Lifshitz transition and modulation of electronic and transport properties of bilayer graphene by sliding and applied normal compressive strain

Using density functional theory (DFT) we investigate the changes in electronic and transport properties of graphene bilayer caused by sliding one of the layers. Change in stacking pattern breaks the lattice symmetry, which results in Lifshitz transition together with the modulation of the electronic structure. Going from AA to AB stacking by sliding along armchair direction leads to a drastic transition in electronic structure from linear to parabolic dispersion. Our transport calculations show a significant change in the overall transmission value for large sliding distances along zigzag direction. The increase in interlayer coupling with normal compressive strain increases the overlapping of conduction and valence band, which leads to further shift in the Dirac points and an enhancement in the Lifshitz transition. The ability to tune the topology of band structure by sliding and/or applying normal compressive strain will open doors for controlled tuning of many physical phenomenon such as Landau levels and quantum Hall effect in graphene. (C) 2015 Elsevier Ltd. All rights reserved.

Effect of current density on the microstructure and corrosion properties of plasma electrolytic oxidation (PEO) coatings on AM50 Mg alloy produced in an electrolyte containing clay additives

Plasma electrolytic oxidation coatings were produced on AM50 Mg alloy in alkaline phosphate based electrolyte with montmorillonite clay additives employing current densities of 30, 60, and 120 mA/cm(2). The effect of current density on the microstructure and corrosion properties of the coating was investigated. The clay additives got melted and reactively incorporated into the coating forming an amorphous phase, at all the current densities. However, the coating was predominantly amorphous only at 30 mA/cm(2) and with increasing current density, increasing fractions of crystalline phases were formed. Higher current densities resulted in increased thickness of the coating, but reduced the compactness of the coatings. Electrochemical impedance spectroscopy tests in 0.5 wt.% (0.08 M) and 3.5 wt.% (0.6 M) NaCl solution revealed that the coatings processed at 30 mA/cm(2) exhibited a relatively better initial corrosion resistance owing to its relatively defect-free barrier layer and compactness of the coating. However, the presence of amorphous phases in significant amounts and lack of MgO in the coating resulted in increased rate of dissolution of the coatings and degradation of corrosion resistance. Coatings produced at higher current densities exhibited initial inferior corrosion resistance due to a more defective barrier layer and increased porosity in pore band and outer porous layer. However, the increased amount of crystalline phases and an increased amount of MgO, which resisted dissolution, counterbalanced the negative effects of defective barrier and increased porosity resulting in a relatively lower rate of the degradation of the corrosion resistance. Thus, the corrosion resistance of all the coatings continuously decreased with time and became similar after prolonged immersion in NaCl solution. Increasing current density, therefore, did not prove to be beneficial for the improvement of the corrosion performance of the PEO coatings. (C) 2016 Elsevier B.V. All rights reserved.

Simultaneous tunability of the electronic and phononic gaps in SnS2 under normal compressive strain

Controlled variation of the electronic properties of. two-dimensional (2D) materials by applying strain has emerged as a promising way to design materials for customized applications. Using density functional theory (DFT) calculations, we show that while the electronic structure and indirect band gap of SnS2 do not change significantly with the number of layers, they can be reversibly tuned by applying biaxial tensile (BT), biaxial compressive (BC), and normal compressive (NC) strains. Mono to multilayered SnS2 exhibit a reversible semiconductor to metal (S-M) transition with applied strain. For bilayer (2L) SnS2, the S-Mtransition occurs at the strain values of 17%,-26%, and -24% under BT, BC, and NC strains, respectively. Due to weaker interlayer coupling, the critical strain value required to achieve the S-Mtransition in SnS2 under NC strain is much higher than for MoS2. From a stability viewpoint, SnS2 becomes unstable at very low strain values on applying BC (-6.5%) and BT strains (4.9%), while it is stable even up to the transition point (-24%) in the case of NC strain. In addition to the reversible tuning of the electronic properties of SnS2, we also show tunability in the phononic band gap of SnS2, which increases with applied NC strain. This gap increases three times faster than for MoS2. This simultaneous tunability of SnS2 at the electronic and phononic levels with strain, makes it a potential candidate in field effect transistors (FETs) and sensors as well as frequency filter applications.

