Optical Spectroscopy of Excitons at the Interfaces of Nanostructures

Atomically thin quasi-two-dimensional materials like graphene and transition metal dichalcogenide (TMDC) layers exhibit extraordinary optical and electrical properties. They have not only been used as testing grounds for fundamental research but also show promise for their viability in optoelectronics, photovoltaics and photocatalysis, to name a few technological applications. In practice, seldom are these materials used in isolation. One often finds them as part of a multicomponent structure, or heterostructure. In a similar spirit as the influence of solvents on the properties of molecular complexes, nanomaterials are also affected by their dielectric environment. Engineering the effect of the surroundings on the excitations in these materials is both a challenge and an opportunity. Moreover, understanding the transport of energy and charge through these heterostructures is crucial for device design. In this dissertation I will explore the properties of excitations in zero-dimensional and two-dimensional nanostructures and their dependence on the details of the environment using optical spectroscopy. Here, I discuss three of the projects that I undertook during my graduate studies. The first project concerns the efficient near-field, non-radiative energy transfer (NRET) of photo-excited carriers from semiconductor nanocrystals to graphene and a TMDC, molybdenum disulfide. Photoluminescence quenching of single quantum dots and time-resolved photoluminescence were used to quantify the rate of energy transfer. The NRET rate exhibited surprisingly opposite trends with increasing number of layers of the acceptor 2D sheet. The rate increased with increasing thickness of adjacent graphene layers but decreased with increasing thickness of MoS₂. A model based on classical electromagnetism could successfully explain the countervailing trends in terms of the competition between the dissipative channels and reduction of the electric field within the 2D material. In the next project, the exciton binding energy and band gap in another TMDC, monolayer WS₂, were tuned via dielectric screening from the environment. Monolayers of WS₂ were capped with graphene layers of varying thickness (1 – 4 layers). The excitonic states of WS₂ in the resulting heterostructures were detected using reflectance contrast spectroscopy and theoretically studied by a semi-classical model. The binding energy of the exciton was halved to 150 meV by placement of a single layer of graphene adjacent to the WS₂. Furthermore, this dramatic decrease in the binding energy is accompanied by a reduction of the band gap by the same amount. Additionally, the average spacing between the graphene and WS₂ was also identified to be a critical parameter with respect to dielectric screening of the electron - hole interaction. This offers a flexible alternative for the external manipulation of the Coulomb interaction. In the final part, I study how excitons in WS₂ couple and scatter with the excitations of the lattice or phonons. The importance of this study stems from the contribution of the scattering rates to the spectral width of the excitonic feature, the dephasing dynamics and thermal transport. The transition from direct to indirect band gap semiconductor from mono- to bilayer is expected to add an additional scattering channel via phonon emission. Through temperature dependent reflectance contrast and photoluminescence spectroscopy, the scattering rate for the phonon emission and absorption processes have been quantified. Comparing the results to data reported in the literature, it is understood that the striking change for the scattering rates is expected only at the mono- to bilayer transition for WS₂. The results suggest material thickness as a handle for engineering exciton - phonon interactions at the nanoscale

Primary cesearean section in multigravidas

Background: Cesarean section is one of the widely performed surgical procedures across the world. Cesarean section is associated with increased risk of maternal morbidity and mortality, despite remarkable improvements in the safety. The objective of the present study is to study the cesearean section in the context of various indications, parity, intraoperative complications, post-operative morbidity, and perinatal morbidity among multigravidae undergoing cesarean section for first time.Methods: The present study was carried out at Yenepoya medical college hospital. All multigravidas who had delivered vaginally once or more and who underwent primary caesarean sections for the first time during time period of August 2015-May 2016 were included in study and various factors are analyzed.Results: In our study most of primary cesearean sections were in second paras who constituted 50%, followed by 4/> paras constituting 29.54%, and it was observed that incidence in third paras was 20.45%. 75% of the patients underwent emergency cesearean section and 25% had elective ceserean section. The most common indication for cesearean in our study was observed to be fetal distress accounting for 25% of the cases, 2nd most common being malpresentations (19.31%), non-progress of labor constituting 11.36% of cases. Intra operative complications were noted in 6.81% of cases, most common complication being extension of uterine incision extension of uterine incision.Conclusions: Complications may occur in women who previously had a normal vaginal delivery requiring interventions in the form of caesarean section and is not uncommon. Though to a small extent, they are contributing to rise is total caesarean section rates seen. There are many cases where a caesarean becomes mandatory for her. The fact that a multipara who has had one or more vaginal deliveries should be regarded as an optimistic historical fact, not as diagnostic-criteria for spontaneous delivery of the pregnancy at hand. A parous woman needs good obstetric care to improve maternal and neonatal outcome and still keeping caesarean section to a lower rate

