bluuebunny/crossref_metadata_2025_split huggingface dataset:
Galatea trap: magnetohydrodynamic stability of plasma surrounding current-carrying conductors
Authors: Medvedev S Yu , Martynov A A , Kozlov A N , Savelyev V V 
Published: September 2020

Abstract
Ideal magnetohydrodynamic (MHD) properties depending on the plasma pressure are considered for axisymmetric equilibrium magnetoplasma configurations in the Galatea trap with three ring current-carrying conductors embedded in plasma. The study of ideal MHD modes with different toroidal wave numbers takes into account the plasma compressibility with an adiabatic index of 5/3 in the perturbed potential energy functional in the framework of the energy principle. The stability calculations are performed in the presence of a vacuum layer between the plasma and the vacuum chamber. The limiting pressure values corresponding to stable multiply connected plasma configurations without an assumption of nested magnetic surfaces are estimated.
Time and space resolved diagnostics for plasma thermal-chemical instability of fuel oxidation in nanosecond plasma discharges
Authors: Rousso Aric C , Goldberg Benjamin M , Chen Timothy Y , Wu Shuqun , Dogariu Arthur , Miles Richard B , Kolemen Egemen , Ju Yiguang 
Published: September 2020

Abstract
An instability in a nanosecond pulsed dielectric barrier discharge plasma occurring in methane–oxygen–argon mixtures is experimentally observed and measured by 1D time-resolved in situ electric field measurements. This instability, which seems to be created by the positive feedback between plasma kinetics and plasma-assisted low temperature fuel oxidation, is studied using electric field induced second harmonic generation and direct ICCD imaging. The rapid formation of streamers from an originally uniform discharge appears to be caused by the chemical kinetics of plasma-assisted low temperature methane oxidation, which may be resulting in a new type of plasma instability: a thermal-chemical instability. The results also revealed that the occurrence of this possible thermal-chemical instability in a reactive flow drastically changes the plasma properties by forming multiple secondary discharges and possibly leads to micron-sized non-uniform electric distributions. Single shot uncalibrated measurements of the electric field of the micron sized streamers appears to show much greater strengths than the average electric field. Furthermore, one-dimensional data analysis shows the positive feedback loop between the streamers and the low temperature plasma assisted oxidation chemistry in the plasma thermal-chemical instability. The present finding advances the understanding plasma instability growth and provides a new way to control plasma uniformity in plasma-assisted combustion and plasma fuel reforming.
Kinetic Monte Carlo simulations of plasma-chemistry
Authors: Dias Tiago C , Guerra Vasco 
Published: September 2020

Abstract
This work presents a kinetic Monte Carlo algorithm to solve the gas-phase chemistry in low-temperature plasmas, as a first effort to achieve a unified formulation of the electron and heavy-particle kinetics based on Monte Carlo techniques. The implemented algorithm is successfully validated in the thermodynamic limit from the comparison with the traditional deterministic description using rate-balance equations. The accuracy of the Monte Carlo description of the rare species strongly depends on the number of particles used in the simulation. To surpass this limitation, two novel variance reduction techniques that significantly reduce the statistical fluctuations on the concentrations of the minor species are proposed and evaluated. These techniques lead to significant gains in computational time, up to factors of the order of 104 times in the cases studied, while ensuring the same quality of the solution.
Interannual variations of the influences of MJO on winter rainfall in southern China
Authors: Chen Xiong , Li Chongyin , Li Lifeng , Yu Peilong , Yang Minghao 
Published: September 2020

Abstract
The influences of Madden-Julian Oscillation (MJO) on the winter rainfall in southern China exhibit prominent interannual variations. In general, when MJO is active over the Indian Ocean (western Pacific), winter rainfall in southern China increases (decreases) substantially; however, it also decreases (increases) significantly in some winters. The anomalous atmospheric circulation, especially the intraseasonal and low-frequency circulation anomalies, like are responsible for these variations. Both the intraseasonal and low-frequency circulation anomalies are almost opposite between wetter and drier winters MJO is active over the Indian Ocean and the western Pacific, which leads to the different moisture convergences in southern China. As a result, the influences of MJO over the same region on winter rainfall in southern China are different. When MJO is active over the Indian Ocean, the moisture convergence (divergence) in wetter (drier) winters is dominated primarily by the meridional (zonal) moisture convergence (divergence) and advection. When MJO is active over the western Pacific, in both wetter and drier winters, the anomalous moisture divergence is controlled by the meridional moisture divergence and advection. Therefore, it is not only the location and intensity of MJO activity that are important; the anomalous circulation and moisture on different timescales (in particular the intraseasonal and low-frequency timescales) should be considered in the operational weather forecast when using MJO as a predictor.
Propagation of periodic wave trains along the magnetic field in a collision-free plasma
Authors: Abbas G , Kevrekidis P G , Allen J E , Koukouloyannis V , Frantzeskakis D J , Karachalios N 
Published: September 2020

