Browsing by Author "Rickey, Dawn, committee member"
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Item Open Access An investigation of the basis of judgments of remembering and knowing (JORKs)(Colorado State University. Libraries, 2012) Soderstrom, Nicholas C., author; Rhodes, Matthew G., advisor; Cleary, Anne M., committee member; Davalos, Deana B., committee member; Rickey, Dawn, committee memberPrevious research indicates that prospective metamemory accuracy can be improved if participants are asked to monitor whether contextual details will be remembered or not (i.e., judgments of remembering and knowing; JORKs), as opposed to monitoring confidence (i.e., judgments of learning; JOLs), an important finding given that accurate memory monitoring has been linked to effective learning. Three experiments investigated whether the advantage for JORK is due to these judgments being based more on retrieval processes than JOLs. Experiment 1 showed that JORKs resemble retrospective confidence judgments (RCJs)--judgments known to be based on retrieval processes--in some ways but not in others. Experiment 2 demonstrated that JORKs benefit less from a delay than JOLs when judgments are made under some circumstances but not others, and Experiment 3 showed that JORKs are less susceptible to a manipulation of encoding fluency than JOLs. Thus, overall, the results provide mixed support for the idea that JORKs are more reliant on retrieval processes than JOLs, reinforcing the need for future research on this topic.Item Open Access Contributions of gas-phase plasma chemistry to surface modifications and gas-surface interactions: investigations of fluorocarbon rf plasmas(Colorado State University. Libraries, 2012) Cuddy, Michael F., author; Fisher, Ellen R., advisor; Levinger, Nancy E., committee member; Rickey, Dawn, committee member; Krummel, Amber, committee member; Yalin, Azer P., committee memberThe fundamental aspects of inductively coupled fluorocarbon (FC) plasma chemistry were examined, with special emphasis on the contributions of gas-phase species to surface modifications. Characterization of the gas-phase constituents of single-source CF4-, C2F6-, C3F8-, and C3F6-based plasmas was performed using spectroscopic and mass spectrometric techniques. The effects of varying plasma parameters, including applied rf power (P) and system pressure (p) were examined. Optical emission spectroscopy (OES) and laser-induced fluorescence (LIF) spectroscopy were employed to monitor the behavior of excited and ground CFx (x = 1,2) radicals, respectively. Mass spectrometric techniques, including ion energy analyses, elucidated behaviors of nascent ions in the FC plasmas. These gas-phase data were correlated with the net effect of substrate processing for Si and ZrO2 surfaces. Surface-specific analyses were performed for post-processed substrates via x-ray photoelectron spectroscopy (XPS) and contact angle goniometry. Generally, precursors with lower F/C ratios tended to deposit robust FC films of high surface energy. Precursors of higher F/C ratio, such as CF4, were associated with etching or removal of material from surfaces. Nonetheless, a net balance between deposition of FC moieties and etching of material exists for each plasma system. The imaging of radicals interacting with surfaces (IRIS) technique provided insight into the phenomena occurring at the interface of the plasma gas-phase and substrate of interest. IRIS results demonstrate that CFx radicals scatter copiously, with surface scatter coefficients, S, generally greater than unity under most experimental conditions. Such considerable S values imply surface-mediated production of the CFx radicals at FC-passivated sites. It is inferred that the primary route to surface production of CFx arises from energetic ion bombardment and ablation of surface FC films. Other factors which may influence the observed CFx scatter coefficient include the surface with which the radical interacts, the vibrational temperature (ΘV) of the radical in its gas phase, and radical interactions in the gas phase. The analyses of ΘV in particular were extended to diatomic radicals from other plasma sources, including nitric oxide and fluorosilane systems, to gauge the contributions of vibrational energy to surface reactivity. In general, a monotonic increase in S is observed for CF, NO, and SiF radicals with increasing ΘV. Preliminary results for mixed plasma precursor systems (i.e. FC/H2, FC/O2) indicate that the choice of feed gas additives has a profound effect on surface modification. Hydrogen additions tend to promote FC film deposition through scavenging of fluorine atoms, whereas oxygen consumes polymerizing species, thus favoring etching regimes. Time-resolved optical emission spectroscopy (TR-OES) studies of gas-phase species elucidate the mechanisms by which these processes occur. Ultimately, the work presented herein expands the fundamental chemical and physical understanding of fluorocarbon plasma systems.Item Open Access Development of a microchip electrophoresis system