Physics Commons^™

Atomic Force Microscopy Cantilever-Based Nanoindentation: Mechanical Property Measurements At The Nanoscale In Air And Fluid, Ashton E. Enrriques, Sean Howard, Raju Timsina, Nawal K. Khadka, Amber N. Hoover, Allison E. Ray, Ling Ding, Chioma Onwumelu, Stephan Nordeng, Laxman Mainali, Gunes Uzer, Paul H. Davis

Physics Faculty Publications and Presentations

An atomic force microscope (AFM) fundamentally measures the interaction between a nanoscale AFM probe tip and the sample surface. If the force applied by the probe tip and its contact area with the sample can be quantified, it is possible to determine the nanoscale mechanical properties (e.g., elastic or Young's modulus) of the surface being probed. A detailed procedure for performing quantitative AFM cantilever-based nanoindentation experiments is provided here, with representative examples of how the technique can be applied to determine the elastic moduli of a wide variety of sample types, ranging from kPa to GPa. These include live mesenchymal …

Kinetic Monte Carlo Simulations Of Quantum Dot Self-Assembly, Matthew Abramson, Hunter J. Coleman, Paul J. Simmonds, Tim P. Schulze, Christian Ratsch

Physics Faculty Publications and Presentations

In the Stranski–Krastanov growth mode for heteroepitaxial systems, layer-by-layer growth is followed by the formation and growth of three-dimensional (3D) islands. In this paper, we use a kinetic Monte Carlo method to simulate this growth mode behavior. We present a detailed and systematic investigation into the effects of key model parameters including strain, growth temperature, and deposition rate on this phenomenon. We show that increasing the strain lowers the apparent critical thickness that is defined by the onset of 3D island formation. Similarly, increasing the growth temperature lowers the apparent critical thickness, until intermixing, and the resulting relevance of entropic …

Binding Of Alpha-Crystallin To Cortical And Nuclear Lens Lipid Membranes Derived From A Single Lens, Raju Timsina, Samantha Wellisch, Dieter Haemmerle, Laxman Mainali

Physics Faculty Publications and Presentations

Several studies reported that α-crystallin concentrations in the eye lens cytoplasm decrease with a corresponding increase in membrane-bound α-crystallin with age and cataracts. The influence of the lipid and cholesterol composition difference between cortical membrane (CM) and nuclear membrane (NM) on α-crystallin binding to membranes is still unclear. This study uses the electron paramagnetic resonance (EPR) spin-labeling method to investigate the α-crystallin binding to bovine CM and NM derived from the total lipids extracted from a single lens. Compared to CMs, NMs have a higher percentage of membrane surface occupied by α-crystallin and binding affinity, correlating with less mobility and …

Liposome Formulation For Tumor-Targeted Drug Delivery Using Radiation Therapy, Daniel Fologea

Physics Faculty Publications and Presentations

Targeted delivery of drugs or other therapeutic agents through internal or external triggers has been used to control and accelerate the release from liposomal carriers in a number of studies, but relatively few utilize energy of therapeutic X-rays as a trigger. We have synthesized liposomes that are triggered by ionizing radiation (RTLs) to release their therapeutic payload. These liposomes are composed of natural egg phosphatidylethanolamine (PE), 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC), cholesterol, and 1,2-disteroyl-sn-glycero-3-phosphoethanolamine-N-[methoxy (polyethylene glycol)-2000] (DSPE-PEG-2000), and the mean size of the RTL was in the range of 114 to 133 nm, as measured by nanoparticle tracking analysis (NTA). The trigger mechanism …

Synthesis Of Metastable Ruddlesden–Popper Titanates, (ATio3)NAO, With N ≥ 20 By Molecular-Beam Epitaxy, Matthew R. Barone, Myoungho Jeong, Nicholas Parker, Jiaxin Sun, Dmitri A. Tenne, Kiyoung Lee, Darrell G. Schlom

