Increase In Relaxation Time Research Articles

Binary Collisions of Water Drops in Presence of Horizontal Electric Fields: A Wind Tunnel Study

AbstractCoalescence/breakup characteristics of binary collisions of small water drops (dS = 0.4–1.8 mm diameter) with large drops (dL = 3–3.5 mm diameter) occurring in the absence/presence of horizontal electric field (EH) = 0, 100, and 300 kVm−1 have been investigated in a small vertical wind tunnel using a high‐speed digital camera. The coalescence efficiency (EC) of 0.299 observed for average diameters (dL = 3.2 mm, dS = 1.2 mm) in EH = 0 decreased to 0.244/0.211 when EH is increased to 100/300 kVm−1. The increase in the electric field reduces the probability of coalescence when Weber number (We) < 1. However, when We ≥ 1, an increase in We restricts the probability of coalescence. Our data, when plotted in the regime diagram in the We*‐p plane, delineates the collision outcomes in all‐electric field values but does show the overlapping of some data points in the adjacent categories. After a binary collision, the relaxation time for coalescence is higher than that for the breakup. Further, the relaxation time increases from the filament to sheet to disk mode of breakup in all‐electric field values. Fragment size distributions after the filament and sheet types of breakups differ and are differently affected by the applied electric field. Higher collision kinetic energy has a tendency to increase the number of fragments of the sizes between dL and dS. It is concluded therefore that, the effect of the electric field needs to be included in the estimation of drop growth and precipitation in clouds.

Strain driven anomalous anisotropic enhancement in the thermoelectric performance of monolayer MoS2

First principles density functional theory based calculations have been performed to investigate the strain and temperature induced tunability of the thermoelectric properties of monolayer (ML) MoS2. Modifications in the electronic and phononic transport properties, under two anisotropic uniaxial strains along the armchair (AC) and zigzag (ZZ) directions, have been explored in detail. Considering the intrinsic carrier-phonon scattering, we found that the charge carrier mobility (μ) and relaxation time (τ) increase remarkably for strains along the ZZ direction. Concomitantly, strain along the ZZ direction significantly reduces the lattice thermal conductivity (κL) of ML-MoS2. The combined effect of shortened phonon relaxation time and group velocity, and the reduced Debye temperature is found to be the driving force behind the lowering of κL. The large reduction in κL and increase in τ, associated with the strains along the ZZ direction, act in unison to result in enhanced efficiency and hence, improved thermoelectric performance. Nearly 150% enhancement in the thermoelectric efficiency can be achieved with the optimal doping concentration. We, therefore, highlight the significance of in-plane tensile strains, in general, and strains along the ZZ direction, in particular, in improving the thermoelectric performance of ML-MoS2.

Spin dynamics in ensembles of ultrafine ferrihydrite nanoparticles

Features of the spin dynamics in ensembles of interacting (FH-chem) and weakly interacting (FH-coated) magnetic ultrasmall ($\ensuremath{\langle}d\ensuremath{\rangle}\ensuremath{\sim}2$ nm) ferrihydrite nanoparticles have been explored. The dc and ac magnetic susceptibilities $[{\ensuremath{\chi}}^{\ensuremath{'}}(T)$ and ${\ensuremath{\chi}}^{\ensuremath{'}\ensuremath{'}}(T)]$ of the investigated samples have been thoroughly measured in a weak magnetic field (2 Oe) around the temperatures of superparamagnetic blocking of the nanoparticle magnetic moments (19 and 50.4 K for FH-coated and FH-chem, respectively, according to the dc magnetization data). It has been shown that the magnetic interactions between nanoparticles induce the formation of the cluster spin-glass state below the superparamagnetic blocking temperature (${T}_{g}=18$ and 49.5 K for FH-coated and FH-chem, respectively). It has been found that coating of nanoparticles increases the critical scaling index from $z\ensuremath{\nu}=5.9$ (FH-chem) to $z\ensuremath{\nu}=8.0$ (FH-coated). This indicates a general slowdown of the dynamics of correlated spins, which is also expressed as an increase in relaxation time ${\ensuremath{\tau}}_{0}$ after switching on the interparticle interactions. We attribute this phenomenon to a consequence of a change in the volume of correlated spins with the increasing size of a cluster of interacting nanoparticles. It has been demonstrated using the simulated ${\ensuremath{\chi}}^{\ensuremath{'}\ensuremath{'}}(T)$ dependence that the dissipation of the magnetic energy occurs in two independent stages. The first stage is directly related to the blocking of the nanoparticle magnetic moments, while the second stage reflects the spin-glass behavior of surface spins and depends strongly on the intensity of the interparticle interactions.

