Velocity-dependent friction enhances tribomechanical differences between monolayer and multilayer graphene

The influence of sliding speed in the nanoscale friction forces between a silicon tip and monolayer and multilayer graphene were investigated with the use of an atomic force microscope. We found that the friction forces increase linearly with the logarithm of the sliding speed in a highly layer-dependent way. The increase in friction forces with velocity is amplified at the monolayer. The amplification of the friction forces with velocity results from the introduction of additional corrugation in the interaction potential driven by the tip movement. This effect can be interpreted as a manifestation of local thermally induced surface corrugations in nanoscale influencing the hopping dynamics of the atoms at the contact. These experimental observations were explained by modeling the friction forces with the thermally activated Prandtl-Tomlinson model. The model allowed determination of the interaction potential between tip and graphene, critical forces, and attempt frequencies of slip events. The latter was observed to be dominated by the effective contact stiffness and independent of the number of layers.

Multiple regression analysis to assess the role of plankton on the distribution and speciation of mercury in water of a contaminated lagoon

Spatial and seasonal variation of mercury species aqueous concentrations and distributions was carried out during six sampling campaigns at four locations within Laranjo Bay, the most mercury-contaminated area of the Aveiro Lagoon (Portugal). Inorganic mercury (IHg(II)) and methylmercury (MeHg) were determined in filter-retained (IHgPART, MeHgPART) and filtered (<0.45μm) fractions (IHg(II)DISS, MeHgDISS). The concentrations of IHgPART depended on site and on dilution with downstream particles. Similar processes were evidenced for MeHgPART, however, its concentrations increased for particles rich in phaeophytin (Pha). The concentrations of MeHgDISS, and especially those of IHg(II)DISS, increased with Pha concentrations in the water. Multiple regression models are able to depict MeHgPART, IHg(II)DISS and MeHgDISS concentrations with salinity and Pha concentrations exhibiting additive statistical effects and allowing separation of possible addition and removal processes. A link between phytoplankton/algae and consumers' grazing pressure in the contaminated area can be involved to increase concentrations of IHg(II)DISS and MeHgPART. These processes could lead to suspended particles enriched with MeHg and to the enhancement of IHg(II) and MeHg availability in surface waters and higher transfer to the food web.

Preliminar results of paleontological salvage at Belo Monte Powerplant construction

In this paper some preliminary fossil specimens are presented. They represent a collection sampled by Belo Monte's Programa de Salvamento do Patrimônio Paleontológico (PSPP), which includes unprecedented invertebrate fauna and fossil vertebrates from Pitinga, Jatapu, Manacapuru, Maecuru e Alter do Chão formations from Amazonas basin, Brazil. The Belo Monte paleontological salvage was able to recover 495 microfossil samples and 1744 macrofossil samples on 30 months of sampling activities, and it is still ongoing. The macrofossils identified are possible plant remains, ichnofossils, graptolites, brachiopods, molluscs, athropods, Agnatha, palynomorphs (miosphores, acritarchs, algae cysts, fungi spores and unidentified types) and unidentified fossils. However, deep scientific research is not part of the scope of the program, and this collection must be further studied by researchers who visit Museu Paraense Emilio Goeldi, where the fossils will be housed. More material will be collected until the end of the program. The collection sampled allows a mosaic composition with the necessary elements to assign, in later papers, taxonomic features which may lead to accurate species identification and palaeoenvironmental interpretations.

The use of a Ga+ focused ion beam to modify graphene for device applications

In this work, we clarify the features of the lateral damage of line defects in single layer graphene. The line defects were produced through well-controlled etching of graphene using a Ga(+) focused ion beam. The lateral damage length was obtained from both the integrated intensity of the disorder induced Raman D band and the minimum ion fluence. Also, the line defects were characterized by polarized Raman spectroscopy. It was found that graphene is resilient under the etching conditions since the intensity of the defect induced Raman D peak exhibits a dependence on the direction of the lines relative to the crystalline lattice and also on the direction of the laser polarization relative to the lines. In addition, electrical measurements of the modified graphene were performed. Different ion fluences were used in order to obtain a completely insulating defect line in graphene, which was determined experimentally by means of charge injection and electric force microscopy measurements. These studies demonstrate that a Ga+ ion column combined with Raman spectroscopy is a powerful technique to produce and understand well-defined periodic arrays of defects in graphene, opening possibilities for better control of nanocarbon devices.

