• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 1454
  • 847
  • 259
  • 251
  • 176
  • 133
  • 86
  • 45
  • 29
  • 27
  • 25
  • 22
  • 18
  • 15
  • 11
  • Tagged with
  • 3981
  • 594
  • 341
  • 272
  • 262
  • 240
  • 221
  • 207
  • 196
  • 186
  • 184
  • 176
  • 169
  • 160
  • 156
  • 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.
311

Field evaluation of passive capillary samplers in monitoring the leaching of agrochemicals

Brandi-Dohrn, Florian M. 17 November 1993 (has links)
Soil solution samplers have certain inadequacies that limit their range of possible applications. Passive Capillary Samplers (PCAPS), which apply suction to the soil pore-water via a fiber glass wick, have shown promising results in preliminary experiments in regard to collection efficiency of water and of bromide tracers. The objectives of this study were to evaluate PCAPS under non-steady state field conditions with respect to (1) effect of installation procedure and operational characteristics, (2) ability to estimate the soil-water flux, and (3) ability to estimate the mean concentration of agrochemicals. At the same time, samplers were used to (4) evaluate the effect of a cereal rye (Secale cereale (L.)) cover crop on NO₃⁻ leaching. Thirty-two PCAPS and 32 suction cup samplers were installed below the root zone at a depth of 120 cm in a Willamette Variant loam wet soil (fine loamy mixed mesic Pachic Ultic Argixeroll). Samplers were installed in an ongoing cover crop/crop rotation study. Regarding overall performance, flux measurements were within 20 % of the native values as determined by a water balance. The air release from the sample bottles was a point of concern and might have slowed down the sampling rate. The installation procedure introduced bias into volume and concentration measurements of the part of the PCAPS closest to the refilled trench. The leachate concentration as calculated using the arithmetic mean of suction cup sampler measurements holds a significant bias, deviating by up to 97 % for bromide concentrations. Phosphate was not detected by the suction cup samplers indicating that ceramic cups should not be used for phosphate sampling. Matrix and preferential flow could clearly be distinguished using the PCAPS, showing that PCAPS are a valuable tool to assess the hydrology and solute transport mechanisms of a field site. The cover crop reduced NO₃⁻-N leaching significantly at the recommended N rate as evaluated by PCAPS. The cover crop reduced the seasonal mean NO₃⁻-N concentration at the recommended N rate from 13.5 mg LI to 8.1 mg L⁻¹, which is under the E.P.A. drinking water quality standard of 10 mg L⁻¹. The total NO₃⁻-N mass lost under the fallow treatment at the recommended N rate was 48 kg N ha⁻' which compares to 32 kg N ha⁻' under the cover crop treatment. Given the increasing problems with nitrate contamination of ground water, programs to support the cultivation of catch crops in conjunction with nitrogen soil testing should be considered as a relatively easy, effective, and biologically sound means to reduce nitrate concentrations in the recharge to the ground water in agricultural settings. / Graduation date: 1994
312

Improvement of Passivity of Fe - xCr Alloys (x < 10%) by Cycling Through the Reactivation Potential

Ulaganathan, Jaganathan 26 February 2009 (has links)
Classically 13% Cr is required for stable passivity of steel in acidic and neutral solutions. Some authors (Mansfeld, Fujimoto) have published potential cycling procedures that generate thick Cr-rich films. Fujimoto cycles right to the transpassivity potential and back in H2SO4 solution. Our idea is to work close to the reactivation potential where the passive film (Fe2O3) is reductively dissolved to Fe2+. While using an equimolar acetate buffer (pH 4.7), we have obtained new insights into the reactivation process. It is under a kind of thermodynamic control, in that the film cannot be reduced, and the metal cannot be dissolved, faster than would exceed the equilibrium concentration of Fe2+ at the electrode surface. Reductive dissolution leads to gel-like Cr-rich film, but Fe dissolution occurs through it, if formed in a single step. However alternating formation and reductive dissolution of a Fe-rich film assist the formation of a more robust Cr-rich film
313

