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होकुदाई बिसौनी

नयाँ अंक

अंक ४, कर्तिक २०६१

विषय सुचि

मुख्य पृष्‍ठ
यात्रा संस्मरण

सोध सारंश


































































































































































Hokudai Bisauni is a biannual (Nepali New Year and Dashain) publication of HUNSA.

Opinions expressed herein are those of the authors and do not reflect policy of HUNSA. 

               होकुदाई बिसौनी
अंक ४, कर्तिक २०६१
                          RESEARCH ARTICLE

Experimental Assessment of Microscopic Traffic Flow Models Based on RTK GPS Data

- Prakash Ranjitkar
Graduate School of Engineering,
 Hokkaido University)

Microscopic traffic flow approach has been given more importance in recent years in solving traffic and safety engineering problems. It has two major applications, first in simulation modeling where car following model amongst others controls the motion of vehicle in the network, and second in advance vehicle control and safety system (AVCSS) that is being introduced as a driver safety aid in an effort to minimize traffic accidents due to human errors. In the last five decades, a large number of car following theories has been developed in an effort to imitate the car following behavior more precisely. Although some of these models have been calibrated and validated also, the confusions on their performances are still prevailing as there is not much effort made towards reaching a common understanding in this regard.

This study has investigated some theoretical aspects of car following process based test track experiment data. It has mainly contributed in two research areas: first, human factor with a particular focus on drivers’ perception response time and drivers’ sensitivity in car following process, and second, calibration and validation of microscopic traffic flow models with a more in depth analysis of the General Motor’s (GM) car following model. The latest advancements in data collection and parameter optimization techniques are implemented to investigate the car following dynamics.  Several car following experiments were conducted in a test track under some simple driving conditions using RTK GPS receivers. Genetic algorithm is implemented to optimize the model parameters and compared with least square technique.

Text Box: -4-

The dissertation is organized in eight chapters. Chapter 1 introduces the background, problem statement, objective, scope and limitations of this study. Chapter 2 summarizes the literatures related to this study under the subheadings: traffic flow theories, car following experiments, global positioning system, and optimization techniques. Chapter 3 presents the details of car following experiments conducted in a test track and organized under the subheadings: experiment location, equipments used, drivers’ characteristics, driving conditions, post-experiment data processing, precision of measurement data, data compilation and data samples. Chapter 4 presents the approaches proposed in this study to investigate human factors, traffic stability, and calibrate and evaluate the microscopic traffic flow models. This study was conducted in three different stages: first investigation of human factors and traffic stability, second calibration and evaluation of microscopic traffic flow model, and third investigation of the GM model. Chapter 5 presents the results from the first step i.e. investigations on human factors and traffic stability, while Chapter 6 presents the results on the calibration and evaluation of microscopic traffic flow models. Chapter 7 presents the results from the investigation of the GM model that includes identification of the model parameters, influence of driving conditions, and characterization of the sensitivity parameters. Finally, Chapter 8 concludes this dissertation, highlighting the main contributions of this research along with some recommendations on future research directions.

Some of the contributions are: 1) implementation of instantaneous response time concept in car following analysis. 2) Investigations on the influence of individual drivers, disturbances in speed, and drivers’ position in the platoon on the driving behavior, 3) experimental analysis of traffic stability, 4) setting up a common approach to evaluate the performance of microscopic traffic flow models, 5) evaluation of the performance of some car following models based on how well they fit with the field data, 6) setting up a broader calibration scheme to calibrate the GM model parameters in a consistent manner, and 7) characterization of the GM model parameters.

The major outcomes of this study are: 1) a large number of instantaneous response time and corresponding sensitivity factor data were estimated efficiently using computer program, 2) the statistical analysis to these data have shown that interpersonal variations are dominant factor, while disturbances in speed or, drivers’ position in the platoon do not have much influence on the driving behavior, 3) the average response of the most of the drivers were unstable as they preferred to maintain closer headway, 4) the models fitted well with the speed data than the headway data, 5) interpersonal variations are influential than inter-model variations, 6) the GM model parameters were found sensitive to the approaches, driving conditions and optimization algorithms used for calibration, 7) the GM model parameters were identified with improved consistency and reliability, 8) the optimal values for the sensitivity parameters fitted well in lognormal function.



