The AC fault ride-through and support capability of line commutated converter based high voltage direct current (LCC-HVDC) have significant influence on the safe operation of power system. The ...ability of phase locked loop (PLL) to synchronize with the voltage phase under AC faults would affect the recovery performance of LCC-HVDC systems. This paper analyzes the influence of the conventional PLL on the subsequent commutation failure (SCF) of LCC-HVDC systems and points out that the conventional PLL has some problems such as slow dynamic response, significant frequency fluctuation, and coupling of phase and frequency detection under fault conditions. A novel PLL is proposed to address the problems. Cascade delayed signal cancellation operators are combined with a mathematical filter, forming a hybrid pre-filter to extract fundamental positive sequence voltage for the PLL. To reduce the fluctuation of PLL's frequency during AC faults, the estimated frequency is fixed when the fault is detected by a fault detector. As a consequence, the decoupling between phase detection and frequency detection is realized, and the proposed PLL's dynamic response performance is enhanced. Simulation results show that the proposed PLL can provide accurate phase reference for the DC control system and reduce the probability of SCFs of LCC-HVDC system.
•The phase error of the PLL will increase the risk of commutation failure.•The original control cannot generate firing angle order precisely during AC faults.•An improved PC-EAC is proposed.•The ...proposed control precisely calculated the firing angle order of each valve.•The proposed control can effectively reduce the risk of commutation failure.
In HVDC projects, the predictive calculation-based extinction angle control (PC-EAC) generates the firing angle order by means of open loop. Under the steady-state condition, the result of its calculation is accurate. However, when a fault occurs in AC system, a serious calculation error will exist, which increases the risk of commutation failure. Therefore, an improved control is proposed. In this control, the firing angle order of each converter valve is separately calculated according to its commutation voltage, and considering the influence of the firing pulse control system, a compensation term is added to eliminate the deviation between actual firing angle and its order. In order to ensure the equidistant pulse control of each converter valve, the minimum firing angle order of all valves is taken as the output of the controller. Finally, several simulations are conducted on the CIGRE HVDC Benchmark model and a ±500 kV/3 kA project model to validate the performance of the proposed strategy. The simulation results show that the proposed control can effectively reduce the risk of commutation failure, and make the system recovery more stable.
In the deep Earth, hydrogen mainly occurs as structural hydroxyl and molecular water in minerals and melts, constituting mobile and immobile aqueous components. Hydrous minerals contain hydrogen ...which occupies a specific structural position and constitutes an indispensable component of chemical formulae. On the other hand, nominally anhydrous minerals do not contain hydrogen in their chemical formulae, but can host trace amounts of water in structural position and lattice defect. The molecular water may occur in the lattice defect as fluid/melt inclusions in minerals. Even though the water content of nominally anhydrous minerals is very limited generally in the order of ppm（parts per million）, they may play a significant role in influencing the physicochemical properties of mineral and rock systems. With the continuous improvement of modern instrumentations, the analytical methodology exhibits trends for higher spatial resolution, lower detection limit and integral multiple methods on the water amount and its isotopic ratio. Among these methods, Fourier transform infrared spectrometry remains the most widely used, while secondary ion mass spectrometry, continuous flow mass spectrometry, elastic recoil detection analysis and Raman spectrometry are promising. This paper provides a brief review on the methodological progress and their applications to the analysis of structural water in nominally anhydrous minerals.
