Attenuation of short strongly nonlinear stress pulses in dissipative granular chains.

Attenuation of short, strongly nonlinear stress pulses in chains of spheres and cylinders was investigated experimentally and numerically for two ratios of their masses keeping their contacts identical. The chain with mass ratio 0.98 supports solitary waves and another one (with mass ratio 0.55) supports nonstationary pulses, which preserve their identity only on relatively short distances, but attenuate on longer distances because of radiation of small amplitude tails generated by oscillating small mass particles. Pulse attenuation in experiments in the chain with mass ratio 0.55 was faster at the same number of the particles from the entrance than in the chain with mass ratio 0.98. It is in quantitative agreement with results of numerical calculations with effective damping coefficient 6 kg/s. This level of damping was critical for eliminating the gap openings between particles in the system with mass ratio 0.55 present at lower or no damping. With increase of dissipation numerical results show that the chain with mass ratio 0.98 provides faster attenuation than the chain with mass ratio 0.55 due to the fact that the former system supports the narrower pulse with the larger difference between velocities of neighboring particles. The investigated chains demonstrated similar behavior at large damping coefficient 100 kg/s.

Localized microjetting in the collapse of surface macrocavities.

This paper focuses on the multiscale mechanism of collapse of hemicylindrical annular surface macrocavities in steel caused by high-strain, high-strain rate plastic flow of copper. Experiments and simulations revealed that a two-stage process is responsible for the observed microjetting phenomena: the formation of lateral copper microjets from the localized shear flow in copper at the interface during the filling of the cavity, and their subsequent collision at the apex of the macrocavity generating two additional horizontal microjets. The lengths of these microjets were an order of magnitude smaller than the cavity size but linearly scaled with the cavity radius. This process of microjet development is sensitive to the cavity geometry and is unlike the previously observed jetting phenomena in cavitation, impact crater collapse, or shock-induced cavity collapse.

Transmission and reflection of strongly nonlinear solitary waves at granular interfaces.

The interaction of a solitary wave with an interface formed by two strongly nonlinear noncohesive granular lattices displays rich behavior, characterized by the breakdown of continuum equations of motion in the vicinity of the interface. By treating the solitary wave as a quasiparticle with an effective mass, we construct an intuitive (energy- and linear-momentum-conserving) discrete model to predict the amplitudes of the transmitted solitary waves generated when an incident solitary-wave front, parallel to the interface, moves from a denser to a lighter granular hexagonal lattice. Our findings are corroborated with simulations. We then successfully extend this model to oblique interfaces, where we find that the angle of refraction and reflection of a solitary wave follows, below a critical value, an analogue of Snell's law in which the solitary-wave speed replaces the speed of sound, which is zero in the sonic vacuum.

Propagation of rarefaction pulses in discrete materials with strain-softening behavior.

We report on the dynamic behavior of strongly nonlinear discrete materials with anomalous strain-softening behavior. Rarefaction solitary waves found in numerical calculations agree well with the exact solution to the continuum wave equation. Compression pulses generated by impact quickly disintegrate into a leading rarefaction solitary wave followed by an oscillatory wave train containing localized excitations. Such behavior is favorable for metamaterials design of shock absorption layers as well as tunable information transmission lines for scrambling of acoustic information.

Highly nonlinear pulse splitting and recombination in a two-dimensional granular network.

The propagation of highly nonlinear signals in a branched two-dimensional granular system was investigated experimentally and numerically for a system composed of chains of spherical beads of different materials. The system studied consists of a double Y-shaped guide in which high- and low-modulus/mass chains of spheres are arranged in various geometries. We observed the transformation of a single or a train of solitary pulses crossing the interface between branches. We report fast splitting of the initial pulse, rapid chaotization of the signal and impulse redirection and bending. Pulse and energy trapping was also observed in the branches. Numerical analysis based on Hertzian interaction between the particles and the side walls of the guide was found in agreement with the experimental data, except for nonsymmetric arrangements of particles excited by a large mass striker.

Shock wave structure in a strongly nonlinear lattice with viscous dissipation.

