Acceleration Of Plate Research Articles

A vibration-based method to estimate the low-wavenumber wall pressure field in a turbulent boundary layer

When an elastic structure is excited by a low-speed turbulent flow, it generates flow-induced vibration which is primarily due to the low-wavenumber components of the wall pressure field (WPF) beneath the turbulent boundary layer (TBL). Therefore, to accurately predict the vibration response of the structure, an accurate estimation of the low-wavenumber WPF is needed. While existing TBL models for WPF well predict the convective region, they exhibit significant discrepancies in predicting the low-wavenumber levels. This numerical study aims to explore the feasibility of estimation of the low-wavenumber WPF by analysing vibration data obtained from a structure excited by a TBL. An inverse method is proposed based on the relationship between the TBL forcing function and structural vibrations in the wavenumber domain. The random TBL force is simulated with deterministic loading using the uncorrelated wall plane wave technique. A model of a simply supported plate under a TBL excitation is developed to demonstrate the proposed method. The plate's acceleration data is then used to estimate the WPF in the low-wavenumber range. It is shown how using multiple discrete frequencies in the analysis can reduce the required snapshots for accurate estimation of the WPF.

Effect of oxidizer on the energy release during the initial detonation stage of aluminized explosives

ABSTRACT The addition of an oxidizer to aluminized explosives can promote the reaction of the aluminum particles to release more energy, significantly increasing the energy of the explosion. In this study, metal plate acceleration tests of CL-20-based explosives under strong constraints were performed, and the metal plate velocity was measured by laser interferometry, then the metal plate acceleration processes were simulated. By combining experiment and numerical simulation, the metal acceleration characteristics of the initial detonation stage were obtained, and the energy release and aluminum reaction law of oxidizer-containing cast cured aluminized explosives were investigated. The results showed that, in the initial stage of the detonation product expansion, the energy released from the aluminum reaction in the explosives with an oxidizer was slower than that in the explosives without an oxidizer. As the oxidizer content increased, the acceleration ability decreased, and the energy utilization rate of the explosive decreased. This may be because of the relatively low CL-20 content and high oxidizer content, where the oxidizer does not participate in the initial reaction and absorbs a large amount of the heat released by the CL-20 reaction, resulting in weak acceleration ability in the initial detonation stage of aluminized explosives.

Theoretical velocity of an object frictionally coupled to a two-mode vibrating plate.

Net velocity has been demonstrated for objects frictionally coupled to a flat plate that oscillates periodically in-plane with two frequencies, provided plate displacement is nonantiperiodic: the ratio of frequencies γ cannot be the ratio of two odd integers. We give a mathematical derivation of the experimentally determined dependence of mean velocity on the relative amplitudes of the two frequency modes, and the phase lag between the modes, when γ=2, and when the magnitude of plate acceleration is much larger than the magnitude of acceleration by static friction. The approach uses an analysis of the symmetry properties of the roots of trigonometric polynomials, without explicit determination of those roots. The behavior when γ=1/2, and specific phase lags that inhibit net velocity for general γ, are also determined.

Effects of Pre-Stretching Amount on Motion Characteristics and Screening Efficiency of Flip-Flow Screen Plates

This study systematically investigates the impact of pre-stretching amount (PSA) on the acceleration, motion status, and screening efficiency of the Flip-flow screen plate (FFSP). Initially, a nonlinear spring-multi-body model of the FFSP is established. Subsequently, the acceleration signals at the midpoint of the FFSP under various PSAs are measured and analyzed. The nonlinear stiffness coefficient of FFSP along the vertical direction is then determined and it is found that simplifying the nonlinear spring-multi-body system to a nonlinear spring-tri-body system under the experimental conditions can maintain the calculation error of FFSP’s acceleration within 30%. Phase and Poincaré mapping diagrams of the FFSP under different PSAs are subsequently created to illustrate the impact of PSA on the motion status of the FFSP. Finally, screening experiments are performed to study the optimal PSA for a kind of bituminous coal from Shanxi province.

