147 research outputs found
Magnetic Properties of the Novel Low-Dimensional Cuprate Na5RbCu4(AsO4)4Cl2
The magnetic properties of a new compound, Na5RbCu4(AsO4)4Cl2 are reported.
The material has a layered structure comprised of square Cu4O4 tetramers. The
Cu ions are divalent and the system behaves as a low-dimensional S=1/2
antiferromagnet. Spin exchange in Na5RbCu4(AsO4)4Cl2 appears to be
quasi-two-dimensional and non-frustrated. Measurements of the bulk magnetic
susceptibility and heat capacity are consistent with low-dimensional magnetism.
The compound has an interesting, low-entropy, magnetic transition at T = 17 K.Comment: 4 pages, 5 figure
Duration of tooth alignment with fixed appliances: A systematic review and meta-analysis
INTRODUCTION
A key goal of orthodontic treatment with fixed appliances is alignment of the dentition, and this remains a commonly selected outcome in clinical studies investigating orthodontic tooth movement. This systematic review has evaluated treatment duration to achieve alignment of the mandibular dentition using fixed appliances.
METHODS
Systematic literature searches without restrictions were undertaken in 9 databases for randomized clinical trials (RCTs) assessing duration and rate of tooth alignment using fixed appliances with or without treatment adjuncts published up to January 2021. After duplicate study selection, data extraction, and risk of bias assessment according to Cochrane, random-effects meta-analyses of aggregate data, and individual patient data were conducted.
RESULTS
Thirty-five trials were included with 2258 participants (39% male; mean age 17.8 years), giving a pooled duration to achieve whole-arch alignment of the mandibular dentition of 263.0 days (4 trials; 95% confidence interval [CI], 186.7-339.4 days) and incisor alignment in the mandibular arch of 100.7 days (9 trials; 95% CI, 84.1-117.4 days). Surgical-assisted orthodontics was associated with reduced duration of incisor alignment: mean difference of 44.3 days less (4 trials; 95% CI, 20.0-68.9 days; P <0.001; high quality of evidence), whereas subgroup and meta-regression analyses indicated significant effects of baseline crowding and premolar extractions. Individual patient data analysis from 3 RCTs indicated that for each additional participant age year, whole-arch alignment of the mandibular dentition took 13.7 days longer (3 trials; 95% CI, 7.7-17.7 days; P <0.001) and for each additional mm of irregularity, 17.5 days more were needed (2 trials; 95% CI, 9.8-25.2 days; P <0.001).
CONCLUSIONS
Patient and treatment-related characteristics can significantly affect the duration of tooth alignment and should be taken into account both clinically and when designing trial outcomes. Future research studies investigating rates of orthodontic tooth alignment would benefit from adequate sample sizes and a more consistent methodology in outcome assessment. Data in this systematic review provides a basis for appropriate trial design for future RCTs investigating the rate of orthodontic tooth alignment with fixed appliances
X-Band ESR Determination of Dzyaloshinsky-Moriya Interaction in 2D SrCu(BO) System
X-band ESR measurements on a single crystal of SrCu(BO) system in
a temperature range between 10 K and 580 K are presented. The temperature and
angular dependence of unusually broad ESR spectra can be explained by the
inclusion of antisymmetric Dzyaloshinsky-Moriya (DM) interaction, which yields
by far the largest contribution to the linewidth. However, the well-accepted
picture of only out-of-plane interdimer DM vectors is not sufficient for
explanation of the observed angular dependence. In order to account for the
experimental linewidth anisotropy we had to include sizable in-plane components
of interdimer as well as intradimer DM interaction in addition to the
out-of-plane interdimer one. The nearest-neighbor DM vectors lie perpendicular
to crystal anisotropy c-axis due to crystal symmetry. We also emphasize that
above the structural phase transition occurring at 395 K dynamical mechanism
should be present allowing for instantaneous DM interactions. Moreover, the
linewidth at an arbitrary temperature can be divided into two contributions;
namely, the first part arising from spin dynamics governed by the spin
Hamiltonian of the system and the second part due to significant spin-phonon
coupling. The nature of the latter mechanism is attributed to phonon-modulation
of the antisymmetric interaction, which is responsible for the observed linear
increase of the linewidth at high temperatures.Comment: 17 pages, 4 figures, submitted to PR
Mucosal immunization with ChAd-SARS-CoV-2-S prevents sequential transmission of SARS-CoV-2 to unvaccinated hamsters
