bluuebunny/crossref_metadata_2025 huggingface dataset:
Cerebral endothelial cell‐derived laminin promotes the outgrowth of neurites in CNS neuronal cultures
Authors: Pákáski Magdolna , Kása Péter , Joó Ferenc , Wolff Joachim R.
Published: April 2003

The aim of the present study was to elucidate whether the endothelial cells, besides providing the structural basis for the blood‐brain barrier (M. Bradbury, Concept for a Blood‐Brain Barrier, 1979; F. Joó, Nature321, 197–198, 1986) can also produce laminin and, via its release, regulate the growth of neuntes of neurons originating from the central nervous system (CNS). In immunohistochemical investigations, the presence of laminin‐like immunoreactivity could be detected in the cytoplasm and on the surface of endothelial cells derived from brain microvessels. Further, the neurite‐promoting effect of laminin on CNS neurons was also noted in a co‐culture system designed especially for conditioning nerve cell cultures continuously with materials released from the cerebral endothelial cells. It is suggested that the endothelial cells may be involved via their laminin secretion in the regulation of axonal growth and guidance in the CNS.
The effects of intrauterine growth retardation on the development of neuroglia in fetal guinea pigs. An immunohistochemical and an ultrastructural study
Authors: Nitsos Ilias , Rees Sandra
Published: April 2003

The effects of intrauterine growth retardation on the development of myelinating oligodendrocytes and astrocytes in the brain and spinal cord of the fetal guinea pig have been examined using immunohistochemical and ultrastructural techniques. As judged by immunoreactivity for myelin basic protein, the extent of myelination in the spinal cord, cerebral cortex, corpus cellosum and cerebellum was reduced in the growth‐retarded fetuses compared with controls at both 52 (n = 4) and 62 days (n = 5) of gestation. As assessed by immunoreactivity for glial fibrillary acidic protein, there were no marked differences between control and growth‐retarded brains in the extent or distribution of radial glial cells or astrocytes at 52 or 62 days in the cerebellum. However, in the cerebral cortex at 62 days there was a striking proliferation of astrocytes surrounding cortical blood vessels in growth‐retarded fetuses. Ultrastructural studies showed that at 52 days, myelination of the corticospinal tract had begun in the control but was virtually absent in growth‐retarded fetuses. At 62 days, the total number of myelinated fibres in growth‐retarded fetuses was significantly reduced by 56% (P < 0.01) compared with control fetuses; however, there was no difference between the groups in the total number of fibres in the corticospinal tract. Where fibres were myelinated the myelin sheath was disproportionately reduced relative to axon diameter. Thus, in intrauterine growth retardation there is a delay in the initiation and in the extent of myelination. This could be due to a reduction in the number of myelinating glia formed and the restricted capacity of those which do form to generate myelin.
Studies on brain monoamine and neuropeptide systems after neonatal intracerebroventricular 6‐hydroxydopamine treatment
Authors: Luthman J. , Brodin E. , Sundström E. , Wiehager B.
Published: April 2003

In order to study the effects of a neonatal dopamine lesion on dopaminergic, serotonergic and peptidergic systems, Sprague‐Dawley rats were treated by intracerebroventricular administration of 6‐hydroxydopamine (100 μg, days 3 and 6) following desipramine pretreatment (25 mg/kg s.c.).

At 60–70 days postnatally a profound reduction of dopamine‐ and 3,4‐dihydroxyphenylacetic acid levels was found in striatal and limbic forebrain regions concomitant with an extensive loss of tyrosine hydroxylase‐immunoreactive fibers, while no significant alteration in noradrenaline levels was seen. A marked loss of tyrosine hydroxylase‐immunoreactive cell profiles was also observed in the substantia nigra and ventral tegmental area in mesencephalon. In striatum, but not in other regions analysed, an almost 100% increase in serotonin levels and serotonin‐immunoreactive fiber density was observed following 6‐hydroxydopamine treatment. However, the number of serotonin‐immunoreactive cell profiles in the median and dorsal raphe nuclei was not altered. The 6‐hydroxydopamine treatment also led to reductions in substance P levels in striatum, nucleus accumbens and ventral mesencephalon. The cholecystokinin level in nucleus accumbens and neurotensin level in ventral mesencephalon were also reduced. A neonatal intracerebroventricular 6‐hydroxydopamine treatment thus leads to a les̀ion of dopamine neurons in the mesencephalon with extensive loss of dopamine fibers in several forebrain areas, while localized serotonin fiber sprouting is induced in striatum. Furthermore, concomitant reductions of the levels of peptides related to the dopamine system occur following the 6‐hydroxydopamine treatment. Behavioral disturbances such as hyperactivity and cognitive deficiencies occurring after a dopamine lesion early in life might therefore be due to plastic alterations in several different transmitter/ neuromodulator systems as a direct or indirect consequence of the lesion.
Quantitative histochemical changes in enzymes involved in energy metabolism in the rat brain during postnatal Development. I. Cytochrome oxidase and lactate dehydrogenase
Authors: Bilger Anne , Nehlig Astrid
Published: April 2003

