Thickness effect on electric resistivity on polystyrene and carbon black- based composites

Changes on electrical resistivity were experimentally studied for polystyrene and carbon black-based composites respect to the temperature. 22% w/w carbon black composite films at 30 μm, 2mm y 1cm thick were submitted to thermal heating-cooling cycles from room temperature to 100°C, slightly up to Tg of the composite. For each cycle changes on electrical resistivity constituent a hysteresis loop that depends on the sample thickness. The changes during the heating stage could be explained as a consequence of the thermal expansion and mobility of the polymer chains at Tg, producing a disconnecting of the electrical contacts among carbon black particles and an important increasing (200%) of the electrical resistivity. For each cycle, the hysteresis loop was observed in thicker samples, whereas for 30 ? m thickness sample the hysteresis loop was lost after four cycles.CONACY

Laser ablated carbon nanodots for light emission

The synthesis of fluorescent carbon dots-like nanostructures (CNDs) obtained through the laser ablation of a carbon solid target in liquid environment is reported. The ablation process was induced in acetone with laser pulses of 1064, 532, and 355 nm under different irradiation times. Close-spherical amorphous CNDs with sizes between 5 and 20 nm, whose abundance strongly depends on the ablation parameters were investigated using electron microscopy and was confirmed using absorption and emission spectroscopies. The π- π* electronic transition at 3. 76 eV dominates the absorption for all the CNDs species synthesized under different irradiation conditions. The light emission is most efficient due to excitation at 3.54 eV with the photoluminescence intensity centered at 3. 23 eV. The light emission from the CNDs is most efficient due to ablation at 355 nm. The emission wavelength of the CNDs can be tuned from the near-UV to the green wavelength region by controlling the ablation time and modifying the ablation and excitation laser wavelength

Optical properties of carbon nanostructures produced by laser irradiation on chemically modified multi-walledcarbon nanotubes

Apoyo a la Red Temática de Colaboración Académica: Desarrollo de Materiales Compuestos con propiedades Ópticas, Eléctricas , Magnéticas y sus aplicacionesThis research focused on the nanosecond(Nd:YAG-1064 nm) laser pulse effect on the optical and morphological properties of chemically modified multi-walled carbon nanotubes(MWCNT).Two sus- pensions of MWCNT in tetrahydrofuran (THF) were prepared,one was submitted to laser pulses for 10 min while the other (blank) was only mechanically homogenized during the same time. Following the laser irradiation, the suspension acquired a yellow-amber color,in contrast to the black translucent appearance of the blank. UV-vis spectroscopy confirmed this observation, showing the blank a higher absorption. Additionally, photoluminescence measurements exhibited a broad blue-green emission band both in the blank and irradiated suspension when excited at 369 nm, showing the blank a lower intensity. However, a modification in the excitation wave length produced a violet to green tuningin the irradiated suspension, which did not occurin the blank. Lastly, the electron microscopy analysis of the treated nanotubes showed the abundant formation of amorphous carbon, nanocages, and nanotube unzipping, exhibiting the intense surface modification produced by the laser pulse. Nanotube surface modification and the coexistence with the new carbon nanostructures were considered as the conductive conditions for optical properties modification.PROME

In vitro conservation of Vanilla planifolia hybrids in minimal growth conditions

ABSTRACT Objective: In vitro conservation with minimal growth in interspecific hybrids of Vanilla planifolia. Design / Methodology / Approach: Explants from seven interspecific V. planifolia hybrids were used with parents of different origins. The treatments were different doses of mannitol and sucrose in the culture medium that varied from 0, 5, 10, 15, 20, 25 and 30 g l-1. The number of nodes, shoots and roots was recorded every 30 days for six months. Results: The results indicated that 30 g l-1 of mannitol and without sucrose in the culture medium allowed minimal growth for most hybrids. It was found that with a higher content of mannitol and less sucrose, the length, number of between nodes, shoots and roots of the explants were shorter, results that were different between treatments (P?0.05). Limitations of the study / implications: There is a differential behavior between the biological material and the culture media used, especially when it comes to hybrids due to the new genetic combinations that are generated, so for their conservation the components of the culture medium must be adjusted. Findings/conclusions: It is concluded that the mannitol at 30 g l-1 and without sucrose in the in vitro culture medium of vanilla hybrids is able to reduce its growth significantly during 180 days.Key words: Ex situ conservation, in vitro culture, Vanilla planifolia, mannitol.Objective: To maintain minimal growth in in vitro Vanilla planifolia hybrids. Design/Methodology/Approach: Explants of seven interspecific hybrids of V. planifolia with different origin parents were used. The treatments consisted of different doses of mannitol and sucrose in the culture medium which varied from 0, 5, 10, 15, 20, 25 and 30 g L-1.The number of nodes, shoots and roots was recorded every 30 d for six months. Results: 30 g L-1 mannitol and no sucrose in the culture medium allowed minimal growth in most of the hybrids. The higher the mannitol and lower the sucrose content, the length, number of between nodes, shoots and roots of the explants was lower (P?0.05). Limitations of the study/implications: There is a differential behavior between the biological material and the used culture medium, particularly in hybrids, due to their new genetic combinations. Therefore, for their conservation, the culture medium components must be adjusted. Conclusions: 30 g L-1 mannitol without sucrose in in vitro culture medium significantly reduces growth during 180 d in vanilla hybrids

