Faculty of Engineering Sciences and Technology

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    Auto-resonant peniotron amplifier with a down tapered DC magnetic field
    (Taylor & Francis, 1990-02) Musyoki, Stephen; Yokoo, Kuniyoshi; Sato, Nabuyi; Ono, Shoichi
    High efficiency operation of an auto-resonant peniotron amplifier operating with a down tapered DC magnetic field is discussed and the basic design concepts for a 200 GHz experimental prototype tube are described.
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    Auto-resonant eniotron oscillator using a magnetron type cavity
    (1991) Musyoki, Stephen; Yokoo, Kuniyoshi; Sato, Nobuyuki; Ono, Shoichi
    In an ideal auto-resonant eniotron oscillator (ARPO), all the electrons are able to give almost all their kinetic energy to an electromagnetic wave, resulting in a conversion efficiency of nearly 100%. However, the electric field strength required to drive a highly efficient interaction is difficult to achieve in an ordinary rectangular or circular waveguide cavity because of the low interaction coupling between electrons and the electromagnetic wave in the cavity. In this aper, we describe our investigation of an ARPO with a magnetron type cavity in lace of that above. In this cavity, the coupling becomes sufficiently strong to confirm experimentally the romising features of an ARPO. Additionally, the experiments should be useful for developing highly efficient medium-power oscillators in the microwave region. Here we resent our rocedure for designing such an experimental tube and our computer simulation results for its operational characteristics
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    Design of a high power, 10 GHz auto-resonant peniotron amplifier
    (1992) Musyoki, Stephen; Sakamoto, Keishi; Watanabe, Akihiko
    The autoresonant peniotron amplifier is a suitable source of high power RF radiation because of its high gain, high power, high frequency and high efficiency operation features. In this report we present our simulation results of a 10 GHz, 2.2 GW autoresonant peniotron amplifier with an electron energy conversion efficiency of 72.5 % and a gain of about 58 dB
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    Design of a high power, 2.75 GHz relativistic peniotron oscillator
    (1992-10) Musyoki, Stephen; Sakamoto, Keishi; Watanabe, Akihiko
    In the peniotron oscillator, the kinetic energy of relativistic electrons can be efficiently converted to an electromagnetic wave. This feature makes the peniotron a very attractive source of high power microwaves, which is required in heating of fusion plasma in tokamaks and high gradient particle accelerators. In this report we present the design of a 2.75 GHz relativistic peniotron oscillator which is capable of generating a microwave radiation of 30 megawatt with an efficiency of about 60 %. The experimental test results of the designed cavity are also presented
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    A static dynamic model for densification of geodetic networks.
    (1993) Aduol, Francis O.
    in the tradition of several joint papers by the honoree and myself, including E. Grafarend and B. Schaffrin (1974, 1976, 1988) and E. Grafarend, B. Schaffrin, and E. Knickmeyer (1982), I took up the subject again in B. Schaffrin (1984, 1989), N. Tamim and B. Schaffrin (1995) and B. Schaffrin and J. Cothren (1998), now with the emphasis on network densification methods which are rigorous, but which leave tie points unchanged along with their variances and covariances. Such a requirement led to the notion of “reproducing estimators” as first presented by B. Schaffrin (1997). It has been known for a long time that the so-called “dynamic adjustment” of geodetic networks can be interpreted as least-squares collocation, according to H. J. Buiten (1978), which would not yield estimates with the “reproducing property.” Also the “free net adjustment” followed by a Helmert transformation would not per se guarantee identical tie point coordinate estimates unless we “forget” about the deviations whose norm we had minimized, but usually not to zero. So the only “reprodu c - ing” alternative seemed to be given by the formulas of a classical least-squares adjustment with fixed constraint even though the tie points are “ fiducial” in their nature, having typically a full dispersion matrix. Therefore, in the formula for the corresponding variance-covariance matrix we find an add i - tional term which vanishes as soon as the “ fiducial” points become real “fixed” points; see, for i n - stance, B. Schaffrin (1984, 1989). This apparently has been the method, applied by JPL over the years, when they talked about “ fiducial network strategies” as in S. M. Lichten et al. (1989), for instance, without spelling out exactly what they did. In any case, as could have been expected, the latter one was shown not to be the optimal estimator with the “reproducing property” by B. Schaffrin (1997). Instead, the optimum turned out to be the “forgetful dynamic adjustment” where every densification point is found conventionally through least- squares collocation, but the tie points remain unchanged. Consequently, a free adjustment followed by a “forgetful Helmert transformation” must be considered inferior and may no longer be carried out routinely; see also K. R. Koch (1983) and F. W. O. Aduol (1993). Here we try to employ least-squares methodology to generate that “reproducing estimator” which, as we already know, will be optimal in this class
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    A model for the establishment of an integrated regional geodetic datum
    (1993) Aduol, Francis O.
