Instability Domain Research Articles

Cellular transport through nonlinear mechanical waves in fibrous and absorbing biological tissues

The present paper investigates the spatiotemporal evolution of a population of mesenchymal cells during invasion. In that end, a mathematical model accounting for haptotaxis, chemotaxis, zero-proliferation, viscous, and traction forces is considered. Injecting plane wave ansatz in the model reveals viscoelastic properties of the medium, as well as the existence of parameters regions where expansive and compressive waves may be found. The model reduction leads to a cubic complex Ginzburg-Landau equation. Stability line versus envelope wave vector is plotted to prove that instability domains may be controlled by increasing traction or by reducing substrate attachment. Analytical solutions constructed reveal that the number of particles carried increases with increasing values of substrate attachment or by reduction of traction forces. Our solutions keep their positivity, and do not deviate from their numerical counterparts. Our investigations summarize the fact that mechanical behaviors coupled with biochemical processes of cells are at great interplay during the invasion in biological tissues.

Compressive response and microstructural evolution of in-situ TiB2 particle-reinforced 7075 aluminum matrix composite

The hot forming behavior, failure mechanism, and microstructure evolution of in-situ TiB2 particle-reinforced 7075 aluminum matrix composite were investigated by isothermal compression test under different deformation conditions of deformation temperatures of 300–450 °C and strain rates of 0.001-1 s−1. The results demonstrate that the failure behavior of the composite exhibits both particle fracture and interface debonding at low temperature and high strain rate, and dimple rupture of the matrix at high temperature and low strain rate. Full dynamic recrystallization, which improves the composite formability, occurs under conditions of high temperature (450 °C) and low strain rate (0.001 s−1); the grain size of the matrix after hot compression was significantly smaller than that of traditional 7075Al and ex-situ particle reinforced 7075Al matrix composite. Based on the flow stress curves, a constitutive model describing the relationship of the flow stress, true strain, strain rate and temperature was proposed. Furthermore, the processing maps based on both the dynamic material modeling (DMM) and modified DMM (MDMM) were established to analyze flow instability domain of the composite and optimize hot forming processing parameters. The optimum processing domain was determined at temperatures of 425-450 °C and strain rates of 0.001-0.01 s−1, in which the fine grain microstructure can be gained and particle crack and interface debonding can be avoided.

Regional cerebral cholinergic nerve terminal integrity and cardinal motor features in Parkinson's disease.

Clinical effects of anti-cholinergic drugs implicate cholinergic systems alterations in the pathophysiology of some cardinal motor impairments in Parkinson’s disease. The topography of affected cholinergic systems deficits and motor domain specificity are poorly understood. Parkinson's disease patients (n = 108) underwent clinical and motor assessment and vesicular acetylcholine transporter [18F]-fluoroethoxybenzovesamicol PET imaging. Volumes-of-interest-based analyses included detailed thalamic and cerebellar parcellations. Successful PET sampling for most of the small-sized parcellations was available in 88 patients. A data-driven approach, stepwise regression using the forward selection method, was used to identify cholinergic brain regions associating with cardinal domain-specific motor ratings. Regressions with motor domain scores for model-selected regions followed by confounder analysis for effects of age of onset, duration of motor disease and levodopa equivalent dose were performed. Among 7 model-derived regions associating with postural instability and gait difficulties domain scores three retained significance in confounder variable analysis: medial geniculate nucleus (standardized β = −0.34, t = −3.78, P = 0.0003), lateral geniculate nucleus (β = −0.32, t = −3.4, P = 0.001) and entorhinal cortex (β = −0.23, t = −2.6, P = 0.011). A sub-analysis of non-episodic postural instability and gait difficulties scores demonstrated significant effects of the medial geniculate nucleus, entorhinal cortex and globus pallidus pars interna. Among 6 tremor domain model-selected regions two regions retained significance in confounder variable analysis: cerebellar vermis section of lobule VIIIb (β = −0.22, t = −2.4, P = 0.021) and the putamen (β = −0.23, t = −2.3, P = 0.024). None of the three model-selected variables for the rigidity domain survived confounder analysis. Two out of the four model-selected regions for the distal limb bradykinesia domain survived confounder analysis: globus pallidus pars externa (β = 0.36, t = 3.9, P = 0.0097) and the paracentral lobule (β = 0.26, t = 2.5, P = 0.013). Emphasizing the utility of a systems-network conception of the pathophysiology of Parkinson's disease cardinal motor features, our results are consistent with specific deficits in basal forebrain corticopetal, peduncupontine-laterodorsal tegmental complex, and medial vestibular nucleus cholinergic pathways, against the background of nigrostriatal dopaminergic deficits, contributing significantly to postural instability, gait difficulties, tremor and distal limb bradykinesia cardinal motor features of Parkinson’s disease. Our results suggest significant and distinct consequences of degeneration of cholinergic peduncupontine-laterodorsal tegmental complex afferents to both segments of the globus pallidus. Non-specific regional cholinergic nerve terminal associations with rigidity scores likely reflect more complex multifactorial signalling mechanisms with smaller contributions from cholinergic pathways.

