• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 1103
  • 351
  • 333
  • 127
  • 88
  • 64
  • 46
  • 32
  • 24
  • 20
  • 12
  • 12
  • 11
  • 9
  • 8
  • Tagged with
  • 2811
  • 330
  • 278
  • 246
  • 235
  • 222
  • 188
  • 173
  • 169
  • 144
  • 127
  • 124
  • 122
  • 122
  • 121
  • 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.
421

Influence of ankle orthoses on ankle joint motion and postural stability before and after exercise

Jorden, Ryan A. 05 May 2000 (has links)
Ankle injuries comprise more than 15% of all sports injuries worldwide. The efficacy of the ankle taping for injury prevention has long been under scrutiny as numerous studies have shown that tape rapidly loses its ability to constrain ankle motion with exercise. Consequently, ankle braces (orthoses) are being used with increasing frequency for the prevention and functional management of ankle injuries. However, the motion restraining qualities of ankle orthoses have not been widely evaluated in closed kinetic chain environments under physiologic loads. The primary purpose of this study was to compare the abilities of four ankle orthoses (ankle taping, lace-up brace, semirigid orthosis and hybrid brace) against a control condition (no brace or tape) to control subtalar and talocrural motion during running on a laterally-tilted treadmill at 16.2 km/h before and after exercise. It has been hypothesized that ankle orthoses make a secondary contribution to injury prevention through enhanced proprioception. The secondary purpose of this study was to quantify the effects of the aforementioned ankle orthoses on postural stability during single-limb stance following a bout of exercise. Fifteen healthy university students (8 men and 7 women) with no history of significant ankle injuries (age, mean �� SD: 22.9 �� 3.9 years) volunteered to participate in this study. Three-dimensional kinematic data were captured with an active infrared digital camera system sampling at 120 Hz. To address the first question, data analyses were performed using 2way univariate (Ankle Orthoses x Pre/Post-Exercise x Subjects) (5 x 2 x 15) repeated measures analysis of variance (ANOVA) to determine the existence of differences among three closed and four open kinematic chain dependent measures before and after exercise. Maximum inversion angles (MAXINV) were similar for all ankle orthoses, with no orthosis limiting inversion during tilted treadmill running significantly more than another, or compared to the control condition, either before or after exercise (p>.05). Pre-exercise MAXINV group means and standard deviations during treadmill running ranged from 6.8 �� 3.4 deg with the Royce Medical Speed Brace to 9.5 �� 4.1 deg in the tape condition; post-exercise MAXINV mean values ranged from 7.6 �� 3.2 deg for the Aircast Sport Stirrup to 9.1 �� 4.6 deg with closed basketweave tape. While not statistically significant (p=0.10), ankle taping provided the least amount of inversion restraint, both before and after the exercise bout. The MAXINV angles measured during treadmill running (8.2 �� 4.0 deg) and open chain inversion AROM measured with a goniometer (34.5 �� 6.2 deg) were not related (r=-0.0003). The compressive forces present during closed kinetic chain activity are known to increase joint stability and thus may explain why MAXINV under dynamic varus loads was so much less in magnitude than inversion AROM measured under open kinetic chain conditions. The nonlinear relationship of these two variables supports our contention that reports of the motion controlling properties of ankle orthoses measured in open kinetic chain environments should not be used to infer the response characteristics of these same orthoses under dynamic, physiologic loads. To address the second question, data were analyzed using 3-way univariate (Ankle Orthoses x Pre/Post-Exercise x Eyes Open/Closed x Subjects) (5 x 2 x 2 x 15) repeated measures ANOVAs. Subjects' postural stability was assessed using a Biodex Balance System with eyes open and eyes closed conditions, before and after an exercise bout. The ankle orthoses evaluated did not influence postural stability as measured by mediolateral sway index, anteroposterior sway index, and overall sway index. Removal of visual perception via blindfolding resulted in significant decreases in all three measures of postural stability (p=.001). There was poor association among the closed chain postural stability parameters and the open chain AROM measures. These correlations ranged from r=.04 to .17, indicating minimal relationship between the amount of AROM permitted by the orthoses and postural stability as quantified by this method. / Graduation date: 2000
422

