4,854 research outputs found
Unsteady characteristics of cloud cavitating flow near the free surface
No full textThe effect of free surface on unsteady cloud cavitation is important for high-speed surface vehicles, However, previously published experimental and numerical works regarding this topic are limited. In this paper, a typical launching experiment is performed with the presence of free surface. A numerical approach is established by using large eddy simulation and volume-of-fluid methods. Firstly, unsteady evolutions of the cavity and re-entry jet are obtained in both experimental and numerical results, which agree well with each other. Results indicate that the cavity evolution on the upper side of projectile is remarkably different compared to the lower side under the free-surface effect. For instance, on the upper side, cavity growth is slower, the velocity of the re-entry jet is higher, the cavity sheds faster, and the position of shedding cavity collapse is closer to the main cavity. Secondly, the effect of the free surface is studied by analyzing the constraint variation. Because the flow stream around the upper surface is thin, changing its direction under the effect of pressure difference inside and outside the cavity is easy. Non-axisymmetric collapse features generate a mass of strong vortexes on the cylindrical surface, and the non-uniform distribution of high pressure region is also one of the most important factors to induce lateral and vertical forces on the projectile. Finally, the heights of wave elevation in cases with and without cavitation are compared. The presence of cavitation leads to an increase in wave height, but the increment is about half the thickness of the cavity. This finding indicates that the actual constraint effect is between the effects of the infinite water field and the fully free condition.</span
Prolog+CG: A Maintainer's Perspective
No full text Prolog+CG is an implementation of Prolog with Conceptual Graphs as first-class datastructures, on a par with terms. As such, it lends itself well to applications in which reasoning with Conceptual Graphs and/or ontologies plays a role. It as originally developed by Prof. Dr. Adil Kabbaj, who in 2004 turned over maintainership of Prolog+ CG to the present author. In this paper, Prolog+CG is described in terms of its history, evolution, and maintenance. A special web-enabled version of Prolog+CG is also described. Possible interoperability with CGIF and the CharGer tool are explored. Finally, we offer some general observations about the tenets that make Prolog+CG a success.</p
Voluntary corporate governance disclosure by post-apartheid South African corporations
No full textPurpose – The purpose of this paper is to investigate as to whether post-Apartheid South African (SA) listed corporations voluntarily comply with and disclose recommended good corporate governance (CG) practices and, if so, the major factors that influence such voluntary CG disclosure behaviour. Design/methodology/approach – The paper constructs a broad voluntary CG disclosure index containing 50 CG provisions from the 2002 King Report using a sample of 169 SA listed corporations from 2002 to 2006. The authors also conduct regression analysis to identify the main drivers of voluntary CG disclosure. Findings – The results suggest that while compliance with, and disclosure of, good CG practices varies substantially among the sampled companies, CG standards have generally improved over the five-year period examined. The authors also find that block ownership is negatively associated with voluntary CG disclosure, while board size, audit firm size, cross-listing, the presence of a CG committee, government ownership and institutional ownership are positively related to voluntary CG disclosure. Practical implications – These findings have important implications for policy-makers and regulators. Evidence of improving CG standards implies that efforts by various stakeholders at improving CG standards in SA companies have had some positive impact on CG practices of SA firms. However, the substantial variation in the levels of compliance implies that enforcement may need to be strengthened further. Originality/value – There is a dearth of evidence on the level of compliance with the King Report. This study fills this gap by providing evidence for the first time on the level of compliance achieved, as well as contributing generally to the literature on compliance with codes of good governance and voluntary disclosure.<br/
Effect of wing flexibility on aircraft flight dynamics
Get PDFThe purpose of this thesis is to give a preliminary investigation into the effect of wing deformation on flight dynamics. The candidate vehicle is FW-11 which is a flying wing configuration aircraft with high altitude and long endurance characteristics. The aeroelastic effect may be significant for this type of configuration. Two cases, the effect of flexible wing on lift distribution and on roll effectiveness during the cruise condition with different inertial parameters are investigated.
For the first case, as the wing bending and twisting depend on the interaction between the wing structural deflections and the aerodynamic loads, the equilibrium condition should be calculated. In order to get that condition, mass, structure characteristics and aerodynamic characteristics are estimated first. Then load model and aerodynamic model are built. Next the interaction calculation program is applied and the equilibrium condition of the aircraft is calculated. After that, effect of wing flexibility on lift parameters is investigated. The influence of CG, location of lift and location of flexural axis are investigated.
