651 research outputs found
Instability and dynamics of two nonlinearly coupled laser beams in a plasma
We investigate the nonlinear interaction between two laser beams in a plasma
in the weakly nonlinear and relativistic regime. The evolution of the laser
beams is governed by two nonlinear Schroedinger equations that are coupled with
the slow plasma density response. We study the growth rates of the Raman
forward and backward scattering instabilities as well of the Brillouin and
self-focusing/modulational instabilities. The nonlinear evolution of the
instabilities is investigated by means of direct simulations of the
time-dependent system of nonlinear equations.Comment: 18 pages, 8 figure
Exoplanet Transmission Spectroscopy using KMOS
KMOS (K-Band Multi Object Spectrograph) is a novel integral field
spectrograph installed in the VLT's ANTU unit. The instrument offers an ability
to observe 24 2.8"2.8" sub-fields positionable within a 7.2' patrol
field, each sub-field producing a spectrum with a 1414-pixel spatial
resolution. The main science drivers for KMOS are the study of galaxies, star
formation, and molecular clouds, but its ability to simultaneously measure
spectra of multiple stars makes KMOS an interesting instrument for exoplanet
atmosphere characterization via transmission spectroscopy. We set to test
whether transmission spectroscopy is practical with KMOS, and what are the
conditions required to achieve the photometric precision needed, based on
observations of a partial transit of WASP-19b, and full transits of GJ 1214b
and HD 209458b. Our analysis uses the simultaneously observed comparison stars
to reduce the effects from instrumental and atmospheric sources, and Gaussian
processes to model the residual systematics. We show that KMOS can, in theory,
deliver the photometric precision required for transmission spectroscopy.
However, this is shown to require a) pre-imaging to ensure accurate centering
and b) a very stable night with optimal observing conditions (seeing
0.8"). Combining these two factors with the need to observe several
transits, each with a sufficient out-of-transit baseline (and with the fact
that similar or better precision can be reached with telescopes and instruments
with smaller pressure,) we conclude that transmission spectroscopy is not the
optimal science case to take advantage of the abilities offered by KMOS and
VLT.Comment: 11 pages, accepted to MNRA
Does fluid loading influence measurements of intestinal permeability?
INTRODUCTION: Urinary recovery of enterally administered probes is used as a clinical test of intestinal mucosal permeability. Recently, evidence has been provided that the recovery of some but not all sugar probes is dependent on the amount of diuresis and renal function. The aim of this study was to assess the effect of fluid loading on the urinary recovery of sugar probes in healthy volunteers. METHODS: In a cross-over study, 10 healthy volunteers ingested 100 ml of a solution containing 0.2 g of 3-O-methyl-D-glucose (3-OMG), 0.5 g of D-xylose, 1.0 g of L-rhamnose, and 5.0 g of lactulose on two different days. The volunteers were randomized to receive either 2 litres of Ringer acetate or no fluid during the following 3 hours. The sugar concentrations were measured in 5-hour urine samples period. RESULTS: Fluid loading increased urine production and urinary recovery of xylose. Fluid loading did not influence the urinary recovery of 3-OMG, L-rhamnose, or lactulose. Neither the lactulose/rhamnose ratio nor the 3-OMG/rhamnose ratio changed. CONCLUSION: Fluid loading increases mediated carbohydrate transport but not the lactulose/rhamnose ratio, after oral sugar administration in healthy volunteers. It remains to be determined whether sugar probes are handled differently in response to fluids in patients with organ dysfunctions
Electrostatic pair creation and recombination in quantum plasmas
The collective production of electron-positron pairs by electrostatic waves
in quantum plasmas is investigated. In particular, a semi-classical governing
set of equation for a self-consistent treatment of pair creation by the
Schwinger mechanism in a quantum plasma is derived.Comment: 4 pages, 3 figures, to appear in JETP Letter
Left hemisphere enhancement of auditory activation in language impaired children
