Current density mapping approach for design of clinical magnetic resonance imaging magnets

Novel current density mapping (CDM) schemes are developed for the design of new actively shielded, clinical magnetic resonance imaging (MRI) magnets. This is an extended inverse method in which the entire potential solution space for the superconductors has been considered, rather than single current density layers. The solution provides an insight into the required superconducting coil pattern for a desired magnet configuration. This information is then used as an initial set of parameters for the magnet structure, and a previously developed hybrid numerical optimization technique is used to obtain the final geometry of the magnet. The CDM scheme is applied to the design of compact symmetric, asymmetric, and open architecture 1.0-1.5 T MRI magnet systems of novel geometry and utility. A new symmetric 1.0-T system that is just I m in length with a full 50-cm diameter of the active, or sensitive, volume (DSV) is detailed, as well as an asymmetric system in which a 50-cm DSV begins just 14 cm from the end of the coil structure. Finally a 1.0-T open magnet system with a full 50-cm DSV is presented. These new designs provide clinically useful homogeneous regions and have appropriately restricted stray fields but, in some of the designs, the DSV is much closer to the end of the magnet system than in conventional designs. These new designs have the potential to reduce patient claustrophobia and improve physician access to patients undergoing scans. (C) 2002 Wiley Periodicals, Inc.

An inverse design of an open, head/neck RF coil for MRI

Radio-frequency (RF) coils are a necessary component of magnetic resonance imaging (MRI) systems. When used in transmit operation, they act to generate a homogeneous RF magnetic field within a volume of interest and when in receive operation, they act to receive the nuclear magnetic resonance signal from the RF-excited specimen. This paper outlines a procedure for the design of open RF coils using the time-harmonic inverse method. This method entails the calculation of an ideal current density on a multipaned planar surface that would generate a specified magnetic field within the volume of interest. Because of the averaging effect of the regularization technique in the matrix solution, the specified magnetic field is shaped within an iterative procedure until the generated magnetic field matches the desired magnetic field. The stream-function technique is used to ascertain conductor positions and a method of moments package is then used to finalize the design. An open head/neck coil was designed to operate in a clinical 2T MRI system and the presented results prove the efficacy of this design methodology.

Analysis of an array of monopoles with the use of a radial waveguide approach

A radial guide field matching method (RGFMM) is used to analyze a circular array antenna consisting of one active monopole surrounded by a concentric array of passive monopoles terminated in arbarary loads. An equivalent admittance matrix for this antenna system is determined to study the input admittance of the active monopole when the peripheral elements are terminated in open or short circuits. RGFMM results are compared with free-space method of moments (FS-MoM) results for a small switched-beam array a seven monopoles. Good agreement is noted. (C) 2002 Wiley Periodicals, Inc.

2,6,,9-trioxabicyclo[3.3.1]nona-3,7-dienes and 2,4,6,8-tetraoxaadamantanes: Novel chiral spacer units in macrocyclic polyethers

The unusual chiral heterocyclic systems, trioxabicyclo[3.3.1]nona-3,7-dienes (bridged bisdioxines), are incorporated as novel spacer molecules into macrocyclic polyether ring systems of various sizes (8, 9 as well as 11-15) by cyclocondensation reaction of the! bisacid chloride 4b or bisesters 6,7 and 10, with several ethylene glycols. The 2:2 macrocycles 12-14 are obtained in approximately 50:50 mixtures of diastereomers. These conclusions are mainly based on HPLC data presented in Table I as well as X-ray analyses of (1R,5R)-8c (space group Pbca, a = 10.163(3) Angstrom, b = 18.999(4) Angstrom, c = 36.187(10) Angstrom, V = 6987(3) Angstrom(3), Z = 8, d(calc) = 1.218 g cm(-3), 6974 reflections, R = 0.0553.), mesolrac-11 (space group P (1) over bar, a = 10.472(5) Angstrom, b = 16.390(5) Angstrom, c = 17.211(5) Angstrom, alpha = 98.69(2)degrees, beta = 93.04(2)degrees, gamma = 98.52(2)degrees, V = 2879.3(18) Angstrom(3), Z = 2, d(calc) = 1.173 g cm(-3), 11,162 reflections, R = 0.0945) and meso-12 (space group P2(1)/c, a = 9.927(2), b = 18.166(3), c = 17.820(3) Angstrom, beta = 96.590(10)degrees, V = 3192.3(10)Angstrom(3), Z = 4, D-c = 1.109 g cm(-3), 3490 reflections, R = 0.0646). The 1:1 macrocycles 8b,c are also formed by intramolecular transesterification of the open-chain bisesters 7b,c and their formation is favored by the use of metal ions as templates. The bridged bisdioxine moieties in 8b and 12 are converted into the corresponding chiral tetra-oxaadamantane spacers to afford macrocycles 16 and 17. Preliminary metal ion complexation studies with selected species (8c, 11-14) were also performed.

