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Search Results: 1 - 10 of 1340 matches for " Miroslav Grajcar "
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How to test the “quantumness” of a quantum computer?
Alexandre M. Zagoskin,Miroslav Grajcar,Joseph J. Betouras,Franco Nori
Frontiers in Physics , 2014, DOI: 10.3389/fphy.2014.00033
Abstract: Recent devices, using hundreds of superconducting quantum bits, claim to perform quantum computing. However, it is not an easy task to determine and quantify the degree of quantum coherence and control used by these devices. Namely, it is a difficult task to know with certainty whether or not a given device (e.g., the D-Wave One or D-Wave Two) is a quantum computer. Such a verification of quantum computing would be more accessible if we already had some kind of working quantum computer, to be able to compare the outputs of these various computing devices. Moreover, the verification process itself could strongly depend on whether the tested device is a standard (gate-based) or, e.g., an adiabatic quantum computer. Here we do not propose a technical solution to this quantum-computing “verification problem,” but rather outline the problem in a way which would help both specialists and non-experts to see the scale of this difficult task, and indicate some possible paths toward its solution.
Simulating long-distance entanglement in quantum spin chains by superconducting flux qubits
Stefano Zippilli,Miroslav Grajcar,Evgeni Il'ichev,Fabrizio Illuminati
Physics , 2014, DOI: 10.1103/PhysRevA.91.022315
Abstract: We investigate the performance of superconducting flux qubits for the adiabatic quantum simulation of long distance entanglement (LDE), namely a finite ground-state entanglement between the end spins of a quantum spin chain with open boundary conditions. As such, LDE can be considered an elementary precursor of edge modes and topological order. We discuss two possible implementations which simulate open chains with uniform bulk and weak end bonds, either with Ising or with XX nearest-neighbor interactions. In both cases we discuss a suitable protocol for the adiabatic preparation of the ground state in the physical regimes featuring LDE. In the first case the adiabatic manipulation and the Ising interactions are realized using dc currents, while in the second case microwaves fields are used to control the smoothness of the transformation and to realize the effective XX interactions. We demonstrate the adiabatic preparation of the end-to-end entanglement in chains of four qubits with realistic parameters and on a relatively fast time scale.
Segregation Behaviour of Third Generation Advanced High-Strength Mn-Al Steels
A. Grajcar
Archives of Foundry Engineering , 2012,
Abstract: The paper addresses the macro- and microsegregation of alloying elements in the new-developed Mn-Al TRIP steels, which belong to the third generation of advanced high-strength steels (AHSS) used in the automotive industry. The segregation behaviour both in the as-cast state and after hot forging was assessed in the macro scale by OES and by EDS measurements in different structural constituents. The structural investigations were carried out using light and scanning electron microscopy. A special attention was paid to the effect of Nb microaddition on the structure and the segregation of alloying elements. The tendency of Mn and Al to macrosegregation was found. It is difficult to remove in Nb-free steels. Microsegregation of Mn and Al between austenite and ferritic structural constituents can be removed.
Selection of the hot-working conditions for TRIP-type microalloyed steel
A. Grajcar
Archives of Materials Science and Engineering , 2008,
Abstract: Purpose: The aim of the paper is to develop hot-working conditions for a low-carbon Mn-Si-Al TRIP-type steel basing on axial compression tests.Design/methodology/approach: The influence of the austenitizing temperature on a grain size of austenite was determined on a basis of the dissolution kinetics in the austenite of MX-type interstitial phases. The identification of processes controlling the strain hardening was carried out in hot-compression tests. Specimens were deformed up to a true strain of 1.0 in a temperature range of 850 to 1150°C with strain rates of 0.1, 1.0 and 10s-1. The σ-ε curves were useful for developing conditions of multi-stage axial compression. The plastic deformation was realized by the use of the DSI Gleeble 3800 equipment.Findings: It was found that the investigated steel has a fine-grained structure of austenite to a temperature of 1050°C. The obtained -! curves indicate that used plastic deformation conditions influence substantially the εmax strain corresponding to a maximum value of flow stress. It increases with lowering the temperature of plastic deformation. The -! curves obtained during multi-stage compression tests confirmed that under used conditions of temperature and strain a dynamic recovery is a process controlling the strain hardening in a whole strain range.Research limitations/implications: To design in detail hot-rolling conditions, the analysis of the influence of time between successive strains on a fraction of statically recrystallized austenite should be carried out.Practical implications: The obtained -! curves are useful in determining force-energetic parameters of rolling and processes controlling the strain hardening during the hot-rolling.Originality/value: The determined true stress – true strain curves were obtained for the low-carbon TRIP-type steel containing Nb and Ti microadditions.
