bluuebunny/crossref_metadata_2025 huggingface dataset:
Determinants of Increased Replicative Capacity of Serially Passaged Simian Immunodeficiency Virus with
nef
Deleted in Rhesus Monkeys
Authors: Alexander Louis , Illyinskii Petr O. , Lang Sabine M. , Means Robert E. , Lifson Jeffrey , Mansfield Keith , Desrosiers Ronald C.
Published: May 2003

Most rhesus macaques infected with simian immunodeficiency virus SIVmac239 with
nef
deleted (either Δ
nef
or Δ
nef
Δ
vpr
ΔUS [Δ3]) control viral replication and do not progress to AIDS. Some monkeys, however, develop moderate viral load set points and progress to AIDS. When simian immunodeficiency viruses (SIVs) recovered from two such animals (one Δ
nef
and the other Δ3) were serially passaged in rhesus monkeys, the SIVs derived from both lineages were found to consistently induce moderate viral loads and disease progression. Analysis of viral sequences in the serially passaged derivatives revealed interesting changes in three regions: (i) an unusually high number of predicted amino acid changes (12 to 14) in the cytoplasmic domain of gp41, most of which were in regions that are usually conserved; these changes were observed in both lineages; (ii) an extreme shortening of
nef
sequences in the region of overlap with U3; these changes were observed in both lineages; and (iii) duplication of the NF-κB binding site in one lineage only. Neither the polymorphic gp41 changes alone nor the U3 deletion alone appeared to be responsible for increased replicative capacity because recombinant SIVmac239Δnef, engineered to contain either of these changes, induced moderate viral loads in only one of six monkeys. However, five of six monkeys infected with recombinant SIVmac239Δnef containing both TM and U3 changes did develop persisting moderate viral loads. These genetic changes did not increase lymphoid cell-activating properties in the monkey interleukin-2-dependent T-cell line 221, but the gp41 changes did increase the fusogenic activity of the SIV envelope two- to threefold. These results delineate sequence changes in SIV that can compensate for the loss of the
nef
gene to partially restore replicative and pathogenic potential in rhesus monkeys.
Herpes Simplex Virus Glycoprotein K, but Not Its Syncytial Allele, Inhibits Cell-Cell Fusion Mediated by the Four Fusogenic Glycoproteins, gD, gB, gH, and gL
Authors: Avitabile Elisa , Lombardi Giulia , Campadelli-Fiume Gabriella
Published: May 2003

A Myc epitope was inserted at residue 283 of herpes simplex virus type 1 (HSV-1) glycoprotein K (gK), a position previously shown not to interfere with gK activity. The Myc-tagged gK localized predominantly to the endoplasmic reticulum, both in uninfected and in HSV-infected cells. gK, coexpressed with the four HSV fusogenic glycoproteins, gD, gB, gH, and gL, inhibited cell-cell fusion. The effect was partially dose dependent and was observed both in baby hamster kidney (BHK) and in Vero cells, indicating that the antifusion activity of gK may be cell line independent. The antifusion activity of gK did not require viral proteins other than the four fusogenic glycoproteins. A syncytial (
syn
) allele of gK (
syn
-gK) carrying the A40V substitution present in HSV-1(MP) did not block fusion to the extent seen with the wild-type (wt) gK, indicating that the
syn
mutation ablated, at least in part, the antifusogenic activity of wt gK. We conclude that gK is part of the mechanism whereby HSV negatively regulates its own fusion activity. Its effect accounts for the notion that cells infected with wt HSV do not fuse with adjacent, uninfected cells into multinucleated giant cells or syncytia. gK may also function to preclude fusion between virion envelope and the virion-encasing vesicles during virus transport to the extracellular compartment, thus preventing nucleocapsid de-envelopment in the cytoplasm.
Expression of Simian Immunodeficiency Virus (SIV) Nef in Astrocytes during Acute and Terminal Infection and Requirement of Nef for Optimal Replication of Neurovirulent SIV In Vitro
Authors: Overholser Emily D. , Coleman Gary D. , Bennett Jennifer L. , Casaday Rebecca J. , Zink M. Christine , Barber Sheila A. , Clements Janice E.
Published: May 2003

As the most numerous cells in the brain, astrocytes play a critical role in maintaining central nervous system homeostasis, and therefore, infection of astrocytes by human immunodeficiency virus (HIV) or simian immunodeficiency virus (SIV) in vivo could have important consequences for the development of HIV encephalitis. In this study, we establish that astrocytes are infected in macaques during acute SIV infection (10 days postinoculation) and during terminal infection when there is evidence of SIV-induced encephalitis. Additionally, with primary adult rhesus macaque astrocytes in vitro, we demonstrate that the macrophage-tropic, neurovirulent viruses SIV/17E-Br and SIV/17E-Fr replicate efficiently in astrocytes, while the lymphocyte-tropic, nonneurovirulent virus SIV
mac
239
open
-
nef
does not establish productive infection. Furthermore, aminoxypentane-RANTES abolishes virus replication, suggesting that these SIV strains utilize the chemokine receptor CCR5 for entry into astrocytes. Importantly, we show that SIV Nef is required for optimal replication in primary rhesus macaque astrocytes and that normalizing input virus by particle number rather than by infectivity reveals a disparity between the ability of a Nef-deficient virus and a virus encoding a nonmyristoylated form of Nef to replicate in these central nervous system cells. Since the myristoylated form of Nef has been implicated in functions such as CD4 and major histocompatibility complex I downregulation, kinase association, and enhancement of virion infectivity, these data suggest that an as yet unidentified function of Nef may exist to facilitate SIV replication in astrocytes that may have important implications for in vivo pathogenesis.
Human Immunodeficiency Virus Type 1 Envelope-Mediated Neuronal Death: Uncoupling of Viral Replication and Neurotoxicity
Authors: Zhang Kunyan , Rana Farazana , Silva Claudia , Ethier Julie , Wehrly Kathy , Chesebro Bruce , Power Christopher
Published: May 2003

