Dauphiné twinning and texture memory in polycrystalline quartz. Part 3: texture memory during phase transformation

Samples of quartz-bearing rocks were heated above the α (trigonal)–β (hexagonal) phase transformation of quartz (625–950°C) to explore changes in preferred orientation patterns. Textures were measured both in situ and ex situ with neutron, synchrotron X-ray and electron backscatter diffraction. The trigonal–hexagonal phase transformation does not change the orientation of c- and a-axes, but positive and negative rhombs become equal in the hexagonal β-phase. In naturally deformed quartzites measured by neutron diffraction a perfect texture memory was observed, i.e. crystals returned to the same trigonal orientation they started from, with no evidence of twin boundaries. Samples measured by electron back-scattered diffraction on surfaces show considerable twinning and memory loss after the phase transformation. In experimentally deformed quartz rocks, where twinning was induced mechanically before heating, the orientation memory is lost. A mechanical model can explain the memory loss but so far it does not account for the persistence of the memory in quartzites. Stresses imposed by neighboring grains remain a likely cause of texture memory in this mineral with a very high elastic anisotropy. If stresses are imposed experimentally the internal stresses are released during the phase transformation and the material returns to its original state prior to deformation. Similarly, on surfaces there are no tractions and thus texture memory is partially lost.     

Direct observations of bipolar outflow from HM sagittae

We observed HM Sagittae with theMulti-Element Radio Linked Interferometer Network (MERLIN) at 6 cm and 18cm. We find non-thermal bipolar outflow in the eastwest direction, associated with optical emission lines, and thermal ridges to the north and south associated with the UV nebulosity detected by the HST.     

voboz: an almost-parameter-free halo-finding algorithm

We have developed an algorithm, called voboz (VOronoi BOund Zones), to find haloes in an N -body dark matter simulation; it has as little dependence on free parameters as we can manage. By using the Voronoi diagram, we achieve non-parametric, 'natural' measurements of each particle's density and set of neighbours. We then eliminate much of the ambiguity in merging sets of particles together by identifying every possible density peak, and measuring the probability that each does not arise from Poisson noise. The main halo in a cluster tends to have a high probability, while its subhaloes tend to have lower probabilities. The first parameter in voboz controls the subtlety of particle unbinding, and may be eliminated if one is cavalier with processor time; even if one is not, the results saturate to the parameter-free answer when the parameter is sufficiently small. The only parameter that remains, an outer density cut-off, does not influence whether or not haloes are identified, nor does it have any effect on subhaloes; it only affects the masses returned for supercluster haloes.     

High resolution radio images of the symbiotic system R aquarii

We present MERLIN images of the symbiotic system R Aquarii obtained at 1.7 and 5 GHz. We identify the emission from the binary system and derive a mass loss rate for the Mira that is commensurate with that in typical Miras. We show that variations in the radio emission over the last decade are consistent with the jet model for the system originally presented by Solf (1992). In addition, we calculate the spectral index distribution and find that there is no evidence of non-thermal emission.     

Detecting shadows in multi-temporal aerial imagery to support near-real-time change detection

Multi-temporal aerial imagery captured via an approach called repeat station imaging (RSI) facilitates post-hazard assessment of damage to infrastructure. Spectral-radiometric (SR) variations caused by differences in shadowing may inhibit successful change detection based on image differencing. This study evaluates a novel approach to shadow classification based on bi-temporal imagery, which exploits SR change signatures associated with transient shadows. Changes in intensity (brightness from red–green–blue images) and intensity-normalized blue waveband values provide a basis for classifying transient shadows across a range of material types with unique reflectance properties, using thresholds that proved versatile for very different scenes. We derive classification thresholds for persistent shadows based on hue to intensity ratio (H/I) images, by exploiting statistics obtained from transient shadow areas. We assess shadow classification accuracy based on this procedure, and compare it to the more conventional approach of thresholding individual H/I images based on frequency distributions. Our efficient and semi-automated shadow classification procedure shows improved mean accuracy (93.3%) and versatility with different image sets over the conventional approach (84.7%). For proof-of-concept, we demonstrate that overlaying bi-temporal imagery also facilitates normalization of intensity values in transient shadow areas, as part of an integrated procedure to support near-real-time change detection.     

