Department of Mathematics and PhysicsMathematics and Physics PDF Documentshttp://elibrary.pu.ac.ke/handle/123456789/2822021-02-25T02:39:59Z2021-02-25T02:39:59ZMECHANICAL AND OPTO - ELECTRICAL CHARACTERIZATION OF CHITOSAN - A MARINE BASED BIOMATERIALHanif, Juma, D.http://elibrary.pu.ac.ke/handle/123456789/8112020-10-12T12:38:28Z2016-07-01T00:00:00ZMECHANICAL AND OPTO - ELECTRICAL CHARACTERIZATION OF CHITOSAN - A MARINE BASED BIOMATERIAL
Hanif, Juma, D.
Mechanical, electrical and optical properties of chitosan thin films extracted from the squid
gladius found along the coastal areas of Kilifi and Mombasa were investigated in this study.
The films were prepared by the solution cast technique. The room temperature ionic
conductivity of the film was measured by the two electrodes conductivity measurement
technique and was found to be ca.1525μScm − 1. DMA analysis showed two dynamic
processes; the beta relaxation process which generally seemed to increase with frequency and
chitosan concentration and the alpha relaxation process (Tg). The temperature range between
these two transitions (30 - 120oC ) gave an insight of the operating temperature range of the
biomaterial. Arrhenius plots gave the activation energy of the biomaterial at ca.259kJ/mol
which increased with chitosan concentration. Structural characteristics of the sample were
discussed on the basis of the DMA, AFM, X-ray, infrared and NMR analysis data. DMA
results showed that the material under investigation is viscoelastic with very low mechanical
damping which means its rigidity and resistance to deformation is very high.
X-ray diffraction indicated the molecular form at two strongest peaks; 2θ ≈ 10.5o and 2θ
≈19.8o with minor reflections at 2 '6o and 2θ ≈35o and crystalline structure with an index of
ca:66%. A DDA value of ca:75% was obtained from the integral values of proton NMR.
Optical properties obtained from the UV vis absorbance spectra gave the optical density of
the material at about 0.8, the absorption coefficient of ca.2.909 and the band gap of
ca.2.75eV. The refractive index of the chitosan thin films was determined by the real and
apparent depth method using a traveling microscope. To determine the relaxation time and
frequency, the permittivity of the material was plotted as a function of frequency and gave a
value of ca:1:58μs. Measured value indicates the dielectric loss decreases with increasing
frequency and temperature. The activation plot confirms that the relaxation processes follow
the Arrhenius law and gave the activation energy of the squid pen gladius at ca.54.7kJ/mole.
Key Words: Tapping mode AFM, Deacetylation, Biomaterial, Cantilever.
Mechanical, electrical and optical properties of chitosan thin films extracted from the squid
gladius found along the coastal areas of Kilifi and Mombasa were investigated in this study.
The films were prepared by the solution cast technique. The room temperature ionic
conductivity of the film was measured by the two electrodes conductivity measurement
technique and was found to be ca.1525μScm − 1. DMA analysis showed two dynamic
processes; the beta relaxation process which generally seemed to increase with frequency and
chitosan concentration and the alpha relaxation process (Tg). The temperature range between
these two transitions (30 - 120oC ) gave an insight of the operating temperature range of the
biomaterial. Arrhenius plots gave the activation energy of the biomaterial at ca.259kJ/mol
which increased with chitosan concentration. Structural characteristics of the sample were
discussed on the basis of the DMA, AFM, X-ray, infrared and NMR analysis data. DMA
results showed that the material under investigation is viscoelastic with very low mechanical
damping which means its rigidity and resistance to deformation is very high.
X-ray diffraction indicated the molecular form at two strongest peaks; 2θ ≈ 10.5o and 2θ
≈19.8o with minor reflections at 2 '6o and 2θ ≈35o and crystalline structure with an index of
ca:66%. A DDA value of ca:75% was obtained from the integral values of proton NMR.
