Ion condensation on charged patterned surfaces

We study ion condensation onto a patterned surface of alternating charges. The competition between self-energy and ion-surface interactions leads to the formation of ionic crystalline structures at low temperatures. We consider different arrangements of underlying ionic crystals, including single ion adsorption, as well as the formation of dipoles at the interface between charged domains. Molecular dynamic simulation illustrates existence of single and mixed phases. Our results contribute to understanding pattern recognition, and molecular separation and synthesis near patterned surfaces.Comment: 3 figure

Electrostatic attraction between cationic-anionic assemblies with surface compositional heterogeneities

Electrostatics plays a key role in biomolecular assembly. Oppositely charged biomolecules, for instance, can co-assembled into functional units, such as DNA and histone proteins into nucleosomes and actin-binding protein complexes into cytoskeleton components, at appropriate ionic conditions. These cationic-anionic co-assemblies often have surface charge heterogeneities that result from the delicate balance between electrostatics and packing constraints. Despite their importance, the precise role of surface charge heterogeneities in the organization of cationic-anionic co-assemblies is not well understood. We show here that co-assemblies with charge heterogeneities strongly interact through polarization of the domains. We find that this leads to symmetry breaking, which is important for functional capabilities, and structural changes, which is crucial in the organization of co-assemblies. We determine the range and strength of the attraction as a function of the competition between the steric and hydrophobic constraints and electrostatic interactions.Comment: JCP June/200

Pattern formation on the surface of cationic-anionic cylindrical aggregates

Charged pattern formation on the surfaces of self--assembled cylindrical micelles formed from oppositely charged heterogeneous molecules such as cationic and anionic peptide amphiphiles is investigated. The net incompatibility $\chi$ among different components results in the formation of segregated domains, whose growth is inhibited by electrostatics. The transition to striped phases proceeds through an intermediate structure governed by fluctuations, followed by states with various lamellar orientations, which depend on cylinder radius $R_c$ and $\chi$. We analyze the specific heat, susceptibility $S(q^*)$, domain size $\Lambda=2\pi/q^*$ and morphology as a function of $R_c$ and $\chi$.Comment: Sent to PRL 11Jan05 Transferred from PRL to PRE 10Jun0

Effects of Colored Light on Growth and Nutritional Composition of Tilapia, and Biofloc as a Food Source

Light stimulation and biofloc technology can be combined to improve the efficiency and sustainability of tilapia production. A 73-day pilot experiment was conducted to investigate the effect of colored light on growth rates and nutritional composition of the Nile tilapia fingerlings (Oreochromis niloticus) in biofloc systems. The effect of colored light on the nutritional composition of bioflocs as a food source for fish was measured. Three groups were illuminated in addition to natural sunlight with colored light using RGB light emitting diodes (LEDs) with peak wavelengths ( ) of 627.27 nm for red (R), 513.33 nm for green (G), and 451.67 nm for blue (B) light. LED light intensity was constant (0.832 mW/cm2), and had an 18-h photoperiod of light per day throughout the study. The control group was illuminated only with natural sunlight (natural). Tilapia had an average initial weight of 0.242 g. There was a significant effect of colored light on tilapia growth and composition. The R group showed the best growth rate, highest survival, and highest lipid content. The B group showed homogeneous growth with the lowest growth rate and lipid content, but the highest protein level. On the other hand, the biofloc composition was influenced by the green light in the highest content of lipids, protein, and nitrogen-free extract

Attractive Interactions Between Rod-like Polyelectrolytes: Polarization, Crystallization, and Packing

We study the attractive interactions between rod-like charged polymers in solution that appear in the presence of multi-valence counterions. The counterions condensed to the rods exhibit both a strong transversal polarization and a longitudinal crystalline arrangement. At short distances between the rods, the fraction of condensed counterions increases, and the majority of these occupy the region between the rods, where they minimize their repulsive interactions by arranging themselves into packing structures. The attractive interaction is strongest for multivalent counterions. Our model takes into account the hard-core volume of the condensed counterions and their angular distribution around the rods. The hard core constraint strongly suppresses longitudinal charge fluctuations.Comment: 4 figures, uses revtex, psfig and epsf. The new version contains a different introduction, and the bibliography has been expande

Rumo a uma caracterização da competência algébrica: Um estudo exploratório com estudantes

