867 research outputs found
Semi-Parametrics Dose Finding Methods
We describe a new class of dose finding methods to be used in early phase clinical trials. Under some added parametric conditions the class reduces to the family of continual reassessment method (CRM) designs. Under some relaxation of the underlying structure the method is equivalent to the CCD, mTPI or BOIN classes of designs. These latter designs are non-parametric in nature whereas the CRM class can be viewed as being strongly parametric. The proposed class is characterized as being semi-parametric since it corresponds to CRM with a nuisance parameter. Performance is good, matching that of the CRM class and improving on it in some cases. The structure allows theoretical questions to be more easily investigated and to better understand how different classes of methods relate to one another
Improved modelling of liquid GeSe: the impact of the exchange-correlation functional
The structural properties of liquid GeSe are studied by using
first-principles molecular dynamics in conjuncton with the Becke, Lee, Yang and
Parr (BLYP) generalized gradient approximation for the exchange and correlation
energy. The results on partial pair correlation functions, coordination
numbers, bond angle distributions and partial structure factors are compared
with available experimental data and with previous first-principle molecular
dynamics results obtained within the Perdew and Wang (PW) generalized gradient
approximation for the exchange and correlation energy. We found that the BLYP
approach substantially improves upon the PW one in the case of the short-range
properties. In particular, the GeGe pair correlation function takes a more
structured profile that includes a marked first peak due to homopolar bonds, a
first maximum exhibiting a clear shoulder and a deep minimum, all these
features being absent in the previous PW results. Overall, the amount of
tetrahedral order is significantly increased, in spite of a larger number of
GeGe homopolar connections. Due to the smaller number of miscoordinations,
diffusion coefficients obtained by the present BLYP calculation are smaller by
at least one order of magnitude than in the PW case.Comment: 6 figure
Low energy phases of bilayer Bi predicted by structure search in two dimensions
We employ an ab-initio structure search algorithm to explore the
configurational space of Bi in quasi two dimensions. A confinement potential
restricts the movement of atoms within a pre-defined thickness during structure
search calculations within the minima hopping method to find the stable and
metastable forms of bilayer Bi. In addition to recovering the two known
low-energy structures (puckered monoclinic and buckled hexagonal), our
calculations predict three new structures of bilayer Bi. We call these
structures the , , and phases of bilayer Bi, which are,
respectively, 63, 72, and 83 meV/atom higher in energy than that of the
monoclinic ground state, and thus potentially synthesizable using appropriate
substrates. We also compare the structural, electronic, and vibrational
properties of the different phases. The puckered monoclinic, buckled hexagonal,
and phases exhibit a semiconducting energy gap, whereas and
phases are metallic. We notice an unusual Mexican-hat type band
dispersion leading to a van Hove singularity in the buckled hexagonal bilayer
Bi. Notably, we find symmetry-protected topological Dirac points in the
electronic spectrum of the phase. The new structures suggest that
bilayer Bi provides a novel playground to study distortion-mediated
metal-insulator phase transitions
Rigidity and intermediate phases in glasses driven by speciation
The rigid to floppy transitions and the associated intermediate phase in
glasses are studied in the case where the local structure is not fully
determined from the macroscopic concentration. The approach uses size
increasing cluster approximations and constraint counting algorithms. It is
shown that the location and the width of the intermediate phase and the
corresponding structural, mechanical and energetical properties of the network
depend crucially on the way local structures are selected at a given
concentration. The broadening of the intermediate phase is obtained for
networks combining a large amount of flexible local structural units and a high
rate of medium range order.Comment: 4 pages, 4 figure
Model-based demosaicking for acquisitions by a RGBW color filter array
Microsatellites and drones are often equipped with digital cameras whose
sensing system is based on color filter arrays (CFAs), which define a pattern
of color filter overlaid over the focal plane. Recent commercial cameras have
started implementing RGBW patterns, which include some filters with a wideband
spectral response together with the more classical RGB ones. This allows for
additional light energy to be captured by the relevant pixels and increases the
overall SNR of the acquisition. Demosaicking defines reconstructing a
