bluuebunny/crossref_metadata_2025 huggingface dataset:
Cerebellar granule cells express a specific isoform of agrin that lacks the acetylcholine receptor aggregating activity
Authors: So K.L. , Pun S. , Wan D.C.C. , Tsim K.W.K.
Published: April 2003

Agrin is a synapse‐organizing molecule that mediates nerve‐induced aggregation of acetylcholine receptors and other postsynaptic components at the developing and regenerating vertebrate neuromuscular junctions. Several lines of evidence indicate that agrin might play a similar role in directing the organization of postsynaptic specifications of neuron‐neuron synapse formation. Here we used immunological methods and polymerase chain reaction to identify the expression of agrin protein and alternatively spliced mRNA isoforms in the culture of rat granule cells. Anti‐agrin polyclonal antibody labeled the cultured granule cells and it detected a protein of over 200 kDa in size from the lysate of the cultured cells. Analysis by polymerase chain reaction showed that the granule cells in culture expressed predominantly the B0 isoform of agrin mRNA. When granule cells were cocultured with primary chick myotubes, there was no detectable effect on the aggregation of acetylcholine receptors on the surface of the myotubes. These results show that the cerebellar granule cells, similar to motor neurons in vitro, express and secrete agrin but it lacks the acetylcholine receptor aggregating activity.
Change in membrane permeability induced by protegrin 1: implication of disulphide bridges for pore formation
Authors: Mangoni Matteo E. , Aumelas André , Charnet Pierre , Roumestand Christian , Chiche Laurent , Despaux Ernest , Grassy Gerard , Calas Bernard , Chavanieu Alain
Published: April 2003

Protegrin 1 (PG‐1) is a naturally occurring cationic antimicrobial peptide that is 18 residues long, has an aminated carboxy terminus and contains two disulphide bridges. Here, we investigated the antimicrobial activity of PG‐1 and three linear analogues. Then, the membrane permeabilisation induced by these peptides was studied upon Xenopus laevis oocytes by electrophysiological methods. From the results obtained, we concluded that protegrin is able to form anion channels. Moreover, it seems clear that the presence of disulphide bridges is a prerequisite for the pore formation at the membrane level and not for the antimicrobial activity.
Mast cell chymase in complex with heparin proteoglycan is regulated by protamine
Authors: Pejler Gunnar
Published: April 2003

Protamines are polycationic proteins that are widely used for neutralisation of the anticoagulant action of heparin. However, several reports have shown adverse, mast cell‐dependent reactions to protamine. The exact mechanism by which protamine causes these adverse effects is not clear. In the present study, the possibility that protamine may influence mast cell chymase function was investigated. Mast cell chymase is in vivo recovered in a macromolecular complex with heparin proteoglycan, and this interaction is essential for expression of optimal enzymatic activity. Protamine was shown to strongly reduce the activity of mast cell chymase by a mechanism that involved displacement of the chymase from heparin proteoglycan.
Epitope topology of Na,K‐ATPase α subunit analyzed in basolateral cell membranes of rat kidney tubules
Authors: Fujimoto Kazushi , Møller Jesper Vuust , Maunsbach Arvid B.
Published: April 2003

For topological analysis of integral membrane protein in situ, we used a novel immunoelectron microscopic technique, SDS‐digested freeze‐fracture replica labeling (SDS‐FRL), and oligopeptide‐specific antibodies to clarify the sidedness of Na,K‐ATPase α subunit epitopes in basolateral cell membranes of kidney tubules. Unfixed tissue slices from rat kidney outer medulla were frozen with liquid helium, freeze‐fractured, and replicated. After digestion with SDS to solubilize unfractured membranes and cytoplasm, the platinum/carbon replicas, along with attached cytoplasmic and exoplasmic membrane halves, were processed for immunocytochemistry. Immunogold labeling using antibodies against the N‐terminus (Gly1‐His13), Leu815‐Gln828 and the C‐terminus (Ile1002‐Tyr1006) was superimposed on the images of the electron microscope protoplasmic fracture face of the basolateral plasma membranes, thus demonstrating cytoplasmic locations of these epitopes. On the contrary, SDS‐FRL showed specific binding of Asn889‐Gln903 to cross‐fractured basolateral plasma membranes suggesting that this epitope is located on the extracellular side of the membrane.
Disulphide structure of a sunflower seed albumin: conserved and variant disulphide bonds in the cereal prolamin superfamily
Authors: Egorov T.A. , Odintsova T.I. , Musolyamov A.Kh. , Fido R. , Tatham A.S. , Shewry P.R.
Published: April 2003

Disulphide mapping of a methionine‐rich 2S albumin from sunflower seeds showed four intra‐chain disulphide bonds which are homologous with those in a related heterodimeric albumin from lupin seeds (conglutin δ). Similar conserved disulphide bonds are also present in α‐gliadin and γ‐gliadin storage proteins of wheat, but a lower level of conservation is present in a further related group of proteins, the cereal inhibitors of α‐amylase and trypsin. These differences may relate to the different functions of the proteins.
Developmental studies on the uptake of tyrosine by synaptosomes and plasma membrane vesicles derived from rat brain. Effect of thyroid hormones
Authors: Herrero E. , Diez‐Guerra J. , Aragon M.C. , Valdivieso F. , Gimenfz C.
Published: April 2003