Although brain tissue from patients with human immunodeficiency virus (HIV) and/or AIDS is consistently infected by HIV type 1 (HIV-1), only 20 to 30% of patients exhibit clinical or neuropathological evidence of brain injury. Extensive HIV-1 sequence diversity is present in the brain, which may account in part for the variability in the occurrence of HIV-induced brain disease. Neurological injury caused by HIV-1 is mediated directly by neurotoxic viral proteins or indirectly through excess production of host molecules by infected or activated glial cells. To elucidate the relationship between HIV-1 infection and neuronal death, we examined the neurotoxic effects of supernatants from human 293T cells or macrophages expressing recombinant HIV-1 virions or gp120 proteins containing the V1V3 or C2V3 envelope region from non-clade B, brain-derived HIV-1 sequences. Neurotoxicity was measured separately as apoptosis or total neuronal death, with apoptosis representing 30 to 80% of the total neuron death observed, depending on the individual virus. In addition, neurotoxicity was dependent on expression of HIV-1 gp120 and could be blocked by anti-gp120 antibodies, as well as by antibodies to the human CCR5 and CXCR4 chemokine receptors. Despite extensive sequence diversity in the recombinant envelope region (V1V3 or C2V3), there was limited variation in the neurotoxicity induced by supernatants from transfected 293T cells. Conversely, supernatants from infected macrophages caused a broader range of neurotoxicity levels that depended on each virus and was independent of the replicative ability of the virus. These findings underscore the importance of HIV-1 envelope protein expression in neurotoxic pathways associated with HIV-induced brain disease and highlight the envelope as a target for neuroprotective therapeutic interventions.
The PDZ Ligand Domain of the Human Papillomavirus Type 16 E6 Protein Is Required for E6's Induction of Epithelial Hyperplasia In Vivo
Authors: Nguyen Marie L. , Nguyen Minh M. , Lee Denis , Griep Anne E. , Lambert Paul F.
Published: May 2003

Human papillomaviruses (HPVs) are the causative agent of warts. Infections with high-risk HPVs are associated with anogenital and head and neck cancers. One of the viral genes responsible for HPV's oncogenic activity is E6. Mice expressing the HPV-16 E6 protein in their epidermis (K14E6
WT
) develop epithelial hyperplasia and squamous carcinomas. Numerous cellular proteins interact with E6, some of which can be grouped based on common amino acid motifs in their E6-binding domains. One such group, the PDZ partners, including hDLG, hSCRIBBLE, MUPP1, and MAGI, bind to the carboxy-terminal four amino acids of E6 through their PDZ domains. E6's interaction with the PDZ partners leads to their degradation. Additionally, E6's binding to PDZ proteins has been correlated with its ability to transform baby rat kidney cells in tissue culture and to confer tumorigenicity onto cells in xenograft experiments. To address whether the ability of E6 to bind PDZ domain partners is necessary for E6 to confer epithelial hyperproliferation in vivo, we generated transgenic mice that express in stratified squamous epithelia a mutant of E6 lacking the last six amino acids at its carboxyl terminus, E6
Δ146-151
, from the human keratin 14 (K14) promoter. The K14E6
Δ146-151
mice exhibit a radiation response similar to that of the K14E6
WT
mice, demonstrating that this protein, as predicted, retains an ability to inactivate p53. However, the K14E6
Δ146-151
mice fail to display epithelial hyperplasia. These results indicate that an interaction of E6 with PDZ partners is necessary for its induction of epithelial hyperplasia.
Varicella-Zoster Virus DNA in Cells Isolated from Human Trigeminal Ganglia
Authors: Levin Myron J. , Cai Guang-Yun , Manchak Michael D. , Pizer Lewis I.
Published: May 2003

To determine the type of cell(s) that contain latent varicella-zoster virus (VZV) DNA, we prepared pure populations of neurons and satellite cells from trigeminal ganglia of 18 humans who had previously had a VZV infection. VZV DNA was present in 34 of 2,226 neurons (1.5%) and in none of 20,700 satellite cells. There was an average of 4.7 (range of 2 to 9) copies of VZV DNA per latently infected neuron. Latent VZV DNA was primarily present in large neurons, whereas the size distribution of herpes simplex virus DNA was markedly different.
Characterization of H9 Subtype Influenza Viruses from the Ducks of Southern China: a Candidate for the Next Influenza Pandemic in Humans?
Authors: Li K. S. , Xu K. M. , Peiris J. S. M. , Poon L. L. M. , Yu K. Z. , Yuen K. Y. , Shortridge K. F. , Webster R. G. , Guan Y.
Published: May 2003

