313 research outputs found
Scale-invariant alternatives to general relativity
We study the general class of gravitational field theories constructed on the
basis of scale invariance (and therefore absence of any mass parameters) and
invariance under transverse diffeomorphisms (TDiff), which are the 4-volume
conserving coordinate transformations. We show that these theories are
equivalent to a specific type of scalar-tensor theories of gravity (invariant
under all diffeomorphisms) with a number of properties, making them
phenomenologically interesting. They contain, in addition to the dimensionless
coupling constants of the original theory, an arbitrary dimensionful parameter
. This parameter is associated with an integration constant of the
equations of motion, similar to the arbitrary cosmological constant appearing
in unimodular gravity. We focus on the theories where Newton's constant and the
electroweak scale emerge from the spontaneous breaking of scale invariance and
are unrelated to . The massless particle spectrum of these theories
contains the graviton and a new particle -- dilaton. For , the
massless dilaton has only derivative couplings to matter fields and the bounds
on the existence of a 5th force are easily satisfied. As for the matter fields,
we determine the conditions leading to a renormalizable low-energy theory. If
, scale invariance is broken. The arbitrary constant
produces a "run-away" potential for the dilaton. As a consequence,
the dilaton can act as a dynamical dark energy component. We elucidate the
origin of the cosmological constant in the class of theories under
consideration and formulate the condition leading to its absence. If this
condition is satisfied, dark energy is purely dynamical and associated to the
dilaton.Comment: 39 pages, no figure
Quelle intégration pour les requérants d'asile mineurs non accompagnés en Valais
L’accueil et l’intégration des personnes migrantes est un enjeu sociétal actuel. Le canton du Valais a mis sur pied la structure du RADOS, institution destinée à l’accompagnement spécifique des mineurs non accompagnés. Ce travail s’intéresse particulièrement à l’intégration des requérants d’asile mineurs non accompagnés (RMNAs) attribués au canton du Valais et à leur point de vue face à leur intégration
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Candidate gene biodosimetry markers of exposure to external ionizing radiation in human blood: A systematic review
Purpose
To compile a list of genes that have been reported to be affected by external ionizing radiation (IR) and to assess their performance as candidate biomarkers for individual human radiation dosimetry.
Methods
Eligible studies were identified through extensive searches of the online databases from 1978 to 2017. Original English-language publications of microarray studies assessing radiation-induced changes in gene expression levels in human blood after external IR were included. Genes identified in at least half of the selected studies were retained for bio-statistical analysis in order to evaluate their diagnostic ability.
Results
24 studies met the criteria and were included in this study. Radiation-induced expression of 10,170 unique genes was identified and the 31 genes that have been identified in at least 50% of studies (12/24 studies) were selected for diagnostic power analysis. Twenty-seven genes showed a significant Spearman’s correlation with radiation dose. Individually, TNFSF4, FDXR, MYC, ZMAT3 and GADD45A provided the best discrimination of radiation dose < 2 Gy and dose ≥ 2 Gy according to according to their maximized Youden’s index (0.67, 0.55, 0.55, 0.55 and 0.53 respectively). Moreover, 12 combinations of three genes display an area under the Receiver Operating Curve (ROC) curve (AUC) = 1 reinforcing the concept of biomarker combinations instead of looking for an ideal and unique biomarker.
