Width Scaling Research Articles

Performance of an attention-demanding task during treadmill walking shifts the noise qualities of step-to-step variation in step width

BackgroundThe fractal scaling evident in the step-to-step fluctuations of stepping-related time series reflects, to some degree, neuromotor noise. Research questionThe primary purpose of this study was to determine the extent to which the fractal scaling of step width, step width and step width variability are affected by performance of an attention-demanding task. We hypothesized that the attention-demanding task would shift the structure of the step width time series toward white, uncorrelated noise. MethodsSubjects performed two 10-min treadmill walking trials, a control trial of undisturbed walking and a trial during which they performed a mental arithmetic/texting task. Motion capture data was converted to step width time series, the fractal scaling of which were determined from their power spectra. ResultsFractal scaling decreased by 22% during the texting condition (p < 0.001) supporting the hypothesized shift toward white uncorrelated noise. Step width and step width variability increased 19% and five percent, respectively (p < 0.001). However, a stepwise discriminant analysis to which all three variables were input revealed that the control and dual task conditions were discriminated only by step width fractal scaling. SignificanceThe change of the fractal scaling of step width is consistent with increased cognitive demand and suggests a transition in the characteristics of the signal noise. This may reflect an important advance toward the understanding of the manner in which neuromotor noise contributes to some types of falls. However, further investigation of the repeatability of the results, the sensitivity of the results to progressive increases in cognitive load imposed by attention-demanding tasks, and the extent to which the results can be generalized to the gait of older adults seems warranted.

Interstellar scintillation observations for PSR B0355+54

In this paper, we report our investigation of pulsar scintillation phenomena by monitoring PSR B0355$+$54 at 2.25 GHz for three successive months using \emph{Kunming 40-m radio telescope}. We have measured the dynamic spectrum, the two-dimensional correlation function, and the secondary spectrum. In those observations with high signal-to-noise ratio ($S/N\ge100$), we have detected the scintillation arcs, which are rarely observable using such a small telescope. The sub-microsecond scale width of the scintillation arc indicates that the transverse scale of structures on scattering screen is as compact as AU size. Our monitoring has also shown that both the scintillation bandwidth, timescale, and arc curvature of PSR B0355$+$54 were varying temporally. The plausible explanation would need to invoke multiple-scattering-screen or multiple-scattering-structure scenario that different screens or ray paths dominate the scintillation process at different epochs.

Operator Spreading in Random Unitary Circuits

Random quantum circuits yield minimally structured models for chaotic quantum dynamics, able to capture for example universal properties of entanglement growth. We provide exact results and coarse-grained models for the spreading of operators by quantum circuits made of Haar-random unitaries. We study both 1+1D and higher dimensions, and argue that the coarse-grained pictures carry over to operator spreading in generic many-body systems. In 1+1D, we demonstrate that the out-of-time-order correlator (OTOC) satisfies a biased diffusion equation, which gives exact results for the spatial profile of the OTOC, and the butterfly speed $v_{B}$. We find that in 1+1D the `front' of the OTOC broadens diffusively, with a width scaling in time as $t^{1/2}$. We address fluctuations in the OTOC between different realizations of the random circuit, arguing that they are negligible in comparison to the broadening of the front. Turning to higher D, we show that the averaged OTOC can be understood exactly via a remarkable correspondence with a classical droplet growth problem. This implies that the width of the front of the averaged OTOC scales as $t^{1/3}$ in 2+1D and $t^{0.24}$ in 3+1D (KPZ exponents). We support our analytic argument with simulations in 2+1D. We point out that, in a lattice model, the late time shape of the spreading operator is in general not spherical. However when full spatial rotational symmetry is present in 2+1D, our mapping implies an exact asymptotic form for the OTOC in terms of the Tracy-Widom distribution. For an alternative perspective on the OTOC in 1+1D, we map it to the partition function of an Ising-like model. As a result of special structure arising from unitarity, this partition function reduces to a random walk calculation which can be performed exactly. We also use this mapping to give exact results for entanglement growth in 1+1D circuits.