The uptake of l‐tyrosine at various stages of development was examined in synaptosomes and in plasma membrane vesicles derived from rat bruin. The total uptake has two components. Na+ dependent and Na+‐independent, respectively. The Na+‐dependent component of the transport system appears around the 5th postnatal day and increases with age. The affinity of the transport system for tyrosine does not vary substantially during development. The Vmax increases more than six‐fold between day 15 and adulthood. Plasma membrane vesicles derived from T3‐treated rats accumulate more tyrosine than those obtained from the control animals. The results support the view that thyroid hormones during development promote the establishment of the systems implicated in neurotransmission in the developing nervous system.
Alteration of cerebral ganglioside metabolism in developing Snell dwarf mice
Authors: Sugisaki Tetsuro , Noguchi Tetsuya , Kanamatsu Tomoyuki , Nishikawa Naoto
Published: April 2003

The ganglioside metabolism of the Snell dwarf cerebrum was examined on postnatal days 15 and 20, by monitoring the rate of incorporation of radioactivity into each ganglioside species from tritiated N‐acetyl‐d‐mannosamine. It was found that the turnover rate of the GM3 ganglioside was reduced throughout the entire period of development, resulting in retardation of A pathway metabolism which becomes abundant during late cerebral development. In addition, the turnover rate of the GM4 species, which is considered related to myelin formation, was also found to be reduced throughout the entire period of cerebral development.
Development of excitatory amino acid induced cytotoxicity in cultured neurons
Authors: Frandsen Aase , Schousboe Arne
Published: April 2003

The neurotoxicity of the excitatory amino acids (EAAs) l‐glutamate (l‐glu), l‐aspartate (l‐asp), N‐methyl‐d‐aspartate (NMDA), kainate (KA), quisqualate (QA) and RS‐α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolopropionate (AMPA) was followed as a function of development in primary cultures of cerebral cortex neurons and cerebellar granule cells. These two types of neurons express, respectively, glutamate receptor subtypes with sensitivity to all of these excitatory amino acids or only to glutamate and aspartate. None of the EAAs were toxic in cerebral cortex neurons at 2 days in culture, whereas at culture day 4 the neurons became sensitive to glutamate, at day 5 to KA followed by sensitivity to QA at day 6, and finally to NMDA, l‐asp and AMPA at day 7. The rank order of potency of the EAAs was in cerebral cortex neurons cultured for 12 days: l‐asp (ed50 = 0.5 μM) = l‐glu (ed50 = 1 μM) > AMPA(ed50 = 10 μM) > NMDA (ed50 = 65 μM) > QA = KA (ed50 = 100 μM). Cerebellar granule cells were insensitive to all of the EAAs at 3 and 5 days in culture but at day 8 the cells became sensitive to toxicity induced by l‐glu (ed50 = 70 μM) and l‐asp (ed50 = 30 μM). In order to determine Ed50 values for l‐asp and l‐glu accurately, media in these experiments also contained 500 μM of the glutamate uptake inhibitor l‐aspartate‐β‐hydroxamate. It is concluded that the EAA‐induced cytotoxicity is strictly related to the glutamate receptor subtype expression in the neurons. Furthermore, based on the differences in temporal development of toxicity of the different EAAs in cortex neurons, it is evident that all glutamate receptor subtypes independently mediate the cytotoxic action of EAAs. Finally, it seems justified to conclude that QA and AMPA do not have strictly analogous actions.
Involvement of gaba receptors in the regulation of neurite growth in cultured embryonic chick tectum
Authors: Michler Angelika
Published: April 2003

Modulation of neurite growth by γ‐aminobutyric acid (GABA) and several agonists and antagonists to its receptors was analysed in neuronal cultures of embryonic chick tectum and rat cerebellum, respectively, using morphometric methods. In each case, modulation of growth by GABA was similar in both types of neurons. However, data on neunte elongation suggest differential effects depending on the culture medium used. In serum‐containing medium GABA stimulated neurite growth. In serum‐free, defined medium the opposite effect was observed, i.e. GABA inhibited neurite elongation in tectal as well as in cerebellar cultures. When agonists of the GABAA‐receptor were employed stimulation of neurite outgrowth was observed in serum‐supplemented medium but not in serum‐free medium. These ligands could not influence the inhibition of neurite growth caused by GABA. In contrast, the GABAB‐receptor agonist (−)baclofen inhibited neurite elongation in serum‐free medium without affecting cells in the presence of serum. Phaclofen, a GABAB‐receptor antagonist, induced quite the opposite effect. It stimulated neurite elongation in serum‐free culture conditions and prevented the inhibition induced by GABA in a concentration‐dependent manner. In serum‐supplemented medium it had no effect. The data suggest that GABAA‐receptors may be involved in the GABA‐induced neurite elongation in serum‐supplemented medium only, although this subtype of receptors is present in serumfree conditions as well as revealed in binding studies using [3H]muscimol. Whether GABAB‐receptors and/or as yet undefined mechanisms are responsible for the different action of GABA in serum‐free medium is subject of further investigations.
Immunofluorescent labeling of tight junctions in the rat brain and spinal cord
Authors: Smith George M. , Shine H. David
Published: April 2003

