1,631 research outputs found
From band insulator to Mott insulator in one dimension
We derive the phase diagram for the one-dimensional model of a ferroelectric
perovskite recently introduced by Egami, Ishihara and Tachiki [Science, {\bf
261}, 1307 (1993)]. We show that the interplay between covalency, ionicity and
strong correlations results in a spontaneously dimerized phase which separates
the weak-coupling band insulator from the strong-coupling Mott insulator. The
transition from the band insulator to the dimerized phase is identified as an
Ising critical point. The charge gap vanishes at this single point with the
optical conductivity diverging as . The spin
excitations are gapless above the second transition to the Mott insulator
phase.Comment: 4 pages LaTex (RevTex) and 1 postscript figure included by eps
The relationship between verve and the academic achievement of African American and European American middle school students
The purpose of this study was to examine if verve had any impact on the
academic achievement of African American middle school students. The three guiding
questions of this research were:
1. Is there a significant difference in the verve levels between African
American and European American students?
2. Is there a significant difference in verve levels of African American male
and African American female students in middle school?
3. Is there a significant difference in the academic achievement of African
American and European American students who possess high and low
verve in the areas of reading and math?
A 24-item questionnaire was administered to 211 middle school students to
determine if any verve levels were present, and if so, to what degree did the verve
levels impact academic performance? The findings were:
1. The verve levels were different between the African American and the
European American students. The African American students in this study
possessed higher amounts of verve.
2. The verve levels were different between the African American males and
the African American females. The African American females in this study
had higher amounts of verve than the African American males.
3. There was no relationship between the higher verve levels among the
African American and European American students and their academic
achievement in reading and math
Spin-orbit induced mixed-spin ground state in NiO perovskites probed by XAS: new insight into the metal to insulator transition
We report on a Ni L edges x-ray absorption spectroscopy (XAS) study
in NiO perovskites. These compounds exhibit a metal to insulator ()
transition as temperature decreases. The L edge presents a clear
splitting in the insulating state, associated to a less hybridized ground
state. Using charge transfer multiplet calculations, we establish the
importance of the crystal field and 3d spin-orbit coupling to create a
mixed-spin ground state. We explain the transition in NiO
perovskites in terms of modifications in the Ni crystal field splitting
that induces a spin transition from an essentially low-spin (LS) to a
mixed-spin state.Comment: 4 pages, 4 figures, accepted as PRB - Rapid Comm. Dez. 200
Assessing with e-Ase
The Educational Development Unit have produced a guide to assist academic staff in transforming assessment practices underpinned by technology. 'Assessing with e-Ase' highlights how technology combined with sound pedagogy has the potential to enhance the student experience of learning, teaching and assessment.
Drawing on the experiences, knowledge and understanding of the e-assessment project at Middlesex University, it offers a consideration of contextual, procedural and logistical factors that may impact when using e-assessment practices. Key issues for consideration when developing and implementing e-assessment are included along with the part played by policy and strategy. Examples of departmental case studies, an outline of the support available to staff and links to resources that may provide useful additional information are also included
Short-range charge-order in NiO perovskites (=Pr,Nd,Eu) probed by X-ray absorption spectroscopy
The short-range organization around Ni atoms in orthorhombic NiO
(=Pr,Nd,Eu) perovskites has been studied over a wide temperature range by Ni
K-edge x-ray absorption spectroscopy. Our results demonstrate that two
different Ni sites, with different average Ni-O bond lengths, coexist in those
orthorhombic compounds and that important modifications in the Ni nearest
neighbors environment take place across the metal-insulator transition. We
report evidences for the existence of short-range charge-order in the
insulating state, as found in the monoclinic compounds. Moreover, our results
suggest that the two different Ni sites coexists even in the metallic state.
The coexistence of two different Ni sites, independently on the ion,
provides a common ground to describe these compounds and shed new light in the
understanding of the phonon-assisted conduction mechanism and unusual
antiferromagnetism present in all NiO compounds.Comment: 4 pages, 3 figures, accepted PRB - Brief Report Dec.200
Phase diagram of the Hubbard chain with two atoms per cell
We obtain the quantum phase diagram of the Hubbard chain with alternating
on-site energy at half filling. The model is relevant for the ferroelectric
perovskites and organic mixed-stack donor-acceptor crystals. For any values of
the parameters, the band insulator is separated from the Mott insulator by a
dimer phase. The boundaries are determined accurately by crossing of excited
levels with particular discrete symmetries. We show that these crossings
coincide with jumps of charge and spin Berry phases with a clear geometrical
meaning.Comment: 5 pages including 2 figures To be published in Phys. Rev. B (Rapid
Communications
Bluebelle pilot randomised controlled trial of three wound dressing strategies to reduce surgical site infection in primary surgical wounds
Objective Surgical site infection (SSI) affects up to 25% of primary surgical wounds. Dressing strategies may influence SSI risk. The Bluebelle study assessed the feasibility of a multicentre randomised controlled trial (RCT) to evaluate the effectiveness and cost-effectiveness of different dressing strategies to reduce SSI in primary surgical wounds.
Design A pilot, factorial RCT.
Setting Five UK hospitals.
Participants Adults undergoing abdominal surgery with a primary surgical wound.