Perturbational Finite Volume Method For The Solution of 2-D Navier-Stokes Equations on Unstructured and Structured Colocated Meshes

Based on the first-order upwind and second-order central type of finite volume( UFV and CFV) scheme, upwind and central type of perturbation finite volume ( UPFV and CPFV) schemes of the Navier-Stokes equations were developed. In PFV method, the mass fluxes of across the cell faces of the control volume (CV) were expanded into power series of the grid spacing and the coefficients of the power series were determined by means of the conservation equation itself. The UPFV and CPFV scheme respectively uses the same nodes and expressions as those of the normal first-order upwind and second-order central scheme, which is apt to programming. The results of numerical experiments about the flow in a lid-driven cavity and the problem of transport of a scalar quantity in a known velocity field show that compared to the first-order UFV and second-order CFV schemes, upwind PFV scheme is higher accuracy and resolution, especially better robustness. The numerical computation to flow in a lid-driven cavity shows that the under-relaxation factor can be arbitrarily selected ranging from 0.3 to 0. 8 and convergence perform excellent with Reynolds number variation from 102 to 104.

Kinetics of Glass Transition and Crystallization in Carbon Nanotube Reinforced Mg-Cu-Gd Bulk Metallic Glass

Mg65 Cu25 Gdlo bulk metallic glass and its carbon nanotube reinforced composite were prepared. Differential scanning calorimeter (DSC) was used to investigate the kinetics of glass transition and crystallization processes. The influence of CNTs addition to the glass matrix on the glass transition and crystallization kinetics was studied. It is shown that the kinetic effect on glass transition and crystallization are preserved for both the monothetic glass and its glass composite. Adding CNTs in to the glass matrix reduces the influence of the heating rate on the crystallization process. In addition, the CNTs increase the energetic barrier for the glass transition. This results in the decrease of GFA . The mechanism of the GFA decrease was also discussed.

Mechanism of nucleation and precipitation in Li containing Al-Zn-Mg-Cu alloys

Investigations on the aging hardening behavior of four Al-Li-Zn-Mg-Cu alloys were carried out using differential scanning calorimetry, transmission electron microscopy and hardness measurement. It is shown that the addition of Li inhibits the formation of Zn-rich G.P. zones in Al-Zn-Mg-Cu alloys. The dominant aging hardening precipitates is delta'(Al3Li) phase. Coarse T ((AlZn)(49)Mg-32) phase, instead of MgZn2, precipitates primarily on grain boundaries, and provides little strengthening. The multi-stop aging involving plastic deformation introduces in the matrix a high concentration of structural defects. These defects play different role on the nucleation of Zn-rich G.P. zones in different alloys. For the Li free alloy, structural defects act as vacancy sinks and tend to suppress the homogeneous precipitation of G.P. zones, while for the Li containing alloys, these defects promote the heterogeneous nucleation of G.P. zones and metastable MgZn2. A significant aging hardening effect is attained in deformed Li containing alloys due to the extra precipitation of fine MgZn2 in the matrix combined with deformation hardening.

Experimental study on two-phase gas-liquid flow patterns at normal and reduced gravity conditions

Experimental studies have been performed for horizontal two-phase air-water flows at normal and reduced gravity conditions in a square cross-section channel. The experiments at reduced gravity are conducted on board the Russian IL-76 reduced gravity airplane. Four flow patterns, namely bubble, slug, slug-annular transition and annular flows, are observed depending on the liquid and gas superficial velocities at both conditions. Semi-theoretical Weber number model is developed to include the shape influence on the slug-annular transition. It is shown that its prediction is in reasonable agreement with the experimental slug-annular transition under both conditions. For the case of two-phase gas-liquid flow with large value of the Froude number, the drift-flux model can predict well the observed boundary between bubble and slug flows.

Estudio preliminar del cultivo in vitro de ��pices caulinares de quequisque (Xanthosoma sagittifolium L. Shott)

