bluuebunny/crossref_metadata_2025 huggingface dataset:
Gangliosides of the mouse spinal cord: A comparison in in vivo and in vitro tissues
Authors: Baker R. E. , Guérold B. , Dreyfus H.
Published: April 2003

Ganglioside profiles in spinal cord from 13‐day mouse fetuses, 21‐day postnatal and adult mice were compared with those harvested from organotypic cross‐sections of fetal mouse spinal cord grown for 28 days in vitro in a serum‐free medium. All the major species of gangliosides reported for brain were present both in the in vivo tissue and cultured spinal cord, though not necessarily at each developmental stage examined. Fresh tissues showed increases and decreases in various gangliosides as have been reported for higher brain centers at similar stages of development in mammals and birds. However, qualitative and quantitative differences exist between fresh spinal cord and cultured cord explants as well as between galactose‐grown and galactose‐free cultures. Spinal cord explants grown in the presence of galactose showed measurable amounts of GM2 and GM3 which were not detected in the control‐defined medium‐grown cultures. The differences between the two culture groups may be related to interneuronal connectivity patterns.
In vitro experiments on neuronal and glial cell lineages among the ventricular cells of the mouse neural plate
Authors: Buse Eberhard , Kindler‐Röhrborn Andrea , Rajewsky Manfred F.
Published: April 2003

The proliferative ventricular cells of the early neural plate of the mouse are generally assumed to be pluripotent and equivalent to one another in their developmental capability. Ventricular cells from the rostral parts of the neural plates of mice (Theiler stages 11 and 12, embryonic days 71/2 and 8) were studied in tissue culture with respect to their potential to give rise to neurons or glial cells, or both. Auto‐radiographic and immunohistochemical analyses showed that ventricular cells developing into neuronal phenotypes stopped proliferating immediately upon transfer to cell culture. Using polyclonal anti‐GFAP antibodies, a small proportion of immunoreactive cells could be detected after 4 days of culture. These cells retained their proliferative activity, displayed morphological characteristics of radial glial cells and may have either developed from specific glial progenitor cells or have been induced to proceed along the glial differentiation pathway at the beginning of culture. Therefore, two distinct types of progenitor cells, committed either to neuronal or glial lineages, appear to co‐exist among the cultured neural plate ventricular cells.
Regional maturation of neurotransmitter‐related and glial markers during postnatal development in the rat
Authors: Virgili M. , Barnabei O. , Contestabile A.
Published: April 2003

Neurotransmitter‐related (choline acetyltransferase, acetylcholinesterase, glutamate decarboxylase, l‐glutamate and GABA high affinity uptake) and glial neurochemical markers (glutamine synthetase, β‐alanine uptake and 2′,3′ cyclic nucleotide phosphohydrolase) have been quantitatively assayed in various regions of the rat CNS during normal postnatal development: spinal cord, cerebellum, superior colliculus, hippocampus, striatum, visual cortex, frontal sensory‐motor cortex and prefrontal cortex. In general, neurochemical markers show an obvious trend toward increasing levels in parallel with brain maturation. However, some relevant exceptions have been observed and discussed. Detailed knowledge of regional neurochemical brain maturation is important since it gives us information concerning some key events of brain development. In addition, this knowledge is the essential pre‐requisite for studies aimed at the alteration of specific regional and temporal parameters through experimental manipulation.
Synapse formation on quail trochlear neurons transplanted in duck embryos before naturally occurring motor neuron death
Authors: Sohal G. S. , Bal H. S. , Campbell L. R. , Husain I. , Arumugam T. , Kumaresan K.
Published: April 2003

About half of the trochlear motor neurons in duck and quail embryos die during normal development. In a previous study the role of target muscle in controlling the number of surviving motor neurons was investigated by reducing the number of neurons innervating the muscle. This was accomplished by removing the midbrain of the duck embryo and grafting in its place the midbrain of the quail embryo before motor neuron death begins. It was observed that the number of surviving trochlear motor neurons in the quail‐duck chimera embryos was not significantly different from that of the normal quail. The present investigation was undertaken to determine whether trochlear motor neurons in the chimera embryos received afferent synapses. Brains of duck, quail and chimera embryos on days 16 and 20 were processed for electron microscopical observations. Synapses formed on motor neurons of the chimera embryos. Surprisingly, synapses on motor neurons of quail differed from those of duck, both qualitatively and quantitatively. Synapses on the motor neurons of the chimera embryos developed in a fashion similar to that for the duck motor neurons. Our failure to rescue trochlear motor neurons in the chimera embryos suggests that the developing motor neurons may respond to a larger target muscle only if they received a normal complement of afferent synaptic input.
Subcellular and regional distribution of casein kinase II and initiation factor 2 activities during rat brain development
Authors: Martín Maria Elena , Alćazar Alberto , Salinas Matilde
Published: April 2003

The possible relationship between the subcellular and regional distribution of the activities of initiation factor 2 and casein kinase II, responsible for the phosphorylation of the β subunit of the factor, has been studied during postnatal rat brain development. Both activities have been measured in four brain regions: diencephalon, hemispheres, cerebellum and brain stem, and in two subcellular fractions: postmicrosomal supernatant and the protein fraction associated with ribosomes, or crude initiation factors fraction.

