Browsing by Author "Getachew, Anteneh"

Now showing 1 - 7 of 7
  • No Thumbnail Available
    Item
    Compa(ct Linear Operators on Blilbert Space and their App[ication to Integral Equations
    (Addis Ababa,, 2011-01) Getachew, Anteneh; Mohammed, Seid (PhD)
    Perhap the most theory developed about eigenvalue, eigenve t rand exi ten f oluti on of a certain operator equ ation i for matrix operator , but th fir t part t b con idered apart from matrices are integral operators, since the cia ical form ul ation from phy ics, chemistry, engineerin.g, stati stics are of thi nature and the tudy of an integral operators gives birth to the modern functional analysi . And the mo t common problem in appli ed mathematic are diffe rential operators which are fruitful source of integral equat ions. Due to various advantages of having integral equation rather than di ffere nti al equation usually we would like to convert and formulate differential equation in to integral equ ation. Many of integral operators encountered in application are bounded operators and many of them are, in fac t, in special classes of bounded operator called compact operators and again the most important classes of compact are the HilbertSchmidt operators.
  • No Thumbnail Available
    Item
    Correlating Dynamic Cone Penetration Index (Dcpi) with Undrained Shear Strength for Clayey Soils
    (Addis Ababa University, 2012-11) Getachew, Anteneh; Teferra, Alemayehu (Professor)
    Determination of the in situ engineering properties of foundation materials has always been a challenge for engineers practicing in developing countries. This usually leads to usage of unreliable designing methods. To avoid such problems, this research introduces the use of Dynamic Cone Penetration (DCP) which is a simple test device that is inexpensive, portable, and easy to operate and understand. In this thesis, field tests were conducted by locally manufactured dynamic cone penetration equipment from available materials. Laboratory tests needed to classify the soil and study the parameters that affect the dynamic cone penetration index were conducted. After analysing the data by categorising in to three categories, it has been found out that parameters like unconfined compression strength, liquidity index, depth, natural moisture content and bulk density have influence on the Dynamic Cone Penetration Index (DCPI). Undrained shear strength can be estimated by UCS=-197ln(DCPI)+735.5 with coefficient of determination (R2) of 71.1% for red clay soils of Addis Ababa and by UCS=895.8*DCPI-0.56 with R2 of 52.4%, for clayey soils including both red clay and black cotton soils of Addis Ababa combined. These good correlations were used to develop bearing capacity equation based on bearing capacity theory. The equation found were qult=-506.5ln(DCPI)+h+1891 for red clay soils of Addis Ababa and qult=2303.1*DCPI-0.56+h for clayey soils including both red clay and black cotton soils of Addis Ababa combined. The results are expected to have wide application in the construction sector.
  • No Thumbnail Available
    Item
    Dynamics of Carbon Dioxide Flux Over Africa: Insight from Observations and Model Simulations
    (Addis Ababa University, 2020-12-29) Getachew, Anteneh; Mengistu, Gizaw (Professor)
    The carbon cycle of tropical terrestrial vegetation plays a vital role in the storage and exchange of atmospheric carbon dioxide (CO2). However, large uncertainties surround the impacts of land-use change, climate warming, the frequency of droughts, and CO2 fertilization. This culminates in poorly quantified carbon stocks and carbon fluxes even for the major ecosystems in Africa’s carbon cycle (savannas and tropical evergreen forests). Contributors to this uncertainty are the sparsity of (micro-)meteorological observations across Africa’s vast land area, a lack of sufficient ground-based observation networks and validation data for CO2, and incomplete representation of important processes in numerical models. Satellite retrievals are strongly influenced by land-use changes, cloud cover, and aerosol loading. Moreover, Africa is a continent with wide extremes in surface type (which ranges from desert, rainforest, and Savannah) and aerosol loading. Therefore, the comparison of satellite observations with model and available in-situ observations will be useful to prove the performance of satellites and show how