El presente trabajo se realiz�� en el Laboratorio de Cultivo de Tejidos Vegetales del Programa Recursos Gen��ticos Nicaraguenses (REGEN-UNA). En los ensayos realizados fueron estudiados 9 Concentraciones de hipoclorito de sodio en la desinfectaci��n de los explantes de quequisque y se determin�� que concentraciones entre 55% y 70% v/v, fueron las m��s adecuadas. Sin embargo, al estudiar el efecto del BAP, ANA y el efecto del Hipoclorito de Sodio sobre la tasa de crecimiento del tallo, se observ�� que las altas concentraciones de cloro utilizados en el proceso de desinfecci��n del explante y la utilizaci��n de ANA en el medio nutritivo de establecimiento reducen la tasa de crecimiento. Por otra parte se observ�� que las concentraciones de BAP utilizadas no tuvieron ning��n efecto sobre la tasa de crecimiento. En el estudio del efecto de 4 concentraciones de sacarosa (23 g, 30 g, 37 g y 44 g) las plantas mostraron una tasa de crecimiento similar. En la tasa de multiplicaci��n acelerada, donde se estudi�� el efecto de la consistencia del medio sobre el ahijamiento no se observ�� diferencias y en la tasa de enraizamiento donde se evaluaron 3 niveles de AIA (0.0 mg/l y 0.1 mg/l). Tambi��n no se encontr�� diferencia en cuanto a la formacion de ra��ces. El comportamiento de las Vitroplantas de quequisque en condiciones de vivero reflejo resultados satisfactorios las cuales mostraron una buena capacidad de adaptaci��n siguiendo un normal crecimiento y desarrollo.

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���������������������������������������������������������(LiCl,NaCl���KCl������������Mg-Al-NO_3������������������������������Mg-Al-NO_3LDH)���������$\Xi$������������������������������������������������������������������������������������������������������pH������������������������Mg-Al-NO_3LDH������������������������������������������������Li+���Na+,K+���Mg-Al-NO_3LDH������������������������������������������������������������������������������������������������������������������������������������������Al���������������������������������������������������������������������������������������������������������

Evaluaci��n de dieciseis variedades de maiz (Zea mays L.) normal y de alta calidad de proteina en cinco ambientes de Nicaragua

Con el fin de identificar variedades de ma��z que respondan consistentemente a las diferentes condiciones ambientales y con buen potencial de rendimiento se realiz�� el presente estudio en ��poca de primera (Mayo-Junio) del 2004, donde se evaluaron 16 genotipos de alta calidad de prote��na y normales en cinco localidades de Nicaragua. El dise��o utilizado fue un L��tice simple 4 x 4 con 3 r��plicas, cada tratamiento estuvo formado por 2 hileras de 5 metros de longitud con separaci��n de 0.25 y 0.80 metros entre plantas e hileras, respectivamente. La parcela ��til estuvo formada por las dos hileras. Se realiz�� an��lisis de varianza para el rendimiento de grano por localidad y a trav��s de las localidades; y se calcul�� la Diferencia M��nima Significativa (���=0.05). La interacci��n genotipo x ambiente (G-A) se determin�� a trav��s del an��lisis Efectos Principales Aditivos e Interacciones Multiplicativas(AMMI). El modelo AMMI identific�� las localidades de Santa Rosa, Jucuapa y Melchorita como ambientes desfavorables (con rendimientos de 2.40, 3.17 y 4.48 t ha-1 y puntuaciones AMMI de 0.44, 1.07 y 0.11, respectivamente) y a Campos Azules y Quilal�� (con rendimientos de 8.46 y 7.40 t ha-1 y puntuaciones AMMI de -1.02 y -0.60, respectivamente) como ambientes favorables o productivos. Las variedades que menos interactuaron con el ambiente(-0.04, 0.03 y-0.10 valores AMMI, respectivamente) fueron ACROS0043, S00TLWQ-B, y S00SEQTLW. En general ninguna variedad estudiada super�� significativamente al testigo TLAYOLLY (5.59 tha-1) en cuanto a rendimiento de grano, aunque algunas variedades fueron superiores al testigo NB-NUTRINTA (4.38 t ha-1), pero con niveles de estabilidad inferior a ACROS0043, S00TLWQ-B, y S00SEQTLW.

Normal shock boundary layer control with various vortex generator geometries

Various vortex generators which include ramp, split-ramp and a new hybrid concept "ramped-vane" are investigated under normal shock conditions with a diffuser at Mach number of 1.3. The dimensions of the computational domain were designed using Reynolds Average Navier-Stokes studies to be representative of the flow in an external-compression supersonic inlet. Using this flow geometry, various vortex generator concepts were studied with Implicit Large Eddy Simulation. In general, the ramped-vane provided increased vorticity compared to the other devices and reduced the separation length downstream of the device centerline. In addition, the size, edge gap and streamwise position respect to the shock were studied for the ramped-vane and it was found that a height of about half the boundary thickness and a large trailing edge gap yielded a fully attached flow downstream of the device. This ramped-vane also provided the largest reduction in the turbulent kinetic energy and pressure fluctuations. Additional benefits include negligible drag while the reductions in boundary layer displacement thickness and shape factor were seen compared to other devices. �� 2010 by Sang Lee.

