167 research outputs found
Decoherence of Friedmann-Robertson-Walker Geometries in the Presence of Massive Vector Fields with U(1) or SO(3) Global Symmetries
Retrieval of classical behaviour in quantum cosmology is usually discussed in
the framework of {\em midi}superspace models in the presence of scalar fields
and the inhomogeneous modes corresponding either to gravitational or scalar
fields. In this work, we propose an alternative model to study the decoherence
of homogeneous and isotropic geometries where the scalar field is replaced by a
massive vector field with a global internal symmetry. We study here the cases
with and global internal symmetries. The presence of a mass term
breaks the conformal invariance and allows for the longitudinal modes of the
spin-1 field to be present in the Wheeler-DeWitt equation. In the case of the
U(1) global internal symmetry, we have only one single ``classical'' degree of
freedom while in the case of the SO(3) global symmetry, we are led to consider
a simple two-dimensional minisuperspace model. These minisuperspaces are shown
to be equivalent to a set of coupled harmonic oscillators where the kinetic
term of the longitudinal modes has a coefficient proportional to the inverse of
the scale factor. The conditions for a suitable decoherence process and
correlations between coordinate and momenta are established. The validity of
the semi-classical Einstein equations when massive vector fields (Abelian and
non-Abelian) are present is also discussed.Comment: 26 pages, CERN-TH.7241/94 DAMTP R-94/2
Multi-orbital and density-induced tunneling of bosons in optical lattices
We show that multi-orbital and density-induced tunneling have a significant
impact on the phase diagram of bosonic atoms in optical lattices. Off-site
interactions lead to density-induced hopping, the so-called bond-charge
interactions, which can be identified with an effective tunneling potential and
can reach the same order of magnitude as conventional tunneling. In addition,
interaction-induced higher-band processes also give rise to strongly modified
tunneling, on-site and bond-charge interactions. We derive an extended
occupation-dependent Hubbard model with multi-orbitally renormalized processes
and compute the corresponding phase diagram. It substantially deviates from the
single-band Bose-Hubbard model and predicts strong changes of the superfluid to
Mott-insulator transition. In general, the presented beyond-Hubbard physics
plays an essential role in bosonic lattice systems and has an observable
influence on experiments with tunable interactions.Comment: 21 pages, 7 figure
Impact of COVID-19 on the oncological outcomes of colorectal cancer surgery in northern Italy in 2019 and 2020: multicentre comparative cohort study
BACKGROUND: This study compared patients undergoing colorectal cancer surgery in 20 hospitals of northern Italy in 2019 versus 2020, in order to evaluate whether COVID-19-related delays of colorectal cancer screening resulted in more advanced cancers at diagnosis and worse clinical outcomes. METHOD: This was a retrospective multicentre cohort analysis of patients undergoing colorectal cancer surgery in March to December 2019 versus March to December 2020. Independent predictors of disease stage (oncological stage, associated symptoms, clinical T4 stage, metastasis) and outcome (surgical complications, palliative surgery, 30-day death) were evaluated using logistic regression. RESULTS: The sample consisted of 1755 patients operated in 2019, and 1481 in 2020 (both mean age 69.6 years). The proportion of cancers with symptoms, clinical T4 stage, liver and lung metastases in 2019 and 2020 were respectively: 80.8 versus 84.5 per cent; 6.2 versus 8.7 per cent; 10.2 versus 10.3 per cent; and 3.0 versus 4.4 per cent. The proportions of surgical complications, palliative surgery and death in 2019 and 2020 were, respectively: 34.4 versus 31.9 per cent; 5.0 versus 7.5 per cent; and 1.7 versus 2.4 per cent. Cancers in 2020 (versus 2019) were more likely to be symptomatic (odds ratio 1.36 (95 per cent c.i. 1.09 to 1.69)), clinical T4 stage (odds ratio 1.38 (95 per cent c.i. 1.03 to 1.85)) and have multiple liver metastases (odds ratio 2.21 (95 per cent c.i. 1.24 to 3.94)), but were not more likely to be associated with surgical complications (odds ratio 0.79 (95 per cent c.i. 0.68 to 0.93)). CONCLUSION: Colorectal cancer patients who had surgery between March and December 2020 had an increased risk of advanced disease in terms of associated symptoms, cancer location, clinical T4 stage and number of liver metastases
From transformation to chronification of migraine: Pathophysiological and clinical aspects
