748 research outputs found
On the disorder-driven quantum transition in three-dimensional relativistic metals
The Weyl semimetals are topologically protected from a gap opening against
weak disorder in three dimensions. However, a strong disorder drives this
relativistic semimetal through a quantum transition towards a diffusive
metallic phase characterized by a finite density of states at the band
crossing. This transition is usually described by a perturbative
renormalization group in of a Gross-Neveu model in the
limit . Unfortunately, this model is not multiplicatively
renormalizable in dimensions: An infinite number of relevant
operators are required to describe the critical behavior. Hence its use in a
quantitative description of the transition beyond one-loop is at least
questionable. We propose an alternative route, building on the correspondence
between the Gross-Neveu and Gross-Neveu-Yukawa models developed in the context
of high energy physics. It results in a model of Weyl fermions with a random
non-Gaussian imaginary potential which allows one to study the critical
properties of the transition within a expansion. We also
discuss the characterization of the transition by the multifractal spectrum of
wave functions.Comment: 5+8 pages, 1+5 figure
Minimal conductivity, topological Berry winding and duality in three-band semimetals
The physics of massless relativistic quantum particles has recently arisen in
the electronic properties of solids following the discovery of graphene. Around
the accidental crossing of two energy bands, the electronic excitations are
described by a Weyl equation initially derived for ultra-relativistic
particles. Similar three and four band semimetals have recently been discovered
in two and three dimensions. Among the remarkable features of graphene are the
characterization of the band crossings by a topological Berry winding, leading
to an anomalous quantum Hall effect, and a finite minimal conductivity at the
band crossing while the electronic density vanishes. Here we show that these
two properties are intimately related: this result paves the way to a direct
measure of the topological nature of a semi-metal. By considering three band
semimetals with a flat band in two dimensions, we find that only few of them
support a topological Berry phase. The same semimetals are the only ones
displaying a non vanishing minimal conductivity at the band crossing. The
existence of both a minimal conductivity and a topological robustness
originates from properties of the underlying lattice, which are encoded not by
a symmetry of their Bloch Hamiltonian, but by a duality
Liver fibrogenesis and genetic factors
SummaryChronic liver diseases lead to the accumulation of fibrosis in the liver with eventual progression to cirrhosis and its complications. However, there is a wide range of inter-individual variation in the liver fibrogenesis process, thus posing a challenge to physicians to identify patients with poor prognosis. As demographic and environmental factors only account for a small portion of fibrogenesis variability, host genetic factors have been suggested as playing an important role. Due to technical limitations, the first genetic studies were restricted to the evaluation of candidate genes having a known or supposed function in liver fibrogenesis. Recently, technological improvements have made it possible to study the whole human genome in a single scan. Genome-wide association studies have considerably heightened the interest in genetics as part of the study of liver fibrogenesis through their identification of previously unsuspected genes that are statistically associated with liver fibrosis. It is thus possible to determine new diagnostic or prognostic genetic markers for the management of patients with chronic liver diseases. Moreover, functional analyses of these genes may provide new insights into the pathophysiology of liver fibrogenesis
The W43-MM1 mini-starburst ridge, a test for star formation efficiency models
Context: Star formation efficiency (SFE) theories are currently based on
statistical distributions of turbulent cloud structures and a simple model of
star formation from cores. They remain poorly tested, especially at the highest
densities. Aims: We investigate the effects of gas density on the SFE through
measurements of the core formation efficiency (CFE). With a total mass of
M, the W43-MM1 ridge is one of the most convincing
candidate precursor of starburst clusters and thus one of the best place to
investigate star formation. Methods: We used high-angular resolution maps
obtained at 3 mm and 1 mm within W43-MM1 with the IRAM Plateau de Bure
Interferometer to reveal a cluster of 11 massive dense cores (MDCs), and, one
of the most massive protostellar cores known. An Herschel column density image
provided the mass distribution of the cloud gas. We then measured the
'instantaneous' CFE and estimated the SFE and the star formation rate (SFR)
within subregions of the W43-MM1 ridge. Results: The high SFE found in the
ridge (6% enclosed in 8 pc) confirms its ability to form a
starburst cluster. There is however a clear lack of dense cores in the northern
part of the ridge, which may be currently assembling. The CFE and the SFE are
observed to increase with volume gas density while the SFR steeply decreases
with the virial parameter, . Statistical models of the SFR may
well describe the outskirts of the W43-MM1 ridge but struggle to reproduce its
inner part, which corresponds to measurements at low . It may be
that ridges do not follow the log-normal density distribution, Larson
relations, and stationary conditions forced in the statistical SFR models.Comment: 13 pages, 7 figures. Accepted by A&
Multiple shells driven by disk winds: ALMA observations in the HH 30 outflow
We present archive Atacama Large Millimeter/Submillimeter Array (ALMA) Band 6
observations of the CO (J=2-1) and CO (J=2-1) molecular line
emission of the protostellar system associated with HH 30. The CO
molecular line shows the accretion disk while the molecular outflow is traced
by the emission of the CO molecular line. We estimated a dynamical mass
for the central object of M, and a mass for the molecular
outflow of M. The molecular outflow presents
an internal cavity as well as multiple outflowing shell structures. We
distinguish three different shells with constant expansion ( km
s) and possible rotation signatures ( km s). We find
that the shells can be explained by magnetocentrifugal disk winds with
launching radii au and a small magnetic lever arm
. The multiple shell structure may be the result of
episodic ejections of the material from the accretion disk associated with
three different epochs with dynamical ages of yr, yr, and
yr for the first, second, and third shells, respectively. The
outermost shell was ejected yr before the medium shell, while the
medium shell was launched yr before the innermost shell. Our
estimations of the linear and angular momentum rates of the outflow as well as
the accretion luminosity are consistent with the expected values if the outflow
of HH 30 is produced by a wide-angle disk wind
Surveying activated sludge changes during acclimation with artificial wastewater
Many processes in the chemical and pharmaceutical industries generate wastewater containing organic
toxic compounds and other kinds of xenobiotics. Usually, biological treatments are used to degrade a
great quantity of these substances. However, most of the time, the microorganisms are not adapted and
the treatment can be blocked. Therefore, the first step to make a continuous reactor operative is the
acclimation, i.e., the adaptation of the microorganisms to a specific substrate. During this particular step
of the process there is a selection and a multiplication of specialized microorganisms and physiological
transformations can occur in their metabolic system. Furthermore, combining image processing
techniques have already been successfully used to elucidate the activated sludge morphological changes
for both aggregated and filamentous bacteria contents, during such processes.