Physics Faculty Publications and Presentations

We outline a method to synthesize (ATiO₃)_nAO Ruddlesden–Popper phases with high-n, where the A-site is a mixture of barium and strontium, by molecular-beam epitaxy. The precision and consistency of the method described is demonstrated by the growth of an unprecedented (SrTiO₃)₅₀SrO epitaxial film. We proceed to investigate barium incorporation into the Ruddlesden–Popper structure, which is limited to a few percent in bulk, and we find that the amount of barium that can be incorporated depends on both the substrate temperature and the strain state of the …

Optical Selection Bias And Projection Effects In Stacked Galaxy Cluster Weak Lensing, Hao-Yi Wu

Physics Faculty Publications and Presentations

Cosmological constraints from current and upcoming galaxy cluster surveys are limited by the accuracy of cluster mass calibration. In particular, optically identified galaxy clusters are prone to selection effects that can bias the weak lensing mass calibration. We investigate the selection bias of the stacked cluster lensing signal associated with optically selected clusters, using clusters identified by the redMaPPer algorithm in the Buzzard simulations as a case study. We find that at a given cluster halo mass, the residuals of redMaPPer richness and weak lensing signal are positively correlated. As a result, for a given richness selection, the stacked lensing …

Membrane Elasticity Modulated By Cholesterol In Model Of Porcine Eye Lens-Lipid Membrane, Nawal K. Khadka, Max-Florian Mortimer, Mason Marosvari, Raju Timsina, Laxman Mainali

Physics Faculty Publications and Presentations

Experimental evidence shows that the eye lens loses its elasticity dramatically with age. It has also been reported that the cholesterol (Chol) content in the eye lens fiber cell plasma membrane increases significantly with age. High Chol content leads to the formation of cholesterol bilayer domains (CBDs) in the lens membrane. The role of high Chol associated with lens elasticity is unclear. The purpose of this research is to investigate the membrane elasticity of the model of porcine lens-lipid (MPLL) membrane with increasing Chol content to elucidate the role of high Chol in lens membrane elasticity. In this study, we …

Alpha-Crystallin Association With The Model Of Human And Animal Eye Lens-Lipid Membranes Is Modulated By Surface Hydrophobicity Of Membranes, Raju Timsina, Geraline Trossi-Torres, Jackson Thieme, Matthew O'Dell, Nawal K. Khadka, Laxman Mainali

Physics Faculty Publications and Presentations

Purpose

This research aims to probe the interaction of α-crystallin with a model of human, porcine, and mouse lens-lipid membranes.

Methods

Cholesterol/model of human lens-lipid (Chol/MHLL), cholesterol/model of porcine lens-lipid (Chol/MPLL), and cholesterol/model of mouse lens-lipid (Chol/MMLL) membranes with 0–60 mol% Chol were prepared using the rapid solvent exchange method and probe-tip sonication. The hydrophobicity near the surface of model lens-lipid membranes and α-crystallin association with these membranes were investigated using the electron paramagnetic resonance spin-labeling approach.

Results

With increased Chol content, the hydrophobicity near the surface of Chol/MHLL, Chol/MPLL, and Chol/MMLL membranes, the maximum percentage of membrane surface occupied …

Experimental Investigations On The Conductance Of Lipid Membranes Under Differential Hydrostatic Pressure, Rose Whiting, Pangaea W. Finn, Andrew Bogard, Fulton Mckinney, Dallin Pankratz, Aviana R. Smith, Elen A. Gardner, Daniel Fologea

Physics Faculty Publications and Presentations

The unassisted transport of inorganic ions through lipid membranes has become increasingly relevant to an expansive range of biological phenomena. Recent simulations indicate a strong influence of a lipid membrane’s curvature on its permeability, which may be part of the overall cell sensitivity to mechanical stimulation. However, most ionic permeability experiments employ a flat, uncurved lipid membrane, which disregards the physiological relevance of curvature on such investigations. To fill this gap in our knowledge, we adapted a traditional experimental system consisting of a planar lipid membrane, which we exposed to a controlled, differential hydrostatic pressure. Our electrophysiology experiments indicate a …

Alpha-Crystallin-Membrane Association Modulated By Phospholipid Acyl Chain Length And Degree Of Unsaturation, Geraline Trossi-Torres, Raju Timsina, Laxman Mainali

