Spelling suggestions: "subject:"eonformal"" "subject:"amongnormal""
921 |
Active Health Monitoring of Aerospace Composite Structures by Embedded Piezoceramic TransducersPaget, Christophe January 2001 (has links)
The objectives of the thesis work were to study theinteraction between embedded piezoceramic transducers andcomposite structures as well as determine techniques tosimplify the Lamb waves analysis. Firstly, this studyconsidered the design of the embedded piezoceramic transducers.Secondly, the effect of the embedded transducer on thecomposite strength as well as the influence of the mechanicallyloaded composite on the characteristics of the embeddedtransducer were investigated. Finally, to simplify the analysisof such complex Lamb wave responses, two techniques weredeveloped. They were based on the wavelet technique and amodelling technique, respectively. The design of the embedded piezoceramic transducers wasimproved by reducing the stress concentrations in the compositeas well as in all components constituting the piezoceramictransducer, that is, the piezoceramic element, interconnectorand conductive adhesive. The numerical analysis showed that thethickness of the interconnector had no significant influence onthe stress state of the piezoceramic transducer. It was alsofound that a compliant conductive adhesive reduced the stressconcentration located at the edge of the piezoceramic element.The structural integrity of composites embedded with theimproved piezoceramic transducer was investigated. Theexperiments, performed in tensile and compressive staticloading, indicated that the strength of the composite was notsignificantly reduced by the embedded piezoceramic transducer.Further investigations were conducted to evaluate theperformance of the improved piezoceramic transducer used as aLamb wave generator embedded in composites subjected tomechanical loading. The tests were conducted in tensile andcompressive static loading as well as fatigue loading. Thestudy showed a large working range of the embedded piezoceramictransducer. A post processing technique based on the waveletswas further assessed in the detection of damage and in thedamage size evaluation. A new wavelet basis was developedspecially for processing the Lamb wave response. This method,focused on the wavelet coefficients from the decomposition Lambwave response, showed promising results in evaluating thedamage size. The wavelets offered a sensitive tool to detectsmall damage, compared to other detection methods, improvingthe damage detection capabilities. The other technique wasdevoted to the simplification of the generated Lamb waves bythe use of multi-element transducers. The transducers weredesigned using both a normal-mode expansion and a FE-method.This technique allowed reducing the effect of a Lamb wave modetowards another. This technique was successfully implemented ina damage detection system in composites. <b>Keywords:</b>Embedded piezoceramic, transducer, composite,structural integrity, health monitoring, damage detection, Lambwaves, wavelets, normal-mode expansion, FE-method
|
922 |
Structural and Spectroscopic Studies of Solvated Metal IonsAbbasi, Alireza January 2005 (has links)
Crystallographic and spectroscopic studies have been performed of structures, coordination and chemical bonding for series of trivalent metal ions solvated by two oxygen-coordinating solvents, water and dimethyl sulfoxide (DMSO). The hydrated scandium(III) and lanthanoid(III) ions, La to Lu, are surrounded by tricapped trigonal prisms of aqua ligands in the isomorphous series of trifluoromethanesulfonates, [M(H2O)n](CF3SO3)3. For the smallest ions, M = Er, Tm, Yb, Lu, Sc, the hydration numbers decrease, n = 8.96(5), 8.8(1), 8.7(1), 8.5(1), 8.0(1), respectively, with decreasing size of the ion. The crystal structures at ambient temperature indicate randomly distributed vacancies of the capping oxygen atoms, and 2H solid-state NMR of the diamagnetic [M(H2O)n](CF3SO3)3, M = Sc, Lu, Y and La compounds revealed increasing mobility of the water ligands in the coordination sphere with increasing temperature, also for the fully nonahydrated LaIII and YIII ions. The stretching force constants of the Ln-O bonds, evaluated from vibrational spectroscopy, increased from 0.81 to 1.16 N cm-1 for the Ln-6O trigonal prism in a smooth correlation with the bond distances from La to Lu. For the capping Ln-3O bonds the increase from 0.49 to 0.65 N cm-1 reflects the increased ligand-ligand repulsion with decreasing ion size. This is also the reason for the water deficiency of the Er, Tm, Yb, Lu and Sc salts, and for [Sc(H2O)8.0](CF3SO3)3 the repulsion induced a phase transition at about 185 K that, by low temperature crystallography, was found to distort the coordination of water molecules toward a monocapped trigonal prism around the scandium(III) ion. All crystal structures of the octakis(dimethyl sulfoxide)lanthanoid(III) iodides comprise discrete [Ln(dmso)8]3+ complexes surrounded by iodide ions. The lanthanum(III) and praseodymium(III) compounds crystallize in the orthorhombic space group Pbca with more efficient packing than for the heavier and smaller ions in the lanthanoid series, which crystallize in the monoclinic space group P21/n. The group 13 metal ions, aluminium(III), gallium(III), indium(III), thallium(III), and also scandium(III) of group 3, form crystalline hexakis(dimethyl sulfoxide) solvates in the space group R 3, with octahedral MO6 coordination entities, which are increasingly compressed along one threefold axis for increasing ionic size. EXAFS measurements on the solvated ions display similar M-O bond distances in dimethyl sulfoxide solution as in the solid solvates. For all the solid dimethyl sulfoxide solvates the strength and nature of the metal-oxygen bond has been evaluated by normal coordinate analysis of vibrational spectra, and correlated with the S-O stretching vibrational mode. Distortions from regular octahedral six coordination are discussed for the hydrated isoelectronic soft mercury(II) and thallium(III) ions in the solid bisaquamercury(II) and trisaquatallium(III) trifluoromethanesulfonates, in terms of pseudo Jahn-Teller effects (PJTE). Mercury(II), generally more strongly influenced by PJTE distortions, displays a 2 + 4 Hg-O coordination forming chains that are held together in sheets by hydrogen bonds and in layers by van der Waals interactions, which explain the fragile structure of the crystals.
