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Prediction models for enteric methane (CH4) emissions from beef cattle proposed by various groups may not perform with similar accuracy for the low- and middle-income countries in South-east Asia (SE-Asia) because beef cattle in these countries are raised under different climatic conditions with diverse feeding systems, and have different CH4 emission characteristics. The objectives of this study were to: i) predict CH4 emission (g d−1 animal−1), yield [g kg−1 dry matter intake; DMI)−1], intensity [g kg−1 average daily gain)−1], and CH4 conversion factor (Ym) using an intercountry database of individual animal records from SE-Asia; ii) evaluate the impact of different dietary forage contents (all-, high- and low-forage) representing the diverse feeding systems on CH4 emission, yield, intensity and Ym in SE-Asia; and iii) cross-validate equations from this study with published data. A total of 398 individual animal observations of beef cattle from SE-Asia were used for this analysis. Linear models developed by incrementally adding covariates revealed that CH4 emission model using only DMI fitted to all data had a root mean square prediction error (RMSPE) of 16.9%. Subsets containing data with 100% forage in the diet (all-forage), 50–85% (high-forage) and < 50% (low-forage) had an RMSPE of 16.5%, 14.7%, and 17.4%, respectively. Linear multiple equation based on DMI and dietary NDF concentration (DMI + NDF_C, RMSPE = 15.2%; all-data) improved prediction accuracy over that of DMI alone. The DMI + NDF_C models for all-forage (RMSPE = 14.6%) and high-forage subsets (RMSPE = 13.3%) except for low-forage (RMSPE = 16.4%), improved the precision and accuracy of CH4 emission prediction. Methane yield and CH4 emission intensity could not be reliably modelled with the current database. The present study provides improved CH4 prediction models for beef cattle managed under diverse feeding systems in SE-Asia and affirmed that region-specific models are needed to reliably predict beef cattle CH4 emission at national or regional levels, particularly for low- and middle-income countries.

The experiment was conducted to investigate degradation of dry matter (DM) and protein of mulberry and rice bran when incubated in nylon bag in the rumen at different incubation times and different rumen environments of rumen-cannulated adult sheep. Three different rumen conditions were created by feeding the three rumen-cannulated sheep with urea-treated rice straw as basal diet and offered with three supplemental treatment diets on different source of energy and nitrogen. Mulberry, urea and rice bran were used as source of fermentable energy and protein. Treatments consisted of control diet mulberry and molasses (T0); 50% mulberry was replaced by rice bran and urea (T1); and 100% of mulberry was replaced with rice bran and urea (T2). The diets were formulated in iso protein and iso energy. Supplemental diets were offered at 1.2% BW. The study was conducted in three periods. For each period, the sheep was offered with one of three supplemental treatment diets. The nylon bags each, contains sample of either mulberrry or rice bran were incubated in the rumen of sheep at different incubation times in reverse order (48, 24, 12, 9, 6, and 3h). Degradation characteristic data were obtained by analyzing degradability data with the equation of p = a+b(1-e-ct) using Neway computer package. Data of degradation characteristic, degradability of DM and CP, DMI, rumen NH3-N and pH were subjected to analysis of variance (ANOVA) using a SAS software package. The results showed that the dry matter intake (DMI) and rumen pH were not significantly different between diets. The rumen ammonia concentration of T1 and T2 was significantly higher than that of T0. However, the rumen ammonia concentration was higher than that of critical value for rumen microbial synthesis (>5mg/100ml). The rate (c value) of DM degradability of mulberry and rice bran was affected by diet treaments, where T2 diet resulted in lower c of mulberry and rice bran. Only CP degradability of mulberry on the other hand was affected by diet treatments. But, both CP mulberry and rice bran had high degradability (>80% after 24 hs incubation) in all diet treatments. It is concluded that the three diets of this study were capable of creating the optimum condition for rumen fermentation. Supplementation of mulberry or urea-rice bran mixture had similar effect on protein degradability of rice bran. On the other hand, the rate of protein degradability of mulberry was reduced when it was incubated in the rumen of sheep fed urea rice bran mix supplement.

