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In this manuscript, we have continued the work of Herrera et al. (Gen. Relativ. Gravit. 44, 1143, 2012) to investigate the instability of non-static spheres supported by anisotropic matter configuration in the background of D-dimensional Einstein gravity. For this purpose, we assume that our relativistic sphere undergoes adiabatic evolution with a vanishing expansion scalar condition. We compute gravitational field equations, conservation equations, and junction conditions in D-dimensional Einstein theory. After considering the evolution of the systems under an expansion-free background, some significant constraints are established by using a perturbation scheme. This leads us to develop the dynamical instability of expansion-free anisotropic fluid spheres in the Newtonian (N) and Post-Newtonian (PN) domains. After focusing on the N and PN eras, our study reveals that the adiabatic index (Γ ), does not contribute to the instability ranges in these domains. Instead, these ranges are being determined solely by the anisotropy of fluid pressure, D-dimensional Einstein gravity parameter, and the radial energy density profile. [ABSTRACT FROM AUTHOR]

Electrically charged anisotropic fluid spheres with vanishing expansion scalar condition under the influence of a newly established gravitational scheme are investigated in this study, i.e., 4D$4\textsf {D}$ Einstein‐Gauss‐Bonnet (EGB) gravity. Glavan and Lin introduced this framework, in which they rescaled the coupling factor α$\alpha$ using αD−4$\frac{\alpha }{D-4}$ and derived the gravitational field equations. The work of Herrera et al. is extended to explore the dynamical instability of charged spherically symmetric matter distribution in the context of 4D$4\textsf {D}$ EGB gravity. In this respect, dynamical equations, conservation equations, and junction conditions for charged sphere are computed. To study the evolution of considered system in the Newtonian and post‐Newtonian regimes against an expansion‐free background, several substantial restrictions are imposed employing a perturbation approach. This study showed that the adiabatic index (Γ$\Gamma$) has no effect on the instability ranges in the aforementioned approximations. It is analyzed that the determination of these ranges solely attributed to the anisotropy of fluid surface pressures, radial profile, 4D$4\textsf {D}$ EGB factors, and charged intensity parameters along with the radial distribution of energy density. Electrically charged anisotropic fluid spheres with vanishing expansion scalar condition under the influence of a newly established gravitational scheme are investigated in this study, i.e., 4D Einstein‐Gauss‐Bonnet (EGB) gravity. Glavan and Lin introduced this framework, in which they rescaled the coupling factor α using α/(D‐4) and derived the gravitational field equations. The work of Herrera et al. is extended to explore the dynamical instability of charged spherically symmetric matter distribution in the context of 4D EGB gravity. In this respect, dynamical equations, conservation equations, and junction conditions for charged sphere are computed. To study the evolution of considered system in the Newtonian and post‐Newtonian regimes against an expansion‐free background, several substantial restrictions are imposed employing a perturbation approach. This study showed that the adiabatic index (Γ) has no effect on the instability ranges in the aforementioned approximations. It is analyzed that the determination of these ranges solely attributed to the anisotropy of fluid surface pressures, radial profile, 4D EGB factors, and charged intensity parameters along with the radial distribution of energy density. [ABSTRACT FROM AUTHOR]

This work is related to the stability of a nonstatic, very restricted class of axially symmetric cosmic matter configuration under the influence of modified gravitational theory (AGT) with a realistic model in anisotropic conditions. We construct dynamically modified equations, continuity equations, mass functions and collapse equations in the scenario of considered AGT. We continue our analysis under the influence of f(R,T) gravity along with a minimally coupled gravitational function of the form f (R , T) = R + β R c (1 − (1 + R 2 R c 2 ) − n) + λ T , where R c indicates constant entity. In this gravitational model, f is a function of Ricci scalar invariant R and the trace of the stress–energy tensor T. This gravitational function gives significant findings only for β > 0 , n > 0 , and both belong to the set of positive real numbers and also λ ≪ 1. We establish expressions of an adiabatic index, i.e. stiffness parameter of fluid (Γ) utilizing relevant perturbation technique with the help of collapse equation in Newtonian (ℕ) and post-Newtonian (ℙ ℕ) domains. We consider the particular form of metric as well as material functions in (ℕ) and (ℙ ℕ) eras, and impose some constraints on physical quantities (i.e. pressure, density, mass, etc.) to carry out the stable behavior of a considered restricted geometry. [ABSTRACT FROM AUTHOR]

