A previous study showed that the diffraction from cubic crystals of an icosahedral virus, cowpea mosaic virus (CPMV), was dramatically improved under elevated hydrostatic pressure. This use of pressure may have a significant impact on structural biology if it is found to be generally applicable. There were two types of cubic crystals assigned in either an I23 or P23 space group. They show the same rhombic dodecahedral morphology at atmospheric pressure. The crystals assigned to the 123 space group diffracted X-rays to higher resolution than those with P23 space group. The assignment of P23 space group was owing to the presence of reflections with indices of h + k + l = (2n + 1) (odd reflections), which are forbidden in space group I23. Analysis of the odd reflections from the P23 crystals at atmospheric pressure showed that they can originate from a rotational disorder in the 123 crystals. The odd reflections were eliminated with the application of 3.5 kbar of pressure, which transformed the crystals from the apparently primitive cell to the body-centered I23 space group with dramatic improvement in diffraction. A mechanistic model is proposed to describe the induction of order by rectifying the imperfection, which is consistent with the experimental data.

RATIONALE: Induction module cavity ring-down spectroscopy (IM-CRDS) has been proposed as a rapid and cost-effective alternative to cryogenic vacuum distillation (CVD) and isotope ratio mass spectrometry (IRMS) for the measurement of delta O-18 and delta H-2 values in matrix-bound waters. In the current study, we characterized the performance of IM-CRDS relative to CVD and IRMS and investigated the mechanisms responsible for differences between the methods.

Soil pH regulates the capacity of soils to store and supply nutrients, and thus contributes substantially to controlling productivity in terrestrial ecosystems(1). However, soil pH is not an independent regulator of soil fertility-rather, it is ultimately controlled by environmental forcing. In particular, small changes in water balance cause a steep transition from alkaline to acid soils across natural climate gradients(2,3). Although the processes governing this threshold in soil pH are well understood, the threshold has not been quantified at the global scale, where the influence of climate may be confounded by the effects of topography and mineralogy. Here we evaluate the global relationship between water balance and soil pH by extracting a spatially random sample (n = 20,000) from an extensive compilation of 60,291 soil pH measurements. We show that there is an abrupt transition from alkaline to acid soil pH that occurs at the point where mean annual precipitation begins to exceed mean annual potential evapotranspiration. We evaluate deviations from this global pattern, showing that they may result from seasonality, climate history, erosion and mineralogy. These results demonstrate that climate creates a nonlinear pattern in soil solution chemistry at the global scale; they also reveal conditions under which soils maintain pH out of equilibrium with modern climate.

Cavity ring-down spectrometers have generally been designed to operate under conditions in which the background gas has a constant composition. However, there are a number of observational and experimental situations of interest in which the background gas has a variable composition. In this study, we examine the effect of background gas composition on a cavity ring-down spectrometer that measures delta O-18-H2O and delta H-2-H2O values based on the amplitude of water isotopologue absorption features around 7184 cm(-1) (L2120-i, Picarro, Inc.). For background mixtures balanced with N-2, the apparent delta O-18 values deviate from true values by 0.50 +/- 0.001 parts per thousand O-2%(-1) and -0.57 +/- 0.001 parts per thousand Ar%(-1), and apparent delta H-2 values deviate from true values by 0.26 +/- 0.004 parts per thousand O-2 %(-1) and 0.42 +/- 0.004 parts per thousand Ar %(-1). The artifacts are the result of broadening, narrowing, and shifting of both the target absorption lines and strong neighboring lines. While the background-induced isotopic artifacts can largely be corrected with simple empirical or semimechanistic models, neither type of model is capable of completely correcting the isotopic artifacts to within the inherent instrument precision. The development of strategies for dynamically detecting and accommodating background variation in N-2, O-2, and/or Ar would facilitate the application of cavity ring-down spectrometers to a new class of observations and experiments.

