567 research outputs found
Functionalization of semiconductor surfaces by organic layers: Concerted cycloaddition versus stepwise free-radical reaction mechanism
In the age when the miniaturization trend that has driven the semiconductor industry is reaching its limits, organic modification of semiconductors is emerging as a field that could give much-needed impetus. We review the current state of understanding of the functionalization of C(100), Si(100), and Ge(100) surfaces through chemisorption of alkenes and alkynes, focussing on adsorbate structural control. While reactions on C(100) show most of the properties expected for concerted cycloaddition reactions such as [2+2] and [4+2] (Diels-Alder) processes, reactions on Si(100) present a wide range of variant behaviour, including in some cases the prominence of non-cycloaddition products. More general stepwise free-radical addition processes are seen to provide a better description of reactions on Si(100), their prominence being attributed to either the non-existence or ineffectiveness of p bonding within surface silicon dimers. The investigations of these systems provide not only insight into driving mechanisms for chemisorption but also motivation for the development of new techniques of organic functionalization on semiconductors
Single photon production by rephased amplified spontaneous emission
The production of single photons using rephased amplified spontaneous
emission is examined. This process produces single photons on demand with high
efficiency by detecting the spontaneous emission from an atomic ensemble, then
applying a population-inverting pulse to rephase the ensemble and produce a
photon echo of the spontaneous emission events. The theoretical limits on the
efficiency of the production are determined for several variants of the scheme.
For an ensemble of uniform optical density, generating the initial spontaneous
emission and its echo using transitions of different strengths is shown to
produce single photons at 70% efficiency, limited by reabsorption. Tailoring
the spatial and spectral density of the atomic ensemble is then shown to
prevent reabsorption of the rephased photon, resulting in emission efficiency
near unity
Quantum tunneling dynamics of an interacting Bose-Einstein condensate through a Gaussian barrier
The transmission of an interacting Bose-Einstein condensate incident on a
repulsive Gaussian barrier is investigated through numerical simulation. The
dynamics associated with interatomic interactions are studied across a broad
parameter range not previously explored. Effective 1D Gross-Pitaevskii equation
(GPE) simulations are compared to classical Boltzmann-Vlasov equation (BVE)
simulations in order to isolate purely coherent matterwave effects. Quantum
tunneling is then defined as the portion of the GPE transmission not described
by the classical BVE. An exponential dependence of transmission on barrier
height is observed in the purely classical simulation, suggesting that
observing such exponential dependence is not a sufficient condition for quantum
tunneling. Furthermore, the transmission is found to be predominately described
by classical effects, although interatomic interactions are shown to modify the
magnitude of the quantum tunneling. Interactions are also seen to affect the
amount of classical transmission, producing transmission in regions where the
non-interacting equivalent has none. This theoretical investigation clarifies
the contribution quantum tunneling makes to overall transmission in
many-particle interacting systems, potentially informing future tunneling
experiments with ultracold atoms.Comment: Close to the published versio
Non-destructive shadowgraph imaging of ultracold atoms
An imaging system is presented that is capable of far-detuned non-destructive
imaging of a Bose-Einstein condensate with the signal proportional to the
second spatial derivative of the density. Whilst demonstrated with application
to , the technique generalizes to other atomic species and is
shown to be capable of a signal to noise of at GHz detuning with
in-trap images showing no observable heating or atom loss. The technique
is also applied to the observation of individual trajectories of stochastic
dynamics inaccessible to single shot imaging. Coupled with a fast optical phase
lock loop, the system is capable of dynamically switching to resonant
absorption imaging during the experiment.Comment: 4 pages, 5 figure
Lattice Relaxation and Charge-Transfer Optical Transitions Due to Self-Trapped Holes in Non-Stoichiometric LaMnO Crystal
We use the Mott-Littleton approach to evaluate polarisation energies in
LaMnO lattice associated with holes localized on both Mn cation and
O anion. The full (electronic and ionic) lattice relaxation energy for a
hole localized at the O-site is estimated as 2.4 eV which is appreciably
greater than that of 0.8 eV for a hole localized at the Mn-site, indicating on
the strong electron-phonon interaction in the former case. Using a Born-Haber
cycle we examine thermal and optical energies of the hole formation associated