We analyzed the C-structures in the mesospheric metal layers. We used two datasets: one from a narrow band Sodium (Na) Density and Temperature LIDAR and the other from a high-resolution dual band Na and Potassium (K) LIDAR, both operated at São José dos Campos, Brazil (23° S, 46° W). We also investigated the Es layer occurrence and wind shear influences forming these structures. We found three C-type events over 82 analyzed nights in the first data set. They all showed lower temperatures inside C-structures compared to the borders. The squared Brunt-Väissälä frequency analyses showed positive values in the region of C-structures. In two out of three cases, dynamical instability was present (Ri < 0.25). We compared these results with the nine simultaneous C-type events identified in the 185 nights from the second data set. They showed height and time simultaneity correspondence as observed in the Na and K layers. Our results showed a low correlation between Es occurrence and C-structures. Additionally, strong wind shears in the altitude and time where C-structures appeared were always present. The advection of a metal cloud to the LIDAR station and a wind distortion seems to be the plausible mechanism that can explain all the observations. [ABSTRACT FROM AUTHOR]

This paper deals with stability analysis of anisotropic-charged cylindrical geometry coupled with f (R , T) modified gravity theory (ℳ ). In this ℳ , the Lagrangian is a varying function of traces of Ricci and stress tensors. In order to examine the stable behavior of the anisotropic cylindrical cosmic object under the electromagnetic effects, we calculated the modified equations of motion and equations of continuity. in the background of f (R , T) theory. By utilizing the perturbation technique, we constitute a modified collapse equation (ℳ ℰ), which contains geometrical and physical variables in the charged scenario. Our investigation continues under the nonminimally coupled function of ℳ . Furthermore, we investigate the dynamically stable phases of charged geometry at Newtonian () and post-Newtonian (p ) epochs with the help of the rigidity parameter of fluid (Γ) by imposing some constraints on physical parameters. [ABSTRACT FROM AUTHOR]

While the glass transition is easy to identify macroscopically, the underlying atomic mechanisms which facilitate the transition from amorphous solid to fluid are still poorly understood. We conduct classical molecular dynamics simulations on a variety of inorganic glasses in order to identify these mechanisms. While also modelling larger systems, we find that the essential qualities which constitute a glass and its transition to a liquid are present even in systems containing only a few hundred atoms. The transition is therefore a local phenomenon. Atomic mobility, the ability of an atom to escape its local coordination environment, is identified as a universal marker of the glass transition. In the solid state, the fraction of mobile atoms is negligible, whereas in the liquid state, effectively all atoms are mobile. The glass transition is continuous between these limiting states, with half of the network forming atoms attaining mobility exactly at the glass transition temperature, over a specific mobility half life, informed by thermodynamics. Over time, network forming atoms which were immobile may swap to become mobile and vice versa, though the population of mobile atoms remains a half., (Creative Commons Attribution license.)

This paper aims to investigate the stability constraints under the influence of particular modified gravity theory , i.e. f (R , T) gravity in which the Lagrangian is a varying function of R and trace of energy momentum tensor (T). We examine stable behavior for compact cylindrical star having anisotropic symmetric configuration. We establish dynamical equations as well as equations of continuity in the background of this particular non-minimal coupled . We utilize perturbation technique which will be applied on geometrical as well as material physical quantities to constitute collapse equation. We continue this significant investigation to understand the dynamical behavior of considered cylindrical system under non-minimal coupled f (R , T) functional, i.e. f (R , T) = R + ξ R c [ 1 − { 1 + R 2 R c 2 } − n ] + λ R T. This gravitational function gives compatible findings only for ξ > 0 , n ∈ R + , also 0 < λ ≪ 1 and λ R T considered in this astrophysical model as coupling entity. This model contains R c which is constant entity, having the values of order of the effective Ricci scalar R. Furthermore, we impose some physical constraints to determine and maintain the stability criteria by establishing the expression of adiabatic index, i.e. Γ for cylindrical anisotropic configuration, in Newtonian (N) and post-Newtonian (p N) eras. [ABSTRACT FROM AUTHOR]

The existence of Chandrasekhar’s limit has played various decisive roles in astronomical observations for many decades. However, various recent theoretical investigations suggest that gravitational collapse of white dwarfs is withheld for arbitrarily high masses beyond Chandrasekhar’s limit if the equation of state incorporates the effect of quantum gravity via the generalized uncertainty principle. There have been a few attempts to restore the Chandrasekhar limit but they are found to be inadequate. In this paper, we rigorously resolve this problem by analysing the dynamical instability in general relativity. We confirm the existence of Chandrasekhar’s limit as well as stable mass–radius curves that behave consistently with astronomical observations. Moreover, this stability analysis suggests gravitational collapse beyond the Chandrasekhar limit signifying the possibility of compact objects denser than white dwarfs.