La vid silvestre en México. Actualidades y potencial

En ocho capítulos se aborda el estado del arte de la vid silvestre en MéxicoEl estudio de las especies vegetales nativas de México representa un reto que cada día más investigadores mexicanos asumen. Durante muchos años, el apoyo a la investigación pública ha sido mínimo; desde el punto de vista agronómico es insuficiente para avanzar a la velocidad que requiere nuestro país para afrontar problemas de producción y distribución de alimentos. Por esa razón, entre otras, me es grato presentar esta obra que compila parte de los trabajos de la Red de Vid Silvestre patrocinada por el Sistema Nacional de Recursos Fitogenéticos (sinarefi) dependiente de la sagarpa; trabajos apuntalados por investigadores que sin pertenecer a la red han colaborado en el estudio de las plantas del género Vitis. En este libro se muestra el potencial del país para aprovechar el recurso vid, empleado desde antes de la conquista española por nativos mexicanos que conocían sus bondades. Es necesario continuar el avance en el conocimiento de este recurso, por ello el presente libro pretende invitar a toda persona interesada en contribuir con el rescate y conservación de las vides mexicanas. Los autores y editores, así como las instituciones en donde laboramos y aquellas que patrocinan estas investigaciones, esperamos se cumpla este objetivo y que el lector, alumno, profesor, investigador, público en general, disfrute esta lectura y, sobre todo, se interese en el recurso VitisSEP, SINAREFI, UAEME

Circulating microRNAs in sera correlate with soluble biomarkers of immune activation but do not predict mortality in ART treated individuals with HIV-1 infection: A case control study

Introduction: The use of anti-retroviral therapy (ART) has dramatically reduced HIV-1 associated morbidity and mortality. However, HIV-1 infected individuals have increased rates of morbidity and mortality compared to the non-HIV-1 infected population and this appears to be related to end-organ diseases collectively referred to as Serious Non-AIDS Events (SNAEs). Circulating miRNAs are reported as promising biomarkers for a number of human disease conditions including those that constitute SNAEs. Our study sought to investigate the potential of selected miRNAs in predicting mortality in HIV-1 infected ART treated individuals. Materials and Methods: A set of miRNAs was chosen based on published associations with human disease conditions that constitute SNAEs. This case: control study compared 126 cases (individuals who died whilst on therapy), and 247 matched controls (individuals who remained alive). Cases and controls were ART treated participants of two pivotal HIV-1 trials. The relative abundance of each miRNA in serum was measured, by RTqPCR. Associations with mortality (all-cause, cardiovascular and malignancy) were assessed by logistic regression analysis. Correlations between miRNAs and CD4+ T cell count, hs-CRP, IL-6 and D-dimer were also assessed. Results: None of the selected miRNAs was associated with all-cause, cardiovascular or malignancy mortality. The levels of three miRNAs (miRs -21, -122 and -200a) correlated with IL-6 while miR-21 also correlated with D-dimer. Additionally, the abundance of miRs -31, -150 and -223, correlated with baseline CD4+ T cell count while the same three miRNAs plus miR- 145 correlated with nadir CD4+ T cell count. Discussion: No associations with mortality were found with any circulating miRNA studied. These results cast doubt onto the effectiveness of circulating miRNA as early predictors of mortality or the major underlying diseases that contribute to mortality in participants treated for HIV-1 infection

Development and Validation of a Risk Score for Chronic Kidney Disease in HIV Infection Using Prospective Cohort Data from the D:A:D Study

