Papers by Gabriel Dumitru
<title>Calibration procedures for a 10.6-μm laser calorimeter</title>
ROMOPTO '97: Fifth Conference on Optics, 1998
ABSTRACT
The article intends to provide a picture of hydrogen economy potential in Romania, in the Europea... more The article intends to provide a picture of hydrogen economy potential in Romania, in the European context. Also, were identified and analyzed some scenarios with opportunities and possibilities for implementing this technology. The working assumptions taken into consideration the hydrogen production from renewable energy surplus and coverage a part of Romania's natural gas needs. For each situation was calculated hydrogen production cost according with investment and operating costs. The last scenario depicts a possible infrastructure for hydrogen distribution and storage integrated with both European markets and national electricity and natural gas networks.
This paper reports the results of measurements performed on a digital thermohygrometer by several... more This paper reports the results of measurements performed on a digital thermohygrometer by several metrology laboratories throughout Romania. The comparison began in 2013 and concluded in 2014. Temperature Laboratory of National Institute of Metrology (INM) acted as pilot laboratory (PL) and reference laboratory (RL) for the programme. The measurements were conducted at temperature integer values in the range of (10…30)º C. The results obtained in this comparison by participating laboratories are used to validate and transmitting traceability measurement according to quality management system.
The characterization of the metallic layers deposited through thermal spraying can be done with d... more The characterization of the metallic layers deposited through thermal spraying can be done with different destructive and nondestructive techniques. In this article the authors describe ultrasound immersion. The purpose of the paper is to characterize the quality of thermal spray deposited layer adhesion to the base material. The parameters of the technological process of deposition through thermal metal spraying which have been taken into consideration to establish the quality of adhesion are deposited material granulation, deposition pressure, nozzle diameter of the torch used for deposition, spraying distance, and deposition angle. A series of tests to determine the influence of changes of certain parameters of technological process deposition thermal metal spraying on the quality of adhesion were performed.
Fiabilitate şi Durabilitate, 2017
Studies of groundwater consist in data acquisition, their processing and interpretation. In areas... more Studies of groundwater consist in data acquisition, their processing and interpretation. In areas of interest hydrogeological is assumed that there is a network of wells drilled. This network provides a first in the hydrogeological information. Electromagnetic (EM) mapping through the use of such areas, using data obtained from existing network of wells drilled, calibration and confirmation. Measurements using the EM can highlight the existence of several layers with different characteristics: clay, limestone, sand, etc. Studies of groundwater interpretation are used for developing a regional hydrogeologic model. The application of electromagnetic techniques for measuring soil resistivity or conductivity has been known for a long time. Conductivity is preferable in inductive techniques, as instrumentation readings are generally directly proportional to conductivity and inversely proportional to resistivity. The operating principle of this method is: a Tx coil transmitter, supplied with alternating current at an audio frequency, is placed on the ground. An Rx coil receiver is located at a short distance, s, away from the Tx coil. The magnetic field varies in time and the Tx coil induces very small currents in the ground. These currents generate a secondary magnetic field, Hs, which is sensed by the Rx receiver coil, together, with primary magnetic field Hp. The ratio of the secondary field, Hs, to the primary magnetic field, Hp, (Hs/Hp) is directly proportional to terrain conductivity. Measuring this ratio, it is possible to construct a device which measures the terrain conductivity by contactless, direct-reading electromagnetic technique (linear meter). This technique for measuring conductivity by electromagnetic induction, using Very Low Frequency (VLF), is a non-intrusive, non-destructive sampling method. The measurements can be done quickly and are not expensive. The Electromagnetic induction technology was originally developed for the mining industry, and has been used in mineral, oil, and gas exploration, and archaeology. In these applications, differences in conductivity of subsurface layers of rock or soil may indicate stratified layers or voids that could be of interest.
