Search results for "dynamics"

Recognition of Chip Forms by Means of Dynamic Force Spectrum Analysis

1993

In this study the ability to identify chip forms occurrs in the turning of austenitic stainless steel using dynamic force spectrum analysis has been tested. For this purpose the frequency spectra obtained from various metal cutting tests were recorded along with the static cutting forces. A dual channel analysis, based on the Fast Fourier Transform (FFT), was adopted to help identify the continuous/discontinuous (favourable/unfavourable) chip forming boundary. The results showed an acceptable correlation between the types of the frequency spectra and the types of chip forms. Finally, an original classification of the spectra obtained during turning of AISI 304 (DIN 1.4301) stainless steel i…

Numerical 3D study of FZ growth: dependence on growth parameters and melt instability

2001

Three-dimensional modelling of the floating zone (needle-eye) crystal growth process is carried out to analyse numerically the stability of the melt flow and the influence of the crystal rotation rate and inductor slit width on the 3D flow field and on the grown crystal resistivity. The unsteadiness of the melt is simulated and it is found that for the considered growth parameters a steady-state flow can be a reasonable approximation to the unsteady melt motion. The parametric studies have shown that increasing the rotation rate essentially changes the flow pattern and weakens the rotational striations, while the inductor slit width has a more local influence on these characteristics.

Measurement of haemodynamics of exercising and non-exercising vastus lateralis muscle with hybrid diffuse optics

2016

We present simultaneous diffuse correlation spectroscopy (DCS) and time resolved spectroscopy (TR NIRS) measurements on exercising and non-exercising vastus lateralis muscle. We discuss the results at two different exercise levels.

Comprehensive Strategy for Proton Chemical Shift Prediction: Linear Prediction with Nonlinear Corrections

2014

A fast 3D/4D structure-sensitive procedure was developed and assessed for the chemical shift prediction of protons bonded to sp3carbons, which poses the maybe greatest challenge in the NMR spectral parameter prediction. The LPNC (Linear Prediction with Nonlinear Corrections) approach combines three well-established multivariate methods viz. the principal component regression (PCR), the random forest (RF) algorithm, and the k nearest neighbors (kNN) method. The role of RF is to find nonlinear corrections for the PCR predicted shifts, while kNN is used to take full advantage of similar chemical environments. Two basic molecular models were also compared and discussed: in the MC model the desc…

A comparative molecular dynamics-phase-field modeling approach to brittle fracture

2016

Abstract In this work, a novel comparative method for highly brittle materials such as aragonite crystals is proposed, which provides an efficient and accurate in-sight understanding for multi-scale fracture modeling. In particular, physically-motivated molecular dynamics (MD) simulations are performed to model quasi-static brittle crack propagation on the nano-scale and followingly compared to macroscopic modeling of fracture using the phase-field modeling (PFM) technique. A link between the two modeling schemes is later proposed by deriving PFM parameters from the MD atomistic simulations. Thus, in this combined approach, MD simulations provide a more realistic meaning and physical estima…

On stiffness and damping of vibro-impact dynamics of backlash

2021

We consider the instantaneous stiffness and damping of the vibro-impact in a backlash pair. Opposed to the existing and mostly used models of the backlash, we address the problem of contact and separation, and the associated force propagation within a mechanical pair, from a viewpoint of the vibro-impact dynamics. We discuss the impact forces with the coefficient of restitution as a principal factor which shapes the transient backlash response.We show that a common approach to modeling the backlash by means of a dead-zone in a restoring force is unsuitable for correctly capturing the mechanical impact. We exemplary demonstrate a qualitative accord between an experimental backlash response a…

Using System Dynamics to Model Student Performance in an Intelligent Tutoring System

2017

One basic adaptation function of an Intelligent Tutoring System (ITS) consists of selecting the most appropriate next task to be offered to the learner. This decision can be based on estimates, such as the expected performance of the student, or the probability that the student successfully solves each particular task. However, the computation of these values is intrinsically difficult, as they may depend on other complex latent variables that also need to be estimated from observable quantities, e.g. the current student's ability. In this work, we have used system dynamics to model learning and predict the student's performance in a given exercise, in an existing ITS that was developed to …

Dynamics of Vertebral Column Observed by Stereovision and Recurrent Neural Network Model

2005

A new non-invasive method for investigation of movement of selected points on the vertebral column is presented. The registration of position of points marked on patient's body is performed by 4 infrared cameras. This experiment enables to reconstruct 3-dimensional trajectories of displacement of marked points. We introduce recurrent neural networks as formal nonlinear dynamical models of each point trajectory. These models are based only on experimental data and are set up of minimal number of parameters. Therefore they are suitable for pattern recognition problems.

DYNAMIC MODELING TOOLS FOR SOLAR POWERED DESALINATION PROCESSES DURING TRANSIENT OPERATIONS

2007

Intubationsbedingungen nach Rocuronium und Succinylcholin

1996

OBJECTIVE Rocuronium is a new non-depolarising steroidal muscle relaxant with a short onset time. The present study was undertaken to compare intubating conditions as well as onset and clinical duration of a single dose of 0.6 mg/kg (2 x ED95) with a single dose of 1 mg/kg suxamethonium (3 x ED95). METHODS After obtaining informed consent and approval of the Ethics Committee, 40 adult patients (ASA I-III) participated in this study. After premedication with oxazepam, anaesthesia was induced with fentanyl and propofol and maintained with propofol, N2O and supplements of fentanyl as needed. Muscular relaxation was assessed by EMG recording of adductor pollicis muscle after supramaximal single…