|
923 |
Self-concept, inner residue of past relationships and current social functioning. : A study of age and gender differences in normal and antisocial adolescents.Östgård-Ybrandt, Helene January 2004 (has links)
This thesis presents several studies of normative development in adolescence, focusing specifically on internalized perceptions of parents’ early behavior and how these perceptions affect the self-concept and social functioning during. Questions of possible age and gender differences in relation to perceptions of self-concept and early parental behavior are addressed. The patterns found in a normal adolescent group are compared with those in a group of adolescents with antisocial problems. Two hundred seventy-seven normal adolescents aged 12 to18 and 30 adolescents with antisocial problems aged 13-19 were investigated. The following self-administered instruments were used: self-concept assessments, the Structural Analysis of Social Behavior (SASB) introject questionnaire, perception of early parental behavior assessment, the SASB mother/father questionnaires, and the EMBU (A Swedish acronym for “own memories of upbringing”). The Youth Self Report checklist (YSR) was used to assess internalizing and externalizing problems. Studies I and II showed that the normal adolescent self-concept and perception of early parental behavior were positive and that there were no age or gender differences. The antisocial group of adolescents, and particularly the antisocial girls, showed a more autonomous and negative self-concept and more negative perceptions of early parental behaviors. Study III showed that a positive self-concept was related to a positive perception of parent’s early behavior. Study IV showed that an adolescent’s positive self-concept was influenced by a mix of mother acting positively and father acting with control. Adolescent self-control was indirectly influenced by parental control behavior mediated through self-affiliation. Study V showed that a positive self-concept was important for adjustment. A negative self-concept combined with female gender was a risk factor for internalizing problems. Self-control had only a small effect on social adjustment in adolescence. The relationship between a negative self-concept and externalizing problem behavior was stronger for adolescents aged 15 to 16 than for younger or older adolescents. Internalizing problem behavior influenced externalizing problems. The results presented in this thesis support a modified “storm-and-stress” view of adolescence and highlight the importance of promoting a positive self-concept in every adolescent in various psychosocial contexts.
|
924 |
ARCON in experimental and clinical radiotherapyRojas Callejas, Ana Maria January 2004 (has links)
xHypoxia and repopulation of tumour clonogens are two important determinants of treatment outcome in radiotherapy. In general clinical evidence indicates that loco-regional control may be reduced with long overall treatment times and for tumours with low pre-treatment levels of oxygen. Experimental studies with normobaric carbogen and oxygen showed a two-fold enhancement of the efficacy of radiation in a mouse tumour model when combining oxygen with treatment acceleration. It was then demonstrated that substituting carbogen for oxygen and adding high-dose nicotinamide (NAM) further increased the effect. These findings became the basis for a multi-factorial approach designed to overcome the radioprotective effect of tumour repopulation and that of perfusion–limited and diffusion–limited hypoxia. The strategy, named ARCON, combines Accelerated Radiotherapy with CarbOgen and Nicotinamide. Experimental evaluation of ARCON The therapeutic potential of carbogen combined with NAM (CON) focusing on treatment schedules that use clinically relevant radiation and drug dose levels was evaluated in tumour and normal tissue animal models. Some of the conditions under which ARCON gives the largest degree of tumour radiosensitization and therapeutic benefit were identified. Specifically, NAM-dose level, pharmacokinetics and scheduling, and the effect of NAM on repair processes in vivo were also investigated. The results showed that in conventional and accelerated radiotherapy, carbogen and CON are effective and relatively non-toxic tumour sensitizers. They also demonstrated that tumour sensitization with CON was independent of time of NAM administration but that it was drug dose dependent. Some degree of normal tissue sensitization was observed but even relative to mouse skin a significant therapeutic gain was achieved. The mechanism of action for NAM sensitization originally proposed was that of repair inhibition. In the in vivo mouse models tested, namely skin and kidney, NAM did not alter the rate nor the magnitude of repair of radiation induced damage. Clinical evaluation of ARCON In the early 90s, various centres, particularly in the UK, Sweden, Holland and Switzerland, undertook clinical trials of ARCON. The protocols were designed based on detailed considerations of the rodent and human radiation and pharmacokinetic studies. This document also discusses the findings of a phase II non-randomized trial in advanced bladder cancer of accelerated radiotherapy combined with carbogen alone and ARCON. The aim of the study was to establish the feasibility of administering carbogen and NAM to patients and to determine the extent of early and late normal tissue damage. Historical comparisons suggested no overt increase in normal tissue radiosensitivity and the data indicate that ARCON could achieve a therapeutic gain in advanced bladder cancer.
