Dynamic Collapse Research Articles

Enhanced image steganalysis through reinforcement learning and generative adversarial networks

With the surging prominence of digital communication platforms, there has been an intensified emphasis on ensuring robust security and privacy measures. Against this backdrop, image steganalysis has emerged as a critical discipline, employing advanced methods to detect clandestine data within image files. At the core of our research is an innovative exploration into image steganalysis using an amalgamation of enhanced reinforcement learning techniques and online data augmentation. This methodology ensures the meticulous identification of concealed data within images. Our design integrates triple parallel dilated convolutions, enabling concurrent extraction of feature vectors from the input images. Once extracted, these vectors are synthesized, paving the way for subsequent classification tasks. To substantiate the efficacy of our approach, we conducted tests on a comprehensive dataset sourced from BossBase 1.01. Furthermore, to discern the influence of transfer learning on our proposed model, the BOWS dataset was employed. Notably, these datasets present a challenge due to its inherent imbalance. To counteract this, we incorporated an advanced Reinforcement Learning (RL) framework. Herein, the dataset samples are envisioned as states in a sequence of interrelated decisions, with the neural network playing the role of the decision-making agent. This agent is then incentivized or reprimanded based on its accuracy in discerning between the minority and majority classes. To bolster our classification capabilities, we innovatively employed data augmentation using images generated by a Generative Adversarial Network (GAN). Concurrently, a regularization mechanism was instituted to alleviate prevalent GAN-related challenges, such as mode collapse and unstable training dynamics. Our experimental outcomes underscore the potency of our methodology. The results highlight a remarkable capability to discern between pristine and steganographic images, registering an average accuracy rate of 85%.

The role of radiological imaging in the management of severe and difficult-to-treat asthma.

Radiological imaging has proven to be a useful tool in the assessment of asthma, its comorbidities and potential complications. Characteristic chest radiograph and computed tomography scan findings can be seen in asthma and in other conditions that can coexist with or be misdiagnosed as asthma, including chronic rhinosinusitis, inducible laryngeal obstruction, excessive dynamic airway collapse, tracheobronchomalacia, concomitant COPD, bronchiectasis, allergic bronchopulmonary aspergillosis, eosinophilic granulomatosis with polyangiitis, and eosinophilic pneumonia. The identification of the characteristic radiological findings of these conditions is often essential in making the correct diagnosis and provision of appropriate management and treatment. Furthermore, radiological imaging modalities can be used to monitor response to therapy.

The ALMA-QUARKS Survey. II. The ACA 1.3 mm Continuum Source Catalog and the Assembly of Dense Gas in Massive Star-Forming Clumps

Leveraging the high resolution, sensitivity, and wide frequency coverage of the Atacama Large Millimeter/submillimeter Array (ALMA), the QUARKS survey, standing for “Querying Underlying mechanisms of massive star formation with ALMA-Resolved gas Kinematics and Structures”, is observing 139 massive star-forming clumps at ALMA Band 6 (λ ∼ 1.3 mm). This paper introduces the Atacama Compact Array (ACA) 7 m data of the QUARKS survey, describing the ACA observations and data reduction. Combining multi-wavelength data, we provide the first edition of QUARKS atlas, offering insights into the multiscale and multiphase interstellar medium in high-mass star formation. The ACA 1.3 mm catalog includes 207 continuum sources that are called ACA sources. Their gas kinetic temperatures are estimated using three formaldehyde transitions with a non-LTE radiation transfer model, and the mass and density are derived from a dust emission model. The ACA sources are massive (16–84 percentile values of 6–160 M ⊙), gravity-dominated (M ∝ R 1.1) fragments within massive clumps, with supersonic turbulence ( M>1 ) and embedded star-forming protoclusters. We find a linear correlation between the masses of the fragments and the massive clumps, with a ratio of 6% between the two. When considering fragments as representative of dense gas, the ratio indicates a dense gas fraction (DGF) of 6%, although with a wide scatter ranging from 1% to 10%. If we consider the QUARKS massive clumps to be what is observed at various scales, then the size-independent DGF indicates a self-similar fragmentation or collapsing mode in protocluster formation. With the ACA data over four orders of magnitude of luminosity-to-mass ratio (L/M), we find that the DGF increases significantly with L/M, which indicates clump evolutionary stage. We observed a limited fragmentation at the subclump scale, which can be explained by a dynamic global collapse process.