with electron ionization from Mn, O and La ions in
LaMnO lattice. For these calculations we derive a phenomenological value
for the second electron affinity of oxygen in LaMnO lattice by matching the
optical energies of La and O hole formation with maxima of binding
energies in the experimental photoemission spectra. The calculated thermal
energies predict that the electronic hole is marginally more stable in the
Mn state in LaMnO host lattice, but the energy of a hole in the
O state is only higher by a small amount, 0.75 eV, rather suggesting that
both possibilities should be treated seriously. We examine the energies of a
number of fundamental optical transitions, as well as those involving
self-trapped holes of Mn and O in LaMnO lattice. The reasonable
agreement with experiment of our predicted energies, linewidths and oscillator
strengths leads us to plausible assignments of the optical bands observed. We
deduce that the optical band near 5 eV is associated with O(2p) - Mn(3d)
transition of charge-transfer character, whereas the band near 2.3 eV is rather
associated with the presence of Mn and/or O self-trapped holes in
non-stoichiometric LaMnO compound.Comment: 18 pages, 6 figures, it was presented partially at SCES-2001
conference in Ann Arbor, Michiga
Effect of Intensive Patient Education vs Placebo Patient Education on Outcomes in Patients with Acute Low Back Pain: A Randomized Clinical Trial
© 2018 2018 American Medical Association. All rights reserved. Importance: Many patients with acute low back pain do not recover with basic first-line care (advice, reassurance, and simple analgesia, if necessary). It is unclear whether intensive patient education improves clinical outcomes for those patients already receiving first-line care. Objective: To determine the effectiveness of intensive patient education for patients with acute low back pain. Design, Setting, and Participants: This randomized, placebo-controlled clinical trial recruited patients from general practices, physiotherapy clinics, and a research center in Sydney, Australia, between September 10, 2013, and December 2, 2015. Trial follow-up was completed in December 17, 2016. Primary care practitioners invited 618 patients presenting with acute low back pain to participate. Researchers excluded 416 potential participants. All of the 202 eligible participants had low back pain of fewer than 6 weeks' duration and a high risk of developing chronic low back pain according to Predicting the Inception of Chronic Pain (PICKUP) Tool, a validated prognostic model. Participants were randomized in a 1:1 ratio to either patient education or placebo patient education. Interventions: All participants received recommended first-line care for acute low back pain from their usual practitioner. Participants received additional 2 × 1-hour sessions of patient education (information on pain and biopsychosocial contributors plus self-management techniques, such as remaining active and pacing) or placebo patient education (active listening, without information or advice). Main Outcomes and Measures: The primary outcome was pain intensity (11-point numeric rating scale) at 3 months. Secondary outcomes included disability (24-point Roland Morris Disability Questionnaire) at 1 week, and at 3, 6, and 12 months. Results: Of 202 participants randomized for the trial, the mean (SD) age of participants was 45 (14.5) years and 103 (51.0%) were female. Retention rates were greater than 90% at all time points. Intensive patient education was not more effective than placebo patient education at reducing pain intensity (3-month mean [SD] pain intensity: 2.1 [2.4] vs 2.4 [2.2]; mean difference at 3 months, -0.3 [95% CI, -1.0 to 0.3]). There was a small effect of intensive patient education on the secondary outcome of disability at 1 week (mean difference, -1.6 points on a 24-point scale [95% CI, -3.1 to -0.1]) and 3 months (mean difference, -1.7 points, [95% CI, -3.2 to -0.2]) but not at 6 or 12 months. Conclusions and Relevance: Adding 2 hours of patient education to recommended first-line care for patients with acute low back pain did not improve pain outcomes. Clinical guideline recommendations to provide complex and intensive support to high-risk patients with acute low back pain may have been premature. Trial Registration: Australian Clinical Trial Registration Number: 12612001180808
A systematic review and meta-synthesis of the impact of low back pain on people's lives
Copyright @ 2014 Froud et al.; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative
Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and
reproduction in any medium, provided the original work is properly credited.Background - Low back pain (LBP) is a common and costly problem that many interpret within a biopsychosocial model. There is renewed concern that core-sets of outcome measures do not capture what is important. To inform debate about the coverage of back pain outcome measure core-sets, and to suggest areas worthy of exploration within healthcare consultations, we have synthesised the qualitative literature on the impact of low back pain on people’s lives.