A current view of the emergence of pandemic influenza viruses envisages a gene flow from the aquatic avian reservoir to humans via reassortment in pigs, the hypothetical “mixing vessel.” Understanding arising from recent H5N1 influenza outbreaks in Hong Kong since 1997 and the isolation of avian H9N2 virus from humans raises alternative options for the emergence of a new pandemic virus. Here we report that H9N2 influenza viruses established in terrestrial poultry in southern China are transmitted back to domestic ducks, in which the viruses generate multiple reassortants. These novel H9N2 viruses are double or even triple reassortants that have amino acid signatures in their hemagglutinin, indicating their potential to directly infect humans. Some of them contain gene segments that are closely related to those of A/Hong Kong/156/97 (H5N1/97, H5N1) or A/Quail/Hong Kong/G1/97 (G1-like, H9N2). More importantly, some of their internal genes are closely related to those of novel H5N1 viruses isolated during the outbreak in Hong Kong in 2001. This study reveals a two-way transmission of influenza virus between terrestrial and aquatic birds that facilitates the generation of novel reassortant H9N2 influenza viruses. Such reassortants may directly or indirectly play a role in the emergence of the next pandemic virus.
Functional Characterization of the Nuclear Localization Signal for a Suppressor of Posttranscriptional Gene Silencing
Authors: Dong Xiangli , van Wezel Rene , Stanley John , Hong Yiguo
Published: May 2003

The nucleus-localized C2 protein ofTomato yellow leaf curl virus-China(TYLCV-C) is an active suppressor of posttranscriptional gene silencing (PTGS). Consistently, infection with TYLCV-C resulted in PTGS arrest in plants. The C2 protein possesses a functional, arginine-rich nuclear localization signal within the basic amino acid-rich region17KVQHRIAKKTTRRRR31. When expressed from potato virus X, C2-RRRR31DVGG (in which the four consecutive arginine residues28RRRR31were replaced with DVGG) that had been tagged with a green fluorescent protein (GFP) failed to transport GFP into nuclei and was dysfunctional in inducing necrosis and suppressing PTGS in plants. Amino acid substitution mutants C2-K17D-GFP, C2-HR21DV-GFP, and C2-KK25DI-GFP localized to nuclei and produced necrosis, but only C2-K17D-GFP suppressed PTGS. The N-terminal portions C21-31and C217-31fused in frame to GFP were capable of targeting GFP to nuclei, but neither caused necrosis nor affected PTGS. Our data establish that nuclear localization is likely required for C2 protein to function in C2-mediated induction of necrosis and suppression of PTGS, which may follow diverse pathways in plants. Possible mechanisms of how the C2 protein involves these biological functions are discussed.
Impairment of Interferon-Induced IRF-7 Gene Expression due to Inhibition of ISGF3 Formation by Trichostatin A
Authors: Génin Pierre , Morin Pierre , Civas Ahmet
Published: May 2003

Two members of the signal transducer and activator of transcription family, STAT1 and STAT2, form, together with interferon regulatory factor 9 (IRF-9), the ISGF3 complex that activates the expression of the interferon-stimulated genes (ISG). The ISGF3 complex also participates in the virus-induced alpha/beta interferon (IFN-α/β) gene amplification cascade by up-regulating IRF-7 gene expression. Here, we show that treatment of cells with trichostatin A (TSA), a deacetylase inhibitor, inhibits the virus-induced activation of IFN-α/β promoters and dramatically reduces the ability of different ISG promoters to respond to IFN stimulation. Impairment of IFN-α/β and ISG expression by TSA in infected cells is due to the blockage of interferon-stimulated ISGF3 complex formation, which leads to the abolition of IRF-7 gene expression. We also show that the TSA-dependent inhibition of ISGF3 is related to impaired nuclear accumulation of STAT2. Our data suggest that an acetylation/deacetylation mechanism participates in the regulation of cellular distribution and function of STAT2 in IFN-α/β signaling.
Flavivirus Capsid Is a Dimeric Alpha-Helical Protein
Authors: Jones Christopher T. , Ma Lixin , Burgner John W. , Groesch Teresa D. , Post Carol B. , Kuhn Richard J.
Published: May 2003

The capsid proteins of two flaviviruses, yellow fever virus and dengue virus, were expressed in
Escherichia coli
and purified to near homogeneity suitable for biochemical characterization and structure determination by nuclear magnetic resonance. The oligomeric properties of the capsid protein in solution were investigated. In the absence of nucleic acid, both proteins were predominately dimeric in solution. Further analysis of both proteins with far-UV circular dichroism spectroscopy indicated that they were largely alpha-helical. The secondary structure elements of the dengue virus capsid were determined by chemical shift indexing of the sequence-specific backbone resonance assignments. The dengue virus capsid protein devoid of its C-terminal signal sequence was found to be composed of four alpha helices. The longest alpha helix, 20 residues, is located at the C terminus and has an amphipathic character. In contrast, the N terminus was found to be unstructured and could be removed without disrupting the structural integrity of the protein.
The hind limb ofCaptorhinus agutiand the step cycle of basal amniotes
Authors: Holmes Robert B
Published: May 2003

Exquisitely preserved limb elements of Captorhinus aguti from the Lower Permian locality of Richards Spur, Oklahoma, form an excellent basis for analysing the step cycle of the hind limb of basal amniotes. An articulated composite hind limb skeleton is moved through the step cycle. These movements are constrained by the intrinsic skeletal anatomy and data from fossilized footprints attributed to Palaeozoic amniotes. Two well-defined hinge joints are evident: a distal tarsometatarsal joint, and a mesotarsal joint between the calcaneumastragaluscentrale unit and distal tarsals. A strict homology between the latter and mesotarsal joint in lepidosaurs is uncertain. The conspicuous size disparity between the distal end of the tibia and the much larger tibial facet of the astragalus, a widespread feature of archaic amniotes, permits considerable movement between the distal end of the tibia and astragalus during the stance phase. Differential dorsoflexion, concentrated at the preaxial side of the mesotarsal joint, allows the pes to remain stationary (rather than slide laterally) on the substrate as the femur is retracted and the tarsus shifts from an anterior to lateral orientation. The distal end of the femur describes an arc of only ~60° during the stance phase, but could rotate about 60° about its long axis, a figure comparable to that recorded for living lizards.
A new microsaur (Tetrapoda: Lepospondyli) from the Lower Permian of Richards Spur (Fort Sill), Oklahoma
Authors: Anderson Jason S , Reisz Robert R
Published: May 2003