Food value, nutritional and biochemical evaluation of wild yam (Dioscorea species) tubers of Nepal

- Megh Raj Bhandari
Laboratory of Food Biochemistry, Research Group of Food Science
Graduate School of Agriculture, Hokkaido University

In Nepal, yams still exist only in wild uncultivated forms. However, they have a significant contribution both as staple as well as vegetables in the diet of local people, especially in village and remote areas. The sampled wild yams are, at present, not well known. Information on their nutritional and biochemical characteristics does not exist. Hence, present research work has attempted to evaluate these poorly utilized wild tubers, found in parts of mid-hill and Terai region of Nepal. The research lays ground for their commercial exploitation. The outcome of the research can be summarized briefly as follows:

1.  Examination of the food value and nutritional characteristics of some lesser known, under exploited wild yam tubers, reveals that the tubers are highly nutritious and are adequate to meet the protein and calorie needs of the target consumer populations. The protein content in yam tubers was found comparatively higher than reported protein value of potato and sweet potato. Yams were found to be good in amino acid composition. However, lysine and sulfur-containing amino acids were the most limiting amino acids in these wild tubers.  Wild yams were found to contain both dietary macro and micro minerals in good amount. The higher level of potassium and low sodium in these wild tubers can be advantageous to hypertensive patients, but are not suitable for renal failure patients.

2.  Assessment of antinutritional factors in these wild tubers indicated that oxalate, phytate, cyanogens, trypsin and a-amylase inhibitors occurred in varying concentrations in these tubers. In general, all four studied wild tubers were high in oxalate and phytate. The high level of oxalate does not make yams suitable for daily consumption for person suffering from kidney stone. This is one of the major barriers to use these tubers. Further, results indicated that the bioavailability of calcium and zinc in these wild yams could have been low, due to high level of oxalate and phytate.

3.  Cooking methods showed variable effect on the antinutritional factors in yam tubers. Among the cooking methods, boiling was found to be the most effective means of reducing most of antinutrients, followed by pressure cooking. Therefore, it is possible to reduce the activity of most of the antinutritional factors by boiling before consumption. This implies that the presence of antinutritional factors identified in this current study should not pose a problem to human health if the tubers are properly cooked before consumption.

4.  Bitter components were identified as furanoid norditerpenes, diosbulbins A and B. Results demonstrated that diosbulbin B, with average value of 31.4 mg/100 g FW, was the principal bitter compound compared to diosbulbin A (3.8 mg/100 g FW). The toxic alkaloid dioscorine and histamine (an allergen), reported in some other toxic yam species, were not detected in these wild tubers. Wild yam tubers contained substantial level of saponin ranging from 5 to 50 mg/100 g FW. Results indicated that these tubers are not toxic varieties. However, the observed bitterness in these tubers was synergistic from both furanoid norditerpenes and saponins, whereas the inflammation and toxicity observed could possibly due to the presence of cyanogens and high level of calcium oxalate.

5.  Wild yam tubers contained remarkable levels of organic acids and polyphenols. The latter were found to have significant antioxidant activities as evaluated by different methods such as DPPH free radical scavenging, ferrous ion chelating, reducing power and total antioxidant activity tests. The consumption of yam tubers may thus serve as a good source of antioxidant in its natural form; and may have roles in preventing human diseases, in which free radicals are involved, such as cancer, cardiovascular disease, and aging-related diseases. The high antioxidant activity of yams increases their potential to be used in producing different products as nutraceutical and pharmacological agents.

In conclusion, Nepali wild yam tubers contain essential dietary nutrients and substantial level of some phytochemicals, which could be useful for health promotion. The results may therefore offer a scientific basis for use of these wild tubers, both in human diet and some commercial products. These wild yams are, at present, not well known and have been collected only in the wild. This has limited their potential uses. Therefore, the research advocates for their commercial cultivation and recommends for breeding programs and popularized them for mass cultivation and consumption, particularly in food-deficit countries like Nepal to alleviate hunger and poverty. As its domestication for commercial exploitation is to be considered in a number of biogeographical regions, such nutritional and biochemical information is also very crucial to overcome the food crisis of ever expanding world's population. It is hoped that this research will serve as the basis for detailed study on nutritional and biochemical characteristics of these wild yams, both at national and international levels, particularly in case where such wild tubers are important for local food security.


