• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 315
  • 52
  • 50
  • 30
  • 8
  • 6
  • 2
  • 1
  • 1
  • Tagged with
  • 466
  • 196
  • 98
  • 81
  • 55
  • 45
  • 45
  • 43
  • 39
  • 38
  • 37
  • 33
  • 31
  • 29
  • 29
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
231

Analýza mechanických vlastností balzového dřeva na mesoúrovni pomocí zkušebního stroje iErudio

Grossová, Olga January 2015 (has links)
This thesis analysis the mechanical properties of balsa wood mesolevel using the test machine iErudio. The thesis aim is to experimentally determine the mechanical properties of balsa wood (Ochroma lagopus). On the prototype minimachine iErudio is a set of measurements. Specifically, tensile and bending tests. Another objective is to determine the Poisson ratio on measured levels. These properties will be obtained from image data recorded device iErudio and calculated using the digital image correlation. Another objective is to evaluate the work done with the prototype device, point out the advantages and disadvantages. To analyse data using a commercial computer program VIC 3D and Mercury RT, which process the results using digital image correlation. The work has provided us with confirmation of mechanical characteristics of balsa and the suitability of using "minimachine" iErudio the performed tests.
232

Zkoumání vybraných vlastností neupraveného a tepelně upraveného smrkového a modřínového dřeva z pohledu vhodnosti na výrobu šindele

Hlobil, Vladimír January 2015 (has links)
The aim of this thesis is the analysis and comparison of selected material properties of spruce, larch, heat-treated spruce and larch in terms of suitability for the production of wood roof shingles. Monitoring and comparing characteristics are durability of the wood material against the brown rot fungus, compressive strength across the fiber, bending strength and modulus of elasticity. Tested material and its selected properties are compared as for use in the manufacture and installation of wooden shingles.
233

Influence of wood structure on wood properties of tropical species

Baar, Jan January 2014 (has links)
The presented thesis is focused on aesthetical and acoustic properties of tropical wood. The discussed tropical species are utilized in Europe mainly for their unusual appearance and colour in joinery and furniture production. The irreplacable acoustic properties like low internal friction predestine specific species for production of musical instruments. The colour of six selected tropical species - jatoba (Hymenea courbaril L.), massaranduba (Manilkara bidentata A. Chev.), muiracatiara (Astronium graveolens Jacq.), angelim amargoso (Vatairea spp.), angelim pedra (Hymenolobium spp.) and angelim vermelho (Dinizia excelsa Ducke) - were analyzed and expressed in CIEL*a*b* colour space. Subsequently the samples were exposed to artificial sunlight and the light-induced discolouration rate and progress was evaluated. The colour change was rapid in zhe first hours of exposure and all species showed a similar trend in lightness (L*) change - initial darkening replaced by gradual fading. The change in chromatic parameters (a* and b*) change was specific for individual species and probably related to the chemical composition of the extractives. The overall discolouration of lighter coloured wood samples is more distinctive. The extractive content of tropical species is usually high and determines wood colour. The wood of African Padauk (Pterocarpus soyauxii Taub) and Jatoba (Hymenaea courbaril L.) was extracted in a mixture of methanol, water and acetone. The total extractives and total phenolic content was measured. Extractive content was related to colour parameters and above all to lightness in both species. The increase in extractive content leads to a lighter and more yellow colouration of Jatoba wood while African Padauk was darker with a higher amount of extractives. In Jatoba, a positive correlation was found between extractive content and the rate of discolouration. The extractives are responsible for intensive discolouration of tropical woods in contrast to light coloured woods from the temperate zone, where the yellowing is primarily caused by lignin photodegradation. The sound velocity was measured by ultrasound and resonance longitudinal method in heartwood of doussie (Afzelia bipindensis), merbau (Intsia bijuga), wengé (Millettia stuhlmannii Taub.), muiracatiara (Astronium graveolens Jacq.) and zebrano (Microberlinia brazzavillensis). The sound velocity was not related to the density in any case. Although anatomical structural characteristics as fiber length or ray ratio positively influenced it. With longer fibers and slender rays the sound velocity increased. Other acoustic properties like dynamic young modulus of elasticity, specific modulus of elasticity, internal friction and acoustic conversion efficiency (ACE) were determined and were related to measured anatomical features. The differences in composition of wood tissue of individual species were the main source of departure between the assessed relationships. The wood with longer fibers and lower frequency of rays reached lower values of internal friction. The stiffness of wood characterized by the dynamic modulus of elasticity was correlated with fiber and ray tissue. A higher volume of fibers influenced the stiffness positively, while ray volume had the opposite effect on stiffness. Positive effects of fiber length and ray ratio were found for dynamic modulus of elasticity and for acoustic conversion efficiency as well. Both values increased with longer fibers and higher ray ratio. The sound velocity is the basis of some nondestructive techniques for determination of wood mechanical properties. The comparison of density and three dynamic moduli of elasticity (longitudinal and flexural resonance method and ultrasound method) in prediction of mechanical properties was carried out. The density was evaluated as a poor predictor when the samples are not straight-grained and defect free. The interlocked grain often occurred in tropical species and its presence influences the mechanical properties of wood but not wood density. The dynamic moduli of elasticity showed strong correlation with the static modulus of elasticity. Among nondestructive techniques, the weakest correlation was found for the ultrasound method, which is probably partially explained by different measuring mechanism. The prediction of the modulus of rupture is less accurate when the dynamic modulus of elasticity is compared with the static modulus of elasticity; however, it was still good in comparison with the density model.
234