Three-dimensional space-borne synthetic aperture radar (SAR) imaging with multiple pass processing

Three-dimensional (3D) synthetic aperture radar (SAR) imaging via multiple-pass processing is an extension of interferometric SAR imaging. It exploits more than two flight passes to achieve a desired resolution in elevation. In this paper, a novel approach is developed to reconstruct a 3D space-borne SAR image with multiple-pass processing. It involves image registration, phase correction and elevational imaging. An image model matching is developed for multiple image registration, an eigenvector method is proposed for the phase correction and the elevational imaging is conducted using a Fourier transform or a super-resolution method for enhancement of elevational resolution. 3D SAR images are obtained by processing simulated data and real data from the first European Remote Sensing satellite (ERS-1) with the proposed approaches.

Design of microchannel free-space optical interconnects based on vertical-cavity surface-emitting laser arrays

We investigate the design of free-space optical interconnects (FSOIs) based on arrays of vertical-cavity surface-emitting lasers (VCSELs), microlenses, and photodetectors. We explain the effect of the modal structure of a multimodeVCSEL beam on the performance of a FSOI with microchannel architecture. A Gaussian-beam diffraction model is used in combination with the experimentally obtained spectrally resolved VCSEL beam profiles to determine the optical channel crosstalk and the signal-to-noise ratio (SNR) in the system. The dependence of the SNR on the feature parameters of a FSOI is investigated. We found that the presence of higher-order modes reduces the SNR and the maximum feasible interconnect distance. We also found that the positioning of a VCSEL array relative to the transmitter microlens has a significant impact on the SNR and the maximum feasible interconnect distance. Our analysis shows that the departure from the traditional confocal system yields several advantages including the extended interconnect distance and/or improved SNR. The results show that FSOIs based on multimode VCSELs can be efficiently utilized in both chip-level and board-level interconnects. (C) 2002 Optical Society of America.

Effect of a control burn on lizards and their structural environment in a eucalypt open-forest

The composition of an open-forest lizard assemblage in eastern Australia was examined before and after a low-intensity controlled fire and concurrently compared with that in an adjoining unburnt area. The effect of fire on the available structural environment and the habitat used by two focal species, Carlia vivax and Lygisaurus foliorum, was also examined. Lizard species richness was unaffected by the controlled burn as was the abundance of most species. C. vivax was the only species to display a significant reduction in abundance after fire. While the low-intensity fire resulted in significant changes to the available structural environment, there were no compensatory shifts in the habitat preferences of either C. vivax or L. foliorum. The reduction in abundance of C. vivax was congruent with this species' avoidance of burnt areas. C. vivax displayed a non-random preference for ground cover and litter cover, which were reduced in burnt areas. Changes in the availability of preferred structural habitat features are likely to contribute to changes in the abundance of some lizard species. Therefore, even low-intensity disturbances can have an impact on lizard assemblages if critical habitat features are lost or become limiting.

Recoverable reserves and support effects when optimizing open pit mine designs

Orebody modelling, support effects and the estimation of recoverable reserves are key parts of open pit optimization studies. A case study is presented on the estimation of recoverable reserves using an implementation of indicator kriging where metal quantity is used to select cutoffs, and support corrections founded on a conditional simulation approach. Mining selectivity is explored in the subsequent optimization study to compare results from indicator kriging of grade estimates on a regular size blocks and indicator kriging estimates on small size blocks. The use of indicator kriging models adjusted for a given selectivity and the use of grade proportions in each block for the optimization study, provide a presentation of the expected ore recovery for a predefined level of selectivity. The case study shows that indicator kriging estimation with full accounting of block grade distributions generates substantially better results in the pit optimization study. In addition, the adverse effects of small blocks and over-smoothing on optimization results are illustrated.

pido, a non-long terminal repeat retrotransposon of the chicken repeat 1 family from the genome of the Oriental blood fluke, Schistosoma japonicum