Flow, turbulence and erosion induced by river structures

Sanjay Giri
Division of Environment & Resources Engineering
Hokkaido University

Construction of structures is usual practice in river engineering. River structures are supposed to be incorporated with a clear understanding of river variables that constitute the stable form and enable to avoid negative environmental impacts and, at the same time, provide their own stability. However, investigation on their effectiveness has indicated that many structures, contrary to the intended design, caused river instability and adverse environmental impacts. It clearly indicates that river structures are often selected and installed without an understanding of structure-induced flow, bed deformation and sediment transport. Of the most problems that have been facing in river engineering since long, riverbank erosion is of great significance from practical engineering point of view, in particular, in the context of Nepal. Lack of proper construction technique in consideration of specific hydraulic and morphological condition of rivers and precise assessment of structure-induced impact on equilibrium river regime has thought to be underlying causes of negative environmental consequences as well as failure of structures. For an instance, field study made for 50 sites with river training structures in Nepal to evaluate their performance, more than 60% was found as failure sites. Such evidences point out towards the necessity for an integrated and state-of-the-art approach to be undertaken in understanding the causes.

   Present research was prompted by the need to determine the structure-induced hydraulic and morphological evolution in consideration of channel plan-form. Extensive and explorative investigations on structure-induced flow, turbulence and morphological impact have been undergone within the framework of this research. Physical investigations have been carried out taking into account the complication associated with such phenomenon in the sense that there was no existence of a consistent theory explaining physically what in fact happens over the whole range of the phenomenon and, consequently, no consistent formulation. Basic objectives of this study were - to shed light and clearly recognize the evidences by means of extensive physical observation considering range of variables, strive for the implementation of possible modeling approach, mathematical and physical, in the context of its practical applicability. Experiments have been conducted in a large laboratory meandering channel where flow field, temporal morphological changes and bed-form pattern were mapped extensively using cutting-edge devices and data acquisition systems.

   Some new attempts at similar problems have been made despite their complication. Significant physical evidences have been revealed regarding the downstream hydraulic and morphologic impact that was found to be associated with structures, their combinations and quantity as well as channel plan-form. In addition, a model has been developed to assess the temporal evolution of bed erosion at river structures based on comprehensive physical observations. Some new parameters have been introduced. The proposed model is widely generalized and possesses considerable preference over earlier developed methods, since it takes into account range of variables overlooked in previous studies and more importantly time factor, which has been able to be generalized extensively in terms of a newly proposed parameter referred to as sediment Strouhal number. It is noteworthy to be mentioned that proposed model can be applied for cohesive sediment as well. The method has been validated using large range of independent physical investigations that have been carried out by several researchers during last 40 years along with some significant field data on erosion at spurs as well as bridge structures. Result is rather promising. Likewise, a simplified relationship has been proposed to assess the incipient of sediment near structures using very rare and valuable experimental data. Furthermore, a field investigation on consequences of flood event in Hokkaido (Typhoon No.15, 2003), and its morphological impact near river structures, in particular bridge structures has been carried out. Valuable data has been collected and used to validate developed method. In addition an extensive database (apparently first of this kind) has been created that can be of great use to researchers and practitioners who are involved in concerning subject matter.

   One of the important constituents of this research is the development of a 2D mathematical model. A novel numerical method referred to as Cubic- Interpolated Pseudo-particle (CIP) has been used to develop this model. Furthermore, continuity and momentum equations have been transferred to a physical coordinate system referred to as Moving Boundary Coordinate System (MBCS). The model has been validated using large range of physical data. The computational time is very efficient and thereby reliable to use in field scale phenomena, however still remains to be determined.  

   Based on these investigations, it can be inferred that the selection of structural solutions for river training, restoration and even installation of bridge structures should be based upon the underlying problems. At present there are no cookbook and unique solutions to these problems, nonetheless findings of this research must be applied as general guiding principles in a flexible design strategy that ensures their adequacy, safety, and environmentally acceptability. Likewise, findings of this research can be considered during decision-making process in practical river engineering issues and would be of significant bench mark for further investigations as well.

   So far as the context of Nepal is concerned, following modus operandi for the proper functioning of river engineering structures can be outlined:

Ř      Scientific approach to the problem.

Ř      Application of appropriate criteria considering all parameters and factors (in macro- level), e.g. precise assessment of characteristic of the rivers with two-phase motion.

Ř      Database management that enables countermeasure against the problem to be carried out efficiently and effectively.

Ř      Application of the achievements of modern science and technology, in particular, hydroinformatics.

Ř      Knowledge information distribution in regard to the problem.

Unified approach to the issue; i.e. remains a breast with other specialists like geologist, geomorphologist, ecologist etc.



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