Au & Pd surfaces: From capping agents to methane oxidation

This thesis uses Density Functional Theory (DFT) to study the applications of transition metal surfaces in the fields of catalysis and nanoparticle synthesis. Chapter 1 provides the reader with a detailed literature review on methane oxidation, methanol synthesis, and an outlook on the different catalysts that have been used for methane activation. Chapter two then addresses the theoretical background of DFT and the different methods used. The work produced in this thesis is then split into two main sections: Section 1 which encompasses chapters 3 and 4 covers the partial oxidation of methane to methanol on Au and Pd surfaces. By modelling two low index surfaces of Au and Pd, we studied the partial oxidation of methane to methanol using hydrogen peroxide and molecular oxygen as oxidants. We performed a detailed study of the reaction mechanism by modelling the adsorption of intermediary species and the activation energy barriers for each of the steps. The results obtained were then used to explain why the alloy is catalytically superior to the pure metals and the different steps at which the pure surfaces fail to catalyse. Once identified, we then model doped surfaces in order understand how the alloy would tackle the problems associated with the pure metal surfaces. The results obtained show that the Pd surfaces are too active for molecular oxygen to an extent that upon adsorption, the molecule cleaves on the surface with a small barrier to from two oxygen metal-bound atoms. The Au surfaces on the other hand, show an opposite effect with a very endothermic energy of reaction for the displacement of water by molecular oxygen. Upon modelling the doped system, an improved binding of molecular oxygen on the Pd-doped Au surfaces is observed along with a decrease in the affinity of the Au-doped Pd surfaces to molecular oxygen. Section 2 which comprises of chapter 5 discusses the use of capping agents in nanoparticle synthesis. The chapter first describes the importance of the use of capping agents in the stabilisation of nanoparticles in nanoparticle synthesis. Hetero-atom containing ligands provide a main class of capping agents used experimentally and thus using DFT, we study how aminopropanol can be used as a capping agent for the synthesis of Pd nanoparticles. By modelling the adsorption of aminopropanol on Pd surfaces and plotting IR spectra, we rationalise how aminopropanol, a ligand made of two heteroatoms, binds to Pd nanoparticles. Our adsorption energies and IR spectra show that 3-amino-propan-1-ol prefers viii to bind to the Pd surfaces through the amino-group. This was further supported by a comparison of the computed IR and experimental spectra which show strong correlation. Chapter 6 provides general conclusions regarding the significance of the results in all three chapter

Numerical study of turbulent normal diffusion flame CH4-air stabilized by coaxial burner

The practical combustion systems such as combustion furnaces, gas turbine, engines, etc. employ non-premixed combustion due to its better flame stability, safety, and wide operating range as compared to premixed combustion. The present numerical study characterizes the turbulent flame of methane-air in a coaxial burner in order to determine the effect of airflow on the distribution of temperature, on gas consumption and on the emission of NOx. The results in this study are obtained by simulation on FLUENT code. The results demonstrate the influence of different parameters on the flame structure, temperature distribution and gas emissions, such as turbulence, fuel jet velocity, air jet velocity, equivalence ratio and mixture fraction. The lift-off height for a fixed fuel jet velocity is observed to increase monotonically with air jet velocity. Temperature and NOx emission decrease of important values with the equivalence ratio, it is maximum about the unity

The impact of conventional and nonconventional inhalants on children and adolescents

AimInhalant abuse in the adolescent population is a growing concern for care givers, communities, physicians, and medical providers. The aim of this article is to provide a review of the literature about this new challenge. In addition, it raises awareness about recent health policy rulings.MethodsReview of the literature was done.ResultsIn this review article, the prevalence of different modes of inhalant use and abuse in children and young adults and their potential health implications will be examined: Cigarettes, ENDS (E Cigarettes), Hookah, Marijuana, and Huffing. Additionally, marketing and advertising tactics will be reviewed to understand how they target this population. A review of current health policy recommendations from the FDA, American Thoracic Society, and the American Academy of Pediatrics will also be discussed.ConclusionThe rapid rise in e‐cigarette and hookah use in school aged children should trigger a call to action in the medical and public health communities. Health policy recommendations need to be made to reduce the level of adolescent substance abuse.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/142898/1/ppul23836_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/142898/2/ppul23836.pd

