Search results for "dynamics"
showing 10 items of 9782 documents
Numerical modeling of blood flow in the internal jugular vein with the use of computational fluid mechanics software.
2021
ObjectivesTo determine the site and nature of altered hemodynamics in pathological internal jugular veins.MethodWith the use of computational fluid mechanics software we simulated blood flow in 3 D models of the internal jugular veins that exhibited different morphologies, including nozzle-like strictures in their upper parts and valves in the lower parts.ResultsIn a majority of models with nozzle-like strictures, especially those positioned asymmetrically, abnormal flow pattern was revealed, with significant flow separation and regions with reversed flow. Abnormal valves had no significant impact on flow in a case of already altered flow evoked by stricture in upper part of the vein.Conclu…
Network Dynamics of an Energy Supply Chain: Applicability of the Network Approach to Analysing the Industrial Ecology Practices of Companies
2006
Currently firms face environmental challenges, which require more emphasis on inter-organisational environmental improvement efforts. A field of study of industrial ecology offers some novel approaches for inter-organisational environmental management. It emphasises symbiotic linkages between firms or other organisations in which waste of one actor is used as raw material by others. The industrial network approach has been suggested as a possible framework for developing managerial implications for industrial ecology. This study analyses an example of an industrial ecosystem with notions of the network theory, and concludes that the industrial network approach is useful in analysing and des…
Dynamic Modeling of the Cyber Security Threat Problem
2009
This chapter discusses the possible growth of black markets (BMs) for software vulnerabilities and factors affecting their spread. It is difficult to collect statistics about BMs for vulnerabilities and their associated transactions, as they are hidden from general view. We conduct a disguised observation of online BM trading sites to identify causal models of the ongoing viability of BMs. Our observation results are expressed as a system dynamic model. We implement simulations to observe the effects of possible actions to disrupt BMs. The results suggest that without interventions the number and size of BMs is likely to increase. A simulation scenario with a policy to halt BM operations re…
Spatial dispersion intensity measure of phase concentration distributions and its applications to quantitative characterization, distinguishing and c…
2008
A method of evaluation of spatial dispersion of structures is presented. A quantitative parameter measuring spatial dispersion is introduced. It is shown that this parameter indeed measures spatial dispersion. A classification of bubble flow structures based on values of this parameter is proposed. An example of application of the method to real flow structures is presented.
157 Patient satisfaction and safety of sedation using perineurial dexmedetomidine in axillary brachial plexus block for wrist surgery
2021
Background and Aims Dexmedetomidine is known to prolong the duration of regional block while its sedative effect when administered perineurally is unknown.[1] We aim to evaluate the effect of perineural Dexmedetomidine on the systemic sedation in patients after axillary brachial plexus block (ABPB). Methods This prospective randomized control trial includes 78 patients undergoing wrist surgery receiving ABPB. The study was conducted with the approval of Ethics Committee of Riga Stradins University. Patients were randomized into two groups – control (CG) (N=39) and study group (SG) (N=39). Both groups received ABPB with a standard dose of local anaesthetics. The study group also received 100…
Signal processing procedures for the evaluation of the cardiovascular effects in the obstructive sleep apnea syndrome
2002
A new index, the cross-power index (CPI), is proposed to quantify the severity of obstructive sleep apnea syndrome (OSAS) in terms of its cardiovascular effects. On the basis of the influences that recurring drops in oxygen saturation have on systolic blood pressure variability of OSAS patients, CPI is defined as the integral of the cross-spectrum modulus between systolic blood pressure and oxygen saturation. In a test group of 22 subjects, CPI correctly identified all 15 OSAS patients included in the pool. Moreover, evaluation of CPI in six OSAS patients sleeping with and without a CPAP (continuous positive airway pressure) device demonstrated that CPAP treatment substantially reduced the …
Large-eddy simulations of turbulent flow with heat transfer in simple and complex geometries using Harwell-FLOW3D
1996
Abstract Large-eddy simulation (LES) results are presented and discussed for the turbulent flow with heat transfer in different geometrical configurations, including a plane channel, a channel bearing transverse square ribs on one of the walls, and a crossed-corrugated air heater. They were obtained using the computational fluid dynamics (CFD) code Harwell-FLOW3D (Release 2), finite-volume grids having up to 423 nodes, and the Smagorinsky subgrid model with several variants regarding near-wall damping and wall boundary conditions. The first problem (plane turbulent Poiseuille flow with heat transfer) was mainly used as a benchmark to investigate the influence of numerical methods (pressure-…
Ventilation/perfusion ratios measured by multiple inert gas elimination during experimental cardiopulmonary resuscitation
2014
Background During cardiopulmonary resuscitation (CPR) the ventilation/perfusion distribution (VA/Q) within the lung is difficult to assess. This experimental study examines the capability of multiple inert gas elimination (MIGET) to determine VA/Q under CPR conditions in a pig model. Methods Twenty-one anaesthetised pigs were randomised to three fractions of inspired oxygen (1.0, 0.7 or 0.21). VA/Q by micropore membrane inlet mass spectrometry-derived MIGET was determined at baseline and during CPR following induction of ventricular fibrillation. Haemodynamics, blood gases, ventilation distribution by electrical impedance tomography and return of spontaneous circulation were assessed. Inter…
A particle based simulation model for glacier dynamics
2013
This publication is contribution number 22 of the Nordic Centre of Excellence SVALI, “Stability and Variations of Arctic Land Ice”, funded by the Nordic Top-level Research Initiative (TRI). The work has been supported by the SVALI project through the University of Lapland, Arctic Centre, and through the University Centre in Svalbard. Funding was also provided by the Conoco-Phillips and Lunding High North Research Program (CRIOS: Calving Rates and Impact on Society). A particle-based computer simulation model was developed for investigating the dynamics of glaciers. In the model, large ice bodies are made of discrete elastic particles which are bound together by massless elastic beams. These…
Il governo del capitale intellettuale attraverso il raccordo tra modelli contabili e di System Dynamics. Una prospettiva di programmazione e controll…
2004
Il presente scritto tenta di far luce sul tema del capitale intellettuale in una prospettiva economico-aziendale, focalizzando in particolare il concetto di governo della conoscenza aziendale. La tesi sostenuta dagli autori è che i processi inerziali di sviluppo e declino della conoscenza non devono essere astrattamente ignorati, relegando l’area Organizzazione e Sistemi al rango di centro di spesa discrezionale. Questa semplicistica prospettiva di analisi può indurre il management all’adozione di politiche miopi, che portino cioè a rinviare investimenti necessari in sviluppo della conoscenza, con l’unico obiettivo di non deprimere i risultati reddituali di breve andare. A tal riguardo, si …