Newtonian gravity predicts the existence of white dwarfs with masses far exceeding the Chandrasekhar limit when the equation of state of the degenerate electron gas incorporates the effect of quantum spacetime fluctuations (via a modified dispersion relation) even when the strength of the fluctuations is taken to be very small. In this paper, we show that this Newtonian "super-stability" does not hold true when the gravity is treated in the general relativistic framework. Employing dynamical instability analysis, we find that the Chandrasekhar limit can be reassured even for a range of high strengths of quantum spacetime fluctuations with the onset density for gravitational collapse practically remaining unaffected. [ABSTRACT FROM AUTHOR]

Highlights • Diagnostic investigation of an extreme rainfall event is carried out over central and Northern Indian region. • Implication of tropical-extratropical interactions to severe weather is highlighted. • The role of dynamical and thermodynamical instabilities in triggering the extreme event is discussed. Abstract A diagnostic investigation of an extreme rainfall episode that occurred over the central and north Indian region is carried out in this study using data from a suite of observations from space-borne instruments and the reanalysis datasets. This event is unique in the sense that the organized tropical and extratropical forcing stimulated the intense rainfall on 01 Jan 2012. The WindSat (multi-frequency polarimetric microwave radiometer) observations indicate the source of the moisture flux coming from the adjoining tropical Ocean. The dynamical and thermo-dynamical contributions are evaluated based on the atmospheric instability analysis using the Atmospheric Infrared Sounder (AIRS) and reanalysis datasets by computing various stability indices such as total totals (TT) index, Potential Vorticity (PV), static stability and the Convective Available Potential Energy (CAPE). High TT index values (>40 K) are observed both in satellite and reanalysis data indicating thermodynamic instability. PV intrusion to low latitudes is also observed with extreme rainfall occurrence ahead of the PV tongue. The vertical structure of PV intrusion shows remarkable features with enhanced upward motions ahead of the intrusion representing the dynamical instability. The reduced static stability, increased CAPE and upper-level cyclonic anomalies together with enhanced moisture in the lower troposphere coming from the adjoining tropical Indian Ocean regulate the amplitude and region of occurrence of the extreme rainfall. Therefore, this study identifies the significant implications of tropical and extra-tropical influences that generate the thermodynamical and dynamical instabilities for the occurrence of the extreme rainfall event over the Central and Northern parts of India. [ABSTRACT FROM AUTHOR]

We investigate the effects of Zeeman field on the dynamical instability of flat states for F = 2 spinor Bose–Einstein condensates in an optical lattice. The instability criteria for the ferromagnetic, uniaxial nematic, biaxial nematic-like and cyclic-like states are obtained analytically. It is shown that the linear Zeeman splitting shift only changes the dynamical instability of the biaxial nematic-like phase, but the quadratic Zeeman splitting shift can stabilize or induce additional dynamical instability to all the phases except the first-type ferromagnetic phase. The interaction strength of the spin–singlet pair term can change the dynamical instability of the cyclic-like state only when the quadratic Zeeman splitting is included. We also provide the experimental parameters to observe these interesting phenomena in future experiments. [ABSTRACT FROM AUTHOR]

