bluuebunny/crossref_metadata_2025 huggingface dataset:
Maintenance and Availability Study of a Manufacturing Company: Case Study of a Flour Mill Company
Authors: Edokpia Ralph O. , Oparah P.C.
Published: September 2013

The focus of this study is to carry out a maintenance and availability study of a manufacturing company using a flour mill company as a case study. To properly evaluate the maintenance activities of the company, some sets of performance ratios were used. The performance ratios used in the assessment include; equipment availability, maintenance to production ratio, equipment shutdown intensity, overall equipment effectiveness. The result obtained showed that equipment availability was 93.7%, 93.38%, 93.18%, 92.42%, 91.28%, for year 2006, 2007, 2008, 2009 and 2010 respectively. Maintenance to production ratio was 0.03, 0.04, 0.04, 0.05, and 0.06 for year 2006, 2007, 2008, 2009 and 2010 respectively. Intensity of shutdown ranged from 0.07, 0.7, 0.07, 0.08, and 0.10 for year 2006, 2007, 2008, 2009 and 2010 respectively. Overall equipment effectiveness was 86.30%, 85.10%, 84.92%, 83.33%, 81.40% for year 2006, 2007, 2008, 2009 and 2010 respectively. Comparing the results obtained, revealed the following; the availability of the mill declined with age, from 93.7% in 2006 to 91.28% in 2010. The proportion of time spent on maintenance as against production was on the increase from 0.03 in 2006 to 0.06 in 2010. The intensity of shutdown of the mill increased by the years from 0.07 in 2006 to 0.10 in 2010. The overall equipment effectiveness of the mill was unsatisfactory from the year when optimal replacement was supposed to have been done (year 2009), according to existing standards. OEE was 83.33% in 2009 and 81.40% in 2010. Further study also revealed that an average of 244 million was lost annually due to down time. For optimal availability, the most effective maintenance strategy needs to be adopted and preventive maintenance is recommended.
Effect of Rice Husk Ash Treatment on the Strength Properties of Oil Contaminated Soils
Authors: Ijimdiya Thomas Stephen
Published: September 2013

Oil contaminated soils (PCS) was treated with up to 6% rice husk ash (RHA) by dry weight of soil. Specimens of treated soil compacted at the energy of the standard Proctor (relative compaction = 100%) were subjected to compaction, unconfined compressive strength (UCS) and California bearing ratio (CBR) tests. The results of laboratory tests show that properties of the treated soil improved with RHA treatment. Peak unconfined compressive strength value of 410kN/m2 was obtained at 2% oil/ Applying the conventional evaluation criteria reveals that soil-oil RHA mixture containing 2% oil/4% RHA, 4% oil/4% RHA and 6% oil/4% RHA yields optimum CBR values of 4.6, 4.4 and 3.5% which does not satisfy the minimum required CBR of 15% for use as a subgrade material in road foundation.
Determination of Hydraulic and Hydrological Parameters of Available Streams in Okada Town and its Environs for Viable Source of Water Supply
Authors: Eze Avemaria Matthew , Ezugwu Maryann Ogoamaka , Okorie Tonye G.
Published: September 2013

The study area comprises Okada Town and its environs located in the South Western part of Edo State in Nigeria. The study area is primarily, an agricultural and commercial area with prospects of becoming a big town with attendant water supply problems. The study identified viable sources for sustainable community based water supply with the objectives to determine hydraulic parameters of the existing streams. The method used to measure the stream hydraulic parameters was Current Meter Discharge Method. The mean dry weather widths are: Okada Stream (3.6m and 10.2m at narrow and upstream sections); Iguedo and Okhai Streams (10.6m and 2.8m at typical upstream sections respectively). The corresponding stream stages and discharges are: Okada (0.57m; 100,656m3/day); Iguedo (1.23m; 117,590m3/day) and Okhai (0.21m; 8,294m3/day). From the obtained, and plotted data, the derived stream stage-discharge equations of the form Q = CHn are: Q = 1.543H0.5 for Okada Stream; Q = 1.062H1.2 for Iguedo Stream; and Q = 0.1334H0.21 for Okhai Stream. This study established only 1-year hydrological frequency. A 5-year or 10-year return period is needed for greater risks from probable worst condition scenarios. The recorded maximum combined discharge was 552,441m3/day in September 2011 and minimum flow was 226,540m3/day in January 2012. The reliable yield is estimated at 103,886m3/day and maximum allowable abstraction is 81,455m3/day. The results show that the three source streams will be adequate for sustainable water supply for the study area.
The Hydrometeorology of Niger River Basin
Authors: Okoli Chucks
Published: September 2013

