413 research outputs found
Development of a non-living model system for cell membranes and investigation of its mechanical and tribological properties
No full textWhile our exposure to nanomaterials (NMs) has increased with advancements in nanotechnology, understanding harmful effects of such materials on humans is still wanting. Here we have proposed and developed a non-living model system for cell membranes which is suitable for elucidating interactions between NMs and living cells. In contrast to existing model systems for cell membranes, PAAm hydrogel was used as soft support for the lipid. Grafting of lipid with PAAm was achieved through layer by layer deposition of alternating poly(allylamine hydrochloride) (PAH)and poly(sodium 4-styrenesulfonate) (PSS) polyelectrolyte multilayers (PEM). Single step bilayer formation was observed under QCM on the PAAm-PEM support owing to high electrostatic interactions between the PEM and lipid vesicles with frequency and dissipation changes of ~-30 Hz and ~0.8x10-6, respectively. It is also shown that the PEM architecture is robust and reproducible on gels of different elastic modulus. AFM images confirm bilayer formation on top of PAAm-PEM supports with uniform bilayer patches of ~ 0.5 μm. AFM indentation experiments show significant differences in the elastic modulus and adhesion forces for systems with soft underlying supports compared to systems having a hard substrate. The physiological relevance of the developed system is clear from its mechanical characterization via AFM, where the system undergoes considerable deformation before and after bilayer rupture. This behavior is similar to behavior of real cells, in which deformation of cytoskeleton is dominant over that of the cell membrane. The model cell membrane system was also used to study shear forces at the interface of the lipid bilayer on hydrogel, which gave insights into the frictional behavior of the system and its mechanical interactions with nanoprobes.Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2018-12-01The student, Tooba Shoaib, accepted the attached license on 2016-07-22 at 08:53.The student, Tooba Shoaib, submitted this Thesis for approval on 2016-07-22 at 10:40.This Thesis was approved for publication on 2016-07-22 at 15:06.DSpace SAF Submission Ingestion Package generated from Vireo submission #10071 on 2017-02-28 at 14:35:29Made available in DSpace on 2017-03-01T16:36:31Z (GMT). No. of bitstreams: 2
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Prospects of Saline agriculture in the Arabian Peninsula: Proceedings of the International Symposium on "Prospects of Saline Agriculture in the GCC Countries"
No full textThis Proceedings presents a comprehensive review of the prospects for saline agriculture in the Gulf Cooperation Council countries. In the six Gulf Cooperation Council countries of Bahrain. Kuwait. Oman. Qatar. Saudi Arabia and the United Arab Emirates. only 170-200 cubic meters of renewable water resources are available per person per year. This is less than 3 percent of the global average. Nevertheless. agriculture still consumes the largest proportion of the freshwater in the region. The withdrawal for irrigation in the six Gulf Cooperation Council countries is 85 percent. Only 15 percent is used for domestic and industrial purposes.
Unfortunately, the use of freshwater for agriculture per person is higher in the Gulf Cooperation Council countries than the global use per person because of the aridity and high summer temperatures over much of the region. Thus. irrigation in agriculture assumes a greater significance. Even in areas where the environmental conditions preclude intensive agriculture, there is a growing demand for water in horticulture and landscaping. In the six Gulf Cooperation Council countries. the area planted to horticultural crops increased by 12-15 percent per annum from 1980 to 1999.
Hence, saline agriculture will become increasingly important because. in the Arabian peninsula. water resources will be exhausted within the next 20 years unless consumption of freshwater is reduced.
Recent advances in biosaline agriculture and salt-tolerant crops now merit assessment of saline water resources and their potential for agricultural use. Moreover. there have been rapid advances around the world in the use of saline water for irrigation. including development of irrigation systems. improved water management. and control of salinity within the root zone.
