• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 1716
  • 685
  • 345
  • 236
  • 194
  • 153
  • 55
  • 31
  • 25
  • 23
  • 19
  • 18
  • 16
  • 16
  • 15
  • Tagged with
  • 4400
  • 418
  • 383
  • 382
  • 324
  • 315
  • 292
  • 283
  • 265
  • 244
  • 229
  • 187
  • 179
  • 174
  • 165
  • 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.
241

Stress recovery during exposure to natural sounds and environmental noise

Alvarsson, Jesper, J. January 2009 (has links)
<p>Research suggests that physiological stress reactions may be reduced by visual impressions from natural environments as compared to urban or built-up environments. The present experiment tested whether similar effects might be found by auditory stimulation. Forty university students were tested in an experiment with four consecutive recovery sessions after stressful mental arithmetic tests. The independent variables were type of sound during recovery. The sound was either a natural sound environment (sounds from water and birdsong, at 50 dBA), or three types of noisy environments (traffic noises at 50 or 80 dBA or ambient background sound at 40 dBA). The main dependent variables were physiological recovery from stress, as measured by decrease in heart rate (HR) and skin conductance level (SCL) after the stressful arithmetic test. The main result was that SCL reduction was faster during nature sounds than during the various noises. For HR, no systematic effects of experimental sounds were found. The result for SCL lends some support the hypothesis that exposure to natural sounds facilitate physiological stress recovery.</p> / Sarcade
242

Tillväxt utan nyanställningar

Wirenstål, Mats, Olsson, Marcus January 2006 (has links)
<p>När IT-kraschen inträffade under 2001 fick den påtagliga konsekvenser för svensk ekonomi. Tillväxten, som tidigare varit hög, fick negativa värden och sysselsättningsökningen avstannade. När sedan tillväxten återhämtade sig, efter knappt ett år, förblev sysselsättningsnivån oförändrad. Ännu idag (dec 2005) har sysselsättningen inte visat några markanta förbättringar. Vi vill med vår uppsats närmare kartlägga var denna tillväxt utan nyanställningar uppkommer. Detta har vi gjort genom att skapa oss en överblick över hela arbetsmarknaden och därefter analyserat vilka sektorer som markant ökat sin produktion per anställd utan att nyanställa. Vi har även använt oss av en analys för hela tillverkningsindustrin där vi undersökt om det skett en arbetskraftomfördelning inom sektorn som lett till en produktionsökning. Vi fann att den enda riktigt tydliga tillväxten utan nyanställningar har skett i sektorn ”fastigheter och företagstjänster”. Arbetskraftsförflyttning mellan branscherna inom tillverkningsindustrin har inte påverkat produktiviteten nämnvärt.</p>
243

Micro Raman Spectroscopy of Annealed Erbium Implanted GaN

Vajpeyi, Agam P., Chua, Soo-Jin, Fitzgerald, Eugene A., Tripathy, S. 01 1900 (has links)
Wurtzite GaN epilayers grown by metal organic chemical vapor deposition on sapphire substrates were subsequently ion implanted with Er to a dose of 5×10¹⁵ cm⁻². The implanted samples were annealed in nitrogen atmosphere at different temperatures to facilitate recovery from implantation related damage. In this paper we report the annealing behavior of Erbium implanted GaN by using micro Raman spectroscopy and optimized annealing condition. We have observed almost full damage recovery of the crystalline quality of Er implanted GaN after annealing at 1000°C for 2 minute. This observation is further confirmed by using AFM images. / Singapore-MIT Alliance (SMA)
244

Two-stage heat engine for converting waste heat to useful work /

Finger, Erik J. January 2005 (has links)
Thesis (Ph. D.)--University of Rhode Island, 2005. / Typescript. Includes bibliographical references (leaves 120-121).
245

Mineral Nutrient Recovery from Pyrolysis Co-Products

Wise, Jatara Rob 2012 May 1900 (has links)
Pyrolysis is the thermo-chemical degradation of biomass in an oxygen-free environment to product liquid, gaseous, and solid co-products. The liquid co-product, known as bio-oil, can be used as a transportation fuel. The gaseous co-product, known as synthesis gas, can be used to power the pyrolysis reactor or other machinery. The solid co-product, known as bio-char, has been studied as an amendment to enhance soil physical and chemical properties and nutrient status. Although previous publications have described the beneficial effects of pyrolysis bio-char on soil physical and chemical properties, relatively little has been published on the recovery of mineral nutrients from pyrolysis co-products. This work quantified the recovery of feedstock nutrients (P, K, Ca, and Mg) and micronutrients (Na, Zn, Fe, Cu, and Mn) from pyrolysis co-products from various feedstocks using three distinct pyrolysis reactor designs. The reactors comprised a laboratory-scale fixed-bed reactor and two fluidized-bed reactors located in College Station, TX and Wyndmoor, PA. Nutrient recoveries, on a feedstock basis, were calculated for a comparison of reactor efficiencies. In addition to nutrient recoveries, physical and chemical properties of input biomass and of bio-char generated by each reactor were characterized through ultimate and proximate analyses. For the fixed-bed reactor, results revealed variation among feedstocks for the recoveries of feedstock sources of macronutrients and Na, Fe, and Cu in pyrolysis co-products. Variation among species was also detected for the recoveries of feedstock sources of P, K, Ca, Mg, and Fe in pyrolysis co-products for samples pyrolyzed using the Wyndmoor reactor. For the College Station reactor, recoveries of feedstock sources of P, K, Ca, and Mg in pyrolysis co-products did not vary among species, but Zn did vary. Ultimate and proximate analyses of biomass and bio-chars generated by the three reactors revealed variation among species. Additionally, the results showed that the recovery of feedstock nutrients varied by reactor design. Statistical analysis revealed high correlations and linear relationships between the recovery of nutrients and reactor mass and energy efficiency and feedstock fiber properties.
246

