Rigid Barrier Research Articles

Dynamical regimes of lipids in additivated liposomes with enhanced elasticity: A field-cycling NMR relaxometry approach

We study the molecular dynamics of lipids in binary large unilamellar liposomes suspended in D2O composed of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) or soy phosphatidylcholine (SPC) additivated with different percentiles of sodium deoxycholate (SDC). We use the fast field-cycling proton NMR relaxometry technique over a wide timescale and at diverse temperatures. A model previously validated in different formulations is here employed for the relaxometric analysis of elastic vesicles. A new dynamical regime is observed for the first time in additivated DMPC and additivated/non-additivated SPC liposomes. This surprising feature is discussed in terms of vesicle shape fluctuations, enhanced elasticity and lipid & additive diffusion within the membrane. The continuum elastic theory is revisited for a better understanding of recent experiments and those here presented. We address the point of deformability measurements across rigid permeable barriers versus measurements of the bending elastic modulus in free-standing vesicles.

PREPARATION AND PROPERTIES OF EXFOLIATED VERMICULITE-POLYAMIDE 6 NANOCOMPOSITE

Ion-exchange treatment of natural vermiculite (VER) with dodecylammonium (DDA) ions and subsequent preparation of a polyamide 6 (PA6) based nanocomposite was conducted to investigate the potential suitability of VER for use in polymer nanocomposites. In order to investigate the ion-exchange behavior, ground VER powder and DDA were treated at 60°C for 12 h, in which time the intercalation reaction was completed. DDA intercalation was rapid and complete for VER even in dilute DDA solution (0.5 mass%) at a low suspension VER concentration of 1 mass%. The VER-PA6 nanocomposite was formed via exfoliation of a DDA modified VER (DDAVER) layer. DDAVER was melt-kneaded with PA6 in a twin-screw extruder at 260°C. The morphology of the nanocomposite was characterized using X-ray diffraction and transmission electron microscopy. Measurements of the mechanical properties and methanol permeability were also carried out. The DDAVER-PA6 nanocomposite exhibits a high degree of VER exfoliation and the rigidity and gas barrier properties also appear to reflect the nanocomposite morphology. Addition of a small amount of DDAVER with 3 mass% sili- cate was sufficient to improve the rigidity, heat resistance and barrier properties of the nanocomposite.

An Impact Oscillator with A Grazing Cycle

An oscillator which impacts against a rigid barrier is taken into account. A cycle with zero impact velocity is discussed. The main result of this article concerns stability of the grazing cycle. A significant attention to a model with the variable coefficient of restitution depending on velocity is paid. The mechanical reasons for that are provided as well as new theoretical advantages have been discovered for the investigation of dynamics near a grazing cycle. The W-map which reduces the system with variable moments of impacts to that with fixed moments and simplifies the analysis, is defined. A new type of linearization system with two compounds is applied to investigate the stability of the grazing cycle whose existence is easily examined. A new approach to suppress a singularity, caused by the tangency, in linearization has been developed. Simulations are provided to visualize the stability of the grazing cycle.

Seismic-induced rockfalls and landslide dam following the October 30, 2016 earthquake in Central Italy

On October 30, 2016, a seismic event and its aftershocks produced diffuse landslides along the SP 209 road in the Nera River Gorge (Central Italy). Due to the steep slopes and the outcropping of highly fractured and bedded limestone, several rockfalls were triggered, of which the main event occurred on the slope of Mount Sasso Pizzuto. The seismic shock acted on a rock wedge that, after an initial slide, developed into a rockfall. The debris accumulation blocked the SP 209 road and dammed the Nera River, forming a small lake. The river discharge was around 3.6 m3/s; the water overtopped the dam and flooded the road. By a preliminary topographic survey, we estimated that the debris accumulation covers an area of about 16,500 m2, while the volume is around 70,000 m3. The maximum volume occupied by the pre-existing talus mobilized by the rockfall is about 20% of the total volume. Besides blocking the road, the rockfall damaged a bridge severely, while, downstream of the dam, the water flow caused erosion of a road embankment. A rockfall protection gallery, a few hundred meters downstream of the dam, was damaged during the event. Other elastic nets and rigid barriers were not sufficient to protect the road from single-block rockfalls, with volumes around 1–2 m3. Considering the geological and geomorphological conditions, as well as the high seismicity and the socioeconomic importance of the area, a review of the entire rockfall protection systems is required to ensure protection of critical infrastructure and local communities.

