Search Results: geometry

A Hybrid Antenna Array Design for 3-D Direction of Arrival Estimation

dx.plos.org/10.1371/journal.pone.0118914
A 3-D beam scanning antenna array design is proposed that gives a whole 3-D spherical coverage and also suitable for various radar and body-worn devices in the Body Area Networks applications. The Array Factor (AF) of the proposed antenna is derived and its various parameters like directivity, Half Power Beam Width (HPBW) and Side Lobe Level (SLL) are calculated by varying the size of the proposed antenna array. Simulations were carried out in MATLAB 2012b. The radiators are considere...

DNA Unwinding by Ring-Shaped T4 Helicase gp41 Is Hindered by Tension on the Occluded Strand

dx.plos.org/10.1371/journal.pone.0079237
The replicative helicase for bacteriophage T4 is gp41, which is a ring-shaped hexameric motor protein that achieves unwinding of dsDNA by translocating along one strand of ssDNA while forcing the opposite strand to the outside of the ring. While much study has been dedicated to the mechanism of binding and translocation along the ssDNA strand encircled by ring-shaped helicases, relatively little is known about the nature of the interaction with the opposite, ‘occluded’ strand. Her...

Optimization of SPECT-CT Hybrid Imaging Using Iterative Image Reconstruction for Low-Dose CT: A Phantom Study

dx.plos.org/10.1371/journal.pone.0138658
Background: Hybrid imaging combines nuclear medicine imaging such as single photon emission computed tomography (SPECT) or positron emission tomography (PET) with computed tomography (CT). Through this hybrid design, scanned patients accumulate radiation exposure from both applications. Imaging modalities have been the subject of long-term optimization efforts, focusing on diagnostic applications. It was the aim of this study to investigate the influence of an iterative CT image recons...

Movement Timing and Invariance Arise from Several Geometries

dx.plos.org/10.1371/journal.pcbi.1000426
Human movements show several prominent features; movement duration is nearly independent of movement size (the isochrony principle), instantaneous speed depends on movement curvature (captured by the 2/3 power law), and complex movements are composed of simpler elements (movement compositionality). No existing theory can successfully account for all of these features, and the nature of the underlying motion primitives is still unknown. Also unknown is how the brain selects movement du...

Data Mechanics and Coupling Geometry on Binary Bipartite Networks

dx.plos.org/10.1371/journal.pone.0106154
We quantify the notion of pattern and formalize the process of pattern discovery under the framework of binary bipartite networks. Patterns of particular focus are interrelated global interactions between clusters on its row and column axes. A binary bipartite network is built into a thermodynamic system embracing all up-and-down spin configurations defined by product-permutations on rows and columns. This system is equipped with its ferromagnetic energy ground state under Ising model...

Effects of Fiber Type and Size on the Heterogeneity of Oxygen Distribution in Exercising Skeletal Muscle

dx.plos.org/10.1371/journal.pone.0044375
The process of oxygen delivery from capillary to muscle fiber is essential for a tissue with variable oxygen demand, such as skeletal muscle. Oxygen distribution in exercising skeletal muscle is regulated by convective oxygen transport in the blood vessels, oxygen diffusion and consumption in the tissue. Spatial heterogeneities in oxygen supply, such as microvascular architecture and hemodynamic variables, had been observed experimentally and their marked effects on oxygen exc...

Asymmetrical Inheritance of Plasmids Depends on Dynamic Cellular Geometry and Volume Exclusion Effects

dx.plos.org/10.1371/journal.pone.0139443
The asymmetrical inheritance of plasmid DNA, as well as other cellular components, has been shown to be involved in replicative aging. In Saccharomyces cerevisiae, there is an ongoing debate regarding the mechanisms underlying this important asymmetry. Currently proposed models suggest it is established via diffusion, but differ on whether a diffusion barrier is necessary or not. However, no study so far incorporated key aspects to segregation, such as dynamic morphology changes throu...

Water use efficiency and evapotranspiration in maize-soybean relay strip intercrop systems as affected by planting geometries

dx.plos.org/10.1371/journal.pone.0178332
Optimum planting geometries have been shown to increase crop yields in maize-soybean intercrop systems. However, little is known about whether changes in planting geometry improve the seasonal water use of maize and soybean intercrops. We conducted two different field experiments in 2013 and 2014 to investigate the effects of changes in planting geometry on water use efficiency (WUE) and evapotranspiration (ETc) of maize (Zea mays L.) and soybean [Glycine max (L.) Merr.] relay strip i...

Control of Whole Heart Geometry by Intramyocardial Mechano-Feedback: A Model Study

dx.plos.org/10.1371/journal.pcbi.1002369
Geometry of the heart adapts to mechanical load, imposed by pressures and volumes of the cavities. We regarded preservation of cardiac geometry as a homeostatic control system. The control loop was simulated by a chain of models, starting with geometry of the cardiac walls, sequentially simulating circulation hemodynamics, myofiber stress and strain in the walls, transfer of mechano-sensed signals to structural changes of the myocardium, and finalized by calculation of resulti...

Orienteering in Knowledge Spaces: The Hyperbolic Geometry of Wikipedia Mathematics

dx.plos.org/10.1371/journal.pone.0067508
In this paper we show how the coupling of the notion of a network with directions with the adaptation of the four-point probe from materials testing gives rise to a natural geometry on such networks. This four-point probe geometry shares many of the properties of hyperbolic geometry wherein the network directions take the place of the sphere at infinity, enabling a navigation of the network in terms of pairs of directions: the geodesic through a pair of points is oriented from one dir...

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