Molecular engineering of torsional potentials in fluorogenic dyes via electronic substituent effects

Fluorogenic dyes such as thiazole orange (TO) and malachite green have been used in live cellular imaging due to their low quantum yield in solution but large fluorescence enhancements when bound to cellular nucleic acids or to a specific surface-expressed protein partner. Better understanding of the structure-property relationships that establish this fluorogenic behavior could benefit the design of improved dyes. In TO the fluorogenic properties are related to twisting of the dye, following electronic excitation in solution, from an emissive planar structure to a nonemissive twisted structure. Herein we develop a computational approach to identify electron acceptor/donor substitution patterns that impart desirable properties to the dye, such as inducing spectral shifts while maintaining an excited-state torsional surface that will lead to fluorogenic behavior. Additivity of substituent effects, on properties such as spectral shifts and excited-state torsional barriers, is tested and found to be sufficiently accurate that it can be used to identify promising dye candidates. Although additivity suggests an underlying linearity in the substituent effects, additional simplifications stemming from linearity could not be identified. The approach is tested on TO, considering seven different substituents at seven substitution positions, to identify fluorogenic dyes that will span a range of wavelengths. Additivity allows quantum chemical calculations on singly substituted molecules (49 molecules) to be used to make estimates for all substitution patterns (nearly 10(6) molecules).     

Interior regularity criteria for suitable weak solutions of the magnetohydrodynamic equations

We present new interior regularity criteria for suitable weak solutions of the magnetohydrodynamic equations in dimension three: a suitable weak solution is regular near an interior point z if the scaled -norm of the velocity with 1?3/p+2/q?2, 1?q?∞ is sufficiently small near z and if the scaled -norm of the magnetic field with 1?3/l+2/m?2, 1?m?∞ is bounded near z. Similar results are also obtained for the vorticity and for the gradient of the vorticity. Furthermore, with the aid of the regularity criteria, we exhibit some regularity conditions involving pressure for weak solutions of the magnetohydrodynamic equations.     

Viscosity and dispersion state of magnetic suspensions

We investigate the viscosity behavior of a magnetic suspension in which magnetic particles are dispersed in a mixture of polyacrylic liquids. The size of magnetite particles is nearly 300 nm and the volume fraction of the magnetic particles is in the range of 0.003-0.03. The particle concentration dependence of the suspension viscosity yields the intrinsic viscosity [η], which varies from 25.6 at 5 s⁻¹ to 5.1 at 400 s⁻¹. The yield stress and the infinite shear viscosity of the suspension increase non-linearly as the particle concentration ? increases. We examine the effect of process conditions such as milling time and amount of dispersant on the viscosity behavior of the suspension. As milling time elapses, yield stress and low shear viscosity decrease and then reach constant values while the infinite shear viscosity remains constant. When oleic acid is added as a dispersant, the yield stress and low shear viscosity of the suspension show minimum values as the amount of oleic acid increases. These results agree with experimental results of sedimentation tests, which enable us to estimate the aggregate size of magnetic suspension. The yield stress and the low shear viscosity of the magnetic suspension are found to be useful in evaluating the dispersion state of the magnetic suspension.     

Silica‐Polymethacrylate Hybrid Particles Synthesized Using High‐Pressure Atom Transfer Radical Polymerization

Hybrid nanoparticles with a silica core and grafted poly(methyl methacrylate) (PMMA) or poly(n‐butyl methacrylate) (PBMA) chains were prepared via activators generated by electron transfer for atom transfer radical polymerization (AGET ATRP) at room temperature under high pressure. Due to enhanced propagation rate constant and reduced termination rate constant for polymerizations conducted under high pressure, the rate of polymerization was increased, while preserving good control over polymerization when compared to ATRP under ambient pressure. Molecular weights of greater than 1 million were obtained. The PMMA and PBMA brushes exhibited “semi‐diluted” or “diluted” brush architecture with the highest grafting densities ≈0.3 chain·nm⁻².

     

Newly Synthesized Nonvacuum Processed High-k Polymeric Dielectrics with Carboxyl Functionality for Highly Stable Operating Printed Transistor Applications

Solution-processed polar hydroxyl containing polymers such as poly(4-vinylphenol) are widely utilized in organic filed-effect transistors (OFETs) due to their high dielectric constant (k) and excellent insulating properties owing to the crosslinking through their hydroxyl groups. However, hydroxyl functionalities can function as trapsites, and their crosslinking reactions decrease the k value of materials. Hence, in this study, new solution-processable copolymers containing both carboxyl and hydrophobic functionalities are synthesized. A fluorophenyl azide (FPA) based UV-assisted crosslinker is also employed to promote the movement of polar carboxyl groups toward the bulk region and the hydrophobic functionalities to the surface region, thereby maintaining the high-k characteristics and hydrophobic surface in thin film. Thus, the addition of an FPA crosslinker eliminates the trapsites on the surface, allowing a stable operation and efficient charge transport. Additionally, the solution-processability enables the production of uniform and thin films to yield OFETs with stable and low-voltage driving characteristics. The printed layers are also applied as gate dielectrics for floating gate memory devices and in integrated one-transistor-one-transistor based memory cells, displaying their excellent memory performance. The synthesis and fabrication strategies employed in this study can become useful guidelines for the production of high-k dielectrics for stable OFETs and other applications.     

