529 research outputs found
Cloned mouse cells with natural killer function and cloned suppressor T cells express ultrastructural and biochemical features not shared by cloned inducer T cells.
We have examined the morphology, cytochemistry, and biochemistry of mouse leukocyte subsets by analyzing cloned leukocyte populations specialized to perform different immunologic functions. Cloned cells expressing high-affinity plasma membrane receptors for IgE and mediating natural killer (NK) lysis and cloned antigen-specific suppressor T cells contained prominent osmiophilic cytoplasmic granules similar by ultrastructure to those of mouse basophils. Both clones also incorporated 35SO4 into granule-associated sulfated glycosaminoglycans, expressed a characteristic ultrastructural pattern of nonspecific esterase activity, incorporated exogenous [3H]5-hydroxytryptamine, and contained cytoplasmic deposits of particulate glycogen. By contrast, cloned inducer T cells lacked cytoplasmic granules and glycogen, incorporated neither 35SO4 nor [3H]5-hydroxytryptamine, and differed from the other clones in pattern of nonspecific esterase activity. These findings establish that certain cloned cells with NK activity and cloned suppressor T cells express morphologic and biochemical characteristics heretofore associated with basophilic granulocytes. However, these clones differ in surface glycoprotein expression and immunologic function, and the full extent of the similarities and differences among these populations and basophils remains to be determined
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Mast cell clones: a model for the analysis of cellular maturation.
Cloned mouse mast cells resemble, by ultrastructure, immature mast cells observed in vivo. These mast cell clones can be grown in the absence of any other cells, facilitating direct investigations of their biochemistry and function. We find that cloned mast cells express plasma membrane receptors (Fc epsilon R) that bind mouse IgE with an equilibrium constant (KA) similar to that of normal mouse peritoneal mast cells. In addition, cloned mast cells do not display detectable la antigens and cannot enhance lg secretion when added to lymphocyte cultures or mediate natural killer lysis. In the presence of 1 mM sodium butyrate, cloned mast cells stop dividing and acquire abundant electron-dense cytoplasmic granules similar to those of mature mast cells. Their histamine content increases concomitant with cytoplasmic granule maturation and may exceed that of untreated mast cells by 50-fold. Unlike peritoneal mast cells, cloned mast cells incorporate 35SO4 into chondroitin sulfates rather than heparin. These findings demonstrate that, unlike fully differentiated mouse peritoneal mast cells, cloned immature mouse mast cells contain no heparin and low levels of histamine. In addition, they establish that high-affinity Fc epsilon R are expressed early in mast cell maturation, well before completion of cytoplasmic granule synthesis and mediator storage
Kinetics of the helix-coil transition
Based on the Zimm-Bragg model we study cooperative helix-coil transition
driven by a finite-speed change of temperature. There is an asymmetry between
the coil-to-helix and helix-to-coil transition: the latter is displayed already
for finite speeds, and takes shorter time than the former. This hysteresis
effect has been observed experimentally, and it is explained here via
quantifying system's stability in the vicinity of the critical temperature. A
finite-speed cooling induces a non-equilibrium helical phase with the
correlation length larger than in equilibrium. In this phase the characteristic
length of the coiled domain and the non-equilibrium specific heat can display
an anomalous response to temperature changes. Several pertinent experimental
results on the kinetics helical biopolymers are discussed in detail.Comment: 6 pages, 8 figure
Aluminum Oxide Layers as Possible Components for Layered Tunnel Barriers
We have studied transport properties of Nb/Al/AlOx/Nb tunnel junctions with
ultrathin aluminum oxide layers formed by (i) thermal oxidation and (ii) plasma
oxidation, before and after rapid thermal post-annealing of the completed
structures at temperatures up to 550 deg C. Post-annealing at temperatures
above 300 deg C results in a significant decrease of the tunneling conductance
of thermally-grown barriers, while plasma-grown barriers start to change only
at annealing temperatures above 450 deg C. Fitting the experimental I-V curves
of the junctions using the results of the microscopic theory of direct
tunneling shows that the annealing of thermally-grown oxides at temperatures
above 300 deg C results in a substantial increase of their average tunnel
barriers height, from ~1.8 eV to ~2.45 eV, versus the practically unchanged
height of ~2.0 eV for plasma-grown layers. This difference, together with high
endurance of annealed barriers under electric stress (breakdown field above 10
MV/cm) may enable all-AlOx and SiO2/AlOx layered "crested" barriers for
advanced floating-gate memory applications.Comment: 7 pages, 6 figure
Metal-Insulator Transition and Spin Degree of Freedom in Silicon 2D Electron Systems
Magnetotransport in 2DES's formed in Si-MOSFET's and Si/SiGe quantum wells at
low temperatures is reported. Metallic temperature dependence of resistivity is
observed for the n-Si/SiGe sample even in a parallel magnetic field of 9T,
where the spins of electrons are expected to be polarized completely.
Correlation between the spin polarization and minima in the diagonal
resistivity observed by rotating the samples for various total strength of the
magnetic field is also investigated.Comment: 3 pages, RevTeX, 4 eps-figures, conference paper (EP2DS-13
Parallel magnetic field induced giant magnetoresistance in low density {\it quasi}-two dimensional layers
We provide a possible theoretical explanation for the recently observed giant
positive magnetoresistance in high mobility low density {\it quasi}-two
dimensional electron and hole systems. Our explanation is based on the strong
coupling of the parallel field to the {\it orbital} motion arising from the
{\it finite} layer thickness and the large Fermi wavelength of the {\it
quasi}-two dimensional system at low carrier densities.Comment: 4 pages with 4 figures. Accepted for Publication in Physical Review
Letter
Classical versus Quantum Effects in the B=0 Conducting Phase in Two Dimensions
In the dilute two-dimensional electron system in silicon, we show that the
temperature below which Shubnikov-de Haas oscillations become apparent is
approximately the same as the temperature below which an exponential decrease
in resistance is seen in B=0, suggesting that the anomalous behavior in zero
field is observed only when the system is in a degenerate (quantum) state. The
temperature dependence of the resistance is found to be qualitatively similar
in B=0 and at integer Landau level filling factors.Comment: 3 pages, 3 figure
Femoral neck fracture following intramedullary nailing with misplacement of an end cup: report of two cases
Femoral neck fracture is an unusual complication of intramedullary fixation of a broken femur. We report on two cases of femoral neck fractures attributed to misplacement of an end cup and subsequent invasive maneuvers in an effort to remove it. Iatrogenic fractures of the femoral neck during or after intramedullary nailing are reported in the medical literature. Authors associate it with many possible technical mistakes performed during the procedure, yet no complications after missed end cup placement were noted. We suggest that the fractures described below were a consequence of injury to the vascular supply and bone stock of the initially intact femoral neck
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