The collapse of linear polyelectrolyte chains in a poor solvent: When does a collapsing polyelectrolyte collect its counter ions?

The collapse of linear polyelectrolyte chains in a poor solvent: When does a collapsing polyelectrolyte collect its counter ions? The collapse of polyions in a poor solvent is a complex system and is an active research subject in the theoretical polyelectrolyte community. The complexity is due to the subtle interplay between hydrophobic effects, electrostatic interactions, entropy elasticity, intrinsic excluded volume as well as specific counter-ion and co-ion properties. Long range Coulomb forces can obscure single molecule properties. The here presented approach is to use just a small amount of screening salt in combination with a very high sample dilution in order to screen intermolecular interaction whereas keeping intramolecular interaction as much as possible (polyelectrolyte concentration cp ≤ 12 mg/L, salt concentration; Cs = 10^-5 mol/L). This is so far not described in literature. During collapse, the polyion is subject to a drastic change in size along with strong reduction of free counterions in solution. Therefore light scattering was utilized to obtain the size of the polyion whereas a conductivity setup was developed to monitor the proceeding of counterion collection by the polyion. Partially quaternized PVP’s below and above the Manning limit were investigated and compared to the collapse of their uncharged precursor. The collapses were induced by an isorefractive solvent/non-solvent mixture consisting of 1-propanol and 2-pentanone, with nearly constant dielectric constant. The solvent quality for the uncharged polyion could be quantified which, for the first time, allowed the experimental investigation of the effect of electrostatic interaction prior and during polyion collapse. Given that the Manning parameter M for QPVP4.3 is as low as lB / c = 0.6 (lB the Bjerrum length and c the mean contour distance between two charges), no counterion binding should occur. However the Walden product reduces with first addition of non solvent and accelerates when the structural collapse sets in. Since the dielectric constant of the solvent remains virtually constant during the chain collapse, the counterion binding is entirely caused by the reduction in the polyion chain dimension. The collapse is shifted to lower wns with higher degrees of quaternization as the samples QPVP20 and QPVP35 show (M = 2.8 respectively 4.9). The combination of light scattering and conductivity measurement revealed for the first time that polyion chains already collect their counter ions well above the theta-dimension when the dimensions start to shrink. Due to only small amounts of screening salt, strong electrostatic interactions bias dynamic as well as static light scattering measurements. An extended Zimm formula was derived to account for this interaction and to obtain the real chain dimensions. The effective degree of dissociation g could be obtained semi quantitatively using this extrapolated static in combination with conductivity measurements. One can conclude the expansion factor a and the effective degree of ionization of the polyion to be mutually dependent. In the good solvent regime g of QPVP4.3, QPVP20 and QPVP35 exhibited a decreasing value in the order 1 > g4.3 > g20 > g35. The low values of g for QPVP20 and QPVP35 are assumed to be responsible for the prior collapse of the higher quaternized samples. Collapse theory predicts dipole-dipole attraction to increase accordingly and even predicts a collapse in the good solvent regime. This could be exactly observed for the QPVP35 sample. The experimental results were compared to a newly developed theory of uniform spherical collapse induced by concomitant counterion binding developed by M. Muthukumar and A. Kundagrami. The theory agrees qualitatively with the location of the phase boundary as well as the trend of an increasing expansion with an increase of the degree of quaternization. However experimental determined g for the samples QPVP4.3, QPVP20 and QPVP35 decreases linearly with the degree of quaternization whereas this theory predicts an almost constant value.

Probing the Mechanical Properties of Magnetosome Chains in Living Magnetotactic Bacteria

The mechanical properties of cytoskeletal networks are intimately involved in determining how forces and cellular processes are generated, directed, and transmitted in living cells. However, determining the mechanical properties of subcellular molecular complexes in vivo has proven to be difficult. Here, we combine in vivo measurements by optical microscopy, X-ray diffraction, and transmission electron microscopy with theoretical modeling to decipher the mechanical properties of the magnetosome chain system encountered in magnetotactic bacteria. We exploit the magnetic properties of the endogenous intracellular nanoparticles to apply a force on the filament-connector pair involved in the backbone formation and stabilization. We show that the magnetosome chain can be broken by the application of external field strength higher than 30 mT and suggest that this originates from the rupture of the magnetosome connector MamJ. In addition, we calculate that the biological determinants can withstand in vivo a force of 25 pN. This quantitative understanding provides insights for the design of functional materials such as actuators and sensors using cellular components.