multi-spectral image from the raw image and recovering the full color
components for all pixels. However, this operation is often tailored for the
most widespread patterns, such as the Bayer pattern. Consequently, less common
patterns that are still employed in commercial cameras are often neglected. In
this work, we present a generalized framework to represent the image formation
model of such cameras. This model is then exploited by our proposed
demosaicking algorithm to reconstruct the datacube of interest with a Bayesian
approach, using a total variation regularizer as prior. Some preliminary
experimental results are also presented, which apply to the reconstruction of
acquisitions of various RGBW cameras
Evaluation of levels of antibiotic resistance in groundwater-derived E. coli isolates in the Midwest of Ireland and elucidation of potential predictors of resistance
Antibiotic-resistant (pathogenic and non-pathogenic) organisms and genes are now acknowledged as significant emerging aquatic contaminants with potentially adverse human and ecological health impacts, and thus require monitoring. This study is the first to investigate levels of resistance among Irish groundwater (private wells) samples; Escherichia coli isolates were examined against a panel of commonly prescribed human and veterinary therapeutic antibiotics, followed by determination of the causative factors of resistance. Overall, 42 confirmed E. coli isolates were recovered from a groundwater-sampling cohort. Resistance to the human panel of antibiotics was moderate; nine (21.4%) E. coli isolates demonstrated resistance to one or more human antibiotics. Conversely, extremely high levels of resistance to veterinary antibiotics were found, with all isolates presenting resistance to one or more veterinary antibiotics. Particularly high levels of resistance (93%) were found with respect to the aminoglycoside class of antibiotics. Results of statistical analysis indicate a significant association between the presence of human (multiple) antibiotic resistance (p = 0.002–0.011) and both septic tank density and the presence of vulnerable sub-populations (\u3c5 years). For the veterinary antibiotics, results point to a significant relationship (p = \u3c0.001) between livestock (cattle) density and the prevalence of multiple antibiotic resistant E. coli. Groundwater continues to be an important resource in Ireland, particularly in rural areas; thus, results of this preliminary study offer a valuable insight into the prevalence of antibiotic resistance in the hydrogeological environment and establish a need for further research with a larger geological diversity
Observables in Topological Yang-Mills Theories
Using topological Yang-Mills theory as example, we discuss the definition and
determination of observables in topological field theories (of Witten-type)
within the superspace formulation proposed by Horne. This approach to the
equivariant cohomology leads to a set of bi-descent equations involving the
BRST and supersymmetry operators as well as the exterior derivative. This
allows us to determine superspace expressions for all observables, and thereby
to recover the Donaldson-Witten polynomials when choosing a Wess-Zumino-type
gauge.Comment: 39 pages, Late
Analyse 3d de la marche en pratique clinique après ligamentoplastie du genou par DIDT : utilisation du système KNEE KG
Pnictogens Allotropy and Phase Transformation during van der Waals Growth
Pnictogens have multiple allotropic forms resulting from their ns2 np3
valence electronic configuration, making them the only elemental materials to
crystallize in layered van der Waals (vdW) and quasi-vdW structures throughout
the group. Light group VA elements are found in the layered orthorhombic A17
phase such as black phosphorus, and can transition to the layered rhombohedral
A7 phase at high pressure. On the other hand, bulk heavier elements are only
stable in the A7 phase. Herein, we demonstrate that these two phases not only
co-exist during the vdW growth of antimony on weakly interacting surfaces, but
also undertake a spontaneous transformation from the A17 phase to the
thermodynamically stable A7 phase. This metastability of the A17 phase is
revealed by real-time studies unraveling its thickness-driven transition to the
A7 phase and the concomitant evolution of its electronic properties. At a
critical thickness of ~4 nm, A17 antimony undergoes a diffusionless shuffle
transition from AB to AA stacked alpha-antimonene followed by a gradual
relaxation to the A7 bulk-like phase. Furthermore, the electronic structure of
this intermediate phase is found to be determined by surface self-passivation
and the associated competition between A7- and A17-like bonding in the bulk.
These results highlight the critical role of the atomic structure and
interfacial interactions in shaping the stability and electronic
characteristics of vdW layered materials, thus enabling a new degree of freedom
to engineer their properties using scalable processes
- …