scholarly journals Infrasonic Nanocrystal Formation in Amorphous NiTi Film: Physical Mechanism, Reasons and Conditions

Metals ◽  
2021 ◽  
Vol 11 (9) ◽  
pp. 1390
Author(s):  
Evgeny E. Slyadnikov
Keyword(s):  
Inelastic Deformation ◽  
Physical Mechanism ◽  
Amorphous State ◽  
Thermal Fluctuations ◽  
Critical Value ◽  
Mechanical Action ◽  
Potential Well ◽  
Nanostructured State ◽  
Two Level Systems ◽  
Nanocrystal Formation

The physical mechanism, reasons and conditions of nanocrystal formation in an amorphous NiTi metal film, stimulated by infrasonic action, are formulated. Nanostructural elements of an amorphous medium (relaxation centers) containing disordered nanoregions with two-level systems are considered to be responsible for this process. When exposed to infrasound, a large number of two-level systems are excited, significantly contributing to inelastic deformation and the formation of nanocrystals. The physical mechanism of the nanocrystallization of metallic glass under mechanical action includes both local thermal fluctuations and the additional quantum tunneling of atoms stimulated by shear deformation. A crystalline nanocluster appears as a result of local atomic rearrangement growing increasingly exposed to infrasound. It is possibly unstable in the absence of infrasound. When the radius of the nanocluster reaches a critical value, a potential well appears, in which a conducting electron is localized to form a phason (stable nanocrystal). Estimated values of the phason’s radius and the depth of the nanometer potential well is about 0.5 nm and 1 eV, respectively. It forms a condition of stable phason formation. The occurrence of the instability of the amorphous state and following transformation to the nanostructured state is based on the accumulation of the potential energy of inelastic deformation to a critical value equal to the latent heat of the transformation of the amorphous state into the nanostructured state.

scholarly journals О возможном механизме внешнего инфразвукового механического стимулирования процесса формирования нанокристаллов в аморфной металлической пленке

2021 ◽  
Vol 91 (11) ◽  
pp. 1662
Author(s):  
Е.Е. Слядников ◽  
И.Ю. Турчановский
Keyword(s):  
Quantum Tunneling ◽  
Inelastic Deformation ◽  
Metal Film ◽  
Significant Contribution ◽  
Physical Mechanism ◽  
Thermal Fluctuations ◽  
Mechanical Vibrations ◽  
Physical Reason ◽  
Amorphous Medium ◽  
Two Level Systems

A kinetic model, a physical reason and a condition for stimulated by external infrasonic mechanical vibrations of the formation of nanocrystals in an amorphous metal film. The nanostructural elements of the amorphous medium are responsible for these processes: locally ordered nanoclusters and nanoregions containing free volume, which contain two-level systems. When glass is deformed, two-level systems are excited, due to which they make a significant contribution to inelastic deformation, structural relaxation, formation of nanoclusters and nanocrystals. The physical mechanism of nanocrystallization of metallic glass during mechanical exposure includes, in addition to the mechanism of local thermal fluctuations, also athermal mechanism of quantum tunneling of atoms or atomic groups stimulated by inelastic deformation.

What happens to the vortex structures when the rising bubble transits from zigzag to spiral?

2017 ◽  
Vol 828 ◽  
pp. 353-373 ◽  
Author(s):  
Jie Zhang ◽  
Ming-Jiu Ni
Keyword(s):  
Angular Velocity ◽  
Magnetic Fields ◽  
Physical Mechanism ◽  
Critical Value ◽  
Theoretical Explanation ◽  
Vortex Structures ◽  
Direct Numerical Simulations ◽  
Vortex Pairs ◽  
Spiral Path ◽  
Rising Bubble

