Estimation of aboveground biomass of a production forest reserve in Malaysian Borneo using K-nearest neighbor method

This study examined the use of the k-nearest neighbour (k-NN) method to estimate aboveground biomass of a logged-over tropical forest in Sabah, Malaysia. To estimate aboveground biomass, field data as well as digital number and normalised difference vegetation index (NDVI) values from Landsat TM-5 data were used to determine the optimum horizontal reference area and the number of reference sample plots (k). An accuracy assessment showed that enhancing the digital number value was superior to enhancing the NDVI value. Root mean square errors of no filtering and 3 × 3 filtering were minimum when k = 4 and k = 5 respectively, when a horizontal reference area of 17 km was applied. The bias was underestimated by 2.01 and 1.62 tonnes ha-1 for k = 4 and k = 5 respectively. Total aboveground biomass of the forest management unit estimated by enhancing the digital number value was 6,873,299 tonnes and average biomass density was 248.8 tonnes ha-1. The results suggest that the k-NN method is an alternative way to estimate and map aboveground biomass of a forest management unit

Gallium vacancy and the residual acceptor in undoped GaSb studied by positron lifetime spectroscopy and photoluminescence

Positron lifetime, photoluminescence (PL), and Hall measurements were performed to study undoped p-type gallium antimonide materials. A 314 ps positron lifetime component was attributed to Ga vacancy (V Ga) related defect. Isochronal annealing studies showed at 300°C annealing, the 314 ps positron lifetime component and the two observed PL signals (777 and 797 meV) disappeared, which gave clear and strong evidence for their correlation. However, the hole concentration (∼2×10 17cm -3) was observed to be independent of the annealing temperature. Although the residual acceptor is generally related to the V Ga defect, at least for cases with annealing temperatures above 300°C, V Ga is not the acceptor responsible for the p-type conduction. © 2002 American Institute of Physics.published_or_final_versio

Notorious places: image, reputation, stigma: the role of newspapers in area reputations for social housing estates

This paper reviews work in several disciplines to distinguish between image, reputation and stigma. It also shows that there has been little research on the process by which area reputations are established and sustained through transmission processes. This paper reports on research into the portrayal of two social housing estates in the printed media over an extended period of time (14 years). It was found that negative and mixed coverage of the estates dominated, with the amount of positive coverage being very small. By examining the way in which dominant themes were used by newspapers in respect of each estate, questions are raised about the mode of operation of the press and the communities' collective right to challenge this. By identifying the way regeneration stories are covered and the nature of the content of positive stories, lessons are drawn for programmes of area transformation. The need for social regeneration activities is identified as an important ingredient for changing deprived-area reputations

A lattice model for the kinetics of rupture of fluid bilayer membranes

We have constructed a model for the kinetics of rupture of membranes under tension, applying physical principles relevant to lipid bilayers held together by hydrophobic interactions. The membrane is characterized by the bulk compressibility (for expansion), the thickness of the hydrophobic part of the bilayer, the hydrophobicity and a parameter characterizing the tail rigidity of the lipids. The model is a lattice model which incorporates strain relaxation, and considers the nucleation of pores at constant area, constant temperature, and constant particle number. The particle number is conserved by allowing multiple occupancy of the sites. An equilibrium ``phase diagram'' is constructed as a function of temperature and strain with the total pore surface and distribution as the order parameters. A first order rupture line is found with increasing tension, and a continuous increase in proto-pore concentration with rising temperature till instability. The model explains current results on saturated and unsaturated PC lipid bilayers and thicker artificial bilayers made of diblock copolymers. Pore size distributions are presented for various values of area expansion and temperature, and the fractal dimension of the pore edge is evaluated.Comment: 15 pages, 8 figure

Biomimicking Fiber Platform with Tunable Stiffness to Study Mechanotransduction Reveals Stiffness Enhances Oligodendrocyte Differentiation but Impedes Myelination through YAP-dependent Regulation