The specific activity of both the factor and the protein kinase is much higher in the protein fraction associated with ribosomes than in the soluble fraction and slightly higher in the hemispheres than in the other three regions. Changes in the activity of both proteins are in parallel with development, the activities increase in the postmicrosomal supernatant and decrease in the fraction associated with ribosomes from suckling (5‐day‐old) to adult (60‐day‐old) animals.

The total activity of the factor and its kinase, calculated by summation of the activities of both sub cellular fractions, does not change during development, and the distribution of activities between the two subcellular fractions observed during brain development, appears as an attractive regulation mechanism for the function of both proteins.
Analysis of the ontogeny of galanin in the rat central nervous system by immunohistochemistry and radioimmunoassay
Authors: Sizer A. R. , Ro̊kaeus Å. , Foster G. A.
Published: April 2003

The development of galanin‐like immunoreactivity in the rat central nervous system has been investigated immunologically. Galanin‐positive processes in the central nervous system were first recognized at day 1 post‐natal, in the dorsal horn of the spinal cord. At day 2, the first galaninimmunoreactive neuronal somata were visualized in several regions of the diencephalon; at later stages of maturation positive cells were also detected in many brain stem areas. The number, density and staining intensity of galanin‐positive structures in these and other regions increased steadily until day 28, by which age the adult disposition was attained. Increases in the concentrations of galanin‐like immunoreactivity during maturation of the animals closely paralleled the immunohistochemical findings. No reduction in galanin‐like immunoreactivity was noted in any area during later post‐natal ages.

The present study indicates that the ontogeny of galanin‐like immunoreactivity in the rat central nervous system occurs entirely post‐natally. The developmental profile is consistent with the rôle of galanin as a putative neurotransmitter/neuromodulator in the rat brain and spinal cord.
Immunocytochemical detection of calcitonin gene‐related peptide in the postnatal developing rat cochlea
Authors: Merchan‐Perez Angel , Gil‐Loyzaga Pablo , Eybalin Michel
Published: April 2003

Using the immunofluorescence technique, three populations of fibers staining for calcitonin gene‐related peptide are identified in postnatal developing cochleas and in adult rat cochleas. During the maturation of the cochlea, the immunostaining first appears in the basal turn and then extends toward the apex of the cochlea. The first population of immunostained fibers belongs to the lateral olivocochlear innervation. It is observed at postnatal day 4 within the inner spiral bundle of the organ of Corti. The second population of calcitonin gene‐related peptide‐like immunostained fibers belongs to the medial olivocochlear innervation. It is first identified at postnatal day 6 under the outer hair cells, generally in the first row. In the older stages, this population of fibers progressively extends toward the external row of outer hair cells. Finally, the third population of immunostained fibers belongs to the sympathetic supply of the cochlea. They can be identified at postnatal day 6 around the cochlear artery and its branches, and also within the entire modiolus.

Our results confirm the presence of calcitonin gene‐related peptide in fibers of the lateral and medial efferent innervations of the cochlea. They indicate an early appearance of calcitonin gene‐related peptide in the developing cochlea, before the onset of the cochlear function, suggesting for this peptide either a neurotrophic function or a regulation of the early cochlear potentials at the level of the lateral efferent synapses.
Sex‐specific schedule in steroid response of rhombencephalic catecholaminergic neurons in vitro
Authors: Küppers Eva , Pilgrim Christoph , Reisert Ingrid
Published: April 2003

Morphological differentiation of tyrosine hydroxylase‐immunoreactive neurons was investigated in dissociated cell cultures of rhombencephalon of male and female day 14 rat embryos grown in the presence or absence of sex steroids. Numbers of cells were counted and morphometrical measurements carried out of soma size and length of tyrosine hydroxylase‐immunoreactive neurites (processes). Subtle sex differences in length of stained neurites, which were not yet present after 3 days in vitro, were observed after 6 days in cultures grown in the absence of sex steroids. Female tyrosine hydroxylase‐immunoreactive neurites could be traced over longer distances than male ones. Daily treatment of cultures with testosterone or 17β‐estradiol resulted in an increase of lengths of stained neurites of female neurons after 3 days and of male neurons after 6 days in vitro. Regarding cell numbers or soma size, there were no differences between genders or between controls and hormone‐treated cultures.

It is concluded that sex steroids promote the outgrowth of neurites from noradrenergic neurons within a gender‐specific time frame. It appears that the critical period for developmental effects of sex steroids differs between males and females.
Quantitative autoradiographic study of the postnatal development of benzodiazepine binding sites and their coupling to GABA receptors in the rat brain
Authors: Daval Jean‐Luc , Werck Marie‐Christine , Nehlig Astrid , de Vasconcelos Anne Pereira
Published: April 2003

The postnatal development of benzodiazepine binding sites in the rat brain was studied by quantitative receptor autoradiography using [3H]flunitrazepam. The coupling of these sites to GABA receptors was assessed in 43 cerebral structures by examining the effects of in vitro addition of GABA on flunitrazepam specific binding. Benzodiazepine‐specific binding was relatively high at birth and exhibited an heterogeneous distribution pattern, anatomically different from the adult one. Data showed a sequential development of benzodiazepine receptors in relation to the time course of maturation of cerebral structures. A proliferation peak which paralleled rapid brain growth was noticed. High levels of benzodiazepine sites were transiently observed in some areas, e.g. thalamus and hypothalamus, and might be related to maturational events. In every brain structure examined, benzodiazepine binding sites were linked to GABA receptors. However, enhancement of flunitrazepam specific binding by exogenous GABA differed according to the structures studied and decreased during development, suggesting some changes in the control of GABA/benzodiazepine regulation during postnatal maturation.
Postnatal development of descending motor pathways studied in man by percutaneous stimulation of the motor cortex and the spinal cord
Authors: Khater‐Boidin Josette , Duron Bernard
Published: April 2003

