Growth and characterization of novel, III-V semiconductor heterostructures

The material presented in this thesis concerns the growth and characterization of III-V semiconductor heterostructures. Studies of the interactions between bound states in coupled quantum wells and between well and barrier bound states in AlAs/GaAs heterostructures are presented. We also demonstrate the broad array of novel tunnel structures realizable in the InAs/GaSb/AlSb material system. Because of the unique broken-gap band alignment of InAs/GaSb these structures involve transport between the conduction- and valence-bands of adjacent layers. These devices possess a wide range of electrical properties and are fundamentally different from conventional AlAs/GaAs tunnel devices. We report on the fabrication of a novel tunnel transistor with the largest reported room temperature current gains. We also present time-resolved studies of the growth fronts of InAs/GainSb strained layer superlattices and investigations of surface anion exchange reactions.

Chapter 2 covers tunneling studies of conventional AlAs/GaAs RTD's. The results of two studies are presented: (i) A test of coherent vs. sequential tunneling in triple barrier heterostructures, (ii) An optical measurement of the effect of barrier X-point states on Γ-point well states. In the first it was found if two quantum wells are separated by a sufficiently thin barrier, then the eigenstates of the system extend coherently across both wells and the central barriers. For thicker barriers between the wells, the electrons become localized in the individual wells and transport is best described by the electrons hopping between the wells. In the second, it was found that Γ-point well states and X-point barrier states interact strongly. The barrier X-point states modify the energies of the well states and increase the escape rate for carriers in the quantum well.

The results of several experimental studies of a novel class of tunnel devices realized in the InAs/GaSb/AlSb material system are presented in Chapter 3. These interband tunnel structures involve transport between conduction- and valence-band states in adjacent material layers. These devices are compared and contrasted with the conventional AlAs/GaAs structures discussed in Chapter 2 and experimental results are presented for both resonant and nonresonant devices. These results are compared with theoretical simulations and necessary extensions to the theoretical models are discussed.

In chapter 4 experimental results from a novel tunnel transistor are reported. The measured current gains in this transistor exceed 100 at room temperature. This is the highest reported gain at room temperature for any tunnel transistor. The device is analyzed and the current conduction and gain mechanisms are discussed.

Chapters 5 and 6 are studies of the growth of structures involving layers with different anions. Chapter 5 covers the growth of InAs/GainSb superlattices for far infrared detectors and time resolved, in-situ studies of their growth fronts. It was found that the bandgap of superlattices with identical layer thicknesses and compositions varied by as much as 40 meV depending on how their internal interfaces are formed. The absorption lengths in superlattices with identical bandgaps but whose interfaces were formed in different ways varied by as much as a factor of two. First the superlattice is discussed including an explanation of the device and the complications involved in its growth. The experimental technique of reflection high energy electron diffraction (RHEED) is reviewed, and the results of RHEED studies of the growth of these complicated structures are presented. The development of a time resolved, in-situ characterization of the internal interfaces of these superlattices is described. Chapter 6 describes the result of a detailed study of some of the phenomena described in chapter 5. X-ray photoelectron spectroscopy (XPS) studies of anion exchange reactions on the growth fronts of these superlattices are reported. Concurrent RHEED studies of the same physical systems studied with XPS are presented. Using the RHEED and XPS results, a real-time, indirect measurement of surface exchange reactions was developed.

Coastal plant growth and CO2 enrichment: Can the productivity of black needle rush keep pace with sea level rise?

The rate of sea level change has varied considerably over geological time, with rapid increases (0.25 cm yr-1) at the end of the last ice age to more modest increases over the last 4,000 years (0.04 cm yr-1; Hendry 1993). Due to anthropogenic contributions to climate change, however, the rate of sea level rise is expected to increase between 0.10 and 0.25 cm year-1 for many coastal areas (Warrick et al. 1996). Notwithstanding, it has been predicted that over the next 100 years, sea levels along the northeastern coast of North Carolina may increase by an astonishing 0.8 m (0.8 cm yr-1); through a combination of sea-level rise and coastal subsidence (Titus and Richman 2001; Parham et al. 2006). As North Carolina ranks third in the United States with land at or just above sea level, any additional sea rise may promote further deterioration of vital coastal wetland systems. (PDF contains 4 pages)

