433 research outputs found
Light cone dynamics and reverse Kibble-Zurek mechanism in two-dimensional superfluids following a quantum quench
We study the dynamics of the relative phase of a bilayer of two-dimensional
superfluids after the two superfluids have been decoupled. We find that on
short time scales the relative phase shows "light cone" like dynamics and
creates a metastable superfluid state, which can be supercritical. We also
demonstrate similar light cone dynamics for the transverse field Ising model.
On longer time scales the supercritical state relaxes to a disordered state due
to dynamical vortex unbinding. This scenario of dynamically suppressed vortex
proliferation constitutes a reverse-Kibble-Zurek effect. We study this effect
both numerically using truncated Wigner approximation and analytically within a
newly suggested time dependent renormalization group approach (RG). In
particular, within RG we show that there are two possible fixed points for the
real time evolution corresponding to the superfluid and normal steady states.
So depending on the initial conditions and the microscopic parameters of the
Hamiltonian the system undergoes a non-equilibrium phase transition of the
Kosterlitz-Thouless type. The time scales for the vortex unbinding near the
critical point are exponentially divergent, similar to the equilibrium case.Comment: 14 pages, 10 figure
Decoherence in an exactly solvable qubit model with initial qubit-environment correlations
We study a model of dephasing (decoherence) in a two-state quantum system
(qubit) coupled to a bath of harmonic oscillators. An exact analytic solution
for the reduced dynamics of a two-state system in this model has been obtained
previously for factorizing initial states of the combined system. We show that
the model admits exact solutions for a large class of correlated initial states
which are typical in the theory of quantum measurements. We derive exact
expressions for the off-diagonal elements of the qubit density matrix, which
hold for an arbitrary strength of coupling between the qubit and the bath. The
influence of initial correlations on decoherence is considered for different
bath spectral densities. Time behavior of the qubit entropy in the decoherence
process is discussed.Comment: 10 pages, 5 figure
Maternal neurofascin-specific autoantibodies bind to structures of the fetal nervous system during pregnancy, but have no long term effect on development in the rat
Neurofascin was recently reported as a target for axopathic autoantibodies in patients with multiple sclerosis (MS), a response that will exacerbate axonal pathology and disease severity in an animal model of multiple sclerosis. As transplacental transfer of maternal autoantibodies can permanently damage the developing nervous system we investigated whether intrauterine exposure to this neurofascin-specific response had any detrimental effect on white matter tract development. To address this question we intravenously injected pregnant rats with either a pathogenic anti-neurofascin monoclonal antibody or an appropriate isotype control on days 15 and 18 of pregnancy, respectively, to mimic the physiological concentration of maternal antibodies in the circulation of the fetus towards the end of pregnancy. Pups were monitored daily with respect to litter size, birth weight, growth and motor development. Histological studies were performed on E20 embryos and pups sacrificed on days 2, 10, 21, 32 and 45 days post partum. Results: Immunohistochemistry for light and confocal microscopy confirmed passively transferred anti-neurofascin antibody had crossed the placenta to bind to distinct structures in the developing cortex and cerebellum. However, this did not result in any significant differences in litter size, birth weight, or general physical development between litters from control mothers or those treated with the neurofascin-specific antibody. Histological analysis also failed to identify any neuronal or white matter tract abnormalities induced by the neurofascin-specific antibody. Conclusions: We show that transplacental transfer of circulating anti-neurofascin antibodies can occur and targets specific structures in the CNS of the developing fetus. However, this did not result in any pre- or post-natal abnormalities in the offspring of the treated mothers. These results assure that even if anti-neurofascin responses are detected in pregnant women with multiple sclerosis these are unlikely to have a negative effect on their children
Review: ‘Gimme five’: future challenges in multiple sclerosis. ECTRIMS Lecture 2009
This article is based on the ECTRIMS lecture given at the 25th ECTRIMS meeting which was held in Düsseldorf, Germany, from 9 to 12 September 2009. Five challenges have been identified: (1) safeguarding the principles of medical ethics; (2) optimizing the risk/benefit ratio; (3) bridging the gap between multiple sclerosis and experimental autoimmune encephalitis; (4) promoting neuroprotection and repair; and (5) tailoring multiple sclerosis therapy to the individual patient. Each of these challenges will be discussed and placed in the context of current research into the pathogenesis and treatment of multiple sclerosis
Momentum-Resolved Bragg Spectroscopy in Optical Lattices
Strongly correlated many-body systems show various exciting phenomena in
condensed matter physics such as high-temperature superconductivity and
colossal magnetoresistance. Recently, strongly correlated phases could also be
studied in ultracold quantum gases possessing analogies to solid-state physics,
but moreover exhibiting new systems such as Fermi-Bose mixtures and magnetic
quantum phases with high spin values. Particularly interesting systems here are
quantum gases in optical lattices with fully tunable lattice and atomic
interaction parameters. While in this context several concepts and ideas have
already been studied theoretically and experimentally, there is still great
demand for new detection techniques to explore these complex phases in detail.