Abstract
In this work, a systematic study, examining the propagation of periodic and solitary waves along the magnetic field in a cold collision-free plasma, is presented. Employing the quasi-neutral approximation and the conservation of momentum flux and energy flux in the frame co-traveling with the wave, the exact analytical solution of the stationary solitary pulse is found analytically in terms of particle densities, parallel and transverse velocities, as well as transverse magnetic fields. Subsequently, this solution is generalized in the form of periodic waveforms represented by cnoidal-type waves. These considerations are fully analytical in the case where the total angular momentum flux L, due to the ion and electron motion together with the contribution due to the Maxwell stresses, vanishes. A graphical representation of all associated fields is also provided.
An Evaluation of Barriers obstructing the Applicability of Standard Bidding Documents (SBDs) in Public Procurement of Iraq
Authors: Hasan Sadeq AbdulHamza , Mohammed Sawsan Rasheed 
Published: September 2020

Abstract
According to Order Number 87 of 2004 which had been issued by Dissolved Coalition Provisional Authority in Iraq, the Ministry of Planning MoP in the Iraqi Government started its efforts toward enhancing and developing the federal level of Public Procurement System by issuing a stream of procedures to the contractual entities (Standard Bidding Documents SBDs, procurement Planning Forms, Performance Indicators, Guide of Archiving Process… etc.). The financial crises which hit the international economy and the noted reduction in crude oil prices and the war against ISIS on the local level reflected an obvious shortage in funding process to the implementation of the project to the very minimums. At 2018 the Iraqi government allocated more funds to compensate the shortage in initial services projects at a time when the SBDs became mandatory to apply by all the public contractual entities, as a result, the local contractors were not able to meet the standard requirements and criteria of a modern experiment in the bidding process which led to more delay by re-announcing these projects. This research is to determine if the Iraqi contractual environment can be considered as healthy and supportive for the SBDs or not? Nine evaluation criteria for the SBDs projects were listed in the questionnaire targeted 100 private sector respondents and 130 public contractual entities, the mean comparison and relative important index RII were used to rank and match respondent agreement on assessing the importance mentioned criteria evaluation. The findings indicated that all respondents had agreed on ranking the average of annual revenues and financial liquidity as the top hurdles that need to be considered by MoP to ensure the success of the SBDs system.
Dynamic Performance of Various Thermal Energy Storage Materials
Authors: Alhamdo M H , Theeb M A , Alani H S 
Published: September 2020

Abstract
The thermal effects of metal partitions inside Porous Thermal Energy Storage (PTES) have been investigated experimentally and theoretically. Four circular cross-sectional area matrices have been studied and comparison was made between them. These include; storage with Flat Plate partitions (FP), storage with Corrugated Plate partitions (CP), storage with Wire Mesh partitions (WM), and storage Without Partitions (WP). A numerical model has been developed to simulate dynamic thermal energy transfer within (PTES) to include the important thermal effects of the partitions within porous matrices. The developed numerical model is characterized by system of differential energy conservation equations, these equations are solved numerically by time marching implicit method. The theoretical analysis and computational scheme validity has been verified through comparisons with measured data from the experimental work conducted in this work. The investigation has been done for Reynolds number, Re, of 1270 <Re < 8050. A convenient agreement was found between theoretical and experimental results for all of the tested matrices. The metal partitions were specified to have considerable effect on the thermal response for each type of the tested materials. From the comparison of different matrices concerning their ratio between pressure drop and heat transfer, it was found that the (CP) matrix has the highest performance. In this work, an improved transient method was presented for the calculation of the average heat transfer coefficient for porous flow channels along the axial direction with the thermal effects of the metal partitions. A correlation equation been developed for the J-factor have for each matrix material at the range of Reynold’s number under investigation. The new (three) correlations predicting the J-factor are found to be in reasonable agreement with the limited published data. However, these correlations have been included the effect of the inside partitions, which have been ignored in all previous published data.
Experimental Researches on Obtaining Sintered Composite Materials with Copper Matrix
Authors: Caliman R 
Published: September 2020

