Ligand Interactions and Nanoparticle Shapes Guide the Pathways toward Interfacial Self-Assembly.

Non-equilibrium molecular dynamics simulations are used to probe the driving forces behind the formation of highly ordered, epitaxially connected superlattices of polyhedral-shaped nanoparticles (NPs) at fluid-fluid interfaces. By explicitly modeling coarse-grained ligands that cap the NP surface, it is shown that differences in NP shapes and time-dependent facet-specific ligand densities give rise to drastically different transformation mechanisms. Our results indicate that the extent of screening of the inter-particle interactions by the surrounding solvation environment has a significant impact on reversibility and ultimately the coherence of the final two-dimensional superlattice obtained. For the particle shapes examined, a hexagonal pre-assembly and a square superlattice final assembly (upon preferential ligand desorption from {100} facets) were prevalent; however, cuboctahedral NPs formed intermediate epitaxially bonded branched clusters, which eventually grew and rearranged into a square lattice; in contrast, truncated octahedral NPs exhibited an abrupt rhombic-to-square transition driven by the clustering of their numerous {111}-ligands that favored the stacking of linear NP rods. To track the incipient order in the system, we also outline a set of novel order parameters that measure the local orientation alignment between nearest-neighbor pairs. The simulation protocols advanced in this work could pave the way forward for exploration of the vast phase space associated with the interfacial self-assembly of NPs.

An Implicit-Solvent Model for the Interfacial Configuration of Colloidal Nanoparticles and Application to the Self-Assembly of Truncated Cubes.

This study outlines the development of an implicit-solvent model that reproduces the behavior of colloidal nanoparticles at a fluid-fluid interface. The center point of this formulation is the generalized quaternion-based orientational constraint (QOCO) method. The model captures three major energetic characteristics that define the nanoparticle configuration-position (orthogonal to the interfacial plane), orientation, and inter-nanoparticle interaction. The framework encodes physically relevant parameters that provide an intuitive means to simulate a broad spectrum of interfacial conditions. Results show that for a wide range of shapes, our model is able to replicate the behavior of an isolated nanoparticle at an explicit fluid-fluid interface, both qualitatively and often nearly quantitatively. Furthermore, the family of truncated cubes is used as a test bed to analyze the effect of changes in the degree of truncation on the potential-of-mean-force landscape. Finally, our results for the self-assembly of an array of cuboctahedra provide corroboration to the experimentally observed honeycomb and square lattices.

Entropic self-assembly of freely rotating polyhedral particles confined to a flat interface.

The self-assembly of hard polyhedral particles confined to a flat interface is studied using Monte Carlo simulations. The particles are pinned to the interface by restricting their movement in the direction perpendicular to it while allowing their free rotations. The six different polyhedral shapes studied in this work are selected from a family of truncated cubes defined by a truncation parameter, s, which varies from cubes (s = 0) via cuboctahedra (s = 0.5) to octahedra (s = 1). Our results suggest that shapes with small values of s show square-like behavior whereas shapes with large values of s tend to show more disc-like behavior. At an intermediate value of s = 0.4, the phase behavior of the system shows both square-like and disc-like features. The results are also compared with the phase behavior of 3D bulk polyhedra and of 2D rounded hard squares. Both comparisons reveal key similarities in the number and sequence of mesophases and solid phases observed. These insights on 2D entropic self-assembly of polyhedral particles is a first step toward understanding the self-assembly of particles at fluid-fluid interfaces, which is driven by a complex interplay of entropic and enthalpic forces. A first-order analysis of the particle-surface energies associated with a fluid-fluid interface indicates that such enthalpic interactions will be particularly important in determining particle orientation behavior at low to intermediate concentrations.

Phase behaviour of PMMA-b-PHEMA with solvents methanol and THF: modelling and comparison to the experiment.

Self-consistent field theory is used to model the self-assembly of a symmetric PMMA-block-PHEMA in the presence of two solvents, methanol and tetrahydrofuran (THF). The model predictions are compared to our experimental results of solvent-vapour annealing of thin polymer films, where the sequence of cylinder to gyroid (or micelles) to lamellar phases was found upon increasing the methanol-THF ratio and for particular extents of film swelling. The Hansen solubility parameters are used to estimate the Flory-Huggins interaction parameters (χ) needed in the theoretical model. However, because enacting the experimental range of high (χ)N values is computationally prohibitive, the use of moderate (χ)N values is compensated by employing larger values of the solvent-to-polymer size ratio (α). This approach is validated by showing that the predicted phase diagrams exhibit qualitatively similar trends whether (χ)N or α is increased. Using such an approach, the theory predicts a cylinder to gyroid to lamellar transition on increasing the THF-methanol ratio, a trend consistent with that observed in the experiments.

