Optical properties of arrays of quantum dots with internal disorder

Optical properties of large arrays of isolated quantum dots are discussed in order to interpret the existent photoluminescence data. The presented theory explains the large observed shift between the lowest emission and absorption energies as the average distance between the ground and first excited states of the dots. The lineshape of the spectra is calculated for the case when the fluctuations of the energy levels in quantum dots are due to the alloy composition fluctuations. The calculated lineshape is in good agreement with the experimental data. The influence of fluctuations of the shape of quantum dots on the photoluminescence spectra is also discussed.Comment: 7 pages (twocolumn) LATEX, 6 Postscript figure

Ensemble interactions in strained semiconductor quantum dots

Large variations in InxGa1-xAs quantum dot concentrations were obtained with simultaneous growths on vicinal GaAs [001] substrates with different surface step densities. It was found that decreasing dot-dot separation blueshifts all levels, narrows intersublevel transition energies, shortens luminescence decay times for excited states, and increases inhomogeneous photoluminescence broadening. These changes in optical properties are attributed to a progressive strain deformation of the confining potentials and to the increasing effects of positional disorder in denser dot ensembles

Multi-Exciton Spectroscopy of a Single Self Assembled Quantum Dot

We apply low temperature confocal optical microscopy to spatially resolve, and spectroscopically study a single self assembled quantum dot. By comparing the emission spectra obtained at various excitation levels to a theoretical many body model, we show that: Single exciton radiative recombination is very weak. Sharp spectral lines are due to optical transitions between confined multiexcitonic states among which excitons thermalize within their lifetime. Once these few states are fully occupied, broad bands appear due to transitions between states which contain continuum electrons.Comment: 12 pages, 4 figures, submitted for publication on Jan,28 199

Optimization of heat treatment in cold-drawn 6063 aluminium tubes

The effect of heat treatment condition on mechanical properties and bendability of 6063 aluminium cold-drawn tubes was investigated. The standardized heat treatment presently used in manufacturing of cold-drawn tubes increases the cost and time of the process which ultimately reduces plant productivity. The effects of time, temperature, and furnace heating rate were studied in order to identify an optimized heat treatment for tubes with different cold work levels. Drawn from the as-extruded state, tubes were heat treated to under-aged, peak-aged, and over-aged conditions with time and temperature ranging from 1 min to 24 h and 130\u2013200 \u25e6C, respectively. Mechanical properties were determined with full section tensile tests whereas tube bendability was evaluated on an industrial draw bending machine. These characteristics were evaluated in each condition in order to identify the heat treatment which allows conforming to 6063-T832 temper requirements and gives sufficient bendability. Moreover, bendability was successfully correlated to fracture strain measured during a uniaxial tensile test and a threshold value over which problem-free bending operation was determined.On a \ue9tudi\ue9 l\u2019effet des conditions de traitement thermique sur les propri\ue9t\ue9s m\ue9caniques et la flexibilit\ue9 de tubes en aluminium 6063 \ue9tir\ue9s \ue0 froid. Le traitement thermique standardis\ue9 pr\ue9sentement utilis\ue9 pour la production de tubes \ue9tir\ue9s \ue0 froid fait cro\ueetre le co\ufbt et la dur\ue9e du proc\ue9d\ue9, ce qui finalement r\ue9duit la productivit\ue9 de l\u2019usine. Les effets du temps, de la temp\ue9rature et de la vitesse de chauffage du four ont \ue9t\ue9 \ue9tudi\ue9s afin d\u2019identifier un traitement thermique optimis\ue9 pour les tubes avec diff\ue9rents niveaux de travail \ue0 froid. \uc9tir\ue9s \ue0 partir de l\u2019\ue9tat extrud\ue9 tel quel, les tubes ont \ue9t\ue9 chauff\ue9s dans des conditions de sous-vieillissement, vieillissement pic et sur-vieillissement avec des temps et des temp\ue9ratures allant de 1 min \ue0 24 h et de 130 \ue0 200 \ub0C. On a d\ue9termin\ue9 les propri\ue9t\ue9s m\ue9caniques au moyen d\u2019essais de tension pleine section, alors que la flexibilit\ue9 a \ue9t\ue9 \ue9valu\ue9e sur une machine industrielle de cintrage par enroulement. Ces caract\ue9ristiques ont \ue9t\ue9 \ue9valu\ue9es pour chaque condition afin d\u2019identifier le traitement thermique qui permet de se conformer aux exigences de duret\ue9 du 6063 T832 et donne une flexibilit\ue9 suffisante. En plus de corr\ue9ler avec succ\ue8s la flexibilit\ue9 \ue0 la d\ue9formation de rupture mesur\ue9e au cours d\u2019un essai de tension dans un axe, une valeur seuil au-dessus de laquelle un cintrage sans probl\ue8me est possible a \ue9t\ue9 d\ue9termin\ue9e.Peer reviewed: YesNRC publication: Ye

