Solvent‐free synthesis of 2H‐pyrans: One‐pot reactions of dithiocarbamates,alkyl propiolates,and isocyanides

A novel, convenient, and an efficient approach to the synthesis of 2H‐pyrans has been reported based on the multicomponent reaction. Solvent‐free condition for the reaction of dithiocarbamates, alkyl propiolates and isocyanides lead to the formation of 2H‐pyrans in good yields. In these reactions, synthesis of 2H‐pyrans is possible based on the one‐pot reaction and without using any catalyst. The mild reaction conditions and high yields of the products exhibit the good synthetic advantage of these methods. J. Heterocyclic Chem., lpar;2011).     

Molecular structure and theoretical studies of new stable phosphorus ylides derived from trialkyl phosphites

The reaction between dialkyl acetylenedicarboxylates and NH heterocyclic compounds in the presence of trialkyl phosphite leads to stable phosphorus ylide derivatives in good yields. The x‐ray crystallographic data and theoretical study show that there is a resonance between two bonds of C₉P₁ and C₉₁O₉₁ in phosphorous ylide 4c . This compound crystallizes in the triclinic system, space group ( ), with the following unit cell parameters: a = 8.7522(3)Å, b = 8.8513(5)Å, c = 18.3469(5)Å, α = 99.1220(10)°, β = 90.954(2)°, γ = 118.792(2)°, Z = 2, and V = 1222.72(9)ų. © 2010 Wiley Periodicals, Inc. Heteroatom Chem 22:36–43, 2011; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.20653     

M-type atomic basic cell as a low intensity long wavelength infrared photodetector

A five-level atomic system in M-type configuration has been proposed in this article as a long-wavelength infrared photodetector cell. Coherent population trapping and electromagnetically induced transparency (EIT) is appeared in this kind of atomic structure. In order to overcome the dark current noise problem in the long-wavelength infrared photodetectors, we utilize quantum interference phenomena between the electromagnetic fields and interpret the incoming long-wavelength to short-wavelength detection range, where the dark current noise is not critical. The proposed M-type-arranged atomic system, have high performance in lower intensities of long-wavelength IR which is more interesting from high-sensitive photodetector point of view.     

High efficiency solar cells using quantum interferences

In this paper, we propose a solar cell model that absorbs specific band of sunlight and investigate the effect of noise–induced quantum coherence in enhancing the output power of this cell. We numerically demonstrate that such induced coherence can increase the maximum output power from a nano structured solar cell by more than 25% as compared to the same system with no coherence. We also study the influence of increasing the bandwidth of absorption on the solar cell power and numerically show that in spite of decrease in output power due to enhancement of thermalisation loss, presence of quantum coherence effect still increases the output power of solar cell compared to non-coherence case.     

Demagnetizing fields of crystallites and a method for measuring the thermodynamic fields of quasi-single-crystal and polycrystalline thin YBa2Cu3O7 − x disks

The role of the demagnetizing fields of crystallites in HTSC samples is studied. An increase in the crystallite size is shown to suppress the intra-and intercrystalline critical currents of the sample in lower fields. The demagnetizing fields of crystallites are shown to be one of the main causes of the fact that the Bean model is invalid for HTSC samples. A method is proposed to measure the thermodynamic field of a superconductor; this method allows the first thermodynamic critical magnetic fields of the sample and its crystallites and “subcrystallites” to be measured with a high accuracy. The first thermodynamic critical magnetic fields are used to estimate the critical current density J _c of the sample, crystallites, and subcrystallites.     

Highly enhanced second-order nonlinear susceptibilities in tailored GaN-AlGaN-AlN quantum well structures

A tailoring proposal for design of the strained quantum well structures, optimized with respect to the intersubband resonant second-order nonlinear properties, is presented in this article. A genetic-algorithm-based method is used in order to obtain the optimal potential shape, doping concentration and location in strained GaN-AlGaN-AlN quantum wells, and the structures are analyzed by a numerical solution of the Schrödinger-Poisson self-consistent method. In general form two types of asymmetric structures with remarkable results are obtained with different resonant frequencies, and in both cases results show a considerably high enhancement in the magnitude of the second-order nonlinear susceptibilities in higher resonant frequencies in comparison with a single quantum well structure with the same well width (5.02×10⁻⁸ m/V at to 2.9×10⁻⁵ m/V at and 2.43×10⁻⁵ m/V at ). The optimized structures exhibit considerable absorption coefficient and electroabsorption properties due to high dipole transition matrix element, high dopant concentration and reasonable Fermi level.     

