194 research outputs found
Heavy Quark Thermalization in Classical Lattice Gauge Theory: Lessons for Strongly-Coupled QCD
Thermalization of a heavy quark near rest is controlled by the correlator of
two electric fields along a temporal Wilson line. We address this correlator
within real-time, classical lattice Yang-Mills theory, and elaborate on the
analogies that exist with the dynamics of hot QCD. In the weak-coupling limit,
it can be shown analytically that the dynamics on the two sides are closely
related to each other. For intermediate couplings, we carry out
non-perturbative simulations within the classical theory, showing that the
leading term in the weak-coupling expansion significantly underestimates the
heavy quark thermalization rate. Our analytic and numerical results also yield
a general understanding concerning the overall shape of the spectral function
corresponding to the electric field correlator, which may be helpful in
subsequent efforts to reconstruct it from Euclidean lattice Monte Carlo
simulations.Comment: 22 pages. v2: a reference and clarifications added; published versio
Anisotropy of the Upper Critical Field and Critical Current in Single Crystal MgB
We report on specific heat, high magnetic field transport and
susceptibility measurements on magnesium diboride single crystals. The
upper critical field for magnetic fields perpendicular and parallel to
the Mg and B planes is presented for the first time in the entire temperature
range. A very different temperature dependence has been observed in the two
directions which yields to a temperature dependent anisotropy with 5 at low temperatures and about 2 near . A peak effect is observed
in susceptibility measurements for 2 T parallel to the axis and
the critical current density presnts a sharp maximum for parallel to the
ab-plane.Comment: 6 pages, 5 figure
The Inverse Scattering Method, Lie-Backlund Transformations and Solitons for Low-energy Effective Field Equations of 5D String Theory
In the framework of the 5D low-energy effective field theory of the heterotic
string with no vector fields excited, we combine two non-linear methods in
order to construct a solitonic field configuration. We first apply the inverse
scattering method on a trivial vacuum solution and obtain an stationary
axisymmetric two-soliton configuration consisting of a massless gravitational
field coupled to a non-trivial chargeless dilaton and to an axion field endowed
with charge. The implementation of this method was done following a scheme
previously proposed by Yurova. We also show that within this scheme, is not
possible to get massive gravitational solitons at all. We then apply a
non-linear Lie-Backlund matrix transformation of Ehlers type on this massless
solution and get a massive rotating axisymmetric gravitational soliton coupled
to axion and dilaton fields endowed with charges. We study as well some
physical properties of the constructed massless and massive solitons and
discuss on the effect of the generalized solution generating technique on the
seed solution and its further generalizations.Comment: 17 pages in latex, changed title, improved text, added reference
The endoscope-assisted supraorbital "keyhole" approach for anterior skull base meningiomas: an updated meta-analysis
Introduction The gold-standard treatment for symptomatic anterior skull base meningiomas is surgical resection. The endoscope-assisted supraorbital "keyhole" approach (eSKA) is a promising technique for surgical resection of olfactory groove (OGM) and tuberculum sellae meningioma (TSM) but has yet to be compared with the microscopic transcranial (mTCA) and the expanded endoscopic endonasal approach (EEA) in the context of existing literature. Methods An updated study-level meta-analysis on surgical outcomes and complications of OGM and TSM operated with the eSKA, mTCA, and EEA was conducted using random-effect models. Results A total of 2285 articles were screened, yielding 96 studies (2191 TSM and 1510 OGM patients). In terms of effectiveness, gross total resection incidence was highest in mTCA (89.6% TSM, 91.1% OGM), followed by eSKA (85.2% TSM, 84.9% OGM) and EEA (83.9% TSM, 82.8% OGM). Additionally, the EEA group had the highest incidence of visual improvement (81.9% TSM, 54.6% OGM), followed by eSKA (65.9% TSM, 52.9% OGM) and mTCA (63.9% TSM, 45.7% OGM). However, in terms of safety, the EEA possessed the highest cerebrospinal fluid leak incidence (9.2% TSM, 14.5% OGM), compared with eSKA (2.1% TSM, 1.6% OGM) and mTCA (1.6% TSM, 6.5% OGM). Finally, mortality and intraoperative arterial injury were 1% or lower across all subgroups. Conclusions In the context of diverse study populations, the eSKA appeared not to be associated with increased adverse outcomes when compared with mTCA and EEA and offered comparable effectiveness. Case-selection is paramount in establishing a role for the eSKA in anterior skull base tumours.Scientific Assessment and Innovation in Neurosurgical Treatment Strategie
From bi-layer to tri-layer Fe nanoislands on Cu3Au(001)
Self assembly on suitably chosen substrates is a well exploited root to
control the structure and morphology, hence magnetization, of metal films. In
particular, the Cu3Au(001) surface has been recently singled out as a good
template to grow high spin Fe phases, due to the close matching between the
Cu3Au lattice constant (3.75 Angstrom) and the equilibrium lattice constant for
fcc ferromagnetic Fe (3.65 Angstrom). Growth proceeds almost layer by layer at
room temperature, with a small amount of Au segregation in the early stage of
deposition. Islands of 1-2 nm lateral size and double layer height are formed
when 1 monolayer of Fe is deposited on Cu3Au(001) at low temperature. We used
the PhotoElectron Diffraction technique to investigate the atomic structure and
chemical composition of these nanoislands just after the deposition at 140 K
and after annealing at 400 K. We show that only bi-layer islands are formed at
low temperature, without any surface segregation. After annealing, the Fe atoms
are re-aggregated to form mainly tri-layer islands. Surface segregation is
shown to be inhibited also after the annealing process. The implications for
the film magnetic properties and the growth model are discussed.Comment: Revtex, 5 pages with 4 eps figure
Can ChatGPT outperform a neurosurgical trainee? A prospective comparative study
Purpose
This study aimed to compare the performance of ChatGPT, a large language model (LLM), with human neurosurgical applicants in a neurosurgical national selection interview, to assess the potential of artificial intelligence (AI) and LLMs in healthcare and provide insights into their integration into the field.
