Particle Size,Surface Coating,and PEGylation Influence the Biodistribution of Quantum Dots in Living Mice

This study evaluates the influence of particle size, PEGylation, and surface coating on the quantitative biodistribution of near‐infrared‐emitting quantum dots (QDs) in mice. Polymer‐ or peptide‐coated ⁶⁴Cu‐labeled QDs 2 or 12 nm in diameter, with or without polyethylene glycol (PEG) of molecular weight 2000, are studied by serial micropositron emission tomography imaging and region‐of‐interest analysis, as well as transmission electron microscopy and inductively coupled plasma mass spectrometry. PEGylation and peptide coating slow QD uptake into the organs of the reticuloendothelial system (RES), liver and spleen, by a factor of 6–9 and 2–3, respectively. Small particles are in part renally excreted. Peptide‐coated particles are cleared from liver faster than physical decay alone would suggest. Renal excretion of small QDs and slowing of RES clearance by PEGylation or peptide surface coating are encouraging steps toward the use of modified QDs for imaging living subjects.     

Visual Recognition and Categorization on the Basis of Similarities to Multiple Class Prototypes

One of the difficulties of object recognition stems from the need to overcome the variability in object appearance caused by pose and other factors, such as illumination. The influence of these factors can be countered by learning to interpolate between stored views of the target object, taken under representative combinations of viewing conditions. Difficulties of another kind arise in daily life situations that require categorization, rather than recognition, of objects. Although categorization cannot rely on interpolation between stored examples, we show that knowledge of several representative members, or prototypes, of each of the categories of interest can provide the necessary computational substrate for the categorization of new instances. We describe a system that represents input shapes by their similarities to several prototypical objects, and show that it can recognize new views of the familiar objects, discriminate among views of previously unseen shapes, and attribute the latter to familiar categories.     

Formation of ArCl(B) molecules in a transverse volume discharge

Results of optimizing a λ=175 nm ArCl(B-X) emitter pumped by a transverse volume discharge are presented. The formation of ArCl(B) molecules was investigated in a plasma formed by mixtures of rare gases with HCl and Cl₂ molecules. It is shown that the Cl₂ molecule is the most efficient chlorine carrier and that neon at pressures ≥ 50 kPa is the most efficient buffer gas. Pis’ma Zh. Tekh. Fiz. 25, 29–33 (June 12, 1999)     

Unravelling Light‐Induced Degradation of Layered Perovskite Crystals and Design of Efficient Encapsulation for Improved Photostability

Layered halide perovskites have recently shown extraordinary potential for low‐cost solution‐processable optoelectronic applications because of their superior moisture stability over their 3D counterparts. However, few studies have investigated the effect of light on layered hybrid perovskites. Here, the mechanically exfoliated nanoflakes of the 2D perovskite (PEA)₂PbI₄ (PEA, 2‐phenylethylammonium) are used as a model to investigate their intrinsic photostability. The light‐induced degradation of the flakes is investigated by using in situ techniques including confocal laser scanning microscopy, wide‐field fluorescence microscopy, and atomic force microscopy. Under resonant photoexcitation, (PEA)₂PbI₄ degrades to PbI₂. It is clearly shown that this process is initiated at the crystal edges and from the surface. As a consequence, the photoluminescence of (PEA)₂PbI₄ is progressively quenched by surface traps. Importantly, the light‐induced degradation can be suppressed by encapsulation using hexagonal boron nitride (hBN) flakes and/or polycarbonates. This report sheds light on a specific mechanism of light‐induced degradation in layered perovskites and proposes a new encapsulation method to improve their photostability.     

