294 research outputs found
Phase Diagram for a Luttinger Liquid coupled to Phonons in one dimension
The Green function and the ordering correlation functions of a system of
electrons coupled to acoustic phonons are calculated explicitly. The
sensitivity of the correlation function exponents to the Wentzel-Bardeen
singularity is discussed. A phase diagram is established for the Hubbard model
coupled to phonons, using the integral equations of Lieb and Wu. By increasing
the filling factor towards half filling, the Wentzel-Bardeen singularity can be
reached for arbitrary phonon coupling. This suppresses antiferromagnetic
fluctuations and drives the system in a metallic phase, and ultimately in the
triplet superconducting regime.Comment: 33 pages, REVTex, 6 figures upon request ([email protected]
Phase coherence in the inelastic cotunneling regime
Two quantum dots with tunable mutual tunnel coupling have been embedded in a
two-terminal Aharonov-Bohm geometry. Aharonov-Bohm oscillations are
investigated in the cotunneling regime. Visibilities of more than 0.8 are
measured indicating that phase-coherent processes are involved in the elastic
and inelastic cotunneling. An oscillation-phase change of pi is detected as a
function of bias voltage at the inelastic cotunneling onset.Comment: 4 pages, 4 figure
Cytoreductive surgery and hyperthermic intraperitoneal chemotherapy in peritoneal carcinomatosis from ovarian cancer
BACKGROUND: In selected patients with peritoneal carcinomatosis from ovarian cancer prognosis can be improved by cytoreductive surgery and hyperthermic intraperitoneal chemotherapy (HIPEC). METHODS: Between September 1995 and February 1999, 19 patients (mean age 52 years, range 30â72 years) with peritoneal carcinomatosis from primary or recurrent epithelial ovarian carcinoma were operated with the aim of complete macroscopical cytoreduction. Surgery was followed by intraoperative HIPEC. The data was analyzed retrospectively. RESULTS: Eleven patients had recurrent and 8 primary ovarian cancer. The median progression free interval was 18 months (range 6â36 months). Macroscopically complete cytoreduction was achieved in 9 patients. Cisplatin (n = 16) or mitoxantrone (n = 3) were used for the intraoperative chemotherapy. The median intraabdominal inflow temperature was 41.5°C. Complications occurred in seven patients. Most frequent complications were anastomotic leakage (2/19) and intraabdominal abscess formation (2/19). One patient died postoperatively. The mean (± SD) overall survival time was 33(± 6) months with a 5-year survival rate of 15%. The survival was found to be influenced by the completeness of cytoreduction (44 ± 11 vs. 25 ± 6 months, p = 0.40), tumor volume (54 ± 10 versus 16 ± 4, p = 0.002) and presence of lymph node (38 ± 8 vs. 20 ± 8 months, p= 0.2) or liver metastases (51 ± 9 vs. 21 ± 6 months, p = 0.06). CONCLUSIONS: Cytoreductive surgery combined with HIPEC is feasible and is associated with a reasonable morbidity and mortality. Complete cytoreduction may improve survival in select group of patients with low tumor volume and no organ metastases
How the COVID-19 pandemic and related school closures reduce physical activity among children and adolescents in the WHO European Region: a systematic review and meta-analysis
Background: Emerging research suggests that physical activity among children and adolescents decreased during the COVID-19 pandemic. However, a differentiated overview of European youth is lacking. In particular, no systematic analysis has been conducted to date on the impact of heterogeneous pandemic restrictions and school closures within European countries, and with regard to potentially vulnerable groups.
Methods: We searched seven databases and included studies for children and adolescents (â€â19 years) of the WHO European Region that compared physical activity during the COVID-19 pandemic with a pre-pandemic baseline using validated measurement instruments. We used the Oxford Stringency Index and School Closure Index as indicators of restriction stringency. Screening for eligibility, data extraction, assessment of the study risk of bias (using the âRisk of Bias in Non-randomized Studies - of Exposureâ [ROBINS-E]) and certainty grading of evidence (using the GRADE approach), were all done in duplicate. Unpublished data was requested from study authors. Data were pooled in random effects models. An a priori protocol was published, reporting is carried out in accordance with the âPreferred Reporting Items for Systematic Review and Meta-Analysesâ (PRISMA) statement.