Tight junctions may play an important role in maintaining the integrity of the blood‐brain barrier. These junctions can be individually visualized using electron microscopy but no current technique is able to provide a more global picture of the presence and density of tight junctions in central nervous system tissue. We used an antibody that recognizes a high molecular weight protein (ZO‐1) associated with tight junctions, to identify these specialized junctions within the rat brain and spinal cord. Immunofluorescent labeling showed a network of tight junctions between cells in the brain vasculature, leptomeninges and choroid plexus, and between tanycytes lining the floor of the third ventricle and the central canal of the spinal cord. Anti‐ZO‐1 labeled the majority of cells associated with the blood‐brain barrier and may prove a useful marker, possibly in conjunction with functional dye studies, in evaluating the anatomical and functional integrity of the blood‐brain barrier.
Developmental changes of aminopeptidase activity in the cortex of the cat brain
Authors: Martínez‐Millán L. , de Gandarias J.M. , Irazusta J. , Echevarría E. , Casis L.
Published: April 2003

Aminopeptidase activity has been proposed as a candidate regulator of the degradation of several neuroactive peptides. In this paper, possible changes in Lys‐, Arg‐, Asp‐ and Tyr‐aminopeptidase activities in the cat brain neocortex (frontal, parietal, area 17 and areas 18 and 19 as a whole) were examined during two of the first stages of the critical developmental period (15 and 30 days postbirth). Aminopeptidase activities were studied by measuring the rate of hydrolysis of the artificial substrates Lys‐, Arg‐, Asp‐ and Tyr‐2‐naphthylamides (fluorimetrically detected in triplicate). Lys‐ and Argaminopeptidase activities do not show significant changes between the first the second stage in any of the cortical regions assayed. On the contrary, in all the cortical structures, activity with Tyr‐2‐naphthylamide shows significant increase with age. In contrast, the activity of Asp‐aminopeptidase shows significant decreases on the 30th day (except in area 17). It is suggested that these activities play a part in the neurochemical changes that take place during cat brain maturation.
Expression of NCAM mRNA and polypeptides in aging rat brain
Authors: Linnemann D. , Gaardsvoll H. , Olsen M. , Bock E.
Published: April 2003

In aging brain, degenerative as well as compensatory regenerative processes are believed to occur. The neural cell adhesion molecule NCAM is involved in developmental and regenerative processes in the brain. However, the role of NCAM in aging brain has not been characterized. In this study, the expression of NCAM mRNAs and polypeptides was investigated in aging rat brain. The 7.4 and 6.7 kb NCAM mRNAs were selectively downregulated during postnatal development, and the 5.2 and 2.9 kb NCAM mRNAs were upregulated. However, from postnatal day 40 to old age no change in NCAM mRNA classes was observed. The fraction of NCAM mRNA containing the VASE exon increased postnatally but remained stable during adult life. VASE, which is believed to modulate the binding capacity, seemed to be relatively more abundant in the 7.4 and 6.7 kb NCAM mRNAs, encoding transmembrane NCAM forms, than in the 5.2 and 2.9 kb NCAM mRNAs, coding for glycosyl phosphatidylinositol (GPI) linked NCAM. Conversely, insertion of exons a and AAG between exons 12 and 13, a region containing two fibronectin type III repeats, seemed to be more pronounced in 5.2 and 2.9 kb NCAM mRNAs than in the 7.4 and 6.7 kb mRNAs. During postnatal development an increase in the fraction of 6.7 kb NCAM mRNA containing the exons a and AAG was observed. However, during aging the fraction of NCAM mRNAs containing this exon combination seemed constant. At the protein level, NCAM‐A was downregulated both during development and aging. No changes were observed during aging in the composition of soluble NCAM forms in the brain, cerebrospinal fluid or blood plasma. The amount of NCAM in rat brain decreased during postnatal development, but remained at a constant level from postnatal day 40 to old age.

To conclude, several changes in NCAM expression occur during early postnatal development emphasizing the important role of this molecule in the morphogenetic processes. During aging, a significant selective downregulation of NCAM‐A was observed indicating that in general only minor regenerative processes occur in the brain.
Concurrent isolation and characterization of oligodendrocytes, microglia and astrocytes from adult human spinal cord
Authors: Whittemore Scott R. , Sanon Henry R. , Wood Patrick M.
Published: April 2003

A cellular preparation of highly enriched oligodendrocytes was obtained from adult human spinal cord by Percoll gradient centrifugation followed by either differential adhesion or fluorescence‐activated cell sorting after immunostaining with an antibody against galactocerebroside (Ol). The adherent and O1‐negative cell fractions were ⪢96% microglia. The non‐adherent and O1‐positive fractions were ⪢96% positive for the oligodendrocyte markers O4 and O1, 0–2% positive for glial fibrillary acidic protein, and were devoid of neuronal or microglial markers. If the oligodendrocyte fraction was co‐cultured with purified dissociated rat dorsal root ganglion neurons, the oligodendrocytes adhered to the axons and their numbers increased over a 4 week period. However, myelin sheaths were not produced around axons in these cultures. In contrast, if the oligodendrocyte cell fraction was grown alone in culture for ⪢3 weeks, the number of oligodendrocytes decreased and a layer of astrocytes developed underneath the oligodendrocytes. The oligodendrocytes could be eliminated from these cultures by subsequent passaging, thus producing cultures of pure astrocytes. The astrocytes accumulated both K+ and glutamate with kinetic properties similar to those reported for rodent astrocytes. We suggest that these astrocytes arose in part from an O4/O1‐positive precursor which did not initially express glial fibrillary acidic protein. These results define a relatively simple method by which highly enriched populations of oligodendrocytes, astrocytes and microglia can be obtained from adult human spinal cord.
Interleukin‐1β does not induce reactive astrogliosis, neovascularization or scar formation in the immature rat brain
Authors: Sievers Jobst , Struckhoff Gernot , Puchner Maximilian
Published: April 2003

