78 research outputs found
Model for the alpha and beta shear-mechanical properties of supercooled liquids and its comparison to squalane data
This paper presents data for supercooled squalane's frequency-dependent shear
modulus covering frequencies from 10 mHz to 30 kHz and temperatures from 168 K
to 190 K; measurements are also reported for the glass phase down to 146 K. The
data reveal a strong mechanical beta process. A model is proposed for the shear
response of supercooled liquids. The model is an electrical equivalent-circuit
characterized by additivity of the dynamic shear compliances of the alpha and
beta processes. The nontrivial parts of the alpha and beta processes are
represented by a "Cole-Cole retardation element", resulting in the Cole-Cole
compliance function well-known from dielectrics. The model, which assumes that
the high-frequency decay of the alpha shear compliance loss varies with angular
frequency as , has seven parameters. Assuming time-temperature
superposition for the alpha and the beta processes separately, the number of
parameters varying with temperature is reduced to four. From the temperature
dependence of the best-fit model parameters the following conclusions are
drawn: 1) the alpha relaxation time conforms to the shoving model; 2) the beta
relaxation loss-peak frequency is almost temperature independent; 3) the alpha
compliance magnitude, which in the model equals the inverse of the
instantaneous shear modulus, is only weakly temperature dependent; 4) the beta
compliance magnitude decreases by a factor of three upon cooling in the
temperature range studied. The final part of the paper briefly presents
measurements of the dynamic adiabatic bulk modulus covering frequencies from 10
mHz to 10 kHz in the temperature range 172 K to 200 K. The data are
qualitatively similar to the shear data by having a significant beta process. A
single-order-parameter framework is suggested to rationalize these
similarities
Shear-Modulus Investigations of Monohydroxy Alcohols: Evidence for a Short-Chain-Polymer Rheological Response
In addition to the ubiquitous structural relaxation of viscous supercooled
liquids, monohydroxy alcohols and several other hydrogen-bonded systems display
a strong single-exponential electrical low-frequency absorption. So far, this
so-called Debye process could be observed only using dielectric techniques.
Exploiting a combination of broad-band and high-resolution rheology experiments
for three isomeric octanols, unambiguous mechanical evidence for the Debye
process is found. Its spectral signature is similar to the viscoelastic
fingerprint of small-chain polymers, enabling us to estimate the effective
molecular weight for the supramolecular structure formed by the studied
monohydroxy alcohols. This finding opens the venue for the application of
further non-dielectric techniques directed at unraveling the microscopic nature
of the Debye process and for an understanding of this phenomenon in terms of
polymer concepts.Comment: 12 pages, 4 figure
Corresponding States of Structural Glass Formers
The variation with respect to temperature T of transport properties of 58
fragile structural glass forming liquids (68 data sets in total) are analyzed
and shown to exhibit a remarkable degree of universality. In particular,
super-Arrhenius behaviors of all super-cooled liquids appear to collapse to one
parabola for which there is no singular behavior at any finite temperature.
This behavior is bounded by an onset temperature To above which liquid
transport has a much weaker temperature dependence. A similar collapse is also
demonstrated, over the smaller available range, for existing numerical
simulation data.Comment: 6 pages, 2 figures. Updated References, Table Values, Submitted for
Publicatio
Pancreatic β-cell imaging in humans: Fiction or option?
