Experimental Analysis and Reconstruction of the Morphology of Particulate and Monolithic Chromatographic Beds

This dissertation is concerned with the acquisition of three-dimensional image data of chromatography columns in capillary format using confocal laser scanning microscopy as well as with the reconstruction and analysis of the acquired image data in view of the dispersive properties of the separation column. Key aspect in the characterization are radial heterogeneities because in UHPLC these heterogeneities contribute in large part to dispersive band broadening. Therefore, radial heterogeneities carry a particular significance in the development of chromatography columns of improved separation efficiency. Consecutively, the topics that are covered in the individual chapters of this work are being summarized: - Chapter 1 and 2 deal with the development of a sample setup for the aberration free optical imaging of capillary chromatography columns via confocal laser scanning microscopy. Additionally, image processing methods are presented that enable image restoration, particle detection, and segmentation of acquired image data. The image data were analyzed using chord length distributions and radial porosity profiles. Subsequent chapters are concerned with the application of the presented method. Herein, focus lies on a characterization of local structural density on the length scales used in J.C. Giddings’ eddy dispersion theory. - In Chapter 3 the separation efficiencies of eleven MTMS-hybrid monoliths were correlated with pore size distribution and wall attachment which outlines a fundamental problem that accompanies the preparation of capillary monoliths. - A first study on the influence of packing parameters on separation efficiency and bed morphology of packed beds was performed in Chapter 4. Six capillary columns of varying inner diameter from 10 µm to 75 µm were packed with 1.7 µm Acquity BEH particles and evaluated for their chromatographic and morphological properties. It was observed that separation efficiency would drop with increasing capillary i.d.. This could be explained by a lower packing density in the wall region of these capillaries. Furthermore, size segregation of particles was observed. - Chapter 5 discusses morphological differences between capillaries packed with core–shell particles and capillaries packed with fully porous particles. Owed to their differing production process the former do have a particle size distribution that is much narrower than the particle size distribution of fully porous particles, which yields a substantially different ordering of the particles in the wall region of the capillaries. - Chapter 6 compares a silica monolith and a sub-2 µm packing in 20 µm i.d. capillaries. The study discusses the microstructure of these columns with regard to transchannel, short-range interchannel, and transcolumn dispersion using the already established descriptors and discusses the potential of each kind of bed structure. - Chapter 7 picks up the results of Chapter 4 and shows how bed microstructure is affected by the slurry concentration used in the slurry packing process. The study showed that the previously observed size segregation of particles can be suppressed by increasing the slurry concentration yielding improved separation efficiency. The trade-off with higher slurry concentrations was an increased number of packing gaps, both in fully porous and core–shell packed beds. Once again, the chapter highlights the potential of using microscopic reconstruction and an analysis of macroscopic separation efficiency comprehensively and illustrates that the packing of beds of increasing inner diameter requires higher slurry concentrations. The concentrations should be chosen to suppress particle size segregation while keeping the amount of packing gaps as small as possible

A receiver-compatible noise reduction system

Also issued as Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1990.Includes bibliographical references (p. 111-113).Supported in part by the National Science Foundation. MIP 87-14969 Supported in part by the Maryland Procurement Office. MDA 904-89-C-3009Matthew M. Bace

LASER Tech Briefs, September 1993

This edition of LASER Tech briefs contains a feature on photonics. The other topics include: Electronic Components and Circuits. Electronic Systems, Physical Sciences, Materials, Computer Programs, Mechanics, Machinery, Fabrication Technology, Mathematics and Information Sciences, Life Sciences and books and reports

Shape Resonances as a Probe of an Evolving Nuclear and Electronic Structure in Molecules

