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1.
Med Teach ; : 1-9, 2023 Sep 23.
Artigo em Inglês | MEDLINE | ID: mdl-37740944

RESUMO

In this critical narrative review, we challenge the belief that single-moment-in-time high-stakes examinations (SMITHSEx) are an essential component of contemporary specialist training. We explore the arguments both for and against SMITHSEx, examine potential alternatives, and discuss the barriers to change.SMITHSEx are viewed as the "gold standard" assessment of competence but focus excessively on knowledge assessment rather than capturing essential competencies required for safe and competent workplace performance. Contrary to popular belief, regulatory bodies do not mandate SMITHSEx in specialist training. Though acting as significant drivers of learning and professional identity formation, these attributes are not exclusive to SMITHSEx.Skills such as crisis management, procedural skills, professionalism, communication, collaboration, lifelong learning, reflection on practice, and judgement are often overlooked by SMITHSEx. Their inherent design raises questions about the validity and objectivity of SMITHSEx as a measure of workplace competence. They have a detrimental impact on trainee well-being, contributing to burnout and differential attainment.Alternatives to SMITHSEx include continuous low-stakes assessments throughout training, ongoing evaluation of competence in the workplace, and competency-based medical education (CBME) concepts. These aim to provide a more comprehensive and context-specific assessment of trainees' competence while also improving trainee welfare.Specialist training colleges should evolve from exam providers to holistic education sources. Assessments should emphasise essential practical knowledge over trivia, align with clinical practice, aid learning, and be part of a diverse toolkit. Eliminating SMITHSEx from specialist training will foster a competency-based approach, benefiting future medical professionals' well-being and success.

2.
Postgrad Med J ; 98(1163): 710-717, 2022 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-37062974

RESUMO

INTRODUCTION: The COVID-19 pandemic has impacted students learning, with the time off resulting in students 'de-skilling', increasing concerns for upcoming observed structured clinical examinations. Foundation Year 1 (F1) doctors (F1s), despite being expected to teach, rarely receive formal preparation, with COVID-19 exacerbating opportunities to practice. As such, a national orthopaedic teaching programme was designed to provide F1s with opportunities to develop their teaching skills and to synergistically teach medical students how to perform clinical orthopaedic examinations. METHODS: Six weekly sessions, each delivered by two newly qualified F1 tutors, on each joint examination were delivered online via Zoom Video Communications (USA). Presession and postsession multiple choice questions (MCQs) were provided to students to assess improvement in knowledge. Anonymous feedback forms were provided to both students and tutors. RESULTS: Of the 341 students that attended, 87.1% provided feedback. 86.2% felt that they had de-skilled due to time off, with a mean 15 weeks off from placement. Based on a 5-point Likert scale, students displayed a mean improvement in confidence (1.9±1.1, p<0.001) and MCQ scores (1.4±1.3, p<0.001) before and after the sessions. 91.6% and 95.3% agreed that the use of online teaching increased attendance and laid the foundation for practice. Of the six tutors, all reported improvement in confidence to teach and teaching skills. CONCLUSION: We demonstrate that online delivery of clinical orthopaedic examinations is effective, increasing the knowledge and confidence of students, while providing opportunities for F1s to teach. We present our findings to encourage similar teaching programmes to be adopted at other locations and specialties, to synergistically benefit students, doctors and ultimately, patients.


Assuntos
COVID-19 , Educação de Graduação em Medicina , Ortopedia , Estudantes de Medicina , Humanos , Pandemias , Educação de Graduação em Medicina/métodos , COVID-19/epidemiologia , Ensino
3.
BMC Health Serv Res ; 21(1): 262, 2021 Mar 21.
Artigo em Inglês | MEDLINE | ID: mdl-33743674