Bolterpeton carrolli n.gen. n.sp. is described from the Lower Permian fissure-fill deposits of Richards Spur, Oklahoma. Bolterpeton is united with the gymnarthrid microsaur Cardiocephalus by having teeth compressed labiolingually, a narrow anterior process of the prearticular penetrating the splenial, and the arrangement of the contacts among the splenial, prearticular, and coronoids. It is united with both Cardiocephalus and Euryodus by the size and distribution of the coronoid teeth and the presence of longitudinal striations of enamel on the lingual tooth surface. Unlike those two genera Bolterpeton has peg-like teeth, but it remains unknown whether this represents the primitive condition or a reversal of the massive conical teeth typical of gymnarthrids. Bolterpeton possesses a flat lamina that runs along the lingual surface of the tooth margin. Where two laminae meet at the point of the tooth a labiolingual ridge is formed, which is most pronounced at smaller sizes. Reexamination of Cardiocephalus shows it to have the same morphology on its "incisors." Previous authors have defined teeth bearing this ridge as "weakly bicuspid." If this ridge were homologous with the "strongly bicuspid" condition of lissamphibians, Bolterpeton would provide the first example of this tooth morphology in lepospondyls and would strengthen recent hypotheses suggesting lepospondyls gave rise to some, if not all, modern amphibians.
"Without a leg to stand on": on the evolution and development of axial elongation and limblessness in tetrapods
Authors: Caldwell Michael W
Published: May 2003

A review of the osteology of the axial and appendicular skeleton of fossil and extant tetrapods, in the context of tetrapod phylogenetic patterns, reveals common patterns of limb loss and axial elongation. A threshold number of 3540 presacral vertebrae is linked to minor reductions in digit number and the phalangeal count. Presacral vertebral counts do not increase gradually, rather, presacral counts jump from 3540 to 6070. At this point, limb loss is extreme, with forelimbs being reduced to tiny appendages or lost altogether. Higher presacral counts (>90) are linked to total forelimb loss and radical rear-limb reductions culminating in total loss. A pattern of this sort is recognized in Paleozoic lepospondyls and Mesozoic to modern squamates. Developmental genetic models illuminate gene systems that are associated with morphogenesis and are linked to the evolution of limb reduction and leglessness in these tetrapods.
Allometric growth in tyrannosaurids (Dinosauria: Theropoda) from the Upper Cretaceous of North America and Asia
Authors: Currie Philip J
Published: May 2003

Many tyrannosaurid skeletons have been collected in Canada, the United States, and Mongolia. These fossils tend to represent mature individuals, but juveniles are also known. Skeletons of five genera of tyrannosaurids representing two distinct clades (albertosaurines and tyrannosaurines) were measured, and bivariate analysis was done on 85 dimensions. Allometric differences among mature specimens of different species are shown to be trivial when compared with the allometric differences associated with growth. Nevertheless, albertosaurines tend to be more lightly built than tyrannosaurines. When compared with a tyrannosaurine of the same absolute size, albertosaurines had slightly shorter, lower skulls, shorter ilia, longer tibiae, longer metatarsals, and longer toes. The arms of albertosaurines and tyrannosaurines are the same size, with the exception of Tarbosaurus, which has shorter front limb elements. Tooth counts show individual and interspecific variation, but there is no evidence that tooth numbers are controlled by the size or age of an animal. Dinotyrannus, Jenghizkhan, Maleevosaurus, Shanshanosaurus, Stygivenator, and possibly Nanotyrannus have proportions that suggest they are ontogenetic stages of either Tarbosaurus or Tyrannosaurus.
The Touquoy Zone deposit: an example of "unusual" orogenic gold mineralisation in the Meguma Terrane, Nova Scotia, Canada
Authors: Bierlein Frank P , Smith Paul K
Published: May 2003

The Touquoy Zone deposit is host to disseminated gold mineralisation in metasiltstones of lower Palaeozoic age. From the close correlation between ore grades and the intersection of favourable stratigraphy and bounding faults, it is apparent that mineralisation is controlled by both structural and lithological influences. Within the ore zone, disseminated gold, arsenopyrite, pyrite, and rare base-metal sulphides are associated with a network of widely spaced, millimetre-scale, quartzcarbonate veinlets. Quasi-pervasive fluid flow and prolonged interaction with the host rocks resulted in a diffuse, but pronounced halo of wall-rock alteration that is characterized by the breakdown of detrital feldspar and metamorphic chlorite and the development of hydrothermal carbonate phases, K-mica, and disseminated sulphides. These mineralogical changes are accompanied by enrichment in CO2, K, Au, As, and S and depletion in Na across the ore zone. Vein formation occurred at between 250° and 350°C and pressures of less than 12 kbar (1 kbar = 100 MPa), corresponding to an estimated depth of between <2.8 and 6 km. Mineralisation resulted from the unmixing of an overpressured (low-salinity, CO2-rich) fluid in response to decreasing pressure during its ascent and penetration into permeable host rocks. Geological and geochemical features of mineralisation in the Touquoy Zone deposit are seen as convincing evidence for a close genetic association between disseminated-style and lode gold mineralisation in orogenic terrains, with the resulting style of mineralisation largely controlled by the overall structural geometry of the mineralising site, rheological properties, permeability and chemical receptiveness of the host rock, and structural level of emplacement.
Structural evolution of the Hemlo greenstone belt in the vicinity of the world-class Hemlo gold deposit
Authors: Muir T L
Published: May 2003