Experimental and numerical study of corrugated steel-plain concrete composite structures under contact explosions

This paper investigates the dynamic response and blast resistance of corrugated steel-plain concrete (CSPC) composite structures subjected to contact blast. A series of explosive tests were conducted to investigate the acceleration, deformation, and damage patterns of CSPC plates under varying blast loads and arrangements of shear connectors, and these findings were compared with reinforced concrete (RC) plates. The results suggested that CSPC plates exhibited superior ductility and blast resistance, and effectively mitigated concrete collapse. The CSPC slab primarily underwent elastic deformation when the TNT charge was small, with the rebound deformation of the concrete and steel plates acting as a significant mode of energy dissipation. As for larger TNT charges, the maximum deformation of the plate progressively increased, especially when exceeding 0.3 kg, the deformation rebound ratio decreased significantly, and the plastic deformation increased. For further increased explosive loads, the concrete and steel plates exhibited a pronounced strain rate effect with a slowed growth rate of deformation. By examining different configurations of shear connectors, it was discovered that the adhesive strength between concrete and steel plates was closely related to the energy dissipation mode, and the elastic recovery capability and deformation resistance of the CSPC structure significantly deteriorated when the shear connectors were shorter, sparser or thinner. A numerical model based on LS-DYNA was designed to further analyze the blast resistance characteristics of CSPC plates. An engineering collapse coefficient Kz was established to predict the failure level of the CSPC plates. This paper provides useful insights for the optimal design and damage assessment of CSPC composite structures.

Numerical computation of damped vibration and sound radiation for structures having a porous layer sandwiched by double walls with an acoustic black hole

Vibration and noise reduction are important technology to realize comfort products with safe structures. In this paper, we carry out numerical simulation of damped vibration and sound radiation for structures having a porous material sandwiched by double walls. The double walls are consisted of a steel base plate and a steel cover plate. The cover plate in double walls has a Krylov type acoustic black hole. Damping material is on the surface of the black hole. One point in the base plate is excited by white noise. Numerical analysis is performed to clarify changes of vibration transmission from the base plate to the cover plate due to the acoustic black hole using FEM and MSKE method(Modal Strain and Kinetic Energy method) proposed by Yamaguchi et al. Sound radiation from the cover plate is also investigated. The vibration transmission were reduced for the model having acoustic black hole in the cover plate. Vibration energy flows into the black hole in the cover plate. This causes that vibration acceleration of the cover plate is damped effectively. Sound radiation from the cover plate also decreased. This is because high damping and shorter wave length of vibration in the acoustic black hole.

Estimation of the low-wavenumber component of turbulent boundary layer pressure field using vibration data

In structures subjected to a high-speed flow, the convective region of the wall pressure field (WPF) beneath a turbulent boundary layer (TBL) plays a crucial role in their vibration behaviour. However, when it comes to underwater structures experiencing low-speed flow, they effectively filter out the convective domain of WPF and the bending wavenumber of structures align with the low-wavenumber domain of the WPF. As a result, the primary cause of vibration in this case is the low-wavenumber components of the WPF. Thus, accurate estimation of the WPF at low-wavenumber domain is crucial for predicting vibration responses of these structures. Existing models for WPF accurately predict the convective region but differ significantly in predicting the low-wavenumber levels. This numerical study aims to investigate the feasibility of estimating the low-wavenumber WPF by analysing measured vibration data from a flat plate excited by a TBL. The WPF's cross spectrum in the wavenumber domain can be linked to the cross spectrum of the plate's acceleration. By employing regularization techniques and solving an inverse problem, the low-wavenumber components of the WPF can be then estimated. Virtual experiments are performed to evaluate the accuracy of the studied process by comparing its prediction to the input WPF model.

Blast Absorption Capacity of Brittle Mineral Foam: an Experimental Evaluation

Cellular materials, such as aluminum foam, have proven to be effective energy absorbents. They can be used as the crushable core for blast mitigation sacrificial cladding. In this paper insights into the blast response of a brittle mineral foam-based sacrificial cladding are presented. The experimental set-up used consists of a rigid steel frame (1000 mm × 1000 mm × 15 mm) with a square cavity of 300 mm x 300 mm in the center. An aluminum plate, representing the structure, with a total surface of 400 mm × 400 mm and a thickness of 2 mm is clamped into the steel frame. Two synchronized high-speed cameras in a stereoscopic configuration are used to capture the dynamic response of the aluminum plate at a frame rate of 20000 frames per second. The transient deformation fields are computed using a three-dimensional digital image correlation technique. The blast load is obtained by detonating 20 g of C4 placed at a distance of 250 mm from the center of the tested aluminum plate. The absorption capacity of the brittle mineral foam is assessed by comparing the out-of-plane displacement, the velocity, the acceleration and the major principal strain of the thin aluminum plate with and without the protective mineral foam. Two foam configurations with different thicknesses are considered: 60 mm and 120 mm. It is shown that adding the brittle mineral foam reduces the out-of-plane displacement together with the displacement velocity and acceleration of the aluminum plate at least by a factor of two. Post-mortem analysis of the foams shows that mitigation of the blast load in the present set-up and under the considered loading is partially obtained by crushing of the cell walls but mostly though the growth of cracks in the specimen.

