Fluctuations and Pattern Formation in Fluids with Competing Interactions

One of the most interesting phenomena in the soft-matter realm consists in the spontaneous formation of super-molecular structures (microphases) in condition of thermodynamic equilibrium. A simple mechanism responsible for this self-organization or pattern formation is based on the competition between attractive and repulsive forces with different length scales in the microscopic potential, typically, a short-range attraction against a longer-range repulsion. We analyse this problem by simulations in 2D fluids. We find that, as the temperature is lowered, liquid-vapor phase separation is inhibited by the competition between attraction and repulsion, and replaced by a transition to non-homogeneous phases. The structure of the fluid shows well defined signatures of the presence of both intra- and inter-cluster correlations. Even when the competition between attraction and repulsion is not so strong as to cause microphase formation, it still induces large density fluctuations in a wide region of the temperature-density plane. In this large-fluctuation regime, pattern formation can be triggered by a weak external modulating field.Comment: To appear in the proceedings of the "International workshop on collective phenomena in macroscopic systems", 2006 Villa Olmo (Como), Ital

Force calculation on walls and embedded particles in multiparticle collision dynamics simulations

Colloidal solutions posses a wide range of time and length scales, so that it is unfeasible to keep track of all of them within a single simulation. As a consequence some form of coarse-graining must be applied. In this work we use the Multi-Particle Collision Dynamics scheme. We describe a particular implementation of no-slip boundary conditions upon a solid surface, capable of providing correct force s on the solid bypassing the calculation of the velocity profile or the stre ss tensor in the fluid near the surface. As an application we measure the friction on a spherical particle, when it is placed in a bulk fluid and when it is confined in a slit. We show that the implementation of the no-slip boundary conditions leads to an enhanced Ensko g friction, which can be understood analytically. Because of the long-range nature of hydrodynamic interactions, the Stokes friction obtained from the simulations is sensitive of the simulation box size. We address this topic for the slit geometry, showing that that the dependence on the system size differs very much from what is expected in a 3D system, where periodic boundary conditions are used in all directions.Comment: To appear in Physical Review

Mode-coupling theory predictions for a limited valency attractive square-well model

Recently we have studied, using numerical simulations, a limited valency model, i.e. an attractive square well model with a constraint on the maximum number of bonded neighbors. Studying a large region of temperatures $T$ and packing fractions $\phi$, we have estimated the location of the liquid-gas phase separation spinodal and the loci of dynamic arrest, where the system is trapped in a disordered non-ergodic state. Two distinct arrest lines for the system are present in the system: a {\it (repulsive) glass} line at high packing fraction, and a {\it gel} line at low $\phi$ and $T$. The former is essentially vertical ($\phi$-controlled), while the latter is rather horizontal ($T$-controlled) in the $(\phi-T)$ plane. We here complement the molecular dynamics results with mode coupling theory calculations, using the numerical structure factors as input. We find that the theory predicts a repulsive glass line -- in satisfactory agreement with the simulation results -- and an attractive glass line which appears to be unrelated to the gel line.Comment: 12 pages, 6 figures. To appear in J. Phys. Condens. Matter, special issue: "Topics in Application of Scattering Methods for Investigation of Structure and Dynamics of Soft Condensed Matter", Fiesole, November 200