Hydrogen-Atom Transfer Oxidation with H2O2 Catalyzed by [FeII(1,2-bis(2,2′-bipyridyl-6-yl)ethane(H2O)2]2+: Likely Involvement of a (μ-Hydroxo)(μ-1,2-peroxo)diiron(III) Intermediate

The iron(II) triflate complex ( 1 ) of 1,2-bis(2,2′-bipyridyl-6-yl)ethane, with two bipyridine moieties connected by an ethane bridge, was prepared. Addition of aqueous 30 % H₂O₂ to an acetonitrile solution of 1 yielded 2 , a green compound with λ_max=710 nm. Moessbauer measurements on 2 showed a doublet with an isomer shift (δ) of 0.35 mm/s and a quadrupole splitting (ΔE_Q) of 0.86 mm/s, indicative of an antiferromagnetically coupled diferric complex. Resonance Raman spectra showed peaks at 883, 556 and 451 cm⁻¹ that downshifted to 832, 540 and 441 cm⁻¹ when 1 was treated with H₂¹⁸O₂. All the spectroscopic data support the initial formation of a (μ-hydroxo)(μ-1,2-peroxo)diiron(III) complex that oxidizes carbon-hydrogen bonds. At 0 °C 2 reacted with cyclohexene to yield allylic oxidation products but not epoxide. Weak benzylic C−H bonds of alkylarenes were also oxidized. A plot of the logarithms of the second order rate constants versus the bond dissociation energies of the cleaved C−H bond showed an excellent linear correlation. Along with the observation that oxidation of the probe substrate 2,2-dimethyl-1-phenylpropan-1-ol yielded the corresponding ketone but no benzaldehyde, and the kinetic isotope effect, k_H/k_D, of 2.8 found for the oxidation of xanthene, the results support the hypothesis for a metal-based H-atom abstraction mechanism. Complex 2 is a rare example of a (μ-hydroxo)(μ-1,2-peroxo)diiron(III) complex that can elicit the oxidation of carbon-hydrogen bonds.     

Representation,similarity, and the chorus of prototypes

It is proposed to conceive of representation as an emergent phenomenon that is supervenient on patterns of activity of coarsely tuned and highly redundant feature detectors. The computational underpinnings of the outlined concept of representation are (1) the properties of collections of overlapping graded receptive fields, as in the biological perceptual systems that exhibit hyperacuity-level performance, and (2) the sufficiency of a set of proximal distances between stimulus representations for the recovery of the corresponding distal contrasts between stimuli, as in multidimensional scaling. The present preliminary study appears to indicate that this concept of representation is computationally viable, and is compatible with psychological and neurobiological data.     

Analysis of effectiveness and benefits of collaboration modes with information- and knowledge-sharing

This study addresses an empirical analysis of information- and knowledge-sharing among collaborative decision makers. In this research, each decision maker represents one of three distributed centers in ERP systems: Sales, Production, and Procurement Centers. Their respective objectives and decision policies are defined to design collaborative decision-making environments. MICSS-LAN, an ERP simulation tool, was applied for the experiments, generating explicit numerical results that enable the measurement of the effectiveness and benefits by collaborative decision making. The experimental results indicate that total profit and due date performance have been improved by information- and knowledge-sharing. It implies that better design and utilization of ERP structures can be achieved by a certain level of information- and knowledge-sharing.     

A high-frequency UV-VUV radiation source operating on a mixture of argon with chlorine molecules

We present the working optical characteristics of a short-wavelength electric-discharge lamp operating at 150–270 nm (UV-VUV spectral range). The working medium is a mixture of argon with chlorine molecules (Ar-Cl₂) excited in a high-frequency transverse discharge between a metal electrode and a semitransparent nickel grid with an interelectrode distance of 2.2 cm. The proposed UV-VUV radiation source operates on the broadened emission lines of chlorine (Cl₂) and argon chloride (ArCl) molecules, which form a continuum in the 150–270 nm wavelength range. The source operation was optimized depending on the pumping power and the pressure and composition of the Ar-Cl₂ mixture. For a discharge excitation power within 50–300 W, the optimum working media were Ar-Cl₂ mixtures with the partial pressures P(Ar) = 300?400 Pa and P(Cl₂) = 30?40 Pa. The average total output power of the UV-VUV radiation extracted from the optimized source amounted to 15 W.