Tissue-pappersmarknaden växer fort och är konkurrenskraftig, det finns i dagsläget intresse att producera ett papper med hög mjukhet till ett lägre pris. Vid tissue-papper produktionen står fibrerna för en stor andel av den totala kostnaden, därför finns det en efterfrågan att kunna minska materialkostnaderna. Barrveden ger främst styrka till tissue-pappret och lövveden bidrar med mjukhet till pappret. Tissue-papper tillverkas vid låga ytvikter, därför fokuserade studien på de mekaniska egenskaperna vid lägre ytvikter. Tidigare forskning har påvisat att mekaniska egenskaperna minskar kraftig vid lägre ytvikter [5]. Att jämföra löv-och barrvedsmassor för att erhålla information om fiberegenskaper och mekaniska egenskaper är därför intressant, speciellt vid lägre ytvikter. I denna studie har de mekaniska egenskaperna testats på ark som tillverkats i Innventias massaprovningslabb, för att se hur egenskaperna ändras med ändrad ytvikt och hur olika massatyper skiljer sig. Relationer mellan barr-och lövvedsmassorna kommer uppmärksammas och trender åskådliggöras. Studien delades upp i tre tester. Första testet var utvärdering av finmaterialretentionen med slutet bakvatten vid arkning, vilket utfördes för att veta när finmaterialhalten i bakvattnet nått jämvikt. Andra testet var utvärdering av massor och mekaniska egenskaper. Ark tillverkades av 3 barrvedsmassor och 3 lövvedsmassor med olika ursprung och fiberegenskaper. De mekaniska egenskaperna testades i dragprovare, Ball Burst Strength och fibrerna karaktäriserades i fibertester. Tester för att erhålla avvattningsegenskaper och fibersvällningsgrad utfördes även i massaprovningslabbet. Det tredje testet var utvärdering av björkmassa vid olika malningsnivåer. Testet utfördes på en björkmassa som malts vid 3 olika malningsnivåer (50, 100, 150 kWh/ton), för att undersöka malningens inverkan och om malningen kunde optimeras. Testerna på massorna var precis som i det andra testet. Finmaterialretentionen i första testet nådde en jämvikt vid ungefär 4 – 6 tillverkade ark och då visade de mekaniska egenskaperna stabila värden. Finmaterialuppbyggnaden fortsattes därför med 10 labark i resterande försök för att säkerställa att finmaterialjämvikt nås. De mekaniska egenskaperna i test 2 var högst för barrvedsarken och de relativa skillnaderna mellan olika råvaror var tydliga för barrvedsarken, även vid lägre ytvikter. Lövvedarkens relativa skillnader var svåra att tyda vid lägre ytvikter, över 30 g/m2 kunde skillnader ses. Lövvedarkens mekaniska egenskaper nådde ett maximum vid 30 g/m2 därefter nådde alla mekaniska egenskaper en platå, medan ingen platå kunde identifieras hos barrveden. Barrvedsarken når förmodligen ett maximum efter 60 g/m2. De massor som erhöll högst mekaniska egenskaper var de med långa och flexibla fibrer, medan de med korta och styva fibrer fick lägre mekaniska egenskaper. Ball Burst-styrkorna var generellt sett högre hos barrvedsarken, vilket berodde på barrvedens längre fibrer. De malda björkmassorna erhöll högre mekaniska egenskaper än både barr-och lövvedsarken, vilket berodde på den ökade bindningsgraden som uppstått. Malda massornas egenskaper ökade kraftigt vid den första malningsgraden (50 kWh/ton) för att sedan avta. Ju längre malningen fortgår desto sämre blir bulken och mjukheten hos pappret [1]. En högre malning än 100 kWh/ton ansågs därför onödig eftersom avvattningsegenskaperna försämrades och ingen markant skillnad i mekaniska egenskaper erhölls. Ett optimum för malningen verkade finnas mellan 0 – 100 kWh/ton. / The tissue paper market is growing fast and is very competitive. The interest right now is to produce a paper with high softness at a lower cost. During the production of tissue paper the fibers stands for a large portion of the total cost, therefore there is a demand to reduce the material costs. Softwood mainly provides with strength to the tissue paper whilst hardwood contributes with softness to the paper. Tissue paper is manufactured at a low grammage, therefore the study is focusing on the mechanical properties at lower grammages. Previous research has shown that the mechanical properties decrease rapidly at lower basis weight. To compare hardwood and softwood pulps to obtain information on the fiber properties and mechanical properties is therefore interesting, especially at lower basis weights. In this study the mechanical properties has been tested on sheets that was manufactured at Innventias pulp testing lab, to see how the properties change with modified basis weight and when pulp types differs. Relations between hardwood and softwood pulps were recognized and trends were illustrated. The study was divided into three tests. The first test was to evaluate the fines retention in a closed white water system with recirculation, whilst making sheets. The evaluation was performed in order to know when the fines reached equilibrium in the system. The second test was the evaluation of different pulps and mechanical properties. The sheets were made with 3 softwood pulps and 3 hardwood pulps, all the pulps had different origin and fiber properties. The mechanical properties were tested in a tensile tester, Ball Burst Strength and the fiber characterization was performed in a fibertester. There were also tests to obtain the dewatering and fiber swelling properties. The third test was the evaluation of birch pulp at different refining levels. The test was conducted on a birch pulp which had 3 different refining levels (50, 100, 150 kWh/ton), to investigate the effect of the refining and if the refining process could be optimized. The paper testing and characterization was exactly as the second test. The fines retention in the first test reached equilibrium at 4 – 6 sheets and the mechanical properties showed stable values after the equilibrium was reached. The fines retention process was therefore decided to be made with 10 laboratory sheets to ensure that the fines reached equilibrium. The mechanical properties in test 2 were highest for the softwood sheets and the relative changes between various pulps were clear, even at lower basis weight. The hardwoods relative changes were hard to decipher at lower basis weights, differences could be seen at grammages higher than 30 g/m2. The hardwood sheets mechanical properties reached a maximum at 30 g/m2, followed by a plateau, whilst no plateau was identified for the softwood sheets. The softwood sheets probably reach a maximum after 60 g/m2. The pulps that obtained highest mechanical properties were those with long and flexible fibers, whilst those with shorter and stiffer fibers had lower mechanical properties. Ball Burst Strength was generally higher for the softwood sheets, due to the long fibers that the softwood had. The refined birch pulps received higher mechanical properties than the unrefined hardwood and softwood pulps, due to the increased degree of bonding that has occurred in the sheets. The refined pulps properties increased vigorously at the first refining degree (50 kWh/ton) and then decreased. The longer the refining proceeds, the worse the paper bulk and softness become [2]. A higher refining than 100 kWh/ton was considered unnecessary as the dewatering properties became worse and no significant difference was received in mechanical properties. An optimum for the refining process seemed to be in the interval 0 – 100 kWh/ton.