The effect of running speed and turning direction on lower extremity joint moment

Lee, Ki-Kwang 19 November 1998 (has links)
Fast medio-lateral movements, frequent in a number of sports activities, are associated with lower extremity injuries. These injuries may occur as a result of excessive musculoskeletal stresses on the joints and their associate structures. The purpose of this study was to investigate the effect of running speed and turning movement on the three-dimensional moments at the ankle, knee, and hip joints. Data were collected using video cameras and force plate. Eight male recreational basketball players were tested during slow (1.5 m/s), moderate (3.0 m/s), and fast running (4.5 m/s) and when cutting to the right or left (+60, +30, 0, -30, and -60��). The inverse dynamics approach was used to integrate the body segment parameter, kinematic and force plate data, and to solve the resultant joint moments. At the ankle joint, inversion/eversion, dorsi/plantar flexion, and internal/external rotation moments of the ankle joint increased with running speed (p<.05). At the knee joint, flexion/extension and abduction/adduction moments increased with running speed except flexion moment that decreased with running speed (p<.05). At the hip joint, internal/external rotation, flexion/extension, and abduction/adduction moments increased with running speed (p<.05). In medial cutting movements, greater abduction moments of the ankle, adduction moments of the knee and external rotation and adduction of the hip were found (p<.05). In lateral cutting movements, greater inversion and adduction moments of the ankle, abduction moments of the knee and hip were found (p<.05). These findings reinforce the intuitive notion that fast medio-lateral turning movements produce substantially greater musculoskeletal loading on the joint structures than does straight running and consequently have greater potential for inducing lower extremity injuries such as ankle sprain or anterior cruciate ligament injury. / Graduation date: 1999
423

Some fundamental considerations concerning noise reduction and range in radar and communication

January 1948 (has links)
Stanford Goldman. / "December 15, 1947." "Presented at the National Electronics Conference, Chicago, Illinois, November, 1947." / Includes bibliographical references. / Army Signal Corps Contract No. W-36-039 sc-32037.
424

Sound Transmission Through A Fluctuating Ocean: A Modal Approach

Udovydchenkov, Ilya A. 21 December 2007 (has links)
Sound transmission through a fluctuating deep ocean environment is considered. It is assumed that the environment consists of a range-independent background, on which a small-scale perturbation, due for example to internal waves, is superimposed. The modal description of underwater sound propagation is used extensively. The temporal spread of modal group arrivals in weakly range-dependent deep ocean environments is considered. The phrase "modal group arrival" refers to the contribution to a transient wavefield corresponding to a fixed mode number. It is shown that there are three contributions to modal group time spreads which combine approximately in quadrature. These are the reciprocal bandwidth, a deterministic dispersive contribution, and a scattering-induced contribution. The latter two contributions are shown to be proportional to the waveguide invariant beta, a property of the background sound speed profile. The results presented are based mostly on asymptotic theory. Some extensions of the asymptotic modal theory are developed. These theoretical results are shown to agree well with full-wave numerical wavefield simulations and available exact mode theoretical results. Theoretical predictions of modal group time spreads are compared to estimates derived from data that was collected during the 2004 LOAPEX experiment. The effects of deficiencies in the receiving array on estimates of modal group time spreads are discussed. It is shown that in spite of array deficiencies in the LOAPEX measurements it is possible to estimate modal group time spreads for almost all propagating modes and these estimates agree well with results obtained from numerical simulations and the developed theory. The effect of ocean internal waves on sound speed fluctuations is also considered, motivated by the observation that the amount of energy being scattered along the propagation path is sometimes greater in the experimental data than predicted by numerical simulations and theory. It is shown that the usual assumption that the potential sound speed gradient is proportional to the squared buoyancy frequency is often not a good approximation.
425