First-principles calculations are employed to determine the mechanical properties of rock-salt structure binary and ternary transition metal nitrides, carbides, and carbonitrides from groups 4 to 12, predicting a unified indicator for mechanical properties: the valence electron concentration (VEC). Pugh's and Poisson's ratios indicate an increasing ductility with increasing VEC, with a brittle-to-ductile transition at a critical VEC = 10. The calculated C 44 of carbonitrides and ternary nitrides monotonically decreases from 164 ± 12 GPa at VEC = 8 to −39 ± 46 GPa at VEC = 11, indicating a transition to mechanical instability at VEC = 10.6. Similarly, the average isotropic elastic modulus decreases slightly from 420 GPa for VEC = 8 to 388 GPa for VEC = 10, but then steeply to −98 GPa for VEC = 11, while the corresponding hardness decreases from 25 to 12 to 2 GPa. The overall softening with increasing VEC is attributed to the increasing electron density in d – t 2g orbitals, which overlap upon shear and cause a decrease in C 44 . Phonon dispersion curves, calculated at 0 K for binary nitrides and carbides, exhibit imaginary frequencies for VEC ≥10, indicating a dynamical stability-to-instability transition between VEC = 9 and 10, which is smaller than the critical VEC = 10.6 for the mechanical stability-instability transition. In addition, mechanical stability is increased by magnetic ordering but decreased when accounting for on-site Coulomb repulsion, while temperature and vacancies cause a reduction in the magnitude of C 44 for both stable and unstable compounds, likely leading to an increase in the critical VEC for the stability-instability transition. The overall results indicate a narrow region between VEC = 9 and 10 where rocksalt carbonitrides are ductile but also exhibit a high hardness, mechanical and dynamical stability, and therefore are expected to exhibit the highest toughness. [ABSTRACT FROM AUTHOR]

The dynamical and energetic instabilities of the F = 2 spinor Bose–Einstein condensates in an optical lattice are investigated theoretically and numerically. By analyzing the dynamical response of different carrier waves to an additional linear perturbation, we obtain the instability criteria for the ferromagnetic, uniaxial nematic, biaxial nematic and cyclic states, respectively. When an external magnetic field is taken into account, we find that the linear or quadratic Zeeman effects obviously affect the dynamical instability properties of uniaxial nematic, biaxial nematic and cyclic states, but not for the ferromagnetic one. In particular, it is found that the faster moving F = 2 spinor BEC has a larger energetic instability region than lower one in all the four states. In addition, it is seen that for most states there probably exists a critical value k c > 0 , for which k > k c causes the energetic instability to arise under appreciative parameters. [ABSTRACT FROM AUTHOR]

Recently, we have revealed an intrinsic instability of metals due to surface plasma waves (SPWs) and raised the prospect of using it to create lossless SPWs. The counter-intuitive nature of this finding prompts one to ask, why had not this instability been disclosed before, given the long history of this subject? If this instability does exist, how far is it from reality? The present work is devoted to answering these questions. To this end, we derive a unified macroscopic theory of SPWs that applies to any type of electron dynamics, be they local or non-local, classical or quantum-mechanical. In light of this theory, we analyze the behaviors of SPWs according to several electron dynamics models, including the widely used local dielectric model, the hydrodynamic model and the specular reflection model, in addition to the less common semi-classical model. We find that, in order to unveil the instability, one must (i) self-consistently treat surface effects without any of the usually imposed auxiliary conditions and (ii) include translation symmetry breaking effects in electron dynamics. As far as we are concerned, none existing work had fulfilled both (i) and (ii). To assess the possibility of realizing the instability, we analyze two very important factors: the dielectric interfacing the metal and inter-band transitions, which both were ignored in our recent work. Whereas inter-band absorption—together with Landau damping—is shown adverse to the instability, a dielectric brings it closer to occurrence. One may even attain it in common plasmonic materials such as silver under not so tough conditions.

The dynamical stability and its connection with phase structures of binary Bose-Einstein condensates (BECs) are systematically studied within framework of the Gross-Pitaevskii (GP) theory. We find that (a) the dynamical stability is the main factor governing both the symmetry breaking and the formation of various phases associated with the scenarios: symmetry restoration (SR) and inverse symmetry breaking (ISB); (b) the condensation of Bose gases might occur at constant temperature for chemical potentials varying in some definite regions. We suggest how to experimentally observe the foregoing phenomena whose possible existences in nature are theoretically confirmed. [ABSTRACT FROM AUTHOR]