Another look at zonal flows: Resonance, shearing, and frictionless saturation

We show that shear is not the exclusive parameter that represents all aspects of flow structure effects on turbulence. Rather, wave-flow resonance enters turbulence regulation, both linearly and nonlinearly. Resonance suppresses the linear instability by wave absorption. Flow shear can weaken the resonance, and thus destabilize drift waves, in contrast to the near-universal conventional shear suppression paradigm. Furthermore, consideration of wave-flow resonance resolves the long-standing problem of how zonal flows (ZFs) saturate in the limit of weak or zero frictional drag, and also determines the ZF scale. We show that resonant vorticity mixing, which conserves potential enstrophy, enables ZF saturation in the absence of drag, and so is effective at regulating the Dimits up-shift regime. Vorticity mixing is incorporated as a nonlinear, self-regulation effect in an extended 0D predator-prey model of drift-ZF turbulence. This analysis determines the saturated ZF shear and shows that the mesoscopic ZF width scales as LZF∼f3/16(1−f)1/8ρs5/8l03/8 in the (relevant) adiabatic limit (i.e., τckk‖2D‖≫1). f is the fraction of turbulence energy coupled to ZF and l0 is the base state mixing length, absent ZF shears. We calculate and compare the stationary flow and turbulence level in frictionless, weakly frictional, and strongly frictional regimes. In the frictionless limit, the results differ significantly from conventionally quoted scalings derived for frictional regimes. To leading order, the flow is independent of turbulence intensity. The turbulence level scales as E∼(γL/εc)2, which indicates the extent of the “near-marginal” regime to be γL&amp;lt;εc, for the case of avalanche-induced profile variability. Here, εc is the rate of dissipation of potential enstrophy and γL is the characteristic linear growth rate of fluctuations. The implications for dynamics near marginality of the strong scaling of saturated E with γL are discussed.

Vessel scaling in evergreen angiosperm leaves conforms with Murray's law and area-filling assumptions: implications for plant size, leaf size and cold tolerance.

Water transport in leaf vasculature is a fundamental process affecting plant growth, ecological interactions and ecosystem productivity, yet the architecture of leaf vascular networks is poorly understood. Although Murray's law and the West-Brown-Enquist (WBE) theories predict convergent scaling of conduit width and number, it is not known how conduit scaling is affected by habitat aridity or temperature. We measured the scaling of leaf size, conduit width and conduit number within the leaves of 36 evergreen Angiosperms spanning a large range in aridity and temperature in eastern Australia. Scaling of conduit width and number in midribs and 2° veins did not differ across species and habitats (P>0.786), and did not differ from that predicted by Murray's law (P=0.151). Leaf size was strongly correlated with the hydraulic radius of petiole conduits (r2 =0.83, P<0.001) and did not differ among habitats (P>0.064), nor did the scaling exponent differ significantly from that predicted by hydraulic theory (P=0.086). The maximum radius of conduits in petioles was positively correlated with the temperature of the coldest quarter (r2 =0.67; P<0.001), suggesting that habitat temperature restricts the occurrence of wide-conduit species in cold habitats.

Graphene FETs Based on High Resolution Nanoribbons for HF Low Power Applications

In this paper we present high frequency field effect transistors based on graphene nanoribbons arrays (GNRFETs). The nanoribbons serve as a channel for the transistors and are fabricated with a process based on e-beam lithography and dry etching of high mobility hydrogen intercalated epitaxial graphene. The widths of the nanoribbons vary from 50 to 20 nm, less than half those measured in previous reports for GNRFETs. Hall measurements reveal that the devices are p-doped, with mobility on the order of 2300 cm2/Vs. From DC characteristics, we find that the maximum ratio IMAX/IMIN is 5 obtained at 50 nm ribbons width. The IV characteristics of the GNRFETs are slightly non-linear at high bias without a full saturation. Therefore, despite the aggressive scaling of the graphene nanoribbon width, a bandgap is still not observed in our measurements. The high frequency performances of our GNRFETs are already significant at low bias. At 300 mV drain source voltage, the highest intrinsic (extrinsic) cut-off frequency ft reaches 82 (18) GHz and the extrinsic maximum oscillation frequency fmax is 20 GHz, which is promising for low power applications.

