842 research outputs found
The thickness of a liquid layer on the free surface of ice as obtained from computer simulation
Molecular dynamic simulations were performed for ice Ih with a free surface
by using four water models, SPC/E, TIP4P, TIP4P/Ice and TIP4P/2005. The
behavior of the basal plane, the primary prismatic plane and of the secondary
prismatic plane when exposed to vacuum was analyzed. We observe the formation
of a thin liquid layer at the ice surface at temperatures below the melting
point for all models and the three planes considered. For a given plane it was
found that the thickness of a liquid layer was similar for different water
models, when the comparison is made at the same undercooling with respect to
the melting point of the model. The liquid layer thickness is found to increase
with temperature. For a fixed temperature it was found that the thickness of
the liquid layer decreases in the following order: the basal plane, the primary
prismatic plane, and the secondary prismatic plane. For the TIP4P/Ice model, a
model reproducing the experimental value of the melting temperature of ice, the
first clear indication of the formation of a liquid layer appears at about -100
Celsius for the basal plane, at about -80 Celsius for the primary prismatic
plane and at about -70 Celsius for the secondary prismatic plane.Comment: 41 pages and 13 figure
A New Species of Agrostis (Poaceae, Pooideae, Poeae, Agrostidinae) from the Andean PĂĄramos of Colombia and Ecuador
Agrostis laegaardii A. M. Molina & RĂșgolo (Poaceae), a new species restricted to the high pĂĄramos from Colombia and Ecuador, is described and illustrated. It is morphologically most similar to A. breviculmis Hitchc. but differs in spikelet length, pedicel apex, glume texture, relative distance between upper glume and floret, lemma and palea length, and the presence of an awn on the lemma. Micromorphology of the spikelet is discussed, and a Trichodium net is reported on the epidermis of the lemma. A distribution map and a key to the Colombian and Ecuadorean species of Agrostis L. with contracted inflorescences are provided.Fil: Palacio, Patricia Candela. Universidad de Buenos Aires. Facultad de AgronomĂa. CĂĄtedra de BotĂĄnica General; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; ArgentinaFil: Molina, Ana M.. Instituto Nacional de TecnologĂa Agropecuaria; ArgentinaFil: RĂșgolo, Zulma Esther. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Instituto de BotĂĄnica Darwinion. Academia Nacional de Ciencias Exactas, FĂsicas y Naturales. Instituto de BotĂĄnica Darwinion; ArgentinaFil: Vega, Andrea Susana. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; Argentina. Universidad de Buenos Aires. Facultad de AgronomĂa. CĂĄtedra de BotĂĄnica General; Argentin
Importance of B4 medium in determining organomineralization potential of bacterial environmental isolates
B4 precipitation medium has been used as the preferred medium for studying mineral precipitation using bacterial strains in vitro since pioneer studies were performed by Boquet and coworkers in 1973. Using this medium, several authors have demonstrated that some environmental isolates were able to precipitate minerals, yet others did not. The main goal of the current study is to understand whether pH and buffer conditions would have a significant effect on mineral precipitation results for environmental isolates grown on B4. For this study, a total of 49 strains isolated from natural environments from Puerto Rico were grown on B4 plates, and their CaCO3 precipitation potential was investigated. Our findings revealed a strong correlation between a lack of CaCO3 precipitation and the acidification of the B4 plates by the colonies. The ability to precipitate CaCO3 could be restored by buffering the B4 medium to a pH of 8.2. Buffering capacity of the medium was proposed to be involved in CaCO3 precipitation: acid-base titrations conducted on the individual ingredients of B4 showed that yeast extract has a poor buffering capacity between pH 6.5?7.5. This pH range corresponds to the pH of B4 plates 6.87 (ĂïżœĂ±0.05)] prior to the inoculation. This might explain why B4 is such a good precipitation medium: a small variation in the H+/OH? balance during microbial growth and precipitation produces rapid changes in the pH of the medium. Finally, an amorphous matrix was distributed within 90% of the examined crystals generated on B4 medium by the environmental strains. Supplemental materials are available for this article. Go to the publisher's online edition of Geomicrobiology Journal to view the free supplemental file.; B4 precipitation medium has been used as the preferred medium for studying mineral precipitation using bacterial strains in vitro since pioneer studies were performed by Boquet and coworkers in 1973. Using this medium, several authors have demonstrated that some environmental isolates were able to precipitate minerals, yet others did not. The main goal of the current study is to understand whether pH and buffer conditions would have a significant effect on mineral precipitation results for environmental isolates grown on B4. For this study, a total of 49 strains isolated from natural environments from Puerto Rico were grown on B4 plates, and their CaCO3 precipitation potential was investigated. Our findings revealed a strong correlation between a lack of CaCO3 precipitation and the acidification of the B4 plates by the colonies. The ability to precipitate CaCO3 could be restored by buffering the B4 medium to a pH of 8.2. Buffering capacity of the medium was proposed to be involved in CaCO3 precipitation: acid-base titrations conducted on the individual ingredients of B4 showed that yeast extract has a poor buffering capacity between pH 6.5?7.5. This pH range corresponds to the pH of B4 plates 6.87 (ĂïżœĂ±0.05)] prior to the inoculation. This might explain why B4 is such a good precipitation medium: a small variation in the H+/OH? balance during microbial growth and precipitation produces rapid changes in the pH of the medium. Finally, an amorphous matrix was distributed within 90% of the examined crystals generated on B4 medium by the environmental strains. Supplemental materials are available for this article. Go to the publisher's online edition of Geomicrobiology Journal to view the free supplemental file