The other case is to calculate the transient roll rate response and estimate the rolling effectiveness of flexible aircraft, and compared with the rigid aircraft’s. A pure roll model is built and derivatives both for the rigid wing and the flexible wing are estimated. It has been found that flexible wing leads to the loss of control effectiveness, even cause reversal when reduces the structure natural frequency. The influence of inertia data for flexible roll is also investigated
Cg-TIMP, an inducible tissue inhibitor of metalloproteinase from the Pacific oyster Crassostrea gigas with a potential role in wound healing and defense mechanisms(1)
No full textWe have cloned and characterized a cDNA encoding Cg-TIMP, the first tissue inhibitor of metalloproteinase identified in mollusks. The isolated cDNA encodes a protein of 221 residues that has a domain organization similar to that of vertebrate TIMPs including a signal sequence, and the 12 cysteines characteristic of the TIMP signature. Analysis of Cg-TIMP expression in adult oyster tissues, by Northern blot and in situ hybridization, indicates that Cg-TIMP was only expressed in hemocytes which are the key components of defense mechanisms in mollusks. We also observed that Cg-TIMP mRNA accumulated during shell damage and bacterial challenge. This pattern of expression suggests that Cg-TIMP may be an important factor in wound healing and defense mechanisms.LR: 20061115; PUBM: Print; GENBANK/AF321279; JID: 0155157; 0 (DNA, Complementary); 0 (RNA, Messenger); 0 (TIMP protein, Crassostrea gigas); 0 (Tissue Inhibitor of Metalloproteinases); ppublishSource type: Electronic(1
Subwavelength spinning of particles in vector cosine-Gaussian field with radial polarization
No full textA new type of radially polarized (RP) cosine-Gaussian (CG) field is proposed. Through the analytical model, it is found that such RP CG beam exhibits completely different focusing properties from the reported RP plane waves. More importantly, a stable three-dimensional trap of Rayleigh particle accompanied by a subwavelength spin motion can be easily achieved using this RP CG beam.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.ImPhys/Optic
CHLAMYDIAL PNEUMONIA IN CHILDREN REQUIRING HOSPITALIZATION: EFFECT OF MIXED INFECTION ON CLINICAL OUTCOME
No full textCross-stream attention enhanced central difference convolutional network for CG image detection
No full textWith the maturation of computer graphics (CG) technology in the field of image generation, the realism of created images has been improved significantly. Although these technologies are widely used in daily life and bring many conveniences, they also come with many security risks. If forged images generated using CG technology are maliciously used and widely spread on the Internet and social media, they may harm the rights of individuals and enterprises. Therefore, an innovative cross-stream attention enhanced central difference convolutional network was proposed, aiming at improving the accuracy of CG image detection. A dual-stream structure was constructed in the model, in order to extract semantic features and non-semantic residual texture features from the image. Vanilla convolutional layers in each stream were replaced by central difference convolutions, which allowed the model to simultaneously extract pixel intensity information and pixel gradient information from the image. Furthermore, by introducing a cross-stream attention enhancement module, the model enhanced feature extraction capability at the global level and promoted complementarity between the two feature streams. Experimental results demonstrate that this method outperforms existing methods. Additionally, a series of ablation experiments further verify the rationality of the proposed model design
Het effect van een anisotropiecoëfficiënt in de Poissonvergelijking op de convergentie van de CG-methode en de ICCG(0)-methode
No full textAllerlei diffusieverschijnselen in de natuurkunde kunnen omschreven wordenmet de Poissonvergelijking op een gebied met te kiezen randvoorwaarden. Er zijn echter ook verschijnselen waarin er een gelaagdheid optreedt zodat er in verticalerichting minder makkelijk diffusie kan plaatsvinden. Dit leidt tot een vergelijkingmet toevoeging van een anisotropiecoëfficiënt epsilon, die dicht bij 0 ligt.Via (onder andere) de Finite Volume Method kunnen deze vergelijkingengediscretiseerd worden, wat leidt tot een stelsel Au = f. Hierbij is A symmetrischen positief deniet (alle eigenwaarden zijn positief). Er zijn tallozemethoden om dit stelsel op te lossen. Een hiervan is de CG-methode, eeniteratieve methode, met als uitbreiding de ICCG(0)-methode. De convergentievan de CG-methode blijkt af te hangen van de eigenwaarden van dematrix A. Hoe dichter de eigenwaarden bij elkaar liggen, hoe sneller deconvergentie. De geschaalde eigenwaarden1 van A liggen min of meer geconcentreerdrond 1. Het is voor een snelle convergentie van belang dat dekleinste eigenwaarden niet al te dicht bij 0 liggen. Dit leidt namelijk tottrage convergentie. Er zijn manieren om de eigenwaarden dichter bij elkaarte brengen. We noemen dat preconditionering. De ICCG(0)-methode is eenvorm van preconditionering en zorgt er (onder andere) voor dat de kleinsteeigenwaarden dichter bij 1 komen te liggen. In dit onderzoek wordt onderzochtwat er gebeurt met de eigenwaarden, zowel in de CG-methode als inde ICCG(0)-methode, als de anisotropiecoëfficiënt heel klein wordt. Hetblijkt dat de ondergrens voor de eigenwaarden van A lineair afhankelijk isvan epsilon. Dit leidt tot een zeer trage convergentie van de CG-methode in hetgeval epsilon klein is. Er blijkt echter ook dat preconditionering met behulp vande ICCG(0)-methode voldoende is om de ondergrens voor de eigenwaardenonafhankelijk te maken van epsilon. Dit betekent dat ook in situaties waarinanisotropie optreedt, ICCG(0) een geschikte methode is om de vergelijkingAu = f op te lossen
- …