Using the percutaneous electrical stimulation of the brain and spinal cord, we have determined central motor pathway conduction velocities in a group of 19 healthy fullterm newborns (average post‐conceptional age 39.8 weeks) and in 19 infants between 2 months and 8 years of age. The newborns were examined during the first postnatal week. The percutaneous stimulation of the motor cortex and of the cervical and lumbar enlargements of the spinal cord was made by means of bipolar electrodes. The evoked compound muscle action potentials were recorded by bipolar surface electrodes fixed on the skin overlying the thenar eminence muscles and the tibialis anterior muscle.

In fullterm newborns, the responses of lower limb muscles to cortical stimulation were more difficult to obtain than those of upper limb muscles. Conduction velocities of central motor fibres along the spinal cord (between vertebrae C7 and L4) were around 10 m/sec in fullterm newborns and 38 m/sec at the age of 4 years. These values are considerably lower than those described for adult man (48–60 m/sec). The adult values are established around the age of 8 years.
Growth of ascending spinal axons in CNS scar tissue
Authors: Frisén Jonas , Fried Kaj , Sjögren Ann Margret , Risling Mårten
Published: April 2003

The aim of the present study was to test the capacity of spinal cord scar tissue to assist and sustain axon regrowth. In adult rats and cats the dorsal funiculus (DF) was cut at mid‐thoracic or lumbar level and a superficial incision in the DF rostral to the lesion was made in order to extend the penetrating lesion. Axonal tracing in rats 50–100 days postinjury with anterogradely transported wheatgerm agglutinin‐conjugated horseradish peroxidase or rhodamine‐conjugated dextran demonstrated that nerve fibers had entered the scar tissue. Axon ingrowth in the scar was further indicated by axonal immunoreactivity to the growth‐associated protein GAP‐43. The scar tissue showed low‐affinity neurotrophin receptor‐like immunoreactivity in association with blood vessels and in the interstitium. The integrity of the blood‐brain barrier in the extended dorsal funiculus lesion was disrupted for at least 11 months postinjury, assessed by i.v. injections of free HRP or Evans blue. The present study shows that penetrating injury in the dorsal funiculus produces a CNS environment permissive for axonal sprouting and that PNS influence is not necessary for spinal tract regrowth. A possible relationship between the absence of an intact BBB and injury‐induced axonal sprouting is discussed.
Migration and differentiation of PC12 cells transplanted into the rat spinal cord
Authors: Zompa E.A. , Pizzo D.P. , Hulsebosch C.E.
Published: April 2003

To test the hypothesis that transplanted neuronal or neuronal‐like cell lines, grown in vitro, might survive and differentiate in the mammalian spinal grey matter, adult male Sprague‐Dawley rats (N=5) were injected with a suspension of between 3 × 105 and 1.0 × 106 DiI labeled, undifferentiated rat pheochromocytoma (PC12) cells in sterile phosphate buffered saline. The PC12 cell line was chosen since, in certain in vitro conditions, this cell line serves as a model of neuronal differentiation, which includes the ability to conduct action potentials and form functional synapses. After a survival time of 7 or 8 days, the spinal cords were removed, cryosectioned longitudinally and examined for detection of DiI labeled PC12 cells using fluorescent microscopy. The number of DiI labeled profiles and the proportions of the DiI cells which were differentiated were counted per section in at least five non‐contiguous sections per animal. Differentiation was defined as cells with neurite‐like extensions which exceeded twice the soma diameter. Results demonstrated the following: (1) from 2 to 15% of the transplanted PC12 cells survived (2) migration within the spinal grey matter occurred since PC12 cells were found as much as 510 μm away from the injection site (3) of the surviving PC12 cell population, a proportion of between 60 and 80% were differentiated, many with two or more neurite‐like processes, in all of the rats (4) no mitotic profiles were observed in DiI labelled cells (5) undifferentiated PC12 cells were juxtaposed to the lumens of small blood vessels or within the lesion cavity. Although the specific factors remain to be elucidated, the observed PC12 migration and differentiation within the host spinal grey matter appears to be controlled by factors in the microenvironment. These data support the use of a homogeneous in vitro population of neuronal or neuronal‐like cells, which are readily accessible to transfection with the appropriate genes, as transplant sources for the injured spinal cord.
Structural maturation, cell proliferation and bioelectric activity in long‐term slice‐cultures of immature rat hippocampus
Authors: Hajós Ferenc , Balázs Robert , Baker Robert E. , Gerics Balázs , Nuijtinck Roger
Published: April 2003

