Accelerator mass spectrometry radiocarbon dating of 1994 Lake Winnipeg cores

Conventional radiocarbon dating of Lake Winnipeg core samples has produced erroneously old ages due to the incorporation of pre-Quaternary carbon derived from carbonaceous rocks, soils and sediments in the watershed, as well as a hard-water effect resulting from leaching of calcareous rocks and soils. To circumvent these problems and develop a reliable chronology for the Lake Winnipeg core series, a total of 64 samples from the Lake Winnipeg core series were processed to isolate well preserved macrofossils suitable for Accelerator Mass Spectrometry (AMS) radiocarbon dating. Here we report six radiocarbon ages derived from plant macrofossils and ostracodes, and reconstruct aspects of the depositional environment of each sample based on the associated macrofossil assemblage.     

Lagrangian Solution of Dynamo Equations and Path Integrals

We discuss an explicit solution of the Cauchy problem for induction equation and suggest its generalization for equations of ²-dynamo. These solutions are based on concepts of multiplicative, Wiener path, and stochastic integrals. Obtained explicit solution can be useful as a tool in investigations of a dynamo with fluctuating helicity.     

浅论马鞍山地区的膨胀土

膨胀土由于粘土矿物含量较多,在一定气候条件下其体积随含水量的增加而膨胀,随含水一的减少而收缩,以膨胀土为地基的低层建筑物常常成群开裂,笔者首次报道了马鞍山地区的膨胀土,并对该区膨胀土的分布,成因,评价方法和防治措施等提出了初步看法。     

The inner Galaxy resolved at IJK using DENIS data

We present the analysis of three-colour optical/near-infrared images, in IJK , taken for the DEep Near Infrared Southern Sky Survey (DENIS) project. The region considered covers 17.4 deg² and lies within <5°, b <1.°5. The adopted methods for deriving photometry and astrometry in these crowded images, together with an analysis of the deficiencies nevertheless remaining, are presented. The numbers of objects extracted in I , J and K are 748 000, 851 000 and 659 000 respectively, to magnitude limits of 17, 15 and 13. Eighty per cent completeness levels typically fall at magnitudes 16, 13 and 10 respectively, fainter by about 2 mag than the usual DENIS limits as a result of the crowded nature of these fields. A simple model to describe the disc contribution to the number counts is constructed, and parameters for the dust layer are derived. We find that a formal fit of parameters for the dust plane, from these data in limited directions, gives a scalelength and scaleheight of 3.4±1.0 kpc and 40±5 pc respectively, and a solar position 14.0±2.5 pc below the plane. This latter value is likely to be affected by localized dust asymmetries. We convolve a detailed model of the systematic and random errors in the photometry with a simple model of the Galactic disc and dust distribution to simulate expected colourmagnitude diagrams. These are in good agreement with the observed diagrams, allowing us to isolate those stars from the inner disc and bulge. After correcting for local dust-induced asymmetries, we find evidence for longitude-dependent asymmetries in the distant J and K sources, consistent with the general predictions of some Galactic bar models. We consider complementary L -band observations in the companion paper.     

The stellar content of a spiral arm of NGC 4321

The effects of the passage of a spiral arm through the disc of the giant Virgo Sc galaxy NGC 4321 are investigated with Hubble Space Telescope WFPC2 images in two colours. Concentrating on a portion of the southern spiral arm of NGC 4321, we have applied a new program to solve for the star formation histories in the arm and interarm regions separately. The observational uncertainties and the variable crowding across the spiral arm are taken into account using the results of artificial star tests. In the interarm regions the data are consistent with a constant star formation rate for the last 50 Myr while the stars in the arm region show a star formation rate four times larger than in the interarm regions in the last 5 Myr.     

The dynamical and liquid water structure of the small cumulus as determined from its environment

This paper examines the evidence for the model of a small cumulus cloud represented as a quasi static but turbulent entity, growing on the upshear side and decaying on the downshear side. While the air just outside the cloudy outline is, on average, stationary relative to the embedding airmass, there is a slight flow, upwards and forward as though the updraft has induced upward motion in the clear air outside the cloud, on the growing side. On the decaying side the motion is downwards and away from the cloud.This is a flow pattern which is not consistent with the air flowing around the cloud as it moves forward but it agrees well with the picture given. Decayed remnants of cloud are found throughout the air previously occupied by the cloud. The cloud outline moves through the embedding air at a velocity which is almost as large as the relative motion of the subcloud feeding airflow (which is almost free from internal wind shear in strong convection).The mixing of dry air from above the inversion yields the observed diluted liquid water content in small cumuli, if such mixing is allowed to proceed until the cloud density equals that of the surrounding air. Quantitative conditions relating the liquid water to inversion temperature and moisture changes, and to the stability of the environment are presented. The strong vertical mixing from the top of the cloud downwards is important to microphysical processes.     

