33,918 research outputs found
Variational study of a two-level system coupled to a harmonic oscillator in a ultrastrong coupling regime
The nonclassical behaviors of a two-level system coupled to a harmonic
oscillator is investigated in the ultrastrong coupling regime. We revisit the
variational solution of the ground state and find that the existing solution do
not account accurately for nonclassical effects such squeezing. We suggest a
new trial wave function and demonstrate that it has an excellent accuracy on
the quantum correlation effects as well as on energy.Comment: 4 pages; 3 figures; to appear in Phys. Rev.
Pressure-Induced Rotational Symmetry Breaking in URuSi
Phase transitions and symmetry are intimately linked. Melting of ice, for
example, restores translation invariance. The mysterious hidden order (HO)
phase of URuSi has, despite relentless research efforts, kept its
symmetry breaking element intangible. Here we present a high-resolution x-ray
diffraction study of the URuSi crystal structure as a function of
hydrostatic pressure. Below a critical pressure threshold kbar,
no tetragonal lattice symmetry breaking is observed even below the HO
transition K. For , however, a pressure-induced rotational
symmetry breaking is identified with an onset temperatures K.
The emergence of an orthorhombic phase is found and discussed in terms of an
electronic nematic order that appears unrelated to the HO, but with possible
relevance for the pressure-induced antiferromagnetic (AF) phase. Existing
theories describe the HO and AF phases through an adiabatic continuity of a
complex order parameter. Since none of these theories predicts a
pressure-induced nematic order, our finding adds an additional symmetry
breaking element to this long-standing problem.Comment: 6 pages, 4 figures and supplemental material
Kondo resonance of a Co atom exchange coupled to a ferromagnetic tip
The Kondo effect of a Co atom on Cu(100) was investigated with a
low-temperature scanning tunneling microscope using a monoatomically sharp
nickel tip. Upon a tip-Co contact, the differential conductance spectra exhibit
a spin-split asymmetric Kondo resonance. The computed ab initio value of the
exchange coupling is too small to suppress the Kondo effect, but sufficiently
large to produce the splitting observed. A quantitative analysis of the line
shape using the numerical renormalization group technique indicates that the
junction spin polarization is weak.Comment: 5 pages, 4 figure
Angular dependent magnetothermopower of alpha-(ET)2KHg(SCN)4
The magnetic field and angular dependencies of the thermopower and Nernst
effect of the quasi-two-dimensional organic conductor alpha-(ET)2KHg(SCN)4 are
experimentally measured at temperatures below (4 K) and above (9 K) the
transition temperature to fields of In addition, a theoretical model which
involves a magnetic breakdown effect between the q1D and q2D bands is proposed
in order to simulate the data. Analysis of the background components of the
thermopower and Nernst effect imply that at low temperatures, in the CDW state,
the properties of alpha-(ET)2KHg(SCN)4 are determined mostly by the orbits on
the new open Fermi sheets. Quantum oscillations observed in the both
thermoelectric effects, at fields above 8 T, originate only from the alpha
orbit.Comment: 25 pages, 18 figure
Cardiac interventions in patients with achondroplasia: a systematic review.
Patients with achondroplasia and other causes of dwarfism suffer from increased rates of cardiovascular disease relative to the remainder of the population. Few studies have examined these patients when undergoing cardiac surgery or percutaneous intervention. This systematic review examines the literature to determine outcomes following cardiac intervention in this unique population. An electronic search was performed in the English literature to identify all reports of achondroplasia, dwarfism, and cardiac intervention. Of the 5,274 articles identified, 14 articles with 14 cases met inclusion criteria. Patient-level data was extracted and analyzed. Median patient age was 55.5 [interquartile ranges (IQR), 43.8, 59.8] years, median height 102.0 [98.8, 112.5] cm, median BMI 32.1 [27.0, 45.9], and 57.1% (8/14) were male. Of these 14 patients, nine had the following documented skeletal abnormalities: 66.7% (6/9) had scoliosis, 66.7% (6/9) had kyphosis, 11.1% (1/9) had lordosis, 11.1% (1/9) pectus carinatum and 11.1% (1/9) spinal stenosis. Coronary artery disease was present in 53.8% (7/13), and 30.8% (4/13) patients previously suffered a myocardial infarction. Of the eight patients who underwent cardiac surgery, 37.5% (3/8) underwent multivessel coronary artery bypass grafting, 37.5% (3/8) underwent aortic valve replacement, 25.0% (2/8) underwent type A aortic dissection repair, and the remaining 12.5% (1/8) underwent pulmonary thromboendarterectomy. Six patients underwent percutaneous intervention. Median cardiopulmonary bypass time was 136.5 [110.0, 178.8] minutes. Median arterial cannula size was 20.0 [20.0, 24.0] Fr. Bicaval cannulation was performed in all cases describing cannulation strategy (5/5). Median superior vena cava cannula size was 28.0 [28.0, 28.0] Fr, and inferior vena cava cannula size was 28.0 [28.0, 28.0] Fr. No mortality was reported with a median follow up time of 6.0 [6.0, 10.5] months. In conclusion, Common cardiac procedures can be performed with reasonable safety in this patient population. Operative adjustments may need to be made with respect to equipment to accommodate patient-specific needs
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