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Uniform finite facets are frequently observed at grain boundaries (GBs) and are usually attributed to equilibrium stabilization by GB stress. We report calculations for an aluminum twin GB using density functional theory, the embedded-atom method, and continuum elasticity theory. These methods show that GB stress is much too small to stabilize finite facets, suggesting that the usual explanation is incorrect.
Size-dependent magnetic single-domain versus vortex state stability of Co/Ru(0001) nanodots is explored with spin-polarized low-energy electron microscopy, analytical modeling, and micromagnetic simulations. We show that both single-domain and vortex states can be stabilized in a broad region near the phase boundary. The calculated width of the bistability region and temperature dependent heights of the energy barriers between both states agree well with our experimental findings.
Model-based deformable organ registration techniques using the finite element method (FEM) have recently been investigated intensively and applied to image-guided adaptive radiotherapy (IGART). These techniques assume that human organs are linearly elastic material, and their mechanical properties are predetermined. Unfortunately, the accurate measurement of the tissue material properties is challenging and the properties usually vary between patients. A common issue is therefore the achievable accuracy of the calculation due to the limited access to tissue elastic material constants. In this study, we performed a systematic investigation on this subject based on tissue biomechanics and computer simulations to establish the relationships between achievable registration accuracy and tissue mechanical and organ geometrical properties. Primarily we focused on image registration for three organs: rectal wall, bladder wall, and prostate. The tissue anisotropy due to orientation preference in tissue fiber alignment is captured by using an orthotropic or a transversely isotropic elastic model. First we developed biomechanical models for the rectal wall, bladder wall, and prostate using simplified geometries and investigated the effect of varying material parameters on the resulting organ deformation. Then computer models based on patient image data were constructed, and image registrations were performed. The sensitivity of registration errors was studied by perturbating the tissue material properties from their mean values while fixing the boundary conditions. The simulation results demonstrated that registration error for a subvolume increases as its distance from the boundary increases. Also, a variable associated with material stability was found to be a dominant factor in registration accuracy in the context of material uncertainty. For hollow thin organs such as rectal walls and bladder walls, the registration errors are limited. Given 30% in material uncertainty, the registration error is limited to within 1.3 mm. For a solid organ such as the prostate, the registration errors are much larger. Given 30% in material uncertainty, the registration error can reach 4.5 mm. However, the registration error distribution for prostates shows that most of the subvolumes have a much smaller registration error. A deformable organ registration technique that uses FEM is a good candidate in IGART if the mean material parameters are available.
A method for simulation of acoustical bores, useful in the context of sound synthesis by physical modeling of woodwind instruments, is presented. As with previously developed methods, such as digital waveguide modeling (DWM) [Smith, Comput. Music J. 16, 74-91 (1992)] and the multi convolution algorithm (MCA) [Martinez et al., J. Acoust. Soc. Am. 84, 1620-1627 (1988)], the approach is based on a one-dimensional model of wave propagation in the bore. Both the DWM method and the MCA explicitly compute the transmission and reflection of wave variables that represent actual traveling pressure waves. The method presented in this report, the wave digital modeling (WDM) method, avoids the typical limitations associated with these methods by using a more general definition of the wave variables. An efficient and spatially modular discrete-time model is constructed from the digital representations of elemental bore units such as cylindrical sections, conical sections, and toneholes. Frequency-dependent phenomena, such as boundary losses, are approximated with digital filters. The stability of a simulation of a complete acoustic bore is investigated empirically. Results of the simulation of a full clarinet show that a very good concordance with classic transmission-line theory is obtained.
This paper examines the effects of morpheme boundaries on intergestural timing, and demonstrates that low-level phonetic realization is influenced by morphological structure, i.e. compounding and affixation. It reports two experiments, one using electromagnetic midsagittal articulography (EMA) and one electropalatography (EPG), examining Korean data. The results of the EMA study show that intergestural timing is less variable for adjacent gestures across the word boundary inside a lexicalized compound than inside a nonlexicalized compound, and inside a monomorphemic word than across a morpheme boundary. The EPG study (which examined the timing in palatalization of a coronal) shows that both [ti] and [ni] have more variability in gestural timing when heteromorphemic than when tautomorphemic. Furthermore, the phonetic details of gestural overlap shed light on the asymmetry on palatalization between tautomorphemic and heteromorphemic gestural sequences (e.g. ni vs. n-i), presumably driven by paradigmatic contrast and preference of overlap. In short, what emerges from two experiments is that gestures are coordinated more stably within a single lexical item (a morpheme or a lexicalized compound) than across a boundary between lexical items. In accounting for the stability of intergestural timing within a lexical entry, several hypotheses were discussed including the Phase Window, Bonding Strength, Phonological Timing and Extended Phase Window model newly proposed here. The implication is that the morphological structure may be encoded in the phonetic realization, as is the case with other linguistic structure (e.g. prosodic structure).