Výuková sestava pro práci s mikrokontroléry AVR Atmel / Educastion kit for working with microcontrolers AVR Atmel

KUBEŠ, Miroslav January 2012 (has links)
This thesis deals with design and production of teaching kits with Atmel AVR microcontroller. This kit includes a processor board and modules, which will connect to the board. It describes the equipment needed for software design and programming of microcontroller and technological processes to create a kit. Also, it will find the basic theoretical knowledge to work with the ATmega8535 microcontroller. Kit along with a disc on which are recorded all the diagrams, pictures and programs created by me, will be attached to the thesis.
235

Využití modulu zesilovače ve výuce / Application module of universal amplifier in education process

CHALOUPEK, Pavel January 2013 (has links)
This thesis deals with the teaching and implementation module for teaching in secondary schools and their role in education. Following the theory being discussed in relation to a valid educational program. Learning amplifier module implemented by the assignment to DPS. The activity of the amplifier module to simulate in Multisim simulation program. Next is made circuitry design in discrete amplifier module. There evaluated the feasibility and simulation of realizations amplifier module in secondary school following the educational program. Comparison of application module amplifier for teaching at primary and secondary schools. At each level of education.
236

Systém nasazení a řízení záchranářské humanitární pomoci poskytované do zahraničí. / The system of deployment of provided rescue humanitarian assistence abroad.

SOJKA, Hynek January 2013 (has links)
This thesis deals with humanitarian assistance from the Czech Republic abroad. The issue of humanitarian assistance is viewed in terms of its own management system and by providing this assistance. The humanitarian assistance has not been compiled into a comprehensive publication before. The constant increasing importance of this problem comes mainly from an increase in the number of disasters caused by the nature on the one hand, and human activities on the other.The issue of the thesis was to define, describe and evaluate the system of management of rescue humanitarian assistance that is provided by Czech Republic abroad and possibly propose some changes in management with the aim to make the humanitarian assistance most effective and fastest to be provided in the affected country. The next issue is to recommend changes in the structure of management to be useful in the praxis and also that the thesis will be appropriate for studying mentioned problems. The research question was if it´s possible to make more effective the procedure of providing rescue humanitarian assistance to the country which was striken by disaster. In relation to the described theory the folllowing assumption was introduced: is it possible to realize the providing and managing of the rescue humanitarian assistance abroad?Research work with the focus on solving practical problem was selected as a processing type of the thesis, it will results in more effective proceeding operation in the mentioned sphere. In this point of view of methodology it´s ?mixed research? in its simple way, qualitative and quantitative research is combined. The analysis of case study and nonstandarized dialogue were applied for solution of research question. The form of analysis, comparation and description in the theoretical part of the thesis was choosen from general to concrete. The first part, mainly characterizes two basic concepts ? The Humanitarian assistance and The Emergency, including definitions of legislation of this issue from the perspective of the European Union and the Czech Republic. There are also identified and described the major practical mechanisms of the assistance - The civil protection modules which send the member states of The European Union, including the Czech Republic, to countries affected by the emergency.This theoretical part of the thesis is followed by a research based on real case studies - provided humanitarian assistance during the floods in Poland in 2010, identifies and defines the system of strategic and operational management, supplement with data and own knowledgement from sphere of service execution ? operation officer of Fire and Rescue Service - procedure of management is formed and followed with the identification of 15 issues from solved sphere. The solution is own proposal which gives with its followed proceeding steps manual (instructions) to crisis managment how to proceed in the first level of management. This procedure is shown here in the form of a practical document that can serve as a ?check-list events? the Checklist. The important point here is a summary of the steps that must not be omitted during proceeding and management of this mechanism, with the only aim ? to provide the humanitarian assistance quickly and efficiently to the affected area.In the chapter titled the Discussion are into the context given knowledges about described issue.In the end of the thesis the outcomes and results are formulated, the research question if it´s possible to make more effective the procedure of providing rescue humanitarian assistance to the country which was striken by disaster is affirmatived answered with the confirmed assumption. Finally the author´s principle is mentioned which is useable for crisis manager´s work in early decision procedure of providing humanitarian assistance and other recommended steps in this procedure.
237

