Microstructure and oxidation behaviour of Fe–Cr–silicide coating on a niobium alloy

The cyclic oxidation performance of a Fe–Cr-modified silicide coating on Nb-alloy C-103 was evaluated in air at temperatures between 1100 and 1500°C and the microstructural changes examined. The coating was oxidation resistant and the duration of protection increased from 60 minutes at 1100°C to 255 minutes at 1500°C. The formation of the surface glassy silica layer and its ability to heal the cracks in the coating enhanced the oxidation performance at high temperatures. The outer NbSi₂ layer served as a reservoir of Si and sustained the formation of the protective silica scale. Spallation of the silica scale and the concomitant depletion of the NbSi₂ layer towards the regeneration of the silica scale limit the oxidation life of the coating.     

Enhanced radiation from an electrically small radiator using an array of sub-wavelength holes

An experimental demonstration of radiation enhancement from an electrically small antenna (ESA) using an array of sub-wavelength holes engraved on a metallic plate is presented in this paper. A weakly radiating, chip inductor loaded open coplanar waveguide transmission line is used as the reference ESA. We show that an array of sub-wavelength hole loaded metallic aperture, placed near the antenna, can significantly enhance radiated power from the source. The hole array converts the high spatial reactive spectrum existing in the near-field of the antenna into a far-field propagating spectrum. The theory is validated by experiments and simulations in the microwave frequency regime. This novel radiation enhancement scheme is seen to enhance the gain of the antenna from ?8.5 to ?2.5?dBi and radiation efficiency from 13 to 33% around resonance.     

Dual material gate doping-less tunnel FET with hetero gate dielectric for enhancement of analog/RF performance

In this paper, charge-plasma-based tunnel FET is proposed by employing dual material gate with hetero gate dielectric technique and it is named hetero-dielectric dual material gate doping-less TFET(HD_DMG_DLTFET). It is compared with conventional doping-less TFET(DLTFET) and dual material gate doping-less TFET(DMG_DLTFET) on the basis of analog and RF performance. The HD_DMG_DLTFET provides better ON state current(I_ON=94 μA/μm), I_ON/I_OFF(≈ 1:36×10¹³), point(≈ 3 mV/dec) and average subthreshold slope(AV-SS=40.40 mV/dec). The proposed device offers low total gate capacitance(C_gg)along with higher drive current. However, with a better transconductance(g_m) and cut-off frequency(f_T), the HD_DMG_DLTFET can be a good candidate for RF circuitry. The early voltage(V_EA) and output conductance(g_d) are also moderate for the proposed device with comparison to other devices and therefore can be a candidate for analog devices. From all these simulation results and their study, it is observed that HD_DMG_DLTFET has improved analog/RF performance compared to DLTFET and DMG_DLTFET.     

Transfusion associated hepatitis: the Indian scenario

The purpose of this study was to evaluate the effect of partial renal shielding used in conjunction with total body irradiation (TBI) on the incidence of bone marrow transplantation nephropathy (BMT Np) seen as a late sequelae after transplantation. Of 402 patients who have undergone bone marrow transplantation (BMT) at the Medical College of Wisconsin (MCW) 157 were greater than 18 years of age, received 14 Gy TBI and survived at least 100 days post-transplant. The incidence of BMT nephropathy was evaluated in these patients by dose to the kidneys. In the 72 patients who received 14 Gy TBI with no renal shielding, the actuarial risk of developing BMT Np at 2 1/2 years (30 months) post-BMT was 29 +/- 7%. Sixty-eight patients received 14 Gy TBI with partial renal shielding of 15% (renal dose = 11.9 Gy), the actuarial risk of developing BMT Np was 14 +/- 5% at 2 1/2 years. Seventeen patients received 14 Gy TBI with renal shielding of 30% (renal dose = 9.8 Gy); none of this group have developed BMT Np despite a median follow-up of over 2 1/2 years (985 days). The trend of decreasing BMT Np with increasing shielding is statistically significant (P = 0.012). Prognostic factors such as age, type of transplant and good-risk vs poor-risk disease status were evaluated and were similar in each cohort of patients described above. We conclude that given the statistically significant benefit seen here in the reduced incidence of BMT Np by the use of selective renal shielding, this should be seriously considered for all patients who receive TBI, but especially for patients whose renal doses exceed 10 Gy.     