This paper examines the mean annual cycle of rainfall and general circulation features over the Niger River Basin consisting of mainly West Africa and Central Africa regions. Rainfall is examined using a 1400-station archive compiled by earlier workers. Other circulation features are examined using the NCEPNCAR reanalysis dataset. Important features of the reanalysis zonal wind field are shown to compare well with the seasonal evolution described by the radiosonde observations. In addition to the well-known African easterly jet (AEJ) of the Northern Hemisphere, the seasonal evolution of its Southern Hemisphere counterpart is also described. Thermal wind calculations show that although the southern jet is weaker, its existence is also due to a local reversal of the surface temperature gradient. In the upper troposphere, a strong semiannual cycle is shown in the 200-mb easterlies and a feature like the tropical easterly jet (TEJ) is evident south of the equator in January and February. The paper describes the movement of the rainbelt between central and West Africa. An asymmetry in the northward and southward migration of the rainbelt is evident. The paper discusses the influence that the jets may have on rainfall and possible feedback effects of rainfall on the jets. Evidence suggests that the midtropospheric jets influence the development of the rainy season, but also that the rainfall affects the surface temperature gradient and in turn the jets. In the Northern Hemisphere, east of 200E, the axis of the TEJ is located so that it may promote convection by increasing upper-level divergence. However, west of 100E and in the Southern Hemisphere, the location of the TEJ is consistent with the suggestion that it is the equatorward outflow of convection that produces the TEJ. The paper notes that rainfall and river flow is largely influenced by groundwater base flow, and a return to sustained river flow requires replenishment of the aquifers, which is possible only with cumulative raining years. The paper confirms that there is correlation between the decrease in rainfall and low river flows.
Evaluation of Lime Treated Oil Contaminated Soils for Use in Waste Containment Applications
Authors: Ijimdiya Thomas Stephen
Published: September 2013

This paper presents the results of an evaluation of lime treated oil contaminated soil for use in waste containment systems. Soil samples were treated with up 6 % lime contents. Specimens were prepared at optimum moisture content and compacted using British Standard Light (BSL) or Standard Proctor (relative compaction = 100%) to evaluate its effectiveness when used in waste containment applications. The hydraulic conductivity values increased with higher lime contents but were less than 1 x 10-9 m/s required for a liner material.
Geotechnical Properties and Chemical Composition of Black Roof Shale as an Industrial Raw Material
Authors: Eze E.O. , Orie O.U.
Published: September 2013

Cretaceous pyritic roof shale from Onyeama mine in Enugu colliery was studied for the geotechnical and compositional characteristics relevant to its use in civil engineering construction and other industries. Properties investigated included moisture absorption, particle size distribution, plasticity, linear shrinkage, compaction, California bearing ratio (CBR), permeability, consolidation, the pH the sulphate content and chemical composition. The shale had a high fines content of 85%, a liquid limit of 55 %, a good standard Proctor compaction strength of 1690 kg/m3, preconsolidation pressure of 36 kN/m2, pH of 6.1 and sulphate content of 0.37%. The shale-water extract indicated a possibility of sulphate attack on concrete in contact with weathered pyritic shale. Permeability impairment of between 1x10-7cm/s to1x10-8 cm/s was observed on the compacted shale exposed to water and atmosphere. This was attributed to the formation of jarosite and ferric oxide which are the oxidation products of shale weathering. The relatively high silica content of 56% and the low combined potash and sodium content of 1.74% pointed to the potential of the oxidized black shale as a foundation for road bed, as a raw material for brick and a wide range of structural ceramics, and as filler for paints and plastics. The objectionable pyrite in the clay shale can be removed prior to use by treatment with sulphur-and iron-oxidizing bacterium-Thiobacillus ferroxidans or by aging the shale stockpile.
Lawsone Sensitized ZnO Photoelectrodes for Dye Sensitized Solar Cells
Authors: Khadtare Shubhangi S. , Jadkar Sandesh R. , Salunke-Gawali Sunita , Pathan Habib M.
Published: September 2013

Innovations in materials technology in the fields of photovoltaics play an important role in the paradigm shift from fossil fuels to renewable energy sources. The use of solar energy is one of the most important problems in energy utilization. Dye sensitized solar cell (DSSC) technology has been recognized as a competitor to the well developed thin film solar cells. In the present investigation, we have fabricated a device using natural Lawsone (Heena) dye which was used to sensitize zinc oxide (ZnO) films. ZnO seed layer was deposited using chemical bath deposition and slurry was used to deposit ZnO films followed by sintering at 450°C for 30 minutes in air. Performance of nanostructure ZnO photoelectrode using lawsone dye as a function of residence time in the dye solution was studied. For 20 hour dye loading time, we were observed power conversion efficiency around 0.5% which is more as compared to 5 and 14 hours dye loading time.
Structural, Optical and Magnetic Properties of Nanocrystalline Cobalt Doped TiO2 Prepared by Sol-Gel Route
Authors: Siddhapara Kirit S. , Shah D.V.
Published: September 2013

Nanocrystalline Cobalt-doped TiO2was prepared by Sol-Gel technique, followed by freeze-drying treatment at-30°C temperature for 12hrs. The obtained Gel was thermally treated at 200,400,600, 800°C. 1%, 2% and 4% Cobalt doped TiO2nanopowder has been prepared X-ray Powder Diffraction (XRD), Scanning Electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDX), was used to study its structural properties. The XRD pattern shows the coexistence of anatase phase and rutile phase. Thermal gravimetric analysis shows Cobalt concentration affects thermal decomposition. UV-Vis Spectroscopy, Photo luminescence (PL), was used to study its Optical properties. Optical Bandgap were calculated with the incorporation of different concentration of cobalt. UV-Visible spectroscopy show variation in band gap for the sample treated at different temperature for same concentration. All Cobalt doped TiO2nanostructures shows an appearance of Red shift relative to the bulk TiO2. The determination of magnetic properties was also carried out by Vibrating Sample Magnetometer.
Structure of Small Gold Clusters with Si Doping Using DFT (AunSi, n=1-10, 19)
Authors: Priyanka  , Bansal Sumali , Dharamvir Keya
Published: September 2013