Ehrlich ascites tumour cells were extracted in buffers containing Triton X-100 and mono-di- and polyvalent cations and then analysed by phase-contrast and electron microscopy. The results of this ultrastructural analysis confirm those of the biochemical analysis in the accompanying paper that the stability of intermediate-sized filaments is dependent on the ionic environment. Furthermore, the organization of filaments in long parallel arrays is dependent on the presence of divalent cations and can be inhibited, to some extent, by the presence of monovalent cations. The stability of other detergent-resistant structures, the boundary lamina, microfilaments, microtubules, centrioles, polyribosomes and the nuclear cortex, is also affected by the ionic environment but to a lesser extent.
For the analysis of time trends in incidence and mortality rates, the age-period-cohort (apc) model has became a widely accepted method. The considered data are arranged in a two-way table by age group and calendar period, which are mostly subdivided into 5- or 10-year intervals. The disadvantage of this approach is the loss of information by data aggregation and the problems of estimating interactions in the two-way layout without replications. In this article we show how splines can be useful when yearly data, i.e., 1-year age groups and 1-year periods, are given. The estimated spline curves are still smooth and represent yearly changes in the time trends. Further, it is straightforward to include interaction terms by the tensor product of the spline functions. If the data are given in a nonrectangular table, e.g., 5-year age groups and 1-year periods, the period and cohort variables can be parameterized by splines, while the age variable is parameterized as fixed effect levels, which leads to a semiparametric apc model. An important methodological issue in developing the nonparametric and semiparametric models is stability of the estimated spline curve at the boundaries. Here cubic regression splines will be used, which are constrained to be linear in the tails. Another point of importance is the nonidentifiability problem due to the linear dependency of the three time variables. This will be handled by decomposing the basis of each spline by orthogonal projection into constant, linear, and nonlinear terms, as suggested by Holford (1983, Biometrics 39, 311-324) for the traditional apc model. The advantage of using splines for yearly data compared to the traditional approach for aggregated data is the more accurate curve estimation for the nonlinear trend changes and the simple way of modeling interactions between the time variables. The method will be demonstrated with hypothetical data as well as with cancer mortality data.
Boundary extension is the tendency to remember more of a scene than was actually shown. The dominant interpretation of this memory illusion is that it originates from schemata that people construct when viewing a scene. Evidence of boundary extension has been obtained primarily with adult participants who remember neutral pictures. The current study addressed the developmental stability of this phenomenon. Therefore, we investigated whether children aged 10-12 years display boundary extension for neutral pictures. Moreover, we examined emotional scene memory. Eighty-seven children drew pictures from memory after they had seen either neutral or emotional pictures. Both their neutral and emotional drawings revealed boundary extension. Apparently, the schema construction that underlies boundary extension is a robust and ubiquitous process.
The natural convection in inclined side-heated rectangular boxes with adiabatic walls is theoretically and numerically investigated. The study is focused on the characterization of the convection patterns arising at the core of the basic steady unicellular flow and covers the whole range of Prandtl numbers (0< or = Pr < or = infinity) and inclinations (from alpha=0 degrees, heated-from-below vertical cavities, to alpha=180 degrees ). The onset of the flow instabilities depends on the core Rayleigh number R identical with K Ra, defined in terms of the local streamwise temperature gradient, K Delta T/L. The critical value of R for transversal and longitudinal modes is determined by the linear stability analysis of the basic plane-parallel flow, which also provides the stability diagram in the (Pr-alpha) chart. Anyhow, the effect of confinement can decisively change the stability properties of the core: if the steady unicell reaches the boundary layer regime (BLR) the local temperature gradient vanishes at the core leaving a completely stable core region. A theoretical determination of the frontier of the BLR in the space of parameters (alpha, R, and cavity size) yields an extra criterion of stability that has been displayed in the stability diagram. As confirmed by numerical calculations, the core-flow instabilities can only develop for Pr<O(1) whereas, at larger Pr the core region remains stable and the instabilities may only develop at the boundary layers. The analysis of the instability mechanisms reveals several couplings between the momentum and temperature fields that are not possible in the horizontal (alpha=90 degrees ) or vertical limits. For instance, by tilting the cavity with respect to alpha=0 degrees, the (Rayleigh-Bérnard) stationary thermal mode is suppressed in cavities whose depth is smaller than a theoretically predicted cutoff wavelength. The inclination also alters the properties of the oscillatory longitudinal instability, extensively investigated in the horizontal Hadley configuration at low Pr (liquid metals). An analytical relationship for its frequency in terms of alpha, Ra, and Pr is derived. Throughout the paper, numerical calculations in two- and three-dimensional enclosures illustrate each type of multicellular flow and examples of instability interactions near the codimension-2 lines predicted by the theory.
