Photoluminescence scanning on InAs/InGaAs quantum dot structures

The photoluminescence spectra of InAs quantum dots (QDs) embedded into four types of In_xGa_1−xAs/GaAs (x = 0.10, 0.15, 0.20 and 0.25) multi quantum well MBE structures have been investigated at 300 K in dependence on the QD position on the wafer. PL mapping was performed with 325 nm HeCd laser (35 mW) focused down to 200 μm (110 W/cm²) as the excitation source. The structures with x = 0.15 In/Ga composition in the In_xGa_1−xAs capping layer exhibited the maximum photoluminescence intensity. Strong inhomogeneity of the PL intensity is observed by mapping samples with the In/Ga composition of x ≥ 0.20-0.25. The reduction of the PL intensity is accompanied by a gradual “blue” shift of the luminescence maximum at 300 K as follows from the quantum dot PL mapping. The mechanism of this effect has been analyzed. PL peak shifts versus capping layer composition are discussed as well.     

Surface characterization of heat-treated electrolytic manganese dioxide

In this work a titration technique was used to determine the amphoteric surface properties of a series of heat-treated electrolytic manganese dioxide (EMD) samples (up to 500 degrees C). The surface of each sample was found to consist of independent acidic and basic hydroxyl sites, which could be characterized by their respective equilibrium constants and site concentrations. It was found that the acidic sites could not be characterized by a single equilibrium constant, but rather by a distribution indicating the subtle differences between individual sites, while a single equilibrium constant adequately represented the basic sites. For EMD, K(a) varied between 0.1 and 6.3x10(-5), with a corresponding [MnOH((a)T)] value varying between 9.1 and 6.4x10(-6) mol m(-2) over the pH range considered. K(b) and [MnOH((b)T)] were found to be 1.81x10(-9) and 1.93x10(-5) mol m(-2), respectively. With heat treatment, K(a) increased, suggesting a strengthening of the MnO bond via the removal of defects such as Mn(3+) ions and cation vacancies. The fact that K(b) also increased was initially counterintuitive because it suggested that the MnO bond had been weakened by heat treatment. However, assuming that the acidic and basic hydroxyl groups are independent, the trends in K(b) could be rationalized in terms of oxygen ion coordination in the progressively heat-treated samples. The number of surface sites (N(s)) was determined crystallographically and from the sum [MnOH((a)T)] + [MnOH((b)T)]. The data from both methods were of the same order of magnitude but exhibited different trends due to certain inadequacies in both methods. However, the data trends did indicate that the crystal planes at the particle surface could be changing with heat treatment due to a decrease in the value of N(s) determined from the surface titrations. Electrochemical analysis of the samples in 9 M KOH indicated that their performance degraded considerably with heat treatment. In comparison with the surface titration data, it was concluded that proton insertion into the structure occurred only through basic surface sites, the decreasing number of which could limit performance.     

The microwave spectrum,structure and centrifugal distortion constants of 2-chloroacrylonitrile

The microwave spectrum of 2-chloroacrylonitrile has been studied in the 26.5–40 GHz region. A total of 99 a- and b-type rotational transitions have been measured and assigned for CH₂ =C³⁵Cl(CN),yielding values for the rotational constants (in MHz): A = 6973.27, B = 3148.16, C = 2165.95. For CH₂=C³⁷Cl(CN) a total of 53 transitions have been measured and assigned and the rotational constants obtained are (in MHz): A = 6909.35, B = 3081.17, C = 2127.98. The distortion effects have also been studied and the quartic distortion constants have been evaluated. From the observed hyperfine structure, the chlorine nuclear quadrupole coupling constants have been obtained. The structure of vinyl cyanide and vinyl chloride can be transferred to account remarkably well for the observed rotational constants.     

Experimental demonstration of near-infrared negative-index metamaterials

Metal-based negative refractive-index materials have been extensively studied in the microwave region. However, negative-index metamaterials have not been realized at near-IR or visible frequencies due to difficulties of fabrication and to the generally poor optical properties of metals at these wavelengths. In this Letter, we report the first fabrication and experimental verification of a transversely structured metal-dielectric-metal multilayer exhibiting a negative refractive index around 2 microm. Both the amplitude and the phase of the transmission and reflection were measured experimentally, and are in good agreement with a rigorous coupled wave analysis.     

