Anisotropic Magnetoresistance in Charge-Ordering Na0.34(H3O)0.15CoO2Na_{0.34}(H_3O)_{0.15}CoO_2:Strong Spin-Charge Coupling and Spin Ordering

Angular-dependent in-plane magnetoresistance (AMR) for single crystal $Na_{0.34}(H_3O)_{0.15}CoO_2$ with charge ordering is studied systematically. The anisotropic magnetoresistance shows a twofold symmetry at high temperature with rotating H in the Co-O plane, while a sixfold symmetry below a certain temperature ($T_\rho$). At $T_\rho$, the symmetry of AMR changes from twofold to fourfold with rotating magnetic field (H) in the plane consisting of the current and c-axis. The variation of AMR symmetry with temperature arises from the subtle changes of the spin structure. These results give a direct evidence for the itinerant electrons directly coupled to the localized spins.Comment: 4 pages, 4 figure

Large enhancement of the thermopower in Nax_xCoO2_2 at high Na doping

Research on the oxide perovskites has uncovered electronic properties that are strikingly enhanced compared with those in conventional metals. Examples are the high critical temperatures of the cuprate superconductors and the colossal magnetoresistance in the manganites. The conducting layered cobaltate $\rm Na_xCoO_2$ displays several interesting electronic phases as $x$ is varied including water-induced superconductivity and an insulating state that is destroyed by field. Initial measurements showed that, in the as-grown composition, $\rm Na_xCoO_2$ displays moderately large thermopower $S$ and conductivity $\sigma$. However, the prospects for thermoelectric cooling applications faded when the figure of merit $Z$ was found to be small at this composition (0.6$<x<$0.7). Here we report that, in the poorly-explored high-doping region $x>$0.75, $S$ undergoes an even steeper enhancement. At the critical doping $x_p\sim$ 0.85, $Z$ (at 80 K) reaches values $\sim$40 times larger than in the as-grown crystals. We discuss prospects for low-temperature thermoelectric applications.Comment: 6 pages, 7 figure

Bulk antiferromagnetism in Na0.82CoO2\bf Na_{0.82}CoO_2 single crystals

Susceptibility, specific heat, and muon spin rotation measurements on high-quality single crystals of $\rm Na_{0.82}CoO_2$ have revealed bulk antiferromagnetism with N\'{e}el temperature $\rm T_N = 19.8 \pm 0.1$ K and an ordered moment perpendicular to the $\rm CoO_2$ layers. The magnetic order encompasses nearly 100% of the crystal volume. The susceptibility exhibits a broad peak around 30 K, characteristic of two-dimensional antiferromagnetic fluctuations. The in-plane resistivity is metallic at high temperatures and exhibits a minimum at $\rm T_N$.Comment: published versio

Phase segregation in NaxCoO2 for large Na contents

We have investigated a set of sodium cobaltates (NaxCoO2) samples with various sodium content (0.67 \le x \le 0.75) using Nuclear Quadrupole Resonance (NQR). The four different stable phases and an intermediate one have been recognized. The NQR spectra of 59Co allowed us to clearly differentiate the pure phase samples which could be easily distinguished from multi-phase samples. Moreover, we have found that keeping samples at room temperature in contact with humid air leads to destruction of the phase purity and loss of sodium content. The high sodium content sample evolves progressively into a mixture of the detected stable phases until it reaches the x=2/3 composition which appears to be the most stable phase in this part of phase diagram.Comment: 5 pages, 4 figure

Drastic ground state changes induced by Ni substitution in NaxCoO2

We report on the effect of Ni substitution at the Co site on the physical properties of NaxCoO2 system by investigating the series NaxCo1-yNiyO2 (x=0.75, 0<y<0.15). An upturn in the resistivity is observed in all Ni substituted samples as the temperature is lowered, suggestive of the occurrence of a Metal-Insulator Transition (MIT). The temperature at which this transition occurs increases with Ni content. The temperature dependence of the resistivity in the metallic region in the Ni substituted samples shows a T2 dependence, which is qualitatively different from that observed in the pristine sample. The evolution of the Fano asymmetry parameter, extracted by analyzing the lineshape of the IR active in-plane Co-O mode, both as a function of Ni concentration and temperature corroborates the occurrence of the MIT. It is argued that the progressive substitution of the Co4+ ions with Ni increases the probability of double occupancy and therefore the on-site Coulomb interaction energy leading to a shift in the thermodynamically driven MIT to higher temperatures.Comment: 17 pages 9 figures; submitted to Journal Of Phys. Cond. Ma

