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1.  The effects of porosity on optical properties of semiconductor chalcogenide films obtained by the chemical bath deposition 
Nanoscale Research Letters  2012;7(1):483.
This paper is dedicated to study the thin polycrystalline films of semiconductor chalcogenide materials (CdS, CdSe, and PbS) obtained by ammonia-free chemical bath deposition. The obtained material is of polycrystalline nature with crystallite of a size that, from a general point of view, should not result in any noticeable quantum confinement. Nevertheless, we were able to observe blueshift of the fundamental absorption edge and reduced refractive index in comparison with the corresponding bulk materials. Both effects are attributed to the material porosity which is a typical feature of chemical bath deposition technique. The blueshift is caused by quantum confinement in pores, whereas the refractive index variation is the evident result of the density reduction. Quantum mechanical description of the nanopores in semiconductor is given based on the application of even mirror boundary conditions for the solution of the Schrödinger equation; the results of calculations give a reasonable explanation of the experimental data.
doi:10.1186/1556-276X-7-483
PMCID: PMC3475102  PMID: 22931255
polycrystalline films; chalcogenide materials; nanopores; quantum confinement in pores
2.  Theory of free electron vortices 
Ultramicroscopy  2011;111(9-10):1461-1468.
The recent creation of electron vortex beams and their first practical application motivates a better understanding of their properties. Here, we develop the theory of free electron vortices with quantized angular momentum, based on solutions of the Schrödinger equation for cylindrical boundary conditions. The principle of transformation of a plane wave into vortices with quantized angular momentum, their paraxial propagation through round magnetic lenses, and the effect of partial coherence are discussed.
Highlights
► Theory of vortex electrons. ► Proof that free electrons can carry quantized orbital momentum. ► Proof that electron vortices are stable and robust under spherical aberration. ► Demonstration of the strong influence of partial coherence.
doi:10.1016/j.ultramic.2011.07.004
PMCID: PMC3279051  PMID: 21930017
TEM; Coherence; Angular momentum; Vortex beams
3.  3-D Quantum Transport Solver Based on the Perfectly Matched Layer and Spectral Element Methods for the Simulation of Semiconductor Nanodevices 
Journal of computational physics  2007;227(1):455-471.
A 3-D quantum transport solver based on the spectral element method (SEM) and perfectly matched layer (PML) is introduced to solve the 3-D Schrödinger equation with a tensor effective mass. In this solver, the influence of the environment is replaced with the artificial PML open boundary extended beyond the contact regions of the device. These contact regions are treated as waveguides with known incident waves from waveguide mode solutions. As the transmitted wave function is treated as a total wave, there is no need to decompose it into waveguide modes, thus significantly simplifying the problem in comparison with conventional open boundary conditions. The spectral element method leads to an exponentially improving accuracy with the increase in the polynomial order and sampling points. The PML region can be designed such that less than −100 dB outgoing waves are reflected by this artificial material. The computational efficiency of the SEM solver is demonstrated by comparing the numerical and analytical results from waveguide and plane-wave examples, and its utility is illustrated by multiple-terminal devices and semiconductor nanotube devices.
doi:10.1016/j.jcp.2007.07.028
PMCID: PMC2083569  PMID: 18037971
Perfectly matched layer (PML); spectral element method (SEM); open boundary condition; quantum transport; nanodevice simulation; Schrödinger equation; tensor effective mass
4.  Motion of a Cylindrical Dielectric Boundary 
The interplay between geometry and electrostatics contributes significantly to hydrophobic interactions of biomolecules in an aqueous solution. With an implicit solvent, such a system can be described macroscopically by the dielectric boundary that separates the high-dielectric solvent from low-dielectric solutes. This work concerns the motion of a model cylindrical dielectric boundary as the steepest descent of a free-energy functional that consists of both the surface and electrostatic energies. The effective dielectric boundary force is defined and an explicit formula of the force is obtained. It is found that such a force always points from the solvent region to solute region. In the case that the interior of a cylinder is of a lower dielectric, the motion of the dielectric boundary is initially driven dominantly by the surface force but is then driven inward quickly to the cylindrical axis by both the surface and electrostatic forces. In the case that the interior of a cylinder is of a higher dielectric, the competition between the geometrical and electrostatic contributions leads to the existence of equilibrium boundaries that are circular cylinders. Linear stability analysis is presented to show that such an equilibrium is only stable for a perturbation with a wavenumber larger than a critical value. Numerical simulations are reported for both of the cases, confirming the analysis on the role of each component of the driving force. Implications of the mathematical findings to the understanding of charged molecular systems are discussed.
