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A model for analyzing dynamic large-signal characteristics of double-barrier resonant-tunneling diodes (RTDs) is presented. The model is based on the analysis of dynamical trajectories in phase space, defined by the RTD bias and electron density in the RTD quantum well. We show that an accurate dynamic model can be reformulated in an approximate way, relying only on a directly measurable DC I–V curve and on few other RTD parameters, which could be easily estimated with simple DC calculations. We further demonstrate that a simple equivalent circuit, composed of a capacitor, inductor, and two resistors (RLRC), accurately describes the large-signal admittance of RTDs. The circuit elements can be described in terms of relaxation time, geometrical RTD capacitance, and low- and high-frequency resistors. The circuit has the very same structure as that previously derived for small-signal RTD admittance, although with deviating parameters, which are now dependent on the AC-signal amplitude. We show that the large-signal RTD relaxation time can be shorter and longer than the small-signal one. In the context of RTD oscillators, a shorter RTD relaxation time allows one to get higher output power at high frequencies. The availability of an accurate, general, but rather simple, physics-based model for analyzing large-signal RTD dynamics removes one of the major hindrances to the further development of sub-THz and THz RTD oscillators. [ABSTRACT FROM AUTHOR]

Vernonia amygdalina L., commonly utilized in traditional Vietnamese folk medicine for the management of afflictions including liver diseases, hypertension, diabetes, and elevated cholesterol levels. Despite its extensive employment in local herbal remedies, there exists a scarcity of scientific investigations elucidating its pharmacological and therapeutic potential. This research investigated the antioxidant activity of leaf extracts using a range of solvents, including n-hexane, chloroform, ethyl acetate, n-butanol, ethanol, and water. The ethyl acetate extract was identified as the most potent antioxidant, exhibiting EC50 values of 8.42 and 71.88 µg/mL in ferric reduction and DPPH assays, respectively. The hepatoprotective activity, as measured using the cellular lipid peroxidation method of ethanol leaf extract (IC50 = 5.87 µg/mL) is 4.75 times stronger than the trolox. Additionally, the ethanol extract demonstrated significant inhibitory potential against α-amylase and α-glucosidase enzymes (IC50 of 480.00 and 72.53 µg/mL, respectively). The acute oral toxicity study conducted on a mouse model indicates a safety margin at the experimental dose Dmax = 18.44 g extract/kg. Additionally, this study encompassed a leaf microdissection of V. amygdalina, elucidating pivotal morphological features. So, it is safe for further studies and producing functional products for disease prevention. [ABSTRACT FROM AUTHOR]

We demonstrate an "island" design of on-chip slot-antenna resonant-tunneling-diode (RTD) oscillators, where the contact n++ layer is removed everywhere except for a small island under the RTD. At frequencies around 2 THz, this design leads to a significant reduction (by a factor of ≈ 2) in the total Ohmic losses at the conducting surfaces of the slot antenna. With this design, we achieved the highest radiated power for RTD oscillators in the frequency range of 1.6–1.74 THz with around 2.2 μW at the fundamental frequency of 1.74 THz. Theoretical analysis of the oscillators indicates that with the utilized RTD design, the operating frequencies beyond 2 THz should be reached if the RTD contact resistance is reduced to 1–1.5 Ω μ m2. [ABSTRACT FROM AUTHOR]

Youths and adolescents are vulnerable to HIV/STIs from unprotected sex. Promotion of young population's awareness about risky sexual behaviors is essential to develop contextualized interventions. A cross-sectional study was conducted in five Vietnamese provinces to document current attitudes and practices regarding sexual behaviors among youths. The information on sociodemographic characteristics, substance use, and sexual behaviors was collected via self-reported questionnaires. The factors associated with risky sexual behaviors were identified by the multivariate logistic regression. Among the 1200 participants, 73.5% reported having sex in their lifetime, and 48.1% used condoms at their latest sexual intercourse. Participants in urban areas were more likely not to intend to use condoms and had a higher unintended pregnancy rate than in rural areas. Older age was positively associated with not wanting to use and not using condoms. Substance-using participants were more likely to not use condoms. The participants taking alcohol or other stimulants before sex had a higher likelihood of unintended pregnancy. Respondents' attitudes and practices regarding sexual behaviors were associated with gender and employment. This study indicated that young population's awareness in Vietnam is high, however, risky sexual behaviors also remain common. Sex-related educational programs about the consequences of substance use, multiple sex partners, and unprotected sex should be developed.