Kansas State University Salina Aerospace and Technology Campus
K-State Research ExchangeNot a member yet
43997 research outputs found
Sort by
Photoelectron Diffraction Imaging of a Molecular Breakup Using an X-Ray Free-Electron Laser
Get PDFA central motivation for the development of x-ray free-electron lasers has been the prospect of time-resolved single-molecule imaging with atomic resolution. Here, we show that x-ray photoelectron diffraction—where a photoelectron emitted after x-ray absorption illuminates the molecular structure from within—can be used to image the increase of the internuclear distance during the x-ray-induced fragmentation of an O2 molecule. By measuring the molecular-frame photoelectron emission patterns for a two-photon sequential K-shell ionization in coincidence with the fragment ions, and by sorting the data as a function of the measured kinetic energy release, we can resolve the elongation of the molecular bond by approximately 1.2 a.u. within the duration of the x-ray pulse. The experiment paves the road toward time-resolved pump-probe photoelectron diffraction imaging at high-repetition-rate x-ray free-electron lasers
Shaping attosecond pulses by controlling the minima in high-order harmonic generation through alignment of CO2 molecules
Get PDFWe report a simple method for generating shaped attosecond pulses by using a CO2 molecule. Unlike most other molecules, owing to its unique energy and angle dependence and the presence of deep minima in the photoionization transition dipole moment, the shape of harmonic spectra, especially the position and depth of minima, can be readily controlled by tuning the degree of alignment. The sensitive alignment dependence of the minima is due to the coherent interference of a laser-induced dipole from each molecule when CO2 molecules are moderately aligned, but not when they are well aligned or when they are isotropically distributed. Such a sensitivity offers a simple way of controlling the spectral amplitude and phase of the generated harmonics and thus shaping the generated attosecond pulses, for example, producing structured attosecond pulses by splitting a single burst into two. We illustrate how such pulses are generated and how to characterize them. This method offers a simple way to shape attosecond pulses at the generation step. It can be easily implemented experimentally to generate attosecond pulses with strong phase variations for unique applications
Validity of the static-exchange approximation for inner-shell photoionization of polyatomic molecules
Get PDFThe simple single-channel static-exchange approximation completely ignores correlation between the continuum and molecular ion electrons. In molecular systems with symmetry equivalent atoms, the single-channel approximation can seriously fail in core ionization when using delocalized orbitals to represent the core hole states. We present cross sections and molecular frame photoelectron angular distributions with both localized and delocalized core orbitals in CF4 F (1s) ionization. We show that only a full coupled-channel calculation can recover an accurate description of the physics of inner-shell photoionization when using delocalized orbitals, whereas nearly the same result can be obtained from independent single-channel static-exchange calculations when localized core orbitals are used. A grid-based variational method described here makes such single-channel calculations possible on larger systems without local-exchange approximations. Illustrative calculations on the core ionization of SF6 are presented to illustrate the power of the grid-based method
Characterization of light-induced potentials in the strong-field dissociation of O2+
Get PDFWe investigate theoretically the imprints of light-induced potentials (LIPs) on the dissociation dynamics of O2+ molecular ions, as observable in angle-resolved fragment kinetic-energy-release (KER) spectra. Following the vibrational and rotational dynamics of the initial pump-laser-excited cationic nuclear wave packet, while accounting for the dipole coupling between the O2+(a4Πu) and O2+(f4Πg) electronic states in 800-nm 40-fs probe-laser pulses with peak intensities between 1013 and 1014 W/cm2, we calculate angle-resolved KER spectra which reveal characteristic energy- and angle-dependent fringe structures. These fringes shift downward in energy as the molecular alignment angle θ relative to the probe-pulse polarization direction increases from 0 to π/2. The angle-dependent shifts in the KER fringes increase for larger probe-pulse peak intensities and follow the angle and light-wave-intensity dependence of the vibrational spectrum in the associated Floquet bond-hardening well, which is a manifestation of transient O2+ nuclear-probability trapping in the LIP during dissociation. By examining the rovibrational dynamics of the dissociating molecular cation near the light-induced conical intersection (LICI) in the cationic LIP surface at θ=π/2, we identify related angle-dependent structures in the KER spectra, suggesting a means for assessing the significance of LICIs in molecular dissociation pathways
Angle-dependent strong-field ionization and fragmentation of carbon dioxide measured using rotational wave packets
Get PDFIn this work, we experimentally study the angle-dependent single ionization of carbon dioxide (CO2) by linearly and circularly polarized pulses. The angle dependence of the ionization probability by linearly polarized pulses extracted from time-domain measurements on an impulsively excited rotational wave packet is compared with data obtained from a direct angle-scan measurement. The results from the measurement with linear and circular polarization are consistent with the adiabatic ionization approximation. We extend the time-domain method to extract the dependence of the asymptotic momentum distribution of fragment ions on the orientation of the molecular axis, and apply it to investigate dissociative double ionization of CO2. We show that such measurements can directly test the validity of the axial recoil approximation
