Effects of temperature and input energy on a quasi-three-level emission cross section of Nd3＋：yAG pumped by a flashlamp

The influence of temperature and input energy on the fluorescence emission cross section of Nd 3+ :YAG crystal is studied. The stimulated emission cross sections of quasi-three-level systems are determined in a temperature range from 30 to 60℃ and an input energy range from 18 to 75 J. The cross section is found to be decreased when the temperature and the input energy are increased. This is attributed to the thermal broadening mechanism of the emission line. This study is relevant for the development of laser design.     

Deep eutectic solvent promoted highly efficient synthesis of N,N’-diarylamidines and formamides

A deep eutectic solvent was used as a dual catalyst and reaction medium for the efficient N-formylation of aromatic amines without hazardous organic solvent and catalyst. Treatment of aromatic amines with trimethyl orthoformate and formic acid in deep eutectic solvent at 70 °C gives the corresponding N-formyl derivatives in good to excellent yields. This simple ammonium deep eutectic solvent, easily synthesized from choline chloride and SnCl₂, with 100% atom economy and making it applicable to industry and laboratory. Furthermore, heating the trimethyl orthoformate and aromatic primary amines in the deep eutectic solvent results in formation of the corresponding N,N’-diarylamidines in high yields.     

Cops and Robber Game with a Fast Robber on Expander Graphs and Random Graphs

We consider a variant of the Cops and Robber game, in which the robber has unbounded speed, i.e., can take any path from her vertex in her turn, but she is not allowed to pass through a vertex occupied by a cop. Let ${c_{\infty}(G)}$ denote the number of cops needed to capture the robber in a graph G in this variant. We characterize graphs G with c _??(G) =? 1, and give an ${O( \mid V(G)\mid^2)}$ algorithm for their detection. We prove a lower bound for c _?? of expander graphs, and use it to prove three things. The first is that if ${np \geq 4.2 {\rm log}n}$ then the random graph ${G= \mathcal{G}(n, p)}$ asymptotically almost surely has ${\eta_{1}/p \leq \eta_{2}{\rm log}(np)/p}$ , for suitable positive constants ${\eta_{1}}$ and ${\eta_{2}}$ . The second is that a fixed-degree random regular graph G with n vertices asymptotically almost surely has ${c_{\infty}(G) = \Theta(n)}$ . The third is that if G is a Cartesian product of m paths, then ${n/4km^2 \leq c_{\infty}(G) \leq n/k}$ , where ${n = \mid V(G)\mid}$ and k is the number of vertices of the longest path.     

A beam shaping design for coupling high power diode laser stack to fiber with capability of spectral narrowing and stabilizing

We applied a VHG-FAC lens in our design in this work to collimate the fast axis and lock the output spectrally. We used a beam shaping technique to improve the beam symmetry and power density of a high power diode laser stack with a stripe mirror plate, a V-Stack mirror and polarization beam combining elements. By this technique, the beam of a high power diode laser stack is effectively coupled into a standard 365 μmcore diameter and a NA = 0.22 fiber. By this technique, compactness, higher efficiency, narrower spectral line width and lower production cost of the diodes are possible.     

Low irradiance background limited type-II superlattice MWIR M-barrier imager

We report a type-II superlattice mid-wave infrared 320×256 imager at 81 K with the M-barrier design that achieved background limited performance (BLIP) and ～99% operability. The 280 K blackbody's photon irradiance was limited by an aperture and a band-pass filter from 3.6 μm to 3.8 μm resulting in a total flux of ～5×10(12) ph.cm(-2).s(-1). Under these low-light conditions, and consequently the use of a 13.5 ms integration time, the imager was observed to be BLIP thanks to a ～5 pA dark current from the 27 μm wide pixels. The total noise was dominated by the photon flux and read-out circuit which gave the imager a noise equivalent input of ～5×10(10) ph.cm(-2).s(-1) and temperature sensitivity of 9 mK with F/2.3 optics. Excellent imagery obtained using a 1-point correction alludes to the array's uniform responsivity.     

Flow Maldistribution in Dense- and Sock-Loaded Trilobe Catalyst Trickle-Bed Reactors: Experimental Data and Modeling Using Neural Network

In order to experimentally study the catalyst loading method (dense and sock) influence on liquid distribution, a trickle-bed reactor (TBR) packed with extrudate trilobe catalysts was used. Furthermore, an artificial neural network (ANN) algorithm has been applied; the results show acceptable agreement between the ANN model prediction and experimental data. Due to the isotropic distribution of porosity in sock-loaded bed with trilobe catalysts, the results illustrate that with the same operating conditions the sock-packed beds spread liquid better than dense ones. The effects of bed height and variations of gas/liquid flow rate on liquid distribution in sock- and dense-loaded TBRs have been investigated.     

Two-temperature generalized thermoelasticity under ramp-type heating by finite element method

In this work, a general finite element model is proposed to analyze transient phenomena in thermoelastic half-space filled with an elastic material, which has constant elastic parameters. The governing equations are taken in the context of the two-temperature generalized thermoelasticity theory (Youssef in IMA J. Appl. Math. 71(3):383–390, 2006). A linear temperature ramping function is used to more realistically model thermal loading of the half-space surface. The medium is assumed initially quiescent. A finite element scheme is presented for the high accuracy numerical purpose. The numerical solutions of the non-dimensional governing partial differential equations of the problem have been shown graphically and some comparisons have been shown in figures to estimate the effect of the ramping parameter of heating and the parameter of two-temperature.     

Almost periodic solution of a non-autonomous model of phytoplankton allelopathy

In this paper, a non-autonomous two species competitive allelopathic phytoplankton model in presence of a discrete time delay is considered. We have obtained the sufficient conditions for permanence along with existence-uniqueness of an almost periodic solution. Sufficient conditions are derived for the existence of unique almost periodic solution. Analytical findings are supported through exhaustive numerical simulations. With the help of the numerical example, we have demonstrated that initial density dependent almost periodic co-existence is possible in some situations when parameter values fail to satisfy all the conditions of permanence.     

Flow pattern and stability of pseudoplastic axial Taylor–Couette flow

The effect of an axial flow on the stability of the Taylor–Couette flow is explored for pseudoplastic fluids. The fluid is assumed to follow the Carreau–Bird model and mixed boundary conditions are imposed while the axial flow can be independent of rotational flow. The four-dimensional low-order dynamical system, resulted from Galerkin projection of the conservation of mass and momentum equations, includes additional non-linear terms in the velocity components originated from the shear-dependent viscosity. In absence of axial flow the base flow loses its radial flow stability to the vortex structure at a lower critical Taylor number, as the pseudoplasticity effects increases. The emergence of the vortices corresponds to the onset of a supercritical bifurcation which is also seen in the flow of a linear fluid. However, unlike the Newtonian case, pseudoplastic Taylor vortices lose their stability as the Taylor number reaches a second critical number corresponding to the onset of a Hopf bifurcation. Existence of an axial flow, induced by a pressure gradient appears to further advance each critical point on the bifurcation diagram. Complete flow field together with viscosity maps are given for stability regions in the bifurcation diagram.