Characterization of Biomaterials by Atomic Force Microscopy

AFM microscopy is a very promising tool for the understanding and the study of biological materials. This abstract briefly shows the results obtained during the period of my Ph.D. studies in the Chemistry and Industrial Chemistry Department at the University of Pisa. A commercial atomic force microscope (AFM) was used to investigate different kinds of biomaterials such as oligo peptides, polymers and proteins but also some hard materials as silicon and metals. The AFM consists of a microsized cantilever with a sharp tip (probe) at its end that is used to scan the specimen surface. The cantilever is typically made of silicon or silicon nitride with a tip radius of curvature on the order of few nanometers. When the tip is brought into proximity of a sample surface, forces between the tip and the sample lead to a deflection of the cantilever ruled by Hooke's law. Depending on the situation, forces that are measured in AFM include mechanical contact force, Van der Waals forces, capillary forces, chemical bonding, electrostatic forces etc. Traditionally, the sample is mounted on a piezoelectric scanner, that can move the object under examination in the z direction for maintaining a constant force, and in the x and y directions for scanning the sample. An image of the surface is obtained by mechanically moving the probe in a raster scan (that is the pattern of image detection and reconstruction in a computer image) over the specimen, line by line, and recording the probe-surface interaction as a function of position. The operating mode described above represents the typical way to use the atomic force microscope. But a whole world of capabilities of the instrument can be used. In particular we focused our attention on three research lines: • The phase imaging • The mechanical analysis of materials • The chemical force microscopy The AFM, developed first to explore atomic details on hard materials, has evolved to an imaging method capable of achieving fine structural details on biological samples and soft matter. The first one in fact, was used in order to characterize the shape and the morphology of particular bio samples: some oligopeptides that could auto aggregate on complex structures depending on the concentration of the starting solutions from which they are prepared and on the presence or not buffer salt. The measurements were performed in the so called “tapping mode” which is capable of acquiring both the morphological maps and also the phase maps. This signal is a powerful extension of AFM that provides nanometer-scale information about surface structure and properties often not revealed by traditional techniques. In phase imaging, the phase lag of the cantilever oscillation, relative to the drive signal, is simultaneously monitored with topography data. The phase lag is very sensitive to variations in many material properties such as viscoelastic properties and this allows for a precise determination of the presence of organic materials What we have found is a dependence of peptide aggregates dimensions from the starting concentration. Essentially a growing trend is found with the augmentation of concentration regarding both the mean dimension and the dispersion of aggregates. Moreover a similar trend was found also in peptides prepared from a salt solution. Nevertheless in this case the dispersion was quite minimal: the presence of the salt strongly influences the dimension of peptides structures. For a better understanding of the aggregation process it would be interesting, for future works, to monitor the dynamics of the peptide aggregations during the cast of the solvent and to make more measurements of samples from solution at different concentration. The second argument we deal with was the mechanical analysis of materials. Tissues are a challenging class of materials as they are composed in hierarchical structures with important features down to the nanometer scale. Continuing developments in indentation data model and analysis will increase the usefulness of the method for the characterisation of biomaterials and in particular for tissue regeneration. The nanoindentation, also known as depth sensing indentation (DSI), involves the application of a controlled load over the surface to induce local deformations. Load and displacement are monitored during the loading- unloading curves enabling the calculation of the interested mechanical properties. Some theoretical models were considered and new ones were developed in order to get a better understanding of phenomena involved during the indentation process. A technique that can probe mechanical properties at these scales has the potential to answer numerous questions that are relevant in the field of nanotribology and nanomechanics. Several tests were performed over a large variety of materials including PMMA, polystyrene, silicon, metals and so on in order to obtain two of the most important mechanical properties: the hardness and the Young modulus. Moreover other deeper studies allow for the determination of the hardness in function of the indentation depth, the stiffness and other important features. Anyway the results obtained have to be fully understood due the large variety of theories and method of analysis of the data. We have also to take in account the instrument data distortion and the different materials response to indentation tests that could affect the final results. The last research addressed to biomaterials in this work is the chemical force microscope, exploited to monitor the forces involved in a protein swelling experiment. The potential of the AFM to reveal ultra low forces at high lateral resolution has opened an exciting way for measuring inter and intra molecular forces at the single molecule level. In particular Human Serum Albumin was used for this test. The idea is to detect and study the binding of ligands on tips to surface-bound receptors by applying an increasing force to the complex that reduces its lifetime until it dissociates at a measurable unbinding force. During the loading unloading curves a couple of step (revealing the sudden change) have been found revealing the first a small detachment of the protein from the surface, while the second is properly due to the uncoiling of albumin. Several measurements were collected in order to have statistically significant data

