Thèses sur le sujet « Beam characteristics »
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1
Bor, Sheau-Shong. « Phase conjugation characteristics of Gaussian beam / ». The Ohio State University, 1986. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487262825076392.
Texte intégral
2
Mourka, Areti. « Probing the modal characteristics of novel beam shapes ». Thesis, University of St Andrews, 2014. http://hdl.handle.net/10023/4287.
Texte intégralRésumé :
In this thesis, an investigation into the modal characteristics of novel beam shapes is presented. Sculpting the phase profile of a Gaussian beam can result in the generation of a beam with unique properties. Described in this thesis are Laguerre-Gaussian (LG), Hermite-Gaussian (HG) and Bessel beams (BBs). The diffraction of LG beam modes from a triangular aperture is explored and this effect can be used for the efficient measurement of the azimuthal mode index l that indicates the number of multiples of 2π of phase changes that the field displays around one circumference of the optical axis. In this study, only LG beams with zero radial mode index p, with p + 1 denoting the number of bright high intensity concentric rings around the optical axis, were considered. Then, a powerful approach to simultaneously determine both mode indices of a pure LG beam using the principal component analysis (PCA) algorithm on the observed far-field diffraction patterns was demonstrated. Owing to PCA algorithm, the shape of the diffracting element used to measure the mode indices is in fact of little importance and the crucial step is ‘training' any diffracting optical system and transforming the observed far-field diffraction patterns into the uncorrelated variables (principal components). Our PCA method is generic and it was extended to other families of light fields such as HG, Bessel and superposed beams. This reinforces the widespread applicability of this method for various applications. Finally, both theoretically and experimentally investigations using interferometry show the definitive linkage between both the radial and azimuthal mode indices of a partially coherent LG beam and the dislocation rings in the far-field cross-correlation function (CCF).
3
Leong, Mun-Foo. « MOMENT-ROTATION CHARACTERISTICS OF BEAM-TO-COLUMN CONNECTIONS ». Thesis, The University of Arizona, 1985. http://hdl.handle.net/10150/275028.
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4
Salzmann, Angela, et n/a. « Damping Characteristics of Reinforced and Prestressed Normal- and High-Strength Concrete Beams ». Griffith University. School of Engineering, 2003. http://www4.gu.edu.au:8080/adt-root/public/adt-QGU20040430.133844.
Texte intégralRésumé :
In the last few decades there has been a significant increase in the design strength and performance of different building materials. In particular, new methods, materials and admixtures for the production of concrete have allowed for strengths as high as 100 MPa to be readily available. In addition, the standard manufactured yield strength of reinforcing steel in Australia has increased from 400 MPa to 500 MPa. A perceived design advantage of higher-strength materials is that structural elements can have longer spans and be more slender than previously possible. An emerging problem with slender concrete members is that they can be more vulnerable to loading induced vibration. The damping capacity is an inherent fundamental quantity of all structural concrete members that affects their vibrational response. It is defined as the rate at which a structural member can dissipate the vibrational energy imparted to it. Generally damping capacity measurements, to indicate the integrity of structural members, are taken once the structure is in service. This type of non-destructive testing has been the subject of much research. The published non-destructive testing research on damping capacity is conflicting and a unified method to describe the effect of damage on damping capacity has not yet been proposed. Significantly, there is not one method in the published literature or national design codes, including the Australian Standard AS 3600-2001, available to predict the damping capacity of concrete beam members at the design stage. Further, little research has implemented full-scale testing with a view to developing damping capacity design equations, which is the primary focus of this thesis. To examine the full-range damping behaviour of concrete beams, two categories of testing were proposed. The categories are the 'untested' and 'tested' beam states. These beam states have not been separately investigated in previous work and are considered a major shortcoming of previous research on the damping behaviour of concrete beams. An extensive experimental programme was undertaken to obtain residual deflection and damping capacity data for thirty-one reinforced and ten prestressed concrete beams. The concrete beams had compressive strengths ranging between 23.1 MPa and 90.7 MPa, reinforcement with yield strengths of 400 MPa or 500 MPa, and tensile reinforcement ratios between 0.76% and 2.90%. The full- and half-scale beams tested had lengths of 6.0 m and 2.4 m, respectively. The testing regime consisted of a series of on-off load increments, increasing until failure, designed to induce residual deflections with increasing amounts of internal damage at which damping capacity (logarithmic decrement) was measured. The inconsistencies that were found between the experimental damping capacity of the beams and previous research prompted an initial investigation into the data obtained. It was found that the discrepancies were due to the various interpretations of the method used to extract damping capacity from the free-vibration decay curve. Therefore, a logarithmic decrement calculation method was proposed to ensure consistency and accuracy of the extracted damping capacity data to be used in the subsequent analytical research phase. The experimental test data confirmed that the 'untested' damping capacity of reinforced concrete beams is dependent upon the beam reinforcement ratio and distribution. This quantity was termed the total longitudinal reinforcement distribution. For the prestressed concrete beams, the 'untested' damping capacity was shown to be proportional to the product of the prestressing force and prestressing eccentricity. Separate 'untested' damping capacity equations for reinforced and prestressed concrete beams were developed to reflect these quantities. To account for the variation in damping capacity due to damage in 'tested' beams, a residual deflection mechanism was utilised. The proposed residual deflection mechanism estimates the magnitude of permanent deformation in the beam and attempts to overcome traditional difficulties in calculating the damping capacity during low loading levels. Residual deflection equations, based on the instantaneous deflection data for the current experimental programme, were proposed for both the reinforced and prestressed concrete beams, which in turn were utilised with the proposed 'untested' damping equation to calculate the total damping capacity. The proposed 'untested' damping, residual deflection and total damping capacity equations were compared to published test data and an additional series of test beams. These verification investigations have shown that the proposed equations are reliable and applicable for a range of beam designs, test setups, constituent materials and loading regimes.
5
Salzmann, Angela. « Damping Characteristics of Reinforced and Prestressed Normal- and High-Strength Concrete Beams ». Thesis, Griffith University, 2003. http://hdl.handle.net/10072/366888.
Texte intégralRésumé :
In the last few decades there has been a significant increase in the design strength and performance of different building materials. In particular, new methods, materials and admixtures for the production of concrete have allowed for strengths as high as 100 MPa to be readily available. In addition, the standard manufactured yield strength of reinforcing steel in Australia has increased from 400 MPa to 500 MPa. A perceived design advantage of higher-strength materials is that structural elements can have longer spans and be more slender than previously possible. An emerging problem with slender concrete members is that they can be more vulnerable to loading induced vibration. The damping capacity is an inherent fundamental quantity of all structural concrete members that affects their vibrational response. It is defined as the rate at which a structural member can dissipate the vibrational energy imparted to it. Generally damping capacity measurements, to indicate the integrity of structural members, are taken once the structure is in service. This type of non-destructive testing has been the subject of much research. The published non-destructive testing research on damping capacity is conflicting and a unified method to describe the effect of damage on damping capacity has not yet been proposed. Significantly, there is not one method in the published literature or national design codes, including the Australian Standard AS 3600-2001, available to predict the damping capacity of concrete beam members at the design stage. Further, little research has implemented full-scale testing with a view to developing damping capacity design equations, which is the primary focus of this thesis. To examine the full-range damping behaviour of concrete beams, two categories of testing were proposed. The categories are the 'untested' and 'tested' beam states. These beam states have not been separately investigated in previous work and are considered a major shortcoming of previous research on the damping behaviour of concrete beams. An extensive experimental programme was undertaken to obtain residual deflection and damping capacity data for thirty-one reinforced and ten prestressed concrete beams. The concrete beams had compressive strengths ranging between 23.1 MPa and 90.7 MPa, reinforcement with yield strengths of 400 MPa or 500 MPa, and tensile reinforcement ratios between 0.76% and 2.90%. The full- and half-scale beams tested had lengths of 6.0 m and 2.4 m, respectively. The testing regime consisted of a series of on-off load increments, increasing until failure, designed to induce residual deflections with increasing amounts of internal damage at which damping capacity (logarithmic decrement) was measured. The inconsistencies that were found between the experimental damping capacity of the beams and previous research prompted an initial investigation into the data obtained. It was found that the discrepancies were due to the various interpretations of the method used to extract damping capacity from the free-vibration decay curve. Therefore, a logarithmic decrement calculation method was proposed to ensure consistency and accuracy of the extracted damping capacity data to be used in the subsequent analytical research phase. The experimental test data confirmed that the 'untested' damping capacity of reinforced concrete beams is dependent upon the beam reinforcement ratio and distribution. This quantity was termed the total longitudinal reinforcement distribution. For the prestressed concrete beams, the 'untested' damping capacity was shown to be proportional to the product of the prestressing force and prestressing eccentricity. Separate 'untested' damping capacity equations for reinforced and prestressed concrete beams were developed to reflect these quantities. To account for the variation in damping capacity due to damage in 'tested' beams, a residual deflection mechanism was utilised. The proposed residual deflection mechanism estimates the magnitude of permanent deformation in the beam and attempts to overcome traditional difficulties in calculating the damping capacity during low loading levels. Residual deflection equations, based on the instantaneous deflection data for the current experimental programme, were proposed for both the reinforced and prestressed concrete beams, which in turn were utilised with the proposed 'untested' damping equation to calculate the total damping capacity. The proposed 'untested' damping, residual deflection and total damping capacity equations were compared to published test data and an additional series of test beams. These verification investigations have shown that the proposed equations are reliable and applicable for a range of beam designs, test setups, constituent materials and loading regimes.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Engineering
Full Text
6
Jackson, Rahsean LaNaul. « Vibration and Flexural Strength Characteristics of Composite Castellated Beams ». Thesis, Virginia Tech, 2002. http://hdl.handle.net/10919/31242.