Simulation Assisted Robotic Orthopedic Surgery in Femoroacetabular Impingement

Chang, Ta-Cheng 27 July 2011 (has links)
Femoroacetabular impingement (FAI) has been increasingly recognized as a cause of early hip osteoarthritis. FAI is characterized by pathologic contact between the femur and acetabular rim during hip join movement, caused by morphological abnormalities. Arthroscopic technique has become increasingly popular for FAI surgical treatment because of its minimal invasiveness. However, it involves cumbersome procedures and over- or under-resection are likely to occur. To tackle this issue, robot-assisted FAI arthroscopy is a well suited approach because it results in high accuracy and reproducible surgical outcomes. This dissertation provides new approaches and methods for the current challenges in the development of robot-assisted FAI arthroscopy. The study has three objectives: 1) to develop a robust calibration method for the A-mode ultrasound probe used for noninvasive bone registration, 2) to develop a bone registration simulator for verifying the registration accuracy and consistency for any given registration point-pattern, and 3) to develop a hip range of motion simulation system that returns the virtual range of motion and determines the bone resection volume. Carefully designed calibration procedures and simulation experiments have been conducted during the study of this research. From the experimental results, the developed ultrasound calibration method successfully reduces the registration errors and is proved to be robust. The results from the registration simulator indicate that the pattern with widely distributed points lead to better registration accuracy and consistency. The hip range of motion simulation system results in acceptable accuracy and successfully generates the resection volume. With further modifications, the ultrasound probe can be successfully calibrated with the developed method, and will be applied for noninvasive bone registration. The registration simulator can also be served as a useful tool for determining the optimized registration point-pattern, which can lead to reduced surgical trauma and registration time. Finally, the developed range of motion simulation system can allow the surgeon to evaluate the surgical outcome and to determine the resection volume even before the surgery begins. To conclude, this dissertation provides useful approaches, methods, and software for developing robot-assisted FAI arthroscopy.
426

Asymmetry in Elite Snowboarders : A Study comparing Range of Motion in the Hip and Spine, Power in Lower Extremities and Circumference of Thigh

Danielsson, Tommy January 2010 (has links)
Snowboarding is a relatively young sport and has grown since the birth in the 1960-70. Today, snowboarding still is a lifestyle to many, but also an accepted mainstream sport and has been an Olympic sport since the Olympic Winter Games in Nagano, Japan 1998 (18,35,36). The movement pattern and body position is asymmetric, since you stand sideways with the front foot ahead of the rear foot in the line of direction (14,18,28). Several studies that have investigated the biomechanics of snowboarding have showed that the loading of the lower extremities are different in the front leg compared to the rear leg during riding (14,18, 22,23,28). The purpose of this study was to investigate if the asymmetric body position in snowboarding causes differences between front and rear leg considering; circumference of thigh, range of motion (ROM) in the hip joints, power in lower extremities, or causes asymmetrical ROM in the spine in the test group compared to the control group. Two groups were used, one test group consisting of ten elite snowboarders (n=10) with an average age of 18 years, and one control group consisting of eight high level skiers (n=8), average age 17,25 years. All subjects were students at Malung/Sälen Alpine Elite Gymnasium. Measurements of ROM in hip and spine were made with a myrin incline goniometer and universal plastic goniometer. A one leg countermovement jump (CMJ) was made as a test of power in the lower extremities using Ivar ump &amp; speed analyzer. Measurements of circumference of thighs were made using a soft tape measure. The results show significant differences in four of the ten measurements in test group and in two of the ten measurements in the control group. There are significant differences in hip passive flexion (P&lt;0,05) and adduction(P&lt;0,05) in both groups (Tables 2,3) suggesting that in these movements there are individual differences. The one leg CMJ and circumference of thigh shows significant differences, (P&gt;0,05) and (P&lt;0,001), between front and rear leg in the test group (Table 2), but no such differences can be seen in the control group (Table 3) suggesting that these differences may be caused by the asymmetrical body position during snowboarding.
427

