RESUMO
Hysteresis loops exhibited by the thermal properties of undoped and 0.8 at.% W-doped nanocrystalline powders of VO2 synthesized by means of the solution combustion method and compacted in pellets, are experimentally measured by photothermal radiometry. It is shown that: (i) the W doping reduces both the hysteresis loops of VO2 and its transition temperature up to 15 °C. (ii) The thermal diffusivity decreases (increases) until (after) the metallic domains become dominant in the VO2 insulating matrix, such that its variation across the metal-insulation transition is enhanced by 23.5% with W-0.8 at.% doping. By contrast, thermal conductivity (thermal effusivity) increases up to 45% (40%) as the metallic phase emerges in the VO2 structure due to the insulator-to-metal transition, and it enhances up to 11% (25%) in the insulator state when the local rutile phase is induced by the tungsten doping. (iii) The characteristic peak of the VO2 specific heat capacity is observed in both heating and cooling processes, such that the phase transition of the 0.8 at.% W-doped sample requires about 24% less thermal energy than the undoped one. (iv) The impact of the W doping on the four above-mentioned thermal properties of VO2 mainly shows up in its insulator phase, as a result of the distortion of the local lattice induced by the electrons of tungsten. W doping at 0.8 at.% thus enhances the VO2 capability to transport heat but diminishes its thermal switching efficiency.
RESUMO
Hysteresis loops in the emissivity of VO2 thin films grown on sapphire and silicon substrates by a pulsed laser deposition process are experimentally measured through the thermal-wave resonant cavity technique. Remarkable variations of about 43% are observed in the emissivity of both VO2 films, within their insulator-to-metal and metal-to-insulator transitions. It is shown that: i) The principal hysteresis width (maximum slope) in the VO2 emissivity of the VO2 + silicon sample is around 3 times higher (lower) than the corresponding one of the VO2 + sapphire sample. VO2 synthesized on silicon thus exhibits a wider principal hysteresis loop with slower MIT than VO2 on sapphire, as a result of the significant differences on the VO2 film microstructures induced by the silicon or sapphire substrates. ii) The hysteresis width along with the rate of change of the VO2 emissivity in a VO2 + substrate sample can be tuned with its secondary hysteresis loop. iii) VO2 samples can be used to build a radiative thermal diode able to operate with a rectification factor as high as 87%, when the temperature difference of its two terminals is around 17 °C. This record-breaking rectification constitutes the highest one reported in literature, for a relatively small temperature change of diode terminals.
RESUMO
Antecedentes: Las roturas bilaterales de tendones cuadricipitales son enfermedades de muy baja frecuencia. Las reparaciones quirúrgicas suelen ser los tratamientos más adecuados y exigen tiempos de recuperación de varios meses. Métodos: Presentamos el caso de un paciente con rotura bilateral de tendones cuadricipitales tras un traumatismo de baja energía, que fue tratado mediante sutura transpatelar quirúrgica reforzada con plasma rico en factores de crecimiento (PRGF-Endoret). Resultados: Los resultados a corto plazo evidenciaron una recuperación funcional y mediante imagen en poco más de dos meses. Conclusiones: La utilización de PRGF asociado a la cirugía habitual puede ayudar a la realización de una rehabilitación precoz.
Background: Bilateral quadriceps tendon tears are infrequent conditions. Surgical repairs are the most appropriate treatments and they involve several months of recovery. Methods: We report the case of a patient with bilateral quadriceps tendon tear resulting from low energy trauma. He was treated with surgical transpatellar suturing reinforced with plasma rich in growth factors (PRGF-Endoret). Results: Short-term results showed functional and radiological recovery at the two-months follow-up. The use of PRGF together with usual surgery may contribute to early rehabilitation.
Assuntos
Idoso , Humanos , Masculino , Peptídeos e Proteínas de Sinalização Intercelular/uso terapêutico , Plasma , Traumatismos dos Tendões/terapia , Músculo Quadríceps , RupturaRESUMO
BACKGROUND: Bilateral quadriceps tendon tears are infrequent conditions. Surgical repairs are the most appropriate treatments and they involve several months of recovery. METHODS: We report the case of a patient with bilateral quadriceps tendon tear resulting from low energy trauma. He was treated with surgical transpatellar suturing reinforced with plasma rich in growth factors (PRGF-Endoret). RESULTS: Short-term results showed functional and radiological recovery at the two-months follow-up. The use of PRGF together with usual surgery may contribute to early rehabilitation.
Assuntos
Peptídeos e Proteínas de Sinalização Intercelular/uso terapêutico , Plasma , Traumatismos dos Tendões/terapia , Idoso , Humanos , Masculino , Músculo Quadríceps , RupturaRESUMO
Intraarticular ganglions are rare and they are usually incidental findings of MRIs and arthroscopies. We report the case of a male athlete with this condition affecting the anterior cruciate ligament. The most frequent symptoms include pain that worsens with activity, and motion limitations. The MRI shows the typical signs of a ganglion and it is the most specific and sensitive test. Arthroscopy is used for both the diagnosis and the treatment of this condition. A late diagnosis turns arthroscopic resection into a complicated or impossible procedure that at times warrants extensive debridement of the anterior cruzate ligament.
Assuntos
Ligamento Cruzado Anterior , Cistos Glanglionares , Adolescente , Cistos Glanglionares/diagnóstico , Cistos Glanglionares/cirurgia , Humanos , MasculinoRESUMO
BACKGROUND: The prognosis of late onset Perthes cases is usually poor and the proposed treatments vary based on the surgeon's preferences and experience, as well as on the available resources. Most of them are salvage procedures with a short follow-up and non-standardized application criteria. METHODS: Hip arthroscopy and arthrodiastasis with external fixator are indicated for certain situations in Perthes disease. Based on the results obtained with each of these techniques separately, both of them were used to treat a case of Perthes disease involving a poor prognosis. RESULTS: Results two years after surgery are good. CONCLUSIONS: The use of both techniques together may produce a good result in these patients.
Assuntos
Artroscopia , Fixadores Externos , Doença de Legg-Calve-Perthes/cirurgia , Adolescente , Fatores Etários , Humanos , Masculino , Procedimentos Ortopédicos/métodosRESUMO
INTRODUCTION: Anterior tibial tubercle fractures are relatively infrequent and occur mainly in young athletes 14 to 17 years old. Most fractures result from jumping during sports activities. METHODS: We describe two cases of anterior tibial tubercle fractures. The latter were Ogden IIIA and IIIB. In both cases treatment consisted of open reduction and internal fixation with cannulated screws. DISCUSSION: The mechanism of injury in the first case is more common than the one in the second case. The first case occurred after jumping to receive a pass during a basketball game. The second one occurred while playing soccer. The patient was kicked on the quadriceps musculature. Both cases involved functional disability. CONCLUSION: Biomechanically, the mechanism of injury in the second case increased the tension on the extensor apparatus. We performed synthesis with cannulated screws and obtained good results without complications.