Unsteady natural convection in an enclosure with vertical wavy walls

In this paper, unsteady heat transfer and fluid flow characteristics in an enclosure are investigated. The enclosure consists of two vertical wavy and two horizontal straight walls. The top and the bottom walls are considered adiabatic. Two wavy walls are kept isothermal and their boundaries are approximated by a cosine function. Governing equations including continuity, momentum and energy were discretized using the finite-volume method and solved by SIMPLE method in curvilinear coordinate. Simulation was carried out for a range of Grashof number Gr = 10³–10⁶, Prandtl number Pr = 0.5–4.0, wave ratio A (defined by amplitude/wavelength) 0.0–0.35 and aspect ratio W (defined by average width/wavelength) 0.5–1.0. Streamlines and isothermal lines are presented to corresponding flow and thermal fields. Local and average Nusselt number distributions are presented. The obtained results are in good agreement with available numerical and experimental data.     

Efficient Routes for the Synthesis of Dinaphthosulfide (BINOL Derivatives) and Dibenzosulfide Aza Podands Containing Ethanolamine

Four new dinaphthosulfide and dibenzosulfide aza podands were synthesized. The synthesis of these podands was performed under three different reaction conditions: 1) diester, K ₂ CO ₃ , methanol, and RT; 2) diester, ethanolamine, and microwave (MW); and 3) diacid dichloride, ethanolamine, Et ₃ N, CH ₂ Cl ₂ , RT. Two kinds of diester (dinaphthosulfide and dibenzosulfide) were used for the preparation of dihydroxy podands. These dihydroxy podands were reacted with thionyl chloride to afford dichloro podands. The second route gave excellent yields of dihydroxy podands. Dichloro podands are more soluble than dihydroxy podands in conventional solvents such as methanol, chloroform, and acetonitrile.     

On automorphisms and embeddings of free periodic groups

The paper gives a construction of a free monoid of rank 2 in the group of automorphisms of free periodic groups B(m, n) of any odd period n ≥ 665 and any rank m > 1.Moreover, it is proved that if the period is any prime numbern > 1003 and the group B(m, n) is nested in some n-periodic group G as a normal subgroup, then B(m, n) is a direct factor in G.     

Solid polymer nanocomposite electrolytes based on poly(ε-caprolactone)-based waterborne polyurethane–polyethylene oxide and fluorine-doped carbon quantum dot-MXene

The need for higher energy storage capability has encouraged researchers to move toward lithium-metal batteries (LMBs). Due to the safety issue associated with liquid electrolytes, solid polymer electrolytes (SPEs) the main focus on polyethylene oxide (PEO) were at the center of the research. However, high crystallization, fast decomposition, and low thermomechanical stability has limited its application. Low lithium-ion transference number ( $$) is another issue leading to polarization of the SPEs and consequently, triggering dendrite nucleation and growth. Here, we developed a series of SPEs based on PEO-waterborne polyurethane (WPU) and nanoparticles of fluorine-doped carbon quantum dot (fCQD) and MXene. The host polymer matrix was a blend of poly(ε-caprolactone) (PCL)-based WPU and PEO. The use of WPU and the nanoparticles increased the thermomechanical stability and suppressed PEO crystallinity through disrupting the spherulites growth and reducing the thermal stability of the crystallites. Using the WPU led to significant increase in $$ ( $$) compared with previous reports. The prepared SPEs showed high-electrochemical stability and ionic conductivity at $$ and based on the results of cycling performance, a discharge capacity of 120.58 mAh/g and coulombic efficiency of 99.1% was achieved after 200 cycles.