No abstract

No abstract

We report on the dynamics of propagation of rotating OAM-carrying beams past partial and total obstructions. We demonstrate a simple experimental technique for generating rotating Helicon beams and for investigating the propagation of the obstructed field. In this technique we create digital holograms, imprinted on a spatial light modulator, that simultaneously vary the amplitude and phase of the light to create a digital equivalent of multiple ring slit apertures. Our method allows for the controlled generation of Helicon beams of any order, and any radial wavevector, thus controlling the rotation rate of the beams. We further study the reconstruction properties for total on-axis obstructions as compared to partial off-axis obstructions and show that the results obtained are in good agreement with theoretical predictions.

We report on application of conductive silver paste smeared glass slides as Raman spectroscopy sample substrates for label-free detection of HIV-1 p24 antigen in blood plasma. We also show that the same substrates can be applied in Raman spectroscopic screening of blood plasma for presence of HIV. The characteristic Raman spectrum of HIV-1 p24 antigen displayed prominent bands that were assigned to ribonucleic acids (RNA) and proteins that constitute the antigen. This spectrum can be used as reference during Raman spectroscopic screening for HIV in plasma within the first few days after exposure (<7 days). The Raman spectra obtained from HIV+ plasma displayed unique peaks centered at wavenumbers 928, 990, 1270, 1397, and 1446 cm attributed to the Raman active vibrations in the virion carbohydrates, lipids, and proteins. Other bands similar to those reported in literature were also seen and assignments made. The attachment of the HIV virions to silver nanoparticles via gp120 glycoprotein knobs was thought to be responsible for the enhanced Raman signals of proteins associated with the virus. The principal component analysis (PCA) applied on the combined spectral data showed that HIV- and HIV+ spectra had differing spectral patterns. This indicated the great power of Raman spectroscopy in HIV detection when plasma samples are deposited onto silver paste smeared glass substrates. The Raman peaks responsible for the segregation of the spectral data in PCA were mainly those assigned to the viral proteins (645, 725, 813, 1270, and 1658 cm). Excellent results were obtained from Artificial Neural Network (ANN) applied on the HIV+ Raman spectral data around the prominent peak centered at 1270 cm with R (coefficient of correlation) and R (coefficient of determination) values of 0.9958 and 0.9895, respectively. The method has the potential of being used as quick blood screening for HIV before blood transfusion with the Raman peaks assigned to the virion proteins acting as reference. Graphical Abstract The HIV type 1 virus particle gets attached to the silver nanoparticle contained in the conductive silver paste smear onto a glass slide. This results in strong Raman signals associated with the components of the virion. The signals are collected, dispersed in a spectrometer and displayed on a computer screen. Method can be used as a label-free and rapid HIV screening in blood plasma.

The wide range of applications of collagenbased materials has triggered research interest especially on the effect of environmental factors in that these materials are exposed to during processing and application. As the applications of these collagenous materials continue to increase such as in the field of medicine, more studies are required to gain more insight into their properties. Collagen is a natural biopolymer whose structure is sensitive to ultraviolet (UV) radiations, which alters its mechanical properties. In this study, the influence of artificial UV irradiations, wavelength 254 nm, on the viscoelastic properties and dynamic viscosity of both pickled and tanned hide was investigated by dynamic mechanical analysis. The influence of tanning on the viscoelastic properties and dynamic viscosity was also investigated. Freshly flayed bovine hide was conventionally prepared to pickling stage and split into two identical halves along the backline. One half was tanned using chromium sulfate, while the other half was left at the pickled stage. Samples of appropriate dimensions from both the pickled and tanned hides were cut and irradiated with artificial UV light for different time duration of 6-30 h. The irradiated samples were then analyzed using the DMA in the multi-frequency mode. It was found that irradiation caused an increase in the storage modulus (E 0 ) of pickled hide over the entire irradiation of 6 h followed by consistent decrease up to a duration of 30 h. Tanning caused an increase in tand that consistently decreased with the increase in the duration of irradiation. In addition, UV irradiation caused an increase in dynamic viscosity of pickled hide, but a decrease in tanned hide. The results show the predominant elastic nature of bovine hides as indicated by tand magnitudes less than a unit.