194 research outputs found
Limited effect of patient and disease characteristics on compliance with hospital antimicrobial guidelines
Full text linkObjective: Physicians frequently deviate from guidelines that promote prudent use of antimicrobials. We explored to what extent patient and disease characteristics were associated with compliance with guideline recommendations for three common infections. Methods: In a 1-year prospective observational study, 1,125 antimicrobial prescriptions were analysed for compliance with university hospital guidelines. Results: Compliance varied significantly between and within the groups of infections studied. Compliance was much higher for lower respiratory tract infections (LRTIs; 79%) than for sepsis (53%) and urinary tract infections (UTIs; 40%). Only predisposing illnesses and active malignancies were associated with more compliant prescribing, whereas alcohol/ intravenous drug abuse and serum creatinine levels > 130 mu mol/l were associated with less compliant prescribing. Availability of culture results had no impact on compliance with guidelines for sepsis but was associated with more compliance in UTIs and less in LRTIs. Narrowing initial broad-spectrum antimicrobial therapy to cultured pathogens was seldom practised. Most noncompliant prescribing concerned a too broad spectrum of activity when compared with guideline-recommended therapy. Conclusion: Patient characteristics had only a limited impact on compliant prescribing for a variety of reasons. Physicians seemed to practise defensive prescribing behaviour, favouring treatment success in current patients over loss of effectiveness due to resistance in future patients
La Osa y Hécate en la Invocación del PGM VII 686-702
Full text linkA study on the Bear Charm (PGM VII 686-702) which goal is guessing the highest divinity to which the Bear has been associated by the author of this charm. To this aim, first of all I will focus on analysing of the epithets, voces magicae and theonyms included in the text and then I will pay attention to two Bear charms in PGM IV (1275-1330 and 1331-1389) to see the similar features between deities which are involved and the epithets referred to them. I propose that in PGM VII 686-702 the Bear has been either associated with Hecate or identified with her. Estudio de la invocación a la Osa en el PGM VII 686-702 cuyo objetivo es averiguar la divinidad superior con la que el autor de la práctica mágica asocia a la Osa en este caso. Para ello recurro principalmente al análisis de los epítetos, voces magicae y teónimos presentes en el texto y, en segundo lugar, a la comparación con otras dos invocaciones a la Osa en el PGM IV (1275-1330 y 1331-1389). Mi propuesta es que se trata de Hécate, bien porque la Osa se asocia a ella o bien porque se identifica con ella (sincretismo Osa-Hécate)
Atmospheric leach process of high-chromitite PGM-bearing oxidized mineralized ore through a single-stage and two-stage techniques
No full text© 2018 Elsevier Ltd The fast depletion of sulfide PGM-bearing minerals and the deteriorating socio-political environments in most primary PGM producing countries have triggered interest in exploring the recovery of these metals from high-chromium PGM-bearing oxidized ores – sometimes contain relatively high marketable PGM values – which have proven to be more difficult to process by conventional metallurgical practice which involves grinding, milling, froth flotation into a sulfide concentrate, smelting and matte production and chemical refining. This paper reports the results of an extensive evaluation campaign performed in both acidic sulfuric and chloride media. Leach tests were conducted in either a single-stage or a two-stage process and the results are compared and contrasted. Using a high-chromium PGM oxidized mineralized ore, the hybrid pyro-hydrometallurgical and low-temperature single-stage salt chlorination process proved successful for simultaneously and efficiently leaching Cu, Ni, Pt and Pd without the need and/or addition of further oxidizing agents. The technique is expected to be a direct treatment route from flotation concentrate to PGM refinery feed. Various chlorinating agents, including CaCl2, MgCl2, SnCl2and AlCl3, were tested. A CaCl2and MgCl2mixture acted synergistically for simultaneous dissolution of both Pt and Pd, achieving 99.7% Pt and 100% Pd recovery when thermally calcined at 650 °C, at a heating rate of 5.42 °C/minute for 6 h, and then leached at 90 °C for a minimum of 3 h in 6 M HCl. Copper and nickel extraction were lower but had not plateaued even after 24 h reaching 75.4 and 90.9% extraction respectively. It was also observed that when MgCl2was used on its own, it dissolves more platinum than palladium, while the opposite was true using CaCl2. The leaching process was controlled by surface chemical reactions with a determined activation energy of 46 kJ/mol. The dissolution rate was limited by the ratio of HCl volume-to-solid content. The recovery mechanism of Pt from PtAs2and some recommendations for future prospects have been suggested
