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Search Results: 1 - 10 of 717565 matches for " A.M.;Figueiredo "
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A Histone Methyltransferase Modulates Antigenic Variation in African Trypanosomes
Luisa M. Figueiredo,Christian J. Janzen,George A.M Cross
PLOS Biology , 2012, DOI: 10.1371/journal.pbio.0060161
Abstract: To evade the host immune system, several pathogens periodically change their cell-surface epitopes. In the African trypanosomes, antigenic variation is achieved by tightly regulating the expression of a multigene family encoding a large repertoire of variant surface glycoproteins (VSGs). Immune evasion relies on two important features: exposing a single type of VSG at the cell surface and periodically and very rapidly switching the expressed VSG. Transcriptional switching between resident telomeric VSG genes does not involve DNA rearrangements, and regulation is probably epigenetic. The histone methyltransferase DOT1B is a nonessential protein that trimethylates lysine 76 of histone H3 in Trypanosoma brucei. Here we report that transcriptionally silent telomeric VSGs become partially derepressed when DOT1B is deleted, whereas nontelomeric loci are unaffected. DOT1B also is involved in the kinetics of VSG switching: in ΔDOT1B cells, the transcriptional switch is so slow that cells expressing two VSGs persist for several weeks, indicating that monoallelic transcription is compromised. We conclude that DOT1B is required to maintain strict VSG silencing and to ensure rapid transcriptional VSG switching, demonstrating that epigenetics plays an important role in regulating antigenic variation in T. brucei.
A Histone Methyltransferase Modulates Antigenic Variation in African Trypanosomes
Luisa M Figueiredo,Christian J Janzen,George A.M Cross
PLOS Biology , 2008, DOI: 10.1371/journal.pbio.0060161
Abstract: To evade the host immune system, several pathogens periodically change their cell-surface epitopes. In the African trypanosomes, antigenic variation is achieved by tightly regulating the expression of a multigene family encoding a large repertoire of variant surface glycoproteins (VSGs). Immune evasion relies on two important features: exposing a single type of VSG at the cell surface and periodically and very rapidly switching the expressed VSG. Transcriptional switching between resident telomeric VSG genes does not involve DNA rearrangements, and regulation is probably epigenetic. The histone methyltransferase DOT1B is a nonessential protein that trimethylates lysine 76 of histone H3 in Trypanosoma brucei. Here we report that transcriptionally silent telomeric VSGs become partially derepressed when DOT1B is deleted, whereas nontelomeric loci are unaffected. DOT1B also is involved in the kinetics of VSG switching: in ΔDOT1B cells, the transcriptional switch is so slow that cells expressing two VSGs persist for several weeks, indicating that monoallelic transcription is compromised. We conclude that DOT1B is required to maintain strict VSG silencing and to ensure rapid transcriptional VSG switching, demonstrating that epigenetics plays an important role in regulating antigenic variation in T. brucei.
Nonlinear optical properties of liquid crystals probed by Z-scan technique
Gómez, S.L.;Cuppo, F.L.S.;Figueiredo Neto, A.M.;
Brazilian Journal of Physics , 2003, DOI: 10.1590/S0103-97332003000400035
Abstract: we present a review of experimental data on the nonlinear optical properties of thermotropic and lyotropic liquid crystals probed by the z-scan technique. depending on the time scale, different processes originate a nonlinear optical response. particularly, at nanosecond range, the physical processes associated with the nonlinear response in thermotropics are not completely understood. in lyotropics, the nonlinear response at ms time scale is from thermal origin and depends on the particular mesophase, relative concentration of the components, and temperature.
Nonlinear optical properties of liquid crystals probed by Z-scan technique
Gómez S.L.,Cuppo F.L.S.,Figueiredo Neto A.M.
Brazilian Journal of Physics , 2003,
Abstract: We present a review of experimental data on the nonlinear optical properties of thermotropic and lyotropic liquid crystals probed by the Z-scan technique. Depending on the time scale, different processes originate a nonlinear optical response. Particularly, at nanosecond range, the physical processes associated with the nonlinear response in thermotropics are not completely understood. In lyotropics, the nonlinear response at ms time scale is from thermal origin and depends on the particular mesophase, relative concentration of the components, and temperature.
Optical, magnetic and dielectric properties of non-liquid crystalline elastomers doped with magnetic colloids
Figueiredo Neto, A.M.;Godinho, M.H.;Toth-Katona, T.;Palffy-Muhoray, P.;
Brazilian Journal of Physics , 2005, DOI: 10.1590/S0103-97332005000100016
Abstract: magnetic nanoparticles from magnetic colloidal suspensions were incorporated in the urethane/urea elastomer (pu/pbdo) by swelling fully crosslinked elastomer samples with a toluene and ferrofluid mixture. it is shown that ferrofluid grains can be efficiently incorporated into the matrix of elastomers. the dependence of the birefringence of both the pure and ferrofluid-doped elastomer samples on strain is linear. the ratio of birefringence to strain of the ferrofluid-doped samples is greater than that of the pure elastomer samples, indicating that ferrofluid grains are oriented by the strained polymer network. we propose that this strain-induced orientation is due to the shape anisotropy of the nanoparticles.