Abstract
Conventional and natural materials, limited in quantity or for which high energy consumption is required, are increasingly being replaced by composite materials, as a very good alternative to the exploitation, energy and environmental problems caused by the production of classic. The relative shape and dimensions of the reinforcing component as well as the structure delimit the composite materials reinforced with particles, the filamentary composite materials and the stratified ones. The general properties of the composite materials are decisively influenced by the nature and properties of the constituents, by the volumetric fraction of the reinforcing component and by its orientation in the composite material, as well, as by the mechanical strength of the matrix - fiber/particle interface. The pieces sintered from metallic powders have special physical and chemical characteristics, determined both by the composition and structure of the existing phases, as well as by the size, shape and distribution of the grains. This paper aims to highlight the particularities of the process of obtaining by sintering a category of composite materials with the copper matrix as well as their characterization with regard to the physical-mechanical properties acquired as a result of sintering. Thus, for the production of parts with advanced compactness, the process of double pressing and double sintering is applied. The first pressing is performed with moderate pressures (3000 daN/cm2) and the sintering, at 800°C, with a bearing of about 30 minutes. The second pressing is performed at high pressures (5000 ÷ 6000 daN/cm2) and is followed by the final sintering, under normal regime. Regarding the sintered metal composite materials, with the role of friction, the most important mechanical property is the hardness. This is a function of the bonding forces between the particles, density and degree of resistance of the material at the test site and can be determined by the Brinell method.
Experimental Researches on the Tribological Behavior of Composite Materials Sintered with Copper Matrix
Authors: Caliman R 
Published: September 2020

Abstract
Particulate materials (fillers) can be used within resistance structures only embedded in a support material called a matrix. Most often, in composite constructions, completely different materials can be combined in such a way that their individual properties reach optimum action. Usually, these are pairs of materials to which one has a bearing function, while the other has the purpose of contributing to taking over the moment of inertia. In this paper, a study is carried out regarding the behavior of abrasive wear of some composite materials with the copper matrix, testing the samples obtained by sintering making for different values of the applied load as well as of the relative sliding speed. Starting from the studied literature, fractions of sintered metallic composite materials were developed and having the copper matrix, which were tested in terms of physical - mechanical and tribological properties. The prepared powders were dosed according to the recipes (Cu 60 ÷ 66.4%, Fe 10%, Sn 7.4%, graphite 3.5 ÷ 25%, SiC 3 ÷ 4%, SiO2 9.7%), and the resulting mixtures have been homogenized in order to achieve homogeneous mixtures that will ensure, finally, a good reproducibility of the physical-mechanical properties for the sintered material. For forming, a cylindrical die having a surface area of 2 cm2 was used. The working pressures varied in the range 5000 ÷ 6000 daN/cm2. The densities obtained for the compressed samples were determined by weighing using the METTLER analytical balance and measured with the micrometer, for volume calculation. The density values for “raw” are in the range 4.47 ÷ 5.01 g/cm3.
Cloud manufacturing - the connection between RAMI 4.0 and IoT
Authors: Ciortea E M 
Published: September 2020

Abstract
The paper presents an empirical analysis regarding the advantages offered by cloud manufacturing, the need to analyze RAMI 4.0 and not least IoT applications. The latter using high performance platforms can lead to the modernization of the automation, tracking and control systems, but they also add to the optimization systems in order to increase the performance. RAMI offers a 3D analysis of the entire manufacturing flow, a system that can be more effectively analyzed, interpreted and can be intervened to grant mandatory maintenance. Cloud manufacturing offers an overview of the entire manufacturing process with all the resources and resources used, as well as an overall analysis regarding any possible interventions needed to optimize the manufacturing system. In order to be able to draw the most relevant conclusions in real time, we simulated such a system with the help offered by Petri nets. We chose the Petri nets because they are easier to interpret, they provide real-time information, modifications can be made relatively easily so that decisions can be made in the shortest time so as not to disturb the manufacturing system. Because cloud manufacturing, the manufacturing system and the IoT platforms have been presented in previous works on the same manufacturing system, in this paper I will review them and focus more on the cloud manufacturing relationship and RAMI 4.0.
“Virtual Pole” method applied at the profiling of the rotary cutter tool for processing of ball screw
Authors: Costin G A , Teodor V G , Oancea N 
Published: September 2020

Abstract

“Virtual pole” method represents a variant of the normals theorem, which can be used for profiling of tools that generate by enwrapping, by the rolling method. This variant of determining the enveloping condition allows to avoid the need to write, in explicit form, the relative movements between the piece and the tool, while remaining scientifically rigorous. In the paper, an application of the „virtual pole” method is presented, for the profiling of the rotary cutter tool designed to process a ball screw type piece. The specific form of the enwrapping condition was compared with a specific form obtained by a classical theorem.
Aerodynamic development of a high-pressure ratio compressor for an advanced microturbine powerplant
Authors: Dumitrescu O , Drăgan V , Gherman B 
Published: September 2020

Abstract
Microturbine engines are increasing in popularity both for small poly-generation power plants and unmanned aerial vehicle; however, their overall efficiency is severely limited by their thermodynamic cycle and component efficiency. This compressor allows the real cycle of the engine to operate with lower specific fuel consumption, extending the rage of the vehicle and lowering pollutant emissions. Optimization methods were implemented in the compressor design, in order to increase the aerodynamic efficiency. A 4.5:1 pressure ratio was selected in order to keep the exhaust jet subsonic. Linear models were used to optimize the speed and gross geometry while the TEIS and later fully viscous 3D models were used successively to optimize the end walls and blade shapes. For all numerical simulations, the Menter SST turbulence model was used. In order to minimize modelling errors, the rotor-stator interface was placed as far as possible downstream of the impeller.
Maintenance of recovery boilers from VLCC shipboard
Authors: Faităr C , Nedelcu A , Buzbuchi N , Stan L , Dumitrache C 
Published: September 2020