RESUMO

BACKGROUND: The association of workplace factors on mental health of healthcare workers (HCWs) during the COVID-19 pandemic needs to be urgently established. This will enable governments and policy-makers to make evidence-based decisions. This international study reports the association between workplace factors and the mental health of HCWs during the pandemic. METHODS: An international, cross-sectional study was conducted in 41 countries. The primary outcome was depressive symptoms, derived from the validated Patient Health Questionnaire-2 (PHQ-2). Multivariable logistic regression identified factors associated with mental health outcomes. Inter-country differences were also evaluated. RESULTS: A total of 2527 responses were received, from 41 countries, including China (n = 1213; 48.0%), UK (n = 891; 35.3%), and USA (n = 252; 10.0%). Of all participants, 1343 (57.1%) were aged 26 to 40 years, and 2021 (80.0%) were female; 874 (34.6%) were doctors, and 1367 (54.1%) were nurses. Factors associated with an increased likelihood of depressive symptoms were: working in the UK (OR = 3.63; CI = [2.90-4.54]; p < 0.001) and USA (OR = 4.10; CI = [3.03-5.54]), p < 0.001); being female (OR = 1.74; CI = [1.42-2.13]; p < 0.001); being a nurse (OR = 1.64; CI = [1.34-2.01]; p < 0.001); and caring for a COVID-19 positive patient who subsequently died (OR = 1.20; CI = [1.01-1.43]; p = 0.040). Workplace factors associated with depressive symptoms were: redeployment to Intensive Care Unit (ICU) (OR = 1.67; CI = [1.14-2.46]; p = 0.009); redeployment with perceived unsatisfactory training (OR = 1.67; CI = [1.32-2.11]; p < 0.001); not being issued with appropriate personal protective equipment (PPE) (OR = 2.49; CI = [2.03-3.04]; p < 0.001); perceived poor workplace support within area/specialty (OR = 2.49; CI = [2.03-3.04]; p < 0.001); and perceived poor mental health support (OR = 1.63; CI = [1.38-1.92]; p < 0.001). CONCLUSION: This is the first international study, demonstrating that workplace factors, including PPE availability, staff training pre-redeployment, and provision of mental health support, are significantly associated with mental health during COVID-19. Governments, policy-makers and other stakeholders need to ensure provision of these to safeguard HCWs' mental health, for future waves and other pandemics.


Assuntos
COVID-19/psicologia , Pessoal de Saúde/psicologia , Saúde Mental , Pandemias/prevenção & controle , Local de Trabalho/psicologia , Adulto , COVID-19/epidemiologia , Estudos Transversais , Feminino , Humanos , Masculino , Equipamento de Proteção Individual , SARS-CoV-2
4.
Educ Prim Care ; 32(2): 66-69, 2021 03.
Artigo em Inglês | MEDLINE | ID: mdl-33054573

RESUMO

High quality medical education requires committed and skilled educators, researchers, and leaders. Capacity building for future educationalists is fundamental in the pursuit of excellence in medical education. Medical education as a discipline is undervalued, underfunded, and often badmouthed. In order to pave the way to excellence, we must lay down the correct career pathways and foster a supportive climate in our speciality. In order to attract and support tomorrow's educationalists we argue that we need to champion the field, develop integrated clinical and educational training programmes, and promote role modelling and mentorship.


Assuntos
Educação Médica , Humanos , Mentores
5.
Am J Physiol Endocrinol Metab ; 318(4): E504-E513, 2020 04 01.
Artigo em Inglês | MEDLINE | ID: mdl-32069071

RESUMO

We hypothesized that probiotic supplementation (PRO) increases the absorption and oxidation of orally ingested maltodextrin during 2 h endurance cycling, thereby sparing muscle glycogen for a subsequent time trial (simulating a road race). Measurements were made of lipid and carbohydrate oxidation, plasma metabolites and insulin, gastrointestinal (GI) permeability, and subjective symptoms of discomfort. Seven male cyclists were randomized to PRO (bacterial composition given in methods) or placebo for 4 wk, separated by a 14-day washout period. After each period, cyclists consumed a 10% maltodextrin solution (initial 8 mL/kg bolus and 2 mL/kg every 15 min) while exercising for 2 h at 55% maximal aerobic power output, followed by a 100-kJ time trial. PRO resulted in small increases in peak oxidation rates of the ingested maltodextrin (0.84 ± 0.10 vs. 0.77 ± 0.09 g/min; P = 0.016) and mean total carbohydrate oxidation (2.20 ± 0.25 vs. 1.87 ± 0.39 g/min; P = 0.038), whereas fat oxidation was reduced (0.40 ± 0.11 vs. 0.55 ± 0.10 g/min; P = 0.021). During PRO, small but significant increases were seen in glucose absorption, plasma glucose, and insulin concentration and decreases in nonesterified fatty acid and glycerol. Differences between markers of GI damage and permeability and time-trial performance were not significant (P > 0.05). In contrast to the hypothesis, PRO led to minimal increases in absorption and oxidation of the ingested maltodextrin and small reductions in fat oxidation, whereas having no effect on subsequent time-trial performance.


