Computational Approach to Electrocatalysis

The main objective of this work is to understand the theoretical basis of the working principle of the Hydrogen fuel cell. We seek the physical basis of the Rational Design Technique, the smart way of preselecting materials from the material-pool, implemented in our study anticipating highly promising electrocatalysts for promoting the conversion of chemical energy stored in hydrogen molecules into the electrical energy. It needs the understanding of the relationship among the compositions of the materials under consideration, their electronic structure and catalytic activities. We performed the first principle DFT calculations to achieve the goal. Our work is focused first on the issues in hydrogen oxidation reaction taking place in anode compartment of the cell. Next comes up with the issues with Oxygen Reduction Reaction taking place in cathode compartment. Finally, we focus on mechanisms underlying binding of small molecules on substrates. Platinum perfectly catalyzes hydrogen oxidation reaction on the hydrogen fuel cell anodes. However, it has at least two drawbacks: a) it is too expensive; b) it has a low tolerance to CO poisoning. Pt-Ru bi-functional catalysts are more tolerant to CO, but they are still very expensive. In this work, we performed first-principle studies of stability and reactivity of M/W (110) structures, where M = Pd, Ru, Au monolayers. All three systems are found to be stable: formation energy of MLs is significantly higher than cohesive energy of the M-elements. The calculated binding energies of H, H2, OH, CO, and H2O were used to obtain the reaction free energies. Analysis of the free energies suggests that Au-W bonding does not activate sufficiently Au monolayer, whereas Ru/W (110) is still too reactive for the CO removal. Meanwhile, Pd/W (110) is found to catalyze hydrogen oxidation and at the same time to be highly tolerant to the CO poisoning. The latter finding is explained by the fact that CO binds much weaker to Pd on W (110) than to Pt, while the OH binding is strong enough to ensure CO oxidation. The obtained results are traced to the electronic structure of the systems. Oxygen Reduction Reaction (ORR) is the heart core reaction in fuel cells, Proton Exchange Membrane Fuel cell and DEMFC. However, the reaction is not so obvious and need suitable electrocatalyst. Pt or Pt-based catalysts are found to be the best catalyst so far. But, its cost and shortage make it not feasible economically. Moreover, lower onset potential (maximal electrode potential at which the reaction can proceed) of such catalysts is offering another limitation to fuel cell performance. Research has been conducted in many directions for lowering the cost by replacing the Pt with some other elements of lower cost or reducing the Pt-load in the material; and even more finding the material performing better than Pt. In this paper, we’ve tried to understand the ORR mechanism and look for the material that could be potential option to Pt. Our calculations suggest that for monolayer of Pt on 5 layered slab of Nb or Mo the onset potential is the same as for Pt, while cost of these systems are much lower than that of Pt. Presence of water changes the reaction rate very minimum. Rational design method facilitates the research of selecting the appropriate catalyst and saves time and effort significantly. The result shows that the d-band center model is not accurate to describe the reactivity of the catalyst. For decades, adsorbates’ binding energy (EB) has been used as an indicator of the adsorbate-substrate bond strength (EBF). Thus, although one can compute accurately any E models to gauge bond-strength are developed and applied to rationalize and anticipate EB\u27s because that is a key aspect in the rational search for efficient catalysts. Yet bond-strength alone fails to predict EB trends. Therefore, quantifying and understanding the difference between EB and EBF is essential to catalysts design. Indeed, the adsorbate-substrate bond formation perturbs the substrate’s electronic charge density, which reduces EB by the energy attached to such perturbation:Epert. Here, with the example of carbon monoxide adsorption on metal-doped graphene, we show that Epert may exceed 1 eV and render an unusual situation: although the EB of CO to the Au-doped graphene indicates that binding does not happen, we find evidence of a strong bond between CO and the substrate. Thus, in this case, the large Epert totally disrupt the equivalency between EBF and EB we also propose a method to compute Epert that bypasses dealing with an excited electronic state of the system