The postnatal maturation of cytochrome oxidase and lactate dehydrogenase activity was assessed by histochemistry in rats at 8 postnatal stages, P0, P5, P10, P14, P17, P21, P35 and the adult stage. Enzyme activities were revealed on cryostat brain sections with diaminobenzidine for cytochrome oxidase and nitroblue tetrazolium for lactate dehydrogenase. Lactate dehydrogenase activity remained unchanged between P0 and P10, significantly increased in 8 areas of the 14 studied between P10 and P14 and in 6 structures from P14 to P17. These were mainly parietal, auditory and cerebellar cortices, hippocampus, thalamus, hypothalamus and medial geniculate body. There was no further change until P35 and lactate dehydrogenase activity increased then significantly to reach higher adult levels in hippocampus and medial geniculate body. Cytochrome oxidase activity was low from P0 to P10 and increased in 8 regions between P10 and P14. These were all cortices, caudate nucleus, hippocampus, inferior colliculus and genu. Enzyme activity further increased between P14 and P17 in auditory cortex, medial geniculate body and brainstem, did not vary from P17 to P21 but increased by 92 to 371% in all areas between P21 and P35. Cytochrome oxidase activity rose further from P35 to adult stage in hippocampus and medial geniculate body. From birth to adulthood, cytochrome oxidase activity increased 5 to 19 fold and lactate dehydrogenase activity 1.8 to 3.0. The present study shows that there is a quite good correlation between postnatal changes in regional cerebral glucose utilization and activity of enzymes involved in glycolytic and oxidative glucose metabolism in the rat.
Ontogeny of corticotropin releasing hormone gene expression in rat hypothalamus — comparison with somatostatin
Authors: Baram Tallie Z. , Lerner Stephen P.
Published: April 2003

Using in situ hybridization histochemistry, corticotropin‐releasing hormone gene expression is first detectable in the parvocellular portion of the rat paraventricular nucleus on the 17th fetal day. The prevalence of messenger RNA for corticotropin releasing hormone decreases perinatally, specifically between the 19th and 21st fetal days. By the 4th postnatal day, CRH gene expression is similar to that of the adult rat. Somatostatin messenger‐RNA is detectable on the 14th fetal day in the periventricular nucleus. No perinatal hiatus in somatostatin gene expression is evident.
Effects of selective inhibition of protein kinase C, cyclic AMP‐dependent protein kinase, and Ca2+‐calmodulin‐dependent protein kinase on neurite development in cultured rat hippocampal neurons
Authors: Cabell Leigh , Audesirk Gerald
Published: April 2003

A variety of experimental evidence suggests that calmodulin and protein kinases, especially protein kinase C, may participate in regulating neurite development in cultured neurons, particularly neurite initiation. However, the results are somewhat contradictory. Further, the roles of calmodulin and protein kinases on many aspects of neurite development, such as branching or elongation of axons vs dendrites, have not been extensively studied. Cultured embryonic rat hippocampal pyramidal neurons develop readily identifiable axons and dendrites. We used this culture system and the new generation of highly specific protein kinase inhibitors to investigate the roles of protein kinases and calmodulin in neurite development. Neurons were cultured for 2 days in the continuous presence of calphostin C (a specific inhibitor of protein kinase C), KT5720 (inhibitor of cyclic AMP‐dependent protein kinase), KN62 (inhibitor of Ca2+‐calmodulin‐dependent protein kinase II), or calmidazolium (inhibitor of calmodulin), each at concentrations from approximately 1 to 10 times the concentration reported in the literature to inhibit each kinase by 50%. The effects of phorbol 12‐myristate 13‐acetate (an activator of protein kinase C) and 4α‐phorbol 12,13‐didecanoate (an inactive phorbol ester) were also tested.

At concentrations that had no effect on neuronal viability, calphostin C reduced neurite initiation and axon branching without significantly affecting the number of dendrites per neuron, dendrite branching, dendrite length, or axon length. Phorbol 12‐myristate 13‐acetate increased axon branching and the number of dendrites per cell, compared to the inactive 4α‐phorbol 12,13‐didecanoate. KT5720 inhibited only axon branching. KN62 reduced axon length, the number of dendrites per neuron and both axon and dendrite branching. At low concentrations, calmidazolium had no effect on any aspect of neurite development, but at high concentrations, calmidazolium inhibited every parameter that was measured (including viability).

These results suggest that these three protein kinases selectively modulate different aspects of neurite development. The universality of effects caused by calmodulin inhibition make it impossible to determine if there are specific targets of calmodulin action involved in neurite development. Finally, our data indicate that some superficially similar characteristics of neuronal differentiation, such as neurite initiation and branching, may be controlled by quite different molecular mechanisms.
Influence of culture substrata on the differentiation of advanced passage glial cells in cultures from aged mouse cerebral hemispheres
Authors: Kozlova Marina , Kentroti Susan , Vernadakis Antonia
Published: April 2003

We have previously reported that glial cells derived from aged mouse cerebral hemispheres (MACH) in primary cultures and after several passages consist of protoplasmic astrocytes (Type 1), differentiated stellate astrocytes (Type 2), a few oligodendrocytes and also glial precursors.4,33,34 In this study, we examined the influence of culture substrata: plastic, poly‐l‐lysine, laminin or collagen on the differentiation of MACH glial cells of advanced passages (P18–19) using glutamine synthetase (GS) and cyclic nucleotide phosphohydrolase (CNP) activity as biochemical markers for astrocytes and oligodendrocytes, respectively. Cultures were also examined morphologically using light microscopy. In general, GS activity was increased in cultures grown on the three chemical substrata versus plastic alone with the most striking effect being the 2‐fold increase observed in those cells grown in laminin. No differences were noted in CNP activity. Morphologically, proliferation of protoplasmic (Type 1) astrocytes was enhanced by culture day 2 on polylysine substratum and stellate differentiated (Type 2) astrocytes were noted on collagen. The striking feature in cultures grown on laminin was the presence of astrocytes with markedly long processes. Thus, morphological astrocyte differentiation appears to correspond to the increased GS activity. We propose that the extracellular matrix components such as collagen and laminin may play an important role in promoting glial precursors to differentiate into astrocytes.
A developmental study of lactate dehydrogenase isozyme and aspartate aminotransferase activity in organotypic rat hippocampal slice cultures and primary cultures of mouse neocortical and cerebellar neurons
Authors: Schousboe Inger , Tønder Niels , Zimmer Jens , Schousboe Arne
Published: April 2003