A complex history of volcano-sedimentary deposition, polyphase strain, multiple intrusive events, and various stages of porphyroblastesis is indicated for the Hemlo gold deposit area within the Hemlo greenstone belt. Structural elements can be assigned to at least six stages of development (D1D6). D1 generated small-scale folds and low-angle faults (thrusts?) with no planar fabric, except within strain aureoles around the earliest intrusions. D2 was a progressive event resulting from northeast-directed compression, which generated regional, predominantly S-shaped folds (early D2); penetrative planar and linear fabrics, overturned stratigraphy, and formation of an inflection in the strike of the greenstone belt (mid-D2); and development of high-strain zones with dominant sinistral and local dextral shear sense (late D2). D3 was a distinctly separate progressive event resulting from northwest-directed transpression, which generated variably penetrative east- to northeast-striking foliation (S3), ductile dextral shear fabrics, and small-scale Z-shaped folds (early D3), followed by brittleductile to brittle development of cataclasite and pseudotachylite in layer-parallel zones (late D3). D4 resulted in contractional kinks and brittle fractures, locally in conjugate sets. D5 and D6 are represented by brittle to brittleductile faults, which overprint Paleoproterozoic and Mesoproterozoic dikes, respectively. Four granitoid magmatic events span the interval 27202677 Ma, with emplacement mainly during D2, between ca. 2690 and ca. 2684 Ma. A protracted period of regional medium-grade metamorphism likely spanned the D2D3 stages. The Hemlo gold deposit was emplaced during mid-D2 and was largely controlled by D2 structural elements and competency contrast between rock units.
Constraints on early Archean crustal extraction and tholeiitic-komatiitic volcanism in greenstone belts of the Northern Superior Province
Authors: Maurice Charles , Francis Don , Madore Louis
Published: May 2003

Numerous small remnants of Archean greenstone belts in the Northern Superior Province (ca. 28752710 Ma) have chemical characteristics similar to those of the larger greenstone belts of the Southern Superior Province, and preserve direct evidence of crustal conditions prior to the major volcanic events of the late Archean (WawaAbitibi subprovinces; ca. 27602700 Ma). Three of the best preserved belts are engulfed in tonalite intrusions of the Faribault-Thury Complex (FTC) and exhibit common chemical characteristics, which may imply a similar origin. The dominant tholeiitic basalts typically have MgO contents > 7 wt.%, TiO2 < 1 wt.% and nearly flat rare-earth element (REE) patterns (La/Smn = 0.771.22; Gd/Ybn = 0.861.20). Associated komatiites have flat to depleted REE patterns (La/Smn = 0.450.95), high Al2O3/TiO2 (>15), low CaO/Al2O3 (<1.2), and chondritic Gd/Yb ratios similar to 2.7 Ga Al-undepleted komatiites. The trace-element ratios of komatiitic rocks are indistinguishable from those of the associated tholeiites, suggesting either a derivation from similar mantle sources or a comagmatic relationship (Nb/Thpm = 0.81.1; La/Cepm = 0.91.3; Nb/Ce = 0.70.9; Y/Hopm ~1; and Th/Lapm = 0.71.1). Numerical modelling of trace and major elements during low-pressure crystal fractionation reproduces the spectrum of both inferred liquid and cumulate compositions and is consistent with a comagmatic origin between the komatiites and tholeiites. The relatively low Nb/Th ratios of these mid-Archean volcanic rocks relative to both modern day basalts and late Archean basalts may indicate that they were derived from a mantle source that had not lost its crustal components, nor seen significant recycled oceanic crust (high Nb/Th). The extraction of continental crust from this Archean mantle source might then postdate the FTC volcanism, and may be associated with the generation of the voluminous tonalites that engulf the belts.
WAVE PACKET DYNAMICS AND RABI OSCILLATIONS IN TWO-COUPLED BOSE–EINSTEIN CONDENSATES CONFINED IN AN OPTICAL LATTICE
Authors: BHATTACHERJEE ARANYABHUTI , MOHAN MAN
Published: May 2003

We predict the collapse and recurrence of Rabi oscillations in a two-component Bose–Einstein condensate trapped in an optical lattice. The optical trap creates a periodic potential with a periodic coupling. The collapse and revival sequence is explained on the basis of wave-packet dynamics. The collapse and revival sequence is found to be a consequence of competition between the potential energy difference and the driving frequency.
ELECTRONIC STRUCTURE OF SHORT CARBON NANOBELLS
Authors: ZHAO G. L. , BAGAYOKO D. , WANG E. G.
Published: May 2003