Att inkludera räddningstjänsten i träningsverktyget Emergo Train System

Hanson, Linnéa January 2018 (has links)
Med anledning av det förändrade säkerhetspolitiska läget i Sverige arbetar flera myndigheter, på uppdrag av regeringen med att förbättra samhällets beredskap på flera olika sätt. Ett sätt att säkerställa att de aktörer som blir involverade vid någon typ av kris är förberedda är att låta dem träna i simulerade miljöer. Denna studie hade som uppgift att specificera räddningstjänstens roller, uppgifter och verktyg för att sedan kunna utveckla en modul för träningsverktyget Emergo Train SystemÒsom tillåter utökade träningsmöjligheter för räddningstjänstpersonal, enskilt eller i samverkan med övriga blåljusaktörer. Detta gjordes genom att samla in information från fokusgrupper med räddningstjänsten och sedan analysera detta med hjälp av hierarkiska uppgiftsanalyser. Resultatet är tabeller som specificerar roller, hierarkiska uppgiftsanalyser som beskriver räddningstjänstens uppgifter samt tabelluppgiftsanalyser som specificerar dessa i kombination med verktyg. Resultatet kan användas av ETS för att skapa symboler och simuleringsövningar för räddningstjänsten där deras prestation kan mätas såväl som utvecklas. / Due to the changed security policy situation in Sweden, several authorities work on behalf of the government to improve society's preparedness in several different ways. One way to ensure that the actors involved in any kind of crisis are prepared is to let them train in simulated environments. The aim of this study was to specify the roles, tasks and tools of the emergency services to develop a module for the Emergo Train SystemÒtraining tool, which allows for increased training opportunities for emergency staff, individually or in collaboration with other first responders. This was done by collecting information from focus groups with the rescue service and then analyzing it with hierarchical task analyzes. The result is tables that specify roles, hierarchical task analyzes that describe the tasks of rescue services and tabular data analyzes that specify these in combination with tools. The result can be used by ETS to create symbols and simulation exercises for the emergency services where their performance can be measured as well as developed.
238

Dynamisk dimensionering av hög träbyggnad med horisontalstabiliserande kärna av KL-trä och prefabricerade volymelement / Dynamic design of high-rise timber building with horizontally stabilising CLT core and prefabricated volume elements

