bluuebunny/crossref_metadata_2025 huggingface dataset:
Atomic-Scale Analysis of Strain Relaxation Mechanisms in Ultra-Thin Metallic Films
Authors: Gungor M. Rauf , Maroudas Dimitrios
Published: June 2019

A comprehensive computational analysis is presented of the atomistic mechanisms of strain relaxation over a wide range of applied biaxial tensile strain in free-standing Cu thin films. The analysis is based on large-scale isothermal-isostrain MD simulations using slab supercells with cylindrical voids normal to the film plane and extending throughout the film thickness. Our analysis has revealed various regimes in the film's mechanical response as the applied strain level increases. Following an elastic response at low strain (≶ 2%), plastic deformation occurs accompanied by emission of screw dislocations from the void surface and threading dislocations from the film surfaces, in parallel with generation of vacancies due to slip of jogged dislocations. At the lower strain range following the elastic-to-plastic deformation transition (⋚ 6%), void growth is the major strain relaxation mechanism, while at higher levels of applied strain (≥ 8%), a subsequent transition leads to a new plastic deformation regime where void growth plays a negligible role in the film strain relaxation.
Residual Stresses around Indentations in Alumina/SiC Nanocomposites [Abstract + Supplemental Data]
Authors: Limpichaipanit Apichart , Todd Richard Ian
Published: June 2019

Alumina/SiC nanocomposites are more wear resistant and have better surface finish than pure alumina of a similar grain size. Grain pullouts caused by intergranular fracture are observed on worn surfaces of alumina whereas only a few pullouts resulting from transgranular fracture and scratches caused by plastic deformation are the main features of a worn surface of the nanocomposites. Surface mechanical properties were investigated by Cr3+ fluorescence microscopy. The experiments were carried out using a variety of microstructures.
Deformation-induced Nanocomposites
Authors: Wilde Gerhard
Published: June 2019

Composite approaches, e.g. with mutually immiscible constituents or including at least one refractory phase, present a viable and maybe even necessary route for stabilizing massive nanostructured materials against detrimental coarsening under thermal and/or mechanical loading conditions [1]. A different way for nanoscaled composite formation is presented by the nanocrystallization of marginally glass-forming amorphous alloys, such as Al-rich alloys with rare earth and transition metal additions. Such composite systems that are stabilized at nanometer-scaled structure sizes due to diffusion limitations have conventionally been processed by supplying thermal energy for initiating the nanocrystal formation [2]. New opportunities for fabricating massive nanocrystalline composites in bulk quantities and with improved microstructures from such alloys might be based on the plastic deformation of the amorphous quenching products, as indicated by the observation of nanocrystallization in shear bands [3-5].ere, different deformation methods with largely different strain and pressure levels have been applied on rapidly quenched Al-rich metallic glasses in order to investigate the strain-induced nanocrystal formation. The results indicate e.g. that shear straining under a high pressure and to large strain values can produce uniform nanocrystalline structures in bulk samples, which is essential to their functional performance. Moreover, detailed structure analyses indicate that the amorphous structure of the entire sample volume, and not only the shear band regions, might be affected by the plastic deformation. In addition to the significance concerning the understanding of the deformation of glasses, the results also indicate the applicability of the new processing routes for synthesizing massive, porosity-free nanocrystalline materials.[1] G. Wilde, H. Rösner, J. Mater. Sci., in press. [2]G. Wilde, et al., Adv. Engr. Mater. 5 (2003) 125. [3]G. Wilde et al., Mater. Sci. Forum 503-504 (2006) 425. [4] N. Boucharat, et al., Scripta Mater. 53 (2005) 823. [5] R. Hebert, et al., Scripta Mater. 54 (2006) 25.
Microstructure and Mechanical Properties of Combinatorially Prepared Thin Film Aluminum-Silicon Nanocomposites
Authors: Olk Charles H. , Lukitsch Michael , Haddad Daad B
Published: June 2019

e have undertaken the exploration of the AlxSi1-x systems to discover new alloys with enhanced properties. We describe the mechanical properties of thin film AlxSi1-x alloys determined through indentation experiments. Combinatorial methods were used to systematically control thin film microstructure through variations in composition and growth temperature. Discrete libraries of compositionally graded films have been sputter deposited onto silicon substrates to produce two structural phase regions: amorphous Al-Si and amorphous Si plus crystalline Al. The mechanical properties of the thin films were determined by analyzing the load-displacement traces based on the Oliver-Pharr method. X-ray diffraction was used to investigate the microstructures and determine the crystallite sizes.
Microstructure-Property Relationships in Wear Resistant Alumina/SiC 'nanocomposites' the Importance of Plastic Deformation in Ceramics
Authors: Todd Richard Ian , Limpichaipanit Apichart , Ortiz Merino Jose
Published: June 2019

