Crystalline Amorphous Interfaces in Polymer Crystals

Crystalline polymer solids are never ideally crystallized. From the density defect one may formally derive a finite crystalline and amorphous component. The study of polyethylene single crystals by different methods suggests a spatial separation of the components: a crystalline core and two quasi amorphous surface layers containing the chain folds. At the interface the amorphous loops are fixed in the crystal lattice. The space requirement of the amorphous conformations can be only met by the assumption of varying loop length . . This immediately increases the entropy content of the loops and partly compensates for the reduction caused by the loop ends fixed at the interface and by the limitation of space accessible to the loops by the existence of the crystal lattice. The high energy requirement of the shortest loops with an excess of gauche conformations favors large loops and hence increases the thickness of the surface layer. The values obtained for strictly adjacent reentry of all loops are still below the experimental data. A perfect fit seems possible if one assumes that there are a few loops with nonadjacent reentry and some chains with one end free. The former are a consequence of crystallization kinetics and the latter result from the finite number of extremely long loops surpassing the length of single molecules but also from the chain ends of all molecules of the sample because there is a clear tendency of their concentration on the surface of the crystal

Crystalline Amorphous Interfaces in Polymer Crystals

Crystalline polymer solids are never ideally crystallized. From the density defect one may formally derive a finite crystalline and amorphous component. The study of polyethylene single crystals by different methods suggests a spatial separation of the components: a crystalline core and two quasi amorphous surface layers containing the chain folds. At the interface the amorphous loops are fixed in the crystal lattice. The space requirement of the amorphous conformations can be only met by the assumption of varying loop length . . This immediately increases the entropy content of the loops and partly compensates for the reduction caused by the loop ends fixed at the interface and by the limitation of space accessible to the loops by the existence of the crystal lattice. The high energy requirement of the shortest loops with an excess of gauche conformations favors large loops and hence increases the thickness of the surface layer. The values obtained for strictly adjacent reentry of all loops are still below the experimental data. A perfect fit seems possible if one assumes that there are a few loops with nonadjacent reentry and some chains with one end free. The former are a consequence of crystallization kinetics and the latter result from the finite number of extremely long loops surpassing the length of single molecules but also from the chain ends of all molecules of the sample because there is a clear tendency of their concentration on the surface of the crystal

Cataract and optic disk drusen in a patient with glycogenosis and di George syndrome: clinical and molecular report

Background We report the ophthalmic findings of a patient with type Ia glycogen storage disease (GSD Ia), DiGeorge syndrome (DGS), cataract and optic nerve head drusen (ONHD). Case presentation A 26-year-old white woman, born at term by natural delivery presented with a post-natal diagnosis of GSD Ia. Genetic testing by array-comparative genomic hybridization (CGH) for DGS was required because of her low levels of serum calcium. The patient has been followed from birth, attending the day-hospital every six months at the San Paolo Hospital, Milan, outpatient clinic for metabolic diseases and previously at another eye center. During the last day-hospital visit, a complete eye examination showed ONHD and cataract in both eyes. Next Generation Sequencing (NGS) was subsequently done to check for any association between the eye problems and metabolic aspects. Conclusions This is the first description of ocular changes in a patient with GSD Ia and DGS. Mutations explaining GSD Ia and DGS were found but no specific causative mutation for cataract and ONHD. The metabolic etiology of her lens changes is known, whereas the pathogenesis of ONHD is not clear. Although the presence of cataract and ONHD could be a coincidence; the case reported could suggest that hypocalcemia due to DGS could be the common biochemical pathway

Non-linear rheology of active particle suspensions: Insights from an analytical approach

We consider active suspensions in the isotropic phase subjected to a shear flow. Using a set of extended hydrodynamic equations we derive a variety of {\em analytical} expressions for rheological quantities such as shear viscosity and normal stress differences. In agreement to full-blown numerical calculations and experiments we find a shear thickening or -thinning behaviour depending on whether the particles are contractile or extensile. Moreover, our analytical approach predicts that the normal stress differences can change their sign in contrast to passive suspensions.Comment: 11 pages, 10 figures, appear in PR

Influence of Viscoelasticity of Amorphous Layers on Longitudinal Accordion Mode Seattering of Polymers

The normal viscoelasticity of the amorphous component yields a rapid exponential decrease of the amplitude of the longitudinal accordion type oscillations in the defect areas of the macromolecule in the crystalline core and in the amorphous layers on the folds containing surfaces of the lamellae. The macrornolecule in the amorphous layer and in crystal defects changes direction and, hence, cannot conserve the longitudinal oscillation. The jumping of this oscillation to neighboring molecules accelerates so much its decrease that the straight sections between the two surface layers are longitudinally completely, while those between any two defects, or between one defect and the surface layer nearly completely decoupled from the rest of the sample. The effect is enhanced by the fact that the basic wave length of the observed Raman scattering is a little smaller than twice the length of the oscillating straight section. Maximum of the vibration energy occurs inside these sections and not in the amorphous regions. Since the lateral decoupling is guaranteed by the smallness of lateral forces, each straight section oscillates as if it were completely independent of the short and long range crystalline and amorphous environment. Only in such a case a simple conclusion on the distribution of straight chain sections can be deduced from the experiment

