356 research outputs found
Turbulence-induced melting of a nonequilibrium vortex crystal in a forced thin fluid film
To develop an understanding of recent experiments on the turbulence-induced
melting of a periodic array of vortices in a thin fluid film, we perform a
direct numerical simulation of the two-dimensional Navier-Stokes equations
forced such that, at low Reynolds numbers, the steady state of the film is a
square lattice of vortices. We find that, as we increase the Reynolds number,
this lattice undergoes a series of nonequilibrium phase transitions, first to a
crystal with a different reciprocal lattice and then to a sequence of crystals
that oscillate in time. Initially the temporal oscillations are periodic; this
periodic behaviour becomes more and more complicated, with increasing Reynolds
number, until the film enters a spatially disordered nonequilibrium statistical
steady that is turbulent. We study this sequence of transitions by using
fluid-dynamics measures, such as the Okubo-Weiss parameter that distinguishes
between vortical and extensional regions in the flow, ideas from nonlinear
dynamics, e.g., \Poincare maps, and theoretical methods that have been
developed to study the melting of an equilibrium crystal or the freezing of a
liquid and which lead to a natural set of order parameters for the crystalline
phases and spatial autocorrelation functions that characterise short- and
long-range order in the turbulent and crystalline phases, respectively.Comment: 31 pages, 56 figures, movie files not include
Too much of a good thing: how ectopic DNA replication affects bacterial replication dynamics
Copyright Š 2020 Syeda, Dimude, Skovgaard and Rudolph. Each cell division requires the complete and accurate duplication of the entire genome. In bacteria, the duplication process of the often-circular chromosomes is initiated at a single origin per chromosome, resulting in two replication forks that traverse the chromosome in opposite directions. DNA synthesis is completed once the two forks fuse in a region diametrically opposite the origin. In some bacteria, such as Escherichia coli, the region where forks fuse forms a specialized termination area. Polar replication fork pause sites flanking this area can pause the progression of replication forks, thereby allowing forks to enter but not to leave. Transcription of all required genes has to take place simultaneously with genome duplication. As both of these genome trafficking processes share the same template, conflicts are unavoidable. In this review, we focus on recent attempts to add additional origins into various ectopic chromosomal locations of the E. coli chromosome. As ectopic origins disturb the native replichore arrangements, the problems resulting from such perturbations can give important insights into how genome trafficking processes are coordinated and the problems that arise if this coordination is disturbed. The data from these studies highlight that head-on replicationâtranscription conflicts are indeed highly problematic and multiple repair pathways are required to restart replication forks arrested at obstacles. In addition, the existing data also demonstrate that the replication fork trap in E. coli imposes significant constraints to genome duplication if ectopic origins are active. We describe the current models of how replication fork fusion events can cause serious problems for genome duplication, as well as models of how such problems might be alleviated both by a number of repair pathways as well as the replication fork trap system. Considering the problems associated both with head-on replication- transcription conflicts as well as head-on replication fork fusion events might provide clues of how these genome trafficking issues have contributed to shape the distinct architecture of bacterial chromosomes.Biotechnology and Biological Sciences Research CouncilBiotechnology and Biological Sciences Research Council, research grants BB/K015729/1 and BB/N014995/1
Complete Genome Sequences of Extraintestinal Pathogenic <i>Escherichia coli</i> Clinical Isolates from Danish Ulcerative Colitis Patients
Inference for bounded parameters
The estimation of signal frequency count in the presence of background noise
has had much discussion in the recent physics literature, and Mandelkern [1]
brings the central issues to the statistical community, leading in turn to
extensive discussion by statisticians. The primary focus however in [1] and the