Mulberry foliages have high nutritive value (protein content, digestibility and degradability), therefore it is potential to be used as a supplement to poor quality roughages. The objective of this experiment was to evaluate the effect of addition of fermentable energy in the mixed of mulberry and rice straw basal diet. A control diet consisted of either rice straw (RS) or urea treated rice straw mixed with mulberry foliage (URS) with ratio of 60 : 40%. Treatment was formulated by supplementation of control diet with molasses (as sources of fermentable energy) at 3 levels (5, 10 and 15%). The study was conducted in a 2 x 4 factorial experiment, consisted of 2 levels rice straw (untreated and urea treated) and 4 levels molasses supplementation (control and 3 levels for molasses). Diets were evaluated using in vitro gas production. The fermentation kinetics was determined from the incubation of 200 mg sample during 96 hours. The calculation of the kinetics based on exponential equation P = A+ B (1-e-ct). A shorter gas production test was carried out to determine truly degradable fermented substrates (in vitro true organic matter degradability/IVTOMD) by incubating 500 mg of samples 24 hours. The result showed that there was no significant interaction between rice straw treatment and molasses supplementation on fermentation characteristics, in vitro true dry matter digestibility, fermented substrate and total volatile fatty acid (VFA) production. However there was a significant interaction between rice straw treatment on partitioning factor (PF), gas produced, propionic acid production and ratio between acetic acid and propionic acid. Molasses supplementation significantly (P

The reduction of nitrogen (N) excretion in animal production is crucial in intensive farming systems particularly in the developed countries. In this study, a model to predict N excretion in cattle was developed based on existing feeding standards and evaluated using independent N balance experiments for Holstein steers and lactating cows and Japanese Black (JB) steers. Although model predictions for fecal and urinary N excretions appeared to be close to observed values in plot figures, statistical analysis showed that the model tended to over-predict both fecal and urinary N excretions, especially in Holstein lactating cows. This was because body weight changes of cows during lactation period were not considered in the model due to the lack of information (i.e., body weight gain or loss) available in the experimental data for evaluation. There were large mean bias and small line bias for urinary N prediction, but reverse results were obtained for fecal N prediction. The largest mean square prediction errors for both N excretions were due to random variation in all cases. When all data were pooled (combined), the accuracy for predictions for fecal N excretion was considerably high ( r 2 = 0.94), indicating that the model may predict fecal N excretion beyond breeds, sexes and physiological states (growing and lactating). More information and accumulated data will be required to predict urinary N excretion under a wide range of genotype and environmental situation.

We have investigated the temperature and excitation power dependence of photoluminescence properties of InAs self-assembled quantum dots grown between two Al0.5Ga0.5As quantum wells. The temperature evolutions of the lower-and higher-energy transition in the photoluminescence spectra have been observed. The striking result is that a higher-energy peak appears at 105 K and its relative intensity increases with temperature in the 105-291 K range. We demonstrate that the higher-energy peak corresponds to the excited-state transition involving the bound-electron state of quantum dots and the two-dimensional hole continuum of wetting layer. At higher temperature, the carrier transition associated with the wetting layer dominates the photoluminescence spectra. A thermalization model is given to explain the process of hole thermal transfer between wetting layer and quantum dots. (C) 2000 Published by Elsevier Science B.V. All rights reserved.

Postgrowth rapid thermal annealing was performed on InGaAs/GaAs quantum dots grown by molecular beam epitaxy. The blue shift of the emission peak and the narrowing of the luminescence line width are observed at lower annealing temperature. However, when the annealing temperature is increased to 850 degrees C, the emission line width becomes larger. The TEM image of this sample shows that the surface becomes rough, and some large clusters are formed, which is due to the interdiffusion of In, Ga atoms at the InGaAs/GaAs interface and to the strain relaxation. The material is found to degrade dramatically when the annealing temperature is further increased to 900 degrees C, while emission from quantum dots can still be detected, along with the appearance of the emission from excited state. (C) 2000 Elsevier Science B.V. All rights reserved.

Red-emission at similar to 640 nm from self-assembled In0.55Al0.45As/Al0.5Ga0.5As quantum dots grown on GaAs substrate by molecular beam epitaxy (MBE) has been demonstrated. We obtained a double-peak structure of photoluminescence (PL) spectra from quantum dots. An atomic force micrograph (AFM) image for uncapped sample also shows a bimodal distribution of dot sizes. From the temperature and excitation intensity dependence of PL spectra, we found that the double-peak structure of PL spectra from quantum dots was strongly correlated to the two predominant quantum dot families. Taking into account quantum-size effect on the peak energy, we propose that the high (low) energy peak results from a smaller (larger) dot family, and this result is identical with the statistical distribution of dot lateral size from the AFM image.

Atomic force microscopy (AFM) measurements of nanometer-sized islands formed by 2 monolayers of InAs by molecular beam epitaxy have been carried out and the scan line of individual islands was extracted from raw AFM data for investigation. It is found that the base widths of nanometer-sized islands obtained by AFM are not reliable due to the finite size and shape of the contacting probe. A simple model is proposed to analyze the deviation of the measured value From the real value of the base width of InAs islands. (C) 1998 Elsevier Science B.V. All rights reserved.