PMCID: PMC3718573  PMID: 23885130
Charged molecules; dielectric boundaries; surface energy; electrostatic energy; effective dielectric boundary force; linear stability
5.  Dynamic Cylindrical Assembly of Triblock Copolymers by a Hierarchical Process of Covalent and Supramolecular Interactions 
We have developed a hierarchical process that combines linear triblock copolymers into concentric globular sub-units through strong chemical bonds and is followed by their supramolecular assembly via weak non-covalent interactions to afford one-dimensionally-assembled, dynamic cylindrical nanostructures. The molecular brush architecture forces triblock copolymers to adopt some intramolecular interactions within confined frameworks and then drives their intermolecular interactions in the mixtures of organic solvent and water. In contrast, the triblock copolymers, when not pre-connected into the molecular brush architectures, organize only into globular assemblies.
doi:10.1021/ja109191z
PMCID: PMC3033480  PMID: 21204539
6.  Do Twin Boundaries Always Strengthen Metal Nanowires? 
Nanoscale Research Letters  2008;4(1):34-38.
It has been widely reported that twin boundaries strengthen nanowires regardless of their morphology—that is, the strength of nanowires goes up as twin spacing goes down. This article shows that twin boundaries do not always strengthen nanowires. Using classical molecular dynamics simulations, the authors show that whether twin boundaries strengthen nanowires depends on the necessary stress for dislocation nucleation, which in turn depends on surface morphologies. When nanowires are circular cylindrical, the necessary stress of dislocation nucleation is high and the presence of twin boundaries lowers this stress; twin boundaries soften nanowires. In contrast, when nanowires are square cylindrical, the necessary stress of dislocation nucleation is low, and a higher stress is required for dislocations to penetrate twin boundaries; they strengthen nanowires.
doi:10.1007/s11671-008-9198-1
PMCID: PMC2894070  PMID: 20596424
Nanowire; Twin; Strengthening; Dislocation; Simulation
7.  Do Twin Boundaries Always Strengthen Metal Nanowires? 
Nanoscale Research Letters  2008;4(1):34-38.
It has been widely reported that twin boundaries strengthen nanowires regardless of their morphology—that is, the strength of nanowires goes up as twin spacing goes down. This article shows that twin boundaries do not always strengthen nanowires. Using classical molecular dynamics simulations, the authors show that whether twin boundaries strengthen nanowires depends on the necessary stress for dislocation nucleation, which in turn depends on surface morphologies. When nanowires are circular cylindrical, the necessary stress of dislocation nucleation is high and the presence of twin boundaries lowers this stress; twin boundaries soften nanowires. In contrast, when nanowires are square cylindrical, the necessary stress of dislocation nucleation is low, and a higher stress is required for dislocations to penetrate twin boundaries; they strengthen nanowires.
doi:10.1007/s11671-008-9198-1
PMCID: PMC2894070  PMID: 20596424
Nanowire; Twin; Strengthening; Dislocation; Simulation
8.  Wave-packet rectification in nonlinear electronic systems: A tunable Aharonov-Bohm diode 
Scientific Reports  2014;4:4566.
Rectification of electron wave-packets propagating along a quasi-one dimensional chain is commonly achieved via the simultaneous action of nonlinearity and longitudinal asymmetry, both confined to a limited portion of the chain termed wave diode. However, it is conceivable that, in the presence of an external magnetic field, spatial asymmetry perpendicular to the direction of propagation suffices to ensure rectification. This is the case of a nonlinear ring-shaped lattice with different upper and lower halves (diode), which is attached to two elastic chains (leads). The resulting device is mirror symmetric with respect to the ring vertical axis, but mirror asymmetric with respect to the chain direction. Wave propagation along the two diode paths can be modeled for simplicity by a discrete Schrödinger equation with cubic nonlinearities. Numerical simulations demonstrate that, thanks to the Aharonov-Bohm effect, such a diode can be operated by tuning the magnetic flux across the ring.
doi:10.1038/srep04566
PMCID: PMC3972507
9.  Various Quantum- and Nano-Structures by III–V Droplet Epitaxy on GaAs Substrates 
Nanoscale Research Letters  2009;5(2):308-314.