An alternative method for measurement of charge carrier mobility in semiconductors using photocurrent transient response

We report here a simple alternative method for measuring charge carrier drift mobilities in semiconductor devices. A typical falling photocurrent transient formula for switch-off-state was adjusted to obtain simultaneously electron and hole mobilities. For both undoped ZnO film and InAlAs/InGaAs quantum well structure, electron mobilities extracted from our model were compared with those obtained from maximum-entropy mobility-spectrum analysis method (ME-MSA). Our results demonstrated that electron mobility obtained from our photocurrent response model could serve as substitutes for a representative mobility obtained from ME-MSA.     

On the regularity of the axisymmetric solutions of the Navier-Stokes equations

We obtain improved regularity criteria for the axisymmetric weak solutions of the three dimensional Navier-Stokes equations with nonzero swirl. In particular we prove that the integrability of single component of vorticity or velocity fields, in terms of norms with zero scaling dimension give sufficient conditions for the regularity of weak solutions. To obtain these criteria we derive new a priori estimates for the axisymmetric smooth solutions of the Navier-Stokes equations. Received: 11 April 2000; in final firm: 26 November 2000 / Published online: 28 February 2002     

Enhanced Maximum Voiced Frequency Estimation Scheme for HTS Using Two‐Band Excitation Model

In a hidden Markov model–based speech synthesis system using a two‐band excitation model, a maximum voiced frequency (MVF) is the most important feature as an excitation parameter because the synthetic speech quality depends on the MVF. This paper proposes an enhanced MVF estimation scheme based on a peak picking method. In the proposed scheme, both local peaks and peak lobes are picked from the spectrum of a linear predictive residual signal. The average of the normalized distances of local peaks and peak lobes is calculated and utilized as a feature to estimate an MVF. Experimental results of both objective and subjective tests show that the proposed scheme improves the synthetic speech quality compared with that of a conventional one in a mobile device as well as a PC environment.     

Deciphering UV-induced DNA Damage Responses to Prevent and Treat Skin Cancer

Ultraviolet (UV) radiation is among the most prevalent environmental factors that influence human health and disease. Even 1 h of UV irradiation extensively damages the genome. To cope with resulting deleterious DNA lesions, cells activate a multitude of DNA damage response pathways, including DNA repair. Strikingly, UV-induced DNA damage formation and repair are affected by chromatin state. When cells enter S phase with these lesions, a distinct mutation signature is created via error-prone translesion synthesis. Chronic UV exposure leads to high mutation burden in skin and consequently the development of skin cancer, the most common cancer in the United States. Intriguingly, UV-induced oxidative stress has opposing effects on carcinogenesis. Elucidating the molecular mechanisms of UV-induced DNA damage responses will be useful for preventing and treating skin cancer with greater precision. Excitingly, recent studies have uncovered substantial depth of novel findings regarding the molecular and cellular consequences of UV irradiation. In this review, we will discuss updated mechanisms of UV-induced DNA damage responses including the ATR pathway, which maintains genome integrity following UV irradiation. We will also present current strategies for preventing and treating nonmelanoma skin cancer, including ATR pathway inhibition for prevention and photodynamic therapy for treatment.     

Photopatternable High-k Polysilsesquioxane Dielectrics for Organic Integrated Devices: Effects of UV Curing on Chemical and Electrical Properties

Polysilsesquioxanes (PSQs) have generated great interest as solution-processable inorganic polymers for obtaining high-dielectric-constant (k) dielectrics. Engineering the side chains in PSQs can enhance the polarization characteristics and provide different functionalities, such as photopatternability and ferroelectric performance. In this study, two types of UV curable high-k PSQs are prepared by introducing epoxy-containing side chains to the PSQs: 1) glycidyl epoxy-containing linear groups and 2) bulky cycloaliphatic epoxy-containing groups. The physical, chemical, and electrical properties of these two materials after UV curing are investigated. Both PSQ films show high dielectric strength and are successfully patterned after exposure to UV light. The structure of the side chains influences the UV curing behavior and capacitance characteristics of the PSQ dielectrics. These differences determine the driving behavior of the fabricated organic thin-film transistors, which exhibits either stable or ferroelectric operation. Finally, logic gates and memory cells exhibiting low-voltage and non-destructive operations are successfully integrated using UV cured PSQs. This approach for engineering PSQs with the purpose of achieving desirable photopatternability and high dielectric or ferroelectric performance can be used to realize simple and inexpensive solution-processing techniques for next generation integrated electronics.