Farming in Changing Production Conditions: Agricultural Technology, Climate Change and Adaptation in Vietnam

In an era when enormous challenges to food security are imposed on humanity through phenomena such as global climate change, it is important to understand how farming households adapt and respond to a changing production environment. This thesis consists of three empirical studies with a special focus on rural farming households in Vietnam. The first study investigates the pattern and determinants of the use of four agricultural practices – new rice seed varieties, chemical fertilisers, pesticides and mechanisation – in small-scale rice farming. Using a long panel dataset, the study applied a two-stage estimation strategy to determine how and to what extent the changes in agricultural technology have been affected by various factors. The second study examines the changes in climatological variables since 1975 using a comprehensive dataset for a relatively long time period (1975 to 2014) and a high density of climatic records. It first combines statistical methods with geostatistical techniques to graphically represent the distribution of climate patterns, identifying variations and trends and linking to rice production throughout the country. The third study investigates whether or not farmers have altered their farming strategies over time in response to pronounced changes in the climate. Since farmers’ decisions to use certain farming techniques are inherently dynamic, I estimated a dynamic random-effects probit model, controlling for unobserved heterogeneity and state dependence. Vietnamese farmers have been operating their farms under a continuously transforming policy environment. However, new challenges are emerging and their impacts on agricultural production have been increasingly pronounced. The findings and policy implications drawn from these studies will be useful in enhancing farmers’ adaptive capacity in fast changing production conditions

Improvement of Eucalyptus plantations grown for pulp production

The objective of the studies this thesis is based upon was to increase knowledge of the genetics of traits related to wood volume, wood density and pulp yield in Eucalyptus urophylla and E. camaldulensis that could be used to enhance and accelerate tree improvement programs in Vietnam. Two provenance-progeny trials of E. urophylla in northern Vietnam testing 144 families, and three clonal trials of E. camaldulensis in southern, north-central and northern Vietnam testing a total of 172 clones were examined in these studies. In E. urophylla, significant between-provenance differences in growth traits were observed, but not in wood basic density or cellulose content. Estimated within-provenance heritabilities were 0.10-0.30 for growth traits, 0.60 for density and 0.50 for cellulose content. Estimated coefficients of additive genetic variation were 10% for growth traits, 6% for density and 4% for cellulose content. Selection efficiency for growth traits was found to be maximal at an age of 2-3 years, with an anticipated rotation period of 5-10 years. Genetic correlations between growth traits and density (0.10-0.28), growth traits and cellulose content (0.28-0.45), and cellulose content and density (-0.02) did not differ significantly from zero. Genetic correlations between the two sites in northern Vietnam, which were 60 km apart and had similar climate and soils, were high for both growth traits and wood density. In E. camaldulensis, clonal repeatabilities at ages 3 and 5 years were 0.18-0.42 for growth traits and 0.71-0.78 for density. The coefficient of genotypic variation was about 13% for growth traits and 6% for density. Genotypic correlations between growth traits and density (-0.16-0.24) did not differ significantly from zero. Between-site genotypic correlations were in the ranges of 0.32-0.56 for growth traits and 0.72-0.88 for density. Selection gains for diameter at breast height at each site at a selection proportion of 5% were 22-32%, with minor effects on density. Selection for diameter based on rankings of material at one site would yield gains in diameter at the other two sites that were only 40-60% of the gains obtainable from direct selection at those sites. Results from the studies suggest that considerable genetic improvement in eucalypt plantations grown for pulp production in Vietnam can be achieved through breeding and appropriate deployment. Strategies for management of genotype by environment interactions in breeding and clonal deployment of these species are discussed

An Effective Metaheuristic for Multiple Traveling Repairman Problem with Distance Constraints

Multiple Traveling Repairman Problem with Distance Constraints (MTRPD) is an extension of the NP-hard Multiple Traveling Repairman Problem. In MTRPD, a fleet of identical vehicles is dispatched to serve a set of customers with the following constraints. First, each vehicle's travel distance is limited by a threshold. Second, each customer must be visited exactly once. Our goal is to find the visiting order that minimizes the sum of waiting times. To solve MTRPD we propose to combine the Insertion Heuristic (IH), Variable Neighborhood Search (VNS), and Tabu Search (TS) algorithms into an effective two-phase metaheuristic that includes a construction phase and an improvement phase. In the former phase, IH is used to create an initial solution. In the latter phase, we use VNS to generate various neighborhoods, while TS is employed to mainly prohibit from getting trapped into cycles. By doing so, our algorithm can support the search to escape local optima. In addition, we introduce a novel neighborhoods’ structure and a constant time operation which are efficient for calculating the cost of each neighboring solution. To show the efficiency of our proposed metaheuristic algorithm, we extensively experiment on benchmark instances. The results show that our algorithm can find the optimal solutions for all instances with up to 50 vertices in a fraction of seconds. Moreover, for instances from 60 to 80 vertices, almost all found solutions fall into the range of 0.9 %-1.1 % of the optimal solutions' lower bounds in a reasonable duration. For instances with a larger number of vertices, the algorithm reaches good-quality solutions fast. Moreover, in a comparison to the state-of-the-art metaheuristics, our proposed algorithm can find better solutions