We report on various self-assembled In(Ga)As nanostructures by droplet epitaxy on GaAs substrates using molecular beam epitaxy. Depending on the growth condition and index of surfaces, various nanostructures can be fabricated: quantum dots (QDs), ring-like and holed-triangular nanostructures. At near room temperatures, by limiting surface diffusion of adatoms, the size of In droplets suitable for quantum confinement can be fabricated and thus InAs QDs are demonstrated on GaAs (100) surface. On the other hand, at relatively higher substrate temperatures, by enhancing the surface migrations of In adatoms, super lower density of InGaAs ring-shaped nanostructures can be fabricated on GaAs (100). Under an identical growth condition, holed-triangular InGaAs nanostructures can be fabricated on GaAs type-A surfaces, while ring-shaped nanostructures are formed on GaAs (100). The formation mechanism of various nanostructures can be understood in terms of intermixing, surface diffusion, and surface reconstruction.
doi:10.1007/s11671-009-9481-9
PMCID: PMC2893769  PMID: 20671787
Droplet epitaxy; Nanostructures; High-index GaAs; Atomic force microscope; Molecular beam epitaxy
10.  Various Quantum- and Nano-Structures by III–V Droplet Epitaxy on GaAs Substrates 
Nanoscale Research Letters  2009;5(2):308-314.
We report on various self-assembled In(Ga)As nanostructures by droplet epitaxy on GaAs substrates using molecular beam epitaxy. Depending on the growth condition and index of surfaces, various nanostructures can be fabricated: quantum dots (QDs), ring-like and holed-triangular nanostructures. At near room temperatures, by limiting surface diffusion of adatoms, the size of In droplets suitable for quantum confinement can be fabricated and thus InAs QDs are demonstrated on GaAs (100) surface. On the other hand, at relatively higher substrate temperatures, by enhancing the surface migrations of In adatoms, super lower density of InGaAs ring-shaped nanostructures can be fabricated on GaAs (100). Under an identical growth condition, holed-triangular InGaAs nanostructures can be fabricated on GaAs type-A surfaces, while ring-shaped nanostructures are formed on GaAs (100). The formation mechanism of various nanostructures can be understood in terms of intermixing, surface diffusion, and surface reconstruction.
doi:10.1007/s11671-009-9481-9
PMCID: PMC2893769  PMID: 20671787
Droplet epitaxy; Nanostructures; High-index GaAs; Atomic force microscope; Molecular beam epitaxy
11.  A boundary integral approach to analyze the viscous scattering of a pressure wave by a rigid body 
The paper provides boundary integral equations for solving the problem of viscous scattering of a pressure wave by a rigid body. By using this mathematical tool uniqueness and existence theorems are proved. Since the boundary conditions are written in terms of velocities, vector boundary integral equations are obtained for solving the problem. The paper introduces single-layer viscous potentials and also a stress tensor. Correspondingly, a viscous double-layer potential is defined. The properties of all these potentials are investigated.
By representing the scattered field as a combination of a single-layer viscous potential and a double-layer viscous potential the problem is reduced to the solution of a singular vectorial integral equation of Fredholm type of the second kind.