The development of enzyme activity and isozyme distribution of lactate dehydrogenase (LDH) was studied in murine organotypic hippocampal slice cultures and dissociated cultures of neocortical neurons and cerebellar granule cells and compared with that of the respective brain regions invivo. In the hippocampal slice cultures and the hippocampus invivo, the activity of aspartate aminotransferase (AAT) was also measured. During development in culture the specific activity of LDH increased in all types of cultures reaching values similar to that found in the corresponding brain areas invivo. However, significant differences in the isozyme distribution were observed between the preparations in vitro and invivo. During development invivo, the LDH isozyme pattern changed from a preferential M‐subunit composition to a preferential H‐subunit composition regardless of the brain area. This shift was not observed in the respective cultures where the M4‐isozyme prevailed at all culture periods examined accounting for 30–45% of the total LDH activity. The cultured cerebellar granule cells did not express the H4‐isozyme at all, while in the hippocampal slice cultures and the cultured neo‐cortical neurons this isozyme accounted for about 5% of the total LDH activity. The activity of AAT in the hippocampal organotypic slice cultures increased considerably during the culture period in parallel with the increase in AAT activity during postnatal development of hippocampus invivo. The activity of AAT in the slice cultures was, however, consistently lower than the corresponding activity invivo. The results show that perinatal hippocampal tissue and neurons from neocortex or cerebellum retain their immature LDH‐isoenzyme distribution when grown as organotypic slice cultures or dissociated cell cultures, respectively. This lack of shift from the M4 to the H4 LDH isozyme which is typical of tissues relying on aerobic glycolysis has several implications but does not apparently interfere with the otherwise normal differentiation of morphological, biochemical and electrophysiological characteristics of these preparations.
Combined pre‐ and postnatal ethanol exposure alters the development of bergmann glia in rat cerebellum
Authors: Shetty Ashok K. , Burrows Robert C. , Wall Kenneth A. , Phillips Dwight E.
Published: April 2003

The development and maturation of Bergmann glial cells in the rat cerebellum was evaluated on postnatal day 15 by glial fibrillary acidic protein (GFAP) immunocytochemistry, following combined gestational and 10‐day postnatal ethanol exposure (a full three trimester human equivalency). GFAP‐positive Bergmann glial fibers of lobules I, III, VIb, VII and X of the cerebellar vermis were examined and counted in the molecular layer (ML), the external granular layer (EGL) and the external limiting membrane (ELM). Ethanol exposure reduced: (1) the number of GFAP‐positive fibers (per unit length of folia surface) at all three levels; (2) the percentage of mature fibers; and (3) the cross‐sectional area in all lobules examined. When data from the five lobules were pooled, there were 7% fewer GFAP‐positive fibers in the ML, 15% fewer in the EGL and 20% fewer in the ELM; the percentage of mature fibers was reduced by 16%; and the cross‐sectional areas of lobules were reduced by 16%. The altered development of Bergmann glia could be one of the factors causing delayed migration of granular neurons and reductions in the number of granule cells reported in other studies following developmental ethanol exposures and could help to explain some of the motor dysfunctions reported in FAS victims.
Spatial control of neuronal cell attachment and differentiation on covalently patterned laminin oligopeptide substrates
Authors: Ranieri John P. , Bellamkonda Ravi , Bekos Evan J. , Gardella Joseph A. , Mathieu Hans J. , Ruiz Laurence , Aebischer Patrick
Published: April 2003

The spatial control of neuronal cell attachment and differentiation via specific receptor mediated interactions, may provide an effective means for the in vitro reconstruction of neuronal cell architecture. In this study, receptor‐specific oligopeptide sequences derived from the extracellular matrix (ECM) molecule laminin, a potent neural cell attachment and differentiation promoter were covalently bound on fluorinated ethylene propylene (FEP) films. The degree of receptor‐specific cell attachment and the ability to spatially control neurite outgrowth by covalently patterning the oligopeptide sequences on the FEP film surface were assessed.

FEP films were first chemically activated with a Radio Frequency Glow Discharge (RFGD) process that covalently replaces the surface fluorine atoms with reactive hydroxyl groups. Oligopeptides containing the YIGSR sequence from the B1 chain of laminin and the water soluble oligopeptide containing the IKVAV sequence (CSRARKQAASIKVAVSADR) from the A chain were covalently bound to the hydroxylated FEP films. Electron Spectroscopy for Chemical Analysis (ESCA) verified the covalent attachment of the oligopeptides to the material surface.

The degree of receptor mediated NG108‐15 cell attachment on immobilized CDPGYIGSR films was determined using competitive binding media. A 78% reduction in cell attachment was observed on films containing CDPGYIGSR in the cell plating medium. Only a 23% reduction in cell attachment was noted on films plated in medium containing a mock CDPGYIGSK sequence. FEP films immobilized with the IKVAV oligopeptide sequence were shown to mediate PC12 cell attachment and a competitive binding medium also significantly attenuated cell attachment on the immobilized films.