Specific language impairment (SLI) is a developmental disorder linked to deficient auditory processing. In this magnetoencephalography (MEG) study we investigated a specific prolonged auditory response (N250m) that has been reported predominantly in children and is associated with level of language skills. We recorded auditory responses evoked by sine-wave tones presented alternately to the right and left ear of 9–10-year-old children with SLI (n = 10) and children with typical language development (n = 10). Source analysis was used to isolate the N250m response in the left and right hemisphere. In children with language impairment left-hemisphere N250m responses were enhanced compared to those of controls, while no group difference was found in the right hemisphere. Consequently, language impaired children lacked the typical right-ward asymmetry that was found in control children. Furthermore, left but not right hemisphere N250m responses correlated positively with performance on a phonological processing task in the SLI group exclusively, possibly signifying a compensatory mechanism for delayed maturation of language processing. These results suggest that enhanced left-hemisphere auditory activation reflects a core neurophysiological manifestation of developmental language disorders, and emphasize the relevance of this developmentally specific activation pattern for competent language development. © 2019, The Author(s).Peer reviewe
Confirmation of an exoplanet using the transit color signature: Kepler-418b, a blended giant planet in a multiplanet system
We announce confirmation of Kepler-418b, one of two proposed planets in this
system. This is the first confirmation of an exoplanet based primarily on the
transit color signature technique. We used the Kepler public data archive
combined with multicolor photometry from the Gran Telescopio de Canarias and
radial velocity follow-up using FIES at the Nordic Optical Telescope for
confirmation. We report a confident detection of a transit color signature that
can only be explained by a compact occulting body, entirely ruling out a
contaminating eclipsing binary, a hierarchical triple, or a grazing eclipsing
binary. Those findings are corroborated by our radial velocity measurements,
which put an upper limit of ~1 Mjup on the mass of Kepler-418b. We also report
that the host star is significantly blended, confirming the ~10% light
contamination suspected from the crowding metric in the Kepler light curve
measured by the Kepler team. We report detection of an unresolved light source
that contributes an additional ~40% to the target star, which would not have
been detected without multicolor photometric analysis. The resulting
planet-star radius ratio is 0.110 +/- 0.0025, more than 25% more than the 0.087
measured by Kepler, leading to a radius of 1.20 +/- 0.16 Rjup instead of the
0.94 Rjup measured by the Kepler team. This is the first confirmation of an
exoplanet candidate based primarily on the transit color signature,
demonstrating that this technique is viable from ground for giant planets. It
is particularly useful for planets with long periods such as Kepler-418b, which
tend to have long transit durations. Additionally, multicolor photometric
analysis of transits can reveal unknown stellar neighbors and binary companions
that do not affect the classification of the transiting object but can have a
very significant effect on the perceived planetary radius.Comment: accepted by Astronomy & Astrophysic
Glial cells are functionally impaired in juvenile neuronal ceroid lipofuscinosis and detrimental to neurons.
The neuronal ceroid lipofuscinoses (NCLs or Batten disease) are a group of inherited, fatal neurodegenerative disorders of childhood. In these disorders, glial (microglial and astrocyte) activation typically occurs early in disease progression and predicts where neuron loss subsequently occurs. We have found that in the most common juvenile form of NCL (CLN3 disease or JNCL) this glial response is less pronounced in both mouse models and human autopsy material, with the morphological transformation of both astrocytes and microglia severely attenuated or delayed. To investigate their properties, we isolated glia and neurons from Cln3-deficient mice and studied their basic biology in culture. Upon stimulation, both Cln3-deficient astrocytes and microglia also showed an attenuated ability to transform morphologically, and an altered protein secretion profile. These defects were more pronounced in astrocytes, including the reduced secretion of a range of neuroprotective factors, mitogens, chemokines and cytokines, in addition to impaired calcium signalling and glutamate clearance. Cln3-deficient neurons also displayed an abnormal organization of their neurites. Most importantly, using a co-culture system, Cln3-deficient astrocytes and microglia had a negative impact on the survival and morphology of both Cln3-deficient and wildtype neurons, but these effects were largely reversed by growing mutant neurons with healthy glia. These data provide evidence that CLN3 disease astrocytes are functionally compromised. Together with microglia, they may play an active role in neuron loss in this disorder and can be considered as potential targets for therapeutic interventions
Early non-invasive cardiac output monitoring in hemodynamically unstable intensive care patients: A multi-center randomized controlled trial
Introduction
Acute hemodynamic instability increases morbidity and mortality. We investigated whether early non-invasive cardiac output monitoring enhances hemodynamic stabilization and improves outcome.