Abstract: A complex eigenvalue in the Bogoliubov–de Gennes equations for a stationary Bose–Einstein condensate in the ultracold atomic system indicates the dynamical instability of the system. We also have the modes with zero eigenvalues for the condensate, called the zero modes, which originate from the spontaneous breakdown of symmetries. Although the zero modes are suppressed in many theoretical analyses, we take account of them in this paper and argue that a zero mode can change into one with a pure imaginary eigenvalue by applying a symmetry breaking external perturbation potential. This emergence of a pure imaginary mode adds a new type of scenario of dynamical instability to that characterized by the complex eigenvalue of the usual excitation modes. For illustration, we deal with two one-dimensional homogeneous Bose–Einstein condensate systems with a single dark soliton under a respective perturbation potential, breaking the invariance under translation, to derive pure imaginary modes. [Copyright &y& Elsevier]

This report describes the impulsive dynamics of a system of two coupled oscillators with essential (nonlinearizable) stiffness nonlinearity. The system considered consists of a grounded weakly damped linear oscillator coupled to a lightweight weakly damped oscillating attachment with essential cubic stiffness nonlinearity arising purely from geometry and kinematics. It has been found that under specific impulse excitations the transient damped dynamics of this system tracks a high-frequency impulsive orbit manifold (IOM) in the frequency-energy plane. The IOM extends over finite frequency and energy ranges, consisting of a countable infinity of periodic orbits and an uncountable infinity of quasi -periodic orbits of the underlying Hamiltonian system and being initially at rest and subjected to an impulsive force on the linear oscillator. The damped nonresonant dynamics tracking the IOM then resembles continuous resonance scattering; in effect, quickly transitioning between multiple resonance captures over finite frequency and energy ranges. Dynamic instability arises at bifurcation points along this damped transition, causing bursts in the response of the nonlinear light oscillator, which resemble self-excited resonances. It is shown that for an appropriate parameter design the system remains in a state of sustained high-frequency dynamic instability under the action of repeated impulses. In turn, this sustained instability results in strong energy transfers from the directly excited oscillator to the lightweight nonlinear attachment; a feature that can be employed in energy harvesting applications. The theoretical predictions are confirmed by experimental results. [ABSTRACT FROM AUTHOR]

The onset of dynamical instabilities of Bose-Einstein condensates in optical lattices due to the dephasing of the condensate wavefunction is observed through the decay of the visibility of the interference pattern in time-of-flight and the growth of the radial width of the condensate. [ABSTRACT FROM AUTHOR]

The relationship between community diversity and biomass variability remains a crucial ecological topic, with positive, negative and neutral diversity-stability relationships reported from empirical studies. Theory highlights the relative importance of Species-Species or Species-Environment interactions in driving diversity-stability patterns. Much previous work is based on an assumption of identical (stable) species-level dynamics. We studied ecosystem models incorporating stable, cyclic and more complex species-level dynamics, with either linear or non-linear density dependence, within a locally stable community framework. Species composition varies with increasing diversity, interacting with the correlation of species' environmental responses to drive either positive or negative diversity-stability patterns, which theory based on communities with only stable species-level dynamics fails to predict. Including different dynamics points to new mechanisms that drive the full range of diversity-biomass stability relationships in empirical systems where a wider range of dynamical behaviours are important. [ABSTRACT FROM AUTHOR]

Abstract: An overview of the physics of spinor and dipolar Bose–Einstein condensates (BECs) is given. Mean-field ground states, Bogoliubov spectra, and many-body ground and excited states of spinor BECs are discussed. Properties of spin-polarized dipolar BECs and those of spinor–dipolar BECs are reviewed. Some of the unique features of the vortices in spinor BECs such as fractional vortices and non-Abelian vortices are delineated. The symmetry of the order parameter is classified using group theory, and various topological excitations are investigated based on homotopy theory. Some of the more recent developments in a spinor BEC are discussed. [Copyright &y& Elsevier]

Abstract: We have performed an ab initio study of structural, bonding, and vibrational properties of AgGaO2 and CuGaO2 delafossites. The calculations have been carried out within the density functional theory and linear response formalism using ultrasoft pseudopotentials and a plane wave basis. Structural properties of AgGaO2 and CuGaO2 are in very good agreement with experimental data, and zone centre phonons in CuGaO2 are in excellent agreement with experimental and previous DFT calculation. Two Raman-active modes, E g and A1g in AgGaO2 are found to have frequencies at 367cm−1 and 682cm−1 respectively. A noticeable difference between these calculated and experimentally observed Raman-active modes have been found. Calculated Raman-active modes have been further verified using atomic-orbital basis and norm-conserving pseudopotentials within finite displacement frozen phonon technique. We also present the phonon dispersion relations, phonon density of states, pressure-coefficients, and mode-Grüneisen parameters at high symmetry points in these oxides. Our DFT calculations predict dynamical instability, possibly related to phase transition around 17GPa in AgGaO2 delafossite. [Copyright &y& Elsevier]

