Performance of multi-junction cells due to illumination distribution across the cell surface

This paper addresses the influence of illumination distribution on the performance of a high concentration photovoltaic (HCPV) module. CPV systems comprise of optical elements as well as mechanical tracking to concentrate the solar flux onto the solar receiver as well as to keep the system on track with the sun. The performance of the subcells of the multi-junction concentrator cell depends on the optical alignment of the system. Raster scanning of the incident intensity in the optical plane of the receiver and corresponding I–V measurements were used to investigate the influence of illumination distribution on performance. The results show that the illumination distribution that differs between cells does affect the performance of the module. The performance of the subcells of the multi-junction concentrator cell also depends on the optical alignment of the system.     

Band splitting and relative spin alignment in bilayer systems

It is shown that one-particle spectra of the lower Hubbard band of bilayer correlated 2D systems with different relative alignments of the spin systems in the layers differ significantly. In particular, the bilayer band splitting differs from zero for identically directed alternating spins of different layers (F _z configuration), but tends to zero for antiparallel alignment (AF _z configuration). It is found that the type of the alignment of the ground state changes upon an increase in the doping δ from the lower AF _z configuration to the F _z configuration of the alignment observed for large values of δ. The behavior of bilayer splitting in Bi₂Sr₂CaCu₂O_8+δ suggests that the configuration of the alignment may change from F _z →AF _z simultaneously with the superconducting transition. The effects associated with the influence of spin alignment on the magnetic excitation spectrum as a method of studying the spin structure of bilayer systems are considered for homogeneous solutions of effective spin models.     

Magnetic coherence transfer induced by discharge radiation and the effect of radiation trapping on the lifetime of the hidden alignment of Ne terms

The dichroism of a neon gas discharge plasma in a weak magnetic field is investigated by scanning the 3s ₂-2p ₄ transition by monochromatic laser radiation. Magneto-optical resonances of the intrinsic macroscopic alignment and hidden alignment of the 2p ₄ level are separated. Against the background of these resonances, resonances attributed to coherence transfer from the 1s _{2, 4, 5} levels and the birefringence of the wings of the nearest absorption lines from the 1s _{4, 5} levels are observed. A new type of alignment is revealed—integral hidden alignment, whose lifetime, in contrast to the case with macroscopic alignment, increases without bound with increasing radiation trapping.     

General features of lipid organization

In block systems made of long chair molecules (lipids, detergents, copolymers), attached by one end at an interface, the steric interactions impose a non zero chain alignment even if the chains are very flexible. This may explain why, in recent experiments on deuterated lammellar lipids, the quadrupolar order parameter S appears to be the same for most of the CD₂ groups.     

High spin chemistry underlying organic molecular magnetism: Topological symmetry rule as the first principle of spin alignment in organic open-shell systems of π-conjugation and their ions

This review paper deals with an overview of molecule-based magnetism as a rapidly developing interdisciplinary field, topological symmetry rule as the first principle of spin alignment in organic open-shell systems in the ground state, the proposal of organic through-bond 1D and 2D ferro- and superparamagnets and the detection of the first organic high-spin molecule, m-phenylenebis(phenylmethylene) in the quintet ground state (S = 2), followed by extended organic high-spin systems with π-conjugation such as aromatic hydrocarbons having S = 3, 4, 5. The paper also describes a theoretical approach to the understanding of electronic spin structures of organic high-spin molecules by invoking both Heisenberg and Hubbard model Hamiltonians, weakly interacting intramolecular high-spin systems from both experimental and theoretical sides, the spin density distribution of the first organic high-spin molecule in terms of electron- nuclear multiple resonance spectroscopy and the detection and characterization of ionic high-spin hydrocarbons, emphasizing the establishment of high spin chemistry underlying organic molecular magnetism.     