Expedition 357 Preliminary Report: Atlantis Massif Serpentinization and Life

International Ocean Discovery Program (IODP) Expedition 357 successfully cored an east–west transect across the southern wall of Atlantis Massif on the western flank of the Mid-Atlantic Ridge to study the links between serpentinization processes and microbial activity in the shallow subsurface of highly altered ultramafic and mafic sequences that have been uplifted to the seafloor along a major detachment fault zone. The primary goals of this expedition were to (1) examine the role of serpentinization in driving hydrothermal systems, sustaining microbial communities, and sequestering carbon; (2) characterize the tectonomagmatic processes that lead to lithospheric heterogeneities and detachment faulting; and (3) assess how abiotic and biotic processes change with variations in rock type and progressive exposure on the seafloor. To accomplish these objectives, we developed a coring and sampling strategy based around the use of seabed rock drills—the first time that such systems have been used in the scientific ocean drilling programs. This technology was chosen in hopes of achieving high recovery of the carbonate cap sequences and intact contact and deformation relationships. The expedition plans also included several engineering developments to assess geochemical parameters during drilling; sample bottom water before and after drilling; supply synthetic tracers during drilling for contamination assessment; gather downhole electrical resistivity and magnetic susceptibility logs for assessing fractures, fluid flow, and extent of serpentinization; and seal boreholes to provide opportunities for future experiments. Seventeen holes were drilled at nine sites across Atlantis Massif, with two sites on the eastern end of the southern wall (Sites M0068 and M0075), three sites in the central section of the southern wall north of the Lost City hydrothermal field (Sites M0069, M0072, and M0076), two sites on the western end (Sites M0071 and M0073), and two sites north of the southern wall in the direction of the central dome of the massif and Integrated Ocean Drilling Program Site U1309 (Sites M0070 and M0074). Use of seabed rock drills enabled collection of more than 57 m of core, with borehole penetration ranging from 1.3 to 16.44 meters below seafloor and core recoveries as high as 75% of total penetration. This high level of recovery of shallow mantle sequences is unprecedented in the history of ocean drilling. The cores recovered along the southern wall of Atlantis Massif have highly heterogeneous lithologies, types of alteration, and degrees of deformation. The ultramafic rocks are dominated by harzburgites with intervals of dunite and minor pyroxenite veins, as well as gabbroic rocks occurring as melt impregnations and veins, all of which provide information about early magmatic processes and the magmatic evolution in the southernmost portion of Atlantis Massif. Dolerite dikes and basaltic rocks represent the latest stage of magmatic activity. Overall, the ultramafic rocks recovered during Expedition 357 revealed a high degree of serpentinization, as well as metasomatic talc-amphibole-chlorite overprinting and local rodingitization. Metasomatism postdates an early phase of serpentinization but predates late-stage intrusion and alteration of dolerite dikes and the extrusion of basalt. The intensity of alteration is generally lower in the gabbroic and doleritic rocks. Chilled margins in dolerite intruded into talc-amphibole-chlorite schists are observed at the most eastern Site M0075. Deformation in Expedition 357 cores is variable and dominated by brecciation and formation of localized shear zones; the degree of carbonate veining was lower than anticipated. All types of variably altered and deformed ultramafic and mafic rocks occur as components in sedimentary breccias and as fault scarp rubble. The sedimentary cap rocks include basaltic breccias with a carbonate sand matrix and/or fossiliferous carbonate. Fresh glass on basaltic components was observed in some of the breccias. The expedition also successfully applied new technologies, namely (1) extensively using an in situ sensor package and water sampling system on the seabed drills for evaluating real-time dissolved oxygen and methane, pH, oxidation-reduction potential, temperature, and conductivity during drilling; (2) deploying a borehole plug system for sealing seabed drill boreholes at four sites to allow access for future sampling; and (3) proving that tracers can be delivered into drilling fluids when using seabed drills. The rock drill sensor packages and water sampling enabled detection of elevated dissolved methane and hydrogen concentrations during and/or after drilling, with “hot spots” of hydrogen observed over Sites M0068–M0072 and methane over Sites M0070–M0072. Shipboard determination of contamination tracer delivery confirmed appropriate sample handling procedures for microbiological and geochemical analyses, which will aid all subsequent microbiological investigations that are part of the science party sampling plans, as well as verify this new tracer delivery technology for seabed drill rigs. Shipboard investigation of biomass density in select samples revealed relatively low and variable cell densities, and enrichment experiments set up shipboard reveal growth. Thus, we anticipate achieving many of the deep biosphere–related objectives of the expedition through continued scientific investigation in the coming years. Finally, although not an objective of the expedition, we were serendipitously able to generate a high-resolution (20 m per pixel) multibeam bathymetry map across the entire Atlantis Massif and the nearby fracture zone, Mid-Atlantic Ridge, and eastern conjugate, taking advantage of weather and operational downtime. This will assist science party members in evaluating and interpreting tectonic and mass-wasting processes at Atlantis Massif