Texte intégralRésumé :
With the development of lightweight concrete and design optimizations, floor vibration problems are becoming a serious serviceability problem. The castellated beam is a prime example and was the focus of this study. The vibration and flexural strength performance were verified in this paper.
The vibration characteristics of castellated beams were examined using experimental and analytical test methods. The effective moment of inertia is essential to accurately predict the frequency and deflection of a floor system due to human occupancy. Since castellated beams have non-prismatic cross-sections, their effective moment of inertia is an uncertainty and was verified in this study. This paper confirmed the accuracy of the AISC Design Guide procedures used in for prismatic beam, when applied to castellated beams.
The flexural strength of various composite castellated beam were studied. Three full-scale specimens were tested to failure to evaluate their yield and maximum applied load. Each specimensâ moment strength was verified based on span, beam properties, concrete slab, and amount of shear connection.
Master of Science
7
Ribton, Colin Nigel. « Development of an electron gun design optimisation methodology ». Thesis, Brunel University, 2017. http://bura.brunel.ac.uk/handle/2438/15629.
Texte intégralRésumé :
The design of high quality electron generators to meet specific requirements is important in the application of these devices to a variety of materials processing systems (including welding, cutting and additive manufacture), X-ray tubes for medical, scientific and industrial applications, microscopy and lithography. Designs can be analysed by field solvers, and electron trajectories plotted to provide an indication of the beam quality. Incremental improvement of designs has normally been executed by trial and error, and this can be a time consuming activity requiring expert intervention for each iteration of the design process. The unique contribution made to knowledge by this work is the application of optimisation techniques to the design of electron guns to produce beams with the required optical properties. This thesis presents a review of the design of electron guns, including a discussion of thermionic cathode material properties and their suitability for use in electron guns for processing materials, the influence of space-charge on gun design and the derivation of salient beam metrics to characterise the beam. Beam quality metrics have been developed that allow quantification of electron beam characteristics, allowing objectives to be set for the optimisation process. Additionally, a method is presented that enables real world measurements to be directly compared with modelled beams. Various optimisation methods are reviewed. A genetic algorithm was selected, which would use gun modelling and beam characterisation calculations as the objective function, as a suitable method for application to this problem. However, it was recognised that selections for the best evolutionary parameters, the population size, number of parents, the mutation rate and mutation scale, were not readily determined from published work. An investigation is presented where a range of evolutionary parameters was tested for a set of geometrical problems, which had some similarity to electron gun design but could be computed sufficiently quickly to enable an extensive survey, and the most efficient combination of parameters was identified. Detail is given of the customisation of a genetic evolutionary optimisation method for the design of electron guns. Examples are presented of electron gun design optimisation processes to meet specified beam requirements within defined geometric and electrical constraints. The results of this work show that optimum evolutionary parameter settings for the geometric problem vary with the complexity of the problem and trends have been identified. Application of these parameters to an electron gun optimisation has been successful. The derived beam parameter metrics have been applied to electron guns as an objective function. Comparisons of modelled predictions of the beam characteristics with the measured real world values have been shown to be reasonable.
8
French, Vandy. « Moment - Rotation characteristics of boltedc beam - to - column aluminium connections ». Master's thesis, University of Cape Town, 2009. http://hdl.handle.net/11427/5046.
Texte intégralRésumé :
Structural aluminum provides a unique option to engineers by virtue of both its unique strength to weight ratio and its well known corrosion resistance properties. The development of the Eurocode 9 provides an insight to the design of aluminum structures based on results from various researchers worldwide. However the area of connections remains very sparse with regards to research material as compared to steel as provided by Eurocode 3 part 1-8. This work involves the analysis of the performance of aluminum end plate beam column connections with regards moment rotation behavior as well as the main connection classification criteria, strength, stiffness and ductility. A parametric study is done with the use of the non- linear finite elements program ADINA in which the effects of connection geometry is observed under incremental loading.
9
Hochanadel, Joris Erich. « Effect of Beam Characteristics and Process Parameters on the Penetration and Microstructure of Laser and Electron Beam Welds in Stainless Steel and Titanium ». The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu160503470688313.
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10
Flampouri, Styliani. « Optimisation of megavoltage beam and detector characteristics for portal imaging in radiotherapy ». Thesis, Institute of Cancer Research (University Of London), 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.408859.
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11
Popov, G. F., A. S. Salah et R. V. Lazurik. « Verification of Two-Parametric Fitting Method for Determination of Electron Beam Characteristics ». Thesis, Sumy State University, 2015. http://essuir.sumdu.edu.ua/handle/123456789/41121.
Texte intégralRésumé :
Computer simulation of radiation processing allows correctly to schedule and control the performance of work on radiation processing installations. In particular, for radiation technology using electron beams (EBs) in the calculations it is required the values of energy characteristics of the electron irradiation. The paper [1] describes a method for the twoparametric fitting of semi-empirical model (PFSEM method) to the results of measuring the depth dependence of the absorbed dose for electron radiation performed by dosimetric wedge.
12
Gustavsson, Bengt. « Effect of Beam Scan Length on Microstructure Characteristics of EBM Manufactured Alloy 718 ». Thesis, KTH, Materialvetenskap, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-225416.
Texte intégralRésumé :
Additive Manufacturing (AM) as a method is on the rise and allow for a high freedom to create unique shapes without being limited by conventional machining methods. The Electron Beam Melting method, developed by Arcam AB in Mölndal, Sweden, use Powder Bed Fusion together with an electron beam and at an elevated temperature (+1000ºC) to lower stress due to thermal gradients. The purpose of this paper is to study the influence of Scan Length during Electron Beam Melting of Alloy 718 in regards to the appearance of shrinkage, porosity, primary carbide precipitation (mainly NbC), primary dendrite width and hardness. Samples built had the dimensions of 10x15xVar mm3 (Height x Depth x Width) with widths ranging from 10 mm in steps of 5 mm up to a maximum of 90 mm. The parameters were set as a single entry within the build project and as such each layer was melted as a single unit. A Light-Optical Microscope (LOM) and a Scanning Electron Microscope (SEM) was used to obtain images for manual counting to calculate the fraction of porosity and NbC-precipitates as well as the columnar grain width. The space between lines of interdendritical precipitation of NbC was used to determine the dendrite arm widths and a series of Hardness Vickers (500g for 15s) indents was performed. An Energy-Dispersive X-Ray Spectroscope (EDS) was used to help identify precipitates and phases. Columnar grain width and the spacing between vertical bands of interdendritical NbC was measured according to ASTM112-13 while porosity and hardness was measured according to ASTM562-11. Both of these only looked at the XZ-plane instead of all three planes. The columnar grain width was measured in the 10 mm, 40 mm and 90 mm samples at a distance of 4 mm from the top and with a slight spread over the sample width according to ASTM112-13 but using only one plane for counting. No significant change to columnar width was found. Primary dendrite arm width was measured on the 10 mm, 40 mm and 90 mm samples at about 5 mm from the top. An average for all samples was found to be 7.82 μm ± 2.89. No significant trend could be found with increased sample width. A total average porosity of 0.33% ± 0.16 was found. Variations between samples were less than the standard deviation. Even though the variations were not high enough to be significant, no obvious trend could be seen in regards to sample width, position on the base plate or heat transfer through the build. The presence of NbC was investigated in all samples with a total average of 0.36% ± 0.23 with variations between sample lengths being within the standard deviation. An insignificant trend could be seen between the smaller samples together with the wider samples having a higher degree of NbC compared to the middle samples. No significant trend could be seen in NbC based on row. Across all samples, the mean hardness was found to be 406.75 HV0.5 ± 16.53. No significant trend could be seen with increased sample width. Based on sample rows no significant trend could be seen.