It has been demonstrated by many experiments carried out over the last 60 years that in certain liquids a single millimetre-sized bubble will rise within an unstable path, which is sometimes observed to transit from zigzag to spiral. After performing several groups of direct numerical simulations, the present work gives a theoretical explanation to reveal the physical mechanism causing the transition, and the results are presented in two parts. In the first part, in which a freely rising bubble is simulated, equal-strength vortex pairs are observed to shed twice during a period of the pure zigzag path, and this type of motion is triggered by the amounts of streamwise vorticities accumulated on the bubble interface, when a critical value is reached. However, when the balance between the counter-rotating vortices is broken, an angular velocity is induced between the asymmetric vortex pairs, driving the bubble to rise in an opposite spiral path. Therefore, although there is no preference of the spiral direction as observed in experiments, it is actually determined by the sign of the stronger vortex thread. In the second part, external vertical magnetic fields are imposed onto the spirally rising bubble in order to further confirm the relations between the vortex structures and the unstable path patterns. As shown in our previous studies (Zhang & Ni, Phys. Fluids, vol. 26 (10), 2014, 102102), the strength of the double-threaded vortex pairs, as well as the imbalance between them, will be weakened under magnetic fields. Therefore, as the vortex pairs become more symmetric, the rotating radius of the spirally rising bubble is observed to decrease. We try to answer the question, put forward by Shew et al. (2005, Preprint, ENS, Lyon), ‘what caused the bubble to transit from zigzag to spiral naturally?’

scholarly journals EVOLUTION OF PLASMOID-CHAIN IN POYNTING-DOMINATED PLASMA

2014 ◽  
Vol 28 ◽  
pp. 1460170
Author(s):  
MAKOTO TAKAMOTO
Keyword(s):  
Magnetic Reconnection ◽  
Current Sheet ◽  
Physical Mechanism ◽  
Temporal Evolution ◽  
High Energy ◽  
Critical Value ◽  
Numerical Results ◽  
Background Plasma ◽  
Reconnection Rate ◽  
Tearing Instability

We present our recent results of the evolution of the plasmoid-chain in a Poynting dominated plasma. We model the relativistic current sheet with cold background plasma using the relativistic resistive magnetohydrodynamic approximation, and solve its temporal evolution numerically. Numerical results show that the initially induced plasmoid triggers a secondary tearing instability. We find the plasmoid-chain greatly enhances the reconnection rate, which becomes independent of the Lundquist number, when this exceeds a critical value. Since magnetic reconnection is expected to play an important role in various high energy astrophysical phenomena, our results can be used for explaining the physical mechanism of them.

Dunes and alternate bars in tidal channels

2011 ◽  
Vol 670 ◽  
pp. 558-580 ◽  
Author(s):  
PAOLO BLONDEAUX ◽  
GIOVANNA VITTORI
Keyword(s):  
Eddy Viscosity ◽  
Physical Mechanism ◽  
Three Dimensional ◽  
Critical Value ◽  
Algebraic Model ◽  
Suspended Load ◽  
Tidal Channels ◽  
Second Mode ◽  
Alternate Bars ◽  
Quantitative Results

A simple idealized model is proposed to predict the appearance of alternate bottom forms in tidal channels. The model is based on the linear stability analysis of the flat seabed driven by tidal currents. The hydrodynamics is described by means of the full three-dimensional continuity and Reynolds equations. To quantify turbulent stresses, the Boussinesq assumption is introduced and an algebraic model is used for the eddy viscosity. The morphodynamics is described by the Exner equation and a simple sediment transport predictor. When applied to tidal channels, the model predicts the appearance of alternate bottom forms if the channel width is larger than a critical value. This finding agrees with previous analyses. However, the results obtained show the existence of two different modes. Close to the conditions of incipient sediment motion or when the suspended load is intense, the model suggests the appearance of an alternate sequence of shoals and pools (the first mode), characterized by a wavelength which might be comparable with the horizontal excursion of the tide. However, under such circumstances, to provide accurate quantitative results, the model should be extended to include the effects of the local acceleration and of the possible variations of the depth and width of the channel, which are neglected in the analysis. In all the other conditions, the model predicts the appearance of a second mode, presently termed tidal alternate bars. This mode is geometrically similar to the first mode, i.e. it is characterized by depositional and erosional areas which are found in an alternate arrangement, but it has significantly shorter wavelengths. In this case, the wavelength of the bedforms scales with the water depth. The physical mechanism generating tidal alternate bars appears to be the same as that generating tidal dunes, and it cannot be described by means of a depth-averaged approach.

