Chiral graphene nanoribbon inside a carbon nanotube: ab initio study

The dispersion-corrected density functional theory (DFT-D) is applied for investigation of structure and electronic properties of a sulfur-terminated graphene nanoribbon (S-GNR) encapsulated in a carbon nanotube. Two mechanisms of accommodation of the GNR in the carbon nanotube, distortion of the nanotube cross-section into an elliptic shape accompanied by bending of the GNR and transformation of the GNR to a helical conformation, are analyzed. Three types of elastic distortions of the nanotube and encapsulated GNR are revealed depending on the ratio of the diameter of the nanotube cavity to the GNR width. Helical states of the GNR are shown to be stabilized by the van der Waals attraction of sulfur atoms at neighbouring edges of adjacent turns of the GNR. The results of calculations are correlated with the experimental observations for the S-GNR synthesized recently inside the carbon nanotube. The hybrid DFT calculations of band structures of zigzag GNRs terminated with different atoms demonstrate that as opposed to O- and H-GNRs, the S-GNR is metallic even when deformed inside carbon nanotubes. Possible applications of GNRs encapsulated in carbon nanotubes are discussed.     

Light backscatter by surfaces composed of small spherical particles

We present measurements of phase angle curves of intensity and degree of linear polarization of powdery surfaces at two spectral bands centered near 0.44 and 0.63 microm. Three powder samples consisting of nonabsorbing spherical particles of sizes comparable with the wavelengths 0.5, 1.0, and 1.5 microm were examined. The particulate surfaces were measured in the phase angle range of 0.2 degrees-50 degrees by two different photometers and/or polarimeters. At small phase angles, powdery samples consisting of spherical particles (having very high albedo that resulted in significant multiple scattering) showed prominent features that corresponded to single-particle scattering. These features became more prominent after compressing the surfaces when we changed the packing density of the powders from 0.29 to 0.48. Noticeable differences were observed between polarimetric curves corresponding to different wavelengths. All the samples demonstrated prominent opposition intensity spikes at phase angles <2 degrees likely caused by the coherent backscatter enhancement due to multiple scattering within the particulate surface. The intensity phase curves at these two wavelengths were similar. The photopolarimetric measurements may have broad applications to the interpretation of photometry, spectroscopy, and polarimetry of the ice regoliths of high albedo satellites.     

Nonparaxial scalar treatment of sinusoidal phase gratings

Scalar diffraction theory is frequently considered inadequate for predicting diffraction efficiencies for grating applications where lambda/d>0.1. It has also been stated that scalar theory imposes energy upon the evanescent diffracted orders. These notions, as well as several other common misconceptions, are driven more by an unnecessary paraxial approximation in the traditional Fourier treatment of scalar diffraction theory than by the scalar limitation. By scaling the spatial variables by the wavelength, we have previously shown that diffracted radiance is shift invariant in direction cosine space. Thus simple Fourier techniques can now be used to predict a variety of wide-angle (nonparaxial) diffraction grating effects. These include (1) the redistribution of energy from the evanescent orders to the propagating ones, (2) the angular broadening (and apparent shifting) of wide-angle diffracted orders, and (3) nonparaxial diffraction efficiencies predicted with an accuracy usually thought to require rigorous electromagnetic theory.     

Electrical control of Förster energy transfer

Bringing together compounds of intrinsically different functionality, such as inorganic nanostructures and organic molecules, constitutes a particularly powerful route to creating novel functional devices with synergetic properties found in neither of the constituents. We introduce nanophotonic functional elements combining two classes of materials, semiconductor nanocrystals and dyes, whose physical nature arises as a superposition of the properties of the individual components. The strongly absorbing rod-like nanocrystals focus the incident radiation by photopumping the weakly absorbing dye via energy transfer. The CdSe/CdS nanorods exhibit a large quantum-confined Stark effect on the single-particle level, which enables direct control of the spectral resonance between donor and acceptor required for nanoscopic F?rster-type energy transfer in single nanorod-dye couples. With this far-field manipulation of a near-field phenomenon, the emission from single dye molecules can be controlled electrically. We propose that this effect could lead to the design of single-molecule optoelectronic switches providing building blocks for more complex nanophotonic circuitry.     

Structural studies of amphiphilic 4-helix bundle peptides incorporating designed extended chromophores for nonlinear optical biomolecular materials

Extended conjugated chromophores containing (porphinato)zinc components that exhibit large optical polarizabilities and hyperpolarizabiliites are incorporated into amphiphilic 4-helix bundle peptides via specific axial histidyl ligation of the metal. The bundle's designed amphiphilicity enables vectorial orientation of the chromophore/peptide complex in macroscopic monolayer ensembles. The 4-helix bundle structure is maintained upon incorporation of two different chromophores at stoichiometries of 1-2 per bundle. The axial ligation site appears to effectively control the position of the chromophore along the length of the bundle.     