Black liquor conbustion in Karft Recovery Boiler-Numerical Modelling

Fakhrai, Reza January 2002 (has links)
QC 20100601
247

Stress recovery during exposure to natural sounds and environmental noise

Alvarsson, Jesper, J. January 2009 (has links)
Research suggests that physiological stress reactions may be reduced by visual impressions from natural environments as compared to urban or built-up environments. The present experiment tested whether similar effects might be found by auditory stimulation. Forty university students were tested in an experiment with four consecutive recovery sessions after stressful mental arithmetic tests. The independent variables were type of sound during recovery. The sound was either a natural sound environment (sounds from water and birdsong, at 50 dBA), or three types of noisy environments (traffic noises at 50 or 80 dBA or ambient background sound at 40 dBA). The main dependent variables were physiological recovery from stress, as measured by decrease in heart rate (HR) and skin conductance level (SCL) after the stressful arithmetic test. The main result was that SCL reduction was faster during nature sounds than during the various noises. For HR, no systematic effects of experimental sounds were found. The result for SCL lends some support the hypothesis that exposure to natural sounds facilitate physiological stress recovery. / Sarcade
248

Concepts and definitions for product recovery : analysis and clarification of the terminology used in academia and industry

Lindahl, Mattias, Sundin, Erik, Östlin, Johan, Björkman, Mats January 2006 (has links)
This paper presents and clarifies the academic and industrial terminology used in the area of product recovery. It is concluded that there exist many different concepts and definitions in academia and industry, several of which are unclearly defined. Given this, a new way to define product recovery is presented through the use of a model. This model is based on actual industrial product recovery cases, existing academic product recovery concepts and definitions and product design theory. The presentation contains a holistic model that can be used for describing and analyzing different product recovery scenarios. In addition, several industry cases are presented as a verification of the model.
249

A Study of the Composition of Carryover Particles in Kraft Recovery Boilers

Khalaj-Zadeh, Asghar 19 January 2009 (has links)
Carryover particles are partially/completely burned black liquor particles entrained in the flue gas in kraft recovery boilers. Understanding how carryover particles form and deposit on heat transfer tube surfaces is critically important in the design and operation of a recovery boiler. The tendency for a carryover particle to deposit on a tube surface depends on the particle temperature and composition at the moment of impact. This study was the first to examine systematically how carryover particle composition changes with the black liquor chemistry and burning conditions. The effect of black liquor composition and particle size, gas composition (O2 and SO2 concentrations) and temperature on the composition of carryover particles were studied using an Entrained Flow Reactor (EFR). Field studies were conducted on three operating boilers, where an air-cooled probe was used to collect carryover samples at the superheater entrance. The results show that the chloride (Cl) and potassium (K) contents in carryover particles were linearly proportional to their contents in black liquor. Cl and K were depleted during black liquor combustion due mainly to the vaporization of NaCl and KCl. The depletion of Cl is about three times greater than that of K. The significant depletion of Cl implies that carryover particles contain much less Cl, and hence, are less sticky than previously expected from black liquor composition. A dynamic model was also developed to predict the composition of carryover particles as a function of black liquor composition and burning conditions. Based on the data obtained experimentally in this study, the kinetic equations for the oxidation of sulphide available in the literature were modified and incorporated into the model to improve its sulphide and sulphate predictions. The model predicts the main components of carryover particles formed in both the EFR and three operating recovery boilers reasonably well, except for the K content, which is slightly over-predicted at high O2 concentrations (or high particle temperatures). Based on the predicted composition, it is possible to determine the thermal properties of carryover and to assess its fouling propensity in the boiler. The information helps boiler manufacturers and operators to identify locations in the boiler where massive carryover deposition may occur and to devise appropriate control strategies to minimize fouling and to improve boiler thermal efficiency.
250

Study on the Role of a Cationic Organic Dispersant in Bitumen Recovery from Mineable Oil Sands Ores

Tseng, Henry Unknown Date
No description available.

Page generated in 0.0608 seconds