Erlon H. Martins Ferreira

Raman Signature of Graphene Superlattices

When two identical two-dimensional periodic structures are superposed, a mismatch rotation angle between the structures generates a superlattice. This effect is commonly observed in graphite, where the rotation between graphene layers generates Moiré patterns in scanning tunneling microscopy images. Here, a study of intravalley and intervalley double-resonance Raman processes mediated by static potentials in rotationally stacked bilayer graphene is presented. The peak properties depend on the mismatch rotation angle and can be used as an optical signature for superlattices in bilayer graphene. An atomic force microscopy system is used to produce and identify specific rotationally stacked bilayer graphenes that demonstrate the validity of our model.

Raman study of ion-induced defects in N-layer graphene

Raman scattering is used to study the effect of low energy (90 eV) Ar(+) ion bombardment in graphene samples as a function of the number of layers N. The evolution of the intensity ratio between the G band (1585 cm(-1)) and the disorder-induced D band (1345 cm(-1)) with ion fluence is determined for mono-, bi-, tri- and ∼50-layer graphene samples, providing a spectroscopy-based method to study the penetration of these low energy Ar(+) ions in AB Bernal stacked graphite, and how they affect the graphene sheets. The results clearly depend on the number of layers. We also analyze the evolution of the overall integrated Raman intensity and the integrated intensity for disorder-induced versus Raman-allowed peaks.

Dynamic Negative Compressibility of Few-Layer Graphene, h-BN, and MoS2

We report a novel mechanical response of few-layer graphene, h-BN, and MoS(2) to the simultaneous compression and shear by an atomic force microscope (AFM) tip. The response is characterized by the vertical expansion of these two-dimensional (2D) layered materials upon compression. Such effect is proportional to the applied load, leading to vertical strain values (opposite to the applied force) of up to 150%. The effect is null in the absence of shear, increases with tip velocity, and is anisotropic. It also has similar magnitudes in these solid lubricant materials (few-layer graphene, h-BN, and MoS(2)), but it is absent in single-layer graphene and in few-layer mica and Bi(2)Se(3). We propose a physical mechanism for the effect where the combined compressive and shear stresses from the tip induce dynamical wrinkling on the upper material layers, leading to the observed flake thickening. The new effect (and, therefore, the proposed wrinkling) is reversible in the three materials where it is observed.

Preimplantation development and expression of Hsp-70 and Bax genes in bovine blastocysts derived from oocytes matured in alpha-MEM supplemented with growth factors and synthetic macromolecules.

In vitro culture conditions affect both the maternal and embryonic expression of genes and is likely to alter both oocyte and embryo developmental competence. The search for better and less variable culture conditions simulating those in vivo has led to the development of defined culture media, with lower impact on the molecular reprogramming of oocytes and embryos. We evaluated embryo development and relative abundance (RA) of Hsp-70 and Bax transcripts in bovine blastocysts produced from oocytes matured in a chemically defined IVM system with synthetic polymers. Immature cumulus oocyte complexes (COCs) were matured for 22-24h in alpha-MEM supplemented with IGF-1, insulin, 0.1% polyvinyl alcohol (PVA), or 0.1% polyvinylpyrrolidone (PVP), but without FSH or LH. The control group consisted of COCs matured in TCM plus FSH and 10% estrous cow serum. After fertilization, presumptive zygotes were co-cultured with cumulus cells until 224 h post-insemination. Total RNA was isolated from embryo pools, reverse transcribed into cDNA, and subjected to transcript analysis by real-time PCR. Cleavage rate was higher (P<0.05) for the control group (68.3%) than for the PVA (54.4%) and PVP-40 (58.3%) groups. Nevertheless, there was no difference among the PVA, PVP-40 and control groups in blastocyst or hatching rates. Similarly, no difference in relative abundance of Hsp-70 and Bax transcripts was detected in comparison to the control group. We inferred that bovine oocytes can be matured in serum- and gonadotrophin-free medium supplemented with PVA or PVP, enriched with IGF-I and insulin, without altering post-cleavage development and relative abundance of some genes associated with stress and apoptosis.

