Orientation Averaging Research Articles

A biomechanical assessment of hand/arm force with pneumatic nail gun actuation systems

A biomechanical model is presented to estimate user hand/arm force exertion with two pneumatic nail gun trigger systems. The sequential actuation trigger (SAT) is safer than the contact actuation trigger (CAT) but increases the user's exertion of force because the trigger must be actuated after the safety tip is held pressed against the workpiece. Time integrated hand force was calculated for a single user based on direct measurement of nail gun tip force against the workpiece (tip contact) and from estimated force to support the tool weight during transfer between nails and during idle holding. The model shows that hand/arm force increases when nailing with the SAT (relative to CAT) and with a vertically-oriented workpiece (relative to horizontal). Expressed per nail fired, the user exerted 0.13 Ns (horizontal orientation) and 2.88 Ns (vertical orientation) integrated hand force during tip contact with CAT compared to 26.15 Ns (horizontal) and 46.08 Ns (vertical) with SAT. Depending upon idle holding duration, integrated hand force during tip contact was estimated to have been 1–3% of 48–132 Ns total hand force with CAT and 21–44% of 83–167 Ns total hand force with SAT (average of horizontal and vertical orientations). Based on standard time allowances from work measurement systems it is proposed that efficient application of hand force during tip contact with SAT can reduce this contribution to 6–15% of 55–139 Ns total hand force. The model is useful for considering differences in hand/arm force exertion between the SAT and CAT systems Relevance to industryThis paper presents a model of hand/arm force associated with two types of pneumatic nail gun actuation (trigger) systems. The model clarifies differences in user force exertion with the sequential actuation and contact actuation triggers to inform nail gun trigger selection decisions.

Coupled electron-nuclear wavepacket dynamics in potassium dimers

Recently we have demonstrated control of valence-bond excitation of a molecule due to the interplay of the induced charge oscillation with the precisely tailored phase of the driving laser field (Bayer et al 2013 Phys. Rev. Lett. 110 123003). In this contribution we describe in more detail the two-colour experiment—a control pulse sequence followed by an ionizing probe pulse of a different wavelength. We provide details on the quantum dynamics simulations carried out to reproduce and to analyse the experimental results. The procedure for averaging over the focal intensity distribution in the interaction region and the method for orientation averaging, which are both crucial for the reproduction of our strong-field measurements, are also described in detail. The analysis of the temporal evolution of the expectation values of the wavepackets on the relevant potentials, the induced energetic shifts in the molecule and the modulation in the charge oscillation provides further insights into the interplay of the coupled nuclear-electron dynamics. Because the measured photoelectron spectra reveal the population of the target states we describe the quantum mechanical approach to calculate the photoelectron spectra and rationalize the results using Mulliken's difference potential method.

The stiffness tensor for composites with curved discontinuous fibers

In this paper, we propose a new method for calculating the stiffness tensor for a composite material containing curved discontinuous fibers. We introduce a new concept of configuration for a single curved fiber defined by five dimensionless parameters. An ensemble of curved fibers within a composite material is then described by a configuration probability density function. The proposed stiffness tensor requires three tensors of fourth-order describing the material microstructure and a set of elastic constants. We introduce the concept of configuration averaging and present an analytical method for estimating elastic constants for materials containing curved fibers. We demonstrate that for materials containing only straight fibers, fiber configuration and configuration averaging reduces to standard fiber orientation and orientation averaging. Comparison of stiffness measurements using X-ray digital image correlation against the stiffness calculated with fiber geometry obtained by X-ray tomography shows that accounting for fiber curvature provides better estimate of stiffness.

An original approach for mechanical modelling of short-fibre reinforced composites with complex distributions of fibre orientation

In this paper, an original and effective model of behaviour for short-fibre reinforced composites is presented. In particular, complex fibre distributions of orientation can be dealt with in a very easy way, without orientation averaging or additional homogenisation steps. The matrix material has elastoplastic damage behaviour with non-isochoric plastic flow. Ductile damage can be fully anisotropic depending on the reinforcement characteristics. The model is validated for the case of a polypropylene reinforced with short flax fibres. In addition, simulations are performed to investigate the influence of key parameters like fibre length and interfacial shear strength, as well as the impact of progressive debonding at the fibre tips.