|
925 |
A Domain-Specific Conceptual Query SystemShen, Xiuyun 02 August 2007 (has links)
This thesis presents the architecture and implementation of a query system resulted from a domain-specific conceptual data modeling and querying methodology. The query system is built for a high level conceptual query language that supports dynamically user-defined domain-specific functions and application-specific functions. It is DBMS-independent and can be translated to SQL and OQL through a normal form. Currently, it has been implemented in neuroscience domain and can be applied to any other domain.
|
926 |
Carotid Artery Wall Layer Dimensions during and after Pre-eclampsia : An investigation using non-invasive high-frequency ultrasoundAkhter, Tansim January 2013 (has links)
Pre-eclampsia is associated with increased risk of cardiovascular disease (CVD) later in life. The ‘gold standard’ for estimating cardiovascular risk - ultrasound assessment of the common carotid artery intima-media thickness (CCA-IMT) - does not convincingly demonstrate this increased risk. The aim of this thesis was to examine whether high-frequency (22 MHz) ultrasound assessment of the individual CCA intima and media layers and calculation of the intima/media (I/M) ratio - can indicate the increased cardiovascular risk after pre-eclampsia. After validation of the method in premenopausal women with systemic lupus erythematosus (SLE) who have a recognized increased risk of CVD, women during and after normal and preeclamptic pregnancies were investigated. Assessment of the individual artery wall layers reliably demonstrated the increased cardiovascular risk in premenopausal women with SLE, while CCA-IMT did not. The artery wall layer dimensions in women with SLE were comparable to those of postmenopausal women without SLE and were 30 years older. Among the women with normal pregnancies negative changes to the artery wall later on in the pregnancy were seen in those with lower serum estradiol, older age, higher body mass index or higher blood pressure early in the pregnancy. About one year postpartum, both the mean intima thickness and the I/M ratio had improved, compared to values during pregnancy. These findings support the theory that normal pregnancy is a stress on the vascular system. Women who developed pre-eclampsia (mean age 31 years) had thicker intima layers, thinner media layers and higher I/M ratios, both at diagnosis and one year postpartum, than women with normal pregnancies, indicating increased cardiovascular risk. Women with a history of severe pre-eclampsia (mean age 44 years; mean 11 years since the last delivery) had thicker intima layers and higher I/M ratios than women with a history of normal pregnancies, indicating long-standing negative vascular effects. Assessment of individual CCA wall layers, but not of CCA-IMT, provided clear evidence of the well-known increased cardiovascular risk in women with SLE or pre-eclampsia. The method has the potential to become an important tool in reducing cardiovascular morbidity and mortality in these women through early diagnosis and intervention.
