agriculture and ecosystems (AE) are seen as separate entities, causing entity specific solutions in response to threats. Anthropogenic climate change simultaneously stresses both agriculture and ecosystems along with their interactions. Induced increasing surface temperatures [1], altered precipitation [2], drought intensification [3], altered ground and surface water quantity/quality [4,5], and diminished soil moisture [6] force adaptations for AE, but these adaptations fail to be efficient when interdependencies are not considered. Additional adaptations will be necessary, as future projections anticipate even greater climate change [1]
Die Folgen des Libyen-Konflikts für Afrika: Gräben zwischen der AU und dem Westen, Destabilisierung der Sahelzone
Der Bürgerkrieg und die Nato-Intervention in Libyen haben Auswirkungen auf Afrika und die europäische Afrikapolitik, denen bislang zu wenig Aufmerksamkeit geschenkt wurde. Kurz- und mittelfristig droht eine weitere Destabilisierung der Sahelzone. Der im Januar 2012 neu ausgebrochene Konflikt im Norden Malis ist eine direkte Folge des libyschen Bürgerkriegs, ebenso wie die Rückkehr von Kämpfern aus Libyen und die Zunahme des Waffenschmuggels. Außerdem hat der Libyen-Konflikt neue Hindernisse für regionale Kooperation im Sahel aufgetürmt. Nicht minder gravierend sind die mittel- und langfristigen internationalen Folgen der Nato-Intervention. Sie hat Streit zwischen afrikanischen und westlichen Staaten verursacht, der die oft beschworene »Partnerschaft auf Augenhöhe« als deklaratorische Politik zu entblößen droht. Auch innerhalb der Afrikanischen Union hat der Umgang mit der Krise Spannungen hervorgerufen, die die Handlungsfähigkeit der Organisation nach innen wie außen beeinträchtigen werden.
Aus diesen Gründen muss deutsche und europäische Afrikapolitik auf mehreren Ebenen reagieren. Europa muss seinen Ansatz für den Sahel modifizieren, denn bisher wollte die EU vor allem die Sicherheitskräfte in der Region stärken. Dies geht nicht nur an den eigentlichen Problemen vorbei, sondern könnte Auseinandersetzungen sogar befeuern und regionale Kooperation erschweren. Stattdessen sollte die EU weit mehr Gewicht auf die Förderung regionaler Anstrengungen legen sowie Libyen und Algerien entschlossener in ihre Sahel-Strategie einbeziehen. Für Europa wird eine funktionsfähige AU in Zukunft noch wichtiger werden. Deutschland und die EU sollten sich daher bemühen, die politischen Gräben zuzuschütten, die der Umgang mit dem Libyen-Konflikt aufgerissen hat. (Autorenreferat
RDF Querying
Reactive Web systems, Web services, and Web-based publish/
subscribe systems communicate events as XML messages, and in
many cases require composite event detection: it is not sufficient to react
to single event messages, but events have to be considered in relation to
other events that are received over time.
Emphasizing language design and formal semantics, we describe the
rule-based query language XChangeEQ for detecting composite events.
XChangeEQ is designed to completely cover and integrate the four complementary
querying dimensions: event data, event composition, temporal
relationships, and event accumulation. Semantics are provided as
model and fixpoint theories; while this is an established approach for rule
languages, it has not been applied for event queries before
Genomic diversity of pathogenic Escherichia coli of the EHEC 2 clonal complex
BACKGROUND: Evolutionary analyses of enterohemorrhagic Escherichia coli (EHEC) have identified two distantly related clonal groups: EHEC 1, including serotype O157:H7 and its inferred ancestor O55:H7; and EHEC 2, comprised of several serogroups (O26, O111, O118, etc.). These two clonal groups differ in their virulence and global distribution. Although several fully annotated genomic sequences exist for strains of serotype O157:H7, much less is known about the genomic composition of EHEC 2. In this study, we analyzed a set of 24 clinical EHEC 2 strains representing serotypes O26:H11, O111:H8/H11, O118:H16, O153:H11 and O15:H11 from humans and animals by comparative genomic hybridization (CGH) on an oligoarray based on the O157:H7 Sakai genome. RESULTS: Backbone genes, defined as genes shared by Sakai and K-12, were highly conserved in EHEC 2. The proportion of Sakai phage genes in EHEC 2 was substantially greater than that of Sakai-specific bacterial (non-phage) genes. This proportion was inverted in O55:H7, reiterating that a subset of Sakai bacterial genes is specific to EHEC 1. Split decomposition analysis of gene content revealed that O111:H8 was more genetically uniform and distinct from other EHEC 2 strains, with respect to the Sakai O157:H7 gene distribution. Serotype O26:H11 was the most heterogeneous EHEC 2 subpopulation, comprised of strains with the highest as well as the lowest levels of Sakai gene content conservation. Of the 979 parsimoniously informative genes, 15% were found to be compatible and their distribution in EHEC 2 clustered O111:H8 and O118:H16 strains by serotype. CGH data suggested divergence of the LEE island from the LEE1 to the LEE4 operon, and also between animal and human isolates irrespective of serotype. No correlation was found between gene contents and geographic locations of EHEC 2 strains. CONCLUSION: The gene content variation of phage-related genes in EHEC 2 strains supports the hypothesis that extensive modular shuffling of mobile DNA elements has occurred among EHEC strains. These results suggest that EHEC 2 is a multiform pathogenic clonal complex, characterized by substantial intra-serotype genetic variation. The heterogeneous distribution of mobile elements has impacted the diversification of O26:H11 more than other EHEC 2 serotypes
Sources and nature of ice-nucleating particles in the free troposphere at Jungfraujoch in winter 2017
Primary ice formation in mixed-phase clouds is initiated by a
minute subset of the ambient aerosol population, called ice-nucleating
particles (INPs). The knowledge about their atmospheric concentration,
composition, and source in cloud-relevant environments is still limited.