Ion species stratification within strong shocks in two-ion plasmas

Strong collisional shocks in multi-ion plasmas are featured in many environments, with Inertial Confinement Fusion (ICF) experiments being one prominent example. Recent work [Keenan et al., Phys. Rev. E 96, 053203 (2017)] answered in detail a number of outstanding questions concerning the kinetic structure of steady-state, planar plasma shocks, e.g., the shock width scaling by the Mach number, M. However, it did not discuss shock-driven ion-species stratification (e.g., relative concentration modification and temperature separation). These are important effects since many recent ICF experiments have evaded explanation by standard, single-fluid, radiation-hydrodynamic (rad-hydro) numerical simulations, and shock-driven fuel stratification likely contributes to this discrepancy. Employing the state-of-the-art Vlasov-Fokker-Planck code, iFP, along with multi-ion hydro simulations and semi-analytics, we quantify the ion stratification by planar shocks with the arbitrary Mach number and the relative species concentration for two-ion plasmas in terms of ion mass and charge ratios. In particular, for strong shocks, we find that the structure of the ion temperature separation has a nearly universal character across ion mass and charge ratios. Additionally, we find that the shock fronts are enriched with the lighter ion species and the enrichment scales as M4 for M ≫ 1.

Creation of Rydberg Polarons in a Bose Gas.

We report spectroscopic observation of Rydberg polarons in an atomic Bose gas. Polarons are created by excitation of Rydberg atoms as impurities in a strontium Bose-Einstein condensate. They are distinguished from previously studied polarons by macroscopic occupation of bound molecular states that arise from scattering of the weakly bound Rydberg electron from ground-state atoms. The absence of a p-wave resonance in the low-energy electron-atom scattering in Sr introduces a universal behavior in the Rydberg spectral line shape and in scaling of the spectral width (narrowing) with the Rydberg principal quantum number, n. Spectral features are described with a functional determinant approach (FDA) that solves an extended Fröhlich Hamiltonian for a mobile impurity in a Bose gas. Excited states of polyatomic Rydberg molecules (trimers, tetrameters, and pentamers) are experimentally resolved and accurately reproduced with a FDA.

On link width scaling for energy‐proportional direct interconnection networks

SummaryEnergy consumption is one of the most important design parameters for future large‐scale computing systems. While the end of Dennard scaling demands for increasing energy‐proportional components, interconnection networks have not received much attention regarding this topic. However, these networks are expected to contribute about 20% to the overall power consumption of these systems in the near future. Furthermore, this fraction increases if other energy‐proportional components, such as CPUs, accelerators, and memory, are not fully utilized. To avoid becoming the main contributor to power consumption and to reduce overall power consumption, it is mandatory to improve the energy‐proportionality of interconnection networks. In this work, we analyze different aspects of energy‐proportionality in interconnection networks for systems designed within current technical constraints but also for future systems that might be designed with different parameters. First, we discuss the impact of multiple design parameters and the most feasible approach for improved energy consumption, such as transition time and power state granularity. Based on this study, we introduce three different power saving policies, which try to address different requirements. While an on/off policy allows for large energy savings, it can also cause significant performance losses for adverse setups. In order to meet the demand for sustainable performance, we present two new policies that trade power saving potential for performance. For all three workload classes, we use a power‐aware network simulation to report the impact on execution time and energy consumption compared to the current situation and an idealized network. While we show that a highly regular pattern enables power saving possibilities close to the theoretical minimum, even slight deviations from such a highly iterative and temporal behavior demand for further improvements in all policies.

Kirigami-Inspired Structures for Smart Adhesion.

Spatially controlled layouts of elasticity can provide enhanced adhesion over homogeneous systems. Emerging techniques in kirigami, where designed cuts in materials impart highly tunable stiffness and geometry, offer an intriguing approach to create well-defined layouts of prescribed elastic regions. Here, we show that kirigami-inspired structures at interfaces provide a new mechanism to spatially control and enhance adhesion strength while providing directional characteristics for smart interfaces. We use kirigami-inspired cuts to define stiff and compliant regions, where above a critical, material-defined length scale, bending rigidity and contact width can be tuned to enhance adhesive force capacity by a factor of ∼100 across a spatially patterned adhesive sheet. The directional nature of these designs also imparts anisotropic responses, where peeling in different directions results in anisotropic adhesion ratios of ∼10. Experimental results are well-supported by theoretical predictions in which the bending rigidity and contact width of kirigami-inspired structures and interconnects control the adhesive capacity. These new interfacial structures and design criteria provide diverse routes for advanced adhesive functionality, including spatially controlled systems, wearable kirigami-inspired electronics, and anisotropic kirigami-inspired bandages that enable strong adhesive capacity while maintaining easy release.

