148 research outputs found
Dynamics of nonlinear excitations of helically confined charges
We explore the long-time dynamics of a system of identical charged particles
trapped on a closed helix. This system has recently been found to exhibit an
unconventional deformation of the linear spectrum when tuning the helix radius.
Here we show that the same geometrical parameter can affect significantly also
the dynamical behaviour of an initially broad excitation for long times. In
particular, for small values of the radius, the excitation disperses into the
whole crystal whereas within a specific narrow regime of larger radii the
excitation self-focuses, assuming finally a localized form. Beyond this regime,
the excitation defocuses and the dispersion gradually increases again. We
analyze this geometrically controlled nonlinear behaviour using an effective
discrete nonlinear Schr\"{o}dinger model, which allows us among others to
identify a number of breather-like excitations.Comment: 11 pages, 7 figure
Finite temperature crossover from a crystalline to a cluster phase for a confined finite chain of ions
Employing Monte-Carlo simulation techniques we investigate the statistical
properties of equally charged particles confined in a one-dimensional box trap
and detect a crossover from a crystalline to a cluster phase with increasing
temperature. The corresponding transition temperature depends separately on the
number of particles N and the box size L, implying non-extensivity due to the
long-range character of the interactions. The probability density of the
spacing between the particles exhibits at low temperatures an accumulation of
discrete peaks with an overall asymmetric shape. In the vicinity of the
transition temperature it is of a Gaussian form whereas in the high temperature
regime an exponential decay is observed. The high temperature behaviour shows a
cluster phase with a mean cluster size that first increases with the
temperature and then saturates. The crossover is clearly identifiable also in
the non-linear behaviour of the heat capacity with varying temperature. The
influence of the trapping potential on the observed results as well as possible
experimental realizations are briefly addressed.Comment: 12 pages, 13 figure
Classical scattering of charged particles confined on an inhomogeneous helix
We explore the effects arising due to the coupling of the center of mass and
relative motion of two charged particles confined on an inhomogeneous helix
with a locally modified radius. It is first proven that a separation of the
center of mass and the relative motion is provided if and only if the confining
manifold represents a homogeneous helix. In this case bound states of
repulsively Coulomb interacting particles occur. For an inhomogeneous helix,
the coupling of the center of mass and relative motion induces an energy
transfer between the collective and relative motion, leading to dissociation of
initially bound states in a scattering process. Due to the time reversal
symmetry, a binding of the particles out of the scattering continuum is thus
equally possible. We identify the regimes of dissociation for different initial
conditions and provide an analysis of the underlying phase space via Poincar\'e
surfaces of section. Bound states inside the inhomogeneity as well as resonant
states are identified.Comment: 15 pages, 18 figure
Exploring Rigidly Rotating Vortex Configurations and their Bifurcations in Atomic Bose-Einstein Condensates
In the present work, we consider the problem of a system of few vortices as it emerges from its experimental realization in the field of atomic
Bose-Einstein condensates. Starting from the corresponding equations of motion,
we use a two-pronged approach in order to reveal the configuration space of the
system's preferred dynamical states. On the one hand, we use a Monte-Carlo
method parametrizing the vortex "particles" by means of hyperspherical
coordinates and identifying the minimal energy ground states thereof for and different vortex particle angular momenta. We then complement this
picture with a dynamical systems analysis of the possible rigidly rotating
states. The latter reveals all the supercritical and subcritical pitchfork, as
well as saddle-center bifurcations that arise exposing the full wealth of the
problem even at such low dimensional cases. By corroborating the results of the
two methods, it becomes fairly transparent which branch the Monte-Carlo
approach selects for different values of the angular momentum which is used as
a bifurcation parameter.Comment: 12 pages, 7 figures. New improved result
Buckling of 2D Plasma Crystals with Non-reciprocal Interactions
Laboratory realizations of 2D plasma crystals typically involve monodisperse
microparticles confined into horizontal monolayers in radio-frequency (rf)
plasma sheaths. This gives rise to the so-called plasma wakes beneath the
microparticles. The presence of wakes renders the interactions in such systems
non-reciprocal, a fact that can lead to a quite different behaviour from the
one expected for their reciprocal counterparts. Here we examine the buckling of
a hexagonal 2D plasma crystal, occurring as the confinement strength is
decreased, taking explicitly into account the non-reciprocity of the system via
a well-established point-particle wake model. We observe that for a finite wake
charge, the monolayer hexagonal crystal undergoes a transition first to a
bilayer hexagonal structure, unrealisable in harmonically confined reciprocal
Yukawa systems, and subsequently to a bilayer square structure. Our theoretical
results are confirmed by molecular dynamics simulations for experimentally
relevant parameters, indicating the potential of their observation in
state-of-the-art experiments with 2D complex plasmas.Comment: 13 pages, 6 figure
Guidelines for the functional annotation of microRNAs using the Gene Ontology
MicroRNA regulation of developmental and cellular processes is a relatively new field of study, and the available research data have not been organized to enable its inclusion in pathway and network analysis tools. The association of gene products with terms from the Gene Ontology is an effective method to analyze functional data, but until recently there has been no substantial effort dedicated to applying Gene Ontology terms to microRNAs. Consequently, when performing functional analysis of microRNA data sets, researchers have had to rely instead on the functional annotations associated with the genes encoding microRNA targets. In consultation with experts in the field of microRNA research, we have created comprehensive recommendations for the Gene Ontology curation of microRNAs. This curation manual will enable provision of a high-quality, reliable set of functional annotations for the advancement of microRNA research. Here we describe the key aspects of the work, including development of the Gene Ontology to represent this data, standards for describing the data, and guidelines to support curators making these annotations. The full microRNA curation guidelines are available on the GO Consortium wiki (http://wiki.geneontology.org/index.php/MicroRNA_GO_annotation_manual)
