Photosensitivity-enabled dispersion controllability for quasi-phase-matching in photonic crystal fibers

A novel photonic crystal fiber featured by concentric cores is proposed to induce dispersion controllability by photosensitivity. Chromatic dispersion can be changed from -1827 to 72 ps/nm/km with refractive index modulation of 4 x 10(-4) produced in Ge-doped regions in the fiber. Effective mode area of inner mode is as small as 6.4 mum(2). The proposed fiber enables to achieve quasi-phase-matched nonlinear parametric interaction in a single piece of photonic crystal fiber, by periodically alternating dispersion and compensating for phase mismatching caused by the dispersion.     

Characterization of star polymers in solution by small angle neutron scattering

In this paper we present the small angle neutron scattering characterization of two polyisoprene and one poly(ethylenepropylene) star polymers in solution. In the limit of low scattering vector, Q, and low concentration, φ, the molecular characteristics were determined. The molecular weights obtained are in good agreement with light scattering data. Deviations in second virial coefficients are due to a difference in solvent quality. Radii of gyration of the stars are well determined by the use of Kratky plots as is shown by the good agreement with average values of Zimm and Guinier analysis. Additionally, some thermodynamic properties were investigated in dilute and semidilute solutions. We have found that the concentration dependence of the osmotic compressibility is influenced by an expected step at the overlap concentration in both concentration regions.     

Detection of Metal Ions (Cu2+, Hg2+) and Cocaine by Using Ligation DNAzyme Machinery

The Cu²⁺‐dependent ligation DNAzyme is implemented as a biocatalyst for the colorimetric or chemiluminescence detection of Cu²⁺ ions, Hg²⁺ ions, or cocaine. These sensing platforms are based on the structural tailoring of the sequence of the Cu²⁺‐dependent ligation DNAzyme for specific analytes. The tethering of a subunit of the hemin/G‐quadruplex DNAzyme to the ligation DNAzyme sequence, and the incorporation of an imidazole‐functionalized nucleic‐acid sequence, which acts as a co‐substrate for the ligation DNAzyme that is tethered to the complementary hemin/G‐quadruplex subunit. In the presence of different analytes, Cu²⁺ ions, Hg²⁺ ions, or cocaine, the pretailored Cu²⁺‐dependent ligation DNAzyme sequence stimulates the respective ligation process by combining the imidazole‐functionalized co‐substrate with the ligation DNAzyme sequence. These reactions lead to the self‐assembly of stable hemin/G‐quadruplex DNAzyme nanostructures that enable the colorimetric analysis of the substrate through the DNAzyme‐catalyzed oxidation of 2,2′‐azinobis(3‐ethylbenzothiazoline‐6‐sulfonic acid), ABTS^2?, by H₂O₂ into the colored product ABTS^.?, or the chemiluminescence detection of the substrate through the DNAzyme‐catalyzed oxidation of luminol by H₂O₂. The detection limits for the sensing of Cu²⁺ ions, Hg²⁺ ions, and cocaine correspond to 1 nM , 10 nM and 2.5 μM , respectively. These different sensing platforms also reveal impressive selectivities.     

Bi-laplacian growth patterns in disordered media

Experiments in quasi-two-dimensional geometry (Hele-Shaw cells) in which a fluid is injected into a viscoelastic medium (foam, clay, or associating polymers) show patterns akin to fracture in brittle materials, very different from standard Laplacian growth patterns of viscous fingering. An analytic theory is lacking since a prerequisite to describing the fracture of elastic material is the solution of the bi-Laplace rather than the Laplace equation. In this Letter we close this gap, offering a theory of bi-Laplacian growth patterns based on the method of iterated conformal maps.     

Identification and calculation of the universal asymptote for drag reduction by polymers in wall bounded turbulence

Drag reduction by polymers in wall turbulence is bounded from above by a universal maximal drag reduction (MDR) velocity profile that is a log law, estimated experimentally by Virk as V+(y+) approximately 11.7logy+ - 17. Here V+(y+) and y+ are the mean streamwise velocity and the distance from the wall in "wall" units. In this Letter we propose that this MDR profile is an edge solution of the Navier-Stokes equations (with an effective viscosity profile) beyond which no turbulent solutions exist. This insight rationalizes the universality of the MDR and provides a maximum principle which allows an ab initio calculation of the parameters in this law without any viscoelastic experimental input.     

Aptamer-functionalized Au nanoparticles for the amplified optical detection of thrombin

The catalytic enlargement of aptamer-functionalized Au nanoparticles amplifies the optical detection of aptamer-thrombin complexes in solution and on surfaces.     

In vivo mapping of functional domains and axonal connectivity in cat visual cortex using magnetic resonance imaging

Noninvasive cognitive neuroimaging studies based on functional magnetic resonance imaging (fMRI) are of ever-increasing importance for basic and clinical neurosciences. The explanatory power of fMRI could be greatly expanded, however, if the pattern of the neuronal circuitry underlying functional activation could be made visible in an equally noninvasive manner. In this study, blood oxygenation level-dependent (BOLD)-based fMRI and diffusion tensor imaging (DTI) were performed in the same cat visual cortex, and the foci of fMRI activation utilized as seeding points for 3D DTI fiber reconstruction algorithms, thus providing the map of the axonal circuitry underlying visual information processing. The methods developed in this study will lay the foundation for in vivo neuroanatomy and the ability for noninvasive longitudinal studies of brain development.     

Magnetic control of electrocatalytic and bioelectrocatalytic processes

Bioelectronics is a rapidly progressing interdisciplinary research field that has important implications for the development of biosensors, biofuel cells, biomaterial-based computers, and bioelectronic devices. Magneto-controlled molecular electronics and bioelectronics are new topics that examine the effect of an external magnetic field on electrocatalytic and bioelectrocatalytic processes of functionalized magnetic particles associated with electrodes. In this article we describe the progress in the developments of magneto-switchable electrocatalytic and bioelectrocatalytic transformations, and the effects of the rotation of the magnetic particles on the electrocatalytic and bioelectrocatalytic processes are discussed. Finally, the implications of the results on the development of biosensors, amplified immunosensors, and DNA sensors are described.