1,040 results match your criteria geometrical parameter

Rectification induced by geometry in two-dimensional quantum spin lattices.

Phys Rev E 2021 Mar;103(3-1):032108

Departamento de Matemática, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil.

We address the role of geometrical asymmetry in the occurrence of spin rectification in two-dimensional quantum spin chains subject to two reservoirs at the boundaries, modeled by quantum master equations. We discuss the differences in the rectification for some one-dimensional cases, and present numerical results of the rectification coefficient R for different values of the anisotropy parameter of the XXZ model, and different configurations of boundary drives, including both local and nonlocal dissipators. Our results also show that geometrical asymmetry, along with inhomogeneous magnetic fields, can induce spin current rectification even in the XX model, indicating that the phenomenon of rectification due to geometry may be of general occurrence in quantum spin systems. Read More

View Article and Full-Text PDF

An extended lidar-based cirrus cloud retrieval scheme: first application over an Arctic site.

Opt Express 2021 Mar;29(6):8553-8580

Accurate and precise characterization of cirrus cloud geometrical and optical properties is essential for better constraining their radiative footprint. A lidar-based retrieval scheme is proposed here, with its performance assessed on fine spatio-temporal observations over the Arctic site of Ny-Ålesund, Svalbard. Two contributions related to cirrus geometrical (dynamic Wavelet Covariance Transform (WCT)) and optical properties (constrained Klett) are reported. Read More

View Article and Full-Text PDF

Inner strut morphology is the key parameter in producing highly porous and mechanically stable poly(ε-caprolactone) scaffolds via selective laser sintering.

Mater Sci Eng C Mater Biol Appl 2021 Apr 23;123:111986. Epub 2021 Feb 23.

Julius Wolff Institute, Charité - Universitaetsmedizin Berlin, Augustenburger Platz 1, 13353, Berlin, Germany; Berlin Institute of Health, Center for Regenerative Therapies (BCRT) at Charité - Universitaetsmedizin Berlin, Augustenburger Platz 1, 13353 Berlin, Germany. Electronic address:

Selective laser sintering (SLS) is an established method to produce dimensionally accurate scaffolds for tissue engineering (TE) applications, especially in bone. In this context, the FDA-approved, biodegradable polymer poly(ε-caprolactone) (PCL) has been suggested as a suitable scaffold material. However, PCL scaffold mechanical stability - an attribute of particular importance in the field of bone TE - was not considered as a primary target for SLS process parameters optimization so far. Read More

View Article and Full-Text PDF

Evolution of cardiac geometry and function in women with severe preeclampsia from immediately post-delivery to 1 year postpartum.

Int J Cardiovasc Imaging 2021 Mar 13. Epub 2021 Mar 13.

Department of Cardiology, University Medical Centre Ljubljana, Zaloška 7, 1000, Ljubljana, Slovenia.

Preeclampsia is associated with left ventricular (LV) geometrical and functional changes, which could be related to cardiovascular risk later in life. The purpose of our study was to evaluate evolution of LV dimensions and function in severe preeclamptic women from immediately post-delivery to 1 year postpartum. Twenty-five women with severe preeclampsia and 15 healthy term controls underwent standard and speckle-tracking echocardiography 1 day after delivery and 1 year postpartum. Read More

View Article and Full-Text PDF

Insights into the intraparticle morphology of dendritic mesoporous silica nanoparticles from electron tomographic reconstructions.

J Colloid Interface Sci 2021 Jun 23;592:296-309. Epub 2021 Feb 23.

Department of Chemistry, Philipps-Universität Marburg, Hans-Meerwein-Strasse 4, 35032 Marburg, Germany. Electronic address:

Hypothesis: Although many synthetic pathways allow to fine-tune the morphology of dendritic mesoporous silica nanoparticles (DMSNs), the control of their particle size and mesopore diameter remains a challenge. Our study focuses on either increasing the mean particle size or adjusting the pore size distribution, changing only one parameter (particle or pore size) at a time. The dependence of key morphological features (porosity; pore shape and pore dimensions) on radial distance from the particle center has been investigated in detail. Read More

View Article and Full-Text PDF

How the growth of ice depends on the fluid dynamics underneath.

Proc Natl Acad Sci U S A 2021 Mar;118(10)

Department of Applied Physics, Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands.

