High‐transmission dielectric metasurface with 2π phase control at visible wavelengths

Recently, metasurfaces have received increasing attention due to their ability to locally manipulate the amplitude, phase and polarization of light with high spatial resolution. Transmissive metasurfaces based on high‐index dielectric materials are particularly interesting due to the low intrinsic losses and compatibility with standard industrial processes. Here, it is demonstrated numerically and experimentally that a uniform array of silicon nanodisks can exhibit close‐to‐unity transmission at resonance in the visible spectrum. A single‐layer gradient metasurface utilizing this concept is shown to achieve around 45% transmission into the desired order. These values represent an improvement over existing state‐of‐the‐art, and are the result of simultaneous excitation and mutual interference of magnetic and electric‐dipole resonances in the nanodisks, which enables directional forward scattering with a broad bandwidth. Due to CMOS compatibility and the relative ease of fabrication, this approach is promising for creation of novel flat optical devices.

     

The neuroblast and angioblast chemotaxic factor SDF-1 (CXCL12) expression is briefly up regulated by reactive astrocytes in brain following neonatal hypoxic-ischemic injury

Background  

Stromal cell-derived factor 1 (SDF-1 or CXCL12) is chemotaxic for CXCR4 expressing bone marrow-derived cells. It functions in brain embryonic development and in response to ischemic injury in helping guide neuroblast migration and vasculogenesis. In experimental adult stroke models SDF-1 is expressed perivascularly in the injured region up to 30 days after the injury, suggesting it could be a therapeutic target for tissue repair strategies. We hypothesized that SDF-1 would be expressed in similar temporal and spatial patterns following hypoxic-ischemic (HI) injury in neonatal brain.     

Analysis of the temporal evolution of atmospheric7Be as a vector of the behavior of other radionuclides in the atmosphere

The mean weekly levels of⁷Be in the atmosphere of Cáceres (Spain) was measured for three consecutive years, from 1992 to 1994. The values showed a strongly seasonal behavior, conditioned fundamentally by two effects: (1) the incorporation of⁷Be into the low layers of the troposphere due to the displacement of masses of air from higher layers caused by the solar irradiation, and (2) the washing of⁷Be out of the atmosphere by rain. From the quantification of these two effects, the residence time of⁷Be was determined in the atmosphere at ground level as 10.3 days, with an interval for the standard error of 9.0 and 12.1 days. Modelling the temporal evolution of this radionuclide we were able to explain 90.72% of the variance of the measured activity levels. Using the effective residence time of⁷Be, we were able to justify the diversity of values obtained for the deposition of¹³⁷Cs in different soils of the province of Cáceres due to the fallout from atmospheric nuclear blasts.     

Quantum parameters for guiding the design of Ti alloys with shape memory and/or low elastic modulus

Electronic structure calculations based on density functional theory have been applied to clusters of titanium with different alloying elements in order to obtain quantum parameters that give some information on the interaction between the mother and alloying atoms. Average values of these parameters weighted with the molar fractions have been calculated for 146 titanium alloys that exhibit shape memory and/or low elastic modulus. These values have been mapped in order to identify zones that group the alloys with either property. This information was used as a guide for designing seven new alloys with desired properties. These have been microstructurally and mechanically characterized; the results confirm the usefulness of the method.     

Enhanced performance of fast-response 3-hole wedge probes for transonic flows in axial turbomachinery

The paper presents the development and application of a three-sensor wedge probe to measure unsteady aerodynamics in a transonic turbine. CFD has been used to perform a detailed uncertainty analysis related to probe-induced perturbations, in particular the separation zones appearing on the wedge apex. The effects of the Reynolds and Mach numbers are studied using both experimental data together with CFD simulations. The angular range of the probe and linearity of the calibration maps are enhanced with a novel zonal calibration technique, used for the first time in compressible flows. The data reduction methodology is explained and demonstrated with measurements performed in a single-stage high-pressure turbine mounted in the compression tube facility of the von Karman Institute. The turbine was operated at subsonic and transonic pressure ratios (2.4 and 5.1) for a Reynolds number of 10⁶, representative of modern engine conditions. Complete maps of the unsteady flow angle and rotor outlet Mach number are documented. These data allow the study of secondary flows and rotor trailing edge shocks.     

Gabriel dimension and spectral torsion theories

In the study of Ring Theory, several concepts of dimension have appeared; among others we can find the Krull dimension, the Gabriel dimension and the Goldie dimension. These concepts have provided many interesting constructions. In a general context, these concepts are diffe nt, although there are some relations among them.     

Dehalogenation of α -haloketones and vic-dibromides with nickel boride

α-Haloketones and $\text{vic}$-dibromides are converted to the corresponding ketones and alkenes respectively with nickel boride generated $\text{in situ}$ from sodium borohydride and nickel chloride.     

Influence of geology and soil particle size on the surface-area/volume activity ratio for natural radionuclides

The radioactive concentrations of²²⁶Ra,²³²Th,²³⁵U and⁴⁰K in surface soil of the province of Cáceres (Spain) were studied as a function of the geology and grain size. The activities of the four radionuclides in granitic and metamorphic soils have normal frequency distributions, with the mean value being significantly higher for the granitic soils than for the metamorphic soils. Sedimentary soils present asymmetric distributions, and their activities lie between the previous two types. The specific activities of the four radionuclides rises as the particle radius decreases. The equationA _e =(P ₁/R)+P ₂ describes the dependence of the specific activityA _e on radiusR, P ₁ andP ₂ being parameters that are related to the surface area and volume activities of the grains. The isotopes²²⁶Ra,²³²Th and²³⁵U accumulate with greater intensity on the surface of the grains than⁴⁰K. This effect is more pronounced in granitic and sedimentary soils than in metamorphic soils.     

Transition state spectroscopy of open shell systems: Angle-resolved photodetachment spectra for the adiabatic singlet states of OHF

In this work three-dimensional potential energy surfaces of the first five singlet states of OHF are developed based on fits of more than 10,000 highly accurate ab initio points. An approximate treatment is presented for the calculation of the anisotropy parameter describing the electron angular distribution photodetached from a molecular anion. This method is used to calculate the angle-resolved photoelectron spectra in the photodetachment of OHF⁻. The wave packet formed in the neutral OHF system is placed at the transition state region, and yields the formation of OH + F and HF + O products. The results are compared with the recent experimental measurements published by Neumark [D.M. Neumark, Phys. Chem. Chem. Phys. 7 (2005) 433]. The intensity found at low electron kinetic energy including these five states and the three lower triplet states is found to be low. To analyze the effect of higher electronic states more excited ¹Σ⁻, ³Σ⁺ and ³Δ states are calculated at collinear geometry. The agreement with the experimental data improves, thus demonstrating that the correct simulation of the photodetachment spectrum at 213 nm involves at least 12 electronic states. All the structures of the experimental spectra are semiquantitatively reproduced finding an overall good agreement. It is concluded that the main problem of the simulation is in the intensity and anisotropy parameters. An alternative to their calculation would be to fit their values to reproduce the experimental results, but this would require to separate the contribution arising from different final electronic states.     

Restricted Hartree–Fock approximation. II. Computational aspects of the direct minimization procedure

A RHF energy minimization procedure based on the treatment outlined in Part I of this series of articles is presented. Test calculations performed on several closed- and open-shell systems show that the present procedure is definitely superior to the conventional SCF methods. In particular, the convergence of this procedure is ensured, the rate of convergency is high, and the computational cost of each cycle is low.