Dissipation Strength Research Articles

Probing postsaddle nuclear dissipation with excitation energy at scission

Using the stochastic Langevin model coupled with a statistical decay model, we study postsaddle dissipation properties in fission by analyzing the excitation energy at scission (${E}_{\mathrm{sc}}^{*}$) measured in fissioning nuclei $^{179}\mathrm{Re}$ and $^{254,256}\mathrm{Fm}$. The postsaddle dissipation strength ($\ensuremath{\beta}$) required to fit ${E}_{\mathrm{sc}}^{*}$ data is found to be larger for $^{254,256}\mathrm{Fm}$ than light $^{179}\mathrm{Re}$ which has a smaller postsaddle deformation compared to heavy $^{254,256}\mathrm{Fm}$, showing a rise of nuclear dissipation strength at a greater deformation. Furthermore, we explore the influence of initial excitation energy of a fissioning system $^{246}\mathrm{Cf}$ on the sensitivity of its ${E}_{\mathrm{sc}}^{*}$ to $\ensuremath{\beta}$, and find that the sensitivity is significantly enhanced with increasing the initial excitation energy. Our finding suggests that, on the experimental side, to more accurately probe the postsaddle dissipation strength through the measurement of ${E}_{\mathrm{sc}}^{*}$, it is best to yield those fissioning systems with high energy.

Effects of ionization and ion loss on dust ion-acoustic solitary waves in a collisional dusty plasma with suprathermal electrons

The combined effects of ionization, ion loss, and electron suprathermality on dust ion-acoustic solitary waves in a collisional dusty plasma are examined. Carrying out a small but finite amplitude analysis, a damped Korteweg-de Vries (dK–dV) equation is derived. The damping term decreases with the increase of the spectral index and saturates for Maxwellian electrons. Choosing typical plasma parameters, the analytical approximate solution of the dK-dV equation is numerically analyzed. We first neglect the ionization and ion loss effects and account only for collisions to estimate the relative importance between these damping terms which can act concurrently. Interestingly, we found that as the suprathermal character of the electrons becomes important, the strength of the collisions related dissipation becomes more important and causes the dust ion-acoustic solitary wave amplitude to decay more rapidly. Moreover, the collisional damping may largely prevail over the ionization and ion loss related damping. The latter becomes more effective as the electrons evolve far away from their thermal equilibrium. Our results complement and provide new insights into previously published work on this problem.

Primordial non-Gaussianity in warm inflation using δ N formalism

The δ N formalism is used to study the non-Gaussianity of the primordial curvature perturbation on an uniform density hypersurfaces generated by the warm inflation for the first time. After introducing the framework of warm inflation and δ N formalism, we obtain an analytic expression for the nonlinear parameter fNL that describes the non-Gaussianity in slow roll approximation, and find that the δ N formalism gives a very good result. We analyse the magnitude of fNL and compare our result with those of the standard inflation. Then we discuss two concrete examples: the quartic chaotic model and the hilltop model. The quartic potential model can again be in very good agreement with the Planck results in the warm inflationary scenario, and we give out the concrete results of how the nonlinear parameter depends on the dissipation strength of the warm inflation and the amounts of expansion. We find that the range of the nonlinear parameters in these two cases are both well inside of the allowed region of Planck.

Formation and stellar spin-orbit misalignment of hot Jupiters from Lidov–Kozai oscillations in stellar binaries