Spin interactions and switching in vertically tunnel-coupled quantum dots

We determine the spin exchange coupling J between two electrons located in two vertically tunnel-coupled quantum dots, and its variation when magnetic (B) and electric (E) fields (both in-plane and perpendicular) are applied. We predict a strong decrease of J as the in-plane B field is increased, mainly due to orbital compression. Combined with the Zeeman splitting, this leads to a singlet-triplet crossing, which can be observed as a pronounced jump in the magnetization at in-plane fields of a few Tesla, and perpendicular fields of the order of 10 Tesla for typical self-assembled dots. We use harmonic potentials to model the confining of electrons, and calculate the exchange J using the Heitler-London and Hund-Mulliken technique, including the long-range Coulomb interaction. With our results we provide experimental criteria for the distinction of singlet and triplet states and therefore for microscopic spin measurements. In the case where dots of different sizes are coupled, we present a simple method to switch on and off the spin coupling with exponential sensitivity using an in-plane electric field. Switching the spin coupling is essential for quantum computation using electronic spins as qubits.Comment: 13 pages, 9 figure

What do evidence-based secondary journals tell us about the publication of clinically important articles in primary healthcare journals?

BACKGROUND: We conducted this analysis to determine i) which journals publish high-quality, clinically relevant studies in internal medicine, general/family practice, general practice nursing, and mental health; and ii) the proportion of clinically relevant articles in each journal. METHODS: We performed an analytic survey of a hand search of 170 general medicine, general healthcare, and specialty journals for 2000. Research staff assessed individual articles by using explicit criteria for scientific merit for healthcare application. Practitioners assessed the clinical importance of these articles. Outcome measures were the number of high-quality, clinically relevant studies published in the 170 journal titles and how many of these were published in each of four discipline-specific, secondary "evidence-based" journals (ACP Journal Club for internal medicine and its subspecialties; Evidence-Based Medicine for general/family practice; Evidence-Based Nursing for general practice nursing; and Evidence-Based Mental Health for all aspects of mental health). Original studies and review articles were classified for purpose: therapy and prevention, screening and diagnosis, prognosis, etiology and harm, economics and cost, clinical prediction guides, and qualitative studies. RESULTS: We evaluated 60,352 articles from 170 journal titles. The pass criteria of high-quality methods and clinically relevant material were met by 3059 original articles and 1073 review articles. For ACP Journal Club (internal medicine), four titles supplied 56.5% of the articles and 27 titles supplied the other 43.5%. For Evidence-Based Medicine (general/family practice), five titles supplied 50.7% of the articles and 40 titles supplied the remaining 49.3%. For Evidence-Based Nursing (general practice nursing), seven titles supplied 51.0% of the articles and 34 additional titles supplied 49.0%. For Evidence-Based Mental Health (mental health), nine titles supplied 53.2% of the articles and 34 additional titles supplied 46.8%. For the disciplines of internal medicine, general/family practice, and mental health (but not general practice nursing), the number of clinically important articles was correlated withScience Citation Index (SCI) Impact Factors. CONCLUSIONS: Although many clinical journals publish high-quality, clinically relevant and important original studies and systematic reviews, the articles for each discipline studied were concentrated in a small subset of journals. This subset varied according to healthcare discipline; however, many of the important articles for all disciplines in this study were published in broad-based healthcare journals rather than subspecialty or discipline-specific journals