Diabetes mellitus is a growing worldwide epidemic disease, currently affecting 1 in 12 adults. Treatment of disease complications typically consumes ∼10% of healthcare budgets in developed societies. Whilst immune‐mediated destruction of insulin‐secreting pancreatic β cells is responsible for Type 1 diabetes, both the loss and dysfunction of these cells underly the more prevalent Type 2 diabetes. The establishment of robust drug development programmes aimed at β‐cell restoration is still hampered by the absence of means to measure β‐cell mass prospectively in vivo, an approach which would provide new opportunities for understanding disease mechanisms and ultimately assigning personalized treatments. In the present review, we describe the progress towards this goal achieved by the Innovative Medicines Initiative in Diabetes, a collaborative public–private consortium supported by the European Commission and by dedicated resources of pharmaceutical companies. We compare several of the available imaging methods and molecular targets and provide suggestions as to the likeliest to lead to tractable approaches. Furthermore, we discuss the simultaneous development of animal models that can be used to measure subtle changes in β‐cell mass, a prerequisite for validating the clinical potential of the different imaging tracers
Statistical Mechanics of Glass Formation in Molecular Liquids with OTP as an Example
We extend our statistical mechanical theory of the glass transition from
examples consisting of point particles to molecular liquids with internal
degrees of freedom. As before, the fundamental assertion is that super-cooled
liquids are ergodic, although becoming very viscous at lower temperatures, and
are therefore describable in principle by statistical mechanics. The theory is
based on analyzing the local neighborhoods of each molecule, and a statistical
mechanical weight is assigned to every possible local organization. This
results in an approximate theory that is in very good agreement with
simulations regarding both thermodynamical and dynamical properties
Globalization, multinationals and institutional diversity
This article aims to explore the impact of globalization and in particular multinationals on diversity within national varieties of capitalism. Do the actions of multinationals create more diversity within national systems, do they reduce diversity or do they have relatively little impact on diversity within national systems? The article argues that there are distinctive structures of institutional diversity across different national systems. Therefore, the question is not how do MNCs impact on institutional diversity per se but how do they impact on these different structures of diversity? In order to develop this argument, the paper also differentiates types of multinational. The article uses distinction between market-seeking, resource-seeking, efficiency-seeking and strategic asset-seeking in order to identify a range of different MNC activity across manufacturing, professional and financial sectors. These different sorts of MNC activity vary across time and contexts in terms of their significance. The article looks in detail at four different models of capitalism and examines how the entry of different sorts of multinationals with distinctive objectives impacts on the relationships between key social actors which underpin and reinforce these models. In this way, it suggests how institutional diversity within different types of capitalism may evolve under the impact of MNCs and globalization
The EndoC-βH1 cell line is a valid model of human beta cells and applicable for screenings to identify novel drug target candidates
Objective: To characterize the EndoC-βH1 cell line as a model for human beta cells and evaluate its beta cell functionality, focusing on insulin secretion, proliferation, apoptosis and ER stress, with the objective to assess its potential as a screening platform for identification of novel anti-diabetic drug candidates. Methods: EndoC-βH1 was transplanted into mice for validation of in vivo functionality. Insulin secretion was evaluated in cells cultured as monolayer and as pseudoislets, as well as in diabetic mice. Cytokine induced apoptosis, glucolipotoxicity, and ER stress responses were assessed. Beta cell relevant mRNA and protein expression were investigated by qPCR and antibody staining. Hundreds of proteins or peptides were tested for their effect on insulin secretion and proliferation. Results: Transplantation of EndoC-βH1 cells restored normoglycemia in streptozotocin induced diabetic mice. Both in vitro and in vivo, we observed a clear insulin response to glucose, and, in vitro, we found a significant increase in insulin secretion from EndoC-βH1 pseudoislets compared to monolayer cultures for both glucose and incretins.Apoptosis and ER stress were inducible in the cells and caspase 3/7 activity was elevated in response to cytokines, but not affected by the saturated fatty acid palmitate.By screening of various proteins and peptides, we found Bombesin (BB) receptor agonists and Pituitary Adenylate Cyclase-Activating Polypeptides (PACAP) to significantly induce insulin secretion and the proteins SerpinA6, STC1, and APOH to significantly stimulate proliferation.ER stress was readily induced by Tunicamycin and resulted in a reduction of insulin mRNA. Somatostatin (SST) was found to be expressed by 1% of the cells and manipulation of the SST receptors was found to significantly affect insulin secretion. Conclusions: Overall, the EndoC-βH1 cells strongly resemble human islet beta cells in terms of glucose and incretin stimulated insulin secretion capabilities. The cell line has an active cytokine induced caspase 3/7 apoptotic pathway and is responsive to ER stress initiation factors. The cells' ability to proliferate can be further increased by already known compounds as well as by novel peptides and proteins. Based on its robust performance during the functionality assessment assays, the EndoC-βH1 cell line was successfully used as a screening platform for identification of novel anti-diabetic drug candidates. Keywords: EndoC-βH1, Pseudoislets, Glucose stimulated insulin secretion, Somatostatin signaling, Proliferatio
The Role of Spatially Controlled Cell Proliferation in Limb Bud Morphogenesis
Oriented cell behaviors likely have a more important role in limb bud elongation during development than previously suggested by the “growth-based morphogenesis” hypothesis
Gendering the careers of young professionals: some early findings from a longitudinal study. in Organizing/theorizing: developments in organization theory and practice
Wonders whether companies actually have employees best interests at heart across physical, mental and spiritual spheres. Posits that most organizations ignore their workforce – not even, in many cases, describing workers as assets! Describes many studies to back up this claim in theis work based on the 2002 Employment Research Unit Annual Conference, in Cardiff, Wales
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