• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 123
  • 84
  • 31
  • 21
  • 17
  • 14
  • 6
  • 4
  • 4
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 359
  • 359
  • 62
  • 51
  • 42
  • 35
  • 31
  • 30
  • 27
  • 25
  • 25
  • 24
  • 22
  • 22
  • 20
  • 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.
101

Energy Optimisation of a Building: a Case Study of Ekebyvallen, Uppsala : Profitable investments in a world with rising energy prices

Enarsson, Pär, Hedenmo, Otto, Sillevis Smitt, Dirk-Jan January 2013 (has links)
Energy prices are on the rise, and with it the interest in saving energy. In the housing sector this means that methods for energy optimising buildings, retrofitting, are increasingly important. There are many studies concerning the retrofitting of buildings built before 2000, but less concerning buildings of more recent date. In cooperation with the housing company Uppsalahem, this report explores minor retrofitting solutions for the apartment buildings in Ekebyvallen/Uppsala which were built 2007. The aim was foremost to find solutions for Ekebyvallen but also to assess the possibilities of applying them to a wider range of buildings. A simulation of the energy balance in one of the buildings in Ekebyvallen was performed with the software VIP energy. The simulation together with a field study show weak spots of the energy usage in the buildings and based on these four retrofitting solutions were proposed. The methods; 1) reducing the airflow in the ventilation units, 2) adjusting the heating in common areas, 3) reducing air leakage out of buildings and 4) adjusting the settings of lighting sensors and timers. All are effectively free from investments and also applicable on buildings with similar issues. Thus, these are effective methods of saving energy and consequently, saving money in recently built buildings. The methods are tailored for Ekebyvallen but are with benefit considered for apartment buildings of both recent date and those built before 2000.
102

The Relationship Between Carbohydrate Restrictive Diets And Body Fat Percentage in the Female Athlete

Lorenzo, Lauren L 22 July 2011 (has links)
Purpose: To assess the dietary intake and body composition of recreational and competitive female athletes, for the purpose of analyzing the relationships between macronutrient intake and body composition.. The main aim was to determine the relationship between caloric intake, carbohydrate (CHO) intake and protein intake with body fat percentage in active females. Methods: Using an IRB approved protocol, 44 volunteer female recreational and competitive athletes 18 years of age or older were recruited. Interviews were conducted to gather information on within day energy balance by assessing the time and amount of foods/beverages consumed, and the duration and intensity (using a Rating of Perceived Exertion scale) of activity performed on the day of assessment. All analyses were performed using Nutritiming™ (Calorie and Pulse Technologies, Atlanta, GA) to assess energy surpluses, energy deficits, and end of day energy balance. Information on date of birth, race/ethnicity, menstrual status, sleep and wake times, and prior diagnoses of metabolic disease and/or eating disorders were collected at the time of the interview. Height was assessed using a standard stadiometer. Weight and body composition were assessed via Bioelectrical Impedance Analysis (BIA) using InBody 230 (BioSpace Co. USA). The BIA assessment was performed to determine body fat percentage, Basal Metabolic Rate (BMR), Body Mass Index (BMI), segmental body composition, and fat and lean mass in kilograms. Nutrient data were derived using an interviewer-led, 24-hour recall. Results: CHO intake/kg total mass was significantly and inversely correlated with body fat percentage and BMI, (p=0.018 and p=0.001 respectively). Protein intake/kg total mass was also inversely and significantly correlated with body fat percentage (p=0.006). Fat intake was not significantly associated with BMI, body fat percent, or lean mass in kilograms. Total energy intake/kg total mass was inversely associated with BMI (p=0.001), with fat mass (p=0.001), and with body fat percentage, (p=0.001). CHO intake/kg total mass was positively associated with the total number of hours spent in an anabolic (i.e., EB>0) state (p=0.001), and was inversely associated with the total number of hours spent in a catabolic (i.e., EB < 0) state (p=0.001). CHO intake/kg total mass was the only substrate to be significantly correlated with the number of hours spent ± 400 kcal EB over a 24 hour period (p=0.001). Z-scores were created to establish categories of body composition and energy balance values. Utilizing Chi-Square tests, it was determined that more hours spent in an energy surplus (> 400kcal) was associated with higher body fat percent (p=0.042). Conclusions: CHO restriction, whether done intentionally or as a function of an energy restrictive intake, was commonly observed in this subject pool. Of the females surveyed, 79% did not meet their daily energy needs and, on average, consumed 49% of the recommended daily intake of CHO established for active people. The findings that subjects with lower CHO intakes had higher body fat levels, and that CHO was associated with improved maintenance of energy balance, which was also associated with lower body fat percent, suggest that physically active women should not restrict CHO to achieve a desired body composition. It was also observed that end-of-day energy balance was not associated with either energy substrate consumption or body composition.
103