Tunability of the topological nodal-line semimetal phase in ZrSiX-type materials

The discovery of a topological nodal-line (TNL) semimetal phase in ZrSiS has invigorated the study of other members of this family. Here, we present a comparative electronic structure study of ZrSiX (where X = S, Se, Te) using angle-resolved photoemission spectroscopy (ARPES) and first-principles calculations. Our ARPES studies show that the overall electronic structure of ZrSiX materials comprises of the diamond-shaped Fermi pocket, the nearly elliptical-shaped Fermi pocket, and a small electron pocket encircling the zone center ($\Gamma$) point, the M point, and the X point of the Brillouin zone, respectively. We also observe a small Fermi surface pocket along the M-$\Gamma$-M direction in ZrSiTe, which is absent in both ZrSiS and ZrSiSe. Furthermore, our theoretical studies show a transition from nodal-line to nodeless gapped phase by tuning the chalcogenide from S to Te in these material systems. Our findings provide direct evidence for the tunability of the TNL phase in ZrSiX material systems by adjusting the spin-orbit coupling (SOC) strength via the X anion.Comment: 7 pages, 4 figure

Chapter 12 - Human settlements, infrastructure and spatial planning

Urbanization is a process that involves simultaneous transitions and transformations across multiple dimensions, including demographic, economic, and physical changes in the landscape. Each of these dimensions presents different indicators and definitions of urbanization. The chapter begins with a brief discussion of the multiple dimensions and definitions of urbanization, including implications for GHG emissions accounting, and then continues with an assessment of historical, current, and future trends across different dimensions of urbanization in the context of GHG emissions (12.2). It then discusses GHG accounting approaches and challenges specific to urban areas and human settlements. In Section 12.3, the chapter assesses the drivers of urban GHG emissions in a systemic fashion, and examines the impacts of drivers on individuals sectors as well as the interaction and interdependence of drivers. In this section, the relative magnitude of each driver's impact on urban GHG emissions is discussed both qualitatively and quantitatively, and provides the context for a more detailed assessment of how urban form and infrastructure affect urban GHG emissions (12.4). Here, the section discusses the individual urban form drivers such as density, connectivity, and land use mix, as well as their interactions with each other. Section 12.4 also examines the links between infrastructure and urban form, as well as their combined and interacting effects on GHG emissions. Section 12.5 identifies spatial planning strategies and policy instruments that can affect multiple drivers, and Section 12.6 examines the institutional, governance, and financial requirements to implement such policies. Of particular importance with regard to mitigation potential at the urban or local scale is a discussion of the geographic and administrative scales for which policies are implemented, overlapping, and / or in conflict. The chapter then identifies the scale and range of mitigation actions currently planned and / or implemented by local governments, and assesses the evidence of successful implementation of the plans, as well as barriers to further implementation (12.7). Next, the chapter discusses major co-benefits and adverse side-effects of mitigation at the local scale, including opportunities for sustainable development (12.8). The chapter concludes with a discussion of the major gaps in knowledge with respect to mitigation of climate change in urban areas (12.9)

Gestational Age Specific Postnatal Growth Curves for Singleton Babies in Tertiary Hospital of Western Nepal

Introduction: Measurement of birth weight (BW), crown heel length (CHL), head circumference (HC) and chest circumference used to assess the intrauterine growth of a baby vary with altitude, race, gender, socio economic status, maternal size, and maternal diseases. The study aimed to construct centile charts for BW, CHL and HC for new born at different gestational ages in western Nepal. Methods:  This was a descriptive cross sectional study done over a period of 15 months in a tertiary care hospital of western Nepal. BW, length, HC and CC were measured within 12-24 hours of birth. Gestational age was estimated from first day of last menstrual period, maternal ultrasonology and New Ballard’s scoring system. Microsoft 2007 Excel and SPSS-16 was used for data analysis. Cole’s Lambda Mu Sigma method was used for constructing centile curves. Results: Out of 2000 babies analysed, 1910 samples were used to construct smoothed intrauterine growth curve of BW, CHL, and HC from 33-42 weeks of gestation. 57.35% (1147) were male, mean gestational age was 38.13 ±2.44 weeks, where 21.5% were preterm and 1.7% post term. The means of BW, CHL, HC and CC were 2744.78 gm, 47.80 cm, 33.18 cm, and 30.20 cm with standard deviations of 528.29, 3.124, 1.78, and 2.35 respectively. These data vary as compared to the Kathmandu data, in case of birth weight for 10th and 90th centiles, and at 90th centile in case of length. Conclusions: This necessitates the update in the existing growth charts and develop in different geographical regions of a country

