The role of intramolecular barriers on the glass transition of polymers: computer simulations versus mode coupling theory

We present computer simulations of a simple bead-spring model for polymer melts with intramolecular barriers. By systematically tuning the strength of the barriers, we investigate their role on the glass transition. Dynamic observables are analyzed within the framework of the mode coupling theory (MCT). Critical nonergodicity parameters, critical temperatures, and dynamic exponents are obtained from consistent fits of simulation data to MCT asymptotic laws. The so-obtained MCT λ-exponent increases from standard values for fully flexible chains to values close to the upper limit for stiff chains. In analogy with systems exhibiting higher-order MCT transitions, we suggest that the observed large λ-values arise form the interplay between two distinct mechanisms for dynamic arrest: general packing effects and polymer-specific intramolecular barriers. We compare simulation results with numerical solutions of the MCT equations for polymer systems, within the polymer reference interaction site model (PRISM) for static correlations. We verify that the approximations introduced by the PRISM are fulfilled by simulations, with the same quality for all the range of investigated barrier strength. The numerical solutions reproduce the qualitative trends of simulations for the dependence of the nonergodicity parameters and critical temperatures on the barrier strength. In particular, the increase in the barrier strength at fixed density increases the localization length and the critical temperature. However the qualitative agreement between theory and simulation breaks in the limit of stiff chains. We discuss the possible origin of this feature.

Recombination dynamics in ZnO nanowires: Surfaces states versus mode quality factor

In this work, we investigate the influence of finite size on the recombinations dynamics of ZnO nanowires. We demonstrate that diameter as well as lenght of nanowires determine the lifetime of the neutral donor bound excitons. Our findings suggest that while the length is mainly responsible for different mode quality factors of the cavity-like nanowires, the diameter determines the influence of surface states as alternative recombinations channels for the optical modes trapped in the nanocavity. In addition, comparing nanowires grown using different catalyst we show that the surfaces states strongly depend on each precursor characteristics.

Structural Insight into the Mode of Action of a Direct Inhibitor of Coregulator Binding to the Thyroid Hormone Receptor.

The development of nuclear hormone receptor antagonists that directly inhibit the association of the receptor with its essential coactivators would allow useful manipulation of nuclear hormone receptor signaling. We previously identified 3-(dibutylamino)-1-(4-hexylphenyl)-propan-1-one (DHPPA), an aromatic β-amino ketone that inhibits coactivator recruitment to thyroid hormone receptor β (TRβ), in a high-throughput screen. Initial evidence suggested that the aromatic β-enone 1-(4-hexylphenyl)-prop-2-en-1-one (HPPE), which alkylates a specific cysteine residue on the TRβ surface, is liberated from DHPPA. Nevertheless, aspects of the mechanism and specificity of action of DHPPA remained unclear. Here, we report an x-ray structure of TRβ with the inhibitor HPPE at 2.3-Å resolution. Unreacted HPPE is located at the interface that normally mediates binding between TRβ and its coactivator. Several lines of evidence, including experiments with TRβ mutants and mass spectroscopic analysis, showed that HPPE specifically alkylates cysteine residue 298 of TRβ, which is located near the activation function-2 pocket. We propose that this covalent adduct formation proceeds through a two-step mechanism: 1) β-elimination to form HPPE; and 2) a covalent bond slowly forms between HPPE and TRβ. DHPPA represents a novel class of potent TRβ antagonist, and its crystal structure suggests new ways to design antagonists that target the assembly of nuclear hormone receptor gene-regulatory complexes and block transcription.

A probable dual mode of action for both L- and D-lactate neuroprotection in cerebral ischemia.

