Anomalous microwave conductivity coherence peak in c-axis MgB2 thin film

The temperature dependence of the real part of the microwave complex conductivity at 17.9 GHz obtained from surface impedance measurements of two c-axis oriented MgB2 thin films reveals a pronounced maximum at a temperature around 0.6 times the critical temperature. Calculations in the frame of a two-band model based on Bardeen-Cooper-Schrieffer (BCS) theory suggest that this maximum corresponds to an anomalous coherence peak resembling the two-gap nature of MgB2. Our model assumes there is no interband impurity scattering and a weak interband pairing interaction, as suggested by bandstructure calculations. In addition, the observation of a coherence peak indicates that the pi-band is in the dirty limit and dominates the total conductivity of our filmsComment: 10 pages, 4 figures, to be published in Phys. Rev. Let

Maternal and Perinatal Outcomes among Maternity Waiting Home Users and Non-Users in Rural Rwanda

Most maternal and perinatal deaths could be prevented through timely access to skilled birth attendants. Women should access appropriate obstetric care during pregnancy, labor, and puerperium. Maternity waiting homes (MWHs) permit access to emergency obstetric care when labor starts. This study compared maternal and perinatal outcomes among MWH users and non-users through a retrospective cohort study. Data were collected through obstetric chart reviews and analyzed using STATA version 15. Of the 8144 deliveries reported between 2015 and 2019, 1305 women had high-risk pregnancies and were included in the study. MWH users had more spontaneous vaginal deliveries compared to non-users (38.6% versus 16.8%) and less cesarean sections (57.7% versus 76.7%). Maternal morbidities such as postpartum hemorrhage occurred less frequently among users than non-users (2.13% versus 5.64%). Four women died among non-users while there was no death among users. Non-users had more stillbirths than users (7.68% versus 0.91%). The MWH may have contributed to the observed differences in outcomes. However, many women with high risk pregnancies did not use the MWH, indicating a probable gap in awareness, usefulness, or their inability to stay due to other responsibilities at home. Use of MWHs at scale could improve maternal and perinatal outcomes in Rwanda

Quantum interference and Klein tunneling in graphene heterojunctions

The observation of quantum conductance oscillations in mesoscopic systems has traditionally required the confinement of the carriers to a phase space of reduced dimensionality. While electron optics such as lensing and focusing have been demonstrated experimentally, building a collimated electron interferometer in two unconfined dimensions has remained a challenge due to the difficulty of creating electrostatic barriers that are sharp on the order of the electron wavelength. Here, we report the observation of conductance oscillations in extremely narrow graphene heterostructures where a resonant cavity is formed between two electrostatically created bipolar junctions. Analysis of the oscillations confirms that p-n junctions have a collimating effect on ballistically transmitted carriers. The phase shift observed in the conductance fringes at low magnetic fields is a signature of the perfect transmission of carriers normally incident on the junctions and thus constitutes a direct experimental observation of ``Klein Tunneling.''Comment: 13 pages and 6 figures including supplementary information. The paper has been modified in light of new theoretical results available at arXiv:0808.048

Emergence of Superlattice Dirac Points in Graphene on Hexagonal Boron Nitride

The Schr\"odinger equation dictates that the propagation of nearly free electrons through a weak periodic potential results in the opening of band gaps near points of the reciprocal lattice known as Brillouin zone boundaries. However, in the case of massless Dirac fermions, it has been predicted that the chirality of the charge carriers prevents the opening of a band gap and instead new Dirac points appear in the electronic structure of the material. Graphene on hexagonal boron nitride (hBN) exhibits a rotation dependent Moir\'e pattern. In this letter, we show experimentally and theoretically that this Moir\'e pattern acts as a weak periodic potential and thereby leads to the emergence of a new set of Dirac points at an energy determined by its wavelength. The new massless Dirac fermions generated at these superlattice Dirac points are characterized by a significantly reduced Fermi velocity. The local density of states near these Dirac cones exhibits hexagonal modulations indicating an anisotropic Fermi velocity.Comment: 16 pages, 6 figure

MicroRNAs: the primary cause or a determinant of progression in leukemia?