BACKGROUND: Healthcare workers are among the most injured workers in the United States. This is due to the high rate of patient handling. The low back is the most injured in this population. This study observed biomechanical factors and how these factors affect low back and ground reaction forces. This study further investigated pain and its relationship to low back force, multifidus cross-sectional area, and multifidus activation in healthcare workers. METHODS: The 45 participants included 10 healthy subjects in the preliminary study and 35 active healthcare workers in the main study. Subjects filled out the VAS to determine current pain level. Ultrasound images of the multifidus muscles were taken. The participants were fitted with reflective markers and surface EMG sensors. A series of patient transfers at various bed heights using three different transfer devices was undertaken. The transfer devices included a Cotton sheet, a Skil-Care™ Transfer Sling, and an AirPal® device. RESULTS: There was a downward trend in resultant low back force when comparing lower bed heights to higher. Therefore, the highest bed position was determined to be optimal. There were significant differences in low back force between self-chosen and optimal bed heights among healthcare workers. There was no significant difference between peak low back or ground reaction forces between pain and nonpain groups. There was a significant difference in multifidus cross-sectional area between these groups at S1, a trend toward significance at L5, and no difference at L4. There was a trend toward significance when comparing multifidus activation between these groups as recorded by surface EMG. CONCLUSIONS: Healthcare workers should choose higher bed heights and appropriate equipment to reduce low back force and those who have smaller multifidus have more pain.

The Casimiro Ulloa Hospital is a confined masonry structure more than 60 years old that does not satisfy the requirements of the Peruvian seismic code E.030 and it is located at high seismic zone. Therefore, this hospital is susceptible to collapse and becomes an essential deficient structure. Therefore, the present study is based on a comparative analysis between reinforced concrete wall and CFRP sheets through the nonlinear Push Over method in order to obtain which is the best reinforcement in structural capacity. The reinforcement with eight L-shaped concrete walls of 15 cm thick located at the corners of the structure, increased the strength of the hospital by 115% in longitudinal direction (Axis X) and 108% in transversal direction (Axis Y), and also increased the ductility by 3% and 117% in the directions respectively. The other reinforcement was carried out with CFRP sheets and anchors. The sheets were designed with a width of 9 inches and were placed in an X-shape in the masonry load-bearing walls and the anchors were implemented in the corners of the laminate walls in order to ensure adequate load transfer between the sheets and the surface. This reinforcement increased the strength of the structure by 345% in axis X and 150% in axis Y and increased the ductility by 59% in longitudinal direction and 331% in transversal direction.