Alumina/SiC “nanocomposites" consist of a dispersion of submicron SiC particles in an alumina matrix. The resistance to severe wear of the nanocomposites and the surface finish produced by a given grinding treatment are strikingly superior to those of pure alumina with the same grain size. We have explored the reasons for this by correlating a wide range of variations in the basic microstructure with the wear behaviour observed, including both the wear rate, and quantitative surface fractography of the worn surfaces. These improved properties of the nanocomposites are shown to be a consequence of a reduction in surface grain pullout by brittle fracture. In “dilute” nanocomposites (<10% SiC), this is due largely to a reduction in size of the individual pullouts. With 10% SiC nanoparticles, however, there is also evidence that the SiC directly suppresses the nucleation of cracking by plastic deformation of the surface. The origin of these effects will be discussed.
Depth-dependent defect and residual stress distribution in magnetron sputtered MoN:Cu nanocomposite films by x-ray microdiffraction
Authors: Chen Gang , Singh Dileep , Eryilmaz Osman , Erdemir Ali , Routbort Jules , Liu Wenjun
Published: June 2019

We have developed a synchrotron-based x-ray microdiffraction technique for measuring depth-resolved residual stress distribution in nanocrystalline films with submicron resolution [1]. In this study, we further refined this technique and applied it to low-friction and high-hardness Cu-doped MoN films. These magnetron sputtered nanocomposites films consist of MoN, Mo2N, and Cu phases, whose ratio depends on Cu concentration. By using the microdiffraction technique, we discovered that both the deviatoric and the hydrostatic components of the residual stresses depend on the film depth (Fig.1). The former indicates depth-dependent distribution of biaxial stresses, while the latter implies depth-dependent defect distribution, which also depends on Cu concentration. Thermal annealing of the nanocomposite film partially relives the stress, significantly reduces the lattice spacing, and eliminates the defect gradients. These results suggest that interstitial N may play an important role in the lattice expansion and the defect gradients formed during the non-equilibrium sputtering process. Our study provides fresh insights into understanding the structure-property relations in the magnetron sputtered MoN:Cu nanocomposites films.
Nanoscale Strain Measurements in Polymer Nanocomposites
Authors: Chen Qi , Chasiotis Ioannis , Chen Chenggang , Roy Ajit
Published: June 2019

The paper describes a multiscale experimental investigation of the mechanical behavior of polymer nanocomposites with nanoscale fused silica inclusions with the objective to shed light into the effect of the hard nanoparticles on the quasistatic mechanical behavior of epoxy matrix and the implications of the latter to the effective composite properties. The main variable in this study was the nanofiller volume fraction while the particle size was either 15 nm or 100 nm. Local strain measurements indicated strain field localization in the vicinity of the nanofillers at strains that macroscopically fall in the linearly elastic regime. The matrix strains were as high as three times the applied far field strain at applied effective strains of ∼ 1%. At larger stresses the local strain fields evolved to maxima that were considerably higher than the applied strain, and they were affected by local particle density and distribution. In composites with the largest particle volume fraction, 5 vol.%, 100 nm fillers, neighboring particles located in small proximities behaved as single large particles and often resulted in matrix strain shielding thus decreasing the benefit of the large surface-to-volume ratio and the associated efficiency in load transfer. On the other hand the 15 nm fillers resulted in more uniformly distributed deformation compared to composites with 100 nm particles.
The Influence of Nanosized Molybdenum and Tungsten Fillers on the Physico-Mechanical and Tribological Properties of Polymer-based Composite Materials
Authors: Makaryan Victor
Published: June 2019

The problems of the creation of composite polymer-based materials with the use of nanosized molybdenum and tungsten fillers with the particle size of less than 10 nm are considered. The copolymer of formaldehyde and dioxolane (CFD) and the polyphenylene sulphide (PPS) are chosen as polymeric matrixes. A comparative analysis of the tribological properties of composite materials with fine nanosized fillers (5-10 nm) and nanosized analogues (100-200) is made. It is determined that the use of nanosized isotropic structure Mo fillers leads to improved wear-resistance up to three times for CFD-based composites and up to four times for PPS-based. The highest hardness values were observed while using isotropic nanosized tungsten fillers. The nanosized crystalline fillers also give positive results, but the bigger sized fillers decrease the polymer hardness characteristics comparatively nanosize isotropic analogues.
Power Cycling Effects on the Structural Stability of Thermal Pastes Used in Microelectronics
Authors: Nnebe Ijeoma , Feger Claudius , McGlashan-Powell Maurice
Published: June 2019

Thermal pastes are a class of soft composite materials of great importance to the microelectronics industry. The function of these pastes is two-fold: (i) to transport heat away from the chip; and (ii) to accommodate mechanical stresses in the package arising from the mismatch in the thermal expansion between the chip and the heat spreader or sink. Due to the former requirement, thermal pastes are among some of the most highly-filled composite systems in practice (solids volume fraction > 70%). These materials are expected to withstand the significant normal forces, lateral forces, and temperature variations associated with chip operations and power off/on transitions. The structural changes and degradation of various thermal pastes during power cycling have been characterized using optical microscopy and IR thermography. Correlations between the evolving structures and variables such as thermal paste inhomogeneity and binder-particle dispersability have been successfully made and will be presented.
Preferential Site Precipitation and Subcell Stability in AA6061 Sandwich Cores
Authors: Bouwhuis B. A. , Hibbard G. D.
Published: June 2019

Periodic cellular metal (PCM) sandwich cores can be considered hybrids of the solid and gas type. These can be designed at both the architectural and microstructural levels. PCM cores with 95% open porosity have been constructed from perforated 6061 aluminium alloy (AA6061) sheets using a perforation-stretching method. This method places planar, periodically-perforated sheet metal in an alternating-pin jig. The pins apply force out-of-plane, plastically deforming the sheet metal into a truss-like array of struts (i.e. metal supports) and nodal peaks (i.e. strut intersections). The result is a non-uniform work-hardened profile exhibiting large deformation at the nodes and small deformation at the struts.

