Superconductivity. Quasiparticle mass enhancement approaching optimal doping in a high-T(c) superconductor.

In the quest for superconductors with higher transition temperatures (T(c)), one emerging motif is that electronic interactions favorable for superconductivity can be enhanced by fluctuations of a broken-symmetry phase. Recent experiments have suggested the existence of the requisite broken-symmetry phase in the high-T(c) cuprates, but the impact of such a phase on the ground-state electronic interactions has remained unclear. We used magnetic fields exceeding 90 tesla to access the underlying metallic state of the cuprate YBa2Cu3O(6+δ) over a wide range of doping, and observed magnetic quantum oscillations that reveal a strong enhancement of the quasiparticle effective mass toward optimal doping. This mass enhancement results from increasing electronic interactions approaching optimal doping, and suggests a quantum critical point at a hole doping of p(crit) ≈ 0.18.This work is supported by the US Department of Energy BES \Science at 100 T," the National Science Foundation, the State of Florida, the Natural Science and Engineering Research Council of Canada and the Canadian Institute for Advanced Research. S.E.S. ac- knowledges support from the Royal Society and the European Research Council under the European Union's Seventh Framework Programme (FP7/2007-2013) / ERC Grant Agree- ment no. 337425.This is the accepted manuscript. The final version is available at http://www.sciencemag.org/content/348/6232/317.abstract?sid=a882093c-ded2-481c-b62b-2f79a56b5689

Universal scaling relation in high-temperature superconductors

Scaling laws express a systematic and universal simplicity among complex systems in nature. For example, such laws are of enormous significance in biology. Scaling relations are also important in the physical sciences. The seminal 1986 discovery of high transition-temperature (high-T_c) superconductivity in cuprate materials has sparked an intensive investigation of these and related complex oxides, yet the mechanism for superconductivity is still not agreed upon. In addition, no universal scaling law involving such fundamental properties as T_c and the superfluid density \rho_s, a quantity indicative of the number of charge carriers in the superconducting state, has been discovered. Here we demonstrate that the scaling relation \rho_s \propto \sigma_{dc} T_c, where the conductivity \sigma_{dc} characterizes the unidirectional, constant flow of electric charge carriers just above T_c, universally holds for a wide variety of materials and doping levels. This surprising unifying observation is likely to have important consequences for theories of high-T_c superconductivity.Comment: 11 pages, 2 figures, 2 table

Relationship between temporomandibular joint dynamics and mouthguards: feasibility of a test method

A test system was developed establishing the feasibility of collecting biomechanical data as they relate to the use of mouthguards. Previous experimental studies have examined the physical and mechanical properties of mouthguard materials. This information has been used as a guide for establishing material standards and specifications for the fabrication of mouthguards, but it lacks the key biomechanical parameters required for a thorough mouthguard evaluation. The current study was designed to assess whether the impact force, condylar deflection, and strain superior to the temporomandibular joint region could be measured. A drop test was conducted on a cadaveric specimen to simulate loading at the chin point. To measure the force of impact, an accelerometer was attached to an impactor of known mass. High-speed biplanar (1000 frames per second) radiographs were used to determine condylar displacement. Radio-opaque markers were inserted into the bone at predetermined locations. Total displacement of these markers was determined in reference to anatomical landmarks. Strain gauges were attached to the mandible and skull to monitor the effects of the condyle impacting the base of the skull. Based on the data collected, forces were calculated by determining the product of the time-based acceleration and known mass. A measurable change in force between the mouthguards and the control (no mouthguard) was demonstrated. The average condylar displacement was successfully measured and indicated as an increase in total deflection for impacts conducted with mouthguards. Quantifiable strain was measured in the region above the mandibular fossa with and without the insertion of a mouthguard at all impact conditions. However, it was determined that additional gauges would provide critical data. Key biomechanical parameters for chin-point impacts were determined in the current study. The technique demonstrated that both displacement within the mandibular fossa and loading of the condyles occur during the impact event. Although the current study established a technique that can be used to examine the relationship between mouthguards and jaw-joint injuries, the role, if any, mouthguards play in the reduction of injuries cannot be established until a thorough analysis is completed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/74031/1/j.1600-9657.2004.00213.x.pd

