Rheology and Dynamics of Associative Polymers in Shear and Extension: Theory and Experiment

Submitted to Macromolecules, July 2005We investigate the steady and transient shear and extensional rheological properties of a series of model hydrophobically modified ethoxylate-urethane (HEUR) polymers with varying degrees of hydrophobicity. A new nonlinear two-species network model for these telechelic polymers is described which incorporates appropriate molecular mechanisms for the creation and destruction of elastically-active chains. Like other recent models we incorporate the contributions of both the bridging chains (those between micelles) and the dangling chains to the final stress tensor. This gives rise to two distinct relaxation time scales; a short Rouse time for the relaxing chains and a longer network time–scale that depends on the aggregation number and strength of the micellar junctions. The evolution equations for the fraction of elastically-active chains and for the conformation tensors of each species are solved to obtain the total stress arising from imposed deformations. The model contains a single non-linear parameter and incorporates the non-linear chain extension, the shear-induced enhancement of associations and the stretch-induced dissociation of hydrophobic chains. In contrast to earlier closed-form models, we are able to obtain quantitative agreement between experimental measurements and the model predictions for three different series of telechelic polymers over a range of concentrations. The scaling of both the zero shear viscosity and the effective network relaxation time show good agreement with those measured in experiments. The model also quantitatively captures both the shear-thickening and subsequent shear-thinning observed in the rheology at high deformation rates and predicts transient extensional stress growth curves in close agreement with those measured using a filament stretching rheometer.Schlumberger Foundatio

Changing Dynamics of Constitutionalism: South Asia's Tryst with Constitution

The prevailing view of the constitutional framework in South Asia is seen as secondary and subsidiary to developed constitutional systems worldwide. Meanwhile, South Asian countries have merely re-produced the constitutional framework of developed nations. The emergence and development of South Asian constitutionalism present a range of perspectives and methodological approaches that contribute to comparative constitutional law scholarship in South Asia. The overt attention toward the Western notion of liberalism has often led to an incomplete and unclear approach to South Asian constitutionalism. The paper aimed to explore the elements of South Asian constitutionalism alongside underlying socio-economic and political discourse surrounding its contemporary understanding. It also analyzed the role of courts in affirming and transforming South Asian constitutionalism. Instead of reviving interest in South Asia and Third World Approach to International Law, this paper showed that it is only practical and pragmatic to study constitutionalism with specific reference to the modern discourse of democracy, judicial review, separation of power, and human rights enshrined in their respective constitutions. In terms of its emergence from the colonial history and other prevalent forms of distinct cultural, social, and political practices, South Asia presented a heterogeneous experience in the light of recognition and enforcement of socio-economic rights and transformations and deviations from its past experiences. KEYWORDS: Comparative Constitutional Law, Constitutionalism, South Asia

Homogeneous percolation versus arrested phase separation in attractively-driven nanoemulsion colloidal gels

We elucidate mechanisms for colloidal gelation of attractive nanoemulsions depending on the volume fraction (ϕ) of the colloid. Combining detailed neutron scattering, cryo-transmission electron microscopy and rheological measurements, we demonstrate that gelation proceeds by either of two distinct pathways. For ϕ sufficiently lower than 0.23, gels exhibit homogeneous fractal microstructure, with a broad gel transition resulting from the formation and subsequent percolation of droplet–droplet clusters. In these cases, the gel point measured by rheology corresponds precisely to arrest of the fractal microstructure, and the nonlinear rheology of the gel is characterized by a single yielding process. By contrast, gelation for ϕ sufficiently higher than 0.23 is characterized by an abrupt transition from dispersed droplets to dense clusters with significant long-range correlations well-described by a model for phase separation. The latter phenomenon manifests itself as micron-scale “pores” within the droplet network, and the nonlinear rheology is characterized by a broad yielding transition. Our studies reinforce the similarity of nanoemulsions to solid particulates, and identify important qualitative differences between the microstructure and viscoelastic properties of colloidal gels formed by homogeneous percolation and those formed by phase separation.United States. Army Research Office (Institute for Collaborative Biotechnologies. Grant W911NF- 09-0001)National Science Foundation (U.S.) (Grants CMMI-1120724 and DMR-1006147

Preparation of Tissues and Heterogeneous Cellular Samples for Single-Cell Analysis

While sample preparation techniques for the chemical and biochemical analysis of tissues are fairly well advanced, the preparation of complex, heterogenous samples for single-cell analysis can be difficult and challenging. Nevertheless, there is growing interest in preparing complex cellular samples, particularly tissues, for analysis via single-cell resolution techniques such as single-cell sequencing or flow cytometry. Recent microfluidic tissue dissociation approaches have helped to expedite the preparation of single cells from tissues through the use of optimized, controlled mechanical forces. Cell sorting and selective cellular recovery from heterogenous samples have also gained traction in biosensors, microfluidic systems, and other diagnostic devices. Together, these recent developments in tissue disaggregation and targeted cellular retrieval have contributed to the development of increasingly streamlined sample preparation workflows for single-cell analysis technologies, which minimize equipment requirements, enable lower processing times and costs, and pave the way for high-throughput, automated technologies. In this chapter, we survey recent developments and emerging trends in this field

An automated syringe-based PoC RT-LAMP LFB platform for infectious disease detection from saliva