For identical PCM architectures, this study looks at the interaction of microstructural strengthening mechanisms and the resultant performance of PCM truss cores. Beginning with fabrication, work-hardening induced a subcell network of dislocation tangles within the AA6061 matrix. Following this stage, a variety of microstructures were created through recovery, recrystallization and precipitation mechanisms. Microhardness measurements and electron back-scattered diffraction (EBSD) characterization were employed through truss core cross-sections in order to study the microstructural gradients of subcell size as well as interaction between subcells and precipitates in the truss cores. To determine the effect of microstructure on mechanical performance, PCM cores were compressed to study deformation and collapse mechanisms.

The present data can be used to illustrate engineering at the architectural and microstructural levels to achieve a range of mechanical properties in a hybrid sandwich core.
Threshold crack speed in dynamic fracture of silicon
Authors: Buehler Markus J. , Tang Harvey , van Duin Adri C.T. , Goddard William A.
Published: June 2019

We report a study of dynamic cracking of a silicon single crystal in which the ReaxFF reactive force field is used for about 3,000 atoms near the crack tip while the other 100,000 atoms of the model system are described with a simple nonreactive force field. The ReaxFF is completely derived from quantum mechanical calculations of simple silicon systems without any empirical parameters. This model has been successfully used to study crack dynamics in silicon, capable of reproducing key experimental results such as orientation dependence of crack dynamics (Buehler et al., Phys. Rev. Lett., 2006). Here we focus on crack speeds as a function of loading and crack propagation mechanisms. We find that the steady state crack speed does not increase continuously with applied load, but instead jumps to a finite value immediately after the critical load, followed by a regime of slow increase. Our results quantitatively reproduce experimental observations of crack speeds during fracture in silicon along the (111) planes, confirming the existence of lattice trapping effects. We find that the underlying reason for this behavior is formation of a 5-7-double ring defect at the tip of the crack, effectively hindering nucleation of the crack at the Griffith load. We develop a simple continuum model that explains the qualitative behavior of the fracture dynamics.
Simulation of Directed Nanocrack Patterns for the Fabrication of Nanowires [PowerPoint Submission]
Authors: Salac David , Lu Wei
Published: June 2019

While material fracture is generally considered undesirable, recent experimental work has indicated that cracking can be utilized to create small scale nanowire structures with diameters of 100nm and smaller. Typical nanowire fabrication techniques include the use of a scanning tunneling microscope and electrochemical deposition. Compared to fracture fabricated nanowire structures current fabrication techniques are either extremely slow or require large amounts of post-processing. To become a viable nanowire fabrication technique the cracking of materials must be directed. We propose a computational model to predict propagation paths in large scale crack systems. We utilize the level set method to investigate the creation of nanoscale crack patterns. The level set method allows for large scale simulations of many crack tips while easily accommodating large scale deformations. Unlike traditional methods such as finite elements explicit modeling of the cracks is not needed. We show that the use of multiple materials and etched regions can effectively direct the cracking of a thin film. Using these patterns nanowire structures can be constructed which would be difficult to obtain otherwise.
Modeling the Effect of Oxidation and Etching of Silicon Photonic Crystals
Authors: Thitsa Makhin , Ali Haider , Wu Feng , Peters Kurt M. , Albin Sacharia
Published: June 2019

Tuning the band-gap of photonic crystals has been a challenge because there are few parameters that can be varied to modify the band structure. In this paper we modeled the effect of well controlled complementary metal oxide semiconductor (CMOS) compatible processing techniques, viz. oxidation and oxide etching, on the band-gap and mid-gap frequency of a silicon photonic crystal (PC). By adding silicon dioxide as the third dielectric, oxide thickness serves as a new parameter that influences the band structure. In the case of a PC of Si atoms in air, if silicon is etched to reduce the original atom radius from 0.28a (a = lattice constant) to 0.1a, the band-gap and mid-gap normalized frequencies increase from 0.1 to 1.6 and from 0.28 to 0.49 respectively. During oxidation, silicon is consumed to form silicon dioxide. Thus, if the Si atom of 0.4a radius is oxidized until it reaches 0.1a, the band-gap and mid-gap vary in the range of (0.1-1.5) and (0.28-0.41) respectively. When the oxide is etched back, the band-gap can be tuned in the range of (0.1-1.6) for a new mid-gap frequency in the range of (0.41-0.49). Results are also presented for a triangular lattice of air holes in silicon.
Inelastic Behavior and Grain-Boundary Effects in Polycrystalline Materials
Authors: Shi Jibin , Zikry Mohammed , Hatem Tarek Moustafa
Published: June 2019

Dislocation-density based multiple-slip constitutive formulations and specialized computational schemes are introduced to account for grain-boundary (GB) effects in polycrystalline aggregates. New kinematically based interfacial grain-boundary regions and formulations are introduced to account for dislocation-density transmission, absorption, and pile-ups that may occur due to CSL grain-boundary misorientations.
A Procedure of Determining Parameters to Expand Applicability of Modified Embedded Atom Method to Non-bulk Systems
Authors: Tokumaru Kento , Takahashi Kunio , Saito Shigeki , Yin Yingchen
Published: June 2019

