Multicolored pH-tunable and activatable fluorescence nanoplatform responsive to physiologic pH stimuli

Tunable, ultra-pH responsive fluorescent nanoparticles with multichromatic emissions are highly valuable in a variety of biological studies, such as endocytic trafficking, endosome/lysosome maturation, and pH regulation in subcellular organelles. Small differences (e.g., <1 pH unit) and yet finely regulated physiological pH inside different endocytic compartments present a huge challenge to the design of such a system. Herein, we report a general strategy to produce pH-tunable, highly activatable multicolored fluorescent nanoparticles using commonly available pH-insensitive dyes with emission wavelengths from green to near IR range. The primary driving force of fluorescence activation between the ON (unimer) and OFF (micelle) states is the pH-induced micellization. Among three possible photochemical mechanisms, homo F?rster resonance energy transfer (homoFRET)-enhanced decay was found to be the most facile strategy to render ultra-pH response over the H-dimer and photoinduced electron transfer (PeT) mechanisms. Based on this insight, we selected several fluorophores with small Stoke shifts (<40 nm) and established a panel of multicolored nanoparticles with wide emission range (500-820 nm) and different pH transitions. Each nanoparticle maintained the sharp pH response (ON/OFF < 0.25 pH unit) with corresponding pH transition point at pH 5.2, 6.4, 6.9, and 7.2. Incubation of a mixture of multicolored nanoparticles with human H2009 lung cancer cells demonstrated sequential activation of the nanoparticles inside endocytic compartments directly correlating with their pH transitions. This multicolored, pH-tunable nanoplatform offers exciting opportunities for the study of many important cell physiological processes, such as pH regulation and endocytic trafficking of subcellular organelles.     

A focussed review of scheduling in services

The paper first outlines the special characteristics of services, as compared to those of the manufacturing systems. The second section stresses that each of the service systems has its own major primary objective/objectives, but such primary objectives are invariably in conflict with the well-known cost-minimization objective of manufacturing systems. The paper also discusses the variety of legal, union, and budgetary constraints which must not be violated by the service-system managers under any circumstances. Finally, the paper lists eleven different types of service systems, showing for each the unique constraints, the special sets of conflicting objectives as designated by their respective managements, and the commonly used techniques, methods and procedures. The most important and the most frequently referenced articles related to each type of system are indicated.     

Investigation of bed shear stresses subject to external turbulence

The fluctuating bed shear stress has largely been investigated only for uniform channel flows and boundary layers. In practical engineering, the flow conditions are often modified due to the presence of various hydraulic structures. To what extent the modification affects the known characteristics of the bed shear stress is not clear. This study presents experimental results of the bed shear stress fluctuations, which are obviously subjected to external turbulence generated by superimposing artificial structures in the open channel flows. The statistical analysis of the measurements shows that the probability density function of the bed shear stress can be described by the lognormal function. Some associated relations concerning higher-order moments, skewness and kurtosis, which are derived from the lognormal function, are further compared with the experimental data. Physical implication of the skewed probability density distribution is finally discussed.     

Two-component hot-film probe for measurements of wall shear stress

A two-component, hot-film probe has been developed, to measure the wall shear stress as a vector quantity in time-dependent flows. The probe has been applied for the measurements of the bottom shear stress in a flow generated by combined waves and current in a water basin where the magnitude and the direction of the bottom shear stress varied periodically with respect to time. The probe has also been used to measure the bottom shear stress around a vertical cylinder exposed to water waves generated in a wave flume.     

THE THEORY OF EXCITON DISTRIBUTION IN ORGANIC SOLIDS

Abstract. The present paper gives an account of the phenomenological theory underlying the three dimensional distribution of excitons in solids. General expressions for the steady state distribution are derived taking into account the bulk and surface and annihilation generation of excitons, the influence of sample geometry and fluorescent reabsorption effects. The wave form of the optical excitation has also been included for purposes of generality. Approximations to the general results are provided for certain special cases which may apply to organic solids.     

Four-membered ring cyclic ketene –O,O–, –O,S–, –O,N–, –S,S–, –S,N–, and –N,N–acetals and their corresponding cations: a computational study

A systematic computational study of four-membered cyclic ketene –O,O–, –O,S–, –O,N–, –S,N– and –N,N-acetals as well as their protonated analogs have been performed at the second order M?ller Plesset level with a polarized triple zeta basis set. The main purpose of this study was to make predictions about the nucleophilicity of these systems and the variations in nucleophilicity with the hetero atoms. Our calculations suggest that all six target molecules are good nucleophiles, and that the N,N analog is the strongest and the S,S analog the weakest nucleophile. Our results include molecular geometries, bond lengths, proton affinities, vibrational frequencies, and calculated charges.