Abstract
The integrated maintenance and diagnosis system is intended for the measurement, monitoring, diagnosis, prediction and analysis of the main technical and functional parameters of a mechanical plant for its safe operation. Various software versions are implemented on modern ships that can ensure constant and efficient surveillance of all systems. These integrated systems of maintenance can focus on a category of aggregates and can prevent a great part of the defects that result from the incorrect exploitation of the respective aggregate or the lack of ensuring an efficient maintenance process. Integrated automatic diagnostics systems for onboard installations are the most efficient means of operation used for a wide range of applications. Also, integrated systems for automatic fault diagnosis - ISAFD is intended for measuring, monitoring and analyzing the technical parameters of machines used in the energy, chemical, metallurgical, food, construction or naval.
The influence of fibre orientation and of the adjacent layers on the delamination of laminated composites
Authors: Hudișteanu I , Țăranu N , Isopescu D N , Ungureanu D , Axinte A , Ghiga D A 
Published: September 2020

Abstract
The paper presents a comparative analysis between different configurations of composite laminates with respect to the delamination onset and growth. The results are presented in terms of the total displacement jumps at the crack tip for an initial imposed displacement up to the final delamination. Therefore, the influence of fibre orientation and the suitable selection of the configuration of the composite laminates are discussed. Moreover, the effect of the adjacent layers on the interlaminar damage of composite laminates is analysed. In this context, a significant number of numerical models have been carried out for two different configurations of multi-layered composites, namely [05/+θ/+θ/05] and [05/+θ/-θ/05]. The influence of the orientation of the adjacent layers is investigated, as well as the sign of the fibre orientation angles. The analysed composite laminates are subjected to tensile opening fracture mode, considering a pre-existing initial crack located at the interface between the layers from the middle plane. The variation of the mode I opening displacement with respect to the fibre orientation angle of the adjacent layers is graphically illustrated. The obtained results show similarities in the variation of Poisson’s ratio with respect to the fibre orientation. Therefore, the mismatch of the Poisson’s ratio of the adjacent laminas may involve significant interlaminar stresses which can lead to a delamination failure or an opening fracture mode.
The use of Lean Manufacturing principles to improve production processes by better designing of assembly cells
Authors: Kowalski A , Waszkowski R , Ratushnyi V 
Published: September 2020

Abstract
One of the pillars of Lean Management is continuous improvement of production processes. Thus, while designing new workstations, it is worth taking into account the requirements resulting from this management philosophy. The question remains how to formulate these requirements, at what design stage to use them and how to do it. A very important aspect of work stations’ design is their ergonomics. Considering the ergonomics of a workplace, we should adapt it to the human anatomical and psycho-physical capabilities. The use of takt time to determine the production capacity of the assembly cell makes it easier to organize tooling, working hours and other factors necessary for effective production. After determining the takt time, it is possible to settle the number of assembly stations we need to achieve the required performance in the analysed time horizon. Another important aspect of Lean Manufacturing is enabling continuous flow of materials between successive production processes. Continuous flow at the assembly stage is ensured by the layout of work stations in accordance with the order of technological operations and thoughtful arrangement of production equipment. This will facilitate further acceleration of production orders, elimination of activities that do not add value, and reduction of labour consumption in the assembly process. In accordance with the aforementioned Lean Management recommendations, a conceptual design of an assembly cell for an example product from the electronics industry was developed. In the case of the analysed product, the idea to ensure continuous flow was to build the assembly cell at the stage when the product design was completed and its trial series produced.
The stress analysis of the milling machine structure
Authors: Lysek K , Gwiazda A , Herbuś K 
Published: September 2020

Abstract
The article presents a ways of checking the stress of milling machine construction made of steel profiles. The aim of the article was designation of strength parameters. In order to designate basic parameters like deformation or stress, one of most popular mesh methods was used – finite elements method. In the work, load of the milling machine on the upper and the lower frame was analysed. The models were analyzed due to the quality of the mesh produced, based on the amount of occurrence of a given type of element. For this purpose, the statistics included in the program were used, which allows a scale of 0 to 1 to determine the quality of the element. Despite the use of most of the Tet10 type elements, and the minority of the type We15 and Hex20, the mesh analysis allowed to believe in the accuracy of computational solutions. Process of tension designation went through without errors, and designated properties didn’t get close to yield point for given material. Received deformations are also low therefore they shouldn’t affect the milling machine work precision in required range in any significant way.