Alternatives to the replacement of an electrical heating system

Schumm, Robert, Maier, Christoph January 2008 (has links)
The aim of this master thesis project is to make an energy survey for a group of apartments and suggestions to change the heating system from electricity to a more efficient one. There are in total 73 flats in 21 buildings. All flats are separated in several houses from two to five flats in one building. There are two different kinds of flats. One with three rooms in one floor, in the following referred to as ‘flat A’ and the other one with four rooms in two floors, in the following referred to as ‘flat B’. [1] In the area there are also two buildings for the commonalty. In these buildings there are a shelter and several common rooms like a storage and a laundry. In our work these two buildings are not included because they are used by everyone inside the community and we could not obtain exact values for the used electricity and the water consumption. So our work is specialised only on the residential houses. The first part of this thesis contains the energy balance for the different kinds of flats to see how much energy they consume for heating and hot tap water. To get theses values we have to analyse the total energy flow into one flat and compare it with the energy which is used because of transmission losses, ventilation losses, hot tap water, electricity for the household and natural ventilation and infiltration. The total energy consumption for flat A is about 19000 kWh per year and in flat B about 23200 kWh per year. But the electricity which is used and has to be bought is about 15600 kWh per year in flat A flat and 17600 kWh in flat B. The rest of the energy is from so called free heat caused by solar radiation and internal heat generation. [1] These numbers for the electricity need in one year create annual costs of about 20000 SEK in flat A and 22500 SEK in flat B. To reduce these costs it is necessary to know where this energy goes and for what it is used. The important parts of the energy balance for this thesis are the transmission losses, the losses caused by natural ventilation and infiltration and the used energy for hot tap water. The losses caused by mechanical ventilation have also a significant value, but they would only affect the new heating system if the ventilation system would be connected to the new system. And the electricity used in the household for electrical devices can only be changed by the consumer himself. The part which is affecting the energy costs for the transmission and natural ventilation losses and the hot tap water sums up to 9240 kWh per year in flat A and flat B. This causes costs of about 10000 SEK per year. To reduce these costs it is necessary to change the actual heating system. In the following we analyse the saving potentials with a change to an air-water heat pump or with a connection to the local district heating network. The costs which can be saved with the installation of a heat pump sum up to about 7000 SEK per year. The installation costs are about 100000 SEK to 125000 SEK depending on the different proposed models. If you consider that the existing electrical boiler has to be changed anyway in the next years the investment costs for the combination with a heat pump decreases. The payback time is then between 9½ and 13½ years. With assumed increasing electricity prices of 5 % each year the payback time decreases to 8½ to 11 years. With a connection of each flat to the local district heating network the energy costs for heating and hot tap water decreases to 3200 SEK per year. Although the price per kWh for district heating is much lower than for electricity the costs are not decreasing a lot because of a high annual fixed fee of 7100 SEK. The saved money per year sums up to 300 SEK and 1000 SEK depending on the electricity contract. The payback time for this alternative is between 50 and up to 160 years. An alternative to the exchange of the heating and hot water system is to change the actual heat exchanger of the ventilation system. With this measure the energy consumption can be reduced with less investment costs. The investment costs for a new heat exchanger are about 35000 SEK, including a new exhaust hood from the kitchen outwards to reduce the contamination of the filters in the heat exchanger. [1] The payback time ranges from 13 years in flat A to 21 years in flat B.
104

