bluuebunny/crossref_metadata_2025 huggingface dataset:
NCAM as a differentiation marker of postmigratory immature neurons in the developing human nervous system
Authors: Terkelsen O.B.F. , Janas M. Stagaard , Bock E. , Møllgård K.
Published: April 2003

The regional distribution and cellular localization of the neural cell adhesion molecule were investigated in the developing nervous system of human embryos and fetuses, by using immunocytochemistry with antibodies against the human neural cell adhesion molecule. Embryos and fetuses with crown‐rump lengths ranging from 15 to 80 mm (corresponding approximately to 6–12 ovulation weeks) were examined. In the telencephalon, immunoreactivity was found in the primordial plexiform layer and in the early cortical plate. During later stages, immunoreactivity was present in the marginal zone, cortical plate, developing subplate zone and radiations of the internal capsule. In the mesencephalon and rhombencephalon, neuronal perikarya were outlined and strong staining was present in fiber bundles. In the spinal cord, strong immunostaining was present in fiber tracts and in dorsal and ventral roots. Immunostaining outlined perikarya of dorsal and ventral gray columns; the neuropil of the developing gray matter was also stained. Contrary to findings in some other species, precursor cells in the proliferating zones, i.e. all cells of ventricular zones and the external granular layer in the developing cerebellum, were not stained. Reactivity, however, was also observed in single mature‐looking nerve cell bodies and their processes, which were localized in proliferating zones. All peripheral nervous structures including nerve fibers and peripheral nervous tissue components derived from the neural crest (i.e. sensory and autonomic ganglia) expressed the neural cell adhesion molecule. At the cellular level staining always appeared to be associated with the entire cell membrane of a given neuron including its outgrowing processes. Immunocytochemical staining for neural cell adhesion molecule is an excellent method for the identification of single nerve fibers, nerves and nerve cell bodies in situ in the developing peripheral and early central nervous system. The neural cell adhesion molecule is suggested as a marker of postmigratory immature neurons in the developing human nervous system.
Expression in murine and human neuroblastoma cell lines of VGF, a tissue specific protein
Authors: Rossi Adelaide , Granata Filippo , Augusti‐Tocco Gabriella , Canu Nadia , Levi Andrea , Possenti Roberta
Published: April 2003

Screening by different means has demonstrated the presence, in human and murine neuroblastoma cell lines, of VGF, a gene product identified in a limited number of neuronal and endocrine cells. Indirect immunofluorescence and Western and Northern blot analyses have shown the presence of this protein in some of the tested lines, confirming that VGF is not an ubiquitous molecule. Further studies, using human SK‐N‐BE and murine N18TG2 lines, showed that VGF expression is upregulated during differentiation, suggesting that various species, including man, express VGF and regulate it in a similar manner. The subcellular localization of the protein, which is associated with vesicles, its electrophoretic molecular profile and its specific release under different conditions are all consistent with results reported in other cells. Neuroblastomas are thus added to the class of VGF‐positive cells and provide a new in vitro model for investigation of the structural and functional properties of this protein.
Synaptic ribbons, spheres and intermediate structures in the developing rat retina
Authors: Hermes Birgit , Reuss Stefan , Vollrath Lutz
Published: April 2003

The present study was conducted to investigate the qualitative and quantitative development of synaptic bodies in retinae of Wistar rats during postnatal days 4–28. In addition, the effects of different light regimens and of eye pigmentation on SB numbers were studied. Synaptic bodies were counted and measured in the outer plexiform layer of retinal tissue fixed and processed by routine electron microscopical techniques.

At postnatal days 4 and 5, retinae showed only few synaptic bodies. The main numerical development of synaptic bodies occurred between postnatal days 4 and 9, numbers remaining more or less constant thereafter. The intracellular location of synaptic ribbons changed from predominantly cytoplasmic sites to positions at the membrane. In Wistar rats of postnatal day 15 held under a light/dark regimen, synaptic ribbon numbers and lengths were found to be significantly larger at night than at daytime. This was not observed in animals kept under constant darkness. In retinae of a pigmented rat strain, Brown Norway, total numbers of synaptic bodies were similar to those of Wistar rats, whereas the relative proportions of synaptic ribbons and spheres or sphere‐like structures, respectively, differed between strains. These results are discussed with regard to synaptic body formation and regulation under the influence of light and eye pigmentation.
Transplantation of oligodendrocyte precursors in the adult demyelinated spinal cord: Migration and remyelination
Authors: Vignais L. , Oumesmar B. Nait , Mellouk F. , Gout O. , Labourdette G. , Baron‐Van Evercooren A. , Gumpel M.
Published: April 2003

A demyelinating lesion induced by an injection of lysolecithin into the spinal cord can be partly repaired by oligodendrocyte precursors transplanted at a distance of 6–8 mm from the lesion. Using a non‐toxic fluorescent dye (Hoechst 33342) as a cell marker, we demonstrate that transplanted oligodendrocyte precursors from different origins (periventricular zone fragments from newborn mouse and cultured rat oligodendrocyte progenitor cells) can migrate along specific pathways (i.e. white matter fasciculi, ependymal wall, meninges and blood vessels). These cells can be attracted when passing at the vicinity of the lesion as well as differentiate and remyelinate axons with the lesion. Myelin repair thus appears to be the result of distinct successive events: migration, specific attraction, differentiation and myelination. This can occur in both shiverer and normal adult hosts.
Requirements for schwann cell migration within cns environments: A viewpoint
Authors: Franklin R.J.M. , Blakemore W.F.
Published: April 2003