A new instability domain of CNO-flashing low-mass He-core stars on their early white-dwarf cooling branches

Context. Before reaching their quiescent terminal white-dwarf cooling branch, some low-mass helium-core white dwarf stellar models experience a number of nuclear flashes which greatly reduce their hydrogen envelopes. Just before the occurrence of each flash, stable hydrogen burning may be able to drive global pulsations that could be relevant in shedding some light on the internal structure of these stars through asteroseismology, similarly to what occurs with other classes of pulsating white dwarfs. Aims. We present a pulsational stability analysis applied to low-mass helium-core stars on their early white-dwarf cooling branches going through CNO flashes in order to study the possibility that the ε mechanism is able to excite gravity-mode pulsations. We assess the ranges of unstable periods and the corresponding instability domain in the log g − Teff plane. Methods. We carried out a nonadiabatic pulsation analysis for low-mass helium-core white-dwarf models with stellar masses between 0.2025 and 0.3630 M⊙ going through CNO flashes during their early cooling phases. Results. We found that the ε mechanism due to stable hydrogen burning can excite low-order (ℓ = 1, 2) gravity modes with periods between ∼80 and 500 s for stars with 0.2025 ≲ M⋆/M⊙ ≲ 0.3630 located in an extended region of the log g − Teff diagram, with effective temperature and surface gravity in the ranges 15 000 ≲ Teff ≲ 38 000 K and 5.8 ≲ log g ≲ 7.1, respectively. For the sequences that experience multiple CNO flashes, we found that with every consecutive flash, the region of instability becomes wider and the modes are more strongly excited. The magnitudes of the rate of period change for these modes are in the range of ∼10−10–10−11 [s/s]. Conclusions. Since the timescales required for these modes to reach amplitudes large enough to be observable are shorter than their corresponding evolutionary timescales, the detection of pulsations in these stars is feasible. Given the current problems in distinguishing some stars that populate the same region of the log g − Teff plane, the eventual detection of short-period pulsations may help in the classification of such stars. Furthermore, if a low-mass white dwarf star were found to pulsate with low-order gravity modes in this region of instability, it would confirm our result that such pulsations can be driven by the ε mechanism. In addition, confirming a rapid rate of period change in these pulsations would support the idea that these stars actually experience CNO flashes, as has been predicted by evolutionary calculations.

Hot Deformation Behavior and Processing Map of a Novel Dilute Extruded Mg-Zn-Gd-Y-Nd Alloy

Background: The hot working characteristic of magnesium alloys have received considerable attention in order to evaluate the constitutive behavior of these alloys under hot working conditions with a view to evaluate constitutive conditions to optimize hot workability and control the microstructure so as to obtain consistent mechanical properties. Methods: The hot deformation response of a new dilute Mg alloy was investigated by means of a series of hot compression tests in the temperature and strain rate range of 375-450°C and 0.001-1 s-1, respectively. The stress-strain behavior, microstructure evolution and processing parameters optimization were studied carefully. Micro-structural characterization studies conducted on a series of deformed samples using optical microscopy revealed that during hot deformation, the main restoration mechanism was dynamic recrystallization (DRX). Results: In the final microstructure of the material, grain boundaries were thoroughly covered by layers of fine DRXed grains. Moreover, a strong twinning induced necklace structure was the most significant characteristic at high strain rates which was accompanied by smaller grain size in the domain material. Based on the measured stress-strain data, constitutive model was conducted on two regimes of low and high temperatures. Moreover, the processing map of the studied material was obtained and interpreted using dynamic material model (DMM). Conclusion: The processing map was built and divided into a feasible domain at high temperatures in the whole range of strain rates and two separated instable domains in the temperature range of 375 to 435°C at high and low strain rates of 1 and 0.001 s-1.