Observed hot Jupiter (HJ) systems exhibit a wide range of stellar spin-orbit misalignment angles. The origin of these HJs remains unclear. This paper investigates the inward migration of giant planets due to Lidov-Kozai (LK) oscillations induced by a distant (100-1000 AU) stellar companion. We conduct a large population synthesis study, including the octupole gravitational potential from the stellar companion, mutual precession of the host stellar spin axis and planet orbital axis, tidal dissipation in the planet, and stellar spin-down in the host star due to magnetic braking. We consider a range of planet masses ($0.3-5\,M_J$) and initial semi-major axes ($1-5$AU), different properties for the host star, and varying tidal dissipation strengths. The fraction of systems that result in HJs depends on planet mass and stellar type, with $f_{\rm HJ} = 1-4\%$ (depending on tidal dissipation strength) for $M_p=1\,M_J$, and larger (up to $8\%$) for more massive planets. The production efficiency of "hot Saturns" ($M_p=0.3M_J$) is much lower, because most migrating planets are tidally disrupted. We find that the fraction of systems that result in either HJ formation or tidal disruption, $f_{\rm mig} \simeq 11-14\%$ is roughly constant, having little variation with planet mass, stellar type and tidal dissipation strength. This "universal" migration fraction can be understood qualitatively from analytical migration criteria based on the properties of octupole LK oscillations. The distribution of final HJ stellar obliquities exhibits a complex dependence on the planet mass and stellar type. For $M_p = (1-3)M_J$, the distribution is always bimodal, with peaks around $30^{\circ}$ and $130^{\circ}$. The distribution for $5M_J$ planets depends on host stellar type, with a preference for low obliquities for solar-type stars, and higher obliquities for more massive ($1.4M_{\odot}$) stars.

Dissipation strength of the tilting degree of freedom in fusion-fission reactions

The four-dimensional Langevin model was applied to calculate a wide set of experimental observables for compound nuclei, formed in heavy-ion fusion-fission reactions. A modified one-body mechanism for nuclear dissipation with a reduction coefficient ks of the contribution from a ”wall” formula was used for shapes parameters. Different possibilities of deformation-dependent dissipation coefficient for the K coordinate (γK) were investigated. Presented results demonstrate that the influence of the ks and γK parameters on the calculated quantities can be selectively probed. It was found that it is possible to describe experimental data with the deformation-dependent γK coefficient. One of the possibility is to use large values of γK � 0.2 (MeV zs) −1/2 for compact shapes featuring no neck and small values of γK � 0.0077 (MeV zs) −1/2 for elongated shapes. Fission still is one of the most interesting and challenging topics in nuclear physics providing a perfect opportunity to investigate the large scale evolution of initial compound nucleus into fission products. During the past two decades stochastic approach based on multidimensional Langevin equations has been extensively and rather successfully used to elucidate many problems of collective nuclear dynamics in fusion-fission reactions at high excitation energies [1, 2]. A reasonable choice of collective degrees of freedom for modeling shape evolution and considering particle evaporation allow modeling the complex interplay between static and dynamical effects in fission and succeeding in explaining a wide range of experimental data [3, 4].

Global regularity of logarithmically supercritical 3-D LAMHD-alpha system with zero diffusion

We study the three-dimensional Lagrangian-averaged magnetohydrodynamics-alpha system with zero diffusion. Despite the dissipation strength at the logarithmically supercritical level, using dyadic decomposition techniques we show that given initial data sufficiently smooth, the solution pair remains smooth for all time. This settles the global regularity case suggested by the authors in [27].

Seismic behavior of steel reinforced concrete (SRC) joints with new-type section steel under cyclic loading

No significant improvement has been observed on the seismic performance of the ordinary steel reinforced concrete (SRC) columns compared with the reinforced concrete (RC) columns mainly because I, H or core cross-shaped steel cannot provide sufficient confinement for core concrete. Two improved SRC columns by constructing with new-type section steel were put forward on this background: a cross-shaped steel whose flanges are in contact with concrete cover by extending the geometry of webs, and a rotated cross-shaped steel whose webs coincide with diagonal line of the column's section. The advantages of new-type SRC columns have been proved theoretically and experimentally, while construction measures and seismic behavior remain unclear when the new-type columns are joined onto SRC beams. Seismic behavior of SRC joints with new-type section steel were experimentally investigated by testing 5 specimens subjected to low reversed cyclic loading, mainly including the failure patterns, hysteretic loops, skeleton curves, energy dissipation capacity, strength and stiffness degradation and ductility. Effects of steel shape, load angel and construction measures on seismic behavior of joints were also analyzed. The test results indicate that the new-type joints display shear failure pattern under seismic loading, and steel and concrete of core region could bear larger load and tend to be stable although the specimens are close to failure. The hysteretic curves of new-type joints are plumper whose equivalent viscous damping coefficients and ductility factors are over 0.38 and 3.2 respectively, and this illustrates the energy dissipation capacity and deformation ability of new-type SRC joints are better than that of ordinary ones with shear failure. Bearing capacity and ductility of new-type joints are superior when the diagonal cross-shaped steel is contained and beams are orthogonal to columns, and the two construction measures proposed have little effect on the seismic behavior of joints.

