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Point Group (PG) symmetries play a fundamental role in many aspects of theoretical chemistry and computational materials science. With the objective to automatize the search of PG symmetry operations of generic atomic clusters, we present a new algorithm called Symmetry Operation FInder (SOFI). SOFI addresses the problem of identifying PG symmetry by framing it as a degenerate shape-matching problem, where the multiple solutions correspond to distinct symmetry operations. The developed algorithm is compared against three other algorithms dedicated to PG identification on a large set of atomic clusters. The results, along with some illustrative use cases, showcase the effectiveness of SOFI. The SOFI algorithm is released as part of the iterative rotations and assignments library, accessible at https://github.com/mammasmias/IterativeRotationsAssignments. [ABSTRACT FROM AUTHOR]

Saddle points on high-dimensional potential energy surfaces (PES) play a determining role in the activated dynamics of molecules and materials. Building on approaches dating back more than 50 years, many open-ended transition-state search methods have been developed to follow the direction of negative curvature from a local minimum to an adjacent first-order saddle point. Despite the mathematical justification, these methods can display a high failure rate: using small deformation steps, up to 80% of the explorations can end up in a convex region of the PES, where all directions of negative curvature vanish, while if the deformation is aggressive, a similar fraction of attempts lead to saddle points that are not directly connected to the initial minimum. In high-dimension PES, these reproducible failures were thought to only increase the overall computational cost, without having any effect on the methods' capacity to find all saddle points surrounding a minimum. Using activation-relaxation technique nouveau (ARTn), we characterize the nature of the PES around minima, considerably expanding on previous knowledge. We show that convex regions can lie on activation pathways and that not exploring beyond them can introduce significant bias in the saddle-point search. We introduce an efficient approach for traversing the convex regions, almost eliminating exploration failures, while multiplying by almost 10 the number of identified unique and connected saddle points as compared to the standard ARTn, thus underlining the importance of correctly handling convex regions for completeness of saddle point explorations. [ABSTRACT FROM AUTHOR]

Nocturnal temperature measurements of various infrared selective radiators performing radiative cooling have been carried out. Measured temperature differences between the radiators and ambient temperature were about 10 degrees C. Radiating surfaces have been prepared by applying different kinds of paints on aluminium substrates. It was shown that the addition of a BaSO4 extender in the paint dispersion increased the cooling performance of the paint radiators. Comparisons between predicted cooling performances by calculations and measured ones are discussed in detail.

The degradation of Staphylococcus aureus bacteria during treatment with neutral oxygen atoms was monitored by scanning electron microscopy. Experiments were performed in an afterglow chamber made from borosilicate glass. The source of oxygen atoms was remote inductively coupled radiofrequency oxygen plasma. The density of atoms at the samples was 8×1020 m-3. The treatment was performed at room temperature. The first effect was the removal of dried capsule. Capsule on exposed parts of bacteria was removed after receiving the dose of 6×1023 at./m2, while the parts of capsule filling the gaps between bacteria were removed after receiving the dose of 2.4×1024 m-2. After removing the capsule, degradation continued as etching of bacterial cell wall. The etching was rather nonuniform as holes with diameter of several 10 nm were observed. The cell wall was removed after receiving the dose of about 7×1024 m-2. The etching probabilities were about 2×10-5 for the capsule and 2×10-6 for the cell wall. The results were explained by different compositions of capsule and the cell wall. [ABSTRACT FROM AUTHOR]

Abstract: Molybdenum blue-type materials are usually obtained by partially reducing MoVI+ in acidic solutions, while in the presented method it is formed in ethanol solution of exfoliated MoS2 nanotubes, where the MoS2 flakes are the preferential location for their growth. Material was investigated by means of scanning electron and atomic force microscopy, showing the structure and self assembly, while also confirming that it is stable in high vacuum with molecules as small as 1.6nm and the agglomerates of few tens of nanometres. The ultraviolet–visible and photoelectron spectrometry show the change in absorption properties and oxidation states from MoS2 structure to molybdenum blue, while the presence of sulphur suggests that this is a new type of molybdenum blue material. [Copyright &y& Elsevier]

Silicon paints were prepared from yellow, ochre, dark ochre, green and blue pigments. To improve the solar absorptance, as, of these coatings, an existing black paint was admixed in different ratios. The optical properties of the mixed paints thus formed are expressed in terms of the Kubelka–Munk absorption and scattering coefficients in the spectral region 400–17000 nm. The scattering coefficient obtained for all paints was essentially equal. In the visible region the absorption coefficient follows the spectral characteristics of each respective colour. In the infrared absorption at ∼9000 nm and above 12000 nm are seen in all cases which result in a thickness-dependent increase of the thermal emittance, eT, of the coating. The metric chroma (Cab*) and lightness (L*) in CIELAB colour space were calculated for wide-angle observer in average daylight conditions. A range of non-black spectrally selective solar absorber surfaces with as>0.8 and eT<0.3 have been prepared with L*<45 and Cab*<10. [Copyright &y& Elsevier]

Presents information on a study which investigated the relationship between the macroscopic properties of plasma-enhanced chemical vapour deposition silicon nitride and oxynitride layers. Details of experimental procedures and calculations; Conclusions.