Effect of processing parameters on flow behaviors and microstructure during high temperature deformation of GH4586 superalloy

The apparent activation energy for deformation (Q) and strain rate sensitivity (m) of GH4586 superalloy are calculated and the variation trend is reasonably explained by the microstructure observations. Constitutive modelling of this superalloy is established and the processing maps at different strains are constructed. The results show that the Q value is in the range of 751.22–878.29 kJ/mol. At a temperature of 1060 °C, strain rate of 0.001 s−1, and strain of 0.65, the m value of GH4586 superalloy reaches a maximum of 0.42. The optimal processing parameter of GH4586 superalloy is at a deformation temperature of 1050 °C and a strain rate of 0.001 s−1. The domains of flow instability notably expand with increasing strain during high temperature deformation of GH4586 superalloy.

FORMATION OF CELLULAR-TYPE STRUCTURES DURING PLASTIC DEFORMATION

A theoretical study of patterns of the evolution and formation of dislocation structures during the plastic deformation of crystals is carried out. A nonlinear theory of the formation of cellular dislocation structures in an ensemble of screw dislocations has been developed. The nonlinear dynamics of an ensemble of dislocations is investigated in a two-dimensional domain, taking into account periodic boundary conditions of the Born - Karman type imposed on the initial equation. The local kinetics of dislocations is chosen in the form of multiplication of dislocations by means of their double transverse sliding and annihilation. A homogeneous stationary solution of the system (thermodynamic branch) is found. It is established that at a critical deviation from the thermodynamic branch, an instability of the homogeneous state occurs in the system due to the correlation interaction of dislocations. To obtain solutions in the domain of instability, the system of evolutionary equations is transformed to a system of equations for collective (mode ) variables. The expediency of such transformation lies in the fact that the system can be divided into subsystems of unstable and damped modes and it makes possible to apply the principle of adiabatic exclusion of unstable variables (the principle of subordination). Using the smallness of the values characterizing the increments of unstable modes, the principle of subordination is applied for the system of collective variables. In this case, it is shown that the system can be reduced to solving differential equations for a relatively small number of variables (order parameters). In the vicinity of the bifurcation point, two stable solutions are obtained for the order parameters. The first one is a consequence of the competition of modes and it leads, in the soft excitation regime, to a periodic one-dimensional structure for the dislocation density, the second parameter is a result of the cooperation of unstable modes and it leads to the formation of a hexagonal structure in the hard regime of emergence. The question is solved, which of these two structures is implemented, when the system reaches the bifurcation point. The equations for the order parameters are written in the variational form and the corresponding potential function is determined. Its analysis at the points of minima showed that the hexagonal configuration is more likely at the moment of instability occurrence. As the bifurcation parameter increases, the single-mode structure becomes more likely. Thus, the formation of a dissipative cellular structure serves as an indicator of the attaining of non-equilibrium critical conditions in a local volume, when a deformable crystal begins to change its defective structure minimizing its elastic energy.

Hot deformation behaviours and spheroidization mechanisms of Ti-5322 alloy during hot compression

The hot deformation behavior of Ti-5322 alloy are researched at compression temperatures range of 750–1050 °C and strain rate range of 0.01–10 s−1, to optimize its hot workability. Processing map analysis and microstructure observations reveal that the optimal processing parameters of Ti-5322 alloy are temperatures of 750–825 °C and strain rates of 0.01–0.05 s−1, and temperatures of 925–975 °C and strain rates of 0.01–1 s−1. The peak efficiency of power dissipation can reach 40% owing to the transformation from α phase to β phase, spheroidization behavior and dynamic recrystallization of the β phase. The dynamic recrystallization was the primary form of microstructure evolution above 900 °C, while the spheroidization of α phase below 900 °C. The spheroidization of α lamellae can be attributed to the instability of subgrain boundaries appeared in the α phase during hot deformation. The β phase wadges into the α/α subgrain boundary and α/β interface migration induced the α phase spheroidization. In addition, three instability domains are detected in the processing maps, which confirmed by the presence of microstructures with wedge cracking and adiabatic shear bands.

