2,555 research outputs found
Field-induced quantum fluctuations in the heavy fermion superconductor CeCu2Ge2
Quantum-mechanical fluctuations in strongly correlated electron systems cause
unconventional phenomena such as non-Fermi liquid behavior, and arguably high
temperature superconductivity. Here we report the discovery of a field-tuned
quantum critical phenomenon in stoichiometric CeCu2Ge2, a spin density wave
ordered heavy fermion metal that exhibits unconventional superconductivity
under ~ 10 GPa of applied pressure. Our finding of the associated quantum
critical spin fluctuations of the antiferromagnetic spin density wave order,
dominating the local fluctuations due to single-site Kondo effect, provide new
information about the underlying mechanism that can be important in
understanding superconductivity in this novel compound.Comment: Heavy Fermion, Quantum Critical Phenomeno
The N-representability problem, the pseudo-spectral decomposition of antisymmetric 1-body operators, and collective behaviour
The pseudo--spectral decomposition of an --particle antisymmetric 1--body
positive--semidefinite operator that corresponds to the canonical convex
decomposition into the extreme elements of the dual cone of the set of fermion
--representable --density operators has been derived. An attempt at
constucting a mathematical model for collective behaviour of a system of
--fermions that originates from the pseudo--spectral decomposition is
presented.Comment: 28 pages, compressed and uuencoded Postscript, 2 figure
Two-dimensional models as testing ground for principles and concepts of local quantum physics
In the past two-dimensional models of QFT have served as theoretical
laboratories for testing new concepts under mathematically controllable
condition. In more recent times low-dimensional models (e.g. chiral models,
factorizing models) often have been treated by special recipes in a way which
sometimes led to a loss of unity of QFT. In the present work I try to
counteract this apartheid tendency by reviewing past results within the setting
of the general principles of QFT. To this I add two new ideas: (1) a modular
interpretation of the chiral model Diff(S)-covariance with a close connection
to the recently formulated local covariance principle for QFT in curved
spacetime and (2) a derivation of the chiral model temperature duality from a
suitable operator formulation of the angular Wick rotation (in analogy to the
Nelson-Symanzik duality in the Ostertwalder-Schrader setting) for rational
chiral theories. The SL(2,Z) modular Verlinde relation is a special case of
this thermal duality and (within the family of rational models) the matrix S
appearing in the thermal duality relation becomes identified with the
statistics character matrix S. The relevant angular Euclideanization'' is done
in the setting of the Tomita-Takesaki modular formalism of operator algebras.
I find it appropriate to dedicate this work to the memory of J. A. Swieca
with whom I shared the interest in two-dimensional models as a testing ground
for QFT for more than one decade.
This is a significantly extended version of an ``Encyclopedia of Mathematical
Physics'' contribution hep-th/0502125.Comment: 55 pages, removal of some typos in section
Variations in the oral microbiome are associated with depression in young adults
Abstract A growing body of evidence supports an important role for alterations in the brain-gut-microbiome axis in the aetiology of depression and other psychiatric disorders. The potential role of the oral microbiome in mental health has received little attention, even though it is one of the most diverse microbiomes in the body and oral dysbiosis has been linked to systemic diseases with an underlying inflammatory aetiology. This study examines the structure and composition of the salivary microbiome for the first time in young adults who met the DSM-IV criteria for depression (n = 40) and matched controls (n = 43) using 16S rRNA gene-based next generation sequencing. Subtle but significant differences in alpha and beta diversity of the salivary microbiome were observed, with clear separation of depressed and healthy control cohorts into distinct clusters. A total of 21 bacterial taxa were found to be differentially abundant in the depressed cohort, including increased Neisseria spp. and Prevotella nigrescens, while 19 taxa had a decreased abundance. In this preliminary study we have shown that the composition of the oral microbiome is associated with depression in young adults. Further studies are now warranted, particuarly investigations into whether such shifts play any role in the underling aetiology of depression
Locally critical quantum phase transitions in strongly correlated metals
When a metal undergoes a continuous quantum phase transition, non-Fermi
liquid behaviour arises near the critical point. It is standard to assume that
all low-energy degrees of freedom induced by quantum criticality are spatially
extended, corresponding to long-wavelength fluctuations of the order parameter.
