Understanding the suppression of structure formation from dark matter-dark energy momentum coupling

Models in which scalar field dark energy interacts with dark matter via a pure momentum coupling have previously been found to potentially ease the structure formation tension between early-and late-universe observations. In this article we explore the physical mechanism underlying this feature. We argue analytically that the perturbation growth equations imply the suppression of structure growth, illustrating our discussion with numerical calculations. Then we generalise the previously studied quadratic coupling between the dark energy and dark matter to a more general power law case, also allowing for the slope of the dark energy exponential potential to vary. We find that the structure growth suppression is a generic feature of power law couplings and it can, for a range of parameter values, be larger than previously found

Physical properties and efficiency of GaNP light emitting diodes

GaNP∕GaP is promising for yellow-amber-red light emitting diodes (LEDs). In this study, pressure and temperature dependent electroluminescence and photocurrent measurements on bulk GaP∕GaN0.006P0.994∕GaP LED structures are presented. Below ∼110K⁠, emission is observed from several localized nitrogen states. At room temperature, the band-edge energy increases weakly with pressure at a rate of +1.6meV∕kbar⁠, substantially lower than the Γ band gap of GaP (+9.5meV∕kbar)⁠. Thus, despite the multiplicity of nitrogen levels, the band anticrossing model reasonably describes this system based on an average of the nitrogen states. Furthermore, carrier leakage into the X minima of GaP reduces the efficiency in GaNP-LEDs with increasing pressure

Temperature dependence and physical properties of Ga(NAsP)/GaP semiconductor lasers

We report on the properties of GaNAsP/GaP lasers which offer a potential route to producing lasers monolithically on silicon. Lasing has been observed over a wide temperature range with pulsed threshold current density of 2.5 kA/cm2 at 80 K (λ=890 nm)⁠. Temperature dependence measurements show that the radiative component of the threshold is relatively temperature stable while the overall threshold current is temperature sensitive. A sublinear variation of spontaneous emission versus current coupled with a decrease in external quantum efficiency with increasing temperature and an increase in threshold current with hydrostatic pressure implies that a carrier leakage path is the dominant carrier recombination mechanism

Patients-people-place : developing a framework for researching organizational culture during health service redesign and change

BACKGROUND: Organizational culture is considered by policy-makers, clinicians, health service managers and researchers to be a crucial mediator in the success of implementing health service redesign. It is a challenge to find a method to capture cultural issues that is both theoretically robust and meaningful to those working in the organizations concerned. As part of a comparative study of service redesign in three acute hospital organizations in England, UK, a framework for collecting data reflective of culture was developed that was informed by previous work in the field and social and cultural theory. METHODS: As part of a larger mixed method comparative case study of hospital service redesign, informed by realist evaluation, the authors developed a framework for researching organisational culture during health service redesign and change. This article documents the development of the model, which involved an iterative process of data analysis, critical interdisciplinary discussion in the research team, and feedback from staff in the partner organisations. Data from semi-structured interviews with 77 key informants are used to illustrate the model. RESULTS: In workshops with NHS partners to share and debate the early findings of the study, organizational culture was identified as a key concept to explore because it was perceived to underpin the whole redesign process. The Patients-People-Place framework for studying culture focuses on three thematic areas (‘domains’) and three levels of culture in which the data could be organised. The framework can be used to help explain the relationship between observable behaviours and cultural artefacts, the values and habits of social actors and the basic assumptions underpinning an organization’s culture in each domain. CONCLUSIONS: This paper makes a methodological contribution to the study of culture in health care organizations. It offers guidance and a practical approach to investigating the inherently complex phenomenon of culture in hospital organizations. The Patients-People-Place framework could be applied in other settings as a means of ensuring the three domains and three levels that are important to an organization’s culture are addressed in future health service research

Measurements on Pb27+ Sources for the CERN Heavy Ion Injection Chain

CERN, the world's largest particle physics laboratory near Geneva, is currently in the process of building the Large Hadron Collider (LHC). Lead-208 will be used in this accelerator and to meet the injection requirements much work is required to find a suitable and reliable heavy ion source. The work in this report covers two ion sources, the Laser Ion Source (LIS), and the Electron Cyclotron Resonance Ion Source (ECRIS). An emittance measurement, using a pepper pot and CCD camera, was completed on the recently re-installed LIS, measured and analysed to be 140mm.mrad un-normalised and 0.8mm.mrad normalised 4rms for the maximum intensity charge state, Pb27+. A Visual Basic Program was modified to allow Charge State Distribution (CSD) and other scans of the ECRIS at CERN to be taken. Chapter 5 presents the results of the CSD scans taken. This program provided a new method to take 1 dimensional transverse beam profiles. From this a direct emittance measurement was formed for the first time since the source was on the test bench. This showed the charge state Pb27+ extracted from the source to have 4rms emittance 100mm.mrad un-normalised. This experiment was repeated while the source was providing Indium21+ during the summer of 2003, and the emittance recorded as 125mm.mrad. A 2 dimensional beam profile of the ECRIS is required and in Chapter 7 is a preliminary test to determine the lifetimes of two different types of beam screen. A lifetime was not determined for the Phosphor-47 coated metal plate, due to charge build-up on the surface. A Schott Glass plate, coated with layer of Aluminium of thickness 50nm, was calculated to have a lifetime of 50 minutes when placed after the ECRI

Charge State Distribution Scans on LEBT of Linac 3

Measurements of the ECR4 lead ion source charge state distributio

Measurements of emittance and twiss parameters in LINAC 3 comparison between measurements and simulations

In the framework of Linac 3 restudy, emittance, and transmission measurements are taken at all stage of acceleration. The results of these measurements will help to increase the accuracy of beam dynamic simulations. Two methods of calculation of the emittance and Twiss parameters from beam profile measurements are used. Some aspects of the beam dynamic in the LEBT, MEBT and Filter of Linac 3 are highlighted