Covalent adaptable networks using boronate linkages by incorporating TetraAzaADamantanes.

Boronic esters prepared by condensation of boronic acids and diols have been widely used as dynamic covalent bonds in the synthesis of both discrete assemblies and polymer networks. In this study we investigate the potential of a new dynamic-covalent motif, derived from TetraAzaADamantanes (TAADs), with their adamantane-like triol structure, in boronic ester-based covalent adaptable networks (CANs). The TetraAzaADamantane-boronic ester linkage has recently been reported as a more hydrolytically stable boronic ester variant, while still having a dynamic pH response: small-molecule studies found little exchange at neutral pH, while fast exchange occurred at pH 3.8. In this work, bi- and trifunctional TetraAzaADamantane linkers were synthesised and crosslinked with boronic acids to form rubber-like materials, with a Young's modulus of 1.75MPa. The dynamic nature of the TetraAzaADamantane networks was confirmed by stress relaxation experiments, revealing Arrhenius-like behaviour, with a corresponding activation energy of 142 ± 10kJ/mol. Increasing the crosslinking density of the material from 10% to 33% resulted in reduced relaxation times, as is consistent with a higher degree of crosslinking within the dynamic networks. In contrast to the reported accelerating effect of acid addition to small-molecule TetraAzaADamantane complexes, within the polymer network the addition of acid increased relaxation times, suggesting unanticipated interactions between the acid and the polymer that cannot occur in the corresponding small-molecules analogues. The obtained boronate-TetraAzaADamantane materials were thermally stable up to 150°C. This thermal stability, in combination with the intrinsically dynamic bonds inside the polymer network, allowed these materials to be reprocessed and healed after damage by hot-pressing.

Glassy magnetism of Tm2Cu2In in elevated pressures

Tm2Cu2In belonging to the family of R2T2X intermetallics is a ferromagnet with glassy features. This work describes results of high-pressure studies of its magnetic behavior. While TC exhibits only a weak and non-monotonous response to hydrostatic pressure, the pressure impact on frequency dependence of AC susceptibility can be interpreted as due to gradual increase of relaxation time and decrease of the activation energy barrier. Since the magnetic behavior is strongly related to the details of crystal structure, the temperature and pressure effects on the lattice are presented, as well. First principles calculations based on the density functional theory provide a background information.

Thermal and electrical transport conductivities of novel ordered double two-dimensional MXenes via density functional theory

In this paper, we examined the effects of transition metal replacement and ordering in 2D M3C2O2 MXene on the electronic structure and thermal and electrical conductivities using the density functional theory and also Boltzmann’s transport theory within the constant relaxation time approximation. We derived the following oxygen-functionalized ordered double-metal MXenes Ti2YC2O2, Y2TiC2O2, Sc2YC2O2, and Y2ScC2O2 through the surface and sub-layer tuning. The results revealed that the ordered MXenes give rise to different electronic structure and transport properties. The electronic thermal conductivities obtained in terms of the relaxation time increase with increase in absolute temperature, while the electrical conductivities decrease with increase in temperature. The respective transport properties of Y2TiC2O2 and Sc2YC2O2 were found to be enhanced due to the increased squared band velocity, density of state, and low Seebeck coefficient compared to Ti2YC2O2 and Y2ScC2O2 MXenes. Generally, the MXene materials investigated in this work were found to possess metallic properties with the existence of energy overlap around the Fermi level. The computed formation energies support chemical stability in all the materials.

Variation on propagation of Rayleigh waves in thermo-poroelastic solids

We analyse the dispersion and attenuation of Rayleigh-wave propagation along on isothermal free surface of a thermo-poroelastic medium. The thermo-poroelastic theory, including the Lord-Shulman (LS) and Green-Lindsay (GL) theories, predicts three compressional waves and one shear wave, which induce two Rayleigh-type surface waves, R1 and R2 modes along the interface by evanescent potential functions specified by vertical imaginary wavenumbers. The GL model can give a stronger P1 and P2 wave thermal attenuation and consequently a stronger velocity dispersion than the LS model. We investigate the influence of frequency and surface boundary condition. The additional thermal diffusion exhibits the inverse dispersion in R1 waves, and makes the pseudo surface-wave transition under the closed (CP) and partial permeable (PP) surface toward high frequencies. Another T wave affects the energy inference along the surface and induce the other R2 waves under the open surface (OP). The thermal dispersion occurs at characteristic frequencies around the thermal relaxation peaks, which induces the high-velocity T wave toward low frequencies when the Maxwell–Vernotte–Cattaneo relaxation time increases. Until the T wave propagates faster than the P2 wave, the Rayleigh equations lose the R2 poles making the prohibition of R2-wave propagation.

