Gemini Surfactant-Induced DNA Compaction with Process Similar to Chromatin Assembly and the Kinetic Intermediates Captured by Surface Trapping

The intrachain DNA compaction induced by a cationic gemini surfactant hexyl-α,ω-bisdodecyldimethylammonium bromide (C₁₂C₆C₁₂Br₂) shows a process with high similarity to that of chromatin formation. The kinetic topological intermediates during compaction were successfully captured by surface trapping method. Further atomic force microscopy (AFM) characterization revealed that a phase-segregated state with the coexistence of compacted beadlike structures and elongated regions within a single DNA chain was generated at the first stage. Then more beadlike structures were formed to result in the necklace-like structures, which further assembled into closely packed higher-order structures while maintaining independence of each bead. The cooperative binding of the C₁₂C₆C₁₂Br₂ molecules onto the DNA chain should play crucial roles in such a compaction mode. Moreover, the structures obtained were found to be highly dependent on the sample preparation method.     

Correlation mechanism between force chains and friction mechanism during powder compaction

The relation between friction mechanism and force chains characteristics has not yet been fully studied in the powder metallurgy research area.In this work,a uniaxial compression discrete element model is established based on the compaction process of ferrous powder.Furthermore,the correlation mechanism between force chains and the friction mechanism during powder compaction is investigated.The simulation results reveal a strong correlation between the variation of the friction coefficient and the evolution of force chains.During the powder compaction,the friction coefficient would eventually tend to be stable,a feature which is also closely related to the slip ratio between particles.The side wall friction and the friction between particles would have an important effect on the direction of force chain growth in about one-third of the area near the side wall.The research results provide theoretical guidance for improving the densification process of the powder according to the force chain and friction.     

土体爆炸压密的原理及试验研究

针对目前土体爆炸压密理论研究不够深入、施工中主要依靠工程经验确定爆炸参数的现状,建立了基于塑性力学和爆炸力学的土体爆炸压密模型,推得压密效果(压密范围、压密程度)与爆炸参数之间的关系式,并通过室外试验进行验证.在孔径为48 mm的炮孔中进行了不耦合系数分别为2.000、1.714、1.500、1.333、1.200、1...     

Correlations and aggregate statistics in granular packs

We study how the aggregate statistical properties for density fluctuations in granular aggregates scale with the sample size and how such a scaling is associated with the correlations between grains. Correlations are studied both between grain positions and between Vorono? cell volumes, showing distinct behaviors and properties. A non-linear scaling in the aggregate volume fluctuations as function of the sample size is discovered and the connection between such anomalous scaling and correlations is explained. It emerges that volume fluctuations might be described by means of a single universal equation for all samples at all cluster sizes.     

Tire load rating to reduce soil compaction

Both experience and research warn that heavily loaded wheels of agricultural transport vehicles and heavy machinery may cause severe compaction damage to the farmland. A remedy consists of reducing both the wheel load and the contact pressure.Early in the 1990s, the author suggested an experimental examination of the problem of soil compaction under fully controlled conditions. The ensuing research program, which was sponsored by the Grant Agency of the Czech Republic, included a series of experiments with loaded wheels carried out in the experimental grounds of the Czech University of Agriculture and, subsequently, their physical modelling in the laboratory of the Department of Motor Vehicles, Technical faculty. This program has corroborated the idea that physical modelling under controlled conditions, complemented by an adequate evaluation procedure, has a promising potential to predict full-scale ground compaction and become a sound basis for practical measures. This paper describes the laboratory equipment, testing technique, and the way of evaluating the compaction potential of tires in terms of soil dry bulk density, leading to a Compaction Number (CN) rating of individual tires. Practically, the CN rating is supposed to be included in agricultural tire catalogues to complement the load capacity/inflation pressure values for hard ground (e.g., ETRTO specifications based on tire strength and wear).     