Observation of the spin-polarized surface state in a noncentrosymmetric superconductor BiPd

Recently, noncentrosymmetric superconductor BiPd has attracted considerable research interest due to the possibility of hosting topological superconductivity. Here we report a systematic high-resolution angle-resolved photoemission spectroscopy (ARPES) and spin-resolved ARPES study of the normal state electronic and spin properties of BiPd. Our experimental results show the presence of a surface state at higher-binding energy with the location of Dirac point at around 700 meV below the Fermi level. The detailed photon energy, temperature-dependent and spin-resolved ARPES measurements complemented by our first principles calculations demonstrate the existence of the spin polarized surface states at high-binding energy. The absence of such spin-polarized surface states near the Fermi level negates the possibility of a topological superconducting behavior on the surface. Our direct experimental observation of spin-polarized surface states in BiPd provides critical information that will guide the future search for topological superconductivity in noncentrosymmetric materials.Comment: 30 pages, 12 figures, Expanded version of arXiv:1505.03466, To appear in Nature Communication

On The Elusive Link Between Adsorbate\u27S Binding Energy And Bond Strength: An Illustration From Co Adsorption On Metal-Doped Graphene

Adsorbates’ binding energy is often used as an indicator of the adsorbate-substrate bond strength. Although one can compute any binding energy, models to gauge bond-strength are developed to rationalize and anticipate it for the rational search for efficient catalysts. Unfortunately, bond-strength alone fails to predict trends in binding energy because, as hinted by models since the 1970s, the binding energy is the outcome of a complex response of the system to the created bond. Therefore further understanding the difference between binding energy and bond strength is essential to catalysts design. Indeed, the adsorbate-substrate bond formation perturbs, not only the geometry of the system, but also the substrate and adsorbate\u27s electronic charge density. Both effects overall reduce the binding energy by an energy attached to such perturbations, the so-called perturbation energy. Here, with the example of carbon monoxide adsorption on metal-doped graphene, we show that such perturbation energy may exceed 1 eV and render an unusual situation: Namely, although the binding energy of CO to the Au-doped graphene indicates that binding does not happen, we find evidence of a strong bond between CO and such substrate. Thus, in this case, the large perturbation energy totally disrupts the equivalency between bond strength and binding energy. Here we propose a method to compute the perturbation energy that bypasses dealing with an excited electronic state of the system

Comparative Study of Chikungunya Only and Chikungunya-Scrub Typhus Coinfection in Children: Findings from a Hospital-Based Observational Study from Central Nepal