The shock wave structure in a one-dimensional lattice (e.g., granular chain of elastic particles) with a power law dependence of force on displacement between particles (F proportional to delta(n)) with viscous dissipation is considered and compared to the corresponding long wave approximation. A dissipative term depending on the relative velocity between neighboring particles is included to investigate its influence on the shape of a steady shock. The critical viscosity coefficient p(c), defining the transition from an oscillatory to a monotonic shock profile in strongly nonlinear systems, is obtained from the long-wave approximation for arbitrary values of the exponent n. The expression for the critical viscosity is comparable to the value obtained in the numerical analysis of a discrete system with a Hertzian contact interaction (n=3/2) . The expression for p(c) in the weakly nonlinear case converges to the known equation for the critical viscosity. An initial disturbance in a discrete system approaches a stationary shock profile after traveling a short distance that is comparable to the width of the leading pulse of a stationary shock front. The shock front width is minimized when the viscosity is equal to its critical value.

Tunability of solitary wave properties in one-dimensional strongly nonlinear phononic crystals.

One-dimensional strongly nonlinear phononic crystals were assembled from chains of PTFE (polytetrafluoroethylene) and stainless-steel spheres with gauges installed inside the beads. Trains of strongly nonlinear solitary waves were excited by impacts. A significant modification of the signal shape and an increase of solitary wave speed up to two times (at the same magnitude of dynamic contact force) were achieved through a noncontact magnetically induced precompression of the chains. The data for the PTFE based chains are presented for the first time and the data for the stainless-steel beads chains are extended into a range of maximum dynamic forces more than one order of magnitude lower than previously reported. Experimental results agreed reasonably well with the long-wave approximation and numerical calculations based on the Hertz interaction law for particles interactions.

Strongly nonlinear wave dynamics in a chain of polymer coated beads.

Strongly nonlinear phononic crystals were assembled from a chain of Parylene-C coated steel spheres in a polytetrafluoroethylene holder. This system exhibits strongly nonlinear properties and extends the range of materials supporting sonic-vacuum-type behavior. The combination of a high density core and a soft (low elastic modulus) coating ensures a relatively low velocity of wave propagation. The bead contact interaction caused by the deformation of the Parylene coating can be described by classical nonlinear elastic Hertz theory with an effective value of the elastic modulus equal to 15 GPa for the contact interaction. Strongly nonlinear solitary waves excited by impacts were investigated experimentally and compared to chains composed of uniform steel beads. Fracture of the polymer coating was detected under relatively large pulse amplitude.

Energy trapping and shock disintegration in a composite granular medium.

We report the first experimental observation of impulse confinement and the disintegration of shock and solitary waves in one-dimensional strongly nonlinear composite granular materials. The chains consist of alternating ensembles of beads with high and low elastic moduli (more than 2 orders of magnitude difference) of different masses. The trapped energy is contained within the "softer" sections of the composite chain and is slowly released in the form of weak, separated pulses over an extended period of time. This effect is enhanced by using a specific group assembly and precompression.

Anomalous wave reflection at the interface of two strongly nonlinear granular media.

Granular materials exhibit a strongly nonlinear behavior affecting the propagation of energy and information. Dynamically self-organized strongly nonlinear solitary waves are the main information carriers in granular chains. We report the first experimental observation of the dramatic change of solitary wave reflectivity from the interface of two granular media triggered by a magnetically induced precompression. It may be appropriate to name this phenomenon the "acoustic diode" effect. We explain this effect by the high gradient of particle velocity near the interface.

Strongly nonlinear waves in a chain of Teflon beads.

One-dimensional "sonic vacuum" type phononic crystals were assembled from a chain of polytetrafluoroethylene (PTFE,Teflon) spheres with different diameters in a Teflon holder. It was demonstrated that this polymer-based sonic vacuum, with exceptionally low elastic modulus of particles, supports propagation of strongly nonlinear solitary waves with a very low speed. These solitary waves can be described using the classical nonlinear Hertz law despite the viscoelastic nature of the polymer and high strain rate deformation of the contact area. The experimentally measured speeds of solitary waves at high amplitudes are close to the theoretically estimated values with a Young's modulus of 1.46 GPa obtained from shock wave experiments. This is significantly higher than the Young's modulus of PTFE from ultrasonic measurements. Trains of strongly nonlinear solitary waves excited by an impact were investigated experimentally and were found to be in reasonable agreement with numerical calculations based on Hertz interaction law though exhibiting a significant dissipation.