Quantitative nanoscale vortex-imaging using a cryogenic quantum magnetometer

Microscopic studies of superconductors and their vortices play a pivotal role in our understanding of the mechanisms underlying superconductivity. Local measurements of penetration depths or magnetic stray-fields enable access to fundamental aspects of superconductors such as nanoscale variations of superfluid densities or the symmetry of their order parameter. However, experimental tools, which offer quantitative, nanoscale magnetometry and operate over the large range of temperature and magnetic fields relevant to address many outstanding questions in superconductivity, are still missing. Here, we demonstrate quantitative, nanoscale magnetic imaging of Pearl vortices in the cuprate superconductor YBCO, using a scanning quantum sensor in form of a single Nitrogen-Vacancy (NV) electronic spin in diamond. The sensor-to-sample distance of ~10nm we achieve allows us to observe striking deviations from the prevalent monopole approximation in our vortex stray-field images, while we find excellent quantitative agreement with Pearl's analytic model. Our experiments yield a non-invasive and unambiguous determination of the system's local London penetration depth, and are readily extended to higher temperatures and magnetic fields. These results demonstrate the potential of quantitative quantum sensors in benchmarking microscopic models of complex electronic systems and open the door for further exploration of strongly correlated electron physics using scanning NV magnetometry.Comment: Main text (5 pages, 4 figures) plus supplementary material (5 pages, 6 figures). Comments welcome. Further information under http://www.quantum-sensing.c

One-dimensional nature of the magnetic fluctuations in YBa2_2Cu3_3O6.6_{6.6}

There is increasing evidence that inhomogeneous distributions of charge and spin--so-called "striped phases"--play an important role in determining the properties of the high-temperature superconductors. For example, recent neutron-scattering measurements on the YBa$_2$Cu$_3$O$_{7-x}$ family of materials show both spin and charge fluctuations that are consistent with the striped-phase picture. But the fluctuations associated with a striped phase are expected to be one-dimensional, whereas the magnetic fluctuations observed to date appear to display two-dimensional symmetry. We show here that this apparent two-dimensionality results from measurements on twinned crystals, and that similar measurements on substantially detwinned crystals of YBa$_2$Cu$_3$O$_{6.6}$ reveal the one-dimensional character of the magnetic fluctuations, thus greatly strengthening the striped-phase interpretation. Moreover, our results also suggest that superconductivity originates in charge stripes that extend along the b crystal axis, where the superfluid density is found to be substantially larger than for the a direction.Comment: 3 pages, PDF onl

Failure of dual radius hydroxyapatite-coated acetabular cups

<p>Abstract</p> <p>Introduction</p> <p>Many kind of hydroxyapatite-coated cups were used, with favorable results in short term studies; it was supposed that its use could improve osteointegration of the cup, enhancing thus stability and survivorship. The purpose of this study is to analyze the long term behavior of the hemispheric HA coated, Dual Radius Osteonics cup and to discuss the way of failure through the exam of the revised components and of both periacetabular and osteolysis tissue.</p> <p>Materials and Methods</p> <p>Between 1994 and 1997, at the Department of Orthopedic Sciences of the Insubria University, using the posterolateral approach, were implanted 276 Dual Radius Osteonics^®in 256 patients, with mean age of 63 years.</p> <p>Results</p> <p>At a mean follow-up of 10 years (range 8–12 years), 183 cups in 165 patients, were available for clinical and radiographical evaluation. 22 Cups among the 183 were revised (11%). The cause of revision was aseptic loosening in 17 cases, septic loosening in one case, periprosthetic fracture in another case, osteolysis and polyethylene wear in two cases and, finally, recurrent dislocations in the last one. In the remaining patients, mean HHS increased from a preoperative value of 50,15 to a postoperative value of 92,69. The mean polyethylene wear was 1,25 mm (min. 0,08, max. 3,9 mm), with a mean annual wear of 0,17 mm. The mean acetabular migration on the two axis was 1,6 mm and 1,8 mm. Peri-acetabular osteolysis were recorded in 89% of the implants (163 cases). The cumulative survivorship (revision as endpoint) at the time was 88,9%.</p> <p>Conclusion</p> <p>Our study confirms the bad behavior of this type of cup probably related to the design, to the method of HA fixation. The observations carried out on the revised cup confirm these hypotheses but did not clarify if the third body wear could be a further problem. Another interesting aspect is the high incidence of osteolysis, which are often asymptomatic becoming a problem for the surgeon as the patient refuses the possibility of a revision.</p

Calibration of GENEActiv accelerometer wrist cut-points for the assessment of physical activity intensity of pre-school aged children