Chronic migraine is a neurological disorder characterized by 15 or more headache days per month of which at least 8 days show typical migraine features. The process that describes the development from episodic migraine into chronic migraine is commonly referred to as migraine transformation or chronification. Ample studies have attempted to identify factors associated with migraine transformation fr
Strongly Correlated Quantum Fluids: Ultracold Quantum Gases, Quantum Chromodynamic Plasmas, and Holographic Duality
Strongly correlated quantum fluids are phases of matter that are
intrinsically quantum mechanical, and that do not have a simple description in
terms of weakly interacting quasi-particles. Two systems that have recently
attracted a great deal of interest are the quark-gluon plasma, a plasma of
strongly interacting quarks and gluons produced in relativistic heavy ion
collisions, and ultracold atomic Fermi gases, very dilute clouds of atomic
gases confined in optical or magnetic traps. These systems differ by more than
20 orders of magnitude in temperature, but they were shown to exhibit very
similar hydrodynamic flow. In particular, both fluids exhibit a robustly low
shear viscosity to entropy density ratio which is characteristic of quantum
fluids described by holographic duality, a mapping from strongly correlated
quantum field theories to weakly curved higher dimensional classical gravity.
This review explores the connection between these fields, and it also serves as
an introduction to the Focus Issue of New Journal of Physics on Strongly
Correlated Quantum Fluids: from Ultracold Quantum Gases to QCD Plasmas. The
presentation is made accessible to the general physics reader and includes
discussions of the latest research developments in all three areas.Comment: 138 pages, 25 figures, review associated with New Journal of Physics
special issue "Focus on Strongly Correlated Quantum Fluids: from Ultracold
Quantum Gases to QCD Plasmas"
(http://iopscience.iop.org/1367-2630/focus/Focus%20on%20Strongly%20Correlated%20Quantum%20Fluids%20-%20from%20Ultracold%20Quantum%20Gases%20to%20QCD%20Plasmas
From transformation to chronification of migraine : pathophysiological and clinical aspects
Chronic migraine is a neurological disorder characterized by 15 or more headache days per month of which at least 8 days show typical migraine features. The process that describes the development from episodic migraine into chronic migraine is commonly referred to as migraine transformation or chronification. Ample studies have attempted to identify factors associated with migraine transformation from different perspectives. Understanding CM as a pathological brain state with trigeminovascular participation where biological changes occur, we have completed a comprehensive review on the clinical, epidemiological, genetic, molecular, structural, functional, physiological and preclinical evidence available
Roadmap on Machine learning in electronic structure
AbstractIn recent years, we have been witnessing a paradigm shift in computational materials science. In fact, traditional methods, mostly developed in the second half of the XXth century, are being complemented, extended, and sometimes even completely replaced by faster, simpler, and often more accurate approaches. The new approaches, that we collectively label by machine learning, have their origins in the fields of informatics and artificial intelligence, but are making rapid inroads in all other branches of science. With this in mind, this Roadmap article, consisting of multiple contributions from experts across the field, discusses the use of machine learning in materials science, and share perspectives on current and future challenges in problems as diverse as the prediction of materials properties, the construction of force-fields, the development of exchange correlation functionals for density-functional theory, the solution of the many-body problem, and more. In spite of the already numerous and exciting success stories, we are just at the beginning of a long path that will reshape materials science for the many challenges of the XXIth century
Metabolic effects of elevated temperature on organic acid degradation in ripening <em>Vitis vinifera</em> fruit