Gel-based ionic thermoelectric (i-TE) conversion systems have attracted more attention to harvest energy from ambient waste heat to power sensors in IoT systems, due to their high ionic thermopower, ...cost-effectiveness, and environmental friendliness. However, their thermoelectric performance, particularly output power density, remains low, hindering their further application. To date, there is still a lack of an effective strategy to reverse this serious situation. Herein, we originally designed an ionic thermoelectric-electrochemical (i-TE-EC) cell by combining two asymmetric gels into a double sandwich structure, resulting in high thermoelectric performance. By tailoring gel compositions, including the concentration and ratio of redox couples as well as additive contents, a maximum output power density
P
max
/(Δ
T
)
2
of 10.0 mW m
−2
K
−2
, a cell ionic thermopower of 5.2 mV K
−1
, and an energy density of 3.4 J m
−2
K
−2
in two hours were obtained at 313 K for the i-TE-EC cell Gp | G-
m
/
n
FeCN
4−/3−
| Gp | G-
x
/
y
I
−
/I
3
−
-
z
CF
3
SO
3
K | Gp (
m
/
n
= 0.175/0.025 M,
x
/
y
= 0.10/0.05 M,
z
= 0.4 M). Moreover,
P
max
/(Δ
T
)
2
increased to a higher value of 20.5 mW m
−2
K
−2
for the i-TE-EC cell using a CEM as a built-in electrode. A gel-device assembled by nine single i-TE-EC cells connected in series generated a voltage of 1.55 V and a high
P
max
/(Δ
T
)
2
of 5.2 mW m
−2
K
−2
at 313 K and Δ
T
= 5 K. This work provides a promising route for improving the gel-based thermoelectric performance, available for other energy conversion systems.
An ionic thermoelectric-electrochemical (i-TE-EC) cell constructed using asymmetric gels shows ultra-high thermoelectric performance.
The example of rare-earth metal-catalyzed guanylation/cyclization of amino acid esters and carbodiimides is well-established, forming 4(3H)-2-alkylaminoquinazolinones in 65–96% yields. The ...rare-earth metal amides REN(TMS)23 (RE = Y, Yb, Nd, Sm, La; TMS = SiMe3) showed high activities, and LaN(TMS)23 performed best for a wide scope of the substrates.
Gel thermocells employing redox couple ions as carriers can convert heat into electricity, playing an important role in low-grade heat harvesting. However, a major challenge is maintaining the high ...ionic thermoelectric performance at non-room temperatures due to the limited heat tolerance of gels. Herein, we propose an effective strategy to improve both ionic thermopower and output power density at high temperatures by optimizing the gel composition
via
introducing graphene. Graphene forming a structure like a "bridge" could improve the ion diffusion coefficient and exchange current density, thereby improving performance. A high ionic thermopower of up to 13 mV K
−1
, an output power density of 1.03 mW m
−2
K
−2
, and a continuous discharge energy density of 0.19 J m
−2
K
−2
in 1 h were obtained at 323 K in gels of Gelatin-0.04/0.06 M FeCN
4−/3−
-6 wt% Gr. In addition, a record-high output power density of 1.2 mW m
−2
K
−2
was delivered at 323 K in a device assembled by four gel thermocells in series. This work provides an achievable guide for fabricating and designing high-performance gels to harvest low-grade heat, especially at high operating temperatures.
Graphene forms a structure like a "bridge" to link adjacent free water clusters in gels, accelerating ion diffusion and improving ionic thermoelectric performance.
Osteosarcoma (OS) is the most common malignancy that occurs mainly during childhood and adolescence; however, no clear molecular or biological mechanism has been identified. In this study, we aimed ...to explore new biomarkers for the early diagnosis, targeted treatment, and prognostic determination of osteosarcoma. We first used bioinformatics analysis to show that KIF21B can be used as a biomarker for the diagnosis and prognosis of osteosarcoma. We then examined the expression of KIF21B in human osteosarcoma tissues and cell lines using immunohistochemistry, western blotting, and qRT-PCR. It was found that KIF21B expression was significantly upregulated in osteosarcoma tissues and cell lines. After knocking down the expression of KIF21B in the osteosarcoma cell lines 143B and U2-OS, we used cell fluorescence counting, CCK-8 assays, flow cytometry, and TUNEL staining to examine the effects of KIF21B on osteosarcoma cell proliferation and apoptosis. The results demonstrated that knocking down KIF21B in 143B and U2-OS cells could increase cell apoptosis, inhibit cell proliferation, and reduce tumor formation in nude mice. Subsequently, we used gene chips and bioinformatics to analyze the differential gene expression caused by knocking down KIF21B. The results showed that KIF21B may regulate OS cell proliferation and apoptosis by targeting the PI3K/AKT pathway. We then examined the expression of PI3K/AKT- and apoptosis-related proteins using western blotting. KIF21B knockdown inhibited the PI3K pathway, downregulated Bcl-2, and upregulated Bax. Moreover, the use of PI3K/AKT pathway agonists reversed the regulatory effect of KIF21B on the apoptosis and proliferation of 143B and U2-OS cells. In conclusion, our results indicated that KIF21B plays a key role in osteosarcoma. Low KIF21B expression might indirectly increase the apoptosis and inhibit the proliferation of osteosarcoma cells through the PI3K/AKT pathway.
