Thermoelectric transport properties of nanostructured FeSb2 and Ce-based heavy-fermions CeCu6 and CeAl3

Thesis advisor: Cyril P. OpeilThermoelectric (TE) energy conversion is an all-solid-state technology which can convert waste thermal energy into useful electric power and cool ambience without using harmful gases like CFC. Due to their several advantages over traditional energy conversion technologies, thermoelectric generators (TEG) and coolers (TEC) have drawn enormous research efforts. The objective of this work is to find promising materials for thermoelectric cooling applications and optimize their thermoelectric performances. Finding a material with a good value for the thermoelectric figure-of-merit (ZT) at cryogenic temperatures, specifically below 77 K, has been of great interest. This work demonstrates that FeSb2, CeCu6 and CeAl3, all belonging to a class of materials with strongly correlated electron behavior; exhibit promising thermoelectric properties below 77 K. In general, ZT of a TE material can be increased using two basic approaches: lattice thermal conductivity reduction and power factor (PF) enhancement. The results of this study indicate that nanostructuring effectively decreases the thermal conductivity of FeSb2, CeCu6 and CeAl3 leading to improved ZT. The approach of introducing point-defect scattering to further reduce the thermal conductivity is successfully implemented for Te-substituted FeSb2 nanostructured samples. A semiconductor/metal interface has long been proposed to exhibit enhanced thermoelectric properties. We use this technique by introducing Ag-nanoparticles in the host FeSb2 which further increases ZT by 70%. Additionally, a detailed investigation is made on the phonon-drag effect as a possible mechanism responsible for the large value of the Seebeck coefficient of FeSb2. We show that the phonon-drag mechanism contributes significantly to the large Seebeck effect in FeSb2 and hence this effect cannot be minor as was proposed in literatures previously. A model based on Kapitza-resistance and effective medium approach (EMA) is used to analyze the thermal conductivities of nanostructured FeSb2 samples. We find a notably large value for Kapitza length at low temperatures indicating the dominance of inter-grain thermal resistance over bulk thermal resistance in determining the thermal properties of FeSb2.Thesis (PhD) — Boston College, 2015.Submitted to: Boston College. Graduate School of Arts and Sciences.Discipline: Physics

Spin ordering and electronic texture in the bilayer iridate Sr3_3Ir2_2O7_7

Through a neutron scattering, charge transport, and magnetization study, the correlated ground state in the bilayer iridium oxide Sr$_3$Ir$_2$O$_7$ is explored. Our combined results resolve scattering consistent with a high temperature magnetic phase that persists above 600 K, reorients at the previously defined $T_{AF}=280$ K, and coexists with an electronic ground state whose phase behavior suggests the formation of a fluctuating charge or orbital phase that freezes below $T^{*}\approx70$ K. Our study provides a window into the emergence of multiple electronic order parameters near the boundary of the metal to insulator phase transition of the 5d $J_{eff}=1/2$ Mott phase.Comment: Revised text and figures. 4 pages, 4 figure

Carrier localization and electronic phase separation in a doped spin-orbit driven Mott phase in Sr3(Ir1-xRux)2O7

Interest in many strongly spin-orbit coupled 5d-transition metal oxide insulators stems from mapping their electronic structures to a J=1/2 Mott phase. One of the hopes is to establish their Mott parent states and explore these systems' potential of realizing novel electronic states upon carrier doping. However, once doped, little is understood regarding the role of their reduced Coulomb interaction U relative to their strongly correlated 3d-electron cousins. Here we show that, upon hole-doping a candidate J=1/2 Mott insulator, carriers remain localized within a nanoscale phase separated ground state. A percolative metal-insulator transition occurs with interplay between localized and itinerant regions, stabilizing an antiferromagnetic metallic phase beyond the critical region. Our results demonstrate a surprising parallel between doped 5d- and 3d-electron Mott systems and suggest either through the near degeneracy of nearby electronic phases or direct carrier localization that U is essential to the carrier response of this doped spin-orbit Mott insulator.Comment: 25 pages, 4 figures in main text, 4 figures in supplemental tex

Classroom Management: Glocalized Contexts

This research based article discusses on issues and practices of classroom management from the local perspectives. It is based on the context of public school of Nepal. The participant is an EFL teacher of public school in Kathmandu, teaching in middle school and secondary level there. The classroom management practices in the EFL teacher’s classes are seen using classroom observation tool, in her classes of both the levels for a week using qualitative framework. The findings show the traditional practice still dominating the classroom activities. Therefore the article is based on the issues of classroom management being specific to the seating arrangements, discipline, peer work, group work, space, presentation, and time management in the public school where classroom observation has been done

Myocardial infarction with nonobstructive coronaries (MINOCA) following rabies postexposure prophylaxis: A case report