available in PMC 2011 October 10.Leukemia is a complex disease with many different types and subtypes caused by a huge diversity of genetic and epigenetic aberrations. Until recently, alterations of protein-coding genes were thought to be the sole cause of tumorigenesis. With the recent discovery of multiple types of non-coding RNAs, it has become evident that mutations in these also contribute to the development of cancer. Among the non-coding RNAs, microRNAs play a crucial role in cancer owing to their involvement in fundamental processes such as apoptosis, differentiation and proliferation. MicroRNAs are small noncoding RNAs (approximately 19–25 nucleotides in length) that bind to and downregulate multiple mRNA targets; in mammals, the production of over a third of all proteins is regulated by microRNAs [3]. Several studies demonstrated that microRNAs are involved in leukemia progression but their role as the primary cause or a determinant of progression in leukemia has been unclear. Some have been identified as oncogenes or tumor suppressor genes, which suggests that they are playing a central role in tumorigenesis, while others appear to be associated with a specific stage in disease progression. Deciphering the exact role of microRNAs in oncogenesis is important in order to improve the diagnosis and treatment of leukemia patients.National Institutes of Health (U.S.) (NIH grant DK068348)National Institutes of Health (U.S.) (NIH Grant 5P01 HL066105)Leukemia & Lymphoma Society of America (Recherche sur le Cancer (ARC) fellowship

Estimated Prevalence and Risk Factor for Age-related Maculopathy

PURPOSE: To assess the estimate prevalence and risk factors for age-related maculopathy (ARM) in Seoul, Korea. PATIENTS AND METHODS: We examined 9,530 subjects with, 40 years of age or older between January 2006 and December 2006 in Seoul, Korea. Subjects underwent fundus photography, clinical examinations (including blood analyses), and completed detailed questionnaires. Fundus images were graded according to definitions from the Wisconsin Age-Related Maculopathy Grading System. RESULTS: ARM was present in 235 subjects, corresponding to an estimate prevalence of 2.46%. Hepatitis B infection (positive status for HBsAg and HBcAb), serum triglyceride levels and high density lipoprotein levels remained as significant risk factors after age-adjustment. Multivariate analyses showed that the prevalence of ARM was significantly higher in older subjects [odds ratio (OR) 1.134; 95% CI 1.114-1.154] and those who were seropositive for hepatitis B surface antigen (OR 2.566; 95% CI 1.519-4.335). CONCLUSION: The estimated prevalence of ARM was 2.46%. Age and hepatitis B infection may increase the risk of ARM.ope

Tunable few-electron double quantum dots and Klein tunnelling in ultra-clean carbon nanotubes

Quantum dots defined in carbon nanotubes are a platform for both basic scientific studies and research into new device applications. In particular, they have unique properties that make them attractive for studying the coherent properties of single electron spins. To perform such experiments it is necessary to confine a single electron in a quantum dot with highly tunable barriers, but disorder has until now prevented tunable nanotube-based quantum-dot devices from reaching the single-electron regime. Here, we use local gate voltages applied to an ultra-clean suspended nanotube to confine a single electron in both a single quantum dot and, for the first time, in a tunable double quantum dot. This tunability is limited by a novel type of tunnelling that is analogous to that in the Klein paradox of relativistic quantum mechanics.Comment: 21 pages including supplementary informatio

Shaping bursting by electrical coupling and noise

Gap-junctional coupling is an important way of communication between neurons and other excitable cells. Strong electrical coupling synchronizes activity across cell ensembles. Surprisingly, in the presence of noise synchronous oscillations generated by an electrically coupled network may differ qualitatively from the oscillations produced by uncoupled individual cells forming the network. A prominent example of such behavior is the synchronized bursting in islets of Langerhans formed by pancreatic \beta-cells, which in isolation are known to exhibit irregular spiking. At the heart of this intriguing phenomenon lies denoising, a remarkable ability of electrical coupling to diminish the effects of noise acting on individual cells. In this paper, we derive quantitative estimates characterizing denoising in electrically coupled networks of conductance-based models of square wave bursting cells. Our analysis reveals the interplay of the intrinsic properties of the individual cells and network topology and their respective contributions to this important effect. In particular, we show that networks on graphs with large algebraic connectivity or small total effective resistance are better equipped for implementing denoising. As a by-product of the analysis of denoising, we analytically estimate the rate with which trajectories converge to the synchronization subspace and the stability of the latter to random perturbations. These estimates reveal the role of the network topology in synchronization. The analysis is complemented by numerical simulations of electrically coupled conductance-based networks. Taken together, these results explain the mechanisms underlying synchronization and denoising in an important class of biological models