Brazilian version of the Berg balance scale

The purpose of the present study was to translate and adapt the Berg balance scale, an instrument for functional balance assessment, to Brazilian-Portuguese and to determine the reliability of scores obtained with the Brazilian adaptation. Two persons proficient in English independently translated the original scale into Brazilian-Portuguese and a consensus version was generated. Two translators performed a back translation. Discrepancies were discussed and solved by a panel. Forty patients older than 65 years and 40 therapists were included in the cultural adaptation phase. If more than 15% of therapists or patients reported difficulty in understanding an item, that item was reformulated and reapplied. The final Brazilian version was then tested on 36 elderly patients (over age 65). The average age was 72 years. Reliability of the measure was assessed twice by one physical therapist (1-week interval between assessments) and once by one independent physical therapist. Descriptive analysis was used to characterize the patients. The intraclass correlation coefficient (ICC) and Pearson's correlation coefficient were computed to assess intra- and interobserver reliability. Six questions were modified during the translation stage and cultural adaptation phase. The ICC for intra- and interobserver reliability was 0.99 (P < 0.001) and 0.98 (P < 0.001), respectively. The Pearson correlation coefficient for intra- and interobserver reliability was 0.98 (P < 0.001) and 0.97 (P < 0.001), respectively. We conclude that the Brazilian version of the Berg balance scale is a reliable instrument to be used in balance assessment of elderly Brazilian patients.Universidade Federal de São Paulo (UNIFESP) Escola Paulista de Medicina Disciplina de ReumatologiaUniversidade Federal de São Paulo (UNIFESP) Escola Paulista de Medicina Disciplina de GeriatriaMcGill University Division of Physical and Occupational TherapyUNIFESP, EPM, Disciplina de ReumatologiaUNIFESP, EPM, Disciplina de GeriatriaSciEL

Fluid-fluid demixing transitions in colloid--polyelectrolyte star mixtures

We derive effective interaction potentials between hard, spherical colloidal particles and star-branched polyelectrolytes of various functionalities and smaller size than the colloids. The effective interactions are based on a Derjaguin-like approximation, which is based on previously derived potentials acting between polyelectrolyte stars and planar walls. On the basis of these interactions we subsequently calculate the demixing binodals of the binary colloid--polyelectrolyte star mixture, employing standard tools from liquid-state theory. We find that the mixture is indeed unstable at moderately high overall concentrations. The system becomes more unstable with respect to demixing as the star functionality and the size ratio grow.Comment: 24 pages, 9 figures, submitted to Journal of Physics: Condensed Matte

Assessment of quality of life, muscle strength and functional capacity in women with fibromyalgia

OBJECTIVE: To assess the quality of life, muscle strength and functional capacity in women with fibromyalgia (FM). PATIENTS AND METHODS: Cross-sectional study carried out with 31 female volunteers (age range, 35 to 60 years), paired in two groups (16 with FM, and 15 in the control group). Both groups underwent the following assessments: one-repetition maximum (1RM) of knee flexors and extensors; quality of life (application of the SF-36 questionnaire); 6-minute walk test (6MWT); pinch strengths (tripod, pulp-to-pulp, and key) and handgrip strength. RESULTS: A significant difference between the groups was observed in the following variables: handgrip strength; pulp-to-pulp and tripod pinch strength of both hands; and the 1RM test of knee flexors and extensors in both limbs (P 0.05). The 6MWT also showed a statistical difference between the groups (P 0,05). O TC6 também mostrou uma diferença estatística entre os grupos (P < 0,01). Já no SF-36, observou-se que mulheres com FM têm redução da capacidade funcional, aumento de dor e piora do estado geral de saúde (P < 0,05). CONCLUSÃO: Os resultados revelam redução da força muscular em membros superiores e inferiores, redução na distância percorrida durante o TC6 em mulheres com FM e também da qualidade de vidaUNIFESPUNIFESP Departamento de Ciências da SaúdeUNIFESP, Depto. de Ciências da SaúdeSciEL