The Statistical Conformation of a Highly Flexible Protein: Small Angle X-Ray Scattering of S. Aureus Protein A

Small-angle X-ray scattering (SAXS) is a biophysical technique that allows one to study the statistical conformation of a biopolymer in solution. SAXS data is a low-resolution probe of conformational space because it is a population weighted orientational average of all conformers within a conformational ensemble. Traditional biological SAXS experiments seek to describe an “average” structure of a protein, or enumerate a “minimal ensemble” of a protein at the atomic resolution scale. However, for highly flexible proteins, an average structure or minimal ensemble is insufficient for enumeration of conformational space, and is an over-parameterized model of the statistical conformation. We developed a minimally parameterized model that describes the statistical conformation using polymer physics theory. We have used this model to fit the SAXS data for a highly flexible protein, Staphylococcal protein A (SpA-N). SpA-N is a multi-domain protein consisting of 5 globular IgG binding domains separated by a six residue flexible linker. We collected SAXS data on SpA-N and constructs consisting of 1, 2, 3, 4, and 5 domain modules in order to study the role of the number of modules on the statistical conformation of this important S. aureus virulence factor. Here we define a new polymer physics model and a scattering function with which to fit the SAXS data. We show that the model, which has three adjustable parameters, can fit the SAXS data of SpA-N, and is an analytical description of the statistical conformation. We propose a protocol employing polymer physics to describe the statistical conformation of other flexible proteins. This analytical description of conformational space provides a depiction of the statistical conformation of a flexible protein that, while lacking atomistic detail, properly reflects the information content of the data.

State-Selective Excitation of the CO Stretch in Carboxyhemoglobin by Mid-IR Laser Pulse Shaping: A Theoretical Investigation

We present simulations of the excitation of specific vibrational levels of the CO stretch in carboxyhemoglobin by shaped mid-IR laser pulses. The pulses are calculated using local control theory, adapted to account for the protein fluctuations, which are included using a microscopic model developed previously. We show that efficient selective vibrational state preparation can be obtained, despite the presence of the fluctuations and orientational averaging, and can be monitored using transient absorption spectra. The mid-IR pulses are found to be in a realistic intensity regime and might soon be available by IR pulse shaping. This opens the way to a direct monitoring of vibrational relaxation from individually prepared, high-lying vibrational states of complex systems.

Internal fields of soot fractal aggregates

This work uses the discrete dipole approximation (DDA) to examine the internal electric field within a simulated carbon soot fractal aggregate in fixed and random orientations. For fixed orientations, deviations of the internal field magnitude up to ±50% from that assumed by the Rayleigh-Debye-Gans Approximation (RDGA) are found. Given the refractive index of the aggregate monomers and conditions for the validity of the approximation, such large deviations are no surprise. Yet despite this deviation, the far-field scattered intensity from such aggregates agrees surprisingly well with that described by the RDGA. Moreover, if the average over an ensemble of many random aggregate-orientations is calculated, both the DDA and RDGA scattered intensities obey the well-known power-law functionality in terms of the scattering wave vector and show a forward-angle intensity-maximum proportional to the square of the number of monomers. The explanation for this lies in the over and under estimations made by the approximation of the internal field, which apparently mostly cancel upon integration to yield the scattered intensity. It is shown that this error cancellation is related to the fractal structure of the aggregate and that the agreement between the DDA and RDGA improves with aggregates of increasing size provided the fractal dimension is less than two. Overall, the analysis suggests that both the special fractal character of the aggregate and its orientational averaging is important to account for the experimentally observed validity of the RDGA despite its poor description of the internal fields.