In the case where the stress vector on the boundary is the main quantity of interest the corresponding boundary singular integral equation is proved to have a unique solution.
doi:10.1016/j.enganabound.2007.02.004
PMCID: PMC2516926  PMID: 18709178
Acoustical scattering; Viscous fluid; Integral Equation; MEMS
12.  Evidences For Charge Transfer-Induced Conformational Changes In Carbon Nanostructure-Protein Corona 
The binding of proteins to a nanostructure often alters protein secondary and tertiary structures. However, the main physical mechanisms that elicit protein conformational changes in the presence of the nanostructure have not yet been fully established. Here we performed a comprehensive spectroscopic study to probe the interactions between bovine serum albumin (BSA) and carbon-based nanostructures of graphene and single-walled carbon nanotubes (SWNTs). Our results showed that the BSA “corona” acted as a weak acceptor to facilitate charge transfer from the carbon nanostructures. Notably, we observed that charge transfer occurred only in the case of SWNTs but not in graphene, resulting from the sharp and discrete electronic density of states of the former. Furthermore, the relaxation of external α–helices in BSA secondary structure increased concomitantly with the charge transfer. These results may help guide controlled nanostructure-biomolecular interactions and prove beneficial for developing novel drug delivery systems, biomedical devices and engineering of safe nanomaterials.
doi:10.1021/jp3085028
PMCID: PMC3519440  PMID: 23243478
Protein corona; charge transfer; graphene; carbon nanotubes; Raman spectroscopy; FTIR spectroscopy
13.  Transient Photoinduced Absorption in Ultrathin As-grown Nanocrystalline Silicon Films 
Nanoscale Research Letters  2007;3(1):1-5.
We have studied ultrafast carrier dynamics in nanocrystalline silicon films with thickness of a few nanometers where boundary-related states and quantum confinement play an important role. Transient non-degenerated photoinduced absorption measurements have been employed to investigate the effects of grain boundaries and quantum confinement on the relaxation dynamics of photogenerated carriers. An observed long initial rise of the photoinduced absorption for the thicker films agrees well with the existence of boundary-related states acting as fast traps. With decreasing the thickness of material, the relaxation dynamics become faster since the density of boundary-related states increases. Furthermore, probing with longer wavelengths we are able to time-resolve optical paths with faster relaxations. This fact is strongly correlated with probing in different points of the first Brillouin zone of the band structure of these materials.
doi:10.1007/s11671-007-9105-1
PMCID: PMC3244776
Ultrafast spectroscopy; Nanoscale silicon thin films
14.  Influence of viscosity on the reflection and transmission of an acoustic wave by a periodic array of screens. The general 3-D problem 
An analysis is presented of the diffraction of a pressure wave by a periodic grating including the influence of the air viscosity. The direction of the incoming pressure wave is arbitrary. As opposed to the classical nonviscous case, the problem cannot be reduced to a plane problem having a definite 3-D character. The system of partial differential equations used for solving the problem consists of the compressible Navier-Stokes equations associated with no-slip boundary conditions on solid surfaces. The problem is reduced to a system of two hypersingular integral equations for determining the velocity components in the slits’ plane and a hypersingular integral equation for the normal component of velocity. These equations are solved by using Galerkin’s method with some special trial functions. The results can be applied in designing protective screens for miniature microphones realized in MEMS technology. In this case, the physical dimensions of the device are on the order of the viscous boundary layer so that the viscosity cannot be neglected. The analysis indicates that the openings in the screen should be on the order of 10 microns in order to avoid excessive attenuation of the signal. This paper also provides the variation of the transmission coefficient with frequency in the acoustical domain.
doi:10.1016/j.wavemoti.2007.05.006
PMCID: PMC2441451  PMID: 19122753
15.  Electron cotunneling through doubly occupied quantum dots: effect of spin configuration 
Nanoscale Research Letters  2011;6(1):251.
A microscopic theory is presented for electron cotunneling through doubly occupied quantum dots in the Coulomb blockade regime. Beyond the semiclassic framework of phenomenological models, a fully quantum mechanical solution for cotunneling of electrons through a one-dimensional quantum dot is obtained using a quantum transmitting boundary method without any fitting parameters. It is revealed that the cotunneling conductance exhibits strong dependence on the spin configuration of the electrons confined inside the dot. Especially for the triplet configuration, the conductance shows an obvious deviation from the well-known quadratic dependence on the applied bias voltage. Furthermore, it is found that the cotunneling conductance reveals more sensitive dependence on the barrier width than the height.