Optimization of Sweep Visually Evoked Potential (sVEP) in Adults

Yadav, Naveen Kumar January 2008 (has links)
Purpose and hypothesis: The purpose of this study was to optimize and standardize the following parameters of sweep Visually Evoked Potential (sVEP) in adults: criteria for fitting the regression line to estimate threshold, luminance, electrode placement, temporal frequency, sweep direction, presence of fixation target and stimulus area. The hypothesis is that the parameters chosen will have an impact on the measured visual acuity, contrast threshold and on the number of viable sVEP plots. Methods: The Power Diva software, Version 1.9 was used for this study. Five gold cup active electrodes, one reference electrode and one ground electrode were used to measure the Electroencephalography (EEG) signals. Six adult participants (aged 17 to 35 years), with corrected to normal visual acuity and no history of ocular disease took part in each experiment, except for the repeatability experiment in which 3 subjects participated. Four criteria for regression line fitting were compared. Psychophysical thresholds were used to validate the sVEP measures for the different criterion and repeatability of sVEP was estimated for 10 sessions. The effect of luminance (25 cd/m2, 50 cd/m2, 100 cd/m2), electrode placement (Power Diva and ISCEV), temporal frequency (6 Hz, 7.5 Hz, 10 Hz), sweep direction, fixation target and stimulus area were investigated. A repeated measure ANOVA statistical method was used to analyze the average threshold and the number of viable plots out of five active channels for all subjects. Results: Criterion 2 and 3 gave better visual acuity, higher contrast sensitivity, better repeatability and gave results that were closer to the psychophysical threshold than criterion 0 and 1. Luminance of 25 cd/m2 gave significantly fewer viable readings than 50 and 100 cd/m2 while measuring visual acuity (F = 5.11, df = 2, p = 0.0295). Temporal frequency of 7.5 Hz gave significantly more viable readings than 6 and 10 Hz while measuring visual acuity (F = 50.53, df = 2, p < 0.0001) and contrast threshold (F = 9.87, df = 2,p = 0.0043). There was a highly significant interaction of criterion with temporal frequency (F = 1536.98, df = 6, p < 0.0001) while measuring contrast threshold. There was a significant interaction of criterion with sweep direction (F = 4.26, df = 3, p = 0.0231) and for the number of readings (F = 3.75, df = 3, p = 0.0343) while measuring visual acuity. There was an interaction of criterion with sweep direction (F = 4.97, df = 3, p = 0.0136) while measuring contrast threshold at a spatial frequency of 1 cpd. There was a significant effect of fixation target (F = 7.64, df = 1, p = 0.0396) while measuring visual acuity. There was a significant effect of stimulus area (F = 11.78, df = 4, p < 0.0001) on the number of readings while measuring contrast threshold. Conclusion: The sVEP parameters chosen do have a significant effect on visual acuity, contrast threshold and on the number of viable readings. The following parameters are recommended in adults on the basis of results; Criterion 2 or 3 for fitting regression line (C2 - regression line fitted from the signal peak amplitude to the last data point with a signal to noise ratio (SNR) >1; C3 – similar to criterion 2, but the threshold should be within sweep range used), luminance of 50 or 100 cd/m2 , either Power Diva (PD) or International Society for Clinical Electrophysiology of Vision (ISCEV) electrode placement, temporal frequency of 7.5 Hz, either sweep direction, measurement with the central fixation target, larger stimulus area.
314

Multidimensional generalized-ensemble algorithms for complex systems

Mitsutake, Ayori, Okamoto, Yuko 04 June 2009 (has links)
No description available.
315

Evaluation of a Potential Site for a Small Hydropower Plant Located in the BioBio North Irrigation System, Chile

Gunnar, Sofie January 2010 (has links)
This project considers an evaluation of a potential site for a small hydropower plant located in the BioBio north irrigation system, Chile. The purpose was to analyze the potential and constraints in harnessing the energy of an existing infrastructure of irrigation canals for electrical production. The site was analyzed technically, economically and managerially. Before this project nothing was done and therefore the investigations are a main part of the project. A preliminary design for the plant was proposed and the project was named the Minicentral Quillaileo-Mininco. Investigations showed a flow variation of 1.62-2.2 m3 per second and a gross head of 44.3 meters. Evaluation gave a possible capacity of 840 kW producing 5 800 MWh annually. Appropriate electromechanical equipment is a Francis turbine with a diameter of 0.5 meter directly coupled to a 1000 rpm synchronous generator. The penstock recommended is a DN 1200 Flowtite GRP. The station is to be fully automatic and connected to the national grid. The revenue is based on analysis of the past three year’s electrical market. The costs are based on budget proposals, statistical values and local comparisons. The economical analysis, based on a discount rate of 12% and life span of 35 years, gives a positive cash flow within eight years and a simple payback period of 5 years. The project will have a NPV value of 444 900 USD, IRR 14.70% and B/C of 1.2. Cost per kW will be 2 980 USD. The project is recommended to be further developed.
316