Extended plane wave expansion formulation for 1-D viscoelastic phononic crystals

The extended plane wave expansion (EPWE) method is formulated in order to obtain the complex dispersion diagram of bulk waves in 1-D viscoelastic phononic crystal solids considering the standard linear solid model (SLSM). This new formulation is important to handle evanescent Bloch waves in 1-D viscoelastic periodic structures for mechanical wave attenuation. The viscoelastic effect can increase the unit cell wave attenuation in 1-D periodic structures. In addition, the increase of relaxation time (up to ωa/2πct=7) and the decrease of final state of shear modulus (considering ωa/2πct≤1.9) enhance the unit cell wave attenuation.

Influence of confined phase transition on dielectric relaxation characteristics of thermochromic epoxy insulating materials

The dielectric relaxation characteristic and mechanism of thermochromic microcapsule-epoxy insulating material are investigated. The results show that thermochromic microcapsule-epoxy insulating material exhibits non-monotonic dielectric relaxation characteristic, namely the dielectric relaxation time gradually increases with the temperature rising in a range of about 58–66 ℃, which cannot be depicted by the conventional Arrhenius equation or Vogel-Fulcher-Tammann equation. It is proposed that the non-monotonic dielectric relaxation characteristic is derived from the free volume variation induced by the confined phase transition in microcapsule. With the increase of temperature, the solid-liquid phase transition occurs in the limited space of microcapsule, reducing the free volume inside the microcapsule, which could restrict the reorientation of dipole with the external electric field and lead to the increase of dielectric relaxation time. The non-monotonic dielectric relaxation characteristic of thermochromic epoxy specimen is fitted based on the confined dielectric relaxation model, obtaining the activation energy of dielectric relaxation. The relaxation activation energy values of thermochromic epoxy insulating materials with different microcapsule content are of the same order of magnitude, indicating that the non-monotonic dielectric relaxations occur inside the thermochromic microcapsule, verifying the role of confined phase transition in the non-monotonic dielectric relaxation characteristic.

First-principles study of the thermal transport properties of superconducting NbN

We investigate the thermal transport properties of NbN by considering three-phonon scattering (3ph), four-phonon scattering (4ph), electron-phonon (ep) scattering, and isotope (iso) scattering. By considering 4ph scattering, we find that 4ph scattering has less effect on the lattice thermal conductivity (κph) within 3-9 THz, while ep scattering has a greater effect on κph which is close to 3ph scattering in this frequency range. When the pressure is increased to 15 GPa, the κph by 148%, which is due to the decrease of the scattering phase space resulting in an increase of phonon relaxation time. We find that the κph of NbN is close to 100 W/mK, which is a potential high thermal conductivity material.

Oscillatory convection in viscoelastic ferrofluid layer: Linear and non-linear stability analyses

The problem of ferroconvection in a viscoelastic fluid layer is studied with the aim to investigate oscillatory motions. In this article, a stability analysis for both linear and nonlinear systems is carried out. In the linear stability analysis, the expressions for steady and oscillatory Rayleigh numbers are obtained and the effects of magnetic as well as viscoelastic parameters on the onset of viscoelastic ferromagnetic convection are investigated numerically. From the analysis, we found that the magnetic number (M_1), the stress relaxation time (lambda_1) and the nonlinearity of magnetization (M_3) have destabilizing influences on the onset of ferroconvection, whereas the strain retardation time (lambda_2) has stabilizing influence. In the weakly nonlinear stability analysis, the formula for heat transfer rate in terms of the Nusselt number is derived for oscillatory convection. From the analyses, we found that for increasing values of the magnetic number, stress relaxation time and nonlinearity of magnetization, the heat transfer rate rises, whereas it decreases for larger values of the strain retardation time. Moreover, the pitchfork bifurcation analysis yields that in order to reach the stable positions, the value of amplitude increases as the stress relaxation time increases, whereas a reverse trend is observed for the strain retardation time.