Measuring global value chains and regional economic integration : an international input-output approach

Firms that are expanding their cross-border activities, such as vertical specialization trade, outsourcing, and fragmentation productions, have brought dramatic changes to the global economy during the last two decades. In an attempt to understand the evolution of the interaction among countries or country groups, many trade-statistics-based indicators have been developed. However, most of these statistics focus on showing the direct trade-specific-relationship among countries, rather than considering the roles that intercountry and interindustrial production networks play in a global economy. This paper uses the concepts of trade in value added as measured by the input–output tables of OECD and IDE-JETRO to provide alternative indicators that show the evolution of regional economic integration and global value chains for more than 50 economies. In addition, this paper provides thoughts on how to evaluate comparative advantages on the basis of value added using an international input–output model.

Effects of RoHs and REACH regulations on firm-level production and export, and the role of global value chains : the cases of Malaysia and Vietnam

This paper uses firm-level data to examine the impact of foreign chemical safety regulations such as RoHS and REACH on the production costs and export performance of firms in Malaysia and Vietnam. This paper also investigates the role of global value chains in enhancing the likelihood that a firm complies with RoHS and REACH. We find that in addition to the initial setup costs for compliance, EU RoHS (REACH) implementation imposes on firms additional variable production costs by requiring additional labor and capital expenditures of around 57% (73%) of variable costs. We also find that compliance with RoHS and REACH significantly increases the probability of export and that compliance with EU RoHS and REACH helps firms enter a greater variety of countries. Furthermore, firms participating in global value chains have higher compliance with RoHS and REACH regulations, regardless of whether the firm is directly exporting, when the firm operates in upstream or downstream industries of the countries' supply chain.

A management model for closed-loop supply chains of reusable articles

This PhD dissertation is framed in the emergent fields of Reverse Logistics and ClosedLoop Supply Chain (CLSC) management. This subarea of supply chain management has gained researchers and practitioners' attention over the last 15 years to become a fully recognized subdiscipline of the Operations Management field. More specifically, among all the activities that are included within the CLSC area, the focus of this dissertation is centered in direct reuse aspects. The main contribution of this dissertation to current knowledge is twofold. First, a framework for the so-called reuse CLSC is developed. This conceptual model is grounded in a set of six case studies conducted by the author in real industrial settings. The model has also been contrasted with existing literature and with academic and professional experts on the topic as well. The framework encompasses four building blocks. In the first block, a typology for reusable articles is put forward, distinguishing between Returnable Transport Items (RTI), Reusable Packaging Materials (RPM), and Reusable Products (RP). In the second block, the common characteristics that render reuse CLSC difficult to manage from a logistical standpoint are identified, namely: fleet shrinkage, significant investment and limited visibility. In the third block, the main problems arising in the management of reuse CLSC are analyzed, such as: (1) define fleet size dimension, (2) control cycle time and promote articles rotation, (3) control return rate and prevent shrinkage, (4) define purchase policies for new articles, (5) plan and control reconditioning activities, and (6) balance inventory between depots. Finally, in the fourth block some solutions to those issues are developed. Firstly, problems (2) and (3) are addressed through the comparative analysis of alternative strategies for controlling cycle time and return rate. Secondly, a methodology for calculating the required fleet size is elaborated (problem (1)). This methodology is valid for different configurations of the physical flows in the reuse CLSC. Likewise, some directions are pointed out for further development of a similar method for defining purchase policies for new articles (problem (4)). The second main contribution of this dissertation is embedded in the solutions part (block 4) of the conceptual framework and comprises a two-level decision problem integrating two mixed integer linear programming (MILP) models that have been formulated and solved to optimality using AIMMS as modeling language, CPLEX as solver and Excel spreadsheet for data introduction and output presentation. The results obtained are analyzed in order to measure in a client-supplier system the economic impact of two alternative control strategies (recovery policies) in the context of reuse. In addition, the models support decision-making regarding the selection of the appropriate recovery policy against the characteristics of demand pattern and the structure of the relevant costs in the system. The triangulation of methods used in this thesis has enabled to address the same research topic with different approaches and thus, the robustness of the results obtained is strengthened.