The structures of silicon doped gold clusters AunSi (n = 1-10 and 19) have been investigated using first principle calculations based on density functional theory (DFT). Calculations indicate that the stability of a gold cluster increases with the introduction of a Si atom. In all the low lying geometries, Si prefers peripheral positions. For every ground state configuration with n > 3 (n = 6 and 9 being exceptions) Si has tetra-coordination. In almost all of the tetra coordinated geometries the coordination unit including Si, is in the form of a square pyramid with gold atoms forming the square base. Electronic properties such as HOMO-LUMO gap, ionization potential and electron affinity have also been calculated and support the relative stability of clusters with even n. The study of Au20 cage doped with Si atom has been done .Similar to smaller Si doped gold clusters; the Si atom prefers an exohedral position. The doping of Si atom has enhanced the stability and chemical reactivity of Au20 cluster.
Synthesis of TiO2 – Water Nanofluids for its Viscosity and Dispersion Stability Study
Authors: Khedkar Rohit S. , Sonawane Shriram S. , Wasewar Kalais L.
Published: September 2013

In the present research work, an anatase structure titanium dioxide nanoparticle was synthesized by hydrolysis of titanium isopropoxide in the presence and absence of ultrasonication. The resultant product suspension was peptized for getting narrow size distribution. The synthesized nanoparticles are used for preparation of nanofluids with different volume percent loading of nanoparticles in water ranging from 1% to 5%. The characterization of particles was carried out by TEM, XRD. Our result shows that the use of ultrasonic technique has a significant effect on the homogeneity and then size of TiO2nanoparticles. Viscosity of nanofluids was demonstrated with rheometer (TA instruments). Viscosity results confirmed Newtonian behavior of nanofluids and showing increasing trends with addition of nanoparticles in base fluids. The dispersion of nanoparticles in nanofluids is studied with unique method of UV visible spectrophotometer, which confirm good dispersion stability prepared nanofluid of 50 hrs.
Evaluation of Mechanical Properties of Coconut Coir Fiber Reinforced Polymer Matrix Composites
Authors: Naveen P.N.E. , Dharma Raju T.
Published: September 2013

Fiber-reinforced polymer composites have played a dominant role for a longtime in a variety of applications for their high specific strength and modulus. The fiber which serves as a reinforcement in reinforced plastics may be synthetic or natural. Past studies show that only synthetic fibers such as glass, carbon etc., have been used in fiber-reinforced plastics. Although glass and other synthetic fiber-reinforced plastics possess high specific strength, their fields of application are very limited because of their inherent higher cost of production. An attempt has been made to utilize the coir, as natural fiber abundantly available in India. Natural fibers are not only strong and lightweight but also relatively very cheap. The present work describes the development and characterization of a new set of natural fiber based polyester composites consisting of coir as reinforcement and epoxy resin. Coir composites are developed and their mechanical properties are evaluated, at five different volume fractions and tests were carried out and the results were presented. Experimental results showed tensile, static and Dynamic properties of the composites are greatly influenced by increasing the percentage of reinforcement, and indicate coir can be used as potential reinforcing material for many structural and non-structural applications.
Fatigue Behavior of a Nanocomposite under a Fighter Aircraft Spectrum Load Sequence
Authors: Manjunatha C.M. , Bojja Ramesh , Jagannathan N.
Published: September 2013

Two different E-glass fiber reinforced plastic (GFRP) composite laminates having quasi isotropic [(+45/-45/0/90)2]S layup sequence were fabricated viz., GFRP with neat epoxy matrix (GFRP-neat) and GFRP with modified epoxy matrix (GFRP-nano) containing 9 wt. % of CTBN rubber micro-particles and 10 wt.% of silica nanoparticles. Standard fatigue test specimens were machined from the laminates and end-tabbed. Spectrum fatigue tests under a standard fighter aircraft load spectrum, mini-FALSTAFF, were conducted on both the composites at various reference stress levels and the experimental fatigue life expressed as number of blocks to fail, were determined. The stiffness of the specimen was determined from the load-displacement data acquired at regular intervals during the fatigue test. The matrix cracks development in the test specimens with fatigue cycling was determined through optical photographic images. The fatigue life of GFRP-nanocomposite under mini-FALSTAFF load sequence was observed to be enhanced by about four times when compared to that of GFRP-neat composite due to presence of micro-and nanoparticles in the matrix. The stiffness degradation rate and matrix crack density was considerably lower in GFRP-nanocomposite when compared to that of GFRP-neat composite. The underlying mechanisms for improved fatigue performance of GFRP-nanocomposite are discussed.
Investigation of Residual Stresses in Flame Sprayed Ni-Based Wear Resistant Coatings by the Hole-Drilling and X-Ray Methods
Authors: Ryabchikov Alexander , Lille Harri , Reitsnik Renno , Toropov Stanislav , Surženkov Andrei , Kulu Priit
Published: September 2013