This paper presents the analysis of the layers deposed by thermal spraying in order to identify t... more This paper presents the analysis of the layers deposed by thermal spraying in order to identify the optimum material and thermal process used for crankshafts reconditioning. In the context of evaluating the layers’ properties, the aim of the experiment is to obtain a good wear resistance. One sample was made by S235 steel coated with 100 C6 (Rul1) powder and intermediate layer of Mo, for the second sample being used a non-alloyed quality steel DC01 covered with Stellite and subjected to a re-melting treatment in plasma jet. The results show that the stellite coat presents a significant wear resistance compared to Rul1through high hardness and decreased porosity resulting by plasma jet re-melting treatment.
The purpose of this paper is to determine the quality of the interface between the ceramic layers... more The purpose of this paper is to determine the quality of the interface between the ceramic layers and the base material for the parts that are reconditioned through thermal spraying process. In the first phase, the flaws that may occur between the parent material and the material for coating will be highlighted by a nondestructive testing method using eddy currents, and in the second phase the behavior of the given specimens to thermal shock will be analyzed using finite element method. Two types of finite elements models which correspond to the two types of specimens tested on the experimental stand were created. The analyzed specimens were coated with a ceramic material of Yttria-Stabilized Zirconium. The obtained results allow the selection and evaluation of the technological reconditioning process.
To put into practice the conventional determination of resistivity by the galvanic method, requir... more To put into practice the conventional determination of resistivity by the galvanic method, requires a relatively large amount of labor and is, therefore, expensive. At the basis of any interpretation are the lateral or vertical variations of re sistivity. The high cost of resistivity maps execution generally means that fewer measurements are made than desirable, with the result that, either (i) the explored area is not large enough to establish a reasonable background, against which the anomaly areas are to be delineated, or (ii) the anomaly areas are obscure and lack definition. The application of electromagnetic techniques (EM) for measuring soil resistivity or conductivity has been known for a long time. Conductivity is preferable in inductive techniques, as instrumentation readings are generally directly proportional to conductivity and inversely proportional to resistivity. The operating principle of this method is: a Tx coil transmitter, supplied with alternating current at an...
For the producers of large and medium casted parts the defects management and defects volume redu... more For the producers of large and medium casted parts the defects management and defects volume reduction has proven to be a very important concern, regarding the cost reduction in the manufacturing process and therefore the margin increase in a stable market with long term profits. Given the tendencies for raw materials and energy on the global market this can be seen also as a survival need of the business unit. Modern approaches like the Six Sigma tools are used to diagnose and improve the casting process for large parts. The main tool considered is DMAIC, which guide the project through the steps of improvement, from problem pinpointing to the implementation of result/solutions into the management system of the business unit.
<title>Femtosecond ablation applied to deep-drilling of hard metals</title>
High-Power Laser Ablation V, 2004
Mechanisms responsible for the limitation of the aspect ratio obtained by deep drilling of hard m... more Mechanisms responsible for the limitation of the aspect ratio obtained by deep drilling of hard metals are investigated in the present work. Cemented carbide targets have been irradiated with laser pulses of 100 fs duration and 100 muJ maximum energy delivered by a Ti:sapphire laser system. The experiments are carried out in different gas environments (vacuum, air, helium up to atmospheric pressure) with incident laser fluences ranging from 1 to 20 Jcm-2. During deep drilling, the laser-induced ablation plume is characterized by means of in-situ plasma diagnostics. Fast imaging is used to observe the expansion behavior of the plasma plume whereas time- and space-resolved emission spectroscopy is employed to analyze the plasma composition. After irradiation, the laser-produced craters were examined by optical microscopy. A correlation between the ablation plume characteristics and the morphological changes of the mciro-holes is established. The results indicate that nanoclusters, that present a significant part of the ablated material, are responsbile for the alteration of the crater shape in the high laser fluence regime.
Laser microstructuring of surfaces for improving their tribological performance
Proceedings of SPIE - The International Society for Optical Engineering, 2001
12 The controlled laser microstructuring of solid surfaces improves their wear properties: microh... more 12 The controlled laser microstructuring of solid surfaces improves their wear properties: microholes induced on a friction surface can act like lubricant reservoirs and as traps for debris particles. In generating such microstructures, the laser has the advantage of its great versatility, since it can be used in various environments and it can be adapted to a wide range of
Laser surface microstructuring to improve tribological systems
Proceedings of SPIE - The International Society for Optical Engineering, 2002
The controlled laser patterning of solid surfaces improves their wear properties: laser generated... more The controlled laser patterning of solid surfaces improves their wear properties: laser generated microcraters of defined dimensions and morphology can act as lubricant reservoirs and as traps for wear particles. For generating such microstructures different ...