During the 2017 joint INUIT/CLACE (Ice Nuclei research UnIT/CLoud–Aerosol
Characterization Experiment) field campaign, observations of INPs as
well as of aerosol physical and chemical properties were performed,
complemented by source region modeling. This aimed at investigating the
nature and sources of INPs. The campaign took place at the High-Altitude
Research Station Jungfraujoch (JFJ), a location where mixed-phase clouds
frequently occur. Due to its altitude of 3580 m a.s.l., the station is
usually located in the lower free troposphere, but it can also receive air
masses from terrestrial and marine sources via long-range transport. INP
concentrations were quasi-continuously detected with the Horizontal Ice
Nucleation Chamber (HINC) under conditions representing the formation of
mixed-phase clouds at −31 ∘C. The INP measurements were performed
in parallel to aerosol measurements from two single-particle mass
spectrometers, the Aircraft-based Laser ABlation Aerosol MAss Spectrometer
(ALABAMA) and the laser ablation aerosol particle time-of-flight mass
spectrometer (LAAPTOF). The chemical identity of INPs is inferred by
correlating the time series of ion signals measured by the mass
spectrometers with the time series of INP measurements. Moreover, our
results are complemented by the direct analysis of ice particle residuals
(IPRs) by using an ice-selective inlet (Ice-CVI) coupled with the ALABAMA.
Mineral dust particles and aged sea spray particles showed the highest
correlations with the INP time series. Their role as INPs is further
supported by source emission sensitivity analysis using atmospheric
transport modeling, which confirmed that air masses were advected from the
Sahara and marine environments during times of elevated INP
concentrations and ice-active surface site densities. Indeed, the IPR
analysis showed that, by number, mineral dust particles dominated the IPR
composition (∼58 %), and biological and metallic
particles are also found to a smaller extent (∼10 % each). Sea
spray particles are also found as IPRs (17 %), and their fraction in the
IPRs strongly varied according to the increased presence of small IPRs,
which is likely due to an impact from secondary ice crystal formation. This
study shows the capability of combining INP concentration measurements with
chemical characterization of aerosol particles using single-particle mass
spectrometry, source region modeling, and analysis of ice residuals in an
environment directly relevant for mixed-phase cloud formation.</p
Duhamel versus transanal endorectal pull through (TERPT) for the surgical treatment of Hirschsprung’s disease
For the surgical treatment of Hirschsprung’s disease, several surgical techniques are used to resect the distal aganglionic colon. Two frequently used techniques are the Duhamel procedure and the transanal endorectal pull-through procedure. During the ‘8th Pediatric Colorectal Course’ in Nijmegen, November 2015, a workshop was organized to share experiences of both techniques by several experts in the field and to discuss (long term) outcomes. Specifically, the objective of the meeting was to discuss the main controversies in relation to the technical execution of both procedures in order to make an initial assessment of the limitations of available evidence for clinical decision-making and to formulate a set of preliminary recommendations for current clinical care and future research
The Horizontal Ice Nucleation Chamber (HINC) : INP measurements at conditions relevant for mixed-phase clouds at the High Altitude Research Station Jungfraujoch
In this work we describe the Horizontal Ice Nucleation Chamber (HINC) as a new instrument to measure ambient ice-nucleating particle
(INP) concentrations for conditions relevant to mixed-phase
clouds. Laboratory verification and validation experiments confirm
the accuracy of the thermodynamic conditions of temperature (T)
and relative humidity (RH) in HINC with uncertainties in T
of ±0.4 K and in RH with respect to water
(RHw) of ±1.5 %, which translates
into an uncertainty in RH with respect to ice
(RHi) of ±3.0 % at T > 235 K. For further validation of HINC as a field
instrument, two measurement campaigns were conducted in winters 2015
and 2016 at the High Altitude Research Station Jungfraujoch (JFJ;
Switzerland, 3580 m a. s. l. ) to sample ambient INPs. During
winters 2015 and 2016 the site encountered free-tropospheric
conditions 92 and 79 % of the time, respectively. We measured
INP concentrations at 242 K at water-subsaturated conditions
(RHw = 94 %), relevant for the formation of
ice clouds, and in the water-supersaturated regime
(RHw = 104 %) to represent ice formation
occurring under mixed-phase cloud conditions. In winters 2015 and
2016 the median INP concentrations at RHw = 94 % was below the minimum detectable concentration. At
RHw = 104 %, INP concentrations were an
order of magnitude higher, with median concentrations in winter 2015
of 2.8 per standard liter (std L−1; normalized to
standard T of 273 K and pressure, p, of
1013 hPa) and 4.7 std L−1 in winter 2016. The
measurements are in agreement with previous winter measurements
obtained with the Portable Ice Nucleation Chamber (PINC) of
2.2 std L−1 at the same location. During winter 2015,
two events caused the INP concentrations at RHw = 104 % to significantly increase above the campaign
average. First, an increase to 72.1 std L−1 was measured
during an event influenced by marine air, arriving at the JFJ from
the North Sea and the Norwegian Sea. The contribution from
anthropogenic or other sources can thereby not be ruled out. Second,
INP concentrations up to 146.2 std L−1 were observed
during a Saharan dust event. To our knowledge this is the first time
that a clear enrichment in ambient INP concentration in remote
regions of the atmosphere is observed during a time of marine air
mass influence, suggesting the importance of marine particles on ice
nucleation in the free troposphere
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