477 research outputs found
The t-t'-J model in one dimension using extremely correlated Fermi liquid theory and time dependent density matrix renormalization group
We study the one dimensional t-t'-J model for generic couplings using two
complementary theories, the extremely correlated Fermi liquid theory and
time-dependent density matrix renormalization group over a broad energy scale.
The two methods provide a unique insight into the strong momentum dependence of
the self-energy of this prototypical non-Fermi liquid, described at low
energies as a Tomonaga-Luttinger liquid. We also demonstrate its intimate
relationship to spin-charge separation, i.e. the splitting of Landau
quasiparticles of higher dimensions into two constituents, driven by strong
quantum fluctuations inherent in one dimension. The momentum distribution
function, the spectral function, and the excitation dispersion of these two
methods also compare well
Magnetic Fields Recorded by Chondrules Formed in Nebular Shocks
Recent laboratory efforts (Fu et al., 2014) have constrained the remanent
magnetizations of chondrules and the magnetic field strengths at which the
chondrules were exposed to as they cooled below their Curie points. An
outstanding question is whether the inferred paleofields represent the
background magnetic field of the solar nebula or were unique to the
chondrule-forming environment. We investigate the amplification of the magnetic
field above background values for two proposed chondrule formation mechanisms,
large-scale nebular shocks and planetary bow shocks. Behind large-scale shocks,
the magnetic field parallel to the shock front is amplified by factors , regardless of the magnetic diffusivity. Therefore, chondrules melted in
these shocks probably recorded an amplified magnetic field. Behind planetary
bow shocks, the field amplification is sensitive to the magnetic diffusivity.
We compute the gas properties behind a bow shock around a 3000 km-radius
planetary embryo, with and without atmospheres, using hydrodynamics models. We
calculate the ionization state of the hot, shocked gas, including thermionic
emission from dust, and thermal ionization of gas-phase potassium atoms, and
the magnetic diffusivity due to Ohmic dissipation and ambipolar diffusion. We
find that the diffusivity is sufficiently large that magnetic fields have
already relaxed to background values in the shock downstream where chondrules
acquire magnetizations, and that these locations are sufficiently far from the
planetary embryos that chondrules should not have recorded a significant
putative dynamo field generated on these bodies. We conclude that, if melted in
planetary bow shocks, chondrules probably recorded the background nebular
field.Comment: 17 pages, 11 figures, accepted for publication in Ap
Orbital structure of the effective pairing interaction in the high-temperature superconducting cuprates
The nature of the effective interaction responsible for pairing in the
high-temperature superconducting cuprates remains unsettled. This question has
been studied extensively using the simplified single-band Hubbard model, which
does not explicitly consider the orbital degrees of freedom of the relevant
CuO planes. Here, we use a dynamic cluster quantum Monte Carlo
approximation to study the orbital structure of the pairing interaction in the
three-band Hubbard model, which treats the orbital degrees of freedom
explicitly. We find that the interaction predominately acts between neighboring
copper orbitals, but with significant additional weight appearing on the
surrounding bonding molecular oxygen orbitals. By explicitly comparing these
results to those from the simpler single-band Hubbard model, our study provides
strong support for the single-band framework for describing superconductivity
in the cuprates
SPICED: News Similarity Detection Dataset with Multiple Topics and Complexity Levels
Nowadays, the use of intelligent systems to detect redundant information in
news articles has become especially prevalent with the proliferation of news
media outlets in order to enhance user experience. However, the heterogeneous
nature of news can lead to spurious findings in these systems: Simple
heuristics such as whether a pair of news are both about politics can provide
strong but deceptive downstream performance. Segmenting news similarity
datasets into topics improves the training of these models by forcing them to
learn how to distinguish salient characteristics under more narrow domains.