CO CV CM CI Ryugu A Ryugu C 0.0 0.5 1.0 1.5 44/40CaSRM915a (age corrected) The Hayabusa2 spacecraft has returned samples from the Cb-type asteroid (162173) Ryugu to Earth. Previous petrological and chemical analyses support a close link between Ryugu and CI chondrites that are presumed to be chemically the most primitive meteorites with a solar-like composition. However, Ryugu samples are highly enriched in Ca compared to typical CI chondrites. To identify the cause of this discrepancy, here we report stable Ca isotopic data (expressed as delta 44/40CaSRM915a) for returned Ryugu samples collected from two sites. We found that samples from both sites have similar delta 44/40CaSRM915a (0.58 +/- 0.03 parts per thousand and 0.55 +/- 0.08 parts per thousand, 2 s.d.) that fall within the range defined by CIs. This isotopic similarity suggests that the Ca budget of CIs and Ryugu samples is dominated by carbonates, and the variably higher Ca contents in Ryugu samples are due to the abundant carbonates. Precipitation of carbonates on Ryugu likely coincided with a major episode of aqueous activity dated to have occurred similar to 5 Myr after Solar System formation. Based on the pristine Ryugu samples, the average delta 44/40CaSRM915a of the Solar System is defined to be 0.57 +/- 0.04 parts per thousand (2 s.d.).

Differential travel times, commonly used to eliminate unwanted near-source and near-receiver heterogeneity from travel time studies, can be affected by slabs and hypocentral errors when phase pair slownesses differ greatly. In particular, D'' and core structure studies can be biased if differential PKP times are used. Here we present differential PKP travel time measurements having significant azimuthal travel time anomalies consistent both in size and pattern with a near-source slab effect and explore other sources of error in differential times.

On May 25, 1987, at 11:31, a M = 5.8 earthquake occurred at the southern end of Vatnafjoll volcanic ridge in south Iceland. This is the largest event in the south Iceland lowland since a hi = 7.0 earthquake in 1912 which was located approximately 15 km to the west of the Vatnafjoll earthquake. Vatnafjoll is located at the junction of the south Iceland seismic zone, a left lateral transform zone, and the eastern volcanic zone which is a zone of rifting and volcanism. In May and June 1987, several foreshocks and aftershocks were recorded on the local seismic network as well as the mainshock. A clear coseismic step associated with the mainshock was observed at all operating stations of a volumetric strainmeter network in southern Iceland. Steps associated with some foreshocks and aftershocks were also observed at the closest strain stations. Slow strain changes, before and after the mainshock, lasting a few days, were also observed. Forward modeling of the coseismic strainmeter signals of the mainshock suggests a double couple solution where the slip is mostly right lateral strike slip on a subvertical plane with a northerly strike. The solution has a good fit to observations and is in good agreement with interpretation of seismometer data. This solution indicates a stress field similar to that in the south Iceland seismic zone. The slow strain changes, which start about 10 min after the first foreshock, may indicate magma involvement in the process. Changes, associated with an intrusion and pressure release, may affect the strain held and possibly trigger the mainshock. The strainmeter records open up a new view of the seismic strain event as a combination of seismic strain release and a slower process of magma intrusion.

Tilt and strain continuous monitoring started in October 2002 in the Trizonia Island, in the Gulf of Corinth, in order to detect possible strain transients in the rift. The hydrostatic tiltmeters, developed at IPGP, are 15 m long and buried in trenches at a depth of 2.5 m, with a few 10(-9)-radian noise level at short period. The strain is measured by a Sacks-Evertson dilatometer has cemented in a borehole at a depth of 148 m, with a few 10(-10) resolution at short period. A 1 h-lasting, 10(-7)-strain transient has been recorded on the dilatometer, possibly related to a seismic swarm that occurred 15 km away. To cite this article: R Bernard et al., C. R. Geoscience 336 (2004). (C) 2004 Academie des sciences. Published by Elsevier SAS. All rights reserved.