Ristola M. on työryhmien DAD Study Grp ; Royal Free Hosp Clin Cohort ; INSIGHT Study Grp ; SMART Study Grp ; ESPRIT Study Grp jäsen.Background Chronic kidney disease (CKD) is a major health issue for HIV-positive individuals, associated with increased morbidity and mortality. Development and implementation of a risk score model for CKD would allow comparison of the risks and benefits of adding potentially nephrotoxic antiretrovirals to a treatment regimen and would identify those at greatest risk of CKD. The aims of this study were to develop a simple, externally validated, and widely applicable long-term risk score model for CKD in HIV-positive individuals that can guide decision making in clinical practice. Methods and Findings A total of 17,954 HIV-positive individuals from the Data Collection on Adverse Events of Anti-HIV Drugs (D:A:D) study with >= 3 estimated glomerular filtration rate (eGFR) values after 1 January 2004 were included. Baseline was defined as the first eGFR > 60 ml/min/1.73 m2 after 1 January 2004; individuals with exposure to tenofovir, atazanavir, atazanavir/ritonavir, lopinavir/ritonavir, other boosted protease inhibitors before baseline were excluded. CKD was defined as confirmed (>3 mo apart) eGFR In the D:A:D study, 641 individuals developed CKD during 103,185 person-years of follow-up (PYFU; incidence 6.2/1,000 PYFU, 95% CI 5.7-6.7; median follow-up 6.1 y, range 0.3-9.1 y). Older age, intravenous drug use, hepatitis C coinfection, lower baseline eGFR, female gender, lower CD4 count nadir, hypertension, diabetes, and cardiovascular disease (CVD) predicted CKD. The adjusted incidence rate ratios of these nine categorical variables were scaled and summed to create the risk score. The median risk score at baseline was -2 (interquartile range -4 to 2). There was a 1: 393 chance of developing CKD in the next 5 y in the low risk group (risk score = 5, 505 events), respectively. Number needed to harm (NNTH) at 5 y when starting unboosted atazanavir or lopinavir/ritonavir among those with a low risk score was 1,702 (95% CI 1,166-3,367); NNTH was 202 (95% CI 159-278) and 21 (95% CI 19-23), respectively, for those with a medium and high risk score. NNTH was 739 (95% CI 506-1462), 88 (95% CI 69-121), and 9 (95% CI 8-10) for those with a low, medium, and high risk score, respectively, starting tenofovir, atazanavir/ritonavir, or another boosted protease inhibitor. The Royal Free Hospital Clinic Cohort included 2,548 individuals, of whom 94 individuals developed CKD (3.7%) during 18,376 PYFU (median follow-up 7.4 y, range 0.3-12.7 y). Of 2,013 individuals included from the SMART/ESPRIT control arms, 32 individuals developed CKD (1.6%) during 8,452 PYFU (median follow-up 4.1 y, range 0.6-8.1 y). External validation showed that the risk score predicted well in these cohorts. Limitations of this study included limited data on race and no information on proteinuria. Conclusions Both traditional and HIV-related risk factors were predictive of CKD. These factors were used to develop a risk score for CKD in HIV infection, externally validated, that has direct clinical relevance for patients and clinicians to weigh the benefits of certain antiretrovirals against the risk of CKD and to identify those at greatest risk of CKD.Peer reviewe

METODOLOGÍA PARA CONFORMAR UNA EMPRESA COMERCIALIZADORA DE PRODUCTOS AGROPECUARIOS COMO ESTRATEGIA PARA EL DESARROLLO DE ZONAS AGRÍCOLAS

This work has as fundamental purpose to establish to a general frame of reference that allow to the small producers to give it a better use to the agricultural products of which it prepares in its production units. Having as objective the following one: To design to plan strategic general to conform a productive company, as well as to provide to reference frame that allows the commercialization of products of a Unit of Agricultural Production. The proposed methodology constitutes a systematic model, which indicates logically and drew each of the actions and steps that must be made to achieve an end, which is the essential and basic detonator, in this case for the conformation of a marketing company of agricultural products to support the development of agricultural areas

Changes in the Electrical Resistivity of Thin-Films for Polymer Composites Induced by Heating-Cooling Cycles

This paper is focus on the analysis of the electrical resistivity of polymer composites respect to the temperature when samples are under heating-cooling cycles in two type of experiments namely: (1) at three different heating rates and (2) an isothermic one. Three different films S1, S2 and S3 of Polystyrene + 22 wt% CB were submitted to several heating-cooling cycles until a reversing processof the resistivity behavior was reached for each film. The heating was performed from room temperature, RT (24 °C) to 120 °C at rates of 1, 2 and 5 °C/min, respectively. A fourth film S4 was exposed to isothermic-heating-cooling cycles, consisting on heat from RT to 120 ºC (at 2 °C/min) and keep the filmat 120 °C for 2.5 hours. The cooling rate was 0.2 °C/min for all samples. Results show that the cycle’s number for reaching the electrical stability of films were strongly dependent on the heating rate more than the kind of process (continuous or isothermic). Main analysis shows that as a lower the heating rate (1 °C/min) the number of heating-cooling cycles for reaching the reversibility (electrical stability) are less (6 cycles in our case) than those for higher heating rates (9 and 12 cycles). Results are explained in terms of the redistribution of carbon black particles due to the composite´s structural and thermal relaxation; in other words the dynamic polymer chain mobility during the heating process and the chain relaxation process during the cooling one

A novel route for the preparation of gold nanoparticles in polycaprolactone nanofibers.

Electrospinning has been recognized as an efficent and relatively simple technique for the preparation of polymer nanofibers, wich can be obtained from micrometic or nanometric scale