Assuntos
Ciclismo/fisiologia , Metabolismo dos Carboidratos/efeitos dos fármacos , Suplementos Nutricionais , Probióticos/farmacologia , Adulto , Estudos Cross-Over , Carboidratos da Dieta , Método Duplo-Cego , Exercício Físico , Ácidos Graxos não Esterificados/sangue , Glucose/metabolismo , Glicerol/sangue , Humanos , Insulina/sangue , Metabolismo dos Lipídeos/efeitos dos fármacos , Masculino , Polissacarídeos/farmacocinética , Adulto Jovem
6.
J Gen Intern Med ; 35(11): 3333-3337, 2020 11.
Artigo em Inglês | MEDLINE | ID: mdl-32472485

RESUMO

Since 2011, aviation has revolutionized their approach to safety. The aviation industry has adopted a multi-faceted approach to improve safety through decreasing duty hour limits and implementing processes to mitigate fatigue-related errors as well as creating cultural shifts in responsibility for safety. These changes have been guided by data generated by quality-improvement methodology. In contrast, duty hour limits in graduate medical education have not yet seen dramatic data-driven reform. Key advancements in aviation fatigue mitigation and implications for residency education are explored in this article. Scientifically based processes to optimize duty hours, quality-improvement strategies to iteratively monitor and reform duty limits, systematic change focusing on a just culture, and financial disincentives and incentives as a catalyst for change are discussed.


Assuntos
Internato e Residência , Educação de Pós-Graduação em Medicina , Fadiga , Humanos , Admissão e Escalonamento de Pessoal , Tolerância ao Trabalho Programado , Carga de Trabalho
7.
Eur J Appl Physiol ; 120(10): 2325-2337, 2020 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-32794058

RESUMO

PURPOSE: Exertional-heat stress adversely disrupts gastrointestinal (GI) barrier integrity, whereby subsequent microbial translocation (MT) can result in potentially serious health consequences. To date, the influence of aerobic fitness on GI barrier integrity and MT following exertional-heat stress is poorly characterised. METHOD: Ten untrained (UT; VO2max = 45 ± 3 ml·kg-1·min-1) and ten highly trained (HT; VO2max = 64 ± 4 ml·kg-1·min-1) males completed an ecologically valid (military) 80-min fixed-intensity exertional-heat stress test (EHST). Venous blood was drawn immediately pre- and post-EHST. GI barrier integrity was assessed using the serum dual-sugar absorption test (DSAT) and plasma Intestinal Fatty-Acid Binding Protein (I-FABP). MT was assessed using plasma Bacteroides/total 16S DNA. RESULTS: UT experienced greater thermoregulatory, cardiovascular and perceptual strain (p < 0.05) than HT during the EHST. Serum DSAT responses were similar between the two groups (p = 0.59), although Δ I-FABP was greater (p = 0.04) in the UT (1.14 ± 1.36 ng·ml-1) versus HT (0.20 ± 0.29 ng·ml-1) group. Bacteroides/Total 16S DNA ratio was unchanged (Δ; -0.04 ± 0.18) following the EHST in the HT group, but increased (Δ; 0.19 ± 0.25) in the UT group (p = 0.05). Weekly aerobic training hours had a weak, negative correlation with Δ I-FABP and Bacteroides/total 16S DNA responses. CONCLUSION: When exercising at the same absolute workload, UT individuals are more susceptible to small intestinal epithelial injury and MT than HT individuals. These responses appear partially attributable to greater thermoregulatory, cardiovascular, and perceptual strain.