Schwann cells are able to migrate into the CNS and myelinate CNS axons in a number of developmental and pathological situations. Morphological studies based on normal, mutant and experimentally‐lesioned tissue have indicated that Schwann cells are only able to enter the CNS when the integrity of the astrocytic glia limitans is disrupted. The significance and subtlety of the interactions between Schwann cells and astrocytes have been further explored by glial cell transplantation studies. These studies support in vitro observations on Schwann cell behaviour in highlighting the importance of extracellular matrix for both migration and myelin sheath formation. The failure of Schwann cells to intermix with astrocytes is an important aspect of glial cell biology which will have a bearing on efforts to remyelinate demyelinated axons by Schwann cell‐transplantation.
High gelsolin content of developing oligodendrocytes
Authors: Léna J.Y. , Legrand Ch. , Faivre‐Sarrailh C. , Sarliéve L.L. , Ferraz C. , Rabié A.
Published: April 2003

The actin‐binding protein gelsolin that severs and caps the actin microfilaments under the control of the cytoplasmic free calcium and the membranous phosphatidylinositol 4,5‐bisphosphate, is essentially restricted to the oligodendroglia in the central nervous system. Immunocytochemistry showed that gelsolin is an early marker of oligodendrocytes, both in vivo, in the rat cerebellum, and in vitro, in oligodendrocyte culture. We report the early appearance of gelsolin in A2B5‐positive precursor oligodendrocyte cells and the specific expression of gelsolin in OL‐1‐, GC‐, and MBP‐positive oligodendrocytes in culture. The protein was distributed throughout the cell body and in the branched cell processes of cultured oligodendrocytes, but not in the MBP‐positive membrane sheets. Gelsolin is thus cytosolic and not a myelin component. The quantitative study demonstrated that the cerebellar gelsolin content changes significantly with age, with the maximal value at the age of 21 days, confirming that large amounts of gelsolin are transiently synthesized during development, especially from the first events of myelinogenesis. The results are consistent with gelsolin being involved, through its effects on the actin cytoskeleton, in the motile events occurring during the growth of the oligodendroglial processes towards the axons and the wrapping of the myelin sheaths around the axons.
BRCA1–Sp1 interactions in transcriptional regulation of the IGF‐IR gene
Authors: Abramovitch Shirley , Glaser Tova , Ouchi Toru , Werner Haim
Published: April 2003

The insulin‐like growth factor‐I receptor (IGF‐IR) plays a critical role in breast tumorigenesis and is overexpressed in most primary tumors. BRCA1 is a transcription factor involved in numerous cellular processes, including DNA damage repair, cell growth, and apoptosis. Consistent with its tumor suppressor role, we demonstrated that BRCA1 repressed the activity of co‐transfected IGF‐IR promoter reporter constructs in a number of breast cancer‐derived cell lines. Results of electrophoretic mobility shift assay showed that BRCA1 did not exhibit any specific binding to the IGF‐IR promoter, although it prevented binding of Sp1. Co‐immunoprecipitation experiments demonstrated that BRCA1 action was associated with specific interaction with Sp1 protein. Furthermore, using a series of glutathione S‐transferase‐tagged BRCA1 fragments, we mapped the Sp1‐binding domain to a segment located between aa 260 and 802. In summary, our data suggest that the IGF‐IR gene is a novel downstream target for BRCA1 action.
GDF‐5 deficiency in mice delays Achilles tendon healing
Authors: Chhabra A. , Tsou D. , Clark R. T. , Gaschen V. , Hunziker E. B. , Mikic B.
Published: April 2003

The aim of this study was to examine the role of one of the growth/differentiation factors, GDF‐5, in the process of tendon healing. Specifically, we tested the hypothesis that GDF‐5 deficiency in mice would result in delayed Achilles tendon repair. Using histologic, biochemical, and ultrastructural analyses, we demonstrate that Achilles tendons from 8‐week‐old male GDF‐5 –/– mice exhibit a short‐term delay of 1–2 weeks in the healing process compared to phenotypically normal control littermates. Mutant animals took longer to achieve peak cell density, glycosaminoglycan content, and collagen content in the repair tissue, and the time course of changes in collagen fibril size was also delayed. Revascularization was delayed in the mutant mice by 1 week. GDF‐5 deficient Achilles tendons also contained significantly more fat within the repair tissue at all time points examined, and was significantly weaker than control tissue at 5 weeks after surgery, but strength differences were no longer detectable by 12‐weeks. Together, these data support the hypothesis that GDF‐5 may play an important role in modulating tendon repair, and are consistent with previously posited roles for GDF‐5 in cell recruitment, migration/adhesion, differentiation, proliferation, and angiogenesis. © 2003 Orthopaedic Research Society. Published by Elsevier Science Ltd. All rights reserved.
Quadriceps strength and volitional activation before and after total knee arthroplasty for osteoarthritis
Authors: Stevens Jennifer E. , Mizner Ryan L. , Snyder‐Mackler Lynn
Published: April 2003

Introduction: Patients with osteoarthritis (OA) of the knee have quadriceps weakness and arthrogenous muscle inhibition (AMI). While total knee arthroplasty (TKA) reliably reduces pain and improves function in patients with knee OA, quadriceps weakness persists after surgery. The purpose of this investigation was to assess contributions of AMI to quadriceps weakness before and after TKA and to assess the effect of pain on AMI.