accompanying discussion is on the construction of a confidence interval. We
argue that the likelihood function and -value function provide a
comprehensive presentation of the information available from the model and the
data. This is illustrated for Gaussian and Poisson models with lower bounds for
the mean parameter
Ampicillin-Improved Glucose Tolerance in Diet-Induced Obese C57BL/6NTac Mice Is Age Dependent
Ampicillin has been shown to improve glucose tolerance in mice. We hypothesized that this effect is present only if treatment is initiated prior to weaning and that it disappears when treatment is terminated. High-fat fed C57BL/6NTac mice were divided into groups that received Ampicillin at different ages or not at all. We found that both diet and Ampicillin significantly changed the gut microbiota composition in the animals. Furthermore, there was a significant improvement in glucose tolerance in Ampicillin-treated, five-week-old mice compared to nontreated mice in the control group. At study termination, expressions of mRNA coding for tumor necrosis factor, serum amyloid A, and lactase were upregulated, while the expression of tumor necrosis factor (ligand) superfamily member 15 was downregulated in the ileum of Ampicillin-treated mice. Higher dendritic cell percentages were found systemically in high-fat diet mice, and a lower tolerogenic dendritic cell percentage was found both in relation to high-fat diet and late Ampicillin treatment. The results support our hypothesis that a âwindowâ exists early in life in which an alteration of the gut microbiota affects glucose tolerance as well as development of gut immunity and that this window may disappear after weaning
Switching between dynamic states in intermediate-length Josephson junctions
The appearance of zero-field steps (ZFSâs) in the current-voltage characteristics of intermediate-length overlap-geometry Josephson tunnel junctions described by a perturbed sine-Gordon equation (PSGE) is associated with the growth of parametrically excited instabilities of the McCumber background curve (MCB). A linear stability analysis of a McCumber solution of the PSGE in the asymptotic linear region of the MCB and in the absence of magnetic field yields a Hillâs equation which predicts how the number, locations, and widths of the instability regions depend on the junction parameters. A numerical integration of the PSGE in terms of truncated series of time-dependent Fourier spatial modes verifies that the parametrically excited instabilities of the MCB evolve into the fluxon oscillations characteristic of the ZFSâs. An approximate analysis of the Fourier mode equations in the presence of a small magnetic field yields a field-dependent Hillâs equation which predicts that the major effect of such a field is to reduce the widths of the instability regions. Experimental measurements on Nb-NbxOy-Pb junctions of intermediate length, performed at different operating temperatures in order to vary the junction parameters and for various magnetic field values, verify the physical existence of switching from the MCB to the ZFSâs. Good qualitative, and in many cases quantitative, agreement between analytic, numerical, and experimental results is obtained
GPsâ strategies in exploring the preschool childâs wellbeing in the paediatric consultation
Background:
Although General Practitioners (GPs) are uniquely placed to identify children with emotional, social, and behavioural problems, they succeed in identifying only a small number of them. The aim of this article is to explore the strategies, methods, and tools employed by GPs in the assessment of the preschool childâs emotional, mental, social, and behavioural health. We look at how GPs address parental care of the child in general and in situations where GPs have a particular awareness of the child.
Method:
Twenty-eight Danish GPs were purposively selected to take part in a qualitative study which combined focus-group discussions, observation of child consultations, and individual interviews with GPs.
Results:
Analysis of the data suggests that GPs have developed a set of methods, and strategies to assess the preschool child and parental care of the child. They look beyond paying narrow attention to the physical health of the child and they have expanded their practice to include the relations and interactions in the consultation room. The physical examination of the child continues to play a central role in doctor-child communication.