Issues in Assessing Short-Term Water Supply Capabilities of Reservoir Systems

Schnier, Spencer Thomas 2010 May 1900 (has links)
The Texas Commission on Environmental Quality (TCEQ) uses a Water Availability Modeling System (WAM) to support long-term regional and statewide water resources planning and management. The water availability studies are based on the modeling capabilities of the Water Rights Analysis Package (WRAP). This research improves the understanding of decision support tools for short-term river basin management. Current reservoir storage levels must be considered to assess short-term frequencies and reliabilities. Conditional reliability modeling (CRM) is used to assess the likelihood of meeting targets for instream flow, reservoir storage, water supply diversion and hydroelectric power generation in the near future (next month to next several years), conditioned upon preceding storage. This study uses data for the Brazos River Basin from the TCEQ WAM System to assess key complexities of water supply reliability analysis in general and conditional reliability modeling in particular. These complexities include uncertainties associated with river basin hydrology, estimating yield-reliability relationships for individual reservoirs and multiple reservoir systems, conventional long-term planning versus short-term adaptive management and other modeling and analysis issues. The modeling capabilities of WRAP were expanded to support near real-time operation of dams under various stream flow conditions. The sensitivity to changes in modeling options is assessed for short and long-term simulations. Traditional and newly developed methodologies for estimating firm yields and water supply reliabilities are evaluated. Guidelines are developed regarding the practical application of firm yield analyses and conditional reliability modeling. Important applications of this research include real-time decision support during drought and routinely recurring operational planning activities. A case study of the drought of 2009 uses the CRM features of WRAP for these applications.
428

Local Features for Range and Vision-Based Robotic Automation

Viksten, Fredrik January 2010 (has links)
Robotic automation has been a part of state-of-the-art manufacturing for many decades. Robotic manipulators are used for such tasks as welding, painting, pick and place tasks etc. Robotic manipulators are quite flexible and adaptable to new tasks, but a typical robot-based production cell requires extensive specification of the robot motion and construction of tools and fixtures for material handling. This incurs a large effort both in time and monetary expenses. The task of a vision system in this setting is to simplify the control and guidance of the robot and to reduce the need for supporting material handling machinery. This dissertation examines performance and properties of the current state-of-the-art local features within the setting of object pose estimation. This is done through an extensive set of experiments replicating various potential problems to which a vision system in a robotic cell could be subjected. The dissertation presents new local features which are shown to increase the performance of object pose estimation. A new local descriptor details how to use log-polar sampled image patches for truly rotational invariant matching. This representation is also extended to use a scale-space interest point detector which in turn makes it very competitive in our experiments. A number of variations of already available descriptors are constructed resulting in new and competitive features, among them a scale-space based Patch-duplet. In this dissertation a successful vision-based object pose estimation system is extended for multi-cue integration, yielding increased robustness and accuracy. Robustness is increased through algorithmic multi-cue integration, combining the individual strengths of multiple local features. Increased accuracy is achieved by utilizing manipulator movement and applying temporal multi-cue integration. This is implemented using a real flexible robotic manipulator arm. Besides work done on local features for ordinary image data a number of local features for range data has also been developed. This dissertation describes the theory behind and the application of the scene tensor to the problem of object pose estimation. The scene tensor is a fourth order tensor representation using projective geometry. It is shown how to use the scene tensor as a detector as well as how to apply it to the task of object pose estimation. The object pose estimation system is extended to work with 3D data. A novel way of handling sampling of range data when constructing a detector is discussed. A volume rasterization method is presented and the classic Harris detector is adapted to it. Finally, a novel region detector, called Maximally Robust Range Regions, is presented. All developed detectors are compared in a detector repeatability test.
429

