Comment on "Scalings for radiation from plasma bubbles" [Phys. Plasmas 17, 056708 (2010)]

Thomas has recently derived scaling laws for X-ray radiation from electrons accelerated in plasma bubbles, as well as a threshold for the self-injection of background electrons into the bubble [A. G. R. Thomas, Phys. Plasmas 17, 056708 (2010)]. To obtain this threshold, the equations of motion for a test electron are studied within the frame of the bubble model, where the bubble is described by prescribed electromagnetic fields and has a perfectly spherical shape. The author affirms that any elliptical trajectory of the form x'^2/{\gamma}_p^2 + y'^2 = R^2 is solution of the equations of motion (in the bubble frame), within the approximation p'_y^2/p'_x^2 \ll 1. In addition, he highlights that his result is different from the work of Kostyukov et al. [Phys. Rev. Lett. 103, 175003 (2009)], and explains the error committed by Kostyukov-Nerush-Pukhov-Seredov (KNPS). In this comment, we show that numerically integrated trajectories, based on the same equations than the analytical work of Thomas, lead to a completely different result for the self-injection threshold, the result published by KNPS [Phys. Rev. Lett. 103, 175003 (2009)]. We explain why the analytical analysis of Thomas fails and we provide a discussion based on numerical simulations which show exactly where the difference arises. We also show that the arguments of Thomas concerning the error of KNPS do not hold, and that their analysis is mathematically correct. Finally, we emphasize that if the KNPS threshold is found not to be verified in PIC (Particle In Cell) simulations or experiments, it is due to a deficiency of the model itself, and not to an error in the mathematical derivation.Comment: 5 pages, 5 figure

Mapping the X-Ray Emission Region in a Laser-Plasma Accelerator

The x-ray emission in laser-plasma accelerators can be a powerful tool to understand the physics of relativistic laser-plasma interaction. It is shown here that the mapping of betatron x-ray radiation can be obtained from the x-ray beam profile when an aperture mask is positioned just beyond the end of the emission region. The influence of the plasma density on the position and the longitudinal profile of the x-ray emission is investigated and compared to particle-in-cell simulations. The measurement of the x-ray emission position and length provides insight on the dynamics of the interaction, including the electron self-injection region, possible multiple injection, and the role of the electron beam driven wakefield.Comment: 5 pages, 4 figure

p-type Bi2Se3 for topological insulator and low temperature thermoelectric applications

The growth and elementary properties of p-type Bi2Se3 single crystals are reported. Based on a hypothesis about the defect chemistry of Bi2Se3, the p-type behavior has been induced through low level substitutions (1 percent or less) of Ca for Bi. Scanning tunneling microscopy is employed to image the defects and establish their charge. Tunneling and angle resolved photoemission spectra show that the Fermi level has been lowered into the valence band by about 400 meV in Bi1.98Ca0.02Se3 relative to the n-type material. p-type single crystals with ab plane Seebeck coefficients of +180 microVK-1 at room temperature are reported. These crystals show a giant anomalous peak in the Seebeck coefficient at low temperatures, reaching +120 microVK-1 at 7 K, giving them a high thermoelectric power factor at low temperatures. In addition to its interesting thermoelectric properties, p-type Bi2Se3 is of substantial interest for studies of technologies and phenomena proposed for topological insulators.Comment: v2: STM characterization of n and p type Bi2Se3 is adde

The development of ferromagnetism in the doped topological insulator Bi2-xMnxTe3

The development of ferromagnetism in Mn-doped Bi2Te3 is characterized through measurements on a series of single crystals with different Mn content. Scanning tunneling microscopy analysis shows that the Mn substitutes on the Bi sites, forming compounds of the type Bi2-xMnxTe3, and that the Mn substitutions are randomly distributed, not clustered. Mn doping first gives rise to local magnetic moments with Curie-like behavior, but by the compositions Bi1.96Mn0.04Te3 and Bi1.91Mn0.09Te3 a second order ferromagnetic transition is observed, with Tc ~ 9-12 K. The easy axis of magnetization in the ferromagnetic phase is perpendicular to the Bi2Te3 basal plane. Thermoelectric power and Hall effect measurements show that the Mn-doped Bi2Te3 crystals are p-type. Angle resolved photoemission spectroscopy measurements show that the topological surface states that are present in pristine Bi2Te3 are also present in ferromagnetic Mn-doped Bi2-xMnxTe3, and that the dispersion relations of the surface states are changed in a subtle fashion

