The 2.1 angstrom crystal structure of copGFP, a representative member of the copepod clade within the green fluorescent protein superfamily

The green fluorescent protein (avGFP), its variants, and the closely related GFP-like proteins are characterized structurally by a cyclic tri-peptide chromophore located centrally within a conserved beta-can fold. Traditionally, these GFP family members have been isolated from the Cnidaria although recently, distantly related GFP-like proteins from the Bilateria, a sister group of the Cnidaria have been described, although no representative structure from this phylum has been reported to date. We have determined to 2.1 angstrom resolution the crystal structure of copGFP, a representative GFP-like protein from a copepod, a member of the Bilateria. The structure of copGFP revealed that, despite sharing only 19% sequence identity with GFP, the tri-peptide chromophore (Gly57-Tyr58-Gly59) of copGFP adopted a cis coplanar conformation within the conserved beta-can fold. However, the immediate environment surrounding the chromophore of copGFP was markedly atypical when compared to other members of the GFP-superfamily, with a large network of bulky residues observed to surround the chromophore. Arg87 and Glu222 (GFP numbering 96 and 222), the only two residues conserved between copGFP, GFP and GFP-like proteins are involved in autocatalytic genesis of the chromophore. Accordingly, the copGFP structure provides an alternative platform for the development of a new suite of fluorescent protein tools. Moreover, the structure suggests that the autocatalytic genesis of the chromophore is remarkably tolerant to a high degree of sequence and structural variation within the beta-can fold of the GFP superfamily. (c) 2006 Elsevier Ltd . All rights reserved.

Multi-types of Skyrmions in SU(N) Quantum Hall System

The skyrmions in SU(N) quantum Hall (QH) system are discussed. By analyzing the gauge field structure and the topological properties of this QH system it is pointed out that in the SU(N) QH system there can exist (N-1) types of skyrmion structures, instead of only one type of skyrmions. In this paper, by means of the Abelian projections according to the (N-1) Cartan subalgebra local bases, we obtain the (N-1) U(1) electromagnetic field tensors in the SU(N) gauge field of the QH system, and then derive (N-1) types of skyrmion structures from these U(1) sub-field tensors. Furthermore, in light of the phi-mapping topological current method, the topological charges and the motion of these skyrmions are also discussed.

A planar microwave imaging system with step-frequency synthesized pulse using different calibration methods

An experimental study of a planar microwave imaging system with step-frequency synthesized pulse for possible use in medical applications is described. Simple phantoms, consisting of a cylindrical plastic container with air or oil imitating fatty tissues and small highly reflective objects emulating tumors, are scanned with a probe antenna over a planar surface in the X-band. Different calibration schemes are considered for successful detection of these objects. (c) 2006 Wiley Periodicals, Inc.

Ipsilateral corticocortical projections to the primary and middle temporal visual areas of the primate cerebral cortex: area-specific variations in the morphology of connectionally identified pyramidal cells

We quantified the morphology of over 350 pyramidal neurons with identified ipsilateral corticocortical projections to the primary (V1) and middle temporal (MT) visual areas of the marmoset monkey, following intracellular injection of Lucifer Yellow into retrogradely labelled cells. Paralleling the results of studies in which randomly sampled pyramidal cells were injected, we found that the size of the basal dendritic tree of connectionally identified cells differed between cortical areas, as did the branching complexity and spine density. We found no systematic relationship between dendritic tree structure and axon target or length. Instead, the size of the basal dendritic tree increased roughly in relation to increasing distance from the occipital pole, irrespective of the length of the connection or the cortical layer in which the neurons were located. For example, cells in the second visual area had some of the smallest and least complex dendritic trees irrespective of whether they projected to V1 or MT, while those in the dorsolateral area (DL) were among the largest and most complex. We also observed that systematic differences in spine number were more marked among V1-projecting cells than MT-projecting cells. These data demonstrate that the previously documented systematic differences in pyramidal cell morphology between areas cannot simply be attributed to variable proportions of neurons projecting to different targets, in the various areas. Moreover, they suggest that mechanisms intrinsic to the area in which neurons are located are strong determinants of basal dendritic field structure.

Investigation of the Effect of Array Geometry on the Performance of Free-Space Optical Interconnects

The effect of transmitter and receiver array configurations on the stray-light and diffraction-caused crosstalk in free-space optical interconnects was investigated. The optical system simulation software (Code V) is used to simulate both the stray-light and diffraction-caused crosstalk. Experimentally measured, spectrally-resolved, near-field images of VCSEL higher order modes were used as extended sources in our simulation model. In addition, we have included the electrical and optical noise in our analysis to give more accurate overall performance of the FSOI system. Our results show that by changing the square lattice geometry to a hexagonal configuration, we obtain an overall signal-to-noise ratio improvement of 3 dB. Furthermore, system density is increased by up to 4 channels/mm2.

Novel array geometries for free-space optical interconnects with improved signal-to-noise ratio

We investigate the effect of transmitter and receiver array configurations on the stray-light and diffraction-caused crosstalk in free-space optical interconnects. The optical system simulation software (Code V) is used to simulate both the stray-light and diffraction-caused crosstalk. Experimentally measured, spectrally-resolved, near-field images of VCSEL higher order modes were used as extended sources in our simulation model. Our results show that by changing the square lattice geometry to a hexagonal configuration, we obtain the reduction in the stray-light crosstalk of up to 9 dB and an overall signal-to-noise ratio improvement of 3 dB.

Linking riparian vegetation spatial structure in Australian tropical savannas to ecosystem health indicators: semi-variogram analysis of high spatial resolution satellite imagery

Government agencies responsible for riparian environments are assessing the combined utility of field survey and remote sensing for mapping and monitoring indicators of riparian zone health. The objective of this work was to determine if the structural attributes of savanna riparian zones in northern Australia can be detected from commercially available remotely sensed image data. Two QuickBird images and coincident field data covering sections of the Daly River and the South Alligator River - Barramundie Creek in the Northern Territory were used. Semi-variograms were calculated to determine the characteristic spatial scales of riparian zone features, both vegetative and landform. Interpretation of semi-variograms showed that structural dimensions of riparian environments could be detected and estimated from the QuickBird image data. The results also show that selecting the correct spatial resolution and spectral bands is essential to maximize the accuracy of mapping spatial characteristics of savanna riparian features. The distribution of foliage projective cover of riparian vegetation affected spectral reflectance variations in individual spectral bands differently. Pan-sharpened image data enabled small-scale information extraction (< 6 m) on riparian zone structural parameters. The semi-variogram analysis results provide the basis for an inversion approach using high spatial resolution satellite image data to map indicators of savanna riparian zone health.