Decentralized Point-of-Care (PoC) diagnostics hold momentous potential for rapid and accessible viral infection disease detection. Presented is a unique design application of an easy-to-use (plug-and-play) platform for viral detection. The platform leverages a simplified multiplex Reverse-Transcription Loop-mediated Isothermal Amplification (RT-LAMP) Lateral Flow Biosensor (LFB) assay with a lyophilized master mix, eliminating the need for RNA isolation or special reporting equipment. A user-friendly Saliva Measuring Tube (SMT) ensures accurate saliva volume self-collection, and a Syringe-based PoC (SPoC) platform automates sample treatment, reagent mixing, and temperature control using readily available components and consumables. The platform’s performance was evaluated by multiplexed detection of the SARS-CoV-2 N2 target gene and human ACTB gene from saliva samples. The SPoC platform achieved a detection limit of spiked 500 copies/mL for SARS-CoV-2 and consistent internal control readout. The presented PoC system offers a promising initial step for further development toward a decentralized solution for viral infection testing

The Response of Synechococcus sp. PCC 7002 to Micro-/Nano polyethylene Particles - Investigation of a Key Anthropogenic Stressor

Microplastics or plastic particles less than 5 mm in size are a ubiquitous and damaging pol- lutant in the marine environment. However, the interactions between these plastic particles and marine microorganisms are just starting to be understood. The objective of this study was to measure the responses of a characteristic marine organism (Synechococcus sp. PCC 7002) to an anthropogenic stressor (polyethelene nanoparticles and microparticles) using molecular techniques. This investigation showed that polyethylene microparticles and nanoparticles have genetic, enzymatic and morphological effects on Synechococcus sp. PCC 7002. An RT-PCR analysis showed increases in the expression of esterase and hydro- lase genes at 5 days of exposure to polyethylene nanoparticles and at 10 days of exposure to polyethylene microparticles. A qualitative enzymatic assay also showed esterase activity in nanoparticle exposed samples. Cryo-scanning electron microscopy was used to assess morphological changes in exopolymer formation resulting from exposure to polyethylene microparticles and nanoparticles. The data from this paper suggests that microplastic and nanoplastics could be key microbial stressors and should be investigated in further detail

Atypical Neurofibroma and Osteosclerotic Metastasis

35-year-old male presented with multiple swellings in left leg, headache, weakness of limbs for 4 months, and blurring of vision for the last 15 days. On examination, he was pale, cachexic with generalized lymphadenopathy and lower motor neuron type weakness of limbs sparing right upper limb. Blood investigations showed anemia with high alkaline phosphatase. Chest radiograph revealed osteosclerotic metastatic lesion in humerus. Biopsy of leg lesion revealed atypical neurofibroma. Computed tomography (CT) of thorax revealed osteoblastic metastasis. Bone marrow aspiration showed cells with round to oval nuclei, fine granular chromatin with large central prominent nucleoli and eosinophilic cytoplasm with acini formation. Magnetic resonance imaging (MRI) of brain and spinal cord defined metastatic leptomeningeal deposits. Cerebrospinal fluid (CSF) cytology was positive for malignant cells. Gastroscopy showed an ulceroinfiltrative growth from stomach which on histopathology revealed diffuse adenocarcinoma. Palliative treatment was given with intrathecal methotrexate and systemic corticosteroid with chemotherapy. Patient's symptom improved drastically, but we lost him to followup

High iron-mediated increased oral fungal burden, oral-to-gut transmission, and changes to pathogenicity of Candida albicans in oropharyngeal candidiasis

Background: Iron affects the diversity of the oral microbial landscape. Laboratory-strain CAI4 of Candida albicans that causes oropharyngeal candidiasis (OPC) exhibits iron-induced changes to the cell wall, impacting phagocytosis (by macrophages) and susceptibility of fungal cells to cell wall-perturbing antifungals, in vitro. Aim: To understand the effect of iron on the CAI4-strain, wild type (WT) SC5314-strain, and oral isolates of C. albicans. Methods: An immunosuppressed murine model of OPC was used to assess the effect of iron on oral-to-gut infection and antifungal susceptibility of the CAI4-strain. In vitro antifungal susceptibility, cell wall analysis, and phagocytic assays were performed under low and high iron, for the SC5314-strain and oral isolates. Results: High iron enhanced oral and gut fungal levels for the CAI4-strain in mice; CAI4 cells from low iron mice were more susceptible to antifungals. The SC5314-strain and oral isolates showed enhanced antifungal-resistance towards most antifungals tested, under high iron. Iron-mediated cell wall changes and phagocytic response in the SC5315-strain were similar to CAI4; oral isolates showed a variable response. Conclusion: Host iron can potentially alter infection severity and dissemination, efficacy of antifungal treatment, and host immune response during OPC. Clinical isolates showed most of these effects of iron, despite exhibiting a varied cell wall composition-change response to iron.Kornberg School of DentistryOral Health Science

Determinants of Intravascular Resistance in Indian Diabetic Nephropathy Patients: A Hospital-Based Study

Aims and Objectives. Metabolic dysregulation has failed to explain clinical variability of patients with diabetic nephropathy and hence a renewed interest emerged in haemodynamic factors as determinant of progression and development of diabetic nephropathy. We therefore studied for various factors which can correlate with raised renal vascular resistance in diabetic nephropathy. Material and Methods. Renal vascular resistance was measured in patients with established and incipient diabetic nephropathy and compared with controls using noninvasive color Doppler examinations of intrarenal vasculature. Results. Renal vascular resistance correlated with age, duration of disease, GFR, serum creatinine, and stage of retinopathy. Renal vascular resistance was significantly reduced in patients on treatment with RAAS inhibitors and insulin, than those on OHA and antihypertensives other than RAAS inhibitors. Conclusion. The study implies that renal vascular resistance may help identify diabetics at high risk of developing nephropathy, and these set of patients could be candidates for RAAS inhibition and early insulin therapy even in patients without albuminuria