Attityder till Metrias föreslagna omstrukturering av det samlade produktutbudet

Jonsson, AnnaKatarina, Lund, Kristin January 2009 (has links)
Marknadsföring är ett omfattande begrepp som innefattar mycket mer än bara reklam och försäljning. I praktiken är kommunikationen med interna och externa aktörer en oerhört viktig del i marknadsföringsarbetet. Kommunikation mellan företagets ledning och anställda är viktig så att företagets vision genomsyrar hela verksamheten. Olika enheter/avdelningar bör kommunicera med varandra så att samtliga är bekanta med hela företagets produktutbud. Det är även viktigt att företaget når ut med sitt budskap till sina externa aktörer om hur de vill bli uppfattade. Kundernas uppfattning och känslor inför företaget som helhet skapar företagets profil. Tidigt i köpprocessen spelar marknadsföringen en central roll då den har till uppgift att göra kunden medveten om produktens existens. Informationen som sänds ut till kunden ska även ge en viss kunskap om produkten.   Metria har ett mycket brett utbud av produkter och tjänster. För att presentera det komplexa utbudet på ett tydligt och begripligt sätt har Metrias marknadsgrupp arbetat fram ett produktstrukturförslag. Syftet med produktstrukturen är att skapa medvetenhet hos anställda och kunder om Metrias alla produkter och tjänster. Innan den framtagna produktstrukturen marknadsförs, vill marknadsgruppen veta vad anställda och kunder har för åsikter om den, om den är tydlig och om begreppen som används är begripliga.   Författarna fick i uppdrag av Metria att undersöka hur anställda och kunder uppfattar produktstrukturförslaget. Undersökningen har legat till grund för denna uppsats. Undersökningen skedde främst genom telefonintervjuer och enstaka besöksintervjuer. Metria valde själva ut respondenter som skulle intervjuas och i samarbete med författarna diskuterades aktuella intervjufrågor.   Intervjuerna redovisas var och en för sig i empirikapitlet. I analysdelen sammankopplas empiri med teori kring marknadsföring och kommunikation som författarna anser vara relevant för problemområdet. Författarna diskuterar utifrån detta vikten av att Metria bör bli bättre på att marknadsföra sig alltefter att konkurrensen på marknaden ökar.   I slutsatsen presenterar författarna sina egna tankar och reflektioner kring vad Metria kan göra för att förbättra produktstrukturen utifrån anställdas och kunders synpunkter. / Marketing is a broad concept which includes much more than just advertising and sales. In practice, communication with internal and external stakeholders is a crucial part of marketing efforts. Communication between the management and employees are important to the company's vision permeates the entire operation. Different units / departments should communicate with each other so that all are familiar with the company's entire product range. It is also important that the company reaches out with its message to their external stakeholders on how they want to be perceived. Perceptions and feelings about the enterprise as a whole create the company's profile. Early in the purchasing process plays a central role of marketing as it is to make customers aware of the product's existence. The information sent to the customer should also give certain knowledge of the product. Metria has a very wide range of products and services. To present the complex range in a clear and understandable way Metrias market group prepared a product structure proposal. The purpose of the product structure is to create awareness among employees and customers of Metrias all products and services. Before the resultant product structure marketed, the market group wants to know what employees and customers have to say about it, unless it is clear and whether and if the terms that are used are understandable. The authors received a mandate from Metria to examine how employees and customers perceive the product structure of the proposal. The investigation has been the basis of this thesis. The study was done mainly through telephone interviews and occasional visits interviews. Metria chose themselves out respondents who were interviewed, and in cooperation with the authors they discussed the interview questions. The interviews are reported separately in the empirical chapter. The analytical part linked empirical and theory about marketing and communications, which the authors believe to be relevant to the problem area. The authors discuss on the basis of the importance of Metria should be better at promoting themselves as the competition in the market increases.   In the conclusion the authors present their own thoughts and reflections on what Metria can do to improve the product structure along employees and what customers says.
430

Spatially Varying Image Based Lighting by Light Probe Sequences, Capture, Processing and Rendering

Unger, Jonas, Gustavson, Stefan, Ynnerman, Anders January 2007 (has links)
We present a novel technique for capturing spatially or temporally resolved light probe sequences, and using them for image based lighting. For this purpose we have designed and built a real-time light probe, a catadioptric imaging system that can capture the full dynamic range of the lighting incident at each point in space at video frame rates, while being moved through a scene. The real-time light probe uses a digital imaging system which we have programmed to capture high quality, photometrically accurate color images of 512×512 pixels with a dynamic range of 10000000:1 at 25 frames per second. By tracking the position and orientation of the light probe, it is possible to transform each light probe into a common frame of reference in world coordinates, and map each point and direction in space along the path of motion to a particular frame and pixel in the light probe sequence. We demonstrate our technique by rendering synthetic objects illuminated by complex real world lighting, first by using traditional image based lighting methods and temporally varying light probe illumination, and second an extension to handle spatially varying lighting conditions across large objects and object motion along an extended path.

Page generated in 0.0631 seconds