Linear Push Research Articles

A 56‐GBaud lumped linear push–pull driver for Mach–Zehnder modulator in 130‐nm SiGe technology

AbstractA fully differential lumped linear driver for Mach–Zehnder modulator has been presented and assessed in 130‐nm SiGe BiCMOS technology. Multitopology peaking techniques, especially T‐coil peaking method, have been employed to flatten the frequency response and increase the bandwidth. Degeneration resistors have been used to enhance circuit linearity. Simultaneously, improvements have been made to the output stage of the conventional single emitter follower push–pull) circuit to enhance the output eye diagram quality at higher transmission rates. The fabricated driver achieved a differential gain of 16.2 dB with a bandwidth of over 50 GHz, corresponding to a fixed output swing of over 3.2 Vppd within the automatic gain control loop. Time domain measurements, limited in speed by the measurement setup, reported a data rate up to 56 Gb/s none return to zero and 40‐GBaud 4‐levels pulse amplitude modulation with a bit error rate less than 10−12.

An obstacle separation method for robotic picking of fruits in clusters

Selectively picking a target fruit surrounded by obstacles is one of the major challenges for fruit harvesting robots. Different from traditional obstacle avoidance methods, this paper presents an active obstacle separation strategy that combines push and drag motions based on 3D visual perception to separate obstacles from the target. We define a region of interest 3D point cloud with a number of sub-blocks around the target to determine the presence or absence of obstacles and generate the separation paths accordingly. A linear push is used to clear the obstacles from the area below the target, while a zig-zag push that contains several linear motions is proposed to push aside more dense obstacles. The zig-zag push can generate multi-directional pushes and the side-to-side motion can break the static contact force between the target and obstacles, thus helping the gripper to receive a target in more complex situations. Moreover, we propose a novel drag operation to address the issue of mis-capturing obstacles located above the target, in which the gripper drags the target to a place with fewer obstacles and then pushes back to move the obstacles aside for further detachment. Furthermore, an image processing pipeline consisting of color thresholding, object detection using deep learning and point cloud operation, is developed to implement the proposed method on a newly developed harvesting robot. Field tests show that the proposed method can improve the picking performance substantially. This method helps to enable complex clusters of fruits to be harvested with a higher success rate than conventional methods.

Validity and Reliability of Kinematics Measured with PUSH Band vs. Linear Encoder in Bench Press and Push-Ups.

Background: The aim of this study was to compare the validity and reliability of a PUSH band device with a linear encoder to measure movement velocity with different loads during the push-up and bench press exercises. Methods: Twenty resistance-trained athletes performed push-up and bench press exercises with four different loads: without weight vest, 10-20-30 kg weight vest, bench press: 50–82% of their assumed 1 repetition maximum (1 RM) in steps of 10 kg. A linear encoder (Musclelab) and the PUSH band measured mean and peak velocity during both exercises. Several statistical analyses were used to investigate the validity and reliability of the PUSH band with the linear encoder. Results: The main findings of this study demonstrated only moderate associations between the PUSH band and linear encoder for mean velocity (r = 0.62, 0.70) and peak velocity (r = 0.46, 0.49) for both exercises. Furthermore, a good level of agreement (peak velocity: ICC = 0.60, 0.64; mean velocity: ICC = 0.77, 0.78) was observed between the two measurement devices. However, a significant bias was found with lower velocity values measured with the PUSH band in both exercises. In the push-up, both the linear encoder and PUSH band were deemed very reliable (ICC > 0.98; the coefficient of variation (CV): 5.9–7.3%). Bench press reliability decreased for the PUSH band (ICC < 0.95), and the coefficient of variance increased to (12.8–13.3%) for the velocity measures. Calculated 1 RM with the two devices was the same for the push-up, while in bench press the PUSH band under-estimated the 1 RM by 14 kg compared to the linear encoder. Conclusions: It was concluded that the PUSH band will show decreased reliability from velocity measures in a bench press exercise and underestimate load-velocity based 1 RM predictions. For training, the PUSH band can be used during push-ups, however caution is suggested when using the device for the purposes of feedback in bench press at increasing loads.

Relationship between linear velocity and tangential push force while turning to change the direction of the manual wheelchair.

