Solar Cell Light Trapping beyond the Ray Optic Limit

In 1982, Yablonovitch proposed a thermodynamic limit on light trapping within homogeneous semiconductor slabs, which implied a minimum thickness needed to fully absorb the solar spectrum. However, this limit is valid for geometrical optics but not for a new generation of subwavelength solar absorbers such as ultrathin or inhomogeneously structured cells, wire-based cells, photonic crystal-based cells, and plasmonic cells. Here we show that the key to exceeding the conventional ray optic or so-called ergodic light trapping limit is in designing an elevated local density of optical states (LDOS) for the absorber. Moreover, for any semiconductor we show that it is always possible to exceed the ray optic light trapping limit and use these principles to design a number of new solar absorbers with the key feature of having an elevated LDOS within the absorbing region of the device, opening new avenues for solar cell design and cost reduction

Light trapping beyond the 4n^2 limit in thin waveguides

We describe a method for determining the maximum absorption enhancement in thin film waveguides based on optical dispersion relations. For thin film structures that support one, well-confined guided mode, we find that the absorption enhancement can surpass the traditional limit of 4n^2 when the propagation constant is large and/or the modal group velocity is small compared to the bulk value. We use this relationship as a guide to predicting structures that can exceed the 4n^2 light trapping limit, such as plasmonic and slot waveguides. Finally, we calculate the overall absorption for both single and multimode waveguides, and show examples of absorption enhancements in excess of 4n^2 for both cases

Reconstructing Positions \& Peculiar Velocities of Galaxy Clusters within 25000 km/sec: The Bulk Velocity

Using a dynamical 3-D reconstruction procedure we estimate the peculiar velocities of $R\ge0$ Abell/ACO galaxy clusters from their measured redshift within 25000 km/sec. The reconstruction algorithm relies on the linear gravitational instability hypothesis, assumes linear biasing and requires an input value of the cluster $\beta$-parameter ($\beta_c \equiv \Omega_{\circ}^{0.6}/b_c$), which we estimated in Branchini \& Plionis (1995) to be $\beta_c\simeq 0.21$. The resulting cluster velocity field is dominated by a large scale streaming motion along the Perseus Pisces--Great Attractor base-line directed towards the Shapley concentration, in qualitative agreement with the galaxy velocity field on smaller scales. Fitting the predicted cluster peculiar velocities to a dipole term, in the local group frame and within a distance of $\sim 18000$ km/sec, we recover extremely well both the local group velocity and direction, in disagreement with the Lauer \& Postman (1994) observation. However, we find a $\sim 6\%$ probability that their observed velocity field could be a realization of our corresponding one, if the latter is convolved with their large distance dependent errors. Our predicted cluster bulk velocity amplitude agrees well with that deduced by the POTENT and the da Costa et al. (1995) analyses of observed galaxy motions at $\sim 5000 - 6000$ km/sec; it decreases thereafter while at the Lauer \& Postman limiting depth ($\sim 15000$ km/sec) its amplitude is $\sim 150$ km/sec, in comfortable agreement with most cosmological models.Comment: 8 pages, uuencoded compressed tarred postscript file uncluding text and 3 figures. Accepted in ApJ Letter

Towards A Short to Medium Term Mitigation Strategy to Address the External Air and Sea Connectivity Challenges posed by the COVID-19 Pandemic for Northern Ireland

The overall aim of the research is the preparation of a short to medium term Access Mitigation Strategy to respond to the challenges posed for the business, travel, leisure and tourism sectors by the physical and psychological impacts on travel access to/from Northern Ireland during/post the COVID-19 Pandemic. The research programme reflects the need to understand the implications of the COVID-19 crisis on accessibility to/from Northern Ireland given the region’s heavy reliance on air and sea access for trade, Foreign Direct Investment (FDI) and tourism. This includes the fall-out from COVID-19 (and additional factors including Flybe, Brexit) on the capacity of air and sea routes, how demand has and will be impacted in the future because of changing behaviours and what actions need to be taken to minimise these effects and keep Northern Ireland open for business. The project objectives are as follows: To establish the current position and near to medium term prospects for air and sea connectivity to Northern Ireland (including Irish Sea ports and airports); review the contribution of air and sea links to the performance of the Northern Ireland Economy and Wider Society; assess the factors shaping this position and their impact on demand for external travel before, during and post the Coronavirus Pandemic; develop a range of future scenarios around passenger transport by air and sea to inform the development of a range of mitigation policy interventions to maximise the accessibility of the region; table recommendations for a mitigation policy to maximise accessibility of the region; and assess the potential for funding and financing a Short to Medium Term Access Mitigation Strategy for the region. The research findings and its recommendations are informed by robust empirical evidence bases and include proven public policy interventions to maximise the region’s access and openness to business and tourism related travel going forward