Upgrading of PGM-rich leach residue by high pressure caustic leaching
Full text linkThesis (MEng)--Stellenbosch University, 2015.ENGLISH ABSTRACT: There is a lack of clear understanding of the rate of selenium (Se), arsenic (As) and sulphur (S) dissolution during caustic (NaOH) batch leaching of PGM-rich leach residue in the presence of oxygen. This has been a limitation in the optimisation of hydrometallurgical processes for the upgrading of PGM concentrates before refining the precious metals. Conditions to improve the rate of leaching of amphoteric elements while minimizing PGM losses were examined to enhance the performance of the leaching process. Development of intrinsic leaching rate equations represent the core of the overall batch leaching model developed in this study. The robustness of the model was assessed by its ability to accurately simulate the effects of changing operating parameters on the reaction extents. The effects of the interfacial oxygen mass transfer rate and temperature on the leaching rates were therefore also included in the overall model.
The first part of the experimental program focussed on the interfacial oxygen mass transfer rate in the test autoclave. This enabled an accurate mathematical description of the interfacial mass transfer rate of the primary oxidant, diatomic oxygen (O2) molecule from the gas to the liquid phase. Mass transfer tests were conducted using the sodium sulphite method at 60°C, 100 kPa oxygen partial pressure and agitation speed of between 500 to 1000 rev/min. Cobalt(II) was used as the catalyst with a concentration range of 1 to 5 mg/L.
Oxidation of amphoteric elements was investigated by leaching of PGM-rich leach residue (residue from sulphuric acid leaching of converter matte) in caustic solution. The test work was conducted to determine the intrinsic leaching rates in 0.125, 0.25 and 0.5 mol/L NaOH solutions in the 160° to 190°C temperatures range over a period of 6 hours. Oxygen partial pressure was maintained at 11 atm in the factorial experiments. The effect of oxygen partial pressure was quantified by conducting tests with oxygen partial pressure ranging from 7 to 16 atm. The intrinsic rate constants and activation energies derived from this test work were incorporated in the overall kinetic model to simulate the batch leaching profiles under real plant conditions.
During the caustic pressure oxidation of amphoteric elements, the rate of oxidation was rapid during the first 10 minutes and decreased steadily over the course of experiment. The experimental results suggest that the oxidation kinetics are controlled by product layer diffusion with sulphur, selenium and arsenic (Arrhenius) activation energies of 31.8 kJ/mol, 26.1 kJ/mol and 10.7 kJ/mol respectively over the temperature range of 160 to 190°C. The reaction mechanism, as well as the observed kinetic behaviour, is most likely due to the base metal/PGMs hydroxide layer that formed as a result of precipitation. An increase in temperature increased the sulphur and arsenic reaction rates. The selenium reaction rate also increased as the temperature was increased from 160 to 175°C. A further increase in temperature above 175°C did not yield a significant increase in the reaction rate. An increase in the caustic concentration increased the reaction rates of all the elements. Increased oxygen partial pressure also improved the reaction rates, with the most significant change observed for sulphur oxidation; the extent of sulphur oxidation increased from 75 to 85% when oxygen partial pressure was increased from 7 to 16 atm. Reaction orders of 0.25, 0.12 and 0.21 with respect to hydroxide concentration and 0.37, 0.29 and 0.36 with respect to dissolved oxygen concentration were obtained for sulphur, selenium and arsenic respectively. Kinetic models were developed for sulphur, selenium and arsenic extraction. The sulphur and selenium simulation gave better agreement between the experimental and model predicted values, while the arsenic simulation gave a relatively poor prediction of the extractions.