We performed local density functional calculations for the electronic structure of short carbon nanobells. The calculated local density of states of the nanobells revealed field emission characteristics that agree with experimental observations. We also performed total energy calculations to study the structural stability and a related possible growth mechanism of the nanobells. In the nitrogen-doped carbon nanobells, nitrogen atoms that are attracted to the open-edge sites of the carbon nanobells appear to stop the growth of the nanostructures.
STRUCTURAL INVESTIGATIONS OF MnO-Bi2O3 AND MnO-Bi2O3-As2O3 GLASS SYSTEMS BY IR SPECTROSCOPY
Authors: ARDELEAN I. , TODOR IOANA , PĂŞCUŢĂ P. , IONCU V.
Published: May 2003

Glasses from x MnO · (100-x) Bi2O3 and x MnO · (100-x)[ Bi2O3 · As2O3 ] systems, with 0≤ x≤ 50 mol% were obtained in the same conditions and characterized by IR spectroscopy. The influence of a gradual increase of MnO content on the glass structure and the effect of changing the glass matrix compositions, were projected. The presence and the dependence of the bismuthate structural units BiO3 and BiO6 on the MnO content was analyzed.
DEPOSITION-AND-SUBSTRATE TUNABLE PHOTONIC BANDGAP IN OPTICAL RESPONSES OF HYDROGENATED AMORPHOUS SILICON CARBIDE THIN FILMS
Authors: RAKOV NIKIFOR , MAHMOOD ARSHAD , XIAO MUFEI
Published: May 2003

Amorphous hydrogenated silicon carbide (a-SiC:H) thin films have been prepared by the RF reactive magnetron sputtering technique. The optical properties of the films have been studied by optical spectroscopy with an incoherent light source. The material is commonly regarded as a dielectric. We have discovered however that some films that were prepared under certain deposition conditions and on certain substrates may respond to external light as a metallic thin film, i.e. there are strongly enhanced reflection peaks in the optical spectrum. We have further discovered that some films may have a strong and broadened absorption peak at about 590 nm, which is an apparent photonic bandgap in the visible spectrum. The appearance of the photonic bandgap is very sensitive to two parameters: the substrate and the deposition gas. By changing the two parameters, one shifts the status of the film from with and without the photonic bandgap.
THE APPLICATION OF PETRI NETS TO WORKFLOW MANAGEMENT
Authors: VAN DER AALST W. M. P.
Published: May 2003

Workflow management promises a new solution to an age-old problem: controlling, monitoring, optimizing and supporting business processes. What is new about workflow management is the explicit representation of the business process logic which allows for computerized support. This paper discusses the use of Petri nets in the context of workflow management. Petri nets are an established tool for modeling and analyzing processes. On the one hand, Petri nets can be used as a design language for the specification of complex workflows. On the other hand, Petri net theory provides for powerful analysis techniques which can be used to verify the correctness of workflow procedures. This paper introduces workflow management as an application domain for Petri nets, presents state-of-the-art results with respect to the verification of workflows, and highlights some Petri-net-based workflow tools.
CONTINUOUS AND HYBRID PETRI NETS
Authors: ALLA HASSANE , DAVID RENÉ
Published: May 2003

Petri nets are widely used to model discrete event dynamic systems (computer systems, manufacturing systems, communication systems…). When a PN contains a large number of tokens, the number of reachable states explodes. This is a practical limitation to the use of Petri nets. Continuous models may provide very good approximations for discrete event systems: this is the basic idea leading to the definition of continuous Petri nets. A continuous PN is a model in which the marking of each place is a real number. In a timed continuous PN, a firing speed is associated with each transition (this basic model is unique although the firing speed may be defined in several ways).

Various timed continuous PN models have been defined and they correspond to a specific calculation of the firing speeds. They provide good approximations for performance evaluation when a PN contains a large number of tokens.

Modeling a number of parts in a buffer by a real number may generally be an acceptable approximation. However, the state of a machine, up or down, cannot be modeled by a real number. This naturally leads to the idea of hybrid PNs, containing a discrete part and a continuous part. Autonomous and timed hybrid PNs are presented.

A large of the presentation is informal and intuitive.

Three examples illustrate the application of the different models.
ON LINEAR ALGEBRAIC TECHNIQUES FOR LIVENESS ANALYSIS OF P/T SYSTEMS
Authors: RECALDE LAURA , TERUEL ENRIQUE , SILVA MANUEL
Published: May 2003

Liveness is a basic property that in many discrete event dynamic systems is considered essential for their correct behavior. It expresses that no action (transition in P/T models) will ever become unattainable. A polynomial time necessary condition for the existence of a live and bounded marking of a P/T net is given. This condition is shown to be also sufficient for some subclasses. The applicability of these results is extended by the use of transformation techniques that allow for their exploitation in the analysis of more general nets. Some results for the structural analysis of actual liveness are also overviewed, in particular, sufficient conditions for deadlock-freeness and absence of dead transitions.
UPPER BOUND ON SNR GAIN IN WAVELET TRANSFORM PREDICTIVE-ENTROPY IMAGE CODING
Authors: MILOVANOVIĆ DRAGORAD , BOJKOVIĆ ZORAN , SAMČOVIĆ ANDREJA
Published: May 2003

Using the rate-distortion theory approach and assuming the Laplacian probability density function of the quantizer input signal, we propose a function which gives the signal-to-quantizing-noise ratio (SNR) gain in discrete wavelet transform predictive-entropy coding over fullband predictive image coding. The upper bound on SNR gain is determined as a function of the subband number only. The practical SNR performances of realizable wavelet still image coders are compared with their theoretical bounds. The computer simulation results of wavelet based predictive coded test images show that the SNR gain grows faster with the subband number increment than its theoretical upper bounds do.
TOLERANCE OF ON-CHIP LEARNING TO VARIOUS CIRCUIT INACCURACIES
Authors: CARD HOWARD C. , McNEILL DEAN K. , SCHNEIDER CHRISTIAN R. , SCHNEIDER ROLAND S. , DOLENKO BRION K.
Published: May 2003

