Force Drift Research Articles

Analysis of Using Interlayer Seismic Isolation Technology in Storey-Adding Structure

Comparing with direct storey-adding structure, storey-adding isolated structure has different effect to the seismic performance of original structure. By establishing a multi-mass dynamic analysis model of storey-adding isolated structure in which isolation devices were set up, the damping mechanism of storey-adding isolated structure with different amounts of added floors and various frequency of isolation layer was studied. The results show that, with the increasing of added floors, the inter-storey shearing force and inter-storey drift increased more obviously, and the isolation effect is more desirable when the frequency of isolation layer is lower than 50% of the site characteristic frequency.

Force sensitive carbon nanotube arrays for biologically inspired airflow sensing

The compressive electromechanical response of aligned carbon nanotube (CNT) arrays is evaluated for use as an artificial hair sensor (AHS) transduction element. CNT arrays with heights of 12, 75, and 225 µm are examined. The quasi-static and dynamic sensitivity to force, response time, and signal drift are examined within the range of applied stresses predicted by a mechanical model applicable to the conceptual CNT array-based AHS (0–1 kPa). Each array is highly sensitive to compressive loading, with a maximum observed gauge factor of 114. The arrays demonstrate a repeatable response to dynamic cycling after a break-in period of approximately 50 cycles. Utilizing a four-wire measurement electrode configuration, the change in contact resistance between the array and the electrodes is observed to dominate the electromechanical response of the arrays. The response time of the CNT arrays is of the order of 10 ms. When the arrays are subjected to constant stress, mechanical creep is observed that results in a signal drift that generally diminishes the responsiveness of the arrays, particularly at stress approaching 1 kPa. The results of this study serve as a preliminary proof of concept for utilizing CNT arrays as a transduction mechanism for a proposed artificial hair sensor. Such a low profile and light-weight flow sensor is expected to have application in a number of applications including navigation and state awareness of small air vehicles, similar in function to natural hair cell receptors utilized by insects and bats.

Routine and timely sub-picoNewton force stability and precision for biological applications of atomic force microscopy.

Force drift is a significant, yet unresolved, problem in atomic force microscopy (AFM). We show that the primary source of force drift for a popular class of cantilevers is their gold coating, even though they are coated on both sides to minimize drift. Drift of the zero-force position of the cantilever was reduced from 900 nm for gold-coated cantilevers to 70 nm (N = 10; rms) for uncoated cantilevers over the first 2 h after wetting the tip; a majority of these uncoated cantilevers (60%) showed significantly less drift (12 nm, rms). Removing the gold also led to ∼10-fold reduction in reflected light, yet short-term (0.1-10 s) force precision improved. Moreover, improved force precision did not require extended settling; most of the cantilevers tested (9 out of 15) achieved sub-pN force precision (0.54 ± 0.02 pN) over a broad bandwidth (0.01-10 Hz) just 30 min after loading. Finally, this precision was maintained while stretching DNA. Hence, removing gold enables both routine and timely access to sub-pN force precision in liquid over extended periods (100 s). We expect that many current and future applications of AFM can immediately benefit from these improvements in force stability and precision.

Statistical Characterization of Structural Demand under Earthquake Loading. Part 1: Robust Estimation of the Central Value of the Data

This article is the first of two companion articles addressing the statistical characterization of seismic demand. Performance-based earthquake engineering methodologies often require the characterization of central value estimates of structural demand. Since outliers can occur in the data, central value estimates should be determined by robust estimation methods. The performance of 50 robust central value estimators is evaluated, for different sample sizes, using the chord rotation, curvature, shear force, and inter-story drift demands obtained after analyzing five reinforced concrete structures under real earthquake records scaled to several intensities. Based on the results, seven estimators are proposed for different sample sizes.