Hot deformation of nickel particles reinforced aluminium based composites: flow behaviour, microstructural evolution and processing map analyses

The hot deformation behavior and workability of stir cast Al 6063 alloy reinforced with 6 wt. % Nickel particles was investigated using flow stress-strain plots, microstructural analysis and processing maps. The composites were hot compression tested at temperatures of 200 °C, 250 °C, 300 °C, 350 °C and 400 °C, and strain rates of 0.01, 0.1, 1, and 10 s−1, while scanning electron microscopy was utilized for characterization of the ensuing microstructures. The results show that the flow stress generally decreased with increase in deformation temperature, while anomalous flow stress oscillations, linked to the pattern of particle distribution in the matrix, characterized the flow stress - strain rate relations at 0.01 s−1 strain rate. The Murty’s and Gegel’s criteria utilized to establish domains of instability at the global strain of 0.5 were found to vary considerably and the combination of both left a very narrow safe processing window for the Al6063/Ni p composite. Safe regions with peak power dissipation efficiencies occurred at temperature range of ∼390 °C–400 °C and 0.01 s−1 in the lower domain and 260 °C–350 °C and 10 s−1 in the upper domain. The dominant flow softening mechanisms were established to be dynamic recrystallisation and dynamic recovery at the lower domain and upper domains, respectively.

Quasi-static hot deformation behavior of a novel third-generation Ni-based powder metallurgy superalloy

Quasi-static hot deformation behavior of a novel third-generation Ni-based powder metallurgy superalloy A3 was investigated by hot compression tests and microscopy. The activation energy for hot working of the experimental alloy was about 867 kJ/mol. An instability domain existed in the processing map when the strain was 0.2, implying a plastic instability at the temperature range of 1080–1100°C and the strain rate range of 0.016–0.1 s−1. The power dissipation efficiency in processing maps indicated that optimum parameters for large deformation could be controlled at the temperature range of 1000–1030°C and the strain rate range of 0.001–0.01 s−1. It provided a reliable suggestion for hot processing during the manufacturing of such superalloy.

Modulational instability in a one-dimensional spin–orbit coupled Bose–Bose mixture

We establish the condition of modulational instability (MI) in one-dimensional effective one-component self-bound quantum droplets and Bose–Bose (BB) mixture, coupled through spin–orbit and Rabi couplings. For the self-bound quantum droplets of effective one-component BB mixture, MI occurs for the atom density: , where δg = g + g 12 with g indicate intra-atomic and g 12 inter-atomic interaction strengths. The MI growth rate of BB mixture in the presence of spin–orbit and Rabi couplings shows distinct signatures of the couplings, in the form of multiple domains of instability. In particular, we demonstrate the explicit difference in MI, between the effective one-component self-bound quantum droplets and BB mixture.

18F-THK5351 PET imaging in patients with progressive supranuclear palsy: associations with core domains and diagnostic certainty

The associations of 18F-THK5351 tau positron emission tomography (PET) findings with core domains of progressive supranuclear palsy (PSP) and its diagnostic certainty have yet to be fully elucidated. The 18F-THK5351 PET patterns of 17 patients with PSP (68.9 ± 6.5 years; 8 women) were compared with those observed in 28 age-matched and sex-matched (66.2 ± 4.5 years, 18 women) control subjects (CS). Tracer accumulation—as reflected by standardized uptake value ratios (SUVRs) and z-scores—was correlated with core domains of PSP and different levels of diagnostic certainty. Compared with CS, patients with PSP showed an increased 18F-THK5351 uptake in the globus pallidus and red nucleus. Patients with PSP and oculomotor dysfunction had significantly higher SUVRs in the midbrain, red nucleus, and raphe nucleus than those without. In addition, cases who meet criteria for level 1 (highest) certainty in the postural instability domain showed significantly higher SUVRs in the frontal, parietal, precuneus, and sensory-motor cortex. Patients with probable PSP had significantly higher SUVR values than those with possible PSP in multiple cortical (i.e., frontal, parietal, temporal, anterior cingulate gyrus, precuneus, and sensory-motor gyrus) and subcortical (i.e., putamen, thalamus, and raphe nucleus) regions. Patterns of 18F-THK5351 uptake were correlated to core domains of PSP—including oculomotor dysfunction and postural instability. Moreover, the degree of diagnostic certainty for PSP was appreciably associated with 18F-THK5351 PET findings.

