Influence of Space Charge During the Oxidation of Metal Surfaces

In this work we present a model for the surface oxidation growth of thin films considering the influence of space charge. The space charge field Esp is assumed proportional to the charge of moving metal ions and electrons in the oxide layer. The surface charge field Eox decreases as the Cabrera and Motts’ oxide thickness X grows to its limit X1 (Eox=VM/X). Eox remains constant for further growth of the oxide film (Eox=VM/X1). The obtained equation for the growing rate of the oxide film covers two stages. The first stage is characterized by a negligible space charge and is described by the typical inverse logarithmic law. During transition from thin to thick film the oxidation growth rate is described by a direct logarithmic law which is confirmed by many experiments. At the end of this stage the drift of metal ions is replaced by their diffusion that leads to parabolic law

Field-dependent Behavior of AC Susceptibility in [Y<inf>0.8</inf>Ca<inf>0.2</inf>](Ba<inf>0.5</inf>Sr<inf>0.5</inf>)<inf>2</inf>Cu<inf>3</inf>O<inf>7−δ</inf>

The AC susceptibility of [Y0.8Ca0.2](Ba0.5Sr0.5)2 Cu3O7−δ was investigated as a function of frequency and amplitude of AC magnetic field. The susceptibilities of the sample display the field amplitude dependence. The peak temperature (Tp) of its imaginary part shows not frequency dependence but field amplitude dependence. The frequency effect on AC susceptibility was negligible. As the field amplitude increases, Tp shifts to lower temperature. This effect can be interpreted in terms of bulk pinning hysteresis loss due to the vortices motion in/out grain boundary.The work in Peru has been supported by the Superior Council of Research of the National University of San Marcos (Grant No. 151301031). This work was also supported by the National Research Foundation of President Post-doctoral fellowship Program (NRF-2013R1A6A3A060443). “L. De Los Santos thanks the Ministry of the Production “Programa Nacional de Innovacion´ para la Competitividad y Productividad” for financial support (Project ECIP-1-P-069-14)”.This is the author accepted manuscript. The final version is available from Springer via http://dx.doi.org/10.1007/s10948-015-3238-

Manometric Determination of the Oxygen Diffusion Coefficients in YBa2Cu3−yFeyO6+x

Thermodynamic parameters, such as the activation energy (Ea) and the diffusion coefficient (D0), of weakly bounded oxygen in Fe-doped YBa2Cu3O6+x (YBa2Cu3-yFeyO6+x) system were obtained utilizing the Manometric technique. It is found that under isothermal conditions, oxygen desorption in YBa2Cu3O6+x (YBCO) occurs following an exponential decay trend and in two distinct stages. During the first stage, the majority of absorbed oxygen is released, while the second stage exhibits a delayed degassing kinetics. Ea and D0 were determined for both, pressed and powdered, samples of the YBCO and YBa2Cu3-yFeyO6+x systems, from experimental kinetic curves, depicting gas release P(t) under isothermal vacuum degassing conditions. It is demonstrated that doping with Fe prevents oxygen exchange in YBCO, as evidenced by the reduction in the quantity of released oxygen with increasing iron index (y). The experimental results validate the efficacy of the Manometric method for analyzing and determining the thermodynamic and kinetic properties of the YBCO superconductor

Texture and magnetic anisotropy of YBa 2 Cu 3 O 7-x film on MgO substrate

Funder: University of CambridgeAbstract: The texture and magnetic anisotropy of a YBa2Cu3O7-x (YBCO) film growth onto a MgO substrate are analyzed in order to understand the relation between them. X-ray diffraction shows the presence of the (00l) reflections from the YBCO layer with a grain’s fraction value 98%. Rocking Curves (RC) measurements reveal an out-of-plane texture with a full width at the half maximum of 0.81°, revealing a high uniaxial texture in the YBCO film. The temperature dependence of the susceptibility measurements obtained under many applied fields along Hext ||c-axis and Hext||ab-plane reveals strong relationship between the uniaxial texture and the magnetic anisotropy, confirming the high ordering of the CuO2 superconducting planes. In addition, the critical current density values are obtained from the hysteresis loops and compared to similar YBCO films with uniaxial and biaxial texture reported elsewhere

Landscape-Scale Mining and Water Management in a Hyper-Arid Catchment: The Cuajone Mine, Moquegua, Southern Peru