Lindberg, Albin January 2018 (has links)
Efterfrågan på höga byggnader ökar i städerna och eftersom hållbarhet är ett viktigt ämne i samhället har intresset för och användandet av trä i höga byggnader ökat de senaste åren. Träbyggnaders flexibilitet och låga vikt gör att svängningar orsakade av horisontella dynamiska vindlaster i bruksgränstillståndet kan uppfattas som störande av personer som vistas i byggnaden och därav bli styrande för dimensioneringen av byggnaden. I detta examensarbete studeras en hybridlösning som använder sig av en vertikalt bärande och horisontellt stabiliserande kärna av KL-trä samt byggs upp med lätta prefabricerade volymelement. Syftet med arbetet är att ta fram en lämplig uppbyggnad och studera dess dynamiska egenskaper samt studera hur förändringar av kärnans parametrar och uppbyggnad påverkar de dynamiska egenskaperna. Målet är att erhålla svar på maximalt antal våningar för respektive alternativ uppbyggnad samt utöka förståelsen på kärnans inverkan på byggnadens dynamiska respons. Byggnaden modelleras upp enligt fyra olika huvudstrukturer där Struktur 1 är byggnadens grundmodell enligt dess enklaste uppbyggnad, inom Struktur 2 varierar KL-träkärnans väggtjocklek, inom Struktur 3 varierar KL-träkärnans storlek och inom Struktur 4 adderas horisontalstabiliserande väggar till KL-träkärnan. I alla modeller antas volymelementen ej bidra till byggnadens globala stabilitet och därför modelleras de in som massor. De olika strukturerna modelleras upp i FEM-programvaran Robot Structural Analysis där en modalanalys utförs för att erhålla byggnadens egenfrekvenser och svängningsmoder. Därefter beräknas toppaccelerationen hos svängningarna, orsakade av dynamisk vind, på golvbjälklaget i byggnadens översta våning ut för hand för att jämföras mot komfortkrav i ISO 10137. Resultaten visar att byggnaden generellt sett har låga egenfrekvenser vilket beror på en förhållandevis hög massa och relativt låg styvhet hos strukturen. Struktur kan uppföras till 20 våningar under de förhållanden som använts i beräkningarna. Förändringar i kärnans tjocklek förstyvar byggnaden något vilket gör att Struktur 2 bör kunna uppföras ett par våningar högre. Förändringar i kärnans storlek visar sig ha en relativt stor påverkan på byggnadens styvhet och därför kan Struktur 3 uppföras till 24 våningar då kärnan är 25 % större i alla riktningar. För Struktur 1, 2 och 3 sker svängning först i y-led, sedan i x-led och sist som vridning kring z-axeln. För Struktur 4 visar sig styvheten påverkas mycket av att stabiliserande väggar adderas till kärnan, dock kan även svängningsriktningar för första och andra svängningsmod förändras och det bör kontrolleras så att problem med vridningssvängningar inte uppkommer. Om stabiliserande väggar läggs till i y-riktning, x-riktning samt del av fasad kan Struktur 4 uppföras hela 28 våningar, med förhållandevis god marginal. Som förslag på fortsatt arbete bör en statisk dimensionering utföras för att vidare utreda om uppbyggnaden är lämplig vad gäller bland annat tvärsnittstorlekar och infästningar. Dessutom bör det undersökas om och hur volymelementens styvhet kan användas för att bidra till strukturens globala stabilitet. Då kärnans storlek har en stor påverkan på byggnadens styvhet bör det utredas ifall lämpliga planlösningar kan arbetas fram med större eller till och med dubbel kärna för att sedan utföra en dynamisk dimensionering på strukturen. Då planlösningen enligt denna och andra studier bedöms ha potential för att bygga högt, vore en jämförelse av olika planlösningar intressant där förslagsvis byggnadens yttermått och form samt placering och antal stabiliserande KL-träkärnor varierar. / The demand on high-rise buildings grows in the cities and since sustainability is an important matter in today’s society, the interest for high-rise timber buildings has grown the past years. The flexibility and weight of timber buildings makes wind-induced vibrations in serviceability limit state an issue that can be deciding for the design of the building since people can find the vibrations disturbing. In this study, a building which uses a vertically load-bearing and horizontally stabilising CLT core and is built-up with light prefabricated volume elements. The objective of this study is to produce a suitable structure and study its dynamic properties and how changes of the core’s parameters and design may change the dynamic properties of the building. The goal is to find the maximum number of floors that can be built for each alternative structure and to expand the knowledge on how the CLT core impacts the dynamic response of the building. The building is modelled by four different main structures where Structure 1 is the building’s basic and most simple model, within Structure 2 the CLT core’s wall thickness varies, within Structure 3 the CLT core’s size varies and within Structure 4 horizontally stabilising walls are added to the core. In all of the models, the volume elements are assumed not to contribute to the global horizontal stability of the building which is why they are modelled as masses. The different structures are modelled into the FEM software Robot Structural Analysis where a modal analysis is being carried out to find the building’s natural eigenfrequencies and modes of vibrations. Subsequently, the top acceleration of the wind-induced vibrations is calculated on the floor slab of the top floor by hand to be compared to comfort limits in ISO 10137. The results show that the building has low eigenfrequencies in general, which is due to the structure’s relatively high mass and low stiffness. Structure 1 can be built up to 20 floors under the conditions used in the calculations. Changes of the core’s wall thickness stiffen the building which means that Structure 2 should be able to build a couple of floors higher. Changes in the size of the core have a relatively large impact on the rigidity of the building and therefore Structure 3 can be built up to 24 floors when the core is 25 % larger in all directions. For Structure 1, 2 and 3, swaying occurs first in the y-direction, second in the x-direction and third as twist around the z-axis. For Structure 4, the rigidity is greatly influenced when stabilising walls are added to the core. However, the direction of the first and second modes of vibration can change and it should be verified that problems with twisting oscillation does not occur. If stabilising walls are added in the y-direction, x-direction and part of the façade, Structure 4 can be built up to 28 floors with a relatively good margin. As a proposal for further work, a static design should be performed to further investigate whether the structure is suitable for e.g. cross-sectional sizes and connections. It should also be examined if and how the rigidity of the volumes can be used to contribute to the global stability of the structure. As the size of the core has a major impact on the rigidity of the building, it should be investigated if a suitable floor layout can be arranged with larger or even double cores and then perform a dynamic design on the structure. As the floor layout, according to this and other studies, is considered to have great potential when building high, a comparison of different floor plans would be interesting where e.g. the external dimensions and shape of the building, as well as the placement of the CLT core and number of cores can vary.
239

