Absolute thickness measurement of pyrolytic graphite spheroids by STEM-EELS.

This paper studies the absolute thickness measurement of pyrolytic graphite spheroids (GSs) by using STEM-EELS mode with log-ratio method and Kramers-Kroning (K-K) method, taking the measured thickness from TEM image as reference that is the diameter of GSs ranging from 60 to 250nm. The effect of collection semi-angle (ß) on thickness measurement has been investigated. It is found that in general the thickness obtained by K-K analysis with surface effect corrected shows the best accuracy, followed by K-K sum rule and then log-ratio method for the three different collection semi-angles of 12.4, 17.3 and 21.1mrad applied. Of these angles, the smallest one gives an overestimated result and the largest one gives an underestimated result, whereas between the two, the angle of 17.3mrad that is about 2x convergence semi-angle (9.0mrad) is identified as more appropriate for K-K analysis. The surface-scattering correction, inelastic mean free path of GS and effect of refractive index n on thickness measurement for different ß angles are also investigated. Moreover, the optical property deduced from the data collected at the center of graphite spheroid, which is related to its microstructure, is characterized by K-K analysis.

Pressure-induced transition in magnetoresistance of single-walled carbon nanotubes.

We applied hydrostatic pressure (up to 10 GPa) to single-walled carbon nanotube bundles at low temperature (down to 2 K) to measure their magnetoresistance (MR) in a field up to 12 T. We found a pressure-induced transition in MR from positive to negative in the high-field regime. The onset of the transition occurs at approximately 1.5 GPa, which correlates closely with the tube shape transitions. The characteristics of the high-pressure MR are consistent with a model of pressure-induced two-dimensional weak localization.

Controlled growth of carbon nanotubes.

Carbon nanotubes have extraordinary mechanical and electronic properties and hold great promise for future applications. The most important aspects of this structure are its low density, high aspect ratio, one dimensionality, high mechanical strength and high electrical and thermal conductivity. We present a short, state-of-the-art account of tailored nanotube growth. To provide these properties in real devices there exists a need for producing nanotubes on substrates. The challenge in the creation of mesoscale nanotube-based architectures and tailored nanotube networks consisting of thousands of tubes in a predefined order is obviously great. Currently, chemical vapour deposition (CVD) appears to be the most powerful method for achieving such required structures. We describe our work on a new synthesis method, based on catalytic CVD using mainly gas-phase catalyst delivery. Gas-phase catalyst delivery allows us to assemble single-walled and multi-walled carbon nanotubes in predetermined multiple orientations on substrates to build one- to three-dimensional architectures. We are able to control, to a large extent, the types of nanotubes produced, their lengths, locations and their orientations. The ability to make mesoscale architectures with nanotubes should lead us to develop applications in areas such as nano-electromechanical systems.

Mobility of carbon nanotubes in high electric fields.

The influence of electric fields on carbon nanotubes is experimentally demonstrated. Alignment of nanotubes along field lines, directed motion of nanotubes between electrodes separated by several thousand micrometers, and impressive solid-state actuation behavior of nanotube-embedded structures are demonstrated, taking into account the polarization and charging of the nanotubes. These effects are reported for long strands of nanotubes, nanotubes dispersed on substrates, and nanotube-embedded polymer strips. The relative magnitude of the field responsible for polarization and directed motion was found to be dependent on the morphology of the nanotubes used. These observations may foreshadow novel electromechanical applications for nanotube elements.

Direct synthesis of long single-walled carbon nanotube strands.

In the processes that are used to produce single-walled nanotubes (electric arc, laser ablation, and chemical vapor deposition), the typical lengths of tangled nanotube bundles reach several tens of micrometers. We report that long nanotube strands, up to several centimeters in length, consisting of aligned single-walled nanotubes can be synthesized by the catalytic pyrolysis of n-hexane with an enhanced vertical floating technique. The long strands of nanotubes assemble continuously from arrays of nanotubes, which are intrinsically long.

Microfabrication technology: organized assembly of carbon nanotubes.

Nanoscale structures need to be arranged into well-defined configurations in order to build integrated systems. Here we use a chemical-vapour deposition method with gas-phase catalyst delivery to direct the assembly of carbon nanotubes in a variety of predetermined orientations onto silicon/silica substrates, building them into one-, two- and three-dimensional arrangements. The preference of nanotubes to grow selectively on and normal to silica surfaces forces them to inherit the lithographically machined template topography of their substrates, allowing the sites of nucleation and the direction of growth to be controlled.

Carbon nanotube-magnesium oxide cube networks.

For future applications based on carbon nanotubes, two- and three-dimensional architectures of nanotubes need to be assembled. In many cases this will involve the creation of nanotube units and nodes from which these nanotubes can be distributed in a network. We demonstrate that this idea is plausible by using a template of the correct dimensions and shape, and that has facets that provide the right growth conditions: submicrometer-sized MgO cubes are used to grow nanotubes by chemical vapor deposition. The resulting networks often show that the MgO cubes function as distribution sites for arrays of aligned nanotubes.

[Analysis of residue and regression of metastatic cervical lymph nodes in NPC after radiotherapy].

Follow up results of residue and regression of metastatic cervical lymph nodes in NPC after radiotherapy are presented. All the 453 cases have been followed for more than five years. According to WHO's criteria, the relative 5 year survival rate was 43.9%. 389 of 453 had had lymph node metastases in the neck at the beginning of treatment. At the end of radiation, immediate regression rate of lymph nodes was 53.2%, which was related to lymph node size before radiotherapy. Five year survival rate of those whose lymph node metastases disappeared completely was 48.8% (group 1). There were 182 cases with residual nodes at the conclusion of radiation (140 recorded in detail). The regression rate of nodes was 96.4% (135/140) and the 5 year survival rate of these 140 patients was 40.0% (group 2). There is no significant difference and the long term results are similar in the two groups. Total recurrence rate in the neck was 4.4%: 5.3% in group 1 and 3.8% in group 2 (P greater than 0.05). The treatment results of the local cervical lesions are the same, too. In 182 cases with residual lesions, 121 with 147 clinically evaluable residual nodes, 0.5 approximately 3 cm in diameter, were followed. The regression time of these residual nodes was 2.5 approximately 2.7 months as to geometric mean (the regressive confidence limit 95%). To sum up, according to the routine cervical target dose, some nodes remaining at the of radiation seem to require no boost dose in order to avoid delayed radiation complications. But the residual nodes which recur during follow up would require a prompt retreatment.

[Anatomic foundation of the lateral portal for radiotherapy of nasopharyngeal cancer (NPC)].

Basing on 31 normal skulls, the lateral projections of some points relative to the bony structure near the nasopharynx were located under the simulator, followed by drawing it on a sheet of paper with the aid of geometry and trigonometry. Thus, the relation between external and internal structures is shown on the drawn projection, which can serve as the anatomic basis for designing the routine field and improving radiotherapy technique. In the light of data informed by this study and clinical experiences of the authors and others, it was found logical, in radiotherapy of NPC, that large opposing lateral pre-auriculo-cervical portals with their posterior margin extending beyond the external auditory meatus posteriorly be used in order to avoid geographic miss of the uppermost deep cervical lymph nodes usually involved beneath the jugular foramen and posterior portion of the nasopharynx. In addition, the upper margin of the lateral portal must be parallel but superior to the cantho-auditory line, on which the foramen ovale is projected. Actual locating the upper margin should depend on the extent of the intracranial invasion of the tumor as shown by the CT scan.