The role of sawtooth-shaped nano riblets on nanobubble dynamics and collapse-induced erosion near solid boundary

In this research, surfaces inspired by shark skin were engineered for aluminum (Al) slabs to investigate the influences of riblets on the collapse dynamics of nanobubbles and the resultant erosion on the slab surfaces. These effects were probed through molecular dynamics simulations. Specifically, surfaces with flat profiles as well as those with small and high sawtooth-shaped nano riblets were modelled for analysis. Near the flat surface, due to the absence of riblets, the water nanohammer, with its semi-spherical shape containing water beads under approximately 30 GPa pressure and 5000 K temperature, impulse the Al slab, transferring both temperature and pressure, thereby inducing maximum erosion. Conversely, surfaces containing riblets separate some parts of water vortices, leading to a shorter collapse time of the nanobubble and the creation of a water nanohammer with a smaller volume compared to their values near a flat surface. Moreover, due to the initial impulse of the water nanohammer to the peak of the riblet, the nanohammer splits into two or three inclined shapes. Then, they diagonally impact the main part of the Al slab, resulting in erosion. The decentralization and diagonal impulse of the water nanohammer in the presence of riblets create a lower erosion volume and depth compared to these values on a flat surface. In summary, it can be inferred that riblets can serve as a passive control method for managing erosion, thereby increasing the lifetime of hulls for ships or submarines.

Determination of dynamic collapse limit states using the energy-based method for multi-story RC frames subjected to column removal scenarios

The Alternative Load Path method is widely adopted to perform progressive collapse analyses for reinforced concrete (RC) frame structures subjected to column removal scenarios. Considering that the progressive collapses are usually dynamic phenomena, nonlinear dynamic analyses can yield the most accurate results. However, the associated computational cost is high. Alternatively, the energy-based method (EBM) can be employed to efficiently calculate the maximum dynamic responses. Unfortunately, collapse or dynamic limit states (DLS) cannot be directly determined when the EBM is adopted for the progressive collapse analyses, because it is essentially a quasi-static approach. To tackle this issue, in this paper an EBM-Intersection Point-based (EBM-IP-based) method is proposed to effectively determine the DLS. The method is considering that the dynamic instability will occur once the dynamic capacity curve exceeds the corresponding static capacity curve. Hence, it is possible to determine the DLS by making a correction on the intersection point of the aforementioned two curves without performing nonlinear dynamic time-history analyses. Compared with the other energy components, the kinetic energy at the moment of the peak displacement response is relatively small and the effectiveness of the EBM is verified. Through both static pushdown analyses and incremental dynamic analyses for 48 column removal scenarios of six different multi-story RC frames, the effectiveness of the proposed EBM-IP-based method is verified and the associated coefficients are calibrated. Statistical information and (joint) probabilistic density functions (PDF) of the coefficients are identified. Further, stochastic analyses are carried out in order to quantify the model uncertainties when adopting the EBM-IP-based method. On the basis of all the calculation results, a Gumbel distribution is adopted to capture the PDF of the model uncertainty in relation to displacements, while a lognormal distribution is adopted to fit the PDF of the model uncertainty in terms of resistances. Moreover, a multi-variate Gaussian distribution model with two components is employed to fit the joint PDF.

Microfluidic jet impacts on deep pools transition from capillary-dominated cavity closure to gas pressure-dominated closure at higher Weber numbers.

Studying liquid jet impacts on a liquid pool is crucial for various engineering and environmental applications. During jet impact, the free surface of the pool deforms and a cavity is generated. Simultaneously, the free surface of the cavity extends radially outward and forms a rim. Eventually the cavity collapses by means of gas inertia and surface tension. Our numerical investigation using an axisymmetric model in Basilisk C explores cavity collapse dynamics under different impact velocities and gas densities. We validate our model against theory and experiments across a previously unexplored parameter range. Our results show two distinct regimes in the cavity collapse mechanism. By considering forces pulling along the interface, we derive scaling arguments for the time of closure and maximum radius of the cavity, based on the Weber number. For jets with uniform constant velocity from tip to tail and We ⩽ 150 the cavity closure is capillary dominated and happens below the surface (deep seal). In contrast, for We ⩾ 180 the cavity closure happens above the surface (surface seal) and is dominated by the gas entrainment and the pressure gradient that it causes. Additionally, we monitor gas velocity and pressure throughout the impact process. This analysis reveals three critical moments of maximum gas velocity: before impact, at the instant of cavity collapse, and during droplet ejection following cavity collapse. Our results provide information for understanding pollutant transport during droplet impacts on large bodies of water, and other engineering applications, like additive manufacturing, lithography and needle-free injections.