Energy Audit and Accounting for Riksbyggen Fastighetsservice, Gävle

Liu, Yuanyuan, Shen, Yang January 2009 (has links)
Riksbyggen Fastighetsservice is a company whose businesses cope with building construction and related services. The local office of Riksbyggen Fastighetsservice in Gävle has been studied in this project. The local office locates in Näringen 20:4, which was constructed in 1989.   The aim of this project is to make a diagnosis of the current situation; find out the most applicable way of optimizing the operation of the facility in order to reduce the energy consumption, to study costs and possible savings and provide assistance with future energy management.      Firstly, a study of Energy Balance was conducted. The transmission losses was 57761 KWh; mechanical ventilation losses 3855 KWh; hot tap water heat losses 9579 KWh; natural transmission and infiltration 6897 KWh. On the other hand, heat gain from internal heat was 12707 KWh; solar radiation 8521 KWh; and supply heat 56806 KWh.   Secondly, the energy costs have been checked out. 29655 KWh of electricity was consumed in 2008. 5948 KWh was used by 20 fuses electricity and 23707 KWh was for 25 fuses. Lighting, electrical equipment and machine composed the electricity consumption. Lighting consumes 13278 KWh; equipment consumes 6452 KWh; and machine consumes 9925 KWh. Lighting electricity was composed by office lighting and workshop lighting with 4798 KWh and 8480 KWh respectively.   Electricity cost is very complicated and flexible in Sweden according to effect and consumption. The total cost of electricity consists of electricity commerce fee and electricity transmission net. Electricity commerce fee includes annual fixed fee, electricity fee, energy certificate and tax. Electricity transmission fee includes annual fixed transmission fee, grid fee and tax. Tax plays vital important role which results in huge total cost. The local office spent 43356 kr on electricity in 2008. 4798 kr was spent on office lighting, and 8480 kr was spent on workshop lighting.   On the other hand district heating fee is composed by annual fixed fee, effect fee, energy fee and tax. The local office spent 37142 kr on 56.806 MWh of district heating in 2008. Thus, the local office purchased 86461 KWh of energies and spent 80498 kr in total in 2008.   Thirdly, to assist its energy traces and management, three tables were designed. One table is for annual energy consumption and cost in each month with all information of sub-terms on costs. One table is for annual electricity consumption for each electrical equipment and cost in accordance. Another table is for district heating consumption and cost.    At last, energy saving possibilities was explored. One way is applying improvements or maintenance of the office construction. The result of Energy Balance shows that transmission losses were 57761 KWh which occupies 74% of the total losses, and it is the biggest bite. As the office was constructed in 1989, if improvements and maintenance can be applied to the insulation of floor, roof and walls, or change the windows, the heat losses can be reduced.   However, the other solution might be much more applicable and financial sound. Just go to Clas Ohlson to buy LED 1 W and 3 W lamps to replace the current bulbs. Spending 3009 kr to buy 51 LED incandescent bulbs of 1W effect, and 3576 kr on 24 LED fluorescent of 3W effect, will save 12057 kr every year. The lighting electricity consumption will be reduced from 13278 KWh / year to 264 KWh / year. Instead of spending 16017 kr on lighting, 98% will be reduced, and only 318 kr will be paid. Moreover, the payback is really nice, only 0.42 year. Action! The sooner the better! 20% of energy cost will be saved!
105

A numerical study of energy balances and flow planforms in earth's mantle with radioactive heating, the 660 km-depth phase boundary and continents