Importance of estimation of market potential : a case of Sandvik Tooling

Tegnér, Mi January 2011 (has links)
Abstract   Title: Importance of estimation of market potential- a case of Sandvik Tooling   Level: Bachelor Degree in BusinessAdministration, 15 ECTS-Credits in Marketing   Author: Mi Tegnér   Supervisor: Akmal Hyder   Date: 2011-05   Aim: The aim of this thesis is to study in which waySandvik Tooling and certain other international companies’ measure and estimatethe market potential   Method: I have used a qualitative method. This meansthat I have focused on the big picture rather than solely on parts from thecollected material. The qualitative method was based on interviews with 12respondents, both within Sandvik AB and with employees from other internationalcompanies. Furthermore, I have made an interconnection between my empirical andtheoretical part in order to draw conclusions on the findings.   Result &amp; Conclusions: The study shows some importantfactors, which may affect a company´s effort to measure and estimate the marketpotential. They are; gaps may easily appear when customers and companies havedifferent views on quality, price and productivity, too large amounts ofinformation, the importance of new ideas and perspectives. A company canminimize their problems and any errors within the collected material if theywork after similar framework, consisting of clear structures and methodologies.   Suggestions for future research: Future research could be to do asimilar study, to identify methods to measure and estimate market potential forSandvik Tooling but within an international setting. Then compare this resultwith my result to see in which way the perception of market potential differsin the different countries.   Contribution of the thesis: From my research, I have got an understandingthat the process of measuring and estimating companies market potential is notan easy mission. Especially among the companies, which consist of differentbusiness areas, product areas and segment areas. I hope the study will beinteresting for the employee´s working with market potential and businessdevelopment, to see that people within the same company may have differentviews about this subject. I also believe that managers in general would benefitfrom this study, to understand that their employees would like to see a moresimilar framework within the company, when it comes to measure and estimatemarket potential. During this thesis, I found a deficiency of scientificarticles about the subject, measuring a company´s market potential. It had beeninteresting to see if my results corresponded to previous results in the samesubject.   Key words: business areas, benchmarking, estimation,market potential, market shares, measuring
317

Direct Fitting of Analytical Potential Functions to Diatomic Molecular Spectroscopic Data

Seto, Jenning January 2000 (has links)
The standard practice of spectroscopic data reduction is generally to fit data to level energy expansions in terms of the vibrational and rotational quantum numbers. However, the utility of such expressions is limited because they extrapolate poorly and they need very large sets of parameters, many of which have no independent physical significance. One method of addressing these problems is to fit the spectroscopic data directly to analytical potential energy functions incorporating the natural physical behaviour of the molecule in question. Although there have been a number of successful applications of this approach, there are still certain problems associated with the types of potential forms being used. This thesis will explore some of these problems and determine how effective the potential forms being used are for a number of specific cases.
318