First published online: September 1, 2014Berries of the cultivated grapevine Vitis vinifera are notably responsive to temperature, which can influence fruit quality and hence the future compatibility of varieties with their current growing regions. Organic acids represent a key component of fruit organoleptic quality and their content is significantly influenced by temperature. The objectives of this study were to (i) manipulate thermal regimes to realistically capture warming-driven reduction of malate content in Shiraz berries, and (ii) investigate the mechanisms behind temperature-sensitive malate loss and the potential downstream effects on berry metabolism. In the field we compared untreated controls at ambient temperature with longer and milder warming (2-4 °C differential for three weeks; Experiment 1) or shorter and more severe warming (4-6 °C differential for 11 days; Experiment 2). We complemented field trials with control (25/15 °C) and elevated (35/20 °C) day/night temperature controlled-environment trials using potted vines (Experiment 3). Elevating maximum temperatures (4-10 °C above controls) during pre-véraison stages led to higher malate content, particularly with warmer nights. Heating at véraison and ripening stages reduced malate content, consistent with effects typically seen in warm vintages. However, when minimum temperatures were also raised by 4-6 °C, malate content was not reduced, suggesting that the regulation of malate metabolism differs during the day and night. Increased NAD-dependent malic enzyme activity and decreased phosphoenolpyruvate carboxylase and pyruvate kinase activities, as well as the accumulation of various amino acids and γ-aminobutyric acid, suggest enhanced anaplerotic capacity of the TCA cycle and a need for coping with decreased cytosolic pH in heated fruit.C. Sweetman, V. O. Sadras, R. D. Hancock, K. L. Soole and C. M. For
The mutational impact of culturing human pluripotent and adult stem cells
Genetic changes acquired during in vitro culture pose a risk for the successful application of stem cells in regenerative medicine. To assess the genetic risks induced by culturing, we determined all mutations in individual human stem cells by whole genome sequencing. Individual pluripotent, intestinal, and liver stem cells accumulate 3.5 ± 0.5, 7.2 ± 1.1 and 8.3 ± 3.6 base substitutions per population doubling, respectively. The annual in vitro mutation accumulation rate of adult stem cells is nearly 40-fold higher than the in vivo mutation accumulation rate. Mutational signature analysis reveals that in vitro induced mutations are caused by oxidative stress. Reducing oxygen tension in culture lowers the mutational load. We use the mutation rates, spectra, and genomic distribution to model the accumulation of oncogenic mutations during typical in vitro expansion, manipulation or screening experiments using human stem cells. Our study provides empirically defined parameters to assess the mutational risk of stem cell based therapies
HNF1α inhibition triggers epithelial-mesenchymal transition in human liver cancer cell lines
<p>Abstract</p> <p>Background</p> <p>Hepatocyte Nuclear Factor 1α (HNF1α) is an atypical homeodomain-containing transcription factor that transactivates liver-specific genes including albumin, α-1-antitrypsin and α- and β-fibrinogen. Biallelic inactivating mutations of <it>HNF1A </it>have been frequently identified in hepatocellular adenomas (HCA), rare benign liver tumors usually developed in women under oral contraceptives, and in rare cases of hepatocellular carcinomas developed in non-cirrhotic liver. HNF1α-mutated HCA (H-HCA) are characterized by a marked steatosis and show activation of glycolysis, lipogenesis, translational machinery and mTOR pathway. We studied the consequences of HNF1α silencing in hepatic cell lines, HepG2 and Hep3B and we reproduced most of the deregulations identified in H-HCA.</p> <p>Methods</p> <p>We transfected hepatoma cell lines HepG2 and Hep3B with siRNA targeting HNF1α and obtained a strong inhibition of HNF1α expression. We then looked at the phenotypic changes by microscopy and studied changes in gene expression using qRT-PCR and Western Blot.</p> <p>Results</p> <p>Hepatocytes transfected with HNF1α siRNA underwent severe phenotypic changes with loss of cell-cell contacts and development of migration structures. In HNF1α-inhibited cells, hepatocyte and epithelial markers were diminished and mesenchymal markers were over-expressed. This epithelial-mesenchymal transition (EMT) was related to the up regulation of several EMT transcription factors, in particular <it>SNAIL </it>and <it>SLUG</it>. We also found an overexpression of TGFβ1, an EMT initiator, in both cells transfected with HNF1α siRNA and H-HCA. Moreover, TGFβ1 expression is strongly correlated to HNF1α expression in cell models, suggesting regulation of TGFβ1 expression by HNF1α.</p> <p>Conclusion</p> <p>Our results suggest that HNF1α is not only important for hepatocyte differentiation, but has also a role in the maintenance of epithelial phenotype in hepatocytes.</p
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