Convective flows coupled with solidification or melting in water bodies play a major role in shaping geophysical landscapes. Particularly in relation to the global climate warming scenario, it is essential to be able to accurately quantify how water-body environments dynamically interplay with ice formation or melting process. Previous studies have revealed the complex nature of the icing process, but have often ignored one of the most remarkable particularities of water, its density anomaly, and the induced stratification layers interacting and coupling in a complex way in the presence of turbulence. Read More

View Article and Full-Text PDF

On discrete Lorenz-like attractors.

Chaos 2021 Feb;31(2):023117

National Research University Higher School of Economics, 25/12 Bolshaya Pecherskaya Ulitsa, 603155 Nizhny Novgorod, Russia.

We study geometrical and dynamical properties of the so-called discrete Lorenz-like attractors. We show that such robustly chaotic (pseudohyperbolic) attractors can appear as a result of universal bifurcation scenarios, for which we give a phenomenological description and demonstrate certain examples of their implementation in one-parameter families of three-dimensional Hénon-like maps. We pay special attention to such scenarios that can lead to period-2 Lorenz-like attractors. Read More

View Article and Full-Text PDF
February 2021

Changing the Geometry of Representations: -Embeddings for NLP Tasks.

Entropy (Basel) 2021 Feb 26;23(3). Epub 2021 Feb 26.

Romanian Institute of Science and Technology (RIST), 400022 Cluj-Napoca, Romania.

Word embeddings based on a conditional model are commonly used in Natural Language Processing (NLP) tasks to embed the words of a dictionary in a low dimensional linear space. Their computation is based on the maximization of the likelihood of a conditional probability distribution for each word of the dictionary. These distributions form a Riemannian statistical manifold, where word embeddings can be interpreted as vectors in the tangent space of a specific reference measure on the manifold. Read More

View Article and Full-Text PDF
February 2021

Geometrical characteristics of eggs from 3 poultry species.

Poult Sci 2021 Mar 26;100(3):100965. Epub 2020 Dec 26.

College of Animal Science and Technology, Zhejiang Agriculture & Forestry University, Lin'an 311300, Zhejiang, China. Electronic address:

We studied the correlations between egg geometrical parameters (i.e., egg shape index, sphericity, geometric mean diameter, surface area, and volume) and eggshell qualities, or the organic matrix in eggshell. Read More

View Article and Full-Text PDF

Lumped-Parameter and Finite Element Modeling of Heart Failure with Preserved Ejection Fraction.

J Vis Exp 2021 02 13(168). Epub 2021 Feb 13.

Institute for Medical Engineering and Science, Massachusetts Institute of Technology; Health Science and Technology Program, Harvard/Massachusetts Institute of Technology; Department of Mechanical Engineering, Massachusetts Institute of Technology;

Scientific efforts in the field of computational modeling of cardiovascular diseases have largely focused on heart failure with reduced ejection fraction (HFrEF), broadly overlooking heart failure with preserved ejection fraction (HFpEF), which has more recently become a dominant form of heart failure worldwide. Motivated by the paucity of HFpEF in silico representations, two distinct computational models are presented in this paper to simulate the hemodynamics of HFpEF resulting from left ventricular pressure overload. First, an object-oriented lumped-parameter model was developed using a numerical solver. Read More

View Article and Full-Text PDF
February 2021

Enhancing the performance of micro-biosensors by functionally graded geometrical and material parameters.

Arch Appl Mech 2021 Feb 20:1-15. Epub 2021 Feb 20.

Faculty of Engineering, Helwan University, P.O. Box 11718, Mataria, Cairo, Egypt.

Most recently, the whole world is struggling against the virulent pandemic COVID-19. Due to the unbounded global spread of the disease, having biosensors with high performance such as high sensitivity and accuracy is of utmost importance. In this paper, the effects of various parameters on the behaviors of micro-biosensors are investigated in order to enhance their performance. Read More

View Article and Full-Text PDF
February 2021

Tissue growth constrains root organ outlines into an isometrically scalable shape.

Development 2021 Feb 26;148(4). Epub 2021 Feb 26.

Department of Biological Sciences, Graduate School of Science, Osaka University, Machikaneyama-cho, Toyonaka 560-0043, Japan.

Organ morphologies are diverse but also conserved under shared developmental constraints among species. Any geometrical similarities in the shape behind diversity and the underlying developmental constraints remain unclear. Plant root tip outlines commonly exhibit a dome shape, which likely performs physiological functions, despite the diversity in size and cellular organization among distinct root classes and/or species. Read More

View Article and Full-Text PDF
February 2021

Shrinkage stress and cuspal deflection in MOD restorations: analytical solutions and design guidelines.