|
927 |
Selection and ranking procedures based on likelihood ratiosChotai, Jayanti January 1979 (has links)
This thesis deals with random-size subset selection and ranking procedures• • • )|(derived through likelihood ratios, mainly in terms of the P -approach.Let IT , . .. , IT, be k(> 2) populations such that IR.(i = l, . . . , k) hasJ_ K. — 12the normal distribution with unknwon mean 0. and variance a.a , where a.i i i2 . . is known and a may be unknown; and that a random sample of size n^ istaken from . To begin with, we give procedure (with tables) whichselects IT. if sup L(0;x) >c SUD L(0;X), where SÎ is the parameter space1for 0 = (0-^, 0^) ; where (with c: ß) is the set of all 0 with0. = max 0.; where L(*;x) is the likelihood function based on the total1sample; and where c is the largest constant that makes the rule satisfy theP*-condition. Then, we consider other likelihood ratios, with intuitivelyreasonable subspaces of ß, and derive several new rules. Comparisons amongsome of these rules and rule R of Gupta (1956, 1965) are made using differentcriteria; numerical for k=3, and a Monte-Carlo study for k=10.For the case when the populations have the uniform (0,0^) distributions,and we have unequal sample sizes, we consider selection for the populationwith min 0.. Comparisons with Barr and Rizvi (1966) are made. Generalizai<j<k Jtions are given.Rule R^ is generalized to densities satisfying some reasonable assumptions(mainly unimodality of the likelihood, and monotonicity of the likelihoodratio). An exponential class is considered, and the results are exemplifiedby the gamma density and the Laplace density. Extensions and generalizationsto cover the selection of the t best populations (using various requirements)are given. Finally, a discussion oil the complete ranking problem,and on the relation between subset selection based on likelihood ratios andstatistical inference under order restrictions, is given. / digitalisering@umu
|
928 |
Simplification Techniques for Interactive ApplicationsGonzález Ballester, Carlos 09 July 2010 (has links)
Interactive applications with 3D graphics are used everyday in a lot of different fields, such as games, teaching, learning environments and virtual reality. The scenarios showed in interactive applications usually tend to present detailed worlds and characters, being the most realistic as possible. Detailed 3D models require a lot of geometric complexity. But not always the available graphics hardware can handle and manage all this geometry maintaining a realistic frame rate. Simplification methods attempt to solve this problem, by generating simplified versions of the original 3D models. These simplified models present less geometry than the original ones. This simplification has to be done with a reasonable criterion in order to maintain as possible the appearance of the original models. But the geometry is not the only important factor in 3D models. They are also composed of additional attributes that are important for the final aspect of the models for the viewer. In the literature we can find a lot of work presented about simplification. However, there are still several points without an efficient solution. Therefore, this thesis focuses on simplification techniques for 3D models usually used in interactive applications.
|
929 |
Concurrent Error Detection in Finite Field Arithmetic OperationsBayat Sarmadi, Siavash January 2007 (has links)
With significant advances in wired and wireless technologies and also increased shrinking in the size of VLSI circuits, many devices have become very large because they need to contain several large units. This large number of gates and in turn large number of transistors causes the devices to be more prone to faults. These faults specially in sensitive and critical applications may cause serious failures and hence should be avoided.
On the other hand, some critical applications such as cryptosystems may also be prone to deliberately injected faults by malicious attackers. Some of these faults can produce erroneous results that can reveal some important secret information of the cryptosystems. Furthermore, yield factor improvement is always an important issue in VLSI design and fabrication processes. Digital systems such as cryptosystems and digital signal processors usually contain finite field operations. Therefore, error detection and correction of such operations have become an important issue recently.
In most of the work reported so far, error detection and correction are applied using redundancies in space (hardware), time, and/or information (coding theory). In this work, schemes based on these redundancies are presented to detect errors in important finite field arithmetic operations resulting from hardware faults. Finite fields are used in a number of practical cryptosystems and channel encoders/decoders. The schemes presented here can detect errors in arithmetic operations of finite fields represented in different bases, including polynomial, dual and/or normal basis, and implemented in various architectures, including bit-serial, bit-parallel and/or systolic arrays.
|
930 |
Concurrent Error Detection in Finite Field Arithmetic OperationsBayat Sarmadi, Siavash January 2007 (has links)
With significant advances in wired and wireless technologies and also increased shrinking in the size of VLSI circuits, many devices have become very large because they need to contain several large units. This large number of gates and in turn large number of transistors causes the devices to be more prone to faults. These faults specially in sensitive and critical applications may cause serious failures and hence should be avoided.
On the other hand, some critical applications such as cryptosystems may also be prone to deliberately injected faults by malicious attackers. Some of these faults can produce erroneous results that can reveal some important secret information of the cryptosystems. Furthermore, yield factor improvement is always an important issue in VLSI design and fabrication processes. Digital systems such as cryptosystems and digital signal processors usually contain finite field operations. Therefore, error detection and correction of such operations have become an important issue recently.
In most of the work reported so far, error detection and correction are applied using redundancies in space (hardware), time, and/or information (coding theory). In this work, schemes based on these redundancies are presented to detect errors in important finite field arithmetic operations resulting from hardware faults. Finite fields are used in a number of practical cryptosystems and channel encoders/decoders. The schemes presented here can detect errors in arithmetic operations of finite fields represented in different bases, including polynomial, dual and/or normal basis, and implemented in various architectures, including bit-serial, bit-parallel and/or systolic arrays.
|
Page generated in 0.0387 seconds