Characterizing Shape Variations in Infant Hips Using Statistical Shape Modeling for Ultrasonic Diagnosis of Hip Dysplasia with Graf’s Method

The effective differentiation between global and local modes plays a fundamental role in the selection and application of the most appropriate seismic analysis procedures. This is particularly relevant in the case of historical heritage structures and ensembles of buildings in old city centres: due to the complexity of the structural scheme, the stratification of interventions, and the irregularity of the structural configuration with the absence of seismic details, several local modes frequently characterize the dynamic response of those structures. Distinguishing local and global modes might be challenging even from the experimental point of view in the presence of few measured degrees of freedom. Nevertheless, an accurate analysis of local modes can support the identification of macro-elements and the selection of the most appropriate analysis procedure. The present paper illustrates an original approach addressing the differentiation between global and local modes through the spatial correlation of modal displacements. The proposed approach can be either automated and integrated into software for structural analysis or applied in the context of an experimental campaign, and its application to simulated case studies is discussed.

Mode transitions have been commonly observed in Hall Effect Thruster (HET) operation where a small change in a thruster operating parameter such as discharge voltage, magnetic field or mass flow rate causes the thruster discharge current mean value and oscillation amplitude to increase significantly. Mode transitions in a 6-kW-class HET called the H6 are induced by varying the magnetic field intensity while holding all other operating parameters constant and measurements are acquired with ion saturation probes and ultra-fast imaging. Global and local oscillation modes are identified. In the global mode, the entire discharge channel oscillates in unison and azimuthal perturbations (spokes) are either absent or negligible. Downstream azimuthally spaced probes show no signal delay between each other and are very well correlated to the discharge current signal. In the local mode, signals from the azimuthally spaced probes exhibit a clear delay indicating the passage of and are not well correlated to the discharge current. These spokes are localized oscillations propagating in the E×B direction that are typically 10-20% of the mean value. In contrast, the oscillations in the global mode can be 100% of the mean value. The transition between global and local modes occurs at higher relative magnetic field strengths for higher mass flow rates or higher discharge voltages. The thrust is constant through mode transition but the thrust-to-power decreased by 25% due to increasing discharge current. The plume shows significant differences between modes with the global mode significantly brighter in the channel and the near-field plasma plume as well as exhibiting a luminous spike on thruster centerline. Mode transitions provide valuable insight to thruster operation and suggest improved methods for thruster performance characterization.

The authors present a reliable double-ring metropolitan area network architecture, called DORFMAN, based on an enhanced Fiber Distributed Data Interface (FDDI) protocol. DORFMAN is composed of two local ring networks interconnected via two monitors. The two monitors are used to perform simple routing and error recovery logic as well as mode transitions of DORFMAN. There are three modes defined in DORFMAN: local, global, and transition modes. During the local mode, DORFMAN allows double rings to operate in parallel. During the global mode, DORFMAN behaves as an FDDI network. Modes are dynamically switched between local and global modes on a demand basis. The bandwidth waste resulting from the transition of modes has been reduced to a minimum. Performance analysis and simulation results show that with a reasonable degree of locality assumed, twice the throughput of an FDDI network can be achieved in DORFMAN. An error recovery scheme for DORFMAN is addressed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A semi-analytical method for vibration localization of plates integrated with low-frequency plate-type resonators