Assuntos
Aptidão Cardiorrespiratória , Microbioma Gastrointestinal , Transtornos de Estresse por Calor/fisiopatologia , Absorção Intestinal , Adulto , Bacteroides/isolamento & purificação , Bacteroides/patogenicidade , Ácidos Graxos/metabolismo , Transtornos de Estresse por Calor/metabolismo , Transtornos de Estresse por Calor/microbiologia , Humanos , Mucosa Intestinal/metabolismo , Mucosa Intestinal/microbiologia , Masculino , Esforço Físico , Açúcares/metabolismo
8.
Opt Express ; 27(15): 21420-21434, 2019 Jul 22.
Artigo em Inglês | MEDLINE | ID: mdl-31510220

RESUMO

We describe the fabrication of metamaterial magnifying hyperlenses with subwavelength wire array structures for operation in the mid-infrared (around 3 µm). The metadevices are composed of approximately 500 tin wires embedded in soda-lime glass, where the metallic wires vary in diameter from 500 nm to 1.2 µm along the tapered structure. The modeling of the hyperlenses indicates that the expected overall losses for the high spatial frequency modes in such metadevices are between 20 dB to 45 dB, depending on the structural parameters selected, being promising candidates for far-field subdiffraction imaging in the mid-infrared. Initial far-field subdiffraction imaging attempts are described, and the problems encountered discussed.

9.
Eur J Appl Physiol ; 119(7): 1491-1501, 2019 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-30982100

RESUMO

PURPOSE: To evaluate the effects of probiotic supplementation on gastrointestinal (GI) symptoms, circulatory markers of GI permeability, damage, and markers of immune response during a marathon race. METHODS: Twenty-four recreational runners were randomly assigned to either supplement with a probiotic (PRO) capsule [25 billion CFU Lactobacillus acidophilus (CUL60 and CUL21), Bifidobacterium bifidum (CUL20), and Bifidobacterium animalis subs p. Lactis (CUL34)] or placebo (PLC) for 28 days prior to a marathon race. GI symptoms were recorded during the supplement period and during the race. Serum lactulose:rhamnose ratio, and plasma intestinal-fatty acid binding protein, sCD14, and cytokines were measured pre- and post-races. RESULTS: Prevalence of moderate GI symptoms reported were lower during the third and fourth weeks of the supplement period compared to the first and second weeks in PRO (p < 0.05) but not PLC (p > 0.05). During the marathon, GI symptom severity during the final third was significantly lower in PRO compared to PLC (p = 0.010). The lower symptom severity was associated with a significant difference in reduction of average speed from the first to the last third of the race between PLC (- 14.2 ± 5.8%) and PRO (- 7.9 ± 7.5%) (p = 0.04), although there was no difference in finish times between groups (p > 0.05). Circulatory measures increased to a similar extent between PRO and PLC (p > 0.05). CONCLUSION: Probiotics supplementation was associated with a lower incidence and severity of GI symptoms in marathon runners, although the exact mechanisms are yet to be elucidated. Reducing GI symptoms during marathon running may help maintain running pace during the latter stages of racing.


Assuntos
Citocinas/sangue , Proteínas de Ligação a Ácido Graxo/sangue , Trato Gastrointestinal/fisiologia , Corrida Moderada/fisiologia , Probióticos/administração & dosagem , Adulto , Bifidobacterium , Feminino , Gastroenteropatias/prevenção & controle , Trato Gastrointestinal/microbiologia , Humanos , Lactobacillus acidophilus , Lactose/sangue , Receptores de Lipopolissacarídeos/sangue , Masculino , Probióticos/uso terapêutico , Ramnose/sangue
10.
Med Teach ; 41(4): 398-402, 2019 04.
Artigo em Inglês | MEDLINE | ID: mdl-30761935