The effect of evolving grain shape and alignment on the coercivity in thermomechanically deformed Nd13.9(Fe0.92Co0.08)80.3B5.3Ga0.5 permanent magnets

A series of samples of nominally identical composition have been melt-quenched and thermomechanically deformed to varying degrees, resulting in a variation in crystallographic alignment. The effect of the alignment on the coercivity has been studied using measurements of the temperature dependence of coercivity. The analysis was performed using a well-known phenomenological model which relates the coercivity to the anisotropy field, through a parameter α, and the saturation magnetization, through an effective demagnetization coefficient N_eff. It was discovered that the trends in α and N_eff as a function of crystallographic grain alignment are the opposite to what is expected and measured previously in analogous sintered samples of varying crystallographic alignment. An explanation for this behavior is proposed in which the evolving grain shape and grain boundary topography caused by deformation becomes the controlling factor in the coercivity rather than the crystallographic alignment of the grains.     

Comparison of the texture functions describing the grain alignment in NdFeB magnets

Two types of Gaussian distribution function (`θ type’ and `tan θ type') describing the degree of grain alignment in sintered NdFeB magnets have been compared in the distribution coefficient σ (or σ_g), the distribution probability P(θ) and the grain alignment dependence of coercivity. The results show that when the grain alignment is good (the ratio of remanence-to-saturation polarization J_r/J_s⩾0.90), σ(σ_g) and P(θ) for the two types of Gaussian functions have similar variation tendencies, the calculated values of normalized coercivity based on the starting field theory are basically the same and are consistent with experiments. When the grain alignment is not good (J_r/J_s⩾0.80), the variation tendencies of σ and P(θ) are different. In addition, according to `tan θ type’ Gaussian function, the theoretical values of the normalized coercivity based on the starting field theory are still consistent with the experiments, but according to `θ type’ Gaussian function, the theoretical values seriously deviate from the experiments. This means that the `tan θ type’ Gaussian function is a better texture function for describing the grain alignment.     

Monopole and topological electron dynamics in adiabatic spintronic and graphene systems

A unified theoretical treatment is presented to describe the physics of electron dynamics in semiconductor and graphene systems. Electron spin's fast alignment with the Zeeman magnetic field (physical or effective) is treated as a form of adiabatic spin evolution which necessarily generates a monopole in magnetic space. One could transform this monopole into the physical and intuitive topological magnetic fields in the useful momentum (K) or real spaces (R). The physics of electron dynamics related to spin Hall, torque, oscillations and other technologically useful spinor effects can be inferred from the topological magnetic fields in spintronic, graphene and other SU(2) systems.     

Effect of the intergrain interactions on the coercivity and its angular dependence for Nd(FeCo)B sintered magnets

Effects of interactions between grains with different alignment degrees on the coercivity and its angular dependence for Nd₁₆(Fe_0.8Co_0.2)₇₈B₆ sintered magnets have been studied. The experiments show that the intrinsic coercivity _jH_c decreases with enhancing grain alignment (decreasing alignment coefficient σ), the coercivity _jH_c(θ) increases with increasing angle θ between the applied field and the texture axis of the magnets and the variation ratio is larger for the magnets with better grain alignment. The coercivity of the magnets should be determined by the critical field making the moment of individual grains reverse and the interactions between the grains. For the sintered magnets composed of the grains with μm size, the magnetostatic interaction between the grains is stronger than the exchange coupling interaction and it makes the coercivity of magnet increase with increasing alignment coefficient σ. Taking into account the intergrain interactions, the starting field theory of coercivity is in good agreement with the experimental results for Nd₁₆(Fe_0.8Co_0.2)₇₈B₆ sintered magnets.     

Sequential fission angular distributions from mass-asymmetric heavy-ion reactions

The angular distributions of sequential fission fragments have been measured for the reactions of ⁴⁰Ar with ¹⁹⁷Au and ²³⁸U as a function of reaction Q-value and charge transfer. These angular, distributions are used to study the angular momentum and alignment of the deep-inelastic products which undergo fission. All of the fission fragment angular distributions are strongly focused into the plane defined by the beam and the projectile-like fragment velocity vectors. The in-plane angular distributions from reactions with uranium are isotropic for small energy losses and become anisotropic as the energy loss increases. For large negative Q-values, the in-plane anisotropy increases as the deep-inelastic products become more symmetric. The variation of the in-plane anisotropy with mass asymmetry for the two systems in this work was compared to a compilation of previous work and a consistent pattern was found. These alignment data are compared to equilibrium statistical calculations.     

