1,411 research outputs found
Nondirected axonal growth on basal lamina from avian embryonic neural retina
The vitreous surface of the embryonic avian retinal neuroepithelium was isolated by mechanical disruption of the retina mounted between 2 adhesive substrata. The 200-micron-thick sheath covered an area of up to 1 cm2 and consisted of the vitreal basal lamina with a lamina densa, 2 laminae rarae, and a carpet of ventricular cell endfeet on top of the lamina. The vitreal endfeet were removed by detergent treatment and an extracellular basal lamina was obtained. The laminae were further characterized by immunohistochemistry and immunoblotting. A 190 kDa laminin protein was detected in laminae with and without vitreal endfeet, whereas the membrane-bound neural cell adhesion molecule (N- CAM) was detectable only on the endfeet of the ventricular cells and was absent in the detergent-treated basal laminae. Neither immunoblotting nor immunostaining revealed fibronectin in these preparations. Explants of retina, sensory ganglia, and cerebellum from chick, quail, and mouse were cultured on the basal lamina as a substratum. In all cases axonal outgrowth was excellent, with a growth rate similar to that in situ. Outgrowing axons from sensory ganglia and cerebellar explants were accompanied by migratory cells, which, in the case of sensory ganglia, were flat cells and, in the case of cerebellar explants, resembled granular neurons. Optic axons grew on the laminae in an asymmetric, explant-inherent pattern specific for the position of origin of the explant. On detergent-treated basal laminae, as well as on laminin, the retinal axons grew in a clockwise orientation. This axonal growth pattern was specific for retinal tissue and was not observed with axons from other neural explants. In spite of the excellent substrate properties provided by the substratum, cues for growing axons (toward or away from the optic disk) were not detectable in the basal lamina preparations
Atom Transfer and Single-Adatom Contacts
The point contact of a tunnel tip approaching towards Ag(111) and Cu(111)
surfaces is investigated with a low temperature scanning tunneling microscope.
A sharp jump-to-contact, random in nature, is observed in the conductance.
After point contact, the tip-apex atom is transferred to the surface,
indicating that a one-atom contact is formed during the approach. In sharp
contrast, the conductance over single silver and copper adatoms exhibits a
smooth and reproducible transition from tunneling to contact regime. Numerical
simulations show that this is a consequence of the additional dipolar bonding
between the homoepitaxial adatom and the surface atoms.Comment: 4 pages, 4 figure
Аналитическое описание поверхностей зубьев эволютных передач
Зниження габаритів зубчастих передач є актуальною задачею сучасного машинобудування. Перспективний шлях її розв'язання – застосування еволютних передач із опукло-увігнутим контактом зубців. Отримані рівняння профілів еволютних зубців на основі методу профільних нормалей. Вони необхідні для подальших досліджень якісних показників та міцності еволютних зачеплень.Lowering of dimensions of gears is an actual task of a modern machine industry. The perspective way of its decision is application of evolute gears with the convax-concave contact. On the basis of method of type normal the equations of evolute teeth are got. They are needed for further researches of high-quality indexes and durability of evolute gearings
Nucleation of cracks in a brittle sheet
We use molecular dynamics to study the nucleation of cracks in a two
dimensional material without pre-existing cracks. We study models with zero and
non-zero shear modulus. In both situations the time required for crack
formation obeys an Arrhenius law, from which the energy barrier and pre-factor
are extracted for different system sizes. For large systems, the characteristic
time of rupture is found to decrease with system size, in agreement with
classical Weibull theory. In the case of zero shear modulus, the energy
opposing rupture is identified with the breakage of a single atomic layer. In
the case of non-zero shear modulus, thermally activated fracture can only be
studied within a reasonable time at very high strains. In this case the energy
barrier involves the stretching of bonds within several layers, accounting for
a much higher barrier compared to the zero shear modulus case. This barrier is
understood within adiabatic simulations
Bound States and Critical Behavior of the Yukawa Potential
We investigate the bound states of the Yukawa potential , using different algorithms: solving the Schr\"odinger
equation numerically and our Monte Carlo Hamiltonian approach. There is a