Observation of Leggett's collective mode in a multi-band MgB2 superconductor

We report observation of Leggett's collective mode in a multi-band MgB2 superconductor with T_c=39K arising from the fluctuations in the relative phase between two superconducting condensates. The novel mode is observed by Raman spectroscopy at 9.4 meV in the fully symmetric scattering channel. The observed mode frequency is consistent with theoretical considerations based on the first principle computations.Comment: Accepted for PR

The Kinematic Properties of the Extended Disks of Spiral Galaxies: A Sample of Edge-On Galaxies

We present a kinematic study of the outer regions (R_25<R<2 R_25) of 17 edge-on disk galaxies. Using deep long-slit spectroscopy (flux sensitivity a few 10^-19 erg s^-1 cm^-2 arcsec^-2), we search for H-alpha emission, which must be emitted at these flux levels by any accumulation of hydrogen due to the presence of the extragalactic UV background and any other, local source of UV flux. We present results from the individual galaxy spectra and a stacked composite. We detect H-alpha in many cases well beyond R_25 and sometimes as far as 2 R_25. The combination of sensitivity, spatial resolution, and kinematic resolution of this technique thus provides a powerful complement to 21-cm observations. Kinematics in the outer disk are generally disk-like (flat rotation curves, small velocity dispersions) at all radii, and there is no evidence for a change in the velocity dispersion with radius. We place strong limits, few percent, on the existence of counter-rotating gas out to 1.5 R_25. These results suggest that thin disks extend well beyond R_25; however, we also find a few puzzling anomalies. In ESO 323-G033 we find two emission regions that have velocities close to the systemic velocity rather than the expected rotation velocity. These low relative velocities are unlikely to be simply due to projection effects and so suggest that these regions are not on disk-plane, circular orbits. In MCG-01-31-002 we find emission from gas with a large velocity dispersion that is co-rotating with the inner disk.Comment: 18 pages, 14 figures, accepted for publication in Ap

A systematic review of interventions in primary care to improve health literacy for chronic disease behavioral risk factors

Background: To evaluate the effectiveness of interventions used in primary care to improve health literacy for change in smoking, nutrition, alcohol, physical activity and weight (SNAPW). Methods: A systematic review of intervention studies that included outcomes for health literacy and SNAPW behavioral risk behaviors implemented in primary care settings. We searched the Cochrane Library, Johanna Briggs Institute, Medline, Embase, CINAHL, Psychinfo, Web of Science, Scopus, APAIS, Australasian Medical Index, Google Scholar, Community of Science and four targeted journals (Patient Education and Counseling, Health Education and Behaviour, American Journal of Preventive Medicine and Preventive Medicine). Study inclusion criteria: Adults over 18 years; undertaken in a primary care setting within an Organisation for Economic Co-operation and Development (OECD) country; interventions with at least one measure of health literacy and promoting positive change in smoking, nutrition, alcohol, physical activity and/or weight; measure at least one outcome associated with health literacy and report a SNAPW outcome; and experimental and quasi-experimental studies, cohort, observational and controlled and non-controlled before and after studies. Papers were assessed and screened by two researchers (JT, AW) and uncertain or excluded studies were reviewed by a third researcher (MH). Data were extracted from the included studies by two researchers (JT, AW). Effectiveness studies were quality assessed. A typology of interventions was thematically derived from the studies by grouping the SNAPW interventions into six broad categories: individual motivational interviewing and counseling; group education; multiple interventions (combination of interventions); written materials; telephone coaching or counseling; and computer or web based interventions. Interventions were classified by intensity of contact with the subjects (High ≥ 8 points of contact/hours; Moderate \u3e3 and \u3c8; Low ≤ 3 points of contact hours) and setting (primary health, community or other). Studies were analyzed by intervention category and whether significant positive changes in SNAPW and health literacy outcomes were reported. Results: 52 studies were included. Many different intervention types and settings were associated with change in health literacy (73% of all studies) and change in SNAPW (75% of studies). More low intensity interventions reported significant positive outcomes for SNAPW (43% of studies) compared with high intensity interventions (33% of studies). More interventions in primary health care than the community were effective in supporting smoking cessation whereas the reverse was true for diet and physical activity interventions. Conclusion: Group and individual interventions of varying intensity in primary health care and community settings are useful in supporting sustained change in health literacy for change in behavioral risk factors. Certain aspects of risk behavior may be better handled in clinical settings while others more effectively in the community. Our findings have implications for the design of programs

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