Sinha, Gunjan 13 July 2009 (has links)
It is well established that the temperature gradients in the interiors of internally-heated mantle convection models are subadiabatic (e.g. Parmentier et al., 1994; Bunge et al., 1997, 2001). The subadiabatic gradients have been explained to arise due to a balance between vertical advection and internal heating, however, a detailed analysis of the energy balance in the subadiabatic regions has not been undertaken. In this research, I examine in detail the energy balance in a suite of two-dimensional convection calculations with mixed internal and basal heating, depth-dependent viscosity and continents. I find that there are three causes of subadiabatic gradients. One is the above-mentioned balance, which becomes significant when the ratio of internal heating to surface heat flux is large. The second mechanism involves the growth of the overshoot (maximum and minimum Temperatures along a geotherm) of the geotherm near the lower boundary where the dominant balance is between vertical and horizontal advection. The latter mechanism is significant even in relatively weakly internally heated calculations. For time-dependent calculations, I find that local secular cooling can be a dominant term in the energy equation and can lead to subadiabaticity. However, it does not show its signature on the shape of the time-averaged geotherm. I also compare the basal heat flux with parameterized calculations based on the temperature drop at the core-mantle boundary, calculated both with and without taking the subadiabatic gradient into account and I find a significantly improved fit with its inclusion.<p> I also explore a wide range of parameter space to investigate the dynamical interaction between effects due to surface boundary conditions representing continental and oceanic lithosphere and the endothermic phase boundary at 660 km-depth in two-dimensional Cartesian coordinate convection calculations. I find that phase boundary induced mantle layering is strongly affected by the wavelength of convective flows and mixed surface boundary conditions strongly increase the horizontal wavelength of convection. My study shows that for mixed cases the effects of the surface boundary conditions dominate the effects of the phase boundary. I show that the calculations with complete continental coverage have the most significantly decoupled lower and upper mantle flows and substantial thermal and mechanical layering. Unlike the free-slip case where the surface heat flux decreases substantially with increasing magnitude of the Clapeyron slope, surface heat flux is shown to be almost independent of the Clapeyron slope for mixed boundary condition cases. Although very different when not layered, models with free and mixed surfaces have very similar planforms with very large aspect ratio flows when run with large magnitudes of the Clapeyron slope. I also calculate the critical boundary layer Rayleigh number as a measure of the thermal resistance of the surface boundary layer. My results show that the thermal resistance in the oceanic and the continental regions of the mixed cases are similar to fully free and no-slip cases, respectively. I find that, even for purely basally heated models, the mantle becomes significantly subadiabatic in the presence of partial continental coverage. This is due to the significant horizontal advection of heat that occurs with very large aspect ratio convection cells.
106

Occurrence and Stability of Glaciations in Geologic Time

Zhuang, Kelin 2010 August 1900 (has links)
Earth is characterized by episodes of glaciations and periods of minimal or no ice through geologic time. Using the linear energy balance model (EBM), nonlinear EBM with empirical ice sheet schemes, the general circulation model coupled with an ice sheet model, this study investigates the occurrence and stability of glaciations in geologic time. The simulations since the last glacial maximum (LGM) suggest that the summertime thawline of ice sheets conforms closely to the equatorward edge of the ice sheets and implies the relative stability toward deglaciation. CO2 levels are indispensable in controlling the initiation of ice sheet in the Cretaceous. At low CO2 levels, ice sheets exist in all periods no matter LGM or the last interglacial (LIG) orbital elements; however, at high CO2 levels ice sheets rarely exist. The simulations agree well with recent geological evidence of the hysteresis of glaciations in the Permo-Carboniferous. Gondwanaland reached its glacial maximum when CO2 level was roughly the same or slightly higher than the preindustrial value. With a further increase of CO2, deglaciation dominates and results in an ice free state. Again, if CO2 decreased to the present level, Gondwanaland would be glaciated once more and start a new cycle of glaciation and deglaciation. Simulations from five paleogeography maps in Gondwanaland with a suite of CO2 levels and different orbital elements reveal that paleogeography, CO2 levels and the Milankovitch cycles all contribute to the glaciations of Gondwanaland. This study shows that orbital elements alone are insufficient to account for the evolution of ice sheets. Net radiative forcing caused by greenhouse gases, such as CO2 and solar constant change are the primary drivers to glacial inception or demise. Continental geography, CO2 levels, solar constant change, and the Milankovitch cycles complicate the glacial history of Earth.
107

