Initial Lift Research Articles

From NAFTA to USMCA: Can a Good Idea that Came Too Late Be Born Again?

This article analyzes from the trade perspective the lower-than-expected growth dividends of the export-led strategy adopted by Mexico in the 1990s. Particular attention is given to employment, labor productivity, and regional outcomes. The North American Free Trade Agreement (nafta) caused Mexican exports to skyrocket in the first years of its implementation. This initial lift was quickly sapped by China’s emergence after its entry into the World Trade Organization (wto) in 2001. Recent years witnessed a renewed dynamism of Mexican presence in the U.S. market. In an international context marked by deglobalization and decoupling, this rebound is expected to continue under the United States-Mexico-Canada Agreement (usmca). Yet, in order to deliver economic growth, Mexico needs to diversify the geographical location of its exporting industries. The analysis of Mexican exports shows also that idiosyncratic weaknesses, such as the low contribution of the business services sector or the deficient trade and transport infrastructure, must be addressed.

Mathematical Modelling of the Impact of Non-Pharmacological Strategies to Control the COVID-19 Epidemic in Portugal

In this paper, we present an age-structured SEIR model that uses contact patterns to reflect the physical distance measures implemented in Portugal to control the COVID-19 pandemic. By using these matrices and proper estimates for the parameters in the model, we were able to ascertain the impact of mitigation strategies employed in the past. Results show that the March 2020 lockdown had an impact on disease transmission, bringing the effective reproduction number (R(t)) below 1. We estimate that there was an increase in the transmission after the initial lift of the measures on 6 May 2020 that resulted in a second wave that was curbed by the October and November measures. December 2020 saw an increase in the transmission reaching an R(t) = 1.45 in early January 2021. Simulations indicate that the lockdown imposed on the 15 January 2021 might reduce the intensive care unit (ICU) demand to below 200 cases in early April if it lasts at least 2 months. As it stands, the model was capable of projecting the number of individuals in each infection phase for each age group and moment in time.

Modeling the Flow State Sensitivity of Actuation Response on a Stalled Airfoil

In this work, we perform direct numerical simulations of leading-edge momentum injection of a NACA0009 airfoil at poststall angles of attack. It is found that the lift response is highly dependent upon the instantaneous state of the wake at the time of actuation, which is characterized by the phase of the vortex-shedding limit cycle present in the unactuated system. In particular, we find that actuating at a phase of the limit cycle corresponding to the maximum lift gives the largest maximum in transient lift response, whereas actuating near the lift minimum gives a smaller initial transient lift enhancement and can lead to a significant reduction in the amplitude of the limit cycle. As well as characterizing this phase dependency, we develop a reduced-order model that can capture this behavior. This is achieved by applying dynamic mode decomposition with control to a concatenation of velocity and lift measurements from several training datasets. The resulting models can accurately capture the dynamics of the training datasets as well as for phases not included in the training data. We show that for this method of actuation, multiple control objectives with the same actuator can be achieved.

The interaction between microalgae and membrane surface in filtration by uniform shearing vibration membrane

Membrane fouling is an inevitable problem in the process of using membrane technology to filtrate microalgae. In the present study, a uniform shearing vibration membrane (USVM) system was proposed and utilized in algae filtration. USVM is a uniform circular motion whose induced shear rate is constant, which is more conducive to the mitigation of fouling. In the filtration experiments, as the frequency increased from 1 to 5 Hz, the membrane fouling decreased obviously. When the frequency is 5 Hz, USVM can filtrate algae with a constant flux and less membrane fouling, and few algae deposited on the membrane. Based on “extended Derjaguin, Landau, Verwey, Overbeek” (XDLVO) theory, the interaction force acting on algae and membrane was calculated to explain the mechanism that USVM can filtrate algae stably at the frequency of 5 Hz, and why the increased frequency could effectively mitigate membrane fouling. At 5 Hz, the initial lift force was 0.123 nN, the total interaction force was the repulsive force, and thus the algae could be prevented from being deposited on the membrane to reduce the membrane fouling. As the frequency decreased, the initial lift force and total interaction force declined, which could not effectively prevent algae deposition.