The spatial patterning of these oligopeptide sequences to the FEP surface was shown to localize cell attachment and neurite extension on the patterned pathways. The surrounding unmodified FEP surface was inhibitory in serum containing medium and prevented cellular interactions outside the oligopeptide modifications. The spatial immobilization of laminin oligopeptides on FEP films provides a means to organize the attachment and differentiation of neuronal cells in a receptor‐specific manner.
Leptomeningeal and skin fibroblasts: Two different cell types?
Authors: Colombo J.A. , Napp M.I. , Puissant V.
Published: April 2003

Leptomeningeal and skin fetal (E16‐17) fibroblasts were subcultured in vitro either in DMEM/F12 basal medium (with or without 10% FCS) or in astroglial conditioned medium (ACM). Both populations were characteristically composed of flat, undifferentiated, fibronectin(+), GFAP(‐)cells where cultured in fetal serum supplemented basal media. When exposed to ACM leptomeningeal cells developed a population of thin, elongated, fibronectin(+) cells with radial type long processes while skin fibroblasts did not show significant changes in their characteristic morphotype. Exposure to db cAMP in basal medium resulted within 3 hr in their transformation to an astrocytic‐like morphotype characterized by a condensed soma and multiple, short processes. Twenty‐four hours later skin fibroblasts had returned to their flat appearance while leptomeningeal ones showed elongated, radial‐like forms. Results indicate the possible existence of different receptors (to ACM factors) and/or cytoskeletal properties, and suggest that ACM‐reactive fibroblasts of leptomeningeal origin represent a different cell type from those of skin origin. The hypothetical role of leptomeningeal cells during brain development is considered.
Mitochondria in apoptosis of ischemic heart
Authors: Borutaite Vilmante , Brown Guy C
Published: April 2003

Apoptosis in the heart can be triggered by ischemia and/or reperfusion depending on conditions. This may involve activation of plasma membrane death receptors and/or translocation of Bcl‐2 homologous proteins to mitochondria. However, one of the main mechanisms for triggering this apoptosis appears to be mitochondrial permeability transition followed by cytochrome c release. Cytochrome c release can result in caspase activation and thus apoptosis, but also results in mitochondrial dysfunction, which might contribute to contractile dysfunction or necrosis at reperfusion.
Cytotoxicity of ribosome‐inactivating protein saporin is not mediated through α2‐macroglobulin receptor
Authors: Bagga Shveta , Hosur M.V , Batra Janendra K
Published: April 2003

Saporin is a single chain ribosome‐inactivating protein produced by the plant Saponaria officinalis. Several isoforms of saporin have been isolated from various parts of the plant. In the present study recombinant saporin isoforms 5 and 6 were produced in Escherichia coli. Saporin‐6 was found to be more active than saporin‐5 in its N‐glycosidase, cytotoxic, and genomic DNA fragmentation activities. Earlier, saporin has been shown to bind low‐density lipoprotein receptor‐related protein (LRP), however, in this study the sensitivities of LRP‐negative and LRP‐positive cell lines were found to be similar towards saporin‐6 toxicity suggesting the internalization of saporin not to be solely dependent on the expression of LRP on eukaryotic cells.
Identification of an ion channel activity of the Vpu transmembrane domain and its involvement in the regulation of virus release from HIV‐1‐infected cells
Authors: Schubert Ulrich , Ferrer-Montiel Antonio V. , Oblatt-Montal Myrta , Henklein Peter , Strebel Klaus , Montal Mauricio
Published: April 2003

HIV‐1 Vpu catalyzes two independent functions, degradation of the virus receptor CD4 in the endoplasmic reticulum and enhancement of virus release from the cell surface. These activities are confined to distinct structural domains of Vpu, the cytoplasmic tail and the transmembrane (TM) anchor, respectively. It was recently reported that Vpu forms cationselective ion channels in lipid bilayers. Here we report that this property of Vpu is a characteristic of its TM anchor. Expression of full‐length Vpu in Xenopus oocytes increases membrane conductance. The Vpu‐induced conductance is selective to monovalent cations over anions, does not discriminate Na+ over K+ and shows marginal permeability to divalent cations. Notably, introduction of the scrambled TM sequence into full‐length Vpu abrogates its capacity to increase membrane conductance in oocytes and to promote virus release from infected cells. Reconstitution of synthetic Vpu fragments in lipid bilayers identified an ion channel activity for a sequence corresponding to the TM domain of Vpu. In contrast, a peptide with the same amino acid composition but with a scrambled sequence does not form ion channels. Our findings therefore suggest that the ability of Vpu to increase virus release from infected cells may be correlated with an ion channel activity of the TM domain, thereby providing a potential target for drug intervention based on the development of Vpu‐specific channel blockers.
Kinetic studies on the inhibition of creatine kinase activity by branched‐chain α‐amino acids in the brain cortex of rats
Authors: Pilla Carmen , de Oliveira Cardozo Rui Felipe , Dornelles Paula Karine Barcelos , Dutra‐Filho Carlos Severo , de Souza Wyse Angela Terezinha , Wajner Moacir , Wannmacher Clóvis Milton Duval
Published: April 2003

