RESUMEN
CONTEXT: Graphene has been used as reinforcement of polymeric nanocomposites to increase mechanical and electrical properties. Recently, graphene suspensions have been used for the development of nanofluids in automotive applications, where improvements in convection heat transfer coefficients and pressure drops have been reported. However, dispersions of graphene sheets in a polymeric matrix as well as in a solvent medium are difficult to achieve; that is because Van der Waals, [Formula: see text] and Coulombic interactions cause agglomerations. Surface chemical modifications have been considered as viable options to improve the graphene integration. In this work, we studied the colloidal stability of aqueous solutions of graphene sheets functionalized with (i) carboxylic groups, (ii) 3-amino-propyl tri-ethoxy silane (amphiphilic behavior), (iii) graphene oxide, and (iv) pristine graphene. Results show that the lower sedimentation velocity corresponds to the graphene functionalized with carboxylic groups, which presents the higher colloidal stability. However, the amphiphilic group enhances the interaction energy between graphene and the solvent; we believe that there is a threshold percentage of functionalization that improves the colloidal stability of graphene. METHOD: Transport properties of graphene solutions were estimated by using Non-Equilibrium Molecular Dynamics simulations to generate Poiseuille flow in an NVT ensemble. Simulations were developed in the LAMMPS code. The COMPASS Force Field was used for the graphene systems and the TIP3P for the water molecules. Bonds and angles of hydrogen atoms were kept rigid by using the shake algorithm. The molecular models were built through MedeA and visualized with the Ovito software.
Asunto(s)
Grafito , Simulación de Dinámica Molecular , Agua , Solventes , Algoritmos , PolímerosRESUMEN
OBJECTIVE: To improve understanding of the causes of morbidity and mortality among critically ill children in the countries studied. DESIGN: Survey of hospital records between 1992 and 1994. SETTING: Six pediatric intensive care units (ICUs) (four ICUs in Mexico City and two ICUs in Ecuador). PATIENTS: Consecutive patients (n = 1,061) admitted to the units studied. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: The mortality rate for low-risk patients (pediatric Risk of Mortality [PRISM] score of < or = 10, n = 701) was more than four times the rate predicted by the PRISM score (8.1% vs. 1.8%, p < .001), with an additional 11.3% of this group incurring major morbidity. The mortality rate for moderate-risk patients (PRISM scores of 11 to 20, n = 232) was more than twice predicted (28% vs. 12%, p < .001). For low-risk patients, death was significantly associated with tracheal intubation, central venous cannulation, pneumonia, age of < 2 months, use of more than two antibiotics, and nonsurgical diagnosis (after controlling for PRISM score). Central venous cannulation and tracheal intubation in the lower-risk groups were performed more commonly in units in Mexico than in one comparison unit in the United States (p < .001). CONCLUSIONS: For six pediatric ICUs in Mexico and Ecuador, mortality was significantly higher than predicted among lower-risk patients. Tracheal intubation, central catheters, pneumonia, sepsis, and nonsurgical status were associated with poor outcome for low-risk groups. We speculate that reducing the use of invasive central catheters and endotracheal intubation for lower-risk patients, coupled with improved infection control, could lower mortality rates in the population studied.
Asunto(s)
Enfermedad Crítica/terapia , Mortalidad Hospitalaria , Unidades de Cuidado Intensivo Pediátrico/normas , Evaluación de Resultado en la Atención de Salud , Índice de Severidad de la Enfermedad , Preescolar , Cuidados Críticos , Enfermedad Crítica/mortalidad , Ecuador , Humanos , Lactante , México , Oportunidad Relativa , Valor Predictivo de las Pruebas , Estudios Prospectivos , Factores de RiesgoRESUMEN
Twenty-six adults with acute bacterial meningitis were enrolled in an open randomized comparative study. The organisms isolated from CSF were Streptococcus pneumoniae, Staphylococcus epidermidis, Haemophilus influenzae, Escherichia coli and Salmonella typhi. 13 patients (group A) were treated once daily with intravenous ceftriaxone (Rocephin). The 13 patients in group B received ampicillin or ampicillin plus chloramphenicol in 4 doses/day. The mean duration of therapy in groups A and B was 9.9 and 12.3 days, respectively. This difference in the duration of therapy was statistically significant. All patients from group A showed clinical improvement and all were bacteriologically cured. In group B only 12 patients were clinically and bacteriologically cured; 1 patient had to be withdrawn from the therapy because CSF culture remained positive after 48 h of therapy. Ceftriaxone was well tolerated in all patients; ampicillin or ampicillin plus chloramphenicol were associated with diarrhea and skin rash in 6 patients.