Superparamagnetic particles in ZSM-5-type ferrisilicates

As-synthesized, low iron content, ferrisilicates of ZSM-5-type contain well-separated Fe(III) ions in a tetrahedral environment and display paramagnetic behavior. After hydrothermal treatment, the iron ions are partially extracted from the framework, generating nanosize iron oxide or oxyhydroxide ferrimagnetic particles. This process has been studied by transmission electron microscopy (TEM), Mossbauer spectroscopy, magnetic ac susceptibility (chi(ac)), and field dependent magnetization, on samples containing up to 6.7 wt. % Fe. The experiments evidence the growth of nonaggregated particles, with a typical size around 3 nm, presumably located at the surface of the ferrisilicate crystallites, From a thorough granulometric analysis involving TEM and chi(ac) data, it is concluded that, in the range from 1.5 to 4.6 wt. % Fe, the particle size distributions are significantly independent of the iron content

A cross sectional study of water quality from dental unit water lines in dental practices in the West of Scotland

OBJECTIVE: To determine the microbiological quality of water from dental units in a general practice setting and current practice for disinfection of units. DESIGN: A cross-sectional study of the water quality from 40 dental units in 39 general practices and a questionnaire of the disinfection protocols used in those practices. SETTING: NHS practices in primarydental care. SUBJECTS: Thirty-nine general practices from the West of Scotland. METHODS: Water samples were collected on two separate occasions from dental units and analysed for microbiological quality by the total viable count (TVC) method. Water specimens were collected from the triple syringe, high speed outlet, cup filler and surgery tap. Each participating practitioner was asked to complete a questionnaire. Results Microbial contamination was highest from the high speed outlet followed by the triple syringe and cup filler. On average, the TVC counts from the high speed water lines at 37 degrees C and for the high speed lines, triple syringe and cup filler at 22 degrees C were significantly higher than that from the control tap water specimens. The study included units from 11 different manufacturers with ages ranging from under one year to over eight years. The age of the dental unit analysed did not appear to influence the level of microbial contamination. Five of the practices surveyed used disinfectants to clean the dental units but these had no significant effect on the microbiological quality of the water. The majority of dental units (25 out of 40) were never flushed with water between patients. A number of different non-sterile irrigants were used for surgical procedures. CONCLUSION: The microbiological quality of water from dental units in general dental practice is poor compared with that from drinking water sources. Suitable sterile irrigants should be used for surgical procedures in dental practice. Further work is required for pragmatic decontamination regimens of dental unit water lines in a general dental practice setting

U-Pb SHRIMP zircon dating of Grenvillian metamorphism in Western Sierras Pampeanas (Argentina) : correlation with the Arequipa-Antofalla craton and constraints on the extent of the Precordillera Terrane

The Sierras Pampeanas of Argentina, the largest outcrop of pre-Andean crystalline basement in southern South America, resulted from plate interactions along the proto-Andean margin of Gondwana, from as early as Mesoproterozoic to Late Paleozoic times (e.g., Ramos, 2004, and references therein). Two discrete Paleozoic orogenic belts have been recognized: the Early Cambrian Pampean belt in the eastern sierras, and the Ordovician Famatinian belt, which partially overprints it to the west (e.g., Rapela et al., 1998). In the Western Sierras Pampeanas, Mesoproterozoic igneous rocks (ca. 1.0–1.2 Ga) have been recognized in the Sierra de Pie de Palo (Fig. 1) (McDonough et al., 1993 M.R. McDonough, V.A. Ramos, C.E. Isachsen, S.A. Bowring and G.I. Vujovich, Edades preliminares de circones del basamento de la Sierra de Pie de Palo, Sierras Pampeanas occidentales de San Juán: sus implicancias para el supercontinente proterozoico de Rodinia, 12° Cong. Geol. Argentino, Actas vol. 3 (1993), pp. 340–342.McDonough et al., 1993, Pankhurst and Rapela, 1998 and Vujovich et al., 2004) that are time-coincident with the Grenvillian orogeny of eastern and northeastern North America (e.g., Rivers, 1997 and Corrievau and van Breemen, 2000). These Grenvillian-age rocks have been considered to be the easternmost exposure of basement to the Precordillera Terrane, a supposed Laurentian continental block accreted to Gondwana during the Famatinian orogeny (Thomas and Astini, 2003, and references therein). However, the boundaries of this Grenvillian belt are still poorly defined, and its alleged allochthoneity has been challenged (Galindo et al., 2004). Moreover, most of the Grenvillian ages so far determined relate to igneous protoliths, and there is no conclusive evidence for a Grenvillian orogenic belt, other than inferred from petrographic evidence alone (Casquet et al., 2001). We provide here the first evidence, based on U–Pb SHRIMP zircon dating at Sierra de Maz, for a Grenville-age granulite facies metamorphism, leading to the conclusion that a continuous mobile belt existed throughout the proto-Andean margin of Gondwana in Grenvillian times