doi:10.1186/1556-276X-6-251
PMCID: PMC3211313  PMID: 21711763
16.  Visible and infrared emission from Si/Ge nanowires synthesized by metal-assisted wet etching 
Abstract
Multi-quantum well Si/Ge nanowires (NWs) were realized by combining molecular beam epitaxy deposition and metal-assisted wet etching, which is a low-cost technique for the synthesis of extremely dense (about 1011 cm−2) arrays of NWs with a high and controllable aspect ratio. In particular, we prepared ultrathin Si/Ge NWs having a mean diameter of about 8 nm and lengths spanning from 1.0 to 2.7 μm. NW diameter is compatible with the occurrence of quantum confinement effects and, accordingly, we observed light emission assignable to the presence of Si and Ge nanostructures. We performed a detailed study of the photoluminescence properties of the NWs, with particular attention to the excitation and de-excitation properties as a function of the temperature and of the excitation photon flux, evaluating the excitation cross section and investigating the presence of non-radiative phenomena.
PACS
61.46.Km; 78.55.-m; 78.67.Lt
doi:10.1186/1556-276X-9-74
PMCID: PMC3928609  PMID: 24521284
Nanowires; Photoluminescence; Semiconductor nanostructures
17.  Path Integrals for Electronic Densities, Reactivity Indices, and Localization Functions in Quantum Systems 
The density matrix theory, the ancestor of density functional theory, provides the immediate framework for Path Integral (PI) development, allowing the canonical density be extended for the many-electronic systems through the density functional closure relationship. Yet, the use of path integral formalism for electronic density prescription presents several advantages: assures the inner quantum mechanical description of the system by parameterized paths; averages the quantum fluctuations; behaves as the propagator for time-space evolution of quantum information; resembles Schrödinger equation; allows quantum statistical description of the system through partition function computing. In this framework, four levels of path integral formalism were presented: the Feynman quantum mechanical, the semiclassical, the Feynman-Kleinert effective classical, and the Fokker-Planck non-equilibrium ones. In each case the density matrix or/and the canonical density were rigorously defined and presented. The practical specializations for quantum free and harmonic motions, for statistical high and low temperature limits, the smearing justification for the Bohr’s quantum stability postulate with the paradigmatic Hydrogen atomic excursion, along the quantum chemical calculation of semiclassical electronegativity and hardness, of chemical action and Mulliken electronegativity, as well as by the Markovian generalizations of Becke-Edgecombe electronic focalization functions – all advocate for the reliability of assuming PI formalism of quantum mechanics as a versatile one, suited for analytically and/or computationally modeling of a variety of fundamental physical and chemical reactivity concepts characterizing the (density driving) many-electronic systems.
doi:10.3390/ijms10114816
PMCID: PMC2808013  PMID: 20087467
density matrix and functionals; Feynman integral; partition function; electronegativity; chemical action and hardness; Fokker-Planck equation; electronic localization
18.  Ferromagnetism and semiconducting of boron nanowires 
Nanoscale Research Letters  2012;7(1):678.
More recently, motivated by extensively technical applications of carbon nanostructures, there is a growing interest in exploring novel non-carbon nanostructures. As the nearest neighbor of carbon in the periodic table, boron has exceptional properties of low volatility and high melting point and is stronger than steel, harder than corundum, and lighter than aluminum. Boron nanostructures thus are expected to have broad applications in various circumstances. In this contribution, we have performed a systematical study of the stability and electronic and magnetic properties of boron nanowires using the spin-polarized density functional calculations. Our calculations have revealed that there are six stable configurations of boron nanowires obtained by growing along different base vectors from the unit cell of the bulk α-rhombohedral boron (α-B) and β-rhombohedral boron (β-B). Well known, the boron bulk is usually metallic without magnetism. However, theoretical results about the magnetic and electronic properties showed that, whether for the α-B-based or the β-B-based nanowires, their magnetism is dependent on the growing direction. When the boron nanowires grow along the base vector [001], they exhibit ferromagnetism and have the magnetic moments of 1.98 and 2.62 μB, respectively, for the α-c [001] and β-c [001] directions. Electronically, when the boron nanowire grows along the α-c [001] direction, it shows semiconducting and has the direct bandgap of 0.19 eV. These results showed that boron nanowires possess the unique direction dependence of the magnetic and semiconducting behaviors, which are distinctly different from that of the bulk boron. Therefore, these theoretical findings would bring boron nanowires to have many promising applications that are novel for the boron bulk.