these systematic errors vary geographically over the continent. In this thesis, GOSAT column-averaged dry-air mole fraction of carbon dioxide (XCO2) is compared with the NOAA CT2016 and six flask observations across Africa using five years of data covering the period from May 2009 to April 2014. Besides, XCO2 from OCO-2 is compared with NOAA CT16NRT17 and eight flask observations across Africa using two years of data covering the period from January 2015 to December 2016. The analysis shows that the XCO2 from GOSAT is higher than XCO2 simulated by CT2016 by 0.28 _ 1.05 ppm, whereas OCO-2 XCO2 is lower than CT16NRT17 by 0.34 _ 0.9 ppm on African landmass on average. The mean correlations of 0.83 _ 0.12 and 0.60 _ 0.41 and an average RMSD of 2.30 _ 1.45 and 2.57 _ 0.89 ppm are found between the model and the respective datasets from GOSAT and OCO-2 implying the existence of a reasonably good agreement between CT and the two satellites over Africa’s land region. However, significant variations were observed in some regions. For example, OCO-2 XCO2 is lower than that of CT16NRT17 by up to 3 ppm over some regions in North Africa (e.g., Egypt, Libya, and Mali ) whereas it exceeds CT16NRT17 XCO2 by 2 ppm over Equatorial Africa (10_S - 10_N). This regional difference is also noted in the comparison of model simulations and satellite observations with flask observations over the continent. For example, CT shows a better sensitivity in capturing flask observations over sites located in Northern Africa. In contrast, satellite observations have better sensitivity in capturing flask observations in lower altitude island sites. CT2016 shows a high spatial mean of seasonal mean RMSD of 1.91 ppm during DJF from GOSAT, while CT16NRT17 shows RMSD of 1.75 ppm during MAM from OCO-2. On the other hand, the low RMSD of 1.00 and 1.07 ppm during SON in model XCO2 from GOSAT and OCO-2, respectively, indicate better agreement during autumn. The model simulation and satellite observations exhibit similar seasonal cycles of XCO2 with a small discrepancy over Southern Africa (35_ - 10_S) and during wet seasons over all regions. Two remotely sensed vegetation products that have been shown to correlate highly with Gross Primary Productivity (GPP): Sun-Induced Fluorescence (SIF) and Near-Infrared Reflectance of vegetation (NIRv) are also analyzed to further understand the dynamics of carbon dioxide flux. A comparison against flux tower observations of daytimepartitioned Net Ecosystem Exchange (NEE) from six major biomes in Africa shows that SIF and NIRv reproduce the seasonal patterns of GPP well, resulting in correlation coefficients of >0.9 (N=12 months, 4 sites) over savannas in the northern and southern hemisphere. These coefficients are slightly higher than for the widely used MPI-BGC GPP products and Enhanced Vegetation Index (EVI). Similar to SIF signals in the neighbouring Amazon, peak productivity occurs in the wet season coinciding with peak soil moisture, and is followed by an initial decline during the early dry season that reverses when light availability peaks. This suggests similar leaf dynamics are at play. Spatially, SIF and NIRv show a strong linear relation (R >0.9, N=250+ pixels) with multiyear MPI-BGC GPP even within single biomes. Both MPI-BGC GPP and EVI show saturation relative to peak NIRv and SIF signals during high productivity months, which suggests that GPP in the most productive regions of Africa might be larger than suggested. Africa’s biome integrated productivity is strongly controlled by the seasonality of soil moisture, with a weak influence of light availability superimposed, indicating that the biome productivity of Africa strongly depends on spatiotemporal drivers. Therefore, an understanding of the spatiotemporal ecosystem dynamics together with its relation to meteorological variables is paramount to quantify the responsiveness of the carbon cycle to climate variability. For that reason, an Empirical Ensemble Mode Decomposition (EEMD) was applied on 17 years monthly time series of natural CO2 flux covering the period from January 2000 to December 2016. The EEMD depicts natural CO2 flux has six periodicities over tropical Africa corresponding to seasonal, interannual, and decadal-scale variabilities which are likely driven by atmospheric and oceanic processes. Seasonal variabilities at quasi-3 months, quasi-6 months, and quasi-12 