The adult mammalian central nervous system (CNS) reacts to a penetrating injury with the formation of a glial scar consisting of a newly formed glia limitans accessoria, basement membrane and meningeal fibroblasts. By contrast, in fetal and perinatal mammals a similar injury evokes only a reduced reactive astrogliosis, and a typical astroglial scar begins to develop only when the lesion has been placed beyond a critical developmental period. In the present investigation we have tested the hypothesis that IL‐1β plays a pivotal role in the process of cicatrization, by investigating whether immature animals develop a glial scar after IL‐1β is injected into their CNS. Adult female rats were given injections of 2U recombinant IL‐1β or PBS alone in the contralateral cortex in identical positions of the cerebral hemispheres. Postnatal day 2 (P2) rats received injections of either 1U IL‐β or PBS into the lateral aspect of the frontal cortex on each side. The animals were sacrificed 4 and 14 days post injection and the perilesional area was assessed for astrogliosis (expression of GFAP‐immunoreactivity and the activity of glutamine synthetase), neovascularization (laminin‐immunoreactivity on blood vessels at the lesion site), and the formation of a gliomeningeal scar (GFAP‐ and laminin‐immunoreactivity at the lesion site). Using similar criteria for the evaluation, we found that in adult animals some of the processes associated with cicatrization are augmented. In the immature animals, however, the formation of the glio‐meningeal scar is not altered by IL‐1β, i.e. it remains absent. We conclude that IL‐1β augments some responses of the cells involved in wound healing in the adult CNS, but does not alter key mechanisms operative in the reaction of the brain to a penetrating injury, as shown by its inability to alter the stage specific response of the immature brain.
Retinoic acid specifically activates an oleate‐dependent phospholipase D in the nuclei of LA‐N‐1 neuroblastoma cells
Authors: Antony Pierre , Kanfer Julian N , Freysz Louis
Published: April 2003

Earlier studies showed that treatment of LA‐N‐1 cells with TPA, a tumoral promoter, leads to the stimulation of a G protein‐regulated phospholipase D (PLD) in the nuclei. Now we demonstrate that retinoic acid, a cellular differentiation inducing agent, activates a nuclear oleate‐dependent PLD in LA‐N‐1 cells. Treatment of the nuclei with retinoic acid induces the breakdown of phosphatidylcholine (PtdCho). Our results indicate that PLD is regulated differentially depending on the nature of the stimulatory agent. These results strongly suggest the existence of two nuclear PLD isoforms in LA‐N‐1 nuclei that hydrolyze PtdCho.
A comparison of the ‘American System of Manufactures’ circa 1850 with Just in Time methods
Authors: Wilson James M.
Published: April 2003

The introduction of Just In Time methods in American business often raises issues of cultural change. These questions may be eased by recognizing that JIT shares many characteristics with methods used in the US during the 1800s. A comparative analysis of the American System of Manufactures ca. 1850 with Just in Time systems shows significant similarities in their development and characteristics. Parallels to their reliance on specialised plant and equipment are described, together with the emphasis on the manufacturing importance of quality, recognition of the impact of resource endowments, cultural and behavioural characteristics, use of appropriate facility layout, and general organizational and structural arrangements. Differences arising from reward systems, labour mobility and a number of technical aspects such as power generation and distribution systems are also analysed. The American System of Manufactures provided companies using JIT with a sophisticated managerial and technical capability. Companies that developed and used the American System of Manufactures in the mid‐1800s share many of the characteristics of successful companies today.
Measurement of lesion area and volume by three‐dimensional spoiled gradient‐echo MR imaging in osteonecrosis of the femoral head
Authors: Kishida Yuki , Nishii Takashi , Sugano Nobuhiko , Nakanishi Katsuyuki , Sakai Takashi , Miki Hidenobu , Ochi Takahiro , Yoshikawa Hideki
Published: April 2003

The purpose of this investigation is to evaluate the diagnostic ability of three‐dimensional spoiled gradient‐echo (3D SPGR) magnetic resonance (MR) imaging in cases of osteonecrosis of the femoral head (ONFH), and to determine the accuracy of 3D SPGR imaging in area and volume measurement of ONFH. T1‐weighted spin‐echo (SE) and 3D SPGR imaging were performed on 20 femoral heads obtained from patients with ONFH. After MR imaging, the femoral heads were cut parallel to the imaging plane and were evaluated histologically. Areas and volumes of necrotic lesions were measured with a computer program and the deviation between MR images and anatomical measurements was evaluated. A low signal intensity band on 3D SPGR MR images was observed in all femoral heads and corresponded histologically to repaired marrow with viable fibrous mesenchymal tissue. The area proximate to the low band area coincided with the necrotic region. Both area and volume measurements by T1‐weighted SE and 3D SPGR images showed a strong correlation to histological measurements. The discrepancies between histological and imaging results were minimal in 3D SPGR imaging, especially at the anterior and posterior portions of the femoral head. Three‐dimensional SPGR imaging provides more accurate measurements of the area and volume of a necrotic lesion than T1‐weighted SE imaging. © 2003 Orthopaedic Research Society. Published by Elsevier Science Ltd. All rights reserved.
Cell proliferation in response to GABA in postnatal hippocampal slice culture
Authors: Ben‐Yaakov G. , Golan H.
Published: April 2003