Dynamics of a Landau–Zener transitions in a two-level system driven by a dissipative environment

The paper investigates the effects of a two-level quantum system coupled to transversal and longitudinal dissipative environment. The time-dependent phase accumulation, LZ transition probability and entropy in the presence of fast-ohmic, sub-ohmic and super-ohmic quantum noise are derived. Analytical results are obtained in terms of temperature, dissipation strength, LZ parameter and bath cutoff frequency. The bath is observed to modify the standard occupation difference by a decaying random phase factor and also produces dephasing during the transfer of population. The dephasing characteristics or the initial non-zero decoherence rate are observed to increase in time with the bath temperature and depend on the system-bath coupling strength and cutoff frequency. These parameters are found to strongly affect the memory and thus tailor the coherence process of the system.

Relaxation times of dissipative many-body quantum systems.

We study relaxation times, also called mixing times, of quantum many-body systems described by a Lindblad master equation. We in particular study the scaling of the spectral gap with the system length, the so-called dynamical exponent, identifying a number of transitions in the scaling. For systems with bulk dissipation we generically observe different scaling for small and for strong dissipation strength, with a critical transition strength going to zero in the thermodynamic limit. We also study a related phase transition in the largest decay mode. For systems with only boundary dissipation we show a generic bound that the gap cannot be larger than ∼1/L. In integrable systems with boundary dissipation one typically observes scaling of ∼1/L(3), while in chaotic ones one can have faster relaxation with the gap scaling as ∼1/L and thus saturating the generic bound. We also observe transition from exponential to algebraic gap in systems with localized modes.

Disentangling geometric and dissipative origins of negative Casimir entropies.

Dissipative electromagnetic response and scattering geometry are potential sources for the appearance of a negative Casimir entropy. We show that the dissipative contribution familiar from the plane-plane geometry appears also in the plane-sphere and the sphere-sphere geometries and adds to the negative Casimir entropy known to exist in these geometries even for perfectly reflecting objects. Taking the sphere-sphere geometry as an example, we carry out a scattering-channel analysis, which allows us to distinguish between the contributions of different polarizations. We demonstrate that dissipation and geometry share a common feature making possible negative values of the Casimir entropy. In both cases there exists a scattering channel whose contribution to the Casimir free energy vanishes in the high-temperature limit. While the mode-mixing channel is associated with the geometric origin, the transverse electric channel is associated with the dissipative origin of the negative Casimir entropy. By going beyond the Rayleigh limit, we find even for large distances that negative Casimir entropies can occur also for Drude-type metals provided the dissipation strength is sufficiently small.

Role of hoops on seismic performance of reinforced concrete joints

Four exterior reinforced concrete beam–column joint specimens with varying amounts of joint hoop reinforcement are constructed and tested under reverse cyclic loading to assess their performance during earthquakes. Headed bars are used in all the specimens. Various parameters such as crack pattern, hysteresis behaviour, modes of failure, energy dissipation, displacement ductility, stiffness degradation and maximum shear strength are studied. The effectiveness of headed bars with short embedded length terminating in the exterior beam–column joint is assessed. As headed bars have the advantage of transferring a more uniform distribution of compressive stress to the concrete at the headed end, they enable the development of a wider compressive strut in the joint, which enhances the joint shear strength under seismic loading. This makes it possible to reduce transverse reinforcement in joints when using headed bars as longitudinal beam reinforcement.