months contribute about 91.41% of the variability of natural CO2 flux, suggesting that CO2 flux has a strong variability at the seasonal scale. Moreover, high atmospheric CO2 flux was observed during warm and dry conditions. Precipitation is found to be a dominating driver of CO2 flux at the seasonal scale over the west coast of tropical Africa and East Africa. In addition to the six periodicities, the application of EEMD to a monthly time series of CO2 flux indicates the existence of either a nonlinear downward trend or a possible multidecadal periodicity that cannot be captured by the limited length of the current data set. The later is more likely as revealed by a slight reversal at the beginning of 2013. Moreover, analysis of different regions of tropical Africa shows reduced CO2 uptake over most regions since 2000, with exception for tropical North Africa which is found to have increased CO2 uptake most likely due to enhanced vegetation which exceeds deforestation. At the interannual scale, a quasi-2 year and quasi-5 year fluctuations were obtained from the EEMD with a contribution of 6.93% to the total CO2 flux variability. This interannual fluctuation has a significant correlation with Niño 3.4 index, El Niño induced temperature, precipitation, soil moisture, and enhanced vegetation index. A significant positive correlation between a warming temperature and interannual CO2 flux over tropical North Africa and rainforest regions suggests that temperature is the major driver of CO2 fluctuation at the interannual scale over these regions. Conversely, over Western and Tropical East Africa, precipitation was found as the most dominant driver. The anomalously high interannual CO2 flux was found in response to strong El Niño (Niño 3.4 index greater than 1.0) in the years 2009 and 2015/16 over most of Equatorial Africa. During the peak of 2015/16 El Niño, tropical Africa releases 0.2 mol/m2/month CO2 into the atmosphere due to interannual variability. The strongest (0.5 mol/m2/month) contribution was from the tropical rainforest, most likely driven by the rising temperature. Besides, Ethiopian highlands also release 0.4 mol/m2/month CO2 flux due to dry and warm conditions during this strong El Niño event. The CO2 flux mean over 17 years (2000-2016) shows that tropical Africa is a net CO2 sink (-7.02 gC/m2/year). However, during the 2015/16 El Niño years, tropical Africa releases 29.12 gC/m2/year leading to 487.49 TgC/year which is twice the estimated carbon flux of Africa (240 Tg C y􀀀1 ) for the period covering from 2000 to 2005.
  • No Thumbnail Available
    Item
    Linear Irreversible Thermodynamics, Efficiency and Coefficient of Performance of Thermal Brownian Motors in Tight Coupling
    (Addis Ababa University, 2007-07) Getachew, Anteneh; Bekele, Mulugeta (PhD)
    We analytically study a thermal Brownian motor and calculate exactly the Onsager's coe±cients in equilibrium and steady state conditions. We show that the reciprocity relation holds and the determinant of the Onsager's matrix vanishes. Such a condi- tion implies that the device is built with tight coupling. This tells us why Carnot's e±ciency can be achieved in the limit of in¯nitely slow velocities (quasistatic pro- cess). We also ¯nd the e±ciency and the coe±cient of performance for our model at these conditions using Onsager's coe±cients. The e±ciency and the coe±cient of performance that we found using the tools of LIT is exactly the same as the Carnot's e±ciency and coe±cient of performance. Also we ¯nd the e±ciency (at maximum power) and the maximum coe±cient of performance of the Brownian refrigerator to be exactly identical with the the corrosponding results of Curzon - Alhborn and Carnot's refrgerator for perfectly tight coupling model
  • No Thumbnail Available
    Item
    The Practice of 'Repair' During Conversational Discourse in EFL Classes
    (Addis Ababa University, 2009-06) Getachew, Anteneh; Mohammed, Nuru (PhD)