Modified Embedded Atom Method '92 (MEAM92) developed by Baskes is the most popular among researchers using Embedded Atom Method series, because MEAM92 has high reliability for bulk system, and parameters are determined consistently. However, the applicability of this method to non-bulk systems, such as surface, is still uncertain. In such background, in order to expand the applicability to non-bulk systems, Kunio Takahashi has proposed Dimer Reference Modified Embedded Atom Method (DR-MEAM). The objective of this work is to discuss the applicability to non-bulk systems by determining the DR-MEAM parameters fitted to the results of clusters and bulk calculated by MEAM92. It is suggested as one of the effective methods for lining up the candidates of optimized parameters consistently. Additionally, calculated surface properties by determined parameters for Cu suggest the valid values in comparison with the other methods, and the possibility of DR-MEAM for expanding to non-bulk systems.
Molecular Dynamics Simulation of Nanoparticle Chain Aggregate Sintering
Authors: Hawa Takumi , Zachariah Michael R
Published: June 2019

Sintering of silicon nanoparticle chain aggregates are investigated using molecular dynamics (MD) simulations at 1500 K, which is about melting temperature at the size range we tested. The straight chain aggregates consist of upto 40 particles and the primary particles of 2.5 to 5 nm sizes are considered. The sintering time increases with increase the total volume of the chain aggregate or with increase the exposed initial surface area of the chain. A mathematical model was developed to describe the dynamics of sintering of chain aggregates. The model was able to predict the sintering time with excellent agreement with the results obtained from MD simulations. We also studied the chain aggregate that has a secondary branch coming out from the edge of the primary branch (L-shape) and from the middle of the primary branch (T-shape). In general, sintering time changes as much as 30% of that of a straight chain which contains the same volume of particles.
Chromium Impurity States in Pb1-xGexTe Alloys Under Pressure
Authors: Skipetrov Evgeny , Plastun Alexey , Kovalev Boris , Skipetrova Lyudmila , Topchevskaya Tatyana , Slyn'ko Vasily
Published: June 2019

The galvanomagnetic effects in the n-Pb1-xGexTe:Cr (x=0.02-0.13) alloys at the temperatures 4.2≤T≤300 K and under hydrostatic compression up to 17 kbar have been investigated. The metal-insulator transition under the increase of germanium content in the alloys and insulator-metal transition, induced by pressure in Pb1-xGexTe:Cr (x=0.10) alloy, were revealed. Using the experimental data in the frame of two-band Kane dispersion relation the dependences of the free electron concentration and the Fermi level position on the matrix composition and on the pressure were calculated. The composition and pressure coefficients of chromium deep level movement were obtained and the models of the electronic structure reconstruction under varying the alloy composition and under pressure were proposed.
High Pressure-High Temperature Reactions in Xenon-Chlorine System
Authors: Somayazulu Maddury , Gramsch Steven , Mao Ho-Kwang , Hemley Russell
Published: June 2019

We present results of studies of the xenon-chlorine system to 60 GPa and temperature range 300 to 2000 K. Using a combination of Raman spectroscopy, infrared spectroscopy and synchrotron x-ray diffraction; we characterize the products of diamond cell experiments. In the 2-20 GPa pressure interval, we observe the formation of a deep red crystalline phase. Above 15 GPa, and at high temperature, a solid solution of Xe and Cl2 appears to form. Comparison of the ultraviolet-visible and infrared absorption measurements on the proposed alloy of Xe and Cl2 show that band edge moves into the visible range at high pressure
Bird conservation in Africa: the contributions of the Ibadan Bird Club
Authors: Awoyemi Adewale Gboyega , Bown Deni
Published: June 2019

The Ibadan Bird Club has met 19 times at monthly intervals between February 2016 and August 2017, and 264 people (155 male and 109 female) have registered as members. During this period, the club has successfully built local capacity in bird conservation, and 111 bird species, distributed in 39 families, have been documented in an urban Important Bird Area, southwestern Nigeria. The findings of this citizen science initiative are essential for conservation purposes.
Grain Reconstruction of Palladium and Palladium-Nickel Alloys for Platinum Catchment
Authors: Fjellvåg A. Slagtern , Waller D. , Skjelstad J. , Sjåstad A. Olafsen
Published: June 2019

