986 research outputs found
Spin-Spin Interaction In Artificial Molecules With In-Plane Magnetic Field
We investigate theoretically the spin-spin interaction of two-electrons in
vertically coupled QDs as a function of the angle between magnetic field and
growth axis. Our numerical approach is based on a real-space description of
single-particle states in realistic samples and exact diagonalization of
carrier-carrier Coulomb interaction. In particular, the effect of the in-plane
field component on tunneling and, therefore, spin-spin interaction will be
discussed; the singlet-triplet phase diagram as a function of the field
strength and direction is drawn.Comment: Proc. of EP2DS-15, Nara, Japan - 6 pages, 4 figure
Osteopontin mediates tumorigenic transformation of a preneoplastic murine cell line by suppressing anoikis: An Arg‐Gly‐Asp‐dependent‐focal adhesion kinase‐caspase‐8 axis
Osteopontin (OPN), an adhesive, matricellular glycoprotein, is a rate‐limiting factor in tumor promotion of skin carcinogenesis. With a tumor promotion model, the JB6 Cl41.5a cell line, we have shown that suppressing 12‐O‐tetradecanoylphorbol‐13‐acetate (TPA)‐induced OPN expression markedly inhibits TPA‐induced colony formation in soft agar, an assay indicative of tumorigenic transformation. Further, the addition of exogenous OPN promotes colony formation of these cells. These findings support a function of OPN in mediating TPA‐induced neoplastic transformation of JB6 cells. In regard to the mechanism of action by OPN, we hypothesized that, for JB6 cells grown in soft‐agar, secreted OPN induced by TPA stimulates cell proliferation and/or prevents anoikis to facilitate TPA‐induced colony formation. Analyses of cell cycle and cyclin D1 expression, and direct cell counting of JB6 cells treated with OPN indicate that OPN does not stimulate cell proliferation relative to non‐treated controls. Instead, at 24 h, OPN decreases anoikis by 41%, as assessed by annexin V assays. Further, in suspended cells OPN suppresses caspase‐8 activation, which is mediated specifically through its RGD‐cell binding motif that transduces signals through integrin receptors. Transfection studies with wild‐type and mutant focal adhesion kinases (FAK) and Western blot analyses suggest that OPN suppression of caspase‐8 activation is mediated through phosphorylation of FAK at Tyr861. In summary, these studies indicate that induced OPN is a microenvironment modulator that facilitates tumorigenic transformation of JB6 cells by inhibiting anoikis through its RGD‐dependent suppression of caspase‐8 activity, which is mediated in part through the activation of FAK at Tyr861. © 2013 Wiley Periodicals, Inc.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/111135/1/mc22108.pd
A vertical diatomic artificial molecule in the intermediate coupling regime in a parallel and perpendicular magnetic field
We present experimental results for the ground state electrochemical
potentials of a few electron semiconductor artificial molecule made by
vertically coupling two quantum dots, in the intermediate coupling regime, in
perpendicular and parallel magnetic fields up to 5 T. We perform a quantitative
analysis based on local-spin density functional theory. The agreement between
theoretical and experimental results is good, and the phase transitions are
well reproduced.Comment: Typeset using Revtex, 13 pages and 8 Postscript figure
Dissociation of vertical semiconductor diatomic artificial molecules
We investigate the dissociation of few-electron circular vertical
semiconductor double quantum dot artificial molecules at 0 T as a function of
interdot distance. Slight mismatch introduced in the fabrication of the
artificial molecules from nominally identical constituent quantum wells induces
localization by offsetting the energy levels in the quantum dots by up to 2
meV, and this plays a crucial role in the appearance of the addition energy
spectra as a function of coupling strength particularly in the weak coupling
limit.Comment: Accepted for publication in Phys. Rev. Let
Competing mechanisms for singlet-triplet transition in artificial molecules
We study the magnetic field induced singlet/triplet transition for two
electrons in vertically coupled quantum dots by exact diagonalization of the
Coulomb interaction. We identify the different mechanisms occurring in the
transition, involving either in-plane correlations or localization in opposite
dots, depending on the field direction. Therefore, both spin and orbital
degrees of freedom can be manipulated by field strength and direction. The
phase diagram of realistic devices is determined.Comment: To appear in Phys. Rev. B - Rapid Comm. - 5 pages, 3 figure