The experimental set-up is composed of an aerated reactor and a clarifier. The sludge is recycled from the
clarifier by a peristaltic pump. The complete mixing inside the reactor is guaranteed by the diffusion of
air from its bottom. The reactor was inoculated with biomass collected from a wastewater treatment plant
and fed with an artificial wastewater based on meat extract. During acclimation, chemical parameters
were measured in the influent, reactor and effluent, in order to verify the stability of the process. To
complete the evaluation of the process, microscopy acquisition and image processing and analysis
techniques were performed for aggregates and filamentous bacteria characterization for bright field, Gram
and poly-β-hydroxybutyrate (PHB) staining images. The information extracted from those images
allowed for aggregates and filamentous bacteria contents inspection, identification of PHB storing
microorganisms and, gram-positive and gram-negative filamentous bacteria recognition. Figure 1 presents
activated sludge samples at the beginning and at the end of the acclimation phase. It was found in this
study that biomass changes during the acclimation phase could be effectively monitored, combining
image analysis information and chemical parameters
To buy or not to buy-evaluating commercial AI solutions in radiology (the ECLAIR guidelines).
Artificial intelligence (AI) has made impressive progress over the past few years, including many applications in medical imaging. Numerous commercial solutions based on AI techniques are now available for sale, forcing radiology practices to learn how to properly assess these tools. While several guidelines describing good practices for conducting and reporting AI-based research in medicine and radiology have been published, fewer efforts have focused on recommendations addressing the key questions to consider when critically assessing AI solutions before purchase. Commercial AI solutions are typically complicated software products, for the evaluation of which many factors are to be considered. In this work, authors from academia and industry have joined efforts to propose a practical framework that will help stakeholders evaluate commercial AI solutions in radiology (the ECLAIR guidelines) and reach an informed decision. Topics to consider in the evaluation include the relevance of the solution from the point of view of each stakeholder, issues regarding performance and validation, usability and integration, regulatory and legal aspects, and financial and support services. KEY POINTS: • Numerous commercial solutions based on artificial intelligence techniques are now available for sale, and radiology practices have to learn how to properly assess these tools. • We propose a framework focusing on practical points to consider when assessing an AI solution in medical imaging, allowing all stakeholders to conduct relevant discussions with manufacturers and reach an informed decision as to whether to purchase an AI commercial solution for imaging applications. • Topics to consider in the evaluation include the relevance of the solution from the point of view of each stakeholder, issues regarding performance and validation, usability and integration, regulatory and legal aspects, and financial and support services
Gemcitabine and oxaliplatin (GEMOX) in gemcitabine refractory advanced pancreatic adenocarcinoma: a phase II study
Gemcitabine and oxaliplatin (GEMOX) are active as first-line therapy against advanced pancreatic cancer. This study aims to evaluate the activity and tolerability of this combination in patients refractory to standard gemcitabine (GEM). A total of 33 patients (median age of 57) were included with locally advanced and metastatic evaluable diseases, who had progressed during or following GEM therapy. The GEMOX regimen consisted of 1000 mg m−2 of GEM at a 100-min infusion on day 1, followed on day 2 by 100 mg m−2 of oxaliplatin at a 2-h infusion; a cycle that was given every 2 weeks. All patients received at least one cycle of GEMOX (median 5; range 1–29). Response by 31 evaluable patients was as follows: PR: 7/31(22.6%), s.d. ⩾8 weeks: 11/31(35.5%), s.d. <8 weeks: 1/31(3.2%), PD: 12/31(38.7%). Median duration of response and TTP were 4.5 and 4.2 months, respectively. Median survival was 6 months (range 0.5–21). Clinical benefit response was observed in 17/31 patients (54.8%). Grade III/IV non-neurologic toxicities occurred in 12/33 patients (36.3%), and grade I, II, and III neuropathy in 17(51%), 3(9%), and 4(12%) patients, respectively. GEMOX is a well-tolerated, active regimen that may provide a benefit to patients with advanced pancreatic cancer after progression following standard gemcitabine treatment
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