Sparse modeling of super-resolution near-field structure read-out signals

In this study, super-RENS disc read-out signals were modeled with various nonlinear models. In the results of modeling the nonlinearity, DC offset, and domain bloom phenomena of the super-RENS channel with a second-order Volterra filter, it was identified that the number of significant quadratic coefficients was relatively small. Therefore, a sparse Volterra model and a truncated Volterra model are applied to effectively model the nonlinear channel. In addition, the Hammerstein-type asymmetric conversion model is employed to model the nonlinear channel for the purpose of comparison. The results demonstrate that the sparse model of a simplified polynomial form achieves good modeling performance for the super-RENS disc read-out signals.     

Unexpected consequences of block polydispersity on the self-assembly of ABA triblock copolymers

Controlled/"living" polymerizations and tandem polymerization methodologies offer enticing opportunities to enchain a wide variety of monomers into new, functional block copolymer materials with unusual physical properties. However, the use of these synthetic methods often introduces nontrivial molecular weight polydispersities, a type of chain length heterogeneity, into one or more of the copolymer blocks. While the self-assembly behavior of monodisperse AB diblock and ABA triblock copolymers is both experimentally and theoretically well understood, the effects of broadening the copolymer molecular weight distribution on block copolymer phase behavior are less well-explored. We report the melt-phase self-assembly behavior of SBS triblock copolymers (S = poly(styrene) and B = poly(1,4-butadiene)) comprised of a broad polydispersity B block (M(w)/M(n) = 1.73-2.00) flanked by relatively narrow dispersity S blocks (M(w)/M(n) = 1.09-1.36), in order to identify the effects of chain length heterogeneity on block copolymer self-assembly. Based on synchrotron small-angle X-ray scattering and transmission electron microscopy analyses of seventeen SBS triblock copolymers with poly(1,4-butadiene) volume fractions 0.27 ≤ f(B) ≤ 0.82, we demonstrate that polydisperse SBS triblock copolymers self-assemble into periodic structures with unexpectedly enhanced stabilities that greatly exceed those of equivalent monodisperse copolymers. The unprecedented stabilities of these polydisperse microphase separated melts are discussed in the context of a complete morphology diagram for this system, which demonstrates that narrow dispersity copolymers are not required for periodic nanoscale assembly.     

Discrete electrostatic charge transfer by the electrophoresis of a charged droplet in a dielectric liquid

We have experimentally investigated the electrostatic charging of a water droplet on an electrified electrode surface to explain the detailed inductive charging processes and use them for the detection of droplet position in a lab-on-a-chip system. The periodic bouncing motion of a droplet between two planar electrodes has been examined by using a high-resolution electrometer and an image analysis method. We have found that this charging process consists of three steps. The first step is inductive charge accumulation on the opposite electrode by the charge of a droplet. This induction process occurs while the droplet approaches the electrode, and it produces an induction current signal at the electrometer. The second step is the discharging of the droplet by the accumulated induced charge at the moment of contact. For this second step, there is no charge-transfer detection at the electrometer. The third step is the charging of the neutralized droplet to a certain charged state while the droplet is in contact with the electrode. The charge transfer of the third step is detected as the pulse-type signal of an electrometer. The second and third steps occur simultaneously and rapidly. We have found that the induction current by the movement of a charged droplet can be accurately used to measure the charge of the droplet and can also be used to monitor the position of a droplet under actuation. The implications of the current findings for understanding and measuring the charging process are discussed.     

The effects of surface modification on the electrical properties of p–n+ junction silicon nanowires grown by an aqueous electroless etching method

Although the aqueous electroless etching (AEE) method has received significant attention for the fabrication of silicon nanowires (SiNWs) due to its simplicity and effectiveness, SiNWs grown via the AEE method have a drawback in that their surface roughness is considerably high. Thus, we fabricated surface-modified p–n ⁺ junction SiNWs grown by AEE, wherein the surface roughness was reduced by a sequential processes of oxide growth using the rapid thermal oxidation (RTO) cycling process and oxide removal with a hydrofluoric acid solution. High-resolution transmission electron microscopy analysis confirmed that the surface roughness of the modified SiNWs was significantly decreased compared with that of the as-fabricated SiNWs. After RTO treatment, the wettability of the SiNWs had dramatically changed from superhydrophilic to superhydrophobic, which can be attributed to the formation of siloxane groups on the native oxide/SiNW surfaces and the effect of the nanoscale structure. Due to the enhancement in surface carrier mobility, the current density of the surface-modified p–n ⁺ junction SiNWs was approximately 6.3-fold greater than that of the as-fabricated sample at a forward bias of 4 V. Meanwhile, the photocurrent density of the surface-modified p–n ⁺ junction SiNWs was considerably decreased as a result of the decreases in the light absorption area, light absorption volume, and light scattering.     

Effect of oxyfluorination on gas sensing behavior of polyaniline-coated multi-walled carbon nanotubes

Polyaniline-coated multi-walled carbon nanotubes were prepared by in situ chemical polymerization method for the novel sensing materials of ammonia gas. The thickness of the polyaniline coatings was controlled by the oxyfluorination treatment on the multi-walled carbon nanotubes. The oxyfluorination with higher oxygen content produced the more hydrophilic functional groups on the surface of multi-walled carbon nanotubes. Both the resistivity change and the response time were significantly improved with high repeatability using the more hydrophilic multi-walled carbon nanotubes which were modified with oxyfluorination.     

