Surface Structure Of Hydrated And Iron(Ii) Reacted Hematite(11(-)02) And (0001)

Thesis (Ph.D.) University of Alaska Fairbanks, 2008Reactions on naturally abundant hematite (alpha-Fe2O 3) surfaces significantly influence the transport and bio-availability of a number of important nutrients and contaminants. The surface reactivity of alpha-Fe2O3 is dependent on the surface structure, i.e. the identity and coordination of chemical moieties exposed at the surface. The surface structure is strongly influenced by the presence of water and common aqueous species such as Fe(II). Therefore, it is important to understand how the surface structure evolves in the presence of water and aqueous species (e.g. Fe(II)) in order to model the surface reactivity of hematite in natural aquatic systems. The current study provides a detailed experimental investigation of the surface structure of two predominant natural faces of alpha-Fe2O 3, the (1102) and (0001) surfaces under hydrated conditions in absence and presence of aqueous Fe(II). The surface structure of hydrated alpha-Fe2O3(1102) prepared via a room-temperature wet chemical and mechanical polishing (CMP) procedure is consistent with a surface termination where the top layer of iron atoms is absent compared to the stoichiometric bulk termination. The annealing of CMP prepared alpha-Fe2O3(1 102) in air at 773 K results in transformation of the surface to a structure consistent with the stoichiometric termination. For CMP prepared alpha-Fe2O3(0001), the experimental results show a co-existence of two distinct structural domains on the surface. The first domain corresponds to hydroxylation of surface Fe atoms, and the second domain is formed by complete removal of the surface Fe cation leading to an exposed oxygen layer on the surface. The exposure of CMP prepared alpha-Fe2O3(1 102) and (0001) to aqueous Fe(II) results in structural modification of both surfaces due to adsorption of Fe(II) at crystallographic lattice sites followed by oxidation to Fe(III). Preliminary research conducted to identify the effect of Fe(II) induced surface modification on reactivity using Pb(II) as a reactive probe indicates that the clean and Fe(II)-modified surfaces exhibit significantly different reactivity towards Pb(II). Overall, the systematic structural characterization of hydrated and Fe(II)-modified alpha-Fe 2O3 surfaces presented in the current study will provide a basis to elucidate surface structure-reactivity relationships for hematite and will aid in developing models of mineral-water interfacial reactivity

Ingestion of cylindrical batteries and its management

In contrast to the ingestion of coin batteries, the ingestion of cylindrical batteries is an uncommon medical presentation. Owing to their larger size, cylindrical battery ingestion can lead to serious complications including intestinal haemorrhage, bowel obstruction, bowel perforation, peritonitis and even death. We discuss the case of a 17-year-old girl who presented after swallowing three cylindrical batteries. Her medical history included depression and previous battery ingestion that required surgical removal. During this presentation however, these ingested batteries were removed endoscopically at oesophagogastroduodenoscopy and ileocolonoscopy. The patient was subsequently discharged without complication. This paper discusses the complications and management of cylindrical battery ingestion

DEVELOPMENT AND STATISTICAL OPTIMIZATION OF GASTRORETANTIVE FLOATING MICROSPHERES OF PREGABALIN PREPARED BY W/O/O MULTIPLE EMULSION METHOD

Objective: The aim of this study is to develop a gastroretentive microsphere of pregabalin using design of experiment (DoE) to decrease dosing frequency and increasing bioavailability. Methods: Pregabalin microsphere was prepared by W/O/O multiple emulsion method using a mixture of ethyl cellulose (EC) and polyvinyl pyrrolidone (PVP) as rate-controlling polymer. Mixed solvent system comprising of dichloromethane (DCM) and acetonitrile (ACN) and light liquid paraffin was chosen as primary and secondary oil phase respectively. Taguchi design was employed for factor screening and Box Behnken design was used for the optimisation of critical process parameters. Results: Taguchi design revealed that polymer: drug, DCM: ACN and PVP: EC is the critical factor for the preparation of microspheres. The optimized formulation was prepared using polymer: drug (4.95:1), DCM: ACN (53.76: 46.24) and PVP: EC (2:5) which showed mean particle size of 203.34±4.82 µm, practical yield of 87.52±2.91 %, encapsulation efficiency of 96.43±3.14 %, floating ability up to 90.42±1.64 % and T60% of 332.81±5.84. Drug release from microsphere followed Higuchi Kinetic model. Conclusion: In a nutshell, microspheres with excellent flowability and great encapsulation efficiency were successfully developed. These can be useful in improving patient compliance by reducing frequent dosing

Reactivity descriptors and electron density analysis for ligand chemistry: a case study of 2,2'-bipyridine and its analogues

In this paper, we study the reactivity of diimines like 2,2'-bipyridine and its analogues using reactivity descriptors. We discuss evaluation of local descriptors using relaxed as well as frozen approximation and characterize the σ/π acceptance/donor characteristics of the above ligands. The intermolecular reactivity sequence for the same systems is examined by the global and local philicity index. In addition, electron density analysis has been carried out to highlight the possible strengths of interaction of the bipyridine and its analogues with metal ions

Haemobilia in a previously stented hilar cholangiocarcinoma: successful haemostasis after the insertion of fcSEMS

Haemobilia describes blood loss from the biliary tract and classically presents as Quincke's triad: upper gastrointestinal bleeding (UGIB), jaundice and right upper quadrant abdominal pain. We discuss the case of a 70-year-old male with a previously stented Bismuth 1 hilar cholangiocarcinoma who presented with haematemesis. He had a similar presentation a month ago where a forward viewing gastroscope identified fresh and altered blood in the distal stomach but no clear source of bleeding. During this admission, a side-viewing duodenoscope identified bleeding from the periampullary region, which was managed by inserting a fully covered self-expanding metal stent (fcSEMS) within his pre-existing uncovered SEMS to tamponade the haemorrhage. This case highlights the importance of using a side-viewing duodenoscope for patients with UGIB on a background of a stented cholangiocarcinoma and inserting a fcSEMS within an uncovered SEMS is feasible and effective in managing these patients

Successful Endoscopic Management of Bouveret's Syndrome in a Patient with Cholecystoduodenocolic Fistulae

Bouveret's syndrome, first described in 1896 by Léon Bouveret, is rare, limited to approximately 200 published case reports to date [Ariche et al.: Scand J Gastroenterol 2000;35:781–783]. It is a subgroup of gallstone ileus in which a cholecystoduodenal fistula allows the passage of a gallstone that obstructs the duodenum, causing gastric outlet obstruction. This case is unique as it describes Bouveret's syndrome in a patient with combined cholecystoduodenocolic fistulae. Gastric outlet obstruction was successfully managed endoscopically with lithotripsy. Both fistulae were subsequently managed conservatively without any complications

Analysis of Box Culvert to Reduce Stress Values

At the time of construction of roads, highways a structure is placed (commonly used) to transfer the traffic, rain water, drainage from one side to another of the road is called a culvert placed beneath the road. Due to the structural use, multiple loads are placed on the box causing various types of stress which occurs on it. The paper tries to reduce the stress occurred in the box by flaring the box partially