Recent studies have implicated the inhibitory neurotransmitter GABA in the regulation of cell migration and proliferation in the embryonic brain. Herein, we examine the possibility that these effects are maintained postnatally. Using 5 days postnatal hippocampus, we tested GABA effects on growth into an incision made in CA1 and the possibility that this response to GABA is mediated via GABAA‐receptor. Our data shows that GABA promotes neurite growth, cell proliferation and migration up to day 6 in vitro. GABAA‐receptor is not involved in the trophic response to either exogenous or endogenous GABA. Moreover, GABA induced a 20% increase in NGF secretion to the growth medium, in a similar time frame to its effect on growth. Elevated NGF secretion was suppressed by the inhibition of cell proliferation. These results suggest that GABA can promote growth in postnatal hippocampal tissue. The effect involves cell proliferation and NGF secretion and does not depend on GABAA‐receptor activation.
Beta‐blocker benefit according to severity of heart failure
Authors: Bouzamondo Anissa , Hulot Jean‐Sébastien , Sanchez Paola , Lechat Philippe
Published: April 2003

Background and aims:

Beta‐blockers are an established treatment for chronic heart failure. However, the relationship between their benefit and the severity of the disease remains to be determined.

Methods and results:

We studied the relationship between amplitude of benefit of beta‐blockers and severity of chronic heart failure, based on data for mortality and hospitalizations for worsening heart failure, using a meta‐analysis of randomized controlled trials, complementary subgroup analyses and analysis of individual data from the CIBIS II trial. In the meta‐analysis, mortality was reduced by 22% (95%CI: 16 to 28) and hospitalizations for worsening heart failure by 24% (95%CI: 20 to 29). Benefit was similar with metoprolol, bisoprolol and carvedilol. After exclusion of bucindolol trials, due to the heterogeneity of results for mortality, the reduction in mortality was similar according to the severity of heart failure, assessed either by left ventricular ejection fraction or by New York Heart Association classification. In CIBIS II, beta‐blockers induced a significant reduction in mortality of 45% (95%CI: 9 to 66), 41% (95%CI: 17 to 59) and 23% (95%CI: 1 to 40) in the low, intermediate and high risk groups, respectively. Hospitalizations were reduced by 35% (95%CI: 2 to 57), 41% (95%CI: 18 to 58) and 23% (95%CI: 0 to 41), there was no significant difference between the three score groups.

Conclusion:

We conclude that the amplitude of benefit of the beta‐blockers carvedilol, metoprolol and bisoprolol on mortality and morbidity is similar, regardless of the severity of chronic heart failure.
Thioredoxin peroxidases can foster cytoprotection or cell death in response to different stressors: over- and under-expression of thioredoxin peroxidase in Drosophila cells
Authors: RADYUK Svetlana N. , SOHAL Rajindar S. , ORR William C.
Published: April 2003

Recently, we identified a set of five genes constituting the peroxiredoxin gene family in Drosophila melanogaster [Radyuk, Klichko, Spinola, Sohal and Orr (2001) Free Radical Biol. Med. 31, 1090–1100]. This set includes two abundant thioredoxin peroxidase (TPx) species, namely Drosophila peroxiredoxin DPx-4783, a cytosolic TPx and DPx-5037, a mitochondrial TPx. Overexpression of either one of them in Drosophila S2 cells conferred increased resistance to toxicity induced by hydrogen peroxide, paraquat or cadmium. To understand further the functional roles of these enzymes in vivo, we report in the present study the effects of decreased expression, using RNA interference, on the response of S2 cells to different stressors. When either of the TPxs was blocked, cells became relatively more susceptible to oxidative stress caused by exposure to hydrogen peroxide or paraquat, but were unaffected when challenged with copper and heat stress. In contrast, TPx overexpressing cells were more susceptible to copper and heat stress when compared with control cells and exhibited DNA fragmentation. Furthermore, when cells were supplemented with N-acetyl-l-cysteine together with copper, there was a clear negative effect on cell survival, which was exacerbated by TPx overexpression. Manipulations in the levels of TPxs demonstrated that, under different stress conditions, these enzymes might have both beneficial and detrimental effects on Drosophila cell viability.
Magnetoelectric effect in thin films and layered toroidal structures
Authors: Chupis I. E.
Published: April 2003

A calculation of the magnetoelectric and dielectric susceptibilities is carried out for a layered structure in which thin toroidal layers alternate with dielectric layers not found in a state of spontaneous toroidal ordering. The toroic considered is nickel iodine boracite. It is shown that an anomalous increase of the magnetoelectric and dielectric susceptibilities can occur in the vicinity of the temperature of the induced toroidal phase transition.
Anisotropy of the hopping magnetoresistance of antiferromagnetic La2CuO4+δ single crystals
Authors: Belevtsev B. I. , Dalakova N. V. , Panfilov A. S. , Braude I. S. , Bondarenko A. V.
Published: April 2003

The anisotropy of the hopping conductivity of antiferromagnetic La2CuO4+δ single crystals with TN≈188 K is investigated in the temperature range 5–295 K and the anisotropy of their magnetoresistance, in the temperature range 5–55 K. The resistance is measured by the Montgomery method for different combinations of directions of the transport current and magnetic field relative to the crystallographic axes. For the case when the field and transport current are directed parallel to the CuO2 layers, a transition from negative to positive magnetoresistance is observed when the temperature is raised to T≈20 K. For fields perpendicular to the CuO2 layers, only negative magnetoresistance is observed. The nature of the positive magnetoresistance is discussed. It is shown that the effect is most likely due not to the interaction of the spin of the charge carriers with the surrounding magnetic medium but to the orbital motion of these carriers. The corresponding values of the positive magnetoresistance and its behavior as a function of magnetic field and temperature are found using the well-known model of Shklovskii and Efros, which is based on taking into account the compression of the impurity wave functions of the charge carriers in the magnetic field.
Ray-based methods in multidimensional linear wave conversion
Authors: Tracy Eugene R. , Kaufman Allan N. , Brizard Alain J.
Published: April 2003