Orientationally invariant metrics of apparent compartment eccentricity from double pulsed field gradient diffusion experiments

Pulsed field gradient diffusion sequences (PFG) with multiple diffusion encoding blocks have been indicated to offer new microstructural tissue information, such as the ability to detect nonspherical compartment shapes in macroscopically isotropic samples, i.e. samples with negligible directional signal dependence on diffusion gradients in standard diffusion experiments. However, current acquisition schemes are not rotationally invariant in the sense that the derived metrics depend on the orientation of the sample, and are affected by the interplay of sampling directions and compartment orientation dispersion when applied to macroscopically anisotropic systems. Here we propose a new framework, the d-PFG 5-design, to enable rotationally invariant estimation of double wave vector diffusion metrics (d-PFG). The method is based on the idea that an appropriate orientational average of the signal emulates the signal from a powder preparation of the same sample, where macroscopic anisotropy is absent by construction. Our approach exploits the theory of exact numerical integration (quadrature) of polynomials on the rotation group, and we exemplify the general procedure with a set consisting of 60 pairs of diffusion wave vectors (the d-PFG 5-design) facilitating a theoretically exact determination of the fourth order Taylor or cumulant expansion of the orientationally averaged signal. The d-PFG 5-design is evaluated with numerical simulations and ex vivo high field diffusion MRI experiments in a nonhuman primate brain. Specifically, we demonstrate rotational invariance when estimating compartment eccentricity, which we show offers new microstructural information, complementary to that of fractional anisotropy (FA) from diffusion tensor imaging (DTI). The imaging observations are supported by a new theoretical result, directly relating compartment eccentricity to FA of individual pores.

Optimal numerical methods for determining the orientation averages of single-scattering properties of atmospheric ice crystals

The optimal orientation averaging scheme (regular lattice grid scheme or quasi Monte Carlo (QMC) method), the minimum number of orientations, and the corresponding computing time required to calculate the average single-scattering properties (i.e., asymmetry parameter (g), single-scattering albedo (ωo), extinction efficiency (Qext), scattering efficiency (Qsca), absorption efficiency (Qabs), and scattering phase function at scattering angles of 90° (P11 (90°)), and 180° (P11 (180°))) within a predefined accuracy level (i.e., 1.0%) were determined for four different nonspherical atmospheric ice crystal models (Gaussian random sphere, droxtal, budding Bucky ball, and column) with maximum dimension D=10μm using the Amsterdam discrete dipole approximation at λ=0.55, 3.78, and 11.0μm.The QMC required fewer orientations and less computing time than the lattice grid. The calculations of P11 (90°) and P11 (180°) required more orientations than the calculations of integrated scattering properties (i.e., g, ωo, Qext, Qsca, and Qabs) regardless of the orientation average scheme. The fewest orientations were required for calculating g and ωo. The minimum number of orientations and the corresponding computing time for single-scattering calculations decreased with an increase of wavelength, whereas they increased with the surface-area ratio that defines particle nonsphericity.

Modeling the non-linear deformation of a short-flax-fiber-reinforced polymer composite by orientation averaging

The growing usage of short-flax-fiber-reinforced polymer composites in such applications as automotive industry necessitates the prediction of their mechanical response up to and beyond the limit of elasticity. Due to the imperfect, mechanical interlocking-dominated adhesion of natural fibers to most polymers, both fiber debonding and matrix yielding contribute to the non-linear deformation. In the present study, the deformation under an active loading of a short misaligned fiber composite is modeled by the orientation averaging approach, employing an analytical description of the behavior of a unit cell (UC), the parameters of which are determined using a FEM analysis of UC response under selected loading modes. The model is applied to the prediction of stress–strain diagrams in tension of flax/polypropylene composites with different fiber volume fractions.

Spectral and angular light-scattering from silica fractal aggregates

This work applies a new model based on the discrete dipole approximation to simulate the scattering of coherent broadband light from fixed and randomly oriented silica fractal aggregates. Two classes of aggregate morphology are considered; the standard aggregate with a single fractal dimension and superaggregates with two dimensions, both of which are generated from a Diffusion-Limited Cluster-Aggregation model. Light scattering from these aggregates is simulated over the short wave infrared to ultraviolet spectral range. We find features in the distribution of the spectral and angular scattered-intensities that do not disappear after orientation averaging and are seen for both types of aggregates. The important role played by the wavelength in q-space analysis is observed and we report the utility of a spectral q-space analysis for multi-dimensional objects like superaggregates with spectrally dependent refractive index.