13
BARROS, FABRICIO JOSE BRITO. « THREE-DIMENSIONAL BEAM TRACING METHOD TO OBTAIN ULTRA WIDEBAND INDOOR RADIO CHANNEL CHARACTERISTICS ». PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2010. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=16771@1.
Texte intégralRésumé :
COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOREste trabalho descreve o método de traçado de feixes em três dimensões que permite a caracterização do canal em uma banda ultralarga. As características do canal são acessadas através do retardo médio, espalhamento de retardo RMS e banda de coerência. Uma análise adicional sobre a variação da potência ao longo da distância foi realizada. Os resultados obtidos foram comparados com mediadas realizadas, com o auxílio da técnica de sondagem em frequência, para validação do método utilizado.
This work describes the tridimensional beam tracing method that allows one to characterize the Ultra Wideband (UWB) indoor Radio Channel. The channel characteristics are assessed in terms of mean delay, delay spread and coherence bandwidth. An additional analysis related to power variation through distance was also evaluated. The results were compared to measurements obtained from the frequency sounding technique.
14
Lundberg, Oscar. « Channel Characteristics Variations from Switching Between Narrow Beams ». Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-65628.
Texte intégralRésumé :
The demand for higher throughput and lower latency in telecommunication systems is growing. Upcoming telecommunication systems will operate at higher frequencies (above 15 GHz) compared with previous systems (below 6 GHz). Antenna arrays will be employed in upcoming systems for increased link budget (coverage) and multiple input multiple output channels. This implies that narrow beams will be used. Beam tracking and beam steering is necessary to follow the user equipment. It is hypothesised that changing beam direction changes the channel condition for the communication link. In this work beam changes in data gathered with a 5G testbed is analysed at both 15 GHz and 28 GHz. The results show that the channel is indeed affected by beam changes. Statistical results of the conducted analysis are presented followed by specific examples on how the channel is affected by the beam changes. Knowledge on how the channel is affected by beam changes is of interest when designing systems for beam selection. The results show a nearly threefold increase of rank changes immediately after a beam change at 15 GHz. The probability for a rank change up or down is found to be equal. At 28 GHz the metric used for channel richness is singular value ratio. The statistical results show that the difference in singular value ratio before and after a beam change is increased by a factor 2. It is also shown that grating lobes may have a significant effect on the channel richness when changing beam direction.
15
Wallace, Richard James. « Theoretical, computational and experimental analysis of the deflagration plasma accelerator and plasma beam characteristics ». Diss., This resource online, 1991. http://scholar.lib.vt.edu/theses/available/etd-08062007-094408/.
Texte intégral
16
Catravas, Palmyra E. (Palmyra Evangeline). « MIT 3.3 GHz relativistic klystron amplifier : experimental study of input cavity and beam characteristics ». Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/34063.
Texte intégralRésumé :
Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1994.Includes bibliographical references (leaves 74-75).
by Palmyra E. Catravas.
M.S.
17
Menefy, Luke. « Investigation of Reactive Powder Concrete and it's Damping Characteristics when Utilised in Beam Elements ». Thesis, Griffith University, 2008. http://hdl.handle.net/10072/365692.
Texte intégralRésumé :
Reactive Powder Concrete (RPC) is a relatively new ultra high strength concrete with a
wide range of capabilities. Currently it is used in high performance applications where
either impact resistance, high durability and/or member size are governing factors in
design. The relatively high cost, required production control, and lack of industry
knowledge have generally precluded its widespread use in more common engineering
applications. Accordingly, the major component of this Thesis aims to contribute new
knowledge with respect to the understanding of the material behaviour and damping
characteristics of RPC. To achieve this goal a staged experimental study was
undertaken encompassing the following (1) the production and material behaviour
including a parallel study on the durability of RPC in an aggressive environment (2) the
static performance and damping characteristics of RPC when utilised in beam elements.
The initial component of the investigation involved several trial mix programmes to
ascertain the viability of RPC production using local Queensland materials. A further
large scale production programme of RPC was carried out utilising two mixer types:
(1) vertical pan mixer representing a precast mix and (2) a mobile inclined drum mixer
representing an onsite mix. The results indicated that the onsite application of RPC was
viable and resulted in only a minor reduction in characteristic strengths when
compared to precast operations. A parallel experimental study investigating the relative
performance of RPC immersed in acidic solutions indicated that the range of RPC’s
investigated were more susceptible to sulphuric acid attack when compared to a
standard high strength concrete (HSC) used in the investigation.
Following verification of RPC characteristic strengths, twenty three test beams were
produced as part of a large scale RPC production programme. These test beams were
incrementally loaded to failure under simply supported conditions during which static
measurements were observed both under load and upon the removal of load. The results
indicated that the fibre reinforced (FR) RPC test beams exhibited a higher load
capacity, an increase in first cracking loads, significantly reduced crack widths and an
overall reduction in shear behaviour when compared to the non-fibre reinforced (NF)
RPC and HSC test beams.
Concurrent free vibration tests through the use of an impulse force hammer were
carried out during the static loading of each of the twenty three test beams in an effort
to ascertain the damping characteristics throughout the various levels of test beam
damage. A new program using analytical and theoretical techniques was developed to
analyse the excitation response histories (ERH) obtained at each load increment, the
program was found to be more efficient when compared to previous analysis methods. A
method of assessing the current and previous analysis methods was also incorporated
within the program enabling the user to compare the damping ratio determined through
the various analysis methods.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Griffith School of Engineering
Science, Environment, Engineering and Technology
Full Text
18
Wang, Phillip Hua-Kuan. « The applications of component mode analysis on the response characteristics of a flexible connected beam ». Thesis, Georgia Institute of Technology, 1985. http://hdl.handle.net/1853/17572.
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Ayzatskiy, N., A. Dovbnya, V. Zakutin, N. Reshetnyak, V. Romas'ko, I. Chertishchev, V. N. Boriskin, V. Mitrochenko, A. B. Galat et I. Khodak. « Experimental investigation on the time characteristics of an electron beam formed in the magnetron gun with a secondari-emission cathode ». Thesis, Национальный научный центр "Харьковский физико-технический институт" (ННЦ ХФТИ), 2007. http://openarchive.nure.ua/handle/document/9244.
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20
Osborne, Robert. « A theoretical study of the propagation characteristics of some optical waveguides by the beam propagation method / ». Thesis, McGill University, 1986. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=65992.
Texte intégral
21
Schnur, Christopher. « Electron Beam - Powder Bed Fusion Of Alloy 718 : Influences Of Contour Parameters On Surface And Microstructural Characteristics ». Thesis, Högskolan Väst, Avdelningen för Industriell ekonomi, Elektro- och Maskinteknik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:hv:diva-14318.