Acceleration of metal plates by hybridization of electrical and chemical energy for potential application in high-velocity impact welding

Vaporizing foil actuator welding is employed to connect dissimilar metals by utilizing the energy of an electrical explosion as the driving force for flyer plate acceleration. Herein, the electrical and chemical energies of explosives were combined to increase flyer plate velocity. A metal foil or wire mesh was used as an actuator, and a small amount of explosives was placed on the foil. Uniform acceleration of the flyer plate on the actuator was recorded using a high-speed video camera. The electrical energy applied to the actuator was measured synchronously by filming. The explosion of chemical explosives was successfully initiated owing to the electrical explosion of the actuator. In all experiments, the combination of the electrical explosion and chemical reaction improved the acceleration of the samples, facilitating higher velocities. The impact of the actuator type (mesh or foil) and the electric discharge parameters on the performance was studied. While foil actuators were more efficient in experiments on electric explosions alone, mesh actuators were superior when the chemical explosive was added. Explosions of the mesh actuator could initiate low density pentaerythritol tetranitrate (PETN) (the space-filling rate of PETN was approximately 30%). An explosive force of 0.3 g of PETN was converted into a driving force, imparting the flying plate with a velocity greater than 210 m/s. Electrical energy consumption for PETN initiation may be assumed to have an insignificant impact on flyer plate acceleration. In future, the proposed method may be used to connect heavier and thicker materials without expensive high-performance capacitors.

The interaction between a shaped charge jet and a single moving plate

Reactive armour is a very efficient add-on armour against shaped charge threats. Explosive reactive armour consists of one or several plates that are accelerated by an explosive. Similar but less violent acceleration of plates can also be achieved in a completely inert reactive armour. To be efficient against elongated jets, the motion of the plates needs to be inclined against the jet such that a sliding contact between the jet and the plates is established. This sliding contact causes a deflection and thinning of the jet. Under certain circumstances, the contact will become unstable, leading to severe disturbances on the jet. These disturbances will drastically reduce the jet penetration performance and it is therefore of interest to study the conditions that leads to an unstable contact.Previous studies on the interaction between shaped charge jets and flyer plates have shown that it is mainly the forward moving plate in an explosive reactive armour that is effective in disturbing the jet. This is usually attributed to the higher plate-to-jet mass flux ratio involved in the collision of the forward moving plate compared to the backward moving plate. For slow moving plates, as occurs in inert reactive armour, the difference in mass flux for the forward and backward moving plate is much lesser, and it is therefore of interest to study if other factors than the mass flux influences on the protection capability.In this work, experiments have been performed where a plate is accelerated along its length, interacting with a shaped charge jet that is fired at an oblique angle to the plate’s normal, either against or along the plate’s velocity. The arrangement corresponds to a jet interacting with a flyer plate from a reactive armour, with the exception that the collision velocity is the same for both types of obliquities in these experiments. The experiments show that disturbances on the jet are different in the two cases even though the collision velocities are the same. Numerical simulations of the interaction support the observation. The difference is attributed to the character of the contact pressure in the interaction region. For a backward moving plate, the maximum contact pressure is obtained at the beginning of the interaction zone and the contact pressure is therefore higher upstream than downstream of the jet while the opposite is true for a forward moving plate. A negative interface pressure gradient with respect to the jet motion results in a more stable flow than a positive, which means that the jet-plate contact is more stable for a backward moving plate than for a forward moving plate. A forward moving plate is thus more effective in disturbing the jet than a backward moving plate, not only because of the higher jet to plate mass flux ratio but also because of the character of the contact with the jet.