Expression of αv and β3 integrin chains on murine lymphocytes

The vitronectin receptor is a member of the integrin family of adhesion protein receptors and binds a broad spectrum of ligands, including fibronectin and fibrinogen in addition to vitronectin. We have generated four mAbs that recognize the murine αvβ3 vitronectin receptor. Biochemical and expression analyses showed that two of the mAbs are specific for the αv chain, and two are specific for the β3 chain. The mAbs are effective blocking reagents and inhibited cell adhesion to vitronectin, fibrinogen, and fibronectin. Staining analysis revealed expression of αv and β3 on certain populations of murine thymocytes, splenocytes, and bone marrow cells. The expression of αv and β3 appeared to be modulated at specific stages of thymocyte development, suggesting a possible function for the αvβ3 vitronectin receptor in T cell development.

Posttranslational amino acid epimerization: enzyme-catalyzed isomerization of amino acid residues in peptide chains.

Since ribosomally mediated protein biosynthesis is confined to the L-amino acid pool, the presence of D-amino acids in peptides was considered for many years to be restricted to proteins of prokaryotic origin. Unicellular microorganisms have been responsible for the generation of a host of D-amino acid-containing peptide antibiotics (gramicidin, actinomycin, bacitracin, polymyxins). Recently, a series of mu and delta opioid receptor agonists [dermorphins and deltorphins] and neuroactive tetrapeptides containing a D-amino acid residue have been isolated from amphibian (frog) skin and mollusks. Amino acid sequences obtained from the cDNA libraries coincide with the observed dermorphin and deltorphin sequences, suggesting a stereospecific posttranslational amino acid isomerization of unknown mechanism. A cofactor-independent serine isomerase found in the venom of the Agelenopsis aperta spider provides the first major clue to explain how multicellular organisms are capable of incorporating single D-amino acid residues into these and other eukaryotic peptides. The enzyme is capable of isomerizing serine, cysteine, O-methylserine, and alanine residues in the middle of peptide chains, thereby providing a biochemical capability that, until now, had not been observed. Both D- and L-amino acid residues are susceptible to isomerization. The substrates share a common Leu-Xaa-Phe-Ala recognition site. Early in the reaction sequence, solvent-derived deuterium resides solely with the epimerized product (not substrate) in isomerizations carried out in 2H2O. Significant deuterium isotope effects are obtained in these reactions in addition to isomerizations of isotopically labeled substrates (2H at the epimerizeable serine alpha-carbon atom). The combined kinetic and structural data suggests a two-base mechanism in which abstraction of a proton from one face is concomitant with delivery from the opposite face by the conjugate acid of the second enzymic base.

Role of phospholipids containing docosahexaenoyl chains in modulating the activity of protein kinase C.

It is known that the phospholipids of the brain cells of fish are altered during cold adaptation. In particular, the 1-monounsaturated 2-polyunsaturated phosphatidylethanolamines (PEs) increase 2- to 3-fold upon adaptation to cold. One of the most striking changes is in the 18:1/22:6 species of PE. We determined how this lipid affected the bilayer-to-hexagonal-phase transition temperature of 16:1/16:1 PE. We found that it was more effective in lowering this transition temperature than were other, less unsaturated, PE species. In addition, it was not simply the presence of the 18:1/22:6 acyl chains which caused this effect, since the 18:1/22:6 species of phosphatidylcholine had the opposite effect on this transition temperature. Zwitterionic substances that lower the bilayer-to-hexagonal-phase transition temperature often cause an increase in the activity of protein kinase C (PKC). Indeed, the 18:1/22:6 PE caused an increase in the rate of histone phosphorylation by PKC which was greater than that caused by other, less unsaturated, PEs. The 18:1/22:6 phosphatidylcholine had no effect on this enzyme. The stimulation of the activity of PKC by the 18:1/22:6 PE is a consequence of this lipid's increasing the partitioning of PKC to the membrane.

Nascent polypeptide-associated complex protein prevents mistargeting of nascent chains to the endoplasmic reticulum.