The crystallographic tilt of the epilayers with respect to their substrates has been observed in many heteroepitaxial systems. Many models have been proposed to explain this phenomenon, but none of them is suitable for the large mismatched system, such as GaAs/Si. Here a new model is proposed for GaAs/Si epilayers, which can also be used in other large mismatched systems. The magnitude of the tilt calculated from this model coincide well with the experimental results. Especially, this model can correctly predict the tilt direction of the GaAs/Si epilayers.

A numerical model that combines mass transport and surface kinetics was applied, for the first time, to the chemical vapor epitaxy of GexSi1-x. The temperature, velocity and concentration fields were calculated from the conservation equations for energy, momentum and species coupled with the boundary conditions on the growth surface which were determined by surface kinetics. The deposition rates of Si and Ge were assumed to be limited, respectively, by surface kinetics and mass transport. A theoretical relation between the initial conditions and the Ge composition in the solid was established. The calculated growth rate as well as the Ge composition in the solid and its dependence on growth temperature agree well with experimental data.

We report a novel technique for growing high-quality GaAs on Si substrate. The process involves deposition of a thin amorphous Si film prior to the conventional two-step growth. The GaAs layers grown on Si by this technique using metalorganic chemical vapor deposition exhibit a better surface morphology and higher crystallinity as compared to the samples grown by conventional two-step method. The full width at half maximum (FWHM) of the x-ray (004) rocking curve for 2.2 μm thick GaAs/Si epilayer grown by using this new method is 160 arcsec. The FWHM of the photoluminescence spectrum main peak for this sample is 2.1 meV. These are among the best results reported so far. In addition, the mechanism of this new growth method was studied using high-resolution transmission electron microscopy.

Voluntary food intake, digestibility and water turnover were determined in adult Malaysian lesser mouse-deer (Tragulus javanicus) given unlimited access to lundai foliage (Sapium baccatum). Daily dry matter (DM) intake was 42.4 g/kg metabolic live mass (M0.73) or 3.7% M. Digestible energy intake was 853 kJ/day (571 kJ metabolisable energy per M0.73), calculated to be used with 79% efficiency. Apparent digestibility (%) of organic matter was 83.8, crude fibre 63.7, acid detergent fibre 60.5, neutral detergent fibre 72.1 and crude protein 65.0. Urinary excretion of the purine derivative, allantoin, was 0.05 mg/g digestible DM intake suggesting rumen microbial yield efficiency may be lower than in other ruminant species. Total water intake was 182 ml/M0.82. The body-water content of the fed mouse-deer, from tritiated water dilution, was 77% M, consistent with a very lean carcass. Turnover of body water was 17% per day. The mouse-deer produced relatively dry, well-defined faecal pellets.

Energetic efficiencies of Kedah Kelantan cattle (Bos indicus) and swamp buffalo (Bubalus bubalis) were determined using a double 4 × 4 latin square experiment, replicated four times for each species. The animals were fed at nominal maintenance (M), 1.4M, 1.8M or ad lib. intakes. Retained energy (RE) was estimated for each animal from the difference between initial and final body fat and protein compositions (using the TOH dilution procedure) for each period. Maintenance requirements for energy equilibrium (Em), energetic efficiencies for maintenance (km) and for gain (k) and maximum rates of gain (MAX) were estimated using quadratic equation of RE on metabolisable energy intake (MEI). Em for cattle was higher (P < 0.05) than values for buffalo (335 vs. 313 kJ ME per kg0.75 BW). km for total energy retained (REtotal) for cattle was higher (P < 0.05) than that for buffalo (0.64 vs. 0.48), because of the higher (P < 0.01) km for fat in cattle (0.45) compared to that for buffalo (0.22). k for REtotal and REfat for cattle (0.30 and 0.18, respectively) were also higher (P < 0.05) than those for buffalo (0.25 and 0.12, respectively). MAXtotal and MAXfat for cattle (130.3 and 82.7 kJ per kg0.75 BW, respectively) was higher (P < 0.05) than those for buffalo (108.0 and 69.7 kJ per kg0.75 BW, respectively). Em, km, k and MAX values measured for RE protein (REprot) for the two species were not statistically different.

The thermal stability of GaAs layers grown at low temperature by molecular beam epitaxy and subsequently annealed from 250 to 850 degrees has been investigated by transmission electron microscopy and Hall measurements. The results show that the formation of arsenic precipitates in annealed GaAs epilayers grown at low temperature and their crystallographical configuration are highly dependent on the temperature and duration of the annealing. Thermal annealing at 850 degrees for 30 min causes arsenic precipitates to become amorphous and some fraction of the arsenic precipitates to redissolve in the crystal matrix. An analysis of the dependence of resistivity on anneal temperature by Hall measurements gives an activation energy of about 1.6 eV for the formation of arsenic precipitates. Our results are discussed taking regard of the role electrically active paint defects during the precipitating process.