[DNA-methylases from different strains of Bacillus subtilis and Bacillus natto]. / DNK-metilazy razlichnykh shtammov Bacillus subtilis i Bacillus natto.

DNA-methyltransferase activity has been detected in some of Bacillus subtilis and Bacillus natto strains. Two strains of Bacillus subtilis exhibited DNA-cytosine methyltransferase activity, and the strains of Bacillus natto exhibited DNA-adenine methyltransferase activity. A possible effect of DNA-methyltransferase specificity on transformation efficiency is discussed.

[Effect of 5-azacytidine on E. coli cells with different DNA-methylases]. / Deistvie 5-azatsitidina na kletki E. coli s razlichnymi DNK-metilazami.

A correlation was found between the bacteriocide effect of 5-aza-C and the amount of cytosine DNA-methylases in E. coli cells. 5-Aza-C-DNA induced partial or complete inhibition of bacterial DNA-methylases with different site specificity; cytosine DNA-methylases were inhibited by the DNA more effectively than adenine DNA-methylase Eco dam. The inhibitory influence of 5-aza-C-DNA on cytosine DNA-methylases was due to the formation of stable inactive complexes between the enzyme and the non-methylating cytosine analog in the recognition sites. Cytosine DNA-methylase Eco RII formed a relatively firm bond with 5-aza-C-DNA, which could be disrupted by 1 M KCl; this disruption restores the DNA-methylase activity and the inhibiting capacity of 5-aza-C-DNA. Thus, the binding of cytosine DNA-methylase to 5-aza-C in DNA is noncovalent; the inhibition of the enzyme by 5-aza-C-DNA is reversible.

Does the DNA methylase Eco dam pair nucleotide sequences to form site-specific duplexes?

The Eco dam methylase is active on denatured DNA and single-stranded synthetic oligonucleotides containing GATC sites. The results suggest that on interaction with single-stranded oligonucleotides the Eco dam methylase is able to form a duplex structure within the GATC site, and that this duplex site is a substrate for enzyme.

[The ability of E. coli DNA methylases to modify denatured DNA]. / O sposobnosti DNK-metilaz E. coli modifitsirovat' denaturirovannye DNK.

Adenine and cytosine DNA methylases from different strains of E. coli are able to methylate denaturated and single-stranded DNAs.

[Use of DNA-methylases as reagents for the production of isotopically labeled DNAs]. / Ispol'zovanie DNK-metilaz v kachestve reagenta dlia polucheniia mechennykh izotopami DNK.

The method of incorporation of an isotopic label into DNA by means of DNA-methyltransferases (DNA-methylases) is proposed. DNA was no degraded and retained its biological activity in the DNA-methylase reaction. The specific activity of labelled DNA preparations can be increased, using the mixtures of different DNA-methylases in the enzymatic reaction. An isotopic label was incorporated into DNA, using DNA methylases M. .EcoRII, M.Eco dam and M.EcoMRE600 dcmI. An average activity of 1 microgram of labelled DNA preparations produced by S-adenosylmethionine (methyl-3H) with specific activity of 15 CU/mmol mas about 1 x 10(5) cpm.

[Isolation and properties of DNA-cytosine-methylase I from Escherichia coli MRE 600]. / Vydelenie i svoistva DNK-tsitozin-menilazy I iz Escherichia coli MRE600.

DNA-cytosine-methylase I was isolated and purified to homogeneity. The yield made up to about 30% of total activity. The enzyme molecular weight as determined by centrifugation in a sucrose gradient, by gel filtration and by electrophoresis in polyacrylamide gel in the presence of sodium dodecyl sulfate was found to be 45,000. The Michaelis constant was 1,8 . 10(-6) M for SAM and 2 . 10(-4) M for DNA. DNA-cytosine-methylase I modifies phage lambda DNA in 60 sites. This modification does not protect DNA from the effects of restriction endonucleases HpaII and BsuRI. The enzyme methylates DNA in the nucleotide sequence: 5'...Pur-MC-C-G-G-Pyr...3'.