Experimental Investigations on the Cavitation Bubble Dynamics near the Boundary of a Narrow Gap

Cavitation bubbles near narrow gaps widely exist within microfluidic control devices. In the present paper, a laser-induced cavitation bubble is arranged in a narrow gap composed of two parallel plates. The inception position of the bubble is set to be at the same distance from the two plates so that the dynamic behaviors of the bubble are symmetrical. The collapse and rebound dynamics of the bubble near the boundary of a narrow gap are investigated through high-speed photography. The bubble behaviors (e.g., shape deformation, translational movement, and jet characteristics) are analyzed while considering the influence of the dimensionless distance between the bubble and the boundary and the dimensionless gap width. The principal findings include the following: (1) When the dimensionless distance is small, a violent jet towards the gap is generated during the bubble collapse stage, along with a weak counter-jet towards the boundary appearing during the rebound stage. (2) As the dimensionless distance increases, the translational distance of the bubble during the collapse stage initially decreases, then increases, and finally decreases to zero. (3) Within the parameter range considered in this paper, the dimensionless width mainly affects the expansion degree and movement direction of the bubble cloud during its rebound and subsequent stages. The above research findings can provide experimental support for bubble-driven flow control, pumping, and liquid mixing in microfluidic channels.

Experimental evaluation and numerical investigation on the anti-collapse performance of beam-to-column connections in the minor-axis direction

This study examined the effects of structural resistance in both major- and minor-axis directions on the anti-collapse performance of a fully bolted composite frame. Current research in the field has focused predominantly on the anti-collapse performance of H-columns in the major-axis direction, potentially hindering accurate determination of anti-collapse transmission path within a structure. Herein, monotonic static loading experiments were conducted on two substructures in the minor-axis direction: one equipped with welded flange and bolted web connections and the other with fully bolted connections. The ductility development curve, dynamic collapse response curve, and resistance mechanism correlation curve were employed to evaluate the test results. Fully bolted connections exhibited superior nonlinear rotation capacity, which is essential for the development of a structure's catenary resistance The failure mechanisms and resistance development processes of the structures were reproduced using the ABAQUS/Explicit dynamic quasi-static modeling technique. A full-scale finite element model was developed for the frame with fully bolted connections loaded in the minor-axis direction. This research will contribute to the robust design of fully bolted structural frames that considers the effects of the column stiffness, thickness of the splicing cover plate, number of bolt rows, and bolt apertures of flange connections on deformation and resistance to loading in the minor-axis direction.

Dynamics of bubble collapse near an armored free surface

Armored surfaces refer to a liquid–air interface covered by a layer of floating particles. This paper examines the collapse dynamics of a bubble generated by an electric spark near such an armored surface. The collapse of the bubble near the armored surface is similar to that near a free surface, with the formation of spraying liquid film, upward liquid jet in the forms of water dome, water spike, and water skirt with the change of the vertical distance (l) from the bubble center to the liquid surface. However, on the armored surface, we also observe particle splash and solid–liquid mixture splash. We confirm that the particle splash occurs due to the transfer of shock wave energy during bubble expansion and collapse. The splashing velocity (vp) and the distance (d0) from the bubble center to the particle follow the scaling law of vp ∼ l/d02. Additionally, we discuss the motion of the upward liquid jet and downward vortex ring. We find that the armored surface only affects the initial velocity of the jet without affecting its acceleration. This can be attributed to the additional energy dissipation caused by the splash formed on the armored surface. In contrast, the trajectory of the vortex ring remains unaffected by the armored surface. This study provides valuable insights into the dynamics of bubble collapse near an armored surface and highlights the role of floating particles in altering the behavior of liquid jets.

Feasibility of Continuous Bronchoscopy During Exercise in the assessment of large airway movement in healthy subjects.