Mapping potential carbon and timber losses from hurricanes using a decision tree and ecosystem services driver model.

Information on the effect of direct drivers such as hurricanes on ecosystem services is relevant to landowners and policy makers due to predicted effects from climate change. We identified forest damage risk zones due to hurricanes and estimated the potential loss of 2 key ecosystem services: aboveground carbon storage and timber volume. Using land cover, plot-level forest inventory data, the Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) model, and a decision tree-based framework; we determined potential damage to subtropical forests from hurricanes in the Lower Suwannee River (LS) and Pensacola Bay (PB) watersheds in Florida, US. We used biophysical factors identified in previous studies as being influential in forest damage in our decision tree and hurricane wind risk maps. Results show that 31% and 0.5% of the total aboveground carbon storage in the LS and PB, respectively was located in high forest damage risk (HR) zones. Overall 15% and 0.7% of the total timber net volume in the LS and PB, respectively, was in HR zones. This model can also be used for identifying timber salvage areas, developing ecosystem service provision and management scenarios, and assessing the effect of other drivers on ecosystem services and goods.

Neurocysticercosis: validity of ELISA after storage of whole blood and cerebrospinal fluid on paper.

Cysticercosis is an infestation of Cysticercus cellulosae. When it occurs in the brain, chronic neurological complications can ensue, most commonly seizures. Neurocysticercosis is usually diagnosed by neuroimaging, a technique not available in most endemic countries. Hence immunological tests are valuable for diagnosis and epidemiological surveys. We evaluated the suitability of paper for storing blood and cerebrospinal fluid (CSF) until subsequent testing by enzyme-linked immunosorbent assay (ELISA), by testing whole blood samples on filter paper from 305 patients and CSF samples from 117 patients stored on ordinary white typing paper and on filter paper. Optimal preservation of biological samples is achieved when whole blood is stored on filter paper, CSF on white paper, and when samples are frozen within 1 week after collection. Our results could improve diagnostic capabilities and facilitate epidemiological surveys in endemic countries where immunodiagnostic tests cannot be rapidly performed because of inadequate laboratory infrastructure.

Simulation of phase transitions in fluids.

This review provides a discussion of recent techniques for simulation of phase equilibria of complex fluids. Monte Carlo methods are emphasized over molecular dynamics methods. We describe recent developments, such as the use of expanded-ensemble, tempering, or histogram reweighting techniques. Our discussion of such developments is aimed at a general audience and is intended to provide an overview of the main advantages and limitations of each particular technique. References are provided to allow interested readers to identify and trace back most recent applications of a particular simulation technique. We conclude with general guidelines regarding selection of suitable simulation methods for particular problems and systems of interest.

[Evaluation of hospital emergency service attendance by patients from a basic health district]. / Evaluación de las urgencias hospitalarias desde un área básica de salud (ABS).

OBJECTIVES: To find the sociodemographic characteristics of patients registered at a Health Centre (HC) who attended a hospital Casualty Department, their reasons for attendance, features of their use of facilities and how justified their attendance was. DESIGN: Descriptive study. SETTING: Urban Health Centre, Llefià (Badalona), between February and June, 1995. PARTICIPANTS: We used a questionnaire composed by the research team to survey 360 patients over 14 who attended the HC with a report from a Casualty Department. MEASUREMENTS AND RESULTS: The variables recorded were: sociodemographic characteristics, reasons for attending Casualty, whether they attended on their own initiative, whether they knew about non-hospital Emergencies, the hospital, day and time, chronic pathology, diagnosis and destination on discharge from Casualty, length of stay and justification. 53.7% were women. 57.8% were married. 95% lived with a partner or intimate family member, 56.9% had completed primary education and 39.4% had jobs. 41% suffered a chronic pathology. Monday was the busiest day and physical trauma was the most frequent diagnosis on discharge. We considered 54.7% of all the consultations non-justified emergencies. CONCLUSIONS: There is a high percentage of users who attend Casualty on their own initiative. Most of the emergencies are unjustified.

Comparison of therapeutic regimen of anticysticercal drugs for parenchymal brain cysticercosis.