Platinum-rhodium gauzes are frequently used to catalyse the high temperature ammonia oxidation step for production of synthetic nitrogen-based fertilisers. The gauzes suffer from Pt loss in the form of platinum dioxide (PtO2), due to the highly exothermic nature of the oxidation reaction. Industrially this is mitigated by installing one or more palladium-nickel catchment gauzes directly downstream of the combustion gauzes, to capture the lost Pt. The Pd-Ni catchment gauzes undergo severe structural modification during operation. In this study, we undertake a systematic study in a laboratory-scale furnace system to determine the role of each of the constituent gases O2, H2O and PtO2 on the structural changes of the Pd-Ni gauzes. In addition, some samples are exposed to real industrial conditions in an ammonia combustion pilot plant reactor. Fresh and spent catchment gauzes are analysed by means of scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), thermogravimetric analysis (TGA) and inductively coupled plasma mass spectroscopy/optical emission spectroscopy (ICP-MS/OES). By combining analysis of samples from furnace and pilot scale experiments, the main findings are that Pd-Ni gauzes undergo internal oxidation to nickel(II) oxide (NiO); which in the presence of steam results in Ni depletion and that PtO2 vapour causes severe grain reconstruction. Furthermore, in laboratory-scale experiments no significant Pd loss is observed, which is in contrast to observations from the pilot plant where the samples are exposed to real post-ammonia oxidation conditions. Pd loss is likely attributed to some gas species contained in the real post-ammonia oxidation gas stream.
A Phase Ib Study of Axitinib in Combination with Crizotinib in Patients with Metastatic Renal Cell Cancer or Other Advanced Solid Tumors
Authors: Michaelson M. Dror , Gupta Shilpa , Agarwal Neeraj , Szmulewitz Russell , Powles Thomas , Pili Roberto , Bruce Justine Yang , Vaishampayan Ulka , Larkin James , Rosbrook Brad , Wang Erjian , Murphy Danielle , Wang Panpan , Lechuga Maria Josè , Valota Olga , Shepard Dale R.
Published: June 2019

Lessons Learned

The combination of axitinib and crizotinib has a manageable safety and tolerability profile, consistent with the profiles of the individual agents when administered as monotherapy. The antitumor activity reported here for the combination axitinib/crizotinib does not support further study of this combination treatment in metastatic renal cell carcinoma given the current treatment landscape.

Background

Vascular endothelial growth factor (VEGF) inhibitors have been successfully used to treat metastatic renal cell carcinoma (mRCC); however, resistance eventually develops in most cases. Tyrosine protein kinase Met (MET) expression increases following VEGF inhibition, and inhibition of both has shown additive effects in controlling tumor growth and metastasis. We therefore conducted a study of axitinib plus crizotinib in advanced solid tumors and mRCC.

Methods

This phase Ib study included a dose-escalation phase (starting doses: axitinib 3 mg plus crizotinib 200 mg) to estimate maximum tolerated dose (MTD) in patients with solid tumors and a dose-expansion phase to examine preliminary efficacy in treatment-naïve patients with mRCC. Safety, pharmacokinetics, and biomarkers were also assessed.

Results

No patients in the dose-escalation phase (n = 22) experienced dose-limiting toxicity; MTD was estimated to be axitinib 5 mg plus crizotinib 250 mg. The most common grade ≥3 adverse events were hypertension (18.2%) and fatigue (9.1%). In the dose-expansion phase, overall response rate was 30% (95% confidence interval [CI], 11.9–54.3), and progression-free survival was 5.6 months (95% CI, 3.5–not reached).

Conclusion

The combination of axitinib plus crizotinib, at estimated MTD, had a manageable safety profile and showed evidence of modest antitumor activity in mRCC.
Soluble Urokinase Plasminogen Activator Receptor and Decline in Kidney Function in Autosomal Dominant Polycystic Kidney Disease
Authors: Hayek Salim S. , Landsittel Douglas P. , Wei Changli , Zeier Martin , Yu Alan S.L. , Torres Vicente E. , Roth Sharin , Pao Christina S. , Reiser Jochen
Published: June 2019

Significance Statement

Soluble urokinase plasminogen activator receptor (suPAR), a marker of inflammation, is also an independent marker for incidence and progression of renal diseases. Mechanistically, it has been shown to activate podocytes in glomerular diseases. In this study, the authors provide the first description linking suPAR levels with disease progression for a major genetic renal disease that mainly affects the extraglomerular compartment, autosomal dominant polycystic kidney disease (ADPKD). They found an association between suPAR levels and height-adjusted total kidney volume, independent of age, sex, race, hypertension, and eGFR. In addition, patients with suPAR levels >2.82 ng/ml had a 3.38-fold increase in risk of incident ESRD. These findings suggest that suPAR levels may be useful for early identification of patients with ADPKD at high risk of disease progression.

Background

Levels of soluble urokinase plasminogen activator receptor (suPAR), an inflammation marker, are strongly predictive of incident kidney disease. Patients with autosomal dominant polycystic kidney disease (ADPKD) experience progressive decline in renal function, but rates of decline and outcomes vary greatly. Whether suPAR levels are predictive of declining kidney function in patients with ADPKD is unknown.

Methods

We assessed suPAR levels in 649 patients with ADPKD who underwent scheduled follow-up for at least 3 years, with repeated measurements of height-adjusted total kidney volume and creatinine-derived eGFR. We used linear mixed models for repeated measures and Cox proportional hazards to characterize associations between baseline suPAR levels and follow-up eGFR or incident ESRD.

Results

The median suPAR level was 2.47 ng/ml and median height-adjusted total kidney volume was 778, whereas mean eGFR was 84 ml/min per 1.73 m2. suPAR levels were associated with height-adjusted total kidney volume (β=0.02; 95% confidence interval, 0.01 to 0.03), independent of age, sex, race, hypertension, and eGFR. Patients in the lowest suPAR tertile (<2.18 ng/ml) had a 6.8% decline in eGFR at 3 years and 22% developed CKD stage 3, whereas those in the highest tertile (suPAR>2.83 ng/ml) had a 19.4% decline in eGFR at 3 years and 68% developed CKD stage 3. suPAR levels >2.82 ng/ml had a 3.38-fold increase in the risk of incident ESRD.

