159 research outputs found
Measurement of the penetration depth and coherence length of MgB2 in all directions using transmission electron microscopy
We demonstrate that images of flux vortices in a superconductor taken with a
transmission electron microscope can be used to measure the penetration depth
and coherence length in all directions at the same temperature and magnetic
field. This is particularly useful for MgB, where these quantities vary
with the applied magnetic field and values are difficult to obtain at low field
or in the -direction. We obtained images of flux vortices from an MgB
single crystal cut in the plane by focussed ion beam milling and tilted to
with respect to the electron beam about its axis. A new method
was developed to simulate these images which accounted for vortices with a
non-zero core in a thin, anisotropic superconductor and a simplex algorithm was
used to make a quantitative comparison between the images and simulations to
measure the penetration depths and coherence lengths. This gave penetration
depths nm and nm at 10.8 K in a
field of 4.8 mT. The large error in is a consequence of tilting
the sample about and had it been tilted about , the errors would be
reversed. Thus, obtaining the most precise values requires taking images of the
flux lattice with the sample tilted in more than one direction. In a previous
paper, we obtained a more precise value using a sample cut in the plane.
Using this value gives nm, nm,
nm and nm which agree well with
measurements made using other techniques. The experiment required two days to
conduct and does not require large-scale facilities. It was performed on a very
small sample: microns and 200 nm thick so this method could prove
useful for characterising new superconductors where only small single crystals
are available.This work was funded by the Royal Society. Work at
Eidgenossische Technische Hochschule, Zürich was supported
by the Swiss National Science Foundation and the National
Center of Competence in Research programme “Materials
with Novel Electronic Properties.”This is the accepted manuscript for a paper published in Physical Review B, 91, 054505, 5 February 2015, DOI: 10.1103/PhysRevB.91.05450
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Hall effect and transmission electron microscopy of epitaxial MnSi thin films
We present Hall effect measurements on MnSi/Si(111) epilayers and find an anomalous Hall contribution that is significantly smaller than in bulk crystals, which enables the observation of an additional contribution to the anomalous signal previously overlooked in MnSi. Our measurements indicate the signal is not due to skyrmions in MnSi thin films, which are absent in out-of-plane fields, but rather are the result of scattering from the cone phase. The absence of magnetic contrast in the transmission electron microscopy (TEM) measurements are consistent with this interpretation. We provide a method to model TEM images of skyrmions lattices to determine the conditions necessary for their observation in other B20 epilayers with an anisotropy that is favourable to their formation.T.L.M. and M.N.W. acknowledge support from NSERC and the support of the Canada Foundation for Innovation, the Atlantic Innovation Fund, and other partners which fund the Facilities for Materials Characterization, managed by the Institute for Research in Materials. Work done by J.C.L. was funded by the Royal Society. The work of F.N.R. was supported by RFBR, research project No. 14-02-31012.This is the accepted manuscript of a paper published in Physical Review B (SA Meynell, MN Wilson, JC Loudon, A Spitzig, FN Rybakov, MB Johnson, TL Monchesky, Physical Review B 2014 90, 224419)
Investigations of the size distribution and magnetic properties of nanoparticles of Cu<inf>2</inf>OSeO<inf>3</inf>
Skyrmions in confined geometries have been a subject of increasing interest
due to the different properties that they exhibit compared to their bulk
counterparts. In this study, nanoparticles of skyrmion-hosting
have been synthesised using a precipitation
method followed by thermal treatment. This enables us to produce nanoparticles
whose mean size varies from tens of nanometers to a few micrometers by varying
the temperature and duration of the thermal decomposition of the precursor.
These sizes span the ~nm diameter of skyrmions in
, allowing investigations into how the magnetic
state changes when the size of the geometrical confinement is similar to and
smaller than the size of an isolated magnetic skyrmion. AC susceptibility
measurements performed on nanoparticles with a size distribution from 15 to 250
nm show a change in the magnetic phase diagram compared to bulk
Direct observation of attractive skyrmions and skyrmion clusters in the cubic helimagnet Cu2OSeO3
We report the discovery of attractive magnetic skyrmions and their clusters
in non-centrosymmetric ferromagnets. These three-dimensional solitons have been
predicted to exist in the cone phase of chiral ferromagnets (J. Phys: Condens.
Matter 28 (2016) 35LT01) and are fundamentally different from the more common
repulsive axisymmetric skyrmions that occur in the magnetically saturated
state. We present real-space images of these skyrmion clusters in thin (~70 nm)
single-crystal samples of CuOSeO taken using transmission electron
microscopy and develop a phenomenological theory describing this type of
skyrmion
Sliding charge density wave in manganites
The so-called stripe phase of the manganites is an important example of the
complex behaviour of metal oxides, and has long been interpreted as the
localisation of charge at atomic sites. Here, we demonstrate via resistance
measurements on La_{0.50}Ca_{0.50}MnO_3 that this state is in fact a
prototypical charge density wave (CDW) which undergoes collective transport.