Maple syrup urine disease (MSUD) is a metabolic disorder biochemically characterized by the accumulation of branched‐chain α‐amino acids (BCAA) and their branched‐chain α‐keto acids (BCKA) in blood and tissues. Neurological dysfunction is usually present in the patients, but the mechanisms of brain damage in this disease are far from be understood. The main objective of this study was to investigate the mechanisms by which BCAA inhibit creatine kinase activity, a key enzyme of energy homeostasis, in the brain cortex of 21‐day‐old Wistar rats. For the kinetic studies, Lineweaver–Burk and a modification of the Chevillard et al. plots were used to characterize the mechanisms of enzyme inhibition. The results indicated that BCAA inhibit creatine kinase by competition with the substrates phosphocreatine and ADP at the active site. Considering the crucial role creatine kinase plays in energy homeostasis in brain, if these effects also occur in the brain of MSUD patients, it is possible that inhibition of this enzyme activity may contribute to the brain damage found in this disease. In this case, it is possible that creatine supplementation to the diet might benefit MSUD patients.
The impact of firm size on bank debt use
Authors: Hooks Linda M.
Published: April 2003

I use a sample of US firms to examine the determinants of the concentration of bank debt in total debt. The results indicate that the factors vary by size of the firm. A small‐ to medium‐sized firm has a high concentration of bank debt when it has a low level of discretionary spending. In contrast, a large firm has a high concentration of bank debt when it is difficult for outsiders to observe. The results support the Diamond [J Polit Econ 99 (1991) 689] reputation view that a firm faces different debt choices as it grows. When evaluating bank regulations, policymakers should consider the importance of the reputation‐building services, which a bank provides to businesses.
Transaktives Gedächtnis, Informationsintegration und Entscheidungsfindung im Medienvergleich
Authors: Piontkowski Ursula , Böing-Messing Eva , Hartmann Juliane , Keil Wolfgang , Laus Frank
Published: April 2003

Zusammenfassung. Es ist ein stabiler Forschungsbefund, dass Gruppen, die in computer-basierten Medien kommunizieren, bei Informationsintegrations- und Entscheidungsaufgaben im Vergleich zu Face-to-Face-Gruppen geringere Leistungen aufweisen. In der vorliegenden Untersuchung wurden Chat-, E-Mail- und Face-to-Face-Gruppen hinsichtlich der Konstruktion eines transaktiven Gedächtnisses, ihrer Interaktionsprozesse sowie ihrer Leistung bei der Informationsintegration und Entscheidungsfindung verglichen. Drei-Personen-Gruppen lösten einen Kriminalfall, der als Hidden-Profile-Aufgabe dargeboten wurde. Die Ergebnisse zeigen, dass transaktive Gedächtnisproduktionen die Qualität der Informationsintegration in allen Medien fördern. Obwohl die Informationsqualität in den CMC-Gruppen höher ist, kann dieser Faktor nicht die Prozessverluste ausgleichen, die aus den Restriktionen der text-basierten Medien resultieren.
Factorial and Construct Validity of the Italian Positive and Negative Affect Schedule (PANAS)
Authors: Terracciano Antonio , McCrae Robert R. , Costa Paul T., Jr.
Published: April 2003

Summary: This study provides evidence that an Italian version of the Positive and Negative Affect Schedule (PANAS) is a reliable and valid self-report measure. In an Italian sample (N = 600), the PANAS showed solid psychometric properties, and several American findings with the PANAS were replicated. The replicability of the PANAS factor structure was confirmed by high congruence coefficients between the American and Italian varimax solutions. Alternative models were tested with Confirmatory Factor Analysis; as in previous studies, the two-factor model achieved the best fit, but absolute fit indices varied with the estimation methods used. The independence/bipolarity issue was also explored: Positive and negative affect scales remain substantially independent after accounting for measurement error and acquiescence. Some predictions from the tripartite model of anxiety and depression were confirmed, and external correlates of the PANAS replicated those found in other languages and cultures. These analyses offer strong support for the construct validity of the Italian PANAS.
Transport activity of chimaeric AE2-AE3 chloride/bicarbonate anion exchange proteins
Authors: FUJINAGA Jocelyne , LOISELLE Frederick B. , CASEY Joseph R.
Published: April 2003

Chloride/bicarbonate anion exchangers (AEs), found in the plasma membrane of most mammalian cells, are involved in pH regulation and bicarbonate metabolism. Although AE2 and AE3 are highly similar in sequence, AE2-transport activity was 10-fold higher than AE3 (41 versus 4 mM · min−1 respectively), when expressed by transient transfection of HEK-293 cells. AE2–AE3 chimaeras were constructed to define the region responsible for differences in transport activity. The level of AE2 expression was approx. 30% higher than that of AE3. Processing to the cell surface, studied by chemical labelling and confocal microscopy, showed that AE2 is processed to the cell surface approx. 8-fold more efficiently than AE3. The efficiency of cell-surface processing was dependent on the cytoplasmic domain, since the AE2 domain conferred efficient processing upon the AE3 membrane domain, with a predominant role for amino acids 322–677 of AE2. AE2 that was expressed in HEK-293 cells was glycosylated, but little of AE3 was. However, AE2 expressed in the presence of the glycosylation inhibitor, tunicamycin, was not glycosylated, yet retained 85 ± 8% of anion-transport activity. Therefore glycosylation has little, if any, role in the cell-surface processing or activity of AE2 or AE3. We conclude that the low anion-transport activity of AE3 in HEK-293 cells is due to low level processing to the plasma membrane, possibly owing to protein interactions with the AE3 cytoplasmic domain.
Invasive nature of corona charging on thermal Si/SiO2 structures with nanometer-thick oxides revealed by electron spin resonance
Authors: Stesmans A. , Afanas’ev V. V.
Published: April 2003