The present investigation was carried out in order to determine residual stresses inNi-based self-fluxing alloy based high velocity oxy-fuel (HVOF) coatings with different wearresistant additives. The main components of the alloy were Ni, Cr, Si and B. To increase the wearresistance of self-fluxing NiCrSiB alloy based coatings, different ceramics and hard metals(WC-Co, TiC-NiMo and Cr2C3-Ni) were added. Residual stresses were measured by the holedrillingmethod and the X-ray method. The incremental hole-drilling technique combined with theintegral method was applied. This combined method allows to analyse non-uniform throughthicknessresidual stresses. The results obtained with the incremental hole-drilling method indicatethat through-thickness residual stress distribution is non-uniform. The determined residual stresseswere tensile on the surface of the coating and became compressive toward the interface.The values of the modulus of elasticity and microhardness of the coatings were obtained byinstrumented indentation. The microstructures of the studied coatings were investigated with theSEM technique.
Third Order Elastic Constants and Rayleigh Wave Dispersion of Shot Peened Aero-Engine Materials
Authors: Rjelka Marek , Barth Martin , Reinert Sven , Koehler Bernd , Bamberg Joachim , Baron Hans Uwe , Hessert Roland
Published: September 2013

Aero-engine components exposed to high mechanical stresses are made of high-strength alloys and additionally, they are surface treated by shot peening. This process introduces compressive residual stress into the material making it less sensitive to stress corrosion cracking and fatigue and therefore benefits the components performance and lifetime. Moreover cold work is induced in an amount depending on the peening parameters. To approximate the remaining lifetime, a quantitative, non-destructive method for stress assessment is required. It was shown that surface treatment of such alloys can be characterized by broadband Rayleigh wave dispersion measurements. However, the relative contributions of residual stress and cold work, respectively, remained an open point. This paper presents the determination of third order elastic constants (TOEC) for IN718 and Ti6246, providing, together with a model for the inversion of dispersion data, a quantitative access to the acoustoelastic effect. Finally, some measurements of differently treated samples are given.
Micro Stresses within Cu Bi-Crystal and Al Tri-Crystal after Plastic Deformation Observed by X-Ray and Neutron Diffraction
Authors: Shiro Ayumi , Masayuki Nishida , Muslih M.Refai , Okada Tatsuya , Takao Hanabusa
Published: September 2013

Microscopic residual stresses developed in a copper bi-crystal and in an aluminum tri-crystal after plastic deformation were investigated by X-ray and neutron diffraction. The copper bi-crystal tensile specimen was prepared so as to have a grain boundary along the tensile axis. The aluminum tri-crystal compressive specimen had a triple point and one of the grain boundaries was parallel to the compressive axis. The present study revealed that (1) residual micro-stresses are inhomogeneous within a crystal, (2) average residual stress in each crystal is different from each other, and (3) the direction of principal stress varies from grain to grain. Furthermore, the compatibility of residual stresses existing in both sides of a grain boundary was confirmed in a microscopic scale.
Residual Stress Development in Laser Machined PVD-Coated Carbide Cutting Tools
Authors: Breidenstein Bernd , Gey Christoph , Denkena Berend
Published: September 2013

Abstract. There is growing interest in laser machining as an alternative to abrasive processes for creating cutting tool micro geometries. This technology is also suitable for creating micro geometries on cutting edges of superhard cutting tools. The pulsed nanosecond lasers, which are commonly used for this type of application, induce a high thermal load in the tool. This heat is believed to result in tensile residual stresses at the cutting edge surface, which are generally unfavorable for cutting tool performance because of the tendency to crack formation and propagation. Different levels of compressive residual stress exist after each step (sintering, grinding, shot peening, etching and PVD-coating). From investigations of commercial processes for manufacturing PVD-coated carbide cutting tools it is known that the final residual stress state of the carbide subsurface is a result of superposition of the stress states resulting from the individual process steps. In contrast to that, a laser machining process is expected to produce tensile residual stress due to the heat input. The present work describes the influence of a process chain alteration for PVD-coated carbide cutting tools by a laser machining process on the residual stress state in the finished tools.
Non-Destructive Residual Stress Analysis of Induction Hardened Components by Neutron and X-Ray Diffraction
Authors: Epp Jeremy , Pirling Thilo , Hirsch Thomas
Published: September 2013

In this paper the microstructural and residual-stress analysis of an induction hardened plate of medium carbon steel is described. The stress gradient was determined using laboratory X-ray diffraction (IWT, Bremen, Germany) and neutron strain scanning (ILL, Grenoble, France). Due to slight variations of chemical composition in the depth, matchstick like (cross section 2×2mm²) d0-reference samples were prepared from a similarly treated sample. The d0shift induced by variation of chemical composition was measured by neutron and by X-ray diffraction along the strain free direction (sin²ψ*) and used for the evaluation of the neutron stress calculation. The d0distribution obtained from the neutron measurement did not appear reliable while the method using X-ray diffraction seems to be an efficient and reliable method to determine d0profiles in small samples. The evaluation of neutron measurements was then done using the X-ray diffraction d0distribution. High compressive residual stresses were measured in the hardened layer followed by high tensile residual stresses in the core. A comparison of the neutron measurements with X-ray diffraction (XRD) depth profiles obtained after successive layer removal showed that both methods give similar results. However, these investigations opened the question about the direct comparison of the residual stresses obtained by neutron and XRD. Indeed, a correction of the neutron data regarding the residual stresses in thickness direction might be necessary as these are released in the case of X-ray diffraction measurements after layer removal.
Through-Thickness Stresses in Automotive Sheet Metal after Plane Strain Channel Draw
Authors: Gnäupel-Herold Thomas , Green Daniel E. , Foecke Tim , Iadicola Mark
Published: September 2013

