Earth’s Stratospheric Aerosol Parameters Reconstruction from Polarimetric Measurements of the Sky

Earth’s climate changes are the result of natural changes in the energy balance of Sun irradiation and influence of anthropogenic factors on the variations of ozone layer thickness and stratospheric aerosol abundance. It is developed a miniature polarimeter for satellite polarimetric experiments in the ultraviolet region of the sunlight spectrum. The main task of this device is to the obtain an information on the stratospheric aerosol physical properties. We tested this polarimeter on a bench specially designed and manufactured as well. It is possible to measure by it the phase dependences of the degree of linear polarization (DLP) of solar radiation scattered by the Earth’s atmosphere. A set of special computer programs was developed for comparing the spectral polarimetric measurements DLP data of cloudless sky with model calculations of DLP for the artificial gas-aerosol medium. Thus, the prototype of satellite polarimeter as well as special computer programs make it possible to study the Earth’s atmosphere aerosol physical characteristics.

Thermochromic and opacity behaviors in vanadium dioxide nanofilms: a theoretical study

Vanadium dioxide nanofilms are one of the most essential materials in electronic applications like smart windows. Therefore, studying and understanding the optical properties of such films is crucial to modifying the parameters that control these properties. To this end, this work focuses on investigating the opacity as a function of the energy directed at the nanofilms with different thicknesses (1 – 100) nm. Effective mediator theories (EMTs), which are considered as the application of Bruggeman's formalism and the Looyenga mixing rule, have been used to estimate the dielectric constant of VO2 nanofilms. The results show different opacity behaviors at different wavelength ranges (ultraviolet, visible, and infrared). The results depict that the highest opacity of the insulating phase is achieved at the ultraviolet region and it reduces for the metal phase. Besides, the results demonstrate that the opacity possesses a redshift during the changes at the three phases. Regarding the infrared region, the lowest opacity value is achieved at the insulator phase and it increases to the highest value at the metal phase. In the visible region, the opacity behavior remains similar in the three phases. It is worth noting that the lowest opacity is found for thinner nanofilm. Since both the refractive index and the extinction index are among the most essential optical constants, hence, both of them were compared with the experiment results, and an excellent agreement is achieved between them.

The Interaction of the 2D MoP2 and NbP2 Surfaces with Carbon Dioxide and Carbon Monoxide and Changes in Their Optical Properties

Using first-principles molecular dynamics (FPMD) simulations at atmospheric pressure and 300 K, we investigated the adsorption of the molecules CO and CO2 on each of the surfaces of the 2D materials MoP2 and NbP2. We found that both surfaces adsorbed the carbon monoxide molecule but not the carbon dioxide. The adsorption energy on the MoP2 surface was −0.9398 eV, and on the NbP2 surface, −0.9017 eV. Furthermore, we obtained substantial changes in the optical properties of each 2D material after the CO adsorption. For the two materials, the optical absorption shows significant changes in the ultraviolet region. Furthermore, the two surfaces present essential changes in the ultraviolet range in the case of reflectivity.

Evaluation of two Non-Edible, Wild Indigenous Botswana Crops (Croton megalobotrys (Motsebi/Letsebi/Moshoole) and Ricinus communis (Mokhure)) as Potential Feedstocks for Petroleum and Cosmetic Industries

Croton megalobotrys and Ricinus cummunis plants produce high-quality non-edible seed oils at relatively high quantities of 39.65 ± 0.06 % w/w to 53.74 ± 0.04 % w/w. The Iodine values of 85.97 ± 1.62 g I2/100 g to 96.51 ± 1.31 g I2/100 g; the low acid values of 0.96 ± 0.05 mg KOH/g to 5.31 ± 0.76 mg KOH/g; and high saponification values of 139.65 ± 1.06 mg KOH/g to 153.01 ± 1.67 mg KOH/g show that these seed oils can be useful feedstocks in the petroleum, soap, and cosmetics industries. GC-MS results revealed that R. cummunis seed oil is made up of eight (8) fatty acids with the bulk being ricinoleic acid at 81.51 %. Ricinoleic acid is the main fatty acid used in oleochemical industries. C. megalobotrys seed oil is made up of five (5) fatty acids, the most abundant being Linoleic acid which makes up 58.01 % of the seed oil. The other two significant fatty acids in C. megalobotrys seed oil are palmitic and oleic acids at 19.51 % and 18.37 %, respectively. These acids are important as starting materials in soap, cosmetic, and pharmaceutical industries. The fatty acids of the two seed oils absorb light at the ultraviolet region of the electromagnetic spectrum. This means that cosmetic products made from these seed oils will be effective in protecting the human skin against ultraviolet radiation. The FT-IR peaks for the two seed oils show that even though these seed oils are made up of different fatty acids, the active sites of their fatty acids are similar, implying that these seed oils can be used as starting materials in similar industries.