A tutorial introduction to the topic of linear wave conversion in multiple spatial dimensions is provided. The emphasis is on physical concepts, particularly those features of multidimensional conversion that are new and different from the more familiar “mode conversion” problem in one spatial dimension. After introductory comments, a brief review of WKB theory for vector wave equations in the absence of conversion is provided in order to introduce notation, terminology, and geometrical ideas. A primary theme of the discussion is that, although WKB (ray-based) methods break down in conversion regions, the ray geometry in the conversion region can be used to develop local wave equations that govern the two coupled wave channels undergoing conversion. These methods can be incorporated into ray-tracing algorithms providing, for the first time, the ability to follow the “ray splitting” associated with linear conversion in multidimensions, including the amplitude and phase changes associated with the conversion.
Proof of quasilinear equations in the strongly nonlinear regime of the weak warm beam instability
Authors: Escande D. F. , Elskens Y.
Published: April 2003

Quasilinear (QL) theory was developed in 1962 to describe the saturation of the weak warm beam-plasma instability, which involves the development of a Langmuir turbulence and the formation of a plateau in the electron velocity distribution function. The original derivations assume that particle orbits are weakly perturbed (quasi linear description), though the plateau formation is the result of a strong chaotic diffusion of the beam particles. Over two decades a controversy has developed about the validity of QL equations in the chaotic saturation regime within the Vlasovian description of the problem, and is not yet settled. Here a proof of these equations is proposed that does not resort to this description. Instead the Langmuir wave-beam system is described as a finite-number-of-degrees-of-freedom Hamiltonian system. The calculation of the chaotic drag on a beam particle is performed using Picard fixed point equation derived from Hamilton equations, and by making approximations justified by the spatial speading of chaotic orbits and by the weak mutual influence between any particle and any wave. The same techniques enable the computation of the particle diffusion coefficient and of the wave growth rate.
Plasma physics in clusters of galaxies
Authors: Eilek Jean A.
Published: April 2003

Clusters of galaxies are the largest self-gravitating structures in the universe. Each cluster is filled with a large-scale plasma atmosphere, in which primordial matter is mixed with matter that has been processed inside stars. This is a wonderful plasma physics laboratory. Our diagnostics are the data we obtain from x-ray and radio telescopes. The thermal plasma is a strong x-ray source; from this we determine its density and temperature. Radio data reveal a relativistic component in the plasma, and first measurements of the intracluster magnetic field have now been made. Energization of the particles and the field must be related to the cosmological evolution of the cluster. The situation is made even richer by the few galaxies in each cluster that host radio jets. In these galaxies, electrodynamics near a massive black hole in the core of the galaxy lead to a collimated plasma beam which propagates from the nucleus out to supergalactic scales. These jets interact with the cluster plasma to form the structures known as radio galaxies. The interaction disturbs and energizes the cluster plasma. This complicates the story but also helps us understand both the radio jets and the cluster plasma.
Thermally excited Trivelpiece–Gould modes as a pure electron plasma temperature diagnostic
Authors: Anderegg F. , Shiga N. , Dubin D. H. E. , Driscoll C. F. , Gould R. W.
Published: April 2003

Thermally excited plasma modes are observed in trapped, near-thermal-equilibrium pure electron plasmas over a temperature range of 0.05<kT<5 eV. The modes are excited and damped by thermal fluctuations in both the plasma and the receiver electronics. The thermal emission spectra together with a plasma-antenna coupling coefficient calibration uniquely determine the plasma (and load) temperature. This calibration is obtained from the mode spectra themselves when the receiver-generated noise absorption is measurable; or from separate wave reflection/absorption measurements; or from kinetic theory. This nondestructive temperature diagnostic agrees well with standard diagnostics, and may be useful for expensive species such as antimatter.
Progress in heavy ion fusion research
Authors: Celata C. M. , Bieniosek F. M. , Henestroza E. , Kwan J. W. , Lee E. P. , Logan G. , Prost L. , Seidl P. A. , Vay J-L. , Waldron W. L. , Yu S. S. , Barnard J. J. , Callahan D. A. , Cohen R. H. , Friedman A. , Grote D. P. , Lund S. M. , Molvik A. , Sharp W. M. , Westenskow G. , Davidson Ronald C. , Efthimion Philip , Gilson Erik , Grisham L. R. , Kaganovich Igor , Qin Hong , Startsev Edward A. , Bernal S. , Cui Y. , Feldman D. , Godlove T. F. , Haber I. , Harris J. , Kishek R. A. , Li H. , O’Shea P. G. , Quinn B. , Reiser M. , Valfells A. , Walter M. , Zou Y. , Rose D. V. , Welch D. R.
Published: April 2003