We work with two different mechanisms to generate geometric frustration on thin elastic sheets; isotropic differential growth and folding. We describe how controlled growth and prescribing folding patterns are useful tools for designing three-dimensional objects from information printed in two dimensions. The first mechanism is inspired by the possibility to control shapes by swelling polymer films, where we propose a solution for the problem of shape formation by asking the question, ``what 2D metric should be prescribed to achieve a given 3D shape?'', namely the reverse problem. We choose two different types of initial configurations of sheets, disk-like with one boundary and annular with two boundaries. We demonstrate our technique by choosing four examples of 3D axisymmetric shapes and finding the respective swelling factors to achieve the desired shape. Second, we present a mechanical model for a single curved fold that explains both the buckled shape of a closed fold and its mechanical stiffness. The buckling arises from the geometrical frustration between the prescribed crease angle and the bending energy of the sheet away from the crease. This frustration increases as the sheet's area increases. Stiff folds result in creases with constant space curvature while softer folds inherit the broken symmetry of the buckled shape. We extend the application of our numerical model to show the potential to study multiple fold structures.

<p>In sheet metal forming processes, friction has decisive effects on the strain distribution in the deformed sheets and the quality of the final product due to the large surface/thickness ratio of the blank sheets. It is well known that friction in sheet forming operations is dependent on local contact conditions such as surface roughness, contact pressure and sliding velocity. Adding complexity to this frictional behavior, some rolled sheets have oriented surface roughness and show considerable frictional anisotropy. A constant friction model without consideration of these relevant phenomena is regarded as the reason why sheet metal forming simulations often fail to produce satisfying results despite the well developed material models. </p> <p>To develop a friction model which considers both of the varying conditions of local contact and the frictional anisotropy was the aim of this thesis. For this purpose, the analysis method of the friction test (draw-bend test) had to be examined for the capability to evaluate these parameters independently. Through careful study using finite element simulations, it was found that the conventional method has shortcomings in addressing pressure dependent friction due to the pressure non-uniformity existing in the test. Therefore, a new analysis method, which can evaluate pressure dependency of a friction coefficient, was developed. In the new method, contact pressure maps obtained from simulations were included in the analysis of test data.</p> <p>The new analysis method was applied to friction measurement of aluminum sheets with known anisotropic mill finish, and friction coefficients were obtained as functions of contact pressure, sliding velocity and sliding direction. In the obtained friction model, a friction coefficient is a continuous surface over the domain of contact pressure and sliding velocity. Lastly, the new friction model was implemented into a finite element code and the model was validated through circular cup drawing experiments and simulations. The comparisons showed good agreements in the aspects of punch force, cup size and failure location. Thus, the newly developed model can accurately predict the effects of anisotropic friction in sheet metal forming processes. </p> / Thesis / Doctor of Philosophy (PhD)

<p> Manufacturing processes such as cold-bending flat sheet to a small radius produces a rather complex residual stress state through the thickness of light gauge structural steel sections. When the load-application device is released the sheet exhibits a phenomenon called "spring-back".</p> <p> The purpose of this research was to develop an exact method of computing the residual stresses in a wide sheet of ideal plastic metal after spring back and subsequently to study their effect on the behaviour of cold-formed sections. An approximate analysis based on the assumption of elastic spring back is presented for comparison purposes. It is demonstrated that plastic flow occurs within a thin core of sheet below the neutral axis and that the spring back is not completely elastic beyond a certain curvature. Such behaviour is particularly significant in cases where the radius of bend is of the same order as the thickness. An exact analysis based on a more realistic approach is then performed considering the adjustments in the stress components due to the plastic core. Computer programs have been developed to calculate the residual stresses associated with any given radius of bend. It is found that the choice of one yield criterion rather than the other does not have any effect on the present analysis and the stress components for Von Mises' material are (2/√3) times the components for Tresca's material. Furthermore, the effect of lateral stretching on the behaviour of cold-formed sections is briefly viewed.</p> <p> The purpose of the experimental work in this thesis was to verify the validity of some of the assumptions made in the analysis.</p> <p> Conclusions are drawn and suggestions made for further research.</p> / Thesis / Master of Engineering (MEngr)

No description available.