Excessive dynamic airway collapse (EDAC) is a recognized cause of exertional dyspnea arising due to invagination of the trachea and/ or main bronchi. EDAC is typically assessed by evaluating large airway movement with forced expiratory maneuvers. This differs from the respiratory response to exercise hyperpnea. We aimed to evaluate large airway movement during physical activity, with continuous bronchoscopy during exercise (CBE), in healthy subjects and compare findings with resting bronchoscopic maneuvers and imaging techniques. Twenty-eight individuals were recruited to complete two visits including treadmill-based CBE, to voluntary exhaustion and cine magnetic resonance imaging (MRI) with forced expiratory maneuvers at rest. 25 subjects (aged 29 (26 - 33) years, 52% female) completed the study (n=2 withdrew before bronchoscopy, and one was unable to tolerate insertion of bronchoscope). The majority (76%) achieved a peak heart rate of >90% predicted during CBE. The procedure was prematurely terminated in five subjects (n=3; elevated blood pressure and n=2; minor oxygen desaturation). The CBE assessment enabled adequate tracheal visualization in all cases. Excessive dynamic airway collapse (tracheal collapse ≥50%) was identified in 16 subjects (64%) on MRI, and in 6 (24%) individuals during resting bronchoscopy, but in no cases with CBE. No serious adverse events were reported, but minor adverse events were evident. The CBE procedure permits visualization of large airway movement during physical activity. In healthy subjects, there was no evidence of EDAC during strenuous exercise, despite evidence during forced maneuvers on imaging, thus challenging conventional approaches to diagnosis.

Collapse and expansion kinetics of a single polyelectrolyte chain with hydrodynamic interactions.

We investigate the collapse and expansion dynamics of a linear polyelectrolyte (PE) with hydrodynamic interactions. Using dissipative particle dynamics with a bead-spring PE model, long-range electrostatics, and explicit ions, we examine how the timescales of collapse tcol and expansion texp depend on the chain length N and obtain scaling relationships tcol ∼ Nα and texp ∼ Nβ. For neutral polymers, we derive values of α = 0.94 ± 0.01 and β = 1.97 ± 0.10. Interestingly, the introduction of electrostatic interaction markedly shifts α to α ≈ 1.4 ± 0.1 for salt concentrations within c = 10-4 to 10-2M. A reduction in the ion-to-monomer size ratio noticeably reduces α. On the other hand, the expansion scaling remains approximately constant, β ≈ 2, regardless of the salt concentration or ion size considered. We find β > α for all conditions considered, implying that expansion is always slower than collapse in the limit of long polymers. This asymmetry is explained by distinct kinetic pathways of collapse and expansion processes.

Optimization of a BEGe Detector Setup for Testing Quantum Foundations in the Underground LNGS Laboratory

In this work, we report on tests performed with an experimental apparatus prototype based on a broad-energy germanium detector aimed at investigating topical, foundational issues in quantum mechanics: i.e., possible violations of the spin-statistics connection and models of dynamical wave function collapse. Our recent phenomenological analyses demonstrated the importance of pushing the research of new physics signal, predicted in these fields, to an energy range below 10 keV. We describe the development of the dedicated data acquisition system and of the pulse shape discrimination algorithm, which have already allowed us to get a factor two improvement in the lower energy threshold. Future plans are discussed to further improve the lower energy threshold to the level of a few keV.

Collapse Dynamics of Vector Vortex Beams in Kerr Medium with Parity–Time-Symmetric Lattice Modulation

Based on the two-dimensional (2D) nonlinear Schrödinger equation, we investigate the collapse dynamics of a vector vortex optical field (VVOF) in nonlinear Kerr media with parity–time (PT)-symmetric modulation. The critical power for the collapse of a VVOF in a Kerr-ROLP medium (Kerr medium with a real optical lattice potential) is derived. Numerical simulations indicate that the number, position, propagation distance, and collapse profile of the collapse of a VVOF in sine and cosine parity–time-symmetric potential (SCPT) Kerr media are closely related to the modulation depth, initial powers, and the topological charge number of a VVOF. The VVOF collapses into symmetric shapes during propagation in a Kerr-ROLP medium, and collapse shapes are sensitively related to the density of the PT-symmetric optical lattice potential. In addition, due to gain–loss, the VVOF will be distorted during propagation in the Kerr-SCPT medium, forming an asymmetric shape of collapse. The power evolution of the VVOF in a Kerr-SCPT medium as a function of the transmission distance with different modulating parameters and topological numbers is analyzed in detail. The introduction of PT-symmetric optical lattice potentials into nonlinear Kerr materials may provide a new approach to manipulate the collapse of the VVOF.