Statistical Characterization of Structural Demand under Earthquake Loading. Part 2: Robust Estimation of the Dispersion of the Data

Performance-based earthquake engineering methodologies often require a probabilistic model of structural demand. Since observations masking the probability distribution of the majority of the data are frequently found, robust estimation methods are proposed to estimate the probabilistic model parameters (i.e., central value and dispersion). The performance of thirty-three robust dispersion estimators is evaluated, for different sample sizes, using the chord rotation, curvature, shear force, and inter-story drift demands obtained after analyzing five reinforced concrete structures under real earthquake records scaled to several intensities. Based on the results, combinations involving dispersion and central value (defined in a companion article) estimators are proposed.

Thermal force drift wave

A drift instability of a collisional magnetized plasma, unstable due to the Braginskii thermal force but not requiring any direct dissipation such as resistivity or electron inertia, is examined. Unlike conventional drift-modes, the maximum growth rate of the thermal force drift wave (TFDW) is of order the drift frequency, making for a strongly turbulent nonlinear state. A 3D, magnetized two-fluid code is developed to allow the study of both ideal MHD modes as well as lower frequency drift modes. The governing equations are essentially the ideal MHD equations with the inclusion of Hall and thermal force terms in Ohm’s law. This set of equations is reduced in a finite β, long parallel wavelength, and small but significant Larmor radius ordering and tested for shear Alfven waves, parallel sound waves, and drift modes. The code is employed to recover the TFDW instability, to verify the code against the mode’s analytic linear characteristics, and to study the nonlinear behavior of the TFDW. The TFDW growth is strongly suppressed by parallel thermal conduction and thus this mode is more likely to be observed in low temperature plasmas.

Assessment of the Statistical Distributions of Structural Demand Under Earthquake Loading

Many existing probabilistic seismic safety assessment studies assume that structural demand conditional to a seismic intensity follows a lognormal distribution. Based on the analysis of five reinforced concrete structures subjected to real earthquake records scaled to several intensities, an in-depth analysis of this assumption is performed using adequate statistical methods. The considered demand parameters are the chord rotation, curvature, shear force, and inter-story drift. The results found indicate that the lognormal distribution is suitable for the probabilistic modeling of the considered demand parameters. In addition, the normal distribution was also found suitable for the shear force demand.

Sickle cell anemia pathophysiology: Back to the data

Sickle cell anemia pathophysiology: Back to the data

Drift tube soft-landing for the production and characterization of materials: Applied to Cu clusters

We have recently developed a soft-landing (SL) instrument that is capable of depositing ions onto substrates for preparative and developmental research of new materials using a laser ablation source. This instrument was designed with a custom drift tube and a split-ring ion optic for the isolation of selected ions. The drift tube allows for the separation and thermalization of ions formed after laser ablation through collisions with an inert bath gas. These collisions allow the ions to be landed at energies below 1 eV onto substrates. The split-ring ion optic is capable of directing ions toward the detector or a landing substrate for selected components. Experiments will be shown ablating Cu using an Nd:YAG (1064 and 532 nm) for cluster formation and landing onto a muscovite (mica) surface. The laser ablation of Cu in 8 Torr of He gas gives a spectrum that contains multiple peaks corresponding to Cu(n), Cu(n)O(m) clusters, and their corresponding isomers. Atomic force microscopy and drift tube measurements were performed to characterize the performance characteristics of the instrument.

Automated setpoint adjustment for biological contact mode atomic force microscopyimaging

Contact mode atomic force microscopy (AFM) is the most frequently used AFM imagingmode in biology. It is about 5–10 times faster than oscillating mode imaging (inconventional AFM setups), and provides topographs of biological samples withsub-molecular resolution and at a high signal-to-noise ratio. Unfortunately, contact modeimaging is sensitive to the applied force and intrinsic force drift: inappropriate force appliedby the AFM tip damages the soft biological samples. We present a methodologythat automatically searches for and maintains high resolution imaging forces. Wefound that the vertical and lateral vibrations of the probe during scanning arevaluable signals for the characterization of the actual applied force by the tip.This allows automated adjustment and correction of the setpoint force during anexperiment. A system that permanently performs this methodology steered the AFMtowards high resolution imaging forces and imaged purple membrane at molecularresolution and live cells at high signal-to-noise ratio for hours without an operator.