Here we report on measurements of a fully momentum-resolved excitation
spectrum of a quantum gas in an optical lattice by means of Bragg spectroscopy.
The bandstructure is measured with high resolution at several lattice depths.
Interaction effects are identified and systematically studied varying density
and excitation fraction.Comment: 13 pages, 5 figure
Stability and Hydrolyzation of Metal Organic Frameworks with Paddle-Wheel SBUs upon Hydration
Instability of most prototypical metal organic frameworks (MOFs) in the
presence of moisture is always a limita- tion for industrial scale development.
In this work, we examine the dissociation mechanism of microporous paddle wheel
frameworks M(bdc)(ted)0.5 [M=Cu, Zn, Ni, Co; bdc= 1,4-benzenedicarboxylate;
ted= triethylenediamine] in controlled humidity environments. Combined in-situ
IR spectroscopy, Raman, and Powder x-ray diffraction measurements show that the
stability and modification of isostructual M(bdc)(ted)0.5 compounds upon
exposure to water vapor critically depend on the central metal ion. A
hydrolysis reaction of water molecules with Cu-O-C is observed in the case of
Cu(bdc)(ted)0.5. Displacement reactions of ted linkers by water molecules are
identified with Zn(bdc)(ted)0.5 and Co(bdc)(ted)0.5. In contrast,.
Ni(bdc)(ted)0.5 is less suscept- ible to reaction with water vapors than the
other three compounds. In addition, the condensation of water vapors into the
framework is necessary to initiate the dissociation reaction. These findings,
supported by supported by first principles theoretical van der Waals density
functional (vdW-DF) calculations of overall reaction enthalpies, provide the
necessary information for de- termining operation conditions of this class of
MOFs with paddle wheel secondary building units and guidance for developing
more robust units
Cancer Appetite and Symptom Questionnaire (CASQ) for Brazilian Patients: Cross-Cultural Adaptation and Validation Study
Background
Appetite and symptoms, conditions generally reported by the patients with cancer, are
somewhat challenging for professionals to measure directly in clinical routine (latent conditions).
Therefore, specific instruments are required for this purpose. This study aimed to perform
a cultural adaptation of the Cancer Appetite and Symptom Questionnaire (CASQ), into
Portuguese and evaluate its psychometric properties on a sample of Brazilian cancer
patients.
Methods
This is a validation study with Brazilian cancer patients. The face, content, and construct
(factorial and convergent) validities of the Cancer Appetite and Symptom Questionnaire,
the study tool, were estimated. Further, a confirmatory factor analysis (CFA) was conducted.
The ratio of chi-square and degrees of freedom (χ2
/df), comparative fit index (CFI),
goodness of fit index (GFI) and root mean square error of approximation (RMSEA) were
used for fit model assessment. In addition, the reliability of the instrument was estimated
using the composite reliability (CR) and Cronbach’s alpha coefficient (α), and the invariance
of the model in independent samples was estimated by a multigroup analysis (Δχ2).