Modeling compaction in agricultural soils

Research was conducted to quantify the effect of tire variables (section width, diameter, inflation pressure); soil variables (soil moisture content, initial cone index, initial bulk density); and external variables (travel speed, axle load, number of tire passes) on soil compaction and to develop models to assess compaction in agricultural soils. Experiments were conducted in a laboratory soil bin at the Asian Institute of Technology in three soils, namely: clay soil (CS), silty clay loam soil (SCLS), and silty loam soil (SLS). A dimensional analysis technique was used to develop the compaction models. The axle load and the number of tire passes proved to be the most dominant factors which influenced compaction. Up to 13% increase in bulk density and cone index were observed when working at 3 kN axle load in a single pass using a 8.0–16 tire. Most of the compaction occurred during the first three passes of the tire. It was also found that the aspect ratio, tire inflation pressure and soil moisture content have significant effect on soil compaction. The initial cone index did not show significant effect. The compaction models provided good predictions even when tested with actual field data from previous studies. Thus, using the models, a decision support system could be developed which may be able to provide useful recommendations for appropriate soil management practices and solutions to site-specific compaction problems.     

Statistics of particle interactions in dense granular material under uniaxial compression

Stress evolution in a dense granular material is closely related to interactions of contacting particles. We investigate statistics related to particle interactions and the relationship between the averaged local relative motion and the macroscopic motion. The validity of the Voigt and Reuss assumptions is examined, and extensions to these assumptions are proposed. Effects of history in the dense granular material are investigated. Statistical samples used in this paper are obtained using three-dimensional numerical simulations of dense granular media under uniaxial cyclical compression. The results show that stresses arise mostly from normal forces between particles, and direct contributions from frictional tangential forces between particles are small. Tangential friction, however, significantly increases the particle contact time, and thus reduces the rate of contact breakage. The contact breakage rate is demonstrated to be a stress relaxation rate. Therefore, stress increases significantly with friction between particles as a result of prolonged relaxation time.     

Effects of tillage systems on compaction and crop yield of Albic Luvisol in Croatia

This four-year experiment was conducted in north-west Slavonia (agricultural area of Croatia) to evaluate the effects of different tillage systems on compaction of silty loam soil (Albic Luvisol). The compared tillage systems were: (1) conventional tillage (CT), (2) conservation tillage (CM), (3) no-tillage system (NT), and the crop rotation was corn (Zea mays L.) – winter wheat (Triticum aestivum L.) – corn – winter wheat. For detecting the soil compaction, bulk density and penetration resistance were measured during the growing seasons. In all seasons and tillage systems, the bulk density and penetration resistance increased with depth and the greatest increase from surface to the deepest layer in average was observed at CT system. The bulk density and penetration resistance increased at all tillage systems during the experiment, but the greatest increase was also observed at CT system. The greatest bulk density (1.66 Mg m⁻³) and the greatest increase of 6.4% were observed at CT system in the layer 30–35 cm. In the first season, the bulk density was the greatest at NT system, but during the experiment the lowest average increase of 1.9% was observed at this system. The greatest penetration resistance of all measurements (5.9 MPa) was observed in the last season at CT system in depth of 40 cm. The lowest average increase of penetration resistance 11.4% was also observed at NT system. The highest yield of corn in the first season was achieved with CT system while in other seasons the highest yield of winter wheat and corn was achieved with CM system.     