Lignocellulose pretreatment in a fungus-cultivating termite.

Depolymerizing lignin, the complex phenolic polymer fortifying plant cell walls, is an essential but challenging starting point for the lignocellulosics industries. The variety of ether- and carbon-carbon interunit linkages produced via radical coupling during lignification limit chemical and biological depolymerization efficiency. In an ancient fungus-cultivating termite system, we reveal unprecedentedly rapid lignin depolymerization and degradation by combining laboratory feeding experiments, lignocellulosic compositional measurements, electron microscopy, 2D-NMR, and thermochemolysis. In a gut transit time of under 3.5 h, in young worker termites, poplar lignin sidechains are extensively cleaved and the polymer is significantly depleted, leaving a residue almost completely devoid of various condensed units that are traditionally recognized to be the most recalcitrant. Subsequently, the fungus-comb microbiome preferentially uses xylose and cleaves polysaccharides, thus facilitating final utilization of easily digestible oligosaccharides by old worker termites. This complementary symbiotic pretreatment process in the fungus-growing termite symbiosis reveals a previously unappreciated natural system for efficient lignocellulose degradation.

Prediction Method on Vehicle Acceleration in Frontal Offset Impact Sled Test

Vehicle impact acceleration has been widely used to reproduce the impact process in crash CAE analysis and the sled test. In the sled test for frontal rigid barrier impact, B-pillar lower accelerations were used as input pulses. But for the frontal offset impact, the magnitudes and directions of left and right B-pillar lower accelerations are significantly different, which makes the selection of vehicle acceleration complicated. By simplifying the vehicle impact kinetic model, a new prediction algorithm for calculation the acceleration of any point on vehicle body was deduced. The new method was verified with the full scale impact data and the test results show that both the trends of the acceleration curves and the peaks of the calculated values have a strong consistency with the measured values.

Approximate solutions of some problems of scattering of surface water waves by vertical barriers

A class of mixed boundary value problems (bvps), occurring in the study of scattering of surface water waves by thin vertical rigid barriers placed in water of finite depth, is examined for their approximate solutions. Two different placings of vertical barriers are analyzed, namely, (i) a partially immersed barrier and (ii) a bottom standing barrier. The solutions of the bvps are obtained by utilizing the eigenfunction expansion method, leading to a mathematical problem of solving over-determined systems of linear algebraic equations. The methods of analytical least-square approximation as well as algebraic least-square approximation are employed to solve the corresponding over-determined system of linear algebraic equations and thereby evaluate the physical quantities, namely, the reflection and transmission coefficients. Further, the absolute values of the reflection coefficients are compared to the known results obtained by utilizing a Galerkin type of approximate method after reducing the bvps to integral equations whose complete solutions are difficult to be determined. Various combinations of discretization of the resulting dual series relations obtained in the present analysis are employed to determine the least-square solution.

New insights into the function of a versatile class of membrane molecular motors from studies of Myxococcus xanthus surface (gliding) motility.

Cell motility is a central function of living cells, as it empowers colonization of new environmental niches, cooperation, and development of multicellular organisms. This process is achieved by complex yet precise energy-consuming machineries in both eukaryotes and bacteria. Bacteria move on surfaces using extracellular appendages such as flagella and pili but also by a less-understood process called gliding motility. During this process, rod-shaped bacteria move smoothly along their long axis without any visible morphological changes besides occasional bending. For this reason, the molecular mechanism of gliding motility and its origin have long remained a complete mystery. An important breakthrough in the understanding of gliding motility came from single cell and genetic studies in the delta-proteobacterium Myxococcus xanthus. These early studies revealed, for the first time, the existence of bacterial Focal Adhesion complexes (FA). FAs are formed at the bacterial pole and rapidly move towards the opposite cell pole. Their attachment to the underlying surface is linked to cell propulsion, in a process similar to the rearward translocation of actomyosin complexes in Apicomplexans. The protein machinery that forms at FAs was shown to contain up to seventeen proteins predicted to localize in all layers of the bacterial cell envelope, the cytosolic face, the inner membrane (IM), the periplasmic space and the outer membrane (OM). Among these proteins, a proton-gated channel at the inner membrane was identified as the molecular motor. Thus, thrust generation requires the transduction of traction forces generated at the inner membrane through the cell envelope beyond the rigid barrier of the bacterial peptidoglycan.

