Comparative study on the effect of dietary lipid level on growth and feed utilization for gibel carp (Carassius auratus gibelio) and Chinese longsnout catfish (Leiocassis longirostris Gunther)

An 8-week growth trial investigated the effect of dietary lipid level on growth performance of a carnivorous fish, Chinese longsnout catfish (Leiocassis longirostris Gunther) and an omnivorous fish, gibel carp (Carassius auratus gibelio). For each species, seven isonitrogenous semi-purified diets (455 g kg(-1) crude protein for Chinese longsnout catfish and 385 g kg(-1) crude protein for gibel carp) were formulated to contain 30, 60, 90, 120, 150, 180 or 210 g kg(-1) lipid. For Chinese longsnout catfish, feed intake (FI) decreased with increasing dietary lipid and there was no significant difference in feed intake from 90 to 210 g kg(-1) lipid. Specific growth rate (SGR) increased with dietary lipid level (P < 0.05) and the 150 and 180 g kg(-1) groups were the best. Feed conversion efficiency (FCE), protein retention efficiency (PRE) and energy retention efficiency (ERE) were higher at 180 g kg(-1) lipid. For gibel carp, FI decreased with increased dietary lipid and 180 and 210 g kg(-1) lipid groups showed lower values. SGR increased with dietary lipid level and the 150 and 180 g kg(-1) were the best. FCE was higher at 180 g kg(-1) lipid level. PRE increased with dietary lipid level and there was no significant difference in groups from 120 to 210 g kg(-1) dietary lipid. ERE increased with increasing dietary lipid level, and groups fed 120, 150 and 180 g kg(-1) lipid showed the highest values. In Chinese longsnout catfish, increase in dietary lipid level, resulted in increased carcass dry matter, crude protein, crude lipid and gross energy. In gibel carp, dry matter, crude protein, and crude lipid increased with dietary lipid level. Based on regression between SGR and dietary lipid, dietary lipid requirements for Chinese longsnout catfish and gibel carp were 142.6 and 140.5 g kg(-1), respectively.

Effect of ration on the growth and energy budget of Chinese longsnout catfish, Leiocassis longirostris Gunther

The effect of ration on growth and energy budget of Chinese longsnout catfish was investigated in a growth trial. Fish of initial body weight of 6.5 g were fed at six ration levels (RLs): starvation, 0.8%, 1.6%, 2.4%, 3.2% of body weight per day, and apparent satiation for 8 weeks. Fish were weighed biweekly to adjust feed amount. The results showed that specific growth rate in wet weight, protein and energy increased logarithmically with increased RLs. The relationship of specific growth rate in wet weight (SGRw, % day(-1)) and RL (%) was a decelerating curve: SGRw=-0.62+3.10 Ln(RL+1). The energy budget equation at satiation was: 100 IE=12.94 FE+5.50(ZE+UE)+40.07 HE+41.49 RE, where IE, FE, (ZE+UE), HE, RE are food energy, faecal energy, excretory energy, heat production and recovered energy respectively. Body composition was slightly but significantly affected by ration size except for protein content. The most efficient ration based on the relationship between RL and feed efficiency ratio in energy (FERe) was 1.8% of body weight per day.

Energy budget of Nile tilapia (Oreochromis niloticus) in relation to ration size

Nile tilapia weighing 8.29-11.02 g were fed a practical diet at seven ration levels (starvation, 0.5, 1, 2, 3, 4% body weight per day and satiation) twice a day at 30 degrees C. Feed consumption, apparent digestibility, nitrogenous excretion and growth were determined directly, and heat production was calculated by difference of energy budget. The relationship between specific growth rate in wet weight (SGR(w), percentage per day) and ration size (RL, percentage per day) was a decelerating curve described as SGR(w) = 2.98 (1 - e(-0.61(RL-0.43))). The apparent digestibility coefficients for dry matter and protein showed a decreasing pattern with increasing ration while the apparent digestibility coefficient of energy was not significantly affected by ration size. The proportion of gross energy intake lost in nitrogenous excretion tended to decrease with increasing ration. Feed efficiency was highest, and the proportion of gross energy intake channelled to heat production was lowest, at an intermediate ration level (2% per day). The energy budget at the satiation level was: 100IE = 16.9FE + 1.2(ZE + UE) + 62.3HE + 19.6RE, where IE, FE, (ZE + UE), HE and RE represent gross energy intake, faecal energy, excretory (non-faecal) energy loss, heat production and recovered energy (growth), respectively. (C) 1997 Elsevier Science B.V.