Soil displacement beneath an agricultural tractor drive tire

Soil strain transducers were used to determine strain in an initially loose sandy loam soil in a soil bin beneath the centerline of an 18.4R38 radial-ply tractor drive tire operating at 10% travel reduction. The initial depth of the midpoints of the strain transducers beneath the undisturbed soil surface was 220 mm. Strain was determined in the vertical, longitudinal, and lateral directions. Initial lengths of strain transducers were approximately 118 mm for the longitudinal and lateral transducers and 136 mm for the vertical transducer. The tire dynamic load was 25 kN and the inflation pressure was 110 kPa, which was a recommended pressure corresponding to the load. In each of four replications, as the tire approached and passed over the strain transducers, the soil first compressed in the longitudinal direction, then elongated, and then compressed again. The soil was compressed in the vertical direction and elongated in the lateral direction. Mean natural strains of the soil following the tire pass were −0.200 in the vertical direction, +0.127 in the lateral direction, and −0.027 in the longitudinal direction. The mean final volumetric natural strain from the strain transducer data was −0.099, which was only 35% of the mean change in natural volumetric strain calculated from soil core samples, −0.286. This difference likely resulted from the greater length of the lateral strain transducer relative to the 69 mm lateral dimension of the soil cores. The strain transducer data indicated the occurrence of plastic flow in the soil during one of the four replications. These results indicate the complex nature of soil movement beneath a tire during traffic and emphasize a shortcoming of soil bulk density data because soil deformation can occur during plastic flow while soil bulk density remains constant.     

Comparisons of different procedures of pre-compaction stress determination on weakly structured soils

Compaction is an important component of soil degradation. In this regard, the pre-compaction stress (σ_pc) concept is considered useful in mechanized agriculture nowadays. When the external forces exceed the internal strength (σ_pc) of soil, soil structure and soil physical quality will deteriorate. This concept was introduced at first for confined consolidation of non-structured, homogenized and saturated subsoils in civil engineering, though it is also suitable for agricultural conditions where the topsoil and subsoil are considered and both are often structured, heterogeneous and unsaturated. The best method for predicting σ_pc is by the plate sinkage test (PST) in the field, but it is expensive and time-consuming. This study was conducted to find an alternative laboratory method besides the confined compaction test (CCT) for predicting σ_pc. The CCT may not be a good method, especially at higher water contents, and for soils with low organic matter content, because of low sharpness of the critical region on the stress–strain curves. The study was performed on five soil types with a range of soil textures and organic matter content from central Iran using three loading types and three pF (i.e. Log [soil matric suction in cm]) values of 2.3, 2.7 and 2.9 with two replicates. Loading types consisted of CCT, the semi-confined compaction test (SCCT) and the kneading compaction test (KCT) at three maximum (or pre-compaction) stresses of 200, 400 and 600 kPa. The experiment was a completely randomized factorial design. The aim was to determine how accurately each loading type test could predict σ_pc of soil pre-compacted by one of the other methods. The applied combinations of CCT–SCCT, SCCT–CCT and KCT–CCT mean that the soil was pre-compacted by the first loading type and evaluated by the second one. The results showed that σ_pc and the sharpness of the σ_pc region were significantly affected by loading types as well as the soil conditions. The sharpest σ_pc region was observed in SCCT and the least sharp in CCT with the overall order being CCT–SCCT > SCCT–CCT > KCT–CCT. The sharpness of the σ_pc region was reduced for the soil samples with higher water content and coarser texture. Regardless of the soil and loading conditions, the prediction by SCCT was consistently more accurate than by CCT. The prediction of σ_pc by SCCT was more precise in comparison with CCT especially at higher stresses and soil water contents. However, the prediction of σ_pc by SCCT was very accurate at pF values of 2.7 and 2.9, and with low σ_pc values, when compared with the actual values of the σ_pc. For the clay soil at a pF value of 2.3, no pre-compaction region (i.e. zero σ_pc) could be determined by CCT at a maximum axial stress of 600 kPa. This was because of the incompressibility of soil water at this near-saturated soil condition at high stress. However, the sharpness of the critical region in SCCT was high enough to predict σ_pc satisfactorily. There was no significant difference between the combinations of SCCT–CCT and KCT–CCT in predicting σ_pc. The SCCT is a compromise method that lies between CCT and PST. SCCT has the advantage of using a limited and definite soil volume that can be modeled as a soil element. Marginal effects of disturbance caused by coring/sampling as well as pre-test sample preparation seem to have minor effects on the stress–strain curve determined by SCCT in comparison with CCT. Moreover, the soil volume needed for this test is the same as for CCT.