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.     

Globally convergent DC trust-region methods

In this paper, we investigate the use of DC (Difference of Convex functions) models and algorithms in the application of trust-region methods to the solution of a class of nonlinear optimization problems where the constrained set is closed and convex (and, from a practical point of view, where projecting onto the feasible region is computationally affordable). We consider DC local models for the quadratic model of the objective function used to compute the trust-region step, and apply a primal-dual subgradient method to the solution of the corresponding trust-region subproblems. One is able to prove that the resulting scheme is globally convergent to first-order stationary points. The theory requires the use of exact second-order derivatives but, in turn, the computation of the trust-region step asks only for one projection onto the feasible region (in comparison to the calculation of the generalized Cauchy point which may require more). The numerical efficiency and robustness of the proposed new scheme when applied to bound-constrained problems is measured by comparing its performance against some of the current state-of-the-art nonlinear programming solvers on a vast collection of test problems.     

Concentration of lambda concatemers using a 3D printed device

Identifying significant variations in genomes can be cumbersome, as the variations span a multitude of base pairs and can make genome assembly difficult. However, large DNA molecules that span the variation aid in assembly. Due to the DNA molecule's large size, routine molecular biology techniques can break DNA. Therefore, a method is required to concentrate large DNA. A bis-acrylamide roadblock was cured in a proof-of-principle 3D printed device to concentrate DNA at the interface between the roadblock and solution. Lambda concatemer DNA was stained with YOYO-1 and loaded into the 3D printed device. A dynamic range of voltages and acrylamide concentrations were tested to determine how much DNA was concentrated and recovered. The fluorescence of the original solution and the concentrated solution was measured, the recovery was 37% of the original sample, and the volume decreased by a factor of 3 of the original volume.     

Hybrid Vesicles Enable Mechano-Responsive Hydrogel Degradation

Stimuli-responsive hydrogels are intriguing biomimetic materials. Previous efforts to develop mechano-responsive hydrogels have mostly relied on chemical modifications of the hydrogel structures. Here, we present a simple, generalizable strategy that confers mechano-responsive behavior on hydrogels. Our approach involves embedding hybrid vesicles, composed of phospholipids and amphiphilic block copolymers, within the hydrogel matrix to act as signal transducers. Under mechanical stress, these vesicles undergo deformation and rupture, releasing encapsulated compounds that can control the hydrogel network. To demonstrate this concept, we embedded vesicles containing ethylene glycol tetraacetic acid (EGTA), a calcium chelator, into a calcium-crosslinked alginate hydrogel. When compressed, the released EGTA sequesters calcium ions and degrades the hydrogel. This study provides a novel method for engineering mechano-responsive hydrogels that may be useful in various biomedical applications.     

StereoPHIP: Stereoselective Parahydrogen-Induced Polarization

Parahydrogen-induced polarization (PHIP) followed by polarization transfer to ¹³C is a rapidly developing technique for the generation of ¹³C-hyperpolarized substrates. Chirality plays an essential role in living systems and differential metabolism of enantiomeric pairs of metabolic substrates is well documented. Inspired by asymmetric hydrogenation, here we report stereoPHIP, which involves the addition of parahydrogen to a prochiral substrate with a chiral catalyst followed by polarization transfer to ¹³C spins. We demonstrate that parahydrogen could be rapidly added to the prochiral precursor to both enantiomers of lactic acid (D and L), with both the (R,R) and (S,S) enantiomers of a chiral rhodium(I) catalyst to afford highly ¹³C-hyperpolarized (over 20 %) L- and D-lactate ester derivatives, respectively, with excellent stereoselectivity. We also show that the hyperpolarized ¹H signal decays obtained with the (R,R) and (S,S) catalysts were markedly different. StereoPHIP expands the scope of conventional PHIP to the production of ¹³C hyperpolarized chiral substrates with high stereoselectivity.     

Synthesis of Flavones through NaI-Mediated Electrochemical Cyclization of Chalcones

A mild electrochemical oxidative cyclization for the synthesis of flavones from easy-access 2’-hydroxychalcones was developed using an inexpensive NaI as mediator and electrolyte under ambient temperature in a mixture of EtOH and H₂O as solvent. This method was successfully applied to synthesize 26 examples of flavones from a variety of functionalized 2’-hydroxychalcones. A gram-scale formal synthesis of bioactive scutellarein was successfully demonstrated. Control experiments were conducted to disclose a possible indirect oxidation via in situ generation of iodine. The main advantages of this reaction include its broad substrate scope, scalability, ability to operate with benign solvent, and no requirement for strong oxidizing agents and external additives.     

A survivable design of last mile communication networks using multi-objective genetic algorithms

In this paper, we are interested in the survivable network design problem (SNDP) for last mile communication networks called (L-SNDP). Given a connected, weighted, undirected graph \(\mathrm{{G}} = (\mathrm{V, E})\); a set of infrastructure nodes and a set of customers C including two customer types where customers in the subset C1 require a single connection (type-1) and customers in the subset C2 need to be redundantly connected (type-2). The aim is to seek a sub-graph of G with the smallest weight in which all customers are connected to infrastructure nodes and the connections are protected against failures. This is a NP-hard problem and it has been solved only with the objective of minimizing the network cost. In this paper, we introduce a new multi-objective approach to solve L-SNDP called ML-SNDP. These objectives are to minimize the network cost (total cost) and to minimize the maximal amount of sharing links between connections. Results of computational experiments reported show the efficiency of our proposal.     

Self-assembly and field-responsive optical diffractions of superparamagnetic colloids

Superparamagnetic Fe(3)O(4) colloids with highly charged surfaces have been assembled into ordered structures in water in response to external magnetic fields. The colloids form chainlike structures with regular interparticle spacings of a few hundred nanometers along the direction of the external field so that the system strongly diffracts visible light. The balance between attractive (in this case, magnetic) and repulsive (electrostatic) forces dictates interparticle spacing and therefore optical properties. By changing the relative strength of these two forces, one can tune the peak diffraction wavelength over the entire visible spectrum. We were able to optimize the diffraction intensity and the tuning range through studying their dependence on variables such as the size distribution and concentration of the Fe(3)O(4) colloids or ionic strength of the solutions. The fast, reversible response and the feasibility for miniaturization impart these photonic materials great potential in applications such as optoelectronic devices, sensors, and color displays.     

Pd(II) complexes with mixed benzothiazolin-2-ylidene and phosphine ligands and their catalytic activities toward C-C coupling reactions

Novel Pd(II) mixed N,S-heterocyclic carbene (NSHC)-phosphine complexes of the general formula [PdBr(2)(NSHC)(PR(3))] were obtained from bridge cleavage of dinuclear NSHC complexes of type [PdBr(2)(NSHC)](2) [NSHC = 3-benzylbenzothiazolin-2-ylidene and 3-propylbenzothiazolin-2-ylidene] with triphenylphosphine, tricyclohexylphosphine and 2-diphenylphosphanyl-pyridine. All complexes have been fully characterized by (1)H and (13)C NMR spectroscopy, ESI mass spectrometry and elemental analysis. The X-ray crystal structures of complexes 3-8 are reported. The complexes exhibit moderate to good catalytic activity in the Suzuki-Miyaura coupling reaction of aryl bromides and chlorides.