Analysis of differential plaque depositions in the brains of Tg2576 and Tg-APPswe/PS1dE9 transgenic mouse models of Alzheimer disease

Adequate assessment of plaque deposition levels in the brain of mouse models of Alzheimer disease (AD) is required in many core issues of studies on AD, including studies on the mechanisms underlying plaque pathogenesis, identification of cellular factors modifying plaque pathology, and developments of anti-AD drugs. The present study was undertaken to quantitatively evaluate plaque deposition patterns in the brains of the two popular AD models, Tg2576 and Tg-APPswe/ PS1dE9 mice. Coronally-cut brain sections of Tg2576 and Tg-APPswe/PS1dE9 mice were prepared and plaque depositions were visualized by staining with anti- amyloid β peptides antibody. Microscopic images of plaque depositions in the prefrontal cortex, parietal cortex, piriform cortex and hippocampus were obtained and the number of plaques in each region was determined by a computer-aided image analysis method. A series of optical images representing a gradual increase of plaque deposition levels were selected in the four different brain regions and were assigned in each with a numerical grade of 1-6, where +1 was lowest and +6, highest, so that plaques per unit in mm(2) increased "sigmoidally" over the grading scales. Analyzing plaque depositions using the photographic plaque reference panels and a computer-aid image analysis method, it was demonstrated that the brains of Tg2576 mice started to accumulate predominantly small plaques, while the brains of Tg-APPswe/PS1dE9 mice deposited relatively large plaques.     

Structure–Activity Studies on the Fluorescent Indicator in a Displacement Assay for the Screening of Small Molecules Binding to RNA

A series of xanthone and thioxanthone derivatives with aminoalkoxy substituents were synthesized as fluorescent indicators for a displacement assay in the study of small‐molecule–RNA interactions. The RNA‐binding properties of these molecules were investigated in terms of the improved binding selectivity to the loop region in the RNA secondary structure relative to 2,7‐bis(2‐aminoethoxy)xanthone (X2S) by fluorimetric titration and displacement assay. An 11‐mer double‐stranded RNA and a hairpin RNA mimicking the stem loop IIB of Rev response element (RRE) RNA of HIV‐1 mRNA were used. The X2S derivatives with longer aminoalkyl substituents showed a higher affinity to the double‐stranded RNA than the parent molecule. Introduction of a methyl group on the aminoethoxy moiety of X2S effectively modulated the selectivity to the RNA secondary structure. Methyl group substitution at the C1′ position suppressed the binding to the loop regions. Substitution with two methyl groups on the amino nitrogen atom resulted in reducing the affinity to the double‐stranded region by a factor of 40 %. The effect of methyl substitution on the amino nitrogen atom was also observed for a thioxanthone derivative. Titration experiments, however, suggested that thioxanthone derivatives showed a more prominent tendency of multiple binding to RNA than xanthone derivatives. The selectivity index calculated from the affinity to the double‐stranded and loop regions suggested that the N,N‐dimethyl derivative of X2S would be suitable for the screening of small molecules binding to RRE.     

Remote stereocontrol of intramolecular rhodium carbene addition driven by a small and flexible chiral 2,4-pentanediol tether

Intramolecular rhodium carbenoid additions were studied using 2,4-pentanidiol as a chiral tether between a diazo group, a precursor of the carbene, and an aromatic group to be reacted with the carbene. The reaction was designed to perform the addition at a remote position, conserving the original high stereoselectivity appeared at additions near the tether, in addition to high regioselectivity and sufficient reaction efficiency. Substitution on the near reaction sites, the carbene carbon and aromatic group, in the reactant was effective to relegate the reaction site to a remote position. In the present study, two remote reactions, one dealing with C–H insertion and the other classified in Büchner reaction, were found to give sole products in high yields.     

Oxygen ionic conductivity of La2NiO4+δ via interstitial oxygen defect

The ionic conduction properties of La₂NiO_4+δ were studied from oxygen permeation flux and defect-related transport properties. The effects of the applied oxygen chemical potential gradient and temperature on the oxygen permeability of La₂NiO_4+δ at various thickness are reported. The thermally activated oxygen permeation flux increased monotonically with increasing oxygen chemical potential gradient, yielding a maximum of 0.15 cc min^?1 cm^?2 under air/N₂ conditions for the 0.95 mm-thick La₂NiO_4+δ specimen at 900 °C. The oxygen ion conductivity of La₂NiO_4+δ was calculated as a function of temperature and oxygen partial pressure by differentiating the chemical diffusion equation for the oxygen permeation flux based on the dominant electronic transference number. In addition, the oxygen ion conductivity was extracted successfully by solving the Nernst–Einstein equation combining with the calculated self-diffusion coefficient of oxygen from the chemical diffusivity and thermodynamic enhancement factor from the equilibrium oxygen nonstoichoimetry of a La₂NiO_4+δ specimen, and a deviation of the OPP dependence of 1/6 power was observed.