GIS-BASED SUITABILITY MODELING AND MULTI-CRITERIA DECISION ANALYSIS FOR UTILITY SCALE SOLAR PLANTS IN FOUR STATES IN THE SOUTHEAST US

Photovoltaic (PV) development shows significantly smaller growth in the Southeast U.S., than in the Southwest; which is mainly due to the low cost of fossil-fuel based energy production in the region and the lack of solar incentives. However, the Southeast has appropriate insolation conditions (4.0-6.0 KWh/m2/day) for photovoltaic deployment and in the past decade the region has experienced the highest population growth for the entire country. These factors, combined with new renewable energy portfolio policies, could create an opportunity for PV to provide some of the energy that will be required to sustain this growth. The goal of the study was to investigate the potential for PV generation in the Southeast region by identifying suitable areas for a utility-scale solar power plant deployment. Four states with currently low solar penetration were studied: Georgia, North Carolina, South Carolina and Tennessee. Feasible areas were assessed with Geographic Information Systems (GIS) software using solar, land use and population growth criteria combined with proximity to transmission lines and roads. After the GIS-based assessment of the areas, technological potential was calculated for each state. Multi-decision analysis model (MCDA) was used to simulate the decision making method for a strategic PV installation. The model accounted for all criteria necessary to consider in case of a PV development and also included economic and policy criteria, which is thought to be a strong influence on the PV market. Three different scenarios were established, representing decision makers\u27 theoretical preferences. Map layers created in the first part were used as basis for the MCDA and additional technical, economic and political/market criteria were added. A sensitivity analysis was conducted to test the model\u27s robustness. Finally, weighted criteria were assigned to the GIS map layers, so that the different preference systems could be visualized. As a result, lands suitable for a potential industrial-scale PV deployment were assessed. Moreover, a precise calculation for technical potential was conducted, with a capacity factor determined by the actual insolation of the sum of each specific feasible area. The results of the study showed that, for a utility-scale PV utility deployment, significant amount of feasible areas are available, with good electricity generation potential Moreover, a stable MCDA model was established for supporting strategic decision making in a PV deployment. Also, changes of suitable lands for utility-scale PV installations were visualized in GIS for the state of Tennessee

THE ROLE OF THE ROV WITHIN INTEGRATED GEOTECHNICAL AND HYDROGRAPHIC SITE INVESTIGATION

The acquisition of marine survey data is traditionally undertaken from surface vessels including boats and temporary rigs. Translation of these techniques to the nearshore zone is a complex task and requires equipment adaptation and. often the sacrifice of data coverage. The remotely operated vehicle (ROV) offers the potential for overcoming some of the standard nearshore survey Concems, providing remote intervention and data acquisition in areas of restricted access. In situ testing is the most efficient and reliable method of acquiring data with minimal sediment disturbance effects. Research has been undertaken into the viability of nearshore cone penetration testing (CPT) which has shown the T-Bar flow round penetrometer to be a possible solution. Data could be acquired in sediments with undrained shear strengths of up to 300 kPa from a bottom crawling ROV weighing 260 kgf and measuring 1 m in length by 0.6 m in width. The collection of sediment cores may be necessary in areas requiring ground truthing for geophysical or in situ investigations. A pneumatic piston corer has been designed and manufactured and is capable of collecting sediment cores up to 400 mm in length, 38 mm in diameter, in sediment with undrained shear strength of 17 kPa. To ascertain additional sediment characteristics in situ, a resistivity subbottom profiling system has also been designed and tested and allows for discrimination between sediment types ranging in size from gravel to silt. The integration of equipment and testing procedures can be fiirther developed through the use of integrated data management approaches such as geographical information systems (GIS). An offthe- shelf GIS, Arclnfo 8, was used to create a GIS containing typical nearshore data using the Dart estuary as a case study location.Britannia Royal Naval Colleg