Under the spotlight : understanding the role of the Chief Medical Officer in a pandemic

As the COVID-19 pandemic took hold in 2020, Chief Medical Officers (CMOs) entered the public spotlight like never before. Amidst this increased visibility, the role is deeply contested. Much of the disagreement concerns whether CMOs should act independently of the government: while some argue CMOs should act as independent voices who work to shape government policy to protect public health, others stress that CMOs are civil servants whose job is to support the government. The scope and diversity of debates about the CMO role can be explained by its inherently contradictory nature, which requires incumbents to balance their commitments as physicians with their mandates as civil servants who advise and speak on the government’s behalf. The long-haul COVID-19 pandemic has further tested the CMO role and has shone light on its varying remits and expectations across different jurisdictions, institutions and contexts. It is perhaps unsurprising, then, that calls to amend the CMO role have emerged in some jurisdictions during the pandemic. However, any discussions about changing the CMO role need a stronger understanding of how different institutional and individual approaches impact what incumbents feel able to do, say and achieve. Based on an ongoing comparative analysis of the position across five countries with Westminster-style political systems, we provide an overview of the CMO role, explain its prominence in a pandemic, examine some debates surrounding the role and discuss a few unanswered empirical questions before describing our ongoing study in greater detail

Identification of a novel truncating PALB2 mutation and analysis of its contribution to early-onset breast cancer in French-Canadian women

Abstract Background PALB2 has recently been identified as a breast cancer susceptibility gene. PALB2 mutations are rare causes of hereditary breast cancer but may be important in countries such as Finland where a founder mutation is present. We sought to estimate the contribution of PALB2 mutations to the burden of breast cancer in French Canadians from Quebec. Methods We screened all coding exons of PALB2 in a sample of 50 French-Canadian women diagnosed with either early-onset breast cancer or familial breast cancer at a single Montreal hospital. The genetic variants identified in this sample were then studied in 356 additional women with breast cancer diagnosed before age 50 and in 6,448 newborn controls. Results We identified a single protein-truncating mutation in PALB2 (c.2323 C>T, resulting in Q775X) in 1 of the 50 high-risk women. This variant was present in 2 of 356 breast cancer cases and in none of 6,440 newborn French-Canadian controls (P = 0.003). We also identified two novel new non-synonymous single nucleotide polymorphisms in exon 4 of PALB2 (c.5038 A>G [I76V] and c.5156 G>T [G115V]). G115V was found in 1 of 356 cases and in 15 of 6,442 controls (P = 0.6). The I76V variant was not identified in either the extended case series or the controls. Conclusion We have identified a novel truncating mutation in PALB2. The mutation was found in approximately 0.5% of unselected French-Canadian women with early-onset breast cancer and appears to have a single origin. Although mutations are infrequent, PALB2 can be added to the list of breast cancer susceptibility genes for which founder mutations have been identified in the French-Canadian population

Policy assessment and policy development for physical activity promotion: results of an exploratory intervention study in 15 European Nations

<p>Abstract</p> <p>Background</p> <p>Purpose of the study was to test a theoretical model to assess and develop policies for the promotion of physical activity among older people as part of an international intervention study.</p> <p>Methods</p> <p>248 semi-standardized interviews with policy-makers were conducted in 15 European nations. The questionnaire assessed policy-makers' perceptions of organizational goals, resources, obligations, as well as organizational, political and public opportunities in the area of physical activity promotion among older people. In order to develop policies, workshops with policy-makers were conducted. Workshop outputs and outcomes were assessed for four nations nine months after the workshops.</p> <p>Results</p> <p>Policy assessment: Results of the policy assessment were diverse across nations and policy sectors. For example, organizational goals regarding actions for physical activity promotion were perceived as being most favorably by the sports sector. Organizational obligations for the development of such policies were perceived as being most favorably by the health sector.</p> <p>Policy development: The workshops resulted in different outputs: a national intersectoral action plan (United Kingdom), a national alliance (Sweden), an integrated policy (the Netherlands), and a continuing dialogue (Germany).</p> <p>Conclusions</p> <p>Theory-driven policy assessment and policy-maker workshops might be an important means of scientific engagement in policy development for health promotion.</p