Isochronal Conditions Research Articles

Micro-to-Nanoscale Characterization of Femtosecond Laser Photo-Inscribed Microvoids.

Fiber Bragg gratings are key components for optical fiber sensing applications in harsh environments. This paper investigates the structural and chemical characteristics of femtosecond laser photo-inscribed microvoids. These voids are at the base of type III fs-gratings consisting of a periodic array of microvoids inscribed at the core of an optical fiber. Using high-resolution techniques such as quantitative phase microscopy, electron transmission microscopy, and scattering-type scanning near-field IR optical microscopy, we examined the structure of the microvoids and the densified shells around them. We also investigated the high-temperature behavior of the voids, revealing their evolution in size and shape under step isochronal annealing conditions up to 1250 °C.

Study of the amorphous and crystalline states in Ge(Te1-xSex) thick films (x = 0, 0.50) by in situ temperature-dependent structural analyses

As-deposited and unencapsulated GeTe1-xSex (x = 0, 0.5) 3-μm-thick amorphous films on Si(001) were obtained via the thermal co-evaporation technique. The crystallization and the structure of these phase change materials were examined using in situ temperature-dependent X-ray diffraction (XRD) and grazing-incidence fluorescence X-ray Absorption Near Edge Structure (XANES) in isochronal annealing conditions under nitrogen flow. The results show that the onset temperature of crystallization is highly sensitive to the substitution of the Te atoms by the Se ones and that the rhombohedral structure, with the space group R3m, is the one that crystallized for both samples without Ge or Te rejection. Moreover, the local order around the Ge and Se atoms, probed by Ge and Se K-edge XANES analyses, presents clear modifications from the amorphous state to the crystalline one expecting a Ge four-fold and a Se two-fold coordination in the amorphous state, with an increase of the local disorder with the Se substitution (x = 0.5).

Tracing the slow Arrhenius process deep in the glassy state-quantitative evaluation of the dielectric relaxation of bulk samples and thin polymer films in the temperature domain.

The slow Arrhenius process (SAP) is a dielectric mode connected to thermally activated equilibration mechanisms, allowing for a fast reduction in free energy in liquids and glasses. The SAP, however, is still poorly understood, and so far, this process has mainly been investigated at temperatures above the glass transition. By employing a combination of methods to analyze dielectric measurements under both isochronal and isothermal conditions, we were able to quantitatively reproduce the dielectric response of the SAP of different polymers and to expand the experimental regime over which this process can be observed down to lower temperatures, up to 70K below the glass transition. Employing thin films of thicknesses varying between 10 and 800nm, we further verified that the peak shape and activation energy of the SAP of poly(4-bromostyrene) are not sensitive to temperature, nor do they vary upon confinement at the nanoscale level. These observations confirm the preliminary trends reported for other polymers. We find that one single set of parameters-meaning the activation barrier and the pre-exponential factor, respectively, linked to the enthalpic and entropic components of the process-can describe the dynamics of the SAP in both the supercooled liquid and glassy states, in bulk and thin films. These results are discussed in terms of possible molecular origins of the slow Arrhenius process in polymers.

Thermal stability and crystallisation behavior of newly developed Cu–Zr–Ag–Ti–Ni multicomponent bulk metallic glass

A comprehensive understanding of the thermal stability of multicomponent bulk metallic glasses (MBMGs) is imperative for their possible technological applications. In this study, new MBMGs, Cu39Zr42Ag9Ti10 and Cu32Zr39Ag8Ti9Ni12, were developed employing a multilayer perceptron neural network, intelligently expanding the binary Cu50Zr50 BMG. X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses were used to confirm the amorphous nature of the as-cast alloys. The crystallisation kinetics of the alloys were investigated using differential scanning calorimetry (DSC) under isochronal conditions at different heating rates coupled with microstructural analyses tools. The thermal attributes suggest that glass transition and crystallisation are more sluggish in the case of Cu32Zr39Ag8Ti9Ni12 compared to Cu39Zr42Ag9Ti10. The local activation energies (Eα) and the Avrami exponent (nα) indicate a diffusion-controlled crystallisation mechanism for both alloys. The nucleation rate of the crystalline phase(s) is relatively lower for Cu32Zr39Ag8Ti9Ni12, indicating sluggish crystallisation. Moreover, the rate of change of nα becomes much slower for Cu32Zr39Ag8Ti9Ni12 MBMG during the later stages of crystallisation owing to higher undercooling and, thus, a higher required driving force for the growth of nucleated phases. The free volume of Cu32Zr39Ag8Ti9Ni12 remains smaller at both room and elevated temperatures, pointing towards its better glass forming ability. XRD and TEM analyses of the crystallised alloys suggested progressively increasing precipitation of the topologically disordered Cu10Zr7 phase from Cu42Zr48Ag10 to Cu32Zr39Ag8Ti9Ni12 MBMG, potentially aiding in its increased thermal stability.