Influence of particle size on the mechanism of dry granular run-up on a rigid barrier

Granular flows comprise a wide range of particle sizes. The particle size governs the degree of grain contact and inertial stresses in the flow, thus influencing the mechanism of impact against a rigid barrier. The current commonly adopted design approaches estimating the run-up height are based on the energy principle and the momentum approach. However, both neglect the discrete nature of flows, and do not consider the effects of particle size on the flow regime. In this study, physical experiments using different sizes of monodispersed sand and glass spheres were carried out to investigate the run-up mechanisms on a rigid barrier. Results have shown that the run-up height is not only dependent on the Froude number of the flow before impact, but also on the particle size which principally governs the mechanism of run-up. Inertial flows comprising large particles (the Savage number (NSav) > 0·1) profoundly transfer momentum vertically upon impact, resulting in significant grain saltation and high run-up heights. In contrast, frictional flows comprising fine particles (NSav < 0·1) tend to pile up without significant run-up due to a high degree of contact stresses. This implies that for flows with coarse particles entrained at the front of the flow by way of particle-size segregation, the run-up height is principally influenced by large particles that accumulate at the flow front.

Interaction between dry granular flow and deflectors

The application of seawall deflectors for reflecting inviscid waves into the sea have been well established. Recently, rigid barrier deflectors have been proposed prescriptively for mitigating geophysical landslides, but flow characteristics differ fundamentally from waves and merit investigation. In this study, flume tests were used to calibrate a discrete element model to explore the interaction between dry granular flow and rigid barrier deflectors. The deflector angle and length and the effective height (distance between deflector tip and channel base) were studied and compared to barriers without deflectors. Findings reveal that deflectors initially prevent spilling of vertical runup and reduce flow energy underneath the deflector. However, controlling overflow depends heavily on the deflector angle and length, with the effective height as ultimate governing parameter. The additional height provided by the deflector should therefore be considered as part of the design height rather than a prescriptive add-on. Longer deflector lengths shield deadzones from energy losses through grain shearing, thus resulting in higher peak overflow velocities. It is recommended that deflector lengths should be less than 10% of the expected flow depth to suppress peak overflow velocities. Perpendicular deflectors tend to enhance faster energy dissipation through increased deadzone confining stress.

Impact mechanisms of granular and viscous flows on rigid and flexible barriers

Structural countermeasures such as rigid and flexible barriers are commonly installed in mountainous regions to intercept mass-wasting processes. Without sufficient and reliable comparable physical data, the study of impact mechanisms remains difficult and not well understood. In this study, a newly developed flexible model barrier together with a rigid barrier are used to simulate either dry granular or viscous liquid impacts on these model barriers in a geotechnical centrifuge. The novel flexible barrier is made of four instrumented cables controlled by spring mechanisms to replicate a bilinear prototype loading response. Tests revealed that regardless of barrier type, both dry granular and viscous flows could have similar frontal dynamic impact coefficients around unity. Compared with the kinetic energy of flow mass (∼10 MJ), only 249 kJ of flexible barrier energy capacity was mobilized. This implies that debris-resisting barriers may only be required to intercept the dynamic flow front as the subsequent flow energy may mainly be dissipated through internal shearing. Attributing to the large deformation of the flexible barrier, the granular static load acting on the flexible barrier could be 39% lower than that on the rigid barrier, resulting in an active failure mode and a lower earth pressure.