Wheelchair propulsion is a major cause of upper limb pain and injuries for manual wheelchair users with spinal cord injuries (SCIs). Few studies have investigated wheelchair turning biomechanics on natural ground surfaces. The purpose of this study was to investigate the relationship between tangential push force and linear velocity of the wheelchair during the turning portions of propulsion. Using an instrumented handrim, velocity and push force data were recorded for 25 subjects while they propel their own wheelchairs on a concrete floor along a figure-eight-shaped course at a maximum velocity. The braking force (1.03 N) of the inside wheel while turning was the largest of all other push forces (p<0.05). Larger changes in squared velocity while turning were significantly correlated with higher propulsive and braking forces used at the pre-turning, turning, and post-turning phases (p<0.05). Subjects with less change of velocity while turning needed less braking force to maneuver themselves successfully and safely around the turns. Considering the magnitude and direction of tangential force applied to the wheel, it seems that there are higher risks of injury and instability for upper limb joints when braking the inside wheel to turn. The results provide insight into wheelchair setup and mobility skills training for wheelchair users.

External Hand Forces Exerted by Long-Term Care Staff to Push Floor-Based Lifts: Effects of Flooring System and Resident Weight.

The aim of this study was to investigate the effects of flooring type and resident weight on external hand forces required to push floor-based lifts in long-term care (LTC). Novel compliant flooring is designed to reduce fall-related injuries among LTC residents but may increase forces required for staff to perform pushing tasks. A motorized lift may offset the effect of flooring on push forces. Fourteen female LTC staff performed straight-line pushes with two floor-based lifts (conventional, motor driven) loaded with passengers of average and 90th-percentile resident weights over four flooring systems (concrete+vinyl, compliant+vinyl, concrete+carpet, compliant+carpet). Initial and sustained push forces were measured by a handlebar-mounted triaxial load cell and compared to participant-specific tolerance limits. Participants rated pushing difficulty. Novel compliant flooring increased initial and sustained push forces and subjective ratings compared to concrete flooring. Compared to the conventional lift, the motor-driven lift substantially reduced initial and sustained push forces and perceived difficulty of pushing for all four floors and both resident weights. Participants exerted forces above published tolerance limits only when using the conventional lift on the carpet conditions (concrete+carpet, compliant+carpet). With the motor-driven lift only, resident weight did not affect push forces. Novel compliant flooring increased linear push forces generated by LTC staff using floor-based lifts, but forces did not exceed tolerance limits when pushing over compliant+vinyl. The motor-driven lift substantially reduced push forces compared to the conventional lift. Results may help to address risk of work-related musculoskeletal injury, especially in locations with novel compliant flooring.

Fláajökull (north lobe), Iceland: active temperate piedmont lobe glacial landsystem

ABSTRACTA 1:6250 map of the foreland of Fláajökull's north lobe as it appeared in 1989, together with a 1:350 scale map of a sample area of recently exposed glacial landforms from 2014, enables an assessment of the spatial and temporal evolution of glacial landform assemblages at the margin of an active temperate piedmont lobe terminating at ice-marginal thickening till wedges. The pattern of landform development captured in these maps indicates that the glacier margin developed strong longitudinal crevassing and well-developed ice-marginal pecten (three-dimensional crenulations) during its historical recession. This is recorded by early recessional phase linear push moraines on well-drained distal slopes of the foreland and the later development of interrelated sawtooth moraines, crevasse squeeze ridges and till eskers, indicative of extending ice flow and poorly drained submarginal conditions. This landform record is a palaeoglaciological signature of a changing process–form regime inherent within the active temperate piedmont lobe landsystem model.

STATIC ANALYSIS OF HELICAL COMPRESSION SPRING

A spring is a flexible element used to exert a force or a torque and, at the same time, to store the energy. The force can be a linear push or pull, or it can be radial, acting similarly to a rubber band around a roll of drawings. The spring which is considered in the paper is a part of automobile horn, where the horn is used for maintain safe distance and it is subjected to varying load . The spring is analyzed through analytical and finite element method to check the variation in the deformation value as well as maximum shear stress value. By the results of ANSYS it is observed that analytical results and finite element method results are within the acceptable range.

Non linear push over assessment of heritage buildings in Istanbul to define seismic risk

The objectives of the Istanbul Seismic Risk Mitigation and Emergency Preparedness Project are to improve Istanbul’s preparedness for a potential earthquake. Within this framework “Risk Assessment of Cultural Heritage Buildings” was designed to address the vulnerability of cultural assets, specifically buildings with global cultural heritage value. One of the components of the project was the vulnerability and risk assessment of 170 historical buildings. After a discussion of the choice of the most appropriate earthquake scenario, the methodology used for assessing the effects of local site conditions on the seismic performance of selected cultural heritage buildings is presented. The purpose is to estimate the earthquake characteristics on the ground surface based on the earthquake characteristics on the engineering bedrock outcrop obtained from the probabilistic and deterministic hazard studies. The site specific elastic design spectra for each site are then further manipulated to obtain site specific non linear displacement spectra, so that these can be directly compared with capacity curves for the buildings obtained by using plasticity based limit state analysis. The procedure for obtaining the capacity curves is described and the choice of the most appropriate level of ductility and the equivalent reduction coefficient are discussed. A procedure to evaluate performance points and to define safety factors based on lateral acceleration, drift or expected damage level, is presented. The process of arriving at a risk evaluation and hence recommendation for strengthening or otherwise, is finally highlighted with respect to two comparable case studies.