The two-degree-of-freedom parametric oscillator: A mechanical experimental implementation

We report the observation and quantitative measurements of the parametric resonance of a two-degree-of-freedom harmonic oscillator made of two coupled pendula. When varying the length of one of the pendula, we parametrically excite the whole set. The frequency of this excitation can be tuned and its depth ajusted, enabling us to draw a frequency-depth Cartesian diagram in which the oscillation behaviour, namely finiteness or exponential divergence, can be plotted. As in the well-known case of the one-degree-of-freedom oscillator, the stability and instability domains are demarcated by a tongue centred at twice the oscillator's free frequency. But in the two-degree-of-freedom oscillator case, this tongue has a three-tip fine structure, two tips corresponding to the free oscillator's eigenfrequencies and an extra tip corresponding to the average of both eigenfrequencies. This situation is unravelled theoretically using a classical adaptation of a formalism introduced in quantum optics by Glauber.

Instability of vibrations of an oscillator moving at high speed through a tunnel embedded in soft soil

This paper investigates the instability of vertical vibrations of an object moving uniformly through a tunnel embedded in soft soil. Using the indirect Boundary Element Method in the frequency domain, the equivalent dynamic stiffness of the tunnel-soil system at the point of contact with the moving object, modelled as a mass-spring system or as the limiting case of a single mass, is computed numerically. Using the equivalent stiffness, the original 2.5D model is reduced to an equivalent discrete model, whose parameters depend on the vibration frequency and the object’s velocity. The critical velocity beyond which the instability of the object vibration may occur is found, and it is the same for both the oscillator and the single mass. This critical velocity turns out to be much larger than the operational velocity of high-speed trains and ultra-high-speed transportation vehicles. This means that the model adopted in this paper does not predict the vibrations of Maglev and Hyperloop vehicles to become unstable. Furthermore, the critical velocity for resonance of the system is found to be slightly smaller than the velocity of Rayleigh waves, which is very similar to that for the model of a half-space with a regular track placed on top (with damping). However, for that model, the critical velocity for instability is only slightly larger than the critical velocity for resonance (of the undamped system), while for the current model the critical velocity for instability is much larger than the critical velocity for resonance due to the large stiffness of the tunnel and the radiation damping of the waves excited in the tunnel. A parametric study shows that the thickness and material damping ratio of the tunnel, the stiffness of the soil and the burial depth have a stabilising effect, while the damping of the soil may have a slightly destabilising effect (i.e., lower critical velocity for instability). In order to investigate the instability of the moving object for velocities larger than the identified critical velocity for instability, we employ the D-decomposition method and find instability domains in the space of system parameters. In addition, the dependency of the critical mass and stiffness on the velocity is found. We conclude that the higher the velocity, the smaller the mass of the object should be to ensure stability (single mass case); moreover, the higher the velocity, the larger the stiffness of the spring should be when a spring is added (oscillator case). Finally, in view of the stability assessment of Maglev and Hyperloop vehicles, the approach presented in this paper can be applied to more advanced models with more points of contact between the moving object and the tunnel, which resembles reality even better.

Constitutive modeling and microstructure characterization of 2196 Al-Li alloy in various hot deformation conditions

• A constitutive model with comprehensive consideration of temperature, strain rate and strain compensation was proposed. • Processing maps under different strains were generated. • The peak power dissipation domain is located in high temperature and medium strain rate. • Dynamic recovery is the main softening mechanism with a small amount of continuous dynamic recrystallization. • The optimum deformation parameters of 2196 Al-Li alloy were determined. Isothermal compression tests of 2196 Al-Cu-Li alloy were carried out at different temperatures (633∼793 K) and strain rates (0.001∼10 s −1 ) on Gleeble-3500 thermal simulator until the compression reached 60 %. According to the obtained stress-strain data, the flow behavior of 2196 Al-Li alloy during thermal deformation was investigated. The Arrhenius constitutive equation of the alloy based on the hyperbolic sine function model was established. A modified constitutive model with comprehensive consideration of deformation temperature, strain rate and strain compensation was proposed. Compared with the traditional constitutive model of strain compensation, the modified model had higher prediction accuracy. The hot processing maps under different strains (0.2∼0.8) were established, it was found that the plastic instability domain mainly occurred at the low temperature and high strain rate, while the peak power dissipation domain was located in the high temperature and medium strain rate. The microstructure evolution of 2196 Al-Li alloy under different deformation conditions was characterized and analyzed by electron back scattering diffraction and transmission electron microscope. The results showed that the softening mechanism was mainly dynamic recovery with a small amount of continuous dynamic recrystallization. High temperature and low strain rate were conducive to the occurrence of dynamic recovery and recrystallization, and the microstructure was mainly characterized by low dislocation density, no dislocation entanglement and dislocation wall structure. The grain boundary was straight and smooth. Some discontinuous dynamic recrystallization occurred at low temperature and high strain rate. Based on the analysis of the hot processing maps and microstructure evolution, the optimum deformation parameters of 2196 Al-Li alloy were determined to be 733∼793 K and 0.01∼1 s −1 .