A semi-supervised clustering method for payload extraction
Get PDFMaster of ScienceDepartment of Electrical and Computer EngineeringDon M. GruenbacherWilliam H. HsuThis thesis addresses payload extraction, the information extraction task of capturing the text of an article from a formatted document such as a PDF file, and focuses on the application and improvement of density-based clustering algorithms as an alternative or supplement to rule-based methods for this task domain. While supervised learning performs well on classification-based subtasks of payload extraction such as relevance filtering of documents or sections in a collection, the labeled data which it requires for training are often prohibitively expensive (in terms of the time resources of annotators and developers) to obtain. On the other hand, unlabeled data is often relatively easily available without cost in large quantities, but there have not been many ways to exploit them. Semi-supervised learning addresses this problem by using large amounts of unlabeled data, together with the labeled data, to build better classifiers. In this thesis, I present a semi-supervised learning-driven approach for the analysis of scientific literature which either already contains unlabeled metadata, or from which this metadata can be computed. Furthermore, machine learning-based analysis techniques are exploited to make this system robust and flexible to its data environment. The overall goal of this research is to develop a methodology to support the document analysis functions of layout-based document segmentation and section classification. This is implemented within an information extraction system within which the empirical evaluation and engineering objectives of this work are framed. As an example application, my implementation supports detection and classification of titles, authors, additional author information, abstract, and the titles and body of subsections such as ‘Introduction’, ‘Method’, ‘Result’, ’Discussion’, ‘Acknowledgement’, ’Reference’, etc. The novel contribution of this work also includes payload extraction as an intermediate functional stage within a pipeline for procedural information extraction from the scientific literature. My experimental results show that this approach outperforms a state-of-the-field heuristic pattern analysis system on a corpus from the domain of nanomaterials synthesis
Access, Engagement and Resilience During COVID-19 Remote Learning
Get PDFKansas was the first state to close P-12 schools and move to a continuous learning model in response to the COVID-19 pandemic. A multidisciplinary group of K-State College of Education faculty researchers conducted a survey in May, 2020 to capture the voices and experiences of Kansas teachers, school counselors, and administrators during that time related to technology and broadband access, engagement and educator resiliency and self-care. Survey links were posted on the Remote Learning P-12 platform (https://remote-learning-p-12.mn.co/feed) and on the Kansas Educators Facebook group. These open links provided a sample of convenience, with 829 educators from across the state responding to the survey. The findings have implications for school districts, administrators, school counselors, teachers, and students in the coming school year.
As schools begin to make decisions about what the current and critical needs are, three tenets must be addressed for optimal school re-entry: (1) Educator and student well-being, (2) Delivery models and high-quality instruction that are conducive and responsive to varied learning environments, and (3) School operations: Precautionary measures and logistics around COVID infection and contagion. This white paper provides data, insight, and recommendations in the areas of educator and student well being and delivery models
Report of Progress 1157
Get PDFObjectives of the National Winter Canola Variety Trial (NWCVT) are to evaluate the performance of released and experimental varieties, determine where these varieties are best adapted, and increase visibility of winter canola across the nation. Breeders, marketers, and producers use information collected from the trials. Over the past decade, the number of environments and entries tested have increased. The NWCVT is planted at locations in the Great Plains, Midwest, northern United States, and Southeast. The wide diversity of environments has improved our knowledge and understanding of winter canola variety performance
Report of Progress 1158
Get PDFThe Kansas Agricultural Experiment Station annually compares both new and currently grown varieties in the state’s major crop-producing areas. These performance tests generate unbiased performance information designed to help Kansas growers select wheat varieties suited for their area and conditions
Double Core-Hole Generation in O2 Molecules Using an X-Ray Free-Electron Laser: Molecular-Frame Photoelectron Angular Distributions
Get PDFWe report on a multiparticle coincidence experiment performed at the European X-ray Free-Electron Laser at the Small Quantum Systems instrument using a COLTRIMS reaction microscope. By measuring two ions and two electrons in coincidence, we investigate double core-hole generation in O2 molecules in the gas phase. Single-site and two-site double core holes have been identified and their molecular-frame electron angular distributions have been obtained for a breakup of the oxygen molecule into two doubly charged ions. The measured distributions are compared to results of calculations performed within the frozen- and relaxed-core Hartree-Fock approximations