Optical properties obtained from the UV vis absorbance spectra gave the optical density of
the material at about 0.8, the absorption coefficient of ca.2.909 and the band gap of
ca.2.75eV. The refractive index of the chitosan thin films was determined by the real and
apparent depth method using a traveling microscope. To determine the relaxation time and
frequency, the permittivity of the material was plotted as a function of frequency and gave a
value of ca:1:58μs. Measured value indicates the dielectric loss decreases with increasing
frequency and temperature. The activation plot confirms that the relaxation processes follow
the Arrhenius law and gave the activation energy of the squid pen gladius at ca.54.7kJ/mole.
Key Words: Tapping mode AFM, Deacetylation, Biomaterial, Cantilever.
2016-07-01T00:00:00ZTHE VARIATION OF PHOTOIONIZATION CROSS-SECTION WITH INCIDENT PHOTON FREQUENCY AND WITH POSITION OF A DONOR IMPURITY IN A QUANTUM WELL DOT OF SQUARE CROSS-SECTION USING A VARIATIONAL TECHNIQUEACHIENG’, OTIENO WINNIEhttp://elibrary.pu.ac.ke/handle/123456789/7832020-10-08T12:16:47Z2018-04-08T00:00:00ZTHE VARIATION OF PHOTOIONIZATION CROSS-SECTION WITH INCIDENT PHOTON FREQUENCY AND WITH POSITION OF A DONOR IMPURITY IN A QUANTUM WELL DOT OF SQUARE CROSS-SECTION USING A VARIATIONAL TECHNIQUE
ACHIENG’, OTIENO WINNIE
In the present work, we carried out a theoretical study of the variation of the photoionization cross-section with the position of a hydrogenic donor impurity along the growth axis of a square GaAs quantum well dot. In our calculation, we used a trial wave function in the effective mass approximation. The wave function is constructed with an appropriate envelope wave function that satisfies the boundary conditions, i.e., the wave function vanishes at the boundary. We employed the trial wave function to calculate the total energy of the hydrogenic donor impurity in the ground state. We then minimized the total energy with respect to the variational parameter in the trial wave function to obtain the minimum energy. The minimized total energies were then used to determine the donor binding energies within the quantum well dot. We observed that the binding energy increases with decreasing dot length for constant dot cross-section up to a certain value when it then decreased rapidly towards zero. We used the binding energies obtained to compute the photoionization cross-section of the donor impurity as a function of the incident photon frequency for different positions of the donor impurity. We observed that the photoionization cross-sections rises steeply to their peaks from almost zero value then gradually decrease as the photon frequencies increase until they become almost constant for very high photon frequencies. The photoionization cross-section peak is much higher for the hydrogenic donor impurity located closest to the centre of the quantum well dot than for hydrogenic donor impurity located farther away from the dot centre. This indicates that the photoionization cross-section is sensitive to the location of the hydrogenic donor impurity in the quantum dot and to the incident photon frequency.
In the present work, we carried out a theoretical study of the variation of the photoionization cross-section with the position of a hydrogenic donor impurity along the growth axis of a square GaAs quantum well dot. In our calculation, we used a trial wave function in the effective mass approximation. The wave function is constructed with an appropriate envelope wave function that satisfies the boundary conditions, i.e., the wave function vanishes at the boundary. We employed the trial wave function to calculate the total energy of the hydrogenic donor impurity in the ground state. We then minimized the total energy with respect to the variational parameter in the trial wave function to obtain the minimum energy. The minimized total energies were then used to determine the donor binding energies within the quantum well dot. We observed that the binding energy increases with decreasing dot length for constant dot cross-section up to a certain value when it then decreased rapidly towards zero. We used the binding energies obtained to compute the photoionization cross-section of the donor impurity as a function of the incident photon frequency for different positions of the donor impurity. We observed that the photoionization cross-sections rises steeply to their peaks from almost zero value then gradually decrease as the photon frequencies increase until they become almost constant for very high photon frequencies. The photoionization cross-section peak is much higher for the hydrogenic donor impurity located closest to the centre of the quantum well dot than for hydrogenic donor impurity located farther away from the dot centre. This indicates that the photoionization cross-section is sensitive to the location of the hydrogenic donor impurity in the quantum dot and to the incident photon frequency.