A series of samples from four automotive materials - AKDQ, HSLA50, DP600, and AA6022-T43 - were deformed in a channel draw processes with different levels of draw bead penetration. As a result, varying magnitudes of deformations in plane strain mode and residual stresses were obtained. Through-thickness stress profiles were obtained non-destructively using a novel, high resolution X-ray diffraction technique.
Shaping of Ceramics Using Residual Stresses
Authors: Höpfel Heiko , Pfeiffer Wulf
Published: September 2013

Shot peening is a common procedure used to improve the static and cyclic strength of metal components and for forming of thin walled components. The underlying mechanisms are localized plastic deformation, work hardening and the introduction of compressive stresses into the near-surface region. During the last decade we have been establishing damage-free shot peening processes for brittle materials such as ceramics. Based on these results we are now developing processes for peen-forming of ceramic components. This paper describes the first successful experiments aimed at shaping ceramic specimens using shot peening. Strips of different thicknesses, made of silicon nitride ceramic, were shot-peened using different shot sizes, peening pressures and coverage. The residual stress-depth distributions were determined using X-ray diffraction. Based on the experimentally determined stress states, the curvatures of the strips were calculated analytically and using Finite Element calculations (FEM). The results of the curvature measurements and calculations agree well.
Generation and Determination of Compressive Residual Stresses of Short Penetration Depths
Authors: Weingärtner Regina , Hoffmeister Jürgen , Schulze Volker
Published: September 2013

Generating compressive residual stress states with high gradients and low penetration depths offers high capability regarding increase of fatigue limit of parts. In this work the determination of such specific residual stress distributions by using X-ray diffraction and a little material removal is introduced. Measurements are compared using two interference peaks of different penetration depths, at which confocal microscopy enables high accuracy in determination of the step sizes in electrochemical machining. Furthermore the realisation of these states by two different peening processes using micro blasting media is described. The suitability of the processes micro peening and ultrasonic wet peening as surface treatment methods to improve fatigue limit are shown. Micro peening is based on the shot peening principle with small shots and ultrasonic wet peening on the acceleration of small blasting particles by cavitation. The investigations were conducted at AISI 4140 in a quenched and tempered state. Besides the residual stresses and the integral width of interference peaks as well as the depth distributions, the surface topography was examined. The beneficial effects of these conditions on the fatigue limit in bending tests are described.
Influence of Shot-Peening Parameters on the Sub-Surface Residual Stress Profiles in Al-7075 Alloy Components
Authors: Cecchin Diego , Azanza Ricardo Cristy Leonor , D'Incau Mirco , Bandini Michele , Scardi Paolo
Published: September 2013

Aluminum alloy (Al-7075-T6) samples were analyzed to determine the in-depth residual stress profile induced by a shot-peening treatment. The influence of coverage degree and Almen intensity on the surface residual stress and on the sub-surface residual stress gradient was investigated. Residual stress profiles were obtained using three different techniques: (i) standard laboratory X-ray diffraction (XRD) residual stress analysis with progressive chemical layer-removal; (ii) XRD residual stress analysis with synchrotron radiation using different X-ray energies, thus changing the penetration depths, and (iii) Blind Hole Drilling (BHD). A comprehensive comparison of the results given by the used techniques is shown.
An Experimental Procedure to Determine the Interaction between Applied Loads and Residual Stresses
Authors: Horne Greame , Peel Matthew J. , Hattingh Danie G. , Connolley Thomas , Hart Michael , Kelleher Joe , Zhang Shu Yan , Smith David John
Published: September 2013

This paper presents a novel experiment to quantify both the initial residual stress state in a specimen and its redistribution due to plasticity induced by in-situ loading. The rate of relaxation of the residual stress with respect to permanent deformation is a measure of the elastic follow-up associated with the residual stress field. Residual stress measurements were made using high energy dispersive X-ray diffraction. Digital image correlation, verified by strain gauges, was used to measure full-field deformation on the specimen. The specimen was loaded and unloaded in-situ incrementally to promote plasticity, allowing the relaxation rate of the residual stress to be quantified. An elastic follow-up factor was calculated for the residual stress field, that indicated loading conditions of the residual stress field between fixed-displacement and fixed-load.
Impact of Residual Stresses on the Fatigue Behavior of a Nickel-Based Superalloy
Authors: Morancais Amélie , Fevre Mathieu , Kanoute Pascale , Kruch Serge , François Manuel
Published: September 2013

Aircraft engine components are subjected, voluntarily or not, to the influence of residual stresses (RS). These RS may evolve in service conditions and may have an influence on fatigue life of the component. This paper presents a method to take into account the RS and their relaxation in a finite element calculation to obtain the fatigue life. This method is applied to a representative high-pressure turbine disk specimen made of N18 Nickel-based superalloy. Firstly, residual stresses are measured using X-Ray diffraction technique on the surface and the thickness of specimens. The influence of different surface finishing processes on the intensity and distribution of RS is compared to as-received specimen. Then, using the experimental profile as an initial state, a fatigue life analysis is performed (on fatigue specimen) by applying a multiaxial extension of the Smith-Watson-Topper model. Numerical and experimental results are discussed in detail and it appears that residual compressive stresses have almost no influence for high strain range but they improve the fatigue life for lower ranges.
The nutrition situation of free-living elderly in Umlazi township, South Africa
Authors: Mkhize Xolile , Napier Carin , Oldewage-Theron Wilna
Published: September 2013

