Secondary magnetite in ancient zircon precludes analysis of a Hadean geodynamo.

Zircon crystals from the Jack Hills, Western Australia, are one of the few surviving mineralogical records of Earth's first 500 million years and have been proposed to contain a paleomagnetic record of the Hadean geodynamo. A prerequisite for the preservation of Hadean magnetization is the presence of primary magnetic inclusions within pristine igneous zircon. To date no images of the magnetic recorders within ancient zircon have been presented. Here we use high-resolution transmission electron microscopy to demonstrate that all observed inclusions are secondary features formed via two distinct mechanisms. Magnetite is produced via a pipe-diffusion mechanism whereby iron diffuses into radiation-damaged zircon along the cores of dislocations and is precipitated inside nanopores and also during low-temperature recrystallization of radiation-damaged zircon in the presence of an aqueous fluid. Although these magnetites can be recognized as secondary using transmission electron microscopy, they otherwise occur in regions that are indistinguishable from pristine igneous zircon and carry remanent magnetization that postdates the crystallization age by at least several hundred million years. Without microscopic evidence ruling out secondary magnetite, the paleomagnetic case for a Hadean-Eoarchean geodynamo cannot yet been made.

Multichamber Multipotentiostat System for Cellular Microphysiometry.

Multianalyte microphysiometry is a powerful technique for studying cellular metabolic flux in real time. Monitoring several analytes concurrently in a number of individual chambers, however, requires specific instrumentation that is not available commercially in a single, compact, benchtop form at an affordable cost. We developed a multipotentiostat system capable of performing simultaneous amperometric and potentiometric measurements in up to eight individual chambers. The modular design and custom LabVIEW™ control software provide flexibility and allow for expansion and modification to suit different experimental conditions. Superior accuracy is achieved when operating the instrument in a standalone configuration; however, measurements performed in conjunction with a previously developed multianalyte microphysiometer have shown low levels of crosstalk as well. Calibrations and experiments with primary and immortalized cell cultures demonstrate the performance of the instrument and its capabilities.

Fast automated method for the direct determination of total antimony in grape juice samples by hydride generation and atomic fluorescence spectrometric detection without external pretreatment.

Matrix complexity of fruit juices and their low antimony level requires sensitive, cost-effective instruments, time-consuming and error-prone sample pretreatment methods. Therefore, a flow-batch procedure (HG-FBA-AFS) was developed for the fast and sensitive determination of total inorganic Sb in grape juice samples by hydride generation atomic fluorescence spectrometry. The sample pretreatment, pre-reduction and stibine formation steps run through the mixing chamber. The HCl and NaBH4 concentrations, and carrier gas flowrate were optimized through a Box-Behnken design. The detection limit (LOD) was 20 ng L-1, intra and inter-day precision ranged in 3.0 - 3.5 %, and low errors within (- 2.4 to 6.6 %) for samples containing 1.23 - 4.58 µg L-1 total Sb. Both HG-FBA-AFS and reference method agreed at 95% confidence level. An 87 h-1 sample throughput, and a 1.15 mL total waste per determination attest that HG-FBA-AFS is a fast, and ecofriendly tool for determining Sb in grape juices.

Paleomagnetic evidence for a disk substructure in the early solar system.

Astronomical observations and isotopic measurements of meteorites suggest that substructures are common in protoplanetary disks and may even have existed in the solar nebula. Here, we conduct paleomagnetic measurements of chondrules in CO carbonaceous chondrites to investigate the existence and nature of these disk substructures. We show that the paleomagnetism of chondrules in CO carbonaceous chondrites indicates the presence of a 101 ± 48 µT field in the solar nebula in the outer solar system (~3 to 7 AU from the Sun). The high intensity of this field relative to that inferred from inner solar system (~<3 AU) meteorites indicates a factor of ~5 to 150 mismatch in nebular accretion between the two reservoirs. This suggests substantial mass loss from the disk associated with a major disk substructure, possibly due to a magnetized disk wind.

A fast and sensitive flow-batch method with hydride generating and atomic fluorescence spectrometric detection for automated inorganic antimony speciation in waters.