However, this requires the existence of topic-specific datasets, which are
currently lacking. In this article, we propose a new dataset of similar news,
SPICED, which includes seven topics: Crime & Law, Culture & Entertainment,
Disasters & Accidents, Economy & Business, Politics & Conflicts, Science &
Technology, and Sports. Futhermore, we present four distinct approaches for
generating news pairs, which are used in the creation of datasets specifically
designed for news similarity detection task. We benchmarked the created
datasets using MinHash, BERT, SBERT, and SimCSE models
Bright artificial light subsensitizes a central muscarinic mechanism
Supersensitivity of a muscarinic mechanism is implicated in the pathophysiology of depression. Bright artificial light is efficacious in the treatment of Seasonal Affective Disorder (SAD). We studied the effect of constant bright light (11, 500 lux) on the sensitivity of adult, male rats to oxotremorine, 1.5 mg/kg ip, using a repeated measures design. Oxotremorine challenges were proceeded by the injection of methylscopolamine, 1 mg/kg ip, by 30 minutes. Temperature was telemetrically measured every 10 minutes for 120 minutes starting 10 minutes after the injection of oxotremorine. Prior to and after 7 continuous days of exposure to bright light, the sample exhibited a hypothermic response of 2if2.50 +/- 0.48[deg]C (mean +/- SEM) and 0.29 +/- 0.31[deg]C (mean +/- SEM), respectively (p < 0.0014). All 7 animals exhibited blunting to the thermic response to oxotremorine. Bright light also blocked the capacity of amitriptyline to supersensitize a central muscarinic mechanism. Exposure to light at an intensity of 300 lux for 7 days had no effect on the thermic response to oxotremorine. These data are consistent with the hypotheses that the biology of depression involves supersensitivity of central muscarinic mechanisms and that the effects of bright artificial light are not the consequence of shifting circadian rhythms.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26470/1/0000005.pd
Robust charge-density wave correlations in the electron-doped single-band Hubbard model
There is growing evidence that the hole-doped single-band Hubbard and -
models do not have a superconducting ground state reflective of the
high-temperature cuprate superconductors but instead have striped spin- and
charge-ordered ground states. Nevertheless, it is proposed that these models
may still provide an effective low-energy model for electron-doped materials.
Here we study the finite temperature spin and charge correlations in the
electron-doped Hubbard model using quantum Monte Carlo dynamical cluster
approximation calculations and contrast their behavior with those found on the
hole-doped side of the phase diagram. We find evidence for a charge modulation
with both checkerboard and unidirectional components decoupled from any
spin-density modulations. These correlations are inconsistent with a
weak-coupling description based on Fermi surface nesting, and their doping
dependence agrees qualitatively with resonant inelastic x-ray scattering
measurements. Our results provide evidence that the single-band Hubbard model
describes the electron-doped cuprates
Energy sector development: system dynamics analysis
The development of a complex and dynamic system such as the energy sector requires a comprehensiveunderstanding ofits constituentcomponents andtheir interactions, and thusrequires approaches that can adapt to the dynamic complexity in systems. Previous efforts mainly used reductionist approaches, which examine the components of the system in isolation, neglecting their interdependent nature. Such approaches reduce our ability to understand the system and/or mitigate undesirable outcomes. We adopt a system dynamics approach to construct an integrated model for analysing the behaviour of the energy sector. Although the Australian energy sector is used as a case study, the model can be applied in other context elsewhere around the world The results indicate that the current trajectory of the Australian energy sector is unsustainable and growth is not being controlled. Limits to growth are fast approaching due to excessive fossil fuel extraction, high emissions and high energy dependency. With the current growth, Australia’s global CO2 emissions footprint will increase to unprecedented levels reaching 12% by 2030 (9.5% for exports and 2.5% for domestic). Oil dependency will account for 43% and 47% of total consumption by 2030 and 2050. By 2032, coal will be the only fossil fuel resource available in Australia. Expansion of investment in coal and gas production is a large risk
Effectiveness of Ledipasvir/Sofosbuvir with/without Ribavarin in Liver Transplant Recipients with Hepatitis C.
Background and Aims: Recurrent infection of hepatitis C virus (HCV) in liver transplant (LT) recipients is universal and associated with significant morbidity and mortality. Methods: We retrospectively evaluated the safety and efficacy of ledipasvir/sofosbuvir with and without ribavirin in LT recipients with recurrent genotype 1 hepatitis C. Results: Eighty-five LT recipients were treated for recurrent HCV with ledipasvir/sofosbuvirwith and without ribavirin for 12 or 24 weeks. The mean (± standard deviation [SD]) time from LT to treatment initiation was 68 (±71) months. The mean (± SD) age of the cohort was 63 (±8.6) years old. Most recipients were male (70%). Baseline alanine transaminase, total bilirubin, and HCV ribonucleic acid (RNA) values (± SD) were 76.8 (±126) mg/dL, 0.8 (±1.3) U/L, and 8,010,421.9 (±12,420,985) IU/mL, respectively. Five of 43 recipients who were treated with ribavirin required drug cessation due to side effects, with 4 of those being anemia complications. No recipient discontinued the ledipasvir/sofosbuvir. Eighty-one percent of recipients had undetectable viral levels at 4 weeks after starting therapy, and all recipients had complete viral suppression at the end of therapy. The sustained viral response at 12 weeks after completion of therapy was 94%. Conclusion : Ledipasvir and sofosbuvir with and without ribavirin therapy is an effective and well-tolerated interferon-free treatment for recurrent HCV infection after LT. Anemia is not uncommon in LT recipients receiving ribavirin
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