Thermomechanical Characterization and Modeling of NiTi Shape Memory Alloy Coil Spring.

Today, shape memory alloys (SMAs) have important applications in several fields of science and engineering. This work reports the thermomechanical behavior of NiTi SMA coil springs. The thermomechanical characterization is approached starting from mechanical loading-unloading tests under different electric current intensities, from 0 to 2.5 A. In addition, the material is studied using dynamic mechanical analysis (DMA), which is used to evaluate the complex elastic modulus E* = E' - iE″, obtaining a viscoelastic response under isochronal conditions. This work further evaluates the damping capacity of NiTi SMA using tan δ, showing a maximum around 70 °C. These results are interpreted under the framework of fractional calculus, using the Fractional Zener Model (FZM). The fractional orders, between 0 and 1, reflect the atomic mobility of the NiTi SMA in the martensite (low-temperature) and austenite (high-temperature) phases. The present work compares the results obtained from using the FZM with a proposed phenomenological model, which requires few parameters for the description of the temperature-dependent storage modulus E'.

Constant-tune cyclotrons

In this paper we demonstrate that cyclotrons can be made to have precisely constant betatron tunes over wide energy ranges. In particular, we show that the horizontal tune can be made constant and does not have to follow the Lorentz factor γ, while still perfectly satisfying the isochronous condition. To make this demonstration we developed a technique based on the calculation of the betatron tunes entirely from the geometry of realistic non-hard-edge closed orbits. We present two particular cyclotron designs, one compact cyclotron and one ring cyclotron. The compact cyclotron design is backed up by a 3-dimensional finite element magnet calculation, that we also present here.

Isochronicity Conditions and Lagrangian Formulations of the Hirota Type Oscillator Equations

Isochronicity Conditions and Lagrangian Formulations of the Hirota Type Oscillator Equations

Crystallization behavior and thermal stability mechanism of plasma sprayed Al2O3-GAP amorphous ceramic coatings

A novel Al2O3-GdAlO3 (GAP) amorphous ceramic coating was in-situ deposited via atmospheric plasma spraying (APS). The crystallization behavior and thermal stability mechanism of Al2O3-GAP coating were studied via differential scanning calorimetry (DSC) under isochronal conditions. The nucleation process of Gd4Al2O9 (GAM) and α-Al2O3 phases were more sensitive than the growth process. On the contrary, the nucleation process of GAP phase was duller than the growth process. The activation energy of Al2O3-GAP coating was higher than those of almost all amorphous materials reported so far. GAM and α-Al2O3 phases had a semblable crystallization mechanism: the initial phase evolution was performed by diffusion-controlled growth with a decreasing nucleation rate. As the crystallization fraction increased, the nucleation rate continued to fall. In addition, it was demonstrated that Al2O3-GAP coating showed long failure time (te10%) of 3.0 × 107 min at 1000 K, which was conducive to the application of the coating under high temperature service conditions.

Crystallization and its kinetics of soft magnetic (Fe1−xNix)79B12P5Si3C1 glassy alloy ribbons