RESUMO

Purpose: We examined studies of the clinical learning environment from the fields of sociology and organizational culture to (i) offer insight into how workplace culture has informed research on postgraduate trainee learning and professional development; (ii) highlight limitations of the literature; and (iii) suggest practical ways to apply sociocultural concepts to challenges in the learning environment. Materials and methods: Concepts were explored by participants at a consensus conference in October 2018. Results: We identified three enduring foci for research using a sociocultural lens: the hidden curriculum, exploration of medical errors, and the impact of time pressures on the relational nature of clinical education. Limitations included the lower value attributed to informal learning and a pejorative valuation of the hidden curriculum; and disconnect between practices in clinical settings and the priorities of the larger organization. Conclusions: Research on the learning environment using a sociocultural lens suggest workplace goals, norms and practices determined which learners engage in learning-relevant activities, to what extent, and the degree of guidance provided, with these factors creating "tacit" curricula that may support or compete with formal learning goals. We close with guidance on how sociocultural constructs could inform research to improve the learning environment.


Assuntos
Aculturação , Internato e Residência/organização & administração , Aprendizagem , Cultura Organizacional , Local de Trabalho/psicologia , Competência Clínica/normas , Diversidade Cultural , Currículo , Meio Ambiente , Humanos , Internato e Residência/normas , Erros Médicos/prevenção & controle , Pesquisa Qualitativa , Meio Social , Sociologia , Estudantes de Medicina/psicologia , Fatores de Tempo , Confiança , Local de Trabalho/organização & administração
11.
Opt Express ; 26(2): 674-679, 2018 Jan 22.
Artigo em Inglês | MEDLINE | ID: mdl-29401949

RESUMO

We demonstrate in this paper thermal poling of multi-wire array fibers, which extends poling of fibers with two anodes to ~50 and ~500 wire array anodes. The second harmonic microscopy observations show that second order nonlinearity (SON) layers are developed surrounding all the rings of wires in the ~50 anode array fiber with poling of 1.8kV, 250°C and 30min duration, and the outer rings of the ~500 anode array fiber at lower poling temperature. Our simulations based on a two-dimensional charge dynamics model confirm this can be explained by the self-adjustment mechanism, and show the SON layers are induced from the outer rings to the inner rings.

13.
Appl Opt ; 57(10): 2459-2466, 2018 Apr 01.
Artigo em Inglês | MEDLINE | ID: mdl-29714228

RESUMO

Luminescent solar concentrators (LSCs) utilizing stimulated emission by a seed laser are a promising approach to overcome the limitations of conventional LSCs, with a significant reduction of the photovoltaic material. In our previous work, we demonstrated the principle of a stimulated LSC (s-LSC) and correspondingly developed a model for quantifying the output power of such a system, taking into account different important physical parameters. The model suggested Perylene Red (PR) dye as a potential candidate for s-LSCs. Here, we experimentally investigate the gain of PR-doped polymethyl methacrylate (PMMA) required for s-LSCs using a single pump wavelength (instead of the solar spectrum) as a proof of principle. The results found from the experiment are well matched with the previously developed numerical model except for gain saturation, which occurs at a comparatively small seed laser signal power. To investigate the gain saturation, two approaches were taken: investigating (i) spectral hole burning and (ii) triplet state absorption. Experimental investigation of spectral hole burning with PR dyes showed a small effect on the gain saturation. We developed a general state model considering triplet state absorption of the PR dyes for the second approach. The state model suggests that the PR dyes suffer from significant triplet state absorption loss, which obstructs the normal operation of the PR-based s-LSC system.