A biaxial hysteretic model for a structural system incorporating strength deterioration and pinching phenomena

A biaxial hysteretic model is developed to take into account the commonly observed hysteretic characteristics of strength and stiffness degradation, pinching and biaxial interaction. The concept of zero force point is proposed to develop the biaxial hysteretic model. Two non-linear inelastic springs and one linear elastic spring are connected in parallel to define the cyclic behavior of the proposed biaxial hysteretic model. The proposed biaxial hysteretic model is rate-independent and capable of simulating not only global (such as story shear force versus story drift response of the whole structure) but also the local hysteretic behavior of structural member (such as moment versus curvature or plastic rotation response of a structural element). The biaxial cyclic loading test data of six reinforced concrete columns, which are designed for flexural failure and shear failure, are used to validate the proposed biaxial hysteretic model.

What Theory Is

The word theory covers a multitude of virtues and vices, sometimes counting as knowledge and sometimes contrasting with knowledge. But theory is as important as observation in science. We all take force, gravity, electrons, mass, and continental drift as genuine aspects of reality even though they are theoretical rather than observational (empirical) features. We all also recognize that the concept of luminiferous ether that was generally accepted at the outset of the nineteenth century is a theoretical concept that was discarded because of the Michelson-Morley experiment. The paradigm for scientific theory is Newton's theory of force, which incorporates the two theoretical concepts of force and gravity . Huygens formulated the laws of centrifugal force, Galileo the laws of freely-falling bodies, and Kepler the laws of planetary motion. Newton showed that each was a special case of the general laws of motion. He thereby integrated three apparently disparate fields of mechanics, explained the empirical laws by subsuming them under the general laws of the theory of force, and provided a heuristic model for further explanations. The best theories are explanatory, integrative, and heuristic. Most scholars recognize this paradigm. Nonetheless, theories today are too varied to come under any single rubric. A particular danger in the humanities and social sciences is that explanations there invariably have a moral dimension, raising the specter of moralism hidden in any and every theory. This essay articulates the paradigm and the cautions without attempting to evaluate grand theory in folkloristics.

Characteristics of electromagnetically accelerated plasma flow in an externally applied magnetic field

In order to clarify the acceleration mechanism of applied-field magneto-plasma-dynamic arcjet (MPDA) plasma, the spatial profiles of the flow field and electromagnetic field near the outlet of the MPDA were measured using magnetic probes and the spectroscopic method. The plasma current densities and Lorentz forces acting on the plasma were evaluated experimentally. It was found that the azimuthal rotation of the exhausted plasma in the applied magnetic field is determined by a balance among the E×B drift, the diamagnetic drift, and the centrifugal force drift. Three components of the Lorentz force, i.e., the radial, the azimuthal, and the axial, were measured experimentally for the first time. The radial component Fr was dominant among the three components and the axial one (Fz) was weakened by the deceleration force, which spontaneously appeared in the applied-field MPDA plasma due to a diamagnetic effect of the high-beta plasma. It was demonstrated that the deceleration force can be converted to an acceleration force in an externally applied diverging field.

Prediction of the force–drift envelope for RC columns in flexure by the CAE method

AbstractA non‐parametric empirical approach, called the conditional average estimator (CAE) method, has been applied for the prediction of the normalized lateral force–drift envelope of reinforced concrete (RC) rectangular columns, as well as their characteristic drifts (effective yield drift, capping drift and ultimate drift), and drift‐related parameters (the ratio between the effective yield drift and elastic drift, and two ductility measures). A subset of the PEER RC column database was used. Five input parameters were employed: axial load index, index related to confinement, shear span index, concrete compressive strength, and longitudinal reinforcement index. The results suggest that the relations between the input and output parameters are complex, and that it is difficult to isolate the influence of a single parameter. Nevertheless, some trends were observed. The axial load index is the most influential input parameter. All the results decrease with an increasing axial load index, whereas they increase with an increasing longitudinal reinforcement index. An increase in the index related to confinement results in increases in the ultimate drift and in ductility. The influence of the shear span index is the most complex. The influence of the concrete strength is small with the exception of two output parameters related to elastic drift, which substantially decrease with increasing strength. The dispersion of the results is relatively large. The results of the predictions can be used for mathematical modelling of moment–rotation backbone curves for plastic hinges, and for the estimation of the deformation capacity of columns in seismic performance assessments. Copyright © 2007 John Wiley & Sons, Ltd.