INVESTIGATION OF DIELECTRIC PROPERTIES OF MBBA-5CB NEMATIC LIQUID CRYSTAL STRUCTURES

The dielectric anisotropy (Δε') is the response of the LC molecules to an applied electric field. In this study, the dielectric properties of 4-pentyl-4'-cyanobiphenyl (5CB) and N-(4-methoxybenzylidene)-4-butylaniline (MBBA) nematic liquid crystals with positive and negative dielectric anisotropy were investigated in detail. In addition, a structure with zero dielectric anisotropy was obtained by mixing MBBA and 5CB liquid crystals in certain rate (1:0.02). The behavior of the samples under 0V and 20V voltages was investigated in detail. Dielectric measurements were made with dielectric spectroscopy technique, which is a powerful method to investigate the molecular interaction mechanisms of liquid crystal materials, at a frequency of 1 kHz-10 MHz and a voltage of 0-20 V at room temperature. Some important parameters such as dielectric anisotropy (Δε'), relaxation frequency (fR), relaxation time (τ) were determined for the samples. When electric field is applied to nematic liquid crystals, it is seen that, depending on the voltage, the relaxation frequency decreases, and the relaxation time increases.

Physiological peristaltic flow of Jeffrey fluid inside an elliptic cross section with heat and mass transfer: Exact solutions through Polynomial solution technique

AbstractAn interpretation of heat and mass transfer for the peristaltic flow of a non‐Newtonian Jeffrey fluid inside a duct having an elliptic cross‐section is mathematically investigated. We have considered constant heat absorption for the present study and a descriptive heat as well as mass transfer analysis is carried out. Exact solutions are computed by utilizing a polynomial solution technique to solve the dimensionless partial differential equations appearing in the problem. A purposeful and detailed graphical assessment is provided for the final mathematical results. Velocity as well as temperature profiles attain highest value at the core region of duct while these profiles gradually decline toward duct boundaries. The incrementing value of λ1 is resulting in an increase of flow and since λ1 is the dimensionless ratio of relaxation to retardation time, it means that the increasing value of λ1 results in an increase of relaxation time but it also results in decline of retardation time.

106 A CASE OF COMPLETE ATRIOVENTRICULAR BLOCK AND ALTERNATING BUNDLE BRANCH BLOCK DUE TO FULMINANT MYOCARDITIS

Abstract A 41-year-old man, without previous cardiological history, presented at the emergency department with hypotension and multi-organ failure. Laboratory testing showed elevated white cell blood count (16780/mcL; normal value 4000-11000/mcL; 90% neutrophils), high-sensibility troponin I (23247 ng/L; normal value <18 ng/L) and NT-pro-BNP (21914 pg/mL; normal value <300 pg/mL). At electrocardiogram (EKG) there was sinus rhythm with complete atrioventricular block and alternating right and left bundle branch block. Echocardiography revealed a moderate left ventricular (LV) dilatation, mild LV hypertrophy, severe biventricular dysfunction (LV Ejection Fraction - EF - 30%) with dense spontaneous echo contrast and moderate pulmonary hypertension (systolic pulmonary artery pressure 51 mmHg). After positioning a temporary pacemaker, the patient was transferred to our Cardiac Intensive Care Unit. After initial hemodynamic stabilization with endovenous inotropes, diuretics, and mechanical circulatory support (intra-aortic balloon pump), coronary angiography was performed showing normal coronary arteries. Since fulminant myocarditis was suspected and magnetic resonance was not feasible due to the patient's instability, an endomyocardial biopsy (EMB) was performed with the evidence of myocardial edema, initial myocardial fibrosis, and the concomitant presence of lymphocytic and eosinophilic endo-myocarditis (despite normal eosinophilic blood count) without evidence of active viral replication. After careful exclusion of latent or active infections, high doses of corticosteroids and azathioprine were initiated, with rapid laboratoristic and clinical response. EKG showed AV block regression and QRS width's normalization, so the pacemaker was removed. LVEF rapidly improved and was completely normalized at discharge after two weeks. In the early follow-up, a cardiac magnetic resonance (CMR) was performed with evidence of persistency of mildly dilated LV, normalization of LV wall thickness and biventricular function, a diffuse increase of T1 relaxation time, increased T2 signal of the anterior and septal walls, and intramural anteroseptal late gadolinium enhancement (LGE). Fulminant myocarditis is a rare presentation of acute myocarditis, with low incidence but high mortality. The inflammation of the myocardium itself leads to acute heart failure, cardiogenic shock, and cardiac arrhythmias, including sinus arrest, AV block, ventricular tachycardia, and ventricular fibrillation during the acute phase. In our case, AV block could be an expression of anteroseptal involvement, documented at CMR. This localization has already been associated with worse clinical presentation and could be a marker of poor prognosis. Diagnosis and treatment of fulminant myocarditis require EMB, to obtain information about the etiology and active viral replication in the heart tissue. In our case, the florid inflammatory state and the absence of viral replication allowed prompt treatment with immunosuppressors, with a quick and full recovery of biventricular function in only two weeks.