Effects of Thermodiffusion and Chemical Reaction on Magnetohydrodynamic-Radiated Unsteady Flow Past an Exponentially Accelerated Inclined Permeable Plate Embedded in a Porous Medium

A finite difference computational study is conducted to assess the influence of thermodiffusion and chemical reaction on unsteady free convective radiated magnetohydrodynamic flow past an exponentially accelerated inclined permeable plate embedded in a saturated porous medium of uniform permeability with variable temperature and concentration. The governing nondimensional set of coupled nonlinear partial differential equations with related initial and boundary conditions are solved numerically by using the accurate and efficient DuFort–Frankel’s explicit finite difference method. The physical features of fluid flow, heat, and mass transfer under the influence of the magnetic field, angle of inclination, plate acceleration, radiation, heat source/sink, thermodiffusion, chemical reaction, and time are scrutinized by plotting graphs and then discussed in detail. It was found that the effective magnetic field and angle of inclination tend to decline the fluid motion, whereas the reverse result is detected by increasing the porosity parameter and plate acceleration. The velocity and temperature of the fluid lessen with increasing the radiation parameter. The effect of thermodiffusion raises the fluid velocity and concentration, whereas a chemical reaction has the opposite impact. The Nusselt number increases with increasing the radiation parameter and time. Increasing chemical reaction and time causes to improve the Sherwood number. This kind of problem finds momentous industrial applications such as food processing, polymer production, inclined surfaces in a seepage flow, and design of fins.

Pulsed counterclockwise rotation of the southwestern Sichuan Basin in response to the India-Asia convergence during 128-42 Ma

Deciphering the building history of the eastern Tibetan Plateau since the India-Asia convergence is crucial to understand geodynamic models of plateau formation. The Sichuan Basin adjacent to the eastern Tibetan Plateau margin potentially provides valuable records of when and how the Tibetan Plateau expanded eastward. In this study, we reconstruct ∼128–42 Ma rotation history of the southwestern Sichuan Basin using detailed paleomagnetic declination data from the Early Cretaceous to Eocene sedimentary sequence of ∼2400 m thick. A total of 78 sampling sites (774 samples) yield primary remanent magnetization confirmed by positive paleomagnetic tests. Our results show that the southwestern Sichuan Basin experienced a long-term clockwise rotation during 128–42 Ma which was interrupted by three transient and rapid counterclockwise rotation pulses. The earlier two pulses (86–82 Ma and 66–60 Ma) coincide with two India Plate acceleration episodes which are probably induced by the Marion and/or Réunion mantle plume upwelling, whereas the later pulse (53–46 Ma) temporally corresponds to the sudden slowdown of the India Plate caused by the India-Asia collision. Our findings indicate that the eastern Tibetan Plateau experienced prolonged and episodic building processes since the Late Cretaceous, long predating the traditional view of the late Miocene. The Tibetan Plateau was built synchronously from the Himalayas to its eastern margin. Lateral extrusion, block rotation, and strike-slip deformation collectively contribute to the mountain building in the eastern Tibetan Plateau region.

Railway Track Ballast Layer Stiffness Dynamic Control Elastic-Linear Model

The paper presents the results of mathematical modeling of the shock-elastic interaction process in the dynamic densimeter for dynamic control of the ballast layer of the railroad track. The installation is used to determine the compaction level and to estimate the carrying capacity of the ballast layer during the inter-repair period of tampering, renewal and track stabilization operations. The effect of exposure on the controlled elastic base is considered within a four-element mathematical model. The time intervals of interaction between the model elements are revealed. Each time interval is described by a system of second-order differential equations, for which analytical solutions were obtained. The model verification was evaluated during tests with a dynamic control unit consisting of a loading plate, a falling weight, and an elastic-damping element located between the weight and the loading plate. Tests were conducted on a polyurethane surface with known stiffness. In the process, signals of vertical acceleration of the loading plate when the load strikes the elastic-damping element were recorded. The acceleration was recorded by an accelerometer sensor with a sampling rate of 42 kHz being connected to a computer with specialized software. The acceleration data were obtained for different values of the stiffness of the elastic-damping element in the installation. To evaluate the simulation results, the obtained signals were compared with the theoretical model by the correlation method. According to the results of modeling, the main amplitude and time informative parameters used to determine the degree of compaction of the base layer have been singled out. The dependence of the values of informative parameters on the installation parameters (load weight, loading plate weight, stiffness of an elastic-damping element) in conditions of uncertainty was studied. The obtained dependences are used to estimate the error of each parameter in calculating the rigidity of the base. Informative parameters have been determined that allow you to determine the stiffness of the base with an error of not more than 7%. A method for selecting the optimal characteristics of the unit design and informative parameters to ensure minimum errors has been developed.