Electron spin resonance (ESR) analysis reveals that the versatile noncontacting corona biasing method frequently applied in the electrical analysis of Si/SiO2-based structures is not a noninvasive tool, as usually assumed. In the absence of carrier impact damage, at least five types of ESR-active defects are generated, indicating the drastic impact and jeopardizing inference of intrinsic device properties.
Stimulated Brillouin scattering in the saturated regime
Authors: Froula D. H. , Divol L. , Braun D. G. , Cohen B. I. , Gregori G. , Mackinnon A. , Williams E. A. , Glenzer S. H. , Baldis H. A. , Montgomery D. S. , Johnson R. P.
Published: April 2003

An experimental study of the stimulated Brillouin scattering (SBS) instability has investigated the effects of velocity gradients and kinetic effects on the saturation of ion-acoustic waves in a plasma. For intensities less than I<1.5×1015 W cm−2, SBS is in a linear regime and is moderated primarily by velocity gradients, while for intensities above this threshold, nonlinear trapping is relevant. Direct evidence of detuning of SBS by a velocity gradient was achieved by directly measuring the frequency of the SBS-driven acoustic wave relative to the local resonant acoustic frequency. The frequency and amplitude of the ion-acoustic wave directly responsible for SBS has been measured as a function of space using a 3ω 200 ps Thomson-scattering probe beam. Furthermore, direct evidence of kinetic effects associated with the SBS process in the nonlinear regime has been investigated through a novel use of Thomson scattering. Specifically, a measured twofold increase in the ion temperature has been linked with ion-acoustic waves that have been driven to large amplitudes by the SBS instability. Ion-acoustic waves were excited to large amplitude with a 2ω 1.2-ns-long interaction beam with intensities up to 7×1015 W cm−2. The measured twofold increase in the ion temperature and its correlation with SBS reflectivity measurements provides quantitative evidence of hot ions created by ion trapping in laser plasmas. These detailed and accurate measurements in well-characterized plasma conditions allow a direct test of linear and nonlinear models of the saturation of SBS.
Application of extremely compact capillary discharge soft x-ray lasers to dense plasma diagnostics
Authors: Rocca J. J. , Hammarsten E. C. , Jankowska E. , Filevich J. , Marconi M. C. , Moon S. , Shlyaptsev V. N.
Published: April 2003

Table-top capillary discharge soft x-ray lasers combine the advantages of a small size and a high repetition rate with an extremely high brightness similar to that of their laboratory-size predecessors. When utilized to probe high density plasmas their short wavelength results in a higher critical density, reduced refraction, decreased free-electron absorption, and higher resolution as compared to optical probes. These characteristics allow the design of experiments capable of measuring the evolution of plasmas with density–scale length products that are outside the reach of optical lasers. This paper reviews the use of a 46.9 nm wavelength Ne-like Ar capillary discharge table-top laser in dense plasma diagnostics, and reports soft x-ray laser interferometry results of spot-focus Nd:YAG laser plasmas created at moderate irradiation intensity (∼7×1012 W cm−2) with ∼13 ns pulse width duration laser pulses. The measurements produced electron density maps with densities up to 0.9×1021 cm−3 that show the development of a concave electron density profile that differ significantly from those of a classical expansion. This two-dimensional behavior, that was recently also observed in line-focus plasmas, is analyzed here for the case of spot-focus plasmas with the assistance of hydrodynamic model simulations. The results demonstrate the use of a table-top soft x-ray laser interferometer as a new high resolution tool for the study of high density plasma phenomena and the validation of hydrodynamic codes.
Hydrodynamic growth of shell modulations in the deceleration phase of spherical direct-drive implosions
Authors: Smalyuk V. A. , Delettrez J. A. , Dumanis S. B. , Glebov V. Yu. , Goncharov V. N. , Knauer J. P. , Marshall F. J. , Meyerhofer D. D. , Radha P. B. , Regan S. P. , Roberts S. , Sangster T. C. , Skupsky S. , Soures J. M. , Stoeckl C. , Town R. P. J. , Yaakobi B. , Frenje J. A. , Li C. K. , Petrasso R. D. , Séguin F. H. , McCrorey D. L. , Mancini R. C. , Koch J. A.
Published: April 2003

The evolution of shell modulations was measured in targets with titanium-doped layers using differential imaging [B. Yaakobi et al., Phys. Plasmas 7, 3727 (2000)] near peak compression of direct-drive spherical implosions. Inner-shell modulations grow throughout the deceleration phase of the implosion due to the Rayleigh–Taylor instability with relative modulation levels of ∼20% at peak neutron production and ∼50% at peak compression (∼100 ps later) in targets with 1-mm-diam, 20-μm-thick shells filled with 4 atm of D3He gas. In addition, the shell modulations grow up to about 1.5 times due to Bell–Plesset convergent effects during the same period. At peak compression the inner part of the shell has a higher modulation level than other parts of the shell.
Limits on the efficiency of several electric thruster configurations
Authors: Fruchtman Amnon
Published: April 2003