Metal-Metal Bonding in Uranium-Group 10 Complexes

Heterobimetallic complexes containing short uranium–group 10 metal bonds have been prepared from monometallic IU^IV(OAr^P-κ²<i>O</i>,<i>P</i>)₃ (<b>2</b>) {[Ar^PO]⁻ = 2-<i>tert</i>-butyl-4-methyl-6-(diphenylphosphino)­phenolate}. The U–M bond in IU^IV(μ-OAr^P-1κ¹<i>O</i>,2κ¹<i>P</i>)₃M⁰, M = Ni (<b>3–Ni</b>), Pd (<b>3–Pd</b>), and Pt (<b>3–Pt</b>), has been investigated by experimental and DFT computational methods. Comparisons of <b>3–Ni</b> with two further U–Ni complexes XU^IV(μ-OAr^P-1κ¹<i>O</i>,2κ¹<i>P</i>)₃Ni⁰, X = Me₃SiO (<b>4</b>) and F (<b>5</b>), was also possible via iodide substitution. All complexes were characterized by variable-temperature NMR spectroscopy, electrochemistry, and single crystal X-ray diffraction. The U–M bonds are significantly shorter than any other crystallographically characterized d–f-block bimetallic, even though the ligand flexes to allow a variable U–M separation. Excellent agreement is found between the experimental and computed structures for <b>3–Ni</b> and <b>3–Pd</b>. Natural population analysis and natural localized molecular orbital (NLMO) compositions indicate that U employs both 5f and 6d orbitals in covalent bonding to a significant extent. Quantum theory of atoms-in-molecules analysis reveals U–M bond critical point properties typical of metallic bonding and a larger delocalization index (bond order) for the less polar U–Ni bond than U–Pd. Electrochemical studies agree with the computational analyses and the X-ray structural data for the U–X adducts <b>3–Ni</b>, <b>4</b>, and <b>5</b>. The data show a trend in uranium–metal bond strength that decreases from <b>3–Ni</b> down to <b>3–Pt</b> and suggest that exchanging the iodide for a fluoride strengthens the metal–metal bond. Despite short U–TM (transition metal) distances, four other computational approaches also suggest low U–TM bond orders, reflecting highly transition metal localized valence NLMOs. These are more so for <b>3–Pd</b> than <b>3–Ni</b>, consistent with slightly larger U–TM bond orders in the latter. Computational studies of the model systems (PH₃)₃MU­(OH)₃I (M = Ni, Pd) reveal longer and weaker unsupported U–TM bonds vs <b>3</b>

A Mossbauer study of the spin-flop phase transition in some antiferromagnetic materials

The spin-flop phase transition has long been of interest to both theoretical and experimental physicists, ever since it was first predicted by Louis Neel in 1936. In this work spin-flop transitions in the antiferromagnetic materials K 2 FeF 5 , Rb 2 FeF 5 and a-Fe 2 0 3 have been 57 studied by means of Fe MBssbauer spectroscopy. Spectra of K2FeF5 and Rb2FeF5 single crystals were recorded at 4.2K with external magnetic fields of up to 14T applied in different modes, providing information on the effect of misalignment on the sharpness or 'order' of the observed transition. Directing the applied field parallel to the easy anisotropy axis resulted in a sharp 'first-order' transition, while misaligning the field by ~30o produced a broadened 'second-order' transition. Field-induced spin-flop transitions in a-Fe203 single crystal samples were studied at low temperatures by applying fields of up to lOT either parallel to or perpendicular to the easy anisotropy axis. The observed transitions were found to be of first-order in the 'parallel' case, and second-order in the 'perpendicular' case. The Morin transition, a temperature driven spin-flop which occurs naturally in a-Fe 2 0 3 at ~260K, was also studied and was found to be of first-order. Comparison of the character of the observed transitions with the predictions of several theoretical models of the spin-flop led to the conclusion that the conventional mean-field theory of the transition provides a good qualitative description of the phenomenon

Child work and labour in Ethiopia: literature review and policy implications

This chapter aims to provide a preliminary bibliographical resource, an initial critical review of the literature, new insights on child work and labour in Ethiopia, and suggestions for future lines of research. The first part considers the different disciplinary and methodological approaches used to study the issues; we suggest that the various disciplinary lenses through which child work and labour have been studied result in a fragmented rather than an integrated picture. Moreover, we argue that there is a dichotomy between quantitative approaches, many of which have focused on rural surveys and the linkages between child work and education, and qualitative approaches that have concentrated on urban areas and vulnerable children. The second part briefly reviews findings from quantitative research notably on the prevalence of child work and its distribution, children’s time use and their contribution to the household economy, the impacts of government rural development and food security programmes on child work, and the implications of work for children’s health and wellbeing. The third part considers key findings from qualitative research on the work that children do, in particular that of children at risk focusing on the main categories studied, and discusses the value and meaning of work and changing work norms. The fourth part considers the policy context, international and national legal frameworks, policies and action plans. The fifth part considers interventions within the country to address child labour. The final part draws overall conclusions and identifies research gaps