Quantum-confined Stark effects in a single GaN quantum dot

Using analytical expressions for the polarization field in GaN quantum dot, and an approximation by separating the potential into a radial and an axial, we investigate theoretically the quantum-confined Stark effects. The electron and hole energy levels and optical transition energies are calculated in the presence of an electric field in different directions. The results show that the electron and hole energy levels and the optical transition energies can cause redshifts for the lateral electric field and blueshifts for the vertical field. The rotational direction of electric field can also change the energy shift.

Investigation of Electronic Energy Levels in InAs Quantum Dot with Shape of Lens by Using B-Spline Technique

The dependence of the electronic energy levels on the size of quantum dots (QDs) with the shape of spherical lens is studied by using the B-spline technique for the first time. Within the framework of the effective-mass theory, the values of electronic energy levels are obtained as a function of the height, radius and volume of QDs, respectively. When the height or radius of QDs increases, all the electronic energy levels lower, and the separations between the energy levels decrease. For lens-shape QDs, height is the key factor in dominating the energy levels comparing with the effect of radius, especially in dominating the ground-state level. These computational results are compared with that of other theoretical calculation ways. The B-spline technique is proved to be an effective way in calculating the electronic structure in QDs with the shape of spherical lens.

Asymmetric quantum-confined Stark effects of hierarchical self-assembly of GaAs/AlxGa1-xAs quantum dots

Quantum-confined Stark effects in GaAs/AlxGa1-xAs self-assembled quantum dots are investigated theoretically in the framework of effective-mass envelope function theory. The electron and hole energy levels and optical transition energies are calculated in the presence of an electric field in different directions. In our calculation, the effect of finite offset, valence-band mixing, the effects due to the different effective masses of electrons and holes in different regions, and the real quantum dot structures are all taken into account. The results show that the electron and hole energy levels and the optical transition energies can cause blueshifts when the electric field is applied along the opposite to the growth direction. Our calculated results are useful for the application of hierarchical self-assembly of GaAs/AlxGa1-xAs quantum dots to photoelectric devices. (c) 2005 American Institute of Physics.

Influence of level filling on optical properties of quantum well

In a specially- designed three-barrier-double-well tunneling structure, electron injecting from the emitter in combination with escaping through a resonant-tunneling structure were used to adjust and control the filling of electrons in different subbands. It was observed that the occupation in the first-excited electron state can result in a suppression to quantum confinement Stark effect. Moreover, at very low bias, a series of intrigue photoluminescence peaks appeared as a small quantity of excess electron was filled in the ground state of the quantum well, that cannot be explained by the theory of hand-to-hand transition in the framework of single electron picture.

Anisotropic Zeeman splitting and Stark shift of In1-yMnyAs1-xNx oblate quantum dots

The electronic structure, Zeeman splitting, and Stark shift of In1-yMnyAs1-xNx oblate quantum dots are studied using the ten-band k center dot p model including the sp-d exchange interaction between the carriers and the magnetic ion. The Zeeman splitting of the electron ground states is almost isotropic. The Zeeman splitting of the hole ground states is highly anisotropic, with an anisotropy factor of 918 at B=0.1 T. The Zeeman splittings of some of the electron and hole excited states are also highly anisotropic. It is because of the spin-orbit coupling which couples the spin states with the anisotropic space-wave functions due to the anisotropic shape. It is found that when the magnetic quantum number of total orbital angular momentum is nearly zero, the spin states couple with the space-wave functions very little, and the Zeeman splitting is isotropic. Conversely, if the magnetic quantum number of total orbital angular momentum is not zero, the space-wave functions in the degenerate states are different, and the Zeeman splitting is highly anisotropic. The electron and hole Stark shifts of oblate quantum dots are also highly anisotropic. The decrease of band gap with increasing nitrogen composition is much more obvious in the smaller radius case because the lowest conduction level is increased by the quantum confinement effect and is closer to the nitrogen level. (C) 2007 American Institute of Physics.