This paper investigates the dynamics of regional cyclogenesis from the perspective of local instability of a zonally inhomogeneous baroclinic jet streak in a two-layer quasi-geostrophic beta-plane channel model. When such a representative jet streak is embedded in a background uniform vertical shear UT, there are both local and global unstable normal modes. In the absence of such a background shear (UT = 0), only the local modes are unstable. The shorter the jet is, the fewer local modes would there be. A local mode consists of a group of dominant waves that jointly give rise to a maximum local energy downstream of the jet core. Its existence is independent of the cyclical boundary condition. The growth rate of a local mode diminishes rapidly when the constant part of the basic zonal wind U0 is increased. A global mode, on the other hand, largely consists of a single wave and its growth rate is much less sensitive to U0. These properties are qualitatively similar to those in the WKB solution. The structural characteristics of these modes are identifiable with those of three classes of unstable modes of an observed atmospheric flow reported in Frederiksen and Bell. Our nonmodal analysis shows that a localized disturbance naturally emerges from a zonally unbiased initial state in a relatively short time. The excitation of a local mode within a few days from an initially isolated disturbance also depends strongly upon its initial position relative to the jet core. The two processes that locally generate the perturbation energy depend upon the structural properties of the disturbance relative to the basic thermal and deformation fields. The two processes that redistribute the perturbation energy are the advection of energy by the basic flow and the convergence of energy flux associated with the ageostrophic component of the perturbation. These four processes are comparably important and greatly counteract one another resulting in a net intensification of a disturbance centered downstream of the jet core. The feedback effects of the most unstable mode on the basic flow resemble the observed geopotential tendencies induced by the transient eddies. The feedback results of this analysis differ noticeably from the WKB counterparts.

This paper deals with the nonusual case in structural dynamics for which a complex structure exhibits both the usual global elastic modes and numerous local elastic modes in the low-frequency range. Despite the presence of these local elastic modes, we are interested in constructing a stochastic reduced-order model using only the global modes and in taking into account the local elastic modes with a probabilistic approach. In the first part, a formulation and an algorithm, which allow the “global elastic modes” and the “local elastic modes” to be calculated, are presented. The second part is devoted to the construction of the stochastic reduced-order model with the global elastic modes and in taking into account the uncertainties on the effects of the local elastic modes by the nonparametric probabilistic approach. Finally, an application, which validates the proposed theory is presented.

Mode transitions in a 6 kW laboratory Hall-effect thruster were induced by varying the magnetic field intensity while holding all other operating parameters constant. Ultrafast imaging, discharge current, and thrust measurements were used to characterize the change in discharge channel current density and thruster performance through mode transitions. The modes are described here as global oscillation mode and local oscillation mode. In global mode, the entire discharge channel is oscillating in unison and spokes are either absent or negligible with discharge current oscillation amplitude (root mean square) greater than 10% of the mean value and can even be as high as 100%. In local oscillation mode, perturbations in the discharge current density are seen to propagate in the direction. Spokes are localized oscillations that are typically 10–20% of the mean discharge current density value. The discharge current oscillation amplitude and mean values are significantly lower than global mode. The mode transitions changed with operating conditions, where the transition between global mode and local mode occurred at higher relative magnetic field strengths for higher mass flow rate or higher discharge voltage. The thrust was approximately constant through the mode transition, but the thrust-to-power ratio and anode efficiency decreased significantly in global mode. The peaks in thrust to power and anode efficiency typically occur near the transition point. Thruster performance maps should include variation in discharge current, discharge voltage, and magnetic field, known as maps, at different flow rates to identify transition regions throughout the life of a thruster. These results are used to calculate a transition surface for use by operators to keep the thruster operating in an optimal mode.

This paper is concerned with overlapping mode-dependent H∞ control for a discrete-time Markov jump linear system in the presence of overlapping local operation modes and incomplete mode transition probabilities. By developing a randomly overlapping decomposition method, the system with deficient global operation modes is reformulated by a set of locally overlapping switched groups with accessible group and local modes. An overlapping group- and local-mode-dependent state feedback controller is delicately constructed. Unlike some existing controllers proposed in the literature, we do not require complete global mode information, but take full advantage of the knowledge of group and local modes of the reformulated system. Moreover, overlapping local modes are allowed to be existed in the formed groups. The stability analysis and control design procedures are developed based on the stochastic Lyapunov functional approach. The proposed framework is shown to be more general, which covers the traditional Markovian jump linear system with completely available global modes as a special case. In the case of only one local group, it is also shown that some existing results from the literature can be regarded as a special case of our derived results. A simulation example is finally presented to show the effectiveness and merits of the proposed method.

