Risk based lifetime costs assessment of a ground source heat pump (GSHP) system design: Methodology and case study

Space heating accounts for a large portion of the world's carbon dioxide emissions. Ground Source Heat Pumps (GSHPs) are a technology which can reduce carbon emissions from heating and cooling. GSHP system performance is however highly sensitive to deviation from design values of the actual annual energy extraction/rejection rates from/to the ground. In order to prevent failure and/or performance deterioration of GSHP systems it is possible to incorporate a safety factor in the design of the GSHP by over-sizing the ground heat exchanger (GHE). A methodology to evaluate the financial risk involved in over-sizing the GHE is proposed is this paper. A probability based approach is used to evaluate the economic feasibility of a hypothetical full-size GSHP system as compared to four alternative Heating Ventilation and Air Conditioning (HVAC) system configurations. The model of the GSHP system is developed in the TRNSYS energy simulation platform and calibrated with data from an actual hybrid GSHP system installed in the Department of Earth Science, University of Oxford, UK. Results of the analysis show that potential savings from a full-size GSHP system largely depend on projected HVAC system efficiencies and gas and electricity prices. Results of the risk analysis also suggest that a full-size GSHP with auxiliary back up is potentially the most economical system configuration. © 2012 Elsevier Ltd.

Study by Hall probe mapping of the trapped flux modification produced by local heating in YBCO HTS bulks for different surface/volume ratios

The aim of this report is to compare the trapped field distribution under a local heating created at the sample edge for different sample morphologies. Hall probe mappings of the magnetic induction trapped in YBCO bulk samples maintained out of thermal equilibrium were performed on YBCO bulk single domains, YBCO single domains with regularly spaced hole arrays, and YBCO superconducting foams. The capability of heat draining was quantified by two criteria: the average induction decay and the size of the thermally affected zone caused by a local heating of the sample. Among the three investigated sample shapes, the drilled single domain displays a trapped induction which is weakly affected by the local heating while displaying a high trapped field. Finally, a simple numerical modelling of the heat flux spreading into a drilled sample is used to suggest some design rules about the hole configuration and their size. © 2005 IOP Publishing Ltd.

Strong carrier lifetime enhancement in GaAs nanowires coated with semiconducting polymer.

The ultrafast charge carrier dynamics in GaAs/conjugated polymer type II heterojunctions are investigated using time-resolved photoluminescence spectroscopy at 10 K. By probing the photoluminescence at the band edge of GaAs, we observe strong carrier lifetime enhancement for nanowires blended with semiconducting polymers. The enhancement is found to depend crucially on the ionization potential of the polymers with respect to the Fermi energy level at the surface of the GaAs nanowires. We attribute these effects to electron doping by the polymer which reduces the unsaturated surface-state density in GaAs. We find that when the surface of nanowires is terminated by native oxide, the electron injection across the interface is greatly reduced and such surface doping is absent. Our results suggest that surface engineering via π-conjugated polymers can substantially improve the carrier lifetime in nanowire hybrid heterojunctions with applications in photovoltaics and nanoscale photodetectors.

Carrier lifetime and mobility enhancement in nearly defect-free core-shell nanowires measured using time-resolved terahertz spectroscopy.

We have used transient terahertz photoconductivity measurements to assess the efficacy of two-temperature growth and core-shell encapsulation techniques on the electronic properties of GaAs nanowires. We demonstrate that two-temperature growth of the GaAs core leads to an almost doubling in charge-carrier mobility and a tripling of carrier lifetime. In addition, overcoating the GaAs core with a larger-bandgap material is shown to reduce the density of surface traps by 82%, thereby enhancing the charge conductivity.

Noncontact measurement of charge carrier lifetime and mobility in GaN nanowires

The first noncontact photoconductivity measurements of gallium nitride nanowires (NWs) are presented, revealing a high crystallographic and optoelectronic quality achieved by use of catalyst-free molecular beam epitaxy. In comparison with bulk material, the NWs exhibit a long conductivity lifetime (>2 ns) and a high mobility (820 ± 120 cm 2/(V s)). This is due to the weak influence of surface traps with respect to other III-V semiconducting NWs and to the favorable crystalline structure of the NWs achieved via strain-relieved growth. © 2012 American Chemical Society.

Seasonal variations in stable isotope ratios of two biomanipulation fishes and seston in a large pen culture in hypereutrophic Meiliang Bay, Lake Taihu

This paper reports on seasonal changes in stable carbon and nitrogen isotope ratios of seston and muscle tissue of silver carp and bighead carp during 2004 and 2005, focusing primarily on the carbon sources and trophic relationships among phytoplankton, zooplankton and silver carp and bighead carp in a large fish pen of Meiliang Bay (Lake Taihu, China). delta C-13 showed a minimal value in March 2005 and a maximal value in August 2005 in seston both inside and outside the pen, whereas delta N-15 of seston showed the minimum in winter and the maximum during algal blooms. A positive correlation between delta C-13 of silver carp and that of seston suggested that temporal variation Of delta C-13 in seston was preserved in fish via the food chain. The differences of delta C-13 among seston, zooplankton and muscle tissue of silver carp and bighead carp ranged only 0.2-1.7%, indicating that plankton production was the primary food source of filter-feeding fishes. According to a mass balance model, we estimated that the contributions of zooplankton to the diets of silver carp and bighead carp were 45.7% and 54.3%, respectively, based on the delta N-15 values of zooplankton and planktivorous fishes. (C) 2007 Elsevier B.V. All rights reserved

Local lifetime engineering in 600V pin diode using mix-mode simulation

This paper reports a detailed analysis of the effect of local lifetime killing (LLK) within the drift region on the reverse recovery (RR) characteristics and on-state performance of 600V Silicon PiN diodes. The paper also discusses the influence of the measurement circuit on the reverse recovery of the high voltage diodes and it proposes a simple and effective mix-mode simulation tool for an accurate assessment of the diode performance in reverse recovery mode. © 2013 IEEE.

