Hue University Journal of Science: Natural Science

Some remarks on Pixley-Roy hyperspaces

Luong Quoc Tuyen, Ong Van Tuyen, Nguyen Xuan Truc* — Mon, 16 Jun 2025 00:00:00 +0000

In this paper, we study cellular-compact, cellular-Lindel\"of, strongly star-Hurewicz, strongly star-Rothberger, strongly star-Menger spaces on hyperspaces with the Pixley-Roy topology. For a space $X$ and $n\in\mathbb N$, we prove that
(1) If $\texttt{PR}[X]$ or $\texttt{PR}_n[X]$ is cellular-compact, then $X$ is cellular-compact. However, there exists a compact space $X$ such that $|X|=\omega$, but $\texttt{PR}_n[X]$ for all $n\in\mathbb N$ and $\texttt{PR}[X]$ are not cellular-compact spaces.
(2) If $\texttt{PR}[X]$ or $\texttt{PR}_n[X]$ is cellular-Lindel\"of, then $X$ is cellular-Lindel\"of.
(3) $X$ is countable if and only if $\texttt{PR}[X]$ is a strongly star-Hurewicz space, if and only if $\texttt{PR}[X]$ is a strongly star-Rothberger space if and only if$\texttt{PR}[X]$ is a strongly star-Menger space.

Second main theorem for Holomorphic curves intersecting a Fermat-type hypersurface in projective spacel

Nguyen Thi Xuan Mai*, Pham Truc Lam, Nguyen Dang Khai, Tran Nhat Minh — Mon, 16 Jun 2025 00:00:00 +0000

Let $s, b, d$ be positive integers with $(s+bd)-(n+1)(s+bn)>0$. Let $R_{i}$ be homogeneous polynomials of degree $s$ and $Q_i$ be homogeneous polynomials of degree $b$. For an algebraically non-degenerate holomorphic curve $f\colon\mathbb{C}\rightarrow\mathbb{C} \mathbb{P}^n$, for a Fermat-type hypersurface of the form $\sum_{i=0}^{n} Q_i R_{i}^{d}=0$, we obtain a Second Main Theorem type estimate in which the counting function are truncated to level $n$.

Modifications of major pigment content of Chlorella vulgaris cultured in different media

Thi Dong Phuong Nguyen* — Mon, 16 Jun 2025 00:00:00 +0000

Currently, to avoid the harmful effects of artificial dyes, scientists strongly encourage the use of natural pigments derived from organisms such as microalgae. Although microalgae are known to outperform all other microorganisms in terms of pigment production, their natural occurrence is insufficient for the increasing commercial demand. Therefore, further enhancing the pigment production in the algae cells is of tremendous significance. Some environmental factors known to regulate natural pigment synthesis are changes in pH, temperature, light, salinity and nutrients of the environment. This study indicates that further manipulation of major nutrient parameters, such as nitrogen (N), phosphorus (P), and carbon (C), in the culture medium can be the easiest way to intervene among other physical parameters with the aim of cultivating microalgae at an industrial scale and commercial production. It also emphasises that if the N content is doubled compared with the standard Bold’s Basal Medium (BBM), the Chlorophyll a content obtained will be higher, reaching (37 ± 0.08) mg/L, while doubling the P content cannot increase chlorophyll production but increases carotenoid synthesis with the highest content compared with the remaining media. Similarly, replacing the C source of glucose with NaHCO₃ also changes the synthesis of pigments, and the concentrations of chlorophyll a, b and carotenoids are all higher than in BBM. Therefore, the results of this study might indicate that if the N/P ratio is doubled compared with its ratio in the BBM medium, the ability to synthesise chlorophyll and carotenoids will increase. This will be the basis for cultivating microalgae in other environments besides the traditional BBM medium to collect chlorophyll or pigments.

Synthesis and characterization of ZnxMn(1–x)Fe2O4

Nguyen Le My Linh*, Do Mai Nguyen — Mon, 16 Jun 2025 00:00:00 +0000

Zn_xMn₍₁_–x)Fe₂O₄ nanoparticles were successfully prepared in the isopropanol solvent with the hydrothermal method and the hydrothermal method combined with impregnation. The characterization of the samples by using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier Transform Infrared (FTIR), and surface area analysis (BET) was conducted. The samples synthesized with the hydrothermal method had a phase composition of franklinite (Zn,Mn,Fe)(Fe,Mn)₂O₄. Meanwhile, the samples synthesized with the hydrothermal method combined with impregnation had the main phase composition of Zn_xMn₍₁_–x)Fe₂O₄_.The Zn_0.8Mn_0.2Fe₂O₄(ZnFe₂O₄/MnSO₄molar ratio = 4:1) sample exhibited the highest degree of structural order, with a BET surface area of 25.7 m²/g.