    The main aim of Ihis slUdy is to investigale Ihe practice of repair during conversational discourse in a foreign language classroom. Thus, il is mea11l to assess the nature of repair and repair-initiation patterns practiced during conversalional discourse in EFL classes, see the extent to which students and teachers use repair-initiation strategies during S-S and T-S interactions respectively, examine where the repair-initiations occur with reference to the trouble-source (I'S) in the observed palterns, find out the most fi'equent repair and repairinitial ion strategies used during classroom conversational discourse. The main subjects of the study were first year English major students taking the course Communicative English Skills-II and their teacher. Eight lessons recordings were made, fi'om all four sections students, fi'om whichfour lessons were transcribedfor analysis. The analysis of the transcribed data shows that all of the four repair initiation patterns were used during conversational discourse in EFL classes except a variation in frequency of use. In addition, the qua11litative analysis reveals that both slUdents and teachers play repair-initiation roles in S-S and T-S interactions respectively fi'om which other-initiation stralegy is more fi'equently used than self-initiation. Moreover, other initiated self repair pattern is most fi'equently used during conversational discourse in EFL classes. Along with this, concerning the position where repair-initiations occur in the observed patterns, in self initiated patterns the repair-initiations mostly occur in same turn; whereas in other initiated repair patterns the repair-initiations fi'equently occur in next turn immediately after the trouble-source. Finally, the thesis concludes by considering the implications of the .findings forfurther researches as to why other repair-initiation mechanism is highly apparent as well as other initiated self repair pal/ern is most fi'equently occur during conversational discourse in EFL classes. So, the study recommends EFL teachers to conduct CA researches in their classrooms to see the meaning negotiation strategies, in light with the practice of repair, and thereby 10 get feed back for remedial works and enhance students ' communicative competence.
  • No Thumbnail Available
    Item
    Segmental and Non-Segmental Phonology of Kūnámá ̄
    (Addis Ababa University, 2018-06) Getachew, Anteneh; Yigezu, Moges (PhD)
    This dissertation presents the descriptions of the segmental and non-segmental phonology of Kunama, a Nilo-Saharan dialect cluster spoken in Western Eritrea and Northern Ethiopia. It also provides an annotated multimedia corpus of the names and description of the Kunama cultural artifacts. The study uses primary data recorded from speakers of the Kunama Shukre dialect, spoken by an isolated minority group living in Tahtay Addi Yabo Woreda of Northwestern Zone of the Tigray Regional State, Ethiopia. The data was collected in three-round fieldworks in a period of two years (2014-15). The study has applied both impressionistic and instrumental analyses methods. The segmental phonology part covers the description of consonant and vowel sounds, phonotactics and syllable structure, phonological and morphophonological process and phonological adaptation of loanwords. Kunama (Shukre) has 18 consonant phonemes, whereas, the glottal fricative /h/ consonant, which has previously been proposed as the 19th consonant phoneme of Kunama, is found to be marginal. Two labialized velar consonants are attested to be the allophonic variants of the basic velar phonemes. The language has five phonemic vowels with an equal number of longer counterparts. The schwa and the central high-close vowel have a phonetic status despite that they are frequent. The analysis of phonotactics and syllable structure shows that the language has a richer and moderately complex inventory of syllable shapes. The productive and the most frequent consonant clusters (CC) follow sonorant-obstruent pattern, in which the prenasalized sequences (Nasal-Obstruent) are the commonest of all. Clusters and geminates occur only word-medially, so more than one consonant is severely marked, word-initially while three consonant sequences (CCC) are disallowed. Typologically, Kunama syllables are specified as light-open, heavy-open, light-closed and heavy-closed structures. Syllable weight specification is based on the mora count in the rhyme constituents of a syllable. Kunama light syllables are mono-moraic, i.e. having either a short vowel or a short vowel with a non-sonorant coda; whereas, the heavy syllables are bi-moraic having a long vowel, a diphthong, or a short vowel with a sonorant coda. A (C) V (C) template that makes an obligatory nucleus and optional margins, therefore, represents the Kunama basic syllable