Enzyme-linked immunosorbent assay quantification of cytokine concentrations in human meningiomas

OBJECTIVE: To gain insight into the network of cytokine gene expression in the brain tumor microenvironment, we investigated the presence of the following cytokines in freshly excised brain tumors: interleukin (IL)-1 beta, IL-2, IL-4, and IL-6. METHODS: Tumor specimens from nine meningiomas were grown as tissue explants. The supernatants from the explants were tested for the presence of the aforementioned cytokines via the enzyme-linked immunosorbent assay method. RESULTS: IL-6, which is thought to stimulate acute protein phase synthesis, neovascularization, and cell proliferation, was found in all of the samples in greater concentrations than the other cytokines tested. IL-1 beta, another stimulatory cytokine thought to be involved in acute protein phase synthesis and cell proliferation, was also found in 100% of the samples tested, in concentrations significantly lower than those of IL-6. As expected, the presence of IL-2 and IL-4 was not detectable in any of the samples. CONCLUSION: This study is the first to clearly determine the relative concentrations of IL-1 beta and IL-6, using enzyme-linked immunosorbent assay quantification. These findings are an important precursor to future studies using antibodies to IL-1 beta and IL-6 and antibodies to IL-6 receptors to modulate neoplastic growth both in vitro and in vivo.     

Mechanical behavior of 3Al2O3·2SiO2 films under nanoindentation

A complete and systematic nanoindentation study was conducted on a mullite (3Al₂O₃·2SiO₂) coating ～1 μm thick, deposited by means of chemical vapor deposition on a silicon carbide (SiC) substrate. The investigation included using different indenter tip geometries (Berkovich, spherical and cube-corner), complemented with atomic force microscopy and three-dimensional focused ion beam tomography to characterize the indentation response, deformation and damage micromechanisms. The intrinsic mechanical properties of the 3Al₂O₃·2SiO₂ film and the interfacial toughness of the coated (3Al₂O₃·2SiO₂/SiC) system were critically evaluated to assess the influence of substrate and film residual stresses. Through appropriate implementation of specific indenter tip geometry, different length-scale mechanical properties in the materials studied were successfully determined: yield strength and fracture toughness for the film, together with energy of adhesion per unit area and interface fracture toughness for the coated system.     

Injection Locked Millimeter Wave Oscillators at Ka, V, and W-Bands

Injection locked Gunn oscillators have been developed to amplify the upconverted millimeter wave frequencies. They are being used in millimeter wave communication systems at Ka, V and W-Bands respectively.     

Inspection of compositionally graded mullite coatings using laser based ultrasonics

Functionally graded materials (FGMs) have spatial variations in composition and structure resulting in corresponding changes in material properties. These materials can be developed for applications in which the functional requirements of a component are position dependent. In this paper, we evaluate the feasibility of using a laser based ultrasonic technique to determine the distribution of elastic properties in FGMs. A model for the laser generation of ultrasound in a compositionally graded coating on a semi-infinite substrate is used to explore the relationship between the acoustic wave propagation and depth dependent elastic property profile. Surface acoustic waves (SAW) generated in such a system are dispersive, and the dispersion characteristics are highly dependent on the mechanical property profile. A high-resolution laser ultrasonic system has been developed, and experimental measurements of the mechanical properties of single layer mullite coatings are presented. Using compositionally graded mullite coatings as a model system, numerical results are reported showing the sensitivity of SAW dispersion behavior to various composition profiles.