Gas and seismicity within the Istanbul seismic gap

Understanding micro-seismicity is a critical question for earthquake hazard assessment. Since the devastating earthquakes of Izmit and Duzce in 1999, the seismicity along the submerged section of North Anatolian Fault within the Sea of Marmara (comprising the “Istanbul seismic gap”) has been extensively studied in order to infer its mechanical behaviour (creeping vs locked). So far, the seismicity has been interpreted only in terms of being tectonic-driven, although the Main Marmara Fault (MMF) is known to strike across multiple hydrocarbon gas sources. Here, we show that a large number of the aftershocks that followed the M 5.1 earthquake of July, 25th 2011 in the western Sea of Marmara, occurred within a zone of gas overpressuring in the 1.5–5 km depth range, from where pressurized gas is expected to migrate along the MMF, up to the surface sediment layers. Hence, gas-related processes should also be considered for a complete interpretation of the micro-seismicity (~M < 3) within the Istanbul offshore domain

Assessment of long-term renal complications in extremely low birth weight children

We assessed the long-term renal complications in a regional cohort of extremely low birth weight (ELBW) children born in 2002–2004. The study group, comprising 78 children born as ELBW infants (88% of the available cohort), was evaluated with measurement of serum cystatin C, urinary albumin excretion, renal ultrasound, and 24-h ambulatory blood pressure measurements. The control group included 38 children born full-term selected from one general practice in the district. Study patients were evaluated at a mean age of 6.7 years, and had a median birthweight of 890 g (25th–75th percentile: 760–950 g) and a median gestational age of 27 weeks (25th–75th percentile: 26–29 weeks). Mean serum cystatin C levels were significantly higher (0.64 vs. 0.59 mg/l; p = 0.01) in the ELBW group. Hypertension was diagnosed in 8/78 ELBW and 2/38 of the control children (p = 0.5). Microalbuminuria (>20 mg/g of creatinine) was detected only in five ELBW children (p = 0.17). The mean renal volume was significantly lower in the ELBW group (absolute kidney volume 81 ml vs. 113 ml; p < 0.001, relative kidney volume 85 vs. 97%; p < 0.001). Abnormally small kidneys (<2/3 of predicted size) were detected in 19 ELBW and four control children (p = 0.08). Multivariate logistic regression revealed that the only independent risk factor for renal complications was weight gained during neonatal hospitalization (odds ratio: 0.67; 95% confidence interval: 0.39–0.94). Serum cystatin C and kidney volume are significantly lower in school-age ELBW children. It is important to include systematic renal evaluation in the follow-up programs of ELBW infants

Disease recurrence in paediatric renal transplantation

Renal transplantation (Tx) is the treatment of choice for end-stage renal disease. The incidence of acute rejection after renal Tx has decreased because of improving early immunosuppression, but the risk of disease recurrence (DR) is becoming relatively high, with a greater prevalence in children than in adults, thereby increasing patient morbidity, graft loss (GL) and, sometimes, mortality rate. The current overall graft loss to DR is 7–8%, mainly due to primary glomerulonephritis (70–80%) and inherited metabolic diseases. The more typical presentation is a recurrence of the full disease, either with a high risk of GL (focal and segmental glomerulosclerosis 14–50% DR, 40–60% GL; atypical haemolytic uraemic syndrome 20–80% DR, 10–83% GL; membranoproliferative glomerulonephritis 30–100% DR, 17–61% GL; membranous nephropathy ∼30% DR, ∼50% GL; lipoprotein glomerulopathy ∼100% DR and GL; primary hyperoxaluria type 1 80–100% DR and GL) or with a low risk of GL [immunoglobulin (Ig)A nephropathy 36–60% DR, 7–10% GL; systemic lupus erythematosus 0–30% DR, 0–5% GL; anti-neutrophilic cytoplasmic antibody (ANCA)-associated glomerulonephritis]. Recurrence may also occur with a delayed risk of GL, such as insulin-dependent diabetes mellitus, sickle cell disease, endemic nephropathy, and sarcoidosis. In other primary diseases, the post-Tx course may be complicated by specific events that are different from overt recurrence: proteinuria or cancer in some genetic forms of nephrotic syndrome, anti-glomerular basement membrane antibodies-associated glomerulonephritis (Alport syndrome, Goodpasture syndrome), and graft involvement as a consequence of lower urinary tract abnormality or human immunodeficiency virus (HIV) nephropathy. Some other post-Tx conditions may mimic recurrence, such as de novo membranous glomerulonephritis, IgA nephropathy, microangiopathy, or isolated specific deposits (cystinosis, Fabry disease). Adequate strategies should therefore be added to kidney Tx, such as donor selection, associated liver Tx, plasmatherapy, specific immunosuppression protocols. In such conditions, very few patients may be excluded from kidney Tx only because of a major risk of DR and repeated GL. In the near future the issue of DR after kidney Tx may benefit from alternatives to organ Tx, such as recombinant proteins, specific monoclonal antibodies, cell/gene therapy, and chaperone molecules