Superlight small bipolarons

Recent angle-resolved photoemission spectroscopy (ARPES) has identified that a finite-range Fr\"ohlich electron-phonon interaction (EPI) with c-axis polarized optical phonons is important in cuprate superconductors, in agreement with an earlier proposal by Alexandrov and Kornilovitch. The estimated unscreened EPI is so strong that it could easily transform doped holes into mobile lattice bipolarons in narrow-band Mott insulators such as cuprates. Applying a continuous-time quantum Monte-Carlo algorithm (CTQMC) we compute the total energy, effective mass, pair radius, number of phonons and isotope exponent of lattice bipolarons in the region of parameters where any approximation might fail taking into account the Coulomb repulsion and the finite-range EPI. The effects of modifying the interaction range and different lattice geometries are discussed with regards to analytical strong-coupling/non-adiabatic results. We demonstrate that bipolarons can be simultaneously small and light, provided suitable conditions on the electron-phonon and electron-electron interaction are satisfied. Such light small bipolarons are a necessary precursor to high-temperature Bose-Einstein condensation in solids. The light bipolaron mass is shown to be universal in systems made of triangular plaquettes, due to a novel crab-like motion. Another surprising result is that the triplet-singlet exchange energy is of the first order in the hopping integral and triplet bipolarons are heavier than singlets in certain lattice structures at variance with intuitive expectations. Finally, we identify a range of lattices where superlight small bipolarons may be formed, and give estimates for their masses in the anti-adiabatic approximation.Comment: 31 pages. To appear in J. Phys.: Condens. Matter, Special Issue 'Mott's Physics

Modulation of triglyceride and cholesterol ester synthesis impairs assembly of infectious hepatitis C virus

In hepatitis C virus infection, replication of the viral genome and virion assembly are linked to cellular metabolic processes. In particular, lipid droplets, which store principally triacylglycerides (TAGs) and cholesterol esters (CEs), have been implicated in production of infectious virus. Here, we examine the effect on productive infection of triacsin C and YIC-C8-434, which inhibit synthesis of TAGs and CEs by targeting long-chain acyl-CoA synthetase and acyl-CoA:cholesterol acyltransferase, respectively. Our results present high resolution data on the acylglycerol and cholesterol ester species that were affected by the compounds. Moreover, triacsin C, which blocks both triglyceride and cholesterol ester synthesis, cleared most of the lipid droplets in cells. By contrast, YIC-C8-434, which only abrogates production of cholesterol esters, induced an increase in size of droplets. Although both compounds slightly reduced viral RNA synthesis, they significantly impaired assembly of infectious virions in infected cells. In the case of triacsin C, reduced stability of the viral core protein, which forms the virion nucleocapsid and is targeted to the surface of lipid droplets, correlated with lower virion assembly. In addition, the virus particles that were released from cells had reduced specific infectivity. YIC-C8-434 did not alter the association of core with lipid droplets but appeared to decrease production of infectious virus particles, suggesting a block in virion assembly. Thus, the compounds have antiviral properties, indicating that targeting synthesis of lipids stored in lipid droplets might be an option for therapeutic intervention in treating chronic hepatitis C virus infection

Hole-depletion of ladders in Sr14_{14}Cu24_{24}O41_{41} induced by correlation effects

The hole distribution in Sr$_{14}$Cu$_{24}$O$_{41}$ is studied by low temperature polarization dependent O K Near-Edge X-ray Absorption Fine Structure measurements and state of the art electronic structure calculations that include core-hole and correlation effects in a mean-field approach. Contrary to all previous analysis, based on semi-empirical models, we show that correlations and antiferromagnetic ordering favor the strong chain hole-attraction. For the remaining small number of holes accommodated on ladders, leg-sites are preferred to rung-sites. The small hole affinity of rung-sites explains naturally the 1D - 2D cross-over in the phase diagram of (La,Y,Sr,Ca)$_{14}$Cu$_{24}$O$_{41}$Comment: 6 pages, 8 figure

Blood pressure measurement at two years in offspring of women randomized to a trial of metformin for GDM: follow up data from the MiG trial