A new class of macrocyclic lanthanide complexes for cell labeling and magnetic resonance imaging applications

Lanthanide complexes have wide applications in biochemical research and biomedical imaging. We have designed and synthesized a new class of macrocyclic lanthanide chelates, Ln/DTPA-PDA-C(n), for cell labeling and magnetic resonance imaging (MRI) applications. Two lipophilic Gd3+ complexes, Gd/DTPA-PDA-C(n) (n = 10, 12), labeled a number of cultured mammalian cells noninvasively at concentrations as low as a few micromolar. Cells took up these agents rapidly and showed robust intensity increases in T1-weighed MR images. Labeled cells showed normal morphology and doubling time as control cells. In addition to cultured cells, these agents also labeled primary cells in tissues such as dissected pancreatic islets. To study the mechanism of cellular uptake, we applied the technique of diffusion enhanced fluorescence resonance energy transfer (DEFRET) to determine the cellular localization of these lipophilic lanthanide complexes. After loading cells with a luminescent complex, Tb/DTPA-PDA-C10, we observed DEFRET between the Tb3+ complex and extracellular, but not intracellular, calcein. We concluded that these cyclic lanthanide complexes label cells by inserting two hydrophobic alkyl chains into cell membranes with the hydrophilic metal binding site facing the extracellular medium. As the first imaging application of these macrocyclic lanthanide chelates, we labeled insulin secreting beta-cells with Gd/DTPA-PDA-C12. Labeled cells were encapsulated in hollow fibers and were implanted in a nude mouse. MR imaging of implanted beta-cells showed that these cells could be followed in vivo for up to two weeks. The combined advantages of this new class of macrocyclic contrast agents ensure future imaging applications to track cell movement and localization in different biological systems.     

A general chemical shift decomposition method for hyperpolarized 13C metabolite magnetic resonance imaging

Metabolic imaging with hyperpolarized carbon‐13 allows sequential steps of metabolism to be detected in vivo. Potential applications in cancer, brain, muscular, myocardial, and hepatic metabolism suggest that clinical applications could be readily developed. A primary concern in imaging hyperpolarized nuclei is the irreversible decay of the enhanced magnetization back to thermal equilibrium. Multiple methods for rapid imaging of hyperpolarized substrates and their products have been proposed with a multi‐point Dixon method distinguishing itself as a robust protocol for imaging [1‐¹³C]pyruvate. We describe here a generalized chemical shift decomposition method that incorporates a single‐shot spiral imaging sequence plus a spectroscopic sequence to retain as much spin polarization as possible while allowing detection of metabolites that have a wide range of chemical shift values. The new method is demonstrated for hyperpolarized [1‐¹³C]pyruvate, [1‐¹³C]acetoacetate, and [2‐¹³C]dihydroxyacetone. Copyright © 2016 John Wiley & Sons, Ltd.     

Midinfrared resonant magnetic nanostructures exhibiting a negative permeability

We experimentally demonstrate the first midinfrared (mid-IR) resonant magnetic nanostructures exhibiting a strong magnetic response corresponding to a negative permeability. This result is an important step toward the achievement of a negative refractive index in the IR. The possibility of extending negative permeability to higher frequencies is discussed; a structure with a negative effective permeability at a near-IR resonance frequency of 230 THz (1.3 microm) is proposed.     

Detection of human and rodent 5-HT3B receptor subunits by anti-peptide polyclonal antibodies

Background  

The 5-HT₃ receptor is a member of a neurotransmitter-gated ion channel family which includes nicotinic acetylcholine, GABA_A, and glycine receptors. While antibodies specific for the 5-HT_3A receptor subunit are plentiful, and have revealed a wealth of structural and functional information, few antisera exist for the detection of 5-HT_3B receptor subunits. Here we describe the generation and characterisation of a rabbit polyclonal antiserum that specifically recognises 5-HT_3B receptor subunits     

The emergence of dynamic form through phase relations in dynamical systems

Theories of visual form have been plagued with the problem of the correspondence between aspects of the form across time and across spatial location. Following Bateson's idea that knowledge emerges from the relations among multiple flows of difference, our computational model illustrates how visual form can emerge from the phase relations between two such flows in a way that eliminates the correspondence problem. Computationally, the first flow of process in a Boolean network falls into one among many different attractor cycles each of which cycles at a given fundamental frequency. A second cyclic systemic flow, with its own frequency, is computationally necessary before a person can experience the patterns (transients, attractors) of the first flow on a computer monitor; and the frequency of this second flow is a control variable. Dynamic visual form, in this computational logic, emerges from the phase relations between the frequencies of the two flows. These dynamic forms exhibit, simultaneously, many kinds of apparent motion suggesting that the processes generating apparent motion are not merely illusions but are in the service of dynamic form perception. This model of perceptual organization and moving form is discussed in relation to other approaches.     

Dibenzyl Structuresin a Macromolecular Chain. III. Dibenzyldiisocyanates Reactivity

The reactivity of the 2,2′-, 2,4′-, 4,4′-dibenzyldiisocyanate (2,2′-, 2,4′-, 4,4′-DBDI) with n-butanol in benzene has been studied. The concentrations of all species were monitored by using high performance liquid chromatography (HPLC). The reactivity of 4,4′-DBDI is similar to that of 4,4′-diphenylmethanediisocyanate (4,4′-MDI). Very strong intramolecular catalytic effects were noticed in the case of 2,2′-DBDI, probably due to the variable molecular geometry. These effects are responsible for the whole reaction pattern. The 2,4′-DBDI NCO ortho and para groups reactivities are different and comparable to that of 2,4-toluylenediisocyanate (2,4-TDI).