Resonant X-ray diffraction studies on the charge ordering in magnetite

Here we show that the low temperature phase of magnetite is associated with an effective, although fractional, ordering of the charge. Evidence and a quantitative evaluation of the atomic charges are achieved by using resonant x-ray diffraction (RXD) experiments whose results are further analyzed with the help of ab initio calculations of the scattering factors involved. By confirming the results obtained from X-ray crystallography we have shown that RXD is able to probe quantitatively the electronic structure in very complex oxides, whose importance covers a wide domain of applications.Comment: 4 pages 4 figures, accepted for publication in PR

Exploring the antimicrobial efficacy of silver acetate against Acinetobacter baumannii and development of an in vitro biofilm model

Acinetobacter baumannii is a nosocomial pathogen with a remarkable capacity for antimicrobial resistance. This bacterial species possesses the ability to form biofilms and survive on abiotic surfaces within hospitals, which makes it a common cause of ventilator associated pneumonia, bacteraemia, catheter associated urinary tract infections , and wound and burn infections. As A. baumannii can cause catheter associated urinary tract infections via biofilm formation on catheters and silver acetate coated catheters are used commercially for prevention of infection, this thesis aimed to explore first the efficacy of silver acetate as an antimicrobial, and then to develop a modified Drip Flow Biofilm Reactor® tubing model to mimic biofilm formation within a catheter. A. baumannii NCTC 13302 was first determined to be the best biofilm forming strain out of the five isolates in the study, and it contained the OXA-24-like gene that provides carbapenem resistance. This strain was then utilised to test the minimum inhibitory concentration of silver acetate, its biofilm prevention capabilities, and its growth inhibitory effects. This provided raw data which did not exist for silver acetate against A. baumannii as there were no other studies stating the antimicrobial activity of silver acetate against this species. A further test of in vivo toxicity of silver acetate was carried out using Galleria mellonella larvae which validated the low toxicity of the silver salt. A further test where the larvae were infected with A. baumannii and then treated with silver acetate showed a significant increase in the survival of the larvae, showing the effectiveness of silver acetate as a treatment. The modified Drip Flow Biofilm Reactor® tubing model was developed first with A. baumannii NCTC 13302 in Mueller-Hinton Broth and subsequently with a modified Artificial Urine Media to move the model towards an imitation of a catheter associated urinary tract infection. During development, it was found that the most efficient way to assess biofilms grown within silicone tubing for five days was to run two samples in parallel and assess viability with cell counts and live/dead staining and to image with Scanning Electron Microscopy. The model developed herein will allow the study of A. baumannii biofilm formation on catheter tubing in conditions that begin to mimic the clinical environment. Future developments will focus on testing the antimicrobial activity of silver acetate coated catheter tubing against A. baumannii, and adaptation of the model to imitate bladder mechanics with a catheter fitted, which would provide a novel model to better study prevention of catheter associated urinary tract infections

Mothers' perceptions of overweight and obesity in their children

Background: Childhood obesity is a growing health concern and the literature implicates parents, particularly mothers. Aim: To develop understandings into the views of a group of mothers with an overweight or obese child, about their child's overweight or obesity. Method: A qualitative design informed by feminist insights. Eleven English speaking mothers of at least one overweight or obese child were drawn from a large urban community in metropolitan Australia to participate in this study. Results: Participants attributed their child's obesity to factors such as slow metabolism, sedentary lifestyle, familial or cultural factors, genetics, eating habits such as not drinking enough water, or not chewing food adequately. Participants were very concerned about their child's weight problems and their immediate concerns focussed on social problems associated with obesity/overweight. Conclusion: Understanding parental views about their children's overweight and obesity is a key step in forming effective liaisons between health professionals and parents

The antimicrobial activity of silver acetate against Acinetobacter baumannii in a Galleria mellonella infection model

Background: The increasing prevalence of bacterial infections that are resistant to antibiotic treatment has caused the scientific and medical communities to look for alternate remedies aimed at prevention and treatment. In addition to researching novel antimicrobials, there has also been much interest in revisiting some of the earliest therapies used by man. One such antimicrobial is silver; its use stretches back to the ancient Greeks but interest in its medicinal properties has increased in recent years due to the rise in antibiotic resistance. Currently antimicrobial silver is found in everything from lunch boxes to medical device implants. Though much is claimed about the antimicrobial efficacy of silver salts the research in this area is mixed. Methods: Herein we investigated the efficacy of silver acetate against a carbapenem resistant strain of Acinetobacter baumannii to determine the in vitro activity of this silver salt against a World Health Organisation designated category I critical pathogen. Furthermore, we use the Galleria mellonella larvae model to assess toxicity of the compound and its efficacy in treating infections in a live host. Results: We found that silver acetate can be delivered safely to Galleria at medically relevant and antimicrobial levels without detriment to the larvae and that administration of silver acetate to an infection model significantly improved survival. This demonstrates the selective toxicity of silver acetate for bacterial pathogens but also highlights the need for administration of well-defined doses of the antimicrobial to provide an efficacious treatment