Conclusions

suPAR levels were associated with progressive decline in renal function and incident ESRD in patients with ADPKD, and may aid early identification of patients at high risk of disease progression.
Leaf morpho-anatomical diversity in Echeveria aff. gigantea (Crassulaceae)
Authors: Sandoval-Zapotitla Estela , Martínez-Quezada Daniel M. , Reyes-Santiago Jerónimo , Islas-Luna María de los Ángeles , Rosas Ulises
Published: June 2019

Background. Distinguishing species and populations in Crassulaceae is challenging because of the morphological variability and inter-specific hybridization. Currently our understanding of the morphological and anatomical features in Echeveria is poor, and therefore it is difficult to delimit species, and morphotypes within the species. Question. Our objective was to describe the foliar anatomy and the shape of accessions in E. gigantea. We used E. gibbiflora , another species in the series as a comparison group. Comparing the two species allowed us to evaluate the relationship between anatomy and morphology in E. gigantea .Methods. We performed a survey of anatomical features in seven accessions of E. gigantea , and one accession of E. gibbiflora . We obtained epidermal prints, leaf sections, performed geometric and morphometric analyses.Results. We found that 65  % of the anatomical traits are heterogeneous among the taxonomic units. Our analysis showed that E. gibbiflora and some E. gigantea accessions share extensive anatomical similarities. There was variation within the E. gigantea , suggesting that at least one of the accessions is an independent taxonomic group. The traits with the largest contribution to variation between the groups were related to the epidermis, the hypodermis, the type of vascular bundles and the collenchyma associated to the vascular bundles. In addition we quantified the variation in leaf shape. Interestingly, we found correlations between the organ shape and anatomical traits.Conclusion. These analyses provide information about traits towards the morpho-anatomical definition of E. gigantea variation and suggest developmental correlation yet to be explained.
Licofitas y helechos del bosque meso?filo de montan?a del estado de Hidalgo, Me?xico
Authors: Hernández-Álvarez Adriana Gisela , Sánchez-González Arturo , Tejero-Díez José Daniel
Published: June 2019

Antecedentes: El bosque mesófilo de montaña (BMM) de México posee alta riqueza de licofitas y helechos. Sin embargo, existen amplias zonas sin inventarios florísticos en este ecosistema, que en la actualidad está severamente afectado por actividades humanas y el calentamiento global.Preguntas: ¿Cuál es la composición y riqueza de especies de licofitas y helechos del BMM de Hidalgo? ¿Cómo es la diversidad de licofitas y helechos del BMM de Hidalgo, con respecto a la de otras entidades del país con el mismo tipo de vegetación?Sitio de estudio y periodo de investigación: El estudio incluye 19 municipios de Hidalgo con BMM, entre los años 2015 y 2018.Métodos: El trabajo de campo se realizó en 14 municipios y se obtuvo información bibliográfica de otros cinco. La determinación fue a nivel de especie y se estimó la diversidad por unidad de área.Resultados: Se identificaron 279 especies, 91 géneros y 29 familias de pteridobiontes; 10 especies fueron nuevos registros a nivel estatal. El sustrato preferido fue el terrestre, seguido por el epífito y rupícola; ocho de las especies se consideran en alguna categoría de riesgo en la NOM-059-2010.Conclusiones: El BMM de Hidalgo ocupa el tercer lugar nacional en número de especies de pteridobiontes, superado por Oaxaca y Veracruz. Las familias y géneros más comunes tienen amplia distribución en México. La densidad baja y distribución restringida de algunas especies, por el elevado grado de perturbación del bosque, indican la necesidad de establecer programas de manejo y conservación.
Shifts in tree allometry in a tropical dry forest: implications for above-ground biomass estimation
Authors: Ramírez-Ramírez Gustavo , Ramírez y Avilés Luis , Solorio-Sánchez Francisco Javier , Navarro-Alberto Jorge Augusto , Dupuy-Rada Juan Manuel
Published: June 2019

Background: Accurate estimations of aboveground biomass (AGB) based on allometric models are needed to implement climate-change mitigation strategies. However, allometry can change with tree size.Questions: Does allometry in a tropical dry forest change with tree size? Does combining different allometric equations provide better AGB estimates than using a single equation?Study site and dates: San Agustín Ejido, Yucatán, México, 2016.Methods: Forty-seven trees of 18 species with 2.5 to 41.5 cm in diameter at breast height (DBH) were sampled. Stems and branches were sectioned, and samples were dried and weighed to estimate tree AGB. Segmented linear regression was used to evaluate changes in allometry between DBH, height and AGB. Different equations were tested for each size category identified, and the best models and model-combinations selected.Results: A shift in the AGB-height relationship was found, defining two tree-size categories (2.5-9.9 cm and ? 10 cm in DBH), with the inflection point corresponding to the average canopy height (12.2 m). The best models were AGB = exp(-2.769+0.937ln(D2HPw)) for trees < 10 cm DBH and AGB = exp(-9.171+1.591lnD+3.902lnH+0.496lnPw) for trees ? 10 cm DBH ( R 2 = 0.85 and R 2 = 0.92, respectively). The combination of these models produced more accurate AGB estimates than a single model or combinations involving regional models with larger sample sizes.Conclusions: These results highlight the importance of locally-developed models and suggest changes in allometry and resource allocation: towards height growth for small trees, thereby reducing the risk of suppression, versus towards AGB growth for larger trees, thereby maximizing stability and resource acquisition.
On the identity of two Mexican species of Ageratina (Eupatorieae, Asteraceae): A. grandifolia and A. rivalis
Authors: Hinojosa-Espinosa Oscar , Villaseñor José Luis , Ortiz Enrique
Published: June 2019