The efficacy of different regimens of therapy for parenchymal brain cysticercosis either with praziquantel (PZQ) or with albendazole (ALB) was compared in 114 patients. Four schemes of treatment were used: PZQ 50 mg/kg per day for 15 days, PZQ 50 mg/kg per day for 8 days, ALB 15 mg/kg per day for 30 days, and ALB 15 mg/kg per day for 8 days. Three months after therapy, it was apparent that both PZQ and ALB were effective, as shown by the disappearance of cystic lesions in computed tomographic scans. Thirty-three control patients followed for a mean of 11 months had no spontaneous remission of lesions. When comparing PZQ with ALB, the latter was found to be more effective than the former for both the full and the short course of treatment: 85% vs 60% and 85% vs 48% disappearance of lesions, respectively (P less than 0.001). Comparison of the full vs the short course of PZQ showed that the short course had a further 12% reduction in drug effectiveness. In contrast, the length of ALB therapy could be shortened without lessening its efficacy. Based on these results, an 8-day course of ALB is recommended as treatment for parenchymal brain cysticercosis; a 15-day course of PZQ could be subsequently used in those patients who show only partial response to ALB.

Albendazole therapy for human neurocysticercosis, a controlled study with computerized tomography and magnetic resonance.

Until recently, there was no specific pharmacologic treatment for neurocysticercosis (NC). Surgery and steroids were the only medical alternatives for this disorder, which in some areas of the world affects between 3% and 4% of the general population, and in many cases is a major cause of neurologic disability. Praziquantel, an isoquinoline, was the first drug to show a potential efficacy for treatment of NC. In 1984, we reported the therapeutic effectiveness of praziquantel for brain cysticercosis. In this report we present the results of a study of 3 groups of patients treated for parenchymal NC with Albendazole, a benzimidazole active against most intestinal helminths, with proven activity at high doses against human hydatidosis.

Short course of albendazole therapy for neurocysticercosis.

Albendazole is now used for therapy of neurocysticercosis; however, duration of treatment has usually been empirically determined. In this study we shortened the length of therapy from one month in previous reports, to one week. Twelve patients with parenchymal brain cysticercosis were treated with albendazole for eight days at daily doses of 15 mg/kg of body weight. After three months of treatment the number of cysts on computed tomography had decreased from 185 to six; a 97% reduction in the number of lesions. Total remission of all cysts was seen in nine patients. Two cases had been unsuccessfully treated before with praziquantel, in both instances albendazole therapy was effective with 100% improvement. Our results indicated that a short course of albendazole is highly effective for treatment of neurocysticercosis.

Albendazole vs praziquantel for therapy for neurocysticercosis. A controlled trial.

Praziquantel and albendazole have been recently described as effective drugs for treating cysticercosis of the brain. In this study, effectiveness of each drug for therapy for parenchymal brain cysticercosis was compared. Twenty patients were treated either with albendazole or with praziquantel; in addition, five patients were taken as controls and treated only with symptomatic drugs. Three months after therapy, results showed that both drugs, albendazole and praziquantel, were highly effective, as seen by the disappearance of cystic lesions in computed tomographic scans. All lesions in control patients remained unchanged. Albendazole, when compared with praziquantel, showed a 76% vs 73% disappearance of lesions, respectively. It was concluded that both drugs have similar equivalent efficacy and greatly improve the therapeutics of cysticercosis.

Albendazole therapy for neurocysticercosis.

Seven patients with chronic parenchymal brain cysticercosis were treated with albendazole for one month at daily doses of 15 mg/kg of body weight. Computed tomographic follow-up studies were made at the following times: a mean of 16 months before the trial; the beginning of treatment; the end of treatment; and three months afterward. Computed tomographic studies at the beginning of treatment showed a total of 157 cysts, the last day of treatment the number had decreased to 39 cysts, and three months later, the total number of lesions was 22; this represents 86% improvement in the number of cystic lesions. Control studies in the same group of patients had shown chronic persistence of lesions without spontaneous improvement in most cases. Two patients had been treated with praziquantel previously with partial response; in both cases albendazole therapy was effective with 100% and 77% improvement. We conclude that albendazole is highly effective for the treatment of parenchymal brain cysticercosis. It is also effective in patients who had shown poor therapeutic response to praziquantel.

Praziquantel in the treatment of neurocysticercosis: long-term follow-up.

Thirty-five patients with active neurocysticercosis were treated with praziquantel and followed for 1 year after therapy. CT and CSF analysis showed that 91% of patients with parenchymal cysts improved, and 47% of patients with chronic arachnoiditis had remission. A single treatment with praziquantel for 2 weeks, administered in a daily dose of 50 mg/kg of body weight, was highly effective in parenchymal cysticercosis but less effective in meningeal cysticercosis. The benefits were sustained for at least 1 year.