Shaking Table Test for Seismic Isolation Performance of Adjustable Height Seismic Isolation Rubber Bearing

To study the seismic isolation effect of adjustable height seismic isolation rubber bearing, a continuous girder bridge was subjected to a shaking table test study with full bridge scaling to compare the seismic isolation effects of plate rubber bearings, natural rubber bearings (LNR) and adjustable height seismic isolation rubber bearings under different types of seismic waves, loading directions and seismic intensities.The test results show that when the seismic intensity is small, the seismic isolation performance of the three types of bearings is relatively close. But when the seismic intensity is large, the seismic isolation effect of the adjustable height isolation bearing is better than that of the plate rubber bearing and LNR bearing. Adjustable height isolation rubber bearing can significantly reduce the acceleration of the bridge deck plate, shear force and bending moment in the bottom of piers.

Analysis on dynamic behavior of 400 km/h high-speed train system under differential settlement of subgrade

Whether the existing ballastless track subgrade settlement control standard of 350 km/h is applicable to the high-speed train of 400 km/h remains to be further research. This paper established a complete rigid flexible coupling dynamic model of vehicle-track-subgrade space based on the finite element method and multi-body dynamics theory. Combined with the fixed interface modal synthesis method and wheel/rail contact theory, the joint simulation of ABAQUS and UM is realized. The dynamic response of 400 km/h high-speed train under the condition of subgrade differential settlement is analyzed and compared with the current 350 km/h high-speed train. The results show that under the same subgrade differential settlement condition, when the train speed increases from 350 km/h to 400 km/h, the wheel rail interaction increases significantly, but does not exceed the specification limit. The amplitude of derailment coefficient is far lower than the maximum specification limit, while the amplitude of wheel load reduction rate exceeds the quasi-static limit in the specification. The impact of the increase of train speed on the lateral stability of the vehicle is greater than that on the vertical stability of the vehicle. At 400 km/h, each stability index of the train does not exceed the maximum specification limit, and sufficient safety margin is reserved. The increase of train speed has a great impact on the vertical acceleration of rail, and has little impact on the vertical acceleration of track plate and baseplate. In summary, the current subgrade settlement control standard of 350 km/h high-speed railway is also applicable to 400 km/h high-speed trains, and there is room for further speed increase.

Influence of external load on forced vibration of rectangular plate

Rectangular plate is one typical structure with wild application in engineering, and the force vibration is the basis for analysis of sound radiation of plate. In this work, numerical simulation is conducted for force vibration of rectangular plate, and the influence of external load is also studied. Numerical results show that, the rectangular plate will resonate under external load at certain driven frequency, and it’s strictly related to structural modal frequencies. Structural vibration response will change obvious with the change of location of external load. When the location is fixed, with the increase of action region of external load, the acceleration of plate will decrease and some new resonance frequencies will be observed. Conclusions here will lay foundation for further work on sound radiation of plate.

RANS simulations of plane impinging jets: On the influence of plate velocity in the Nusselt number secondary peak

In the present work, heat transfer characteristics of a turbulent confined slot jet impinging on a heated moving plate are studied by means of time-averaged Navier-Stokes simulations. Three different plate conditions are considered: zero plate velocity (stationary plate), plate moving with a constant velocity, and plate moving with a constant acceleration. The jet nozzle-to-plate ratio and the jet inlet Reynolds number are equal to 4 and 2 ? 104, respectively. The objective of the present research is to investigate the role of the plate velocity condition on the development of the second peak in the Nusselt number profile along the impingement plate. The k-kl-? transition RANS model was validated against direct numerical simulation and experimental data and was able to correctly predict both the size and location of the Nusselt number secondary peak. A third re-circulation zone appears as the plate velocity increases and the Nusselt number secondary peaks location shifts slightly downstream. The development of the third re-circulation zone induces an accentuated decrease in the local and average Nusselt numbers. Furthermore, the plate acceleration delays the movement of the transition in the wall jets and the appearance of the third re-circulation zone. Consequently, the average Nusselt number increases with time, and the heat transfer from the plate is enhanced up to 8%.