Key Clinical Message This case underscores the importance of considering myocardial infarction with nonobstructive coronary arteries (MINOCA) in patients experiencing acute chest pain following rabies vaccination, emphasizing the need for heightened awareness and further research into the association between MINOCA and Rabies vaccination. Abstract Rabies is a vaccine‐preventable deadly viral disease prevalent in Asia and Africa that causes thousands of deaths annually. Rabies pre (PrEP) and postexposure prophylaxis (PEP) is highly effective in annulling rabies‐associated deaths. The adverse reactions following rabies vaccination are typically mild. Myocardial infarction with non‐obstructive coronary arteries (MINOCA) is a rare condition, and its association with rabies vaccination is unprecedented. We present a case of a 43‐year‐old male with MINOCA following Rabies PEP. A 43‐year‐old male, nonsmoker and nonalcoholic, presented to the ER with complaints of acute onset left sided chest pain following the completion of the third dose of intradermal rabies vaccine, whose clinical features, ECG changes and lab reports were suggestive of acute presentation of inferior wall MI. Coronary angiography was performed, which however revealed normal coronaries with only slow flow being noted in the left anterior descending (LAD) artery. Echocardiography later showed a normal study with no other relevant diagnosis unveiled on further investigations. Hence a diagnosis of vaccine‐induced MINOCA was made. Treatment included antiplatelet therapy, statins, and beta‐blockers. MINOCA following rabies vaccination is an unprecedented finding. The clear etiology behind this couldn't be ascertained. The patient's treatment was conventional, emphasizing the need for further research and clinical trials in MINOCA diagnosis and management. This case highlights the need for clinicians to consider MINOCA in patients with acute chest pain post‐rabies vaccination. Further research is essential to unravel the association between MINOCA and rabies vaccination, paving the way for optimal management strategies

Prevalence of and risk factors for diabetic retinopathy among the patients with diabetes mellitus in Dharan municipality, Nepal

Background &amp; Objectives: The individuals with diabetes have 29 times higher chance of becoming blind due to diabetic retinopathy than non-diabetic of similar age and gender. The knowledge on the factors for it can help detect the disease in its early course. The study was conducted with objectives to study the prevalence of diabetic retinopathy and its risk factors in a diabetic population.Materials and Methods: A community based cross-sectional study that involved 418 subjects with type 2 diabetes, living in the Dharan municipality of Nepal was carried out using convenient sampling method.Results: The prevalence of diabetic retinopathy was 38.8%. Prevalence of mild, moderate, severe and very severe non-proliferative diabetic retinopathy was 9.1%, 16.3%, 6.2% and 17.2% respectively. Prevalence of proliferative diabetic retinopathy and clinically significant macular edema was 3.8% and 1.9% respectively. Among the risk factors studied age, hypoglycemic drug intake, family history and duration of diabetes mellitus had a significant association with the occurrence of diabetic retinopathy (p&lt;0.05).Conclusions: The prevalence of diabetic retinopathy in patients with diabetes mellitus was 38.8% and increase risk factors for it are age, hypoglycemic drug intake, family history of diabetes, duration of diabetes.JCMS Nepal. 2015;11(1): 17-21</p

Toxoplasma gondii bradyzoites and tachyzoites isolation from vitreous of atypical necrotizing retinitis

Abstract Background Detection of Toxoplasma gondii cysts in vitreous of immunocompetent patient with necrotizing retinitis is extremely rare. We herein report the isolation of Toxoplasma bradyzoites and tachyzoites from the vitreous of healthy person. Results A 19-year-old immunocompetent female presented with sudden loss of vision in left eye since 1 week. The BCVA was 6/6 and HM in right and left eye. The left eye finding was suggestive of diffuse necrotizing retinitis with retinal detachment. The IgM and IgG for TORCH infection were negative and HIV, HCV and HBsAg tests were also non reactive. The patient underwent diagnostic and therapeutic vitrectomy with silicon oil installation. The vitreous toxoplasma IgG titre was found to be significantly raised to 1:16. Bradyzoites of toxoplasma were identified in H&E staining and tachyzoites of Toxoplasma were identified in Giemsa staining of vitreous sample. She received oral clindamycin and oral corticosteroid but the vision could not be restored in left eye. Conclusion Hence, atypical toxoplasmosis with necrotizing retinitis is a fulminant condition with the diagnostic and therapeutic challenge

Clinicomycological Characterization of Superficial Mycoses from a Tertiary Care Hospital in Nepal

Background. Superficial mycosis is a common fungal infection worldwide, mainly caused by dermatophytes. However, the prevalence of species varies geographically. In addition, fungal treatment is best guided according to species isolated. This study was carried out to determine the clinical as well as mycological profile of superficial mycoses in a tertiary care hospital, Nepal. Methods. This was a prospective case-control laboratory based study conducted over a period of six months from January to June 2014 at Tribhuvan University Teaching Hospital, Nepal. A total of 200 specimens were collected from the patients suspected of superficial mycoses. The specimens were macroscopically as well as microscopically examined. The growth was observed up to 4 weeks. Results. Out of total 200 specimens from the patients suspected of superficial mycoses, tinea corporis 50 (25%) was most common clinical types. KOH mount was positive in 89 (44.5%) and culture was positive in 111 (55.5%). Trichophyton mentagrophytes 44 (39.6%) was the most common isolate. Conclusions. The diagnostic yields of KOH mount and culture were found to be complementary to each other. Thus both the methods added with clinical findings are equally important to establish superficial mycosis