Stress compensation by gap monolayers for stacked InAs/GaAs quantum dots solar cells
In this work we report the stacking of 10 and 50 InAs quantum dots layers using 2 monolayers of GaP for stress compensation and a stack period of 18 nm on GaAs (001) substrates. Very good structural and optical quality is found in both samples. Vertical alignment of the dots is observed by transmission electron microscopy suggesting the existence of residual stress around them. Photocurrent measurements show light absorption up to 1.2 ÎŒm in the nanostructures together with a reduction in the blue response of the device. As a result of the phosphorus incorporation in the barriers, a very high thermal activation energy (431 meV) has also been obtained for the quantum dot emission
Funcionamiento y mantenimiento de molinos de viento
NĂșmero especial de la serie ABC de la tecnologĂa en el que se describen generalidades del molino de viento, tipos de molinos de viento, componentes, funcionamiento, mantenimiento preventivo y reparacionesSpecial number of the ABC series of the technology in which are described generalities of the windmill, types of windmills, components, operation, preventive maintenance and repairsNociones Generales -- DescripciĂłn del molino de viento -- ClasificaciĂłn y usos -- Componentes del molino lento -- Funcionamiento -- Parte Molino en movimiento -- Parte Molino frenado -- Mantenimiento -- Mantenimiento preventivo -- Mantenimiento reparativonaDocumento producto del convenio SENA â Universidad Nacional de Colombia46 pĂĄgina
Pupil size differences between female and male patients after cataract surgery
Purpose To evaluate the changes in pupil diameter in women and men after cataract surgery. The correlation of pupillary changes with the variables age and anterior chamber depth will be analyzed. Methods The values of 109 randomized eyes who underwent cataract surgery were obtained and divided into two groups, 71 women and 38 men. Pupil diameter was measured preoperatively and 3-months postoperatively using the pupillometer software of the Topolyzer Vario (Wavelight Laser Technologie AG). Anterior chamber depth was obtained with PentacamÂź (Oculus). Differences in pupillary diameters were investigated and correlations with age and anterior chamber depth were analyzed. Results For mesopic pupils, the male group had greater reduction in their postoperative pupillary diameter, -0.56 mm (-12.4%), than the female group, -0.38 mm (-8.2%), P = 0.025. Photopic postoperative pupils reduced to a lesser extent, yet more in men than in women (-0.11mm [-4.5%] vs. -0.04 [-1.6%], P = 0.048). Weak significant negative correlation was found between photopic pupillary changes in women with age (r = -0.24, P = 0.041), and positive correlation for mesopic pupillary changes in men with age (r = +0.34, P = 0.039). Conclusions Patients experience pupil reduction after cataract surgery in general, but more in men than in women and for both photopic and mesopic lighting conditions. The differences are statistically significant and have moderate clinical relevance. Concerning pupillary changes, weak but opposite sign correlations were found between male/female gender and age.This work was supported by the Spanish Ministerio de EconomĂa y Competitividad and FEDERfunds under project Ref. DPI2016-76019-RPeer ReviewedPostprint (author's final draft
ACTN3 R577X Polymorphism does not Influence Explosive Leg Muscle Power in Elite Volleyball Players
We examined the association of R577X polymorphism (rs1815739) in the α-actinin-3 (ACTN3) gene with âexplosiveâ leg muscle power performance in a group of male and female elite volleyball players (n=66, 31 men, 35 women) and in a group of non-athletic male and female young adults (n=334, 243 men, 91 women). We assessed power performance by means of the vertical squat and counter-movement jump tests. We also determined whether the genotypic frequencies of the ACTN3 R577X genotypes differed between groups. We did not observe any effect of the ACTN3 R577X polymorphism on study phenotypes in both groups, regardless of gender (all P>0.05). Genotype frequencies were similar between volleyball and control groups (P=0.095). Moreover, we did not find an association between the ACTN3 R577X polymorphism and the likelihood of being an elite volleyball player using the dominant (RR vs RX+XX) and the recessive model (RR+RX vs XX). In summary, these findings suggest that the ACTN3 R577X polymorphism does not influence explosive leg muscle power in elite volleyball players
Benchmarking a wide spectrum of metaheuristic techniques for the radio network design problem
The radio network design (RND) is an NP-hard optimization problem which consists of the maximization of the coverage of a given area while minimizing the base station deployment. Solving RND problems efficiently is relevant to many fields of application and has a direct impact in the engineering, telecommunication, scientific, and industrial areas. Numerous works can be found in the literature dealing with the RND problem, although they all suffer from the same shortfall: a noncomparable efficiency. Therefore, the aim of this paper is twofold: first, to offer a reliable RND comparison base reference in order to cover a wide algorithmic spectrum, and, second, to offer a comprehensible insight into accurate comparisons of efficiency, reliability, and swiftness of the different techniques applied to solve the RND problem. In order to achieve the first aim we propose a canonical RND problem formulation driven by two main directives: technology independence and a normalized comparison criterion. Following this, we have included an exhaustive behavior comparison between 14 different techniques. Finally, this paper indicates algorithmic trends and different patterns that can be observed through this analysis.Publicad
Tolerability Profile and Discontinuation Causes of Sacubitril/Valsartan Treatment in âReal-lifeâ Patients with Heart Failure and Reduced Ejection Fraction
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