Lactate has been shown to offer neuroprotection in several pathologic conditions. This beneficial effect has been attributed to its use as an alternative energy substrate. However, recent description of the expression of the HCA1 receptor for lactate in the central nervous system calls for reassessment of the mechanism by which lactate exerts its neuroprotective effects. Here, we show that HCA1 receptor expression is enhanced 24 hours after reperfusion in an middle cerebral artery occlusion stroke model, in the ischemic cortex. Interestingly, intravenous injection of L-lactate at reperfusion led to further enhancement of HCA1 receptor expression in the cortex and striatum. Using an in vitro oxygen-glucose deprivation model, we show that the HCA1 receptor agonist 3,5-dihydroxybenzoic acid reduces cell death. We also observed that D-lactate, a reputedly non-metabolizable substrate but partial HCA1 receptor agonist, also provided neuroprotection in both in vitro and in vivo ischemia models. Quite unexpectedly, we show D-lactate to be partly extracted and oxidized by the rodent brain. Finally, pyruvate offered neuroprotection in vitro whereas acetate was ineffective. Our data suggest that L- and D-lactate offer neuroprotection in ischemia most likely by acting as both an HCA1 receptor agonist for non-astrocytic (most likely neuronal) cells as well as an energy substrate.

Catalogue-tarif à prix forts et nets des journaux, revues et publications périodiques parus à Paris ... : contenant les titres complets par ordre alphabétique, les noms des rédacteurs, le format, la tomaison, la date d'origine, le mode de publication... : suivi d'une table systématique et du tarif postal pour la France et l'étranger / publié par Henri Le Soudier

1897 (A18).

Catalogue-tarif à prix forts et nets des journaux, revues et publications périodiques parus à Paris ... : contenant les titres complets par ordre alphabétique, les noms des rédacteurs, le format, la tomaison, la date d'origine, le mode de publication... : suivi d'une table systématique et du tarif postal pour la France et l'étranger / publié par Henri Le Soudier

Variante(s) de titre : Annuaire-tarif des journaux, revues et publications périodiques parus à Paris

Entry Mode Choice in a Hard Service Company

Pro gradun tavoitteena oli löytää tärkeimmät seikat, jotka vaikuttavat kansainvälisen operaatiomuodon valintaan. Tutkimuskohteena olivat suomalaiset pienet tai keskisuuret tuotteistetut ohjelmistopalveluyritykset. Tutkimusmenetelmänä käytettiin kvalitatiivista tutkimusta sekä case-tutkimusta. Tutkimus koostui kahdesta osasta: teoreettinen osa sekä empiirinen kahden case yrityksen analyysi. Operaatiomuodon valintaan vaikuttavat tekijät jaettiin sisäisiin (yritys, tuote ja päätöksentekijä), ulkoisiin (ala ja maa) ja operaatiomuodon (kontrolli, riski, resurssit, joustavuus, tuotot ja kulut) tekijöihin. Teoreettisesti operaatiomuodon valinta on erittäin monimutkainen päätös ja sitä on tutkittu monelta kannalta. Tämä empiirinen tutkimus osoittaa, että yrityksen resurssit olivat tärkein vaikuttava tekijä molemmissa yrityksissä.

Epigenetic regulatory elements: Recent advances in understanding their mode of action and use for recombinant protein production in mammalian cells.

Successful generation of high producing cell lines requires the generation of cell clones expressing the recombinant protein at high levels and the characterization of the clones' ability to maintain stable expression levels. The use of cis-acting epigenetic regulatory elements that improve this otherwise long and uncertain process has revolutionized recombinant protein production. Here we review and discuss new insights into the molecular mode of action of the matrix attachment regions (MARs) and ubiquitously-acting chromatin opening elements (UCOEs), i.e. cis-acting elements, and how these elements are being used to improve recombinant protein production. These elements can help maintain the chromatin environment of the transgene genomic integration locus in a transcriptionally favorable state, which increases the numbers of positive clones and the transgene expression levels. Moreover, the high producing clones tend to be more stable in long-term cultures even in the absence of selection pressure. Therefore, by increasing the probability of isolating a high producing clone, as well as by increasing transcription efficiency and stability, these elements can significantly reduce the time and cost required for producing large quantities of recombinant proteins.

A probable dual mode of action for both L- and D-lactate neuroprotection in cerebral ischemia.