Texte intégralRésumé :
Additive Manufacturing (AM) is an uprising manufacturing process for parts with complex geometries and low production quantities. Within the layer-wise building process, less additional processes are needed, to produce the parts. This allows a building of parts within a reasonable time- and costs-range. Especially industries, such as aerospace industry, can profit from AM. Electron beam – Powder bed fusion (EB-PBF) is a common technique, within AM, to produce metallic parts out of special alloys such as Alloy 718. This superalloy is a Nickle-Iron based alloy that has high mechanical properties, even in elevated temperatures (up to 650ºC). The combination of such material properties with high geometrical freedom creates new opportunities for the industry. However, it must be noted that a significant drawback of AM-techniques is the need for post-processing because of surface roughness- and microstructural characteristics. Commonly, the produced parts utilize mechanical post process such as milling to provide good surface roughness and dimensional accuracy. To reduce the surface roughness in the contour region, and therefore reduce the amount of mechanical post-processing, the present survey elaborates the effect of relevant parameters on contours such as the number of contours, scanning speed, focus offset and beam current. By using Design of Experiments (DOE), two batches were carried out: one screening batch and a two-level-full factorial design. In those batches, 15×15×15 mm cubes were printed with various parameters and, after that, analysed by using White light interferometry (WLI), Optical microscopy (OM) and Scanning electron microscopy (SEM). Furthermore, the program ImageJ was used to perform porosity and melt pool measurements. It had been observed that the number of contours had quite a considerable impact on the final surface roughness and the number of defects. Samples with two contours, instead of only one, tend to have a lower surface roughness. Nevertheless, the parameters and their interaction were found to have fundamental effects on the resulting surface roughness and microstructure.
22
Shahali, Hesam. « Assessment of the bactericidal effect of biomimicked nanopillars of cicada wings on titanium implants ». Thesis, Queensland University of Technology, 2020. https://eprints.qut.edu.au/204245/1/Hesam_Shahali_Thesis.pdf.
Texte intégralRésumé :
Biofilm formation is the major causes of infection in implants. This research presented nanopillars architecture to eliminate the bacteria attachment based on mechanical interaction. Advanced microscopy techniques (e.g. HIM and SEM and AFM) were employed to characterize the cicada wings' nanopillars and find the optimum geometry with the highest bactericidal effect. Electron beam lithography was used to mimic and fabricate versatile geometry of titanium nanopillars for orthopaedic application. It is proposed that the biomimicked titanium nanopillars have an excellent bactericidal effect in the same manner as cicada wings. The titanium nanopillars were biocompatible with human cells.
23
Nowakowski, Krzysztof A. « Laser beam interaction with materials for microscale applications ». Link to electronic thesis, 2005. http://www.wpi.edu/Pubs/ETD/Available/etd-121205-135626/.
Texte intégralRésumé :
Dissertation (Ph.D.)--Worcester Polytechnic Institute.Keywords: laser beam characteristics; heat transfer; hole profile; MEMS; hole formation; laser micromachining; laser microdrilling; plasma effects; silicon; 304 stainless steel; Fourier theory; lattice-phonon vibration. Includes bibliographical references. (p.379-390)
24
Lopez, Jay. « Optimizing the Mechanical Characteristics of Bamboo to Improve the Flexural Behavior for Biocomposite Structural Application ». DigitalCommons@CalPoly, 2012. https://digitalcommons.calpoly.edu/theses/902.
Texte intégralRésumé :
Global awareness and preservation have spurred increasing interest in utilizing environmentally friendly materials for high-performance structural applications. Biocomposites pose an appealing solution to this issue and are characterized by their sustainable lifecycles, biodegradable qualities, light weight, remarkable strength, and exceptional stiffness. Many of these structural qualities are found in applications that exhibit flexural loading conditions, and this study focuses on improving the bending performance of engineered biocomposite structures. The current application of biocomposites is increasing rapidly, so this expanding research explores other natural constituent materials for biocomposite structures under flexural loading.
The renewable material investigated in this study was experimentally and numerically validated by optimizing the mechanical characteristics of bamboo fibers in biocomposite structures under flexural loading conditions through various thermal and organic chemical treatment methods. Therefore, bending performance of a biocomposite truss and I-beam are analyzed to demonstrate the benefits of utilizing optimally treated bamboos in their design.
To accomplish this goal, the first task consisted of treating bamboos by thermal and chemical means to determine the resulting effects on the compressive and tensile mechanical properties through experimental testing. Results indicated a significant improvement in strength, stiffness, and weight reduction. An extensive analysis determined the optimal treatment method that was utilized for flexural loading conditions.
The second task entailed studying the flexural behavior of the optimally treated bamboo in two geometric configurations, a hollow cylinder and veneer strip, to determine the resultant properties for the truss and I-beam structure. The effect of node location on flexural performance was also studied to establish design guidelines for the applied structures. Bending tests indicated that node location affects the strength and stiffness of the hollow cylindrical configuration but has minimal effects on the veneer strip. Observations discovered by this study were employed into the designs of the applied structures that yielded excellent mechanical performance through flexural testing.
The final task required conducting a finite element analysis in Abaqus/CAE on the performance of each structural application to validate experimental results. A conclusive analysis revealed good agreement between the numerical method and experimental result.
25
Spickermann, Sven [Verfasser], Oswald [Gutachter] Willi et Alexander [Gutachter] Pukhov. « Laser-Driven Ion Beam Characteristics and Dose Measurements for Medical Applications / Sven Spickermann ; Gutachter : Oswald Willi, Alexander Pukhov ». Düsseldorf : Universitäts- und Landesbibliothek der Heinrich-Heine-Universität Düsseldorf, 2019. http://d-nb.info/119960724X/34.
Texte intégral
26
Shih, Hoi Wai. « Damage assessment in structures using vibration characteristics ». Thesis, Queensland University of Technology, 2009. https://eprints.qut.edu.au/30319/1/Hoi_Shih_Thesis.pdf.
Texte intégralRésumé :
Changes in load characteristics, deterioration with age, environmental influences and random actions may cause local or global damage in structures, especially in bridges, which are designed for long life spans. Continuous health monitoring of structures will enable the early identification of distress and allow appropriate retrofitting in order to avoid failure or collapse of the structures. In recent times, structural health monitoring (SHM) has attracted much attention in both research and development. Local and global methods of damage assessment using the monitored information are an integral part of SHM techniques. In the local case, the assessment of the state of a structure is done either by direct visual inspection or using experimental techniques such as acoustic emission, ultrasonic, magnetic particle inspection, radiography and eddy current. A characteristic of all these techniques is that their application requires a prior localization of the damaged zones. The limitations of the local methodologies can be overcome by using vibration-based methods, which give a global damage assessment. The vibration-based damage detection methods use measured changes in dynamic characteristics to evaluate changes in physical properties that may indicate structural damage or degradation. The basic idea is that modal parameters (notably frequencies, mode shapes, and modal damping) are functions of the physical properties of the structure (mass, damping, and stiffness). Changes in the physical properties will therefore cause changes in the modal properties. Any reduction in structural stiffness and increase in damping in the structure may indicate structural damage. This research uses the variations in vibration parameters to develop a multi-criteria method for damage assessment. It incorporates the changes in natural frequencies, modal flexibility and modal strain energy to locate damage in the main load bearing elements in bridge structures such as beams, slabs and trusses and simple bridges involving these elements. Dynamic computer simulation techniques are used to develop and apply the multi-criteria procedure under different damage scenarios. The effectiveness of the procedure is demonstrated through numerical examples. Results show that the proposed method incorporating modal flexibility and modal strain energy changes is competent in damage assessment in the structures treated herein.
27
Shih, Hoi Wai. « Damage assessment in structures using vibration characteristics ». Queensland University of Technology, 2009. http://eprints.qut.edu.au/30319/.
Texte intégralRésumé :
Changes in load characteristics, deterioration with age, environmental influences and random actions may cause local or global damage in structures, especially in bridges, which are designed for long life spans. Continuous health monitoring of structures will enable the early identification of distress and allow appropriate retrofitting in order to avoid failure or collapse of the structures. In recent times, structural health monitoring (SHM) has attracted much attention in both research and development. Local and global methods of damage assessment using the monitored information are an integral part of SHM techniques. In the local case, the assessment of the state of a structure is done either by direct visual inspection or using experimental techniques such as acoustic emission, ultrasonic, magnetic particle inspection, radiography and eddy current. A characteristic of all these techniques is that their application requires a prior localization of the damaged zones. The limitations of the local methodologies can be overcome by using vibration-based methods, which give a global damage assessment. The vibration-based damage detection methods use measured changes in dynamic characteristics to evaluate changes in physical properties that may indicate structural damage or degradation. The basic idea is that modal parameters (notably frequencies, mode shapes, and modal damping) are functions of the physical properties of the structure (mass, damping, and stiffness). Changes in the physical properties will therefore cause changes in the modal properties. Any reduction in structural stiffness and increase in damping in the structure may indicate structural damage. This research uses the variations in vibration parameters to develop a multi-criteria method for damage assessment. It incorporates the changes in natural frequencies, modal flexibility and modal strain energy to locate damage in the main load bearing elements in bridge structures such as beams, slabs and trusses and simple bridges involving these elements. Dynamic computer simulation techniques are used to develop and apply the multi-criteria procedure under different damage scenarios. The effectiveness of the procedure is demonstrated through numerical examples. Results show that the proposed method incorporating modal flexibility and modal strain energy changes is competent in damage assessment in the structures treated herein.