structures. While CV syllable is the unmarked structure, closed syllables (VC and CVC) are constrained word-finally. The morphophonemic processes comprise of terminal vowel deletion, vowel and glide epenthesis, glide formation, vowel rounding assimilation, gemination and degemination. Post-lexical alterations may cause constraint violations and necessitate resyllabification as such some constraints that operate on non-derived lexical items may not diametrically encode onto derivations. The analysis of phonological adaptation of loanwords explores the adjustment of word shapes and the mapping of sound segments of borrowed terms. Accordingly, consonant final loanwords are adapted with epenthesis of the nominal vowel suffix [a], and sound segments are adapted via substitution, deletion and retention strategies. The vowel adaptation is asymmetrical as both phonetically and phonologically grounded changes have been observed; nonetheless, the consonant adaptation is phonologically grounded. The non-segmental phonology part covers the analyses of gemination, vowel length and tone, in the lexicon and in the grammar. Kunama is a tone language with quantity contrast of vowel and consonant length. It has three phonemic tone levels (High, Mid and Low) that combine in nine ways on the surface of bi-moraic syllables and on sequences of two light syllables. These level combinations are claimed to be the basic melodies of the language. Complex (polysyllabic) contour melodies that combine simple rises and falls are attested on polysyllabic words. The study attempts to show the importance of pitch scaling in Kunama tone production as such it proposes a four-point pitch height scale in the tonal space of three distinctive level heights. The F0 scaling splits the high tone into extra-high and high pitches though no evidence shows the prominence of the former in underlying contrast. Tone plays a grammatical role as well, and it marks number of the possessor, in a range of possessive constructions, and number of person object in verbs. It also identifies inclusive vs. exclusive possessor, copula vs. genitive, and used as an intensifier morpheme on adjectives in attributive function. The salient tonal processes in Kunama are triggered by morpheme boundary phenomena. These include spreading and floating of tones, re-linking of floating tones, high tone shifting and docking, contour formation, tone assimilation and a low tone terrace.
  • No Thumbnail Available
    Item
    The Study of Aerosol Microphysical and Optical Parameters, Total Columnar Ozone and Water Vapor Content Derived from Sunphotometer
    (Addis Ababa University, 2009-07) Getachew, Anteneh; Mengistu, Gizaw (PhD)
    The spectral aerosol optical depth measurements are estimated over Addis Ababa (09.033N , 38.7E) at 2445m a.m.s.l. from the measurements of direct solar irradiance at different wavelengthes in the range between 305.3-1020nm using a hand held 5-channel Microtops II sunphotometer (Solar light co. USA) for the first time. Results show wavelength dependence of aerosol optical depth (AOD) which gradually decreases with increasing wavelength, having mean value of 0.209 (±0.0625) at 1020 nm optical channel. The °Angstrom exponent and turbidity were found to be inversely related with a good anticorrelation (R = −0.807) and the °Angstrom exponent was observed to be small in the range from (0.204) to (0.993) with a mean value of (0.627) indicates the presence of coarse mode particles over the site. Temporal variation of both AOD and retrieved columnar size distribution (ASD) show minimum value during the noon time. Large value with large variability in AOD and ASD are observed in April, 2009 as compered to March and May, 2009. This is attributed to the long range transported aerosols from different source. A good positive correlation between aerosol optical depth (AOD) and precipitable water content (PWC) were observed during the measurements of March and may which attributed to the presence of hygroscopic aerosols over the site. The day-to-day variations in total columnar ozone (TCO) were found to be in fair agreement (10−14%) deviation from TOMS satellite data for all the experimental days, having mean observed value of 294.45 (±6.61) DU over the station. Keywords: Aerosols; Aerosol optical depth; Aerosol size distribution; °Angstrm parameters; total columnar ozone; and precipitable water content