Background: Ageratina , with 167 species, constitutes the most diverse genus of the Mexican Asteraceae and the sixth most diverse of the vascular plants in Mexico. The taxonomy of the genus is complex, due to its number of species and the numerous inadequately delimited taxa or with intricate and confusing nomenclature. In addition, little known species have sometimes remained under the synonymy of another different species, as in the case of A. rivalis , which has been considered as a synonym of A. grandifolia .Question: Is it possible to recognize Ageratina rivalis as a distinct species of A. grandifolia by critically analyzing its circumscription, nomenclature and geographical distribution?Taxon: Ageratina grandifolia and A. rivalis .Study site: Mexico.Method: A thorough review of herbarium specimens, field material, descriptions and geographic distribution of the species was made to contrast them.Results: Several differences exist in the morphology and geographical distribution of Ageratina rivalis and A. grandifolia . Descriptions, pictures, distribution maps, synonymy and a key to distinguish them from similar species are provided. The presence of A. grandifolia in Mexico City is also documented. Lectotypes are designated for Eupatorium conspicuum, E . conspicuum var. pueblense , E . grandifolium , and E . rivale .Conclusions: Morphology and geography support the distinction between A . grandifolia and A . rivalis . However, further research is desirable to corroborate or refute this statement, and especially to clearly circumscribe several similar species that seem to be related. This work contributes to a better understanding of the taxonomy and biogeography of the genus Ageratina in Mexico.
White Certificates and White Certificate Trading Schemes as greenhouse gas mitigation policy options for South Africa
Authors: Tyler Emily , Du Toit Michelle , Burchell Zelda
Published: June 2019

AbstractEnergy efficiency activities driven by White Certificate Trading schemes (WCT) achieve the objective of conserving energy, and in most circumstances, also that of reducing greenhouse gas (GHG) emissions. The potential therefore exists that both objectives could be targeted by a single policy mechanism. Energy efficiency activities are important from a GHG mitigation perspective as they represent some of the least costly GHG mitigation activities available to economies. However, there are some significant differences between the use of a direct policy instrument to target GHG emissions mitigation, and the use of an indirect instrument such as WCT, whose direct policy objective is to achieve energy efficiency. Most importantly, WCT utilises intensity targets, whereas GHG mitigation is required by science to comprise absolute reductions. International experience does however suggest that white certificates can be fully fungible with a GHG mitigation policy instrument such as an emissions trading scheme, as long as double counting rules are firmly in place, and the design of the schemes are compatible.Given that 80 percent of the South African GHG emissions are energy related, with energy efficiency measures in industry, commerce and the residential sector representing the bulk of negative cost mitigation options available in the economy, energy efficiency has an important role to play in the country’s mitigation strategy.This paper presents results on research into WCT as a policy option for South Africa conducted in 2008 and presented at the Climate Change Summit 2009.  It investigates in particular the Electricity Conservation Scheme (ECS) as an option for incorporating a WCT mechanism.There is limited experience and therefore analysis on WCS available to date, and even less on the potential interaction and linkages of WCS and emissions trading schemes. This paper therefore identifies significa
Enhancing consumers’ voluntary use of small-scale wind turbines to generate their own electricity in South Africa
Authors: Whelan Brendan , Muchapondwa Edwin
Published: June 2019

This paper investigates whether households and small businesses can voluntarily take advantage of the South Africa’s substantial wind resources to produce their own power from small-scale wind turbines in a viable way. The viability of small-scale wind turbines used to displace electricity consumption from the grid is assessed by means of a financial analysis based on the internal rate of return method. The benefits of small-scale wind turbines output is valued at the grid power tariff which is saved rather than at the wind feed-in tariff rate. The analysis found the small-scale wind turbines to be robustly viable in locations with a mean annual wind speed of at least 8m/s, which is only a few of the windiest locations in South Africa. The competiveness of the wind turbines is seriously challenged by the relatively low coal-based electricity tariffs in South Africa. As such, the financial analysis also considers alternative scenarios where the turbines are supported by financial mechanisms, namely: a tariff subsidy; a capital subsidy and revenue from carbon credits. The analysis reveals that a tariff subsidy of between R1.00 and R1.60/kWh or a capital subsidy of between R25.95 and R32.330/kW or a carbon credit price of between R2.135 and R3.200 will be needed to boost the viability of consumer-based small-scale wind turbines in areas with a mean annual wind speed of at least 5m/s, which is considered to be above average. Thus, there is a need for subsidizing all producers of renewable energy including those who produce it for their own consumption as they equally contribute to renewable energy expansion in the country. A tariff subsidy is however likely to be met with both political and public resistance if it means that consumers have to cross-subsidize the tariff, while the significant funds required for capital subsidies might not be freely available. Carbon credit prices have yet to mature to the required high levels. Thus, the removal of distortionary support to coal-based electricity generation might be the only currently available alternative of enhancing viability of consumer-based small-scale wind turbines.
The effect of open sun and indoor forced convection on heat transfer coefficients for the drying of papad
Authors: Kumar Mahesh , Khatak Pankaj , Sahdev Ravinder Kumar , Prakash Om
Published: June 2019