doi:10.1186/1556-276X-7-678
PMCID: PMC3549899  PMID: 23244063
Boron nanowires; Ferromagnetism; Semiconducting
19.  Optoelectronic Properties of Carbon Nanorings: Excitonic Effects from Time-Dependent Density Functional Theory 
The electronic structure and size-scaling of optoelectronic properties in cycloparaphenylene carbon nanorings are investigated using time-dependent density functional theory (TDDFT). The TDDFT calculations on these molecular nanostructures indicate that the lowest excitation energy surprisingly becomes larger as the carbon nanoring size is increased, in contradiction with typical quantum confinement effects. In order to understand their unusual electronic properties, I performed an extensive investigation of excitonic effects by analyzing electron-hole transition density matrices and exciton binding energies as a function of size in these nanoring systems. The transition density matrices allow a global view of electronic coherence during an electronic excitation, and the exciton binding energies give a quantitative measure of electron-hole interaction energies in the nanorings. Based on overall trends in exciton binding energies and their spatial delocalization, I find that excitonic effects play a vital role in understanding the unique photoinduced dynamics in these carbon nanoring systems.
doi:10.1021/jp9074674
PMCID: PMC3317592  PMID: 22481999
20.  A Nonadiabatic Theory for Ultrafast Catalytic Electron Transfer: A Model for the Photosynthetic Reaction Center 
Journal of Biological Physics  2005;31(3-4):375-402.
A non-adiabatic theory of Electron Transfer (ET), which improves the standard theory near the inversion point and becomes equivalent to it far from the inversion point, is presented. The complex amplitudes of the electronic wavefunctions at different sites are used as Kramers variables for describing the quantum tunneling of the electron in the deformable potential generated by its environment (nonadiabaticity) which is modeled as a harmonic classical thermal bath. After exact elimination of the bath, the effective electron dynamics is described by a discrete nonlinear Schrödinger equation with norm preserving dissipative terms and a Langevin random force, with a frequency cut-off, due to the thermalized phonons.
This theory reveals the existence of a specially interesting marginal case when the linear and nonlinear coefficients of a two electronic states system are appropriately tuned for forming a Coherent Electron-Phonon Oscillator (CEPO). An electron injected on one of the electronic states of a CEPO generates large amplitude charge oscillations (even at zero temperature) associated with coherent phonon oscillations and electronic level oscillations. This fluctuating electronic level may resonate with a third site which captures the electron so that Ultrafast Electron Transfer (UFET) becomes possible. Numerical results are shown where two weakly interacting sites, a donor and a catalyst, form a CEPO that triggers an UFET to an acceptor. Without a catalytic site, a very large energy barrier prevents any direct ET. This UFET is shown to have many qualitative features similar to those observed in the primary charge separation in photosynthetic reaction centers. We suggest that more generally, CEPO could be a paradigm for understanding many selective chemical reactions involving electron transfer in biosystems.
doi:10.1007/s10867-005-1283-4
PMCID: PMC3456328  PMID: 23345905
electron transfer; ultrafast electron transfer; catalysis; photosynthetic reaction center; coherent oscillations; nonlinear phenomena
21.  Strongly Enhanced THz Emission caused by Localized Surface Charges in Semiconducting Germanium Nanowires 
Scientific Reports  2013;3:1984.
A principal cause of THz emission in semiconductor nanostructures is deeply involved with geometry, which stimulates the utilization of indirect bandgap semiconductors for THz applications. To date, applications for optoelectronic devices, such as emitters and detectors, using THz radiation have focused only on direct bandgap materials. This paper reports the first observation of strongly enhanced THz emission from Germanium nanowires (Ge NWs). The origin of THz generation from Ge NWs can be interpreted using two terms: high photoexcited electron-hole carriers (Δn) and strong built-in electric field (Eb) at the wire surface based on the relation . The first is related to the extensive surface area needed to trigger an irradiated photon due to high aspect ratio. The second corresponds to the variation of Fermi-level determined by confined surface charges. Moreover, the carrier dynamics of optically excited electrons and holes give rise to phonon emission according to the THz region.
doi:10.1038/srep01984
PMCID: PMC3680808  PMID: 23760467
22.  Singly ionized double-donor complex in vertically coupled quantum dots 
Nanoscale Research Letters  2012;7(1):489.