Role of upper airway evaluation in the multidisciplinary management of obstructive sleep apnea in children below two years of age.

Diagnosis and treatment of obstructive sleep apnea (OSA) in infants and young children is challenging because of its clinical heterogeneity and lack of age-specific guidelines. We report the management and treatment outcome of OSA in children below 2 years of age. Treatment decisions were based upon the pattern of upper airway (UA) obstruction, clinical presentation and OSA severity. Retrospective, non-randomized observational cohort study at a tertiary center. Children with OSA who underwent an UA evaluation (drug-induced sleep endoscopy or direct laryngoscopy) were included. We studied 100 patients, 57 boys and 43 girls, age 0.72 years (0.0-2.0) and OSA confirmed by polysomnography. Multilevel UA collapse was present in 26%, (adeno)tonsillar hypertrophy in 31% and 21% had laryngomalacia. Laryngomalacia was more common in children below 6 months of age and adenotonsillar hypertrophy was observed mainly in children >1.5 year of age. Surgical and nonsurgical treatment guided by UA findings, improved OSA severity at group level with a significant reduction (p < 0.001) in obstructive apnea/hypopnea index from 10.8/h (2.1-99.1) to 1.7/h (0.0-73.0), an improvement in mean oxygen saturation from 96.9% (88.9-98.4) to 97.4% (92.3-99.0), in minimal oxygen saturation from 85.4% (37.0-96.0) to 88.8% (51.0-95.5) and oxygen desaturation index from 5.1/h (0.2-52.0) to 1.3/h (0.0-47.8). Multidisciplinary management of young children with OSA guided by the pattern of UA obstruction and OSA severity, reduces OSA severity. The pattern of UA obstruction changes in the first 2 years of life from a dynamic collapse to structural abnormalities.

Nonlinear dynamic collapse analysis of space semi-rigid frames using finite particle method

Based on the finite particle method, this work presents a general numerical method to perform the nonlinear dynamic collapse analysis of space semi-rigid structures. A space connection element composed of two particles and six zero-length springs is proposed to simulate the space semi-rigid connection. Geometrical nonlinearity is addressed through fictitious motion, while material and connection behavior nonlinearities are captured by updating the element stiffness matrix and the connection stiffness matrix, respectively. Member and connection fracture models are convenient for simulating fracture behaviors during collapse processes. To verify the effectiveness of the proposed method, the numerical results are compared with those from previous studies, and energy conversion analyses are adopted. The analysis results indicate that only member fractures occur at beam ends in the rigid and linear semi-rigid frames, while only connection fractures occur at beam ends in the nonlinear semi-rigid frame.

The minimum mass for star formation by dynamical fragmentation: dependence on epoch, dust abundance, and environment

ABSTRACT We estimate the minimum mass of a star formed by dynamical collapse and fragmentation, as a function of epoch, dust abundance, and environment. Epoch is parametrized by redshift, zred, through the variation in the temperature of the cosmic microwave background. The dust abundance is parametrized by the mass-fraction in dust, ZD, with the additional simplifying assumption that the intrinsic properties of dust do not change with ZD, only the amount of dust. Environment is parametrized by the energy-density of the ambient suprathermal radiation fields through a dilution factor ω⋆ (applied to a blackbody radiation field at $T_{\star }=10^4\, {\rm K}$). The critical condition is that a spherical proto-fragment should be able to cool, and therefore contract, fast enough to detach from neighbouring proto-fragments. The minimum mass increases with increasing redshift, increasing dust abundance, and increasing suprathermal background. Values in the range from $M_{{\rm MIN}}\sim 0.002\, {\rm M}_{\odot }$ to $M_{{\rm MIN}}\sim 0.2\, {\rm M}_{\odot }$ are obtained at the extremes of the parameter ranges we have considered (0 ≤ zred ≤ 8, 0.00016 &amp;lt; ZD &amp;lt; 0.04, and 10−15 ≤ ω⋆ ≤ 10−8). Our results agree quite well with the predictions of detailed numerical simulations invoking similar redshifts and dust abundances, but our estimates are somewhat lower; we attribute this difference to resolution issues and the small-number statistics from the simulations. The increased minimum masses predicted at high redshift and/or high suprathermal background result in significantly bottom-light initial mass functions, and therefore low mass-to-light ratios, provided that the dust abundance is not too low. The changes due to high suprathermal background may be particularly important for star formation in galactic nuclei and at high redshift.