Results: Of 14,897 non-duplicate records, 26 publications (nâ=â15,038 pre-pandemic, nâ=â13,041 during pandemic) met full inclusion criteria. Comparison before and during the COVID-19 pandemic revealed a significant reduction in total physical activity (standardized mean difference [SMD], -0.57 [95%CI, -0.95; -0.20]) and moderate-to-vigorous physical activity (SMD, -0.43 [95% CI, -0.75; -0.10]), corresponding to a decrease of 12 min per day (a 20% reduction of the WHO recommendation). A decrease in sporting activity was also recorded. Subgroup analyses suggested that middle childhood (aged 8â12) and adolescents were particularly affected by the decline. School closures were associated with a reduction in physical activity. The certainty of evidence for all outcomes was low.
Conclusions: A sharp decline in all forms of physical activity was recorded among European children and adolescents during the COVID-19 pandemic. This decline was higher during periods of school closure and mainly affected younger schoolchildren and adolescents. Immediate action by policy-makers and practitioners, as well as evidence-based public health strategies, are imperative in reversing this trend
Conductance Increase by Electron-Phonon Interaction in Quantum Wires
We investigate the influence of electron-phonon interactions on the
DC-conductance of a quantum wire in the limit of one occupied
subband. At zero temperature, a Tomonaga-Luttinger-like renormalization of
to a value slightly larger than is calculated for a
realistic quantum wire model.Comment: 12 pages RevTeX, no figure. Appears in Phys. Rev.
Heavy hole states in Germanium hut wires
Hole spins have gained considerable interest in the past few years due to
their potential for fast electrically controlled qubits. Here, we study holes
confined in Ge hut wires, a so far unexplored type of nanostructure. Low
temperature magnetotransport measurements reveal a large anisotropy between the
in-plane and out-of-plane g-factors of up to 18. Numerical simulations verify
that this large anisotropy originates from a confined wave function which is of
heavy hole character. A light hole admixture of less than 1% is estimated for
the states of lowest energy, leading to a surprisingly large reduction of the
out-of-plane g-factors. However, this tiny light hole contribution does not
influence the spin lifetimes, which are expected to be very long, even in non
isotopically purified samples
Decoherence of Schrodinger cat states in a Luttinger liquid
Schrodinger cat states built from quantum superpositions of left or right
Luttinger fermions located at different positions in a spinless Luttinger
liquid are considered. Their decoherence rates are computed within the
bosonization approach using as environments the quantum electromagnetic field
or two or three dimensionnal acoustic phonon baths. Emphasis is put on the
differences between the electromagnetic and acoustic environments.Comment: 22 pages revtex4, 7 figures in a separate PS fil
Spin current shot noise as a probe of interactions in mesoscopic systems
It is shown that the spin resolved current shot noise can probe attractive or
repulsive interactions in mesoscopic systems. This is illustrated in two
physical situations : i) a normal-superconducting junction where the spin
current noise is found to be zero, and ii) a single electron transistor (SET),
where the spin current noise is found to be Poissonian. Repulsive interactions
may also lead to weak attractive correlations (bunching of opposite spins) in
conditions far from equilibrium. Spin current shot noise can be used to measure
the spin relaxation time , and a set-up is proposed in a quantum dot
geometry.Comment: 5 pages, 4 Figures, revised version, added reference
Entangled Hanbury Brown Twiss effects with edge states
Electronic Hanbury Brown Twiss correlations are discussed for geometries in
which transport is along adiabatically guided edge channels. We briefly discuss
partition noise experiments and discuss the effect of inelastic scattering and
dephasing on current correlations. We then consider a two-source Hanbury Brown
Twiss experiment which demonstrates strikingly that even in geometries without
an Aharonov-Bohm effect in the conductance matrix (second-order interference),
correlation functions can (due to fourth-order interference) be sensitive to a
flux. Interestingly we find that this fourth-order interference effect is
closely related to orbital entanglement. The entanglement can be detected via
violation of a Bell Inequality in this geometry even so particles emanate from
uncorrelated sources.Comment: International Symposium "Quantum Hall Effect: Past, Present and
Future
Competing mechanisms for singlet-triplet transition in artificial molecules
We study the magnetic field induced singlet/triplet transition for two
electrons in vertically coupled quantum dots by exact diagonalization of the
Coulomb interaction. We identify the different mechanisms occurring in the
transition, involving either in-plane correlations or localization in opposite
dots, depending on the field direction. Therefore, both spin and orbital
degrees of freedom can be manipulated by field strength and direction. The
phase diagram of realistic devices is determined.Comment: To appear in Phys. Rev. B - Rapid Comm. - 5 pages, 3 figure
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