A glassy phase is formed over the whole composition range for melt-spun (Fe1−xNix)79B12P5Si3C1 with x = 0; 0.2; 0.4; 0.5; 0.6 alloy ribbons and these glassy ribbons exhibit good bending plasticity. The Ni-containing glassy alloys show glass transition, followed by a supercooled liquid (SCL) region and then multistage crystallization for the alloys with x = 0.5 and 0.6 (hereafter 0.5Ni and 0.6Ni alloys). The 0.5Ni glassy alloy exhibits the largest SCL region of 43 K and good soft magnetic properties even in as-spun state, i.e., low coercive force of 4.8 A/m, effective permeability of 7400 at 1 kHz and saturation magnetization of 0.80 T. The bending plasticity remains unchanged in the wide annealing temperature range below Tg. The crystallization proceeds in the processes of glassy (G) → bcc(α)Fe(Si) + Fe3B for the 0–0.2 Ni alloys, G → fcc(γ)(Fe,Ni) + Fe3(B,C) + Fe3Ni3(B,C) for the 0.4Ni alloy and G → G’ + γ(Fe,Ni) → γ(Fe,Ni) + Ni5P2 + Fe4P + Fe3Ni3(B,C) for the 0.5Ni and 0.6Ni alloys. Analyses of crystallization reaction in isochronal and isothermal conditions were performed via Kissinger and JMAK models and the activation energy for crystallization is much larger for the 0.5Ni glassy alloy. The appearance of the largest SCL region as well as the highest activation energy for the 0.5Ni alloy is due to the necessity of the simultaneous decomposition to the four crystalline phases. The better magnetic softness for the 0.5Ni alloy is presumably due to the development of medium-range ordered atomic configurations which enable the appearances of the largest SCL region as well as the lower internal stress state. The combination of useful properties for the 0.5Ni glassy alloy is promising for useful soft magnetic materials with mass production ability.

Statistical Approach to Crystal Nucleation in Glass-Forming Liquids.

In this work, methods of description of crystal nucleation by using the statistical approach are analyzed. Findings from classical nucleation theory (CNT) for the average time of formation of the first supercritical nucleus are linked with experimental data on nucleation in glass-forming liquids stemming from repetitive cooling protocols both under isothermal and isochronal conditions. It is shown that statistical methods of lifetime analysis, frequently used in medicine, public health, and social and behavioral sciences, are applicable to crystal nucleation problems in glass-forming liquids and are very useful tools for their exploration. Identifying lifetime with the time to nucleate as a random variable in homogeneous and non-homogeneous Poisson processes, solutions for the nucleation rate under steady-state conditions are presented using the hazard rate and related parameters. This approach supplies us with a more detailed description of nucleation going beyond CNT. In particular, we show that cumulative hazard estimation enables one to derive the plotting positions for visually examining distributional model assumptions. As the crystallization of glass-forming melts can involve more than one type of nucleation processes, linear dependencies of the cumulative hazard function are used to facilitate assignment of lifetimes to each nucleation mechanism.

Neural signatures of temporal regularity and recurring patterns in random tonal sound sequences.

The auditory system is highly sensitive to recurring patterns in the acoustic input - even in otherwise unstructured material, such as white noise or random tonal sequences. Electroencephalography (EEG) research revealed a characteristic negative potential to periodically recurring auditory patterns - a response, which has been interpreted as memory trace-related and specific, rather than as a sign of periodicity-driven entrainment. Here, we aim to disentangle these two possible contributions by investigating the influence of a periodic sound sequence's inherent temporal regularity on event-related potentials. Participants were presented continuous sequences of short tones of random pitch, with some sequences containing a recurring pattern, and asked to indicate whether they heard a repetition. Patterns were either spaced equally across the random sequence (isochronous condition) or with a temporal jitter (jittered condition), which enabled us to differentiate between event-related potentials (and thus processing operations associated with a memory trace for a repeated pattern) and the periodic nature of the repetitions. A negative recurrence-related component could be observed independently of temporal regularity, was pattern-specific, and modulated by across trial repetition of the pattern. Critically, isochronous pattern repetition induced an additional early periodicity-related positive component, which started to build up already before the pattern onset and which was elicited undampedly even when the repeated pattern was occasionally not presented. This positive component likely reflects a sensory driven entrainment process that could be the foundation of a behavioural benefit in detecting temporally regular repetitions.

Effect of cobalt content on non­isothermal crystallization kinetics of Fe­based amorphous alloys

In the present study, FeSiBP and FeCoSiBP ribbons with a fully amorphous structure were made by melt spinning technique. A detailed analysis of the isochronal crystallization behavior is presented in this paper. The influence of cobalt on the crystallization kinetics of the alloys was studied under isochronal conditions using differential scanning calorimetry (DSC). Apparent and local activation energy values were determined by Kissinger, Ozawa and Kissinger-Akahira-Sunose (KAS) methods. The results indicate that appropriate amounts of cobalt can significantly enhance the thermal stability of Fe-based alloys, through an increase in nucleation activation energy from 538kJ/mol to 701kJ/mol, obtained by Kissinger method. Furthermore, with the method proposed by Matusita, it was possible to obtain global values for the Avrami exponent, noting that from a general perspective, Co changes the mechanism from diffusion controlled to interface controlled. This leads to the conclusion that the crystallization process is complex and takes place in more than one stage. Therefore, the determination of nucleation mechanisms and dimensional growth is difficult due to the inapplicability of the Johnson-Melh-Avrami (JMA) model. As such, a study under isothermal conditions is suggested, in order to achieve a full understanding of the mechanisms involved.