Design and Analysis of the US ITER Central Solenoid Module Lifting Fixture

The central solenoid (CS) consists of six large high field superconducting magnets (also known as modules) approximately 4 m in diameter and 2 m tall that weigh approximately 120 tonnes each. These large and complex modules create challenges during assembly of the CS that require the development of custom assembly tooling such as the CS lifting fixture. The CS module lifting fixture is designed to lift and stack the six CS modules in the assembly building on the ITER site. Because of its unique design, fabrication, and assembly features, no lifting attachments could be incorporated within or under the CS modules. This limitation motivated the development of a friction-based lift fixture. The design and evaluation of the CS module lifting fixture considered both worker safety and investment protection, and the assessments were performed to international codes and standards. The CS module lifting fixture consists of two principal subassemblies: spider assembly and ring weldment. These subassemblies allow the frictional force to be augmented by the mechanical advantage of shallow-angle wedges. Large radial preloads created by both screw jack assemblies and the weight of a CS module develop frictional forces capable of performing a lift with a safety factor of at least 2. The design effort resulted in the use of low friction linear bearings on angle surfaces to ensure constant pressure, integrated jacks for pretensioning the fixture prior to lifting, and load pin strain gauges for monitoring the normal force. Testing of various materials and surface treatments led to the selection of laminated aluminum and rubber pads as the friction interface on the CS lifting fixture side and a grit-blasted Nitronic 50 stainless steel band on the CS module side. A redundant lifting method using the module slings between the spider and module is also utilized after the initial friction lift. The CS lifting fixture provides a safe and reliable solution for lifting and stacking the CS module during assembly.

Aerodynamic characteristics of flexible wings with leading-edge veins in pitch motions

To demonstrate the effects of wing deformations on aerodynamic performances during the wing reversal, aerodynamic force/torque and flow vector-fields were measured. Wing models consisted of wing planes with various thicknesses and two leading-edge veins, which obstructed spanwise deformations (Case 1 as a rigid wing and Cases 2 to 4 as flexible wings). They also underwent three different pitching periods (t/TR,α=0.1,0.2, and 0.4) to determine the distinct changes in vortical structures and corresponding aerodynamic characteristics. Flexible wings generally showed a negative camber in the stroke motion, causing poor aerodynamic performance relative to a rigid wing. This was also related to the positive camber and camber change to the negative during the pitch motions. After the start of the stroke, the positive camber caused separated and weakened tip vortex (TV) structures, hindering leading-edge vortex (LEV) formations around the wingtip. Depending on the LEV shedding, the flexible wings generated less aerodynamic forces than the rigid wing in stroke motion. During the pitch motions, on the other hand, the dynamic cambers influenced rotational mechanisms such as the wing–wake interaction and rotational force, causing higher or less initial lift increment. As the t/TR,α increased, the amount of the lift augmentation decreased due to the weakened wing–wake interaction, instead showing a downwash. At t/TR,α=0.4, however, the higher initial lift peak was occurred due to the absence of distinct trailing-edge vortex (TEV) generation during the wing-reversal. This lack of the U_TEV2 led to the decline of the downwash. Thus, the delayed U_LEV1 dispersal and the U_TEV2 traces generated similar induced flows to the wing–wake interaction, resulting in higher lift augmentation. Furthermore, Case 2 achieved higher lift augmentations than the other cases in all pitching periods. The slight wing deformations not only reduced the distance between the vortices and the wing surface, but also caused the delayed vortex dispersals. These induced the stronger rapid flows toward the wing surface, causing the higher initial lift peaks. Case 2 also had the highest C¯L/C¯P,t at t/TR,α=0.1 than the other cases. These results suggest that the flexible wing with leading-edge veins can have higher aerodynamic efficiency in its specific chordwise flexibility range.