The caustic concentration had a notable effect on the dissolution of the PGMs. An increase in the caustic concentration increased the dissolution of platinum, palladium and ruthenium. Ruthenium dissolution also increased with an increase in temperature. To the contrary, platinum and palladium dissolution decreased with an increase in temperature. Rhodium and iridium precipitated and did not report in the solution phase while osmium could not be traced. The oxygen partial pressure did not have a significant effect on the dissolution rate of platinum, palladium and ruthenium.AFRIKAANSE OPSOMMING: Daar is ‘n tekort aan die begrip van die tempo van seleen (Se), arseen (As) en swawel (S) oplosbaarheid gedurende bytsoda (NaOH) enkelladingsloging van platinum groep metaal (PGM)-ryk oorskot materiaal in die teenwoordigheid van suurstof. Hierdie inligting word benodig wanneer die optimisering van tipiese hidrometallurgiese prosesse wat PGM oorskot materiaal opgradeer verlang word. Hierdie bytsoda druklogingsproses vind tipies voor raffinering van die PGM metale plaas. Kondisies wat die tempo van amfoteriese element-loging verbeter, terwyl die PGM verliese geminimaliseer word, was in hierdie werk geondersoek om sodoende die effektiwiteit van die logingsproses te verbeter. Die ontwikkeling van intrinsieke logingtempo vergelykings vorm die kern van die algemene enkelladingsloging model wat ontwikkel was. Die robuustheid van hierdie model word geevalueer op sy vermoë om akkuraat die effekte van veranderende bedryfstelsel parameters op die logingstempo van betrokke reaksies te simuleer. Die effekte van suurstof tussenvlak massaoordrag en temperatuur was ook in die algehele model ingesluit.
Die eerste deel van die eksperimentele program het gefokus op die suurstof tussenvlak massaoordrag in die outoklaaf. ‘n Akkurate wiskundige model wat die massaoordrag van die primêre oksidant, diatomiese suurstof (O2), van die gas fase na die vloeistof fase beskryf, was gebruik om die suurstof oordragtempo te kwantifiseer. Suurstof massaoordrag toetse het van die natrium sulfiet metode gebruik gemaak by 60°C, 100 kPa suurstof parsiële druk en tussen 500 en 1000 rev/min roerspoed. Kobalt(II) het gedien as katalis wat tussen 1 tot 5 mg/L gevarieer was.
Die amfoteriese element oksidasie was volgende ondersoek deur die PGM-ryk oorskot materiaal te loog met bytsoda (wat stroomop onderwerp was aan swawelsuur loging van omskakelaar mat). Die toetswerk wou die intrinsieke logingtempo’s met 0.125, 0.25 en 0.5 mol/L NaOH oplossings by temperature 160 en 190°C oor 6 uur residensie tyd vasstel. Die suurstof parsiële druk was konstant gehou op 11 atm in hierdie faktoriale eksperimente. Die effek van suurstof parsiële druk was apart vasgestel, deur die suurstof parsiële druk te varieër vanaf 6 tot 16 atm. Die intrinsieke tempokonstantes en aktiveringsenergieë wat in hierdie toetswerk afgelei is, was in ‘n algehele kinetiese model ingekorporeer wat die enkellading logingsprofiele gesimuleer het by aanleg kondisies.