Conclusion
Gene expression is a promising approach for radiation dosimetry assessment. A list of robust candidate biomarkers has been identified from analysis of the studies published to date, confirming for example the potential of well-known genes such as FDXR and TNFSF4 or highlighting other promising gene such as ZMAT3. However, heterogeneity in protocols and analysis methods will require additional studies to confirm these results
Resolution and enhancement in nanoantenna-based fluorescence microscopy
Single gold nanoparticles can act as nanoantennas for enhancing the
fluorescence of emitters in their near-fields. Here we present experimental and
theoretical studies of scanning antenna-based fluorescence microscopy as a
function of the diameter of the gold nanoparticle. We examine the interplay
between fluorescence enhancement and spatial resolution and discuss the
requirements for deciphering single molecules in a dense sample. Resolutions
better than 20 nm and fluorescence enhancement up to 30 times are demonstrated
experimentally. By accounting for the tip shaft and the sample interface in
finite-difference time-domain calculations, we explain why the measured
fluorescence enhancements are higher in the presence of an interface than the
values predicted for a homogeneous environment.Comment: 10 pages, 3 figures. accepted for publication in Nano Letter
Optical microscopy via spectral modifications of a nano-antenna
The existing optical microscopes form an image by collecting photons emitted
from an object. Here we report on the experimental realization of microscopy
without the need for direct optical communication with the sample. To achieve
this, we have scanned a single gold nanoparticle acting as a nano-antenna in
the near field of a sample and have studied the modification of its intrinsic
radiative properties by monitoring its plasmon spectrum.Comment: 6 pages, 4 figures (color
Biomolecular interactions control the shape of stains from drying droplets of complex fluids
When a sessile droplet of a complex fluid dries, a stain forms on the solid surface. The structure and pattern of the stain can be used to detect the presence of a specific chemical compound in the sessile droplet. In the present work, we investigate what parameters of the stain or its formation can be used to characterize the specific interaction between an aqueous dispersion of beads and its receptor immobilized on the surface. We use the biotin-streptavidin system as an experimental model. Clear dissimilarities were observed in the drying sequences on streptavidin-coated substrates of droplets of aqueous solutions containing biotin-coated or streptavidin-coated beads. Fluorescent beads are used in order to visualize the fluid flow field. We show differences in the distribution of the particles on the surface depending on biomolecular interactions between beads and the solid surface. A mechanistic model is proposed to explain the different patterns obtained during drying. The model describes that the beads are left behind the receding wetting line rather than pulled towards the drop center if the biological binding force is comparable to the surface tension of the receding wetting line. Other forces such as the viscous drag, van der Waals forces, and solid–solid friction forces are found negligible. Simple microfluidics experiments are performed to further illustrate the difference in behavior where is adhesion or friction are present between the bead and substrate due to the biological force. The results of the model are in agreement with the experimental observations which provide insight and design capabilities. A better understanding of the effects of the droplet–surface interaction on the drying mechanism is a crucial first step before the identification of drying patterns can be promisingly applied to areas such as immunology and biomarker detection
Comparison of established and emerging biodosimetry assays
Rapid biodosimetry tools are required to assist with triage in the case of a large-scale radiation incident. Here, we aimed to determine the dose-assessment accuracy of the well-established dicentric chromosome assay (DCA) and cytokinesis-block micronucleus assay (CBMN) in comparison to the emerging γ-H2AX foci and gene expression assays for triage mode biodosimetry and radiation injury assessment. Coded blood samples exposed to 10 X-ray doses (240 kVp, 1 Gy/min) of up to 6.4 Gy were sent to participants for dose estimation. Report times were documented for each laboratory and assay. The mean absolute difference (MAD) of estimated doses relative to the true doses was calculated. We also merged doses into binary dose categories of clinical relevance and examined accuracy, sensitivity and specificity of the assays. Dose estimates were reported by the first laboratories within 0.3-0.4 days of receipt of samples for the γ-H2AX and gene expression assays compared to 2.4 and 4 days for the DCA and CBMN assays, respectively. Irrespective of the assay we found a 2.5-4-fold variation of interlaboratory accuracy per assay and lowest MAD values for the DCA assay (0.16 Gy) followed by CBMN (0.34 Gy), gene expression (0.34 Gy) and γ-H2AX (0.45 Gy) foci assay. Binary categories of dose estimates could be discriminated with equal efficiency for all assays, but at doses ≥1.5 Gy a 10% decrease in efficiency was observed for the foci assay, which was still comparable to the CBMN assay. In conclusion, the DCA has been confirmed as the gold standard biodosimetry method, but in situations where speed and throughput are more important than ultimate accuracy, the emerging rapid molecular assays have the potential to become useful triage tools
Selective nanomanipulation using optical forces
We present a detailed theoretical study of the recent proposal for selective
nanomanipulation of nanometric particles above a substrate using near-field
optical forces [Chaumet {\it et al.} Phys. Rev. Lett. {\bf 88}, 123601 (2002)].
Evanescent light scattering at the apex of an apertureless near-field probe is
used to create an optical trap. The position of the trap is controlled on a
nanometric scale via the probe and small objects can be selectively trapped and
manipulated. We discuss the influence of the geometry of the particles and the
probe on the efficiency of the trap. We also consider the influence of multiple
scattering among the particles on the substrate and its effect on the
robustness of the trap.Comment: 12 pages, 17 figure
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