14.
Eur J Orthop Surg Traumatol ; 28(1): 9-14, 2018 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-28798994

RESUMO

INTRODUCTION: Radiation exposure from intra-operative fluoroscopy in orthopaedic trauma surgery is a common occupational hazard. References for fluoroscopy use in the operating room for commonly performed operations have not been reported adequately. This study aimed to report appropriate intra-operative fluoroscopy use in orthopaedic trauma and compare the effect of surgery type and surgeon grade on radiation exposure. METHODS: Data on 849 cases over an 18-month period were analysed retrospectively. Median and 75th centile values for dose area product (DAP), screening time (ST), and number of fluoroscopy images were calculated for procedures where n > 9 (n = 808). RESULTS: Median DAP for dynamic hip screws for extracapsular femoral neck fractures was 668 mGy/cm2 (ST 36 s), 1040 mGy/cm2 (ST 49 s) for short proximal femoral nail, 1720 mGy/cm2 (ST 2 m 36 s) for long femoral nail for diaphyseal fractures, 25 mGy/cm2 (ST 25 s) for manipulation and Kirschner wire fixation in distal radius fractures, and 27 mGy/cm2 (ST 23 s) for volar locking plate fixation in distal radius fractures. These represented the five commonest procedures performed in the trauma operating room in our hospital. Experienced surgeons utilized less radiation in the operating room than junior surgeons (DAP 90.55 vs. 366.5 mGy/cm2, p = 0.001) and took fewer fluoroscopic images (49 vs. 66, p = 0.008) overall. CONCLUSIONS: This study reports reference values for common trauma operations. These can be utilized by surgeons in the operating room to raise awareness and perform clinical audits of appropriate fluoroscopy use for orthopaedic trauma, using this study as guidance for standards. We demonstrated a significant reduction in fluoroscopy usage with increasing surgeon experience.


Assuntos
Competência Clínica , Fluoroscopia , Fixação Interna de Fraturas/métodos , Fraturas Ósseas/cirurgia , Exposição Ocupacional , Doses de Radiação , Pinos Ortopédicos , Placas Ósseas , Parafusos Ósseos , Fios Ortopédicos , Fraturas do Colo Femoral/cirurgia , Fluoroscopia/efeitos adversos , Fixação Interna de Fraturas/instrumentação , Humanos , Período Intraoperatório , Exposição Ocupacional/prevenção & controle , Fraturas do Rádio/cirurgia , Valores de Referência , Estudos Retrospectivos
15.
Opt Lett ; 42(4): 819-822, 2017 Feb 15.
Artigo em Inglês | MEDLINE | ID: mdl-28198873

RESUMO

In thermally poled optical fibers, the second-order nonlinearity has been observed to be distributed in a narrow layer more than 10 µm beneath the anode surface, a result that cannot be explained by current models. In this Letter, we propose a new model based on slow migration of H3O+ and fast H+ migration related to the H3O+ concentration. The numerical simulation results show a narrow layer-shaped distribution of the induced second-order nonlinearity, which retains its magnitude and distribution profile in the migration process, and is in good agreement with the experimental observations.

16.
Eur J Appl Physiol ; 117(12): 2569-2577, 2017 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-29058112

RESUMO

PURPOSE: To examine the dose-response effects of acute glutamine supplementation on markers of gastrointestinal (GI) permeability, damage and, secondary, subjective symptoms of GI discomfort in response to running in the heat. METHODS: Ten recreationally active males completed a total of four exercise trials; a placebo trial and three glutamine trials at 0.25, 0.5 and 0.9 g kg-1 of fat-free mass (FFM) consumed 2 h before exercise. Each exercise trial consisted of a 60-min treadmill run at 70% of [Formula: see text] in an environmental chamber set at 30 °C. GI permeability was measured using ratio of lactulose to rhamnose (L:R) in serum. Plasma glutamine and intestinal fatty acid binding protein (I-FABP) concentrations were determined pre and post exercise. Subjective GI symptoms were assessed 45 min and 24 h post-exercise. RESULTS: Relative to placebo, L:R was likely lower following 0.25 g kg-1 (mean difference: - 0.023; ± 0.021) and 0.5 g kg-1 (- 0.019; ± 0.019) and very likely following 0.9 g kg- 1 (- 0.034; ± 0.024). GI symptoms were typically low and there was no effect of supplementation. DISCUSSION: Acute oral glutamine consumption attenuates GI permeability relative to placebo even at lower doses of 0.25 g kg-1, although larger doses may be more effective. It remains unclear if this will lead to reductions in GI symptoms. Athletes competing in the heat may, therefore, benefit from acute glutamine supplementation prior to exercise in order to maintain gastrointestinal integrity.