for online monitoring of atmospheric aerosol composition(Colorado State University. Libraries, 2011) Noblitt, Scott Douglas, author; Henry, Charles S., 1972-, advisor; Collett, Jeffrey L., committee member; Elliott, C. Michael, committee member; Strauss, Steven H., committee member; Rickey, Dawn, committee memberAtmospheric aerosols are solid or liquid particles that remain suspended in the environment for an extended time because of their size. Due to their high number concentration, low mass concentration, unique size range, and high temporal and spatial variability, atmospheric aerosols represent a significant unknown in both environmental impact and human health. Despite the importance of aerosols, current instrumentation for monitoring their chemical composition is often limited by poor temporal resolution, inadequate detection limits, lack of chemical speciation, and/or high cost. To help address these shortcomings, microchip electrophoresis (MCE) has been introduced for the semi-continuous monitoring of water-soluble aerosol composition. The MCE instrument was coupled to a water condensation particle collector (growth tube), and the integrated system is termed Aerosol Chip Electrophoresis (ACE). ACE is capable of measuring particle composition with temporal resolution of 1 min and detection limits of ~100 ng m-3. This dissertation covers the development process of the prototype ACE instrument, including the novel separation chemistry, necessary modifications to traditional microfluidic devices, and the interface between the growth tube and the microchip.Item Open Access Framing metamemory judgments: judgments of retention intervals (JORIs)(Colorado State University. Libraries, 2010) Tauber, Sarah K., author; Rhodes, Matthew, advisor; McCabe, David, committee member; Kraiger, Kurt, committee member; Rickey, Dawn, committee memberPrior research has shown that participants’ predictions of memory performance are not sensitive to the time between study and test. However, this work has largely relied in one metacognitive measure, Judgments of Learning (JOLs), to assess such awareness. Thus, in three experiments I explored a new metacognitive measure. Judgments of Retention Interval (JORIs), in which participants determine how long (in minutes) information will be remembered. Results demonstrated that the metacognitive measure itself influences assessments of monitoring and control. For example participants chose to restudy more items when JORIs were made, compared with fewer restudy choices from participants who made JOLs (Experiment 2). However, participants demonstrated difficulty incorporating information about a retention interval into their judgments regardless of the type of judgment made (i.e., JOLs or JORIs). Results are considered within existing theoretical frameworks. I suggest that the metacognitive measure needs to be considered in order to accurately assess metacognitive awareness, and additional work is needed to assess metacognitive awareness of RI.Item Open Access Isolating partial recollection as a distinct entity in recognition memory using a modified recognition without identification (RWI) paradigm(Colorado State University. Libraries, 2012) Ryals, Anthony J., author; Cleary, Anne M., advisor; Seger, Carol A., committee member; Clegg, Benjamin A., committee member; Volbrecht, Vicki J., committee member; Rickey, Dawn, committee memberIn dual-process recognition memory research, recollection is believed to involve bringing to mind a specific prior occurrence, a target item, or the contextual details surrounding a past experience. Prior research has suggested that when recollection fails, individuals can still rely on a sense of familiarity to judge whether something has been experienced before, and the two processes may be dissociable. However, many recognition memory methods index recollection in a binary fashion such that it is treated as an all-or none occurrence. To the contrary, some research suggests that recollection may actually be a variable (i.e., a "some-or-none") process. In the present study, three experiments were conducted to explore the nature of partial recollection using a variation of the recognition without identification procedure (RWI) (Cleary, 2006; Cleary & Greene, 2000; Peynircioglu, 1990). In Experiment 1, I explored the hypothesis that manipulating the amount of perceptual information present at encoding in a recognition task can modulate the likelihood of partial recollection (Parks et al., 2011). In Experiment 2, I examined whether partial recollection responds to word frequency in a manner similar or different than full target recollection or familiarity. In Experiment 3, I explored whether partial recollection, like full target recollection, could also be affected by manipulating degree of target emotionality. In this work, I demonstrate that partial recollection is a distinct, albeit rare, factor in studies of human recognition memory.Item Open Access Part 1: Synthesis and characterization of magnetic Cr5Te8 nanoparticles. Part 2: Local atomic