Variability of quadriceps femoris motor neuron discharge and muscle force in human aging

The purpose was to determine the contribution of visual feedback and the effect of aging on the variability of knee extensor (KE) muscle force and motor unit (MU) discharge. Single MUs were recorded during two types of isometric trials, (1) visual feedback provided (VIS) and then removed (NOVIS) during the trial (34 MUs from young, 32 from elderly), and (2) only NOVIS (66 MUs from young, 77 from elderly) during the trial. Recruitment threshold (RT) ranged from 0-37% MVC. Standard deviation (SD) and coefficient of variation (CV) of muscle force and MU interspike interval (ISI) was measured during steady contractions at target forces ranging from 0.3 to 54% MVC. Force drift (<0.5 Hz) was removed before analysis. VIS/NOVIS trials: the decrease in the CV of ISI from VIS to NOVIS was greater for MUs from elderly (12.5 +/- 4.1 to 9.94 +/- 2.6%) than young (10.6 +/- 3.3 to 10.3 +/- 2.8%, age group x vision interaction, P = 0.006). The change in CV of force from VIS to NOVIS was significantly greater for elderly (1.45 to 1.05%) than young (1.42 to 1.41%). NOVIS only trials: for all MUs, the average RT (6.6 +/- 7.7 % MVC), target force above RT (1.20 +/- 2.7% MVC), SD of ISI (0.012 +/- 0.005 s), and CV of ISI (11.1 +/- 3.3%) were similar for young and elderly MUs. The CV of force was similar between age groups for trials between 0 and 3% MVC (1.74 +/- 0.74%) and was greater for young subjects from 3 to 10% MVC (1.47 +/- 0.5 vs. 1.21 +/- 0.4%) and >10% MVC (1.44 +/- 0.6 vs. 1.01 +/- 0.3%). The CV of ISI was similar between age groups for MUs in 0-3, 3-10, and >10% bins of RT. Thus, the contribution of visuomotor correction to the variability of motor unit discharge and force is greater for elderly adults. The presence of visual feedback appears to be necessary to find greater discharge variability in motor units from the knee extensors of elderly adults.

Development and Evaluation of a New Bicycle Instrument for Measurements of Pedal Forces and Power Output in Cycling

Determination of pedal forces is a prerequisite to analyse cycling performance capability from a biomechanical point of view. Comparing existing pedal force measurement systems, there are methodological or practical limitations regarding the requirements of scientific sports performance research and enhancement. Therefore, the aim of this study was to develop and to validate a new bicycle instrument that enables pedal forces as well as power output measurements with a free choice of pedal system. The instrument (Powertec-System) is based on force transducer devices, using the Hall-Effect and being mounted between the crank and the pedal. Validation of the method was evaluated by determining the accuracy, the cross talk effect, the influence of lateral forces, the reproducibility and, finally, a possible drift under static conditions. Dynamic tests were conducted to validate the power output measurement in reference to the SRM-System. The mean error of the present system was -0.87 +/- 4.09 % and -1.86 +/- 6.61 % for, respectively, the tangential and radial direction. Cross talk, lateral force influence, reproducibility and drift mean values were < +/- 7 %, < or = 2.4 %, < 0.8 % and 0.02 N x min (-1), respectively. In dynamic conditions, the power output measurement error could be kept below 2.35 %. In conclusion, this method offers the possibility for both valid pedal forces and power output measurements. Moreover, the instrument allows measurements with every pedal system. This method has an interesting potential for biomechanical analyses in cycling research and performance enhancement.