Interventions Participants were randomised to âsimple dressingâ, âglue-as-a-dressingâ or âno dressingâ, and to the time at which the treatment allocation was disclosed to the surgeon (disclosure time, before or after wound closure).
Primary and secondary outcome measures Feasibility outcomes focused on recruitment, adherence to randomised allocations, reference assessment of SSI and response rates to participant-completed and observer-completed questionnaires to assess SSI (proposed primary outcome for main trial), wound experience and symptoms, and quality of life (EQ-5D-5L).
Results Between March and November 2016, 1115 patients were screened; 699 (73.4%) were eligible and approached, 415 (59.4%) consented and 394 (35.3%) were randomised (simple dressing=133, glue=129 and âno dressingâ=132). Non-adherence to dressing allocation was 2% (3/133), 6% (8/129) and 15% (20/132), respectively. Adherence to disclosure time was 99% and 86% before and after wound closure, respectively. The overall rate of SSI (reference assessment) was 18.1% (51/281). Response rates to the Wound Healing Questionnaire and other questionnaires ranged from >90% at 4 days to 68% at 4â8 weeks.
Conclusions A definitive RCT of dressing strategies including âno dressingâ is feasible. Further work is needed to optimise questionnaire response rates
Excitation Spectrum of One-dimensional Extended Ionic Hubbard Model
We use Perturbative Continuous Unitary Transformations (PCUT) to study the
one dimensional Extended Ionic Hubbard Model (EIHM) at half-filling in the band
insulator region. The extended ionic Hubbard model, in addition to the usual
ionic Hubbard model, includes an inter-site nearest-neighbor (n.n.) repulsion,
. We consider the ionic potential as unperturbed part of the Hamiltonian,
while the hopping and interaction (quartic) terms are treated as perturbation.
We calculate total energy and ionicity in the ground state. Above the ground
state, (i) we calculate the single particle excitation spectrum by adding an
electron or a hole to the system. (ii) the coherence-length and spectrum of
electron-hole excitation are obtained. Our calculations reveal that for V=0,
there are two triplet bound state modes and three singlet modes, two anti-bound
states and one bound state, while for finite values of there are four
excitonic bound states corresponding to two singlet and two triplet modes. The
major role of on-site Coulomb repulsion is to split singlet and triplet
collective excitation branches, while tends to pull the singlet branches
below the continuum to make them bound states.Comment: 10 eps figure
Lived experience of work and long COVID in healthcare staff.
Healthcare workers (HCWs) had a greater occupational risk of exposure to coronavirus disease 2019 (COVID-19) and reported higher rates of long COVID (LC). This has implications for the provision of health care in already stretched health services. This study explored the impact of LC on a range of UK National Health Service (NHS) HCWs, their health and well-being, the effect on work patterns, and occupational support received. This research was conducted through a mixed-methods study, online survey and qualitative interviews. Participants self-reporting LC symptoms were recruited through social media and NHS channels. Interviews used maximum variation sampling of 50 HCWs including healthcare professionals, ancillary and administration staff. Thematic analysis was conducted using NVivo software. A total of 471 HCWs completed the online survey. Multiple LC symptoms were reported, revealing activity limitations for 90%. Two-thirds had taken sick leave, 18% were off-work and 33% reported changes in work duties. There were few differences in work practices by occupational group. Most participants were working but managing complex and dynamic symptoms, with periods of improvement and exacerbation. They engaged in a range of strategies: rest, pacing, planning and prioritizing, with work prioritized over other aspects of life. Symptom improvements were often linked to occupational medicine, managerial, colleague support and flexible workplace adjustments. The study concluded that LC has a significant impact on the lives of HCWs suffering prolonged symptoms. Due to the variability and dynamic nature of symptoms, workplace support and flexible policies are needed to help retain staff
A prospective, randomized, pragmatic, health outcomes trial evaluating the incorporation of hylan G-F 20 into the treatment paradigm for patients with knee osteoarthritis (Part 2 of 2): economic results
AbstractObjective Viscosupplementation with hylan G-F 20 has recently become registered for treatment of patients with osteoarthritis (OA) of the knee in most parts of the world. The cost effectiveness and cost utility of this new therapeutic modality were determined as part of a Canadian prospective, randomized, 1-year, open-label, multicentered trial.Design A total of 255 patients were randomized to âAppropriate care with hylan G-F 20â (AC+H) or âAppropriate care without hylan G-F 20â (AC). Costs (1999 Canadian dollars) were collected from the societal viewpoint and included all costs related to OA of the knee and OA in all joints. Patients completed a number of outcomes questionnaires including the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and the Health Utilities Index Mark 3 (HUI3). Data were collected at clinic visits (baseline, 12 months) and by telephone (1, 2, 4, 6, 8, 10, and 12 months).Results The AC+H group over the year had higher costs (1415=2505/patient improved. The incremental costâutility ratio was $10000/QALY gained. Sensitivity analyses and a second cost perspective gave similar results.Conclusion The costâutility ratio is below the suggested Canadian adoption threshold. The results provide strong evidence for adoption of treatment with hylan G-F 20 in the patients and settings studied in the trial. Copyright 2002 OsteoArthritis Research Society International. Published by Elsevier Science Ltd. All rights reserved
- âŠ