The risk for non-communicable diseases such as hypertension, diabetes, stroke and ischaemic heart disease in the elderly continues to be on the increase. It is shaped and modified by factors such as economic status and experiences across the whole lifespan. Although malnutrition in this population could be due to poor dietary practices, the nutrition transition of communities in South Africa is partially responsible for nutritional problems. Because of the degree of dependency on others for help and care in communities, the elderly are at risk for malnutrition. The elderly of the Umlazi community are overburdened with the social responsibility of grandchildren and trying to bring stability by managing various households. This becomes a double burden and puts more strain on their quality of life, further impacting on their nutritional status.Die risiko vir chroniese siektes soos hipertensie, diabetes, beroerte en hartkwaal is steeds baie hoog in die bejaardes in Suid Afrika. Dit word deur faktore soos ekonomiese status en ervarings oor die hele lewesiklus gevorm en verander. Voedings probleme wat geïndentifiseer is in die studie hou verband met dieettekorte, alhoewel probleme met oorvoeding verband kan hou met die voedings oorgang wat plaasvind in Suid Afrikaanse gemeenskappe. In verskeie gemeenskappe, as gevolg van die graad van afhanklikheid van ander vir hulp en sorg, is die bejaardes blootgestel aan die risiko van wanvoeding. Die bejaardes van die Umlazi gemeenskap is oorlaai met die sosiale verantwoordelikheid van kleinkinders en probeer om verskeie huishoudings te stabiliseer, wat ‘n dubbele las op hulle plaas en dit kan hulle lewenskwaliteit affekteer wat dan hul voedingstatus verder kan vererger.
A Lattice Boltzmann Method for the Advection-Diffusion Equation with Neumann Boundary Conditions
Authors: Gebäck Tobias , Heintz Alexei
Published: September 2013

In this paper, we study a lattice Boltzmann method for the advection-diffusion equation with Neumann boundary conditions on general boundaries. A novel mass conservative scheme is introduced for implementing such boundary conditions, and is analyzed both theoretically and numerically.

Second order convergence is predicted by the theoretical analysis, and numerical investigations show that the convergence is at or close to the predicted rate. The numerical investigations include time-dependent problems and a steady-state diffusion problem for computation of effective diffusion coefficients.
Phase Field Models Versus Parametric Front Tracking Methods: Are They Accurate and Computationally Efficient?
Authors: Barrett John W. , Garcke Harald , Nürnberg Robert
Published: September 2013

We critically compare the practicality and accuracy of numerical approximations of phase field models and sharp interface models of solidification. Here we focus on Stefan problems, and their quasi-static variants, with applications to crystal growth. New approaches with a high mesh quality for the parametric approximations of the resulting free boundary problems and new stable discretizations of the anisotropic phase field system are taken into account in a comparison involving benchmark problems based on exact solutions of the free boundary problem.
Estimating neutral nanoparticle steady-state size distribution and growth according to measurements of intermediate air ions
Authors: Tammet H. , Komsaare K. , Hõrrak U.
Published: September 2013

Abstract. Continuous measurements of intermediate air ion size distributions were carried out in the small town Tartu, Estonia, from 1 April 2010 through 7 November 2011. The intermediate ions are charged aerosol particles of diameter 1.5–7.5 nm. In this paper we study what information about neutral nanoparticles of atmospheric aerosols can be drawn from the air ion measurements. Rough estimates of the growth rate and the size distribution of neutral nanoparticles were derived for the subset of measurements while the concentration of the intermediate ions was close to the median and remains in the range of 21 ± 2 cm−3. This criterion excludes the specific new particle formation events characterized with high concentration of intermediate ions and includes only most typical quiet periods between the events when the simultaneous growth, depletion and recharging of particles are described with steady-state equations. We estimated the growth rate of nanoparticles to be about 2 nm h−1 while the growth flux or apparent nucleation rate proved to be about 0.5 cm−3 s−1 at 3 nm and about 0.08 cm−3 s−1 at 7 nm. The results suggest that the process of new particle formation is not interrupted during the quiet periods between events of intensive nucleation of atmospheric aerosols.
The impact of emission and climate change on ozone in the United States under representative concentration pathways (RCPs)
Authors: Gao Y. , Fu J. S. , Drake J. B. , Lamarque J.-F. , Liu Y.
Published: September 2013