History of climate and forests in tropical Africa during the last 8 million years

There have been major changes in climate and in the composition and distribution of forest during the last 8 Myr. During the last world glacial maximum (peak 18 000 yr B.P.) the climate was dry and cold and forest much reduced and fragmented. The last glacial period as a whole (12000–70000 B.P.) was dry in tropical Africa and so too were most of the other 20 major ice ages which have occurred since 2.43 Myr B.P., in comparison with intervening interglacials. The extent of forest must have oscillated greatly. There has been a general drying in climate since 8 Myr.     

Habitat use by small mammals in coastal marshes of Southwestern Louisiana

A short-term study based on snap-trap capture rates of small mammals in the marsh and levee system in southwestern Louisiana was conducted in the winter-spring period. Marsh rice rats (Oryzomys palustris) dominated marsh habitats and rice rats and fulvous harvest mice (Reithrodontomys fulvescens) were co-dominants on levees. Least shrews (Cryptotis parva) and house mice (Mus musculus) were also taken. Although rice rat capture rate in marshes was twice that from levees, the difference was not significant (p=0.1428). When found on levees, rice rats preferred portions of levees adjacent to marshes and canals (p<0.0001). We found few differences in rice rat capture rates from marsh and levee habitats, although capture rates from fresh marsh and adjacent levees were select levee ridges over the marsh and canal edges (0.1≥p≥0.05). The abundance of harvest mice on levees adjacent to intermediate marshes exceeded all other levee habitats. For reasons as yet unexplained, intermediate marshes and adjacent levees had the highest small mammal abundance and species richness. Conversely, fresh marshes and their adjacent levees had the lowest abundance and variety of small mammals.     

The GF algorithm for reservoir storage, yield and spillage distributions for non-seasonal and seasonal independent inflow processes

a well-known generating function formula for the equilibrium storage distribution in a finite Moran reservoir having IID inflows and unit release is extended to apply to a class of nondecreasing staircase-like release policies withm unit increments,m>1, and to seasonal inflows. The analysis is conducted in terms of an alternative to the Moran inflow-outflow sequencing scheme, with the release during a working interval controlled by the water level at the beginning of that interval.In addition to the storage, the equilibrium distributions of yield and spillage are obtained. Illustrative examples are provided.     

Fluid Borders: Rethinking Historical Geography and Fixed Map Boundaries in Contested Regions

This article introduces a quantitative methodology for analyzing contested map borders. The article applies the new analytical technique to a data set of thirty maps showing Bulgaria in ca. 800 CE, a disputed state and period in medieval historiography with relevance to modern national politics and territorial claims. Based on the data set, we generate a series of new maps that make explicit the fluid medieval boundaries and general disagreement among geographers and historiographers. Our analysis begins with a simple point-in-polygon procedure to create a majority map that depicts the points included within the borders of the Bulgarian polity in sixteen or more of the maps (>50 percent). The majority map is then combined with percentage maps, confidence interval map boundaries, and cluster maps. The confidence interval maps are created via a spatial bootstrapping procedure and measure the uncertainty in the majority map. The cluster maps are developed via a radial basis function and provide insight into the potential affectivity based on the cartographers' countries of origin. The final map reflects the general modern consensus of the borders of the Bulgarian polity around 800 CE. Besides its quantitative contribution to medieval and modern cartographic, historiographical, and political debates, this article has developed a widely applicable methodology for synthesizing map borders and territories in cases of cartographic disagreement.     

Absolute measurements and computed values for Martian irradiance between 10.5 and 12.5 μm

The combination of seasonal and orbital changes in Martian insolation result in complex latitude dependent surface temperature variations that effect the total radiance of the planet as seen from the earth. These surface temperature variations have been calculated, based upon a computer simulation of the thermal environment of the planet. The temperature variations are then integrated to yield the total radiance of the planet as seen from the earth as a function of time. The absolute radiance of Mars was measured on April 4, 1971, with a balloon-borne radiometer system operating in the wavelength range between 10.5 and 12.5 μm. The average brightness temperature of the Mars disk determined from these measurements was 254°K with a 1 σ error of 4°K.