Spectroscopic and photophysical properties of dicopper(I) metallocyclophanes

AbstractElectronic properties have been calculated for derivatives of long lived Cu(I) metallocyclophanes, which are self‐assembling coordination complexes that have metal–ligand charge‐transfer excited states. The molecules studied here are not the typical linear push–pull type with electron withdrawing and donating substituents at either end. The central C2 axis is preserved by putting the same type of substituent on one end of the cylindrical molecule. In theory, a pseudo‐octupolar species can be obtained by a proper balance of substituents at either end of the cylinder. DFT/PBE0 geometry optimizations of the quinoxaline/pyridine derivatives show a preference for the enantiomeric C2 isomer over the centrosymmetric Ci one. Geometry optimizations of the first excited state using TD‐DFT indicate loss of C2 symmetry and return to the ground state. First order hyperpolarizabilities were calculated using analytic gradients. Gas phase hyperpolarizabilities were enhanced by an order of magnitude when recalculated using a Polarized Continuum Model for the polar solvent acetonitrile. Electron withdrawing groups gave positive total β and donating groups gave negative β, both approximately 400 × 10−30 esu. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010

Reaction of enamines with trifluoromethyl containing carbonyl reagents

The reaction of linear push–pull enamines bearing a methyl group at the α-position with a set of trifluoromethylated carbonyl compounds was investigated. It has been found that the reaction proceeds at the methyl group of the enamines. The first computational study of the reaction between push–pull enamines and strong electrophilic reagents was reported. Out of three pathways considered DFT and MP2 calculations support ene-mechanism previously suggested based on experimental results only.

ChemInform Abstract: Reaction of Linear Push—Pull Enamines at the β′‐Position

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Nonlinear Optical Properties of the Linear Quadrupolar Molecule: Structure−Function Relationship Based on a Three-State Model

Theoretical descriptions of the molecular polarizability and second hyperpolarizability (α and γ) of the linear quadrupolar molecule are presented. By using a valence-bond and two charge-transfer states, three eigenfunctions of a quadrupolar molecule are obtained as linear combinations of these basis states. The analytic expressions for α and γ are obtained, and the physical picture on the nonlinear optical (NLO) response of the quadrupolar molecule is presented. By introducing the bond-length-alternation coordinates into the model Hamiltonian, the relationships of various vibrational characteristics, such as IR, Raman, and hyper-Raman intensities and vibrational frequencies, with respect to the molecular structure are established. The vibrational second hyperpolarizability is also compared with the electronic one, and the two quantities show similar trends as the charge-transfer character changes. A number of distinctive features are discussed by comparing the results with those of the linear push−pull p...

An elementary description of nonlinear optical properties of octupolar molecules: Four-state model for guanidinium-type molecules

A theoretical description of the molecular polarizability (α) and first and second hyperpolarizabilities (β and γ) of a guanidinium-type octupolar molecule is presented. By using a valence bond and three charge-transfer states with nonzero transfer integrals, the electronic states are obtained as linear combinations of these basis states. It is found that a doubly degenerate excited state is only optically coupled to the ground state. Based on the analytic expressions for α, β, and γ obtained, it is shown that the resultant tensor elements of β satisfy the symmetry requirements of point group D3h. Unlike the linear push–pull polyenes, the magnitudes of α, β, and γ of the guanidinium-type octupolar molecules increase as the charge-transfer character of the electronic ground state increases. Also, their dependences on the distance (d) between the donor and acceptor are briefly discussed.

Logarithmic-spiral focusing monochromator

A crystal monochromator with a logarithmic-spiral curvature has been designed as part of a low-angle x-ray diffraction camera that uses synchrotron radiation emanating from the storage ring SPEAR at Stanford Linear Accelerator Center. The logarithmic-spiral curvature allows a greater demagnification of the source than is permitted by a cylindrical geometry. Independent bending couples are applied at both ends of a rectangular crystal plate via pairs of parallel rods which rotate under a linear push from differential micrometer screws. Stepping motors control the bending mechanism, theta motion, guard slits, and camera alignment. A tenfold demagnification of the source is readily obtained. Focusing is rapid and easy. The crystal monochromator is combined with a focusing mirror in order to eliminate harmonics and produce a point focus (Webb, Samson, Stroud, Gamble, and Baldeschwieler, 1975).