An investigation is made of the tolerance of various in-circuit learning algorithms to component imprecision and other circuit limitations in artificial neural networks. In contrast with most previous work, the various circuit limitations are treated separately for their effects on learning. Supervised learning mechanisms including backpropagation and contrastive Hebbian learning, and unsupervised soft competitive learning were found to be sufficiently tolerant of those levels of arithmetic inaccuracy, noise, nonlinearity, weight decay, and statistical variation from fabrication that we have experienced in 1.2 μm analog CMOS circuits employing Gilbert multipliers as the primary computational element. These learning circuits also function properly in the presence of offset errors in analog multipliers and adders, provided that the computed weight updates are constrained by the circuitry to be made only when they exceed certain minimum or threshold values. These results may also be relevant for other analog circuit approaches and for compact (low bit rate) digital implementations, although in this case, the minimum weight increment defined by the bit precision could necessitate stochastic updating.
INTERPOLATION OF MULTIPLIER COEFFICIENTS OF AN ELLIPTIC WAVE DIGITAL FILTER
Authors: TAN E. C. , CHIA C. Y.
Published: May 2003

Since the characteristics of an elliptic filter are generally more complex, the required multiplier coefficients of an elliptic wave-digital filter are usually computed from table values. To avoid such an inconvenience and to exploit today's PC capability in terms of storage and speed, we found that it is sufficient to store only a few pre-calculated values and other coefficients can be obtained by employing a computationally simple and fast interpolation routine.
ON A REFINED CYCLIC RESERVATION-BASED MAC SCHEME FOR ULTRA HIGH-SPEED HIERARCHICAL RING MANS
Authors: WANG WEN-FONG , KUNG LING-YANG
Published: May 2003

To support a great number of dispersed users in a wider area with high-speed communication services, we investigate a highly efficient medium access control (MAC) scheme for the hierarchical ring networks. In these networks, traffic congestion may happen due to the mismatch of transmission speed between backbone and outer rings. To cope with the issue, we propose a refined MAC protocol based on the cyclic reservation-based access control method for different network resources, viz. network bandwidth and buffers. By this approach, our protocol can achieve fair access to the network resources and avoid traffic congestion at the same time. Also, the networks will have the properties of extremely high throughput, low delay, fair access, simple implementation, and so forth. To evaluate the network, several simulative experiments are performed and some optimistic results are revealed.
FAST DHT ALGORITHMS FOR COMPOSITE SEQUENCE LENGTHS
Authors: BI GUOAN , CHEN YANQIU
Published: May 2003

This paper presents fast algorithms for the computation of discrete Hartley transform (DHT). When the sequence length N = p*q, where p and q are integers and relatively prime, the one dimensional DHT can be decomposed into p length-q DHT's and q length-p discrete Fourier transforms (DFT). Compared to other reported algorithms, the proposed one has a regular computational structure, provides flexibility for composite sequence lengths and achieves substantial savings on the required number of operations.
SIGMA-DELTA IIR FILTER REALIZATION USING THIRD-ORDER REMODULATORS
Authors: PNEUMATIKAKIS A. G. , CONSTANTINIDES A. G. , DELIYANNIS T. , ANASTASSOPOULOS V.
Published: May 2003

In general, Sigma-Delta (ΣΔ) IIR filters are realized using cascades of second-order sections. The existing biquadratic structures do not exploit the high signal-to-noise ratio (SNR) of the higher-order ΣΔ modulators. A second-order IIR structure which achieves this high SNR is proposed. For this purpose a third-order ΣΔ remodulator, necessary to provide the ΣΔ output samples and eliminate the multipliers, is incorporated into the filter structure. The performance of the proposed biquadratic section is investigated and compared to existing counterparts. A cascade of three such sections is used to implement a sixth-order IIR filter.
A CMOS LOW-VOLTAGE TRANSCONDUCTOR FOR VHF CONTINUOUS-TIME FILTERS
Authors: LEE T. S.
Published: May 2003

A new CMOS low-voltage transconductor suitable for VHF continuous-time filters is proposed. The transconductance is tunable with the tunable input common-mode voltage. The output resistance of the transconductor is compensated and the resulting output resistance can be fine-tuned by means of a separate voltage. The transconductor has a large bandwidth due to excess phase compensation. Further, it exhibits low distortion due to the square-law linearization technique used. The performance of the transconductor is shown by simulation results.
ACTIVE RC FILTERS USING OPERATIONAL TRANSRESISTANCE AMPLIFIERS
Authors: SALAMA K. N. , SOLIMAN A. M.
Published: May 2003

A new generalized universal filter configuration using the Operational Transresistance Amplifier is proposed. Twelve different filter circuits are derived from the general configuration. The circuits are designed to provide Low-pass, Band-pass, High-pass, All-pass and Notch responses through appropriate choice of admittances. The feasibility of this configuration in operating at high frequencies is presented. A detailed analysis taking the effect of the finite transresistance gain into consideration is presented. Self-compensation that requires no additional elements of some of the proposed filters is presented. The effectiveness of the proposed configuration is demonstrated by HSpice simulations.
IMPLEMENTATION ISSUES FOR HIGH-BANDWIDTH FIELD-PROGRAMMABLE ANALOG ARRAYS
Authors: GAUDET VINCENT C. , GULAK P. GLENN
Published: May 2003

