Synthesis and Characterization of Nanostructures in Porous Anodic Aluminum Oxide Templates

In this study, template-based methods are used for the fabrication of various nanostructures such as nandots, nanorods, nanowires, nanotubes, and core-shell structures. Porous alumina membranes were employed as templates and metal nanostructures were synthesized in the templates by electrodeposition. By using lithography techniques, controlled patterned nanostructures were also fabricated on alumina templates. The magnetic properties of the various metal nanostructures were investigated. The pore size, interpore distance, and pore geometry highly affect magnetic properties of nanostructures grown in the templates. Hexagonally ordered porous alumina templates can be fabricated by two-step anodization. The pore diameters and interpore distances were readily controlled by appropriately changing anodization conditions and pore widening time. Alumina templates with various pore geometries were also successfully synthesized by changing applied voltage, increasing and decreasing, during a third anodization step. To understand magnetic properties of nanostructures with different aspect rations in the form of nanodots, nanorods, or nanowires, Fe nanostructures were fabricated in the templates by controlling of electrodeposition times. The coercivity of nanostructures increased with increasing aspect ratio. The anisotropy of the arrays was governed by the shape anisotropy of the magnetic objects with different aspect ratios. nanowires in mild-hard alumina and conventional alumina templates showed distinct differences in the squareness of hysteresis loops and coercivity both as a function of pore structure and magnetic component. Iron oxide nanotubes with a unique inner-surface were also fabricated by an electrodeposition method. β-FeOOH nanotubes were grown in alumina templates and transformed into hematite and magnetite structures during various heating processes. Hematite nanotubes are composed of small nanoparticles less than 20 nm diameters and the hysteresis loops and FC-ZFC curves show superparamagnetic properties without the Morin transition. In the case of magnetite nanotubes, which consist of slightly larger nanoparticles, hysteresis loops show ferromagnetism with weak coercivity at room temperature while FC-ZFC curves exhibit the Verwey transition at 125 K. For the patterning of nanowires, lithography techniques including nanosphere lithography and e-beam lithography were used. Nanosphere lithography used self-assembled PS spheres as a mask creates holes between spheres and the size of the holes is determined by the size and geometry of ordered PS spheres on the templates. This method can grow patterned nanowires arrays and also produce unique cup-shaped nanostructures with sizes ranging from micrometer down to several nanometers. E-beam lithography was also combined with template-based electrodeposition. Of these two lithographic methods, this one is the most powerful in the fabrication of patterned nanostructures with high aspect ratios. Various features and the sizes of patterned structures can be readily controlled. By the directing the pore diameters and interpore distances of the alumina template, the size and number of patterned nanowires are also adjustable

Facilitatory neural dynamics for predictive extrapolation

Neural conduction delay is a serious issue for organisms that need to act in real time. Perceptual phenomena such as the flash-lag effect (FLE, where the position of a moving object is perceived to be ahead of a brief flash when they are actually colocalized) suggest that the nervous system may perform extrapolation to compensate for delay. However, the precise neural mechanism for extrapolation has not been fully investigated. The main hypothesis of this dissertation is that facilitating synapses, with their dynamic sensitivity to the rate of change in the input, can serve as a neural basis for extrapolation. To test this hypothesis, computational and biologically inspired models are proposed in this dissertation. (1) The facilitatory activation model (FAM) was derived and tested in the motion FLE domain, showing that FAM with smoothing can account for human data. (2) FAM was given a neurophysiological ground by incorporating a spike-based model of facilitating synapses. The spike-based FAM was tested in the luminance FLE domain, successfully explaining extrapolation in both increasing and decreasing luminance conditions. Also, inhibitory backward masking was suggested as a potential cellular mechanism accounting for the smoothing effect. (3) The spike-based FAM was extended by combining it with spike-timing-dependent plasticity (STDP), which allows facilitation to go across multiple neurons. Through STDP, facilitation can selectively propagate to a specific direction, which enables the multi-neuron FAM to express behavior consistent with orientation FLE. (4) FAM was applied to a modified 2D pole-balancing problem to test whether the biologically inspired delay compensation model can be utilized in engineering domains. Experimental results suggest that facilitating activity greatly enhances real time control performance under various forms of input delay as well as under increasing delay and input blank-out conditions. The main contribution of this dissertation is that it shows an intimate link between the organism-level problem of delay compensation, perceptual phenomenon of FLE, computational function of extrapolation, and neurophysiological mechanisms of facilitating synapses (and STDP). The results are expected to shed new light on real-time and predictive processing in the brain, and help understand specific neural processes such as facilitating synapses