[Objetivo] El presente artículo tiene por objetivo evidenciar la competencia algebraica exhibida por un grupo de 27 estudiantes de universidad, en México, al trabajar con una tarea algebraica. Para esto se propone, desde las investigaciones de la competencia matemática y los niveles de algebrización, un marco para su estudio articulado en tres acciones: resolver, interpretar y validar. [Metodología]La investigación fue de corte cualitativa y exploratoria con una selección de estudiantes de tipo incidental, la implementación de la tarea se llevó a cabo durante una clase habitual con duración de dos horas. El profesor titular y el investigador estuvieron presentes durante el desarrollo de la tarea en el aula. [Resultados] Los resultados muestran que estos estudiantes presentan dificultades en la acción de resolver dado que no manipulan eficazmente expresiones simbólico-literales y no alcanzan el nivel de algebrización esperado. También, presentan inconsistencias en la acción de interpretar, es decir, no identifican ni conectan los conocimientos sobre las propiedades de las operaciones que se ponen en juego en la tarea algebraica. En la acción de validar, comunican comprobaciones o verificaciones de carácter descriptivo. [Conclusiones] Los hallazgos sugieren que la mayoría de los participantes no alcanzaron un primer nivel de competencia algebraica y se plantea la necesidad de formular estadios de desarrollo basados en las tres acciones.[Objective] The present article seeks to determine the algebraic competence displayed by a group of 27 university students in Mexico when they worked on an algebraic problem. A study framework is proposed based on the investigation of mathematical competence and levels of algebrization  in three areas: solving, interpreting and validating. [Methodology] A qualitative and exploratory study with convenience-based selection of students was implemented during a regular two-hour class. The professor and the researcher were present when the task was carried out in the classroom. [Results] The results show that the students had difficulties in problem solving because they did not effectively manipulate symbolic-literal expressions, and did not achieve the expected level of algebraization. They were also inconsistent in interpreting the task – that is, they did not identify or connect knowledge about the properties of the operations necessary to solve the algebraic problem. When validating their responses, they provided descriptive proofs or verifications. [Conclusions] The findings suggest that most of the participants did not display a basic level of algebraic competence, and the necessity of formulating stages of development based on the three actions is discussed.[Objetivo] O objetivo deste artigo é demonstrar a competência algébrica exposta por um grupo de 27 estudantes universitários no México quando se trabalha com uma tarefa algébrica. Para este fim, propomos, a partir da pesquisa sobre competência matemática e níveis de algebrização, uma estrutura para seu estudo articulada em três ações: resolver, interpretar e validar. [Metodologia] A pesquisa foi de coorte qualitativa e exploratória com uma seleção incidental de estudantes, a implementação da tarefa foi realizada durante uma aula regular com duração de duas horas. O professor principal e o pesquisador estiveram presentes durante o desenvolvimento da tarefa na sala de aula. [Resultados] Os resultados mostram que estes estudantes apresentam dificuldades na ação de resolver, uma vez que não manipulam efetivamente as expressões simbólico-literárias e não atingem o nível de algebrização esperado. Além disso, mostram inconsistências na ação de interpretar, ou seja, não identificam e nem conectam o conhecimento sobre as propriedades das operações em jogo na tarefa algébrica. Na ação de validar, eles relatam testes ou verificações de caráter descritivo. [Conclusões] As constatações sugerem que a maioria dos participantes não atingiu um primeiro nível de competência algébrica e surge a necessidade de formular etapas de desenvolvimento com base nas três ações

Depression in Mexican Americans with Diagnosed and Undiagnosed Diabetes

Background: Depression and diabetes commonly co-occur; however, the strength of the physiological effects of diabetes as mediating factors towards depression is uncertain. Method: We analyzed extensive clinical, epidemiological and laboratory data from n = 2081 Mexican Americans aged 35-64 years, recruited from the community as part of the Cameron County Hispanic Cohort (CCHC) divided into three groups: Diagnosed (self-reported) diabetes (DD, n = 335), Undiagnosed diabetes (UD, n = 227) and No diabetes (ND, n = 1519). UD participants denied being diagnosed with diabetes, but on testing met the 2010 American Diabetes Association and World Health Organization definitions of diabetes. Depression was measured using the Center for Epidemiological Studies - Depression (CES-D) scale. Weighted data were analyzed using dimensional and categorical outcomes using univariate and multivariate models. Results: The DD group had significantly higher CES-D scores than both the ND and UD (p ⩽ 0.001) groups, whereas the ND and UD groups did not significantly differ from each other. The DD subjects were more likely to meet the CES-D cut-off score for depression compared to both the ND and UD groups (p = 0.001), respectively. The UD group was also less likely to meet the cut-off score for depression than the ND group (p = 0.003). Our main findings remained significant in models that controlled for socio-demographic and clinical confounders. Conclusions: Meeting clinical criteria for diabetes was not sufficient for increased depressive symptoms. Our findings suggest that the \u27knowing that one is ill\u27 is associated with depressive symptoms in diabetic subjects

Depression, Obesity, and Metabolic Syndrome: Prevalence and Risks of Comorbidity in a Population-Based Study of Mexican Americans

Introduction: We examined the prevalence of depression, obesity, and metabolic syndrome and associations between them in a population-based representative cohort of Mexican Americans living on the United States-Mexico border. Method: The sample in this cross-sectional analysis consisted of 1,768 Mexican American adults (≥ 18 years of age) assessed between the years 2004 and 2010, with whom we tested our central hypothesis of a significant relationship between obesity and depression. Depression was measured using the Center for Epidemiologic Studies-Depression scale (CES-D) with a cutoff score of ≥ 16 for depression and a cutoff score of ≥ 27 for severe depression. We categorized body mass index (BMI) values as obese (≥ 30kg/m(2)) and later subdivided the obese subjects into obese (30-39 kg/m(2)[inclusive]) and morbidly obese (≥ 40 kg/m(2)). Metabolic syndrome was defined using the American Heart Association definition requiring at least 3 of the following: increased waist circumference, elevated triglycerides, reduced high-density lipoprotein (HDL) cholesterol, elevated blood pressure, and elevated fasting glucose. Weighted data were analyzed to establish prevalence of depression, obesity, and metabolic syndrome. Univariate and multivariable weighted regression models were used to test potential associations between these disorders. Results: Using weighted prevalence, we observed high rates of depression (30%), obesity (52%), and metabolic syndrome (45%). Univariate models revealed female gender (P = .0004), low education (P = .003), low HDL level (P = .009), and increased waist circumference (P = .03) were associated with depression. Female gender (P = .01), low education (P = .003), and morbid obesity (P = .002) were risk factors for severe depression and remained significant in multivariable models. Conclusions: In this large cohort of Mexican Americans, obesity, female gender, and low education were identified risk factors for depression. These indicators may serve as targets for early detection, prevention, and intervention in this population