In this paper, a flow-batch analysis (FBA) system, hydride generation (HG), and atomic fluorescence spectrometry (AFS) are coupled for the first time to develop a fast and sensitive FBA-HG-AFS method for automated inorganic antimony speciation in waters, whether from the sea, mineral water, tap water, or lakes. Unlike previous automated flow methods that use confluent fluids and complex devices, the main advantage of the proposed FBA-HG-AFS method is an innovative use of a simple laboratory made flow-batch chamber to simultaneously perform mixing, homogenization, reactions, antimony hydride formation, and gas-liquid separation. The FBA-HG-AFS method was optimized using two-level full factorial and Box-Behnken designs, and validated on the basis of real repeated measurements and analysis of variance, yielding a satisfactory working range (100-2000 ng L-1), precision (RSD = 4%), sensitivity, and limit of detection (6 ng L-1) for the water samples analyzed. Accuracy was evaluated by recovery tests and analysis of a standard reference material (SRM 1643e) of trace elements in water (NIST, USA), resulting in recovery rates of from 90 to 114%, and relative error = 0.7%. The high sampling throughput (54 speciations h-1), together with low waste generation, low costs, low reagent and sample consumption make this FBA-HG-AFS method an interesting proposal for fast large-scale analysis in routine laboratoy according to the principles of green analytical chemistry.

Reevaluating the evidence for a Hadean-Eoarchean dynamo.

The time of origin of the geodynamo has important implications for the thermal evolution of the planetary interior and the habitability of early Earth. It has been proposed that detrital zircon grains from Jack Hills, Western Australia, provide evidence for an active geodynamo as early as 4.2 billion years (Ga) ago. However, our combined paleomagnetic, geochemical, and mineralogical studies on Jack Hills zircons indicate that most have poor magnetic recording properties and secondary magnetization carriers that postdate the formation of the zircons. Therefore, the existence of the geodynamo before 3.5 Ga ago remains unknown.

Multi-scale magnetic mapping of serpentinite carbonation.

Peridotite carbonation represents a critical step within the long-term carbon cycle by sequestering volatile CO2 in solid carbonate. This has been proposed as one potential pathway to mitigate the effects of greenhouse gas release. Most of our current understanding of reaction mechanisms is based on hand specimen and laboratory-scale analyses. Linking laboratory-scale observations to field scale processes remains challenging. Here we present the first geophysical characterization of serpentinite carbonation across scales ranging from km to sub-mm by combining aeromagnetic observations, outcrop- and thin section-scale magnetic mapping. At all scales, magnetic anomalies coherently change across reaction fronts separating assemblages indicative of incipient, intermittent, and final reaction progress. The abundance of magnetic minerals correlates with reaction progress, causing amplitude and wavelength variations in associated magnetic anomalies. This correlation represents a foundation for characterizing the extent and degree of in situ ultramafic rock carbonation in space and time.

Thin-film IrOx pH microelectrode for microfluidic-based microsystems.

Microsensors are valuable tools to monitor cell metabolism in cell culture volumes. The present research describes the fabrication and characterization of on-chip thin-film iridium oxide pH microsensors with dimensions of 20 microm x 20 microm and 20 microm x 40 microm suitable to be incorporated into nl volumes. IrOx thin films were formed on platinum microelectrodes by electrochemical deposition in galvanostatic mode. Anodically grown iridium oxide films showed a near super-Nernstian response with a slope of -77.6+/-2 mV/pH at 22 degrees C, and linear responses within the pH range of 4-11. Freshly deposited electrodes showed response times as low as 6s. Long-term studies showed a baseline drift of 2-3 mV/month, which could easily be compensated by calibration. This work demonstrated for the first time the use of planar IrOx pH microelectrodes to measure the acidification rate of CHO and fibroblast cells in an on chip cell culture volume of 25 nl with microfluidic control.

A microfluidic device to confine a single cardiac myocyte in a sub-nanoliter volume on planar microelectrodes for extracellular potential recordings.

A hybrid chip is described which combines a microfluidic network fabricated in a silicone elastomer (PDMS) with planar microelectrodes. It was used to measure extracellular potentials from single adult murine cardiac myocytes in a restricted extracellular space. The recorded variations in the extracellular potentials were caused by transmembrane currents associated with spontaneously initiated intracellular calcium waves. Single cells were trapped inside the 100 pl microchamber by pressure gradients and maintained for several hours by continuous perfusion. In addition, the localized delivery of drugs to a portion of the cell was demonstrated. The impedance of the electrodes was reduced by a factor of 10 to 20 after the electrodeposition of platinum black. Biopotentials recorded from single cells with platinum black electrodes showed a three-fold decrease in the noise, resulting in a maximum signal-to-noise ratio of 15:1. Characteristic variations in the frequency and shape of the extracellular potentials were observed among different cells which are most likely due to differences in the sarcoplasmic reticulum Ca(2+) load. Our device architecture permits the integration of electrochemical and optical sensors for multiparameter recordings.

Paleomagnetism. Solar nebula magnetic fields recorded in the Semarkona meteorite.