Effect of dietary carbohydrate-to-lipid ratios on growth and feed utilization in Chinese longsnout catfish (Leiocassis longirostris Gunther)

An 8-week growth trial was carried out in a semi-recirculation system at 26 +/- 0.5 degrees C to investigate the optimal dietary carbohydrate-to-lipid (CHO:L) ratio for carnivorous Chinese longsnout catfish (Leiocassis longirostris Gunther). Triplicate tanks of fish were assigned to each of five isocaloric and isonitrogenous diets with different carbohydrate-to-lipid ratios (0.75, 1.48, 1.98, 2.99 and 5.07). The results showed that a higher specific growth rate (SGR) and feed rate (FR) were observed in the fish fed diet ratios of 1.98 CHO:L (P < 0.05). Overloading dietary carbohydrate (5.07 CHO:L ratio) caused skeletal malformations. Apparent digestibility of dry matter (ADC(d)) significantly increased with dietary CHO:L ratio (P < 0.05), while significantly higher apparent digestibility of protein (ADC(p)) and apparent digestibility of energy (ACD(e)) was observed only in the 1.98 CHO:L group (P < 0.05). Whole body contents of dry matter, lipid and energy significantly increased as the CHO:L ratio decreased (P < 0.05). The hepatosomatic index (HSI) was highest at 1.98 CHO:L ratio (P < 0.05). Highest dietary CHO:L ratio resulted in lower liver glycogen, liver lipid, plasma glucose and plasma triacylglycerol (P < 0.05), whereas there was no significant difference in plasma total cholesterol (P > 0.05). High dietary CHO:L ratio caused pathological changes in fish morphology and liver histology. Based on maximum growth, the optimal carbohydrate-to-lipid ratio was 1.98 for Chinese longsnout catfish.

Studies on the food web structure of Lake Donghu using stable carbon and nitrogen isotope ratios

Food web structure was studied by using carbon and nitrogen isotope ratios in a hypereutrophic subtropical Chinese lake, Lake Donghu. High external nutrient loading and the presence of abundant detritus from submersed macrophytes were responsible for the high sediment delta(15)N and delta(13)C, respectively. C-13 was significantly higher in submersed macrophytes than in other macrophytes. The similar delta(13)C values in phytoplankton, zooplankton, zoobenthos, and planktivorous fish indicate that phytoplankton was the major food source for the consumers. By using a delta(15)N mass balance model, we estimate that the contributions of zooplankton to the diet of silver carp and bighead carp were 54% and 74%, respectively, which is in agreement with previous microscopic observations on intestinal contents of these fishes.

Lifetime distribution of spontaneous emission from line antennas in two-dimensional quasi-periodic photonic crystals

We investigate the lifetime distribution functions of spontaneous emission from line antennas embedded in finite-size two-dimensional 12-fold quasi-periodic photonic crystals. Our calculations indicate that two-dimensional quasi-periodic crystals lead to the coexistence of both accelerated and inhibited decay processes. The decay behaviors of line antennas are drastically changed as the locations of the antennas are varied from the center to the edge in quasi-periodic photonic crystals and the location of transition frequency is varied.

Proton irradiation-induced defects in undoped GaSb studied by positron lifetime spectroscopy and photoluminescence

Undoped GaSb was irradiated by 2.6 MeV protons. The irradiation-induced defects were studied by positron lifetime spectroscopy (PLS) and photoluminescence (PL). Positron lifetime measurements showed that vacancy-type defects were introduced after irradiation, and divacancies were formed at higher irradiation dose. Annealing experiments revealed there were different annealing steps between the as grown and proton-irradiated samples, the reason for which was tentatively attributed to the formation of divacancies in the proton-irradiated samples during annealing. All the vacancy defects could be annealed out at around 500 degrees C. The PL intensity quickly fell down after proton irradiation and decreased with increasing irradiation dose, indicating that irradiation induced non-irradiative recombination centers, whose candidates were assigned to the vacancy defects induced by proton irradiation.

Decay lifetime and evolution of semiconductor quantum dots in photonic crystals

Spontaneous emission from GaAs/AlGaAs quantum dots (QDs) embedded in photonic crystals with a narrow photonic band gap is studied theoretically. The results show that the decay lifetime is very sensitive to the sizes of QDs, and both inhibited and accelerated emission can occur, which had been indicated in a previous experiment. The Weisskopf-Wigner approximation, good for atoms and molecules, may be incorrect for QDs. A damped Rabi oscillation of the excited state with the transition frequency outside the photonic band gap may appear, which is impossible for atoms and molecules. (c) 2008 Elsevier Ltd. All rights reserved.

Spontaneous emission lifetime distribution of infinite line antennas in two-dimensional photonic crystals with finite size

The authors calculate the lifetime distribution functions of spontaneous emission from infinite line antennas embedded in two-dimensional disordered photonic crystals with finite size. The calculations indicate the coexistence of both accelerated and inhibited decay processes in disordered photonic crystals with finite size. The decay behavior of the spontaneous emission from infinite line antennas changes significantly by varying factors such as the line antennas' positions in the disordered photonic crystal, the shape of the crystal, the filling fraction, and the dielectric constant. Moreover, the authors analyze the effect of the degree of disorder on spontaneous emission. (c) 2007 American Institute of Physics.