We show that, after removal of the nascent polypeptide-associated complex (NAC) from ribosome-associated nascent chains, ribosomes synthesizing proteins lacking signal peptides are efficiently targeted to the endoplasmic reticulum (ER) membrane. After this mistargeting, translocation across the ER membrane occurs, albeit less efficiently than for a nascent secretory polypeptide, perhaps because the signal peptide is needed to catalyze the opening of the translocation pore. The mistargeting was prevented by the addition of purified NAC and was shown not to be mediated by the signal recognition particle and its receptor. Instead, it appears to be a consequence of the intrinsic affinity of ribosomes for membrane binding sites, since it can be blocked by competing ribosomes that lack associated nascent polypeptides. We propose that, when bound to a signalless ribosome-associated nascent polypeptide, NAC sterically blocks the site in the ribosome for membrane binding.

Geodynamic events reconstructed in the Betic, Maghrebian, and Apennine chains (central-western Tethys)

A synthetic study has been made to identify main tectono-sedimentary and geodynamic events in central-western Tethys. For this, an interdisciplinary analysis has been performed on successions belonging to tectonic units derived from Betic-Maghrebian-southern Apennine “Flysch basin” domain. The stratigraphic records of the internal, external, and mixed successions deposited in lateral basins of different chains show very similar characters, especially regarding: (a) lithostratigraphy and ages; (b) kind and provenance of supplies (immature and supermature petrofacies from internal and external margins, respectively); (c) presence of “mixed successions” (composed of alternating internal and external petrofacies) attesting to clear palaeogeographic relationships between opposite depositional systems; and (d) timing of the deformation. In addition, specific lithofacies reveal correspondence with similar sedimentary events, such as: (1) very thick silicoclastic supply concentrated in restricted time ranges indicating the main deformational phases in the margin/basin systems; (2) levels rich in black-shales, glauconian, siliceous-producers, and volcaniclastic intercalations, widespread in the studied successions and linked to particular events at the Tethyan scale (anoxic periods, starvation-upwelling, acid-intermediate penecontemporaneous volcanic activity, respectively). Tectonic influence has also been recorded by means of unconformities and tectofacies (such as turbidites, slumps, or olisthostromes, etc.), being correlated with the main deformational phases. Similar stratigraphic and tectonic events have also been found in the Calvana unit of Val Marecchia nappe (Ligurides, northern Apennine). Correlations of stratigraphic and tectonic events support the proposal of an evolutionary geodynamic model involving the presence of a “Mesomediterranean microplate” in intermediate position during Africa-Europe convergence. The closure of central-western Tethys occasioned the Betic-Maghrebian-southern Apennine oceanic branch deformation and the birth of perimediterranean chains during middle-late Miocene.

Quality certification, performance and size in hotel chains

This paper examines the relationship between quality certification and performance, and quality certification and size in hotel chains operating in Spain. In an initial phase, a quantitative study is made with secondary and objective data to analyse these relationships. In a second phase, a qualitative analysis is applied to reach a better understanding of the quantitative results. The findings show that chains with certified hotels achieve better performance levels; that better performance levels increase with the percentage of certified hotels within the chain; and that quality certification has positive effects on some performance variables. In addition, size is not a key factor for certification, although it could be an enabler.

Controlled Radical Polymerization of Styrene and Methyl Acrylate in the Presence of Reversible Addition-Fragmentation Chain Transfer Agents, Phenylethyl Phenyl Dithioacetate and Phenyldithioacetic Acid

The use of phenyldithioacetic acid (PDA) in homopolymerizations of styrene or methyl acrylate produced only a small fraction of chains with dithioester end groups. The polymerizations using 1-phenylentyl phenyldithioacetate (PEPDTA) and PDA in the same reaction showed that PDA had little or no influence on the rate or molecular weight distribution even when a 1:1 ratio is used. The mechanistic pathway for the polymerizations in the presence of PDA seemed to be different for each monomer. Styrene favors addition of styrene to PDA via a Markovnikov type addition to form a reactive RAFT agent. The polymer was shown by double detection SEC to contain dithioester end groups over the whole distribution. This polymer was then used in a chain extension experiment and the M-n was close to theory. A unique feature of this work was that PDA could be used to form a RAFT agent in situ by heating a mixture of styrene and PDA for 24 h at 70 degrees C and then polymerizing in the presence of AIBN to give a linear increase in Mn and low values of PDI (< 1.14). In the case of the polymerization of MA with PDA, the mechanism was proposed to be via degradative chain transfer. (c) 2005 Wiley Periodicals, Inc.

