Framework Cationization by Preemptive Coordination of Open Metal Sites for Anion‐Exchange Encapsulation of Nucleotides and Coenzymes

Cationic frameworks can selectively trap anions through ion exchange, and have applications in ion chromatography and drug delivery. However, cationic frameworks are much rarer than anionic or neutral ones. Herein, we propose a concept, preemptive coordination (PC), for targeting positively charged metal–organic frameworks (P‐MOFs). PC refers to proactive blocking of metal coordination sites to preclude their occupation by neutralizing ligands such as OH^?. We use 20 MOFs to show that this PC concept is an effective approach for developing P‐MOFs whose high stability, porosity, and anion‐exchange capability allow immobilization of anionic nucleotides and coenzymes, in addition to charge‐ and size‐selective capture or separation of organic dyes. The CO₂ and C₂H₂ uptake capacity of 117.9 cm³ g^?1 and 148.5 cm³ g^?1, respectively, at 273 K and 1 atm, is exceptionally high among cationic framework materials.     

Group 13 Element Trihalide Complexes of Anionic N‐Heterocyclic Carbenes

A series of group 13 complexes of the general type [{(WCA‐IDipp)EX₃}Li(solv)] (E=B, Al, Ga, In; X=Cl, Br) that bear an anionic N‐heterocyclic carbene ligand with a weakly coordinating borate moiety (WCA‐IDipp, WCA=B(C₆F₅)₃ and IDipp=1,3‐bis(2,6‐diisopropylphenyl)imidazolin‐2‐ylidene) were prepared by the reaction of the respective group 13 trihalides (EX₃) with the lithium salt [(WCA‐IDipp)Li ? toluene]. The molecular structures of the BBr₃, AlCl₃, AlBr₃, GaCl₃ and InCl₃ adducts were established by X‐ray diffraction analyses, revealing the formation of coordination polymers linked by halide‐lithium interactions, except for the indium derivative, which consists of isolated [Li(THF)₄]⁺ and [(WCA‐IDipp)InCl₃]^? ions in the solid state.     

Electrochemically-assisted deposition of oxidases on platinum nanoparticle/multi-walled carbon nanotube-modified electrodes

Platinum nanoparticles were electrodeposited by a multi-potential step technique onto a multi-walled carbon nanotube (MWCNT) film pre-casted on a glassy carbon (GC) or boron-doped diamond (BDD) electrode. The MWCNT network consisted of Pt nanoparticles with an average diameter of 120 nm after an optimization of 36 deposition cycles. The resulting electrochemical sensors were capable of detecting hydrogen peroxide as low as 25 nM. Five different enzymes: glucose, lactate, glutamate, amino acid and xanthine oxidases, respectively, were deposited by a constant current technique for 5-10 min to form a stable and active biolayer for the analysis of their corresponding analytes. The glucose oxidase-based biosensor was linear up to 10 mM glucose with a detection limit of 250 nM and a response time of 5 s. Similar response times and detection limits were observed with glutamate, lactate, and amino acid oxidase despite the fact that the linear ranges were noticeably narrower. The mechanism of deposition was attributed to the decrease of local pH, created by oxygen evolution and effected enzyme precipitation.     

Sum Squeezing, Difference Squeezing, Higher-Order Antibunching and Entanglement of Two-Mode Photon-Added Displaced Squeezed States

In this paper, we study some higher-order nonclassical properties and intermodal entanglement that may arise in the so called two-mode photon-added displaced squeezed state. We derive analytical expressions for the degree of sum squeezing and difference squeezing, which are interesting kinds of two-mode squeezing, as well as for the degree of antibunching to any orders. We also examine the degree of entanglement between the two modes using the existing Hillery-Zubairy criterion. Based on the derived expressions we analyze in detail the behavior of these nonclassical effects and entanglement depending on the parameters involved.     

Confined-acoustic-phonon-assisted cyclotron resonance via multi-photon absorption process in GaAs quantum well structure

Phonon-assisted cyclotron resonance (PACR) in GaAs quantum well (QW) structure is investigated via multi-photon absorption process when electrons interact with the confined acoustic phonon through deformation potential. The additional peaks in the absorption spectrum due to transitions between Landau levels accompanied with the emission and absorption of phonons are indicated. The dependence of absorption power on the temperature, magnetic field and well width is presented. Using profile method, we obtain PACR-linewidth as profiles of the curves. The temperature, magnetic field and well width dependences of the PACR-linewidth are investigated. The results are compared with those in the case of mono-photon absorption process, as well as in the electron-bulk acoustic phonon interaction. The results show that the multi-photon absorption process is strong enough to be detected in PACR.     