Limits on the efficiency of several thruster configurations are discussed. The efficiency of the Pulsed Plasma Thruster is reduced when part of the magnetic field energy that is converted into particle energy does not become directed kinetic energy but rather thermal energy. The partitioning of the power when the propellant exhibits slug, snowplow or specular-reflection acceleration is analyzed. It is suggested how to distribute the propellant mass along the accelerating channel so as to efficiently use this thermal energy. Steady acceleration to supersonic velocities is examined in two configurations: the Magneto-Plasma Dynamics (MPD) thruster and the Hall thruster. Limits on the efficiency of the MPD thruster in a nondiverging geometry are derived. The efficiency in the self-field acceleration is higher than in the azimuthal applied-field acceleration. These limits can be overcome in a converging–diverging geometry, analogous to the Laval nozzle, in which the efficiency can approach unity. The acceleration efficiency in the Hall thruster becomes unity for an infinite magnetic Reynolds number even in a nondiverging geometry. The efficiency can be enhanced by the pressure that results from electron heating or by employing segmented emitting electrodes.
Subsonic ion flow at the presheath entrance in tokamak divertors
Authors: Gao Qingdi , Chen Xiaoping
Published: April 2003

At the interface between a magnetized plasma and solid surface, a magnetic presheath region exists before the Debye sheath. The subsonic ion flow at the entrance to the magnetic presheath is investigated under divertor-relevant plasma conditions. The collisional sheath problem is investigated with a simple fluid model. Reasonable boundary conditions at the Debye sheath edge are found based on the analysis of the Sagdeev potential. By using a fluid model, the relationship between ion flow at the presheath entrance and the presheath length is evaluated. It is found that the starting value of the ion velocity along the magnetic field lines decreases with the increase of the presheath length for a fixed collisionality, which has a limitation imposed only by the presheath length. Chodura’s sonic ion flow is approached when the presheath length L→0. For a fixed presheath length, the required ion velocity at the presheath entrance decreases with increasing collisionality.
Comment on “On the consistency of the collisionless sheath model” [Phys. Plasmas 9, 4427 (2002)]
Authors: Allen J. E.
Published: April 2003

The recently published paper on the collisionless sheath model is not correct. The present Comment points out that the sheath model is in fact valid and consistent because it describes the situation where λD/L→0 and not to nonzero values of λD as supposed by the authors.
The electron–electron instability in a spherical plasma structure with an intermediate double layer
Authors: Lapuerta V. , Ahedo E.
Published: April 2003

A linear dynamic model of a spherical plasma structure with an intermediate double layer is analyzed in the high-frequency range. The two ion populations tend to stay frozen in their stationary response and this prevents the displacement of the double layer. Different electron modes dominate the plasma dynamics in each quasineutral region. The electrostatic potential and the electron current are the magnitudes most perturbed. The structure develops a reactive electron–electron instability, which is made up of a countable family of eigenmodes. Space-charge effects must be included in the quasineutral regions to determine the eigenmode carrying the maximum growth rate. Except for very small Debye lengths, the fundamental eigenmode governs the instability. The growth rate for the higher harmonics approaches that of an infinite plasma. The instability modes develop mainly on the plasma at the high-potential side of the double layer. The influence of the parameters defining the stationary solution on the instability growth rate is investigated, and the parametric regions of stability are found. The comparison with a couple of experiments on plasma contactors is satisfactory.
Aerodynamic flow acceleration using paraelectric and peristaltic electrohydrodynamic effects of a One Atmosphere Uniform Glow Discharge Plasma
Authors: Roth J. Reece
Published: April 2003

The development of the One Atmosphere Uniform Glow Discharge Plasma has made it possible to cover the wings and fuselage of aircraft with a thin layer of glow discharge plasma at low energy cost. This plasma layer provides, through Lorentzian collisions, a purely electrohydrodynamic coupling between an electric field and the neutral gas in the boundary layer. This coupling is strong enough to cause aerodynamically significant acceleration and manipulation of the boundary layer and free stream flow, including re-attachment of flow to an airfoil at high angles of attack, and the peristaltic induction of neutral gas flow by a traveling electrostatic wave on the surface of a flat plate.
Dynamic hohlraum driven inertial fusion capsules
Authors: Slutz S. A. , Bailey J. E. , Chandler G. A. , Bennett G. R. , Cooper G. , Lash J. S. , Lazier S. , Lake P. , Lemke R. W. , Mehlhorn T. A. , Nash T. J. , Nielson D. S. , McGurn J. , Moore T. C. , Ruiz C. L. , Schroen D. G. , Torres J. , Varnum W. , Vesey R. A.
Published: April 2003

A dynamic hohlraum is formed when an imploding annular cylindrical Z-pinch driven plasma collides with an internal low density convertor. This collision generates an inward traveling shock wave that emits x rays, which are trapped by the optically thick Z-pinch plasma and can be used to drive an inertial fusion capsule embedded in the convertor. This scheme has the potential to efficiently drive high yield capsules due to the close coupling between the intense radiation generation and the capsule. In prior dynamic hohlraum experiments [J. E. Bailey et al., Phys. Rev Lett. 89, 095004 (2002)] the convertor shock wave has been imaged with gated x-ray pinhole cameras. The shock emission was observed to be very circular and to be quite narrow in the radial direction. This implies that there is minimal Rayleigh–Taylor imprinting on the shock wave. Thus, the dominant source of radiation asymmetry is not random and in principle could be significantly decreased by proper design. Due to the closed geometry of the dynamic hohlraum, the most convenient way to diagnose the radiation symmetry is to image the x rays from the core of an imploded capsule. However, the core temperatures in the prior experiments were not high enough to obtain images. Using numerical simulations we have redesigned the dynamic hohlraum to obtain higher capsule core temperatures. This has enabled us to obtain x-ray pinhole images and Ar K-shell spectra from the imploded cores of 1.7–2.0 mm diameter CH-wall capsules filled with either D2 or CD4 and doped with a small amount of Ar. These capsules absorbed approximately 20 kJ of x-ray energy from the radiation drive, which peaked at a temperature of about 200 eV. Core temperatures of approximately 1 keV were inferred from the Ar spectrum. Our present understanding of the physics of dynamic hohlraums is presented along with our plans to improve this system.
Coupled cluster calculations of the vertical excitation energies of tetracyanoethylene
Authors: Garcı́a-Cuesta I. , Sánchez de Merás Alfredo M. J. , Koch Henrik
Published: April 2003