A transition from a large open pit into a novel “macroblock variant” block caving geometry at Chuquicamata mine, Codelco Chile

With a history of more than 100 years, Chuquicamata has become one of the largest open pits in the world. Its current depth of 1100 m, length of 4500 m and width of 3000 m, resulting in haulage distances of over 11,000 m from pit bottom to the processing plant or waste dumps, with waste/ore ratio greater than 4 and much lower grades, are effectively determining its profitable limit by the end of this decade. Currently, there are over 4300 Mt of geological resources containing 0.7% of copper and 340 ppm (1 ppm = 1 g/t) of molybdenum below the final pit shell. The corresponding orebody geometry is 3000 m northsouth, 300–800 m eastwest and the drilling campaign suggested the existence of more than 900 m of mineable ore from the final pit bottom. This is in spite of the fact that the Chuquicamata orebody is still open at depth. The business case to continue with the mining of the Chuquicamata orebody is to change from the current large open pit to a novel macroblock variant block caving geometry. This requires a production rate of 140,000 t/d (50 Mt per annum), with a continuous material handling system to achieve the 7-year ramp-up to full production. The resolution of a number of known technical, operational and logistical challenges outside current industry practises which Chuquicamata will face over its projected 40-year mine life is therefore essential. These challenges include simultaneous operations of open pit and underground macroblocks and from the initial lift to the second lift, rapid ramp-up and optimum sequencing of the planned macroblocks, early dilution from the west fault and late dilution from potential slope failures, and the potential for major operational hazards. An equally important issue to be addressed is cultural given that the mining history in the northern region of Chile, which includes Chuquicamata, is predominantly open pit. This paper presents a synopsis of the main challenges that the Chuquicamata underground project will face in order to meet the objectives of its corresponding business case. Those discussed and how they were resolved are: simultaneous operations, rapid ramp-up and optimum sequencing of the planned macroblocks, and early and late dilutions. The project is an example of the fact that there are no recipes or cook books in cave mining.

Predictability of walking ability and of bed-chair transfers at the end of inpatient rehabilitation period of elderly patients after stroke

Walking independently is one of the most important goals for patients post-stroke and their families. Standing up is an essential function for walking independently. The aim was to explore initial physical evaluation component that predict patients ability to stand up and walk independently at discharge from rehabilitation, in older adults’ post-stroke. One hundred and thirty-one elderly patients post-stroke admitted to rehabilitation. Excluded were patients with debilitating orthopedic conditions, or previous progressive neurological diseases. Initial evaluation, within 3–7 days of admission, included motor function, lower extremities muscle strength, sitting balance and cognitive assessment. Patients had a follow-up one week before discharge, the follow-up included two parts of the Functional Independence Measure (FIM) test: walking and chair-bed transition. Initial pelvic lift, bed rolling performance were significantly correlate ( r > 0.7, P < 0.01) to patients’ outcome measures at discharge and had highly significant prediction value. A combination of the inadequate static balance upon admission, dependence of rolling to the affected side and lack of independence at pre-stroke daily function predicted 85% chance that a patient will be dependent in walking at discharge. Inadequate static balance upon admission, major/full dependence of rolling to the less affected side and major/full dependence in pelvic lift at bed predicted 89% chance that patient will be dependent in chair-bed transfer at discharge. Initial physiotherapists evaluation to evaluate patient current functional status have a significant predictive value for patients’ outcome at discharge in terms of standing and walking. These clinical predictors can help in setting treatment goals, educating families, and coordinating expectations.

Particle resuspension by a periodically forced impinging jet

When hovering over sandy terrain, the rotor of helicopters generates a downward jet that induces resuspension of dust and debris. We investigate the mechanisms that govern particle resuspension in such flow using an Eulerian–Lagrangian approach based on large-eddy simulation of turbulence. The wake generated by the helicopter is modelled as a vertical impinging jet, to which a sequence of periodically forced azimuthal vortices is superposed. The resulting flow field provides a unique range of flow scales with which the particles can interact. Downstream of the impingement region, layers of negative azimuthal vorticity (secondary vortices) form on the upwash side of the primary azimuthal (large-scale) vortices. These layers then detach from the surface together with the near-wall (small-scale) vortices populating the wall-jet region. We show how the dynamics of sediments is governed by its interaction with these structures. After initial lift off from the impingement surface, particles accumulate in regions where near-wall vortices roll around the impinging azimuthal vortex, forming rib-like structures that either propel particles away from the azimuthal vortex or entrap them in the shear layer between the azimuthal and secondary vortices. We demonstrate that these trapped particles are more likely to reach the outer flow region and generate a persistent cloud of airborne particles. We also show that, in a time-averaged sense, particle resuspension and deposition fluxes balance each other near the impingement surface.