Hot-working in the γ+α region of TRIP-aided microalloyed steel
A. Grajcar
Archives of Materials Science and Engineering , 2007,
Abstract: Purpose: The aim of the paper is to investigate the influence of hot-working in the γ+α range and isothermal holding temperature in a bainitic range on a stability of retained austenite in a TRIP-aided microalloyed steel.Design/methodology/approach: The thermomechanical processing in the γ+α range to obtain multiphase structures with the retained austenite in a microalloyed steel was realized. It consisted of plastic deformation of specimens at 750°C or 780°C, oil cooling and isothermal holding in a bainitic region. Degree of deformation was 28 or 50%. To reveal the multiphase structure optical and transmission electron microscopy were used. X-ray diffraction method was employed to determine a volume fraction of retained austenite.Findings: It was found that hot-working in the two-phase region influences essentially a multiphase structure of investigated steel. The ferrite fraction is comparable for heat-treated and thermo-mechanically processed specimens but the ferrite grain size is twice smaller in a case of plastically-deformed specimens. The optimum isothermal holding temperature in a bainitic range is 300°C, independent on austenitizing temperature. The specimens forged in the γ+α range and isothermally held at this temperature made it possible to obtain about 10% of retained austenite.Research limitations/implications: Investigations concerning the influence of isothermal holding time in a bainitic range on the stability of retained austenite should be carried out.Practical implications: The established conditions of the thermomechanical processing can be useful in a development of the hot-rolling technology for TRIP-aided microalloyed steels.Originality/value: The realized thermomechanical processing enabled to obtain about 10% fraction of retained austenite in a steel containing 0.5% Si.
Heat treatment and mechanical stability behaviour of medium-carbon TRIP-aided bainitic steel
A. Grajcar
Archives of Materials Science and Engineering , 2008,
Abstract: bainitic transformation on the mechanical stability of retained austenite for medium-carbon TRIP-aided steel.Design/methodology/approach: The examinations were carried out on medium-carbon steel containing 0.55%C and 1.35%Si. The conditions of heat treatment consisted of isothermal quenching of the specimens to a temperature range of 250 to 550°C, where they were held for 600 and 1800 s. Tensile deformation of steel to the given strain equal 0.25, 0.5 and 0.75 of total elongation of samples was conducted in order to determine the kinetics of retained austenite transformation into martensite. The retained fraction of the γ phase was determined by the use of the quantitative X-ray phase analysis.Findings: Increasing the carbon concentration to 0.55% in TRIP-type steels makes possible to obtain very high strength properties without a deterioration of the ductility. The retained austenite of the 19% volume fraction can be obtained after the isothermal quenching of the steel to a temperature of 250°C. In these conditions, the matrix of the steel is the ferritic bainite. The size of regular grains of retained austenite is equal up to 3μm, while the rest of γ phase is present in a form of thin films between individual laths of bainite. Diversification of retained austenite form has a reflection in its mechanical stability, connected with two-stage kinetics of martensitic transformation of γ phase.Research limitations/implications: To determine with more detail the stability of retained austenite the knowledge of lattice parameter changes with an isothermal holding temperature is needed.Practical implications: The proposed heat treatment can be useful for manufacturing reinforced structural elements characterized by high strength and ductile properties in the automobile industry.Originality/value: The developed conditions of the heat treatment concern the medium-carbon TRIP-type bainitic steel, offering higher product of UTS UEl compared with usually investigated TRIP-type ferritic-bainitic steels.
Effect of hot-working in the γ+α range on a retained austenite fraction in TRIP-aided steel
A. Grajcar
Journal of Achievements in Materials and Manufacturing Engineering , 2007,
Abstract: Purpose: The aim of the paper is to determine the influence of thermomechanical processing conditions on an austenite stability in a TRIP-aided microalloyed steel.Design/methodology/approach: The heat treatment and thermomechanical processing in a two-phase region to obtain ferritic – bainitic structures with the retained austenite in a low-carbon microalloyed steel were conducted. The heat treatment consisted of austenitizing of specimens at 750°C, oil cooling, isothermal holding in a temperature range from 300°C to 500°C and slow cooling to room temperature. A part of the specimens was forged with a degree of deformation of 28% before cooling. Optical and transmission electron microscopy were employed for structure observations. The retained austenite amount was determined by X-ray diffraction method.Findings: It was found that hot-working in the γ+α range contributes to a considerable refinement of a ferritic matrix. The grain size of the α phase is about 4 μm and its volume fraction equals from 60 to 68%. The optimum structure containing 10% fraction of retained austenite was obtained for the specimen forged in the two-phase region and isothermally held at a temperature of 300°C.Research limitations/implications: To determine with more detail the relationship between hot-working conditions and the stability of retained austenite investigations in a wider deformation temperature range should be carried out.Practical implications: The proposed thermomechanical treatment route can be useful in a development of the technology for TRIP-aided low-carbon microalloyed steels with a reduced silicon content.Originality/value: The design thermomechanical treatment conditions made for obtaining the 10% fraction of retained austenite in a steel containing 0.5% Si only in comparison to 1.5% Si concentration used in TRIP-aided steels usually.