Background: Offspring born following maternal gestational diabetes are at risk of excessive childhood weight gain and Type 2 diabetes in childhood, which in turn is associated with an increased rate of hypertension. We aimed to determine the systolic and diastolic blood pressure at two years of age in a cohort of children exposed to gestational diabetes mellitus using data from the MiG trial of metformin use in gestational diabetes. The secondary aim was to analyze these data by randomization of treatment to insulin or metformin. Methods: The offspring of women who had gestational diabetes and had been assigned to either open treatment with metformin (with supplemental insulin if required) or insulin in the MiG trial were followed up at 2 years of age. Oscillometric measurement of BP in the right arm was performed by a researcher using an appropriately sized cuff. Results: A total of 489 measurement blood pressure measurements were obtained in 170 of the 222 children who were seen at a median (range) age of 29 (22-38) months corrected gestational age. At the time of assessment the mean (SD) weight and height was 13.8(2) kg and 90 (4.2) cm respectively. For the whole group the mean (SD) systolic pressure was 90.9 (9.9) mmHg and mean (SD) diastolic pressure was 55.7 (8.1) mmHg. No difference was found between the metformin and insulin treatment arms. In a regression model, height and weight were only two factors associated with the levels of systolic blood pressure. For each additional kg the systolic blood pressure increased by 1.0 mmHg. For each additional cm of height the systolic blood pressure increased by 0.42 mmHg. Conclusions: Blood pressure data was obtained at approximately two years of age in a substantial cohort of children whose mothers received treatment for GDM. These novel data compare favorably with published norms. Clinical Trials Registry: This study was registered under the Australian New Zealand Clinical Trials Registry ( ACTRN12605000311651 ).Malcolm R Battin, Victor Obolonkin, Elaine Rush, William Hague, Suzette Coat and Janet Rowa

Modification of a charged-Bose-gas model for observed room-temperature superconductivity in narrow channels through films of oxidised atactic polypropylene

Reasons have been found for thinking that the minimum diameter of channels of a given length to support superconductivity at room temperature through films of oxidised atactic polypropylene (OAPP) is considerably larger than found in a model for Bose condensation in an array of nanofilaments [D.M. Eagles, Phil. Mag. 85, 1931 (2005)] used previously. This model was introduced to interpret experimental results dating from 1988 on OAPP. The channels are thought to be of larger diameter than believed before because, for an N-S-N system where the superconductor consists of an array of single-walled carbon nanotubes, the resistance, for good contacts, is R_Q/2N, where N is the number of nanotubes and R_Q=12.9 kOhm [See e.g. M. Ferrier et al., Solid State Commun. 131, 615 (2004)]. We assume this would be 2R_Q/N for a triplet superconductor with all spins in the same direction and no orbital degeneracy, which may be the case for nanofilaments in OAPP. Hence one may infer a minimum number of filaments for a given resistance. In the present model, the E(K) curve for the bosons is taken to be of a Bogoliubov form, but with a less steep initial linear term in the dispersion at T_c than occurs at low T. This form is different from the simple linear plus quadratic dispersion, with a steeper initial slope, used in my 2005 paper. A combination of theory and experimental data has been used to find approximate constraints on parameters appearing in the theory.Comment: Publication details added. Correction to bracketing in Eq. (1), which was incorrect in v1 of preprint and in the published articl

Observation of magnetic circular dichroism in Fe L_{2,3} x-ray-fluorescence spectra

We report experiments demonstrating circular dichroism in the x-ray-fluorescence spectra of magnetic systems, as predicted by a recent theory. The data, on the L_{2,3} edges of ferromagnetic iron, are compared with fully relativistic local spin density functional calculations, and the relationship between the dichroic spectra and the spin-resolved local density of occupied states is discussed

Metformin in gestational diabetes: The Offspring Follow-Up (MiG TOFU): body composition at 2 years of age

OBJECTIVE: In women with gestational diabetes mellitus, who were randomized to metformin or insulin treatment, pregnancy outcomes were similar (Metformin in Gestational diabetes [MiG] trial). Metformin crosses the placenta, so it is important to assess potential effects on growth of the children. RESEARCH DESIGN AND METHODS: In Auckland, New Zealand, and Adelaide, Australia, women who had participated in the MiG trial were reviewed when their children were 2 years old. Body composition was measured in 154 and 164 children whose mothers had been randomized to metformin and insulin, respectively. Children were assessed with anthropometry, bioimpedance, and dual energy X-ray absorptiometry (DEXA), using standard methods. RESULTS: The children were similar for baseline maternal characteristics and pregnancy outcomes. In the metformin group, compared with the insulin group, children had larger mid-upper arm circumferences (17.2 6 1.5 vs. 16.7 6 1.5 cm; P = 0.002) and subscapular (6.3 6 1.9 vs. 6.0 6 1.7 mm; P = 0.02) and biceps skinfolds (6.03 6 1.9 vs. 5.6 6 1.7 mm; P = 0.04). Total fat mass and percentage body fat assessed by bioimpedance (n = 221) and DEXA (n = 114) were not different. CONCLUSIONS: Children exposed to metformin had larger measures of subcutaneous fat, but overall body fat was the same as in children whose mothers were treated with insulin alone. Further follow-up is required to examine whether these findings persist into later life and whether children exposed to metformin will develop less visceral fat and be more insulin sensitive. If so, this would have significant implications for the current pandemic of diabetes.Janet A. Rowan, Elaine C. Rush, Victor Obolonkin, Malcolm Battin, Trecia Wouldes and William M. Hagu

Neurological impact of emboli during adult cardiac surgery.