    A model for the establishment of an integrated geodetic datum covering a region is treated. The integrated geodetic datum is understood here to comprise the geoid, the reference ellipsoid, and the positional coordinates. A comprehensive unified solution model including the three parameters comprising the datum is considered. The estimation model adopted rigorously incorporates determined prior information in the estimation of the datum parameters. Mathematical models together with the pertinent observation equations are presented, followed by a description of the procedure for the actual setting up of the datum. The observational scheme is based on a system of modular traverses anchored on a trilateration of GPS baselines.
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    A new method of emittance measurement for electron beams from the Micro-emitter
    (1994) Ishizuka, Hiroshi; Nakahara, Yuriko; Kawasaki, Sunao; Musyoki, Stephen; Shimizu, Hiroshi; Watanabe, Akihiko; Shiho, Makoto
    Recently a new type of cathode called Micor-emitter has been put in progress. This cathode is a microfabricated field emitter having the characteristics of very low emittance and high brightness. We cannot measure the emittance of the cathode with conventional methods like the pepper-pot method. The reasons are: (1) the angle between the electron orbit and the axis is very small and (2) we cannot focus the electron beam in the vacuum or on the surface of the material since the current density of the cathode is extremely high. For the emittance measurement for such low emittance and high brightness cathode, we need to expand the beam, and measure the beam's cross section without any slits or apertures. We studied and proposed a new emittance measurement method for the Micro-emitter.
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    Robust geodetic parameter estimation through iterative weighting
    (1994) Aduol, Francis O.
    A procedure for robust linear estimation of parameters on the basis of iterative weighting of observations is presented. The approach considers the weights of observations as not just functions of the observational variances, but as functions of both the observational variances and estimates of the observational residuals. However, as the residuals are themselves functions of the estimates of the unknown parameters, the entire estimation procedure is performed iteratively. Three test examples comprising a linear point estimation, a linear regression case, and a geodetic network have been adopted to demonstrate the procedure. The results indicate that the proposed approach is effective in the isolation and management of outliers, and further that the robust estimation is in general a more efficient estimation procedure than the ordinary least squares.
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    Emittance measurement of high-brightness microbeams
    (Japanese Journal of Applied Physics, 1994) Musyoki, Stephen; Ishizuka, Hiroshi; Nakahara, Yuriko; Kawasaki, Sunao; Shimizu, Hiroshi; Watanabe, Akihiko; Shiho, Makoto
    Arrays of microtriodes have recently become available due to the development of microfabricated field-emission electron sources. Computer simulation has shown that the brightness of beams emitted by them is significantly higher than that of the common microbeams, and possible application of the accelerated beam to free electron lasers has been discussed. Experimentation on beam generation has started, but methods for diagnosing the beam have not yet been established. Difficulty is predicted, because of the high brightness, in applying the conventional methods of emittance measurement. In this paper we propose a new method that determines the emittance without using apertures. The cross section of a converging beam is elongated by a quadrupole lens, and parameters of the emittance ellipse are obtained from the beam size on a screen when changing either the strength or the axial position of the quadrupole lens.
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    An evaluation of some robust estimation techniques in the estimation of geodetic parameters.
    (1999) Aduol, Francis O.