A diplotype in the lymphotoxin alpha gene is associated with differential expression of LTA mRNA induced by Gram-positive and Gram-negative bacteria

We sequenced the lymphotoxin alpha (LTA) promoter and identified LTA10G>A in strong linkage with LTA252G>A and LTA723C>A. Stimulated cells from LTA723AA: LTA252GG:LTA10AA individuals had significantly higher LTA mRNA levels than LTA723CC:LTA252AA:LTA10GG and LTA723AA:LTA252AG:LTA10GA individuals, suggesting that this diplotype may contain a functional polymorphism explaining the observed disease associations with LTA252G>A.

Polymorphisms in lymphotoxin alpha and CD14 genes influence TNFalpha production induced by Gram-positive and Gram-negative bacteria

Improved understanding of how host genetic variation affects resistance to microbial pathogens could lead to better treatment and/or prevention of infectious diseases. The lymphotoxin alpha (LTA)+250 and CD14-159 polymorphisms are associated with differences in susceptibility or outcome to several infections. We stimulated peripheral blood mononuclear cells (PBMC) from 22 healthy individuals with purified lipopolysaccharide (LPS), heat-killed Escherichia coli or Streptococcus pneumoniae. TNF alpha intracellular protein levels were measured by flow cytometry and mRNA was quantitated by RT-PCR. TNF alpha mRNA levels were higher in LTA+250GG subjects after 4 h incubation with LPS compared with LTA+250AA (T test, P=0.001). In contrast, after 8 h incubation with S. pneumoniae, there was slightly more TNF alpha mRNA in cells from LTA+250AA subjects. After 4 h incubation with LPS or E. coli, CD14-159TT subjects had higher TNF alpha mRNA levels than CD14-159CC (P=0.05, 0.033, respectively). Neither polymorphism affected the proportion of cells expressing intracellular TNF alpha protein. This suggests that the polymorphisms affected transcription and that other regulatory mechanisms affect production of TNF alpha protein. The effect of these two polymorphisms on TNF alpha mRNA production is stimulus dependent, with opposite effects observed for Gram-positive and Gram-negative stimuli.

[Cerebral venous thrombosis and homocystinuria: case report]

Homocystinuria presenting as cerebral venous thrombosis is not usual. We report on a 13-year-old boy who was admitted to the hospital due to severe headache, nausea, vomiting and fever (38 degrees C). The patient was Marfan like and presented left hemiparesis and meningeal irritation sings. He was mentally retarded, had severe myopia, and had right lens dislocation one month before. Cranial CT scan was suggestive of cerebral venous infarct. MRI and magnetic resonance angiography showed venous infarcts more prominent in the right thalamic projection with hemorrhagic transformation and multiple foci of cortical (occipital and parietal bilaterally) deep parietal and left capsular bleeding, secondary of thrombosis of the transverse and sigmoid venous sinuses. High levels of homocysteine were detected in the blood and urine. Homocystinuria is an autosomal recessive inborn error of methionine metabolism caused by cystathionine-beta-synthase defect in most cases. We discuss the clinical and radiological findings in this patient, analyzing the pathophysiology of the thrombotic events related to homocystinuria.

Considerations on methodology used in the World Health Organization 2000 Report

The article analyzes the World Health Organization Report for 2000, with emphasis placed on the methodology used to analyze the indicators utilized to compare and classify the performance of the health systems of the 191 member countries. The Report's contribution was the compromise of monitoring the performance of the health systems of member countries, but because of the inconsistent way it was elaborated, and the utilization of questionable scientific evaluation methodologies, the Report fails to give a clear picture. A criterion-based methodology revision is imposed. The main problems in evidence are the choice of individual indicators of disparity in health that discount the population profile, the inadequate control of the impact of social disparities over the performance of the systems, the evaluation of the responsibility of systems that are only partially articulated to the right of the citizens, the lack of data for a great number of countries, consequently having inconsistent estimations, and the lack of transparency in the methodological procedures in the calculation of some indicators. The article suggests a wide methodological revision of the Report.