Antibiotic Resistance Pattern of Shigella spp. Among Gastroenteritis Patients at Tertiary Care Hospital in Pokhara, Nepal

Shigellosis, a disease caused by Shigella species. It is a major public health problem in developing nations like Nepal, where communities having poverty; poor sanitation, personal hygiene, and water supplies. The main aim of our study is to isolate and identify Shigella spp. from gastroenteritis patients and to find out its drug resistance pattern.A cross-sectional study was carried out based on routinely attending outpatients and inpatients.  A total of 225 stool samples collected from gastroenteritis patients were processed from 20 April to 24 September 2014 in Western Regional Hospital, Pokhara, Nepal. Standard microbiological procedures were followed for the isolation of Shigella spp. After that slide agglutination kit method was used for identification of Shigella spp.  Finally, Kirby-Bauer disc diffusion method was done for an antimicrobial resistance test.Of the total 225 gastroenteritis patients, 133 were detected as bacterial positive cases.  Among positive cases, Shigella spp. was identified in 10.5%.  Age wise, an infection rate of Shigella in patients <15-years old was found higher i.e. 7.3% than in patients ≥ 15 years old i.e. 4.5% with the (p = 0.432) at 95% CI. The infection rate of S. dysenteriae, S. flexneri, and S. sonnei was detected in 28.6%, 57.1%, and 14.3% respectively. For the antimicrobial test, eight types of antibiotics were used.  The most resistance pattern of isolated Shigella spp. was found in nalidixic acid, and co-trimoxazole 92.8% followed by ampicillin 64.3% and ciprofloxacin 42.8% etc.Our study reported that endemicity of Shigellosis with S. flexneri is the predominant group in gastroenteritis patients. This finding suggests that co-trimoxazole, nalidixic acid, ciprofloxacin and ampicillin should not be used experimentally as first-line drugs for shigellosis treatment

Idiopathic multicentric Castleman disease: a mysterious case of generalized lymphadenopathy

Castleman disease is a syndrome with significant clinico-pathological overlap between malignancy, autoimmune causes and infectious etiologies. It is a spectrum and can vary in extent from unicentric to multicentric disease with generalized lymphadenopathy, organ involvement, constitutional symptoms and cytopenias, and in severity from non-severe to severe disease with TAFRO symptoms. Idiopathic multicentric Castleman disease (iMCD) is a diagnosis of exclusion after multiple causes as per diagnostic criteria are excluded. Treatment varies between the disease severity types with anti-IL 6 antibodies for non-severe disease to cytotoxic chemotherapy agents for severe disease with TAFRO symptoms. We hereby report a case of a non-severe type of iMCD with a prolonged course and delayed arrival at the diagnosis, owing to the rarity of this condition, which stresses the need for a reduced threshold to consider MCD, early in the differential diagnosis. Interestingly there were positive auto-antibodies and elevated IgG4 levels in this patient, but applying strict criteria helps to distinguish the diagnosis

Development of a panel of recombinase polymerase amplification assays for detection of common bacterial urinary tract infection pathogens

Aims: To develop and evaluate the performance of a panel of isothermal real?time recombinase polymerase amplification (RPA) assays for detection of common bacterial urinary tract infection (UTI) pathogens. Methods and Results: The panel included RPAs for Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, Pseudomonas aeruginosa and Enterococcus faecalis. All five RPAs required reaction times of under 12 min to reach their lower limit of detection of 100 genomes per reaction or less, and did not cross?react with high concentrations of nontarget bacterial genomic DNA. In a 50?sample retrospective clinical study, the five?RPA assay panel was found to have a specificity of 100% (95% CI, 78�0%) and a sensitivity of 89% (95% CI, 75�%) for UTI detection. Conclusions:The analytical and clinical validity of RPA for the rapid and sensitive detection of common UTI pathogens was established. Significance and Impact of the Study: Rapid identification of the causative pathogens of UTIs can be valuable in preventing serious complications by helping avoid the empirical treatment necessitated by traditional urine culture's 48�?h turnaround time. The routine and widespread use of RPA to supplement or replace culture?based methods could profoundly impact UTI management and the emergence of multidrug?resistant pathogens

Advancements in Solar-Powered UAV Design Leveraging Machine Learning: A Comprehensive Review

Unmanned Aerial Vehicles (UAVs), commonly known as drones, have seen significant innovations in recent years. Among these innovations, the integration of solar power and machine learning has opened up new horizons for enhancing UAV capabilities. This review article provides a comprehensive overview of the state-of-the-art in solarpowered UAV design and its synergy with machine learning techniques. We delve into the various aspects of solar-powered UAVs, from their design principles and energy harvesting technologies to their applications across different domains, all while emphasizing the pivotal role that machine learning plays in optimizing their performance and expanding their functionality. By examining recent advancements and challenges, this review aims to shed light on the future prospects of this transformative technology