Coupled cluster linear-response formalism has been used to compute the vertical spectrum of ethylene and tetracyanoethylene (TCNE). We show that for both molecules the ππ* excitation A11g→1B1u of the experimental spectrum is not vertical nor the 0-0 transition. For TCNE this excitation is the only experimentally observed band. We have computed vertical excitations of 5.2 eV in gas phase and 5.1 eV in acetonitrile and estimated a lower bound for the 0-0 transition in the gas phase of 4.3 eV.
Nonlinear effects in inductively coupled plasmas
Authors: Smolyakov A. I. , Godyak V. A. , Tyshetskiy Y. O.
Published: April 2003

Nonlinear effects in an inductive discharge have been studied experimentally and theoretically in a low pressure and low frequency operational regime. Plasma dynamics at these conditions is strongly nonlinear due to inertial and Lorentz forces. Nonlinear plasma polarization at the second harmonic and mean (ponderomotive) potential as well as generation of the electric current at the second harmonic have been measured experimentally and analyzed theoretically. It has been found experimentally that classical expression for the ponderomotive force is not applicable for warm plasmas in the inductive discharges that are typically in the regime of the anomalous skin effect. A new expression for the ponderomotive force in a warm plasma had been derived and was shown to be in a good agreement with experimental data. The influence of nonlinear effects on the plasma heating in the low frequency regime has been investigated theoretically.
Dust grain acceleration by the ponderomotive force of Alfvén waves in cosmic plasmas
Authors: Shukla P. K. , Schlickeiser R.
Published: April 2003

It is shown that the ponderomotive force of shear Alfvén waves in astrophysical plasmas can create intense space charge electric fields which can accelerate charged dust grains. A specific example for the magnetic field aligned dust grain acceleration has been worked out. It is found that the dust acceleration is proportional to the product of ωpi2/ωci2 and the gradient of the shear Alfvén wave intensity, where ωpi(ωci) is the ion plasma (ion gyro) frequency. The result may help in understanding the origin of high energy dust in cosmic environments.
High tunability in compositionally graded epitaxial barium strontium titanate thin films by pulsed-laser deposition
Authors: Lu S. G. , Zhu X. H. , Mak C. L. , Wong K. H. , Chan H. L. W. , Choy C. L.
Published: April 2003

Compositionally graded barium strontium titanate [(BaxSr1−x)TiO3—BST, x=0.75, 0.8, 0.9, and 1.0] thin films are fabricated by pulsed-laser deposition on a LaAlO3 substrate with (La0.7Sr0.3)MnO3 as the bottom electrode. A high dielectric permittivity and temperature characteristic without Curie–Weiss law are obtained. A tunability of over 70% is obtained at frequency of 1 MHz, which is higher than that of single BST layer with the same compositions. All the results indicate that the graded thin films have better electrical properties than a single-layer film.
Nanobelts as nanocantilevers
Authors: Hughes William L. , Wang Zhong L.
Published: April 2003

Semiconducting oxide nanobelts of ZnO have been sectioned and manipulated, for microelectromechanical systems, using an atomic force microscopy probe. Structurally modified nanobelts demonstrate potential for nanocantilever based technologies. With dimensions ∼35–1800 times smaller than conventional cantilevers, the nanocantilevers are expected to have improved physical, chemical, and biological sensitivity for scanning probe microscopy and sensor applications.
Electron emission from diamond nanoparticles on metal tips
Authors: Tyler T. , Zhirnov V. V. , Kvit A. V. , Kang D. , Hren J. J.
Published: April 2003

Single-crystalline diamond nanoparticles (∼5 nm in scale) have been deposited onto molybdenum needles (with radii <100 nm), and their effects on field emission behavior were measured. Combined transmission electron microscopy observations, field emission measurements, and diamond depositions allowed for direct comparison of the effects of various amounts of nanodiamond coating on the field emission properties of a coated metal field emitter. In the limit, field emission from a single isolated diamond nanoparticle is compared here with that from an uncoated metal emitter and from a coating comprised of several layers of nanoparticles.
Hot isostatic pressing of powder in tube MgB2 wires
Authors: Serquis A. , Civale L. , Hammon D. L. , Liao X. Z. , Coulter J. Y. , Zhu Y. T. , Jaime M. , Peterson D. E. , Mueller F. M. , Nesterenko V. F. , Gu Y.
Published: April 2003

The critical current density (Jc) of hot isostatic pressed (HIPed) MgB2 wires, measured by dc transport and magnetization, is compared with that of similar wires annealed at ambient pressure. The HIPed wires have a higher Jc than the annealed wires, especially at high temperatures and magnetic fields, and higher irreversibility field (Hirr). The HIPed wires are promising for applications, with Jc>106 A/cm2 at 5 K and zero field and >104 A/cm2 at 1.5 T and 26.5 K, and Hirr∼17 T at 4 K. The improvement is attributed to a high density of structural defects, which are the likely source of vortex pinning. These defects, observed by transmission electron microscopy, include small angle twisting, tilting, and bending boundaries, resulting in the formation of subgrains within MgB2 crystallites.