critical , above which no bound state exists. We study the
relation between and for various angular momentum quantum
number , and find in atomic units, , with , ,
, and .Comment: 15 pages, 12 figures, 5 tables. Version to appear in Sciences in
China
Adsorption structure of glycine on TiO2(1 1 0): a photoelectron diffraction determination
High-resolution core-level photoemission and scanned-energy mode photoelectron diffraction (PhD) of the O 1s and N 1s states have been used to investigate the interaction of glycine with the rutile TiO2(1 1 0) surface. Whilst there is clear evidence for the presence of the zwitterion View the MathML sourceCH2COO− with multilayer deposition, at low coverage only the deprotonated glycinate species, NH2CH2COO is present. Multiple-scattering simulations of the O 1s PhD data show the glycinate is bonded to the surface through the two carboxylate O atoms which occupy near-atop sites above the five-fold-coordinated surface Ti atoms, with a Ti–O bondlength of 2.12 ± 0.06 Å. Atomic hydrogen arising from the deprotonation is coadsorbed to form hydroxyl species at the bridging oxygen sites with an associated Ti–O bondlength of 2.01 ± 0.03 Å. Absence of any significant PhD modulations of the N 1s emission is consistent with the amino N atom not being involved in the surface bonding, unlike the case of glycinate on Cu(1 1 0) and Cu(1 0 0)
Pattern formation from consistent dynamical closures of uniaxial nematic liquid crystals
Pattern formation in uniaxial polymeric liquid crystals is studied for
different dynamic closure approximations. Using the principles of mesoscopic
non-equilibrium thermodynamics in a mean-field approach, we derive a
Fokker-Planck equation for the single-particle non-homogeneous distribution
function of particle orientations and the evolution equations for the second
and fourth order orientational tensor parameters. Afterwards, two dynamic
closure approximations are discussed, one of them considering the relaxation of
the fourth order orientational parameter and leading to a novel expression for
the free-energy like function in terms of the scalar order parameter.
Considering the evolution equation of the density of the system and values of
the interaction parameter for which isotropic and nematic phases coexist, our
analysis predicts that patterns and traveling waves can be produced in
lyotropic uniaxial nematics even in the absence of external driving.Comment: 34 pages, 7 figure
Expression of human milk fat globulin proteins in cells of haemopoietic origin
Lineage-specific gene expression has been used for the identification of metastasis of cancers with unknown primary site or of disseminated cancer cells in haemopoietic compartments such as bone marrow or in lymph nodes. For the muc1, cytokeratin-19 and the CEA genes, the transcription in haemopoietic cells has been shown recently. Here, the expression of the mammary epithelium related antigens BA46 (lactadherin) and BA70 in lymphoid and myeloid cell lines, and in clinical specimens is analysed. By Northern-hybridization with specific oligonucleotides an ubiquitous transcription of both genes, independent from the provenance of cells or the chromosomal gender was found. Both mRNA molecules were amplified by rtPCR from the samples and the specificity could be confirmed by sequence analysis. Peptide-specific antibodies were raised in rabbits and used for Western-blot analysis and for immunocytochemical studies. Both antibodies reacted with total cell lysates from myeloid and lymphatic cells. In immunocytochemistry antibody P717 (anti-lactadherin) had a significant strong staining of the myeloid cell lines K562 and HL60 suggesting a participation of lactadherin in leukocyte-function. Using antibody P718, strong stains were seen in myeloid line K562 and lymphoid line ST486. In conclusion, our findings expand the results that the concept of lineage-specific gene expression is no longer valid at the molecular level. © 2000 Cancer Research Campaig
Does the 1/f frequency-scaling of brain signals reflect self-organized critical states?
Many complex systems display self-organized critical states characterized by
1/f frequency scaling of power spectra. Global variables such as the
electroencephalogram, scale as 1/f, which could be the sign of self-organized
critical states in neuronal activity. By analyzing simultaneous recordings of
global and neuronal activities, we confirm the 1/f scaling of global variables
for selected frequency bands, but show that neuronal activity is not consistent
with critical states. We propose a model of 1/f scaling which does not rely on
critical states, and which is testable experimentally.Comment: 3 figures, 6 page
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