Methods: Twenty‐eight patients with unilateral, end‐stage, primary knee OA were tested an average of 10 days before and 26 days after TKA. The mean age at time of operation was 63 years (range 49–82 years). Measurements on the involved and uninvolved knees were performed using the burst‐superimposition technique, where supramaximal electrical stimulation is superimposed on a voluntary contraction. Knee pain during contraction was measured using a numeric rating scale.

Results: The involved quadriceps were significantly weaker than the uninvolved prior to TKA (p < 0.05). Quadriceps strength decreased by 60% (p < 0.001) and activation decreased 17% (p < 0.001) after TKA. Changes in muscle activation accounted for 65% of the variability in the change in quadriceps strength (r2 = 0.65) (p < 0.001). Knee pain during muscle contraction accounted for a small, but significant portion of the change in voluntary activation (r2 = 0.22) (p = 0.006).

Discussion: Exercise regimens that emphasize strong muscle contraction and clinical tools that facilitate muscle activation like biofeedback and neuromuscular electrical stimulation may be necessary to reverse the quadriceps activation failure and weakness in the patients with knee OA that worsens after TKA. The failure of current rehabilitation regimens to directly address activation deficits within the first months after surgery may explain the persistent quadriceps weakness in patients after TKA. © 2003 Orthopaedic Research Society. Published by Elsevier Science Ltd. All rights reserved.
Differential effects of static and dynamic compression on meniscal cell gene expression
Authors: Upton Maureen L. , Chen Jun , Guilak Farshid , Setton Lori A.
Published: April 2003

Cells of the meniscus are exposed to a wide range of time‐varying mechanical stimuli that may regulate their metabolic activity in vivo. In this study, the biological response of the meniscus to compressive stimuli was evaluated in vitro, using a well‐controlled explant culture system. Gene expression for relevant extracellular matrix proteins was quantified using real‐time RT‐PCR following a 24 h period of applied static (0.1 MPa compressive stress) or dynamic compression (0.08–0.16 MPa). Static and dynamic compression were found to differentially regulate mRNA levels for specific proteins of the extracellular matrix. Decreased mRNA levels were observed for decorin (∼︁2.1 fold‐difference) and type II collagen (∼︁4.0 fold‐difference) following 24 h of dynamic compression. Decorin mRNA levels also decreased following static compression (∼︁4.5 fold‐difference), as did mRNA levels for both types I (∼︁3.3 fold‐difference) and II collagen (∼︁4.0 fold‐difference). Following either static or dynamic compression, mRNA levels for aggrecan, biglycan and cytoskeletal proteins were unchanged. It is noteworthy that static compression was associated with a 2.6 fold‐increase in mRNA levels for collagenase, or MMP‐1, suggesting that the homeostatic balance between collagen biosynthesis and catabolism was altered by the mechanical stimuli. These findings demonstrate that the biosynthetic response of the meniscus to compression is regulated, in part, at the transcriptional level and that transcription of types I and II collagen as well as decorin may be regulated by common mechanical stimuli. © 2003 Orthopaedic Research Society. Published by Elsevier Science Ltd. All rights reserved.
The postnatal development of the hypothalamic–pituitary–adrenal axis in the mouse
Authors: Schmidt M. , Enthoven L. , van der Mark M. , Levine S. , de Kloet E.R. , Oitzl M.S.
Published: April 2003

The main characteristic of the postnatal development of the stress system in the rat is the so‐called stress hypo‐responsive period (SHRP). Lasting from postnatal day (pnd) 4 to pnd 14, this period is characterized by very low basal corticosterone levels and an inability of mild stressors to induce an enhanced ACTH and corticosterone release. During the last years, the mouse has become a generally used animal in stress research, also due to the wide availability of genetically modified mouse strains. However, very few data are available on the ontogeny of the stress system in the mouse. This study therefore describes the postnatal ontogeny of peripheral and central aspects of the hypothalamic–pituitary–adrenal (HPA) axis in the mouse. We measured ACTH and corticosterone in blood and CRH, urocortin 3 (UCN3), mineralocorticoid receptor (MR) and glucocorticoid receptor (GR) transcripts in the brain at postnatal days 1, 2, 4, 6, 9, 12, 14 and 16. Our results show that we can subdivide the postnatal development of the HPA axis in the mouse in two phases. The first phase corresponds to the SHRP in the rat and lasts from right after birth (pnd 1) until pnd 12. Basal corticosterone levels were low and novelty exposure did not enhance corticosterone or ACTH levels. This period is further characterized by a high expression of CRH in the paraventricular nucleus (PVN) of the hypothalamus. Expression levels of GR in the hippocampus and UCN3 in the perifornical area are low at birth but increase significantly during the SHRP, both reaching the highest expression level at pnd 12. In the second phase, the mice have developed past the SHRP and were now exhibiting enhanced corticosterone basal levels and a response of ACTH and corticosterone to mild novelty stress. CRH expression was decreased significantly, while expression of UCN3 and GR remained high, with a small decrease at pnd 16. The expression of MR in the hippocampus was very dynamic throughout the postnatal development of the HPA axis and changed in a time and subregion specific manner. These results demonstrate for the first time the correlation between the postnatal endocrine development of the mouse and gene expression changes of central regulators of HPA axis function.
Is presidential cycle in security returns merely a reflection of business conditions?
Authors: Booth James R , Booth Lena Chua
Published: April 2003