structure studies using theory to simulate polarons in superconducting cuprates and experiment to analyze alternative energy nanomaterials(Colorado State University. Libraries, 2012) Martucci, Mary B., author; Prieto, Amy L., advisor; Elliott, C. Michael, committee member; Fisher, Ellen R., committee member; Rickey, Dawn, committee member; Patton, Carl E., committee memberThe field of spintronics, the development of spin-based devices that utilize the spin degree of freedom to increase memory capacity, has emerged as a solution to faster more efficient memory storage for electronic devices. One class of materials that has been extensively studied is the half-metallic ferromagnets, compounds that are 100% spin-polarized at the Fermi level. One material in this group that has been investigated is chromium telluride (Cr1-xTe), whose family of compounds is known to exhibit a wide range of interesting magnetic and electronic properties. We have developed a hot injection solution synthesis of Cr5Te8 nanoplatlets which show similar magnetic behavior to the bulk material. It has also been shown that selenium and sulfur analogues can be obtained without changing the reaction conditions, making progress toward a better understanding of the reaction as well as an interesting family of compounds. Using real-space simulations, the effect of polarons in the high-Tc superconducting cuprates has been studied. The simulations demonstrate energetically favorable sites for the defects and show evidence of longer-range pairing interactions. Variations of the stripe show similar energetic results. X-ray absorption fine structure spectroscopy and neutron scattering have been utilized to examine the local structure of Ni-doped Mg nanoparticles, a hydrogen storage material as well as Cu2ZnSnS4 (CZTS) nanoparticles, a photovoltaic material. The Mg-Ni material shows much local disorder upon hydrogen cycling. The CZTS data demonstrate a loss of sulfur from around the copper sites upon annealing, helping to explain the changes observed in the optical absorption properties resulting from the annealing process.Item Open Access Part I: Development of plasma surface modification and characterization strategies for three-dimensional polymer constructs used in biological applications and Part II: Exploring general chemistry students' metacognitive monitoring on examinations(Colorado State University. Libraries, 2016) Hawker, Morgan Johanna, author; Fisher, Ellen R., advisor; Rickey, Dawn, committee member; Menoni, Carmen S., committee member; Barisas, George, committee member; Rhodes, Matthew G., committee memberTo view the abstract, please see the full text of the document.Item Open Access Recognition without identification (RWI) and the feeling of knowing (FOK): a comparison of retrospective and prospective-based familiarity judgments(Colorado State University. Libraries, 2010) Nomi, Jason S., author; Cleary, Anne M., advisor; Rhodes, Matthew, committee member; Rickey, Dawn, committee memberRecognition without identification (RWI) and the feeling of knowing (FOK) are two memory paradigms that attempt to tap awareness of memory states in the absence of identification of a target. Although both RWI and FOKs have been described using the example of recognizing a face as familiar without recalling who that person is, no empirical evidence has yet demonstrated that they are based on a common underlying mechanism. The presented studies attempted to directly compare RWI and FOK judgments by utilizing a hybrid paradigm containing commonly used RWI and FOK methodologies that differed by a single manipulation of instruction type. The data demonstrated that participants gave significantly different patterns of ratings in the RWI condition than the FOK condition, suggesting different underlying mechanisms of RWI and FOK judgments.Item Open Access Role of homotropic association of luteinizing hormone receptors in hormone mediated signaling(Colorado State University. Libraries, 2012) Crenshaw, Shirley Ann, author; Barisas, B. George, advisor; van Orden, Alan, committee member; Rickey, Dawn, committee member; Levinger, Nancy, committee member; Roess, Deborah, committee memberG protein-coupled receptors (GPCR) are plasma membrane receptors involved in signal transduction and are an important target for drug discovery. Luteinizing hormone receptors (LHR) are GPCRs found on the reproductive organs of both males and females and promote spermatogenesis and ovulation. Understanding how these protein receptors function on the plasma membrane will lead to better understanding of the mammalian reproduction system and other GPCR systems. Studies in the past suggested that these receptors oligomerize after hormone binding, but recent studies performed with LHRs suggest that these receptors maybe constitutively oligomerized in the endoplasmic reticulum and on the plasma membrane. However, these experiments were performed on receptors expressed by transient transfection and using bioluminescence resonance energy transfer (BRET). These methods have potential