Explants of transverse slices of the 6‐day‐old rat hippocampus were grown in a serum‐free medium for 2–14 days. Histology performed after various culturing periods demonstrated that these slices maintain a high degree of 3‐dimensional organotypy, while undergoing growth and differentiation of the main cellular elements similar to that seen in vivo. Histological indications of continuing cell proliferation were verified by autoradiography showing a labelling of neuroblasts in the dentate gyrus and of glioblasts at the sites of gliogenesis observed in vivo. Spontaneous bioelectric activity and evoked potentials were recorded, both indicating the development of impulse generation and neuronal connectivity within the explant. Silver impregnation and electron microscopic studies lent further support for the presence of neuronal networks intrinsic to the hippocampus. These findings suggest that within the period studied the hippocampal slice cultures mature in a fashion similar to that seen in situ.
Stimulatory effect of opioid peptides and naloxone on rat spinal cord cells in primary dissociated culture
Authors: Kozlova Marina , Kalentchuk Vyachieslav
Published: April 2003

Opioid peptides leu‐enkephalin, a synthetic analog of enkephalin dalargin and an opiate receptor blocker naloxone were studied for their morphological effect on the cells of dissociated cultures of rat spinal cord.

Low density seeding of cells (3.105; 6.105 cells/ml) on collagen substrate was performed to document that opioid peptides increase the number of cultured cells and neurite outgrowth and lead to the activation of the initiated processes of aggregate formation. Upon higher density of plating (5.106 cells/ml) with poly‐l‐lysine as a substrate, activation of the aggregate formation process was demonstrated, both opioid peptides and naloxone leading to an increase in the size of aggregates. Statistical treatment of the results obtained in this set of experiments documented that leu‐enkephalin, dalargin and naloxone increased 2.2‐, 2.2–2.6‐, 2.4‐fold, respectively, the size of aggregates compared to the control, i.e. the reaction of spinal cord cells to opioid peptides and opiate receptor blocker naloxon was unidirected. The total effect of opioid peptides and naloxon resulted in a 3.6‐fold increase in the size of the aggregates compared to the control. The data obtained in this study allow the assumption that opioid peptides and naloxone, while activating spinal cord cells via receptors of a different type, manifest the properties of factors thus increasing survival and adhesion of spinal cord cells in culture.
Presenilin 1 gene silencing by S‐adenosylmethionine: a treatment for Alzheimer disease?
Authors: Scarpa Sigfrido , Fuso Andrea , D'Anselmi Fabrizio , Cavallaro Rosaria A
Published: April 2003

Presenilin 1 (PS1) is a key factor for β‐amyloid (Ab) formation in Alzheimer disease (AD). Homocysteine accumulation, frequently observed in AD patients, may be a sign of a metabolic alteration in the S‐adenosylmethionine (SAM) cycle, which generates the overexpression of genes controlled by methylation of their promoters, when the cytosine in CpG moieties becomes unmethylated. The methylation of a gene involved in the processing of amyloid precursor protein may prevent Ab formation by silencing the gene. Here we report that SAM administration, in human neuroblastoma SK‐N‐SH cell cultures, downregulates PS1 gene expression and Ab production.
Nitric oxide released from zwitterionic polyamine/NO adducts inhibits Cu2+‐induced low density lipoprotein oxidation
Authors: Yamanaka Naoki , Oda Osamu , Nagao Seiji
Published: April 2003

The effects of nitrix oxide (NO) released from zwitterionic polyamine/NO adducts on Cu2+‐induced low density lipoprotein (LDL) oxidation were studied. When each of the two kinds of NO releasing zwitterionic polyamine/NO adducts (NOC5 and NOC7) was incubated at 5 μM with isolated human LDL (0.25 mg/ml) and Cu2+, the formation of thiobarbituric acid reactive substances (TBARS) was inhibited. The duration of inhibition by NOC7 (20 min) and NOC5 (100 min) corresponded to the NO generation lives of respective zwitterionic polyamine/NO adducts. The duration of inhibition was dependent on the amount of NOC5 added (2.5–20 μM). Repeated additions of 5 μM NOC5 at 100 min intervals worked as inhibitor in the same manner. NOC5 broke to inhibit at any process of the Cu2+‐induced LDL oxidation reaction. Fragmentation of apolipoprotein B derived from Cu2+‐induced LDL oxidation was also prevented by the addition of NOC5. These results clearly indicate that NO inhibits the oxidative modification of LDL induced by Cu2+. NO releasing zwitterionic polyamine/NO adducts are good reagents for NO studies.
Linking performance drivers in production planning and inventory control to process choice
Authors: Safizadeh M.Hossein , Ritzman Larry P.
Published: April 2003

This study investigates how process choice relates to production planning and inventory control decisions. We empirically examine the validity of deductively derived patterns about these types of decisions. More importantly, we look for normative insights by exploring how production planning and inventory control decisions affect operations performance. Our findings show that production line and continuous flow plants use more of a level production strategy, and carry less raw material and work‐in‐process inventory. The performance drivers for these plants, through which the operations function excels, are effective utilization of equipment, reduced finished goods inventory, and reduced setup down time. To gain forward demand visibility and batching economies, job and batch shops rely much more on backlogs in their planning process. These plants use more of a production chase strategy and position inventory lower in the bills of materials. Four performance drivers for top‐performing job and batch shops are to find ways that better anticipate customers' orders, have a more responsive chase strategy, carry less raw material or purchased inventory, and shorten production planning horizon, partly through less reliance on backlogs. It is intriguing that top‐performing plants not only do the expected things, given their choice of process, but also excel in selected dimensions—some of which fit the profile normally associated with a different process choice. To monitor and continuously improve operations, evaluation ‘scorecards’ should pay particular attention to performance drivers, which change depending on the plant's process choice.
Platelet counts in depressed patients treated with amitriptyline or paroxetine
Authors: Lederbogen F. , Hörer E. , Hellweg R. , Heuser I. , Deuschle M.
Published: April 2003

Objective

To assess whether therapy with two widely used antidepressants influences platelet counts.

