59 research outputs found
Entanglement study of the 1D Ising model with Added Dzyaloshinsky-Moriya interaction
We have studied occurrence of quantum phase transition in the one-dimensional
spin-1/2 Ising model with added Dzyaloshinsky-Moriya (DM) interaction from bi-
partite and multi-partite entanglement point of view. Using exact numerical
solutions, we are able to study such systems up to 24 qubits. The minimum of
the entanglement ratio R \tau 2/\tau 1 < 1, as a novel estimator of
QPT, has been used to detect QPT and our calculations have shown that its
minimum took place at the critical point. We have also shown both the
global-entanglement (GE) and multipartite entanglement (ME) are maximal at the
critical point for the Ising chain with added DM interaction. Using matrix
product state approach, we have calculated the tangle and concurrence of the
model and it is able to capture and confirm our numerical experiment result.
Lack of inversion symmetry in the presence of DM interaction stimulated us to
study entanglement of three qubits in symmetric and antisymmetric way which
brings some surprising results.Comment: 18 pages, 9 figures, submitte
Non-diagonal reflection for the non-critical XXZ model
The most general physical boundary -matrix for the open XXZ spin chain in
the non-critical regime () is derived starting from the bare
Bethe ansazt equations. The boundary -matrix as expected is expressed in
terms of -functions. In the isotropic limit corresponding results for
the open XXX chain are also reproduced.Comment: 8 pages Late
Excitation spectrum and critical exponents of a one-dimensional integrable model of fermions with correlated hopping
We investigate the excitation spectrum of a model of colour fermions with
correlated hopping which can be solved by a nested Bethe ansatz. The gapless
excitations of particle-hole type are calculated as well as the spin-wave like
excitations which have a gap. Using general predictions of conformal field
theory the long distance behaviour of some groundstate correlation functions
are derived from a finite-size analysis of the gapless excitations. From the
algebraic decay we show that for increasing particle density the correlation of
so-called -multiplets of particles dominates over the density-density
correlation. This indicates the presence of bound complexes of these
-multiplets. This picture is also supported by the calculation of the
effective mass of charge carriers.Comment: 15 pages, 3 PostScript figures appende
Association between COVID-19 lockdown measures and the incidence of iatrogenic versus spontaneous very preterm births in the Netherlands:a retrospective study
Background: The COVID-19 pandemic led to regional or nationwide lockdowns as part of risk mitigation measurements in many countries worldwide. Recent studies suggest an unexpected and unprecedented decrease in preterm births during the initial COVID-19 lockdowns in the first half of 2020. The objective of the current study was to assess the effects of the two months of the initial national COVID-19 lockdown period on the incidence of very and extremely preterm birth in the Netherlands, stratified by either spontaneous or iatrogenic onset of delivery, in both singleton and multiple pregnancies. Methods: Retrospective cohort study using data from all 10 perinatal centers in the Netherlands on very and extremely preterm births during the initial COVID-19 lockdown from March 15 to May 15, 2020. Incidences of very and extremely preterm birth were calculated using an estimate of the total number of births in the Netherlands in this period. As reference, we used data from the corresponding calendar period in 2015β2018 from the national perinatal registry (Perined). We differentiated between spontaneous versus iatrogenic onset of delivery and between singleton versus multiple pregnancies. Results: The incidence of total preterm birth < 32 weeks in singleton pregnancies was 6.1β° in the study period in 2020 versus 6.5β° in the corresponding period in 2015β2018. The decrease in preterm births in singletons was solely due to a significant decrease in iatrogenic preterm births, both < 32 weeks (OR 0.71; 95%CI 0.53 to 0.95) and < 28 weeks (OR 0.53; 95%CI 0.29 to 0.97). For multiple pregnancies, an increase in preterm births < 28 weeks was observed (OR 2.43; 95%CI 1.35 to 4.39). Conclusion: This study shows a decrease in iatrogenic preterm births during the initial COVID-19-related lockdown in the Netherlands in singletons. Future studies should focus on the mechanism of action of lockdown measures and reduction of preterm birth and the effects of perinatal outcome
Thermal Conductivity of Spin-1/2 Chains
We study the low-temperature transport properties of clean one-dimensional
spin-1/2 chains coupled to phonons. Due to the presence of approximate
conservation laws, the heat current decays very slowly giving rise to an
exponentially large heat conductivity, . As a result of an
interplay of Umklapp scattering and spinon-phonon coupling, the characteristic
energy scale turns out to be of order , where is
the Debye energy, rather than the magnetic exchange interaction -- in
agreement with recent measurements in SrCuO compounds. A large magnetic field
strongly affects the heat transport by two distinct mechanisms. First, it
induces a LINEAR spinon--phonon coupling, which alters the nature of the fixed point: the elementary excitations of the system are COMPOSITE
SPINON-PHONON objects. Second, the change of the magnetization and the
corresponding change of the wave vector of the spinons strongly affects the way
in which various Umklapp processes can relax the heat current, leading to a