Analysis and design of a crash attenuator for a lightweight racing car

In this paper, the crash safety performance of a racing car is evaluated focusing on the optimisation of its frontal impact attenuator from the geometrical and material point of view. After the definition of the CAD model of the full vehicle, it was possible to convert it into finite elements applying properties, materials, contacts, boundary and initial conditions for each body components in order to conduct a dynamic analysis through LS-DYNA code. The full vehicle front impact simulation against a rigid barrier is carried out considering different attenuator structures. With respect to the previous literary works, geometries taken into account are much more complex. Moreover, conventional and CFRP composite materials are used during modelling in order to do a comparison between them in term of safety. The results show that the composite attenuators can be more competitive than conventional absorbers of similar geometry in terms of intrusion and energy absorption.

Analysis and design of a crash attenuator for a lightweight racing car

In this paper, the crash safety performance of a racing car is evaluated focusing on the optimisation of its frontal impact attenuator from the geometrical and material point of view. After the definition of the CAD model of the full vehicle, it was possible to convert it into finite elements applying properties, materials, contacts, boundary and initial conditions for each body components in order to conduct a dynamic analysis through LS-DYNA code. The full vehicle front impact simulation against a rigid barrier is carried out considering different attenuator structures. With respect to the previous literary works, geometries taken into account are much more complex. Moreover, conventional and CFRP composite materials are used during modelling in order to do a comparison between them in term of safety. The results show that the composite attenuators can be more competitive than conventional absorbers of similar geometry in terms of intrusion and energy absorption.

Coagulation of carbon clusters in a detonation wave

The effect of the parameters of a charge of TNT/RDX alloys and their detonation conditions on the coagulation of carbon on the isentrope of the detonation products is analyzed. In the region of liquid nanocarbon, coagulation occurs by coalescence of nanodroplets and in the region of solid nanocarbon, by their joining (sintering) simultaneously with crystallization. Therefore, the specific surface area of nanodiamonds calculated from their sizes is always larger than the measured value. Separation of nanodroplets in detonation products accelerates their coagulation and cooling due to the flow of cooler products around them. Evaluation of the distance between the surfaces of nanodroplets in various TNT/RDX alloys shows that they are small, smaller than nanodroplets. The conditions of rapid coalescence of nanodroplets during different deceleration of the products by rigid barriers are analyzed. An increase of up to five orders of magnitude in the size of diamond particles was established experimentally. The factors responsible for the change in the coagulation rate with the transition from heterogeneous to homogeneous TNT/RDX alloy with decreasing size of TNT/RDX particles are discussed.

The Characteristics and Origins of Koryŏ's Pluralist Society

Koryŏ, much more than the preceding Silla kingdom and the ensuing Chosŏn kingdom, was a vibrant society that embraced pluralism. From its founding that saw the unification under one state of the immediately preceding Three Kingdoms to its support of many competing philosophical beliefs, Koryŏ flourished within a truly international milieu. The start of the tenth century, witnessing the collapse of the Tang dynasty, opened much of East Asia to change, which Koryŏ readily accepted. As a maritime state, that received new ideas and goods from around the region, international trade flourished and rigid social barriers were relaxed. Koryŏ exemplified the idea of unity within variety.

The Characteristics and Origins of Koryŏ’s Pluralist Society

Abstract Koryŏ, much more than the preceding Silla kingdom and the ensuing Chosŏn kingdom, was a vibrant society that embraced pluralism. From its founding that saw the unification under one state of the immediately preceding Three Kingdoms to its support of many competing philosophical beliefs, Koryŏ flourished within a truly international milieu. The start of the tenth century, witnessing the collapse of the Tang dynasty, opened much of East Asia to change, which Koryŏ readily accepted. As a maritime state, that received new ideas and goods from around the region, international trade flourished and rigid social barriers were relaxed. Koryŏ exemplified the idea of unity within variety.