Biosaline agriculture technologies use salty water productively. Plants that tolerate salt in water and soil are being evaluated for productive use. perhaps replacing varieties that will only grow in sweet soil irrigated by fresh water. If economically useful plants are grown with salty water and on saline land, more food and feed can be made available globally and land abandoned because the soil has become saline can be put to economic and sustainable agricultural use. Making use of saline water for agriculture will relieve pressure on scarce freshwater resources
A stabilized discontinuous Galerkin method for variational embedding of physics-based data
No full textA stabilized variational framework that admits overlapping as well as non overlapping coupling of domains for a variety of Partial Differential Equations (PDEs) is employed in this work. This method accommodates non-matching meshes across the interfaces between the subdomain boundaries and allows for sharp changes in mechanical material properties. Interface coupling operators that emanate via embedding of Discontinuous Galerkin ideas in the continuous Galerkin framework provide a unique avenue to embed physics-based data in the modeling and analysis of the system. Physics-based data, either in discrete or in distributed form can be embedded via the interface operators that are otherwise devised to enforce continuity of the fields across internal discontinuities. The least-squares form of the interface coupling operators is exploited for its inherent linear regression type structure, and it is shown that it helps improve the overall accuracy of the numerical solution. Method is applicable to multi-PDE class of problems wherein different PDEs are operational on adjacent domains across the common interface. The method also comes equipped with a residual based error estimation method which is shown to be applicable to test problems employed. Different test cases are employed to investigate the mathematical attributes of the method.Submission published under a 24 month embargo labeled 'Closed Access', the embargo will last until 2021-08-01The student, Shoaib Ahmad Goraya, accepted the attached license on 2019-07-12 at 16:53.The student, Shoaib Ahmad Goraya, submitted this Thesis for approval on 2019-07-12 at 16:54.This Thesis was approved for publication on 2019-07-15 at 14:47.DSpace SAF Submission Ingestion Package generated from Vireo submission #14260 on 2019-11-26 at 14:03:50Made available in DSpace on 2019-11-26T20:59:45Z (GMT). No. of bitstreams: 3
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Softmatter tribology: Understanding the microstructure to property relationships of hydrogel-like materials
No full textBiological tribosystems are excellent examples of nature leveraging soft matter properties to achieve exceptional lubrication for prolonged periods of activity. In these systems, lubrication is provided by sparsely crosslinked, polymeric surface layers imbibed with an aqueous lubricant. A prominent biological tribosystem is the articular cartilage, an avascular tissue consisting of an extracellular matrix made of collagen fibrils and proteoglycans, with a small number of chondrocyte cells. However, in this tissue, there exists a gradient in the orientation of the collagen fibers and water content as a function of the distance from the bone, which emphasizes the importance of the microstructure in cartilage’s functionality, i.e. a load-bearing tissue that maintains low friction and wear. In fact, recent studies have shown that the cartilage’s articulating surface comprises of a network of highly hydrated mucins, polysaccharides, glycoproteins, and phospholipids, which play a key role in maintaining low friction in boundary lubrication. This has been evident in studies performed on multiple other biphasic, non-biological hydrogels as well, where a prominent effect of the interfacial microstructure is observed on their mechanical and tribological properties. Yet, not only there is a lack of knowledge but also wide discrepancy about the fundamental underlying mechanisms relating the dynamic and static frictional dissipation to the microstructure of these materials. Conversely, this fundamental gap in knowledge also limits progress in the design of functional replacements, based on hydrogel-like materials.
Our aim was to not only advance the existing knowledge about the frictional dissipation of hydrogels, by precisely correlating the role of microstructure to the tribological performance, but also, to establish design principles that can help combat some of the existing challenges related to their application as tribological biomaterials. In light of this, the doctoral work presented here has achieved the following specific goals:
I. Studied, modeled and quantified influence of the microstructure, crosslinking degree and stiffness of the polymer on the dynamic and static frictional response
II. Scrutinized the relation between friction force and interfacial rheology of hydrogels
III. Elucidated the pathways of network formation in double network hydrogels which lead to enhanced mechanical and frictional response
IV. Scrutinized mechanical and tribological response of biological hydrogels in physiologically relevant conditions
By combining powerful state-of-the-art experimental techniques such as the Dynamic Light Scattering (DLS), Atomic Force Microscopy (AFM) and extended surface forces apparatus (SFA), we have demonstrated that the main mechanisms behind the frictional dissipation of hydrogels arise directly from their biphasic nature – the polymeric network and the imbibing fluid. In the context of dynamic friction, the viscous-adhesive model developed here quantifies the hydrogel’s frictional response by considering an interplay of adhesive and viscous dissipation directly arising from the hydrogel’s microstructure. The model accounts for confinement effects, poroelastic deformation, and the influence of the polymer on the viscous friction force, and helps reconcile seemingly contradictory models proposed previously. The adhesive contribution was modeled as a combination of reversible, transient adhesive bonds between the hydrogel and the countersurface and the poroelastic deformation of the hydrogel during shear, while the role of viscous dissipation was revealed to be directly related to the rheological performance of the hydrogel’s interface. In the latter, the polymer and imbibed fluid, both dictated viscous dissipation. Scrutiny of the rheological behavior of hydrogel thin films in tandem with nanotribology was conducted to show that the effective viscosity measured in rheology agrees with the friction behavior, although it is not sufficient to capture the rich frictional response of hydrogels as a function of sliding velocity. In the context of static friction, the combined effects of microstructure, interfacial shear stresses, interfacial ageing, and temperature were all tied together into a conceptual phase diagram for the static friction of hydrogels. Feasibility of the models developed for the dynamic and static friction was validated by extending the concepts to other hydrogel systems such as physically crosslinked agarose and cartilage, thereby demonstrating the universality of the proposed mechanisms for biphasic soft materials.