Methods
A multicenter, randomized controlled trial was conducted in three European university hospital intensive care units in 2006 and 2007. A total of 388 hemodynamically unstable patients identified during their first six hours in the intensive care unit (ICU) were randomized to receive either non-invasive cardiac output monitoring for 24 hrs (minimally invasive cardiac output/MICO group; n = 201) or usual care (control group; n = 187). The main outcome measure was the proportion of patients achieving hemodynamic stability within six hours of starting the study.
Results
The number of hemodynamic instability criteria at baseline (MICO group mean 2.0 (SD 1.0), control group 1.8 (1.0); P = .06) and severity of illness (SAPS II score; MICO group 48 (18), control group 48 (15); P = .86)) were similar. At 6 hrs, 45 patients (22%) in the MICO group and 52 patients (28%) in the control group were hemodynamically stable (mean difference 5%; 95% confidence interval of the difference -3 to 14%; P = .24). Hemodynamic support with fluids and vasoactive drugs, and pulmonary artery catheter use (MICO group: 19%, control group: 26%; P = .11) were similar in the two groups. The median length of ICU stay was 2.0 (interquartile range 1.2 to 4.6) days in the MICO group and 2.5 (1.1 to 5.0) days in the control group (P = .38). The hospital mortality was 26% in the MICO group and 21% in the control group (P = .34).
Conclusions
Minimally-invasive cardiac output monitoring added to usual care does not facilitate early hemodynamic stabilization in the ICU, nor does it alter the hemodynamic support or outcome. Our results emphasize the need to evaluate technologies used to measure stroke volume and cardiac output--especially their impact on the process of care--before any large-scale outcome studies are attempted
Critical surfaces for general inhomogeneous bond percolation problems
We present a method of general applicability for finding exact or accurate
approximations to bond percolation thresholds for a wide class of lattices. To
every lattice we sytematically associate a polynomial, the root of which in
is the conjectured critical point. The method makes the correct
prediction for every exactly solved problem, and comparison with numerical
results shows that it is very close, but not exact, for many others. We focus
primarily on the Archimedean lattices, in which all vertices are equivalent,
but this restriction is not crucial. Some results we find are kagome:
, , ,
, , :
. The results are generally within of numerical
estimates. For the inhomogeneous checkerboard and bowtie lattices, errors in
the formulas (if they are not exact) are less than .Comment: Submitted to J. Stat. Mec
Upper limb dysfunction and activities in daily living in idiopathic normal pressure hydrocephalus
Background Idiopathic normal pressure hydrocephalus (iNPH) is a neurodegenerative disease with a characteristic symptom triad of gait disturbance, cognitive decline, and incontinence. Recently, also dysfunctions in upper limbs have been described in iNPH and reported to improve after shunt surgery. We aim to describe the role of upper limb motor function in the clinical assessment of iNPH patients and its influence on activities of daily living (ADL). Methods Seventy-five consecutive patients with probable iNPH were studied pre-operatively and at 3 and 12 months after shunt surgery. The pre-operative evaluation included lumbar drainage of cerebrospinal fluid (tap test). Motor functions were assessed in upper and lower limbs with Grooved Pegboard Test (GPT), Box & Block Test (BBT), Total Score of Gait (TSG), and balance test. ADL was assessed with Barthel's index and cognition in accordance with the Consortium to Establish a Registry for Alzheimer's Disease (CERAD). Results Patients showed improvement in all motor tests and ADL at 3 months after shunt surgery. The improvement remained stable during the 12-month post-operative follow-up. The motor function tests correlated with each other and with ADL. Conclusions A 3-month follow-up period after shunt surgery is adequate to show improvement in motor tasks, and a positive outcome will last for at least 12 months. A shunt-responsive dysfunction of upper limb motor performance plays a major role in ADL of iNPH patients. Therefore, we suggest an evaluation of upper limb motor performance to be included in routine evaluation of iNPH patients.Peer reviewe
- …