Neurolinguistic analysis: aspects of language and speech deviations in Palestinian Arabic aphasics

The characteristics of aphasics’ speech in various languages have been the core of numerous studies, but Arabic in general, and Palestinian Arabic in particular, is still a virgin field in this respect. However, it is of vital importance to have a clear picture of the specific aspects of Palestinian Arabic that might be affected in the speech of aphasics in order to establish screening, diagnosis and therapy programs based on a clinical linguistic database. Hence the central questions of this study are what are the main neurolinguistic features of the Palestinian aphasics’ speech at the phonetic-acoustic level and to what extent are the results similar or not to those obtained from other languages. In general, this study is a survey of the most prominent features of Palestinian Broca’s aphasics’ speech. The main acoustic parameters of vowels and consonants are analysed such as vowel duration, formant frequency, Voice Onset Time (VOT), intensity and frication duration. The deviant patterns among the Broca’s aphasics are displayed and compared with those of normal speakers. The nature of deficit, whether phonetic or phonological, is also discussed. Moreover, the coarticulatory characteristics and some prosodic patterns of Broca’s aphasics are addressed. Samples were collected from six Broca’s aphasics from the same local region. The acoustic analysis conducted on a range of consonant and vowel parameters displayed differences between the speech patterns of Broca’s aphasics and normal speakers. For example, impairments in voicing contrast between the voiced and voiceless stops were found in Broca’s aphasics. This feature does not exist for the fricatives produced by the Palestinian Broca’s aphasics and hence deviates from data obtained for aphasics’ speech from other languages. The Palestinian Broca’s aphasics displayed particular problems with the emphatic sounds. They exhibited deviant coarticulation patterns, another feature that is inconsistent with data obtained from studies from other languages. However, several other findings are in accordance with those reported from various other languages such as impairments in the VOT. The results are in accordance with the suggestions that speech production deficits in Broca’s aphasics are not related to phoneme selection but rather to articulatory implementation and some speech output impairments are related to timing and planning deficits.

Computational studies on the structure and stabilities of magnetic inter-metallic compounds

The purpose of this thesis is to further the understanding of the structural, electronic and magnetic properties of ternary inter-metallic compounds using density functional theory (DFT). Four main problems are addressed. First, a detailed analysis on the ternary Heusler compounds is made. It has long been known that many Heusler compounds ($X_2YZ$; $X$ and $Y$ transition elements, $Z$ main group element) exhibit interesting half-metallic and ferromagnetic properties. In order to understand these, the dependence of magnetic and electronic properties on the structural parameters, the type of exchange-correlation functional and electron-electron correlation was examined. It was found that almost all Co$_2YZ$ Heusler compounds exhibit half-metallic ferromagnetism. It is also observed that $X$ and $Y$ atoms mainly contribute to the total magnetic moment. The magnitude of the total magnetic moment is determined only indirectly by the nature of $Z$ atoms, and shows a trend consistent with Slater-Pauling behaviour in several classes of these compounds. In contrast to experiments, calculations give a non-integer value of the magnetic moment in certain Co$_2$-based Heusler compounds. To explain deviations of the calculated magnetic moment, the LDA+$U$ scheme was applied and it was found that the inclusion of electron-electron correlation beyond the LSDA and GGA is necessary to obtain theoretical description of some Heusler compounds that are half-metallic ferromagnets. The electronic structure and magnetic properties of substitutional series of the quaternary Heusler compound Co$_2$Mn$_{1-x}$Fe$_x$Si were investigated under LDA+$U$. The calculated band structure suggest that the most stable compound in a half-metallic state will occur at an intermediate Fe concentration. These calculated findings are qualitatively confirmed by experimental studies. Second, the effect of antisite disordering in the Co$_2$TiSn system was investigated theoretically as well as experimentally. Preservation of half-metallicity for Co$_2$TiSn was observed with moderate antisite disordering and experimental findings suggest that the Co and Ti antisites disorder amounts to approximately 10~% in the compound. Third, a systematic examination was carried out for band gaps and the nature (covalent or ionic) of bonding in semiconducting 8- and 18-electron or half-metallic ferromagnet half-Heusler compounds. It was found that the most appropriate description of these compounds from the viewpoint of electronic structures is one of a $YZ$ zinc blende lattice stuffed by the $X$ ion. Simple valence rules are obeyed for bonding in the 8- and 18-electron compounds. Fourth, hexagonal analogues of half-Heusler compounds have been searched. Three series of compounds were investigated: GdPdSb, GdAutextit{X} (textit{X} = Mn, Cd and In) and EuNiP. GdPdSb is suggested as a possible half-metallic weak ferromagnet at low temperature. GdAutextit{X} (textit{X} = Mn, Cd and In) and EuNiP were investigated because they exhibit interesting bonding, structural and magnetic properties. The results qualitatively confirm experimental studies on magnetic and structural behaviour in GdPdSb, GdAutextit{X} (textit{X} = Mn, Cd and In) and EuNiP compounds. ~