Structure changes in steels and hard metal induced by nanosecond and femtosecond laser processing
Proceedings of SPIE - The International Society for Optical Engineering, 2003
Investigations on the occurrence of structure and hardness changes (for two sorts of steel and fo... more Investigations on the occurrence of structure and hardness changes (for two sorts of steel and for a hard metal substrate) in the immediate vicinity of laser induced craters are presented in this work. Experiments with femtosecond pulses were performed in air with a Ti:sapphire laser (800 nm, 100 fs) at mean fluences of 2, 5 and 10 J/cm2. Series of
Femtosecond laser ablation of materials
Proceedings of SPIE - The International Society for Optical Engineering, 2003
Polycrystalline SiGe is attracting more and more attention in micro and optoelectronics devices b... more Polycrystalline SiGe is attracting more and more attention in micro and optoelectronics devices both at industrial and university level. Research on both devices and material growth techniques continues at a very rapid pace in the scientific world. Low cost production techniques, capable to produce such alloys with uniform and controlled grain size, becomes of particular attention. Excimer laser crystallization has
Applied Surface Science, 2004
Diamond-like carbon (DLC) coatings were deposited on Si substrates using a hot filament diode dis... more Diamond-like carbon (DLC) coatings were deposited on Si substrates using a hot filament diode discharge and they were irradiated with ultrashort laser pulses (800 nm, 150 fs, <4 J/cm 2). The laser-treated films were examined using optical microscopy, Raman spectroscopy, SEM, AFM and white-light interferometery. Damage threshold of 0.16 J/cm 2 and ablation rates below 110 nm/pulse were determined. Changes in the structure of the laser-irradiated films were showed by means of Raman investigations. The laser-treated samples were etched and the depths of modified material layers were determined. Ablation experiments with longer laser pulses (1064 nm, 100 ns, <3 J/cm 2) were also performed and the irradiated DLC films were afterwards analyzed using the same procedures. Dissimilarities in the structure changes induced by fs-and ns-laser irradiation were observed and comments are given.
Rezumat. În scopul identificării surselor de risc, managerul de proiect va trebui să definească t... more Rezumat. În scopul identificării surselor de risc, managerul de proiect va trebui să definească tipul de proiect ce face obiectul analizei care poate să-i ofere variante și mai ales surse de analiză a factorilor specifici de risc. Pentru proiecte, pentru obiective industriale, sisteme tehnice/tehnologice analiza de identificare a surselor de risc, evaluarea și monitorizarea în vederea reducerii și/sau neutralizarea riscurilor, se vor avea în vedere cel puțin următoarele: factorii de risc intrinseci sistemelor tehnice/tehnologice, factori de risc externi și/sau de natura conjuncturală, factori de risc asociați erorilor umane, organigrama conținutului minimal al analizei de risc în fazele de proiectare, execuție, montaj și funcționare a sistemelor tehnice/tehnologice. Abstract. In order to identify sources of risk, the project manager will have to define the type of project which is the subject analysis which can offer options and especially sources of analysis of the specific risk fa...
<title>Computation algorithms for laser beam visualization</title>
ICONO '98: Quantum Optics, Interference Phenomena in Atomic Systems, and High-Precision Measurements, 1999
wseas.us
GHEORGHE AMZA, ZOIA APOSTOLESCU, GABRIEL MARIUS DUMITRU Faculty of Engineering and Technological ... more GHEORGHE AMZA, ZOIA APOSTOLESCU, GABRIEL MARIUS DUMITRU Faculty of Engineering and Technological Systems Management, University POLITEHNICA of Bucharest, Spl.IndependenŃei nr.313, sector 6, Bucharest, ROMANIA, amza@camis.pub.ro VALENTIN PETRESCU ...
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Papers by Gabriel Dumitru