Simón Bolívar University

About: Simón Bolívar University is a education organization based out in Caracas, Venezuela. It is known for research contribution in the topics: Population & Crystallization. The organization has 5912 authors who have published 8294 publications receiving 126152 citations.

Immunology: Autoimmunity to spermatozoa, asymptomatic Chlamydia trachomatis genital tract infection and γδ T lymphocytes in seminal fluid from the male partners of couples with unexplained infertility

Abstract: The relationship between an undetected, asymptomatic Chlamydia trachomatis genital tract infection, the concentration of gamma delta and alpha b T cells in semen and sperm autoimmunity was examined in 48 male partners of couples with unexplained infertility. Immunoglobulin A (IgA) antibodies to C. trachomatis were detected in seminal fluids from 14 (29.2%) of the men. Only four of these were positive for circulating anti-chlamydial IgA, suggesting that the stimulus for antibody production was within the genital tract. In contrast, four men were positive for anti-chlamydial IgG in their semen; all were also seropositive for anti-chlamydial IgG. T lymphocytes bearing the alpha beta and gamma delta antigen receptors were present in every semen sample. Men with seminal anti-chlamydial IgA, however, had significantly (P = 0.035) elevated semen gamma delta T cell concentrations (median 3100 cells/ml) than did men lacking this antibody (median 1400 cells/ml); concentrations of alpha beta T cells were comparable in both groups. Genital tract sperm autoimmunity, as shown by antibodies bound to motile ejaculated spermatozoa, was detected in 13 (27.1%) men. The presence of these antibodies was associated with elevated concentrations of both gamma delta (median 4200 versus 700 cells/ml) and alpha beta (median 5000 versus 850 cells/ml) T cells (P = 0.0002 and 0.0001 respectively). Men with antisperm antibodies only in their serum had seminal T cell concentrations comparable with men testing negative for antisperm antibodies. Anti-chlamydial IgA was identified in semen from four of 10 men with IgA bound to their spermatozoa and in none of the men with only spermatozoa-bound IgG.(ABSTRACT TRUNCATED AT 250 WORDS)

Surface Modification of Multiwalled Carbon Nanotubes with Biocompatible Polymers via Ring Opening and Living Anionic Surface Initiated Polymerization. Kinetics and Crystallization Behavior

Abstract: Multiwalled carbon nanotubes (MWNTs) were functionalized with 2-hydroxyethyl benzocyclobutene (BCB-EO) through a Diels–Alder cycloaddition reaction. The functionalized MWNTs were utilized for the surface initiated ring opening (ROP) catalyzed and anionic polymerization of e-caprolactone (e-CL) and ethylene oxide (EO), respectively. The kinetics of the ROP of e-CL was monitored through thermogravimetric analysis (TGA) which revealed that the polymerization proceeds very fast as compared to that of EO and that both polymerizations could be controlled with time. 1H NMR, Raman and FTIR spectroscopy, TGA, DSC, and transmission electron microscopy (TEM) were employed for the characterization of these polymer/CNT hybrids. DSC results showed that a remarkable nucleation effect is produced by MWNTs that reduced the supercooling needed for crystallization of both PeCL and PEO. Furthermore, the isothermal crystallization kinetics of the grafted PeCL and PEO was substantially accelerated compared to the neat polymers. The strong impact on the nucleation and crystallization kinetics is attributed to the covalent MWNT-polymer bonding. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4379–4390, 2009

The evaluation of the state of dispersion in immiscible blends where the minor phase exhibits fractionated crystallization

Abstract: Differential Scanning Calorimetry (DSC) can provide a qualitative measure of the state of dispersion of an immiscible blend if the minor phase exhibits fractionated crystallization when dispersed into fine particles. The technique is only sensitive to the volume of the dispersed particle and not to its shape and can only be used when the exotherms of interest do not overlap with other thermal transitions present in the multicomponent system. Selfnucleation is a valuable tool to ascertain the presence of fractionated crystallization. The morphology induced by fractionated crystallization in immiscible blends could lead to enhanced plastic deformation during yielding of the matrix.

Pruning conformant plans by counting models on compiled d-DNNF representations

Abstract: Optimal planners in the classical setting are built around two notions: branching and pruning. SAT-based planners for example branch by trying the values of a selected variable, and prune by propagating constraints and checking consistency. In the conformant setting, a similar branching scheme can be used if restricted to action variables, but the pruning scheme must be modified. Indeed, pruning branches that encode inconsistent partial plans is not sufficient since a partial plan may be consistent and complete (covering all the action variables) and still fail to be a conformant plan. This happens indeed when the plan does not conform to some possible initial state or transition. A remedy to this problem is to use a criterion stronger than consistency for pruning. This is actually what we do in this paper where the consistency-based pruning criterion used in classical planning is replaced by a validity-based criterion suitable for conformant planning. Under the assumption that actions are deterministic, a partial plan can be defined as valid when it is logically consistent with the theory and each possible initial state. A valid partial plan that is complete is guaranteed to encode a conformant plan, and vice versa. Checking validity, however, while useful for pruning can be very expensive. We show then that such validity checks can be performed in linear time provided that the theory encoding the problem is transformed into a logically equivalent theory in deterministic decomposable negation normal form (d-DNNF). In d-DNNF, plan validity checks can be reduced to two linear-time operations: projection (finding the strongest consequence of a formula over some of its variables) and model counting (finding the number of satisfying assignments). We then define and evaluate a conformant planner that branches on action variables, and prunes invalid partial plans in linear time. The empirical results are encouraging, showing the potential benefits of stronger forms of inference in planning tasks that are not reducible to SAT.