Об ударно-волновом разгоне материала в системе пластин с уменьшающейся акустической жесткостью

To obtain the high-speed metal particles in simulating the impact of meteoroids and fragments of space debris on the spacecraft protective screens, shock-wave acceleration of thin metal plates is used at their collision with the impact element accelerated by a light-gas ballistic installation. Such an element is provided at the front end with an insert of layers with acoustic stiffness decreasing outwards. The effect of increasing speed of a plate accelerated by the plate impact is considered, when an intermediate system of plates with monotonically decreasing acoustic impedance is installed between it and the impact element, which values are between the impact element and the accelerated plate impedances. Based on numerical simulation in the framework of a plane one-dimensional problem of continuum mechanics, the shock-wave acceleration of an aluminum plate was studied in its direct collision with a tantalum impact element, as well as in the presence of one intermediate plate of copper or two intermediate plates of copper and titanium between them. An increase in the coefficient of accelerated plate raising speed relative to the impact element speed was registered with an increase in the number of intermediate plates. Using acoustic approximation, an analytical solution to the problem of plate acceleration in the presence of a system of the infinite number of infinitely thin plates with the continuously decreasing acoustic impedance between it and the impact element was obtained.

Late Eocene subduction initiation of the Indian Ocean in the North Sulawesi Arc, Indonesia, induced by abrupt Australian plate acceleration

Subduction of oceanic lithosphere is the main driving force of plate tectonics on Earth, yet, how subduction began (i.e. subduction initiation; SI) remains enigmatic, due to limited SI examples. Here, we report new whole-rock geochemical and zircon U-Pb-Hf isotopic data of arc magmatism from the North Sulawesi Arc, Indonesia, to constrain the petrogenesis, magmatic tempo, and tectonic setting, as well as the timing and trigger of SI. Zircon U-Pb dating yielded crystallization ages of ~29.7–16.7 Ma for parental magmas, which are calc-alkaline I-type in nature and show typical subduction-related signatures. Geochemical data and high positive zircon ε Hf (t) values indicate magma generation by partial melting of preexisting mafic basement rocks. Our new results, together with literature data, allow the identification of an Indian SI in the Late Eocene, as evidenced by the last vanishing of BAB-type mafic basement rocks at ~37 Ma and the first appearance of calc-alkaline felsic arc magmatism at ~30 Ma in the North Sulawesi Arc, as well as ~36–32 Ma ophiolite and ~34–29 Ma metamorphic sole in the nearby East Sulawesi Ophiolite. Such a temporal duration (maximum of ~7 Ma) from SI to typical arc magmatism is identical to that (~8–7 Ma) of the Izu-Bonin-Mariana system. Given the contemporaneousness of a sudden increase (from ~4–5 to ~8–9 cm/y) in northward drifting rate of the Australian plate, we propose that Late Eocene Indian SI was probably linked to the sharp Australian plate acceleration. Such plate reorganization may have played a significant role in driving SI in Earth history. • Calc-alkaline I-type felsic rocks in the North Sulawesi Arc developed at ~30–16 Ma. • Arc magmatism formed by melting of preexisting mafic rocks during Indian subduction. • Indian SI occurred in the Late Eocene, driven by Australian plate acceleration.

Shock Initiation and Detonation Parameters of Hexanitrohexaazaisowurtzitane (CL‐20)

AbstractExperimental studies of the reaction zone structure in hexanitrohexaazaisowurtzitane (CL‐20) at different initial densities with a multichannel VISAR laser interferometer have been carried out. It is shown that the flow in the reaction zone corresponds to the Zeldovich‐von Neumann‐ Döring theory with a characteristic reaction time of 50 ns. The dependence of the detonation velocity on the initial density is well approximated by a similar line for HMX with a charge diameter of 20 mm. With a decrease in diameter to 4 mm, a sharp drop in the detonation parameters of CL‐20 has been recorded. The initiation of detonation under shockwave action is investigated, and the comparison of data for CL‐20 and PETN has shown that their shockwave sensitivity is quite close. The experiments on the acceleration of thin steel plates by detonating CL‐20 charges have been performed, and it is found that its accelerating ability is higher than that of HMX and retarded RDX.