weaknesses. Transient transfections typically yield a fraction of cells with very high receptor expression and BRET measurements are strongly weighted towards those cells. Hence, this overall approach may have yielded misleading results. Fluorescence energy transfer (FRET) is a similar technique to BRET but has advantages such as allowing imaging examination of single cells. Using FRET, LHR oligomerization was evaluated on cells treated with human chorionic gonadotropin (hCG) or deglycosylated-hCG, hormones which activate and inhibit the receptor function, respectively. FRET measurements demonstrated that, on the surfaces of transiently transfected cells, LHRs exhibit substantial intermolecular FRET which is very slightly increased by hCG treatment and very slightly reduced by exposure to DG-hCG. Closer examination of these data showed that all observed FRET depended linearly on receptor expression and approach zero at low expression levels. This suggests that FRET between LHR on these transiently-transfected cells may arise from inter-molecular proximity induced non-specifically by high receptor surface concentrations. To evaluate the receptor density on cells flow cytometry was used. Flow cytometry revealed that transiently-transfected LHRs are expressed over a broad range of surface densities, including very high expression levels. Using a mathematical model, the FRET efficiencies expected for various receptor surface densities were calculated. These calculations suggest that expression levels observed cytometrically could cause substantial amounts of FRET from molecular crowding and, particularly if the receptors are additionally concentrated in lipid rafts, most of the observed FRET signal could be attributed to non-specific concentration effects.Item Open Access Synthesis and characterization of multidentate iminopyridine and polypyridine transition metal complexes(Colorado State University. Libraries, 2013) McDaniel, Ashley M., author; Shores, Matthew, advisor; Anderson, Oren, committee member; Borch, Thomas, committee member; Finke, Richard, committee member; Rickey, Dawn, committee memberThe work described in this dissertation details the syntheses and characterization of transition metal complexes featuring polypyridyl and iminopyridine ligands. The primary focus has been the synthesis of 3d metal complexes of multidentate iminopyridine ligands bearing functionalizations relevant to spin crossover and photochemistry. These seemingly disparate areas of research are linked by the facts that subtle metal-ligand interactions play enormous roles in determining complex properties and that understanding these types of interactions is crucial for eventual property control. In Chapter 1, the underpinnings of spin crossover in transition metals with d4-d7 configurations are discussed along with progress toward linking spin-switching events with host-guest interactions in solution. My research on Fe(II) hexadentate iminopyridine complexes is placed into context with extending anion sensing to biologically and environmentally relevant media. Also in Chapter 1, my work on hexadentate iminopyridine and polypyridine Cr complexes is related to the current understanding of the excited state behavior of 3d iminopyridine complexes, specifically, and 3d aromatic diimines in general. Additionally, the redox non-innocence of iminopyridine and polypyridine ligands is discussed. In Chapter 2, the preparation and characterization of a series of divalent 3d transition metal complexes (Cr to Zn), featuring an ester functionalized multidentate, tripodal iminopyridine Schiff-base L5-OOMe is reported. X-ray structural studies reveal complex geometries ranging from local octahedral coordination to significant distortion towards trigonal prismatic geometry to heptacoordinate environments. Regardless of coordination mode, magnetic and spectroscopic studies show the ligand to provide moderately strong ligand fields: the Fe complex is low-spin, while the Co and Mn complexes are high-spin at all temperatures proved. Cyclic voltammograms exhibit multiple reversible ligand-based reductions, which are relatively consistent throughout the series; however, the electrochemical behavior of the Cr complex is fundamentally different from those of the other complexes. Time-dependent (TD) DFT and natural transition orbital (NTO) computational analyses for the ligand, its anion, and complexes were provided by Prof. Anthony Rappé: the computed spectra reproduce the major differential features of the observed visible absorption spectra, and NTOs provide viable interpretations for the observed features. The combined studies indicate that for Mn-Zn complexes, neutral ligands are bound to M(II) ions, but Cr is best described as a Cr(III) species bound to a radical anionic ligand. In Chapter 3, the syntheses and characterizations of Fe(II) complexes of hexadentate ligands poised for anion-triggered spin-state switching in polar solution media are reported. The tripodal iminopyridine ligands L5-OH, L6-OH and L5-ONHtBu, L6-ONHtBu contain methanolic