Uplink Channel Allocation Scheme and QoS Management Mechanism for Cognitive Cellular-Femtocell Networks

Cognitive radio and femtocell are promising technologies which can satisfy the requirements of future mobile communications in terms of dynamic spectrum sharing and high user density areas. Providing quality-of-service (QoS) guaranteed realtime services is challenging issue of future cognitive cellular-femtocell mobile networks. In this paper, we introduce a user’s QoS management mechanism used to protect SINR of macro users from QoS violation caused by femtocell users. We design a novel uplink channel allocation scheme (denoted as “flexible scheme”) for real-time connections. The scheme uses the information of interference level and channel occupancy collected at  cognitive femtocell access points and their covering macro base station (MBS) and apply relevant selection criteria to select an appropriate channel which causes the minimums interference to macro users of the covering MBS. Performance results prove that comparing with femtocell-access-point (FAP)-based and MBS-based uplink channel allocation schemes, the novel “flexible scheme” can provide lower unsuccessful probability of new connection requests

Study on Designing and Manufacturing a Radio-Frequency Generator Used in Drying Technology and Efficiency of a Radio Frequency-Assisted Heat Pump Dryer in Drying of <em>Ganoderma lucidum</em>

A radio-frequency (RF) generator applied in drying technology was designed and manufactured for drying Ganoderma lucidum. The drying experiments were conducted by drying method of RF-assisted heat pump in order to inspect the operating parameters of the RF generator and investigate the effects of the input drying parameters on drying rate in the RF-assisted heat pump drying of Ganoderma lucidum. The results have shown that the RF generator achieved the required operating parameters as design such as RF power of 3 kW and operating frequency of 27 MHz. In RF-assisted heat pump drying, increase in RF power and drying air temperature increases the drying rate. Meanwhile, drying air velocity does not significantly affect the drying rate. At RF power of 1.95 kW, the drying time reduces by 9, 17, and 33% in comparison with RF power of 1.3, 0.65, and 0 kW (heat pump drying). At drying air temperature of 50°C, the drying time reduces by 10% and 21% in comparison with drying air temperature of 40 and 45°C. Besides, increasing RF power retains the higher content of polysaccharide in Ganoderma lucidum, and the Ganoderma lucidum samples retain the color better after drying

The influences of the number of concrete dowels to shear resistance based on push out tests

To reduce the depth of floor-beam structures and to save the cost of headed-shear studs, many types of shallow composite beam have been developed during the last few years. Among them, the shallow-hollow steel beam consists of web openings, infilled with in-situ concrete (named concrete dowel) has been increasingly focused recently. In this new kind of structure, this concrete dowel plays an important role as the principal shear connector. This article presents an investigation on the shear transferring mechanism and failure behavior of the trapezoid shape concrete dowel. An experimental campaign of static push-out tests has been conducted with variability in the number of web openings (WOs). The results indicate that the mechanical behavior of concrete dowel could be divided into crushing, compression, and tension zones and exhibits brittle behavior. The longitudinal shear resistance and specimen's stiffness are strongly affected by the number of considered WO

On the performance of the time reversal SM-MIMO-UWB system on correlated channels

The impact of spatial correlation on the multi-input multi-output ultrawide band (MIMO-UWB) system using the time reversal (TR) technique is investigated. Thanks to TR, several data streams can be transmitted by using only one antenna in a system named virtual MIMO-TRUWB. Since the virtual MIMO-TR-UWB system is not affected by the transmit correlation, under the condition of the high spatial correlation, it outperforms the true MIMO-UWB system with multiple transmit antennas. The channel measurements are performed in short-range indoor environment, both line-of-sight and non-line-of-sight to verify the adopted correlated channel model.Vietnamese National Foundation for Science and Technology Development (NAFOSTED)/102.02.07.0