Magnetic fields are proposed to have played a critical role in some of the most enigmatic processes of planetary formation by mediating the rapid accretion of disk material onto the central star and the formation of the first solids. However, there have been no experimental constraints on the intensity of these fields. Here we show that dusty olivine-bearing chondrules from the Semarkona meteorite were magnetized in a nebular field of 54 ± 21 microteslas. This intensity supports chondrule formation by nebular shocks or planetesimal collisions rather than by electric currents, the x-wind, or other mechanisms near the Sun. This implies that background magnetic fields in the terrestrial planet-forming region were likely 5 to 54 microteslas, which is sufficient to account for measured rates of mass and angular momentum transport in protoplanetary disks.

An ancient core dynamo in asteroid Vesta.

The asteroid Vesta is the smallest known planetary body that has experienced large-scale igneous differentiation. However, it has been previously uncertain whether Vesta and similarly sized planetesimals formed advecting metallic cores and dynamo magnetic fields. Here we show that remanent magnetization in the eucrite meteorite Allan Hills A81001 formed during cooling on Vesta 3.69 billion years ago in a surface magnetic field of at least 2 microteslas. This field most likely originated from crustal remanence produced by an earlier dynamo, suggesting that Vesta formed an advecting liquid metallic core. Furthermore, the inferred present-day crustal fields can account for the lack of solar wind ion-generated space weathering effects on Vesta.

Universal serial bus powered and controlled isolated constant-current physiological stimulator.

We have developed a compact, isolated, physiological, constant-current stimulator that is powered and controlled by a universal serial bus (USB) interface. The stimulator is designed to be used in ex vivo cardiac experiments but is suitable for a wide variety of settings. The cost and features compare very favorably with commercial stimulators usually used in research and student laboratories. In addition to being USB powered, other novel aspects of our stimulator include the ability to produce large currents, up to 100 mA through a typical 1 kOmega load, by means of a single high-voltage dc-to-dc converter; user-specified variable period, magnitude, and duration of complex monophasic or biphasic sequences; and easy integration via hardware or software into existing experimental setups.

Magnetism on the angrite parent body and the early differentiation of planetesimals.

Angrites are among the oldest known pristine basaltic meteorites and record the earliest stages of planet formation and differentiation. Our paleomagnetic analysis of three angrites found that they record a past magnetic field of approximately 10 microteslas on the angrite parent body extending from 4564 to at least 4558 million years ago. Because the angrite paleomagnetic record extends beyond the expected lifetime of the early circumstellar disk, these paleofields were probably generated internally on the angrite parent body, possibly by an early dynamo in a rapidly formed metallic core.

Differential effects of phospholamban and Ca2+/calmodulin-dependent kinase II on [Ca2+]i transients in cardiac myocytes at physiological stimulation frequencies.

In cardiac myocytes, the activity of the Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) is hypothesized to regulate Ca(2+) release from and Ca(2+) uptake into the sarcoplasmic reticulum via the phosphorylation of the ryanodine receptor 2 and phospholamban (PLN), respectively. We tested the role of CaMKII and PLN on the frequency adaptation of cytosolic Ca(2+) concentration ([Ca(2+)](i)) transients in nearly 500 isolated cardiac myocytes from transgenic mice chronically expressing a specific CaMKII inhibitor, interbred into wild-type or PLN null backgrounds under physiologically relevant pacing conditions (frequencies from 0.2 to 10 Hz and at 37 degrees C). When compared with that of mice lacking PLN only, the combined chronic CaMKII inhibition and PLN ablation decreased the maximum Ca(2+) release rate by more than 50% at 10 Hz. Although PLN ablation increased the rate of Ca(2+) uptake at all frequencies, its combination with CaMKII inhibition did not prevent a frequency-dependent reduction of the amplitude and the duration of the [Ca(2+)](i) transient. High stimulation frequencies in the physiological range diminished the effects of PLN ablation on the decay time constant and on the maximum decay rate of the [Ca(2+)](i) transient, indicating that the PLN-mediated feedback on [Ca(2+)](i) removal is limited by high stimulation frequencies. Taken together, our results suggest that in isolated mouse ventricular cardiac myocytes, the combined chronic CaMKII inhibition and PLN ablation slowed Ca(2+) release at physiological frequencies: the frequency-dependent decay of the amplitude and shortening of the [Ca(2+)](i) transient occurs independent of chronic CaMKII inhibition and PLN ablation, and the PLN-mediated regulation of Ca(2+) uptake is diminished at higher stimulation frequencies within the physiological range.