This paper is a tutorial introduction to field-programmable analog arrays, as well as a review of existing field-programmable analog array architectures, of both educational and industrial origin. Circuit issues relevant to the development of high-bandwidth FPAAs are presented. A current conveyor-based architecture, which promises to achieve video bandwidths, is described. Test results are presented for the CMOS current conveyor-based FPAA building block, with programmable transconductors and capacitors. Measurements indicate bandwidths in excess of 10 MHz, and functionality of amplifiers, integrators, differentiators, and adders. The die area is 1.5 mm× 3.5 mm in a 0.8 μm CMOS technology.
TWO CELLULAR ARCHITECTURES FOR INTEGRATED IMAGE SENSING AND PROCESSING ON A SINGLE CHIP
Authors: ERTEN GAIL , SALAM FATHI M.
Published: May 2003

Two architectures for a programmable image processor with on-chip light sensing capability are described. The first is a VLSI implementation of a cellular neural network. The second is a distributed dual-structure mutation of the first architecture. The distributed dual architecture leverages the speed of silicon against the large silicon area requirements. Moreover, the innovative integrated nature of the dual-structure design significantly reduces the bottleneck and computational overload caused by data transfer from sensory focal plane to the image processor. The paper also describes VLSI chip prototypes and test results.
Efflux and Atherosclerosis
Authors: Singaraja Roshni R. , Brunham Liam R. , Visscher Henk , Kastelein John J.P. , Hayden Michael R.
Published: May 2003

Approximately 50 mutations and many single nucleotide polymorphisms have been described in the ABCA1 gene, with mutations leading to Tangier disease and familial hypoalphalipoproteinemia. Homozygotes and heterozygotes for mutations in ABCA1 display a wide range of phenotypes. Identification of ABCA1 as the molecular defect in these diseases has allowed for ascertainment based on genetic status and determination of genotype-phenotype correlations and has permitted us to identify mutations conferring a range of severity of cellular, biochemical, and clinical phenotypes. In this study we review how genetic variation at the ABCA1 locus affects its role in the maintenance of lipid homeostasis and the natural progression of atherosclerosis.
Periodontal Disease Is Associated With Brachial Artery Endothelial Dysfunction and Systemic Inflammation
Authors: Amar Salomon , Gokce Noyan , Morgan Sonia , Loukideli Mariana , Van Dyke Thomas E. , Vita Joseph A.
Published: May 2003

Objective—

The purpose of this study was to determine whether periodontal disease is associated with endothelial dysfunction and systemic inflammation. Epidemiological studies suggest that severe periodontal disease is associated with increased cardiovascular disease risk, but the mechanisms remain unknown.

Methods and Results—

We assessed flow-mediated dilation and nitroglycerin-mediated dilation of the brachial artery using vascular ultrasound in 26 subjects with advanced periodontal disease and 29 control subjects. The groups were matched for age and sex, and patients with hypercholesterolemia, diabetes mellitus, hypertension, and history of cigarette smoking were excluded. We also examined serum levels of C-reactive protein using an established high-sensitivity method. Subjects with advanced periodontal disease had lower flow-mediated dilation compared with control patients (7.8±4.6% versus 11.7±5.3%,
P
=0.005). Nitroglycerin-mediated dilation was equivalent in the two groups. Subjects with advanced periodontitis exhibited higher serum levels of high-sensitivity C-reactive protein compared with healthy controls patients (2.3±2.3 versus 1.0±1.0 mg/L,
P
=0.03).

Conclusions—

Subjects with advanced periodontal disease exhibit endothelial dysfunction and evidence of systemic inflammation, possibly placing them at increased risk for cardiovascular disease.
Novel pathways of F-actin polymerization in the human neutrophil
Authors: Chodniewicz David , Zhelev Doncho V.
Published: May 2003

Recently we demonstrated the existence of a phosphatidylinositol 3-kinase (PI3K)–independent F-actin polymerization during neutrophil pseudopod extension. Here we examine the use of the PI3K-dependent and PI3K-independent pathways of activation by the N-formyl peptide receptor and the chemokine receptors, and the priming of the 2 pathways by granulocyte-macrophage colony-stimulating factor (GM-CSF) and insulin. The inhibition of PI3K activity with wortmannin showed that rate of pseudopod extension stimulated with N-formyl-Met-Leu-Phe (fMLP was mostly dependent on PI3K, while the rate of interleukin-8 (IL-8)–stimulated pseudopod extension was less dependent on PI3K. The incubation of cells with either GM-CSF or insulin increased the rate of pseudopod extension by 50% when the cells were stimulated with IL-8 but not with fMLP. The stimulation with IL-8 phosphorylated the PI3K regulatory subunit. This phosphorylation was enhanced by GM-CSF, which increased PI3K activity and total phosphatidylinositol 3,4,5-trisphosphate (PtdIns(3,4,5)P3) production. The effect of GM-CSF was blocked with wortmannin. In contrast, insulin did not increase p85 phosphorylation and did not enhance PI3K activity or PtdIns(3,4,5)P3 production. The effect of insulin was insensitive to wortmannin; however, it was blocked by an Src homology 2 (SH2)–binding peptide. These data indicate that priming of IL-8 activation with GM-CSF was mediated via the PI3Ks of class IA, while priming with insulin used a PI3K-independent pathway.