Orientations of Cells on Compliant Substrates under Biaxial Stretches: A Theoretical Study

Mechanical cues from the microenvironments play a regulating role in many physiological and pathological processes, such as stem cell differentiation and cancer cell metastasis. Experiments showed that cells adhered on a compliant substrate may change orientation with an externally applied strain in the substrate. By accounting for actin polymerization, actin retrograde flow, and integrin binding dynamics, here we develop a mechanism-based tensegrity model to study the orientations of polarized cells on a compliant substrate under biaxial stretches. We show that the cell can actively regulate its mechanical state by generating different traction force levels along its polarized direction. Under static or ultralow-frequency cyclic stretches, stretching a softer substrate leads to a higher increase in the traction force and induces a narrower distribution of cell alignment. Compared to static loadings, high-frequency cyclic loadings have a more significant influence on cell reorientation on a stiff substrate. In addition, the width of the cellular angular distribution scales inversely with the stretch amplitude under both static and cyclic stretches. Our results are in agreement with a wide range of experimental observations, and provide fundamental insights into the functioning of cellular mechanosensing systems.

Geometrical Properties of Antiparallel Arrays Regulate Microtubule Sliding and Stalling by PRC1 and Kif4A

Motor and non-motor crosslinking proteins play critical roles in determining the size and stability of microtubule-based architectures. However, we have a limited understanding of how the geometrical properties of microtubule arrays, in turn, regulate the output of crosslinking proteins. Here we investigate the relative sliding of antiparallel microtubules by two interacting proteins: the non-motor crosslinker PRC1 and kinesin Kif4A. The collective activity of PRC1 and Kif4A also results in the accumulation of both proteins at the microtubule plus-end (‘end-tag’). Sliding stalls when the end-tags on the antiparallel microtubules collide. Interestingly, we find that structural properties of the initial array regulate two aspects of PRC1-Kif4A mediated microtubule organization. First, sliding velocity scales with initial microtubule-overlap length. Second, the width of the final stable overlap scales with microtubule lengths. Our analyses reveal how nanometer-sized proteins can decode micron-scale geometrical features of antiparallel bundles to define the structure and mechanics of microtubule-based architectures.

Submicron scale tissue multifractal anisotropy in polarized laser light scattering

The spatial fluctuations of the refractive index within biological tissues exhibit multifractal anisotropy, leaving its signature as a spectral linear diattenuation of scattered polarized light. The multifractal anisotropy has been quantitatively assessed by the processing of relevant Mueller matrix elements in the Fourier domain, utilizing the Born approximation and subsequent multifractal analysis. The differential scaling exponent and width of the singularity spectrum appear to be highly sensitive to the structural multifractal anisotropy at the micron/sub-micron length scales. An immediate practical use of these multifractal anisotropy parameters was explored for non-invasive screening of cervical precancerous alterations ex vivo, with the indication of a strong potential for clinical diagnostic purposes.

Radiographic measurement of cardiac size in laboratory mice

This study was to establish quantitative reference range measurements that could be used to support basic data of cardiac size in the laboratory animals. Right and left lateral recumbency (R/L view) and ventral and dorsal recumbency (VD/DV view) radiographs were obtained in 6 normally laboratory mice (Mus musculus). The R/L view heart measurements were the apicobasal length (AB); the maximum width (CD); the distance between the cranial edge of the fifth rib and the caudal edge of the seventh rib (R5-7); the vertical depth of the thorax (H). The VD/DV view cardiac silhouette measurements were maximum length (L); maximum width (W); the width of the thorax (T). In order to determine vertebral heart scale score (VHS), the length and width of the heart were measured and then superimposed to the thoracic vertebrae starting at fourth vertebral (T4) caudally. In order to determine intercostals space (ICS), the CD were measured perpendicularly and superimposed on the intercostals space from fourth costal caudally. The cardiac silhouette was evaluated objectively to describe the cardiac appearance. Lengths of the parameter were determined with a caliper and a ruler in millimeters scale. The result showed that all measurements have not differed significantly between radiographic views (p&gt;0.05).