Die tempo van oksidasie was vinnig in die eerste 10 minute en het geleidelik afgeplat, gedurende die bytsoda druk oksidasie van amfoteriese elemente. Die eksperimentele resultate suggereer dat produklaagdiffusie die oksidasie kinetika beheer met swawel, seleen en arseen (Arrhenius) aktiveringsenergieë as volg bereken in die temperatuur interval 160 tot 190°C: 31.8 kJ/mol, 26.1 kJ/mol en 10.7 kJ/mol. Die reaksie meganisme en kinetiese gedrag word hoogs waarskynlik veroorsaak deur die onedelmetaal/PGM hidroksied laag wat deur middel van presipitasie gevorm het. Temperatuur toename het die swawel en arseen se reaksietempo’s verhoog. Met seleen het die reaksietempo met temperatuur toename tussen 160 en 175°C ook verhoog, maar afplatting het by 175°C opwaarts plaasgevind. Oor die algemeen het die bytsoda konsentrasie die amfoteriese elemente se reaksietempo’s verhoog. Die verhoging van die suurstof parsiële druk het ook die reaksietempo’s verhoog. Swawel oksidasie het van 75 tot 85% verhoog vanaf 6 tot 16 atm, wat die mees noemenswaardige verandering was. Swawel, seleen en arseen reaksieordes van 0.25, 0.12 en 0.21 met hidroksied konsentrasie en 0.37, 0.29 en 0.36 met opgeloste suurstof konsentrasie het die beste paslyn op die eksperimentele data tot gevolg gehad. Hierdie data was gebruik om die kinetiese modelle van swawel, seleen en arseen ekstraksie te ontwikkel. Terwyl swawel en seleen ‘n goeie paslyn vir die eksperimentele data tot gevolg gehad het, kon passing van arseen ekstraksie nie ‘n goeie model oplewer nie.
Varierende bytsoda konsentrasie het ‘n noemenswaardige effek op die PGM ontbinding gehad. Wanneer die bytsoda se konsentrasie vermeerder word, los daar meer platinum, palladium en rutenium op. Rutenium ontbinding het tydens ‘n temperatuur toename verhoog. In kontras het platinum en palladium ontbinding velaag tydens temperatuur toename. Rodium en iridium het gepresipiteer en was nie ontbind nie. Osmium kon nie gemeet word nie. Die suurstof parsiële druk het nie ‘n noemenswaardige effek op platinum, palladium en rutenium ontbinding gehad nie
Christ and Charon: PGM P13 Reconsidered
No full textPGM P13 consists of a long invocation to Jesus and a request for protection against all possible evils, and can be dated to the early fifth century. Although its reference to Charon and description of the descent of Jesus to the underworld makes it one of the most exciting pieces in Preisendanz's collection of Christian magical texts, it has not been treated in detail since its publication in 1900 by Adolf Jacoby. This article presents some corrections to the previous editions on the basis of a black-and-white image of the papyrus available online. The text is followed by a detailed line-by-line commentary, which aims at situating the text in the context of the literature read and produced in the period in Egypt, as well as of the Christian ritual texts. The article finishes with a discussion of the salient features of this remarkable text, as the creedal formulas, the reference to the descent, and the mention of Charon, which allows us to catch a glimpse of the author, a Christian intellectual in search of ritual efficacy.
This is an Accepted Manuscript of an article published by Taylor & Francis Group in Symbolae Osloenses on 12 Jan 2016
Jesus, Morton Smith, and the Eighth Book of Moses (PGM 13.1-734)
No full textThe late Morton Q. Smith's innovative interpretation of PGM 13.1-734 as containing not merely two but three different versions of the Eighth Book of Moses (hereafter MosesVIII) was built on assumptions which have not been critically examined either in scholarship on that text or in critical discussion of Smith's use of the magical papyri in his book Jesus the Magician. Critical examination of those assumptions would suggest that Smith's negative evaluation of MosesVIII's world-view exercised inappropriate influence both on his translation of the text and on his views concerning its sources and literary structure. As a critical alternative to Smith's views, the present article provides new lines of support for holding, in agreement with pre-Smith scholarship, that only two versions of MosesVIII are present in PGM 13.1-734. A comparative analysis of the two versions is also offered, wherein version B (lines 343-734) is seen as representing the earlier stage in the development of the tradition, and version A (lines 1-343) is contextualized as a fourth-century CE Christianized redaction that belongs in part to the reception history of the New Testament Gospels and Acts. © 2011 The Author(s)
Chalcogenide - mold interactions during Precision Glass Molding (PGM) of GeAsSe glasses