Thermoelectric transport in Bi2Te3/Sb2Te3\text{Bi}_2\text{Te}_3/\text{Sb}_2\text{Te}_3 superlattices

The thermoelectric transport properties of $\text{Bi}_2\text{Te}_3/\text{Sb}_2\text{Te}_3$superlattices are analyzed on the basis of first-principles calculations and semi-classical Boltzmann theory. The anisotropy of the thermoelectric transport under electron and hole-doping was studied in detail for different superlattice periods at changing temperature and charge carrier concentrations. A clear preference for thermoelectric transport under hole-doping, as well as for the in-plane transport direction was found for all superlattice periods. At hole-doping the electrical transport anisotropies remain bulk-like for all investigated systems, while under electron-doping quantum confinement leads to strong suppression of the cross-plane thermoelectric transport at several superlattice periods. In addition, insights on the Lorenz function, the electronic contribution to the thermal conductivity and the resulting figure of merit are given

Structural, Vibrational, and Electronic Study of α‑As2Te3 under Compression

This document is the Accepted Manuscript version of a Published Work that appeared in final form in Journal of Physical Chemistry C, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://dx.doi.org/10.1021/acs.jpcc.6b06049We report a study of the structural, vibrational, and electronic properties of layered monoclinic arsenic telluride (α-As2Te3) at high pressures. Powder X-ray diffraction and Raman scattering measurements up to 17 GPa have been complemented with ab initio total-energy, lattice dynamics, and electronic band structure calculations. Our measurements, which include previously unreported Raman scattering measurements for crystalline α-As2Te3, show that this compound undergoes a reversible phase transition above 14 GPa at room temperature. The monoclinic crystalline structure of α-As2Te3 and its behavior under compression are analyzed by means of the compressibility tensor. Major structural and vibrational changes are observed in the range between 2 and 4 GPa and can be ascribed to the strengthening of interlayer bonds. No evidence of any isostructural phase transition has been observed in α-As2Te3. A comparison with other group 15 sesquichalcogenides allows understanding the structure of α-As2Te3 and its behavior under compression based on the activity of the cation lone electron pair in these compounds. Finally, our electronic band structure calculations show that α-As2Te3 is a semiconductor at 1 atm, which undergoes a trivial semiconducting−metal transition above 4 GPa. The absence of a pressure-induced electronic topological transition in α-As2Te3 is discussed.This work has been performed under financial support from Projects MAT2013-46649-C4-2-P, MAT2013-46649-C4-3-P, MAT2015-71070-REDC, FIS2013-48286-C2-1-P, and FIS2013-48286-C2-2-P of the Spanish Ministry of Economy and Competitiveness (MINECO), and the Department of Education, Universities and Research of the Basque Government and UPV/EHU (Grant No. IT756-13). This publication is also fruit of "Programa de Valoracion y Recursos Conjuntos de I+D+i VLC/CAMPUS" and has been financed by the Spanish Ministerio de Educacion, Cultura y Deporte as part of "Programa Campus de Excelencia Internacional" through Projects SP20140701 and SP20140871. Finally, authors thank ALBA Light Source for beam allocation at beamline MSPD.Cuenca Gotor, VP.; Sans-Tresserras, JÁ.; Ibáñez, J.; Popescu, C.; Gomis, O.; Vilaplana Cerda, RI.; Manjón Herrera, FJ.... (2016). Structural, Vibrational, and Electronic Study of α‑As2Te3 under Compression. Journal of Physical Chemistry C. 120(34):19340-19352. https://doi.org/10.1021/acs.jpcc.6b06049S19340193521203

