[en] Dark energy can be studied by its influence on the expansion of the Universe. We investigate current constraints on early dark energy (EDE) achievable by the combined observational data from type Ia supernovae (557), baryon acoustic oscillations, the current cosmic microwave background and the observed Hubble parameter. We find that combining these data sets provides powerful constraints on early dark energy and the best fit values of the parameters in 68% and 95% confidence-level regions are: Ω_m0 = 0.2897^{+0.0149+0.0207}_{-0.0138-0.0194}, Ω_e = 0.0129^{+0.0272+0.0381}_{-0.0129-0.0129}, w₀ = -1.0415^{+0.0891+0.1182}_{-0.109-0.1604}, and h = 0.6988^{+0.0059+0.0083}_{-0.0058-0.0081}.

[en] Taking a college building corridor as an example, the fire simulation software FDS is used to study the fire characteristics of narrow space. By creating a numerical model, the temperature field in the space is monitored, moreover the effect of ventilation conditions on the distribution of temperature in the channel is researched to provide a reference for the setting of the temperature detector in the channel. (paper)

[en] Highly sensitive detection of nitrite has drawn considerable concern owing to their destructive effect on both human health and the environment. A simple but sensitive electrocatalytic method for nitrite determination is significantly important in its real operation. Herein, a novel electrochemical nitrite sensor is synthetized by combining CuO with H-C₃N₄ and reduced graphene oxide (rGO). The N-doped carbon layer derived from H-C₃N₄ acting as “bridge” distributes evenly on the surface of rGO substrate and tunes the growth of CuO. The H-C₃N₄ acting as nucleation site could combine the catalytic center (CuO) and the substrate rGO to improve the electro-catalytic properties. The CuO/H-C₃N₄/rGO hybrid modified glassy carbon electrode exhibits remarkable sensing ability toward nitrite with a low detection limit of 0.025 μM (S/N = 3), wide linear response ranging from 0.2 μM–110 μM and a high sensitivity of 0.093 μAμM⁻¹.

[en] We derive the upper limit on the dark matter (DM) fraction in primordial black holes (PBHs) in the mixed DM scenarios. In this scenarios, a PBH can accrete weakly interacting massive particles (WIMPs) to form a ultracompact minihalo (UCMH) with a density profile of ρ${}_{DM}$(r) ∼ r${}^{-<!--\; ???\; -->9/4}$. The energy released from UCMHs due to dark matter annihilation has influence on the photodissociation of ${}^4$He, producing the ${}^3$He and the D. By requiring that the ratio (${}^3$He+D)/H caused by UCMHs does not exceed the measured value, we derive the upper limit on the dark matter fraction in PBHs. For the canonical value of DM thermally averaged annihilation cross section $⟨<!--\; ???\; -->$σv$⟩<!--\; ???\; -->$ = 3×10${}^{-<!--\; ???\; -->26}$ cm${}^3$ s${}^{-<!--\; ???\; -->1}$, we find that the upper limit is $f_{PBH}$< 0.35(0.75) for DM mass m${}_{\mathrm{\chi <!--\; ??\; -->}}$ = 1(10) GeV. Compared with other limits obtained by different astronomical measurements, although our limit is not the strongest, we provide a different way of constraining the cosmological abundance of PBHs.

[en] It has been proposed that ultracompact minihalos (UCMHs) might be formed in earlier epoch. If dark matter consists of Weakly Interacting Massive Particles (WIMPs), UCMHs can be treated as the γ-ray sources due to dark matter annihilation within them. In this paper, we investigate the contributions of UCMHs formed during three phase transitions (i.e., electroweak symmetry breaking, QCD confinement and e⁺e⁻ annihilation) to the extragalactic γ-ray background. Moreover, we use the Fermi-LAT observation data of the extragalactic γ-ray background to get the constraints on the current abundance of UCMHs produced during these phase transitions. We also compare these results with those obtained from Cosmic Microwave Background (CMB) observations and find that the constraints from the Fermi-LAT are more stringent than those from CMB

[en] Charge trap flash memory capacitors incorporating various (ZrO_2)_x(SiO_2)_1_−_x films (x = 1.0, 0.92, 0.79, 0.63, 0.46, 0.28, 0.17 and 0.08) as the charge trapping layer were fabricated, and the dependence of the memory window, data retention and program/erase speed on the mole fraction value x were investigated. It was observed that changing the elemental composition affects the dielectric constant and equivalent oxide thickness of (ZrO_2)_x(SiO_2)_1_−_x films, and the memory capacitor (x = 0.63) exhibits a memory window as large as 10.7 V for a ±10 V sweeping voltage range, and a low extrapolated charge loss of 9.0% over a period of 10 years. A faster program/erase speed can be obtained for memory capacitors when x = 0.79 and 0.63. The results should be attributed to the different (ZrO_2)_x(SiO_2)_1_−_x microstructures, defect state densities and energy band alignments resulting from the change of compositions. In order to achieve the trade-off between the memory window, data retention, and program/erase speed, the optimal x values of the (ZrO_2)_x(SiO_2)_1_−_x trapping layer are in the range of 0.63 to 0.79 for charge trap flash memory applications. The present study provides useful insights for the composition selection for a complex oxide-based charge trap flash memory. (paper)

[en] It was proposed that the massive compact halo objects (MCHOs) would be produced during an earlier epoch of cosmology if the density perturbations are between 3x10^-4 and 0.3. Then these objects can accrete dark matter particles onto them due to their high density. If the dark matter is in the form of the weakly interacting massive particles, the MCHOs can have a significant effect on the evolution of cosmology due to the dark matter annihilation within them. Using the WMAP-7 years data, we investigated the constraints on the current abundance of MCHOs (f_MCHOs) formed during the e⁺e^- annihilation phase transition. We have found that the 2σ constraint is f_MCHOs < or approx. 10^-4 for dark matter masses in the range between 1 GeV and 1 TeV.