We study the stability of spatiotemporally periodic orbits in 1-d lattices of piecewise monotonic maps coupled via translationally invariant coupling and periodic boundary conditions. States of such systems have independent spatial and temporal periodicities and their stability can be studied through the analysis of a single, uniquely identified reduced matrix of size kxk when the system size is MxM, for M=kN, a multiple of k. This result applies for arbitrary temporal periods and is valid for all coupled map lattice systems coupled in a translationally invariant manner with stability matrices which are irreducible and non-negative, as in the present case. Our analysis could be useful in the analysis of stability regions and bifurcation behavior in a variety of spatially extended systems.
Chaotic properties of the one-parameter family of oval billiards with parabolic boundaries are investigated. Classical dynamics of such billiard is mixed and depends sensitively on the value of the shape parameter. Deviation matrices of some low period orbits are analyzed. Special attention is paid to the stability of orbits bouncing at the singular joining points of the parabolic arcs, where the boundary curvature is discontinuous. The existence of such orbits is connected with the segmentation of the phase space into two or more chaotic components. The obtained results are illustrated by numerical calculations of the Poincaré sections and compared with the properties of the elliptical stadium billiards.
We use highly efficient transition-matrix Monte Carlo simulations to determine equilibrium unfolding curves and fluid phase boundaries for solutions of coarse-grained globular proteins. The model we analyze derives the intrinsic stability of the native state and protein-protein interactions from basic information about protein sequence using heteropolymer collapse theory. It predicts that solutions of low hydrophobicity proteins generally exhibit a single liquid phase near their midpoint temperatures for unfolding, while solutions of proteins with high sequence hydrophobicity display the type of temperature-inverted, liquid-liquid transition associated with aggregation processes of proteins and other amphiphilic molecules. The phase transition occurring in solutions of the most hydrophobic protein we study extends below the unfolding curve, creating an immiscibility gap between a dilute, mostly native phase and a concentrated, mostly denatured phase. The results are qualitatively consistent with the solution behavior of hemoglobin (HbA) and its sickle variant (HbS), and they suggest that a liquid-liquid transition resulting in significant protein denaturation should generally be expected on the phase diagram of high-hydrophobicity protein solutions. The concentration fluctuations associated with this transition could be a driving force for the nonnative aggregation that can occur below the midpoint temperature.
The stability of the rotor of ultrasonic motor driving fluid directly is a key to its applications and control. This paper introduced the acoustic streaming and acoustic viscous stress near the boundary layer. Following this, the effect of acoustic viscous force on the stability of the rotor of ultrasonic motor driving fluid directly was presented in detail. The result showed that this system can be equivalent to a mass-spring and the spring constant can be used to weigh the stability of the rotor. By this model and relevant experiments, factors that affect the stability of the rotor such as the driving frequency, the rotor's weight and radius, the saturated acoustic streaming velocity, the mode number of stator vibration, the fluid's height and type are investigated and useful guidelines for design and application are obtained.
We investigated the effect on host-parasitoid dynamics of prolonged diapause, a feature of the life history of many animals living in unpredictable environments, by modifying the classical May (J. Anim. Ecol. 47 (1978) 833) host-parasitoid model. We considered three patterns of development of host and parasitoid: (a) prolonged parasitoid diapause controlled by host physiology, (b) parasitoid interference in host development, preventing parasitized hosts from prolonging diapause, and (c) host diapause independent of parasitoid attack. We found that single-year prolonged diapause shifted the boundaries of the May model towards a slight increase in stability. Longer periods of diapause prolongation had a stronger influence, but this influence remained modest if we considered realistic parameter values. In contrast to other recent studies, our results suggest that prolonged diapause does not necessarily compensate for the destabilizing effects of time lags on the influence of parasitoids on population dynamics.
We investigate the dynamics of the Josephson vortex lattice in layered high- T(c) superconductors at high magnetic fields. It is shown that the average electric current depends on the lattice structure and is resonantly enhanced when the Josephson frequency matches the frequency of the plasma mode. We find the stability regions of a moving lattice. It is shown that a specific lattice structure at a given velocity is uniquely selected by the boundary conditions; at small velocities a periodic triangular lattice is stable and looses its stability at some critical velocity. At even higher velocities, a structure close to a rectangular lattice is restored.