OBJECTIVES: This study draws on advances in Doppler ultrasound bubble sizing to investigate whether high volumes of macro-bubbles entering the brain during cardiac surgery increase the risk of new cerebral microbleeds (CMBs), ischemic MR lesions, or post-operative cognitive decline (POCD). METHODS: Transcranial Doppler (TCD) ultrasound recordings were analysed to estimate numbers of emboli and macrobubbles (>100 μm) entering the brain during cardiac surgery. Logistic regression was used to explore the hypothesis that emboli characteristics affect the incidence of new brain injuries identified through pre- and post-operative MRI and neuropsychological testing. RESULTS: TCD, MRI, and neuropsychological test data were compared between 28 valve and 18 CABG patients. Although valve patients received over twice as many emboli per procedure [median: 1995 vs. 859, p = .004], and seven times as many macro-bubbles [median: 218 vs. 28, p = .001], high volumes of macrobubbles were not found to be significantly associated with new CMBs, new ischaemic lesions, or POCD. The odds of acquiring new CMBs increased by approximately 5% [95% CI: 1 to 10%] for every embolus detected in the first minute after the release of the aortic cross-clamp (AxC). Logistic regression models also confirmed previous findings that cardiopulmonary bypass time and valve surgery were significant predictors for new CMBs (both p = .03). Logistic regression analysis estimated an increase in the odds of acquiring new CMBs of 6% [95% CI: 1 to 12%] for every minute of bypass time over 91 mins. CONCLUSIONS: This small study provides new information about the properties and numbers of bubbles entering the brain during surgery, but found no evidence to substantiate a direct link between large numbers of macrobubbles and adverse cognitive or MR outcome. Clinical Trial Registration URL - http://www.isrctn.com. Unique identifier: 66022965

Metformin in gestational diabetes: the offspring follow-up (MiG TOFU): body composition and metabolic outcomes at 7-9 years of age

Objective: To compare body composition and metabolic outcomes at 7–9 years in offspring of women with gestational diabetes (GDM) randomized to metformin (±insulin) or insulin treatment during pregnancy. Research design and methods: Children were assessed at 7 years in Adelaide (n=109/181) and 9 years in Auckland (n=99/396) by anthropometry, bioimpedance analysis (BIA), dual-energy X-ray absorptiometry (DXA), magnetic resonance imaging (MRI) (n=92/99) and fasting bloods (n=82/99). Results: In the Adelaide subgroup, mothers were similar at enrollment. Women randomized to metformin versus insulin had higher treatment glycemia (p=0.002) and more infants with birth weight >90th percentile (20.7% vs 5.9%; p=0.029). At 7 years, there were no differences in offspring measures. In Auckland, at enrollment, women randomized to metformin had a higher body mass index (BMI) (p=0.08) but gained less weight during treatment (p=0.07). Offspring birth measures were similar. At 9 years, metformin offspring were larger by measures of weight, arm and waist circumferences, waist:height (p<0.05); BMI, triceps skinfold (p=0.05); DXA fat mass and lean mass (p=0.07); MRI abdominal fat volume (p=0.051). Body fat percent was similar between treatment groups by DXA and BIA. Abdominal fat percentages (visceral adipose tissue, subcutaneous adipose tissue and liver) were similar by MRI. Fasting glucose, triglyceride, insulin, insulin resistance, glycosylated hemoglobin (HbA1c), cholesterol, liver transaminases, leptin and adiponectin were similar. Conclusions: Metformin or insulin for GDM was associated with similar offspring total and abdominal body fat percent and metabolic measures at 7–9 years. Metformin-exposed children were larger at 9 years. Metformin may interact with fetal environmental factors to influence offspring outcomes.Janet A Rowan, Elaine C Rush, Lindsay D Plank, Jun Lu, Victor Obolonkin, Suzette Coat, William M Hagu

Numerical optimization of spherical variable-line-spacing grating X-ray spectrometers

Operation of an X-ray spectrometer based on a spherical variable-line-spacing grating is analyzed using dedicated ray-tracing software allowing fast optimization of the grating parameters and spectrometer geometry