or t-butylamide functional groups, respectively. Solid-state evidence for anion-cation hydrogen bonding interactions are observed for halide complexes of [Fe(L6-OH)]2+ and [Fe(L5-ONHtBu)]2+; [Fe(L5-ONHtBu)]2+ forms a preorganized pocket which strongly binds Cl-. Strong anion binding events in the 5-position complexes are also observed in solution via 1H NMR monitored chloride titrations in acetonitrile. And while no temperature dependence or anion dependence on spin-state is apparent for 6-position complexes in solution, a small but significant increase in magnetic susceptibility is observed for [Fe(L5-ONHtBu)]2+ as up to one equivalent of tetrabutylammonium chloride is added; suggesting that spin-state control by anion-cation interactions may be accessible for this class of compounds. In Chapter 4, the preparation and characterization of homo- and heteroleptic Cr(III) coordination complexes featuring the dimethyl 2,2'-bipyridine-4,4'-dicarboxylate (4-dmcbpy) ligand are discussed. Static and nanosecond time-resolved absorption and emission properties of these complexes dissolved in acidic aqueous (1 M HCl(aq)) solutions were investigated by Huan-Wei Tseng and Prof. Niels Damrauer. The photophysical data suggest that in these acidic aqueous environments these complexes store ~1.7 eV for multiple microseconds at room temperature. The electrochemical properties of these polypyridyl complexes were investigated by cyclic voltammetry. It is found that inclusion of 4-dmcbpy shifts the 'CrIII/II' E1/2 by +0.22 V compared to those of homoleptic parent complexes. The electrochemical and photophysical data allow for excited state potentials to be determined: for [Cr(4-dmcbpy)3]3+, CrIII*/II lies at +1.44 V versus Fc+/0 (~+2 V vs NHE), suggesting it would act as one of the most powerful photooxidants reported. In Chapter 5, the preparation, photophysical characterization, and computed excited state energies for Cr(III) complexes of a family of tripodal hexadentate and tris(bidentate) iminopyridine ligands are reported. Cyclic voltammograms reveal that the hexadentate and tris(bidentate) analogues have almost identical reduction potentials, and overall electrochemical behavior similar to the polypyridyl complexes described in Chapter 3. The absorption spectra of the hexadentate complexes show improved absorption of visible light compared to the tris(bidentate) analogues. Photophysical characterization provided by Huan-Wei Tesng and Prof. Niels Damrauer show a doublet excited state with 17 to 19 μs lifetime at room temperature for the ester functionalized tris(bidentate) complex, while no doublet states are observed for the ester functionalized hexadentate analogue under the same conditions. The electronic structure contributions to the differences in observed photophysical properties are compared by extensive computational analyses provided by Prof. Anthony Rappé. These studies indicate that the presence of non-ligated bridgehead nitrogen atoms in the complexes of tripodal hexadentate iminopyridines significantly reduce excited state doublet, quartet, and sextet energies and change the character of the low lying doublet states in compared to species that show population of doublet excited states. In Chapter 6 the syntheses and characterization of reduced forms of Cr complexes of 4-dmcbpy (described in Chapter 4), [Cr(4-dmcbpy)3]n+ (n = 2, 1), and tren(py)3 (L1, described in Chapter 5) [Cr(tren(py)3)]n+ (n = 2) are reported. Comparison of electrochemical data for the series (n = 3, 2, 1) and solid state structures of the divalent complexes are consistent with consecutive reducing equivalents added to Cr polypyridine or iminopyridine complexes not residing on the metal, and that these complexes are best described as Cr(III) ions ligated to anionic radical ligands. Final remarks about the work in Chapters 2-6 and suggested directions for future work are presented in Chapter 7.Item Open Access Towards the total synthesis of 14-acetoxygelsenicine and synthesis of largazole analogs(Colorado State University. Libraries, 2009) Newkirk, Tenaya L., author; Williams, Robert M., advisor; Stermitz, Frank R., committee member; Ferreira, Eric M., committee member; Rickey, Dawn, committee member; Thamm, Douglas H., committee memberHerein are documented our efforts in two projects, beginning with studies towards the total synthesis of 14-acetoxygelsenicine. We have developed different strategies towards this complex natural product, wherein we have developed routes towards an appropriate substrate for a novel, intramolecular hetero Diels-Alder cyclization. The developed route would also lead to related members of this family of alkaloids, and helps set the stage for future efforts. In the second project discussed, we have successfully pursued the synthesis of numerous, biologically active analogs of the natural product (+)-largazole. Synthetic efforts have led to the design of inhibitors with unprecedented biological activity, as well as providing information regarding the structure-activity relationship of these molecules.