scholarly journals Supercurrents in lead—copper—-lead sandwiches

1969 ◽  
Vol 308 (1495) ◽  
pp. 447-471 ◽  
Keyword(s):  
Magnetic Field ◽  
Critical Current ◽  
Proximity Effect ◽  
Mean Free Path ◽  
Thermal Fluctuations ◽  
Critical Value ◽  
Decay Length ◽  
The Mean ◽  
Copper Lead ◽  
Gennes Theory

The resistance of thin-film lead-copper-lead junctions has been studied with the lead in the superconducting state. The junctions will sustain a supercurrent up to a certain critical value above which a voltage appears, rising smoothly from zero as the current is increased. The effect of a magnetic field upon the critical current has demonstrated that the sandwiches behave phenomenologically as Josephson junctions. The critical current rises rapidly as the temperature is lowered, decreases exponentially with increasing thickness of copper and increases with increase of the mean free path of the copper. A simplified version of the de Gennes theory of the proximity effect has been used to account quantitatively for this behaviour. The experiments show that the coherence length of the paired electrons in the copper increases as the temperature decreases, implying that thermal fluctuations govern the decay of the pairs. From the value of the decay length, the interaction parameter in copper is estimated to lie between +0·06 and +0·14. The properties of these junctions are compared with those of junctions with insulating barriers.

scholarly journals Coherently amplifying photon production from vacuum with a dense cloud of accelerating photodetectors

2021 ◽  
Author(s):  
Hui Wang ◽  
Miles Blencowe
Keyword(s):  
Phase Transition ◽  
Critical Value ◽  
Normal Phase ◽  
Photon Production ◽  
Optically Active ◽  
Microwave Cavity ◽  
Type Model ◽  
Two Level Systems ◽  
System Maps ◽  
Dense Concentration

Abstract We consider N>>1 accelerating (i.e., oscillating) photodetectors modeled as two level systems (TLSs) that are contained within a microwave cavity and show that the resulting photon production from vacuum can be collectively enhanced such as to be measurable. The cavity-accelerating TLSs system maps onto a parametrically driven Dicke-type model and when the detector number N exceeds a certain critical value, the vacuum photon production undergoes a phase transition from a normal phase to an enhanced superradiant-like, inverted lasing phase. Such a model may be realized as a mechanical membrane with a dense concentration of optically active defects undergoing GHz flexural motion and contained within a 3D, superconducting microwave cavity. We show that recent related experimental devices are close to demonstrating this inverted, vacuum photon lasing phase.

RESHAPING-INDUCED CHAOTIC ESCAPE FROM A POTENTIAL WELL

2005 ◽  
Vol 15 (08) ◽  
pp. 2587-2592
Author(s):  
R. CHACÓN ◽  
J. A. MARTÍNEZ
Keyword(s):  
Pulse Shape ◽  
Physical Mechanism ◽  
Numerical Results ◽  
Finite Width ◽  
Potential Well ◽  
External Excitation ◽  
Wide Range ◽  
Melnikov Analysis ◽  
Threshold Amplitude ◽  
Damped Oscillator

The chaotic escape of a damped oscillator excited by a periodic string of symmetric pulses of finite width and amplitude from a cubic potential well that typically models a metastable system close to a fold is investigated. Analytical (Melnikov analysis) and numerical results show that chaotic escapes are typically induced over a wide range of parameters by hump-doubling of an external excitation which is initially formed by a periodic string of single-humped symmetric pulses. The analysis reveals that the threshold amplitude for chaotic escape when altering solely the pulse shape presents a minimum as a single-humped pulse transforms into a double-humped pulse, the remaining parameters being held constant. We discuss a physical mechanism concerning the impulse transmitted by the pulse which explains the aforementioned results.