28
Aridogan, Mustafa Ugur. « Performance Evaluation Of Piezoelectric Sensor/actuator On Investigation Of Vibration Characteristics And Active Vibration Control Of A Smart Beam ». Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12612005/index.pdf.
Texte intégralRésumé :
In this thesis, the performance of piezoelectric patches on investigation of vibration characteristics and active vibration control of a smart beam is presented. The smart beam is composed of eight surface-bonded piezoelectric patches symmetrically located on each side of a cantilever aluminium beam.
At first, vibration characteristics of the smart beam is investigated by employment of piezoelectric patches as sensors and actuators. Smart beam is excited by either impact hammer or piezoelectric patch and the response of the smart beam particular to these excitations is measured by piezoelectric patches used as sensors. In order to investigate the performance of piezoelectric patches in sensing, the measurements are also conducted by commercially available sensing devices.
Secondly, active vibration suppression of the smart beam via piezoelectric sensor/actuator pair is
considered. For this purpose, system identification of the smart beam is conducted by using four piezoelectric patches as actuators and another piezoelectric patch as a sensor. The designed robust controller is experimentally implemented and active vibration suppression of the free and first resonance forced vibration is presented.
Thirdly, active vibration control of the smart beam is studied by employment of piezoelectric patches as self-sensing actuators. Following the same approach used in the piezoelectric sensor/actuator pair case, system identification is conducted via self-sensing piezoelectric actuators and robust controller is designed for active vibration suppression of the smart beam. Finally, active vibration suppression via self-sensing piezoelectric actuators is experimentally presented.
29
Huang, Chih-Jen, et 黃志仁. « Characteristics of electron beam and dosimetry in total skin electron beam irradiation ». Thesis, 1995. http://ndltd.ncl.edu.tw/handle/58284506278150191409.
Texte intégral
30
Shen, Chan-Han, et 沈昌翰. « Characteristics of ion-beam-sputtered optical thin films ». Thesis, 1995. http://ndltd.ncl.edu.tw/handle/04278710086474026162.
Texte intégral
31
Gwo-Guey, Wu, et 吳國貴. « Effects of characteristics of on R.C cantilever beam ». Thesis, 1993. http://ndltd.ncl.edu.tw/handle/44111468012952557388.
Texte intégral
32
Yu, Chi-Sheng, et 余齊盛. « On the vibration characteristics of micro free-free beam ». Thesis, 2004. http://ndltd.ncl.edu.tw/handle/42076224917442882527.
Texte intégral
33
Huang, Ying-Hsiu, et 黃英修. « Localized Electrochemically Deposited Cantilever Beam and It’s Fatigue Characteristics ». Thesis, 2005. http://ndltd.ncl.edu.tw/handle/33949616806044319155.
Texte intégralRésumé :
碩士大葉大學
機械工程研究所碩士班
93
Localized electrochemical deposition method can be used in the fabrication of micro-sized structure with high aspect ratio. As the process is getting more and more popular, the automatic control utilizing computer programming not only can speed up the process but also increase the variety of the fabricated structures. A new methodology in controlling the movement of the anode in order to improve the surface uniformity and reduce the porosity inside the deposited structure was proposed in this thesis. This control algorithm was implemented employing LabVIEW. The fundamental resonance frequency of the fabricated microstructure in cantilever configuration was determined by using base excitation of a piezoelectric actuator platform. Therefore, the apparent Young’s modulus and porosity of the microstructure can be inferred from the measured resonance frequency. Furthermore, the outer appearance of the microstructure was also examined employing SEM. Finally, the fatigue strength of the deposited material was evaluated by exciting the microcantilever beam in harmonic oscillation with an attached mass at the free end to increase the dynamic loading effect.
34
WU, CHAO KAI, et 吳朝凱. « Pilot Decontamination Techniques Based on Beam-domain Channel Characteristics ». Thesis, 2016. http://ndltd.ncl.edu.tw/handle/35302487185669831016.
Texte intégralRésumé :
碩士國立中正大學
通訊工程研究所
104
The upcoming 5G systems is expected to use large-scale antenna arrays to increase the user’s data rate and system capacity. With a large number of antennas, channel estimation becomes a very critical design issue due to the adverse effects of pilot contamination. The following are some of the problems facing the existing channel estimation methods studied in the literature: 1. The complexity of signal processing on spatial domain is very high, because UEs have to estimate all the channels of each antenna. 2. Channels are frequency selective. 3. It is not easy to obtain the second-order statistics of channels and the correlation between the UEs that are needed in some of the existing methods. In this thesis, the channel estimation issue is investigated using the signal processing in the beam-domain; thanks to the salient feature of channel sparsity of high-frequency bands, only a few beam channels need to be estimated for a user and that can be exploited to reduce the pilot contamination. In this thesis, the following pilot decontamination techniques are proposed. 1. Beam-set Overlapping Allocation (BOLA) 2. Inter-cell Interference Mitigation Allocation (ICIMA) 3. Maximum Beam Power Based Allocation (MBPBA) 4. Less Aggressive Pilot Reuse Allocation (LAPRA) 5. Random Pilot Allocation (RPA) The only required information of the above five methods is the user’s beam channel energy. After the performance evaluation on the ray-tracing channel model of Bern city of Switzerland, we observe that the best method is MBPBA. The RPA method has the least complexity yet has a rather good performance in terms of overhead and normalized square error.
35
Pu, Ta-Chun, et 浦大鈞. « A Planar Shaped-Beam Antenna using Leaky-Wave Characteristics ». Thesis, 2007. http://ndltd.ncl.edu.tw/handle/33171150912397895774.
Texte intégralRésumé :
博士國立交通大學
電信工程系所
95
In this thesis, the shaped-beam antennas were investigated systematically using theoretical analysis and experimental measurement. The basic structure of the shaped-beam antenna contains a line source, taken as an excitation source, embedded in an air substrate sandwiched between a metal reflector and a grating made of metallic or dielectric material. Due to the contribution of leaky wave caused by the grating and direct wave radiating directly from the line source, such a shaped-beam antenna can radiate uniform electromagnetic field pattern over a rectangular plane in front of the antenna. In addition to the fabrication and measurement for the radiation characteristics of this antenna, the rigorous mode-matching method was employed to study the electromagnetic fields within the structure and the radiation far-field pattern, as well. Furthermore, the sensitivity analysis for the parameters including the geometric structure and electrical property of the dielectric material was taken into account to understand the tolerance of this antenna during fabrication. Since this antenna can radiate uniform coverage over a rectangle footprint, it can be a good candidate for serving as the antenna of a hyper LAN (local area network) access point in millimeter wave applications.
36
Chen, Yu-Chia, et 陳佑嘉. « Study on Fundamental Dynamic Characteristics of Axially Loaded Beam Members ». Thesis, 2009. http://ndltd.ncl.edu.tw/handle/78055823162546891039.
Texte intégralRésumé :
碩士朝陽科技大學
營建工程系碩士班
97
Bernoulli and Timoshenko beam theories are the two common theories used in structural practices. The differences between two theories are generally minor but they can be significant for results associated with slender members and within the relatively high frequency region. It is investigated in this study, the difference of responses predicted by the two theories with various slenderness ratios and under different levels of axial forces, emphasizing the varying trends of the natural frequencies. It is concluded that frequencies by Bernoulli beam are irrelevant to the slenderness ratio while Timoshenko theory includes effect of such factor. Besides, frequencies by Timoshenko beam approach limiting values regardless the boundary conditions applied to the member. Applications of simple trends of dynamic characteristics or relations of certain quantities may potentially be useful to serve as a reference method in evaluating member integrity.