Results
Participants included 1,140 cancer patients with a mean age of 53.95 (SD = 13.25) years;
61.3% were women. After the CFA of the original CASQ structure, 2 items with inadequate
factor weights were removed. Four correlations between errors were included to provide
adequate fit to the sample (χ2
/df = 8.532, CFI = .94, GFI = .95, and RMSEA = .08). Themodel exhibited a low convergent validity (AVE = .32). The reliability was adequate
(CR = .82 α = .82). The refined model showed strong invariance in two independent samples
(Δχ2
: λ: p = .855; i: p = .824; Res: p = .390). A weak stability was obtained between
patients undergoing chemotherapy and radiotherapy (Δχ2
: λ: p = .155; i: p < .001; Res:
p < .001), and between patients undergoing chemotherapy combined with radiotherapy
and palliative care (Δχ2
: λ: p = .058; i: p < .001; Res: p < .001).
Conclusion
The Portuguese version of the CASQ had good face and construct validity and reliability.
However, the CASQ still presented invariance in independent samples of Brazilian patients
with cancer. However, the tool has low convergent validity and weak invariance in samples
with different treatment
Treatment of MOG-IgG-associated disorder with rituximab: An international study of 121 patients
OBJECTIVE: To assess the effect of anti-CD20 B-cell depletion with rituximab (RTX) on relapse rates in myelin oligodendrocyte glycoprotein antibody-associated disorder (MOGAD). METHODS: Retrospective review of RTX-treated MOGAD patients from 29 centres in 13 countries. The primary outcome measure was change in relapse rate after starting rituximab (Poisson regression model). RESULTS: Data on 121 patients were analysed, including 30 (24.8%) children. Twenty/121 (16.5%) were treated after one attack, of whom 14/20 (70.0%) remained relapse-free after median (IQR) 11.2 (6.3-14.1) months. The remainder (101/121, 83.5%) were treated after two or more attacks, of whom 53/101 (52.5%) remained relapse-free after median 12.1 (6.3-24.9) months. In this 'relapsing group', relapse rate declined by 37% (95%CI=19-52%, p<0.001) overall, 63% (95%CI=35-79%, p = 0.001) when RTX was used first line (n = 47), and 26% (95%CI=2-44%, p = 0.038) when used after other steroid-sparing immunotherapies (n = 54). Predicted 1-year and 2-year relapse-free survival was 79% and 55% for first-line RTX therapy, and 38% and 18% for second-/third-line therapy. Circulating CD19+B-cells were suppressed to <1% of total circulating lymphocyte population at the time of 45/57 (78.9%) relapses. CONCLUSION: RTX reduced relapse rates in MOGAD. However, many patients continued to relapse despite apparent B-cell depletion. Prospective controlled studies are needed to validate these results
Relapses in Patients Treated with High-Dose Biotin for Progressive Multiple Sclerosis
High-dose biotin (HDB) is a therapy used in non-active progressive multiple sclerosis (PMS). Several reports have suggested that HDB treatment may be associated with an increased risk of relapse. We aimed to determine whether HDB increases the risk of clinical relapse in PMS and describe the characteristics of the patients who experience it. We conducted a French, multicenter, retrospective study, comparing a group of PMS patients treated with HDB to a matched control group. Poisson regression was applied to model the specific statistical distribution of the annualized relapse rate (ARR). A propensity score (PS), based on the inverse probability of treatment weighting (IPTW), was used to adjust for indication bias and included the following variables: gender, primary PMS or not, age, EDSS, time since the last relapse, and co-prescription of a DMT. Two thousand six hundred twenty-eight patients treated with HDB and 654 controls were analyzed with a follow-up of 17 ± 8 months. Among them, 148 validated relapses were observed in the group treated with biotin and 38 in the control group (p = 0.62). After adjustment based on the PS, the ARR was 0.044 ± 0.23 for the biotin-treated group and 0.028 ± 0.16 for the control group (p = 0.18). The more relapses there were before biotin, the higher the risk of relapse during treatment, independently from the use of HDB. While the number of relapses reported for patients with no previous inflammatory activity receiving biotin has gradually increased, the present retrospective study is adequately powered to exclude an elevated risk of relapse for patients with PMS treated with HDB.Observatoire Français de la Sclérose en Plaque
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