Reduced magnetic disorder at low temperature in Ca3Co2O6 via zinc substitution

ABSTRACT

The compound Ca₃Co₂O₆ undergoes a transition into a spin-density wave (SDW) state near 24?K. Below ～10?K, this unstable SDW state coexists with a nearly- degenerate commensurate antiferromagnetic state as well as short-range magnetic order. Clear signatures of this strong magnetic disorder have been observed in the response of entropy to changing magnetic field and temperature. We performed a calorimetry study of Ca₃Co₂O₆ and Ca₃Co_1.9Zn_0.1O₆ in order to compare their entropic responses at low temperature. Our results for Ca₃Co₂O₆ reveal that ΔS(T, H)?≡?S(T, H)?S(T, H?=?0) increases as either temperature or magnetic field increase. In contrast, ΔS data for Ca₃Co_1.9Zn_0.1O₆ were relatively unresponsive to changes in temperature or field, suggesting that Zn substitution may reduce the low-temperature magnetic disorder observed in Ca₃Co₂O₆. These results are discussed within the context of two cases (Ca₃Co₂O₆ under applied pressure and Ca_2.75R_0.25Co₂O₆ (R?=?Dy, Lu)) in which a single magnetic ground state is stabilised.     

Turing pattern formation for reaction–convection–diffusion systems in fixed domains submitted to toroidal velocity fields

We have studied the effect of advection on reaction–diffusion equations by using toroidal velocity fields. Turing patterns formation in diffusion–advection–reaction problems was studied specifically, considering the Schnackenberg and glycolysis reaction kinetics models. Four cases were analyzed and solved numerically using finite elements. For glycolysis models, the advective effect modified the form of Turing patterns obtained with diffusion–reaction; whereas for Schnackenberg problems, the original patterns distorted themselves slightly, making them rotate in direction of the velocity field. We have also determined that the advective effect surpassed the diffusive one for high values of velocity and instability driven by diffusion was eliminated. On the other hand the advective effect is not considerable for very low values in the velocity field, and there was no modification in the original Turing pattern.     

Hölder Estimates of Solutions on the Equation u t = Δ G ( u )

In this paper we are concerned with the Hölder estimates of solutions of the Cauchy problem for the degenerate parabolic Eq. (1) with the initial data (2), where the diffusion function G ( u ) can be a constant on a non-zero measure set, such as the equations of two-phase Stefan's type. Under the condition | GG "/ G ' 2 | h g , g 2 h 1/2 N , the global estimates | o ( G f ( u ))| h M , on R N ‐ R + , is obtained by using the maximum principle, where f is a constant given in (9).     

Recurrence plots and unstable periodic orbits

A recurrence plot is a two-dimensional visualization technique for sequential data. These plots are useful in that they bring out correlations at all scales in a manner that is obvious to the human eye, but their rich geometric structure can make them hard to interpret. In this paper, we suggest that the unstable periodic orbits embedded in a chaotic attractor are a useful basis set for the geometry of a recurrence plot of those data. This provides not only a simple way to locate unstable periodic orbits in chaotic time-series data, but also a potentially effective way to use a recurrence plot to identify a dynamical system. (c) 2002 American Institute of Physics.     

Room temperature olefins oligomerization over sulfated titania

Oligomerization reaction was carried out at room temperature using sulfated titania as catalyst. Total isobutene conversion was obtained with high stability for a long period of time. In case of deactivation, total reactivation of the catalyst was reached.     

Modular deposition chamber for in situ X‐ray experiments during RF and DC magnetron sputtering

A new sputtering system for in situ X‐ray experiments during DC and RF magnetron sputtering is described. The outstanding features of the system are the modular design of the vacuum chamber, the adjustable deposition angle, the option for plasma diagnostics, and the UHV sample transfer in order to access complementary surface analysis methods. First in situ diffraction and reflectivity measurements during RF and DC deposition of vanadium carbide demonstrate the performance of the set‐up.     

Characterization of Phenolic Compounds Contained in Bio-Oil Stemming from Agricultural Biomass Wastes

JPC – Journal of Planar Chromatography – Modern TLC - Bio-oil is produced by biomass pyrolysis. It contains hundreds of chemical compounds including alkanes, aromatic hydrocarbons,...     

Photoprotective and Antigenotoxic Effects of the Flavonoids Apigenin,Naringenin and Pinocembrin

This work evaluated the photoprotective and antigenotoxic effects against ultraviolet B (UVB) radiation of flavonoid compounds apigenin, naringenin and pinocembrin. The photoprotective efficacy of these compounds was estimated using in vitro photoprotection indices, and the antigenotoxicity against UVB radiation was evaluated using the SOS chromotest and an enzymatic (proteinase K/T4 endonuclease V enzyme) comet assay in UV‐treated Escherichia coli and human (HEK‐293) cells, respectively. Naringenin and pinocembrin showed maximum UV‐absorption peak in UVC and UVB zones, while apigenin showed UV‐absorption capability from UVC to UVA range. These compounds acted as UV filters reducing UV‐induced genotoxicity, both in bacteria and in human cells. The enzymatic comet assay resulted highly sensitive for detection of UVB‐induced DNA damage in HEK‐293 cells. In this work, the photoprotective potential of these flavonoids was widely discussed.     

Computational examples of reaction–convection–diffusion equations solution under the influence of fluid flow: First example

This paper presents several numerical tests on reaction–diffusion equations in the Turing space, affected by convective fields present in incompressible flows under the Schnakenberg reaction mechanism. The tests are performed in 2D on square unit, to which we impose an advective field from the solution of the problem of the flow in a cavity. The model developed consists of a decoupled system of equations of reaction–advection–diffusion, along with the Navier–Stokes equations of incompressible flow, which is solved simultaneously using the finite element method. The results show that the pattern generated by the concentrations of the reacting system varies both in time and space due to the effect exerted by the advective field.