The effects of Moina artificial diet and nutrase xyla supplemented artificial diet on growth and survival of Clarias gariepinus larvae

An experiment was carried out to investigate the effects of Moina, artificial diet (55% CP) and nutrase xyla supplemented artificial diet on growth performances and survival rates of Clarias gariepinus larvae. A combination of Moina and artificial diet (with or without nutrass xyla) resulted in higher growth performance and survival rates during a 12-day nursing time with specific growth rates of 30.04-32.15% d super(-1) and survival rates of 87.5-90%. Best growth performance and survival rate was obtained with a combination of Moina and artificial diet supplemented with nutrias xylem. Feeding of Moina and artificial diet supplemented, with nutrias xyla alone to the larval led to a lower growth performance of 25.60-27.04% d super(-1). However, the survival rate of Monia of larvae fed a combination of Moina and artificial diet (with or without nutrias xylem supplementation) artificial diet without nutrias xylem addition proved relatively less suitable for larval rearing of Clarias gariepinus owing to a low survival rate of 69% and growth performance of 19.7% d super(-1). This study showed the feasibility of feeding a combination of Moina and nutrias xylem supplemented artificial diet to the larvae of Clarias gariepinus

Effects of fermented fluted pumpkin leaf (Telfaria occidentalis) on the growth and nutrient utilization of Clarias (Clarias gariepinus)

Clarias (Clarias gariepinus) (Burshell, 1821) fingerlings were fed isonitrogenous diets (38.9% crude protein) with fermented fluted pumpkin leaves (FFPL) replacing different proportion (0,50,75,100%) of extruded soybean meal (ESM) for 8 weeks. Growth responses at the different substitution levels measured. Increasing FFPL intake resulted in better weight gains and higher specific growth rates (SGR) of 0.29, 0.36 and 0.38% per day respectively. The increase in growth from feeding diets containing 75% and 100% of the ESM replaced with FFPL were significantly higher (P<0.05) than those of other diets. Further more fish tissue protein deposition consistently increased with increasing level of FFPL concentration in their diets. Fish fed diets where whole ESM was replace 100% FFPL gave the best overall response in terms of their weight gain, food conversion ratio, protein efficiency ratio, and specific growth rate. Economic considerations indicate the replacement of ESM with FFPL, which is a cheaper ingredient in feeds for Clarias

Effect of salinity on growth and survival of Clarias gariepinus (Burchell, 1822): Clariidae fry

The effect of different salinity levels on the growth and survival of Clarais gariepinus fry was studied in indoor hatchery system for a period of three weeks. 1000 Clarias gariepinus fry of an average weight 0.37~c0.06g were stocked at 100 fry in five replicated 20 liters plastic bowls. Five salinity levels of 0.2, 0.4, 1.1, 2.1 and 4.2ppt were tested. The results indicated that significant difference P~.0.05 highest weight gain of 0.89~c0.05g was presented by fry in 0.2ppt medium. All fry raised in 4.2ppt died within 24 hours. No significant difference P~,0.05 in weight gain is presented in fry raised in 0.2ppt-2.1ppt. From this study, the weight gain decreases with increase in salinity. Also the survival rate decreases from 0.2ppt to 1.1ppt raised fry while the lowest significant difference P~.0.05 survivals were presented in fry raised in 2.1 and 4.2ppt. Based on these results and foregoing, salinity rate of 0.4ppt is favourable for growth and survival of C.gariepinus fry

Effects of substituting fish meal with grasshopper meal on growth and food utilization of the Nile Tilapia, Oreochromis niloticus fingerlings

The effects of substituting fish meal with grasshopper meal in fish diets on the growth, food utilization and survival of the Nile tilapia, Oreochromis niloticus (mean weight = 40.1g) were investigated. The results show that the best growth and food utilization were recorded in the fingerlings fed in the 10% grasshopper meal and 30% fish meal while the poorest growth and food utilization indexes were recorded with the 25% grasshopper meal and 15% fish meal. In general, at 10% inclusion, the fingerlings performed even better than the control (40% fishmeal and no grasshopper meal)

Low Climate Stabilisation under Diverse Growth and Convergence Scenarios

4 p.