Copper(II) complexation properties and surfactant activity of 3-[N, N-bis(2-hydroxyethyl)amino]-2-hydroxypropanesulfonic acid and N-(2-Hydroxyethyl)piperazine-N'-2-hydroxypropanesulfonic acid pH buffers which may affect trace metal speciation in in vitro studies

Disadvantages of the some zwitterionic pH buffers are (i) that they can interact with metal ions as well as protons, and (ii) that they may have a surfactant effect in chemical or in vitro biological or biochemical studies. This has to be taken into account when a buffer is selected. Here, the copper-complexing capacity and the surfactant activity of three compounds, 3-[N,N-bis (2-hydroxyethyl)amino]-2-hydroxypropanesulfonic acid (DIPSO), N-(2-hydroxyethyl)piperazine-N'-(2-hydroxypropanesulfonic acid) (HEPPSO), and piperazine-N,N'-bis(2-ethanesulfonic acid) (Pipes), were investigated. Global stability constants (log betaabc) of copper(II)-buffer complexes were determined, at 25 degrees C, 0.5 M ionic strength, and at 0.8 mM buffer concentration, by pH and pCu ion-selective electrode measurements. Here, betaabc corresponds to the equilibrium: aCu2+ + bL- + cH+ left and right arrow (CuaLbHc)(2a-b+c); HL = DIPSO or HEPPSO; c: +1 = proton; -1 = hydroxide. Using SUPERQUAD constants were calculated, giving: DIPSO: log beta110 = 5.02, log beta120 = 8.99, log beta130 = 13.0, log beta140 = 16.3, log beta14-1 = 9.26, log beta14-2 = 0.645, log beta150 = 20.5, log beta160 = 24.3, log beta16-1 = 16.1, log beta16-2 = 8.98; HEPPSO: log beta110 = 4.29, log beta120 = 8.35, log beta130 = 12.1, log beta140 = 15.9, log beta150 = 19.6, log beta160 = 23.4, log beta16-1 = 14.9. The pKa values were determined at higher buffer concentrations, giving a value 7.33 for DIPSO and 7.84 for HEPPSO at 2.0 mM buffer concentration. Effects of buffer concentration on stability and acidity constants were investigated and compared with measurements using voltammetric and potentiometric stripping analysis, confirming no copper(II) complexation by Pipes. Surfactant activities were determined using alternating current polarography, confirming marked surface activity of 10 mM of DIPSO or HEPPSO.

Development of snake antivenom antibodies in chickens and their purification from yolk

Adult white leghorn hens hyperimmunised with Brazilian snake venoms of the genus Bothrops and/or Crotalus produced antibodies capable of recognising, combining with and neutralising the toxic and lethal components of the venoms. The antibodies were first detected by an enzyme-linked immunosorbent assay two weeks after starting the immunisation schedule, reached the highest titres by the third week and remained high for at least 24 weeks. These antibodies are transferred to the egg yolk from which they were isolated as enriched IgY preparations by a combination of methods using positive and negative precipitation with sodium sulphate and/or caprylic acid. The yolk-derived IgY preparations contained antibodies which blocked the phospholipase A2-dependent haemolytic activity of both venoms and the haemorrhagic activity of Bothrops venom, and neutralised the toxic lethal activities of the venoms with good efficacy. The median effective dose (ED50) of the IgY anti-Bothrops venom was 592.5 microliters/2LD50 and, 1.0 ml neutralised 0.0675 mg of venom. The ED50 of the IgY anti-Crotalus venom was 457.5 microliters/3LD50 and 1.0 ml neutralised 0.075 mg of venom.

Grief among parents of children with diabetes

The observation that parents respond with grief when their children are diagnosed with diabetes is supported in the medical literature. Dysfunctional family dynamics that disrupt the process of adapting to a diagnosis of diabetes can be attributed to unresolved grief. Group work is advocated as an effective means of promoting healthy familial interactions and adjusting to life with diabetes.

The cervical window as an aid in root canal access

Access to the coronal opening of root canals may be very difficult in cases where cervical caries, whether treated or not, has developed. A direct view through a buccal opening, called a buccal window, was successfully used on two patients and is proposed for similar cases.