124 research outputs found
Forbidden island heights in stress-driven coherent Stranski-Krastanov growth
The observed height distribution of clusters obtained in strained epitaxy has
been often interpreted in terms of electronic effects. We show that some
aspects can be explained classically by the interplay of strain and edge
energies. We find that soft materials can transform directly from monolayer
into thicker islands by two-dimensional (2D) multilayer nucleation and growth.
There is a critical thickness decreasing with the force constant. Thinner
islands are thermodynamically forbidden, due to the insufficient stress
relaxation upon clustering particularly under tensile stress. At sufficiently
large misfits the barrier for 2D multilayer nucleation is significantly smaller
than the barrier for subsequent single-layer nucleation. The effects are found
to be quantitatively reasonable and offer a plausible explanation for the
absence of thin islands and 2D growth of flattop islands usually attributed to
quantum size effects.Comment: 4 pages, 4 figures. Accepted version. Includes quantitative
estimations comparing with experiments plus minor change
Effect of the lattice misfit on the equilibrium shape of strained islands in Volmer-Weber growth
We have studied the effect of the misfit on the equilibrium shape of
three-dimensional pyramidal islands grown on a foreign substrate in the case of
incomplete wetting (Volmer-Weber mode of growth). We have found that tensile
islands have smaller aspect ratios compared with compressed islands owing to
its better adhesion to the substrate. The average strains of consecutive layers
decrease faster with thickness in compressed than in tensile islands. The
strains decrease rapidly with thickness, with the consequence that above a
certain height, the upper layers of the pyramid become practically unstrained
and does not contribute to a further reduction in the upper base. As a result,
the truncated pyramids are not expected to transform into full pyramids. Our
results are in good agreement with experimental observations in different
systems.Comment: 6 pages, 7 figures. Accepted version, minor change
Second-layer nucleation in coherent Stranski-Krastanov growth of quantum dots
We have studied the monolayer-bilayer transformation in the case of the
coherent Stranski-Krastanov growth. We have found that the energy of formation
of a second layer nucleus is largest at the center of the first-layer island
and smallest on its corners. Thus nucleation is expected to take place at the
corners (or the edges) rather than at the center of the islands as in the case
of homoepitaxy. The critical nuclei have one atom in addition to a compact
shape, which is either a square of i*i or a rectangle of i*(i-1) atoms, with
i>1 an integer. When the edge of the initial monolayer island is much larger
than the critical nucleus size, the latter is always a rectangle plus an
additional atom, adsorbed at the longer edge, which gives rise to a new atomic
row in order to transform the rectangle into the equilibrium square shape.Comment: 6 pages, 4 figures. Accepted version, minor change
Computing unite of a mobile computer vision system
The work is devoted to the computing unite of a mobile computer vision system and developing his algorithmic software. We developed hardware-implemented the convolutional neural networks on a field programmable gate array. A study of the performance and power consumption of variants of the computing unite
Optimization of a therapeutic electromagnetic field (EMF) to retard breast cancer tumor growth and vascularity
Background: This study provided additional data on the effects of a therapeutic electromagnetic field (EMF) device on growth and vascularization of murine 16/C mammary adenocarcinoma cells implanted in C3H/HeJ mice.
Methods: The therapeutic EMF device generated a defined 120 Hz semi sine wave pulse signal of variable intensity. Murine 16/C mammary adenocarcinoma tumor fragments were implanted subcutaneously between the scapulae of syngeneic C3H mice. Once the tumor grew to 100 mm3, daily EMF treatments were started by placing the cage of mice within the EMF field. Treatment ranged from 10 to 20 milli-Tesla (mT) and was given for 3 to 80 minutes either once or twice a day for 12 days. Tumors were measured and volumes calculated each 3–4 days.
Results: Therapeutic EMF treatment significantly suppressed tumor growth in all 7 EMF treated groups. Exposure to 20mT for 10 minutes twice a day was the most effective tumor growth suppressor. The effect of EMF treatment on extent of tumor vascularization, necrosis and viable area was determined after euthanasia. The EMF reduced the vascular (CD31 immunohistochemically positive) volume fraction and increased the necrotic volume of the tumor. Treatment with 15 mT for 10 min/ d gave the maximum anti-angiogenic effect. Lack of a significant correlation between tumor CD 31 positive area and tumor growth rate indicates a mechanism for suppression of tumor growth in addition to suppression of tumor vascularization.
Conclusion: It is proposed that EMF therapy aimed at suppression of tumor growth and vascularization may prove a safe alternative for patients whether they are or are not candidates for conventional cancer therapy
- …