In this research paper, a simulation study has been carried out for the determination of convective heat transfer coefficients of papad under open sun drying and indoor forced convection drying modes. Experimental data obtained from open sun and indoor forced convection drying modes for papad were used to determine the values of the constants (C and n) in Nusselt number expression by using linear regression analysis, and consequently convective heat transfer coefficients were evaluated. The average values of convective heat transfer coefficients were found to be 3.54 and 1.56 W/m2 oC under open sun drying and indoor forced convection drying modes respectively. The experimental errors in terms of percent uncertainty were also evaluated.
Outdoor testing of amorphous and crystalline silicon solar panels at Thohoyandou
Authors: Maluta Eric , Sankaran Vaithianathaswami
Published: June 2019

The use of solar panels is becoming one of the options for some of the rural communities in Limpopo Province, South Africa, to get electrical energy for their radio and television sets as the national grid may not reach them in the near future. Hence, dissemination of knowledge of how to use the solar devices and their maintenance is crucial for these communities. This will be possible only if there is appropriate information available for the potential end-users, installers and extension workers. With this in mind, an attempt has been made to evaluate the performance of an amorphous and a crystalline solar panel at our experimental site. Outdoor tests were conducted to measure solar radiation, open-circuit voltage, short circuit current, current-voltage (I-V) curve, fill-factor and conversion efficiency and hence to compare the performance of the two types of panels. It was found that both types give a satisfactory performance for the climate of this region.
Renewable energy, poverty alleviation and developing nations: Evidence from Senegal
Authors: Thiam Djiby Racine
Published: June 2019

The desire to increase energy access remains a strong driving force for poverty alleviation in rural areas of developing countries. The supply of modern energy facilitates the improvement of human living conditions and the productivity of sectors. It also contributes by reducing the time spent, mainly for women and children, in collecting biomass and therefore can provide an opportunity for an increase in the education level of children and for women empowerment. This paper shows how renewable energy facilitates the improvement of the standard of living in a Sahelian developing country of Senegal. Using a life-cycle-cost approach while integrating an assessment of the environmental externalities, I argue that in remote rural areas where grid-connection is non-existent, photovoltaic (PV) renewable technologies provide suitable solutions for delivering energy services although wind technology has been considered as well. In this framework, policies promoting the adoption of clean technologies in developing nations like Sen-egal could be considered as being the main components on the agenda of poverty reduction.
Regression-SARIMA modelling of daily peak electricity demand in South Africa
Authors: Chikobvu Delson , Sigauke Caston
Published: June 2019

In this paper, seasonal autoregressive integrated moving average (SARIMA) and regression with SARIMA errors (regression-SARIMA) models are developed to predict daily peak electricity demand in South Africa using data for the period 1996 to 2009. The performance of the developed models is evaluated by comparing them with Winter’s triple exponential smoothing model. Empirical results from the study show that the SARIMA model produces more accurate short-term forecasts. The regression-SARIMA modelling framework captures important drivers of electricity demand. These results are important to decision makers, load forecasters and systems operators in load flow analysis and scheduling of electricity.
Application of artificial neural networks for short term wind speed forecasting in Mardin, Turkey
Authors: Nogay H. Selcuk , Akinci Tahir Cetin , Eidukeviciute Marija
Published: June 2019

Artificial neural network models were used for short term wind speed forecasting in the Mardin area, located in the Southeast Anatolia region of Turkey. Using data that was obtained from the State Meteorological Service and that encompassed a ten year period, short term wind speed forecasting for the Mardin area was performed. A number of different ANN models were developed in this study. The model with 60 neurons is the most successful model for short term wind speed forecasting. The mean squared error and approximation values for training of this model were 0.378088 and 0.970490, respectively. The ANN models developed in the study have produced satisfactory results. The most successful among those models constitutes a model that can be used by the Mardin Electric Utility Control Centre.
Climate change: The opportunity cost of Medupi and Kusile power stations
Authors: Blignaut James
Published: June 2019

Eskom has embarked on the construction of two coal-fired power stations (Medupi and Kusile) that use a new dry-cooling process with flue gas desulphurisation (FGD). While the introduction of these new technologies does have meaningful environmental benefits beyond the conventional coal-fired power stations, they still emit greenhouse gasses. The question at stake here is what is the opportunity cost, viewed from a climate change perspective, of these two new power stations? This question is answered by considering the carbon footprint of the two power stations and a range of unit values for CO2. From this analysis, it is evident that the most likely range of the opportunity cost is between R6.3 billion and R10.7 billion per year. This converts to a damage cost of between R0.10 and R0.17/kWh when assuming a net combined generation capacity of 8 677 MW and a load factor of 85%.