Untypical changes of electrical resistivity and viscosity of the La60Ni10Al25Cu5 metallic glass during crystallization

Clarifying the crystallization behaviors of metallic glasses can not only provide useful information to understand the origin of high thermal stability and good glass-forming ability but also help to tailor the properties of composite materials. The untypical changes of both electrical resistivity and viscosity in the La60Ni10Al25Cu5 metallic glass during crystallization were studied. Electrical resistivity possesses a rise before the normal declining stage under both continuous heating and isothermal annealing. Meanwhile, the viscosity firstly remains almost constant, then changes with applied stresses under isochronal condition. Increase in viscosity proceeds in two stages when annealing at 488 K while that still shows stress-depended behavior at 510 K. DSC and TEM analysis suggest the much slower grain-growth crystallization kinetics which contributes to the untypical changes of this amorphous alloy. The results indicate that glass-forming systems with similar phenomenon still have good processing ability to fabricate composite materials with versatile geometries even after crystallization.

A note on the paper “Center and isochronous center conditions for switching systems associated with elementary singular points”

In this note, we correct an error in our paper published in Communications in Nonlinear Science and Numerical Simulation in 2015 [5], in which the form of a Z2-equivariant cubic planar switching system is not correct. In this note, we add one more switching line and use the same equations given in [5] to construct a correct Z2-equivariant cubic system. Then, we prove that the new system can exhibit 15 limit cycles and therefore the conclusion given in [5] still holds.

Enhancement of the Physical Stability of Amorphous Sildenafil in a Binary Mixture, with either a Plasticizing or Antiplasticizing Compound.

The main purpose of this paper was to evaluate the impact of both high- and low-Tg polymer additives on the physical stability of an amorphous drug, sildenafil (SIL). The molecular mobility of neat amorphous SIL was strongly affected by the polymeric excipients used (Kollidon VA64 (KVA) and poly(vinylacetate) (PVAc)). The addition of KVA slowed down the molecular dynamics of amorphous SIL (antiplasticizing effect), however, the addition of PVAc accelerated the molecular motions of the neat drug (plasticizing effect). Therefore, in order to properly assess the effect of the polymer on the physical stability of SIL, the amorphous samples at both: isothermal (at constant temperature—353 K) and isochronal (at constant relaxation time—τα = 1.5 ms) conditions were compared. Our studies showed that KVA suppressed the recrystallization of amorphous SIL more efficiently than PVAc. KVA improved the physical stability of the amorphous drug, regardless of the chosen concentration. On the other hand, in the case of PVAc, a low polymer content (i.e., 25 wt.%) destabilized amorphous SIL, when stored at 353 K. Nevertheless, at high concentrations of this excipient (i.e., 75 wt.%), its effect on the amorphous pharmaceutical seemed to be the opposite. Therefore, above a certain concentration, the PVAc presence no longer accelerates the SIL recrystallization process, but inhibits it.

Non-Isothermal Crystallization Kinetics of a Rapidly Solidified as-Cast TiZrHfNiCu High Entropy Bulk Metallic Glass

This paper aims to investigate the thermal behavior and crystallization kinetics of TiZrHfNiCu high entropy bulk metallic glass (HE-BMG) alloy using the standard procedure of Differential Scanning Calorimetric (DSC) annealing technique. The alloy was produced using an arc melting machine with a critical diameter of 1.5 mm. The crystallization kinetics and phase transformation mechanism of TiZrHfNiCu HE-BMG was investigated under the isochronal condition at a single heating run based on the Johnson-Mehl- Avrami (JMA) theory. In isochronal heating, the apparent activation energy for glass transition and crystallization events was analyzed by Kissinger and Ozawa methods. The average activation energy value for crystallization of TiZrHfNiCu amorphous alloys in isochronal modes was 226.41 kJ/mol for the first crystallization and 297.72 kJ/mol for second crystallization stages. The crystallization mechanism of the first step was dominated by two- and three-dimensional growth with increasing nucleation rate, while the crystallization mechanism in the second stage was dominated by two-dimensional crystallization growth with a constant nucleation rate. The diffusion mechanism result proved the theory of sluggish atomic diffusion of HEA at elevated temperature.