Subjects and methods

In 90 patients hospitalized for treatment of a major depressive episode according to DSM-IV, platelet counts were performed after a 6 d antidepressant-free run-in period and again after 35 d of active standardized treatment with amitriptyline (n = 40) or paroxetine (n = 50).

Results

There was a trend for platelet counts to increase during treatment with amitriptyline (from 245.5 ± 68.6 to 256.8 ± 69 cells × 109 L-1, P < 0.06); no change was observed during treatment with paroxetine (from 232.6 ± 58.3 to 234.6 ± 68.9 cells × 109 L-1, n.s).

Conclusions

Treatment with amitriptyline tends to be associated with elevated platelet counts. The cause for this increase is not known, but may be relevant in terms of patients’ long-term thromboembolic risk.
Selective interaction of LAT (linker of activated T cells) with the open-active form of Lck in lipid rafts reveals a new mechanism for the regulation of Lck in T cells
Authors: KABOURIDIS Panagiotis S.
Published: April 2003

In T cells, the lipid raft-associated Lck is strongly tyrosine phosphorylated and has reduced enzymic activity in contrast with the detergent-soluble pool, which has substantial activity. Lck tagged at the C-terminus (Lck/V5-His) was efficiently captured by epitope-specific reagents from the detergent-soluble fraction but not from lipid rafts. Binding was restored following urea denaturation, suggesting that Lck/V5-His is in a ‘closed’ conformation in these domains. In agreement with this hypothesis, the Tyr505 → Phe/V5-His and Arg154 → Lys/V5-His mutants, which disrupt the SH2-Tyr505 intramolecular interaction, were efficiently precipitated from lipid rafts. In contrast to Lck, Fyn/V5-His was precipitated equally well from both fractions. In the LAT (linker of activated T cells)-deficient J.CaM2 cells, Tyr505 phosphorylation of raft-associated Lck was reduced whereas its enzymic activity was elevated. This correlated with decreased levels of raft-localized Csk (C-terminal Src kinase) kinase. Increased tyrosine phosphorylation of Lck was restored in LAT-reconstituted J.CaM2 cells suggesting that LAT negatively regulates Lck activity in lipid rafts. Co-immunoprecipitation experiments from Tyr505 → Phe/V5-His-expressing cells revealed that LAT preferentially interacts with the ‘open’ form of Lck in T cell raft domains. These results demonstrate that, unlike the non-raft pool, Lck in lipid rafts has a ‘closed’-inactive structure, and that LAT plays a role in maintaining this conformation, possibly by facilitating critical associations within lipid rafts via its capacity to interact with the ‘open’ form of the kinase.
Accretion disks: The magnetohydrodynamic powerhouse
Authors: Hawley John F.
Published: April 2003

Accretion disks orbiting around compact objects such as white dwarfs, neutron stars and black holes are a central paradigm of high energy astrophysics. Accretion disks are believed to power systems such as x-ray binaries, active galactic nuclei, and quasars through the release of gravitational potential energy as gas spirals in. This infall requires the transfer of angular momentum outward from one fluid element to another. Thus the dynamics and evolution of accretion disks depend fundamentally upon this angular momentum transport process. Because accretion disks are composed of highly ionized conducting plasma with very high Reynolds number, the equations governing their evolution are those of (inviscid) magnetohydrodynamics (MHD). In disks the combination of a subthermal magnetic field and outwardly decreasing differential rotation leads to a powerful linear instability (the magnetorotational instability) which, in turn, generates MHD turbulence that produces a net Maxwell stress and the required angular momentum transport. The turbulence generates heat through dissipation at the viscous and resistive length-scales. Thus, accretion disks are systems where the power generation mechanism derives directly from a magnetohydrodynamic process. Fully global three-dimensional MHD simulations are now beginning to probe the properties of accretion disks from first principles.
Mean shear flows, zonal flows, and generalized Kelvin–Helmholtz modes in drift wave turbulence: A minimal model for L→H transition
Authors: Kim Eun-jin , Diamond P. H.
Published: April 2003

The dynamics of and an interplay among structures (mean shear flows, zonal flows, and generalized Kelvin–Helmholtz modes) are studied in drift wave turbulence. Mean shear flows are found to inhibit the nonlinear generation of zonal flows by weakening the coherent modulation response of the drift wave spectrum. Based on this result, a minimal model for the L→H (low- to high-confinement) transition is proposed, which involves the amplitude of drift waves, zonal flows, and the density gradient. A transition to quiescent H-mode sets in as the profile becomes sufficiently steep to completely damp out drift waves, following an oscillatory transition phase where zonal flows regulate drift wave turbulence. The different roles of mean flows and zonal flows are elucidated. Finally, the effect of poloidally nonaxisymmetric structures (generalized Kelvin–Helmholtz mode) on anomalous transport is investigated, especially in reference to damping of collisionless zonal flows. Results indicate that nonlinear excitation of this structure can be potentially important in enhancing anomalous transport as well as in damping zonal flows.
Plasma parameter scaling of the error-field penetration threshold in tokamaks
Authors: Fitzpatrick Richard
Published: April 2003

