Viscous fingering in liquid crystals: Anisotropy and morphological transitions

We show that a minimal model for viscous fingering with a nematic liquid crystal in which anisotropy is considered to enter through two different viscosities in two perpendicular directions can be mapped to a two-fold anisotropy in the surface tension. We numerically integrate the dynamics of the resulting problem with the phase-field approach to find and characterize a transition between tip-splitting and side-branching as a function of both anisotropy and dimensionless surface tension. This anisotropy dependence could explain the experimentally observed (reentrant) transition as temperature and applied pressure are varied. Our observations are also consistent with previous experimental evidence in viscous fingering within an etched cell and simulations of solidification.Comment: 12 pages, 3 figures. Submitted to PR

Periodic forcing in viscous fingering of a nematic liquid crystal

We study viscous fingering of an air-nematic interface in a radial Hele-Shaw cell when periodically switching on and off an electric field, which reorients the nematic and thus changes its viscosity, as well as the surface tension and its anisotropy (mainly enforced by a single groove in the cell). We observe undulations at the sides of the fingers which correlate with the switching frequency and with tip oscillations which give maximal velocity to smallest curvatures. These lateral undulations appear to be decoupled from spontaneous (noise-induced) side branching. We conclude that the lateral undulations are generated by successive relaxations between two limiting finger widths. The change between these two selected pattern scales is mainly due to the change in the anisotropy. This scenario is confirmed by numerical simulations in the channel geometry, using a phase-field model for anisotropic viscous fingering.Comment: completely rewritten version, more clear exposition of results (14 pages in Revtex + 7 eps figures

Application of remote sensing technique in biomass change detection: a case study of Bromley and Chihota, Zimbabwe

Biomass is defined as the total mass of living plant matter in a given unit of an environment area.  Several factors influence the change in biomass content of an area. The rate of change varies from mass seasonal drying of grasslands to gradual degradation of forestry area.  It is in the interest of environmental monitoring and sustainable development that biomass change be constantly determined. There are various field methods used worldwide to determine density of forest resources but have several limitations because of the nature of factors influencing biomass change.  These include seasonal changes, human activities, forest fires etc.  Remote Sensing as an enabling technology provides an efficient avenue of assessment of biomass content of any area.  This research focused on biomass content that constituted forest resources. Two main methods used were qualitative analysis involving visual image interpretation relying on knowledge of spectral reflectance characteristics of ground cover types and quantitative analysis involving use of mathematical capacity of the computer to extract information on pixel digital number The techniques employed in these methods were complementary and were combined in a systematic manner to optimize the potential of remotely sensed data in biomass change. Comparison of two methods information, revealed that biomass content obtained from the remotely sensed data from the two study areas were almost identical. Extra ancillary data like population information and detailed land use data, can be integrated into GIS together with results from remote sensing analysis to enhance the decision making process.Keywords:  Biomass, Forest, Image, Interpretation, Qualitative, Quantitativ

A comparison of Google Earth extracted points with GPS surveyed points

Surveying has become the most effective way of taking measurement in or/and on the earth surface. There is an exponential rise in techniques of taking measurements on the earth for different reasons and purposes. Google Earth offers an open source service, easy to access and cost free image data that supports map interests and provides data which are crucial for engineering purposes. Google earth has become so popular not because of its high accuracy, but because it is easily accessible to anyone. Google Earth, virtual globe uses World Geodetic Coordinate System 1984 WGS84 as a global coordinate system. However, in this research, the transformations made from those data obtained using Global Positioning Systems (GPS) and those obtained from Google Earth were made and analyzed. The same points were uploaded to Global Positioning Systems and Google Earth for extraction of heights. The resultant coordinate generated contours obtained from both systems were analyzed and conclusions made. The height difference obtained from both system was 15.138m

Mapping wetland characteristics for sustainable development in Harare: The case of Borrowdale West, Highlands, National Sport stadium and Mukuvisi Woodlands wetlands

Wetland ecosystems are under threat from agriculture and urbanisation, affecting water supply and quality in urban areas like the City of Harare. With the need to protect wetlands that remain, the spatial extent of the Highlands, Borrowdale West, Mukuvisi and National Sports wetlands was established. LANDSAT and SPOT Satellite imagery were used to map the spatial extent on the wetlands and to take note of the temporal changes that occurred between 1989 and 2009. Supervised classification was used to classify the images. High resolution Google earth imagery were then downloaded and used as baseline data for mapping the wetlands using the Cowardin wetland classification system 1979 and the Land Capability Classification system for wetness. Maps showing the physical characteristic of the wetlands were then produced. Results indicated that area under wetlands has been shrinking over the years. Using the wetland classification system it was found out that much of the area under wetland should not be used for any other landuse purpose other than wetland protection. However the study found out that urban expansion projects are currently modifying the wetlands. The Highlands wetland has been drained and road construction is currently in progress while a Hotel is under construction on the National sports wetland covering 287 012 m2 of the wetland. This study provides information on the current physical state of the wetlands, which can be the basis for wetland protection and management by policy makers and managers. Key Words:  Wetland, Spatial extent, Physical characteristics, Classification, Landuse, Protection and Managemen