Normal shock boundary layer control with various vortex generator geometries

Various vortex generators which include ramp, split-ramp and a new hybrid concept "ramped-vane" are investigated under normal shock conditions with a diffuser at Mach number of 1.3. The dimensions of the computational domain were designed using Reynolds Average Navier-Stokes studies to be representative of the flow in an external-compression supersonic inlet. Using this flow geometry, various vortex generator concepts were studied with Implicit Large Eddy Simulation. In general, the ramped-vane provided increased vorticity compared to the other devices and reduced the separation length downstream of the device centerline. In addition, the size, edge gap and streamwise position respect to the shock were studied for the ramped-vane and it was found that a height of about half the boundary thickness and a large trailing edge gap yielded a fully attached flow downstream of the device. This ramped-vane also provided the largest reduction in the turbulent kinetic energy and pressure fluctuations. Additional benefits include negligible drag while the reductions in boundary layer displacement thickness and shape factor were seen compared to other devices. �� 2011 Elsevier Ltd.

Fracture statistics of brittle materials: Weibull or normal distribution

The fit of fracture strength data of brittle materials (Si3N4, SiC, and ZnO) to the Weibull and normal distributions is compared in terms of the Akaike information criterion. For Si3N4, the Weibull distribution fits the data better than the normal distribution, but for ZnO the result is just the opposite. In the case of SiC, the difference is not large enough to make a clear distinction between the two distributions. There is not sufficient evidence to show that the Weibull distribution is always preferred to other distributions, and the uncritical use of the Weibull distribution for strength data is questioned.

Crecimiento y acumulaci��n de nutrientes por los frutos de caf�� (Coffea arabica L.) variedad pacas bajo combinaciones de especies de ��rboles de sombra y diferentes niveles de fertilizaci��n, Masatepe, Nicaragua, 2012

De abril a diciembre de 2012, de un ensayo ya establecido se realizaron dos estudios en el cultivo de caf�� variedad pacas, con el objetivo de determinar las curvas de crecimiento, peso seco y acumulaci��n de nutrientes (N, P, K, Ca y Mg) por los frutos de caf��. El ensayo de sistemas fue establecido en el a��o 2000 en el Centro Nacional de Cooperativismo (CENECCOP), Masatepe, Nicaragua donde se establecieron cuatro parcelas grandes con combinaci��n de ��rboles de sombra maderables y de servicio y una parcela a pleno sol. En las parcelas grandes se establecieron cuatro sub parcelas o niveles de fertilizaci��n org��nica (org��nico intensivo y org��nico moderado) y fertilizaci��n convencional (convencional intensivo y convencional moderado) para un total de 14 tratamientos. De este ensayo se seleccionaron para el primer experimento dos niveles de sombra (Inga laurina ��� Samanea saman y Tabebuia rosea ��� Simaruba glauca) cada parcela grande con los cuatro niveles de insumo. Para el segundo experimento se tomaron los cuatro niveles de sombra (Inga laurina y Simaruba glauca), (Samanea saman y Tabebuia rosea), (Samanea saman e Inga laurina), (Tabebuia rosea y Simaruba glauca) y una parcela a pleno sol. Las variables evaluadas en los frutos de caf�� fueron di��metro polar, di��metro ecuatorial y peso seco. Los frutos se secaron en el horno a 70 ��C y posteriormente se utiliz�� el molino Foss Tecator Cyclotec para obtener una muestra fina. De la muestra molida de los frutos, en el laboratorio de suelo y Agua de la UNA se determin�� las concentraciones de N, P, K, Ca y Mg. Se realiz�� una correlaci��n entre el di��metro polar y di��metro ecuatorial de los frutos en ambos ensayos. Las curvas de crecimiento y peso se ajustaron a regresiones no lineales. El programa usado fue SAS vs 9.1. Los frutos de caf�� con especies leguminosas y combinaciones de leguminosas y no leguminosas y la aplicaci��n de fertilizaci��n OI y CM presentaron el mayor crecimiento, mayor peso seco y las m��s altas concentraciones de nutrientes. El mayor crecimiento de los frutos se da durante la formaci��n, a los primeros 90 d��as y la mayor acumulaci��n de nutrientes se da entre los 90 y 210 d��as. Los modelos utilizados para el ajuste de curvas fueron el No Lineal Exponencial y el modelo Probit normal.