Lactate has been shown to offer neuroprotection in several pathologic conditions. This beneficial effect has been attributed to its use as an alternative energy substrate. However, recent description of the expression of the HCA1 receptor for lactate in the central nervous system calls for reassessment of the mechanism by which lactate exerts its neuroprotective effects. Here, we show that HCA1 receptor expression is enhanced 24 hours after reperfusion in an middle cerebral artery occlusion stroke model, in the ischemic cortex. Interestingly, intravenous injection of L-lactate at reperfusion led to further enhancement of HCA1 receptor expression in the cortex and striatum. Using an in vitro oxygen-glucose deprivation model, we show that the HCA1 receptor agonist 3,5-dihydroxybenzoic acid reduces cell death. We also observed that D-lactate, a reputedly non-metabolizable substrate but partial HCA1 receptor agonist, also provided neuroprotection in both in vitro and in vivo ischemia models. Quite unexpectedly, we show D-lactate to be partly extracted and oxidized by the rodent brain. Finally, pyruvate offered neuroprotection in vitro whereas acetate was ineffective. Our data suggest that L- and D-lactate offer neuroprotection in ischemia most likely by acting as both an HCA1 receptor agonist for non-astrocytic (most likely neuronal) cells as well as an energy substrate.

Targeted cell elimination reveals an auxin-guided biphasic mode of lateral root initiation.

To sustain a lifelong ability to initiate organs, plants retain pools of undifferentiated cells with a preserved proliferation capacity. The root pericycle represents a unique tissue with conditional meristematic activity, and its tight control determines initiation of lateral organs. Here we show that the meristematic activity of the pericycle is constrained by the interaction with the adjacent endodermis. Release of these restraints by elimination of endodermal cells by single-cell ablation triggers the pericycle to re-enter the cell cycle. We found that endodermis removal substitutes for the phytohormone auxin-dependent initiation of the pericycle meristematic activity. However, auxin is indispensable to steer the cell division plane orientation of new organ-defining divisions. We propose a dual, spatiotemporally distinct role for auxin during lateral root initiation. In the endodermis, auxin releases constraints arising from cell-to-cell interactions that compromise the pericycle meristematic activity, whereas, in the pericycle, auxin defines the orientation of the cell division plane to initiate lateral roots.

Governance mode vs. governance fit: Performance implications of make-or-ally choices for product innovation in the worldwide aircraft industry, 1942-2000

We examine the impact of governance mode and governance fit on performance in make-or-ally decisions. We argue that while horizontal collaboration and autonomous governance have direct and countervailing performance implications, the alignment of make-or-ally choices with the focal firm's resource endowment and the activity's resource requirements leads to better performance. Data on the aircraft industry show that relative to aircraft developed autonomously, collaborative aircraft exhibit greater sales but require longer time-to-market. However, governance fit increases unit sales and reduces time-to-market. We contribute to the alliance and economic organization literatures. (Copyright © 2013 John Wiley & Sons, Ltd.)

Screening of breast lesions: a comparative study between mammography, B-mode ultrasonography, sonoelastography and histological results

Objective To compare the capacity of mammography, sonoelastography, B-mode ultrasonography and histological analysis to differentiate benign from malignant breast lesions. Materials and Methods A total of 12 histopathologically confirmed breast lesions were documented. The lesions were assessed by means of mammography, B-mode ultrasonography and sonoelastography, and histopathological analysis was utilized as a gold standard. Sensitivity and specificity were calculated. A receiver operating characteristic (ROC) curve was constructed to evaluate the diagnostic performance of the mentioned techniques. Results Sensitivity and specificity in the differentiation between benign and malignant lesions were respectively 100% and 50% for mammography, 100% and 71% for B-mode ultrasonography, and 67% and 83% for sonoelastography. The area under the ROC curve was calculated for the three imaging modalities and corresponded to 0.792 for mammography, 0.847 for B-mode ultrasonography, and 0.806 for sonoelastography. Conclusion Sonoelastography demonstrated higher specificity and lower sensitivity as compared with mammography and B-mode ultrasonography. On the other hand, B-mode ultrasonography had the largest area under the ROC curve. Sonoelastography has demonstrated to be a promising technique to detect and evaluate breast lesions, and could potentially reduce the number of unnecessary biopsies.