COVID-19 vaccines have successfully reduced severe disease and death after severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Nonetheless, COVID-19 vaccines are variably effective in preventing transmission and symptomatic SARS-CoV-2 infection. Here, we evaluated the impact of mucosal or intramuscular vaccine immunization on airborne infection and transmission of SARS-CoV-2 in Syrian hamsters. Immunization of the primary contact hamsters with a mucosal chimpanzee adenoviral-vectored vaccine (ChAd-CoV-2-S), but not intramuscular messenger RNA (mRNA) vaccine, reduced infectious virus titers ~100-fold and 100,000-fold in the upper and lower respiratory tract of the primary contact hamster following SARS-CoV-2 exposure. This reduction in virus titer in the mucosal immunized contact animals was sufficient to eliminate subsequent transmission to vaccinated and unvaccinated hamsters. In contrast, sequential transmission occurred after systemic immunization with the mRNA vaccine. Thus, immunization with a mucosal COVID-19 vaccine protects against cycles of respiratory transmission of SARS-CoV-2 and can potentially limit the community spread of the virus
Magnetic properties of the frustrated AFM spinel ZnCr_2O_4 and the spin-glass Zn_{1-x}Cd_xCr_2O_4 (x=0.05,0.10)
The -dependence (2- 400 K) of the electron paramagnetic resonance (EPR),
magnetic susceptibility, , and specific heat, , of the
antiferromagnetic (AFM) spinel ZnCrO and the spin-glass
(SG) ZnCdCrO () is reported. These
systems behave as a strongly frustrated AFM and SG with K and -400 K K. At high-
the EPR intensity follows the and the -value is -independent.
The linewidth broadens as the temperature is lowered, suggesting the existence
of short range AFM correlations in the paramagnetic phase. For
ZnCrO the EPR intensity and decreases below 90 K and 50
K, respectively. These results are discussed in terms of nearest-neighbor
Cr (S %) spin-coupled pairs with an exchange coupling of 50 K. The appearance of small resonance modes for K,
the observation of a sharp drop in and a strong peak in
at K confirms, as previously reported, the existence of long range
AFM correlations in the low- phase. A comparison with recent neutron
diffraction experiments that found a near dispersionless excitation at 4.5 meV
for and a continuous gapless spectrum for ,
is also given.Comment: 17 pages, 8 figures, 1 Table. Submitted to Physical Review
What is the value of orthodontic treatment?
Orthodontic treatment is as popular as ever. Orthodontists frequently have long lists of people wanting treatment and the cost to the NHS in England was £258m in 2010-2011 (approximately 10% of the NHS annual spend on dentistry). It is important that clinicians and healthcare commissioners constantly question the contribution of interventions towards improving the health of the population. In this article, the authors outline some of the evidence for and against the claims that people with a malocclusion are at a disadvantage compared with those without a malocclusion and that orthodontic treatment has significant health benefits. The authors would like to point out that this is not a comprehensive and systematic review of the entire scientific literature. Rather the evidence is presented in order to stimulate discussion and debate
Development of a core outcome set for orthodontic trials using a mixed-methods approach: Protocol for a multicentre study
© 2017 The Author(s). Background: Orthodontic treatment is commonly undertaken in young people, with over 40% of children in the UK needing treatment and currently one third having treatment, at a cost to the National Health Service in England and Wales of £273 million each year. Most current research about orthodontic care does not consider what patients truly feel about, or want, from treatment, and a diverse range of outcomes is being used with little consistency between studies. This study aims to address these problems, using established methodology to develop a core outcome set for use in future clinical trials of orthodontic interventions in children and young people. Methods/design: This is a mixed-methods study incorporating four distinct stages. The first stage will include a scoping review of the scientific literature to identify primary and secondary outcome measures that have been used in previous orthodontic clinical trials. The second stage will involve qualitative interviews and focus groups with orthodontic patients aged 10 to 16 years to determine what outcomes are important to them. The outcomes elicited from these two stages will inform the third stage of the study in which a long-list of outcomes will be ranked in terms of importance using electronic Delphi surveys involving clinicians and patients. The final stage of the study will involve face-to-face consensus meetings with all stakeholders to discuss and agree on the outcome measures that should be included in the final core outcome set. Discussion: This research will help to inform patients, parents, clinicians and commissioners about outcomes that are important to young people undergoing orthodontic treatment. Adoption of the core outcome set in future clinical trials of orthodontic treatment will make it easier for results to be compared, contrasted and combined. This should translate into improved decision-making by all stakeholders involved. Trial registration: The project has been registered on the Core Outcome Measures in Effectiveness Trials (COMET) website, January 2016
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