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•Aerobic granular sludge with the filamentous bacterium Kouleothrix was obtained.•Kouleothrix acted as skeleton and fermenting bacteria for granulation.•The functional genes involved ...in VFA production and PHA synthesis increased.•A collaborative pathway between Kouleothrix and Ca. Competibacter was proposed.
Forming and maintaining stable aerobic granular sludge (AGS) at a low superficial gas velocity (SGV) is challenging, particularly with polymeric substrates. This study cultivated filamentous aerobic granular sludge (FAGS) with filamentous Kouleothrix (Type 1851) at low SGV (0.15 cm/s) utilizing mixed acetate-soluble starch. Within approximately 260 days, notable increases in the relative abundance of Kouleothrix (from 4 % to 10 %) and Ca. Competibacter (from 1 % to 26 %) were observed through 16S rRNA gene analysis. Metagenomic analysis revealed increased expression of functional genes involved in volatile fatty acid (VFA) production (e.g., ackA and pta) and polyhydroxyalkanoate synthesis (e.g., phbB and phbC). Kouleothrix acted as a skeleton for bacterial attachment and was the key fermenting bacteria promoting granulation and maintaining granule stability. This study provides insight into the formation of FAGS with low-energy and non-VFA substrates.
The stabilization mechanism of water-in-oil (W/O) emulsions has been studied by measuring the interactions between two water droplets in n-tetradecane using atomic force microscopy. The effects of ...water-soluble surfactants (SDS/CTAB/Tween 80), an oil-soluble surfactant (Span 20), and the coexistence of the water and oil-soluble surfactants on the stability of water droplets in oil were investigated separately. It is found that the addition of oil-soluble surfactants (Span 20) prevents the coalescence of water droplets in oil. To discuss the role of an oil-soluble surfactant, we analyzed the force curve by applying the theoretical model. The results demonstrate that the oil-soluble surfactant (Span 20) stabilizes dispersed droplets by adsorbing onto the interface and forming a relatively tighter layer with the increase in surfactant concentration, which hinders film rupture. This behavior of the surfactant could also be properly characterized by steric hindrance. A further step was taken by introducing another water-soluble surfactant. It is found that the addition of either SDS or CTAB into the water phase is futile in inducing droplet coalescence in the presence of Span 20. In contrast, Tween 80 was found to be effective in destabilizing water droplets, which could be due to the competitive adsorption between Tween 80 and Span 20 at the interface. By characterizing the interfacial adsorption of Tween 80 and Span 20 with a theoretical adsorption isotherm model, the result indicates that interface replacement would result in a loose adsorption layer that is insufficient to hinder droplet coalescence. Our study provides an intriguing understanding of the role of surfactants in the stabilization and destabilization of water-in-oil emulsions.
![RE[N(SiMe3)2]3‑Catalyzed Gu...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0022-3263/small "RE[N(SiMe3)2]3‑Catalyzed Guanylation/Cyclization of Amino Acid Esters and Carbodiimides")
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