Electron transfer dynamics of bistable single-molecule junctions

We present transport measurements of single-molecule junctions bridged by a molecule with three benzene rings connected by two double bonds and with thiol end-groups that allow chemical binding to gold electrodes. The I-V curves show switching behavior between two distinct states. By statistical analysis of the switching events, we show that a 300 meV mode mediates the transition between the two states. We propose that breaking and reformation of a S-H bond in the contact zone between molecule and electrode explains the observed bistability.     

Exploring three-dimensional matrix-assisted laser desorption/ionization imaging mass spectrometry data: three-dimensional spatial segmentation of mouse kidney

Three-dimensional (3D) imaging has a significant impact on many challenges of life sciences. Three-dimensional matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI-IMS) is an emerging label-free bioanalytical technique capturing the spatial distribution of hundreds of molecular compounds in 3D by providing a MALDI mass spectrum for each spatial point of a 3D sample. Currently, 3D MALDI-IMS cannot tap its full potential due to the lack efficient computational methods for constructing, processing, and visualizing large and complex 3D MALDI-IMS data. We present a new pipeline of efficient computational methods, which enables analysis and interpretation of a 3D MALDI-IMS data set. Construction of a MALDI-IMS data set was done according to the state-of-the-art protocols and involved sample preparation, spectra acquisition, spectra preprocessing, and registration of serial sections. For analysis and interpretation of 3D MALDI-IMS data, we applied the spatial segmentation approach which is well-accepted in analysis of two-dimensional (2D) MALDI-IMS data. In line with 2D data analysis, we used edge-preserving 3D image denoising prior to segmentation to reduce strong and chaotic spectrum-to-spectrum variation. For segmentation, we used an efficient clustering method, called bisecting k-means, which is optimized for hierarchical clustering of a large 3D MALDI-IMS data set. Using the proposed pipeline, we analyzed a central part of a mouse kidney using 33 serial sections of 3.5 μm thickness after the PAXgene tissue fixation and paraffin embedding. For each serial section, a 2D MALDI-IMS data set was acquired following the standard protocols with the high spatial resolution of 50 μm. Altogether, 512?495 mass spectra were acquired that corresponds to approximately 50 gigabytes of data. After registration of serial sections into a 3D data set, our computational pipeline allowed us to reveal the 3D kidney anatomical structure based on mass spectrometry data only. Finally, automated analysis discovered molecular masses colocalized with major anatomical regions. In the same way, the proposed pipeline can be used for analysis and interpretation of any 3D MALDI-IMS data set in particular of pathological cases.     

Tautochronism principle and grating dispersive delay lines

Dispersion delay lines (DDLs) are used for dispersion compensation in ultrafast optics. Note that the correct determination of the time delay of DDLs is based on the tautochronism principle: in an optical system consisting of refracting and reflecting elements the time delay between any two wavefronts is the same for all rays. But for diffraction gratings this principle is not valid; the time delay between the wavefronts of incident and diffracted waves for different light rays is different. However, fortunately, a pair of diffraction gratings can be combined so that the input and the output wavefronts of the system still satisfy the tautochronism principle. There are only two such grating systems: Treacy's system and Martinez's system. Both these systems are closely related to each other: in Martinez's system one can see virtual Treacy's system. Note that according to the tautochronism principle, dispersion Martinez's system and virtual Treacy's system are equal in value but opposite in sign.     

Low-temperature microwave sintering of TiN–SiC nanocomposites

Densification kinetics study during microwave sintering of titanium nitride-based nanocomposite has been conducted. A series of TiN–SiC compositions with 1, 3, 5 wt% of silicon carbide were microwave sintered at relatively low sintering temperatures (900–1,300 °C) for 0–30 min. The SiC content influenced on heating uniformity and final density and grain-size achieved. Densification process during microwave sintering obeyed the mechanism of grain-boundary diffusion with activation energy of 235 kJ mol⁻¹. Microwave sintering resulted in fine microstructure (~300 nm) and hence high values of micro hardness (~20 GPa).     

Solitonic lattice and Yukawa forces in the rare-earth orthoferrite TbFeO3

The random fluctuations of spins give rise to many interesting physical phenomena, such as the 'order-from-disorder' arising in frustrated magnets and unconventional Cooper pairing in magnetic superconductors. Here we show that the exchange of spin waves between extended topological defects, such as domain walls, can result in novel magnetic states. We report the discovery of an unusual incommensurate phase in the orthoferrite TbFeO(3) using neutron diffraction under an applied magnetic field. The magnetic modulation has a very long period of 340?? at 3?K and exhibits an anomalously large number of higher-order harmonics. These domain walls are formed by Ising-like Tb spins. They interact by exchanging magnons propagating through the Fe magnetic sublattice. The resulting force between the domain walls has a rather long range that determines the period of the incommensurate state and is analogous to the pion-mediated Yukawa interaction between protons and neutrons in nuclei.