2018-04-08T00:00:00ZTHE EFFECT OF HERMANSON’S SPATIAL DIELECTRIC FUNCTION ON THE DENSITY OF IMPURITY STATES IN A GALLIUM ARSENIDE QUANTUM DOT (GaAs QD) OF RECTANGULAR CROSS-SECTIONMACHUKA, LEONARDhttp://elibrary.pu.ac.ke/handle/123456789/7822020-10-08T11:58:15Z2018-04-08T00:00:00ZTHE EFFECT OF HERMANSON’S SPATIAL DIELECTRIC FUNCTION ON THE DENSITY OF IMPURITY STATES IN A GALLIUM ARSENIDE QUANTUM DOT (GaAs QD) OF RECTANGULAR CROSS-SECTION
MACHUKA, LEONARD
In this work, a theoretical study of the effect of Hermansons dielectric function (screening) on the density of impurity states (DOIS) of a donor impurity located in the center of a Gallium Arsenide (GaAs) Quantum Well Dot (QWD) of rectangular cross-section has been done. The density of impurity states (DOIS) of an unscreened (hydrogenic) donor impurity was calculated and compared with that of the screened (non-hydrogenic) donor impurity for the same system. The calculations were carried out using a trial wave function in the effective mass approximation. Calculations of the binding energies for the hydrogenic and non hydrogenic donor impurity as a function of the axial (growth) length of the QWD was done and the results used to compute the density of impurity states. The results show that impurity binding energies increase with decreasing quantum well axial length until about 20 nm for a constant QWD cross-section. The binding energies for the non-hydrogenic donor impurity were found to be higher than in the hydrogenic type. These results are in agreement with previous results obtained for donor impurities in quantum well wires and quantum well dots of similar geometry .The results for the density of impurity states clearly show an important feature that is a peak at lower binding energies coming from the contribution of impurities near the axial edge of the quantum well dot. It was also observed that the DOIS obtained for the non-hydrogenic donor impurities is markedly enhanced over that for purely hydrogenic donor impurities. In fact, the enhanced DOIS of the non-hydrogenic donor impurities is observed throughout the range of binding energy values considered. The findings of this research are in agreement with the results obtained by F. J. Ribeiro and A. Latge ‘In their work on the density of impurity states in spherical and cubic quantum dots, the DOIS exhibited a similar trend with a sharp peak of density of states at low binding energy followed by an almost exponential decrease with increasing binding energy. In our case, we have applied a spatial dielectric function and found that it enhances the DOIS. It is therefore, important that the effect of spatial dielectric function should be considered when designing optoelectronic devices.
In this work, a theoretical study of the effect of Hermansons dielectric function (screening) on the density of impurity states (DOIS) of a donor impurity located in the center of a Gallium Arsenide (GaAs) Quantum Well Dot (QWD) of rectangular cross-section has been done. The density of impurity states (DOIS) of an unscreened (hydrogenic) donor impurity was calculated and compared with that of the screened (non-hydrogenic) donor impurity for the same system. The calculations were carried out using a trial wave function in the effective mass approximation. Calculations of the binding energies for the hydrogenic and non hydrogenic donor impurity as a function of the axial (growth) length of the QWD was done and the results used to compute the density of impurity states. The results show that impurity binding energies increase with decreasing quantum well axial length until about 20 nm for a constant QWD cross-section. The binding energies for the non-hydrogenic donor impurity were found to be higher than in the hydrogenic type. These results are in agreement with previous results obtained for donor impurities in quantum well wires and quantum well dots of similar geometry .The results for the density of impurity states clearly show an important feature that is a peak at lower binding energies coming from the contribution of impurities near the axial edge of the quantum well dot. It was also observed that the DOIS obtained for the non-hydrogenic donor impurities is markedly enhanced over that for purely hydrogenic donor impurities. In fact, the enhanced DOIS of the non-hydrogenic donor impurities is observed throughout the range of binding energy values considered. The findings of this research are in agreement with the results obtained by F. J. Ribeiro and A. Latge ‘In their work on the density of impurity states in spherical and cubic quantum dots, the DOIS exhibited a similar trend with a sharp peak of density of states at low binding energy followed by an almost exponential decrease with increasing binding energy. In our case, we have applied a spatial dielectric function and found that it enhances the DOIS. It is therefore, important that the effect of spatial dielectric function should be considered when designing optoelectronic devices.