No full textPaper 88841UFive chalcogenide glasses in the GeAsSe ternary glass system were melted, fabricated into flats, and molded between planar, uncoated, binderless WC molds using a laboratory-scale precision glass molding machine. The five glasses originate at the binary arsenic triselenide (As 40 Se 60 ) and are modified by replacing As with Se in 5 mol% increments, or by locking the As:Se ratio and adding Ge, also in 5 mol% increments. The glasses are separated into two groups, one for the Ge-free compositions and the other for the Ge-containing compositions. This effort analyzes the differences between the Ge-containing and the Ge-free glasses on the post-molded glass and mold surface behavior, as well as the mold lifetime. Fabrication features, such as scratch and/or dig marks were present on the glass and mold surfaces prior to the PGM process. White light interferometry analysis of the surfaces shows an overall reduction in the RMS roughness of the glass after molding, and an increase of the roughness of the molds, after 15 molding cycles. After molding, the quantity of observable defects, primarily deposits and dig marks are increased for both the glass and mold surfaces. Deposits found on the WC molds and glasses were analyzed using Electron Dispersive X-ray Spectroscopy (EDS) and showed no evidence of being due to material transfer between the WC molds and the glass constituents. In general the main observable difference in the analysis of the two post molded sets, despite the changes in chemistry, is the quantity of molding induced defects near the edge of the GeAsSe samples
Chalcogenide-mold interactions during precision glass molding (PGM) of GeAsSe glasses
No full textFive chalcogenide glasses in the GeAsSe ternary glass system were melted, fabricated into flats, and molded between planar, uncoated, binderless WC molds using a laboratory-scale precision glass molding machine. The five glasses originate at the binary arsenic triselenide (As40Se60) and are modified by replacing As with Se in 5 mol% increments, or by locking the As:Se ratio and adding Ge, also in 5 mol% increments. The glasses are separated into two groups, one for the Ge-free compositions and the other for the Ge-containing compositions. This effort analyzes the differences between the Ge-containing and the Ge-free glasses on the post-molded glass and mold surface behavior, as well as the mold lifetime. Fabrication features, such as scratch and/or dig marks were present on the glass and mold surfaces prior to the PGM process. White light interferometry analysis of the surfaces shows an overall reduction in the RMS roughness of the glass after molding, and an increase of the roughness of the molds, after 15 molding cycles. After molding, the quantity of observable defects, primarily deposits and dig marks are increased for both the glass and mold surfaces. Deposits found on the WC molds and glasses were analyzed using Electron Dispersive X-ray Spectroscopy (EDS) and showed no evidence of being due to material transfer between the WC molds and the glass constituents. In general the main observable difference in the analysis of the two post molded sets, despite the changes in chemistry, is the quantity of molding induced defects near the edge of the GeAsSe samples. © 2013 SPIE
Condensed phase properties of platinum group metal complexes from computational simulations
Full text linkThesis (MSc)--University of Stellenbosch, 2004ENGLISH ABSTRACT: A variety of computational techniques are used to calculate structural, thermodynamic and transport
properties of two specific Platinum Group Metal (PGM) complex systems. The first system consists of
a PGM complex ([PdCl4]2-; [PtCl4]2-; [PtCl6]2- or [RhCl6]3-) with sodium counter-ions in a water
solution at 30ºC and at a concentration of 0.106 mol/dm3. The second system under consideration is
that of a PGM complex ([PdCl4]2-; [PtCl4]2-; [PtCl6]2- or [RhCl6]3-) with sodium counter-ions in a water
solution in the presence of four poly (ethylene oxide) (PEO) chains at 30ºC and at a concentration of
0.013 mol/dm3. A conformational study of the two types of dihedral angles in a PEO chain (-C-O-C-Cand
-O-C-C-O-) is performed and the extreme flexibility of the polymer is confirmed. Dihedral angle
distributions of the two dihedral angles are calculated and explained in terms of the potential energy
surface obtained from the conformational study. The solvation geometries of the PGM complexes are
confirmed and the results are contrasted with those in the system where the polymer (PEO) is present.