Calvert Casey's Wasted Narratives

In the 1960s, Calvert Casey wrote fiction and essays in support of the Cuban Revolution as a member of Lunes de Revolucion and Casa de las Americas before going into exile. This essay argues that he developed a revolutionary, though ultimately wasted, model by which individuals can form a political community despite the rigid social barriers that persisted from Cuba's colonial and neocolonial past. In his writings, Casey explores Havana's sewers and the forgotten stories of the capital city. His focus on literal and figurative waste is not an isolated moment in the history of Cuban aesthetics, but one that he locates in the works of nineteenth-and early twentieth-century Cuban authors, including Cirilo Villaverde, Ramon Meza, and Miguel de Carrion. Casey critiques a certain Romantic vision of the past that, in his view, idealized pre-Revolutionary Cuba as a tropical paradise set for epic struggles and sublime realizations. Against this mythical, Romantic image of the Cuban nation, he proposes an aesthetics and politics without the lofty, normative values that exclude images of sullied objects, disreputable places, and people getting wasted. The essay concludes with an analysis of the film P.M. alongside Casey's posthumously published short story Piazza Margana to situate both of these seemingly aberrant texts within a long-standing, though infrequently celebrated, national tradition of reveling in filthy places packed with writhing, drunken bodies.

Bifurcation analysis of a stochastically excited vibro-impact Duffing-Van der Pol oscillator with bilateral rigid barriers

This study focuses on the bifurcation analysis of a Duffing-Van der Pol (DVDP) oscillator with rigid barriers, subjected to additive white noise excitations. This involves mapping the non-smooth vibro-impact system on a continuous phase plane through non-smooth variable transformations. The formulation considers the general case of asymmetrically positioned both sided rigid barriers. The probabilistic description of the system dynamics is subsequently defined through the corresponding Fokker-Planck (FP) equation. The stationary probability density function of the response is numerically obtained by solving the FP equation using finite element method. The stochastic stability of the vibro-impact DVPD oscillator is examined both in terms of D- and P-bifurcations.

Acoustic impact on the laminated plates placed between barriers

On the basis of previously derived equations, analytical solutions are established on the forced vibrations of two-layer and three-layers rectangular plates hinged in an opening of absolutely rigid walls during the transmission of monoharmonic sound waves. It is assumed that the partition wall is situated between two absolutely rigid barriers, one of them by harmonic oscillation with a given displacements amplitude on the plate forms the incident sound wave, and the other is stationary and has a coating of deformable energy absorbing material with high damping properties. The behavior of acoustic environments in the spaces between the deformable plate and the barriers described by classical wave equation based on the ideal compressible fluid model. To describe the process of dynamic deformation of the energy absorbing coating of fixed barrier, two-dimensional equations of motion based on the use of models transversely soft layer are derived with a linear approximation of the displacement field in the thickness direction of the coating and taking into account the damping properties of the material and the hysteresis model for it. The influence of the physical and mechanical properties of the concerned mechanical system and the frequency of the incident sound wave on the parameters of its insulation properties of the plate, as well as on the parameters of the stress-strain state of the plate has been analyzed.

Flume investigation of the influence of rigid barrier deflector angle on dry granular overflow mechanisms

Mass-wasting processes are often intercepted using rigid barriers, which are sometimes equipped with deflectors to prevent overspilling. Despite the engineering value of deflectors, they are currently only installed using empirical and prescriptive approaches because flow interaction mechanisms are not well understood. A 5 m flume was used to study dry granular flow deposition and overflow processes with and without deflectors of varying angles. The deflector angle was varied as 0°, 30°, 45°, and 60° with respect to the horizontal plane. For the geometric and material parameters adopted in this study, experimental results reveal that deflector angles greater than 45° develop steep ramp-like deadzones that result in effective energy dissipation as approaching flow impacts the deflector, whereas deflectors less than 45° rapidly develop shallow ramp-like deadzones, which promote high-energy overflow. Deflectors of at least 45° are required to develop upward overflow launch angles, whilst deflectors of 30° or less result in downward overflow launch angles. Upward launch angles indicate that a steep deadzone develops and effectively dissipates flow energy. An orthogonal deflector increases launch lengths by 40% compared to a bare rigid barrier.