Modulational instability and soliton control in a cubic–quintic dissipative Gross–Pitaevskii equation with distributed coefficients* *The first author, EK dedicates this work to the memory of his Father-in-law, His Majesty Sado Jean Le Prince, Deceased on the June 2nd, 2020

In this work, we consider the generalized cubic–quintic dissipative Gross–Pitaevskii equation, which governs the dynamics of matter wave solitons in Bose–Einstein condensates with two- and three-body interatomic interactions in a spatiotemporal-dependent dissipative potential consisting of parabolic, linear, and complex terms. By using the ansatz method, the modulational instability and gray, kink, and bright soliton solutions are presented under certain parametric conditions. We found that the complex potential, related to the feeding or the loss of atoms by the condensates seriously modifies the instability and stability domain, while the linear potential has not effect on the stability of the system. With the use of exact analytical soliton-like solutions, we investigate analytically the solitons control system, and the results show that the soliton control system may relax the limitations to parametric conditions. We found that the motion of matter wave solitons in the systems can be manipulated by controlling both the external harmonic and linear trapping potentials. We have established that the amplitude of the matter wave solitons keep no change in propagating in the system though the total number of the condensate atoms decreases (increases) when the condensate losses (gains) atoms. We also showed that the three-body interatomic interactions is responsible of the soliton compression. Our results also revealed that the found exact soliton-like solutions can be used to describe the compression of matter wave solitons in BEC system with loss of atoms.

Characterization of Hot Deformation Behavior and Processing Map of As-Cast H13 Hot Work Die Steel

The hot-working behavior of as-cast H13 hot work die steel was investigated in the method of isothermal compression test involving the wide deformation temperatures of 900–1150 °C and strain rates of 0.01–10 s−1, with the true strain to 0.8, on the MMS-200 thermo-mechanical simulator. Two characteristic parameters involving the critical strain for DRX initiation ( $$\varepsilon_{c}$$ ) and the strain for peak stress ( $$\varepsilon_{p}$$ ) were identified. The ratio of critical strain to peak strain ranged from 0.26 to 0.6, which decreased with the increase in temperature and decrease in strain rate. Processing maps were established using dynamic material model at strains of 0.2, 0.4, 0.6, 0.8. The power dissipation maps were not significantly affected by the strain, while the instability maps were sensitivity with the strain when it was over 0.4. The area of instability domain at strain of 0.8 was the largest. The instable characteristics contained the mixed grain structure, adiabatic shear band, intense deformation in serious deformation area and brittle elemental segregation area. The chief effect on the power dissipation was the strain rate, the optimum hot working parameters at strain of 0.8 (910–985 °C, 1010–1150 °C and 0.01–0.05 s−1) were determined. In this filed, the original coarse as-cast grains were gradually refined by dynamic recrystallization mechanism and the DRX grain numbers had a significant increase with the increase of power dissipation efficiency.

Hot workability characteristics of low-density Fe–4Al–1Ni ferritic steel

The hot-working behavior of a low-density Fe–4Al–1Ni ferritic steel at the deformation temperature in the range of 700–950 °C and the strain rate in the range of 0.01–10 s-1 was studied on a Gleeble-3800 thermomechanical simulator by means of a compression test. The hot-working behavior of the experimental steel was in accord with a material with intermediate stacking fault energy. The deformation mechanism is controlled by the glide and climb of dislocations. The constitutive equations were established to predict peak stress. The apparent deformation activation energy of experimental steel was about 347.5 kJ/mol. Electron backscatter diffraction was applied to study the microstructure after deformation. The experimental results showed that both continuous dynamic recrystallization and discontinuous dynamic recrystallization could occur, and increasing deformation temperature and strain rate is conducive to the occurrence of discontinuous dynamic recrystallization behavior. According the dynamic materials model, the processing maps of the experimental steel were established. Combined with the microstructure results, the power consumption efficiency of continuous dynamic recrystallization, discontinuous dynamic recrystallization and dynamic recovery decreases gradually. There are two flow instability domains, which are related to mischcrystal microstructure caused by partial dynamic recrystallization. The optimum deformation parameters for industrial processing are as follows: deformation temperature 750–900 °C, strain rate 10 s-1.