Dramatic resistance hysteresis effects and broadband noise properties are
observed, both of which are typical of sliding CDW systems. Moreover, the high
levels of disorder typical of manganites result in behaviour similar to that of
well-known disordered CDW materials. Our discovery that the manganite
superstructure is a CDW shows that unusual transport and structural properties
do not require exotic physics, but can emerge when a well-understood phase (the
CDW) coexists with disorder.Comment: 13 pages; 4 figure
Sociocultural and psychological determinants in migrants for noncompliance with occlusion therapy for amblyopia
Background: Compliance with occlusion therapy for amblyopia in children is low when their parents have a low level of education, speak Dutch poorly, or originate from another country. We determined how sociocultural and psychological determinants affect compliance. Methods: Included we
Combined rotation scarf and Akin osteotomies for hallux valgus: a patient focussed 9 year follow up of 50 patients
<p>Abstract</p> <p>Background</p> <p>The Cochrane review of hallux valgus surgery has disputed the scientific validity of hallux valgus research. Scoring systems and surrogate measures such as x-ray angles are commonly reported at just one year post operatively but these are of dubious relevance to the patient. In this study we extended the follow up to a minimum of 8 years and sought to address patient specific concerns with hallux valgus surgery. The long term follow up also allowed a comprehensive review of the complications associated with the combined rotation scarf and Akin osteotomies.</p> <p>Methods</p> <p>Between 1996 and 1999, 101 patients underwent rotation scarf and Akin osteotomies for the treatment of hallux valgus. All patients were contacted and asked to participate in this study. 50 female participants were available allowing review of 73 procedures. The average follow up was over 9 years and the average age at the time of surgery was 57. The participants were physically examined and interviewed.</p> <p>Results</p> <p>Post-operatively, in 86% of the participants there were no footwear restrictions. Stiffness of the first metatarsophalangeal joint was reported in 8% (6 feet); 10% were unhappy with the cosmetic appearance of their feet, 3 feet had hallux varus, and 2 feet had recurrent hallux valgus. There were no foot-related activity restrictions in 92% of the group. Metatarsalgia occurred in 4% (3 feet). 96% were better than before surgery and 88% were completely satisfied with their post-operative result. Hallux varus was the greatest single cause of dissatisfaction. The most common adverse event in the study was internal fixation irritation. Hallux valgus surgery is not without risk and these findings could be useful in the informed consent process.</p> <p>Conclusions</p> <p>When combined the rotation scarf and Akin osteotomies are an effective treatment for hallux valgus that achieves good long-term correction with a low incidence of recurrence, footwear restriction or metatarsalgia. The nature of the osteotomies allows early return to normal shoes and activity without the need for postoperative immobilisation in a plaster cast.</p
Genetic variability and ontogeny predict microbiome structure in a disease-challenged montane amphibian
Amphibian populations worldwide are at risk of extinction from infectious diseases, including chytridiomycosis caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd). Amphibian cutaneous microbiomes interact with Bd and can confer protective benefits to the host. The composition of the microbiome itself is influenced by many environment- and host-related factors. However, little is known about the interacting effects of host population structure, genetic variation and developmental stage on microbiome composition and Bd prevalence across multiple sites. Here we explore these questions in Amietia hymenopus, a disease-affected frog in southern Africa. We use microsatellite genotyping and 16S amplicon sequencing to show that the microbiome associated with tadpole mouthparts is structured spatially, and is influenced by host genotype and developmental stage. We observed strong genetic structure in host populations based on rivers and geographic distances, but this did not correspond to spatial patterns in microbiome composition. These results indicate that demographic and host genetic factors affect microbiome composition within sites, but different factors are responsible for host population structure and microbiome structure at the between-site level. Our results help to elucidate complex within- and among- population drivers of microbiome structure in amphibian populations. That there is a genetic basis to microbiome composition in amphibians could help to inform amphibian conservation efforts against infectious diseases
Role of Factor VII in Correcting Dilutional Coagulopathy and Reducing Re-operations for Bleeding Following Non-traumatic Major Gastrointestinal and Abdominal Surgery
Objective The objective of this study is to evaluate the effectiveness of rfVIIa in reducing blood product requirements and re-operation for postoperative bleeding after major abdominal surgery. Background Hemorrhage is a significant complication after major gastrointestinal and abdominal surgery. Clinically significant bleeding can lead to shock, transfusion of blood products, and re-operation. Recent reports suggest that activated rfVIIa may be effective in correcting coagulopathy and decreasing the need for re-operation. Methods This study was a retrospective review over a 4-year period of 17 consecutive bleeding postoperative patients who received rfVIIa to control hemorrhage and avoid re-operation. Outcome measures were blood and clotting factor transfusions, deaths, thromboembolic complications, and number of re-operations for bleeding. Results Seventeen patients with postoperative hemorrhage following major abdominal gastrointestinal surgery (nine pancreas, four sarcoma, two gastric, one carcinoid, and one fistula) were treated with rfVIIa. In these 17 patients, rfVIIa was administered for 18 episodes of bleeding (dose 2,400-9,600 mcg, 29.8-100.8 mcg/kg). Transfusion requirement of pRBC and FFP were each significantly less than pre-rfVIIa. Out of the 18 episodes, bleeding was controlled in 17 (94%) without surgery, and only one patient returned to the operating room for hemorrhage. There were no deaths and two thrombotic complications. Coagulopathy was corrected by rfVIIa from 1.37 to 0.96 (p<0.0001). Conclusion Use of rfVIIa in resuscitation for hemorrhage after non-traumatic major abdominal and gastrointestinal surgery can correct dilutional coagulopathy, reducing blood product requirements and need for re-operation
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