Shape resonances are a ubiquitous phenomenon in electron–molecule scattering, in which the impinging electron is resonantly captured in a pseudo-bound state that is supported by the molecular potential. To study the electron scattering dynamics, we use time- and angle- resolved photoelectron spectroscopy here. With this technique, the transient evolution of the photoelectron angular distributions (PADs) from the ionization of an excited-state species can be measured. In the PADs, the electron–molecular-ion scattering dynamics are contained because the photoelectron necessarily interacts with the potential of the parent molecule as it escapes. The aim of this thesis is to investigate to what extent molecular dynamics, which are triggered by a pump laser pulse, are reflected in the PADs of the photoelectron spectra generated by an ionizing probe pulse, and how these effects can be rationalized in a photoelectron-scattering picture. Three experimental studies are covered in this thesis: In the first experiment, CF3I molecules are impulsively aligned in space by a short near-infrared pulse, which creates a rotational wave packet. During the revival of the rotational wave packet, PADs are measured for different molecular-axes distributions by photoionization with an ultrashort XUV pulse generated through high-order harmonic generation (HHG). Comparing the PADs thus obtained to the results of quantum-scattering calculations carried out with the ePolyScat suite of programs, we show that the alignment-dependent change in the PADs can be largely explained by two prominent shape resonances that contribute to the PADs in a distinctly different way geometrically. In the second experiment, we investigate the laser-assisted photoelectron recollisions that occur in strong-field ionization of atoms and molecules. We show how the differential scattering cross sections (DCSs) for the electron–molecular-ion collision process can be extracted from the resulting photoelectron spectrum. Then, we apply this approach to the investigation of the excited-state dynamics of I2 molecules that are prepared in the A or B state, leading to photodissociation and the creation of a vibrational wave packet, respectively. Again, by comparing to calculations carried out with ePolyScat, we conclude that the observed modulations in the DCSs of the rescattered electrons can be very well explained by considering two prominent shape resonances involved, the l=6 resonance of the diatomic molecular ion and the l=3 resonance of the free iodine atomic ion. In the third study, the time-resolved core-shell photoionization of dissociating halomethane molecules, namely CH3I and CH2ICl, is investigated employing ultrashort soft x-ray pulses provided by the free-electron laser FLASH in Hamburg, which are able to ionize the 4d shell of iodine close to the well-known “giant” photoionization resonance (again related to the l=3 shape resonance). We find that the dissociation clearly manifests as a shift of the 4d core-level binding energy, and that the time scale and temporal onset of this effect is distinctly different from that of the photoion measurements, which are commonly exploited to quantify the dissociation dynamics

Restoration of color images subjected to interchannel blurring

This paper deals with the restoration of colored images, distorted by both intra- and inter-channel blur, and corrupted by additive white Gaussian noise. The image is modeled as a Markov Random Field (MRF), and color image restoration is cast as a maximum a posteriori (MAP) estimation problem. We propose a First Order Interchannel Interaction (FOII) model for image restoration. Simulated annealing algorithm is then used to minimize the posterior energy function. We compare the simulation results of conventional non interaction (NI) approach and the proposed FOII approach. Proposed model is fairly general, and the results are satisfactory even when interchannel degradation parameter is unknown

Restoration of color images subjected to interchannel blurring

This paper deals with the restoration of colored images, distorted by both intra- and inter-channel blur, and corrupted by additive white Gaussian noise. The image is modeled as a Markov Random Field (MRF), and color image restoration is cast as a maximum a posteriori (MAP) estimation problem. We propose a First Order Interchannel Interaction (FOII) model for image restoration. Simulated annealing algorithm is then used to minimize the posterior energy function. We compare the simulation results of the conventional non-interaction (NI) approach and the proposed FOII approach. The proposed model is fairly general, and the results are satisfactory even when interchannel degradation parameter is unknown.© IEE

NASA Tech Briefs, Fall 1979

Topics include: NASA TU Services: Technology Utilization services that can assist you in learning about and applying NASA technology; New Product Ideas: A summary of selected innovations of value to manufacturers for the development of new products; Electronic Components and Circuits; Electronic Systems; Physical Sciences; Materials; Life Sciences; Mechanics; Machinery; Fabrication Technology; Mathematics and Information Sciences

Abstracts on Radio Direction Finding (1899 - 1995)

The files on this record represent the various databases that originally composed the CD-ROM issue of "Abstracts on Radio Direction Finding" database, which is now part of the Dudley Knox Library's Abstracts and Selected Full Text Documents on Radio Direction Finding (1899 - 1995) Collection. (See Calhoun record https://calhoun.nps.edu/handle/10945/57364 for further information on this collection and the bibliography). Due to issues of technological obsolescence preventing current and future audiences from accessing the bibliography, DKL exported and converted into the three files on this record the various databases contained in the CD-ROM. The contents of these files are: 1) RDFA_CompleteBibliography_xls.zip [RDFA_CompleteBibliography.xls: Metadata for the complete bibliography, in Excel 97-2003 Workbook format; RDFA_Glossary.xls: Glossary of terms, in Excel 97-2003 Workbookformat; RDFA_Biographies.xls: Biographies of leading figures, in Excel 97-2003 Workbook format]; 2) RDFA_CompleteBibliography_csv.zip [RDFA_CompleteBibliography.TXT: Metadata for the complete bibliography, in CSV format; RDFA_Glossary.TXT: Glossary of terms, in CSV format; RDFA_Biographies.TXT: Biographies of leading figures, in CSV format]; 3) RDFA_CompleteBibliography.pdf: A human readable display of the bibliographic data, as a means of double-checking any possible deviations due to conversion