A comparative study of functional outcome of transtibial and transportal femoral tunneling techniques for arthroscopic ACL reconstruction

Introduction:Acl reconstruction has revolutionarised the sports medicine world lately. Various methods of reconstruction have been advocated in the literature recently. ACL injury results in severe morbidity to an athletes career. The aim for anatomical reconstruction is to harvest the ACL graft at a more anatomical location on both the tibia and the femur. The purpose of this study is to compare the functional outcomes of the two methods of the graft harvestis to compare the functional outcomes of the two methods of the graft harvestHypotheses:60 patients were included in the study with complete ACL tear and were assessed at 3 6 and 9 months on the basis of various scores and relevant elements.Methods:All patients who were planned for arthroscopic ACL reconstruction surgery from the OPD, who were willing and fit the inclusion criteria were included in the study. They were then examined clinically with special tests i.e. Lachman’s test, anterior drawer test, pivot shift test and McMurray’s test and the findings were recorded including any associated meniscal injuries. They were then evaluated using 3 different evaluation systems i.e. IKDC, Lysholm and pain VAS.Results:Average mean age of the patients undergoing ACL reconstruction was (26%) in Transtibial and 23.3%. 90% of them were males. Majority of them were males (58%). The average IKDC score of transportal patients was significantly higher than transtibial patients at 6 months followup [P=0.001]. The average Lysholm knee score of transportal patients was significantly higher than the transtibial patients [P=0.047].The average pain on VAS score of transportal group was significantly lower than transtibial at 6 months followup [P<0.001].Complication of instability was more common in transtibial patients, 11(36.7%), when compared to transportal patients, 9(30%), however this difference was not significant [P=0.58].Conclusion:Our study clearly stated that the transportal technique for acl reconstruction fetched superior results as compared to the transtibial technique in terms of knee instability, pain and other domains.

Effect of Ag Addition on the Hot Deformation, Constitutive Equations and Processing Maps of a Hot Extruded Mg-Gd-Y Alloy

Hot deformation behavior of the extruded Mg-6Gd-3Y (GW63) and Mg-6Gd-3Y-1Ag (GW63-1Ag) alloys was assessed by shear punch testing (SPT) method in the temperature range of 623 K to 723 K and shear strain rate of 1.6 × 10−2 to 1.3 × 10−1 s−1. Microstructural examinations showed that Ag addition decreased the initial grain size from 10.1 to 2.9 µm. According to the hot deformation results, hyperbolic-sine exponents (n-values) of 3.39 and 2.54 were obtained for the Ag-free and Ag-containing alloys, respectively. The corresponding activation energies were found to be 321 and 178 kJ mol−1 for these alloys. Therefore, the controlling deformation mechanisms were defined as viscous glide of dislocation for the Mg-6Gd-3Y alloy and grain boundary sliding for Mg-6Gd-3Y-1Ag. Processing maps were developed based on the dynamic material model (DMM) to determine the flow instability domains during hot deformation. Accordingly, the optimum hot working conditions were found to be in the temperature range of 655 K to 723 K and shear strain rate of 3.3 × 10−2 to 1.3 × 10−1 s−1 for the GW63-1Ag alloy, whereas the safe deformation window for the GW63 alloy was narrowed down to a temperature range of 665 K to 705 K and shear strain rate of 7.2 × 10−2 to 1.3 × 10−1 s−1. The Ag-containing alloy exhibited flow instability regions only at low temperatures and high strain rates. On the other hand, the Ag-free alloy demonstrated other instability domains comprising the formation of mechanical twins and cracking. Electron back-scattered diffraction analysis was utilized to correlate the microstructural evolution of the alloys after shear deformation to the hot working parameters. Continuous dynamic recrystallization was suggested as the main mechanism for generation of the dynamically recrystallized grains during hot deformation of both alloys.