Circularly Polarized Light Detection by Chiral Photonic Cellulose Nanocrystal with ZnO Photoconductive Layer in Ultraviolet Region

Circularly polarized light (CPL) detection and polarization state recognition are required for a wide range of applications. Conventional polarization detection with optical components causes difficulties for miniaturization and integration. An effective design strategy is proposed for direct CPL detection with chiral material. Here, we realized direct CPL detection based on the combination of chiral photonic cellulose nanocrystal (CNC) and ultraviolet-sensitive ZnO photoconductive material. The CNC layer deposited by evaporation-induced self-assembly established the left-handed chiral nematic structure with a photonic bandgap (PBG) to recognize left-handed CPL (LCPL) and right-handed CPL (RCPL) at specific wavelengths. The PBG of CNC layer has been modulated by the adjustment of chiral nematic pitch to match the semiconductor bandgap of ZnO film in ultraviolet region. The photocurrents under RCPL and LCPL are 2.23 × 10−6 A and 1.77 × 10−6 A respectively and the anisotropy factor Δgpc of 0.23 is acquired for the CPL detection based on the chiral photonic CNC. This design provides a new approach to the detection of CPL polarization state with competitive performance.

High-harmonic generation in Weyl semimetal β-WP2 crystals

As a quantum material, Weyl semimetal has a series of electronic-band-structure features, including Weyl points with left and right chirality and corresponding Berry curvature, which have been observed in experiments. These band-structure features also lead to some unique nonlinear properties, especially high-order harmonic generation (HHG) due to the dynamic process of electrons under strong laser excitation, which has remained unexplored previously. Herein, we obtain effective HHG in type-II Weyl semimetal β-WP2 crystals, where both odd and even orders are observed, with spectra extending into the vacuum ultraviolet region (190 nm, 10th order), even under fairly low femtosecond laser intensity. In-depth studies have interpreted that odd-order harmonics come from the Bloch electron oscillation, while even orders are attributed to Bloch oscillations under the “spike-like” Berry curvature at Weyl points. With crystallographic orientation-dependent HHG spectra, we further quantitatively retrieved the electronic band structure and Berry curvature of β-WP2. These findings may open the door for exploiting metallic/semimetallic states as solid platforms for deep ultraviolet radiation and offer an all-optical and pragmatic solution to characterize the complicated multiband electronic structure and Berry curvature of quantum topological materials.

Poly(N,N-dimethylacrylamide)-coated upconverting NaYF4:Yb,Er@NaYF4:Nd core–shell nanoparticles for fluorescent labeling of carcinoma cells

Upconverting luminescent lanthanide-doped nanoparticles (UCNP) belong to promising new materials that absorb infrared light able to penetrate in the deep tissue level, while emitting photons in the visible or ultraviolet region, which makes them favorable for bioimaging and cell labeling. Here, we have prepared upconverting NaYF4:Yb,Er@NaYF4:Nd core–shell nanoparticles, which were coated with copolymers of N,N-dimethylacrylamide (DMA) and 2-(acryloylamino)-2-methylpropane-1-sulfonic acid (AMPS) or tert-butyl [2-(acryloylamino)ethyl]carbamate (AEC-Boc) with negative or positive charges, respectively. The copolymers were synthesized by a reversible addition-fragmentation chain transfer (RAFT) polymerization, reaching Mn ~ 11 kDa and containing ~ 5 mol% of reactive groups. All copolymers contained bisphosphonate end-groups to be firmly anchored on the surface of NaYF4:Yb,Er@NaYF4:Nd core–shell nanoparticles. To compare properties of polymer coatings, poly(ethylene glycol)-coated and neat UCNP were used as a control. UCNP with various charges were then studied as labels of carcinoma cells, including human hepatocellular carcinoma HepG2, human cervical cancer HeLa, and rat insulinoma INS-1E cells. All the particles proved to be biocompatible (nontoxic); depending on their ξ-potential, the ability to penetrate the cells differed. This ability together with the upconversion luminescence are basic prerequisites for application of particles in photodynamic therapy (PDT) of various tumors, where emission of nanoparticles in visible light range at ~ 650 nm excites photosensitizer.

Anomalous dependence of ionization probability and electron angular distributions on orientation of molecular axis in photoionization of H+ 2: effect of two-center interference

A theoretical and computational study of photoionization of the one-electron molecular ion H+ 2 initially in the 1σu state is performed. The laser pulse is linearly polarized with the carrier wavelength in the extreme ultraviolet region. The electron wave function is obtained by solving the time-dependent Schrödinger equation with the help of the generalized pseudospectral method. The dependence of the total ionization probability and photoelectron spectra on the orientation of the molecular axis is analyzed. At the wavelength of 12.5 nm, anomalous behavior of the ionization probability is found, where the ionization probability increases with an increase of the angle between the polarization vector of the external field and the molecular axis and reaches a maximum at the perpendicular orientation of the molecule. The phenomenon is explained as resulting from the two-center interference in the wave function of the emitted electron. When the wavelength or internuclear distance change, the effect disappears, and the ionization probability exhibits its usual behavior with the maximum at the parallel orientation of the molecular axis.