A previously published analytical formula for the error-field penetration threshold in rotating tokamak plasmas is successfully benchmarked against nonlinear magnetohydrodynamical simulations in slab geometry. Moreover, the fundamental assumption underlying the derivation of this formula, namely, that the response of a flowing plasma to a low amplitude, quasistatic, resonant magnetic perturbation is governed by linear, constant-ψ layer physics, is verified over a wide range of plasma parameters, which includes the parameter range relevant to Ohmic and neutral beam injection start-up discharges in modern-day tokamaks. It is concluded that the formula in question can be used to estimate error-field penetration thresholds in such plasmas.
Simulations and theories of relativistic ion cyclotron instabilities driven by MeV alpha particles in thermal deuterium plasmas
Authors: Chen K. R.
Published: April 2003

The harmonic relativistic ion cyclotron instabilities driven by MeV alpha particles in magnetized thermal deuterium plasmas are studied with a perturbation theory, a kinetic theory, and particle-in-cell simulations. Due to the mass deficit of alphas, the resonant harmonic cyclotron frequency of the alphas is not smaller than that of the deuterons such that the low harmonics are linearly stabilized by the deuterons. However, the thermal deuterons behave as a cold-gyro-stream plasma at high harmonics so that, by including relativistic streaming in gyro-phase, the alpha particles can drive the high harmonic electrostatic ion cyclotron instability, that is in a quadratic form, although their Lorentz factor is very close to unity (e.g., γ=1.000 94 for 3.5 MeV alphas). The dielectric of the first deuteron cyclotron harmonic determines the alpha harmonic number threshold for instability; the quadratic instability occurs in the lower-hybrid frequency regime. As in a sharp contrast to the nonresistive thermalization of MeV protons due to the two-gyro-stream instability dominating at low harmonics, the high harmonic interaction between the unstable waves and the alphas becomes selective; only alpha particles with its perpendicular momentum above a threshold are involved and the interaction stops when they are slowed down to the threshold. The resultant energy spectrum is in a shape close to the profile of the theoretical interaction strength between the alpha particles and the dominating wave mode; the alpha particles almost loss no net energy. New-born alpha particles experience a similar selective gyro-broadening process in a shorter time scale. A simple explanation for the selective gyro-broadening based on the wave–alpha interaction calculated from the perturbation theory is given.
Compression fluctuations of chain molecules
Authors: Ivlev B. I. , Ramos Cárdenas J. J.
Published: April 2003

Thermal compression fluctuations of a long molecule, like DNA, are accounted when a bead is attached to the end of the molecule. When the bead is acted by some trapping (attractive) potential produced, for example, by optical tweezers, this potential can be essentially renormalized due to compression thermal fluctuations of the long molecule. The effective potential may turn over into a repulsive one for a sufficiently long molecule. The effect should be taken into account for an analysis of bead fluctuations.
Breit–Wigner formula at barrier tops
Authors: Fujiié Setsuro , Ramond Thierry
Published: April 2003

For noncritical energies, the asymptotic behavior of the scattering phase and of the time-delay are known to be described by a Weyl type formula and the Breit–Wigner formula, respectively. We consider here the case of critical energy levels in dimension 1. We obtain the semiclassical asymptotics of the scattering phase and of the time-delay, uniformly with respect to the energy in a neighborhood of a critical value.
Non-neutral plasma equilibria, trapping, separatrices, and separatrix crossing in magnetic mirrors
Authors: Fajans J.
Published: April 2003

The equilibria of non-neutral plasmas confined in Penning–Malmberg traps with axial varying (mirror) magnetic fields exhibit numerous unusual features, including potential differences along field lines, plasma density variations, trapped particles in both the high and low field regions, and unusual separatrices between trapped and untrapped particles. Mirror fields play prominent roles in a number of recent experiments, and overly simplistic models of the equilibria can lead to errors in the interpretation of experimental results.
Short-time dynamics of glass-forming liquids: Phenyl salicylate (salol) in bulk liquid, dilute solution, and confining geometries
Authors: Kalampounias A. G. , Yannopoulos S. N. , Steffen W. , Kirillova L. I. , Kirillov S. A.
Published: April 2003

Raman spectroscopy has been used to investigate picosecond vibrational dynamics of the molecular glass-former phenyl salicylate (salol). The study has concentrated on the elucidation and comparison of molecular dynamics of salol subjected to different local environments, namely in bulk, in a dilute CCl4 solution, and under spatial confinement in nanoporous sol–gel glasses. Contrary to most of the previous picosecond dynamics studies performed by means of Raman line profile analysis, we have employed in this paper a novel approach that enables the extraction of valuable short-time dynamics information through spectra fitting in the frequency domain. As a result, strongly overlapping vibrational lines can be put in focus. The analysis has shown a systematic dependence of vibrational relaxation on the local environment around a salol molecule. The magnitude of the vibrational relaxation time τV decreases in the sequence dilute solution→bulk liquid→confined liquid, indicating the modification of interactions when passing from the dilute solution to confined geometries. This fact has been rationalized by invoking the enhancement of the orientational order of salol molecules under spatial confinement. Similar conclusions can be drawn from the analysis of changes of the frequency modulation time τω upon confinement. The changes in second moments of vibrations as well as the observed blueshifts of the Raman peaks in confinement suggest the strengthening of repulsion between salol molecules in the restricted space.
Inverse mapping of block copolymer morphologies
Authors: Lyakhova K. S. , Zvelindovsky A. V. , Sevink G. J. A. , Fraaije J. G. E. M.
Published: April 2003