The electronic states of a singly ionized on-axis double-donor complex (D2+) confined in two identical vertically coupled, axially symmetrical quantum dots in a threading magnetic field are calculated. The solutions of the Schrödinger equation are obtained by a variational separation of variables in the adiabatic limit. Numerical results are shown for bonding and antibonding lowest-lying artificial molecule states corresponding to different quantum dot morphologies, dimensions, separation between them, thicknesses of the wetting layers, and magnetic field strength.
doi:10.1186/1556-276X-7-489
PMCID: PMC3477053  PMID: 22937880
Quantum dots; Adiabatic approximation; Artificial molecule; 78.67.-n; 78.67.Hc; 3.21.-b
23.  Trion X+ in vertically coupled type II quantum dots in threading magnetic field 
Nanoscale Research Letters  2012;7(1):532.
We analyze the energy spectrum of a positively charged exciton confined in a semiconductor heterostructure formed by two vertically coupled, axially symmetrical type II quantum dots located close to each other. The electron in the structure is mainly located inside the dots, while the holes generally move in the exterior region close to the symmetry axis. The solutions of the Schrödinger equation are obtained by a variational separation of variables in the adiabatic limit. Numerical results are shown for bonding and anti-bonding lowest-lying of the trion states corresponding to the different quantum dots morphologies, dimensions, separation between them, thicknesses of the wetting layers, and the magnetic field strength.
doi:10.1186/1556-276X-7-532
PMCID: PMC3563483  PMID: 23013605
Quantum dots; Adiabatic approximation; Trion; 78.67.-n; 71.35.Pq; 73.21.La
24.  Discontinuous properties of current-induced magnetic domain wall depinning 
Scientific Reports  2013;3:3080.
The current-induced motion of magnetic domain walls (DWs) confined to nanostructures is of great interest for fundamental studies as well as for technological applications in spintronic devices. Here, we present magnetic images showing the depinning properties of pulse-current-driven domain walls in well-shaped Permalloy nanowires obtained using photoemission electron microscopy combined with x-ray magnetic circular dichroism. In the vicinity of the threshold current density (Jth = 4.2 × 1011 A.m−2) for the DW motion, discontinuous DW depinning and motion have been observed as a sequence of “Barkhausen jumps”. A one-dimensional analytical model with a piecewise parabolic pinning potential has been introduced to reproduce the DW hopping between two nearest neighbour sites, which reveals the dynamical nature of the current-driven DW motion in the depinning regime.
doi:10.1038/srep03080
PMCID: PMC3812652  PMID: 24170087
25.  Fuzzy Modeling and Control of HIV Infection 
The present study proposes a fuzzy mathematical model of HIV infection consisting of a linear fuzzy differential equations (FDEs) system describing the ambiguous immune cells level and the viral load which are due to the intrinsic fuzziness of the immune system's strength in HIV-infected patients. The immune cells in question are considered CD4+ T-cells and cytotoxic T-lymphocytes (CTLs). The dynamic behavior of the immune cells level and the viral load within the three groups of patients with weak, moderate, and strong immune systems are analyzed and compared. Moreover, the approximate explicit solutions of the proposed model are derived using a fitting-based method. In particular, a fuzzy control function indicating the drug dosage is incorporated into the proposed model and a fuzzy optimal control problem (FOCP) minimizing both the viral load and the drug costs is constructed. An optimality condition is achieved as a fuzzy boundary value problem (FBVP). In addition, the optimal fuzzy control function is completely characterized and a numerical solution for the optimality system is computed.
doi:10.1155/2012/893474
PMCID: PMC3318236  PMID: 22536298

Results 1-25 (636851)