Stark and rashba effects in GaN nanowires

The effects of an external electric field on the electronic structure of GaN nanowires, as well as GaAs nanowires for comparison, are investigated theoretically. It is found that there is an anti-crossing effect in GaN nanowires caused by a small electric field, the hole energy levels, hole wave functions, and optical oscillator strengths change dramatically when the radius (R) is around a critical radius (R-c), while this effect is absent in GaAs nanowires. When R is slightly smaller than R-c, the highest hole states are optically dark in the absence of the electric field, and a small electric field can change them to be optically bright, due to the coupling of hole states brought by the field. The Rashba spin-orbit effect is also studied. The electron Rashba coefficient alpha increases linearly with the electric field. While the hole Rashba coefficients beta do not increase linearly, but have complicated relationships with the electric field.

Deep level and photoluminescence studies of Er-implanted GaN films

Deep level transient spectroscopy measurements were performed on the metal organic chemical vapor deposition epitaxially grown GaN before and after the implantation with Er. Only one deep level located at 0.270 eV below the conduction band was found in the as-grown GaN films. But four defect levels located at 0.300, 0.188, 0.600 and 0.410 eV below the conduction band were found in the Er-implanted GaN films after annealing at 900 degrees for 30 min. The origins of the deep defect levels were discussed. The photoluminescence (PL) properties of Er-implanted GaN thin films were also studied. After annealing at 900 degrees for 30 min in a nitrogen flow, Er-related 1.54 mu m luminescence peaks could be observed for the Er-implanted GaN sample. Moreover, the energy-transfer and recombination processes of the Er-implanted GaN film were described. (c) 2006 Elsevier B.V. All rights reserved.

The Stark effect on excitons in a bilayer system

The Stark effect on excitons in a bilayer system is investigated theoretically within the framework of the effective-mass approximation. The calculations indicate that the energy of the excitons decreases as the value of the in-plane electric field F increases at a fixed value of the distance d between the layers. However, the energy of the excitons increases with d at a fixed value of F. In particular, it increases linearly at small values of d but increases as 1/d at large values. Therefore, it can be concluded that excitons in a bilayer system have a small binding energy equal to the absolute value of the excitonic energy at large d or small F. In addition, the radiative lifetime of heavy-hole excitons in this system is calculated and is found to be short at small values of both F and d. The radiative lifetime of heavy-hole excitons in a bilayer system can be increased by two orders by an in-plane electric field of 2 kV/cm when d is twice the excitonic Rydberg. (c) 2006 American Institute of Physics.

Deep level transient spectroscopy studies of Er and Pr implanted GaN films

Deep level transient spectroscopy measurements were used to characterize the electrical properties of metal organic chemical vapor deposition grown undoped, Er-implanted and Pr-implanted GaN films. Only one deep level located at 0.270 eV below the conduction band was found in the as-grown GaN films. But four defect levels located at 0.300 eV, 0.188 eV, 0.600 eV and 0.410 eV below the conduction band were found in the Er-implanted GaN films after annealing at 900 degrees C for 30 min, and four defect levels located at 0.280 eV, 0.190 eV, 0.610 eV and 0.390 eV below the conduction band were found in the Pr-implanted GaN films after annealing at 1050 degrees C for 30min. The origins of the deep defect levels are discussed. After annealing at 900 degrees C for 30min in a nitrogen flow, Er-related 1538nm luminescence peaks could be observed for the Er-implanted GaN sample. The energy-transfer and luminescence mechanism of the Er-implanted GaN film are described.

Electronic structure of coupled vertically stacked self-assembled InAs quantum disks in a vertical electric field

In the framework of the effective-mass and adiabatic approximations, by setting the effective-mass of electron in the quantum disks (QDs) different from that in the potential barrier material, we make some improvements in the calculation of the electronic energy levels of vertically stacked self-assembled InAs QD. Comparing with the results when an empirical value was adopted as the effective-mass of electron of the system, we can see that the higher levels become heightened. Furthermore, the Stark shifts of the system of different methods are compared. The Stark shifts of holes are also studied. The vertical electric field changes the splitting between the symmetric level and the antisymmetric one for the same angular momentum. (C) 2003 Elsevier Ltd. All rights reserved.

Quantum-confined stark effect of vertically stacked self-assembled quantum discs

We study the electronic energy levels and probability distribution of vertically stacked self-assembled InAs quantum discs system in the presence of a vertically applied electric field. This field is found to increase the splitting between the symmetric and antisymmetric levels for the same angular momentum. The field along the direction from one disc to another affects the electronic energy levels similarly as that in the opposite direction because the two discs are identical. It is obvious from our calculation that the probability of finding an electron in one disc becomes larger when the field points from this disc to the other one.