Gait Planning Research for an Electrically Driven Large-Load-Ratio Six-Legged Robot

Gait planning is an important basis for the walking of a legged robot. To improve the walking stability of multi-legged robots and to reduce the impact force between the foot and the ground, gait planning strategies are presented for an electrically driven large-load-ratio six-legged robot. First, the configuration and walking gait of the electrically driven large-load-ratio six-legged robot are designed. The higher-stable swing sequences of legs and typical walking modes are respectively obtained. Based on the Denavit–Hartenberg (D–H) method, the analyses of the forward and inverse kinematics are implemented. The mathematical models of the articulated rotation angles are respectively established. In view of the buffer device installed at the end of shin to decrease the impact force between the foot and the ground, an initial lift height of the leg is brought into gait planning when the support phase changes into the transfer phase. The mathematical models of foot trajectories are established. Finally, a prototype of the electrically driven large-load-ratio six-legged robot is developed. The experiments of the prototype are carried out regarding the aspects of the walking speed and surmounting obstacle. Then, the reasonableness of gait planning is verified based on the experimental results. The proposed strategies of gait planning lay the foundation for effectively reducing the foot–ground impact force and can provide a reference for other large-load-ratio multi-legged robots.

Ascending performance analysis for high altitude zero pressure balloon

This paper describes a comprehensive simulation for high altitude zero pressure balloon trajectories. A mathematical model was established to simulate the ascending process which considers the atmospheric conditions and thermodynamic variations. Influences of launch parameters on ascending performance were analyzed. The necessary quantity of initial lift gas was estimated and optimized, so that ensures no ballast consuming during the ascending process. The climbing rate was a governing parameter to evaluate the ascending performance. Based on the simulation, results revealed the apparent different effect on climbing rate at troposphere and stratosphere layers. Change in launch time and site mainly affect the climbing rate at the stratosphere and have no significant effect at the troposphere and tropopause altitudes. Meanwhile, change in launch date has a negligible effect on both layers. Due to the earth’s declination angle, the influence of the same launch latitude and the same launch longitude is not identical within a year. Also, results showed that the optimum lift gas quantity improved the climbing rate stability to obtain an accurate simulation.

Age-related differences in movement strategies and postural control during stooping and crouching tasks

While epidemiologic data suggests that one in four older adults have difficulty performing stooping and crouching (SC) tasks, little is known about how aging affects SC performance. This study investigated differences between young and older adults in lower limb kinematics and underfoot center of pressure (COP) measures when performing a series of SC tasks. Twelve healthy younger and twelve healthy older participants performed object-retrieval tasks varying in: (1) initial lift height, (2) precision demand, and (3) duration. Whole-body center of mass (COM), underfoot COP, and hip and knee angular kinematics (maximum angles and velocities) were analyzed. Compared to younger, older participants moved slower when transitioning into and out of pick-up postures that were characterized by less hip and knee flexion. Older participants also showed a diminished ability to adapt to the changing postural demands of each set of tasks. This was especially evident during longer tasks, whereby older individuals avoided high knee flexion crouching postures that were commonly used by younger participants. Older adults also tended to exhibit faster and more frequent COP trajectory adjustments in the anterior–posterior direction. It is likely that limitations in physical characteristics such as lower limb strength and range of motion contributed to these differences.

Field scale minimization of energy use for groundwater pumping

The limitations on an analytical solution to a groundwater management problem are tested with a field-scale problem and a modification to the analytical solution is proposed. The management problem minimizes the energy used for extracting water from the subsurface. The analytical solution depends on assumptions of linearity, steady state conditions, and adequate water demand to activate all wells and results in a stationarity condition that depends on initial lift and drawdown at each well. The field-scale problem is an aquifer in California with large historical drawdown. Testing of the analytical solution assumptions provides encouragement that the analytical solution may be useful to well-system operators for practical application to minimize energy consumption for pumping.