Methods - Two reviewers searched CINAHL, Embase, PsycINFO, PEDro, and Medline, identifying qualitative studies of people’s experiences of non-specific LBP. Abstracted data were thematic coded and synthesised using a meta-ethnographic, and a meta-narrative approach.
Results - We included 49 papers describing 42 studies. Patients are concerned with engagement in meaningful activities; but they also want to be believed and have their experiences and identity, as someone ‘doing battle’ with pain, validated. Patients seek diagnosis, treatment, and cure, but also reassurance of the absence of pathology. Some struggle to meet social expectations and obligations. When these are achieved, the credibility of their pain/disability claims can be jeopardised. Others withdraw, fearful of disapproval, or unable or unwilling to accommodate social demands. Patients generally seek to regain their pre-pain levels of health, and physical and emotional stability. After time, this can be perceived to become unrealistic and some adjust their expectations accordingly.
Conclusions - The social component of the biopsychosocial model is not well represented in current core-sets of outcome measures. Clinicians should appreciate that the broader impact of low back pain includes social factors; this may be crucial to improving patients’ experiences of health care. Researchers should consider social factors to help develop a portfolio of more relevant outcome measures.Arthritis Research U
Evidence for Quantum Interference in SAMs of Arylethynylene Thiolates in Tunneling Junctions with Eutectic Ga-In (EGaIn) Top-Contacts
This paper compares the current density (J) versus applied bias (V) of self-assembled monolayers (SAMs) of three different ethynylthiophenol-functionalized anthracene derivatives of approximately the same thickness with linear-conjugation (AC), cross-conjugation (AQ), and broken-conjugation (AH) using liquid eutectic Ga-In (EGaIn) supporting a native skin (~1 nm thick) of Ga2O3 as a nondamaging, conformal top-contact. This skin imparts non-Newtonian rheological properties that distinguish EGaIn from other top-contacts; however, it may also have limited the maximum values of J observed for AC. The measured values of J for AH and AQ are not significantly different (J ≈ 10-1 A/cm2 at V = 0.4 V). For AC, however, J is 1 (using log averages) or 2 (using Gaussian fits) orders of magnitude higher than for AH and AQ. These values are in good qualitative agreement with gDFTB calculations on single AC, AQ, and AH molecules chemisorbed between Au contacts that predict currents, I, that are 2 orders of magnitude higher for AC than for AH at 0 < |V| < 0.4 V. The calculations predict a higher value of I for AQ than for AH; however, the magnitude is highly dependent on the position of the Fermi energy, which cannot be calculated precisely. In this sense, the theoretical predictions and experimental conclusions agree that linearly conjugated AC is significantly more conductive than either cross-conjugated AQ or broken conjugate AH and that AQ and AH cannot necessarily be easily differentiated from each other. These observations are ascribed to quantum interference effects. The agreement between the theoretical predictions on single molecules and the measurements on SAMs suggest that molecule-molecule interactions do not play a significant role in the transport properties of AC, AQ, and AH.
Robust statistical properties of the size of large burst events in AE
Geomagnetic indices provide a comprehensive data set with which to quantify space climate, that is, how the statistical likelihood of activity varies with the solar cycle. We characterize space climate by the AE index burst distribution. Burst sizes are constructed by thresholding the AE time series; a burst is the sum of the excess in the time series for each time interval over which the threshold is exceeded. The distribution of burst sizes is two component with a crossover in behavior at thresholds ≈1000 nT. Above this threshold, we find a range over which the mean burst size varies weakly with threshold for both solar maxima and minima. The burst size distribution of the largest events is exponential. The relative likelihood of these large events varies from one solar maximum and minimum to the next. Given the relative overall activity of a solar maximum/minimum, these results constrain the likelihood of extreme events of a given size
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