A newly described non-long terminal repeat (non-LTR) retrotransposon element was isolated from the genome of the Oriental schistosome, Schistosoma japonicum. At least 1000 partial copies of the element, which was named pido, were dispersed throughout the genome of S. japonicum. As is usual with non-LTR retrotransposons, it is expected that many pido elements will be 5'-truncated. A consensus sequence of 3564 bp of the truncated pido element was assembled from several genomic fragments that contained pido-hybridizing sequences. The sequence encoded part of the first open reading frame (ORF), the entire second ORF and, at its 3'-terminus, a tandemly repetitive, A-rich (TA(6)TA(5)TA(8)) tail, The ORF1 of pido encoded a nucleic acid binding protein and ORF2 encoded a retroviral-like polyprotein that included apurinic/apyrimidinic endonuclease (EN) and reverse transcriptase (RT) domains, in that order. Based on its sequence and structure, and phylogenetic analyses of both the RT and EN domains, pido belongs to the chicken repeat 1 (CR1)-like lineage of elements known from the chicken, turtle, puffer fish, mosquitoes and other taxa. pido shared equal similarity with CRI from chicken, an uncharacterized retrotransposon from Caenorhabditis elegans and SR1 (a non-LTR retrotransposon) from the related blood fluke Schistosoma mansoni; the level of similarity between pido and SR1 indicated that these two schistosome retrotransposons were related but not orthologous. The findings indicate that schistosomes have been colonized by at least two discrete CRI-like elements. Whereas pido did not appear to have a tight target site specificity, at least one copy of pido has inserted into the 3'-untranslated region of a protein-encoding gene (GeriBank AW736757) of as yet unknown identity. mRNA encoding the RT of pido was detected by reverse transcription-polymerase chain reaction in the egg, miracidium. and adult developmental stages of S. japonicum, indicating that the RT domain was transcribed and suggesting that pido was replicating actively and mobile within the S. japonicum genome. (C) 2002 Elsevier Science B.V. All rights reserved.

Macropodid herpesvirus 1 encodes genes for both thymidylate synthase and ICP34.5

Macropodid herpesvirus 1 (MaHV-1) is an unclassified alphaherpesvirus linked with the fatal infections of kangaroos and other marsupials. During the characterisation of the internal repeat region of MaHV-1, an open reading frame (ORF) encoding for thymidylate synthase (TS) gene was identified and completely sequenced. Southern blot analysis confirmed the presence of two copies of the TS gene in the MaHV-1 genome as expected. Computer analysis of the TS ORF showed it was 948 nucleotides in length. A putative polyadenylation signal was identified 17-22 bp inside the ORF implying a minimal or absent 3' untranslated region. The predicted polypeptide was 316 amino acid residues in length and contained the highly conserved motifs for folate binding and F-dUMP binding, typical of all TS enzymes. Interestingly, MaHV-1 TS polypeptide had highest similarity to the human TS polypeptide (81%) compared to the TS polypeptides of other herpesviruses (72-75%). Immediately upstream of the TS gene, a second ORF of 510 bp, encoding a polypeptide with 170 amino acid residues, was identified. The carboxyl domain of this MaHV-1 polypeptide shared 68% similarity to a 59 amino acid motif of human herpesvirus 1 ICP34.5, identifying it as the MaHV-1 ICP34.5 homologue. This is the first report of a herpesvirus that encodes for both TS and ICP34.5.

The role of space as both a conflict trigger and a conflict control mechanism in culturally heterogeneous workgroups

The diversity literature is replete with examples of poor outcomes in Culturally Heterogeneous Workgroups (CHWs) caused by relational difficulties. Although it is widely recognised that culture shapes people's interpretation of behavior and their style of interaction with others in the workplace, what is ill understood is what the specific conflict triggers of these conflicts are. In this paper, we argue that differences in cultural norms and views of physical and psychological space are major triggers of conflict in CHWs. Findings from a field study support the proposition that different viewpoints regarding the use of space, the inability to retreat from exposure to others, decreased interpersonal space, and privacy invasion moderate the relationship between cultural diversity in the workgroup and the type, frequency, and duration of conflict events in CHWs. The paper represents a first step in elucidating the role of space in cross-cultural interactions in the workplace and how space may be a potentially important conflict control mechanism for managers of culturally diverse workgroups.