Behavioural differences in response to current: implications for the longitudinal distribution of stream odonates

Different longitudinal distribution patterns occur in closely related running water species. However, the mechanisms that underlie this phenomenon are poorly studied. In European Cordulegaster species (Odonata) two different longitudinal distribution patterns occur: species like C. bidentata and C. insignis are limited to springs and springbrooks, whereas species like C. boltonii and C. picta are less restricted and occur from springs to larger streams and rivulets. To find an explanation for these patterns, experiments in artificial streams were carried out to reveal differences in larval response to current between species of the two types. Larval C. bidentata and C. insignis showed a higher proneness to drift compared to C. boltonii and C. picta. Furthermore, C. bidentata and C. insignis avoided renewed drifting after a forced drift event less effectively and, exposed to strong current, travelled longer distances. It is concluded that, compared to the other pair of species, the behavioural traits of C. bidentata and C. insignis are less effective to withstand strong hydraulic stress, which restricts the distribution of these species to habitats with low discharge and current velocity, namely springs and springbrooks.

中低層鉄骨ラーメン構造の耐震性評価における構造モデルと入力地震動の研究

With dynamic analysis, this paper attempted to illustrate the influence of structural models and input earthquakes on seismic performance evaluation of middle-and-low rise steel moment-resisting frames (SMRFs). Weak-columned SMRFs and artificial waves of an identical Fourier amplitude spectrum were selected to study herein. Analysis results showed that mass-spring models might evaluate as precisely as frame models, only if the relationship of shear force and story drift were setup equivalently. Moreover, the minimum acceleration rates of input earthquakes to have structural models reach the limit states such as elasticity and collapse would remain constant respectively. While the minimum acceleration rate necessary for the limit state of deterioration would significantly increase if the input earthquakes were changed from an epicentral type to an oceanic one.

Finite element formulations and theoretical study for variable curvature friction pendulum system

The friction pendulum system (FPS), a type of base isolation technology, has been recognized as a very efficient tool for controlling the seismic response of a structure during an earthquake. However, previous studies have focused mainly on the seismic behavior of base-isolated structures far from active earthquake faults. In recent years, there have been significant studies on the efficiency of the base isolator when subjected to near-fault ground motions. It is suggested from these studies that the long-duration pulse of near-fault ground motions results in significant response of a base-isolated structure. In view of this, an advanced base isolator called the variable curvature friction pendulum system (VCFPS) is proposed in this study. The radius of the curvature of VCFPS is lengthened with an increase of the isolator displacement. Therefore, the fundamental period of the base-isolated structure can be shifted further away from the predominant period of near-fault ground motions. Finite element formulations for VCFPS have also been proposed in this study. The numerical results show that the base shear force and story drift of the superstructure during near-fault ground motion can be controlled within a desirable range with the installation of VCFPS. Therefore, the VCFPS can be adopted for upgrading the seismic resistance of the structures adjacent to an active fault.

Seismic performance of cover-plate strengthened frames

This paper summarizes results and conclusions of a case study of cover-plate strengthened frames with two, five and ten stories. The study begins with the comparison of a test results from a cover-plate connection assembly specimen with results using a detailed nonlinear finite element analysis (FEA) model. With a strong correlation to the test specimen, more FEA models are generated and analysed in order to (a) examine the local behavior of cover-plate profiles; various and (b) compare their performance to the simplified structural models that will be used in the static and time history analysis of those of the frames. With the reliable simple structural model of the cover-plate connection assemblies capturing both elastic and inelastic behavior, such a model is incorporated into frames to perform nonlinear static and time history analyses. Nine frames (two-, five- and ten-story steel moment frames with and without a cover plate) are the designed for the study. For comparative purposes, the 1940 Imperial Valley (El Centro station, 0·32g PGA) and the 1994 Northridge (Newhall station, 0·59g PGA) ground motions factored to 0·3 and 0·6g are used in time-history analyses. Global and local performance of frames are discussed in terms of plastic deformation distribution, story shear force and inelastic drift ratio. Copyright © 1999 John Wiley & Sons, Ltd.