Raman spectra of multilayer graphene under high temperatures.

For graphitic materials, Raman technique is a common method for temperature measurements through analysis of phonon frequencies. Temperature (T) induced downshift of the bond-stretching G mode (ΔG) is well known, but experimentally obtained thermal coefficients ΔG/ΔT vary considerably between diverse works. Further, ΔG/ΔT coefficients usually were evaluated for relatively low temperatures and found to differ strongly for mono, a few and multilayer graphene. We studied G band behavior in freely suspended multilayer graphene flakes (or graphite nanoflakes) under localized heating by a laser beam. Analysis of Stokes and anti-Stokes signals showed that G band has a complex structure and can be deconvoluted into several peaks that demonstrate distinctly different behavior under heating. A plausible assumption is that these peaks correspond to several groups of graphitic layers (surface, near-surface and bulk) and then different thermal coefficients were determined for these groups. This behavior can be explained by decreasing interaction between surface layers and underlying material at high temperatures that affects especially vibrational properties of a few outermost layers. Estimates of temperatures using anti-Stokes/Stokes intensity ratio (I aS/I S) were also done to give results comparable with those obtained from G band downshift, T ΔG ≈ T aS/S, supporting the proposed model. The range of temperatures obtained by laser heating, as evaluated by both methods, was from 450 to 1200 K.

A wearable, highly stable, strain and bending sensor based on high aspect ratio graphite nanobelts.

A simple and scalable method was developed for the fabrication of wearable strain and bending sensors, based on high aspect ratio (length/thickness ∼10(3)) graphite nanobelt thin films deposited by a modified Langmuir-Blodgett technique onto flexible polymer substrates. The sensing mechanism is based on the changes in contact resistance between individual nanobelts upon substrate deformation. Very high sensor response stability for more than 5000 strain-release cycles and a device power consumption as low as 1 nW were achieved. The device maximum stretchability is limited by the metal electrodes and the polymer substrate; the maximum strain that could be applied to the polymer used in this work was 40%. Bending tests carried out for various radii of curvature demonstrated distinct sensor responses for positive and negative curvatures. The graphite nanobelt thin flexible films were successfully tested for acoustic vibration and heartbeat sensing.

A modern minimally invasive transcallosal approach to the third ventricle. A personal experience of 30 patients.

INTRODUCTION: Expansive processes around the third ventricle have always been a major neurosurgical challenge. Despite all the technological and scientific progress recorded over the last few years, third ventricle tumors are still a very difficult pathology to approach due to their formidable complexity.Treating such a tumor demands a good knowledge of local anatomy, pathophysiology, pathology and a good capacity to integrate all the data gathered from the patient prior to and during surgery. Last but not least, the correct means to approach such a tumor involves using modern neuronavigation technology which might be too expensive to access in certain clinics (1,2). OBJECTIVE: This article presents the personal experience of the authors, gathered while using a novel surgical approach,configured to maximize the success rate of interventions for tumors within the third ventricle, without using neuronavigation technology. MATERIALS AND METHODS: The authors have developed a study of neuroanatomy using 30 adult human brains, without any pathological lesions, harvested during routine autopsies and analysed using a a standard protocol (Protocol of the Ludwig-Maximilians University Clinic of Neurosurgery, Laboratory of Microanatomy - Munich, Germany). The authors assessed a series of anatomic elements which were later used as landmarks to build the neurosurgical operative field. After completing the anatomic study the authors moved on to record morphometric data for 30 volunteers. The authors used sagittal T1 weighted images. The volunteers were males and females, all adults, with the mean age of 45.3 years. (The age interval: 21-83 years, sex distribution: 17 males and 13 females). The images were digitally enhanced and the specific targets were outlined using Corel Draw, thus allowing for a systematic identification of contours and landmarks. Each contour was recorded and saved as a sequence of dots. The next stage of the study, after having studied all the data recorded, consisted of establishing the appropriate transcallosal surgical corridor (transforaminal or inter forniceal) for each of the 30 patients (not to be mistaken with the 30 volunteers)who were admitted for third ventricle tumors and who were included in this study. After having performed surgery for there section of the above mentioned third ventricle tumors, the authors observed pre- and postoperative clinical data which were corroborated with the neuropsychological examination which was also performed prior to and after surgery. CONCLUSIONS: The results obtained through observation and anatomical measurements have proven to be highly valuable in determining a standard access corridor through the corpuscallosum. The data gathered and the patient's MRI exam images helped obtain an optimal surgical corridor of the third ventricle. In what regards the surgical act in 23 cases (77%) the authors managed to achieve a complete resection of the tumor.In 6 cases (20%) the authors managed a subtotal resection of the tumors. In a single case the authors performed only a biopsy. A number of 24 patients (80%) achieved an excellent outcome (Glasgow Outcome Scale - GOS V). Minor deficits were recorded in 5 patients (17%) (disabled but independent)(GOS IV) No cases were recorded with serious impairment(GOS III) or vegetative state (GOS II). One patient with anaplastic glioma died 4 months after surgery after an initial favorable evolution. The tumor had spread to the hypothalamus. A single postoperative complication was linked to the surgical approach in a 73-year-old female patient who suffered a venous infarction due to a venous thrombosis in atributary vein of the superior sagittal sinus in the access area.The patient, after a slow recovery managed to improve her condition reaching GOS IV. There were no other complications connected to the surgical act.