The U.S. Heavy Ion Fusion program has recently commissioned several new experiments. In the High Current Experiment [P. A. Seidl et al., Laser Part. Beams 20, 435 (2003)], a single low-energy beam with driver-scale charge-per-unit-length and space-charge potential is being used to study the limits to transportable current posed by nonlinear fields and secondary atoms, ions, and electrons. The Neutralized Transport Experiment similarly employs a low-energy beam with driver-scale perveance to study final focus of high perveance beams and neutralization for transport in the target chamber. Other scaled experiments—the University of Maryland Electron Ring [P. G. O’Shea et al., accepted for publication in Laser Part. Beams] and the Paul Trap Simulator Experiment [R. C. Davidson, H. Qin, and G. Shvets, Phys. Plasmas 7, 1020 (2000)]—will provide fundamental physics results on processes with longer scale lengths. An experiment to test a new injector concept is also in the design stage. This paper will describe the goals and status of these experiments, as well as progress in theory and simulation. A proposed future proof-of-principle experiment, the Integrated Beam Experiment, will also be described.
Laser imprint reduction with a shaping pulse, oscillatory Richtmyer–Meshkov to Rayleigh–Taylor transition and other coherent effects in plastic-foam targets
Authors: Metzler N. , Velikovich A. L. , Schmitt A. J. , Karasik M. , Serlin V. , Mostovych A. N. , Obenschain S. P. , Gardner J. H. , Aglitskiy Y.
Published: April 2003

A substantial reduction of the laser imprint with a short, low-energy “shaping” laser pulse incident upon a foam–plastic sandwich target prior to the main laser pulse has been demonstrated to be possible [Metzler et al., Phys. Plasmas 9, 5050 (2002)]. Nonuniformity of this shaping pulse, however, produces standing sonic waves in the target. Laser-imprinted seeds for the Rayleigh–Taylor (RT) instability growth then emerge from the interaction of these waves with the strong shock wave launched by the drive laser pulse. Such coherent interaction between different waves and modes perturbed at the same wavelength is shown to be important in a variety of situations relevant to the inertial confinement fusion studies. As an example, an oscillatory transition from the classical Richtmyer–Meshkov shock-interface instability development to the RT growth exhibiting a characteristic phase reversal in a target of finite thickness is described. Another example refers to the feedout mechanism of seeding the perturbations that come from the nonuniformities of the rear (inner) surface of the laser target. The coherent interaction between the strong shock wave from the main laser pulse and the rippled rarefaction wave produced by a low-intensity foot of the pulse produces observable effects, such as an extra phase reversal compared to the case of no foot. Some of these predictions are shown to be consistent with our new experimental results obtained in the feedout geometry on the Nike laser facility [S. P. Obenschain et al. Phys. Plasmas 3, 2098 (1996)].
Trapped ion effect on shielding, current flow, and charging of a small object in a plasma
Authors: Lampe Mártin , Goswami Rajiv , Sternovsky Zoltan , Robertson Scott , Gavrishchaka Valeriy , Ganguli Gurudas , Joyce Glenn
Published: April 2003

The problem of electrostatic shielding around a small spherical collector immersed in nonflowing plasma, and the related problem of electron and ion flow to the collector, date to the origins of plasma physics. Calculations have typically neglected collisions, on the grounds that the mean free path is long compared to the Debye length. However, it has long been suspected that negative-energy trapped ions, created by occasional collisions, could be important. This paper presents self-consistent analytic calculations of the density and distribution function of trapped and untrapped ions, the potential profile, the ion and electron current to the collector, and the floating potential and charge of the collector. Under typical conditions for dust grains immersed in a discharge plasma, trapped ions are found to dominate the shielding near the grain, substantially increase the ion current to the grain, and suppress the floating potential and grain charge, even when the mean free path is much greater than the Debye length.
Geometric discretization of the Koenigs nets
Authors: Doliwa Adam
Published: April 2003

We introduce the Koenigs lattice, which is a new integrable reduction of the quadrilateral lattice (discrete conjugate net) and provides natural integrable discrete analog of the Koenigs net. We construct the Darboux-type transformation of the Koenigs lattice and we show permutability of superpositions of such transformations, thus proving integrability of the Koenigs lattice. We also investigate the geometry of the discrete Koenigs transformation. In particular we characterize the Koenigs transformation in terms of an involution determined by a congruence conjugate to the lattice.
Hybrid functionals based on a screened Coulomb potential
Authors: Heyd Jochen , Scuseria Gustavo E. , Ernzerhof Matthias
Published: April 2003

Hybrid density functionals are very successful in describing a wide range of molecular properties accurately. In large molecules and solids, however, calculating the exact (Hartree–Fock) exchange is computationally expensive, especially for systems with metallic characteristics. In the present work, we develop a new hybrid density functional based on a screened Coulomb potential for the exchange interaction which circumvents this bottleneck. The results obtained for structural and thermodynamic properties of molecules are comparable in quality to the most widely used hybrid functionals. In addition, we present results of periodic boundary condition calculations for both semiconducting and metallic single wall carbon nanotubes. Using a screened Coulomb potential for Hartree–Fock exchange enables fast and accurate hybrid calculations, even of usually difficult metallic systems. The high accuracy of the new screened Coulomb potential hybrid, combined with its computational advantages, makes it widely applicable to large molecules and periodic systems.
Fast linear scaling second-order Møller-Plesset perturbation theory (MP2) using local and density fitting approximations
Authors: Werner Hans-Joachim , Manby Frederick R. , Knowles Peter J.
Published: April 2003