Dent Mater 2021 Feb 18. Epub 2021 Feb 18.

Minnesota Dental Research Center for Biomaterials and Biomechanics, School of Dentistry, University of Minnesota, United States. Electronic address:

Objective: This paper aimed to derive analytical solutions for the shrinkage stress and cuspal deflection in model Class-II mesial-occlusal-distal (MOD) resin-composite restorations to better understand their dependence on geometrical and material parameters. Based on the stress solutions, it was shown how design curves could be obtained to guide the selection of dimensions and materials for the preparation and restoration of this class of cavities.

Methods: The cavity wall was considered as a cantilevered beam while the resin composite was modeled as Winkler's elastic foundation with closely-spaced linear springs. Read More

View Article and Full-Text PDF
February 2021

Planning tool for first metatarsal length in hallux valgus surgery.

Foot (Edinb) 2021 Mar 14;46:101774. Epub 2021 Jan 14.

Department of Orthopaedics, Balgrist University Hospital, Zurich, Switzerland. Electronic address:

Background: The precise planning of metatarsal (MT) I length in hallux valgus surgery is important. However, currently no tool exists which allows the surgeon to reliably predict this parameter.

Methods: 30 virtual 3-dimensional hallux valgus surgeries were performed on varied deformation models based on cadaveric feet scans. Read More

View Article and Full-Text PDF

The geometrical analysis of localization error characteristic in stereo vision systems.

Rev Sci Instrum 2021 Jan;92(1):015122

Beijing Institute of Spacecraft System Engineering CAST, Beijing 100094, China.

The parameters of a stereo camera directly determine the accuracy of a stereo vision positioning system. In this paper, the relationship between camera parameter error and positioning error is established by using the geometric analysis method with a clear physical meaning. The error models of the relative position error and camera resolution error of the stereo camera are established. Read More

View Article and Full-Text PDF
January 2021

Sparse planar arrays for azimuth and elevation using experimental data.

J Acoust Soc Am 2021 Jan;149(1):167

Technical University of Denmark, Kongens Lyngby, Denmark.

Sparse arrays are special geometrical arrangements of sensors which overcome some of the drawbacks associated with dense uniform arrays and require fewer sensors. For direction finding applications, sparse arrays with the same number of sensors can resolve more sources while providing higher resolution than a dense uniform array. This has been verified numerically and with real data for one-dimensional microphone arrays. Read More

View Article and Full-Text PDF
January 2021

Molded Vial Manufacturing and Its Impact on Heat Transfer during Freeze-Drying: Vial Geometry Considerations.

AAPS PharmSciTech 2021 Jan 27;22(2):57. Epub 2021 Jan 27.

Department of Pharmaceutics, Freeze Drying Focus Group (FDFG), Friedrich-Alexander University (FAU) Erlangen-Nuremberg, Cauerstrasse 4, 91058, Erlangen, Germany.

Recent advances in molded vial manufacturing enabled manufacturers to use a new manufacturing technique to achieve superior homogeneity of the vial wall thickness. This study evaluated the influence of the different manufacturing techniques of molded vials and glass compositions on vial heat transfer in freeze-drying. Additionally, the influence of using empty vials as thermal shielding on thermal characteristics of edge and center vials was investigated. Read More

View Article and Full-Text PDF
January 2021

Control Protocols for Range-Based Navigation of a Networked Group of Underwater Vehicles.

Front Robot AI 2020 9;7:519985. Epub 2020 Dec 9.

Department of Innovation Engineering (DII), University of Salento (Interuniversity Center of Integrated Systems for the Marine Environment node), Lecce, Italy.

This paper tackles the problem of formation reconstruction for a team of vehicles based on the knowledge of the range between agents of a subset of the participants. One main peculiarity of the proposed approach is that the relative velocity between agents, which is a fundamental data to solve the problem, is not assumed to be known in advance neither directly communicated. For the purpose of estimating this quantity, a collaborative control protocol is designed in order to mount the velocity data in the motion of each vehicle as a parameter through a dedicated control protocol, so that it can be inferred from the motion of the neighbor agents. Read More

View Article and Full-Text PDF
December 2020

Experimental performance evaluation of an impinging jet with fins type solar air heater.

Environ Sci Pollut Res Int 2021 Jan 6. Epub 2021 Jan 6.