The study was further extended to DN hydrogels and biological hydrogels. Systematic investigations of the DN hydrogels comprising of agarose and polyacrylamide hydrogels as independent, interpenetrating networks revealed the design limitations of achieving high strength and high lubricity, simultaneously. Lastly, the novel experimental study on the gel-like surface of the articular cartilage was conducted as a direct application of this research. The graded response of the cartilage’s gel-like articulating surface in elevated calcium concentrations was traced back to changes in the surface and sub-surface microstructure, which was reported to subsequently modulate the mechanical and tribological response of the material.
In summary, through its collective experimental studies and comprehensive models, this doctoral work provides the basic framework to understand lubrication mechanisms of hydrogel-like materials in light of their microstructure. Furthermore, it also helps provide the basic design principles for fabricating hydrogels capable of achieving low friction coefficients and augmented wear resistance through the precise control of their microstructure. Lastly, the novel methodologies and protocols stemming from this dissertation open up previously unexplored research avenues and hence can influence diverse areas of inquiries, not only limited to biolubrication and biomedical applications but soft robotics and microelectromechanical devices.Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2023-08-01The student, Tooba Shoaib, accepted the attached license on 2021-07-14 at 11:30.The student, Tooba Shoaib, submitted this Dissertation for approval on 2021-07-14 at 11:37.This Dissertation was approved for publication on 2021-07-16 at 11:52.DSpace SAF Submission Ingestion Package generated from Vireo submission #16930 on 2022-01-12 at 12:55:05Made available in DSpace on 2022-01-12T22:35:15Z (GMT). No. of bitstreams: 2
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Electronic properties of corundum-like Ir2O3 and Ir2O3-Ga2O3 alloys
No full textThis article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Shoaib Khalid, Anderson Janotti; Electronic properties of corundum-like Ir2O3 and Ir2O3-Ga2O3 alloys. Appl. Phys. Lett. 11 November 2024; 125 (20): 202102. https://doi.org/10.1063/5.0232445 and may be found at https://doi.org/10.1063/5.0232445.
© 2024 Author(s). Published under an exclusive license by AIP Publishing.
This article will be embargoed until 11/11/2025.In the hexagonal, corundum-like structure, -Ga2O3 has a bandgap of 5.1 eV, which, combined with its relatively small electron effective mass, high Baliga's figure of merit, and high breakdown field, makes it a promising candidate for power electronics. Ga2O3 is easy to dope n-type, but impossible to dope p-type, impeding the realization of some electronic device designs. Developing a lattice-matched p-type material that forms a high-quality heterojunction with n-type Ga2O3 would open new opportunities in electronics and perhaps optoelectronic devices. In this work, we studied Ir2O3 as a candidate for that purpose. Using hybrid density functional theory calculations we predict the electronic band structure of -Ir2O3 and compare that to -Ga2O3, and study the stability and electronic properties of -(IrxGa1−x)2O3 alloys. We discuss the band offset between the two materials and compare it with recently available experimental data. We find that the Ir d bands that compose the top of the valence band in -Ir2O3 are much higher in energy than O p bands in -Ga2O3, possibly enabling effective p-type doping. Our results provide an insight into using the Ir2O3 or Ir2O3-Ga2O3 alloys as p-type material lattice-matched to -Ga2O3 for the realization of p–n heterojunctions.This work was supported by the Laboratory Directed Research and Development (LDRD) Program (Project No. 800025) at Princeton Plasma Physics Laboratory under U.S. Department of Energy Prime Contract No. DE-AC02-09CH11466. A.J. was supported by the NSF through the UD-CHARM University of Delaware Materials Research Science and Engineering Center (MRSEC) Grant No. DMR-2011824. The calculations were carried out at the National Energy Research Scientific Computing Center (NERSC), a U.S. Department of Energy Office of Science User Facility located at the Lawrence Berkeley National Laboratory, operated under Contract No. DE-AC02-05CH11231 using NERSC award BES-ERCAP27253, the Stellar Cluster at Princeton University, and the DARWIN computing system at the University of Delaware, using the NSF Grant No. 1919839
VPR-Bench: An Open-Source Visual Place Recognition Evaluation Framework with Quantifiable Viewpoint and Appearance Change
