Numerical solutions of the isotropic 3-wave kinetic equation

We show that the isotropic 3-wave kinetic equation is equivalent to the mean-field rate equations for an aggregation–fragmentation problem with an unusual fragmentation mechanism. This analogy is used to write the theory of 3-wave turbulence almost entirely in terms of a single scaling parameter. A new numerical method for solving the kinetic equation over a large range of frequencies is developed by extending Lee’s method for solving aggregation equations. The new algorithm is validated against some analytical calculations of the Kolmogorov–Zakharov (KZ) constant for some families of model interaction coefficients. The algorithm is then applied to study some wave turbulence problems in which the finiteness of the dissipation scale is an essential feature. Firstly, it is shown that for finite capacity cascades, the dissipation of energy becomes independent of the cut-off frequency as this cut-off is taken to infinity. This is an explicit indication of the presence of a dissipative anomaly. Secondly, a preliminary numerical study is presented of the so-called bottleneck effect in a wave turbulence context. It is found that the structure of the bottleneck depends non-trivially on the interaction coefficient. Finally, some results are presented on the complementary phenomenon of thermalisation in closed wave systems which demonstrates explicitly for the first time the existence of so-called mixed solutions of the kinetic equation which exhibit aspects of both KZ and equilibrium equipartition spectra.     

Sunshine is an Important Determinant of Vitamin D Status Even Among High‐dose Supplement Users: Secondary Analysis of a Randomized Controlled Trial in Crohn's Disease Patients

Sunshine is considered to be the most important source of vitamin D. Due to an increased risk of skin cancer, sun avoidance is advised, but this directly contributes to the high prevalence of vitamin D deficiency. The simple solution is to advise vitamin D supplementation. The aim of this study was to examine the absolute and relative contribution of sunshine and supplementation to vitamin status. This study was a secondary analysis of an RCT of 92 Crohn's disease patients in remission (49% female, median age = 44). Participants were randomized to 2000 IU day^?1 of vitamin D3 or placebo for 1 year, with 25‐hydroxyvitamin D (25(OH)D) being measured at baseline and every 4 months. Based on participant's place of residence, daily ambient UVB dose at wavelengths that can induce vitamin D synthesis (D‐UVB) was obtained. Cumulative and weighted ambient D‐UVB (cw‐D‐UVB) exposure prior to each blood draw was calculated for each participant. Linear regression analysis and multilevel modeling were used to examine the association between UVB exposure, supplementation and 25(OH)D concentration. There was considerable annual variation in D‐UVB, cw‐D‐UVB and 25(OH)D. Both supplementation and cw‐D‐UVB were found to be strongly associated with 25(OH)D: in multilevel model, an increase of approximately 6 nmol L^?1 for every 100 kJ m^?2 in cw‐D‐UVB was found, among those receiving placebo and supplementation (P < 0.0001). Treatment was associated with increase of 23 nmol L^?1 (P < 0.0001). Sunshine is an important determinant of 25(OH)D concentration, even in those who are taking high‐dose vitamin D supplements and reside at a higher mid‐latitude location.     

Absolute triple differential cross sections for helium at 300 eV

Absolute triple differential cross sections for the ionisation of He by electrons with energies near 300 eV have been measured in asymmetric conditions. The kinematics of the experiment select ionising events which belong to the intermediate regime of energy and momentum transfer. The experiments are compared with the distorted wave Born approximation.     

Design variations of a polymer–enzyme composite biosensor for glucose: Enhanced analyte sensitivity without increased oxygen dependence

The glucose sensitivity and oxygen dependence of a variety of implantable biosensors based on glucose oxidase (GOx), incorporating an electrosynthesized poly-o-phenylenediamine (PPD) permselective barrier on 125-μm diameter Pt disks (Pt_D) and cylinders (Pt_C, 1-mm length), were measured and compared. Full glucose calibrations and experimental monitoring of solution oxygen concentration allowed us to determine apparent Michaelis–Menten parameters for glucose and oxygen. In the linear region of glucose response, the most sensitive biosensor design studied was Pt_D/PPD/GOx (enzyme deposited over polymer) that was 20 times more sensitive than the more widely used Pt_C/GOx/PPD (enzyme immobilized before polymer deposition) configuration. The oxygen dependence, quantified as K_M(O₂), of both active and less active designs was surprisingly similar, a finding that could be rationalized in terms of an increase in K_M(G) with increased enzyme loading. The Pt_D/PPD/GOx design will now enable us to explore glucose concentration dynamics in smaller and layered brain regions with good sensitivity and minimal interference from fluctuations in tissue pO₂.     