We confirm previous findings that both large‐cap and small‐cap stock returns in the US exhibit a presidential cycle pattern, i.e. returns are significantly higher in the last 2 years than in the first 2 years of the presidential term. We attempt to examine if this presidential cycle pattern can be explained away by the traditional business cycle proxies, namely the term spread (TERM), dividend yield (D/P), and default spread (DEF). Our motivation arises from the political business cycle theory that monetary and fiscal measures undertaken by presidents are usually translated into the business cycle. We find that the presidential cycle has explanatory power beyond business conditions proxies shown to be important in explaining stock returns. Tests of slope parameters show that stock returns are less sensitive to only the D/P during the last 2 years of the presidential term. The presidential cycle effect prevails even after controlling for the party in power and the incumbent versus nonincumbent presidents.
The sense of presence in virtual environments:
Authors: Schubert Thomas W.
Published: April 2003

Abstract. The sense of presence is the feeling of being there in a virtual environment. A three-component self report scale to measure sense of presence is described, the components being sense of spatial presence, involvement, and realness. This three-component structure was developed in a survey study with players of 3D games (N = 246) and replicated in a second survey study (N = 296); studies using the scale for measuring the effects of interaction on presence provide evidence for validity. The findings are explained by the Potential Action Coding Theory of presence, which assumes that presence develops from mental model building and suppression of the real environment.
The internal alternative NADH dehydrogenase of Neurospora crassa mitochondria
Authors: DUARTE Margarida , PETERS Markus , SCHULTE Ulrich , VIDEIRA Arnaldo
Published: April 2003

An open reading frame homologous with genes of non-proton-pumping NADH dehydrogenases was identified in the genome of Neurospora crassa. The 57 kDa NADH:ubiquinone oxidoreductase acts as internal (alternative) respiratory NADH dehydrogenase (NDI1) in the fungal mitochondria. The precursor polypeptide includes a pre-sequence of 31 amino acids, and the mature enzyme comprises one FAD molecule as a prosthetic group. It catalyses specifically the oxidation of NADH. Western blot analysis of fungal mitochondria fractionated with digitonin indicated that the protein is located at the inner face of the inner membrane of the organelle (internal enzyme). The corresponding gene was inactivated by the generation of repeat-induced point mutations. The respiratory activity of mitochondria from the resulting null-mutant ndi1 is almost fully inhibited by rotenone, an inhibitor of the proton-pumping complex I, when matrix-generated NADH is used as substrate. Although no effects of the NDI1 defect on vegetative growth and sexual differentiation were observed, the germination of both sexual and asexual ndi1 mutant spores is significantly delayed. Crosses between the ndi1 mutant strain and complex I-deficient mutants yielded no viable double mutants. Our data indicate: (i) that NDI1 represents the sole internal alternative NADH dehydrogenase of Neurospora mitochondria; (ii) that NDI1 and complex I are functionally complementary to each other; and (iii) that NDI1 is specially needed during spore germination.
Curcumin activates the haem oxygenase-1 gene via regulation of Nrf2 and the antioxidant-responsive element
Authors: BALOGUN Elisabeth , HOQUE Martha , GONG Pengfei , KILLEEN Erin , GREEN Colin J. , FORESTI Roberta , ALAM Jawed , MOTTERLINI Roberto
Published: April 2003

The transcription factor Nrf2, which normally exists in an inactive state as a consequence of binding to a cytoskeleton-associated protein Keap1, can be activated by redox-dependent stimuli. Alteration of the Nrf2–Keap1 interaction enables Nrf2 to translocate to the nucleus, bind to the antioxidant-responsive element (ARE) and initiate the transcription of genes coding for detoxifying enzymes and cytoprotective proteins. This response is also triggered by a class of electrophilic compounds including polyphenols and plant-derived constituents. Recently, the natural antioxidants curcumin and caffeic acid phenethyl ester (CAPE) have been identified as potent inducers of haem oxygenase-1 (HO-1), a redox-sensitive inducible protein that provides protection against various forms of stress. Here, we show that in renal epithelial cells both curcumin and CAPE stimulate the expression of Nrf2 in a concentration- and time-dependent manner. This effect was associated with a significant increase in HO-1 protein expression and haem oxygenase activity. From several lines of investigation we also report that curcumin (and, by inference, CAPE) stimulates ho-1 gene activity by promoting inactivation of the Nrf2–Keap1 complex, leading to increased Nrf2 binding to the resident ho-1 AREs. Moreover, using antibodies and specific inhibitors of the mitogen-activated protein kinase (MAPK) pathways, we provide data implicating p38 MAPK in curcumin-mediated ho-1 induction. Taken together, these results demonstrate that induction of HO-1 by curcumin and CAPE requires the activation of the Nrf2/ARE pathway.
Anisotropy of the magnetoresistance in the case of trapping of magnetic fields in granular bismuth-containing high-Tc superconductors
Authors: Sukhanov A. A. , Omelchenko V. I.
Published: April 2003