It is concluded that the effect of the polymer on the structure and degree of solvation is negligible. The
free energy of solvation values of the PGM complexes are calculated to provide insight into their
structural characteristics such as solvation shell volume and geometry. The structural and
thermodynamic properties of the PGM complexes in solution are also used to explain the trends
observed in the calculated diffusion coefficients. Comments are made on the accuracy of the calculated
diffusion coefficients as well as the legitimacy of the mechanistic speculations which results from
them. Suggestions regarding possible future improvements to the computational methods are made.AFRIKAANSE OPSOMMING: Verskeie berekenings tegnieke is aangewend om die strukturele, termodinamiese en verplasings
eienskappe van twee spesifieke Platinumgroep Metaal (PGM)-kompleks sisteme te bereken. Die eerste
sisteem bestaan uit die PGM-kompleks ([PdCl4]2-; [PtCl4]2-; [PtCl6]2- of [RhCl6]3-) met natrium teenione
in water by 30ºC en met ‘n konsentrasie van 0.106 mol/dm3. Die tweede sisteem bestaan uit die
PGM-kompleks ([PdCl4]2-; [PtCl4]2-; [PtCl6]2- of [RhCl6]3-) met natrium teen-ione in water in die
teenwoordigheid van vier poli-etileenoksied (PEO) kettings by 30ºC en met ‘n konsentrasie van 0.013
mol/dm3. ‘n Studie is gemaak van die konformasies van die twee soorte dihedrale-hoeke in ‘n PEOketting
(-C-O-C-C- en -O-C-C-O-) en die insense buigbaarheid van die polimeer is hiermee bevestig.
Die dihedrale-hoek-verspreidings van die twee tipes dihedrale hoeke is bereken en word verduidelik in
terme van die potensiёle energie kromvlakke soos bereken tydens die konformasie analiese. Die
geometrie van die solvasie van die PGM-komplekse is bereken en vergelyk met die sisteme waar die
polimeer (PEO) teenwoordig is. Hieruit word afgelei dat die effek van die polimeer op die struktuur en
graad van solvasie van die komplekse minimal is. Die vrye energie van solvasie van die PGMkomplekse
is bereken met die doel om insig in te win oor die stukturele eienskappe soos byvoorbeeld
die volume van die solvasie sfeer en die geometrie daarvan. Die strukturele en termodinamiese
eienskappe van die PGM-komplekse in oplossing word ook gebruik om die neigings in die berekende
diffusie koёffisiente te verduidelik. Opmerkings word gemaak aangaande die akkuraatheid van die
berekende diffusie koeffisiente asook die geldigheid van die meganistiese spekulasies wat daaruit
gemaak word. Voorstelle word ook gemaak rakende toekomsige verbeterings aan die reken tegnieke
Impact of Heterometallic Cooperativity of Iron and Copper Active Sites on Electrocatalytic Oxygen Reduction Kinetics
Full text linkThe oxygen reduction reaction (ORR) is a key reaction in polymer electrolyte fuel cells and metal–air batteries. In these electrochemical systems, platinum group metals (PGMs) have been widely used as ORR electrocatalysts. Because of material cost and scarcity of platinum group metals, non-PGM electrocatalysts are considered to be an ideal alternative for mass production with low material cost. Many non-PGM electrocatalysts have been intensively studied such as pyrolyzed Fe-, N-doped carbon (Fe–N–C) catalysts. However, many non-PGM electrocatalysts including Fe–N–C still suffer from product selectivity due to the production of H2O2 as the byproduct. In this work, we synthesized an ORR electrocatalyst of Cu-, Fe-, and N-doped carbon nanotubes, (Cu,Fe)–N–CNT. This heterobimetallic catalyst showed the selective 4e– reduction of O2 to H2O with ca. 99%. Kinetic analysis of the electrocatalytic ORR and hydrogen peroxide reduction reaction (HPRR) in acidic media revealed that (Cu,Fe)–N–CNT showed two orders of magnitude higher rate constants for the direct 4e– reduction of O2 to H2O than those for the 2e– reduction of O2 to H2O2, whereas a monometallic Fe–N–CNT showed the same order of magnitude, indicating that the heterometallic cooperativity had a drastic impact on the ORR kinetics. Our findings would open up possibilities to develop non-PGM ORR electrocatalysts with heterobimetallic active sites for the selective ORR
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