However, this picture has been contradicted by recent experiments on a
prototype system: heavy fermion metals at a zero-temperature magnetic
transition. In particular, neutron scattering from CeCuAu has
revealed anomalous dynamics at atomic length scales, leading to much debate as
to the fate of the local moments in the quantum-critical regime. Here we report
our theoretical finding of a locally critical quantum phase transition in a
model of heavy fermions. The dynamics at the critical point are in agreement
with experiment. We also argue that local criticality is a phenomenon of
general relevance to strongly correlated metals, including doped Mott
insulators.Comment: 20 pages, 3 figures; extended version, to appear in Natur
Easing Legal News Monitoring with Learning to Rank and BERT
While ranking approaches have made rapid advances in the Web search, systems that cater to the complex information needs in professional search tasks are not widely developed, common issues and solutions typically rely on dedicated search strategies backed by ad-hoc retrieval models. In this paper we present a legal search problem where professionals monitor news articles with constant queries on a periodic basis. Firstly, we demonstrate the effectiveness of using traditional retrieval models against the Boolean search of documents in chronological order. In an attempt to capture the complex information needs of users, a learning to rank approach is adopted with user specified relevance criteria as features. This approach, however, only achieves mediocre results compared to the traditional models. However, we find that by fine-tuning a contextualised language model (e.g. BERT), significantly improved retrieval performance can be achieved, providing a flexible solution to satisfying complex information needs without explicit feature engineering
Protocol for the Smoking, Nicotine and Pregnancy (SNAP) trial: double-blind, placebo-randomised, controlled trial of nicotine replacement therapy in pregnancy
Background: Smoking in pregnancy remains a public health challenge. Nicotine replacement therapy (NRT) is effective for smoking cessation in non-pregnant people, but because women metabolise nicotine and cotinine much faster in pregnancy, it is unclear whether this will be effective for smoking cessation in pregnancy. The NHS Health Technology Assessment Programme (HTA)-funded smoking, nicotine and pregnancy ( SNAP) trial will investigate whether or not nicotine replacement therapy ( NRT) is effective, cost-effective and safe when used for smoking cessation by pregnant women. Methods/Design: Over two years, in 5 trial centres, 1050 pregnant women who are between 12 and 24 weeks pregnant will be randomised as they attend hospital for ante-natal ultrasound scans. Women will receive either nicotine or placebo transdermal patches with behavioural support. The primary outcome measure is biochemically-validated, self-reported, prolonged and total abstinence from smoking between a quit date ( defined before randomisation and set within two weeks of this) and delivery. At six months after childbirth self-reported maternal smoking status will be ascertained and two years after childbirth, self-reported maternal smoking status and the behaviour, cognitive development and respiratory symptoms of children born in the trial will be compared in both groups. Discussion: This trial is designed to ascertain whether or not standard doses of NRT ( as transdermal patches) are effective and safe when used for smoking cessation during pregnancy
Gauss-Bonnet Black Holes and Heavy Fermion Metals
We consider charged black holes in Einstein-Gauss-Bonnet Gravity with
Lifshitz boundary conditions. We find that this class of models can reproduce
the anomalous specific heat of condensed matter systems exhibiting
non-Fermi-liquid behaviour at low temperatures. We find that the temperature
dependence of the Sommerfeld ratio is sensitive to the choice of Gauss-Bonnet
coupling parameter for a given value of the Lifshitz scaling parameter. We
propose that this class of models is dual to a class of models of
non-Fermi-liquid systems proposed by Castro-Neto et.al.Comment: 17 pages, 6 figures, pdfLatex; small corrections to figure 10 in this
versio
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