RESUMEN
During their production, single-walled carbon nanotubes form bundles. Owing to the weak van der Waals interaction that holds them together in the bundle, the tubes can easily slide on each other, resulting in a shear modulus comparable to that of graphite. This low shear modulus is also a major obstacle in the fabrication of macroscopic fibres composed of carbon nanotubes. Here, we have introduced stable links between neighbouring carbon nanotubes within bundles, using moderate electron-beam irradiation inside a transmission electron microscope. Concurrent measurements of the mechanical properties using an atomic force microscope show a 30-fold increase of the bending modulus, due to the formation of stable crosslinks that effectively eliminate sliding between the nanotubes. Crosslinks were modelled using first-principles calculations, showing that interstitial carbon atoms formed during irradiation in addition to carboxyl groups, can independently lead to bridge formation between neighbouring nanotubes.
Asunto(s)
Nanotubos de Carbono/química , Partículas beta , Reactivos de Enlaces Cruzados , Microscopía Electrónica , Nanotubos de Carbono/efectos de la radiación , Nanotubos de Carbono/ultraestructura , Resistencia a la TracciónRESUMEN
We have determined the mechanical anisotropy of a single microtubule by simultaneously measuring the Young's and the shear moduli in vitro. This was achieved by elastically deforming the microtubule deposited on a substrate tailored by electron-beam lithography with a tip of an atomic force microscope. The shear modulus is 2 orders of magnitude lower than the Young's, giving rise to a length-dependent flexural rigidity of microtubules. The temperature dependence of the microtubule's bending stiffness in the (5-40) degrees C range shows a strong variation upon cooling coming from the increasing interaction between the protofilaments.
Asunto(s)
Microtúbulos/química , Anisotropía , Elasticidad , Microscopía de Fuerza Atómica , Microtúbulos/fisiología , Nanotecnología/métodosRESUMEN
The purpose of this study was to determine the effect of jaw and cheek support on nutritional intake. A 32-month-old child who had experienced a brainstem stroke was spoon fed, with and without jaw and cheek support, in an ABAB single case fashion. Jaw and cheek support elicited an increased amount of solid food consumption by the participant. There was no difference, between control and intervention sessions, in the amount of solid food expelled onto the bib. Jaw and cheek support enabled a 32-month-old child with a brainstem stroke to consume more solid foods than without support.
Asunto(s)
Niños con Discapacidad , Ingestión de Alimentos , Métodos de Alimentación , Rehabilitación de Accidente Cerebrovascular , Preescolar , HumanosRESUMEN
We replicated prior research on Rorschach and MMPI-2 convergent validity by testing 8 hypotheses in a new sample of patients. We also extended prior research by developing criteria to include more patients and by applying the same procedures to 2 self-report tests: the MMPI-2 and the MCMI-II. Results supported our hypotheses and paralleled the prior findings. Furthermore, 3 different tests for methodological artifacts could not account for the results. Thus, the convergence of Rorschach and MMPI-2 constructs seems to be partially a function of how patients interact with the tests. When patients approach each test with a similar style, conceptually aligned constructs tend to correlate. Although this result is less robust, when patients approach each test in an opposing manner, conceptually aligned constructs tend to be negatively correlated. When test interaction styles are ignored, MMPI-2 and Rorschach constructs tend to be uncorrelated, unless a sample just happens to possess a correlation between Rorschach and MMPI-2 stylistic variables. Remaining ambiguities and suggestions for further advances are discussed.
Asunto(s)
MMPI/normas , Trastornos Mentales/diagnóstico , Trastornos Mentales/psicología , Prueba de Rorschach/normas , Análisis Factorial , Humanos , Pacientes Internos/estadística & datos numéricos , Pacientes Ambulatorios/estadística & datos numéricos , Psicometría , Reproducibilidad de los Resultados , Estados UnidosRESUMEN
A case of submucous lipoma of the uterus is described. The suspected location in the curettings was confirmed in the hysterectomy specimen.