Longitudinal contribution to the alignment polarization of quarks produced in e+ e−-annihilation: an O(αs) effect

We calculate the longitudinal contribution to the alignment polarization P ^l of quarks produced in e ⁺ e ^? annihilation. In the Standard Model, the longitudinal alignment polarization vanishes at the Born term level and thus receives its first non-zero contribution from the O(α_s) tree graph process. We provide analytical and numerical results for the longitudinal alignment polarization of massless and massive quarks, in particular for the recently discovered top quark.     

Coexistence of type-I and type-II band alignment in Ga(Sb,P)/GaP heterostructures with pseudomorphic self-assembled quantum dots

Band alignment of heterostructures with pseudomorphic GaSb_{1 ? x} P _x /GaP self-assembled quantum dots (SAQDs) lying on a wetting layer was studied. Coexistence of type-I and type-II band alignment was found within the same heterostructure. Wetting layer has band alignment of type-I with the lowest electronic state belonging to the X _XY valley of GaSb_{1 ? x} P _x conduction band, in contrast to SAQDs, which have band alignment of type-II, independently of the ternary alloy composition x. It is shown that type-I-type-II transition is a result of GaP matrix deformation around the SAQD.     

Angular momentum alignment in the reaction154Sm+214 MeV32S

Angular momentum alignment in the reaction¹⁵⁴Sm+214 MeV³²S has been investigated using discrete-lineγ-ray techniques. The anisotropies of stretchedE2 transitions from the target-like fragments reach approximately three at the largest energy losses, implying rather strong alignment. The results are compared with the predictions of a simple model.     

Aligned rotation of octupole-vibrational states in deformed nuclei

Analysis of level energies in aligned octupole bands in even-even deformed nuclei using the VMI-model expressed in terms of the rotational angular momentumR, show that almost complete alignment is reached at low spin values. It is shown that the alignment is almost spin independant. Using the ground-state band VMI-parameters only a renormalization of the alignment parameter 〈J _⊥〉 is enough to reproduce the level energies of the NPB's.     

Intrinsic fragment spins generated in the reactions of 20Ne with 197Au and 238U at 12.6 MeV/nucleon

The average magnitude and alignment of the intrinsic spin of the heavy partner from the reaction of 252 MeV ²⁰Ne with ¹⁹⁷Au and ²³⁸U were determined as a function of Q-value. These spin values were extracted from sequential fission angular distributions obtained in coincidence with projectile-like products. For all Q-values a large out-of-plane anisotropy was observed, while for large negative Q-values an in-plane anisotropy was observed. A very large entrance-channel mass-asymmetry was chosen to provide a stringent test of equilibrium statistical model predictions for the spin alignment. The importance of determining the direction of the line-of-centers of the dinuclear system at scission is discussed. Large values of P_ZZ were deduced for all Q- values. P_XY was observed to be positive in the quasielastic region and negative in the deep-inelastic region. The extracted alignment data are compared to equilibrium statistical model calculations.     

Study of dependence of quasi-particle alignment on proton and neutron numbers in A = 80 region through g-factor measurements

Dependence of quasi-particle alignment on proton and neutron numbers has been studied in A?=?80 mass region through g-factor measurements by using TMF-IMPAD. The experimental results show that for the nuclides ⁸⁴Zr, ⁸⁵Zr and ⁸⁶Zr with Z?=?40 the proton alignment is followed by the neutron alignment in ⁸⁴Zr and ⁸⁵Zr, while the neutron alignment is followed by the proton alignment in ⁸⁶Zr, and for the nuclides ⁸²Sr, ⁸³Y, ⁸⁴Zr and ⁸⁵Nb with N?=?44 the proton aligns only in ⁸²Sr, the proton alignment occurs first that is followed by the neutron alignment in ⁸³Y and ⁸⁴Zr and the neutron alignment is followed by the proton alignment in ⁸⁵Nb. Proton and/or neutron alignments lead to different patterns of the g-factor variation with spin.     