A method of searching for radial velocity anomalies in the lower mantle using interfering signals

Radial velocity anomalies in the lower mantle that give rise to triplications in the travel-time curve for short-periodP waves will produce arrivals havingdT/d values that differe by roughly 0.2–0.5 s/deg. The first two arrivals associated with such triplications will be separated by less than one second over a distance range of 4°–10° they may not, therefore, be separable visually on single seismograms, so that their presence can only be inferred from some measurable property that depends on their mutual interference. If there are lateral variations in the regions of anomalous velocity gradients, the interfering signals will also have different azimuths of arrival. Using two synthetic wavelets we have investigated the effect of interference on bothdT/d and azimuth measurements at the Yellowknife Array. We found that if the interfering pulses have a dominant frequencyv, there is a range of time separations (0.30/v0.55/v) over which the measureddT/d and azimuth values may fluctuate by much more than the differences indT/d and azimuth between the interfering signals. We have evaluated the following empirically defined functions for three different primary signals, and for three different relative amplitudes of the interfering signals:f (t), the drift function, which expresses how the measured slownesses,p, and azimuths, , differ from the slownesses and azimuths of the primary wavelets; f(), the range function, which describes the behaviour of the upper and lower bounds ofp and as a function of the difference in arrival times of the signals, andf , studied the properties of these functions, and have outlined how these properties provide criteria based on the numerical and statistical characteristics of the arrival vectors, and on the waveform of the signal that will enable small radial velocity anomalies to be more clearly delineated.Contribution No. 863 from the Earth Physics Branch.     

NUMERICAL STUDY OF REMOTE SENSING OF CLOUD LIQUID WATER CONTENT BY SPACE-BORNE COMBINED RADAR-RADIOMETER

A retrieval method of microwave(MW)space-borne remote sensing of cloud liquid watercontent by the combined radar-radiometer is suggested.A three-layer cloud model is chosen torepresent the typical stratified precipitating cloud.The retrieval method mainly follows ourpreviously suggested scheme with some modifications.Numerical comparative study shows that inspace-borne remote sensing of cloud liquid water content by the combined method is much betterthan by radar only;Also the retrieval accuracy of cloud liquid water content may be improvedwhen using the three-layer cloud model in the combined method.     

Migmatite formation at subsolidus conditions–an alternative to anatexis

Abstract This contribution discusses the formation of stromatic high-grade migmatites. Volume considerations require that most of the leucosome material is not added from outside the system. A segregation mechanism is necessary except in those cases where the protolith of the migmatite already had a banded structure. Although partial melting is most often advocated to provide the segregation mechanism, several arguments can be raised against high degrees of melting: mineral compositions and even zoning patterns are similar in both mesosomes and leucosomes; sufficient degrees of melting at reasonable temperatures require more than the available amounts of water; the leucosomes do not always approximate to a minimum melt composition; high degrees of melting cannot occur without an appreciable volume increase; etc. Diffusion works as a segregation mechanism at low temperatures. As diffusion rates increase exponentially with temperature diffusion must become still more important as a segregation mechanism at high temperatures. A model is suggested based on the diffusion of components in response to the gradient δσ/δx, where σ= 1/3∑³_i=1 σ_i is the mean pressure. In homogeneously strained rocks, σ₃ is larger in rock parts rich in incompetent phases than in rock parts depleted in incompetent phases. Accordingly, mechanically competent but chemically incompetent high-volume phases like quartz and feldspars stressed in micadominated parts of a rock (high σσ) migrate to parts of the rock that are depleted in mica (low σ¯). It is suggested that hornblende occurring in many leucosomes may be premigmatitic or early syn-migmatitic and due to its mechanical competency it initiates the segregation. Diffusion occurs along grain boundaries and is enhanced by small amounts of ‘intergranular fluid’;. At the best, semiquantitative estimates of diffusion rates and distances indicate that the process should work over geological times.     

Kinematics and stellar populations of the dwarf elliptical galaxy IC 3653

We present the first 3D observations of a diffuse elliptical galaxy (dE). The good quality data (S/N up to 40) reveal the kinematical signature of an embedded stellar disc, reminiscent of what is commonly observed in elliptical galaxies, though similarity of their origins is questionable. Colour map built from Hubble Space Telescope Advanced Camera for Surveys (ACS) images confirms the presence of this disc. Its characteristic scale (about 3 arcsec =250 pc) is about a half of galaxy's effective radius, and its metallicity is 0.1–0.2 dex larger than the underlying population. Fitting the spectra with synthetic single stellar populations (SSP), we found an SSP-equivalent age of 5 Gyr and nearly solar metallicity [Fe/H]  =−0.06  dex. We checked that these determinations are consistent with those based on Lick indices, but have smaller error bars. The kinematical discovery of a stellar disc in dE gives additional support to an evolutionary link from dwarf irregular galaxies due to stripping of the gas against the intracluster medium.