External circuit integration with electromagnetic particle in cell modeling of plasma focus devices

The pinch performance of a plasma focus (PF) device is sensitive to the physical conditions of the breakdown phase. It is therefore essential to model and study the initial phase in order to optimize device performance. An external circuit is self consistently coupled to the electromagnetic particle in cell code to model the breakdown and initial lift phase of the United Nations University/International Centre for Theoretical Physics (UNU-ICTP) plasma focus device. Gas breakdown during the breakdown phase is simulated successfully, following a drop in the applied voltage across the device and a concurrent substantial rise in the circuit current. As a result, the plasma becomes magnetized, with the growing value of the magnetic field over time leading to the gradual lift off of the well formed current sheath into the axial acceleration phase. This lifting off, with simultaneous outward sheath motion along the anode and vertical cathode, and the strong magnetic fields in the current sheath region, was demonstrated in this work, and hence validates our method of coupling the external circuit to PF devices. Our method produces voltage waveforms that are qualitatively similar to the observed experimental voltage profiles of the UNU-ICTP device. Values of the mean electron energy before and after voltage breakdown turned out to be different, with the values after breakdown being much lower. In both cases, the electron energy density function turned out to be non-Maxwellian.

Optimization of flight distance and robustness in the discus

This paper describes the optimal flight of a discus. Two objective functions are considered. One is the flight distance, and the other is robustness. Robustness is defined as insensitivity to deviations from the local optimal release conditions. The aim of the optimization is to maximize both flight distance and robustness. There are ten control and design variables, which include variables concerned with the skill of the thrower and with the design of the equipment. It was found that there is a trade-off between flight distance and robustness. It was also found that lower drag is preferable in the first half of flight, and greater lift and drag are preferable in the latter half of flight for the world record throw of 77 m. In order to do this, the initial angle between the velocity vector and the discus planform should be negative at the launch, even if the initial lift acts vertically downward. The attitude of the discus should be inclined at launch. The discus rolls with time during the flight, so that the discus planform becomes almost in the horizontal plane in the latter half of the flight. Lower mass is good for achieving longer flight distance, but conversely, mass should be slightly greater for robustness.

Efficiency of selection for body weight in a cooperative village breeding program of Menz sheep under smallholder farming system

We evaluated the efficiency of selection for body weight in a cooperative village breeding program for Menz sheep of Ethiopia under smallholder farming system. The design of the program involved organizing villagers in a cooperative breeding group to implement selective breeding of their sheep. The program was jump-started through a one-time provision of elite rams from a central nucleus flock, but subsequent replacement rams were selected from within the village flocks. We also evaluated body weight trends in a village where cooperative breeding was not implemented and individual farmers managed their flocks under traditional breeding practices. Under traditional breeding practices, genetic progress over 8 years either stagnated or declined in all the weights recorded. In the cooperative villages, selection differentials of 2.44 and 2.45 kg were achieved in 2010 and 2011 selection seasons, respectively. Birth weight, 3-month weight and 6-month weight increased, respectively, by 0.49, 2.29 and 2.46 kg in the third-generation lambs over the base generation. Improved rams supplied from the central nucleus flock gave an initial genetic lift of 14.4% in the 6-month weight. This was higher than the gain achieved from selection in the village flocks, which was 5.2%. Our results showed that village-based genetic improvement in body weights under smallholder conditions could be feasible if appropriate designs are adopted and that commencing with elite central nucleus rams help jump-start village-based programs.

Effects of Transfer Distance on Spine Kinematics for De-palletizing Tasks

One approach to reducing lateral bending and twisting in manual lifting tasks is to separate the lift's origin and destination, thereby encouraging lifters to step and turn their entire bodies. The objective of the current study was to determine how the degree to which one laterally bends and twists changes with transfer distance and initial lift height. Eighteen males lifted 10.9 kg boxes from a conveyor 0.5 m, 0.9 m, and 1.3 m above the floor and placed the boxes on a conveyor .50, .75, 1.00, 1.25, 1.50, or 1.75 m away at a height of .9 m. During picking, lateral bending and trunk extension velocities increased with increasing transfer distances. When placing the box, the degree of twisting decreased with increased transfer distance. In sum, when attempting to control the twisting and lateral bending during de-palletizing, the lift origin and destination should be separated by between 1 and 1.25 meters.