[en] Highlights: • A numerical simulation method for the coupling flow and heat transfer process of liquid metal HCOTSG is proposed. • The correctness of the method is validated by comparing with relevant experimental research, and the maximum error is less than 25%. • The flow and heat transfer characteristics of liquid metal HCOTSG under different working conditions are analyzed. Much attention has been focused on the Liquid Metal Fast Reactor (LMFR) as one of the most promising concepts for GEN-IV reactors. Helical coil once-through tube steam generator (HCOTSG) is a proposed form of steam generator. Due to its unique advantages, HCOTSG is widely used in various reactor power systems, including LMFR. In this paper, a numerical approach is proposed to simulate heat transfer from the primary side (liquid metal) and secondary side (water/steam). The liquid lead-bismuth eutectic (LBE) is flowing in the shell side and pressurized water is flowing in the tube side. FLUENT CFD commercial code is adopted for the simulations. The robustness of the method is validated by comparing it with relevant experimental research, and the maximum error is less than 25%. Based on this method, the distribution of thermal-hydraulic parameters inside HCOTSG is obtained and the flow and heat transfer characteristics are analyzed. The influence of boundary conditions and geometric parameters on the flow and heat transfer in HCOTSG is analyzed. The comprehensive performance of different models is compared with the comprehensive performance evaluation index. The optimal geometric arrangement scheme for the working conditions is recommended. Compared with the reference model, the comprehensive performance can be improved by up to 14%. This study provides a numerical simulation method reference for the study of flow and heat transfer characteristics and structural design optimization of liquid metal HCOTSG.

[en] Highlights: • A numerical simulation method for liquid metal HCOTSG is proposed. • The wall heat flux and comprehensive performance are compared. • The radial pitch has a significant effect on the wall heat flux. • The HCOTSG has the best performance when P_r /D is 0.167 and P_a /D is 0.137. Lead-bismuth Fast Reactor (LFR) has attracted attentions due to its intrinsic characteristics, such as sustainability, safety, and economics. Helical coil once-through tube steam generator (HCOTSG) is a proposed form of steam generator. Due to its unique advantages, HCOTSG is widely used in various reactor power systems, including LMFR. In this paper, FLUENT CFD commercial code is adopted to simulate heat transfer from the primary side (liquid metal) and secondary side (water/steam). The robustness of the method is validated by comparing it with relevant experimental research, and the maximum error is less than 25%. Based on this method, 9 models with different geometrical parameters were established to analyze the effects of geometrical parameters on the performance of liquid metal HCOTSG. The wall heat flux and comprehensive performance factor (En) of different models is compared. The optimal geometric arrangement scheme for the working conditions is recommended. The geometrical parameters of the tube side and shell side are analyzed as sensitivity parameters. Among the established geometric models, the HCOTSG has the best comprehensive performance when P_r /D is 0.167 and P_a /D is 0.137 under the working conditions in this paper. This study provides a numerical simulation method on structural design optimization of liquid metal HCOTSG.

[en] Highlights: • Aspergillus niger residue from citrate fermentation was used for chitosan production. • Chitosan was produced after pretreatment of residue with steam explosion and ion liquid. • Yield of sugar, chitosan deacetylation, and by-product fermentation were improved. • Comprehensive utilization of A. niger waste reduced environmental pollution. • Utilization of industrial waste is important for sustainable development. Aspergillus niger mycelium residues, a citric acid fermentation by-product, is a raw material for fungal chitosan and glucosamine (GlcN). However, traditional chemical extraction of fungal chitosan and GlcN uses strong acid at high temperatures for long periods and has several drawbacks, including high cost and environmental pollution. In this work, the residues were pretreated by the combination of steam explosion (SE) and ionic liquid (IL) to produce fungal chitosan and GlcN hydrochloride. Following chemical extraction, GlcN hydrochloride yield increased by 65.49 ± 8.14%, and soluble sugar release reached 0.36–0.46 g/g via SE pretreatment at 2.5 MPa for 1 min. Fungal chitosan was produced via enzymatic hydrolysis. Combined SE and IL pretreatment increased deacetylation degree (1.29 ± 0.06-fold) of fungal chitosan by chitin deacetylase hydrolysis using Rhodococcus equi CGMCC14861 (ReCDA) at 37 °C for 6 h. Besides, fungal chitosan was produced using a by-product recycling strategy, promoting ReCDA fermentation, using supernatant with soluble sugars and proteins. After mixing 0.2 g by-product supernatant with 100 mL medium, ReCDA production was 1.5-fold higher than that in the control. This study demonstrates a green technology for efficient utilization of fungal chitin from A. niger mycelium residues of citric acid fermentation.