Effektivisering av informationsflödet hos ett företag med produktvariation : Fallstudie på A-hus AB / Streamlining the information flow of a company with product variation : A case study at A-hus AB

Luu, Alan, Ragnarsson, John January 2017 (has links)
Syftet med denna studie är att identifiera ett företags informationsflödet och ta fram förbättringsförslag. Företaget har en hög efterfrågan på deras produkter och en effektivisering av projekteringsarbetet gör att företaget lättare kan möta kommande utmaningar. Vid studier konstaterades det att problem skapas mellan arkitekt och konstruktör när det blir så kallat specialprojekt samtidigt som det saknades standardiserat arbete. Genom de presenterade förbättringsförslagen kan informationsflödet göra betydande effektiviseringar.
240

Influence of the Melt Flow Rate on the Mechanical Properties of Polyoxymethylene (POM) / Einfluss des Schmelzfließindex auf die mechanischen Eigenschaften von Polyoxymethylen (POM)

Faust, Karsten, Bergmann, André, Sumpf, Jens 19 December 2017 (has links) (PDF)
In this article the correlation between the average molar mass and the melt flow rate (MFR) is achieved. Based on the example of Polyoxymethylene (POM) it is shown that a high average molar mass is associated with a low MFR (high viscosity). On the basis of this dependency, the mechanical properties of static and dynamic tensile strength, elastic modulus, hardness and notched impact strength are investigated. It was found that the characteristic values of static tensile strength, elastic modulus and hard-ness increase with increasing MFR (decreasing viscosity). On the other hand the dynamic long-term properties and notched impact strengths decrease with increasing MFR. / Im Beitrag wird der Zusammenhang zwischen der mittleren molaren Masse und des Schmelzfließindex (MFR) hergestellt. Dabei wird am Beispiel von Polyoxymethylen (POM) ersichtlich, dass eine hohe mittlere molare Masse mit einem geringen MFR (hochviskos) einhergeht. Basierend auf dieser Abhängigkeit werden die mechanischen Eigenschaften statische und dynamische Zugfestigkeit, E-Modul, Härte sowie Kerbschlagzähigkeit untersucht. Dabei konnte festgestellt werden, dass die Kenngrößen statische Zugfestigkeit, E-Modul und Härte mit steigendem MFR (abnehmende Viskosität) zunehmen. Die dynamischen Langzeiteigenschaften und Kerbschlagzähigkeiten sinken hingegen mit zunehmendem MFR.

Page generated in 0.0435 seconds