A study is made of the features of the magnetoresistance in ceramic Bi(Pb)-HTSCs containing trapped magnetic fields. It is found that upon trapping of magnetic flux in these granular HTSCs their magnetoresistance becomes anisotropic. For magnetic fields H parallel to the field Hi that has initiated the trapping and for currents perpendicular to Hi, the field dependence of the magnetoresistance ΔR(H) is nonmonotonic, and the magnetoresistance at low magnetic fields H<Hinv is negative. The influence on ΔR(H) of the values and orientation of the trapped field and the transport current is investigated. In particular, it is found that the field Hinv at which inversion of the sign of the magnetoresistance occurs increases in a practically linear manner with increasing effective trapped magnetic fields, decreases to zero as the angle between the directions of the fields H and Hi increases to π/2, and decreases weakly with increasing transport current. The results are explained in the framework of a model of magnetic flux trapping in superconducting granules or superconducting “rings” embedded in a matrix of weak links.
A mechanism for tearing onset near ideal stability boundaries
Authors: Brennan D. P. , La Haye R. J. , Turnbull A. D. , Chu M. S. , Jensen T. H. , Lao L. L. , Luce T. C. , Politzer P. A. , Strait E. J. , Kruger S. E. , Schnack D. D.
Published: April 2003

The prevention of neoclassical tearing modes (NTMs) in tokamak plasmas is a major challenge for fusion. Ideal modes can seed NTMs through forced reconnection, yet in sawtoothing discharges it is not well understood why a particular sawtooth crash seeds a NTM after several preceding sawteeth did not. Also, tearing modes sometimes appear and grow without an obvious ideal mode causing a seed island. Based on theoretical and experimental results a new mechanism for tearing mode onset is proposed and tested which explains these puzzling observations. Tearing stability calculations based on experimental equilibria from the DIII-D tokamak [J. L. Luxon and L. G. Davis, Fusion Technol. 8, 441 (1985)] indicate that tearing modes can be driven unstable by a rapid increase in the linear tearing stability index Δ′ just before onset. Near the ideal kink limit in βN≡β/(I/aBT), Δ′ becomes large and positive as it approaches a pole discontinuity. The relative time scales of the change in Δ′ vs the effects of finite island width will determine the evolution of the island, and the eventual nonlinear state. Theoretical predictions of the onset point, the βN at a specified small island width, and the early evolution characteristics are compared with results from new DIII-D experiments designed specifically to test this hypothesis. Time integration of the island evolution equation shows that these predictions are consistent with the experimental observations. The nonlinear 3D resistive magnetohydrodynamic code NIMROD [A. H. Glasser et al., Plasma Phys. Control. Fusion 41, A747 (1999)] is used to evolve equilibria reconstructed from these experiments in time to provide a more comprehensive prediction of the island evolution during the early nonlinear phase. The simulations are also consistent with the proposed mechanism.
Hot plasma in clusters of galaxies, the largest objects in the Universe
Authors: Sarazin Craig L.
Published: April 2003

Clusters of galaxies are the largest organized structures in the Universe. They are important cosmological probes, since they are large enough to contain a fair sample of the materials in the Universe, but small enough to have achieved dynamical equilibrium. Clusters were first discovered as concentrations of hundreds of bright galaxies in a region about 3 megaparsecs (10 million light years) across. However, the dominant observed form of matter in clusters is hot, diffuse intergalactic gas. This intracluster plasma has typical temperatures of T∼7×107 K, and typical electron densities of ne∼10−3 cm−3. This intracluster plasma mainly emits x rays, and typical cluster x-ray luminosities are LX∼1043–1045 erg/s. The basic properties of and physical processes in the intracluster plasma will be reviewed. Important observational constraints on plasma processes in these systems will be discussed. Recent x-ray observations of clusters of galaxies with the orbiting Chandra X-Ray Observatory will be highlighted.
Nonlinear δ f simulations of collective effects in intense charged particle beams
Authors: Qin Hong
Published: April 2003

A nonlinear δf particle simulation method based on the Vlasov–Maxwell equations has been recently developed to study collective processes in high-intensity beams, where space-charge and magnetic self-field effects play a critical role in determining the nonlinear beam dynamics. Implemented in the Beam Equilibrium, Stability and Transport (BEST) code [H. Qin, R. C. Davidson, and W. W. Lee, Phys. Rev. ST Accel. Beams 3, 084401 (2000); 3, 109901 (2000)], the nonlinear δf method provides a low-noise and self-consistent tool for simulating collective interactions and nonlinear dynamics of high-intensity beams in modern and next generation accelerators and storage rings, such as the Spallation Neutron Source and heavy ion fusion drivers. A wide range of linear eigenmodes of high intensity charged particle beams can be systematically studied using the BEST code. Simulation results for the electron–proton two-stream instability in the Proton Storage Ring experiment [R. Macek et al., in Proceedings of the Particle Accelerator Conference, Chicago, 2001 (IEEE, Piscataway, NJ, 2001), Vol. 1, p. 688] at the Los Alamos National Laboratory agree well with experimental observations. Large-scale parallel simulations have also been carried out for the ion–electron two-stream instability in the very-high-intensity heavy ion beams envisioned for heavy ion fusion applications. In both cases, the simulation results indicate that the dominant two-stream instability has a dipole-mode (hose-like) structure and can be stabilized by a modest axial momentum spread of the beam particles.
Performance and stability of near-unity aspect ratio plasmas in the Pegasus Toroidal Experiment
Authors: Garstka G. D. , Diem S. J. , Fonck R. J. , Lewicki B. T. , Sontag A. C. , Tritz K. L. , Unterberg E. A.
Published: April 2003