Large‐Scale Fabrication of MoS2 Ribbons and Their Light‐Induced Electronic/Thermal Properties: Dichotomies in the Structural and Defect Engineering

AbstractControlled design and patterning of layered transition metal dichalcogenides (TMDs) into specific dimensions and geometries hold great potential for next‐generation micro/nanoscale electronic applications. Herein, the large‐scale fabrication of MoS2 ribbons with widths ranging from micro‐ to nanoscale is reported. Their unique electric and thermal properties introduced by the shape change and defect creation are also demonstrated, with particular focus on the performance associated with light–matter interactions. The theoretical calculation indicates significantly increased absorption and scattering efficiency of the MoS2 ribbons with decreasing width. As a result, enhanced photocarrier generation ability is detected on their phototransistors with defect‐modulated light‐response behavior. The light‐induced thermal transport properties of the MoS2 ribbons are further studied. A decreased thermal conductivity is observed on narrower ribbons, attributed to the defects created during fabrication. It is also found that the effect of phonon scattering at ribbon edges on their thermal conductivity is insignificant, and the thermal transport has no obvious dependence on the ribbon direction at such width scale. This study evaluates the prospects for designing and fabricating TMD semiconductors with specific geometries for future optoelectronic applications.

Strain Localization during Equal-Channel Angular Pressing Analyzed by Finite Element Simulations

Equal-Channel Angular Pressing (ECAP) is a method used to introduce severe plastic deformation into a metallic billet without changing its geometry. In special cases, strain localization occurs and a pattern consisting of regions with high and low deformation (so-called shear and matrix bands) can emerge. This paper studies this phenomenon numerically adopting two-dimensional finite element simulations of one ECAP pass. The mechanical behavior of aluminum is modeled using phenomenological plasticity theory with isotropic or kinematic hardening. The effects of the two different strain hardening types are investigated numerically by systematic parameter studies: while isotropic hardening only causes minor fluctuations in the plastic strain fields, a material with high initial hardening rate and sufficient strain hardening capacity can exhibit pronounced localized deformation after ECAP. The corresponding finite element simulation results show a regular pattern of shear and matrix bands. This result is confirmed experimentally by ECAP-processing of AA6060 material in a severely cold worked condition, where microstructural analysis also reveals the formation of shear and matrix bands. Excellent agreement is found between the experimental and numerical results in terms of shear and matrix band width and length scale. The simulations provide additional insights regarding the evolution of the strain and stress states in shear and matrix bands.

Coexistence of a well-determined kinetic law and a scale-invariant power law during the same physical process

It is generally claimed that physical processes which display scale-invariant power-law distributions are subjected to a dynamic criticality that prohibits a well-defined kinetic law. In this paper, we demonstrate the coexistence of these two apparently contradicting behaviors during the same physical process---the motion of type-II twin boundaries in martensite Ni-Mn-Ga. The process is investigated by combined measurements of the temporal twin-boundary velocity and the acoustic emitted energy. Velocity values are extracted from high-resolution force measurements taken during displacement-driven mechanical tests, as well as from force-driven magnetic tests, and cover an overall range of six orders of magnitude. Acoustic emission (AE) is measured during mechanical tests. Velocity values follow a normal distribution whose characteristic value is determined by the material's kinetic relation, and its width scales with the average velocity. In addition, it is observed that velocity distributions are characterized by a heavy tail at the right (i.e., faster) end that exhibits a power law over more than one and a half orders of magnitude. At the same time, the AE signals follow a scale-invariant power-law distribution, which is not sensitive to the average twin-boundary velocity. The coexistence of these two different statistical behaviors reflects the complex nature of twin-boundary motion and suggests the possibility that the transformation proceeds through physical subprocesses that are close to criticality alongside other processes that are not.