Abstract. Dynamical downscaling was applied in this study to link the global climate-chemistry model Community Atmosphere Model (CAM-Chem) with the regional models Weather Research and Forecasting (WRF) Model and Community Multi-scale Air Quality (CMAQ). Two representative concentration pathway (RCP) scenarios (RCP 4.5 and RCP 8.5) were used to evaluate the climate impact on ozone concentrations in the 2050s. From the CAM-Chem global simulation results, ozone concentrations in the lower to mid-troposphere (surface to ~300 hPa), from mid- to high latitudes in the Northern Hemisphere, decreases by the end of the 2050s (2057–2059) in RCP 4.5 compared to present (2001–2004), with the largest decrease of 4–10 ppbv occurring in the summer and the fall; and an increase as high as 10 ppbv in RCP 8.5 resulting from the increased methane emissions. From the regional model CMAQ simulation results, under the RCP 4.5 scenario (2057–2059), in the summer when photochemical reactions are the most active, the large ozone precursor emissions reduction leads to the greatest decrease of downscaled surface ozone concentrations compared to present (2001–2004), ranging from 6 to 10 ppbv. However, a few major cities show ozone increases of 3 to 7 ppbv due to weakened NO titration. Under the RCP 8.5 scenario, in winter, downscaled ozone concentrations increase across nearly the entire continental US in winter, ranging from 3 to 10 ppbv due to increased methane emissions. More intense heat waves are projected to occur by the end of the 2050s in RCP 8.5, leading to a 0.3 ppbv to 2.0 ppbv increase (statistically significant except in the Southeast) of the mean maximum daily 8 h daily average (MDA8) ozone in nine climate regions in the US. Moreover, the upper 95% limit of MDA8 increase reaches 0.4 ppbv to 1.5 ppbv in RCP 4.5 and 0.6 ppbv to 3.2 ppbv in RCP 8.5. The magnitude differences of increase between RCP 4.5 and 8.5 also reflect that the increase of methane emissions may favor or strengthen the effect of heat waves.
Using ocean-glint scattered sunlight as a diagnostic tool for satellite remote sensing of greenhouse gases
Authors: Butz A. , Guerlet S. , Hasekamp O. P. , Kuze A. , Suto H.
Published: September 2013

Abstract. Spectroscopic measurements of sunlight backscattered by the Earth's surface is a technique widely used for remote sensing of atmospheric constituent concentrations from space. Thereby, remote sensing of greenhouse gases poses particularly challenging accuracy requirements for instrumentation and retrieval algorithms which, in general, suffer from various error sources. Here, we investigate a method that helps disentangle sources of error for observations of sunlight backscattered from the glint spot on the ocean surface. The method exploits the backscattering characteristics of the ocean surface, which is bright for glint geometry but dark for off-glint angles. This property allows for identifying a set of clean scenes where light scattering due to particles in the atmosphere is negligible such that uncertain knowledge of the lightpath can be excluded as a source of error. We apply the method to more than 3 yr of ocean-glint measurements by the Thermal And Near infrared Sensor for carbon Observation (TANSO) Fourier Transform Spectrometer (FTS) onboard the Greenhouse Gases Observing Satellite (GOSAT), which aims at measuring carbon dioxide (CO2) and methane (CH4) concentrations. The proposed method is able to clearly monitor recent improvements in the instrument calibration of the oxygen (O2) A-band channel and suggests some residual uncertainty in our knowledge about the instrument. We further assess the consistency of CO2 retrievals from several absorption bands between 6400 cm−1 (1565 nm) and 4800 cm−1 (2100 nm) and find that the absorption bands commonly used for monitoring of CO2 dry air mole fractions from GOSAT allow for consistency better than 1.5 ppm. Usage of other bands reveals significant inconsistency among retrieved CO2 concentrations pointing at inconsistency of spectroscopic parameters.
Retrieval of nitric oxide in the mesosphere and lower thermosphere from SCIAMACHY limb spectra
Authors: Bender S. , Sinnhuber M. , Burrows J. P. , Langowski M. , Funke B. , López-Puertas M.
Published: September 2013

Abstract. We use the ultra-violet (UV) spectra in the range 230–300 nm from the SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) to retrieve the nitric oxide (NO) number densities from atmospheric emissions in the gamma-bands in the mesosphere and lower thermosphere. Using 3-D ray tracing, a 2-D retrieval grid, and regularisation with respect to altitude and latitude, we retrieve a whole semi-orbit simultaneously for the altitude range from 60 to 160 km. We present details of the retrieval algorithm, first results, and initial comparisons to data from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS). Our results agree on average well with MIPAS data and are in line with previously published measurements from other instruments. For the time of available measurements in 2008–2011, we achieve a vertical resolution of 5–10 km in the altitude range 70–140 km and a horizontal resolution of about 9° from 60° S–60° N. With this we have independent measurements of the NO densities in the mesosphere and lower thermosphere with approximately global coverage. This data can be further used to validate climate models or as input for them.
Effects of solar activity and geomagnetic field on noise in CALIOP profiles above the South Atlantic Anomaly
Authors: Noel V. , Chepfer H. , Hoareau C. , Reverdy M. , Cesana G.
Published: September 2013

Abstract. By documenting noise levels in 6.5 yr of nighttime measurements by the spaceborne lidar CALIOP above the South Atlantic Anomaly (SAA), we show they contain information about the evolution of upwelling high-energy radiation levels in the area. We find the amount of noisy profiles is influenced by the 11 yr cycle of solar activity, fluctuates by ±5% between 2006 and 2013, and is anticorrelated with solar activity with a 1 yr lag. The size of the SAA grows as solar activity decreases, and an overall westward shift of the SAA region is detectable. We predict SAA noise levels will increase anew after 2014, and will affect future spaceborne lidar missions most near 2020. In other areas, supposedly unaffected by incoming sunlight, nighttime noise levels are much weaker but follow the same 11 yr cycle, superimposed with a one-year cycle that affects both hemispheres similarly and could be attributed to geomagnetic activity.
The role of microorganisms in the formation of a stalactite in Botovskaya Cave, Siberia – paleoenvironmental implications
Authors: Pacton M. , Breitenbach S. F. M. , Lechleitner F. A. , Vaks A. , Rollion-Bard C. , Gutareva O. S. , Osintcev A. V. , Vasconcelos C.
Published: September 2013