2018-04-08T00:00:00ZAPPLICATION OF THE JOINT MODELLING OF SERIAL ANTHROPOMETRIC MEASURES AND MORTALITY AMONGST CHILDREN FOLLOWING HOSPITALIZATION WITH A COINCIDENT ACUTE INFECTIOUS DISEASE IN ADDITION TO SEVERE ACUTE MALNUTRITIONNYAWANGA, VICTOR BENEFIThttp://elibrary.pu.ac.ke/handle/123456789/7812020-10-08T11:52:42Z2016-08-08T00:00:00ZAPPLICATION OF THE JOINT MODELLING OF SERIAL ANTHROPOMETRIC MEASURES AND MORTALITY AMONGST CHILDREN FOLLOWING HOSPITALIZATION WITH A COINCIDENT ACUTE INFECTIOUS DISEASE IN ADDITION TO SEVERE ACUTE MALNUTRITION
NYAWANGA, VICTOR BENEFIT
Background: Malnutrition continues to be a major health burden in developing countries. It is
globally the most important risk factor for illness and death, with hundreds of millions of
young children particularly affected. The mid-upper arm circumference (MUAC) and the
standardized weight-for- length Z-score (WFLz) are two anthropometric measures that are
used for the diagnosis of malnutrition. The two anthropometric measures have poor
correlation in terms of their predictive capabilities.
Design: A joint model was applied to data collected recently in a randomized, double blind,
placebo-controlled trial to see which of these two anthropometric measures would be the
better predictor of mortality in infants who were admitted to hospital with severe acute
malnutrition and later discharged and followed up for one year. Typically longitudinal
measures and event time data are modelled jointly by introducing shared random effects or by
considering conditional distributions together with marginal distributions.
Participants: The study population comprised of 1781 children admitted to hospital with
evidence of an acute infectious disease and with severe malnutrition and who had care
initiated and were stabilized.
Results: Joint modelling showed that While WFLz was not significantly associated with
mortality (p=0.202); MUAC had a high association with mortality (p=0.014) and was a
predictor of children at risk of post-discharge mortality.
Conclusion: Using joint modelling approach, MUAC was identified as superior predictor of
mortality amongst children treated for complicated SAM.
Background: Malnutrition continues to be a major health burden in developing countries. It is
globally the most important risk factor for illness and death, with hundreds of millions of
young children particularly affected. The mid-upper arm circumference (MUAC) and the
standardized weight-for- length Z-score (WFLz) are two anthropometric measures that are
used for the diagnosis of malnutrition. The two anthropometric measures have poor
correlation in terms of their predictive capabilities.
Design: A joint model was applied to data collected recently in a randomized, double blind,
placebo-controlled trial to see which of these two anthropometric measures would be the
better predictor of mortality in infants who were admitted to hospital with severe acute
malnutrition and later discharged and followed up for one year. Typically longitudinal
measures and event time data are modelled jointly by introducing shared random effects or by
considering conditional distributions together with marginal distributions.
Participants: The study population comprised of 1781 children admitted to hospital with
evidence of an acute infectious disease and with severe malnutrition and who had care
initiated and were stabilized.
Results: Joint modelling showed that While WFLz was not significantly associated with
mortality (p=0.202); MUAC had a high association with mortality (p=0.014) and was a
predictor of children at risk of post-discharge mortality.
Conclusion: Using joint modelling approach, MUAC was identified as superior predictor of
mortality amongst children treated for complicated SAM.
2016-08-08T00:00:00Z