Multiple prior concussions are associated with symptoms in high school athletes

Objectives: The purpose of this study was to evaluate the association of prior concussion on baseline computerized neurocognitive testing in a large cohort of high school athletes. Methods: This is a retrospective cohort study of student athletes from 49 Maine High Schools in 2010 who underwent baseline computerized neurocognitive evaluation with Immediate Post-Concussion Assessment and Cognitive Testing (ImPACT®). As part of the ImPACT®, subjects reported a prior history of concussion as well as demographic information and a symptom questionnaire. We used linear regression to evaluate the association of prior concussion with baseline: (1) ImPACT® composite scores; and (2) symptom scores. Results: Six thousand seventy-five subjects were included in the study, of whom 57% were boys. The majority of student athletes (85.3%) reported no prior history of concussion while 4.6% reported having sustained two or more prior concussions. On simple linear regression, increasing number of concussions was related to worse performance in verbal memory (P = 0.039) and greater symptoms scores (P < 0.001). On multivariate modeling, only the association with baseline symptoms remained (P < 0.001). Other factors associated with baseline symptom reporting in the multivariate model included mental health history, headache/migraine history, gender, developmental and/or learning problems, and number of prior concussions. Interpretation In this large-scale, retrospective survey study, history of multiple prior concussions was associated with higher symptom burden but not baseline computerized neurocognitive testing. The association between baseline symptom reporting and clinical and demographic factors was greater than the association with a history of multiple concussions

Resonant X-Ray Scattering on the M-Edge Spectra from Triple-k Structure Phase in U_{0.75}Np_{0.25}O_{2} and UO_{2}

We derive an expression for the scattering amplitude of resonant x-ray scattering under the assumption that the Hamiltonian describing the intermediate state preserves spherical symmetry. On the basis of this expression, we demonstrate that the energy profile of the RXS spectra expected near U and Np M_4 edges from the triple-k antiferromagnetic ordering phase in UO_{2} and U_{0.75}Np_{0.25}O_{2} agree well with those from the experiments. We demonstrate that the spectra in the \sigma-\sigma' and \sigma-\pi' channels exhibit quadrupole and dipole natures, respectively.Comment: 3 pages, 3 figures, to be published in J. Phys. Soc. Jpn. Supp

How Changes in Extracellular Matrix Mechanics and Gene Expression Variability Might Combine to Drive Cancer Progression

Changes in extracellular matrix (ECM) structure or mechanics can actively drive cancer progression; however, the underlying mechanism remains unknown. Here we explore whether this process could be mediated by changes in cell shape that lead to increases in genetic noise, given that both factors have been independently shown to alter gene expression and induce cell fate switching. We do this using a computer simulation model that explores the impact of physical changes in the tissue microenvironment under conditions in which physical deformation of cells increases gene expression variability among genetically identical cells. The model reveals that cancerous tissue growth can be driven by physical changes in the microenvironment: when increases in cell shape variability due to growth-dependent increases in cell packing density enhance gene expression variation, heterogeneous autonomous growth and further structural disorganization can result, thereby driving cancer progression via positive feedback. The model parameters that led to this prediction are consistent with experimental measurements of mammary tissues that spontaneously undergo cancer progression in transgenic C3(1)-SV40Tag female mice, which exhibit enhanced stiffness of mammary ducts, as well as progressive increases in variability of cell-cell relations and associated cell shape changes. These results demonstrate the potential for physical changes in the tissue microenvironment (e.g., altered ECM mechanics) to induce a cancerous phenotype or accelerate cancer progression in a clonal population through local changes in cell geometry and increased phenotypic variability, even in the absence of gene mutation

An x-ray resonant diffraction study of multiferroic DyMn2O5

X-ray resonant scattering has been used to measure the magnetic order of the Dy ions below 40K in multiferroic DyMn$_{2}$O$_{5}$. The magnetic order has a complex behaviour. There are several different ordering wavevectors, both incommensurate and commensurate, as the temperature is varied. In addition a non-magnetic signal at twice the wavevector of one of the commensurate signals is observed, the maximum intensity of which occurs at the same temperature as a local maximum in the ferroelectric polarisation. Some of the results, which bear resemblence to the behaviour of other members of the RMn$_{2}$O$_{5}$ family of multiferroic materials, may be explained by a theory based on so-called acentric spin-density waves.Comment: 8 pages, 8 figure

Satellite holmium M-edge spectra from the magnetic phase via resonant x-ray scattering

Developing an expression of resonant x-ray scattering (RXS) amplitude which is convenient for investigating the contributions from the higher rank tensor on the basis of a localized electron picture, we analyze the RXS spectra from the magnetic phases of Ho near the $M_{4,5}$ absorption edges. At the $M_5$ edge in the uniform helical phase, the calculated spectra of the absorption coefficient, the RXS intensities at the first and second satellite spots capture the properties the experimental data possess, such as the spectral shapes and the peak positions. This demonstrates the plausibility of the adoption of the localized picture in this material and the effectiveness of the spectral shape analysis. The latter point is markedly valuable since the azimuthal angle dependence, which is one of the most useful informations RXS can provides, is lacking in the experimental conditions. Then, by focusing on the temperature dependence of the spectral shape at the second satellite spot, we expect that the spectrum is the contribution of the pure rank two profile in the uniform helical and the conical phases while that is dominated by the rank one profile in the intermediate temperature phase, so-called spin slip phase. The change of the spectral shape as a function of temperature indicates a direct evidence of the change of magnetic structures undergoing. Furthermore, we predict that the intensity, which is the same order observed at the second satellite spot, is expected at the fourth satellite spot from the conical phase in the electric dipolar transition.Comment: 24 pages, 5 figure