Structural and functional features of the myocardium in residents of the industrial region of the Far North under the exposure to nickel and arsenic

The study of the role of chemicals of industrial origin in the development of cardiovascular pathology determines the relevance of this study. The purpose of the work is to study the features of cardiac structural and functional disorders in residents of the industrial region of the Far North under the exposure of nickel and arsenic. Materials and methods. The study included one hundred fifty eight women living in the industrial center of the Far North with the location of large metallurgical enterprises (observation group) and 65 women living in similar climatic and geographical conditions, but without the location of industrial enterprises (comparison group). An echocardiographic study was carried out with the measurement of structural and doppler parameters of the heart on an expert-class ultrasonic scanner “Vivid q”. Results. In the observation group the values of myocardial performance indices (MPI) values for mitral annulus (0.55 ± 0.09 vs. 0.48 ± 0.07, p=0.005) and tricuspid annulus (0.57 ± 0.10 vs. 0.48 ± 0.06, p=0.001) were higher than in the comparison group. A gain in the concentration of nickel in the blood is associated with an increase in isovolumic relaxation time (IVRT) of the mitral atrioventricular ring (p=0.0001) and systolic pressure in the pulmonary artery (p=0.00002). An increase in the concentration of arsenic in the blood is associated with an increase in the filling pressure of the left ventricle (E/Em) and end diastolic diameter of the left ventricle (EDD LV) (p=0.0001), the diameters of the right ventricle (RV) and right atrium (RA) (p=0.0001), and rate of late diastolic filling of the RV and MPI of the tricuspid atrio-ventricular ring (p=0.0001). Limitations. This study did not include middle aged and elderly women, and also did not include male patients and did not include the population of other territories except the Far North. Conclusion. The revealed changes in echocardiographic parameters indicate subclinical dysfunctions of the myocardium of the left and right ventricles, affecting both systolic and diastolic function in residents of the industrial city of the Far North, living under the influence of nickel and arsenic.

Semiconductorlike photocarrier dynamics in Dirac-semimetal Cd3As2 films probed with transient terahertz spectroscopy

The topological three-dimensional Dirac semimetal ${\mathrm{Cd}}_{3}{\mathrm{As}}_{2}$ has drawn great attention for the novel physics and promising applications in optoelectronic devices operating in the infrared and terahertz (THz) regimes. Among the extensive studies in the past decades, one intriguing debate is the underlined mechanism governing the nonequilibrium carrier dynamics following photoexcitation. In this study, the temperature-dependent photocarrier dynamics in ${\mathrm{Cd}}_{3}{\mathrm{As}}_{2}$ film has been investigated with time-resolved terahertz spectroscopy. The experimental results demonstrate that photoexcitation results in abrupt increase in THz photoconductivity, and the subsequent relaxation shows a single exponential relaxation for various temperatures and pump fluences. The relaxation time increases from 4.7 ps at 5 K to 7.5 ps at 220 K, while the lifetime remains almost constant at $\ensuremath{\sim}7.5$ ps with temperature above 220 K. A Rothwarf-Taylor model was employed to fit the temperature-dependent relaxation time, and a narrow energy gap of $\ensuremath{\sim}35\ifmmode\pm\else\textpm\fi{}6$ meV is obtained, which occurs around the Dirac node. Our THz spectroscopy results demonstrate that the photocarrier relaxation in ${\mathrm{Cd}}_{3}{\mathrm{As}}_{2}$ shows a semiconductorlike behavior, rather than hot-carrier scatterings in graphene and most of metals.

Combined Triboelectric and Piezoelectric Effect in ZnO/PVDF Hybrid-Based Fiber-Structured Nanogenerator with PDMS:Carbon Black Electrodes.