The Pegasus Toroidal Experiment [R. Fonck et al., Bull. Am. Phys. Soc. 41, 1400 (1996)] is a spherical torus designed to study the limits of plasma behavior as the aspect ratio A approaches unity. Access to near-unity A is achieved through the use of a novel high-stress reinforced solenoid magnet. High toroidal beta βt is obtained in ohmically-heated plasmas by operation at low field with densities up to the Greenwald limit. Values of βt up to 20% and normalized beta up to 5 have been obtained. The ratio of plasma current to toroidal field rod current, known as the toroidal field utilization, reaches values as large as 1 but appears to approach a “soft” boundary at that level related to both ohmic flux limitations and the onset of resistive magnetohydrodynamic (MHD) activity. The m/n=2/1 and 3/2 modes are most frequently observed, in agreement with the inferred safety factor profiles. Experiments are beginning to access the external kink stability boundary at edge safety factor q95=5, which is significantly higher than that observed in conventional tokamaks. Calculations using the DCON code [A. H. Glasser and M. S. Chance, Bull. Am. Phys. Soc. 42, 1848 (1997)] confirm instability to the ideal kink.
Frequency chirp and pulse shape effects in self-modulated laser wakefield accelerators
Authors: Schroeder C. B. , Esarey E. , Geddes C. G. R. , Tóth Cs. , Shadwick B. A. , van Tilborg J. , Faure J. , Leemans W. P.
Published: April 2003

The effect of asymmetric laser pulses on plasma wave excitation in a self-modulated laser wakefield accelerator is examined. Laser pulse shape and frequency chirp asymmetries, controlled experimentally in the laser system through a grating pair compressor, are shown to strongly enhance measured electron yields for certain asymmetries. It is shown analytically that a positive (negative) frequency chirp enhances (suppresses) the growth rate of the Raman forward scattering and near-forward Raman sidescatter instabilities, but is of minimal importance for the experimental parameters. Temporal laser pulse shapes with fast rise times (≲ plasma period) are shown to generate larger wakes (compared to slow rise time pulses) which seed the growth of the plasma wave, resulting in enhanced electron yield.
Hysteresis-like effects in gyrotron oscillators
Authors: Dumbrajs O. , Idehara T. , Iwata Y. , Mitsudo S. , Ogawa I. , Piosczyk B.
Published: April 2003

Special experiments devoted to studying hysteresis in gyrotron oscillators have been performed for the first time. Clear hysteresis-like effects with respect to variation of the cathode voltage have been observed in the mode competition scenario of the Forschungszentrum Karlsruhe coaxial gyrotron [B. Piosczyk et al., IEEE Trans. Plasma Sci. 30, 818 (2002)] and with respect to variation of the magnetic field and voltage in a single-mode operation of the Fukui IV gyrotron [T. Idehara et al., Int. J. Infrared Millim. Waves 19, 793 (1998)]. The observed phenomena are explained theoretically.
Effect of the intermediate state on the loop-to-coil transition of a telechelic chain
Authors: Sheng Yu-Jane , Lin Han-Jou , Chen Jeff Z. Y. , Tsao Heng-Kwong
Published: April 2003

The kinetics of conformational fluctuations of a telechelic chain with two binding sites at both ends is studied by Monte Carlo simulations. The site-to-site binding energy is −ε. An example of the telechelic biopolymer is RNA or ssDNA made of a homogeneous sequence such as poly(T) with complementary bases at both ends. The conformation of such a chain fluctuate from loop (closed) to coil (open) state and the probability of the coil state depends on the temperature. An all-or-none transition between open and closed states is often adopted to depict the melting curves. It is found that the two-state model fails due to the existence of the intermediate state. A three-state model including open, intermediate, and closed states is proposed. The melting curves obtained from such a scenario agree quite well with the simulation results and there are two characteristic temperatures. The rate constants from closed to intermediate states kc,i and from intermediate to open states ki,o are independent of chain length but proportional to e−ε/kT. In contrast, the rate constants from open to intermediate states ko,i is independent of temperature and that from intermediate to closed states ki,c is essentially constant.
Wave scattering in waveguides
Authors: Dacol Dalcio K. , Roy Dilip G.
Published: April 2003

The scattering of scalar waves by objects located inside a waveguide or a cavity is discussed using the method of pseudopotentials. Pseudopotentials were introduced to simulate short-range potentials in quantum mechanics and proved useful in many-body problems and in problems involving multicentered potentials. In this work it is shown that this approach can also be used to describe the scattering of classical scalar waves by objects confined to the interior of a waveguide or a cavity in terms of the scattering amplitudes of those objects in an extended medium.
Electron beam pumped KrF lasers for fusion energy
Authors: Sethian J. D. , Friedman M. , Giuliani J. L. , Lehmberg R. H. , Obenschain S. P. , Kepple P. , Wolford M. , Hegeler F. , Swanekamp S. B. , Weidenheimer D. , Welch D. , Rose D. V. , Searles S.
Published: April 2003

In this paper, we describe the development of electron beam pumped KrF lasers for inertial fusion energy. KrF lasers are an attractive driver for fusion, on account of their demonstrated very high beam quality, which is essential for reducing imprint in direct drive targets; their short wavelength (248 nm), which mitigates the growth of plasma instabilities; and their modular architecture, which reduces development costs. In this paper we present a basic overview of KrF laser technology as well as current research and development in three key areas: electron beam stability and transport; KrF kinetics and laser propagation; and pulsed power. The work will be cast in context of the two KrF lasers at the Naval Research Laboratory, The Nike Laser (5 kJ, single shot), and The Electra Laser (400–700 J repetitively pulsed).
A consistent approach to solving the radiation diffusion equation
Authors: Hammer James H. , Rosen Mordecai D.
Published: April 2003