The limited ability of most human tissues to regenerate has necessitated the interventions namely autograft and allograft, both of which carry the limitations of its own. An alternative to such interventions could be the capability to regenerate the tissue in vivo.Regeneration of tissue using the innate capacity of the cells to regenerate is studied under the discipline of tissue engineering and regenerative medicine (TERM). Besides the cells and growth-controlling bioactives, scaffolds play the central role in TERM which is analogous to the role performed by extracellular matrix (ECM) in the vivo. Mimicking the structure of ECM at the nanoscale is one of the critical attributes demonstrated by nanofibers. This unique feature and its customizable structure to befit different types of tissues make nanofibers a competent candidate for tissue engineering. This review discusses broad range of natural and synthetic biodegradable polymers employed to construct nanofibers as well as biofunctionalization of polymers to improve cellular interaction and tissue integration. Amongst the diverse ways to fabricate nanofibers, electrospinning has been discussed in detail along with advances in this technique. Review also presents a discourse on application of nanofibers for a range of tissues, namely neural, vascular, cartilage, bone, dermal and cardiac.

We propose a versatile, parameter-less approach for solving the shape matching problem, specifically in the context of atomic structures when atomic assignments are not known a priori. The algorithm Iteratively suggests Rotated atom-centered reference frames and Assignments (iterative rotations and assignments (IRA)). The frame for which a permutationally invariant set-set distance, namely, the Hausdorff distance, returns a minimal value is chosen as the solution of the matching problem. IRA is able to find rigid rotations, reflections, translations, and permutations between structures with different numbers of atoms, for any atomic arrangement and pattern, periodic or not. When distortions are present between the structures, optimal rotation and translation are found by further applying a standard singular value decomposition-based method. To compute the atomic assignments under the one-to-one assignment constraint, we develop our own algorithm, constrained shortest distance assignments (CShDA). The overall approach is extensively tested on several structures, including distorted structural fragments. The efficiency of the proposed algorithm is shown as a benchmark comparison against two other shape matching algorithms. We discuss the use of our approach for the identification and comparison of structures and structural fragments through two examples: a replica-exchange trajectory of a cyanine molecule, in which we show how our approach could aid the exploration of relevant collective coordinates for clustering the data, and a SiO 2 amorphous model, in which we compute distortion scores, and compare them with a classical strain-based potential. The source code and benchmark data are available at https://github.com/mammasmias/IterativeRotationsAssignments.

Finding transition states and diffusion pathways is essential to understand the evolution of materials and chemical reactions. Such characterization is hampered by the heavy computation costs associated with exploring energy landscapes at ab initio accuracy. Here, we revisit the activation-relaxation technique (ARTn) to considerably reduce its costs when used with the density functional theory and propose three adapted versions of the algorithm to efficiently (i) explore the energy landscape of complex materials with the knowledge of a single minimum (ARTn); (ii) identify a transition state when two minima or a guess transition state is given (refining ART or r-ART); and (iii) reconstruct complex pathways between two given states (directed ART or d-ART). We show the application of these three variants on benchmark examples and on various complex defects in silicon. For the latter, the presented improvements to ART lead to much more precise transition states while being 2 to 6 times faster than the commonly used string methods such as the climbing image nudged elastic band method (CI-NEB).

In the original publication [Appl. Opt.55, 122 (2016)APOPAI0003-693510.1364/AO.55.000122], Eq. 5(c) was wrong. The correction for it is given here.

Ergonomic science at work and living places should appraise human factors concerning the photobiological effects of lighting. Thorough knowledge on this subject has been gained in the past; however, few attempts have been made to propose suitable evaluation parameters. The blue light hazard and its influence on melatonin secretion in age-dependent observers is considered in this paper and parameters for its evaluation are proposed. New parameters were applied to analyse the effects of white light-emitting diode (LED) light sources and to compare them with the currently applied light sources. The photobiological effects of light sources with the same illuminance but different spectral power distribution were determined for healthy 4-76-year-old observers. The suitability of new parameters is discussed. Correlated colour temperature, the only parameter currently used to assess photobiological effects, is evaluated and compared to new parameters.

Reflectance spectra may show very different and interesting shapes. The most interesting may be connected to Evans holes. Model calculations to reproduce this effect were done applying model dielectric function functions. When a weak oscillator appears within the frequency region of a strong one (i.e. between its TO and LO frequencies), its LO-mode frequency shifts towards higher wavenumbers. As a consequence, the oscillator strength of the corresponding weak mode becomes negative which produces a dip (Evans hole) in the reflectance spectrum. This model was successfully applied to analyze polarized reflectance spectra of potassium hydrogen succinate monocrystal in the ac crystal plane. The crystal symmetry was described by phenomenological model and by full symmetry consideration. The phenomenological approach applies the four-parametric model for dielectric function which allows good evaluation of asymmetric reflectance bands. A cosine dependence of oscillator strength on polarization angle was obtained for some bands, most likely due to small deviation of the crystal symmetry from orthorhombic. This is why the phenomenological approach provides good parameters for almost all phonon modes. The full symmetry consideration applies real description of dielectric tensor in the ac plane and the three-parameter model for dielectric function. This model could give very accurate directions of transition dipole moments, but cannot fit asymmetric bands well to measured reflectance. Both approaches describe all basic spectral features, the wide reflectance of asOH and the two Evans holes appearing on its shoulder.

We propose a novel, to our knowledge, method for characterizing the optical properties of pigment particles or powders. Measurements of the diffuse and the total transmittance as well as the diffuse and the total reflectance are used to obtain effective scattering and absorption coefficients per unit length for the particles that are dispersed in a continuous matrix. For dilute dispersions in the single-scattering regime scattering and absorption cross sections of the particles were obtained. The method was applied to two pigments, namely, FeMnCuO(x) and black carbon. The data were obtained by use of pellets consisting of low concentrations of FeMnCuO(x) or black-carbon pigments dispersed in a KBr matrix. The pigment volume concentrations used to evaluate the scattering and the absorption coefficients ranged from 0.053% to 0.530% for FeMnCuO(x) and 0.076% to 0.310% for the black carbon. These ranges were found to exhibit the linear dependence of the coefficients as a function of volume fraction, as given by single-scattering theory.