Department of Mechanical Engineering, Indian Institute of Technology (Indian School of Mines), Dhanbad, Jharkhand, 826004, India.

The current experimental investigation aimed to evaluate performance of a non-cross flow type solar air heater (SAH). The design comprises of an array of continuous longitudinal fins which extends the bottom of absorber surface and alongside to it a jet plate with inline holes has also been encapsulated. The experiments were performed in natural outdoor conditions for a specified range of flow and geometrical parameters, namely, {[Formula: see text], 5700≤ Re  ≤ 11700, 0. Read More

View Article and Full-Text PDF
January 2021

Viscoelasticity of children and adolescent brains through MR elastography.

J Mech Behav Biomed Mater 2021 03 19;115:104229. Epub 2020 Dec 19.

Department of Mechanical Engineering, Stevens Institute of Technology, Hoboken, NJ, 07030, USA; Biomedical Engineering and Imaging Institute, Mount Sinai Icahn School of Medicine, New York, NY, 10029, USA. Electronic address:

Magnetic Resonance Elastography (MRE) is an elasticity imaging technique that allows a safe, fast, and non-invasive evaluation of the mechanical properties of biological tissues in vivo. Since mechanical properties reflect a tissue's composition and arrangement, MRE is a powerful tool for the investigation of the microstructural changes that take place in the brain during childhood and adolescence. The goal of this study was to evaluate the viscoelastic properties of the brain in a population of healthy children and adolescents in order to identify potential age and sex dependencies. Read More

View Article and Full-Text PDF

Zoomable head-up display with the integration of holographic and geometrical imaging.

Opt Express 2020 Nov;28(24):35716-35723

Head-up displays (HUDs) have already penetrated into vehicle applications and demand keeps growing. Existing head-up displays have their image fixed at a certain distance in front of the windshield. New development could have two images displayed at two different yet fixed distances simultaneously or switchable upon request. Read More

View Article and Full-Text PDF
November 2020

Assessing MMA Welding Process Stability Using Machine Vision-Based Arc Features Tracking System.

Sensors (Basel) 2020 Dec 25;21(1). Epub 2020 Dec 25.

Department of Welding Engineering, Silesian University of Technology, 44-100 Gliwice, Poland.

Arc length is a crucial parameter of the manual metal arc (MMA) welding process, as it influences the arc voltage and the resulting welded joint. In the MMA method, the process' stability is mainly controlled by the skills of a welder. According to that, giving the feedback about the arc length as well as the welding speed to the welder is a valuable property at the stage of weld training and in the production of welded elements. Read More

View Article and Full-Text PDF
December 2020

Improving the characterization of meningioma microstructure in proton therapy from conventional apparent diffusion coefficient measurements using Monte Carlo simulations of diffusion MRI.

Med Phys 2021 Mar 5;48(3):1250-1261. Epub 2021 Feb 5.

Centre for Medical Image Computing (CMIC), Department of Computer Science, University College London (UCL), London, WC1V6LJ, UK.

Purpose: Proton therapy could benefit from noninvasively gaining tumor microstructure information, at both planning and monitoring stages. The anatomical location of brain tumors, such as meningiomas, often hinders the recovery of such information from histopathology, and conventional noninvasive imaging biomarkers, like the apparent diffusion coefficient (ADC) from diffusion-weighted MRI (DW-MRI), are nonspecific. The aim of this study was to retrieve discriminative microstructural markers from conventional ADC for meningiomas treated with proton therapy. Read More

View Article and Full-Text PDF

First-principles calculation of B solid-state NMR parameters of boron-rich compounds I: the rhombohedral boron modifications and BX (X = P, As, O).

Phys Chem Chem Phys 2021 Jan;23(1):470-486

Institut für Anorganische und Analytische Chemie, Albert-Ludwigs-Universität, Albertstr. 21, 79104 Freiburg, Germany. and Freiburger Materialforschungszentrum FMF, Stefan-Meier-Str. 21, 79104 Freiburg, Germany.

In the present study, solid-state nuclear magnetic resonance (NMR) spectra under magic angle spinning conditions of the rhombohedral structures α-B and B12P2 are reported together with the corresponding parameter sets from first principles calculations on α-B B12X2 (X = P, As, O). With the combination of density functional theory (DFT) and the gauge-including projector-augmented wave (GIPAW) approach as the theoretical tools at hand the computed 11B parameters lead to unambiguous explanation of the measurements. Thereby, we overcome common obstacles of processing recorded NMR spectra of solid-state compounds with several crystallographic positions, in particular non-trivial signal assignments and parameter determination due to peak overlap or even unexpected intensity/area ratios. Read More

View Article and Full-Text PDF
January 2021

Impact of needle positioning on ablation success of irreversible electroporation: a unicentric retrospective analysis.