Abstract: This paper explores how the surface permeability of sandstone blocks changes over time in response to repeated salt weathering cycles. Surface permeability controls the amount of moisture and dissolved salt that can penetrate in and facilitate decay. Connected pores permit the movement of moisture (and hence soluble salts) into the stone interior, and where areas are more or less permeable soluble salts may migrate along preferred pathways at differential rates. Previous research has shown that salts can accumulate in the near-surface zone and lead to partial pore blocking which influences subsequent moisture ingress and causes rapid salt accumulation in the near-surface zone. Two parallel salt weathering simulations were carried out on blocks of Peakmoor Sandstone of different volumes. Blocks were removed from simulations after 2, 5, 10, 20 and 60cycles. Permeability measurements were taken for these blocks at a resolution of 20mm, providing a grid of 100 permeability values for each surface. The geostatistical technique of ordinary kriging was applied to the data to produce a smoothed interpolation of permeability for these surfaces, and hence improve understanding of the evolution of permeability over time in response to repeated salt weathering cycles. Results illustrate the different responses of the sandstone blocks of different volumes to repeated salt weathering cycles. In both cases, after an initial subtle decline in the permeability (reflecting pore blocking), the permeability starts to increase — reflected in a rise in mean, maximum and minimum values. However, between 10 and 20cycles, there is a jump in the mean and range permeability of the group A block surfaces coinciding with the onset of meaningful debris release. After 60cycles, the range of permeability in the group A block surface had increased markedly, suggesting the development of a secondary permeability. The concept of dynamic instability and divergent behaviour is applied at the scale of a single block surface, with initial small-scale differences across a surface having larger scale consequences as weathering progresses. After cycle 10, group B blocks show a much smaller increase in mean permeability, and the range stays relatively steady — this may be explained by the capillary conditions set up by the smaller volume of the stone, allowing salts to migrate to the ‘back’ of the blocks and effectively relieving stress at the ‘front’ face. [Copyright &y& Elsevier]

Recently, it was shown that giant vortices with arbitrarily large quantum numbers can possibly created in dilute Bose-Einstein condensates by cyclically pumping vorticity into the condensate. However, multiply quantized vortices are typically dynamically unstable in harmonically trapped nonrotated condensates, which poses a serious challenge to the vortex pump procedure. In this theoretical study, we investigate how the giant vortices can be stabilized by the application of a Gaussian potential peak along the vortex core. We find that achieving dynamical stability is feasible up to high quantum numbers. To demonstrate the efficiency of the stabilization method, we simulate the adiabatic creation of an unsplit 20-quantum vortex with the vortex pump. [ABSTRACT FROM AUTHOR]

Abstract: We study the dynamics of a trapped Bose–Einstein condensate with a multiply-quantized vortex, and investigate the roles of the fluctuations in the dynamical evolution of the system. Using the perturbation theory of the external potential, and assuming the situation of the small coupling constant of self-interaction, we analytically solve the time-dependent Gross–Pitaevskii equation. We introduce the zero mode and its adjoint mode of the Bogoliubov–de Gennes equations. Those modes are known to be essential for the completeness condition. We confirm how the complex eigenvalues induce the vortex splitting. It is shown that the physical role of the adjoint zero mode is to ensure the conservation of the total condensate number. The contribution of the adjoint mode is exponentially enhanced in synchronism with the exponential growth of the complex mode, and is essential in the vortex splitting. [Copyright &y& Elsevier]

This paper investigates the dynamical instability and adiabatic evolution of the atom-homonuclear-trimer dark state of a condensate system in a stimulated Raman adiabatic passage aided by Feshbach resonance. It obtains analytically the regions for the appearance of dynamical instability caused by the interparticle interactions. Moreover, the adiabatic property of the dark state is also studied in terms of a newly defined adiabatic fidelity. It shows that the nonlinear collisions have a negative effect on the adiabaticity of the dark state and hence reduce the conversion efficiency. [ABSTRACT FROM AUTHOR]