Evaluation of Corrosion Behavior of Copper in Chloride Media Using Electrochemical Impedance Spectroscopy (EIS)
Nagiub,A.M.;
Portugaliae Electrochimica Acta , 2005,
Abstract: the corrosion behavior of pure copper rotating cylinder electrode (rce) exposed to 3% nacl or artificial seawater prepared as v?t??nen nine salt solution (vnss) has been studied using electrochemical impedance spectroscopy (eis) and polarization techniques. eis experiments for copper rce were carried out at different rotation rate from 0 rpm to 1600 rpm. polarization resistance (rp) values were obtained from both eis and polarization experiments. excellent agreement between impedance and polarization data is observed. rce experiments demonstrated that ecorr and corrosion rate for copper depend linearly on rotation speed r0.7. the results obtained showed that eis is a powerful electrochemical method to follow the change of corrosion mechanisms.
LAPAROSCOPIC ILEAL LOOP CONDUIT: AN EXPERIMENTAL STUDY IN DOGS
A.M. SHOMA
African Journal of Urology , 2002,
Abstract: Objective This experimental study in dogs aimed at establishing a technique for laparoscopic construction of an ileal loop conduit for urinary diversion. Material and Methods Eight mongrel dogs were included in the study. All of them were subjected to preoperative intravenous urography (IVU) for evaluation of the upper urinary tract. In the first four dogs (Group I) ileal loop conduits were constructed via a transperitoneal approach with implantation of the right ureter only to the newly fashioned conduit. Group II consisted of another four dogs in which the conduits were created and both ureters were reanastomosed to their walls. All procedures were done laparoscopically. Postoperatively, all dogs were evaluated using IVU and diuretic renography. The conduits were further evaluated by loopograms. Results Open conversion was not necessary in any animal. The mean operative time was 5 ± 1.5 hours and 4 ± 0.5 hours for Groups I and II, respectively. One dog of Group I died postoperatively because of urinary leakage. Thus, only three units were evaluable. Two of them showed a perfect configuration on IVU film, while a ureteroileal stricture was detected in one. Mean renographic clearance was 55 ± 10.5 ml/minute. Eight renal units could be assessed in Group II. All showed perfect postoperative configurations during radiological assessment with a mean renographic clearance of 56 ± 8 ml/minute. The loopograms showed adequately fashioned conduits in all dogs with no leakage. Conclusion This experimental study confirmed the feasibility of laparoscopic ileal conduit construction with a satisfactory outcome. Although technically challenging, ongoing technical refinements will make the performance of reconstructive laparoscopy more widely acceptable. La Dérivation Cutanée Trans-Intestinale par Voie Laparoscopique: Une Etude Expérimentale chez le Chien Objectif Cette étude expérimentale avait pour but d'établir une technique pour la confection par voie laparoscopique d'une dérivation urinaire trans-intestinale. Matériel et Méthodes Huit chiens de race Mongrel ont été inclus dans cette étude. Tous ont eu une urographie intra-veineuse (UIV) pour l'évaluation de leur haut appareil urinaire. Chez les 4 premiers chiens (Group I) la dérivation a été réalisée par voie trans-péritonéale avec implantation de l'uretère droit seul dans le conduit nouvellement confectionné. Le groupe II comprenait 4 chiens chez lesquels les conduits étaient crées et les deux uretères anastomosés dans la paroi. Toutes les opérations ont été réalisées par voie laparoscopique. En post-opératoire, tous les chiens ont été évalués par UIV et néphrographie aux diurétiques. Les conduits de dérivation ont été évalués par opacification de l'anse de dérivation. Résultats Une conversion en chirurgie ouverte n'a été nécessaire chez aucun animal. La durée moyenne de l'opération était de 5 ± 1.5 heures et 4 ± 0.5 heures pour les groupes I et II respective-ment. Un des chiens du groupe I décéda en post-
Computer simulation of modulated two-beam interference using monochromatic light
A.M. Hamed
Optica Applicata , 2004,
Abstract: Two different models are suggested to describe the fringe shift obtained from the two beam interference modulated by the phase variations of transparent objects. The first model of the fringe shift assumes a linear triangular distribution, while the second model varies as a truncated Gauss function. The Abel transform enables computation of the refractive index distribution from the theoretical data of the fringe shift. The fringe shift of the phase object is represented in the harmonic term of the intensity distribution formula. A computer program is written to plot both of the fringe shifts of the models described and the corresponding refractive indices of the phase object. Comparative results are cited in the introduction which are based on an algebraic reconstruction technique (ART) using two models; one of them has a cosine phantom field which constructs an asymmetric single peak, while the other model has cosGauss function giving an asymmetric double-peak phantom. These results are compared with our results, which gives only a single peak in both cases of linear and quadratic variations, which is convenient for use in optical fibers.
A demographic model to predict future growth of the Addo elephant population
A.M. Woodd
Koedoe : African Protected Area Conservation and Science , 1999, DOI: 10.4102/koedoe.v42i1.226
Abstract: An age-structured demographic model of the growth of the Addo elephant population was developed using parameters calculated from long-term data on the population. The model was used to provide estimates of future population growth. Expansion of the Addo Elephant National Park is currently underway, and the proposed target population size for elephant within the enlarged park is 2700. The model predicts that this population size will be reached during the year 2043, so that the Addo elephant population can continue to increase for a further 44 years before its target size within the enlarged park is attained.
Intranet/Extranet security
A.M. Niven
South African Journal of Information Management , 2009, DOI: 10.4102/sajim.v2i1.82
Abstract:
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