Measuring Disorder in Graphene with Raman Spectroscopy

Since the experimental discovery of an easy method to produce graphene (Novoselov et al., 2004; 2005), there is a continuous rising of interest on this fascinating material. Due to its own peculiar electronic band structure, graphene is a promising material for the future electronic nanodevice industry. In any production process is of fundamental importance to control the quality of materials in a fast and non-destructive manner. Quantifying defects in graphene related systems is a major problem for the application of such materials (Neto et al., 2009). In the field of carbon-based nanostructures, Raman spectroscopy has shown to be the most suitable technique since it accomplishes those desirable goals and also because it can be used to differentiate the many types of sp2 carbon structures and to identify the presence of defects (Ferrari & Robertson, 2000; Pimenta et al., 2007). Defects are of great importance since they modify the electronic and optical properties of the system, sometimes in a desirable way. Raman spectroscopy is also one of the most sensitive techniques to probe disorder in carbon structures. The development of an accurate methodology to study disorder with Raman spectroscopy will certainly facilitate the control of the amount of induced disorder in a target system. By combining experiment and theory, a phenomelogical model has been established to explain the evolution of the Raman spectrum of graphene with increasing amount of disorder caused by low energy ion bombardment. Using this model one can extract information about the density of defects, the average defect size and also the Raman process relaxation length and its dependence with the laser excitation energy and temperature. How the ion bombardment procedure affects graphene samples with two or more layers and graphene read edges has also been studied.

Involvement of Bone Morphogenetic Proteins (BMPs) in Ovarian Function and Infertility

Advances in assisted reproduction techniques and the treatment of diseases known to be correlated with infer- tility such as polycystic ovary syndrome and premature ovarian failure require a better understanding of ovarian physiol- ogy. Despite the enormous quantity of information produced over the last two decades, the mechanisms controlling fol- licular development are not fully understood. Ovarian function is regulated by interactions between gonadotropins, follicle stimulating hormone, luteinizing hormone and local ovarian factors such as inhibins, activins, bone morphogenetic pro- tein-15 (BMP-15) and growth differentiation factor-9 (GDF-9), all members of the transformation and growth factor-� (TGF-� ) superfamily. There is evidence of a functional ovarian BMP system with countless genes involved in normal fol- licular development and in fertility. The present review summarizes the ligands of the TGF-� superfamily, their receptors and signaling pathways and discusses the ovarian functions of the BMPs secreted by the oocytes as critical regulators of fertility.

Key Aspects for Implementing ISO/IEC 17025 Quality Management Systems at Materials Science Laboratories

Implementing a quality management system based on the requirements specified in ISO/IEC 17025 standard at materials science laboratories is challenging, mainly due to two main factors: (i) the high technical complexity degree of some tests used for materials characterization and (ii) the fact that most materials science laboratories provide materials characterization tests and also carry out research and development activities. In this context, this chapter presents key subjects while implementing a quality management system at materials science laboratories and some considerations on strategies for effectively implementing such systems.

Study of Carbon Nanostructures for Soil Fertility Improvement

Keeping organic matter in the soil is one of the most promising carbon capture and storage methods. Soil organic matter has the longest soil persistence and cause soil amelioration. The “Terra Preta de Indio” (Amazonian Dark Earth) is an anthropogenic Amazonian soil that provides a potential model for such organic matter soil storage, generating a sustainable land-use system that is highly efficient even in the hot and humid tropical regions. The large amount of carbon-based materials in these soils is responsible for their unusually high fertility over long periods of usage. In this chapter, by applying materials science tools, including scanning and transmission electron microscopy, energy dispersive X-ray, electron energy loss spectroscopy and Raman spectroscopy, we show that these millenary carbon materials exhibit a complex morphology, with particles ranging in size from micrometers to nanometers, from the core to the surface of the carbon grains, and are rich on specific elements that are important for fertility and carbon stability. Specifically, calcium and oxygen are abundant in the whole carbon structure, and the role of these elements on carbon stability is studied theoretically. From one side, our results might elucidate how nature solved the problem of keeping high levels of ion exchange capacity in these soils. From the other side, morphology and dimensionality are the key issues in nanotechnology, and the structural aspects revealed here may help generating the “Terra Preta Nova” (New Black Earth), effectively improving world agriculture and ecosystem sustainability.

Hereditary protein C deficiency and portal vein thrombosis

Inherited defects of the natural coagulation inhibitors predispose patients to thrombosis. These disorders have similar clinical presentations with a strong family of thrombosis, episodes of recurrent venous thromboembolism, beginning in early adulthood. We report a case of upper gastrointestinal bleeding in a patient with portal hypertension due to portal-vein thrombosis secondary to hereditary protein C deficiency, an association that has seldom been reported. We conclude that protein C deficiency should be investigated in thrombotic states, namely after more frequent causes have been excluded.