Role of boundaries in the crystallization of amorphous films

1988 ◽  
Vol 46 ◽  
pp. 626-627
Author(s):  
D. A. Smith
Keyword(s):  
Low Temperature ◽  
Amorphous State ◽  
Nucleation And Growth ◽  
Amorphous Films ◽  
Island Nucleation ◽  
Surface Steps ◽  
Transmission Electron ◽  
Component Systems ◽  
Temperature Deposition

The nucleation and growth processes which lead to the formation of a thin film are particularly amenable to investigation by transmission electron microscopy either in situ or subsequent to deposition. In situ studies have enabled the observation of island nucleation and growth, together with addition of atoms to surface steps. This paper is concerned with post-deposition crystallization of amorphous alloys. It will be argued that the processes occurring during low temperature deposition of one component systems are related but the evidence is mainly indirect. Amorphous films result when the deposition conditions such as low temperature or the presence of impurities (intentional or unintentional) preclude the atomic mobility necessary for crystallization. Representative examples of this behavior are CVD silicon grown below about 670°C, metalloids, such as antimony deposited at room temperature, binary alloys or compounds such as Cu-Ag or Cr O2, respectively. Elemental metals are not stable in the amorphous state.

Structures and crystallization of vacuum-deposited amorphous Se and Sb films

1990 ◽  
Vol 48 (4) ◽  
pp. 140-141
Author(s):  
Makoto Shiojiri ◽  
Toshiyuki Isshiki ◽  
Tetsuya Fudaba ◽  
Yoshihiro Hirota
Keyword(s):  
Monte Carlo ◽  
Electron Microscope ◽  
Monte Carlo Method ◽  
Computer Program ◽  
Radial Distribution ◽  
Film Formation ◽  
Amorphous State ◽  
Two Dimensional ◽  
Amorphous Films ◽  
Binding Condition

In hexagonal Se crystal each atom is covalently bound to two others to form an endless spiral chain, and in Sb crystal each atom to three others to form an extended puckered sheet. Such chains and sheets may be regarded as one- and two- dimensional molecules, respectively. In this paper we investigate the structures in amorphous state of these elements and the crystallization.HRTEM and ED images of vacuum-deposited amorphous Se and Sb films were taken with a JEM-200CX electron microscope (Cs=1.2 mm). The structure models of amorphous films were constructed on a computer by Monte Carlo method. Generated atoms were subsequently deposited on a space of 2 nm×2 nm as they fulfiled the binding condition, to form a film 5 nm thick (Fig. 1a-1c). An improvement on a previous computer program has been made as to realize the actual film formation. Radial distribution fuction (RDF) curves, ED intensities and HRTEM images for the constructed structure models were calculated, and compared with the observed ones.

Microstructure of YBa2Cu3O7-x thin films deposited by dc sputtering

1989 ◽  
Vol 47 ◽  
pp. 172-173
Author(s):  
O. Eibl ◽  
G. Gieres ◽  
H. Behner
Keyword(s):  
Thin Films ◽  
Cross Sections ◽  
Intermediate Layer ◽  
Amorphous State ◽  
Critical Currents ◽  
Dc Sputtering ◽  
State Process ◽  
Diffraction Patterns ◽  
Film Substrate ◽  
Substrate Temperatures

The microstructure of high-Tc YBa2Cu3O7-X thin films deposited by DC-sputtering on SrTiO3 substrates was analysed by TEM. Films were either (i) deposited in the amorphous state at substrate temperatures < 450°C and crystallised by a heat treatment at 900°C (process 1) or (ii) deposited at around 740°C in the crystalline state (process 2). Cross sections were prepared for TEM analyses and are especially useful for studying film substrate interdiffusion (fig.1). Films deposited in process 1 were polycristalline and the grain size was approximately 200 nm. Films were porous and the size of voids was approximately 100 nm. Between the SrTiO3 substrate and the YBa2Cu3Ox film a densly grown crystalline intermediate layer approximately 150 nm thick covered the SrTiO3 substrate. EDX microanalyses showed that the layer consisted of Sr, Ba and Ti, however, did not contain Y and Cu. Crystallites of the layer were carefully tilted in the microscope and diffraction patterns were obtained in five different poles for every crystallite. These patterns were consistent with the phase (Ba1-XSrx)2TiO4. The intermediate layer was most likely formed during the annealing at 900°C. Its formation can be understood as a diffusion of Ba from the amorphously deposited film into the substrate and diffusion of Sr from the substrate into the film. Between the intermediate layer and the surface of the film the film consisted of YBa2Cu3O7-x grains. Films prepared in process 1 had Tc(R=0) close to 90 K, however, critical currents were as low as jc = 104A/cm2 at 77 K.

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