On the Reconstructed Fermi Surface in the Underdoped Cuprates

The Fermi surface topologies of underdoped samples the high-Tc superconductor Bi2212 have been measured with angle resolved photoemission. By examining thermally excited states above the Fermi level, we show that the Fermi surfaces in the pseudogap phase of underdoped samples are actually composed of fully enclosed hole pockets. The spectral weight of these pockets is vanishingly small at the anti-ferromagnetic zone boundary, which creates the illusion of Fermi "arcs" in standard photoemission measurements. The area of the pockets as measured in this study is consistent with the doping level, and hence carrier density, of the samples measured. Furthermore, the shape and area of the pockets is well reproduced by a phenomenological model of the pseudogap phase as a spin liquid.Comment: 4 pages, 4 figures. Submitted to Physics Review Letter

High-energy kink in high-temperature superconductors

In conventional metals, electron-phonon coupling, or the phonon-mediated interaction between electrons, has long been known to be the pairing interaction responsible for the superconductivity. The strength of this interaction essentially determines the superconducting transition temperature TC. One manifestation of electron-phonon coupling is a mass renormalization of the electronic dispersion at the energy scale associated with the phonons. This renormalization is directly observable in photoemission experiments. In contrast, there remains little consensus on the pairing mechanism in cuprate high temperature superconductors. The recent observation of similar renormalization effects in cuprates has raised the hope that the mechanism of high temperature superconductivity may finally be resolved. The focus has been on the low energy renormalization and associated "kink" in the dispersion at around 50 meV. However at that energy scale, there are multiple candidates including phonon branches, structure in the spin-fluctuation spectrum, and the superconducting gap itself, making the unique identification of the excitation responsible for the kink difficult. Here we show that the low-energy renormalization at ~50 meV is only a small component of the total renormalization, the majority of which occurs at an order of magnitude higher energy (~350 meV). This high energy kink poses a new challenge for the physics of the cuprates. Its role in superconductivity and relation to the low-energy kink remains to be determined.Comment: 13 pages, 4 figure

THE ANTICOAGULANT AND ANTILYMPHOMA PROPERTIES OF ARSENIC AZOPROTEINS : I. ANTICOAGULANT EFFECTS OF ARSENIC AZOPROTEINS IN VIVO AND IN VITRO: COMPARISON OF ARSENICALS AS ANTICOAGULANTS AND AS ANTILYMPHOMA AGENTS: MOLECULAR STRUCTURE IN RELATION TO ANTICOAGULANT AND ANTILYMPHOMA PROPERTIES

Experiments given in this paper have shown that 4-arsonophenylazoproteins possess marked anticoagulant activity both in vivo and in vitro. Mice and rabbits given moderate amounts of the arsenic azoprotein, for example, often bled to death from injuries that proved trivial in control animals, and their blood remained liquid during many hours' postmortem even when left in contact with transected tissues, fibrinolysis having no part in the outcome. So, too, the addition of minute amounts of 4-arsonophenylazoprotein to plasma procured from citrated rabbit or human blood greatly prolonged the time required for clotting after recalcification. Other arsenic-containing compounds,—for example, those in which arsenic See PDF for Structure was joined to amino acids or peptides through the azo linkage, or to proteins through couplings other than the azo linkage,—were largely devoid of anticoagulant and antilymphoma effects. The findings as a whole show clearly that the structural requirements for anticoagulant and antilymphoma effects are: (a) possession of negatively charged arsonic or arsinoso groups, (b) large molecular size (protein), and (c) linkage of arsenic-containing groups to protein through the azo bond. Two acidic azoproteins that were devoid of arsenic,—namely 4-carboxyphenylazoprotein and 4-sulfonophenylazoprotein,—were also found to have marked anticoagulant effects in vitro, but they had no inhibitory action against cells of Lymphoma 6C3HED in vivo, even when they were given to mice in maximum tolerated amounts. The essential part played by arsenic in the antilymphoma activity of arsenic azoproteins was further emphasized by the action of dimercaprol (BAL) in preventing the antilymphoma effects of 4-arsonophenylazoprotein on Lymphoma 6C3HED cells in vivo. In an associated paper the anticoagulant and antilymphoma effects of 4-arsonophenylazoproteins are studied further, and consideration is given to the ways in which these effects may be brought about

Fine Details of the Nodal Electronic Excitations in Bi2_2Sr2_2CaCu2_2O8+δ_{8+\delta}

Very high energy resolution photoemission experiments on high quality samples of optimally doped Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ show new features in the low-energy electronic excitations. A marked change in the binding energy and temperature dependence of the near-nodal scattering rates is observed near the superconducting transition temperature, $T_C$. The temperature slope of the scattering rate measured at low energy shows a discontinuity at ~$T_C$. In the superconducting state, coherent excitations are found with the scattering rates showing a cubic dependence on frequency and temperature. The superconducting gap has a d-wave magnitude with negligible contribution from higher harmonics. Further, the bi-layer splitting has been found to be finite at the nodal point.Comment: 5 pages, 4 figure

Doping of a One-Dimensional Mott Insulator: Photoemision and Optical Studies of Sr2_2CuO3+δ_{3+\delta}