Optimization of Sweep Visually Evoked Potential (sVEP) in Adults

Yadav, Naveen Kumar January 2008 (has links)
Purpose and hypothesis: The purpose of this study was to optimize and standardize the following parameters of sweep Visually Evoked Potential (sVEP) in adults: criteria for fitting the regression line to estimate threshold, luminance, electrode placement, temporal frequency, sweep direction, presence of fixation target and stimulus area. The hypothesis is that the parameters chosen will have an impact on the measured visual acuity, contrast threshold and on the number of viable sVEP plots. Methods: The Power Diva software, Version 1.9 was used for this study. Five gold cup active electrodes, one reference electrode and one ground electrode were used to measure the Electroencephalography (EEG) signals. Six adult participants (aged 17 to 35 years), with corrected to normal visual acuity and no history of ocular disease took part in each experiment, except for the repeatability experiment in which 3 subjects participated. Four criteria for regression line fitting were compared. Psychophysical thresholds were used to validate the sVEP measures for the different criterion and repeatability of sVEP was estimated for 10 sessions. The effect of luminance (25 cd/m2, 50 cd/m2, 100 cd/m2), electrode placement (Power Diva and ISCEV), temporal frequency (6 Hz, 7.5 Hz, 10 Hz), sweep direction, fixation target and stimulus area were investigated. A repeated measure ANOVA statistical method was used to analyze the average threshold and the number of viable plots out of five active channels for all subjects. Results: Criterion 2 and 3 gave better visual acuity, higher contrast sensitivity, better repeatability and gave results that were closer to the psychophysical threshold than criterion 0 and 1. Luminance of 25 cd/m2 gave significantly fewer viable readings than 50 and 100 cd/m2 while measuring visual acuity (F = 5.11, df = 2, p = 0.0295). Temporal frequency of 7.5 Hz gave significantly more viable readings than 6 and 10 Hz while measuring visual acuity (F = 50.53, df = 2, p < 0.0001) and contrast threshold (F = 9.87, df = 2,p = 0.0043). There was a highly significant interaction of criterion with temporal frequency (F = 1536.98, df = 6, p < 0.0001) while measuring contrast threshold. There was a significant interaction of criterion with sweep direction (F = 4.26, df = 3, p = 0.0231) and for the number of readings (F = 3.75, df = 3, p = 0.0343) while measuring visual acuity. There was an interaction of criterion with sweep direction (F = 4.97, df = 3, p = 0.0136) while measuring contrast threshold at a spatial frequency of 1 cpd. There was a significant effect of fixation target (F = 7.64, df = 1, p = 0.0396) while measuring visual acuity. There was a significant effect of stimulus area (F = 11.78, df = 4, p < 0.0001) on the number of readings while measuring contrast threshold. Conclusion: The sVEP parameters chosen do have a significant effect on visual acuity, contrast threshold and on the number of viable readings. The following parameters are recommended in adults on the basis of results; Criterion 2 or 3 for fitting regression line (C2 - regression line fitted from the signal peak amplitude to the last data point with a signal to noise ratio (SNR) >1; C3 – similar to criterion 2, but the threshold should be within sweep range used), luminance of 50 or 100 cd/m2 , either Power Diva (PD) or International Society for Clinical Electrophysiology of Vision (ISCEV) electrode placement, temporal frequency of 7.5 Hz, either sweep direction, measurement with the central fixation target, larger stimulus area.
319

Model of MOSFET in Delphi

Prokhorov, Andrey, Gerzheva, Olesya January 2011 (has links)
In modern times the increasing complexity of transistors and their constant decreasingsize require more effective techniques to display and interpret the processes that are inside of devices. In this work, we are modeling a two‐dimensional n‐MOSFET with a long channeland uniformly doped substrate. We assume that this device is a large geometry device so that short‐channel and narrow‐width effects can be neglected. As a result of the thesis, a demonstration program was built. In this executable file, the user can choose parameters of the MOSFET‐model: drain and gate voltage, and different geometrical parameters of the device (junction depth and effective channel length). In the advanced regime of the program, the user can also specify the model re‐calculation parameter, doping concentration in n+ and bulk regions. The program shows the channel between the source and drain region with surface diagrams of carrier density and potential energy as an output. It is possible to save all calculated results to a file and process it in any other program, for example, plot graphics in Matlab or Matematica. The model can be used in lectures that are related to semiconductor physics in order to explain the basic working mechanisms of MOSFETs as well as for further detailed analysis of the processes in MOSFETs. It is possible to use our modeling techniques to rebuild the model in another computer language, or even to build other models of transistors, performing similar calculations and approximations. It is possible to download the executable file of the model here: http://studentdevelop.com/projects/MOSFET_model.zip
320

A gravity model for trade between Vietnam and twenty-three European countries

Thai, Tri Do January 2006 (has links)
This thesis examines the bilateral trade between Vietnam and twenty three European countries based on a gravity model and panel data for years 1993 to 2004. Estimates indicate that economic size, market size and real exchange rate of Vietnam and twenty three European countries play major role in bilateral trade between Vietnam and these countries. Distance and history, however, do not seem to drive the bilateral trade. The results of gravity model are also applied to calculate the trade potential between Vietnam and twenty three European countries. It shows that Vietnam’s trade with twenty three European countries has considerable room for growth.

Page generated in 0.0666 seconds