Effects of supraspinal feedback on human gait: rhythmic auditory distortion

BackgroundDifferent types of sound cues have been used to adapt the human gait rhythm. We investigated whether young healthy volunteers followed subliminal metronome rhythm changes during gait.MethodsTwenty-two healthy adults walked at constant speed on a treadmill following a metronome sound cue (period 566 msec). The metronome rhythm was then either increased or decreased, without informing the subjects, at 1 msec increments or decrements to reach, respectively, a low (596 msec) or a high frequency (536 msec) plateaus. After 30 steps at one of these isochronous conditions, the rhythm returned to the original period with decrements or increments of 1 msec. Motion data were recorded with an optical measurement system to determine footfall. The relative phase between sound cue (stimulus) and foot contact (response) were compared.ResultsGait was entrained to the rhythmic auditory stimulus and subjects subconsciously adapted the step time and length to maintain treadmill speed, while following the rhythm changes. In most cases there was a lead error: the foot contact occurred before the sound cue. The mean error or the absolute mean relative phase increased during the isochronous high (536 msec) or low frequencies (596 msec).ConclusionThese results showed that the gait period is strongly “entrained” with the first metronome rhythm while subjects still followed metronome changes with larger error. This suggests two processes: one slow-adapting, supraspinal oscillator with persistence that predicts the foot contact to occur ahead of the stimulus, and a second fast process linked to sensory inputs that adapts to the mismatch between peripheral sensory input (foot contact) and supraspinal sensory input (auditory rhythm).

Bifurcation analysis on a class of three-dimensional quadratic systems with twelve limit cycles

This paper concerns bifurcation of limit cycles in a class of 3-dimensional quadratic systems with a special type of symmetry. Normal form theory is applied to prove that at least 12 limit cycles exist with 6–6 distribution in the vicinity of two singular points, yielding a new lower bound on the number of limit cycles in 3-dimensional quadratic systems. A set of center conditions and isochronous center conditions are obtained for such systems. Moreover, some simulations are performed to support the theoretical results.

Improving the resolving power of Isochronous Mass Spectrometry by employing an in-ring mechanical slit

Isochronous Mass Spectrometry (IMS) in heavy-ion storage rings is an excellent experimental method for precision mass measurements of exotic nuclei. In the IMS, the storage ring is tuned in a special isochronous ion-optical mode. Thus, the mass-over-charge ratios of the stored ions are directly reflected by their respective revolution times in first order. However, the inevitable momentum spread of secondary ions increases the peak widths in the measured spectra and consequently limits the achieved mass precision. In order to achieve a higher mass resolving power, the ring aperture was reduced to 60 mm by applying a mechanical slit system at the dispersive straight section. The momentum acceptance was reduced as well as better isochronous conditions were achieved. The results showed a significant improvement of the mass resolving power reaching 5.2×105, though at the cost of about 40% ion loss.

Elastic Energy Fraction as the Phenomenological Connection Between Electrical, Mechanical and Thermal Properties of the Al–(Nb, Mo, Ta, W) Amorphous Thin Films

Some of mechanical, electrical, and thermal properties of the Al–(Nb, Mo, Ta, W) binary thin films which are important for the stability and usability of the amorphous alloys were examined. Samples were prepared by magnetron deposition technique in wide range of composition onto various substrates held at room temperature. Different experimental techniques were used for the characterization of samples. The results of structural relaxation and crystallization measurements under isochronal conditions are compared with the results of measurements of micro/nano hardness and strain in the films. From the micro/nano hardness measurement, the elastic deformation energy fraction is calculated. The elastic deformation energy fraction is correlated with the various results obtained from electrical resistivity measurements under isochronal conditions. Particular emphasis was placed on the Al–Mo amorphous alloys. It turns out that elastic deformation energy fraction becomes important indicator and phenomenological correlation parameter between various physical properties of examined films.