Role of hoops on seismic performance of reinforced concrete joints

Four exterior reinforced concrete beam–column joint specimens with varying amounts of joint hoop reinforcement are constructed and tested under reverse cyclic loading to assess their performance during earthquakes. Headed bars are used in all the specimens. Various parameters such as crack pattern, hysteresis behaviour, modes of failure, energy dissipation, displacement ductility, stiffness degradation and maximum shear strength are studied. The effectiveness of headed bars with short embedded length terminating in the exterior beam–column joint is assessed. As headed bars have the advantage of transferring a more uniform distribution of compressive stress to the concrete at the headed end, they enable the development of a wider compressive strut in the joint, which enhances the joint shear strength under seismic loading. This makes it possible to reduce transverse reinforcement in joints when using headed bars as longitudinal beam reinforcement.

Fusion measurements for the O+ reaction and search for neutron shell closure effects

Evaporation residue (ER) and fission cross sections were measured for the reaction O+ forming the compound nucleus 212Rn. Fission fragment angular distributions and anisotropies are consistent with the saddle point model predictions. Measured ER cross sections were fitted with statistical model calculations assuming shell-corrected free energy fission barrier height. The non-zero dissipation strength required to fit the ER cross section supports the dissipative nature of fission dynamics in heavy ion fusion. In the present study shell closure effects are not observed in the dissipation strength.

Time Dependence of Entropy Flux and Entropy Production for a Time-Delayed Dynamical System Driven by Cross-Correlated Noises

We study the relaxation of a dissipative dynamical system with time delay and cross-correlated noises in the absence and presence of a non-equilibrium constraint in terms of the information entropy flux and production for the case of small delays. Based on the delay Fokker-Planck equation and the entropy balance equation, the time dependence of the entropy flux and entropy production of the system is derived when the delay time is small. Our calculation shows how the relaxation time depends on the delay time. We also consider how the non-equilibrium constraint is affected by the system parameters, such as the cross-correlation intensity, strength of dissipation, and delay time. The interplay among the non-equilibrium constraint, dissipation, time delay, and inter-correlated noises reveals some interesting extremal nature in the time dependence of the entropy flux and entropy production.

Shear zone broadening controlled by thermal pressurization and poroelastic effects during model earthquakes

AbstractAs a result of the comminution that takes place over numerous earthquake cycles, mature faults are characterized by thick layers of pulverized gouge with finite porosity that is saturated with water at seismogenic depths. The heat generated during earthquakes raises the gouge temperature and thermal expansion of the pore fluid, and surrounding solids produce elevated pore pressures that cause fault strength to decrease in the process known as thermal pressurization. Building upon this framework, we describe a model that imposes a plane‐strain configuration and shows that the stress variations caused by porothermoelasticity promote the Mohr‐Coulomb failure of previously undeformed regions. Except in special cases where the friction is rate strengthening, we find that the frictional strength must vary throughout the post‐failure region, which we identify in our model with the shear zone. We introduce a strain rate function that describes the overall influence of distributed slip on energy dissipation and fault strength as the shear zone thickness expands. Using typical fault parameters at 7 km depth, the shear zone reaches several millimeters of thickness after 1 s sliding at an overall rate of 1 m/s. The expansion of the shear zone limits the temperature rise to several hundred degrees Celsius, and the average fault strength falls to about a tenth of the static frictional strength.