Size and shape distributions of carbon black aggregates by transmission electron microscopy

Carbon black aggregate size and shape affects its performance in many applications. In this interlaboratory comparison, an industry reference carbon black, SRB8, was analysed with a protocol based on ASTM D3849-14a, a method for morphological characterization of carbon black aggregates using electron microscopy. Multiple descriptor types (size, elongation, ruggedness, plus those of ASTM D3849-14a) were assessed for repeatability, reproducibility, and measurement uncertainties. Carbon black aggregates have been characterized using descriptor correlations: two important such correlations are affinity coefficients and fractal exponents. SRB8 aggregates appear to be self-affine, i.e., their width and length descriptors scale anisotropically. ASTM D3849-14a derived descriptors have low interlaboratory reproducibilities and high measurement uncertainties. When these descriptors are used for projected area-based fractal analysis, the estimated fractal exponents do not have realistic values. However, the use of an average nodule diameter generated self-consistent values of fractal exponents with measurement uncertainties of about 9%. Carbon black aggregates can be categorized using shape descriptors into the categories: spheroidal, ellipsoidal, branched, and linear. These shape categories contribute non-uniformly to descriptor values across their data ranges and lead to multimodal distributions. These findings illustrate the importance of assessing data quality and measurement uncertainty for particle size and shape distributions.

Nonlinear forced vibration of FG-CNTs-reinforced curved microbeam based on strain gradient theory considering out-of-plane motion

The main goal of this research is to examine the in-plane and out-of-plane forced vibration of a curved nanocomposite microbeam. The in-plane and out-of-plane displacements of the structure are considered based on the first order shear deformation theory (FSDT). The curved microbeam is reinforced by functionally graded carbon nanotubes (FG-CNTs) and thus the extended rule of mixture is employed to estimate the effective material properties of the structure. Also, the small scale effect is captured using the strain gradient theory. The structure is rested on a nonlinear orthotropic viscoelastic foundation and is subjected to concentrated transverse harmonic external force, thermal and magnetic loads. The derivation of the governing equations is performed using energy method and Hamilton's principle. Differential quadrature (DQ) method along with integral quadrature (IQ) and Newmark methods are employed to solve the problem. The effect of various parameters such as volume fraction and distribution type of CNTs, boundary conditions, elastic foundation, temperature changes, material length scale parameters, magnetic field, central angle and width to thickness ratio are studied on the frequency and force responses of the structure. The results indicate that the highest frequency and lowest vibration amplitude belongs to FGX distribution type while the inverse condition is observed for FGO distribution type. In addition, the hardening-type response of the structure with FGX distribution type is more intense with respect to the other distribution types.

HEMIBRYCON GUEJARENSIS, A NEW SPECIES FROM THE GÜEJAR RIVER, ORINOCO BASIN, COLOMBIA (CHARACIFORMES: CHARACIDAE) WITH A REVIEW THE POPULATIONS IDENTIFIED AS HEMIBRYCON METAE

Hemibrycon guejarensis, new species, is described from the Güejar River, La Macarena mountain range, upper Guaviare River drainage, Colombia. The new species is distinguished from most cis-Andean congeners (H. jabonero Lake Maracaibo and adjacent Caribbean drainages, H. metae which is found in the Guavio River, some Orinoco and Caribbean River drainages in Venezuela, and H. taeniurus from Trinidad and adjacent mainland drainages in Venezuela) in having ii, 7, i dorsal-fin rays (vs. ii, 8). H. guejarensis is further distinguished from H. taeniurus and H. jabonero, in having a wider second pigment layer in the humeral spot (covering 3 vs. 2 scale widths). H. guejarensis is very similar to H. metae (an allopatric species also present in streams of the Orinoco River Basin in Venezuela and Colombia and some Venezuelan Caribbean drainages). Hemibrycon guejarensis is distinguishedby the orientation of the dorsal lateral-line canal which crosses the ventral part of the humeral spot transversely vs. horizontally across dorsal part of spot in the holotype of H. metae and Orinoco and Caribbean populations. H. guejarensis differs from H. metae in having the tip of the pectoral fin passing the pelvic-fin insertions (vs. pectoral fin tip not reaching pelvic-fin insertions). We identify populations previously considered as Hemibrycon metae from Venezuelan Orinoco River Basin piedmont streams and Caribbean drainages to be instead H. jabonero and H. taeniurus. Careful analysis of these populations indicated that all of them differ from the H. metae holotype and topotypic specimens in pelvic fin and postorbital lengths.