Competing interaction effects in recording media

In this work we present a study of the effects of easy axis alignment on coupling effects in recording media. We have studied both particulate and thin film media representing both flexible and rigid disc materials. The texture in the systems has been determined via measurements of the angular dependence of remanence and the coupling determined using the well-established ΔM technique. In particulate media only dipolar coupling is present whereas in thin films intergranular exchange effects also occur. In our thin film samples the exchange coupling is weak so that dipolar effects dominate. We find that the dipolar effects in both systems increase with texture, increasing their dominance over exchange effects.     

Electronic energy alignment at the PbSe quantum dots/ZnO(101̅0) interface

A number of solar energy conversion strategies depend on exciton dissociation across interfaces between semiconductor quantum dots (QDs) and other electron or hole conducting materials. A critical factor governing exciton dissociation and charge transfer in these systems is the alignment of electronic energy levels across the interface. We probe interfacial electronic energy alignment in a model system, sub-monolayer films of PbSe QDs adsorbed on single crystal ZnO(101?0) surfaces using ultraviolet photoemission spectroscopy. We establish electronic energy alignment as a function of quantum dot size and surface chemistry. We find that replacing insulating oleic-acid capping molecules on the QDs by the short hydrazine or ethanedithiol molecules results in pinning of the valence band maximum (VBM) of QDs to ZnO substrate states, independent of QD size. This is in contrast to similar measurements on TiO₂(110) where the alignment of the PbSe QD VBM to that of the TiO₂ substrate depends on QD size. We interpret these findings as indicative of strong electronic coupling of QDs with the ZnO surface but less with the TiO₂ surface. Based on the measured energy alignment, we predict that electron injection from the 1s_e level in photo-excited PbSe QDs to ZnO can occur with small QDs (diameter ? = 3.4 nm), but energetically unfavorably for larger dots (? = 6.7 nm). In the latter, hot electrons above the 1s_e level are necessary for interfacial electron injection.     

Study of the paraelectric behavior of OH− ions in alkali halides with optical and caloric methods-I. Statics of dipole alignment

The electric field induced alignment of substitutional OH^? ions in a variety of alkali halide crystals was studied, using electro-optical and electro-caloric techniques. As basis for the electro-optical studies, the u.v. absorption of OH^? in various crystals was thoroughly investigated at different temperatures, and in several cases oscillator strength values were determined. The energy position of the u.v. absorption of OH^? in 13 alkali halides follows closely an Ivery-relation, which is discussed in terms of a charge-transfer model. The observed electric field induced zero-moment changes of the u.v. absorption, which depend strongly on light polarization, field direction and temperature, can be quantitatively accounted for by a paraelectric alignment model of permanent dipoles with moment p. The anisotropy of the OH^? electro-dichroism reveals <100> dipole orientation in NaCl, KCl, KBr, RBCl, RbBr and RbI, <110> orientation in KI, and <111> orientation in CsBr. The determined dipole moment values p show little variation with the host material, which excludes sizeable contributions to p from off-center shifts of the OH^? ion. The observed saturation of the electro-dichroism indicates a peculiar ‘mixed’ polarization behavior of the optical transition, which will be discussed. Reversible electro-caloric measurements, performed on several OH^? systems, reveal a field dependence and anisotropy in the high field range, which yield dipole orientation and dipole moment values in agreement with the electrooptical results.     

Mutual alignment errors due to localized distortion in free-space laser communication links

Instead of Zernike polynomials, truncated Gaussian function is proposed to express localized wave-front deformation in studying mutual alignment errors in free-space laser communication links, which simplifies the calculation. Mutual alignment errors include pointing and tracking errors which depend on transmitting and receiving optical system, respectively. It is shown that both pointing and tracking errors depend on three parameters (the center value A, the radius a and the distance d) of Gaussian localized distortion and change regularly as they increase. The maximum pointing and tracking errors always appear around A = 0.4λ (rms = π). Moreover, pointing error is more sensitive to localized wave-front deformation than tracking error. Beam truncation ratio has great influence on pointing error, and obscuration ratio has less influence on pointing and tracking errors except that antenna secondary mirror shelters parts of the localized deformation. To reduce the influence of localized aberrations, the principles how to choose the optical devices with large aperture are given, and a method that aligns the pointing direction to compensate pointing and tracking errors is suggested. The work will contribute to the design of free-space laser communication systems.