Morphological features of retained austenite in thermo-mechanically processed C-Mn-Si-Al-Nb-Ti multiphase steel
A. Grajcar
Journal of Achievements in Materials and Manufacturing Engineering , 2010,
Abstract: Purpose: The aim of the paper is to determine the influence of isothermal bainitic transformation temperature on morphological features and a fraction of retained austenite in a new-developed thermo-mechanically processed C-Mn-Si-Al-Nb-Ti multiphase steel.Design/methodology/approach: The thermo-mechanical processing was realized in a multi-stage compression test by the use of the Gleeble thermomechanical simulator. The steel was isothermally held for 600 s in a bainitic transformation temperature range of 250 to 500°C. A fraction and stereological parameters of retained austenite were determined by a computer image analyser using an optical microscope. The details of the retained austenite morphology were revealed in a scanning electron microscope and using EBSD technique.Findings: The maximum fraction of retained austenite (above 14%) was obtained for the temperatures of isothermal bainitic transformation from 400 to 450°C. Below 350°C, the largest grains of retained austenite located in a ferritic matrix transform to martensite and its fraction estimated by the use of computer image analysis is too high compared to X-ray investigations. Blocky, irregular grains located in a ferritic matrix are a main structural constituent of retained austenite in a temperature range up to 350°C. Increasing the isothermal holding temperature to a range of 400-450°C results in increasing a fraction of fine blocky and layer regions of the γ phase.Research limitations/implications: To describe in detail morphological features of retained austenite in fine-grained multiphase structures, a combination of different methods characterized by various resolution is necessary.Practical implications: The revealed morphological features of retained austenite are of great importance for mechanical stability of this phase during cold straining, affecting mechanical properties of advanced TRIP-assisted steels.Originality/value: Combined colour etching, scanning electron microscopy and EBSD (Electron Backscattered Diffraction) methods were applied to characterize retained austenite in a modern group of thermomechanically processed TRIP steels with Nb and Ti microadditions.
Determination of the stability of retained austenite in TRIP-aided bainitic steel
A. Grajcar
Journal of Achievements in Materials and Manufacturing Engineering , 2007,
Abstract: Purpose: The aim of the paper is to determine the influence of the isothermal holding temperature in a bainiticrange of medium-carbon steel on the stability of retained austenite.Design/methodology/approach: The heat treatment of the medium-carbon steel in order to obtain a bainiticstructure with the retained austenite was realized. A range of the holding temperature of the steel underisothermal bainite transformation conditions was from 250 to 550°C. To investigate the structure, optical andtransmission electron microscopy were employed. An amount of the retained austenite was determined usingX-ray diffraction. The mechanical stability of retained austenite was determined by means of the tensile test.Findings: It was found that after the optimum heat treatment the investigated medium-carbon steel has a structureof the ferritic bainite with a 19% fraction of retained austenite. Increasing the isothermal holding temperatureresults in obtaining the lower (350°C) and upper bainite (450°C). The retained austenite occurs as regular grainsor thin foils between bainite laths. The steel is characterized by an excellent strength-ductility balance. A kineticsof the strain-induced martensitic transformation of the retained austenite has a two-stage character.Research limitations/implications: To determine with more detail the stability of retained austenite theknowledge of the austenite carbon content as a function of the isothermal holding is required. Lattice parametermeasurements with X-ray diffraction is planned for this purpose.Practical implications: The established heat treatment conditions can be useful for manufacturing crash-relatedelements in the automobile industry.Originality/value: It should be stressed that the developed conditions of the heat treatment concern themedium-carbon steel, compared with usually investigated low-carbon steels. The kinetics of the strain-inducedtransformation for TRIP-aided bainitic steel was determined, too.
Structural and mechanical behaviour of TRIP-type microalloyed steel in hot-working conditions
A. Grajcar
Journal of Achievements in Materials and Manufacturing Engineering , 2008,
Abstract: Purpose: The aim of the paper is to investigate the influence of various deformation conditions on microstructure evolution and flow curves of TRIP-type steel.Design/methodology/approach: In order to determine the influence of MX-type interstitial phases on limiting the grain growth of primary austenite, samples were quenched in water from a temperature range, from 900 to 1200°C. Determination of processes controlling strain hardening was carried out in compression test using Gleeble 3800 simulator. The σ-ε curves were defined in a temperature range from 850 to 1150°C, for 0.1, 1 and 10s-1 of strain rate. To determine the progress of recrystallization samples were isothermally held for up to 60 s at 900 and 1000°C.Findings: Profitable impact of TiN and NbC particles on austenite grain growth limitation is present up to 1050°C. The values of flow stress are equal from 120 to 270 MPa. The steel is characterized by quite high values of deformation, εmax=0.4-0.65, corresponding to maximum stress on σ-ε curves. Beneficial grain refinement of primary austenite microstructure can be obtained due to static recrystallization. In temperature of 1000°C, t0.5 is equal 35 s and elongates to 43 s after decreasing deformation temperature to 900°C. The σ-ε curves obtained during multi-stage compression tests confirmed that a process controlling the strain hardening is a dynamical recovery.Research limitations/implications: To design hot-rolling conditions, the analysis of the primary austenite microstructure evolution during successive deformation cycles should be carried out.Practical implications: The obtained precipitation kinetics of MX-type phases and σ-ε curves are useful in determining hot-rolling conditions ensuring the fine-grained microstructure of primary austenite.Originality/value: The determined true stress–true strain curves were obtained for the TRIP-type microalloyed steel containing decreased Si concentration.
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