Polymer morphologies can be analyzed by various experimental projection methods. Since most structures live in three dimensions the problem is to extrapolate the underlying 3D morphology from the projection. We propose an approach in which the free energy functional of a 3D sample is minimized to fit experimental 2D information, serving as an additional constraint. The method is very general and can be applied to any physical system described in terms of a density functional theory.
Rigorous proof of isotope effect by Bardeen–Cooper–Schrieffer theory
Authors: Yang Yisong
Published: April 2003

In this article, we present a rigorous proof of the isotope effect within the theory of Bardeen–Cooper–Schrieffer for isotropic superconductors. We show that, when the interaction kernel is a positive constant, the isotope effect is exact; when the interaction kernel is a positive function depending on the energies of the pairing electrons, the isotope effect is no longer exact but lies within a sharp range determined by the varying kernel function. Moreover, we show that our method here may be extended to establish an existence and uniqueness theorem for the transition temperature in the Bogoliubov–Tolmachev–Shirkov model which allows separate phonon and Coulomb dominance in their respective energy regimes.
A new realization for the d=2 topological algebra
Authors: Carvalho M. , Oliveira A. L.
Published: April 2003

We derive topological algebras for two-dimensional models admitting a d=[δ,b] decomposition (with b the BRST operator). In general, the topological algebra we obtain is not derived from the twisting of an N=2 supersymmetry algebra. We show, for the particular case of an Abelian model described by a ladder of matter, how to derive N=2 supersymmetry generators from the odd generators of the topological algebra.
Particle-in-cell simulations of tunneling ionization effects in plasma-based accelerators
Authors: Bruhwiler David L. , Dimitrov D. A. , Cary John R. , Esarey Eric , Leemans Wim , Giacone Rodolfo E.
Published: April 2003

Plasma-based accelerators can sustain accelerating gradients on the order of 100 GV/m. If the plasma is not fully ionized, fields of this magnitude will ionize neutral atoms via electron tunneling, which can completely change the dynamics of the plasma wake. Particle-in-cell simulations of a high-field plasma wakefield accelerator, using the OOPIC code [D. L. Bruhwiler et al., Phys. Rev. ST Accel. Beams 4, 101302 (2001)], which includes field-induced tunneling ionization of neutral Li gas, show that the presence of even moderate neutral gas density significantly degrades the quality of the wakefield. The tunneling ionization model in OOPIC has been validated via a detailed comparison with experimental data from the l’OASIS laboratory [W.P. Leemans et al., Phys. Rev. Lett. 89, 174802 (2002)]. The properties of a wake generated directly from a neutral gas are studied, showing that one can recover the peak fields of the fully ionized plasma simulations, if the density of the electron drive bunch is increased such that the bunch rapidly ionizes the gas.
Observations of low frequency oscillations due to transverse sheared flows
Authors: Thomas Edward , Jackson Jon David , Wallace Edwynn A. , Ganguli Gurudas
Published: April 2003

This Letter details observations of low frequency (i.e., ω⩽Ωi, where Ωi is the ion cyclotron frequency), coherent instabilities in the Auburn Linear Experiment for Instability Studies (ALEXIS). In the ALEXIS device, which is a 1.8-m long magnetized plasma column, the observed instabilities are excited by the presence of sheared flows in the plasma that are transverse to the axial magnetic field. The instabilities have long azimuthal wavelengths (m⩽2) and are localized in the plasma to regions where the sheared flow is maximized and are anticorrelated to both density gradients and field aligned currents.
Generation of ultrahigh intensity laser pulses
Authors: Fisch N. J. , Malkin V. M.
Published: April 2003

Mainly due to the method of chirped pulse amplification, laser intensities have grown remarkably during recent years. However, the attaining of very much higher powers is limited by the material properties of gratings. These limitations might be overcome through the use of plasma, which is an ideal medium for processing very high power and very high total energy. A plasma can be irradiated by a long pump laser pulse, carrying significant energy, which is then quickly depleted in the plasma by a short counterpropagating pulse. This counterpropagating wave effect has already been employed in Raman amplifiers using gases or plasmas at low laser power. Of particular interest here are the new effects which enter in high power regimes. These new effects can be employed so that one high-energy optical system can be used like a flashlamp in what amounts to pumping the plasma, and a second low-power optical system can be used to extract quickly the energy from the plasma and focus it precisely. The combined system can be very compact. Thus, focused intensities more than 1025 W/cm2 can be contemplated using existing optical elements. These intensities are several orders of magnitude higher than what is currently available through chirped pump amplifiers.
Quasi-perpendicular magnetosonic waves in a multi-ion-species plasma
Authors: Irie Shinsuke , Ohsawa Yukiharu
Published: April 2003

