The temperature-dependent (10–300 K) optical band gap ${\mathit{E}}_0$(T) of the epitaxial metastable zinc-blende-structure β-GaN(001)4×1 has been determined by modulated photoreflectance and used to interpret low-temperature photoluminescence spectra. ${\mathit{E}}_0$ in β-GaN was found to vary from 3.302±0.004 eV at 10 K to 3.231±0.008 eV at 300 K with a temperature dependence given by ${\mathit{E}}_0$(T) =3.302–6.697×${10}^{\mathrm{-}4}$ ${\mathit{T}}^2$/(T+600) eV. The spin-orbit splitting ${\mathrm{\Delta }}_0$ in the valence band was determined to be 17±1 meV. The oscillations in the photoreflectance spectra were very sharp with a broadening parameter Γ of only 10 meV at 10 K. The dominant transition observed in temperature-dependent photoluminescence was attributed to radiative recombination between a shallow donor, at ≃11 meV below the conduction-band edge and the valence band.

The COVID-19 pandemic demonstrated the critical need for accurate and rapid testing for virus detection.

The optical energy gap of ${\mathrm{Ge}}_{\text{1−x}}{\mathrm{Sn}}_x$ alloys has been determined from transmittance measurements, using a fast-Fourier-transform infrared interferometer. Our results show that the change from indirect to direct band gap occurs at a lower critical Sn concentration ${\mathrm{(x}}_c)$ than the value predicted from the virtual crystal approximation, tight binding, and pseudopotential models. However, a close agreement between the experimental results and the predictions with deformation potential theory is observed. The concentration $x_c,$ which is theoretically expected to be 0.09, actually it is observed to lie between ${\text{0.10<x}}_c\text{<0.13.}$

Breast cancer is the most common type of malignant tumor among women and their second leading cause of cancer-related deaths. The most common method for screening and diagnosis is mammography. Nonetheless, two main problems have been identified. First, the dose of radiation received during the test prevents the method from the use on women who are < 40 years old. Second, there can be mammogram failure owing to the lack of tumor contrast with the fibrous tissue. Therefore, there is a need for screening methods that will help to identify high-risk cases. We developed a biological marker test that can help to identify them. Increased levels of sialic acid (SA) in saliva are known to correlated with breast cancer. In this study, we evaluated the feasibility of Raman spectroscopy as a method for quantification of SA in saliva, using citrate-reduced silver nanoparticles (cit-Ag-NPs) as a surface-enhanced Raman spectroscopy (SERS) substrate. Quantification of SA was accomplished by measuring its intensity in saliva and comparing it with a calibration curve of SA standards. The mean SA concentration in saliva was found to be significantly higher among 100 breast cancer patients (18.3 ± 9.4 mg·dL^–1; mean ± SD) than among 106 healthy controls (3.5 ± 1.0 mg·dL^–1). The SERS test showed sensitivity of 94% and specificity 98% for detection of patients with breast cancer, assuming that SA concentration >7 mg·dL^–1 is a cutoff for positive test results. Our findings prove the usefulness of this SERS technique as a simple, convenient, and highly sensitive method of quantitative analysis of SA in saliva. The simplicity of this nanotechnological test may help to substantially reduce the mortality among patients with breast cancer by providing women with a simple, noninvasive screening test that can be applied regardless of age or density of breast tissue.