Assuntos
Proteínas de Ligação a Ácido Graxo/sangue , Glutamina/farmacologia , Temperatura Alta , Absorção Intestinal , Intestinos/fisiologia , Corrida/fisiologia , Administração Oral , Adulto , Relação Dose-Resposta a Droga , Glutamina/administração & dosagem , Glutamina/sangue , Humanos , Intestinos/efeitos dos fármacos , Lactose/sangue , Masculino , Ramnose/sangue
17.
Opt Express ; 24(26): A1546-A1559, 2016 Dec 26.
Artigo em Inglês | MEDLINE | ID: mdl-28059284

RESUMO

The efficiency improvement of luminescent solar concentrators (LSCs) necessary for practical realization is currently hindered by one major loss mechanism: reabsorption of emitted photons by the luminophores. Recently, we explored a promising technique for reducing reabsorption and also improving directional emission in LSCs utilizing stimulated emission, rather than only spontaneous emission, with an inexpensive seed laser. In this work, a model is developed to quantify the gain (i.e. the amount of amplification of a low power seed laser propagating through the solar-pumped concentrator) of stimulated-LSCs (s-LSCs) considering the effects of different important physical parameters. The net optical output power, available for a small PV cell, from the concentrator can also be determined from the model, which indicates the performance of s-LSCs. Finally, the performance of different existing material systems is investigated using literature values of the parameters required for the model, and a set of optimal parameters is suggested for practical realization of such a device.

18.
Opt Express ; 24(6): A497-505, 2016 Mar 21.
Artigo em Inglês | MEDLINE | ID: mdl-27136870

RESUMO

Luminescent solar concentrators (LSCs) are an emerging technology that aims primarily to reduce the cost of solar energy, with great potential for building integrated photovoltaic (PV) structures. However, realizing LSCs with commercially viable efficiency is currently hindered by reabsorption losses. Here, we introduce an approach to reducing reabsorption as well as improving directional emission in LSCs by using stimulated emission. Light from a seed laser (potentially an inexpensive laser diode) passes through the entire area of the LSC panel, modifying the emission spectrum of excited dye molecules such that it is spectrally narrower, at wavelengths that minimize reabsorption to allow net gain in the system, and directed towards a small PV cell. A mathematical model, taking into account thermodynamic considerations, of such a system is presented which identifies key parameters and allows evaluation in terms of net effective output power.

19.
Opt Express ; 24(16): 17989-8002, 2016 Aug 08.
Artigo em Inglês | MEDLINE | ID: mdl-27505766

RESUMO

Hyperlenses and hyperbolic media endoscopes can overcome the diffraction limit by supporting propagating high spatial frequency extraordinary waves. While hyperlenses can resolve subwavelength details far below the diffraction limit, images obtained from them are not perfect: resonant high spatial frequency slab modes as well as diffracting ordinary waves cause image distortion and artefacts. In order to use hyperlenses as broad-band subwavelength imaging devices, it is thus necessary to avoid or correct such unwanted artefacts. Here we introduce three methods, namely convolution, field averaging, and power averaging, to remove imaging artefacts over wide frequency bands, and numerically demonstrate their effectiveness based on simulations of a wire medium endoscope. We also define a projection in spatial Fourier space to effectively filter out all ordinary waves, leading to considerable reduction in image distortion. These methods are outlined and demonstrated for simple and complex apertures.

20.
Appl Opt ; 55(1): 178-83, 2016 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-26835639

RESUMO

The optical gain is measured in Perylene Red (PR)-doped polymethyl methacrylate (PMMA) slabs for copropagating and transverse pumping configurations based on a single-pass pump-probe method where a small signal is used as a probe beam. The gain is characterized in terms of the stimulated gain coefficient (g(S)) for both pump configurations. This material property determines the strength of pump absorption and coupling to the probe signal beam through stimulated emission. For copropagating pumping, g(S) was found to be (3.05±0.17)×10(-3) m/W for ∼0.05 mM PR-doped PMMA using a 633 nm probe laser, pumping with a 532 nm CW laser. For transverse pumping, g(S) was found to be (3.28±0.09)×10(-3) m/W for a ∼0.15 mM sample. The small difference in the gain coefficient is attributed to the difference in concentration. The stimulated gain coefficient, a material property of the gain medium independent of the pump configuration and experimental setup, offers a useful and convenient way to characterize the optical gain for solid-state lasers or amplifiers.

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