Association of Cyclooxygenase-2 Expression With Endoplasmic Reticulum Stress and Autophagy in Triple-Negative Breast Cancer

Cyclooxygenase-2 plays a role in oncogenesis and its overexpression is associated with triple-negative breast cancer. However, the mechanisms whereby cyclooxygenase-2 contribute to breast cancer are complex and not well understood. Cyclooxygenase-2 overexpression causes hypoxia, oxidative stress, and endoplasmic reticulum stress. The aim of this study is to investigate the correlations among cyclooxygenase-2 expression, endoplasmic reticulum stress-associated molecules, and autophagy-associated molecules in triple-negative breast cancer. Surgical specimens from two cohorts of triple-negative breast cancer patients without neoadjuvant systemic therapy were analyzed: cohorts 1 and 2 consisted of 218 cases from 2004 to 2006 and 221 cases from 2007 to 2009, respectively. Specimens were evaluated by immunohistochemical examination of cyclooxygenase-2, endoplasmic reticulum stress markers, and autophagy markers expression using tissue microarrays. Cyclooxygenase-2 was overexpressed in 29.8% and 23.9% of cases in cohorts 1 and 2, respectively; and it was positively correlated with two out of three endoplasmic reticulum stress-associated molecules (XBP1, p = 0.025 and p = 0.003 in cohort 1 and cohort 2, respectively; PERK, p \u3c 0.001 in both cohorts). Cyclooxygenase-2 was also positively correlated with two out of three autophagy markers (p62, p = 0.002 and p = 0.003 in cohort 1 and cohort 2, respectively; beclin1, p \u3c 0.001 in both cohorts). Although cyclooxygenase-2 was not an independent prognostic factor for distant metastasis free survival and overall survival, its expression was associated with the expression of endoplasmic reticulum stress and autophagy molecules in triple-negative breast cancer

An Active and Soft Hydrogel Actuator to Stimulate Live Cell Clusters by Self-folding

The hydrogels are widely used in various applications, and their successful uses depend on controlling the mechanical properties. In this study, we present an advanced strategy to develop hydrogel actuator designed to stimulate live cell clusters by self-folding. The hydrogel actuator consisting of two layers with different expansion ratios were fabricated to have various curvatures in self-folding. The expansion ratio of the hydrogel tuned with the molecular weight and concentration of gel-forming polymers, and temperature-sensitive molecules in a controlled manner. As a result, the hydrogel actuator could stimulate live cell clusters by compression and tension repeatedly, in response to temperature. The cell clusters were compressed in the 0.7-fold decreases of the radius of curvature with 1.0 mm in room temperature, as compared to that of 1.4 mm in 37 degrees C. Interestingly, the vascular endothelial growth factor (VEGF) and insulin-like growth factor-binding protein-2 (IGFBP-2) in MCF-7 tumor cells exposed by mechanical stimulation was expressed more than in those without stimulation. Overall, this new strategy to prepare the active and soft hydrogel actuator would be actively used in tissue engineering, drug delivery, and micro-scale actuators

Analysis of Building Energy Savings Potential for Metal Panel Curtain Wall Building by Reducing Thermal Bridges at Joints Between Panels

AbstractTo achieve national greenhouse gas reduction in the building sector, heating and cooling energy in buildings should be reduced. The government has strengthened regulations on insulation performance for building energy savings. However, the building envelope has various thermal bridges. In particular, a metal panel curtain wall comprises a number of thermal bridges at joints between the panels and the fixing units, thus degrading the overall thermal performance. To reduce building energy, it is necessary to reduce thermal bridges in building envelopes. This study aims to analyze the energy saving potential achieved by reducing thermal bridges. For this, the insulation performance and building energy needs of the existing and alternative metal panel curtain wall were evaluated. The alternative metal panel curtain wall that uses plastic molds at joints between panels and the thermally-broken brackets was suggested to reduce heat loss through thermal bridges. As results, the effective U-value of the alternative metal panel curtain wall was reduced by 72% compared with the existing metal panel curtain wall. In addition, annual heating energy needs of the alternative metal panel curtain wall building was reduced by 26%, and annual total energy needs was reduced by 6% because annual cooling energy needs of it slightly increased compared with the existing metal panel curtain wall. In conclusion, the alternative metal panel curtain wall considerably influenced the savings in building energy needs by reducing thermal bridges