Conclusion:
The participating GPsâ strategies helped them to assess the wellbeing of the preschool child but they often find it difficult to share their impressions with parents
Compositional characteristics and spatial distribution of enriched Icelandic mantle components
Author Posting. Š The Authors, 2010. This is the author's version of the work. It is posted here by permission of Oxford University Press for personal use, not for redistribution. The definitive version was published in Journal of Petrology 51 (2010): 1447-1475, doi:10.1093/petrology/egq025.We present compositional data on a suite of 18 primitive neovolcanic alkali basalts from three
flank zone regions in Iceland (Vestmannaeyjar in the south, SnĂŚfell in the east, and SnĂŚfellsnes
in the west) that are peripheral to the main rift zones that are dominated by tholeiitic basalts. This
study integrates He isotope data with radiogenic isotope data (Sr-Nd-Pb-Hf), stable isotope data
(δ18O), and trace element data to characterise the compositional features of the trace-elementenriched
components of the Icelandic mantle. We also present high-precision Pb isotope data on
an additional 57 lava samples from the flank zones (including ĂrĂŚfajĂśkull in the south-east) and
the Northern and Eastern rift zones. Most Icelandic lavas have negative Î207Pb (â4 to â1), with
higher values (â1 to +4) found only in samples from ĂrĂŚfajĂśkull, SnĂŚfell, and parts of the
Reykjanes Peninsula. At SnÌfell, this EM1-type component is characterised by a low δ18Oolivine
signature (+4.1â° to +4.6â°), moderate 206Pb/204Pb values (18.4-18.6) and MORB-like 3He/4He
(6.9-7.5 R/RA). Samples from Vestmannaeyjar and SnÌfellsnes have mantle-like δ18Oolivine
(+4.9â° to +5.0â°), and radiogenic 206Pb/204Pb values (18.9-19.3) that fall on the NHRL for
208Pb/204Pb (Î208Pb â5 to +5). Compared to the Vestmannaeyjar lavas, SnĂŚfellsnes lavas have
higher La/YbN (5-11 vs. 3-5), lower ÎľNd (5.5-6.5 vs. 6.8-7.6) and lower 3He/4He (6.3-8.6 R/RA vs.
11.4-13.5 R/RA). Therefore, the most trace element enriched components in the Icelandic mantle
are not the carriers of the high 3He/4He values (> 15 R/RA) found in some lavas on Iceland and
the adjacent ridges, and instead are consistent with degassed, recycled components. Even after
excluding the EM1-type high Î207Pb samples, high-precision Pb isotope data produce a kinked
array on an 206Pb/204Pb vs. 208Pb/204Pb plot, which is not consistent with simple binary mixing
between two end-members. This requires significant lateral heterogeneity within the Icelandic
mantle and the presence of more than just two compositionally-distinct local mixing end-member
components. Samples from each of the main axial rift zones define different trends. Despite the
tectonic continuity between the Northern Volcanic Zone and the Eastern Volcanic Zone, lavas
from these two rift zones define separate sub-parallel linear arrays. Lavas from the adjacent
Western Volcanic Zone and the Eastern Volcanic Zone define oblique linear arrays that converge
on a common local end-member that is not involved in the magmatism of the Northern Volcanic
Zone. Therefore, there is a distinct NE-SW compositional heterogeneity within the Icelandic
mantle.work was funded primarily by the Danish National Research
Foundation through a grant to the former Danish Lithosphere Centre, with additional funding
from the University of Iowa for the oxygen isotope analyses
Origins left, right and centre: increasing the number of initiation sites in the Escherichia coli chromosome
Š 2018 by the authors. The bacterium Escherichia coli contains a single circular chromosome with a defined architecture. DNA replication initiates at a single origin called oriC. Two replication forks are assembled and proceed in opposite directions until they fuse in a specialised zone opposite the origin. This termination area is flanked by polar replication fork pause sites that allow forks to enter, but not to leave. Thus, the chromosome is divided into two replichores, each replicated by a single replication fork. Recently, we analysed the replication parameters in E. coli cells, in which an ectopic origin termed oriZ was integrated in the right-hand replichore. Two major obstacles to replication were identified: (1) head-on replicationâtranscription conflicts at highly transcribed rrn operons, and (2) the replication fork trap. Here, we describe replication parameters in cells with ectopic origins, termed oriX and oriY, integrated into the left-hand replichore, and a triple origin construct with oriX integrated in the left-hand and oriZ in the right-hand replichore. Our data again highlight both replicationâtranscription conflicts and the replication fork trap as important obstacles to DNA replication, and we describe a number of spontaneous large genomic rearrangements which successfully alleviate some of the problems arising from having an additional origin in an ectopic location. However, our data reveal additional factors that impact efficient chromosome duplication, highlighting the complexity of chromosomal architecture
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