Abstract. Calcitic speleothems in caves can form through abiogenic or biogenic processes, or through a combination of both. Many issues conspire to make the assessment of biogenicity difficult, especially when focusing on old speleothem deposits. This study reports on a multiproxy analysis of a Siberian stalactite, combining high-resolution microscopy, isotope geochemistry and microbially enhanced mineral precipitation laboratory experiments. The contact between growth layers in a stalactite exhibits a biogenic isotopic signature; coupled with morphological evidence, this supports a microbial origin of calcite crystals. SIMS δ13C data suggest that microbially mediated speleothem formation occurred repeatedly at short intervals before abiotic precipitation took over. The studied stalactite also contains iron and manganese oxides that have been mediated by microbial activity through extracellular polymeric substance (EPS)-influenced organomineralization processes. The latter reflect paleoenvironmental changes that occurred more than 500 000 yr ago, possibly related to the presence of a peat bog above the cave at that time. Microbial activity can initiate calcite deposition in the aphotic zone of caves before inorganic precipitation of speleothem carbonates. This study highlights the importance of microbially induced fractionation that can result in large negative δ13C excursions. The microscale biogeochemical processes imply that microbial activity has only negligible effects on the bulk δ13C signature in speleothems, which is more strongly affected by CO2 degassing and the host rock signature.
On the puzzling feature of the silence of precursory electromagnetic emissions
Authors: Eftaxias K. , Potirakis S. M. , Chelidze T.
Published: September 2013

Abstract. It has been suggested that fracture-induced MHz–kHz electromagnetic emissions (EME), which emerge from a few days up to a few hours before the main seismic shock occurrence permit a real-time monitoring of the damage process during the last stages of earthquake preparation, as it happens at the laboratory scale. Despite fairly abundant evidence, electromagnetic (EM) precursors have not been adequately accepted as credible physical phenomena. These negative views are enhanced by the fact that certain "puzzling features" are repetitively observed in candidate fracture-induced pre-seismic EME. More precisely, EM silence in all frequency bands appears before the main seismic shock occurrence, as well as during the aftershock period. Actually, the view that "acceptance of "precursive" EM signals without convincing co-seismic signals should not be expected" seems to be reasonable. In this work we focus on this point. We examine whether the aforementioned features of EM silence are really puzzling ones or, instead, reflect well-documented characteristic features of the fracture process, in terms of universal structural patterns of the fracture process, recent laboratory experiments, numerical and theoretical studies of fracture dynamics, critical phenomena, percolation theory, and micromechanics of granular materials. Our analysis shows that these features should not be considered puzzling.
Numerical investigation of stability of breather-type solutions of the nonlinear Schrödinger equation
Authors: Calini A. , Schober C. M.
Published: September 2013

Abstract. In this article we present the results of a broad numerical investigation on the stability of breather-type solutions of the nonlinear Schrödinger (NLS) equation, specifically the one- and two-mode breathers for an unstable plane wave, which are frequently used to model rogue waves. The numerical experiments involve large ensembles of perturbed initial data for six typical random perturbations. Ensemble estimates of the "closeness", A(t), of the perturbed solution to an element of the respective unperturbed family indicate that the only neutrally stable breathers are the ones of maximal dimension, that is: given an unstable background with N unstable modes, the only neutrally stable breathers are the N-dimensional ones (obtained as a superimposition of N simple breathers via iterated Backlund transformations). Conversely, breathers which are not fully saturated are sensitive to noisy environments and are unstable. Interestingly, A(t) is smallest for the coalesced two-mode breather indicating the coalesced case may be the most robust two-mode breather in a laboratory setting. The numerical simulations confirm and provide a realistic realization of the stability behavior established analytically by the authors.
Global Asymptotic Trajectory Tracking and Point Stabilization of Asymmetric Underactuated Ships with Non-Diagonal Inertia/Damping Matrices
Authors: Bao-Li Ma , Wen-Jing Xie
Published: September 2013

In this work, we investigate the trajectory tracking and point stabilization problems of asymmetric underactuated surface ships with non-diagonal inertia and damping matrices. By combining the novel state and input transformations, the direct Lyapunov approach, and the nonlinear time-varying tools, the trajectory tracking controller is derived, guaranteeing global κ-exponential convergence of state trajectory to the reference one satisfying mild persistent exciting conditions. By properly designing the reference trajectory, the proposed tracking scheme is also generalized to achieve global uniform asymptotic point stabilization. Simulation examples are given to illustrate the effectiveness of the proposed control schemes.
Discovering the Impact of ICT, FDI and Human Capital on GDP: A Cross-sectional Analysis
Authors: Campisi Domenico , De Nicola Arianna , Farhadi Maryam , Mancuso Paolo
Published: September 2013

This paper investigates the impact that human capital, information and communication technology (ICT) and foreign direct investment (FDI) have on GDP. Cross-sectional data from a set of 20 OECD and 24 non-OECD countries in 2007 are analysed employing data envelopment analysis (DEA) and classification and regression tree (CART) techniques. The paper illustrates that the level and quality of access to ICT infrastructures plays an important role in determining a country's level of technical efficiency. The paper also indicates the presence of a catch-up process, led by technological innovation, on the part of emerging countries.