No full textVisual place recognition (VPR) is the process of recognising a previously visited place using visual information, often under varying appearance conditions and viewpoint changes and with computational constraints. VPR is related to the concepts of localisation, loop closure, image retrieval and is a critical component of many autonomous navigation systems ranging from autonomous vehicles to drones and computer vision systems. While the concept of place recognition has been around for many years, VPR research has grown rapidly as a field over the past decade due to improving camera hardware and its potential for deep learning-based techniques, and has become a widely studied topic in both the computer vision and robotics communities. This growth however has led to fragmentation and a lack of standardisation in the field, especially concerning performance evaluation. Moreover, the notion of viewpoint and illumination invariance of VPR techniques has largely been assessed qualitatively and hence ambiguously in the past. In this paper, we address these gaps through a new comprehensive open-source framework for assessing the performance of VPR techniques, dubbed “VPR-Bench”. VPR-Bench (Open-sourced at: https://github.com/MubarizZaffar/VPR-Bench) introduces two much-needed capabilities for VPR researchers: firstly, it contains a benchmark of 12 fully-integrated datasets and 10 VPR techniques, and secondly, it integrates a comprehensive variation-quantified dataset for quantifying viewpoint and illumination invariance. We apply and analyse popular evaluation metrics for VPR from both the computer vision and robotics communities, and discuss how these different metrics complement and/or replace each other, depending upon the underlying applications and system requirements. Our analysis reveals that no universal SOTA VPR technique exists, since: (a) state-of-the-art (SOTA) performance is achieved by 8 out of the 10 techniques on at least one dataset, (b) SOTA technique in one community does not necessarily yield SOTA performance in the other given the differences in datasets and metrics. Furthermore, we identify key open challenges since: (c) all 10 techniques suffer greatly in perceptually-aliased and less-structured environments, (d) all techniques suffer from viewpoint variance where lateral change has less effect than 3D change, and (e) directional illumination change has more adverse effects on matching confidence than uniform illumination change. We also present detailed meta-analyses regarding the roles of varying ground-truths, platforms, application requirements and technique parameters. Finally, VPR-Bench provides a unified implementation to deploy these VPR techniques, metrics and datasets, and is extensible through templates
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No full textLet G be a simple molecular graph without directed and multiple edges and without loops. The vertex and edge-sets of G are denoted by V(G) and E(G), respectively. Suppose G is also a connected molecular graph and let u, v is an element of V(G) be two vertices. The harmonic index H(G) of G is defined as the sum of the weights 2(d(u)+d(v))(-1) of all edges in E(G), where d(v) is the degree of a vertex v in G which is defined as the number of vertices of G adjacent to v. The harmonic polynomial of G is defined as H(G, x) = Sigma(e=uv is an element of E(G)) 2x((du+dv-1)) and there is the following nice relation between these two notions H(G) = integral(1)(0) H(G, x)dx. In this paper, we present an explicit formula for the harmonic indices and harmonic polynomials of carbon nanocones CNCk[n]
Computational modeling and analysis on chemically reacting species in catalytic oxidation reaction mechanism: Novel model reduction and NSFD scheme
No full textMulti-step catalytic mechanisms are an important issue related to chemical kinetics to reduce, and such reduction directly affects the quality and efficiency of modeling complicated reactions. Nevertheless, the currently available literature is using the traditional fractional method that is poorly positioned to address the global non-local and fractal characteristics of catalytic systems. This paper will fill this gap by using fractal-fractional derivatives with generalized Mittag-Leffler kernels and using Nonstandard Finite Difference (NSFD) scheme to study kinetic equations. As a representative model, to study the behavior of numerical solutions, steady-state, and stability to various rate coefficients, the selection of Water-Gas Shift (WGS) reaction is made. Gibbs rule is used to reduce the higher dimensional system to a lower dimensional model by using two model reduction methods known as Spectral Quasi-Equilibrium Manifold (SQEM) and Intrinsic Low-Dimensional Manifold (ILDM). It was found that the fractal-fractional model is more representative of the memory and heterogeneity of the system whereas the NSFD model exhibits stability and positivity better than the existing approaches. Sensitivity analysis also indicates the effect of individual species to the system dynamics. The results are useful on how to effectively model the catalytic mechanism and avenue towards creating more realistic and consistent chemical simulation models
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