Challenges in physician supply planning: the case of Belgium

<p>Abstract</p> <p>Introduction</p> <p>Planning human resources for health (HRH) is a complex process for policy-makers and, as a result, many countries worldwide swing from surplus to shortage. In-depth case studies can help appraising the challenges encountered and the solutions implemented. This paper has two objectives: to identify the key challenges in HRH planning in Belgium and to formulate recommendations for an effective HRH planning, on the basis of the Belgian case study and lessons drawn from an international benchmarking.</p> <p>Case description</p> <p>In Belgium, a numerus clausus set up in 1997 and effective in 2004, aims to limit the total number of physicians working in the curative sector. The assumption of a positive relationship between physician densities and health care utilization was a major argument in favor of medical supply restrictions. This new regulation did not improve recurrent challenges such as specialty imbalances, with uncovered needs particularly among general practitioners, and geographical maldistribution. New difficulties also emerged. In particular, limiting national training of HRH turned out to be ineffective within the open European workforce market. The lack of integration of policies affecting HRH was noteworthy. We described in the paper what strategies were developed to address those challenges in Belgium and in neighboring countries.</p> <p>Discussion and evaluation</p> <p>Planning the medical workforce involves determining the numbers, mix, and distribution of health providers that will be required at some identified future point in time. To succeed in their task, health policy planners have to take a broader perspective on the healthcare system. Focusing on numbers is too restrictive and adopting innovative policies learned from benchmarking without integration and coordination is unfruitful. Evolving towards a strategic planning is essential to control the effects of the complex factors impacting on human resources. This evolution requires an effective monitoring of all key factors affecting supply and demand, a dynamic approach, and a system-level perspective, considering all healthcare professionals, and integrating manpower planning with workforce development.</p> <p>Conclusion</p> <p>To engage in an evidence-based action, policy-makers need a global manpower picture, from their own country and abroad, as well as reliable and comparable manpower databases allowing proper analysis and planning of the workforce.</p

An integrative review of the factors influencing older nurses’ timing of retirement

Aims: To summarise the international empirical literature to provide a comprehensive understanding of older nurses’ decision making surrounding the timing of their retirement. Background: The global nursing shortage is increasing. Amongst some countries it has become an economic imperative to consider raising the state pension age and to extend working lives. Design: An integrative literature review using an integrated design. Data sources: MEDLINE, CINAHL and Business Source Premier databases were searched for studies between January 2007 ‐ October 2019. Review Methods: Quality appraisal of the studies were conducted. Findings were summarised, grouped into categories and themes extracted. Two models were developed for data representation. Results: 132 studies were identified by the search strategy. Of these, 27 articles were included for appraisal and synthesis. 16 papers were quantitative, seven qualitative and four mixed methods. The research took place in 13 different geographical locations. Most studies were of a questionnaire design, followed by interviews and focus groups. The total participant sample was 35,460. Through a synthesis of the studies, four themes were identified: Health, Well‐being and Family factors; Employer factors; Professional factors; Financial factors. Conclusion: This review revealed the heterogeneity of studies on this subject and confirmed previous findings but also established a ranking of criteria that influences nurses’ decision making: age, followed by personal and organisational factors. Four extracted themes of push and pull factors map onto these factors. No ‘one‐size‐fits‐all’ strategy exists to ensure the extension of older nurses’ working lives. Organisations need to foster an environment where older nurses feel respected and heard and where personal and professional needs are addressed

Physician supply forecast: better than peering in a crystal ball?

<p>Abstract</p> <p>Background</p> <p>Anticipating physician supply to tackle future health challenges is a crucial but complex task for policy planners. A number of forecasting tools are available, but the methods, advantages and shortcomings of such tools are not straightforward and not always well appraised. Therefore this paper had two objectives: to present a typology of existing forecasting approaches and to analyse the methodology-related issues.</p> <p>Methods</p> <p>A literature review was carried out in electronic databases Medline-Ovid, Embase and ERIC. Concrete examples of planning experiences in various countries were analysed.</p> <p>Results</p> <p>Four main forecasting approaches were identified. The supply projection approach defines the necessary inflow to maintain or to reach in the future an arbitrary predefined level of service offer. The demand-based approach estimates the quantity of health care services used by the population in the future to project physician requirements. The needs-based approach involves defining and predicting health care deficits so that they can be addressed by an adequate workforce. Benchmarking health systems with similar populations and health profiles is the last approach. These different methods can be combined to perform a gap analysis. The methodological challenges of such projections are numerous: most often static models are used and their uncertainty is not assessed; valid and comprehensive data to feed into the models are often lacking; and a rapidly evolving environment affects the likelihood of projection scenarios. As a result, the internal and external validity of the projections included in our review appeared limited.</p> <p>Conclusion</p> <p>There is no single accepted approach to forecasting physician requirements. The value of projections lies in their utility in identifying the current and emerging trends to which policy-makers need to respond. A genuine gap analysis, an effective monitoring of key parameters and comprehensive workforce planning are key elements to improving the usefulness of physician supply projections.</p