37
Hsueh, I.-Ting, et 薛屹廷. « Characteristics and an Experimental Program of Torsional Type Beam Bracing ». Thesis, 2013. http://ndltd.ncl.edu.tw/handle/55679282913792549847.
Texte intégralRésumé :
碩士國立臺灣科技大學
營建工程系
101
The use of torsional bracings could effectively inhibits instability and increases both strength and ductility of beams. There are two types of torsional bracing: nodal and continuous. This paper presents a parametric study on the continuous torsional bracing of steel beams restrained by floor slab by referring to formulas specified in AISC code. In addition, an experimental program is established. Under the condition of 15 cm solid RC slab and commonly used configuration of shear connectors between steel beam and slab, it is found that: (1) torsional bracing stiffness and the joint stiffness between beam and slab have minor effect on torsional bracing systems; (2) flexural stiffness of web of steel section has significant effect on torsional bracing systems; (3) flexural stiffness of web can be increased by using stiffeners on the web; (4) higher beam width and web thickness reduces the requirement of the torsional bracing systems; (5) larger section depth and flange thickness increase the requirement of the torsional bracing; (5) The experimental program designed 14 beam specimens to investigate beam behavior under different combination of torsional stiffness and section stiffness.
38
Wu, Chia-Hsing, et 吳家興. « Growth and Characteristics of Selenide Compounds by Molecular Beam Epitaxy ». Thesis, 2015. http://ndltd.ncl.edu.tw/handle/03622307654698455672.
Texte intégralRésumé :
博士大同大學
光電工程研究所
103
This dissertation is devoted to CuGaSe2 and GaSe thin films grown using molecular beam epitaxy. For CuGaSe2 thin films, the growth and physical properties were studied. CuGaSe2 were obtained with varying metallic ratio of (Cu/Cu+Ga) from 0.23 to 0.75. When the metallic ratio increases from 0.23 to 0.75, surface morphology of CuGaSe2 thin films implies the transformation of crystal structure from GaSe-like to CuGaSe2 (Cu-rich). The optical performances exhibit the optimum growth condition for CGSe2 is obtained. Following, this condition is used to grow CuGaSe2 thin films on molybdenum coated stainless steel(SS) substrate. Two kinds of stainless steel substrates (304SS、430SS ) were used. The different of stainless 430SS and 304SS is the content with/ without chromium (Cr), respectively. CuGaSe2 and Cu2-xSe phases were observed by Raman scattering measurement. The photoluminescence emission of donor-acceptor pair exhibits a red shift, which implies the different of content ratio in these samples. Temperature dependence PL was used to measure activation energy of CGS grown on two substrates. The activation energy (Ea) of CGS2 grown on 430SS and 304SS were estimated as 41 and 30 meV. The CuGaSe2 thin film growth on 430SS was better than 304SS substrate. The second parts focus on the growth of GaSe epitaxial single crystal thin films. The GaSe epilayer during growth were monitored by in situ reflection high-energy electron diffraction (RHEED). Streak RHEED patterns demonstrated a flat and crystalline sample surface Lattice constant in a-axis was approximately 0.375±0.012 nm, which was correspondedwith single-crystal GaSe. Furthermore, two kinds structure of GaSe thin films which were correlated with the m-axis and a-axis of hexagonal was observed by RHEED after 15 min. The single crystal GaSe was verified using X-ray diffraction and high-resolution cross-section transmission electron microscopy. The full width at half-maximum of peak (0002) which was defined in the XRD rocking-curve spectrum of GaSe epilayer was obtain around 207 arcsec. The epitaxial growth of GaSe demonstrated the feasibility of growing large-area ultrathin epilayers. The surface effect of selenium pretreated sapphire substrate (Se-sapphire) at low temperature (500℃) was investigated. GaSe thin films were deposited on Se-sapphire. The growth rate of GaSe/Se-sapphire was 5 times than GaSe/sapphire. It implies that Se terminated sapphire surface assisted GaSe deposition. Moreover, the improvement conductivity of GaSe was investigated by doping copper and zinc. The conductivity of intrinsic GaSe, GaSe:Cu, and GaSe:Zn were 10-7, 10-6, and 10-4 (Ω×cm)-1, respectively, by four point probe measurement. The reason is the incorporation of metal cations (Cu and Zn) increasing hole concentration. The crystal structure became worse when the concentration of dopant increased, especially in the doped copper series. In future work, based on these works, the ultra-thin film of the epitaxial will be demonstrated. Finally, the photocurrent in metal-semiconductor-metal (MSM) photo-detectors based on layered GaSe will be generated.
39
Chiu, Chung-Yu, et 邱琮祐. « Using Polymer Gel Dosimeter to Assess the Clinical Beam Characteristics ». Thesis, 2014. http://ndltd.ncl.edu.tw/handle/85473051421948598109.
Texte intégralRésumé :
碩士中臺科技大學
醫學影像暨放射科學系暨研究所
102
The introduction of the beam intensity control concept in current radiotherapy techniques has increased the complexity of treatment planning; thus, small-field dose measurement has become increasingly vital. Clinical dose verification tools measure small-field beams, if the spatial resolution is insufficient, then the measured dose values are lower than the actual values because of the volume averaging effect. Polymer gel dosimetry has been widely studied. It is the only dose measurement tool that provides 3D dose distribution, estimates the absorbed dose based on the extent of polymerization reaction after small-field beam irradiation, and evaluates clinical beam performance. Therefore, the objective of this study is to use a N-isopropylacrylamide (NIPAM) gel dosimeter to conduct beam performance measurements of percentage depth dose (PDD), beam flatness, and symmetry for photon beams with field sizes of 3 × 3 cm2 and 4 × 4 cm2 . The computed tomography (CT) scans were used to readout the gel dosimeters. After the gel receives a 0 – 10 Gy dose, the dose response curve exhibits a linear response with an R2 of 0.997. In the PDD measurement, the NIPAM gel dosimeter and GafchromicTM EBT3 radiochromic film display high consistency in the region deeper than build-up region. A gel dosimeter dose profile at a 5-cm depth for different fields has a 3% lower flatness and symmetry measurement compared to that of the GafchromicTM EBT3 film. However, the overall measurement remains similar. During the gamma evaluation under a 3%/3 mm dose-difference/distance-to-agreement (DTA) standard, the pass rates of polymer gel dosimeter to the TPS and EBT3 film were both higher than 96%. Compared to the film, the polymer gel dosimeter obtained all beam characteristic information in only one irradiation and image acquisition, which provides greater convenience than the film does. In addition, because the gel is tissue-equivalent, gel dosimeters do not have the energy dependence problems of radiochromic films; thus, the practical use of NIPAM polymer gel dosimeters is enhanced in clinical dose verification.
40
Lin, Chia-Hung, et 林佳宏. « Optical Characteristics of MQW Nanorod Fabricated by Focused Ion Beam ». Thesis, 2007. http://ndltd.ncl.edu.tw/handle/01249876329832659434.
Texte intégral
41
Chen, Chyn-Jye, et 陳勤傑. « Seismic Resistance Characteristics of Steel Reinforced Concrete Beam-to-Column Connection ». Thesis, 1996. http://ndltd.ncl.edu.tw/handle/04214203472442695569.
Texte intégralRésumé :
碩士國立臺灣科技大學
營建工程技術學系
84
This reported research work is aimed at enhancing the ductility and workability of beam-to-column connection of SRC structure. An enlarged plastic zone around the connection is obtained by utilizing the concept of super ductile connection method. The design of this type connection is based on providing the moment capacity equal to that of moment demand so that a uniform stress state can be achieved around the connection. The workability of this type connection is greatly improved by using steel plates instead of using steel reinforcing bars. Based on large size experimental studies, it is found that the proposed connection method is able to achieve a better ductility and keep the same performance on the stiffness and strength as compared to the conventional method. Improper details are frequently observed in the construction site, and this may affect the workability and the seismic resistance capacity greatly. It is believed that the placements of reinforcing bars need special attention in order to keep good workability and in the same time provide good seismic resistance capability. The reported research also provided suggested detailing for beam-to-column connections of the SRC structure.