Propagation of oblique magnetosonic waves in a multi-ion-species plasma is studied with theory and three-fluid simulations. First, the linear dispersion relation of the high-frequency mode, the upper branch of magnetosonic waves, is examined in detail. Next, nonlinear evolution equation for this mode is derived. This mode can propagate as compressive or rarefactive solitary pulses, depending on the propagation angle. Ion acceleration due to these pulses and resultant pulse damping are analytically discussed. These processes are then demonstrated by fluid simulations for a plasma consisting of H, He, and electrons; either rarefactive or compressive pulses are gradually damped owing to the slight ion acceleration.
Stability analysis of hollow electron columns including compressional and thermal effects: Initial value treatment
Authors: Pariev V. I. , Delzanno G. L.
Published: April 2003

The diocotron spectrum for a simplified fluid model of Malmberg–Penning traps that includes compressional effects due to end curvature with finite temperature is investigated analytically. The general initial value treatment of the l=1 mode is performed and the algebraic growth proportional to t is recovered when the plasma length profile is the integrable one as introduced by Delzanno et al. [Phys. Plasmas 9, 4863 (2002)]. Then, nonintegrable length profiles slightly different from the integrable one are considered (the difference being characterized by ε). It is shown that complex discrete eigenfrequencies appear near the edge of the continuous spectrum of the l=1 mode. Depending on the sign of ε, these discrete eigenfrequencies may or may not lead to exponential instability. The discrete eigenfrequency scales as ε2/3 with respect to the upper edge of the continuum. This confirms and explains the numerical observations of Finn et al. [Phys. Plasmas 6, 3744 (1999)] and Delzanno et al. [Phys. Plasmas 9, 4863 (2002)] and proves that the ε2/3 scaling law is a generic property of the modified drift-Poisson model near the edge of the continuum. The same general treatment is also applied to the l=1 diocotron spectrum in a cylindrical Malmberg–Penning trap with an additional coaxial inner conductor of radius a.
Prediction of large polar Kerr rotation in the Heusler-related alloys AuMnSb and AuMnSn
Authors: Offernes Laila , Ravindran P. , Kjekshus A.
Published: April 2003

Theoretical spectra for the magneto-optical Kerr effect have been obtained for the Heusler-related alloys AuMnSb and AuMnSn, and repeated calculations are performed for the isostructural PtMnSb phase. Using experimental lattice constants, our calculations predict a Kerr rotation exceeding −1° in the 0.5–0.8 eV region for AuMnSb and a somewhat smaller rotation for AuMnSn. Supercell calculations indicate that half-metallic behavior can be induced on hole/electron doping in the AuMnSn1−xSbx solid-solution phase for 0.50<x<0.75.
Formation of lateral quantum dot molecules around self-assembled nanoholes
Authors: Songmuang Rudeesun , Kiravittaya Suwit , Schmidt Oliver G.
Published: April 2003

We fabricate groups of closely spaced self-assembled InAs quantum dots (QDs)—termed lateral QD molecules—on GaAs (001) by a combination of molecular-beam epitaxy and AsBr3 in situ etching. An initial array of homogeneously sized nanoholes is created by locally strain-enhanced etching of a GaAs cap layer above InAs QDs. Deposition of InAs onto the nanoholes causes a preferential formation of the InAs QD molecules around the holes. The number of QDs per QD molecule ranges from 2 to 6, depending on the InAs growth conditions. By decreasing the substrate temperature, the number of QDs per QD molecule increases, but the statistical distribution is wider due to a reduced In atom diffusion length. Our photoluminescence investigation documents the nanohole and QD molecule formation step by step and confirms the high crystal quality of these structures. An analysis of the nanohole geometry as a function of annealing time and InAs filling allows us to propose a model for the QD molecule formation process.
Nonlinear effects at the boundary of an electron plasma
Authors: Gradov O. M. , Stenflo L. , Shukla P. K.
Published: April 2003

Two solutions for nonlinear electron plasma waves propagating along a cold plasma boundary are reported. Thus, the nonlinear frequency shift caused by the harmonic generation as well as new localized nonlinear perturbations are found.
Backbone 15N relaxation analysis of the N‐terminal domain of the HTLV‐I capsid protein and comparison with the capsid protein of HIV‐1
Authors: Cornilescu Claudia C. , Bouamr Fadila , Carter Carol , Tjandra Nico
Published: April 2003

Human T‐cell leukemia virus type 1 (HTLV‐I) is an oncogenic retrovirus that exhibits specific tropism for human T‐cells. The capsid (CA) proteins of retroviruses share highly conserved secondary and tertiary structures. However, they can form quaternary structures (assembled cores) that are conical (e.g., the lentivirus subgroup, including HIV) or spherical (e.g., the oncovirus subgroup, including HTLV). The intrinsic features that drive these differences are not understood. So far, only structural studies have been used as a basis for comparison. Dynamics may play a role in particle formation. High‐resolution nuclear magnetic resonance (NMR) 15N relaxation data (T1, T1ρ, and NOE) have been used to characterize the backbone dynamics of the N‐terminal domain (NTD) of the oncovirus HTLV‐I and to compare with the CA NTD of HIV‐1. Large variations in the 15N heteronuclear NOEs and transversal relaxation rates for individual residues are consistent with the bundle RMSD of the previously calculated NMR structures. The β‐hairpin and CyP‐A loop exhibit different mobility in HTLV‐I and HIV‐1. The overall hydrodynamic property of the HTLV‐I capsid NTD is quite distinct from the HIV‐1.