Quantum dot (QD) lasers are expected to have superior properties over conventional quantum well lasers due to a delta-function like density of states resulting from three dimensional quantum confinements. QD lasers can only be realized with significant improvements in uniformity of QDs free of defects and increasing QD density. In this paper, we first briefly give a review on the techniques for preparing QDs, and emphasis on strain induced self-organized quantum dot growth. Secondly, self-organized In(Ga)As/GaAs, InAlAs/GaAlAs and InAs/InAlAs QDs grown on both GaAs and InP substrates with different orientations by using MBE and the Stranski-Krastanow (SK) growth mode at our labs are presented. Under optimization of the growth conditions such as growth temperature, V/III ratio, the amount of InAs, In/sub x/Ga/sub 1-x/As, In/sub x/Al/sub 1-x/As coverage, the composition x, etc., controlling the thickness of the strained layers, for example, just slightly larger than the critical thickness and choosing the substrate orientation or patterned substrates as well, the sheet density of ODs can reach as high as 10/sup 11/ cm/sup -2/, and the dot size distribution is controlled to be less than 10%. These are very important to obtain a low threshold current density (J/sub th/) of the QD laser. How to improve the dot lateral ordering and the dot vertical alignment for realizing lasing from the ground states of the QDs and further reducing the J/sub th/ Of the QD lasers are also described in detail. Thirdly, based on the optimization of the hand engineering design for the QD laser and the structure geometry and growth conditions of QDs, 1 W continuous-wave (cw) laser operation of a single composite sheet or vertically coupled In(Ga)As quantum dots in a GaAs matrix and a larger than 10 W semiconductor laser module consisting of nineteen QD laser diodes is demonstrated. The lifetime of the QD laser with an emitting wavelength around 960 nm and 0.614 W cw operation at room temperature is over than 3000 hrs, at this point the output power was only reduced to 0.83 db. This is the best result as we know at the moment. Finally the future trends and perspectives of the QD laser are also discussed.

Quantum dot lasers are predicted to have proved lasing characteristics compared to quantum well and quantum wire lasers. We report on quantum dot lasers with active media of vertically stacked InAs quantum dot layers grown by molecular beam epitaxy. The laser diodes were fabricated and the threshold current density of 220 A/cm/sup 2/ was achieved at room temperature with lasing wavelength of 951 nm. The characteristic temperature T/sub 0/ was measured to be 333 K and 157 K for the temperature ranges of 40-180 K and 180-300 K, respectively.

We improved the method previously used to determine the lattice constants and misorientation of GaAs/Si by recording the patterns of X-ray (004) and (220) reflections. The (220) reflection was measured from the (110) cross section of a GaAs/Si epilayer. The structural properties of the GaAs/Si epilayers grown by metal-organic chemical-vapor deposition (MOCVD) using an ultrathin a-Si buffer layer were investigated. The rotation angle of GaAs/Si epilayers grown by MOCVD using an a-Si buffer layer is very small and the lattice constants of these GaAs/Si epilayers agree quite well with elastic theory.

GaAs epilayers grown on Si by metalorganic chemical vapor deposition (MOCVD) using an ultrathin a-Si buffer layer were characterized by deep-level transient spectroscopy (DLTS). Six electron traps with activation energies of 0.79, 0.67, 0.61, 0.55, 0.53 and 0.32 eV below the conduction band were determined by fitting the experimental spectra. Two of the levels, C (0.61 eV) and F (0.32 eV), were first detected in GaAs epilayers on Si and identified as the metastable defects M3 and M4, respectively. In order to improve the quality of GaAs/Si epilayers, another GaAs layer was grown on the GaAs/Si epilayers grown using MOCVD. The deep levels in this regrown GaAs epilayer were also studied using DLTS. Only the EL2 level was found in the regrown GaAs epilayers. These results show that the quality of the GaAs epilayer was greatly improved by applying this growth process.

Both the extrinsic luminescence related to the impurities near the well center and that related to the impurities at the GaAs-GaAlAs interfaces have been observed from all our samples with well widths ranging from 78 to 145 A. This identification has been confirmed by the dependence of the extrinsic photoluminescence on the excitation intensities and temperature. Relatively strong interface-related luminescence is believed to be due to the presence of more trapped impurities at the interfaces.