HMBA Releases P-TEFb from HEXIM1 and 7SK snRNA via PI3K/Akt and Activates HIV Transcription

Hexamethylene bisacetamide (HMBA) is a potent inducer of cell differentiation and HIV production in chronically infected cells. However, its mechanism of action remains poorly defined. In this study, we demonstrate that HMBA activates transiently the PI3K/Akt pathway, which leads to the phosphorylation of HEXIM1 and the subsequent release of active positive transcription elongation factor b (P-TEFb) from its transcriptionally inactive complex with HEXIM1 and 7SK small nuclear RNA (snRNA). As a result, P-TEFb is recruited to the HIV promoter to stimulate transcription elongation and viral production. Despite the continuous presence of HMBA, the released P-TEFb reassembles rapidly with 7SK snRNA and HEXIM1. In contrast, a mutant HEXIM1 protein that cannot be phosphorylated and released from P-TEFb and 7SK snRNA via the PI3K/Akt pathway antagonizes this HMBA-mediated induction of viral production. Thus, our studies reveal how HIV transcription is induced by HMBA and suggest how modifications in the equilibrium between active and inactive P-TEFb could contribute to cell differentiation

Podado del tallo principal como técnica de regulación del crecimiento del Algodón en Sistemas Productivos Minifundistas

El objetivo del trabajo fue determinar la influencia que el podado del tallo principal tiene sobre el crecimiento, rendimiento y calidad de fibra del algodón, cuando es empleado como técnica para regular el crecimiento de la planta. Los tratamientos consistieron en el podado de plantas con machete cuando alcanzaban los 18, 19 y 20 nudos reduciéndole tres nudos en la operación (15, 16 y 17 nudos finales respectivamente) comparándolas con un testigo sin tratar. El mejor momento para realizarlo es cuando la planta alcanza el estado de fin de floración efectiva, caracterizado por la presencia de 20 nudos sobre el tallo principal, en donde la combinación de altos valores de biomasa total manteniendo elevados índices de cosecha, permitió obtener los mejores rendimientos sin afectar la calidad del algodón. El podar demasiado temprano afecta el crecimiento y el rendimiento, pero no la calidad. El podado mecánico puede ser empleado como herramienta de regulación del crecimiento de la planta de algodón en sistemas productivos minifundistas

Agreement of self-reported physician diagnosis of migraine with international classification of headache disorders-II migraine diagnostic criteria in a cross-sectional study of pregnant women

Background: Migraine, a common chronic-intermittent disorder among reproductive age women, has emerged as a novel risk factor for adverse perinatal outcomes. Diagnostic reliability of self-report of physician-diagnosed migraine has not been investigated in pregnancy cohort studies. We investigated agreement of self-report of physician-diagnosed migraine with the diagnostic criteria promoted by the International Classification of Headache Disorders, 2nd edition (ICHD-II). Methods: The cross-sectional study was conducted among 500 women who provided information on a detailed migraine questionnaire that allowed us to apply all ICHD-II diagnostic criteria. Results: Approximately 92% of women reporting a diagnosis of migraine had the diagnosis between the ages of 11 and 40 years (40 years 1.0%). We confirmed self-reported migraine in 81.6% of women when applying the ICHD-II criteria for definitive migraine (63.1%) and probable migraine (18.5%). Conclusion: There is good agreement between self-reported migraine and ICHD-II-based migraine classification in this pregnancy cohort. We demonstrate the feasibility of using questionnaire-based migraine assessment according to full ICHD-II criteria in epidemiological studies of pregnant women

Activation of PAK by HIV and SIV Nef: importance for AIDS in rhesus macaques

AbstractBackground The primate lentiviruses, human immunodeficiency virus types 1 and 2 (HIV-1 and HIV-2) and simian immunodeficiency virus (SIV), encode a conserved accessory gene product, Nef. In vivo, Nef is important for the maintenance of high virus loads and progression to AIDS in SIV-infected adult rhesus macaques. In tissue culture cells expressing Nef, this viral protein interacts with a cellular serine kinase, designated Nef-associated kinase.Results This study identifies the Nef-associated kinase as a member of the p21-activated kinase (PAK) family of kinases and investigates the role of this Nef-associated kinase in vivo. Mutants of Nef that do not associate with the cellular kinase are unable to activate the PAK-related kinase in infected cells. To determine the role of cellular kinase association in viral pathogenesis, macaques were infected with SIV containing point-mutations in Nef that block PAK activation. Virus recovered at early time points after inoculation with mutant virus was found to have reverted to prototype Nef function and sequence. Reversion of the kinase-negative mutant to a kinase-positive genotype in macaques infected with the mutant virus preceded the induction of high virus loads and disease progression.Conclusions Nef associates with and activates a PAK-related kinase in lymphocytes infected in vitro. Moreover, the Nef-mediated activation of a PAK-related kinase correlates with the induction of high virus loads and the development of AIDS in the infected host. These findings reveal that there is a strong selective pressure in vivo for the interaction between Nef and the PAK-related kinase