Layer thickness dependence of the current induced effective field vector in Ta|CoFeB|MgO
The role of current induced effective magnetic field in ultrathin magnetic
heterostructures is increasingly gaining interest since it can provide
efficient ways of manipulating magnetization electrically. Two effects, known
as the Rashba spin orbit field and the spin Hall spin torque, have been
reported to be responsible for the generation of the effective field. However,
quantitative understanding of the effective field, including its direction with
respect to the current flow, is lacking. Here we show vector measurements of
the current induced effective field in Ta|CoFeB|MgO heterostructrures. The
effective field shows significant dependence on the Ta and CoFeB layers'
thickness. In particular, 1 nm thickness variation of the Ta layer can result
in nearly two orders of magnitude difference in the effective field. Moreover,
its sign changes when the Ta layer thickness is reduced, indicating that there
are two competing effects that contribute to the effective field. The relative
size of the effective field vector components, directed transverse and parallel
to the current flow, varies as the Ta thickness is changed. Our results
illustrate the profound characteristics of just a few atomic layer thick metals
and their influence on magnetization dynamics
Quantum phases in artificial molecules
The many-body state of carriers confined in a quantum dot is controlled by
the balance between their kinetic energy and their Coulomb correlation. In
coupled quantum dots, both can be tuned by varying the inter-dot tunneling and
interactions. Using a theoretical approach based on the diagonalization of the
exact Hamiltonian, we show that transitions between different quantum phases
can be induced through inter-dot coupling both for a system of few electrons
(or holes) and for aggregates of electrons and holes. We discuss their
manifestations in addition energy spectra (accessible through capacitance or
transport experiments) and optical spectra.Comment: 29 pages, 8 figures (ps and eps), LaTeX 2e, ELSART package. To appear
in Solid State Communications - Special Issue on Spin Effects in Mesoscopic
System
Adjustable current-induced magnetization switching utilizing interlayer exchange coupling
Electrical current-induced deterministic magnetization switching in a magnetic multilayer structure without external magnetic field is realized by utilizing interlayer exchange coupling. Two ferromagnetic Co layers, with in-plane and out-of-plane anisotropy respectively, are separated by a spacer Ta layer, which plays a dual role of inducing antiferromagnetic interlayer coupling, and contributing to the current-induced effective magnetic field through the spin Hall effect. The current-induced magnetization switching behavior can be tuned by pre-magnetizing the in-plane Co layer. The antiferromagnetic exchange coupling field increases with decreasing thickness of the Ta layer, reaching 630 ±5 Oe for a Ta thickness of 1.5nm. The magnitude of the current-induced perpendicular effective magnetic field from spin-orbit torque is 9.2 Oe/(107Acm-2). The large spin Hall angle of Ta, opposite in sign to that of Pt, results in a low critical current density of 9×106A/cm2. This approach is promising for the electrical switching of magnetic memory elements without external magnetic field
Método automático de clasificación de color en dientes humanos usando aprendizaje de máquina
Trabajo de InvestigaciónActualmente el proceso de identificación del color de los dientes para la fabricación de prótesis dentales es realizado manualmente por un experto que, utilizando un método de identificación visual, determina el color de las piezas dentales en la boca del paciente, usando guías de color como la VITA®. A pesar de que el método visual es el más utilizado para la identificación del color de dientes, este se ve afectado por distintas variables tales como: el cansancio del experto, la luminosidad en el ambiente, salud visual del especialista, entre otras que influyen en la identificación del color en los dientes. Los errores en la clasificación del color de los dientes pueden generar pérdidas de tiempo lo que implicaría en consecuencia sobrecostos que afectarían directamente al fabricante y la satisfacción final del cliente.1. Planteamiento del problema
2. Pregunta de investigación
3. Objetivos
4. Estado del arte
5. Marco de referencia
6. Alcances y limitaciones
7. Metodología
8. Diseño metodológico
9. Discusión y resultados
10. Conclusiones
11. Trabajos futuros
12. Bibliografía
13. ANEXOSPregradoIngeniero de Sistema
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