    In Part 1 of this study, we reported on an evaluation of the performances of four robust estimation techniques, namely: the modified residuals technique, the modified weights technique, the modified residuals-weights technique, and the iterative weighting technique. The methods were then tested on a simulated geodetic network. In this second part of the study, we carry out a further evaluation of the methods with a real geodetic network as the test network. In order that a set of gross-error contaminated observational may be available for the study, gross errors have been simulated into observational set. The results of the study largely corroborate the findings in Part 1 of the study
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    Simulation of the influence of secondary electrons on the performance of potential depressed collectors for TWTs
    (2000) Musyoki, Stephen; Takahashi, M; Uchikawa, T
    Significant differences have been found between measured and simulated data for collectors designed with codes which disregard the influence of secondary electrons. To solve this problem, various codes have been developed. These codes assume that secondary electrons are only emitted in a single direction and ignore their spatial distribution. We have developed a code in which secondary electron yield is calculated from an empirical formula and the emitted secondary electrons are assumed to have cosine spatial distribution. To represent this distribution, for each primary beam point of impact, the emitted secondary beam is split into 3 beams; one beam normal to the impact surface and the other two at an angle to the normal. The normal beam carries half of the current and the rest of the current is divided equally between the side beams. The code uses a two dimensional, axis symmetric Finite Element Method (FEM) for modeling. FEM has been chosen because of its ability to model accurately arbitrary shaped structures. We designed a ku-band (14.25 GHz), 2-stage TWT by using the developed code.
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    Influence of graphite morphology, matrix structure on gray iron machining
    (2000) Marwanga, Reuben O; Robert, C. Voigt; Paul, H. Cohen
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    The surveying profession beyond the Year 2000 and the Kenyan surveyor.
    (2000) Aduol, Francis O.
    An overview of geospatial information education and its development in Kenya in general and Jomo Kenyatta University of Agriculture and Technology (JKUAT) in particular is given. The gradual evolution and conception, design and establishment of Geomatic Engineering and Geospatial Information Systems (GIS) training programmes at Jomo Kenyatta University is discussed. The impetus of this growth, envisaged direction, expected impact on the practice of Geomatic Engineering, GIS and associated disciplines in Kenya and the Eastern Africa Region are explored. The anticipated challenges and strategies for meeting the same are discussed
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    A model for estimating student unit cost and staffing requirements for university programmes with reference to Kenyan public universities.
    (2001) Aduol, Francis O.
    A model for the estimation of student unit costs and the staffing requirements for university academic programmes is presented. The development of the model starts off with the specification of a staff distribution matrix, which sets out the proportions of the various staff levels in a given staff category that are needed to service at a particular degree level. The categories of staff considered are teaching (academic), senior administrative, technical, clerical, and semi-skilled. Within a given category of staff are considered various staff levels, e.g. Professor, Senior Lecturer and Lecturer in the case of the teaching staff category. The academic programmes are considered to be taken at the Bachelor's, Master's and the Doctorate degree levels. Ratios between numbers of staff in a given level within a category, as well as ratios of staff within the category needed to service at the various degree levels are specified a priori. Academic (teaching) student-staff ratios for the various programmes are also set out a priori. Student-staff ratios for the other categories of staff are then computationally derived from the academic student-staff ratios. For each staff category a staff distribution matrix is then worked out. With the staff distribution matrix thus specified, the student unit cost and staffing requirement for a given academic programme are computed through various manipulations on the matrix. As a test example, the model is used to estimate student unit cost and staffing requirements for the six public universities in Kenya
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    Financing public universities in Kenya: a model based on rationalised student unit costs and staffing
    (2001) Aduol, Francis O.
    Whitehead (1967:4) defines the term “Education is t he acquisition of the art of the utilization of knowledge.” The universities are those institutions that teach learners the art of the utilization of knowle dge. For this to be achieved, goals and objectives are set in such a way that at a certain time 3 or 4 years, an individual is said to acquire the basic art at u ndergraduate level. If still interested, the individual can continue to higher l evels. This basic level and other levels above it are referred as higher educa tion. In this paper, the term university will be used to refer higher education. The art of the teaching and learning process requir es the appropriate media to communicate the curriculum content in this paper, the term communication simply refers to the art of sending o r receiving messages. Development of any nations depends on the participa tion of its human resources. This need well qualified personnel to handle all matters pertaining to her specific needs. Education in deve loping countries has expanded tremendously from few secondary schools at independence to the vast numbers that we have today. Most of the Africa n countries had either one or two universities at independence or none at all. However, this trend has changed and the countries can be congratulated for making sure that their people/citizens have access to higher education