SOFI: Finding point group symmetries in atomic clusters as finding the set of degenerate solutions in a shape-matching problem.

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.

Exploring potential energy surfaces to reach saddle points above convex regions.

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.

Biofunctionalization and Applications of Polymeric Nanofibers in Tissue Engineering and Regenerative Medicine.

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).

Deep Eutectic Solvents: Fundamental Aspect, Characterizations and Applications.

Deep eutectic solvents (DESs) containing bioactive have been explored as potential choices for therapeutic efficiency enhancement. DESs are regarded as superior compared to established solvents owing to accessibility, storage conditions, synthesis, and low cost. As such, intensive research has taken place in different disciplines, especially nutraceuticals, foods and pharmaceuticals.

Characterization of fresh PM deposits on calcareous stone surfaces: Seasonality, source apportionment and soiling potential.

Particulate matter (PM) pollution is one of the major threats to cultural heritage outdoors. It has been recently implied that organic aerosols will prevail over inorganic carbon particulates in the future, changing the main mechanisms of damage caused by poor air quality to calcareous heritage in particular. We studied fresh particulate deposits on marble and limestone surfaces exposed to urban air in sheltered and unsheltered configurations.

IRA: A Shape Matching Approach for Recognition and Comparison of Generic Atomic Patterns.

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.

Finding Reaction Pathways and Transition States: r-ARTn and d-ARTn as an Efficient and Versatile Alternative to String Approaches.

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 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).

Analysis of the polarized IR reflectance spectra of the monoclinic α-oxalic acid dihydrate.

In contrast to the extensive molecular and crystal structure investigations on oxalic acid dihydrate (CHO·2HO, α-POX) and its deuterated analogues (α-DOX), stands the absence of a complete vibrational spectra analysis. Such analysis is desirable in view of the proton dynamics in α-POX crystals. In this communication we report the room temperature polarized IR reflectance spectra of a single crystal of α-POX recorded from the ac crystal plane, and from the plane containing the b-crystallographic axis, with polarization along the axis.

Relation between colour- and phase changes of a leuco dye-based thermochromic composite.

Reversible colour change of leuco dye-based composites is in general closely related to their phase change, thus the two phenomena should occur at around the same temperature and should be influenced similarly. However, spatial confinement of the analysed sample affects the change in colour differently compared to its phase transition and the most pronounced effects can be observed during cooling. The bulk composite is coloured while still liquid and the colour hysteresis does not exhibit a loop.

Goniospectrometric space: identifiable presentation of spectral goniometric data for complex diffractive samples.

Optical security takes advantage of complex gonioapparent effects of diffractive samples having strong angular and spectral dependence of reflected light. However, resolving the full angular and spectral properties of these kinds of targets might be a tremendous task. Preferably, one would like to measure a more limited number of illumination-viewing directions, using a multiangle goniometer, and still reveal the complex and unique properties of the target.

Goniospectrometric space curve for coatings with special effect pigments.

Advanced application of eye-catching effects occurring in coatings with special effect pigments requires controlling their appearance. For this purpose, angular dependent reflectance must be analyzed in terms of the used flakes and their distribution inside the coating; it is important to know the size of the surface area they cover, and the position and precision of their orientation. These properties were varied using our numerical model, which gave an angular dependent reflectance factor for each set of coating parameters.

Evaluation of complex gonioapparent samples using a bidirectional spectrometer.

Many applications use gonioapparent targets whose appearance depends on irradiation and viewing angles; the strongest effects are provided by light diffraction. These targets, optically variable devices (OVDs), are used in both security and authentication applications. This study introduces a bidirectional spectrometer, which enables to analyze samples with most complex angular and spectral properties.

High-performance lighting evaluated by photobiological parameters.

The human reception of light includes image-forming and non-image-forming effects which are triggered by spectral distribution and intensity of light. Ideal lighting is similar to daylight, which could be evaluated by spectral or chromaticity match. LED-based and CFL-based lighting were analyzed here, proposed according to spectral and chromaticity match, respectively.