Objectives. Chikungunya and scrub typhus infection are important causes of undifferentiated fever in tropical zones. The clinical manifestations in both conditions are nonspecific and often overlap. This study compares the clinical manifestations and the outcome of chikungunya with chikungunya-scrub typhus coinfection in children. Methods. A hospital-based observational study was conducted in children below 15 years of age over 16-month duration in 2017-2018. Chikungunya was diagnosed by IgM ELISA. All positive chikungunya cases were subjected to scrub typhus testing, dengue testing, leptospira testing, and malaria testing. Clinical manifestations and outcomes of all patients were recorded. Results. Out of the 382 admitted cases with fever, 11% (n=42) were diagnosed with chikungunya, and the majority (n=30, 71.4%) were male. Among the 42 chikungunya cases, 17 (40.5%) tested positive for scrub typhus and one positive for falciparum malaria. Out of a total of 42 chikungunya cases, myalgia, nausea/vomiting, headache, abdominal pain, lymphadenopathy, hepatomegaly, splenomegaly, and edema were 81%, 73.8%, 66.7%, 64.3%, 59.5%, 52.4%, 40.5%, and 38.1%, respectively. Besides, altered sensorium (31%), jaundice (26.2%), dry cough (21.4%), shortness of breath (19%), and seizures (16.7%) were other clinical manifestations present in this group of children. Patients with chikungunya-scrub typhus coinfection reported headaches, pain in the abdomen, dry cough, shortness of breath, seizures, and splenomegaly, significantly more (p value < 0.05) compared to those with chikungunya only. Thirteen (31%) children developed shock, five in the chikungunya group and eight in the chikungunya-scrub typhus coinfection group. Six children in the coinfection group received inotrope. Among the chikungunya-only cases, 22 recovered and one died, whereas in the chikungunya-scrub typhus coinfection group, fourteen recovered and three died. Conclusions. Both the chikungunya and scrub typhus coinfection groups shared many similar clinical manifestations. In children, coinfection with scrub typhus often leads to modification of the clinical profile, complications, and chikungunya outcome

Observation of Dirac-like semi-metallic phase in NdSb

The search of new topological phases of matter is one of the new directions in condensed matter physics. Recent experimental realizations of Dirac semimetal phases pave the way to look for other exotic phases of matter in real materials. Here we present a systematic angle-resolved photoemission spectroscopy (ARPES) study of NdSb, a potential candidate for hosting a Dirac semi-metal phase. Our studies reveal two hole-like Fermi surface pockets present at the zone center ($\Gamma$) point as well as two elliptical electron-pockets present in the zone corner (X) point of the Brillouin zone (BZ). Interestingly, Dirac-like linearly dispersive states are observed about the zone corner (X) point in NdSb. Our first principles calculations agree with the experimentally observed bands at the $\Gamma$ point. Moreover, the Dirac-like state observed in NdSb may be a novel correlated state, not yet predicted in calculations. Our study opens a new direction to look for Dirac semi-metal states in other members of the rare earth monopnictide family.Comment: 6 pages, 3 figures, To appear in Journal of Physics: Condensed Matte

Reducing mental illness stigma in healthcare settings:Proof of concept for a social contact intervention to address what matters most for primary care providers

Initiatives for integration of mental health services into primary care are underway through the World Health Organization’s mental health Gap Action Programme (mhGAP) and related endeavors. However, primary healthcare providers’ stigma against persons with mental illness is a barrier to success of these programs. Therefore, interventions are needed to reduce stigma among primary healthcare providers. We developed REducing Stigma among HealthcAre ProvidErs (RESHAPE), a theoretically-grounded intervention that draws upon the medical anthropology conceptual framework of “what matters most.” RESHAPE addresses three domains of threats to what matters most: survival, social, and professional. In a proof-of-concept study, mental health service users and aspirational healthcare providers (primary healthcare providers actively incorporating mental health services) were trained to co-facilitate the RESHAPE intervention embedded within mhGAP training in Nepal. Two trainings with the RESHAPE anti-stigma component were held with 41 primary healthcare providers in Nepal. Evaluation of the training included four focus groups and 25 key informant interviews. Stigmatizing attitudes and role play-based clinical competency, assessed with the ENhancing Assessment of Common Therapeutic factors tool (ENACT), were evaluated pre-training and followed-up at four and 16 months. The study was conducted from February 2016 through June 2017. In qualitative interviews, primary healthcare providers described changes in perceptions of violence (survival threats) and the ability to treat mental illness effectively (professional threats). Willingness to interact with a person with mental illness increased from 54% pre-training to 81% at 16 months. Observed clinical competency increased from 49% pre-training to 93% at 16-months. This proof-of-concept study supports reducing stigma by addressing what matters most to healthcare providers, predominantly through mitigating survival and professional threats. Additional efforts are needed to address social threats. These findings support further exploration of service user and aspirational figure involvement in mhGAP trainings based on a “what matters most” conceptual framewor