A key hallmark of many diseases, especially those in the central nervous system (CNS), is the change in tissue stiffness due to inflammation and scarring. However, how such changes in microenvironment affect the regenerative process remains poorly understood. Here, a biomimicking fiber platform that provides independent variation of fiber structural and intrinsic stiffness is reported. To demonstrate the functionality of these constructs as a mechanotransduction study platform, these substrates are utilized as artificial axons and the effects of axon structural versus intrinsic stiffness on CNS myelination are independently analyzed. While studies have shown that substrate stiffness affects oligodendrocyte differentiation, the effects of mechanical stiffness on the final functional state of oligodendrocyte (i.e., myelination) has not been shown prior to this. Here, it is demonstrated that a stiff mechanical microenvironment impedes oligodendrocyte myelination, independently and distinctively from oligodendrocyte differentiation. Yes-associated protein is identified to be involved in influencing oligodendrocyte myelination through mechanotransduction. The opposing effects on oligodendrocyte differentiation and myelination provide important implications for current work screening for promyelinating drugs, since these efforts have focused mainly on promoting oligodendrocyte differentiation. Thus, the platform may have considerable utility as part of a drug discovery program in identifying molecules that promote both differentiation and myelination

Synthesis and structural characterization of a mimetic membrane-anchored prion protein

During pathogenesis of transmissible spongiform encephalopathies (TSEs) an abnormal form (PrPSc) of the host encoded prion protein (PrPC) accumulates in insoluble fibrils and plaques. The two forms of PrP appear to have identical covalent structures, but differ in secondary and tertiary structure. Both PrPC and PrPSc have glycosylphospatidylinositol (GPI) anchors through which the protein is tethered to cell membranes. Membrane attachment has been suggested to play a role in the conversion of PrPC to PrPSc, but the majority of in vitro studies of the function, structure, folding and stability of PrP use recombinant protein lacking the GPI anchor. In order to study the effects of membranes on the structure of PrP, we synthesized a GPI anchor mimetic (GPIm), which we have covalently coupled to a genetically engineered cysteine residue at the C-terminus of recombinant PrP. The lipid anchor places the protein at the same distance from the membrane as does the naturally occurring GPI anchor. We demonstrate that PrP coupled to GPIm (PrP-GPIm) inserts into model lipid membranes and that structural information can be obtained from this membrane-anchored PrP. We show that the structure of PrP-GPIm reconstituted in phosphatidylcholine and raft membranes resembles that of PrP, without a GPI anchor, in solution. The results provide experimental evidence in support of previous suggestions that NMR structures of soluble, anchor-free forms of PrP represent the structure of cellular, membrane-anchored PrP. The availability of a lipid-anchored construct of PrP provides a unique model to investigate the effects of different lipid environments on the structure and conversion mechanisms of PrP

T. gondii RP Promoters & Knockdown Reveal Molecular Pathways Associated with Proliferation and Cell-Cycle Arrest

Molecular pathways regulating rapid proliferation and persistence are fundamental for pathogens but are not elucidated fully in Toxoplasma gondii. Promoters of T. gondii ribosomal proteins (RPs) were analyzed by EMSAs and ChIP. One RP promoter domain, known to bind an Apetela 2, bound to nuclear extract proteins. Promoter domains appeared to associate with histone acetyl transferases. To study effects of a RP gene's regulation in T. gondii, mutant parasites (Δrps13) were engineered with integration of tetracycline repressor (TetR) response elements in a critical location in the rps13 promoter and transfection of a yellow fluorescent-tetracycline repressor (YFP-TetR). This permitted conditional knockdown of rps13 expression in a tightly regulated manner. Δrps13 parasites were studied in the presence (+ATc) or absence of anhydrotetracycline (-ATc) in culture. -ATc, transcription of the rps13 gene and expression of RPS13 protein were markedly diminished, with concomitant cessation of parasite replication. Study of Δrps13 expressing Myc-tagged RPL22, -ATc, showed RPL22 diminished but at a slower rate. Quantitation of RNA showed diminution of 18S RNA. Depletion of RPS13 caused arrest of parasites in the G1 cell cycle phase, thereby stopping parasite proliferation. Transcriptional differences ±ATc implicate molecules likely to function in regulation of these processes. In vitro, -ATc, Δrps13 persists for months and the proliferation phenotype can be rescued with ATc. In vivo, however, Δrps13 could only be rescued when ATc was given simultaneously and not at any time after 1 week, even when L-NAME and ATc were administered. Immunization with Δrps13 parasites protects mice completely against subsequent challenge with wildtype clonal Type 1 parasites, and robustly protects mice against wildtype clonal Type 2 parasites. Our results demonstrate that G1 arrest by ribosomal protein depletion is associated with persistence of T. gondii in a model system in vitro and immunization with Δrps13 protects mice against subsequent challenge with wildtype parasites