Empirical Study of PEFT techniques for Winter Wheat Segmentation

Parameter Efficient Fine Tuning (PEFT) techniques have recently experienced significant growth and have been extensively employed to adapt large vision and language models to various domains, enabling satisfactory model performance with minimal computational needs. Despite these advances, more research has yet to delve into potential PEFT applications in real-life scenarios, particularly in the critical domains of remote sensing and crop monitoring. The diversity of climates across different regions and the need for comprehensive large-scale datasets have posed significant obstacles to accurately identify crop types across varying geographic locations and changing growing seasons. This study seeks to bridge this gap by comprehensively exploring the feasibility of cross-area and cross-year out-of-distribution generalization using the State-of-the-Art (SOTA) wheat crop monitoring model. The aim of this work is to explore PEFT approaches for crop monitoring. Specifically, we focus on adapting the SOTA TSViT model to address winter wheat field segmentation, a critical task for crop monitoring and food security. This adaptation process involves integrating different PEFT techniques, including BigFit, LoRA, Adaptformer, and prompt tuning. Using PEFT techniques, we achieved notable results comparable to those achieved using full fine-tuning methods while training only a mere 0.7% parameters of the whole TSViT architecture. The in-house labeled data-set, referred to as the Beqaa-Lebanon dataset, comprises high-quality annotated polygons for wheat and non-wheat classes with a total surface of 170 kmsq, over five consecutive years. Using Sentinel-2 images, our model achieved a 84% F1-score. We intend to publicly release the Lebanese winter wheat data set, code repository, and model weights

Transient transcriptional silencing alters the cell cycle to promote germline stem cell differentiation in Drosophila

Transcriptional silencing is a conserved process used by embryonic germ cells to repress somatic fate and maintain totipotency and immortality. In Drosophila, this transcriptional silencing is mediated by polar granule component (pgc). Here, we show that in the adult ovary, pgc is required for timely germline stem cell (GSC) differentiation. Pgc is expressed transiently in the immediate GSC daughter (pre-cystoblast), where it mediates a pulse of transcriptional silencing. This transcriptional silencing mediated by pgc indirectly promotes the accumulation of Cyclin B (CycB) and cell cycle progression into late-G2 phase, when the differentiation factor bag of marbles (bam) is expressed. Pgc mediated accumulation of CycB is also required for heterochromatin deposition, which protects the germ line genome against selfish DNA elements. Our results suggest that transient transcriptional silencing in the pre-cystoblast re-programs it away from self-renewal and toward the gamete differentiation program

Down-Regulation of Platelet Imidazoline-1-Binding Sites after Bupropion Treatment

An elevation of I1 (imidazoline-1)-binding sites on platelets may be a state marker for depression. Herein, platelet I1 sites were compared in two groups of unipolar depressed patients given different regimens of bupropion treatment : Regimen 1 (n=13 titrated up to 300 mg}d by week 4 and held constant until week 6) ; Regimen 2 (n=15 titrated up to 300 mg}d by week 2, to 450 mg}d by week 6, and held constant until week 8). Platelet I1 sites were quantified by p-[125I]iodoclonidine binding (0.5–15 nm) and displaced by moxonidine under a saturating concentration of norepinephrine to mask α2-adrenoceptors. I1 Bmax values were confirmed to be high at pretreatment in depressed patients (n=28) compared to healthy control subjects (n=18 ; p=0.02). Highest Bmax values at pretreatment were found in patients who responded worst to treatment. More than two-thirds of patients recovered from depression (69 and 80% in Regimens 1 and 2, respectively) after treatment. Dose and/or time of exposure to bupropion were relevant variables since (1) only Regimen 2 led to platelet I1 down-regulation and (2) the extent of down-regulation correlated with plasma concentrations of bupropion. The data suggest a dissociation exists between I1 down-regulation and therapeutic response, or else platelet I1 down-regulation lags behind clinical antidepressant response before becoming measurable

Is it the time for Hepatitis E virus (HEV) Testing for Blood Donors in Qatar?

HEV is the etiologic agent of acute hepatitis E. Although HEV usually causes a self-limiting infection, the disease may develop into a chronic or fulminant form of Hepatitis. Sporadic HEV infections spread in several developed countries; however, outbreaks usually occur in regions where sanitation is low, in particular, in developing countries where water flooding frequently occurs. In addition, religious background, life style, hygienic practices, and the economic status have been linked to HEV infection. Fecal-oral is the established route of transmission, however, infections through blood transfusion were recently documented in many developed and developing countries. This recent finding raises the question: is there is a need for HEV screening prior transfusion or transplantation? Studies related to this issue, in the Middle East are scarce. Although the CDC HEV epidemiological map, classifies the Arabian Gulf countries including Qatar as endemic or highly endemic, to the best of our knowledge, no HEV population –based epidemiological study were conducted in Qatar. HEV infection is usually detected using IgM and IgG serological tests and confirmed by molecular tests for detection of viral RNA. Yet, commercially available HEV serological kits are not validated, and needs further investigation