Elastic constants of single-walled carbon nanotubes (SWCNTs) and single-layer graphene sheets (SLGSs) are determined by studying their free vibration characteristics using molecular mechanics (MM) simulations with the MM3 potential and finding their equivalent continuum structures (ECSs). The computational framework has been validated by comparing the presently computed basal plane stiffness and frequencies of radial breathing modes (RBMs) with those available in the literature. We have considered armchair, zigzag and chiral SWCNTs of aspect ratios (length/ diameter in the unloaded relaxed configuration) ranging from 2 to 15. The wall thickness of ECSs of SWCNTs is determined by applying continuum theories, viz., beam, shell and 3D-linear elasticity to ECSs and equating their frequencies with those of SWCNTs obtained from the MM simulations. An expression for the wall thickness of an ECS of a SWCNT in terms of its chiral indices is deduced. The wall thickness of an ECS of a SWCNT is found to increase with an increase in its radius and to saturate at 1.37 Ã for the radius exceeding 15 Ã . Poisson's ratio for zigzag SWCNTs decreses with an increase in the tube radius, but that for armchair SWCNTs exhibits the opposite trend. For the same radius, Poisson's ratio of a chiral SWCNT is slightly more than that for an armchair tube but a little less than that for a zigzag tube. For zigzag SWCNTs, frequencies of inextensional modes of vibration saturate with an increase in the circumferential wave number but those of their ECSs do not. The MM simulations of uniaxial tensile deformations of SLGSs of aspect ratios (length/width) ~ 10 give the basal plane stiffness of ~ 340 N/m. The MM simulations of free vibrations of clamped SLGSs and the analysis of vibrations of their ECSs with a continuum theory gives a wall thickness of ~ 1 Ã for a SLGS. / Ph. D.

Šiame magistriniame darbe yra pateikiama CSS (Cascading Style Sheeets) apžvalga ir mokymosi galimybių analizė. Taip pat darbe yra pateikiami tyrimo, skirto išsiaiškinti Lietuvoje gyvenančių suinteresuotų asmenų poreikius CSS mokymo kurso teikimui internete ir kurso teikimo aplinkai. Atsižvelgiant į tyrimo rezultatus parengtas pedagoginio kurso teikimo scenarijus ir kursui teikti skirtos virtualios aplinkos projektas bei dirbančios aplinkos vartotojo gidas. / Main aim of this work is to create CSS web-based course pedagogical model and develop web based learning environment ideal for this course. In this document’s project part you will find course, named “CSS usage for web pages creation process”, pedagogical model and web-based learning environment creating process detailed projecting steps. In the end of document you will find created learning environment using and administrating manual.

Our vision is as yet unsurpassed by machines because of the sophisticated representations of objects in our brains. This representation is vastly different from a pixel-based representation used in machine storages. It is this sophisticated representation that enables us to perceive two faces as very different, i.e, they are far apart in the “perceptual space”, even though they are close to each other in their pixel-based representations. Neuroscientists have proposed distances between responses of neurons to the images (as measured in macaque monkeys) as a quantification of the “perceptual distance” between the images. Let us call these neuronal dissimilarity indices of perceptual distances. They have also proposed behavioural experiments to quantify these perceptual distances. Human subjects are asked to identify, as quickly as possible, an oddball image embedded among multiple distractor images. The reciprocal of the search times for identifying the oddball is taken as a measure of perceptual distance between the oddball and the distractor. Let us call such estimates as behavioural dissimilarity indices. In this thesis, we describe a decision-theoretic model for visual search that suggests a connection between these two notions of perceptual distances. In the first part of the thesis, we model visual search as an active sequential hypothesis testing problem. Our analysis suggests an appropriate neuronal dissimilarity index which correlates strongly with the reciprocal of search times. We also consider a number of alternative possibilities such as relative entropy (Kullback-Leibler divergence), the Chernoff entropy and the L1-distance associated with the neuronal firing rate profiles. We then come up with a means to rank the various neuronal dissimilarity indices based on how well they explain the behavioural observations. Our proposed dissimilarity index does better than the other three, followed by relative entropy, then Chernoff entropy and then L1 distance. In the second part of the thesis, we consider a scenario where the subject has to find an oddball image, but without any prior knowledge of the oddball and distractor images. Equivalently, in the neuronal space, the task for the decision maker is to find the image that elicits firing rates different from the others. Here, the decision maker has to “learn” the underlying statistics and then make a decision on the oddball. We model this scenario as one of detecting an odd Poisson point process having a rate different from the common rate of the others. The revised model suggests a new neuronal dissimilarity index. The new dissimilarity index is also strongly correlated with the behavioural data. However, the new dissimilarity index performs worse than the dissimilarity index proposed in the first part on existing behavioural data. The degradation in performance may be attributed to the experimental setup used for the current behavioural tasks, where search tasks associated with a given image pair were sequenced one after another, thereby possibly cueing the subject about the upcoming image pair, and thus violating the assumption of this part on the lack of prior knowledge of the image pairs to the decision maker. In conclusion, the thesis provides a framework for connecting the perceptual distances in the neuronal and the behavioural spaces. Our framework can possibly be used to analyze the connection between the neuronal space and the behavioural space for various other behavioural tasks.