We report a fiber-structured hybrid nanogenerator wearable device fabricated on a single polyethylene terephthalate (PET) textile cylindrical substrate. The device can be described as a capacitor with inner and outer carbon-black-dispersed poly dimethyl siloxane (PDMS:Carbon black) electrodes, and zinc oxide and polyvinylidene fluoride (PVDF) as the dielectric medium between the electrodes. The compositional analysis in terms of X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy of the synthesized ZnO/PVDF has been measured and analyzed. The combined effect of triboelectricity between PDMS:Carbon black and PVDF, and piezoelectricity in a ZnO/PVDF hybrid, was investigated. Current–voltage characteristics were observed with varying load from 0–20 g, and resistance was observed to be decreased with load. Compared to earlier reports, there was a significant enhancement in voltage (≈5.1 V) and current (≈92.5 nA) at 10 g. Due to the introduction of interfacial polarization between PVDF and ZnO, the piezoelectric properties and pressure sensitivity of the hybrid ZnO/PVDF is enhanced. The hysterical behavior in the device’s response while measuring voltage and current with varying time shows the signature of the triboelectric effect between PVDF and ZnO, as well as PDMS:Carbon black and ZnO/PVDF layers. Reduction of triboelectric behavior was confirmed with increasing relaxation time. Because of the enhancement in piezoelectricity, fiber-structured nanogenerator (FNG) ZnO/PVDF proved to a potential candidate to be used for wearable computing devices, such as smart watches and sports bracelets.

Very low levels of n-butyl acrylate comonomer strongly affect residual stress relaxation in styrene/acrylic random copolymer films

Processing-induced residual stresses in polymer films can cause microscopic defects and macroscopic dimensional changes. Although stress relaxation behavior of polymer films has been studied for several decades, little work has addressed random copolymers. We probed the residual stress relaxation in non-equilibrated random copolymer films of styrene (S) and n-butyl acrylate (nBA) using two optical techniques, ellipsometry and fluorescence. Both techniques show that incorporation of very low levels of nBA (2 mol% to 5 mol%) in S/nBA random copolymers can lead to dramatic increases in stress relaxation time of copolymer films relative to neat polystyrene films. For example, relative to polystyrene, the bulk-film stress relaxation time at 130 °C of 95/5 mol% S/nBA copolymer increases by factors of at least six as determined by ellipsometry and three as determined by fluorescence. Nanoconfined, 25-nm-thick films exhibit similar differences. This work provides implications for how low comonomer levels may deleteriously affect stress relaxation in polymer films, and we highlight that these findings are important for applications in which thin polymer films are required.

The propagation characteristics of particle-laden two-phase detonation waves in pyrolysis mixtures of C(s)/H2/CO/CH4/O2/N2

In this paper, numerical simulations are carried out to study the propagation characteristics of detonation waves in carbon particle-laden two-phase pyrolysis mixtures consisting of C(s)/H2/CO/CH4/O2/N2. The results show that the hydrodynamic thickness of the detonation waves changes non-monotonically with the carbon particle mass loading ratio and particle diameter. Both the aerodynamic relaxation time and heterogeneous reaction time increase drastically by enlarging the carbon particles. Small particles with the diameter of less than 1 μm gather and then react near the detonation front, which significantly enhances the propagation velocity of the detonation waves. Under such conditions, the aerodynamic relaxation time scale is smaller than the detonation wave characteristic time scale, which causes both the velocities and temperatures of gas and particles to reach the maximum values at the detonation front. However, such effects diminish gradually as the particles enlarge in size. The investigations show that 50 μm-sized particles have almost no effect on the detonation wave, for which the aerodynamic relaxation and heterogeneous reaction time scales are considerably larger than the detonation wave characteristic time scale. The propagation velocity of the detonation wave in the presence of 50 μm-sized particles is close to the value of the gaseous case. The results also show that increasing the particle mass loading ratio induces nonlinear changes in the detonation propagation velocity, due to changes in the global equivalence ratio of the two-phase mixtures.

Thermal Convection for an Oldroyd-B Fluid in an Anisotropic Porous Medium Underlying a Fluid Layer

Abstract We investigate the thermal convection in a fluid layer overlying an anisotropic porous medium with Oldroyd-B fluids in the paper. The linear stability analysis and the Chebyshev pseudo-spectral method are used to obtain the numerical results. We found that the neutral curves are bimodal at some depth ratios. The proper values of the permeability ratio and the thermal diffusivity ratio are found to stabilize the stationary convection and the oscillatory convection. Furthermore, the variation of permeability ratio does not affect the bimodal nature of the neutral curves. In addition, the increase in the stress relaxation time has an unstable effect on the oscillatory convection, but the strain retardation time has the opposite effect.