Goniospectrophotometric space curves of diffraction gratings and their applicability as appearance fingerprints.

The bidirectional reflectance distribution functions of diffraction gratings were calculated by applying diffraction theory and transformed into goniospectrophotometric space curves. Gratings with parallel sinusoidal grooves having periods of 1-3.5 μm and amplitudes below 0.

Suitability of goniospectrophotometric space curves as appearance fingerprints.

Goniospectrophotometric space curves were obtained by summation of spatially under-sampled bidirectional reflectance distribution function over all directions and repeating this for all wavelengths in the visible spectral region. This gives a 3D goniospectrophotometric curve called an xDNA graph. Systematic analysis applying 19 measurement geometries confirms existence of characteristic shapes of the graph for all optically similar samples.

Optical properties of exfoliated MoS2 coaxial nanotubes - analogues of graphene.

We report on the first exfoliation of MoS2 coaxial nanotubes. The single-layer flakes, as the result of exfoliation, represent the transition metal dichalcogenides' analogue of graphene. They show a very low degree of restacking in comparison with exfoliation of MoS2 plate-like crystals.

Optical behaviour of copper phthalocyanine preparations for inkjet inks.

The present study investigates the preparation of the copper phthalocyanine pigment for inkjet printing inks. The pigment particle size distribution was measured with laser diffraction at different times of wet milling. Simultaneously, the absorbance spectra in a visible-near infrared spectral region of the corresponding diluted pigment dispersions were measured.

Optical characterization method for black pigments applied to solar-selective absorbing paints.

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.

Absorption and scattering of light by pigment particles in solar-absorbing paints.

The optical properties of black-pigmented solar absorbing paint were analyzed phenomenologically by use of the Kubelka-Munk theory, including correction for reflection on front and rear surfaces. The effective absorption and scattering coefficients and the efficiency curves for absorption and scattering were calculated for coatings with different pigment-to-volume concentration ratios. The dependence of absorption and scattering efficiency on the pigment-to-volume concentration ratio was analyzed by reference to theoretical data in the literature.

Color rendering properties of interior lighting influenced by a switchable window.

Switchable windows are being installed into modern buildings. We report on how the variable transmittance of gasochromic and electrochromic switchable windows changes the color rendering properties of the daylight passing through these windows. We present a series of color rendering examples.

The IR reflectance spectra of the nu 3(SO4(2-)) and nu 4(SO4(2-)) band regions of some Tutton salts using polarized radiation: testing the model dielectric function.

The investigation of the vibrational bands of the SO(4)(2-) ions (in the nu(3) and nu(4) frequency regions) of six different Tutton salts was performed with specular IR reflectance spectroscopy using polarized radiation, on single crystal samples. The reflectance function under oblique incidence using dielectric model function as parameter (originally derived for optically uniaxial crystals) appeared to be readily applicable for the investigated monoclinic crystals. The frequencies of the transversal and longitudinal phonons were obtained by fitting of spectra recorded from (0 1 0), (0 0 1) and (1 0 0) crystal planes.

Infrared reflection-absorption spectra of metal-effect coatings.

The results of studies of infrared reflection-absorption spectra of metal-effect coatings are presented in this paper. Such coatings consist of metallic flakes that are dispersed in a polymer binder. The spectra show two distinct phenomena.

Infrared optical constants and roughness factor functions determination: the H(T)H(R)TR method.

This method was developed to determine the complex infrared optical constant of a single free-standing partially absorbing plate as wellas a thin solid film eposited on it. The method is based on exact formulas for normal transmittance T and near-normal reflectance R of the substrate as well as the film-substrate double layer. Coherent multiple reflections throughout the film and incoherent multiple reflections in the substrate as well as the intensity losses on the rough surface are taken into account.