Sci Rep 2020 12 14;10(1):21902. Epub 2020 Dec 14.

Clinic for Diagnostic and Interventional Radiology, Heidelberg University Hospital, Im Neuenheimer Feld 420, 69120, Heidelberg, Germany.

Irreversible electroporation (IRE) is an ablation procedure in which cell death is induced by ultrashort electrical pulses. In this unicentric retrospective study we investigated the influence of needle positioning on ablation success. 15 IREs with residual tumor after ablation, detected in the first follow-up MRI, were included, and compared with 30 successful ablations. Read More

View Article and Full-Text PDF
December 2020

Protein secondary structure motifs: A kinematic construction.

J Comput Chem 2021 Feb 11;42(5):271-292. Epub 2020 Dec 11.

Department of Applied Mathematics and Statistics, Stony Brook University, Stony Brook, New York, USA.

The kinematic geometry of protein backbone structures, constrained by either single or multiple hydrogen bonds (H-bonds), possibly in a periodic array, is discussed. These structures include regular secondary structure elements α-helices and β-sheets but also include other short H-bond stabilized irregular structural elements like β-turns. The work here shows that the variations observed in such structures have simple geometrical correlations consistent with constrained motion kinematics. Read More

View Article and Full-Text PDF
February 2021

Personalized 0D models of normal and stenosed carotid arteries.

Comput Methods Programs Biomed 2021 Mar 1;200:105888. Epub 2020 Dec 1.

COMSATS University Islamabad, Abbottabad Campus, Pakistan. Electronic address:

Background And Objective: Recent advances in medical imaging like MRI, CT-Scan, Doppler ultrasound, etc. have made it possible to study the hemodynamics of cardiovascular system having different levels of vessel abnormalities.

Methods: Within this work, we have developed two different personalized lumped-parameter models of the human carotid arteries having elastic and viscoelastic vessel wall behaviors. Read More

View Article and Full-Text PDF

Inter- and intra-scanner variations in four magnetic resonance imaging image quality parameters.

J Med Imaging (Bellingham) 2020 Nov 4;7(6):065501. Epub 2020 Dec 4.

University of Helsinki and Helsinki University Hospital, HUS Medical Imaging Center, Radiology, Helsinki, Finland.

In addition to less frequent and more comprehensive tests, quality assurance (QA) protocol for a magnetic resonance imaging (MRI) scanner may include cursory daily or weekly phantom checks to verify equipment constancy. With an automatic image analysis workflow, the daily QA images can be further used to study scanner baseline performance and both long- and short-term variations in image quality. With known baselines and variation profiles, automatic error detection can be employed. Read More

View Article and Full-Text PDF
November 2020

Laminar-Turbulent Intermittency in Annular Couette-Poiseuille Flow: Whether a Puff Splits or Not.

Entropy (Basel) 2020 Nov 30;22(12). Epub 2020 Nov 30.

Department of Mechanical Engineering, Tokyo University of Science, Chiba 278-8510, Japan.

Direct numerical simulations were carried out with an emphasis on the intermittency and localized turbulence structure occurring within the subcritical transitional regime of a concentric annular Couette-Poiseuille flow. In the annular system, the ratio of the inner to outer cylinder radius is an important geometrical parameter affecting the large-scale nature of the intermittency. We chose a low radius ratio of 0. Read More

View Article and Full-Text PDF
November 2020

An evaluation of Hamiltonian Monte Carlo performance to calibrate age-structured compartmental SEIR models to incidence data.

Epidemics 2020 12 11;33:100415. Epub 2020 Nov 11.

Data Science Institute and School of Computer Science, National University of Ireland Galway, Ireland. Electronic address:

Hamiltonian Monte Carlo (HMC) is a Markov chain Monte Carlo method to estimate unknown quantities through sample generation from a target distribution for which an analytical solution is difficult. The strength of this method lies in its geometrical foundations, which render it efficient for traversing high-dimensional spaces. First, this paper analyses the performance of HMC in calibrating five variants of inputs to an age-structured SEIR model. Read More

View Article and Full-Text PDF
December 2020