Dynamic Light Scattering Based Microelectrophoresis: Main Prospects and Limitations

Microelectrophoresis based on the dynamic light scattering (DLS) effect has been a major tool for assessing and controlling the conditions for stability of colloidal systems. However, both the DLS methods for characterization of the hydrodynamic size of dispersed submicron particles and the theory behind the electrokinetic phenomena are associated with fundamental and practical approximations that limit their sensitivity and information output. Some of these fundamental limitations, including the spherical approximation of DLS measurements and an inability of microelectrophoretic analyses of colloidal systems to detect discrete charges and differ between differently charged particle surfaces due to rotational diffusion and particle orientation averaging, are revisited in this work. Along with that, the main prospects of these two analytical methods are mentioned. A detailed review of the role of zeta potential in processes of biochemical nature is given too. It is argued that although zeta potential has been used as one of the main parameters in controlling the stability of colloidal dispersions, its application potentials are much broader. Manipulating surface charges of interacting species in designing complex soft matter morphologies using the concept of zeta potential, intensively investigated recently, is given as one of the examples. Branching out from the field of colloid chemistry, DLS and zeta potential analyses are now increasingly finding application in drug delivery, biotechnologies, physical chemistry of nanoscale phenomena and other research fields that stand on the frontier of the contemporary science. Coupling the DLS-based microelectrophoretic systems with complementary characterization methods is mentioned as one of the prosperous paths for increasing the information output of these two analytical techniques.

Does variability affect statistical averaging of length and orientation?

Does variability affect statistical averaging of length and orientation?

Average orientation is more accessible through object boundaries than surface features.

In a glance, the visual system can provide a summary of some kinds of information about objects in a scene. We explore how summary information about orientation is extracted and find that some representations of orientation are privileged over others. Participants judged the average orientation of either a set of 6 bars or 6 circular gratings. For bars, orientation information was carried by object boundary features, while for gratings, orientation was carried by internal surface features. The results showed more accurate averaging performance for bars than for gratings, even when controlling for potential differences in encoding precision for solitary objects. We suggest that, during orientation averaging, the visual system prioritizes object boundaries over surface features. This privilege for boundary features may lead to a better representation of the spatial layout of a scene.

FRET Investigation of Membrane Protein Folding: Evolution of Tertiary Structure of Soluble and Transmembrane Domains during Folding into Synthetic Bilayers

This paper describes an investigation of the folding mechanisms of an integral membrane protein. A key goal is to determine the role of the soluble domain during the insertion of a transmembrane domain into synthetic bilayers. Towards this end, we report Forster resonance energy transfer (FRET) efficiencies between donor (tryptophan) and acceptor (1,5-IAEDANS) pairs that are located on the transmembrane and soluble domains of outer membrane protein A (OmpA). The FRET efficiencies are correlated to the evolution of distances and tertiary structure under the assumption of orientational averaging. Analysis of the kinetics reveals that the full-length protein, which contains both soluble and transmembrane domains, displays slower folding rates compared to the truncated variant, which is comprised of the transmembrane domain only. This difference in rates may reflect an increase in the number of kinetic traps during folding, or indicate alternate pathways. These measurements of the formation of tertiary structure and the role of a soluble domain on the kinetics of folding may aid in the elucidation of the mechanisms of membrane protein folding and dynamics.

A refined strut model for calculating the elastic constants of highly porous cellular plastics by the method of orientational averaging

A model is presented for calculating the linear elastic constants of high-porosity cellular plastics by orientationally averaging the rigidity tensor of a structural element consisting of an air sheath and a loadcarrying element in the form of a straight strut with a piecewise constant cross section. The load-carrying element can resist the axial and shear loads and bending moments applied to its ends. The nonuniform orientational distribution of the elements is also taken into account. The calculation results obtained are compared with some literature data.