Fiber optical parametric amplifer for chirped pump pulses

LAUREA MAGISTRALELo scopo finale di questa tesi è di presentare la realizzazione di nuovi modelli di amplificatori fotonici a banda ultra-larga e frequenza di ripetizione ultra-alta notevolmente superiori ai modelli attuali. In questo progetto sono combinate tecniche innovative di laser in fibre robuste a alta frequenza di ripetizione e tecniche di ottica non-lineare a banda ultra larga che permettono di risolvere i limiti dei materiali tradizionali di lunghezza d’onda e larghezza dello spettro. Il processo generale sfruttato è basato su amplificazione parametrica ottica in fibra utilizzando impulsi di pompa chirpati. L’intero processo si basa su effetti non lineari del terzo ordine che permettono di ottenere alti guadagni con una larga banda spettrale. Le proprietà di due di due distinti impulsi laser, alta energia e banda stretta per la pompa e larga banda e bassa energia per il segnale, sono quindi combinate insieme attraverso un processo di “4-wave-mixing” in condizione di “phase matching” permettendo di generare l’impulso ottimale a larga banda e alta energia. Il trasferimento di energia tra i due impulsi avviene utilizzando una fibra a cristalli fotonici. L’impulso di pompa viene generato da un amplificatore in fibra dopata all’itterbio per sfruttare le sue caratteristiche di alta frequenza di ripetizione e energia. Il segnale a sua volta è allargato tramite effetti non lineari e poi ricompresso a termine del processo per eliminare contributi spuri alla fase spettrale generati durante il processo di amplificazione. In conclusione questa tesi mostra come tale esperimento permette di amplificare impulsi ultrabrevi fino a 30 fs senza allargarne la durata temporale.The broad aim of this thesis is to present the study and development of new kinds of ultra-broad band photonic amplifiers at ultra-high repetition rate that are able to operate well beyond the current state-of-the-art. In the project, are combined new techniques based on compact, robust high repetition rate fiber lasers and ultra-broad band nonlinear optical techniques that elegantly circumvent the bandwidth and wavelength limitation of traditional material. The exploited general principle is based on optical parametric amplification of chirped pulses with a broad band in a fiber. The process relies on the third-order nonlinearity, which can provide both large gain bandwidth and high gain values in a compact, rugged geometry. The useful properties of two distinct laser pulses (one high energy but narrow bandwidth, the other broad spectrum but low energy) are “combined” to engineer a “perfect” targeted pulse (high energy and broad spectrum) through a phase-matched four wave mixing process. The instantaneous energy transfer from an intense pump pulse with narrow bandwidth to a low energy broad bandwidth pulse is achieved by using a photonic crystal fiber. The intense pump is usually generated by an ytterbium doped fiber amplifier to benefit from its high repetition rate and high energy. The signal is stretched beforehand to avoid optical damage in the fiber and then recompressed after amplification since spurious phase generated during the amplification process. This thesis shows in conclusion as such project allows to amplify ultra-fast pulses up to 30 fs without broadening their duration

The impact of network formation on technology use among female headed households in rural Southern Philippines

This study was undertaken to investigate the farming activities of female headed households in the Philippines. In particular. how resource-poor households utilize networks to access resources and technology;To accomplish the above purpose, a survey questionnaire was prepared in the Department of Sociology in Iowa State University. After approval. it was translated and taken to the sampled 8 rural barrios which had previously been stratified according to population and migration status. All female heads of households in these barrios were interviewed by females who were residents of the barrios;Results indicate that FHHs\u27 and households\u27 characteristics are important factors in accessing resources and technology. Among these characteristics are parental land status, origin, age, education and marital status of FHHs, household size and male:female ratio. Specifically, young FHHs had many laborers even if they did not join rotational work groups. FHHs with high educational attainment who joined agricultural related associations had high income. With the husband present, households had high income and consumed more harvested produce. Larger households had higher income when the FHHs joined many associations or when they joined rotational work groups;The advantage in joining agricultural related associations was qualified by the positive relationship with animals raised, value of harvest consumed and higher income. Likewise, joining few associations was related to more draft animals owned and the use of indigenous technology;Rotation work groups complemented the use of indigenous technology which was associated with larger household size that promoted the cultivation of more land. Similar to indigenous technology, attendance in training had a positive effect on cultivated area. Training benefit was also enhanced if this was conducted in small groups. On the other hand, extension visit was dysfunctional in that households that were not visited had higher income and consumed more harvested produce;On the basis of the results, two middle ranged theories are proposed. These are the theory of social loss and the religious connectivity theory