Methods
In a prospective comparative study, a set of neurosurgical national selection-style interview questions were asked to eight human participants and ChatGPT in an online interview. All participants were doctors currently practicing in the UK who had applied for a neurosurgical National Training Number. Interviews were recorded, anonymised, and scored by three neurosurgical consultants with experience as interviewers for national selection. Answers provided by ChatGPT were used as a template for a virtual interview. Interview transcripts were subsequently scored by neurosurgical consultants using criteria utilised in real national selection interviews. Overall interview score and subdomain scores were compared between human participants and ChatGPT.
Results
For overall score, ChatGPT fell behind six human competitors and did not achieve a mean score higher than any individuals who achieved training positions. Several factors, including factual inaccuracies and deviations from expected structure and style may have contributed to ChatGPT's underperformance.
Conclusions
LLMs such as ChatGPT have huge potential for integration in healthcare. However, this study emphasises the need for further development to address limitations and challenges. While LLMs have not surpassed human performance yet, collaboration between humans and AI systems holds promise for the future of healthcare
Skull base repair following endonasal pituitary and skull base tumour resection: a systematic review
Purpose Postoperative cerebrospinal fluid rhinorrhoea (CSFR) remains a frequent complication of endonasal approaches to pituitary and skull base tumours. Watertight skull base reconstruction is important in preventing CSFR. We sought to systematically review the current literature of available skull base repair techniques. Methods Pubmed and Embase databases were searched for studies (2000-2020) that (a) reported on the endonasal resection of pituitary and skull base tumours, (b) focussed on skull base repair techniques and/or postoperative CSFR risk factors, and (c) included CSFR data. Roles, advantages and disadvantages of each repair method were detailed. Random-effects meta-analyses were performed where possible. Results 193 studies were included. Repair methods were categorised based on function and anatomical level. There was absolute heterogeneity in repair methods used, with no independent studies sharing the same repair protocol. Techniques most commonly used for low CSFR risk cases were fat grafts, fascia lata grafts and synthetic grafts. For cases with higher CSFR risk, multilayer regimes were utilized with vascularized flaps, gasket sealing and lumbar drains. Lumbar drain use for high CSFR risk cases was supported by a randomised study (Oxford CEBM: Grade B recommendation), but otherwise there was limited high-level evidence. Pooled CSFR incidence by approach was 3.7% (CI 3-4.5%) for transsphenoidal, 9% (CI 7.2-11.3%) for expanded endonasal, and 5.3% (CI 3.4-7%) for studies describing both. Further meaningful meta-analyses of repair methods were not performed due to significant repair protocol heterogeneity. Conclusions Modern reconstructive protocols are heterogeneous and there is limited evidence to suggest the optimal repair technique after pituitary and skull base tumour resection. Further studies are needed to guide practice.Scientific Assessment and Innovation in Neurosurgical Treatment Strategie
Spectral and transport properties of doped Mott-Hubbard systems with incommensurate magnetic order
We present spectral and optical properties of the Hubbard model on a
two-dimensional square lattice using a generalization of dynamical mean-field
theory to magnetic states in finite dimension. The self-energy includes the
effect of spin fluctuations and screening of the Coulomb interaction due to
particle-particle scattering. At half-filling the quasiparticles reduce the
width of the Mott-Hubbard `gap' and have dispersions and spectral weights that
agree remarkably well with quantum Monte Carlo and exact diagonalization
calculations. Away from half-filling we consider incommensurate magnetic order
with a varying local spin direction, and derive the photoemission and optical
spectra. The incommensurate magnetic order leads to a pseudogap which opens at
the Fermi energy and coexists with a large Mott-Hubbard gap. The quasiparticle
states survive in the doped systems, but their dispersion is modified with the
doping and a rigid band picture does not apply. Spectral weight in the optical
conductivity is transferred to lower energies and the Drude weight increases
linearly with increasing doping. We show that incommensurate magnetic order
leads also to mid-gap states in the optical spectra and to decreased scattering
rates in the transport processes, in qualitative agreement with the
experimental observations in doped systems. The gradual disappearence of the
spiral magnetic order and the vanishing pseudogap with increasing temperature
is found to be responsible for the linear resistivity. We discuss the possible
reasons why these results may only partially explain the features observed in
the optical spectra of high temperature superconductors.Comment: 22 pages, 18 figure
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