Diffusive x-ray-driven heat waves are found in a variety of astrophysical and laboratory settings, e.g., in the heating of a hohlraum used for inertial confinement fusion, and hence are of intrinsic interest. However, accurate analytic diffusion wave (also called Marshak wave) solutions are difficult to obtain due to the strong nonlinearity of the radiation diffusion equation. The typical approach is to solve near the heat front, and by ansatz apply the solution globally. This approach works fairly well due to “steepness” of the heat front, but energy is not conserved and it does not lead to a consistent way of correcting the solution or estimating accuracy. In this work, the steepness of the front is employed through a perturbation expansion in ε=β/(4+α), where the internal energy varies as Tβ and the opacity varies as T−α. The equations are solved using an iterative approach, equivalent to asymptotic methods that match outer (away from the front) and inner (near the front) solutions. Typically ε<0.3. Calculations through first order in ε and are accurate to ∼10%, which is comparable to the inaccuracy from assuming power laws for material properties. Supersonic waves with arbitrary drive time history are solved for, including the case of a rapidly cooling surface. The method is then generalized to arbitrary temperature dependence of opacity and internal energy. Also solved for are subsonic waves with drive temperature varying as a power of time. In the subsonic case, the specific heat (pressure/density) and opacity are each assumed to vary as density to a small power, of order ε. Solutions are obtained through order ε2 and it is found that the theory compares well with radiation hydrodynamics code calculations of the heat front position, absorbed flux, and ablation pressure.
Effect of chain topology of block copolymer on micellization: Ring versus linear block copolymer
Authors: Kim Kwang Hee , Huh June , Jo Won Ho
Published: April 2003

Micellization of ring block copolymer and triblock copolymer in a solvent selective for A-block is investigated by using a mean-field theory and a Brownian dynamics simulation. Theoretically, our findings show that the cmc (critical micelle concentration) of ring block copolymer is lower than that of the triblock copolymer but much higher than that of diblock copolymer. The theoretical prediction qualitatively agrees with the simulation results. This difference of cmc is originated from the difference in architectural constraint imposed to reduce the conformational freedom of copolymer in the micellar state.
Evaporation dynamics of mixed Lennard-Jones atomic clusters
Authors: Parneix P. , Bréchignac Ph.
Published: April 2003

Molecular dynamics (MD) simulations have been run to study the evaporation process of a model Lennard-Jones cluster, namely ArnXm, in which X is an artificial atom whose properties can be adjusted. The influence of changes in its Lennard-Jones parameters (binding energies D and distance σ) and its mass has been explored in a systematic way in the case of various seven-atom clusters on: (i) The outcome of Ar3X4 evaporation (chemical composition of the product cluster) and (ii) the evaporation rate constant in the series of Ar7−mKrm. It is shown that a proper choice of the X atom parameters allows to enhance the evaporation rate constant of ArnX in a way which enables to explore by MD the dynamics at much lower values of internal energy. Consequently the “melting” transition in Ar7 and Ar13 product clusters can be investigated by the analysis of the mean kinetic-energy release. In the latter case it is shown to be in excellent agreement with phase space theory predictions.
Basic and integrated studies for fast ignition
Authors: Tanaka K. A. , Kodama R. , Mima K. , Kitagawa Y. , Fujita H. , Miyanaga N. , Nagai K. , Norimatsu T. , Sato T. , Sentoku Y. , Shigemori K. , Sunahara A. , Shozaki T. , Tanpo M. , Tohyama S. , Yabuuchi T. , Zheng J. , Yamanaka T. , Norreys P. A. , Evanse R. , Zepf M. , Krushelnic K. , Dangor A. , Stephens R. , Hatchett S. , Tabak M. , Turner R.
Published: April 2003

Basic and integrated studies are conducted on fast ignition (FI) using various large laser systems. A Peta watt (PW) laser system is used to study the basic elements relevant to FI and can also be injected to a compressed core to test the FI integrated experiment when coupled with a GEKKO twelve laser beam system. Using a spherical target inserted with a Au cone guide for the PW laser pulse, an imploded core is heated up to 1 keV resulting in neutron increase 1000 times more than that without heating pulse. Details of the implosion are examined at the Omega laser system of this type target with indirect implosion scheme and are compared with simulation results. LASNEX simulation indicates that a 400 g/c.c. high density core could be achieved with this scheme at 1.8 MJ laser input.
Transport of edge localized modes energy and particles into the scrape off layer and divertor of DIII-D
Authors: Leonard A. W. , Osborne T. H. , Fenstermacher M. E. , Groebner R. J. , Groth M. , Lasnier C. J. , Mahdavi M. A. , Petrie T. W. , Snyder P. B. , Watkins J. G. , Zeng L.
Published: April 2003

The reduction in size of Type I edge localized modes (ELMs) with increasing density is explored in DIII-D [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] for the purpose of studying the underlying transport of ELM energy. The separate convective and conductive transport of energy due to an ELM is determined by Thomson scattering measurements of electron density and temperature in the pedestal. The conductive transport from the pedestal during an ELM decreases with increasing density, while the convective transport remains nearly constant. The scaling of the ELM energy loss is compared with an edge stability model. The role of the divertor sheath in limiting energy loss from the pedestal during an ELM is explored. Evidence of outward radial transport to the midplane wall during an ELM is also presented.
GaAs-based near-infrared omnidirectional reflector
Authors: Park Yeonsang , Roh Young-Geun , Cho Chi-O , Jeon Heonsu , Sung Min Gyu , Woo J. C.
Published: April 2003