The Sustainability of `Sustainable´ Energy Use: Historical Evidence on the Relationship between Economic Growth and Renewable Energy

20 p.

Low Climate Stabilisation under Diverse Growth and Convergence Scenarios

9 p.

Estimation of growth and financial analysis through the application of Ipil ipil (Leucaena leucocephala) leaf meal as supplements to soybean and fish meal in the diet of juvenile monosex tilapia (Oreochromis niloticus)

Among plant protein ingredients,ipil ipil (Leucaena leucocephala) leafmeal (ILLM) is considered the most nutritive plant protein source after soybean meal in aquatic feeds. That was proven in a 21-day experiment conducted to assess the response of juvenile Monosex Nile tilapia Oreochromis niloticus with four iso-nitrogenous formulated diets: One control diet was formulated based on fishmeal, one on soybean meal and one on rice bran, ipil ipil leafmeal was also included in experimental diets.

Application of ipil- ipil leaf meal (IILM) as feed Ingredient for Monosex tilapia fry (oreochronis niioticus) : In terms of growth and economics

The Ipil-ipil (Leucaena leucocephal) leaf analyzed for crude protein (CP), fat, crude fibre (CF), ash content, moisture content and nitrogen free extract (NFE). The CP 23± 0.12 % , fat 8 ± 0.11 %, CF 18 ± 0.15 % , ash 10 ± 0.13 %, moisture 14. ± .16% and NFE 29.± 1.10 % were recorded. A twenty one days experiment was conduced to assess the response of juvenile monosex tilapia with different iso-nitrogenous formulated diets for find out the feasibility study of using ipil-ipil leaf meals as feed ingredient for juvenile tilapia. Three experimental diets were formulated by using fish meal, soybean meal, rice bran and ipil ipil leaf meal. One control diet was formulated by using fish meal, soybean meal and rice bran. Considering the high demand, limited availability of fish meal and soybean meal, ipil ipil leaf meal was incorporated in juvenile tilapia feed. Among plant protein ingredients ipil ipil leaf meal was considered as the most nutritive plant protein source after soybean meal. However, high concentration of toxic element limited the incorporation level of ipil ipil leaf meal in fish feed. Use of 15 % ipil ipil leaf meal in fish feed was more significant from the view of growth performance and economics. The higher Absolute Growth was 1119.26 gm, higher Specific Growth Rate was 6.52% /day higher Feed Conversion Efficiency was 41.23% , higher Protein Efficiency Ratio was 1.178 and higher Average Daily Growth rate was 14.00% recorded in diet-4 ( which contained 15% IILM). The lower Feed Conversion Ratio 2.42 and lower cost for per unit production 34.65 taka/kg were recorded in diet-4. The higher cost for per unit fish production 45.6 tk./kg was recorded for diet-1 where no ipil ipil leaf meal.. The results suggest that tree legumes Ipil-ipil (Leucaena leucocephal) leaf has potential and excellent source of feed ingredients as protein supplements for juvenile monosex

Growth and reproduction of Moina rectirostris (Leydig) and Ceriodaphnia quadrangula (O. F. Muller) with feeding on detritus. [Translation from: Sbornik po prudovomu rybovodstvu, 79-89. Moscow, VNIRO, 1969.]

The significance of detritus in the nutrition of aquatic animals, especially of the small representatives of the zooplankton, has been studied very slightly. Research so far has established that in M. rectirostris with feeding on protococcal and single-celled green algae and bacteria the beginning of formation of eggs takes place in 2 - 4 days. The young appear in 4 - 6 days. In this study M. rectirostris and C. quadrangula are fed on detritus of natural origin in laboratory conditions. In order to determine the assimilability and productive: effect of detritus, the author set up experiments, permitting to characterize the rate of growth, speed of maturing and fertility of M. rectirostris and C. quadrangula with feeding of them on detritus of different composition and age.

Mortality, growth and growth rate variability of striped bass larvae in Chesapeake Subestuaries

In this report we develop age-length keys and derive age-frequency data. We estimate striped bass and white perch mortality and growth rates, based on the otolith-aging analysis. We also report on hatch-date frequencies of striped bass and white perch larvae, and we discuss environmental effects on recruitment potential.