단섬유강화 플라스틱 복합재료 구조해석 기법연구

본 연구는 사출 성형 공정을 통하여 제작되는 단섬유강화 플라스틱 복합재료의 구조해석 기법에 관한 내용으로 소재의 이방성 기계물성을 예측하고 이를 구조해석에 적용하도록 하였다. 사출 성형 공정을 통하여 제작되는 단섬유강화 플라스틱 복합재료의 구조해석에 있어서 기존의 경우는 일반적으로 소재의 기계적 물성을 균질 등방성 탄성 모델로 이용하여 왔으나, 실제 부품 파손 모드와 크게 상이한 경우가 많다. 이러한 점을 극복하고자 사출 성형 g,름 해석, 일방향성 복합재료의 Halpin-Tsai 식과 배향 평균 모델을 도입하여 단섬유강화 플라스틱 복합재료의 섬유배향 효과가 고려되도록 새로운 구조해석 시스템을 개발하였다. 해석의 정확도는 시편시험 결과와의 비교를 통하여 검증하였으며, 섬유 배향 및 웰드라인 영향 및 섬유 함량에 따른 변화가 해석에 장 반영됨을 확인하였다. 또한 자동차 부품에 개발된 해석 시스템을 적용하여 균질 등방 모델과 달리 부품의 위치별로 다른 기계적 성능이 반영되고, 사출 게이트 위치에 따라 유리섬유 배향이 변화하여 부품의 성능이 달라짐을 확인하였다. This paper deals with anisotropic property and structural analysis for short fiber reinforced plastic composites manufactured by the injection molding process. The common approach for modeling this type of material is the consideration of the material as homogenous and isotropic. However, the common isotropy approach often results in unexpected failure. To overcome this, new structure analysis methodology was developed in order to consider fiber orientation effect using injection mold flow analysis and Halpin-Tsai equations for unidirectional composites and taking an orientation average. The numerical predictions are compared to experimental data for tensile specimen. The predicted mechanical properties agree well with experimental data for fiber orientation and weld line effect. The analysis system was also applied to an automobile part. The proposed anisotropic model predicted different mechanical properties by position of the part and different mechanical performance of the part was changed according to injection gate position.

Inserção internacional da pesquisa científica em Contabilidade desenvolvida no Brasil

The objective of this study was to analyze the international insertion of scientific production in the Accounting Sciences area developed in Brazil, in addition to identify other attributes that can enhance the international publication. Thereunto, information were collected from the Curricula Lattes of 236 researchers, derived from two groups: (i) doctors from the PhD program on Accounting of the University of Sao Paulo; and (ii) professors linked to 16 national stricto sensu post-graduation programs Accounting Sciences. The option was to analyze the international scientific production of the mentioned groups since it was believed that these are responsible for great part of the national and international publications developed in the Accounting area. After some exclusions, it was arrived to a total of 236 professors to be analyzed. The collected information comprised the whole period of the professor's curriculum (that is, from the beginning of the curriculum) until 2009 and referred to: international and national publication, accomplishment of sandwich PhD and post-doctorate, participation in research groups, orientations completed and PhD course concluded. The main results showed that the professors published 308 articles in international journals and 3,561 articles in national journals; 42 professors had completed post-doctorate degree, most of them at North American institutions; 84% of the professors participate in or act as research groups leaders; the average of master's degree orientations was of 12 students and of PhD's only one student. Although the study is focused on the quantification of publications performed by for the professors in the accounting area, the important question of the quality of the studies is well known, which must be pursued by any researcher, regardless of his area of performance.

Correction: Sejnoha, M. et al. Mori-Tanaka Based Estimates of Effective Thermal Conductivity of Various Engineering Materials. Micromachines 2011, 2, 129–149

We have discovered a mistake in our original derivation related to the definition of the apparent conductivity due to orientation averaging. [...]

Effect of interphase layers on the elastic properties of a carbon-nanotube-reinforced composite

A variant of a stepwise analysis of the elastic properties of a carbon-nanotube-reinforced composite with account of the effect of interphase layers between the nanotubes and the polymer matrix is reported. The preliminary calculation of the elastic constants of a structural element incorporating a nanotube and an interphase layer and the subsequent calculation of independent elastic constants of a composite with such transversely isotropic structural elements oriented in one direction are both performed by using the Mori–Tanaka theory of an equivalent medium. The calculations are carried out for a wide range of ratios between the elastic moduli of the interphase layer and matrix. The elastic constants of a composite with randomly oriented nanotubes are obtained by using the method of orientational averaging.