Measuring cell adhesion forces with the atomic force microscope at the molecular level

In the past 25 years many techniques have been developed to characterize cell adhesion and to quantify adhesion forces. Atomic force microscopy (AFM) has been used to measure forces in the pico-newton range, an experimental technique known as force spectroscopy. We modified such an AFM to measure adhesion forces between live cells or between cells and surfaces. This strategy required functionalizing the surface of the sensors for immobilizing the cell. We used Dictyostelium discoideum cells which respond to starvation by surface expression of the adhesion molecule csA and consequent aggregation to measure the adhesion force of a single csA-csA bond. Relevant experimental parameters include the duration of contact between the interacting surfaces, the force against which this contact is maintained, the number and specificity of interacting adhesion molecules and the constituents of the medium in which the interaction occurs. This technology also permits the measurement of the viscoelastic properties of single cells or cell layers. Copyright (C) 2002 S, Karger AG, Basel

Velocity-Dependent Forces in Atomic Force Microscopy Imaging of Lipid Films

We have imaged adsorbed fluid lipid bilayers by atomic force microscopy. The patches were formed by rupture of phospholipid vesicles onto magnesium fluoride. We show that the membrane patches are fluid but can be stably imaged at scan rates higher than 6 p d s . At lower scan rates the tip penetrates through the layer. The penetrating tip does not destroy the fluid patches, and the previous image can be restored after increasing the scanning velocity. The dynamic forces that possibly explain the effect are discussed

Evaluating Baseflow Recession Behavior using the Integrated Hydrologic Model ParFlow

Hydrologists have long studied the rate of streamflow recession as a means of understanding watershed properties. Historically, recession events were lumped together for analysis. However, more recent work has shown that individual recession events behave differently, and additional insights can be gained by evaluating events individually. The analysis of individual recession events has been shown to be a valuable tool for examining hydrologic processes in large watersheds, however its connection to hydrologic models has not been thoroughly explored. We used the integrated hydrologic model ParFlow to systematically explore the drivers of baseflow recession curves. Using ParFlow we demonstrated that the integrated model can generate shifting between recession events consistent with observational tudies. Furthermore, we found that storage has a major impact on recession curves, causing curves to shift to the right when storage is high. Subsurface configuration was also seen to have a large effect, with hydraulic conductivity influencing recession curves regardless of storage levels

An Arab NATO in the Making? Middle Eastern Military Cooperation Since 2011

Arab military cooperation has been, over the past century, mostly a history of failures. Whether the Arab League’s Defence Pact or the Middle East Command, ideas for collective security in the region all failed to move beyond the state of declarations. Most of the time, Arab states were either at open war or in cold peace. Since the Arab Spring has toppled not only regimes but also brought insecurity, new momentum has come into regional security. From joint exercises to the announcement of first an Arab and more recently an Islamic military alliance, states begin to move further into cooperation. As this Letort Paper shows, several obstacles will have to be overcome before collective security in the Middle East and North Africa can become a reality.https://press.armywarcollege.edu/monographs/1299/thumbnail.jp

After the Spring: Reforming Arab Armies

View the Executive SummaryAs the Arab Spring has renewed Western interest in the political, as well as military, role of Arab armed forces, reform—rather than mere assistance—is crucial. In this monograph, the author focuses on the structural aspects of reform from which the Arab Spring forces would benefit. Seven features are identified which need to be addressed when attempting Arab military reform in the countries affected by large-scale unrest in 2011: an unclear mandate, over-politicization, a challenging ongoing security situation, limited resources, lack of civilian oversight, pockets of paramilitary activity, and, in parts, as well as the lack of an institutional perception of reform need. Their origins are elaborated as much as recommendations for what outside assistance can achieve.https://press.armywarcollege.edu/monographs/1483/thumbnail.jp

The Gulf Moment: Arab Relations Since 2011

This monograph examines the impact that the “Arab Spring” has had on how Arab states relate to each other post-regime change and post-Islamist electoral victory. It shows that the region is undergoing a profound change as some traditional regional policy actors are paralyzed by internal turmoil (such as Syria and Egypt), while others do not have a regional ambition (such as Algeria and Morocco). The region has therefore entered a Gulf moment where key decisions pertaining to the region’s future are now taken in Riyadh, Doha, and Abu Dhabi. From having once been mere bystanders of regional politics, the Gulf States have moved to become players with both the ambition and capability to shape regional dynamics. As the ripple effects of their 2014 rift show, these dynamics will have a wider Arab impact.https://press.armywarcollege.edu/monographs/1453/thumbnail.jp

Polymerized LB films imaged with a combined atomic force microscope-fluorescence microscope

The first results obtained with a new stand-alone atomic force microscope (AFM) integrated with a standard Zeiss optical fluorescence microscope are presented. The optical microscope allows location and selection of objects to be imaged with the high-resolution AFM. Furthermore, the combined microscope enables a direct comparison between features observed in the fluorescence microscope and those observed in the images obtained with the AFM, in air or under liquid. The cracks in polymerized Langmuir-Blodgett films of lO,l2-pentacosadiynoic acid as observed in the fluorescence microscope run parallel to one of the lattice directions of the crystal as revealed by molecular resolution images obtained with the AFM. The orientation of these cracks also coincides with the polarization direction of the fluorescent light, indicating that the cracks run along the polymer backbone. Ripple-like corrugations on a submicrometer scale have been observed, which may be due to mechanical stress created during the polymerization process

Protein-DNA force assay in a microfluidic format

The detailed study of protein-DNA interactions is a core effort to elucidate physiological processes, including gene regulation, DNA repair and the immune response. The molecular force assay (MFA) is an established method to study DNA-binding proteins. In particular, high-affinity binder dissociation is made possible by the application of force. Microfluidic lab-on-a-chip approaches have proven helpful for parallelization, small sample volumes, reproducibility, and low cost. We report the successful combination of these two principles, forming a microfluidic molecular force assay and representing a novel use for the established MITOMI chip design. We present, characterize, validate and apply this integrated method. An alternative confocal fluorescence microscopy readout and analysis method is introduced and validated. In a multiplexing application, EcoRI binding is detected and characterized. This method paves the way for quantitative on-chip force measurements. It is suited for integration with DNA micro-spotting and in vitro expression of transcription factors to form a high-throughput chip for detailed DNA-protein interaction studies