The expansion of copper mining on the hyper-arid pacific slope of Southern Peru has precipitated growing concern for scarce water resources in the region. Located in the headwaters of the Torata river, in the department of Moquegua, the Cuajone mine, owned by Southern Copper, provides a unique opportunity in a little-studied region to examine the relative impact of the landscape-scale mining on water resources in the region. Principal component and cluster analyses of the water chemistry data from 16 sites, collected over three seasons during 2017 and 2018, show distinct statistical groupings indicating that, above the settlement of Torata, water geochemistry is a function of chemical weathering processes acting upon underlying geological units, and confirming that the Cuajone mine does not significantly affect water quality in the Torata river. Impact mitigation strategies that firstly divert channel flow around the mine and secondly divert mine waste to the Toquepala river and tailings dam at Quebrada Honda remove the direct effects on the water quality in the Torata river for the foreseeable future. In the study area, our results further suggest that water quality has been more significantly impacted by urban effluents and agricultural runoff than the Cuajone mine. The increase in total dissolved solids in the waters of the lower catchment reflects the cumulative addition of dissolved ions through chemical weathering of the underlying geological units, supplemented by rapid recharge of surface waters contaminated by residues associated with agricultural and urban runoff through the porous alluvial aquifer. Concentrations in some of the major ions exceeded internationally recommended maxima for agricultural use, especially in the coastal region. Occasionally, arsenic and manganese contamination also reached unsafe levels for domestic consumption. In the lower catchment, below the Cuajone mine, data and multivariate analyses point to urban effluents and agricultural runoff rather than weathering of exposed rock units, natural or otherwise, as the main cause of contamination

Physical and chemical techniques for a comprehensive characterization of river sediment: A case of study, the Moquegua River, Peru

River sediment is comprised of complex mineral systems composed by different kinds of organic and inorganic matter, and thus, is difficult to characterize. Besides, some standard techniques, such as X-ray diffraction (XRD), energy dispersive X-ray (EDX), optical and scanning electron microscopy, Fourier transmission infrared spectroscopy, inductively couple plasma-mass spectrometry (ICP-MS), and simultaneous Thermogravimetric Analysis – Differential Thermal Analysis (TGA-DTA), Mössbauer spectroscopy and magnetometry can provide substancial information about the compositional, physical, and chemical characteristics. In the current study, the versality of these methods is tested and the information provided by these methods for eight sediment samples, collected from the Moquegua River, Peru is compared. Qualitative analysis indicates that the samples consist of sand grains with different shapes, sizes, and colors coexisting with the presence of some diatoms. The chemical and mineralogical analysis reveal that the samples are composed mainly of silicon (Si), aluminium (Al), sodium (Na), potassium (K), aluminon–silicates, and carbonates, typical for river sediment. More detailed information obtained by these techniques include the discovery of adsorbed oxygen–hydrogen (O–H), carbon–H (C–H) and C, from organic matter, the thermal reactions and decomposition of the components, and the identification of the minor iron–oxides components. Further, other properties such as magnetic interaction are also analyzed in detail

Outcomes from elective colorectal cancer surgery during the SARS-CoV-2 pandemic

This study aimed to describe the change in surgical practice and the impact of SARS-CoV-2 on mortality after surgical resection of colorectal cancer during the initial phases of the SARS-CoV-2 pandemic

The magnetic reversal characteristics of 32-bit composite element magnetic barcodes

Magnetic barcodes containing 32 composite element bits have been produced and measured in order to optimize the design of magnetic microcarriers. Focused magneto-optic Kerr effect measurements allow the determination of the change in magnetic hysteresis when the width of magnetic elements is varied between bits, and the electron beam lithography used in production is confirmed to be accurate to ∼6 nm using scanning electron microscopy. The sharp magnetic switching observed, an important prerequisite for a functioning device, is attributed to the expected dipolar interactions between magnetic elements and the use of magnetically soft Permalloy. A crossover between two magnetic reversal behaviors is discovered when the magnetic elements are ∼200 nm wide. From these measurements, 12 bits were selected on which data can be written with a low probability of error, with the prospect of the other 20 bits being employed for error correction. We have therefore developed a nonvolatile magnetic memory on which 4096 unique codes can be programmed.RG85120 RG9297