Evaluation of the efficacy of Alpron disinfectant for dental unit water lines

AIMS: To assess the efficacy of a disinfectant, Alpron, for controlling microbial contamination within dental unit water lines. METHODS: The microbiological quality of water emerging from the triple syringe, high speed handpiece, cup filler and surgery hand wash basin from six dental units was assessed for microbiological total viable counts at 22 degrees C and 37 degrees C before and after treatment with Alpron solutions. RESULTS: The study found that the use of Alpron disinfectant solutions could reduce microbial counts in dental unit water lines to similar levels for drinking water. This effect was maintained in all units for up to six weeks following one course of treatment. In four out of six units the low microbial counts were maintained for 13 weeks. CONCLUSIONS: Disinfectants may have a short term role to play in controlling microbial contamination of dental unit water lines to drinking water quality. However, in the longer term attention must be paid to redesigning dental units to discourage the build up of microbial biofilms

Dynamic phase transition properties and hysteretic behavior of a ferrimagnetic core-shell nanoparticle in the presence of a time dependent magnetic field

We have presented dynamic phase transition features and stationary-state behavior of a ferrimagnetic small nanoparticle system with a core-shell structure. By means of detailed Monte Carlo simulations, a complete picture of the phase diagrams and magnetization profiles have been presented and the conditions for the occurrence of a compensation point $T_{comp}$ in the system have been investigated. According to N\'{e}el nomenclature, the magnetization curves of the particle have been found to obey P-type, N-type and Q-type classification schemes under certain conditions. Much effort has been devoted to investigation of hysteretic response of the particle and we observed the existence of triple hysteresis loop behavior which originates from the existence of a weak ferromagnetic core coupling $J_{c}/J_{sh}$, as well as a strong antiferromagnetic interface exchange interaction $J_{int}/J_{sh}$. Most of the calculations have been performed for a particle in the presence of oscillating fields of very high frequencies and high amplitudes in comparison with exchange interactions which resembles a magnetic system under the influence of ultrafast switching fields. Particular attention has also been paid on the influence of the particle size on the thermal and magnetic properties, as well as magnetic features such as coercivity, remanence and compensation temperature of the particle. We have found that in the presence of ultrafast switching fields, the particle may exhibit a dynamic phase transition from paramagnetic to a dynamically ordered phase with increasing ferromagnetic shell thickness.Comment: 12 pages, 12 figure

Growth and yield responses to amending the sugarcane monoculture: interactions between break history and nitrogen fertiliser

Experiments were established in the Burdekin Irrigation Area in North Queensland, Australia, to measure whether yield improvements from breaking the sugarcane monoculture or fumigating the soil could be modified by the application of different rates of nitrogen (N) fertiliser. Experiments were conducted in consecutive crop cycles (phase 1, planted 1998; phase 2, planted 2001) using the variety Q117, with the interaction between N applications and rotation histories discussed for the two plant crops. Histories consisted of alternate crop, bare fallow or mixed grass-legume pastures for periods of 42-66 months, compared with continuous cane as plough-out replant without (PORP) or with (PORP-F) soil fumigation. The N strategies involved combinations of N rates (0-180kgN/ha) and application times (at planting, 90 days after planting (DAP) or split between these times) in phase 1 and N rates (0-300kgN/ha) in phase 2. Histories had differing effects on N available to the cane crop and hence on response to N fertiliser. Some combinations of history and N rate were N-limited and strong linear relationships between biomass production or cane yield and crop N content could be developed. Critical N contents for biomass production (R2≤0.93) and fresh-weight cane yield (R2≤0.88) were 1.42 and 0.57kgN/t, respectively. Application of N fertiliser was shown to have significant impacts on both tiller addition and the retention of tillers to produce harvestable stalks. However, the application of fertiliser N had limited (phase 1) or no (phase 2) capacity to provide the quantum of yield response in soil health benefits associated with breaking the sugarcane monoculture. Increasing N application rates above that required to optimise crop yield resulted in significant decreases in sugar content of cane and thus lower sugar yields. Yield increases solely from improved soil health (i.e. exclusive of N response) constituted advantages averaging 15% (phase 1) to 20% (phase 2) compared with PORP. These effects were manifest early in the establishment of primary shoots in the plant crops, although the longevity of these benefits was limited. Replanting cane after a 3-year crop cycle (plant, 1st and 2nd ratoon) on land that had been under pasture, crop, bare fallow or PORP-F histories (phase 2, cycle 2) showed carryover effects of histories on N availability and fertiliser N responsiveness, but limited yield impacts attributable to residual soil health benefits. These results reinforce the importance of crop rotation during breaks between sugarcane cycles to maintain soil health and improve crop productivity