488 research outputs found
SIMULATING KNOWLEDGE-GENERATION AND DISTRIBUTION PROCESSES IN INNOVATION COLLABORATIONS AND NETWORKS
Immunohistochemical analysis of spinal cord components in mouse model of experimental autoimmune encephalomyelitis
Introduction. Experimental autoimmune encephalomyelitis (EAE) is a widely used animal model for studying immunopathology of multiple sclerosis (MS) because it repeats the hallmarks of the human disease, such as focal inflammation and demyelination of the central nervous system, subsequently leading to axonal and neuronal loss. The interrelationships, timing and sequence of different pathological processes that lead to histologically observed lesions in SM are still incompletely understood.Material and methods. EAE was induced in female C57Bl/6 mice by active immunization with MOG35-55 antigen. Development of the neurological symptoms in the animals was monitored and on that basis spinal cords were collected in three successive phases of the disease (onset, peak, chronic). Total leukocytes, T cells, macrophages/microglia, oligodendrocytes, damaged axons and surviving neuronal cell bodies were visualized using appropriate immunohistochemical markers and their density was quantitatively assessed using image analysis software.Results. The density of all studied cells except neurons was significantly higher in EAE mice than in the control mice. The density of total leukocytes, T cells, and damaged axons increased from the onset to the peak phase and decreased in the chronic phase to reach values lower than those in the peak phase. The density of macrophages/microglia increased in the peak phase and remained at the elevated level in the chronic phase. Oligodendrocytes showed the highest density in the onset phase and gradually decreased afterwards. The density of neuronal cell bodies decreased only in the chronic phase of the disease.Conclusions. In mouse model of EAE, inflammatory cells predominate in the early phases of the disease. This study shows for the first time that inflammation precedes oligodendrocyte death and neuronal loss and that macrophages/ microglia are the only cells persisting in large numbers in the chronic phase of the disease, probably because of the switch from proinflammatory to anti-inflammatory phenotype
Capability-based governance patterns over the product life-cycle: an agent-based model
In recent literature, there is disagreement over the temporal pattern of vertical governance of firms over the product life-cycle. We use a novel neo-Schumpeterian agent-based simulation model to investigate emerging patterns of vertical governance for different levels of imitability and substitutability of capabilities. We find that, in the mature phase of the product life-cycle, firms generally prefer vertical specialization. However, in the early phase, imitability and substitutability, in interplay, determine the governance form preferred. High imitability frustrates appropriation and thereby discourages integration for synergistic advantages. However, firms need not vertically specialize: under low substitutability, incompatibilities reduce the advantages of specialization. When both substitutability and imitability are low, firms can appropriate the value of their inventions and there is no combinatorial advantage of specialization, so firms predominantly integrate. If substitutability is high and imitability is low, the combinatorial advantage of specialization balances with the synergistic advantage of integration
Capability-based governance patterns over the product life-cycle
We investigate patterns of vertical governance over the product life-cycle as function of the capability regime properties imitability and substitutability. We use a novel neo-Schumpeterian model to study emerging governance patterns. We find that, in the era of incremental change, firms prefer vertical specialization. In the era of ferment, no governance form dominates. Imitability and substitutability, in interplay, determine the governance form preferred. High imitability frustrates appropriation and thereby integration for synergistic advantages. However, firms need not vertically specialize: under low substitutability, incompatibilities reduce the advantages of specialization. When both substitutability and imitability are low, firms can appropriate the value of their inventions and there is no combinatorial advantage of specialization, so firms predominantly integrate. If substitutability is high and imitability is low, the combinatorial advantage of specialization balances with the synergistic advantage of integration
Raman scattering in high temperature superconductors : An integrated view
The common features in the Raman data of high temperature superconductors:
(the cuprates, bismathates, alkali doped fullerides and some organic
superconductors), are analyzed. It was shown that qualitative understanding of
the data can be achieved in terms of non-Fermi liquid models for their normal
state, with appropiate bag mechanisms for the superconducting state.Comment: To appear in Physica B (1996). Invited talk presented by S. N.
Behera, Latex file in revtex style, six figures available on request to first
author (e-mail : [email protected]
Spin-Charge Coupling in lightly doped NdCeCuO
We use neutron scattering to study the influence of a magnetic field on spin
structures of NdCuO. On cooling from room temperature, NdCuO
goes through a series of antiferromagnetic (AF) phase transitions with
different noncollinear spin structures. While a c-axis aligned magnetic field
does not alter the basic zero-field noncollinear spin structures, a field
parallel to the CuO plane can transform the noncollinear structure to a
collinear one ("spin-flop" transition), induce magnetic disorder along the
c-axis, and cause hysteresis in the AF phase transitions. By comparing these
results directly to the magnetoresistance (MR) measurements of
NdCeCuO, which has essentially the same AF structures
as NdCuO, we find that a magnetic-field-induced spin-flop transition,
AF phase hysteresis, and spin c-axis disorder all affect the transport
properties of the material. Our results thus provide direct evidence for the
existence of a strong spin-charge coupling in electron-doped copper oxides.Comment: 12 pages, 12 figure
Polaronic optical absorption in electron-doped and hole-doped cuprates
Polaronic features similar to those previously observed in the photoinduced
spectra of cuprates have been detected in the reflectivity spectra of
chemically doped parent compounds of high-critical-temperature superconductors,
both -type and -type. In NdCuO these features, whose
intensities depend both on doping and temperature, include local vibrational
modes in the far infrared and a broad band centered at 1000 cm.
The latter band is produced by the overtones of two (or three) local modes and
is well described in terms of a small-polaron model, with a binding energy of
about 500 cm. Most of the above infrared features are shown to survive
in the metallic phase of NdCeCu0, BiSrCuO, and
YBaCuO, where they appear as extra-Drude peaks. The occurrence
of polarons is attributed to local modes strongly coupled to carriers, as shown
by a comparison with tunneling results.Comment: File latex, 31 p., submitted to Physical Review B. Figures may be
faxed upon reques
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