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We investigate the signal and noise transform characteristics from the projection domain to the image domain in a linear systems theory framework and predictions of the DQE within this framework are made. A simulation study of a photon counting silicon detector is made from which the energy information is used in order to produce synthetic monoenergetic images. From these images the MTF, NPS, and DQE are estimated and are compared to the respective quantities predicted from the model. Within this model we find that the DQE in the projection domain has similar global characteristics as in the image domain, and that the sampling step in the imaging chain affects the DQE close to the zero frequency., Vi undersöker hur signal och brus egenskaper transformeras från projektionsdomänen till bilddomänen i ett linjärt-skiftinvariant system och förutsägelser av DQE inom detta ramverk görs. Vidare görs en simuleringsstudie av en fotonräknande kiseldetektor från vilken energiinformationen används för att producera syntetiska monoenergetiska bilder. Från dessa bilder uppskattas MTF, NPS och DQE och jämförs med respektive storheter förutspådda från modellen. Inom modellen finner vi att DQE i projektionsdomänen har liknande globala egenskaper som i bilddomänen, och att samplingssteget i bildkedjan påverkar DQE nära nollfrekvensen.

We investigate the signal and noise transform characteristics from the projection domain to the image domain in a linear systems theory framework and predictions of the DQE within this framework are made. A simulation study of a photon counting silicon detector is made from which the energy information is used in order to produce synthetic monoenergetic images. From these images the MTF, NPS, and DQE are estimated and are compared to the respective quantities predicted from the model. Within this model we find that the DQE in the projection domain has similar global characteristics as in the image domain, and that the sampling step in the imaging chain affects the DQE close to the zero frequency., Vi undersöker hur signal och brus egenskaper transformeras från projektionsdomänen till bilddomänen i ett linjärt-skiftinvariant system och förutsägelser av DQE inom detta ramverk görs. Vidare görs en simuleringsstudie av en fotonräknande kiseldetektor från vilken energiinformationen används för att producera syntetiska monoenergetiska bilder. Från dessa bilder uppskattas MTF, NPS och DQE och jämförs med respektive storheter förutspådda från modellen. Inom modellen finner vi att DQE i projektionsdomänen har liknande globala egenskaper som i bilddomänen, och att samplingssteget i bildkedjan påverkar DQE nära nollfrekvensen.

A synthetic strategy was developed for the preparation of porphyrins containing between one and four stereogenic centers, such that their molecular weights vary only as a result of methyl groups which give the chiral forms. The low-dimensional nanoscale aggregates of these compounds Reveal the profound effects of this varying molecular chirality on their supramolecular structure and optical activity. The number of stereogenic centers influences significantly the self-assembly and chiral structure of the aggregates of porphyrin molecules described here. A scanning tunneling microscopy study of monolayers on graphite shows that the degree of structural chirality with respect to the surface increases almost linearly with the number of stereogenic centers, and only one handedness is formed in the monolayers, whereas the achiral compound forms a mixture of mirror-image domains at the surface. In solution, four hydrogen bonds induce the formation of an H-aggregate, and circular dichroism measurements and theoretical studies indicate that the compounds self-assemble into helical structures. Both the chirality and stability of the aggregates depend critically on the number of stereocenters. The chiral porphyrin derivatives gelate methylcyclohexane at concentrations dependent on the number and position of chiral groups at the periphery of the aromatic core, reflecting the different aggregation forces of the molecules in solution. Increasing the number of stereogenic centers requires more material to immobilize the solvent, in all likelihood because of the greater solubility of the porphyrins. The vibrational circular dichroism spectra of the gels show that all compounds have a chiral environment around the amide bonds, confirming the helical model proposed by calculations. The morphologies of the xerogels (studied by scanning electron microscopy and scanning force microscopy) are similar, although more fibrous features are present in the molecules with fewer stereogenic cent, QC 20140826