Clinical Decision Science: Proof of concept

Clinical decision science, a newly identified area of scholarship, describes how clinical research is used for a patient, within the context of their unique social conditions. We hypothesize that physicians use sociocultural context as an important input to their decision making. We performed a prospective, randomized, double-blind mixed methods study. Family medicine faculty and residents at a community hospital family medicine residency were included in the study. After academic journal club discussing a primary research paper, physicians were asked if they would prescribe medication for a patient who was similar to the subjects in a research paper. However, social and cultural context was given to the cases. The physicians were block randomized into two groups; Group A was given a case with a patient who had a social and cultural context more conducive to lifestyle modification, while group B had a case more conducive to prescribing medication. Primary outcome was whether or not physicians prescribed medication, allowing for a 2x2 table for analysis. We also asked a free response question regarding the reasoning for their decision and performed qualitative analysis. In group A (n=14), no subjects prescribed medication. In group B (n=18), six subjects prescribed medication. (chi-square statistic with Yates correction 9.95, p=0.001). Thematic analysis in group A showed 22 statements related to medical practice or disease characteristics, and 25 statements related to familial relationships and patient preferences. In group B, subjects who prescribed medication made 30 statements related to medical practice, and 13 statements related to patient preference. Subjects who did not prescribe medication made 10 statements related to medical practice, and 1 statement related to patient preference. This study demonstrates social context of individual patients, together with evidence, affects clinical decision and management. We propose further study into how this affects physician decision making, a scholarly field we call Clinical Decision Science

Flavin Oxidase-Induced ROS Generation Modulates PKC Biphasic Effect of Resveratrol on Endothelial Cell Survival.

Dietary intake of natural antioxidants is thought to impart protection against oxidative-associated cardiovascular diseases. Despite many in vivo studies and clinical trials, this issue has not been conclusively resolved. Resveratrol (RES) is one of the most extensively studied dietary polyphenolic antioxidants. Paradoxically, we have previously demonstrated that high RES concentrations exert a pro-oxidant effect eventually elevating ROS levels leading to cell death. Here, we further elucidate the molecular determinants underpinning RES-induced oxidative cell death. Using human umbilical vein endothelial cells (HUVECs), the effect of increasing concentrations of RES on DNA synthesis and apoptosis was studied. In addition, mRNA and protein levels of cell survival or apoptosis genes, as well as protein kinase C (PKC) activity were determined. While high concentrations of RES reduce PKC activity, inhibit DNA synthesis and induce apoptosis, low RES concentrations elicit an opposite effect. This biphasic concentration-dependent effect (BCDE) of RES on PKC activity is mirrored at the molecular level. Indeed, high RES concentrations upregulate the proapoptotic , while downregulating the antiapoptotic , at both mRNA and protein levels. Similarly, high RES concentrations downregulate the cell cycle progression genes, , ornithine decarboxylase and cyclin D1 protein levels, while low RES concentrations display an increasing trend. The BCDE of RES on PKC activity is abrogated by the ROS scavenger Tempol, indicating that this enzyme acts downstream of the RES-elicited ROS signaling. The RES-induced BCDE on HUVEC cell cycle machinery was also blunted by the flavin inhibitor diphenyleneiodonium (DPI), implicating flavin oxidase-generated ROS as the mechanistic link in the cellular response to different RES concentrations. Finally, PKC inhibition abrogates the BCDE elicited by RES on both cell cycle progression and pro-apoptotic gene expression in HUVECs, mechanistically implicating PKC in the cellular response to different RES concentrations. Our results provide new molecular insight into the impact of RES on endothelial function/dysfunction, further confirming that obtaining an optimal benefit of RES is concentration-dependent. Importantly, the BCDE of RES could explain why other studies failed to establish the cardio-protective effects mediated by natural antioxidants, thus providing a guide for future investigation looking at cardio-protection by natural antioxidants

Density functional theory study of the partial oxidation of methane to methanol on Au and Pd surfaces

The partial oxidation of methane to methanol has been a goal of heterogeneous catalysis for many years. Recent experimental investigations have shown how AuPd nanoparticle catalysts can give good selectivity to methanol with only limited total oxidation of CH4 using hydrogen peroxide as an oxidant in aqueous media. Interestingly, the use of colloidal nanoparticles alone, without a support material, leads to efficient use of the oxidant and the possibility of introducing oxygen from O2(g) into the CH3O2H primary product. This observation indicates that a radical mechanism is being initiated by H2O2 but then the oxygen addition step, catalyzed by these nanoparticles, can incorporate O2(ads). In this contribution, we use density functional theory (DFT) to study the elementary steps in the partial oxidation of methane to methanol using H2O2 as a radical initiator and molecular oxygen as an oxidant over the low index surfaces of Pd and Au. We are able to show that pure Pd nanoparticles are prone to oxidation by O2(g), whereas the competitive adsorption of water on Au surfaces limits the availability of O2(ads). Calculations with Au added to Pd or vice versa show that both effects can be alleviated by using mixed metal surfaces. This provides a rationalization of the need to use alloy nanoparticles experimentally, and the insights from these results will aid future catalyst development