This article describes an axially symmetric ion trap with one-dimensional ion sorting ('three-dimensional (3D) monopole'). The mass spectrometer can be created by substituting one hyperboloid endcap electrode with a cone-shaped electrode, the vertex of the cone coincides with the cross-over point of the asymptotes of the ion trap electrodes. The potential applied to this cone-shaped electrode is equal to the potential at the centre of the electrode system. The stability zone of the 3D monopole has a shape of a narrow band extending along the z boundary; the mass resolution and the quality factor (the product of resolution and sensitivity) are constant within this stability band which also lowers the requirements for the driving voltage stability. The mass resolution obtained 1s 100 measured at 50% peak height and the relative sensitivity is 3 x 10(-5).
We carried our Poisson-Boltzmann (PB) calculations for the effects of charge reversal at five exposed sites (K16E, R119E, K135E, K147E, and R154E) and charge neutralization and proton titration of the H31-D70 semi-buried salt bridge on the stability of T4 lysozyme. Instead of the widely used solvent-exclusion (SE) surface, we used the van der Waals (vdW) surface as the boundary between the protein and solvent dielectrics (a protocol established in our earlier study on charge mutations in barnase). By including residual charge-charge interactions in the unfolded state, the five charge reversal mutations were found to have DeltaDeltaG(unfold) from -1.6 to 1.3 kcal/mol. This indicates that the variable effects of charge reversal observed by Matthews and co-workers are not unexpected. The H31N, D70N, and H31N/D70N mutations were found to destabilize the protein by 2.9, 1.3, and 1.6 kcal/mol, and the pK(a) values of H31 and D70 were shifted to 9.4 and 0.6, respectively. These results are in good accord with experimental data of Dahlquist and co-workers. In contrast, if the SE surface were used, the H31N/D70N mutant would be more stable than the wild-type protein by 1.3 kcal/mol. From these and additional results for 27 charge mutations on five other proteins, we conclude that 1) the popular view that electrostatic interactions are generally destabilizing may have been based on overestimated desolvation cost as a result of using the SE surface as the dielectric boundary; and 2) while solvent-exposed charges may not reliably contribute to protein stability, semi-buried salt bridges can provide significant stabilization.
Where pain of the musculoskeletal system is present, commonly, this pain is without objective evidence of disease, trauma, or disorder. Absence of an apparent cause for common pain prompts the consideration of mechanical stress as a contributing factor. The principal stress of the musculoskeletal system is postural. By posture it is usually meant the distribution of body mass with respect to gravity. Past efforts to predict chronic pain by postural analysis or to reduce such pain by strengthening, conscious control or splinting of posture has had marginal success. Past failure to relate posture to pain is attributable to (1) ubiquity of sub-optimal posture that precludes clinical comparison to those with optimal posture; (2) presupposition that the causal relation between posture and pain is of the observational class of causality rather than the manipulable kind; (3) a definition of posture that is too narrow to complete the picture; and (4) inadequate methods for reduction of postural asymmetry to an extent that is sufficient to elicit a significant and enduring effect on sub-optimal posture and related pain. Posture can be defined more broadly as the stance of the body performing within the boundaries of posture and which is mediated by the Postural Control System towards greatest stability (Fx. 1). The stance of the body is the arrangement of the body with respect to gravity and other accelerative forces. The postural boundaries are the set of forces that resist acceleration and thereby provide the limits within which one functions stably, and this resistance is currently approximated by six principal sources of resistance to acceleration: viscous, elastic, neuromuscular, rigid, viscoelastic, and inertial. The Postural Control System is located in the brainstem and modulates body stance to more economically and stably effect and resist acceleration. The rigid boundaries can be so with respect to compressive, tractive, or tensile qualities that permits three kinds of motion: translation, rotation and oscillation. An example of postural boundaries that are rigid with respect to compression and tensile character are the bones that bear weight. In contrast, ligaments provide a tractive rigidity and musculotendons a relatively elastic boundary. Joint surfaces are considered boundaries that are rigid but not perfectly so. Of fundamental importance are those joints that arc lowermost in a column of the musculoskeletal system namely: (1) the feet and ankles that support the entirety of the musculoskeletal system and; (2) the base of the sacrum that supports the vertebral spine. This broadened definition of posture leads to a greatly enhanced manipulability of posture in the upright stance and alleviation of more than two-thirds of common pain by the coherent combination of (1) manual manipulation to reduce somatic dysfunction; (2) foot orthotics to optimize the amplitude of the arches of the feet and vertically align the ankle; (3) a heel lift to level the sacral base; (4) and a group of therapeutic postures configured to minimize restriction of peripheral soft tissue reflective of the earlier posture, all aimed to optimize posture. Mediated by the postural control system, manipulation of postural boundaries accordingly modifies the structure and function of the entire musculoskeletal system. Typically, this relief is maintained by foot orthotic and heel lift alone without maintenance by manual manipulation, medication, or exercise.