Circulating MicroRNAs Are Not Eliminated by Hemodialysis
BACKGROUND: Circulating microRNAs are stably detectable in serum/plasma and other body fluids. In patients with acute kidney injury on dialysis therapy changes of miRNA patterns had been detected. It remains unclear if and how the dialysis procedure itself affects circulating microRNA level. METHODS: We quantified miR-21 and miR-210 by quantitative RT-PCR in plasma of patients with acute kidney injury requiring dialysis and measured pre- and post-dialyser miRNA levels as well as their amount in the collected spent dialysate. Single treatments using the following filters were studied: F60 S (1.3 m(2), Molecular Weight Cut Off (MWCO): 30 kDa, n = 8), AV 1000 S (1.8 m(2), MWCO: 30 kDa, n = 6) and EMiC 2 (1.8 m(2), MWCO: 40 kDa, n = 6). RESULTS: Circulating levels of miR-21 or -210 do not differ between pre- and post-dialyzer blood samples independently of the used filter surface and pore size: miR-21: F60S: p = 0.35, AV 1000 S p = 1.0, EMiC2 p = 1.0; miR-210: F60S: p = 0.91, AV 1000 S p = 0.09, EMiC2 p = 0.31. Correspondingly, only traces of both miRNAs could be found in the collected spent dialysate and ultrafiltrate. CONCLUSIONS: In patients with acute kidney injury circulating microRNAs are not removed by dialysis. As only traces of miR-21 and -210 are detected in dialysate and ultrafiltrate, microRNAs in the circulation are likely to be transported by larger structures such as proteins and/or microvesicles. As miRNAs are not affected by dialysis they might be more robust biomarkers of acute kidney injury
Identification of the initial molecular changes in response to circulating angiogenic cells-mediated therapy in critical limb ischemia
BackgroundCritical limb ischemia (CLI) constitutes the most aggressive form of peripheral arterial occlusive disease, characterized by the blockade of arteries supplying blood to the lower extremities, significantly diminishing oxygen and nutrient supply. CLI patients usually undergo amputation of fingers, feet, or extremities, with a high risk of mortality due to associated comorbidities.Circulating angiogenic cells (CACs), also known as early endothelial progenitor cells, constitute promising candidates for cell therapy in CLI due to their assigned vascular regenerative properties. Preclinical and clinical assays with CACs have shown promising results. A better understanding of how these cells participate in vascular regeneration would significantly help to potentiate their role in revascularization.Herein, we analyzed the initial molecular mechanisms triggered by human CACs after being administered to a murine model of CLI, in order to understand how these cells promote angiogenesis within the ischemic tissues.MethodsBalb-c nude mice (n:24) were distributed in four different groups: healthy controls (C, n:4), shams (SH, n:4), and ischemic mice (after femoral ligation) that received either 50 mu l physiological serum (SC, n:8) or 5x10(5) human CACs (SE, n:8). Ischemic mice were sacrificed on days 2 and 4 (n:4/group/day), and immunohistochemistry assays and qPCR amplification of Alu-human-specific sequences were carried out for cell detection and vascular density measurements. Additionally, a label-free MS-based quantitative approach was performed to identify protein changes related.ResultsAdministration of CACs induced in the ischemic tissues an increase in the number of blood vessels as well as the diameter size compared to ischemic, non-treated mice, although the number of CACs decreased within time. The initial protein changes taking place in response to ischemia and more importantly, right after administration of CACs to CLI mice, are shown.ConclusionsOur results indicate that CACs migrate to the injured area; moreover, they trigger protein changes correlated with cell migration, cell death, angiogenesis, and arteriogenesis in the host. These changes indicate that CACs promote from the beginning an increase in the number of vessels as well as the development of an appropriate vascular network.Institute of Health Carlos III, ISCIII; Junta de Andaluci
Is Human Cytomegalovirus Infection Associated with Hypertension? The United States National Health and Nutrition Examination Survey 1999–2002
PURPOSE: Recent studies have implicated the human cytomegalovirus (HCMV) as a possible pathogen for causing hypertension. We aimed to study the association between HCMV infection and hypertension in the United States National Health and Nutrition Examination Survey (NHANES). METHODS: We analyzed data on 2979 men and 3324 women in the NHANES 1999-2002. We included participants aged 16-49 years who had valid data on HCMV infection and hypertension. RESULTS: Of the participants, 54.7% had serologic evidence of HCMV infection and 17.5% had hypertension. There were ethnic differences in the prevalence of HCMV infection (P<0.001) and hypertension (P<0.001). The prevalence of both increased with age (P<0.001). Before adjustment, HCMV seropositivity was significantly associated with hypertension in women (OR = 1.63, 95% CI = 1.25-2.13, P = 0.001) but not in men. After adjustment for race/ethnicity, the association between HCMV seropositivity and hypertension in women remained significant (OR = 1.55, 95% CI = 1.20-2.02, P = 0.002). Further adjustment for body mass index, diabetes status and hypercholesterolemia attenuated the association (OR = 1.44, 95% CI = 1.10-1.90, P = 0.010). However, after adjusting for age, the association was no longer significant (OR = 1.24, 95% CI = 0.91-1.67, P = 0.162). CONCLUSIONS: In this nationally representative population-based survey, HCMV seropositivity is associated with hypertension in women in the NHANES population. This association is largely explained by the association of hypertension with age and the increase in past exposure to HCMV with age.published_or_final_versio
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