Cyclone microbubble flotation for enhanced oil recovery from palm oil mill effluent

Le Van Tuan* — Mon, 16 Jun 2025 00:00:00 +0000

In this study, we investigate cyclone microbubble (CMB) flotation for oil recovery from palm oil mill effluent (POME) under batch and continuous operations. Designed to reduce floated waste and enhance oil separation, the process was tested on a real POME from a Malaysian palm oil mill, with high temperature, low pH, and fluctuating oil and grease (O&G), total solids (TS), and chemical oxygen demand (COD) levels. For a mill processing 1,000 tons of fresh fruit bunches (FFB) daily, the POME discharge contained 7.9 tons of O&G, 36.5 tons of TS, and 59.2 tons of COD. Batch flotation achieved ~63.8% of O&G separation with a 60-minute retention time, whereas continuous flotation (flow rate > 20 L/min) showed a lower efficiency (36 ± 9%). However, O&G was enriched 3 times in the recovery tank, demonstrating an effective oil concentration. Economic analysis confirmed that energy costs were significantly lower than the value of recovered palm oil, highlighting CMB flotation’s cost-effectiveness. The findings support CMB flotation as a scalable and sustainable POME treatment method, with a potential for further efficiency improvements.

Evolution of microscopic domains in Co/Pt multilayers with perpendicular magnetic anisotropy

Duy-Truong Quach* — Mon, 16 Jun 2025 00:00:00 +0000

We investigated the domain evolutions of (0.3nm Co/0.8nm Pt)_n multilayers (n = 5 and 10) with perpendicular magnetic anisotropy. Our direct observation of magnetic domain structures by means of magneto-optical microscopy reveals that under a negative magnetic field, domain evolution happens via domain wall motion at the domains’ boundaries. However, under a reversed field, the domains react differently depending on their domains’ substructures. While the domains shrink solely at their boundaries when n = 5, the domain wall motion was observed mostly inside the domains’ boundaries when n = 10. This could offer an effective way of using magneto-optical microscopy to investigate domain structures of multilayers with fine substructures without using other high-resolution observation methods.

Preparation of natural polymer coating incorporating silver nanoparticles to extend shelf life of passion fruit

Ngoc Duy Nguyen, Thi Bich Phuong Ho, Ho Minh Chau Le, Xuan Du Dang* — Mon, 16 Jun 2025 00:00:00 +0000

Passion fruit is highly perishable because of its vigorous metabolic activity after harvest. Therefore, "green" preservation using safe natural polysaccharides as functional coatings is of significant research interest. This study investigated the combined effects of chitosan and silver nanoparticle coatings at varying concentrations on the quality and shelf life of passion fruit. The results show that the appropriate chitosan concentration to prolong the preservation time was 1%. After 20 days of storage at 25 ± 2 °C, the weight loss was 19.59%. The total yeast and mold, soluble solids, acidity, and vitamin C content were 8.1 × 10⁶ CFU/g, 14.5 °Bₓ, 6.31%, and 0.1583 mg/g, respectively. The coating from chitosan 1%-silver nanoparticles 5 mg/L solution was the most effective in the weight loss of the passion fruit at 17.4%, and the fruit peel colour changed insignificantly. The treated samples exhibited a total yeast and mold count of 1.3 × 10⁵ CFU/g, soluble solids of 14.83 °B_x, the acidity of 6.59%, and vitamin C content of 0.1841 mg/g. Interestingly, no silver nanoparticle residues were detected in the fruit flesh. These findings provided a scientific basis and demonstrated the practical potential of silver nanoparticle-chitosan coatings for effective fruit preservation.

Treatment of urban wastewater discharged into Tinh Tam lake using hydrogen peroxide-supplemented aerated biofilter system

Dang Thi Thanh Loc, Le Van Tuan* — Mon, 16 Jun 2025 00:00:00 +0000

This study investigates the application of a hydrogen peroxide-supplemented aerated biofilter system (ABF-H₂O₂) for the treatment of urban domestic wastewater from the Tinh Tam Lake catchment area, located within the Imperial Citadel of Hue City, Vietnam. In the absence of centralised treatment facilities, untreated sewage from a combined sewer system is directly discharged into this ecologically and historically significant lake. A laboratory-scale ABF-H₂O₂ reactor was designed and operated over 45 days, treating both synthetic and actual urban wastewater. Key operational parameters included organic loading rate, hydraulic retention time, and H₂O₂ dosage. The system achieved removal efficiencies of 69–81% for chemical oxygen demand and 88–94% for five-day biochemical oxygen demand. Ammonium (NH₄⁺–N) removal reached 87% under low-loading conditions but declined to 27% at higher organic loading rates. H₂O₂ supplementation improved dissolved oxygen availability, supporting microbial activity and treatment stability under elevated stress. Microscopic analysis revealed a diverse and well-adapted microbial community, including protozoa and metazoa. These results highlight the potential of the ABF-H₂O₂ approach as a sustainable and decentralised wastewater treatment solution for urban heritage areas such as the Imperial City of Hue City.