New results on the dynamics of critical collapse* *JQG is Supported by the Natural Science Foundation of Shandong Province, China (ZR2019MA068). YH, PPW and CGS are Supported by the National Natural Science Foundation of China (11925503)

We study the dynamics of the critical collapse of a spherically symmetric scalar field. Approximate analytic expressions for the metric functions and matter field in the large-radius region are obtained. In the central region, owing to the boundary conditions, the equation of motion for the scalar field is reduced to the flat-spacetime form.

Predicting the collapse process and tipping points for mutualistic and competitive networks with k-core method

Abstract Ecosystems generally have the self-adapting ability to resist various external pressures or disturbances, which is always called resilience. However, once the external disturbances exceed the tipping points of the system resilience, the consequences would be catastrophic, and eventually lead the ecosystem to complete collapse. We capture the collapse process of ecosystems represented by plant-pollinator networks with the k-core nested structural method, and find that a sufficiently weak interaction strength or a sufficiently large competition weight can cause the structure of the ecosystem to collapse from its smallest k-core towards its largest k-core. Then we give the tipping points of structure and dynamic collapse of the entire system from the one-dimensional dynamic function of the ecosystem. Our work provides an intuitive and precise description of the dynamic process of ecosystem collapse under multiple interactions, and provides theoretical insights for further avoiding the occurrence of ecosystem collapse.

Study on Non-Spherical Deformation Velocity of a Single Cavitation Bubble

Cavitation bubbles commonly exist in shipbuilding engineering, ocean engineering, mechanical engineering, chemical industry, and aerospace. Asymmetric deformation of the bubble occurs near the boundary and then has strong destructiveness, such as high amplitude loading. Therefore, the research on non-spherical deformation is of great significance, and the objective of this paper is to investigate the non-spherical collapse dynamics of laser-induced cavitation bubbles when near different boundaries. In this study, experimental data, such as the bubble pulsation process and bubble surface velocity distribution, were obtained by high-speed camera techniques and full-field velocity calculations. Near the different boundaries, the results show that the bubbles appeared to have different collapse shapes, such as near-hemispherical, near-ellipsoidal, near-cone, and near-pea shapes, and the surface velocity distribution is extremely non-uniform. When the bubble near the free surface or rigid boundary collapses, the smaller the stand-off r is, the more obvious the repulsive effect of the free surface or the attractive effect of the rigid boundary is. As the stand-off r decreases, the larger the Bjerknes force and the bubble surface velocity difference and the more pronounced the non-spherical shape becomes.

The collapse of a sonoluminescent cavitation bubble imaged with X-ray free-electron laser pulses

Single bubble sonoluminescence (SBSL) is the phenomenon of synchronous light emission due to the violent collapse of a single spherical bubble in a liquid, driven by an ultrasonic field. During the bubble collapse, matter inside the bubble reaches extreme conditions of several gigapascals and temperatures on the order of 10000 K, leading to picosecond flashes of visible light. To this day, details regarding the energy focusing mechanism rely on simulations due to the fast dynamics of the bubble collapse and spatial scales below the optical resolution limit. In this work we present phase-contrast holographic imaging with single x-ray free-electron laser (XFEL) pulses of a SBSL cavitation bubble in water. X-rays probe the electron density structure and by that provide a uniquely new view on the bubble interior and its collapse dynamics. The involved fast time-scales are accessed by sub-100 fs XFEL pulses and a custom synchronization scheme for the bubble oscillator. We find that during the whole oscillation cycle the bubble’s density profile can be well described by a simple step-like structure, with the radius R following the dynamics of the Gilmore model. The quantitatively measured internal density and width of the boundary layer exhibit a large variance. Smallest reconstructed bubble sizes reach down to R≃0.8μm , and are consistent with spherical symmetry. While we here achieved a spatial resolution of a few 100 nm, the visibility of the bubble and its internal structure is limited by the total x-ray phase shift which can be scaled with experimental parameters.