The spectral properties of a one-dimensional (1D) single-chain Mott insulator Sr$_2$CuO$_{3}$ have been studied in angle-resolved photoemission and optical spectroscopy, at half filling and with small concentrations of extra charge doped into the chains via high oxygen pressure growth. The single- particle gap is reduced with oxygen doping, but the metallic state is not reached. The bandwidth of the charge-transfer band increases with doping, while the state becomes narrower, allowing unambiguous observation of separated spinon and holon branches in the doped system. The optical gap is not changed upon doping, indicating that a shift of chemical potential rather than decrease of corelation gap is responsible for the apparent reduction of the photoemission gap.Comment: 4 pages, 2 figure

Breeding \u3cem\u3eLotus Australis\u3c/em\u3e Andrews for Low Cyanide Content

Lotus australis Andrews is a native perennial tetraploid legume (2n=4x=28) widely distributed throughout Australia (Figure 1). It is highly variable with 14 botanical varieties reported in the Australian Plant Name Index (http://www.anbg.gov.au). Despite broad adaptation within L. australis no cultivars have been developed for cultivation. One of the main barriers to cultivation is the reported cyanogenic nature of the species (Foulds, 1982), which makes it potentially toxic when plant cyanogenic glycosides are fully hydrolysed to form hydrogen cyanide (HCN). Foulds (1982) also reported that the cyanophoric trait was polymorphic at seedling and adult stages with 12% of plants acyanogenic in some populations. . The Cooperative Research Center for Plant-Based Management of Dryland Salinity, financially supported by Australian Wool Innovation has commenced a breeding program to develop a non-toxic cultivar of L. australis. The selection criterion of the first phase of the breeding programme was for low HCN production. Once this trait is stabilised, forage production and seed yield as well as general plant health will be the main breeding objectives

Impact of an educational video as a consent tool on knowledge about cure research among patients and caregivers at HIV clinics in South Africa

Background: Despite increasing access to antiretroviral therapy in low- and middle-income countries, only 54% of eligible individuals were receiving treatment in Africa by 2015. Recent developments in HIV cure research have been encouraging. However, the complex science and procedures of cure research render the informed consent process challenging. Objective: This study evaluates the impact of a video tool on educating participants about HIV cure. Methods: A questionnaire assessing the content of the video was administered to adults recruited from two clinics in South Africa. Patients and their care partners, who provided voluntary informed consent, were included in the study. The questionnaire was administered in each participant‘s home language before, immediately after and at 3 months after viewing the video, in an uncontrolled quasi-experimental ‘one group pre-test–post-test’ design. Scoring was carried out according to a predetermined scoring grid, with a maximum score of 22. Results: A total of 88 participants, median age 32.0 years and 86% female, were enrolled and completed the pre- and post-video questionnaires. Twenty-nine (33%) completed the follow-up questionnaire 3 months later to assess retention of knowledge. Sixty-three (72%) participants had a known HIV-positive status. A significant increase (10.1 vs 15.1, P=0.001) in knowledge about HIV and HIV cure immediately after viewing the video was noted. No statistically significant difference in knowledge between HIV-positive and -negative patients was noted at baseline. After 3 months, a decrease in performance participation (14 vs 13.5, P=0.19) was noted. However, knowledge scores achieved after 3 months remained significantly higher than scores at baseline (13.5 vs 9.5, P<0.01). Conclusions: This research showed that a video intervention improved participants’ knowledge related to HIV, HIV cure research and ethics, and the improvement was sustained over 3 months. Video intervention may be a useful tool to add to the consent process when dealing with complex medical research questions

Analysis of Mars Analogue Soil Samples Using Solid-Phase Microextraction, Organic Solvent Extraction and Gas Chromatography/Mass Spectrometry

Polycyclic aromatic hydrocarbons (PAHs) are robust and abundant molecules in extraterrestrial environments. They are found ubiquitously in the interstellar medium and have been identified in extracts of meteorites collected on Earth. PAHs are important target molecules for planetary exploration missions that investigate the organic inventory of planets, moons and small bodies. This study is part of an interdisciplinary preparation phase to search for organic molecules and life on Mars. We have investigated PAH compounds in desert soils to determine their composition, distribution and stability. Soil samples (Mars analogue soils) were collected at desert areas of Utah in the vicinity of the Mars Desert Research Station (MDRS), in the Arequipa region in Peru and from the Jutland region of Denmark. The aim of this study was to optimize the solid-phase microextraction (SPME) method for fast screening and determination of PAHs in soil samples. This method minimizes sample handling and preserves the chemical integrity of the sample. Complementary liquid extraction was used to obtain information on five- and six-ring PAH compounds. The measured concentrations of PAHs are, in general, very low, ranging from 1 to 60 ng g(sup -1). The texture of soils is mostly sandy loam with few samples being 100% silt. Collected soils are moderately basic with pH values of 8-9 except for the Salten Skov soil, which is slightly acidic. Although the diverse and variable microbial populations of the samples at the sample sites might have affected the levels and variety of PAHs detected, SPME appears to be a rapid, viable field sampling technique with implications for use on planetary missions