This study sought to validate cut-points for use of wrist worn GENEActiv accelerometer data, to analyse preschool children’s (4 to 5 year olds) physical activity (PA) levels via calibration with oxygen consumption values (VO2). This was a laboratory based calibration study. Twenty-one preschool children, aged 4.7 ± 0.5 years old, completed six activities (ranging from lying supine to running) whilst wearing the GENEActiv accelerometers at two locations (left and right wrist), these being the participants’ non-dominant and dominant wrist, and a Cortex face mask for gas analysis. VO2 data was used for the assessment of criterion validity. Location specific activity intensity cut points were established via Receiver Operator Characteristic curve (ROC) analysis. The GENEActiv accelerometers, irrespective of their location, accurately discriminated between all PA intensities (sedentary, light, and moderate and above), with the dominant wrist monitor providing a slightly more precise discrimination at light PA and the non-dominant at the sedentary behaviour and moderate and above intensity levels (Area Under the Curve (AUC) for non-dominant = 0.749-0.993, compared to AUC dominant = 0.760-0.988). Conclusion: This study establishes wrist-worn physical activity cut points for the GENEActiv accelerometer in pre-schoolers.N/

Collaboration with general practitioners: preferences of medical specialists – a qualitative study

BACKGROUND: Collaboration between general practitioners (GPs) and specialists has been the focus of many collaborative care projects during the past decade. Unfortunately, quite a number of these projects failed. This raises the question of what motivates medical specialists to initiate and continue participating with GPs in new collaborative care models. The following question is addressed in this study: What motivates medical specialists to initiate and sustain new models for collaborating with GPs? METHODS: We conducted semi-structured interviews with eighteen medical specialists in the province of Groningen, in the North of The Netherlands. The sampling criteria were age, gender, type of hospital in which they were practicing, and specialty. The interviews were recorded, fully transcribed, and analysed by three researchers working independently. The resulting motivational factors were grouped into categories. RESULTS: 'Teaching GPs' and 'regulating patient flow' (referrals) appeared to dominate when the motivational factors were considered. In addition, specialists want to develop relationships with the GPs on a more personal level. Most specialists believe that there is not much they can learn from GPs. 'Lack of time', 'no financial compensation', and 'no support from colleagues' were considered to be the main concerns to establishing collaborative care practices. Additionally, projects were often experienced as too complex and time consuming whereas guidelines were experienced as too restrictive. CONCLUSION: Specialists are particularly interested in collaborating because the GP is the gatekeeper for access to secondary health care resources. Specialists feel that they are able to teach the GPs something, but they do not feel that they have anything to learn from the GPs. With respect to professional expertise, therefore, specialists do not consider GPs as equals. Once personal relationships with the GPs have been established, an informal network with incidental professional contact seems to be sufficient to satisfy the collaborative needs of the specialist. The concerns seem to outweigh any positive motivational forces to developing new models of collaborative practice

Motives and preferences of general practitioners for new collaboration models with medical specialists: a qualitative study

BACKGROUND: Collaboration between general practitioners (GPs) and specialists has been the focus of many collaborative care projects during the past decade. Unfortunately, quite a number of these projects failed. This raises the question of what motivates GPs to initiate and continue participating with medical specialists in new collaborative care models. The following two questions are addressed in this study: What motivates GPs to initiate and sustain new models for collaborating with medical specialists? What kind of new collaboration models do GPs suggest? METHODS: A qualitative study design was used. Starting in 2003 and finishing in 2005, we conducted semi-structured interviews with a purposive sample of 21 Dutch GPs. The sampling criteria were age, gender, type of practice, and practice site. The interviews were recorded, fully transcribed, and analysed by two researchers working independently. The resulting motivational factors and preferences were grouped into categories. RESULTS: 'Developing personal relationships' and 'gaining mutual respect' appeared to dominate when the motivational factors were considered. Besides developing personal relationships with specialists, the GPs were also interested in familiarizing specialists with the competencies attached to the profession of family medicine. Additionally, they were eager to increase their medical knowledge to the benefit of their patients. The GPs stated a variety of preferences with respect to the design of new models of collaboration. CONCLUSION: Developing personal relationships with specialists appeared to be one of the dominant motives for increased collaboration. Once the relationships have been formed, an informal network with occasional professional contact seemed sufficient. Although GPs are interested in increasing their knowledge, once they have reached a certain level of expertise, they shift their focus to another specialty. The preferences for new collaboration models are diverse. A possible explanation for the differences in the preferences is that professionals are more knowledge driven than organisation driven as the acquiring of new knowledge is considered more important than the route by which this is achieved. A new collaboration model seems a way to acquire knowledge. Once this is achieved the importance of a model possibly diminishes, whereas the professional relationships last