Biomechanical evaluation of the Eco-Pick lift assist: A device designed to facilitate product selection tasks in distribution centers

Developing lift assist devices to aid workers performing case tasks in distribution centers has been challenging given the movement of workers through a distribution facility. The objective of this work was to biomechanically evaluate a lift assist that can be integrated with pallet jacks and thereby move through the facility with the workers. Twelve participants transferred 16.4 kg boxes from one pallet to another manually and using the Eco-Pick lift assist. Electromyographic (EMG) activities were measured bilaterally in the Bicep, Deltoid, Latissimus Dorsi, and Erector Spinae muscles. The analysis showed that the 90th percentile normalized EMG values were significantly reduced in 4 of the 8 muscles sampled when using the Eco-Pick. Likewise, the 50th percentile normalized EMG data were significantly reduced for the Erector Spinae, Latissimus Dorsi, and the Bicep muscles when using the assist. For some of the muscles the advantage of the Eco-Pick was dependent upon the initial lift height or the placement height. Overall, it appears that this evaluation of the Eco-Pick's efficacy indicates that the device has the potential to be an effective means of reducing worker exposure to risk factors associated with back and shoulder injuries experienced during manual palletizing tasks found in distribution centers.

High-flux membrane separation using fluid skimming dominated convective fluid flow

We here report on the separation of yeast cells, with micro-engineered membranes having pores that are typically five times larger than the cells. The separation is due to neither shear-induced diffusion, nor initial lift, but to an effect similar to fluid skimming. The separation performance is linked to the ratio between cross-flow and transmembrane flux, and could be captured with a dimensionless number relating those. On the basis of this dimensionless number, flux and transmission of the cells could be predicted.The mechanism rests on having a sufficiently high cross-flow velocity, such that particles are not dragged too deep in the pore, but are dragged with the cross-flow back into the feed stream. The separation factor can simply be changed by changing the ratio between crossflow velocity and transmembrane flux.Since the membranes have very large pores, fouling does not play a role. Constant high transmembrane flux values of 200–2200L/m2h were reached for transmembrane pressures ranging from 0.02 to 0.4bar (typical industrial fluxes are 150L/m2hbar with a maximum of 2000L/m2hbar for short periods of time, comparable to 50–400L/m2h [1,2]). Although the effect is strongest with monodispersed pores, it will be possible to exploit the mechanism with conventional membranes. As such, it may open up a new route towards non-fouling crossflow microfiltration.

Synoptic velocity and pressure fields at the water–sediment interface of streambeds

This paper presents a comprehensive study of the near-bed hydrodynamics at non-moving streambeds based on laboratory experiments in open-channel flows. Pressure and velocity measurements were made with an array of up to 15 miniaturized piezo-resistive pressure sensors within the bed and slightly above it, and a two-dimensional particle-image-velocimetry (PIV) system measuring in streamwise vertical or horizontal planes. Three different types of bed materials were studied covering typical natural streambed conditions. The range of the global Reynolds number covered in the experiments was from 20000 to 200000. This study provides new insights into the flow structure over gravel beds based on the PIV measurements in both streamwise vertical and horizontal planes. In a streamwise vertical plane, large-scale wedge-like flow structures were observed where a zone of faster fluid over-rolled a zone with slower fluid. The resulting shear layer was inclined along the flow at an angle of 10°–25° to the bed, and was populated with clockwise rotating eddies. This mechanism occurred with sufficient frequency and shape to leave an ‘imprint’ in the velocity statistics. Typically, the described flow pattern is formed near the bed and is approximately scaled with the height of the logarithmic layer, although the biggest structures extended over the whole flow depth. In a horizontal near-bed plane, turbulent structures formed a patched ‘chessboard’ pattern with regions of lower and higher velocities that were elongated in the streamwise direction. Their lateral extension was typically two to four times the equivalent sand roughness with lengths up to several water depths. The dimensions of the regions were increasing linearly with the distance from the bed. These findings are consistent with conceptual models originally developed for smooth-wall flows. They also support observations made in rough-bed flume experiments, numerical simulations and natural rivers. Spatial fields of bed-pressure fluctuations were reconstructed by applying Taylor's frozen turbulence hypothesis on time data obtained with an array of pressure sensors. Based on the conditional sampling of velocity patterns associated with pressure-drop events a distinct bed-destabilizing flow-pressure pattern was identified. If a high-speed fluid in the wake of a large-scale wedge-like flow structure reaches the vicinity of the bed, a phenomenon akin to a Bernoulli effect leads to a distinctive low-pressure pattern. The resulting force may exceed the particles' submerged weight and is assumed to be able to give an initial lift to the particle. As a result, the exposed area of a particle is amplified and its angle of repose is reduced, increasing the probability for entrainment.