Interference of apoptosis in the pathophysiology of subarachnoid hemorrhage.

Programmed cell death is crucial for the correct development of the organism and the clearance of harmful cells like tumor cells or autoreactive immune cells. Apoptosis is initiated by the activation of cell death receptors and in most cases it is associated with the activation of the cysteine proteases, which lead to apoptotic cell death. Cells shrink, chromatin clumps and forms a large, sharply demarcated, crescent-shaped or round mass; the nucleus condenses, apoptotic bodies are formed and eventually dead cells are engulfed by a neighboring cell or cleared by phagocytosis. The authors have summarized the most important data concerning apoptosis in subarachnoid hemorrhage that have been issued in the medical literature in the last 20 years.

Micro-reactors for characterization of nanostructure-based sensors.

Fabrication and testing of micro-reactors for the characterization of nanosensors is presented in this work. The reactors have a small volume (100 µl) and are equipped with gas input/output channels. They were machined from a single piece of kovar in order to avoid leaks in the system due to additional welding. The contact pins were electrically insulated from the body of the reactor using a borosilicate sealing glass and the reactor was hermetically sealed using a lid and an elastomeric o-ring. One of the advantages of the reactor lies in its simple assembly and ease of use with any vacuum/gas system, allowing the connection of more than one device. Moreover, the lid can be modified in order to fit a window for in situ optical characterization. In order to prove its versatility, carbon nanotube-based sensors were tested using this micro-reactor. The devices were fabricated by depositing carbon nanotubes over 1 µm thick gold electrodes patterned onto Si/SiO(2) substrates. The sensors were tested using oxygen and nitrogen atmospheres, in the pressure range between 10(-5) and 10(-1) mbar. The small chamber volume allowed the measurement of fast sensor characteristic times, with the sensors showing good sensitivity towards gas and pressure as well as high reproducibility.

Thermal evaporation furnace with improved configuration for growing nanostructured inorganic materials.

A tubular furnace specifically designed for growing nanostructured materials is presented in this work. The configuration allows an accurate control of evaporation temperature, substrate temperature, total pressure, oxygen partial pressure, volumetric flow and source-substrate distance, with the possibility of performing both downstream and upstream depositions. In order to illustrate the versatility of the equipment, the furnace was used for growing semiconducting oxide nanostructures under different deposition conditions. Highly crystalline indium oxide nanowires with different morphologies were synthesized by evaporating mixtures of indium oxide and graphite powders with different mass ratios at temperatures between 900 °C and 1050 °C. The nanostructured layers were deposited onto oxidized silicon substrates with patterned gold catalyst in the temperature range from 600 °C to 900 °C. Gas sensors based on these nanowires exhibited enhanced sensitivity towards oxygen, with good response and recovery times.

Resistive-switching behavior in polycrystalline CaCu(3)Ti(4)O(12) nanorods.

Highly aligned CaCu(3)Ti(4)O(12) nanorod arrays were grown on Si/SiO(2)/Ti/Pt substrates by radio-frequency sputtering at a low deposition temperature of 300 °C and room temperature. Structural and morphological studies have shown that the nanostructures have a polycrystalline nature and are oriented perpendicular to the substrate. The high density of grain boundaries in the nanorods is responsible for the nonlinear current behavior observed in these arrays. The current-voltage (I-V) characteristics observed in nanorods were attributed to the resistive memory phenomenon. The electrical resistance of microcapacitors composed of CaCu(3)Ti(4)O(12) nanorods could be reversibly switched between two stable resistance states by varying the applied electric field. In order to explain this switching mechanism, a model based on the increase/decrease of electrical conduction controlled by grain boundary polarization has been proposed.