The Effects of Exercise on Acute Energy Balance and Macronutrient Intake

Jokisch, Emily N 01 May 2010 (has links)
This investigation examined acute energy compensation and macronutrient intake in habitually active and sedentary, college-aged males, following an exercise session as compared to a resting (control) session, to see if habitually active males compensate intake better to an energy deficit incurred by exercise, than sedentary males. Participants were males, aged 18-30 years, of a normal percent body fat and body mass index, and exercised < 60 min per week (sedentary) or > 150 min per week (habitually active). Participants came in for two sessions: 1) 45 minutes of resting (control) and then eating an ad libitum meal; and 2) riding a cycle ergometer for 45 minutes (exercise) and then eating an ad libitum meal. Sessions were counterbalanced across participants. Energy and macronutrient intake were calculated for the meal and over the remaining part of the day. Sedentary individuals ate significantly less during the meal in the exercise session (which expended a mean of 453.5 kcals across both groups) as compared to the control session (934.8 + 222.0 kcals vs. 1073.9 + 470.3 kcals, p < 0.03), which demonstrated negative energy compensation (-30.6%). The habitually active group showed no significant difference in energy intake between sessions at the meal (1016.8 + 396.7 kcal [control] vs. 1105.6 + 389.2 kcal [exercise]). While the habitually active group showed no significant difference in intake at the meal, the slight increase in intake at the meal in the exercise session demonstrated some energy compensation (19.6%), which was significantly better (p < 0.03) than that in the sedentary group. No differences in macronutrient intake at the meal were found between the sessions. Over the day following the sessions, both groups reported a significant increase in energy intake after the exercise session as compared to the control session (1457.5 + 646.2 kcals vs. 1356.1 + 657.2 kcals, p < 0.04), with no difference in macronutrient intake between the sessions. These results indicate that, although complete acute compensation did not occur, the habitually active group acutely compensated intake significantly more so than the sedentary group, demonstrating better energy regulation ability.
108

Dietary energy balance modulates growth factor signaling during multistage epithelial carcinogenesis in mouse skin

Moore, Tricia Wallace 14 February 2012 (has links)
Energy balance refers to the relationship between energy intake and energy expenditure. Epidemiological studies have established a clear association between energy balance and cancer, however the underlying mechanisms are unclear. The objective of the current study was to evaluate the impact of caloric consumption on epithelial carcinogenesis and identify potential mechanisms of inhibition or enhancement. Using ICR female mice, we demonstrated that positive energy balance enhanced, while negative energy balance inhibited susceptibility to multistage carcinogenesis in mouse skin. We next evaluated diet-induced changes in the epidermal proliferative response. Calorie restriction (CR) significantly reduced epidermal hyperproliferation, in the presence and absence of tumor promotion, as compared to diet-induced obesity (DIO). Additional studies were conducted to determine the impact of dietary manipulation on TPA-induced growth factor signaling. CR reduced, while DIO increased insulin like growth factor-1 receptor (IGF-1R) and epidermal growth factor receptor (EGFR) activation, which subsequently modulated signaling downstream to Akt and mTOR. These diet-induced changes in growth factor signaling were confirmed under steady-state conditions in multiple epithelial tissues (i.e., skin, liver and dorsolateral prostate) in multiple mouse strains (FVB/N, C57BL/6 and ICR). Further analyses demonstrated that caloric consumption directly correlated with levels of cell cycle progression related proteins and inversely correlated with levels of cell cycle inhibitory proteins. Genetic reduction of circulating IGF-1, liver IGF-1 deficient (LID) mouse model, inhibited two-stage skin carcinogenesis, reduced epidermal hyperproliferation and attenuated IGF-1R and EGFR growth factor signaling during tumor promotion, similar to CR, suggesting a potential for IGF-1R and EGFR crosstalk. Further studies, demonstrated that IGF-1 induced EGFR activation in cultured mouse keratinocytes, possibly due to IGF-1R and EGFR heterodimerization or IGF-1 induced changes in EGFR mRNA expression. In vivo, CR reduced, while DIO increased IGF-1R and EGFR association during tumor promotion. Furthermore, CR attenuated EGFR ligand mRNA expression both in the presence and absence of TPA treatment. Collectively, these findings suggest that dietary energy balance modulates epithelial carcinogenesis, at least in part due to diet-induced changes in levels of circulating IGF-1, which then modulate IGF-1R and EGFR crosstalk and downstream signaling to cell cycle related proteins, subsequently altering epidermal hyperproliferation. / text
109