We introduce a compound-semiconductor-based omnidirectional reflector. A four-layer-pair stack of GaAs/AlAs was grown epitaxially using molecular-beam epitaxy, and was then converted to a GaAs/Al2O3 multilayer stack by selective oxidation of the AlAs layers. The resultant one-dimensional photonic crystal exhibited omnidirectional reflection properties in near-IR wavelength range below 1 μm. Reflectance spectra measured at various incidence angles and polarizations were observed to be in good agreement with theoretically simulated results.
Surface nanostructuring of borosilicate glass by femtosecond nJ energy pulses
Authors: Vanagas Egidijus , Kudryashov Igor , Tuzhilin Dmitrii , Juodkazis Saulius , Matsuo Shigeki , Misawa Hiroaki
Published: April 2003

We report on a feature, that of hillock-shaped damage, formed on a glass surface by femtosecond pulses of tp=180 fs [full width at half maximum (FWHM) value] duration produced by a recording beam focus with energy of 5 nJ/pulse at 800 nm wavelength (the corresponding irradiance of about 7.6 TW/cm2 was evaluated for a 0.68 μm FWHM spot size). Single hillocks of 40–50 nm height were recorded reproducibly in single-pulse irradiation. Surface nanopatterning over a large, curved area (over 200 μm2) can be achieved by implementing a confocal surface curvature tracking method that utilizes the reflection of a supplementary cw-laser beam. The ablation pattern achieved by this method is consistent with that of a Coulomb explosion.
Carrier leakage in InGaN quantum well light-emitting diodes emitting at 480 nm
Authors: Pope I. A. , Smowton P. M. , Blood P. , Thomson J. D. , Kappers M. J. , Humphreys C. J.
Published: April 2003

Pulsed light–current characteristics of InGaN/GaN quantum well light-emitting diodes have been measured as a function of temperature, with sublinear behavior observed over the whole temperature range, 130–330 K. A distinctive temperature dependence is also noted where the light output, at a fixed current, initially increases with temperature, before reaching a maximum at 250 K and then decreases with subsequent increases in temperature. On the basis of a drift diffusion model, we can explain the sublinear light–current characteristics and the temperature dependence by the influence of the large acceptor ionization energy in Mg-doped GaN together with a triangular density of states function characteristic of localized states. Without the incorporation of localization effects, we are unable to reproduce the temperature dependence whilst maintaining emission at the observed wavelength. This highlights the importance of localization effects on device performance.
Multiple temperature regimes of radiative decay in CdSe nanocrystal quantum dots: Intrinsic limits to the dark-exciton lifetime
Authors: Crooker S. A. , Barrick T. , Hollingsworth J. A. , Klimov V. I.
Published: April 2003

We investigate the strongly temperature-dependent radiative lifetime of electron–hole excitations in colloidal CdSe nanocrystal quantum dots over nearly three orders of magnitude in temperature (300 K to 380 mK). These studies reveal an intrinsic, radiative upper limit of ∼1 μs for the storage of excitons below 2 K. At higher temperatures, exciton lifetimes are consistent with thermal activation from the dark-exciton ground state, but with two different activation thresholds.
The enneagram system for enhancing workplace spirituality
Authors: Kale Sudhir H. , Shrivastava Samir
Published: April 2003

The notion of “spirituality in the workplace” continues to receive growing attention in practitioner as well as academic circles. Realizing that a spiritual workplace is not just a more harmonious workplace but a more profitable workplace as well, companies are looking at means and methods to fulfill spiritual needs of their workforce. This paper makes a case for using the enneagram as a tool for enhancing spirituality in the workplace.
Applying linguistic criteria in FMS selection: fuzzy‐set‐AHP approach
Authors: Shamsuzzaman M. , Sharif Ullah A.M.M. , Bohez Erik L.J.
Published: April 2003

This paper presents a computational framework that combines both fuzzy sets and analytical hierarchy process (AHP) for selecting the best‐ranked flexible manufacturing system from a number of feasible alternatives. Fuzzy sets are employed to recognize the selection criteria as linguistic variables rather than numerical ones, which, in turn, makes the framework quite user‐friendly. AHP is used to determine the due weight of the selection criteria, in accordance with their relative importance. In total, 14 criteria are considered, grouping them into flexibility, cost, productivity, and risk. The criteria under the first three groups are independent (i.e. their own fuzzy sets evaluate them) and the criteria under risk are indirectly evaluated by using the fuzzy sets of the criteria under flexibility. The proposed framework is implemented by developing an expert system called FmsExpert, using Borland C++. The performance of this system is also demonstrated by using an example.
Exploring potential strategic impacts of XML‐related technologies
Authors: Smith Alan D.
Published: April 2003

Extensible Markup Language (XML) made its entry in the late 1990s, but will it deliver real strategic value to businesses? Applying Norman’s and Christensen’s technology s‐curve, XML‐related technologies are currently crossing the transition point, moving from an originally technology‐driven product to predominately customer‐driven, characterized by a more human‐centered product and/or service. A few application areas are developed based on XML technology to satisfy the changing business needs. Companies and organizations will continue to benefit in an ever‐increasing fashion from adopting these technologies as these XML‐related technologies grow and develop in response to the ever‐changing demands of businesses.