Bamboo poles, and other one-dimensional thin-walled structures are usually loaded under compression, which may also be subject to bending arising from eccentric loading. Many of these structures contain diaphragms or circumferential stiffeners to prevent cross-sectional distortions and so enhance overall load-carrying response. Such hierarchical structures can compartmentalize buckling to local regions in addition to withstanding global buckling phenomena. Predicting the buckling mode shapes of such structures for a range of geometric parameters is challenging due to the interaction of these global and local modes. Abaqus finite element software is used to model thousands of circular hollow tubes with random geometric parameters such that the ratios of radius to periodic length range from 1/3-1/7, the ratio of wall thickness to radius varies from 1/4-1/10. The material used in this study is a type of bamboo, where the Young’s and shear moduli are point-wise orthotropic and gradually increase in magnitude in the radial direction. Under eccentric loads with varying eccentricity, the structures can buckle into a global mode or local modes within an internode, i.e. periodic unit. Moreover, the local modes may contain only one wave or multiple waves in the circumferential direction. As expected, numerical results show that the global mode is more likely to occur in small and thick tubes, whereas the local modes are observed in larger tubes with a smaller number of circumferential waves present in thicker walls. Also, greater eccentricity pushes the local mode domains towards smaller tubes. An efficient classification method is developed herein to identify the domains of each mode shape in terms of radius, wall thickness and eccentricity. Based on linear discriminant analysis, explicit boundary surfaces for the three domains are defined for the obtained data, which can help designers in predicting the mode shapes of tubular structures under axial bending.

In-plane modal responses of two-cable networks considering cable bending stiffness effect

Global flexible modes for the model reduction of planar mechanisms using the finite-element floating frame of reference formulation

Linear stability of the non-parallel Batchelor vortex is studied using global modes. This family of swirling wakes and jets has been extensively studied under the parallel-flow approximation, and in this paper we extend to more realistic non-parallel base flows. Our base flow is obtained as an exact steady solution of the Navier–Stokes equations by direct numerical simulation (with imposed axisymmetry to damp all instabilities). Global stability modes are computed by numerical simulation of the linearized equations, using the implicitly restarted Arnoldi method, and we discuss fully the numerical and convergence issues encountered. Emphasis is placed on exploring the general structure of the global spectrum, and in particular the correspondence between global modes and local absolute modes which is anticipated by weakly non-parallel asymptotic theory. We believe that our computed global modes for a weakly non-parallel vortex are the first to display this correspondence with local absolute modes. Superpositions of global modes are also studied, allowing an investigation of the amplifier dynamics of this unstable flow. For an illustrative case we find global non-modal transient growth via a convective mechanism. Generally amplifier dynamics, via convective growth, are prevalent over short time intervals, and resonator dynamics, via global mode growth, become prevalent at later times.

BackgroundInjury is an important risk factor for osteoarthritis (OA), a highly prevalent and disabling joint disease. Joint shape is linked to OA, but the interplay of injury and joint shape and their combined role in OA, particularly at the ankle, is not well known. Therefore, we explored cross-sectional associations between ankle shape and injury in a large community-based cohort.MethodsAnkles without radiographic OA were selected from the current data collection of the Johnston County OA Project. Ankles with self-reported prior injury were included as injury cases (n = 108) along with 1:1 randomly selected non-injured ankles. To define ankle shape, a 68 point model on weight-bearing lateral ankle radiographs was entered into a statistical shape model, producing a mean shape and a set of continuous variables (modes) representing variation in that shape. Nineteen modes, explaining 80% of shape variance, were simultaneously included in a logistic regression model with injury status as the dependent variable, adjusted for intra-person correlation, sex, race, body mass index (BMI), baseline OA radiographic grade, and baseline symptoms.ResultsA total of 194 participants (213 ankles) were included; mean age 71 years, BMI 30 kg/m2, 67% white and 71% women. Injured ankles were more often symptomatic and from whites. In a model adjusted only for intra-person correlation, associations were seen between injury status and modes 1, 6, 13, and 19. In a fully adjusted model, race strongly affected the estimate for mode 1 (which was no longer statistically significant).ConclusionsThis study showed variations in ankle shape and history of injury as well as with race. These novel findings may indicate a change in ankle morphology following injury, or that ankle morphology predisposes to injury, and suggest that ankle shape is a potentially important factor in the development of ankle OA.

An energy-based approach to buckling modal decomposition of thin-walled members with arbitrary cross sections, Part 1: Derivation

Statistical shape and appearance models of bones