Mechanical stresses on cargo during ground operations in air transport

Mechanical stresses from the shocks and vibrations to which air cargo is exposed during transport and handling at airports have been investigated. Field trials were carried out at Arlanda Airport, Stockholm, and John F. Kennedy Airport, New York. It was found that when products are transported in the airport area, they are exposed to much higher stresses than during actual flight. Especially severe conditions were registered during transport at John F. Kennedy Airport. Measured stresses are related to the ground and mode of driving within the airport area, as well as to location on the pallet wagon. Guidelines as regards design of realistic, simulating test programs for product and package design are reported. Future development possibilities and suggestions for further research within the area are discussed.     

Catalytic motors for transport of colloidal cargo

Autonomous micro- and nanomotors should, in principle, deliver materials in a site-directed fashion, powering the assembly of dynamic, nonequilibrium superstructures. Here we demonstrate that catalytic Pt-Au nanomotors can transport a prototypical cargo: polystyrene microspheres. In addition, motors with Ni segments can overcome both Brownian orientational fluctuations and biased rotation of the rod-sphere doublet to enable persistent steerable uniaxial motion in an external magnetic field. Assuming a cargo-independent motive force, the speeds are inversely proportional to the Stokes resistance, which we compute using a completed double-layer boundary integral equation. In addition, we demonstrate motors transporting cargo via chemotaxis toward a H2O2 fuel source.     

Physical factors affecting kinesin-based transport of synthetic nanoparticle cargo

Recently, kinesin biomolecular motors and microtubules filaments (MTs) were used to transport metal and semiconductor nanoparticles with the long-term goal of exploiting this active transport system to dynamically assemble nanostructured materials. In some cases, however, the presence of nanoparticle cargo on MTs was shown to inhibit transport by interfering with kinesin-MT interactions. The primary objectives of this work were (1) to determine what factors affect the ability of kinesin and MTs to transport nanoparticle cargo, and (2) to establish a functional parameter space in which kinesin and MTs can support unimpeded transport of nanoparticles and materials. Of the factors evaluated, nanoparticle density on a given MT was the most significant factor affecting kinesin-based transport of nanoparticles. The density of particles was controlled by limiting the number of available linkage sites (i.e., biotinylated tubulin), and/or the relative concentration of nanoparticles in solution. Nanoparticle size was also a significant factor affecting transport, and attributed to the ability of particles < 40 nm in diameter to bind to the "underside" of the MT, and block kinesin transport. Overall, a generalized method of assembling and transporting a range of nanoparticle cargo using kinesin and MTs was established.     

Statistical characterization of acceleration levels of random vibrations during transport

Random vibration tests are an efficient way to simulate the mechanical vibratory effects caused by transportation. The usual method is only concerned with the frequency distribution pattern of the signal using the average power spectral density. This work offers an additional method based on detailed analysis of instantaneous acceleration levels of a real road transport, which enables modelling of the statistical distribution of these levels. Continuous recording of acceleration signal all along the journey permits confirmation that this statistical distribution is not a Gaussian distribution but a modified Gaussian distribution, for which parameters are estimated and discussed. Therefore, it is possible to evaluate the transport severity by working out the appearance probability of acceleration levels greater than a fixed threshold and also the statistical moments, i.e. second order moment which gives the root mean square value together with fourth order moment (kurtosis) which evaluates the difference between the experimental distribution and the Gaussian distribution. Copyright © 2011 John Wiley & Sons, Ltd.     

Mechanical stresses on products during air cargo transportation

A field study was conducted on board a Boeing 747 Combi (freight and passenger) aircraft on the route Stockholm (Arlanda) via Oslo (Gardermoen) to New York (John F. Kennedy Airport) and return to Stockholm (Arlanda). Shock and vibration, acting on the cargo, during air transportation were measured and analysed. The study encompassed all phases of the flight, including taxiing, climb, cruise during both calm and turbulent conditions, descent and approach, landing including touchdown and taxiing to apron. The field data were analysed by conventional frequency analysis and modelling techniques. In order to generalize the results, flight recorder data from the field trial and from other flights are included. Guide-lines for the development of realistic, simulation test programs for product and package design are included.     

Public transport during pandemic

Clean Technologies and Environmental Policy -     

Charging of molecules during transport

The possibility that a single molecule can acquire charge during steady-state transport is an open issue. We report first-principles calculations in a range of configurations of certain molecules and conclude the following. When a molecule is strongly coupled to the electrodes, charging is not sustainable. On the other hand, by using variable-length tunnel barriers (insulating tethers) one can enable and control charging. In particular, by using different combinations of "tethers", we demonstrate the possibility of charging by a single electron, sustainable over a wide bias range, and also the possibility of continuous linear charging when a gate voltage is applied.     