characteristic fractal--like spiky behavior of when plotted as a
function of magnetization at fixed T.Comment: 16 pages, RevTex4, 2 figures included; revised refs. and some useful
comments on experimental relevance. On July 12 2005, added an appendix
correcting an error in the form of the phonon propagator. The main result is
unchange
Study protocol for a randomised trial for atosiban versus placebo in threatened preterm birth : The APOSTEL 8 study
Peer reviewedPublisher PD
COMPTEL observations of gamma-ray bursts - Imaging and localization
The COMPTEL experiment on GRO images 0.7-30 MeV celestial gamma-radiation that falls within its 1 steradian field of view. During the first eleven months of orbit, preliminary lozalizations from BATSE triggers indicated that about 1 in 6 cosmic events could have fallen within COMPTEL\u27s field of view. WE present COMPTEL positions for four of the brighter of these gamma-ray bursts
First measurements of p11B fusion in a magnetically confined plasma
Proton-boron (p11B) fusion is an attractive potential energy source but technically challenging to implement. Developing techniques to realize its potential requires first developing the experimental capability to produce p11B fusion in the magnetically-confined, thermonuclear plasma environment. Here we report clear experimental measurements supported by simulation of p11B fusion with high-energy neutral beams and boron powder injection in a high-temperature fusion plasma (the Large Helical Device) that have resulted in diagnostically significant levels of alpha particle emission. The injection of boron powder into the plasma edge results in boron accumulation in the core. Three 2 MW, 160 kV hydrogen neutral beam injectors create a large population of well-confined, high -energy protons to react with the boron plasma. The fusion products, MeV alpha particles, are measured with a custom designed particle detector which gives a fusion rate in very good relative agreement with calculations of the global rate. This is the first such realization of p11B fusion in a magnetically confined plasma
Behavioral and neurodevelopmental outcome of children after maternal allopurinol administration during suspected fetal hypoxia:5-year follow up of the ALLO-trial
Objective To evaluate the long-term neurodevelopmental and behavioral outcome of antenatal allopurinol treatment during suspected fetal hypoxia. Study design We studied children born from women who participated in a randomized double-blind placebo controlled multicenter study (ALLO-trial). Labouring women in whom the fetus was suspected to have fetal hypoxia were randomly allocated to receive allopurinol or placebo. At 5 years of age, the children were assessed with 2 parent reported questionnaires, the Ages and Stages Questionnaire (ASQ) and the Child Behavior Checklist (CBCL). A child was marked abnormal for ASQ if it scored below 2 standard deviation under the normative mean of a reference population in at least one domain. For CBCL, a score above the cut-off value (95th percentile for narrowband scale, 85th percentile for broadband scale) in at least one scale was marked as abnormal. Results We obtained data from 138 out of the original 222 mildly asphyxiated children included in the ALLO-trial (response rate 62%, allopurinol n = 73, placebo n = 65). At 5 years of age, the number of children that scored abnormal on the ASQ were 11 (15.1%) in the allopurinol group versus 11 (9.2%) in the placebo group (relative risk (RR) 1.64, 95% confidence interval (CI): 0.64 to 4.17, p = 0.30). On CBCL 21 children (30.4%) scored abnormal in de allopurinol group versus 12 children (20.0%) in the placebo group (RR 1.52, 95% CI: 0.82 to 2.83, p = 0.18). Conclusion We found no proof that allopurinol administered to labouring women with suspected fetal hypoxia improved long-term developmental and behavioral outcome. These findings are limited due to the fact that the study was potentially underpowered
The human equilibrative nucleoside transporter 1 mediates in vitro cytarabine sensitivity in childhood acute myeloid leukaemia
Cytarabine (ara-C) is the most effective agent for the treatment of acute myeloid leukaemia (AML). Aberrant expression of enzymes involved in the transport/metabolism of ara-C could explain drug resistance. We determined mRNA expression of these factors using quantitative-real-time-PCR in leukemic blasts from children diagnosed with de novo AML. Expression of the inactivating enzyme pyrimidine nucleotidase-I (PN-I) was 1.8-fold lower in FAB-M5 as compared to FAB-M1/2 (P=0.007). In vitro sensitivity to deoxynucleoside analogues was determined using the MTT-assay. Human equilibrative nucleoside transporter-1 (hENT1) mRNA expression and ara-C sensitivity were significantly correlated (rp=β0.46; P=0.001), with three-fold lower hENT1 mRNA levels in resistant patients (P=0.003). hENT1 mRNA expression also seemed to correlate inversely with the LC50 values of cladribine (rp=β0.30; P=0.04), decitabine (rp=β0.29; P=0.04) and gemcitabine (rp=β0.33; P=0.02). Deoxycytidine kinase (dCK) and cytidine deaminase (CDA) mRNA expression seemed to correlate with in vitro sensitivity to gemcitabine (rp=β0.31; P=0.03) and decitabine (rp=0.33; P=0.03), respectively. The dCK/PN-I ratio correlated inversely with LC50 values for gemcitabine (rp=β0.45, P=0.001) and the dCK/CDA ratio seemed to correlate with LC50 values for decitabine (rp=β0.29; 0.04). In conclusion, decreased expression of hENT1, which transports ara-C across the cell membrane, appears to be a major factor in ara-C resistance in childhood AML
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