42
He, Feng-Zhou, et 何豐州. « Growth and Characteristics of SnSex Thin Films by Molecular Beam Epitaxy ». Thesis, 2015. http://ndltd.ncl.edu.tw/handle/27209106948700083892.
Texte intégralRésumé :
碩士大同大學
光電工程研究所
103
In this work, the fabrication of SnSex and (001)-oriented SnSe2 thin films on c-sapphire by molecular beam epitaxy (MBE) was studied. The growth processes were monitored by in situ reflection high energy electron diffraction (RHEED). Streaky RHEED patterns of SnSe2 show the films were flat. The lattice constant of a-axis was approximately 3.71 ± 0.1Å, which is consistent with that of SnSe2 crystalline. The crystal structure was also observed by X-ray diffraction (XRD) analysis for lattice constant c of 6.15Å, the c/a = 1.685. The SnSex films were measured by using Raman spectrum, SEM and four point probe method for components, morphology and electric properties. In addition, the relationship between stoichiometry and substrate temperature was investigated by X-ray photoelectron spectroscope (XPS). At temperature < 400℃, SnSe2 phase films was grown. The growth conditions of SnSex thin film were observed in this research, the optimization conditions of SnSe2 thin films are substrate temperature = 300℃, Tin cell temperature = 980℃, Selenium cell temperature = 203℃. At the conditions, the SnSe2 single phase thin films were deposited successfully.
43
Chang, Y.-Hsin, et 張譯心. « Characteristics of Ga2O3/GaSe hetero-structure grown by molecular beam epitaxy ». Thesis, 2016. http://ndltd.ncl.edu.tw/handle/10386775591927283825.
Texte intégralRésumé :
碩士大同大學
電機工程學系(所)
104
Layered semicomductor GaSe is a candidate of ultra thin divice where exhibits a stable atomic-thin layer. In a layer of GaSe, gallium and selenium are bonded in the sequence of Se-Ga-Ga-Se with covelent and ionic bounds. Layer and layer of GaSe are boned by Van der Waals force. It is discovered that the physical properties of GaSe have changed when exposed in atmosphere over time. A thin, uncontrollable native oxide bonding on the surface. It leads us to propose a metal/oxide/semiconductor (MOS) structure. In this work, the growth and characterization of Ga2O3/GaSe hetero-structures grown on c-sapphire by plasma assisted molecular beam epitaxy. Two methods were employed: firstly, we propose the oxygen replace the selenium by oxygen plasma surface treament. Reactive oxygen species are intended to secceed selenium and construct a thin gallium oxide on the surface of GaSe. It is noticed that the structure of GaSe was demaged and etched. GaSe layer was grown under lightly gallium-rich conditions. Native gallium is intended to be provided as a source for constructing Ga2O3. Various growth temperature : 300 oC, 450 oC, 500 oC, 550 oC, was test, to construct high-temperature growth oxide and lower-temperature growth selenium compound. Raman spectra of gallium-rich GaSe and Ga2O3/GaSe show reliable shift at A11g, E12g mode. In photoluminescence (PL) spectrua, luminescence of gallium-rich GaSe was enhanced by constructing heterostructure. X-ray photoelectron spectroscopy (XPS) and Auger depth profile was used to confirm the existence of Ga2O3. At last, crystal structure of the heterostructure was discussed by transmmision electron microscopy (TEM). Heterostructure was obsurved with two different structure of GaSe epitaxy layers. The atomic arrangment of GaSe, which close to gallium oxide, is reconstructed.
44
Lam, Dennis, et F. Fu. « ¿Behaviour of semi-rigid composite beam ¿ column connections with steel beams and precast hollow core slabs ». 2006. http://hdl.handle.net/10454/5777.
Texte intégralRésumé :
This paper is concerned with the behaviour of beam ¿ column connections of steel ¿ concrete composite beams with precast hollow core slabs. Experiments were carried out to investigate the joint rotation characteristics and ultimate moment capacity of these connections. Details of the test specimens, instrumentation, test set-up and test procedures are described. Results obtained for the connection moment capacity, rotation capacity and failure modes are presented. It is found that through proper design and detailing, these simple steel connections display the characteristics of a semi-rigid connection with very little extra cost.
45
Nelligan, Raelene Ann. « Investigation into the dosimetric characteristics of MOSFETs for use for in vivo dosimetry during external beam radiotherapy ». 2009. http://hdl.handle.net/2440/55292.
Texte intégralRésumé :
This thesis investigates the response to ionising radiation, of p-type Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) (REM Oxford (UK)) and a reader system developed by the Centre for Medical Radiation Physics, The University of Wollongong, to determine their feasibility for measurements of dose during radiotherapy treatment (in vivo dosimetry (IVD)). Two types of MOSFET probes were used -"single sensitivity", for measuring low doses, and "dual sensitivity", to measure both high and lose doses. Sensitivity, linearity of response with dose, and response changes with accumulated dose and direction of incident radiation (angular dependence) were investigated. The average sensitivity reduction over the lifetime of the probes was 22.37% with a standard deviation of 0.63%. This reduction in sensitivity can be corrected for by the use of "drift equations". MOSFETs have a limited "lifetime" due to saturation effects with increasing accumulated dose. Saturation occurred at an average of 40 Gray (Gy) accumulated dose, for the high sensitivity probes investigated. The high sensitivity probes were linear within 1.6% for doses between 5 and 140 cGy, and 3.8% for the high sensitivity probes for doses between 50 and 500 cGy. Drift (changes in readings with time since irradiation due to electronic processes) over the long-term (from hours to weeks following irradiation) has been previously well characterised in the literature. This work focuses on shortterm drift, within the first few seconds or minutes following irradiation, being the most clinically relevant for in vivo measurements. Drift is investigated for various reading methods, such as reading frequency, and delays between irradiation and readings. It is shown that sensitivity, and consequently dose determination, is significantly influenced by the reading methodology. During the first five minutes following an irradiation, drift increased inversely with delivered dose, and was greater for probes having accumulated dose of > 20 Gy (2.0 -16.2% compared with 1.2 -7.4% for < 20 Gy probes). During the first five minutes following an irradiation, drift increased inversely with delivered dose, and was greater for probes having accumulated dose of > 20 Gy (2.0 -16.2% compared with 1.2 -7.4% for < 20 Gy probes). When two post-irradiation readings were taken following an irradiation, the difference between them generally increased as the time interval between the two readings increased, by up to 8.8%. Delays in taking pre-and post-irradiation readings resulted in drift of up to 5.7% or 9.3% respectively, compared with readings without a delay. These results emphasise the necessity for consistent methodologies between calibration and measurement in the clinical situation. Greater sensitivity was measured with the epoxy bubble, rather than the substrate side, facing the beam. The greatest variation, for orientations other than the bubble side facing directly towards the beam, was 10%, or 5% uncertainty in dose. The variations with angle were found to be reproducible, so that appropriate correction factors could be applied to correct measurements at angles other than with the sensitive area of the probes facing directly towards the radiation beam.http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1368262
Thesis (M.Sc.) -- University of Adelaide, School of Chemistry and Physics, 2009
46
Nelligan, Raelene Ann. « Investigation into the dosimetric characteristics of MOSFETs for use for in vivo dosimetry during external beam radiotherapy ». Thesis, 2009. http://hdl.handle.net/2440/55292.
Texte intégralRésumé :
This thesis investigates the response to ionising radiation, of p-type Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) (REM Oxford (UK)) and a reader system developed by the Centre for Medical Radiation Physics, The University of Wollongong, to determine their feasibility for measurements of dose during radiotherapy treatment (in vivo dosimetry (IVD)). Two types of MOSFET probes were used -"single sensitivity", for measuring low doses, and "dual sensitivity", to measure both high and lose doses. Sensitivity, linearity of response with dose, and response changes with accumulated dose and direction of incident radiation (angular dependence) were investigated.
The average sensitivity reduction over the lifetime of the probes was 22.37% with a standard deviation of 0.63%. This reduction in sensitivity can be corrected for by the use of "drift equations". MOSFETs have a limited "lifetime" due to saturation effects with increasing accumulated dose. Saturation occurred at an average of 40 Gray (Gy) accumulated dose, for the high sensitivity probes investigated.