Surface-immobilized pyridine-functionalized gamma-cyclodextrin: alkanethiol co-adsorption-induced reorientation

Monolayers of di-6A,6B-deoxy-6-(4-pyridylmethyl)amino-gamma-cyclodextrin (gamma-CD-(py)2) have been formed on polycrystalline platinum electrodes and investigated using electrochemical and surface-enhanced Raman spectroscopy (SERS). The behavior of self-assembled monolayers of (gamma-CD-(py)2) alone, (gamma-CD-(py)2) backfilled with 1-nonanethiol, and 1-nonanethiol are reported. The potential dependence of the capacitance indicates that the film capacitance is higher for the backfilled CD layers than for 1-nonanethiol layers, most likely due to ion flux through the CD cavity. SERS spectra of the backfilled layer exhibit features associated with both pyridine-functionalized CD and alkane moieties. Investigations using [Fe(CN)6]4- as a solution-phase probe indicate that the backfilled CD-alkane thiol layer exhibits enhanced blocking properties compared to gamma-CD-(py)2 films alone. Complete blocking was achieved by a combination of backfilling and insertion of a high-affinity guest 1-adamantylamine into the cavity. Significantly, an electroactive guest with high affinity for gamma-CD, [Co(biptpy)2]2+, does not exhibit a redox response at the gamma-CD-(py)2 layer but molecular recognition is turned on by backfilling the CD layer with 1-nonanethiol molecules. This switching on of the electrochemical activity suggests that the CD hosts are initially inaccessible but reorientate upon backfilling, exposing the CD opening to solution and permitting a supramolecular host-guest complex to form. The binding of [Co(biptpy)2]2+ to gamma-CD in the backfilled monolayer depends on the bulk concentration of guest and is modeled by the Langmuir isotherm, yielding an association constant for the Co2+ state of 1.45 +/- 0.46 x 105 M-1 and a limiting surface coverage 1.49 +/- 0.25 x 10-11 mol cm-2. The surface coverage of the divalent state is higher than the trivalent state, reflecting the dynamic nature of the inclusion.     

Mercury-platinum tunneling junctions incorporating supramolecular host-guest assemblies

Molecular junctions incorporating monolayers of surface-active cyclodextrins have been formed by bringing macroscopic platinum and mercury electrodes together. Monolayers of the host di-6A,6B-deoxy-6-(4-pyridylmethyl)amino-gamma-cyclodextrin (CD) have been formed on platinum electrodes and backfilled with 1-nonanethiol. Significantly, the tunneling current for bilayer junctions in which the mercury surface is modified with a C16 alkane thiol depends markedly on the nature of the CD guest. Junctions where nonconjugated guests, such as adamantane, are included in the CD show an order of magnitude lower current than junctions incorporating the conjugated guest C60. Moreover, monolayer junctions of CD backfilled with 1-nonanethiol exhibit potential-dependent currents in the presence of CD guest molecule [Co(biptpy)2](2+) but not for [Co(tpy)2](2+), which is structurally analogous but cannot associate with CD. Significantly, unlike bilayer systems, when only one electrode is modified, mechanical pressure is required to form a stable tunneling junction and these junctions cannot be formed and separated reversibly.     

A Triphasic Sorting System: Coordination Cages in Ionic Liquids

Host–guest chemistry is usually carried out in either water or organic solvents. To investigate the utility of alternative solvents, three different coordination cages were dissolved in neat ionic liquids. By using ¹⁹F NMR spectroscopy to monitor the presence of free and bound guest molecules, all three cages were demonstrated to be stable and capable of encapsulating guests in ionic solution. Different cages were found to preferentially dissolve in different phases, allowing for the design of a triphasic sorting system. Within this system, three coordination cages, namely Fe₄L₆ 2 , Fe₈L₁₂ 3 , and Fe₄L₄ 4 , each segregated into a distinct layer. Upon the addition of a mixture of three different guests, each cage (in each separate layer) selectively bound its preferred guest.     

Highly Efficient Triplet Photosensitizers: A Systematic Approach to the Application of IrIII Complexes containing Extended Phenanthrolines

A series of Ir^III complexes, based on 1,10‐phenanthroline featuring aryl acetylene chromophores, were prepared and investigated as triplet photosensitizers. The complexes were synthesized by Sonogashira cross‐coupling reactions using a “chemistry‐on‐the‐complex” method. The absorption properties and luminescence lifetimes were successfully tuned by controlling the number and type of light‐harvesting group. Intense UV/Vis absorption was observed for the Ir^III complexes with two light‐harvesting groups at the 3‐ and 8‐positions of the phenanthroline. The asymmetric Ir^III complex (with a triphenylamine (TPA) and a pyrene moiety attached) exhibited the longest lifetime. Red emission was observed for all the complexes in deaerated solutions at room temperature. Their emission at low temperature (77 K) and nanosecond time‐resolved transient difference absorption spectra revealed the origin of their triplet excited states. The singlet‐oxygen (¹O₂) sensitization and triplet‐triplet annihilation (TTA)‐based upconversion were explored. Highly efficient TTA upconversion (Φ_UC=28.1 %) and ¹O₂ sensitization (Φ_Δ=97.0 %) were achieved for the asymmetric Ir^III complex, which showed intense absorption in the visible region (λ_abs=482 nm, ?=50900 m ^?1 cm^?1) and had a long‐lived triplet excited state (53.3 μs at RT).