Energetic Consequences of Thermal and Non-Thermal Food Processing

Carmody, Rachel Naomi January 2012 (has links)
All human societies process their food extensively by thermal and non-thermal means. This feature distinguishes us from other species, and may even be compulsory given that humans are biologically committed to an energy-rich diet that is easy to chew and digest. Yet the energetic consequences of food processing remain largely unknown. This dissertation tests the fundamental hypothesis that thermal and non-thermal processing lead to biologically relevant increases in energy gain from protein-rich meat and starch-rich tubers, two major caloric resources for modern and ancestral humans that present divergent structural and macronutrient profiles. The energetic consequences of food processing are evaluated using three indices of energy gain, each of which account for costs not currently captured by conventional biochemical assessments of dietary energy value. Chapter 2 investigates the effects of cooking and pounding on net energy gain as indexed by changes in body mass, controlling for differences in food intake and activity level. Chapter 3 examines the effect of cooking and pounding on diet-induced thermogenesis, the metabolic cost of food digestion. Chapter 4 considers the effort required to engage in food processing, arguing that the advantageous ratio of benefit to cost has likely had important effects on human life history. By each of these definitions of energy gain, food processing is shown to have substantial energetic significance. Overall, energetic gains due to thermal processing exceeded those of non-thermal processing, consistent with recent proposals that the adoption of cooking had a particularly important influence on human biology. Gains due to food processing were observed in both meat and tuber substrates, supporting a transformative role for habitual food processing in the evolution and maintenance of the human energy budget. / Human Evolutionary Biology
110

Energy expenditure, dietary intake and nutritional knowledge of elite, school-aged gymnasts / C. Joubert

Joubert, Cornel January 2005 (has links)
Objective. To compare energy balance and nutrient intake of elite and non-elite school-aged gymnasts, as well as to evaluate their nutritional knowledge and eating attitude and its effect on dietary intake and practices. Methods. Demographic information, anthropometric measurements, menstrual status, sources of nutritional information, nutritional habits as well as supplement use was documented. Eating attitudes were measured by the EAT26 test and nutritional knowledge by a standardised questionnaire. Dietary intake and practices were determined with a 3-day weighed food record, while energy expenditure was measured with an Actical® accelerometer (Mini Mitter Co., Inc. Bend, OR, USA). Results. The total daily energy intake (non-elite = 6 944.37 ± 1 272.28 kJ vs. elite = 6 543.01 ± 2 570 kJ) in both groups was similar to their daily energy expenditure values (non-elite = 6 393.77 ± 1 244.19 kJ vs. elite = 6 696.09 ± 1 676.58 kJ). Elite gymnasts tended to have higher protein (21.37 vs. 15.4% total energy intake (TE), small effect size, d = 0.1) and lower fat (28.9 vs. 33.6% TE, medium effect size, d = - 0.6) intakes. More non-elite gymnasts (n = 7, 88.88%) used micronutrient supplements than elite gymnasts (n = 4, 45.45%, medium effect size, d = 0.45). Most of the gymnasts (55%) ate snacks during the day, which consisted mostly of refined carbohydrates. In the total group of gymnasts the most frequently used source of nutritional information was the coach (60%). There was no difference in nutritional knowledge between the groups (elite = 61.8% vs. non-elite = 62.8% respectively). Lastly, elite gymnasts had a practically significantly higher risk than non-elite gymnasts to follow a diet (large effect size, d = 1.32), while non-elite gymnasts exercised practically significantly more self-control over their food intake com pared to elite gymnasts (large effect size, d = - 1.03). Conclusions. South African elite gymnasts do not differ from non-elite gymnasts in terms of energy-, carbohydrate-, protein-, or fat intake. There is also no difference in energy expenditure or risk in developing an eating disorder, probably due to less competitiveness compared to other international gymnasts. / Thesis (M.Sc. (Dietetics))--North-West University, Potchefstroom Campus, 2005.

Page generated in 0.0613 seconds