Hsc70-induced changes in clathrin-auxilin cage structure suggest a role for clathrin light chains in cage disassembly

The molecular chaperone, Hsc70, together with its cofactor, auxilin, facilitates the ATP-dependent removal of clathrin during clathrin-mediated endocytosis in cells. We have used cryo-electron microscopy to determine the 3D structure of a complex of clathrin, auxilin401-910 and Hsc70 at pH 6 in the presence of ATP, frozen within 20 seconds of adding Hsc70 in order to visualize events that follow the binding of Hsc70 to clathrin and auxilin before clathrin disassembly. In this map,we observe density beneath the vertex of the cage that we attribute to bound Hsc70. This density emerges asymmetrically from the clathrin vertex, suggesting preferential binding by Hsc70 for one of the three possible sites at the vertex. Statistical comparison with a map of whole auxilin and clathrin previously published by us reveals the location of statistically significant differences which implicate involvement of clathrin light chains in structural rearrangements which occur after Hsc70 is recruited. Clathrin disassembly assays using light scattering suggest that loss of clathrin light chains reduces the efficiency with which auxilin facilitates this reaction. These data support a regulatory role for clathrin light chains in clathrin disassembly in addition to their established role in regulating clathrin assembly. © 2013 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

Designing post-disaster supply chains:learning from housing reconstruction projects

Post-disaster housing reconstruction projects face several challenges. Resources and material supplies are often scarce; several and different types of organizations are involved, while projects must be completed as quickly as possible to foster recovery. Within this context, the chapter aims to increase the understanding of relief supply chain design in reconstruction. In addition, the chapter is introducing a community based and beneficiary perspective to relief supply chains by evaluating the implications of local components for supply chain design in reconstruction. This is achieved through the means of secondary data analysis based on the evaluation reports of two major housing reconstruction projects that took place in Europe the last decade. A comparative analysis of the organizational designs of these projects highlights the ways in which users can be involved. The performance of reconstruction supply chains seems to depend to a large extent on the way beneficiaries are integrated in supply chain design impacting positively on the effectiveness of reconstruction supply chains.

A diagnostic framework for demand amplification problems in supply chains

This dissertation delivers a framework to diagnose the Bull-Whip Effect (BWE) in supply chains and then identify methods to minimize it. Such a framework is needed because in spite of the significant amount of literature discussing the bull-whip effect, many companies continue to experience the wide variations in demand that are indicative of the bull-whip effect. While the theory and knowledge of the bull-whip effect is well established, there still is the lack of an engineering framework and method to systematically identify the problem, diagnose its causes, and identify remedies. ^ The present work seeks to fill this gap by providing a holistic, systems perspective to bull-whip identification and diagnosis. The framework employs the SCOR reference model to examine the supply chain processes with a baseline measure of demand amplification. Then, research of the supply chain structural and behavioral features is conducted by means of the system dynamics modeling method. ^ The contribution of the diagnostic framework, is called Demand Amplification Protocol (DAMP), relies not only on the improvement of existent methods but also contributes with original developments introduced to accomplish successful diagnosis. DAMP contributes a comprehensive methodology that captures the dynamic complexities of supply chain processes. The method also contributes a BWE measurement method that is suitable for actual supply chains because of its low data requirements, and introduces a BWE scorecard for relating established causes to a central BWE metric. In addition, the dissertation makes a methodological contribution to the analysis of system dynamic models with a technique for statistical screening called SS-Opt, which determines the inputs with the greatest impact on the bull-whip effect by means of perturbation analysis and subsequent multivariate optimization. The dissertation describes the implementation of the DAMP framework in an actual case study that exposes the approach, analysis, results and conclusions. The case study suggests a balanced solution between costs and demand amplification can better serve both firms and supply chain interests. Insights pinpoint to supplier network redesign, postponement in manufacturing operations and collaborative forecasting agreements with main distributors.^