Asymmetric hybrid silica nanomotors for capture and cargo transport: towards a novel motion-based DNA sensor

An innovative self-propelled nanodevice able to perform motion, cargo transport, and target recognition is presented. The system is based on a mesoporous motor particle, which is asymmetrically functionalized by the attachment of single-stranded DNA onto one of its faces, while catalase is immobilized on the other face. This enzyme allows catalytic decomposition of hydrogen peroxide to oxygen and water, giving rise to the driving force for the motion of the whole system. Moreover the motor particles are able to capture and transport cargo particles functionalized with a noncomplementary single-stranded DNA molecule, only if a specific oligonucleotide sequence is present in the media. Functionalization with characteristic oligonucleotide sequences in the system implies a potential for further developments for lab-on-chip devices with applications in biomedical applications.     

An engineered virus as a bright fluorescent tag and scaffold for cargo proteins--capture and transport by gliding microtubules

We have demonstrated substantial capture and transport of fluorescently-labeled engineered cowpea mosaic virus (CPMV) using Drosophila kinesin-driven microtubules (MTs). The capture occurred through both NeutrAvidin (NA)-biotin and antibody (IgG)-antigen interactions. The MTs were derivatized with rabbit anti-chicken IgG or biotin, and the virus was conjugated with chicken IgG or NA. The CPMV conjugate was introduced into standard MT motility assays via convective flow at concentrations as high as 1.36 nM, and became bound to the MTs in densities as high as one virus per microm of MT length. When the CPMV conjugate was present at 17 pM, the average speed of the MTs bearing the NA-virus was 0.59 +/- 0.08 microm/sec, and that of those bearing IgG-virus was 0.52 +/- 0.15 microm/sec. These speeds are comparable to those of the unladen MTs (0.61 +/- 0.09 microm/sec), the presence of the virus on the MT causing only a small decrease in MT gliding speeds. The fluorescent CPMV appears to be superior to fluorescent polystyrene spheres of the same size, as both a reporter tag and a scaffold for MT-transported cargo proteins, because of its negligible non-specific adsorption and superior brightness. This work is important for the development of sensors based on nanolocomotion and biological recognition, or new strategies for the nanoassembly of biological structures.     

复合材料货舱地板立柱压溃响应试验

复合材料已经在民用飞机结构上得到广泛应用,并逐渐应用到主承力结构中,复合材料的脆性特点给飞机的适坠性设计和评估提出了新的挑战。复合材料机身货舱地板支撑立柱作为坠撞过程中的重要吸能元件,对机身结构抗坠撞性能有重要影响。复合材料货舱地板支撑立柱在压溃失效模式下吸收的能量明显多于整体弯曲失效模式。根据民用飞机复合材料货舱地板立柱的设计需求,对不同试件触发模式、高度、截面形式、截面面积等设计参数变化的T700GC碳纤维/环氧树脂复合材料立柱开展准静态和动态压溃试验,得到立柱吸能特性的关键影响参数和设计因子。      

空投货物冲击过程的仿真

空投物资方式越来越多地应用于救灾等紧急情况,为使物资安全着陆,往往是通过大量的外场试验来模拟实际情况,根据试验结果逐步改进货物的组合或包装.这种方法会耗费大量的时间和成本.在建立空投货物模型的基础上,利用计算机仿真货物与地面冲击的过程,分析下落速度、货物材料、厚度对最大加速度和脉冲持续时间的影响,用于指导实际的外场试验,从而节约时间和成本.     

Finite rotations in the description of continuum deformation

Finite rotations in continuum mechanics are described by means of either a proper orthogonal tensor or finite rotation vectors. Some algebraic relations concerning the finite rotations are reviewed. Formulae expressing them in terms of displacements are given. Along each of the curvilinear coordinate lines the finite rotations are shown to satisfy some systems of the linear first-order differential equations. Each system of the equations is presented in four different but equivalent forms associated with an intermediate stretched basis or with an intermediate rotated basis. Integrability conditions of the system of equations provide various alternative forms of compatibility conditions in continuum mechanics. The displacement field is expressed through the stretch and rotation fields in the form of three successive line integrals. The formula describes the displacements to within a constant finite translation and a constant finite rotation. The procedure proposed here generalizes the formula derived by Cesàro (1906) within the classical linear theory of elasticity.     

Mass transport during electromigration in aluminum-magnesium thin films

Single-crystal and polycrystalline aluminum thin film conductors, containing up to 6 at.% magnesium, were subjected to electromigration experiments at 175° and 225°C with current densities up to 4 × 10⁶ A/cm² and for times up to 50 000 h. These conductors were subsequently examined in order to obtain quantitative data on mass transport during electromigration.The results indicate that in an alloy containing about 6 at.% magnesium the lattice diffusivity of aluminum is larger by an order of magnitude than the corresponding lattice diffusivity in pure aluminum, whereas the grain boundary diffusivity of aluminum in this alloy is two orders of magnitude smaller than the corresponding value in pure aluminum. Further, the lattice and grain boundary diffusivities of magnesium in this alloy are of the same order of magnitude as the aluminum diffusivities, and appear to be slightly smaller in both cases.