Disposable flow cytometer with high efficiency in particle counting and sizing using an optofluidic lens

Flow cytometers are widely applied to environmental monitoring, industrial testing, and biochemical studies. Integrating a flow cytometer into microfluidic networks helps to miniaturize the system and make it portable for field use. The integration of optical components, such as lenses, further improves the compactness and thus has been intensively studied recently. However, the current designs suffer from severe light scattering due to the roughness of the solid-based lens interface. In this Letter, we propose a flow cytometer using an optofluidic lens to focus the light beam. Benefiting from the smooth liquid-liquid lens interface and the refractive-index matching liquid as cladding streams, a light beam can be well focused without scattering. The variations of the signal peak values are reduced, owing to the small beam width at the beam waist. The device presents an efficient and accurate performance on both the counting and sizing of particles.     

Suppression of slow gain recovery in ultralong quantum-dash semiconductor optical amplifier emitting at 1.55 μm

Gain dynamics in two quantum-dash semiconductor optical amplifiers of different lengths emitting in the 1.55 μm region are investigated experimentally and compared. It is shown that slow gain recovery due to total carrier relaxation is totally suppressed in the ultralong amplifier. Consequently, the 10%-90% gain recovery time is drastically reduced from about 40 ps (short sample) to 10 ps (long one).     

Magneto-transport and magnetic properties of (1-x)La0.7Ca0.3MnO3+xAl2O3 composites

We report magneto-transport and magnetic properties of (1-x)La_0.7Ca_0.3MnO₃+xAl₂O₃ composites synthesized through a solid-state reaction method combined with a high energy milling method. Most interestingly, the effective magnetic anisotropy is found to decrease with increase in the non-magnetic insulating Al₂O₃ phase fraction in the composites. In addition, we observed that the magnitude of low-field magnetoresistance arising from spin-polarized tunneling of conduction electrons, as well as that of high-field magnetoresistance, displays a Curie-Weiss law-like behavior. Finally, we found that the temperature dependence of low and high-field magnetoresistance is controlled predominantly by the nature of temperature response of surface magnetization of the particles.     

Imaging of the oxygen distribution in an isothermal turbulent free jet using two-color toluene LIF imaging

The results of a novel technique for the quantification of oxygen in an isothermal turbulent free jet using toluene laser induced fluorescence (LIF) are presented. This method relies on the red-shift of the toluene LIF emission spectrum with increasing oxygen concentration. Evaluating the LIF signal ratio from two different wavelength regions simultaneously produces results that depend only on the local oxygen concentration. From calibration data, obtained from repeated tests, the oxygen sensitivity of the two-color LIF technique is best for oxygen partial pressures p_O2 ￡ 120 mbarp_{\mathrm{O}_{2}} \leq 120\mbox{ mbar} in the current setup. Quantified images of oxygen distribution are presented for 40.4, 60.5, 80.5, and 103 mbar p_O2p_{\mathrm{O}_{2}} in the toluene-seeded jet flow that is shielded by a toluene-seeded nitrogen co-flow at atmospheric pressure and temperature. Based on the average oxygen concentration images (obtained from 100 instantaneous oxygen images), the error in accuracy of measuring the oxygen concentration was 0.8, 3.0, 7.7, and 7.3% with a precision of ± 8.6, 5.5, 13.3, and 11.6% for the jet p_O2 = 40.4, 60.5, 80.5, and 103 mbarp_{\mathrm{O}_{2}} = 40.4,\, 60.5,\, 80.5,\mbox{ and }103\mbox{ mbar} cases, respectively. The main jet flow characteristics have been captured by the technique as determined from the measured oxygen distribution images. Centerline profiles of average oxygen concentration, normalized to the value at the nozzle exit, demonstrate self-similar behavior from 5 mm above the nozzle exit. Radial oxygen concentration profiles exhibit a Gaussian-type distribution that broadens with distance above the nozzle exit, in agreement with literature.     

Pósa's conjecture for graphs of order at least 2 × 108

In 1962 Pósa conjectured that every graph G on n vertices with minimum degree \begin{align*}\delta(G)\ge \frac{2}{3}n\end{align*} contains the square of a hamiltonian cycle. In 1996 Fan and Kierstead proved the path version of Pósa's Conjecture. They also proved that it would suffice to show that G contains the square of a cycle of length greater than \begin{align*}\frac{2}{3}n\end{align*}. Still in 1996, Komlós, Sárközy, and Szemerédi proved Pósa's Conjecture, using the Regularity and Blow‐up Lemmas, for graphs of order n ≥ n₀, where n₀ is a very large constant. Here we show without using these lemmas that n₀:= 2 × 10⁸ is sufficient. We are motivated by the recent work of Levitt, Sárközy and Szemerédi, but our methods are based on techniques that were available in the 90's. © 2011 Wiley Periodicals, Inc. Random Struct. Alg., 2011