Academic Aspect of the Leather Industry: An Interpretation from the Perspective of Business Science

In the leather industry, a production process that is the subject of many different disciplines is dominant. Many studies on these branches of science have examined the sector in detail in terms of production. On the other hand, studies dealing with the sector in terms of business administration department and sub-disciplines are not common. In this study, academic publications examining the relationship between the leather industry and the business administration department are the subjects. 98 scientific studies obtained after the search in the Web of Science database were examined in terms of the form of publication, the year of publication, the country where the publication was made and the sub-disciplines of the business department

Scanning strategies and spacing effect on laser fusion of H13 tool steel powder using high power Nd : YAG pulsed laser

Layered manufacturing technologies have been used to produce complex parts of diversified materials through different physical/chemical manufacturing principles. Nevertheless only a few materials are commercially available to build parts suitable for engineering applications. In this paper, the powder fusion of H13 tool steel is investigated. A high power Nd:YAG pulsed laser source on a CNC machine was used to fuse the powder, layer by layer, building solid cubes for further analysis. Four different laser vector scanning strategies were evaluated by comparing the results of porosity and layer distortion. The complexity of the laser/powder interaction shows that a complex strategy must be used to avoid porosity and distortion

A new mixed-integer programming model for irregular strip packing based on vertical slices with a reproducible survey

The irregular strip-packing problem, also known as nesting or marker making, is defined as the automatic computation of a non-overlapping placement of a set of non-convex polygons onto a rectangular strip of fixed width and unbounded length, such that the strip length is minimized. Nesting methods based on heuristics are a mature technology, and currently, the only practical solution to this problem. However, recent performance gains of the Mixed-Integer Programming (MIP) solvers, together with the known limitations of the heuristics methods, have encouraged the exploration of exact optimization models for nesting during the last decade. Despite the research effort, the current family of exact MIP models for nesting cannot efficiently solve both large problem instances and instances containing polygons with complex geometries. In order to improve the efficiency of the current MIP models, this work introduces a new family of continuous MIP models based on a novel formulation of the NoFit-Polygon Covering Model (NFP-CM), called NFP-CM based on Vertical Slices (NFP-CM-VS). Our new family of MIP models is based on a new convex decomposition of the feasible space of relative placements between pieces into vertical slices, together with a new family of valid inequalities, symmetry breakings, and variable eliminations derived from the former convex decomposition. Our experiments show that our new NFP-CM-VS models outperform the current state-of-the-art MIP models. Finally, we provide a detailed reproducibility protocol and dataset based on our Java software library as supplementary material to allow the exact replication of our models, experiments, and results

A new technique for 3D modeling of water surfaces using a Geiger mode receiver

It is difficult to accurately and quickly (i.e in real time) create a digital surface model of a water surface using bathymetric lidar when presented with water turbidity. Accurate and consistent modeling of the water surface is required in order to correct for the surface’s volatility when imaging the sea floor. However, this becomes exceedingly difficult due to the limited data return from water, the uneven surface, and noise. For this purpose, we use a highly sensitive Geiger Mode Avalanche PhotoDiode camera to collect this feint data and attempt to create an accurate digital surface model for water which can be utilized in future imaging computations.M.S

Frost Action in Soils

Frost action generally is used, in its broad sense, to include any detrimental effect on engineering works resulting from the penetration of frost below the surface of the ground. Considerable damage is done to roads, airfields, bridges, culverts, pipelines and buildings in regions where the ground and the climatological conditions are favorable to ground freezing and thawing. The writer has reviewed most of the available material pertaining to frost action in an effort to present the problem in an authentic manner, simple, yet reasonably up to date in theory and application. This study has been made from the stand-point of a highway engineer, since the interests of structural engineers and agronomists might be somewhat different. The body of this study is divided into six chapters emphasizing the following: damages and reduction of load carrying capacities in roads due to frost action; soil texture; liquid and gas soil moisture; soil temperatures; permafrost; and potential remedies