The high sensitivity probes were linear within 1.6% for doses between 5 and 140 cGy, and 3.8% for the high sensitivity probes for doses between 50 and 500 cGy.
Drift (changes in readings with time since irradiation due to electronic processes) over the long-term (from hours to weeks following irradiation) has been previously well characterised in the literature. This work focuses on shortterm drift, within the first few seconds or minutes following irradiation, being the most clinically relevant for in vivo measurements. Drift is investigated for various reading methods, such as reading frequency, and delays between irradiation and readings. It is shown that sensitivity, and consequently dose determination, is significantly influenced by the reading methodology.
During the first five minutes following an irradiation, drift increased inversely with delivered dose, and was greater for probes having accumulated dose of > 20 Gy (2.0 -16.2% compared with 1.2 -7.4% for < 20 Gy probes).
During the first five minutes following an irradiation, drift increased inversely with delivered dose, and was greater for probes having accumulated dose of > 20 Gy (2.0 -16.2% compared with 1.2 -7.4% for < 20 Gy probes).
When two post-irradiation readings were taken following an irradiation, the difference between them generally increased as the time interval between the two readings increased, by up to 8.8%.
Delays in taking pre-and post-irradiation readings resulted in drift of up to 5.7% or 9.3% respectively, compared with readings without a delay.
These results emphasise the necessity for consistent methodologies between calibration and measurement in the clinical situation.
Greater sensitivity was measured with the epoxy bubble, rather than the substrate side, facing the beam. The greatest variation, for orientations other than the bubble side facing directly towards the beam, was 10%, or 5% uncertainty in dose. The variations with angle were found to be reproducible, so that appropriate correction factors could be applied to correct measurements at angles other than with the sensitive area of the probes facing directly towards the radiation beam.Thesis (M.Sc.) -- University of Adelaide, School of Chemistry and Physics, 2009
47
Chang, Chieh-Ping, et 張傑評. « Characteristics of Nb Superconducting Quantum Interference Device Fabricated by Focused Ion Beam ». Thesis, 2013. http://ndltd.ncl.edu.tw/handle/9j4tp9.
Texte intégralRésumé :
碩士國立中興大學
物理學系所
101
A low-transition-temperature niobium (Nb) Superconducting Quantum Interference Device (SQUID) was made using nanobridges and nano-trench as weak link. The thickness of Nb thin film was about 150 nm. A 125 nm-thick Au layer was deposited on the Nb film by DC magnetron sputtering. The Au layer served as an electrode and a protective layer on the Nb thin film, and increased the accuracy of focused ion beam (FIB) etching. Microbridges with a width of 5 μm were fabricated by photolithography using an argon ion milling system. Then, nanobridges ranging in 80-180 nm wide were fabricated by FIB etching. The voltage-current and voltage-magnetic field chacteristics of SQUID were measured at different temperature. The critical current of SQUID depends on operating temperature and the width of nanobridge. It was found that the critical current reduces significantly when the width of junction is decreased. The applied magnetic field also affect the critical current of SQUIDs. The SQUID shows a peak-to-peak voltage swing of 25 μV. The electrical transport properties of SQUID were measured and discussed.
48
Chen, Cshnb-Ming, et 陳聰明. « Vibration Characteristics of Spinning Annular Plate with Disordered or Mistuned Beam-Stiffeners ». Thesis, 2006. http://ndltd.ncl.edu.tw/handle/6qvfkd.
Texte intégralRésumé :
碩士國立臺灣科技大學
機械工程系
94
The purpose of this paper is to study the vibration characteristic of a spinning annular plate with disordered of mistuned beam-stiffeners. First, via the principle of energy, we derive the equations of motion of the rotating beam and plate. Galerkin’s method is then employed to discretize the equation. The receptance method follows to join the rotating beam and plate, and yield the natural frequencies and mode shapes. In this paper the beams reinforcement one-side on the plate. Numerical results for three combine situation, perfect, with disordered or mistuned. In the same time, analyze the system’s change of natural frequencies and mode shape. Finally, parametric studies of systems are conducted. The results show that adequate number of beams do stiffen the spinning plate. But a mistuned beam has caused frequencies bifurcation. A mistuned beam has caused frequencies increase and decrease when mistuned error was raised or downed. All the results are well interpreted and illustrated from physical viewpoint.
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Wang, Miao-Ci, et 王妙琪. « Monte Carlo Simulation of Photon Beam Characteristics for a Siemens Linear Accelerator ». Thesis, 2009. http://ndltd.ncl.edu.tw/handle/8ehuz2.
Texte intégralRésumé :
碩士國立陽明大學
生物醫學影像暨放射科學系暨研究所
97
Monte Carlo calculation is presently the most accurate method to calculate dose distributions in patients treated with radiation. A prerequisite for such calculations is to have accurate information of the input data, i.e., the phase space data. The primary task of this study is thus using Monte Carlo simulation to obtain the phase space data of radiation beams generated from a medical linear accelerator. The phase space data contain information about the particles’ position, energy, and direction; these are correspondingly represented as the particle fluence, energy fluence, spectrum, and angular distribution. In our simulation of a Siemens Primus M3375 linear accelerator, the BEAM code subroutines of BEAMnrc, BEAMDP and DOSXYZnrc were used respectively, for treatment head simulation, phase space analysis, and phantom dose calculation. Our simulation comprised three parts: First, the treatment head was simulated and the phase space data within a 50cm field, at 100cm distance from the source were saved in files. These simulations were performed for 6MV and 10MV photons, for both open fields and wedged fields of 15�a, 30�a, 45�a, and 60�a physical wedges. Second, the phase space files were analyzed using BEAMDP for particles’ distribution. Finally, the phase space files were taken as the input sources for dose calculation in a water phantom using the DOSXYZnrc subroutine. Depth doses and lateral dose profiles were calculated and compared with measured data for validation. Measured data were acquired under standard conditions for quality assurance using the IBA water tank and Wellhofer farmer type ion chamber. These measured dose distributions were compared with the simulated results, and free simulation parameters such as the initial electron energy and the spot size can be adjusted to make the simulated results agree with the measured ones. For clinical application, the validated phase space files were used to calculate isodose distributions with three cases of typical radiation technique. The calculated isodose distributions were compared with those computed by the clinical treatment planning system. The results showed that the dose differences between measurements and simulations were less than 2% for depth doses, and less than 3% for dose profiles inside the 80% field size. For clinical cases, comparisons between simulation results and treatment planning system calculations showed that the dose differences were within 3%. It demonstrated that the simulated phase space data were reliable and could be used for clinical patient dose calculations for future investigations.
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CHUNG, CHAO-CHI, et 鐘兆麒. « Quality Characteristics for Effective Source to Surface Distance of LINAC Electron Beam ». Thesis, 2017. http://ndltd.ncl.edu.tw/handle/8h6n34.
Texte intégralRésumé :
碩士中臺科技大學
醫學影像暨放射科學系暨研究所
105
Quality characteristics for effective source to surface distance (SSD) of LINAC electron beam were evaluated in this work. In some cases of extended SSD, output cannot be accurately predicted by using the inverse square law from the nominal source position (X-ray target) because the electrons scatter from various locations such as the scattering foils, the X-ray jaws, and the electron applicator. For most cases of clinical significance, however, the output can be accurately predicted by using the inverse square law from an effective source position. The distance from this effective source position to the patient surface is called the "effective SSD" (SSDeff) and is well known to be a function of beam energy and cone size. We had determined the dependence of SSDeff on various combinations of cone size, and beam energy. An Axesse 6D LINAC was adopted and the four operated factors: beam energy, cone size, dmax, and gap were preset into 3-26 levels, respectively in this work. Thus a total of 6×3×6×26=2808 combinations was considered and condensed to only 207 trials of effective measurements according to Taguchi’s optimal recommendation. Each trial was measured three times to reduce the error and ensure the reproducibility. The derived data were then integrated altogether to compose a 1st-order nonlinear semi-empirical formula with 11 coefficients. The summarized uncertainties were suppressed to below 5 % for the estimation. The comparison between theoretical and practical evaluations was depicted and the correlated discussion were also emphasized point by point to imply the importance of this revised evaluation in clinical field.