We apply density fitting approximations to generate the 2-electron integrals in local MP2 (LMP2) to produce a method denoted DF-LMP2. The method can equally be seen as a local version of the well-known RI-MP2 method, which in this work is referred to as DF-MP2. Local approximations reduce the asymptotic scaling of computational resources to O(N), and the most expensive step of DF-MP2 [the O(N5] assembly) is rendered negligible in DF-LMP2. It is demonstrated that for large molecules DF-LMP2 is much faster (1–2 orders of magnitude) than either LMP2 or DF-MP2. The availablility of LMP2, DF-MP2 and DF-LMP2 has for the first time made it possible to assess the accuracy of local and density fitting approximations for extended molecules using cc-pVDZ and cc-pVTZ basis sets. The density fitting errors are found to be consistently small, but the errors arising from local approximations are somewhat larger than expected from calculations on smaller systems. It is proposed to apply local density fitting approximations also for the Fock matrix construction in Hartree-Fock calculations. Preliminary results demonstrate that this can lead to significant savings in the Hartree-Fock calculation.
Dipole orientation effects on nonlinear optical properties of organic molecular aggregates
Authors: Datta Ayan , Pati Swapan K.
Published: April 2003

We consider a few dipolar organic molecules in several of their packing arrangements to understand the aggregation effect. We have performed an extensive semiempirical calculations based on multireference doubles configuration interactions for the dimer arrangements. This is coupled with a simple theory based on dipole–dipole interactions and hydrogen-bonding effects. We find that the best dimer configuration is the in-line head-to-tail arrangement of the monomer molecules, which gives rise to an enormous increase in nonlinear optical properties compared to its monomer counterparts, at small distances. We have also shown that such dimer configurations have an appreciable absorption intensity, and for an aggregate, the absorption appears deep in the IR region. These excitations are excitonic in character and are associated with a large dipole moment change, along the long axis of the dimer configurations. We suggest the experimental methods by which such tunings can be realized.
Kinetic barrier of pinning in polymer crystallization: Rate equation approach
Authors: Toda Akihiko
Published: April 2003

The numerical solution of a rate equation proposed by Sadler and Gilmer for the pinning of polymer crystallization has been examined to discuss the supercooling dependence of the kinetic barrier in comparison with that of surface nucleation postulated in the standard model. The entropy and free energy of the stems in the pinning region with the fluctuation of stem length have been evaluated from the stationary solution with the expression of conditional entropy of a finite Markov chain. The results have confirmed that the pinning stems form a local minimum in the free energy landscape and the rate-determining process is the detachment of the whole pinning region. The dependence on supercooling of the kinetic barrier is smaller than that of nucleation but not negligible for the parameters of polyethylene crystallization.
Determination of the hydrogen and helium ion densities in the initial and final stages of a plasma in the Large Helical Device by optical spectroscopy
Authors: Goto M. , Morita S. , Sawada K. , Fujimoto T. , Yamamoto S. , Miyazawa J. , Yamada H. , Toi K.
Published: April 2003

Emission line intensities in the UV and visible wavelength range have been measured in the initial and final stages of a discharge in the Large Helical Device (LHD) [O. Motojima et al., Phys. Plasmas 8, 1843 (1999)]. From these results combined with Te and ne, which are determined spectroscopically, the ionization and recombination fluxes of hydrogen and helium are estimated in the region of high line emissivities. The temporal behavior of line-averaged ne which is evaluated from these fluxes is found to be consistent with the results of the interferometer measurement. This implies that in such transient stages of the plasma the temporal variation of ne is dominated by the atomic ionization-recombination processes rather than the particle transport or diffusion. On the basis of that characteristic in LHD, the line-averaged ion densities for hydrogen and helium just before the termination of the plasma heating are determined. Thus, a method of the density determination of the fueling gas and of the ash is suggested for future fusion devices.
Trapped particle bounds on stimulated scatter in the large kλD regime
Authors: Rose Harvey A.
Published: April 2003

In the strongly damped regime, the convective gain rate for stimulated scatter, κ, is customarily maximized by requiring that, taken together, the laser light wave and the daughter light and plasma waves, satisfy wavevector and frequency matching, and then 1/κ∼γ, the plasma wave damping rate. If the bounce frequency in the daughter plasma wave is large compared to the trapped particle loss rate, it would seem, based on naı̈ve extrapolation of the work by Zakharov and Karpman [JETP 16, 351 (1963)] on decaying, one-dimensional Langmuir waves, that κ may be increased indefinitely by increasing the electrostatic wave amplitude, φ, since they calculate that γ varies as φ−3/2. However, for a driven plasma wave in a laser speckle—as is appropriate to stimulated Raman scatter in an optically smoothed laser beam in three dimensions—it has been shown [H. A. Rose and D. A. Russell, Phys. Plasmas 8, 4784 (2001)] that γ varies more slowly, ∝φ−1/2, and asymptotes to a finite value for large φ, when the loss of trapped electrons due to convection out the speckle sides dominates that due to collisions. This behavior, combined with the loss of resonance for φ too large, leads to a maximum value for κ as a function of scattered light frequency and φ, for given laser and plasma parameters. Bounds for stimulated Brillouin scatter gain rate are also obtained. The standard mode-coupling model (MCM) of these scattering processes, when modified to include the trapped particle nonlinear frequency shift, always allows for a propagating plasma wave, and therefore may be qualitatively in error in regimes where the daughter plasma wave loses resonance. A mean field approximation model is proposed which is consistent with the bound on κ and agrees with the MCM in the resonant regime, but differs in the nonresonant regime by respecting this fundamental difference in the plasma mode structure. If a plasma, as it evolves, crosses the resonant/nonresonant regime boundary, a model that is cognizant of both regimes is required to avoid a qualitative overestimate of the scatter.