Spallation reaction versus heavy-ion fusion: Fission excitation functions as a fundamental probe of presaddle nuclear dissipation

Due to nuclear dissipation, fission cross sections drop with respect to standard statistical model predictions. Using the stochastic dynamical model of fission, we calculate the drop of fission cross sections, ${\ensuremath{\sigma}}_{f}^{\mathrm{drop}}$, as a function of presaddle dissipation strength ($\ensuremath{\beta}$) under two contrasting initial conditions for produced $^{224}\mathrm{Th}$ compound nuclei: (i) high excitation energy but low angular momentum (available in spallation reactions) and (ii) low excitation energy but high angular momentum (available in heavy-ion fusion). We find that the former type of conditions not only significantly increases the influence of friction on fission cross sections but also substantially enhances the sensitivity of ${\ensuremath{\sigma}}_{f}^{\mathrm{drop}}$ to $\ensuremath{\beta}$. Our findings suggest that on the experimental side, to accurately obtain information of presaddle friction strength with fission excitation function, it is optimal to choose the spallation reaction approach induced by energetic protons as a way to populate excited nuclear systems.

Dissipation-induced first-order decoherence phase transition in a noninteracting fermionic system

We consider a quantum wire connected to the leads and subjected to dissipation along its length. The dissipation manifests as tunneling into (out of) the chain from (to) a memoryless environment. The evolution of the system is described by the Lindblad equation. Already infinitesimally small dissipation along the chain induces a quantum phase transition (QPT). This is a decoherence QPT: the reduced density matrix of a subsystem in the nonequilibrium steady state (far from the ends of the chain) can be represented as the tensor product of single-site density matrices. The QPT is identified from the jump of the current and the entropy per site as the dissipation becomes nonzero. We also explore the properties of the boundaries of the chain close to the transition point and observe that the boundaries behave as if they undergo a second-order phase transition as a function of the dissipation strength: the particle-particle correlation functions and the response to the electric field exhibit a power-law divergence. Disorder is known to localize one-dimensional systems, but the coupling to the memoryless environment pushes the system back into the delocalized state even in the presence of disorder. Interestingly, we observe a similar transition in the classical dissipative counterflow model: the current has a jump at the ends of the chain introducing an infinitely small dissipation.

Probing nuclear dissipation via evaporation residue excitation functions for theO16,18+Pt198reactions

Evaporation residue (ER) cross sections for the $^{16,18}\mathrm{O}+^{198}\mathrm{Pt}$ reactions are measured in order to investigate fission hindrance. Compound nuclei ($^{214,216}\mathrm{Rn}$) are formed in the above fusion reactions at excitation energies in the range of 40--68 MeV. The experimental ER cross sections are compared with predictions from the statistical model calculations of compound nuclear decay where Kramers' fission width is used. The strength of nuclear dissipation is treated as a free parameter in the statistical model calculations in order to fit the experimental data.

Qubit interference at avoided crossings: The role of driving shape and bath coupling

We derive the structure of the Landau-Zener-St\"uckelberg-Majorana (LZSM) interference pattern for a qubit that experiences quantum dissipation and is additionally subjected to time-periodic but otherwise general driving. A spin-boson Hamiltonian serves as model which we treat with a Bloch-Redfield master equation in Floquet basis. It predicts a peak structure that depends sensitively on the operator through which the qubit couples to the bath. The Fourier transforms of the LZSM patterns exhibit arc structures which reflect the shape of the driving. These features are captured by an effective time-independent Bloch equation which provides an analytical solution. Moreover, we determine the decay of these arcs as a function of dissipation strength and temperature.

Primordial non-Gaussianity in noncanonical warm inflation

We study the bispectrum of the primordial curvature perturbation on uniform-density hypersurfaces generated by a kind of the noncanonical warm inflation, wherein the inflation is provided by a noncanonical scalar inflaton field that is coupled to radiation through a thermal dissipation effect. We obtain an analytic form for the nonlinear parameter $f_{NL}$ that describes the non-Gaussianity in first-order cosmological perturbation theory and analyse the magnitude of this nonlinear parameter. We make a comparison between our result and those of the standard inflation and the canonical warm inflation. We also discuss when the contribution to the non-Gaussianity due to the second-order perturbation theory becomes more important and what effect can be observed. We take the Dirac-Born-Infeld (DBI) inflation as a concrete example to find how the sound speed and the thermal dissipation strength to decide the non-Gaussianity and to get a lower bound of the sound speed constrained by PLANCK.