Physics Faculty Publications and Presentations

α-crystallin-membrane association increases with age and cataracts, with the primary association site of α-crystallin being phospholipids. However, it is unclear if phospholipids’ acyl chain length and degree of unsaturation influence α-crystallin association. We used the electron paramagnetic resonance approach to investigate the association of α-crystallin with phosphatidylcholine (PC) membranes of different acyl chain lengths and degrees of unsaturation and with and without cholesterol (Chol). The association constant (K_a) of α-crystallin follows the trends, i.e., K_a (14:0–14:0 PC) > K_a (18:0–18:1 PC) > K_a (18:1–18:1 PC) ≈ K_a (16:0–20:4 PC) where the presence of Chol decreases K …

An Afm Approach Applied In A Study Of Α-Crystallin Membrane Association: New Insights Into Lens Hardening And Presbyopia Development, Nawal K. Khadka, Raju Timsina, Laxman Mainali

Physics Faculty Publications and Presentations

The lens of the eye loses elasticity with age, while α-crystallin association with the lens membrane increases with age. It is unclear whether there is any correlation between α-crystallin association with the lens membrane and loss in lens elasticity. This research investigated α-crystallin membrane association using atomic force microscopy (AFM) for the first time to study topographical images and mechanical properties (breakthrough force and membrane area compressibility modulus (K_A), as measures of elasticity) of the membrane. α-Crystallin extracted from the bovine lens cortex was incubated with a supported lipid membrane (SLM) prepared on a flat mica surface. The …

Coil-To-Bridge Transitions Of Self-Assembled Water Chains Observed In A Nanoscopic Meniscus, Byung I. Kim, Ryan D. Boehm, Harrison Agrusa

Physics Faculty Publications and Presentations

Ten downward portions in the large oscillatory force–distance curve reported earlier are analyzed to understand a nanoscale water meniscus confined between a sharp probe and a flat substrate in air. The sigmoidal shape of each portion leads to the assumption that the meniscus is made up of n independent transitions of two states: one for a coil state and the other for a bridge state. The analysis reveals that each downward portion occurs due to a coil-to-bridge transition of n self-assembled water chains whose length ranges between 197 and 383 chain units. The transition provides novel insights into water’s unique …

Exploiting Non-Linear Scales In Galaxy–Galaxy Lensing And Galaxy Clustering: A Forecast For The Dark Energy Survey, Andrés N. Salcedo, David H. Weinberg, Hao-Yi Wu, Benjamin D. Wibking

Physics Faculty Publications and Presentations

No abstract provided.

Effect Of As Flux On Inas Submonolayer Quantum Dot Formation For Infrared Photodetectors, K. D. Vallejo, P. J. Simmonds

Physics Faculty Publications and Presentations

The performance of infrared photodetectors based on submonolayer quantum dots was investigated as a function of the arsenic flux. All the devices showed similar figures of merit and a very high specific detectivity above 1 × 10¹¹ cm Hz^1/2/W at 12 K, despite the fact that cross-sectional scanning tunneling microscopy images pointed out a strong reduction in the density of such nanostructures with decreasing arsenic flux. This contrast is a consequence of the small size and low In content of the submonolayer quantum dots that lead to a strong delocalization of the electrons wave function and, therefore, …

Vortices And Dust Devils As Observed By The Mars Environmental Dynamics Analyzer Instruments On Board The Mars 2020 Perseverance Rover, Brian Jackson

Physics Faculty Publications and Presentations

An important and perhaps dominant source of dust in the Martian atmosphere, dust devils play a key role in Mars' climate. Data sets from previous landed missions have revealed dust devil activity, constrained their structures, and elucidated their dust-lifting capacities. However, each landing site and observational season exhibits unique meteorological properties that shape dust devil activity and illuminate their dependence on ambient conditions. The recent release of data from the Mars Environmental Dynamics Analyzer (MEDA) instrument suite on board the Mars 2020 Perseverance rover promises a new treasure trove for dust devil studies. In this study, we sift the time …