Ni‐rich layered oxides are one of the most attractive cathode materials in high‐energy‐density lithium‐ion batteries, their degradation mechanisms are still not completely elucidated. Herein, we ...report a strong dependence of degradation pathways on the long‐range cationic disordering of Co‐free Ni‐rich Li1−m(Ni0.94Al0.06)1+mO2 (NA). Interestingly, a disordered layered phase with lattice mismatch can be easily formed in the near‐surface region of NA particles with very low cation disorder (NA‐LCD, m≤0.06) over electrochemical cycling, while the layered structure is basically maintained in the core of particles forming a “core–shell” structure. Such surface reconstruction triggers a rapid capacity decay during the first 100 cycles between 2.7 and 4.3 V at 1 C or 3 C. On the contrary, the local lattice distortions are gradually accumulated throughout the whole NA particles with higher degrees of cation disorder (NA‐HCD, 0.06≤m≤0.15) that lead to a slow capacity decay upon cycling.
A series of Ni‐rich Li1−m(Ni0.94Al0.06)1+mO2 (NA) oxides are synthesized through tailoring the heating temperature. The NA oxides with high cation disorder experience a comparably homogeneous fatigue process upon extended cycling, while a disordered surface with lattice mismatch is gradually formed in the NA with low cation disorder (i.e. heterogeneous degradation) which results in a rapid capacity decay during the fast charge–discharge cycling.
To quantify the fate of respiratory droplets under different ambient relative humidities, direct numerical simulations of a typical respiratory event are performed. We found that, because small ...droplets (with initial diameter of 10 μm) are swept by turbulent eddies in the expelled humid puff, their lifetime gets extended by a factor of more than 30 times as compared to what is suggested by the classical picture by Wells, for 50% relative humidity. With increasing ambient relative humidity the extension of the lifetimes of the small droplets further increases and goes up to around 150 times for 90% relative humidity, implying more than 2 m advection range of the respiratory droplets within 1 sec. Employing Lagrangian statistics, we demonstrate that the turbulent humid respiratory puff engulfs the small droplets, leading to many orders of magnitude increase in their lifetimes, implying that they can be transported much further during the respiratory events than the large ones. Our findings provide the starting points for larger parameter studies and may be instructive for developing strategies on optimizing ventilation and indoor humidity control. Such strategies are key in mitigating the COVID-19 pandemic in the present autumn and upcoming winter.
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We numerically investigate both single and multiple droplet dissolution with droplets consisting of less dense liquid dissolving in a denser host liquid. In this situation, buoyancy can lead to ...convection and thus plays an important role in the dissolution process. The significance of buoyancy is quantified by the Rayleigh number
$Ra$
, which is the buoyancy force over the viscous damping force. In this study,
$Ra$
spans almost four decades from 0.1 to 400. We focus on how the mass flux, characterized by the Sherwood number
$Sh$
, and the flow morphologies depend on
$Ra$
. For single droplet dissolution, we first show the transition of the
$Sh(Ra)$
scaling from a constant value to
$Sh\sim Ra^{1/4}$
, which confirms the experimental results by Dietrich
et al.
(
J. Fluid Mech.
, vol. 794, 2016, pp. 45–67). The two distinct regimes, namely the diffusively and the convectively dominated regimes, exhibit different flow morphologies: when
$Ra\geqslant 10$
, a buoyant plume is clearly visible, which contrasts sharply with the pure diffusion case at low
$Ra$
. For multiple droplet dissolution, the well-known shielding effect comes into play at low
$Ra$
, so that the dissolution rate is slower as compared to the single droplet case. However, at high
$Ra$
, convection becomes more and more dominant so that a collective plume enhances the mass flux, and remarkably the multiple droplets dissolve faster than a single droplet. This has also been found in the experiments by Laghezza
et al.
(
Soft Matt.
, vol. 12 (26), 2016, pp. 5787–5796). We explain this enhancement by the formation of a single, larger plume rather than several individual plumes. Moreover, there is an optimal
$Ra$
at which the enhancement is maximized, because the single plume is narrower at larger
$Ra$
, which thus hinders the enhancement. Our findings demonstrate a new mechanism in collective droplet dissolution, which is the merging of the plumes, which leads to non-trivial phenomena, contrasting the shielding effect.
Indoor ventilation is essential for a healthy and comfortable living environment. A key issue is to discharge anthropogenic air contamination such as CO$_2$ gas or, of potentially more direct ...consequence, airborne respiratory droplets. Here, by employing direct numerical simulations, we study mechanical displacement ventilation with a wide range of ventilation rates $Q$ from 0.01 to 0.1 m$^3$ s$^{-1}$ person$^{-1}$. For this ventilation scheme, a cool lower zone is established beneath a warm upper zone with interface height $h$, which depends on $Q$. For weak ventilation, we find the scaling relation $h\sim Q^{3/5}$, as suggested by Hunt & Linden (Build. Environ., vol. 34, 1999, pp. 707–720). Also, the CO$_{2}$ concentration decreases with $Q$ within this regime. However, for too strong ventilation, the interface height $h$ becomes insensitive to $Q$, and the ambient averaged CO$_2$ concentration decreases towards the ambient value. At these values of $Q$, the concentrations of pollutants are very low and so further dilution has little effect. We suggest that such scenarios arise when the vertical kinetic energy associated with the ventilation flow is significant compared with the potential energy of the thermal stratification.
•Cooling pipes are embedded in the wall through which water is circulated.•The heat transfer and electric consumption of the system is investigated.•The performance of pipes is satisfactory in the ...three typical Chinese cities.•Cooling pipes can provide greater heat reductions on the sunny sides.
An active pipe-embedded building envelope, which is a kind of external wall with cooling pipes embedded, has been developed recently to reduce heat transfer through building envelopes in summer. However, the method presented in previous studies was not good enough to analyze the thermal performance of this kind of building envelope during the whole cooling season. In this paper, a comprehensive numerical model is employed to simulate the conjugated heat transfer through a pipe-embedded building envelope in the whole summer. The model has been validated by the experimental data and then employed to a case study. The performance of the novel envelope in different orientations in three typical cities in China is analyzed with the cooling water produced from evaporative cooling. The results show that the cooling pipes are effective in the three typical cities in China, especially in Beijing where the reduced heat gain in the cooling season reaches 17.4kWh per square meter of wall. And the reduction rates of overall electricity consumption are 51.9% and 58.9% in Shanghai and Guangzhou, respectively. The embedded pipes are more suitable for orientations with more sunshine such as the roof and west wall. The study will help develop a comprehensive understanding of the dynamic performance of pipe-embedded envelopes utilizing evaporative cooling.
Hydrogel-based microfluidic chips are more biologically relevant than conventional polydimethylsiloxane (PDMS) chips, but the inherent swelling of hydrogels leads to a decrease in mechanical ...performance and deformation of the as-prepared structure in their manufacture and application processing. Non-swelling hydrogel has, for the first time, been utilized to construct microfluidic chips in this study. It was fabricated by covalently cross-linking the biocompatible copolymer of di-acrylated Pluronic F127 (F127-DA). Thanks to their non-swelling property, the hydrogel-based microfluidic chips maintain their as-prepared mechanical strength and channel morphology when equilibrated in aqueous solution at 37 °C. Moreover, the microfluidic chips are autoclavable and show an appropriately slow degradation rate by remaining stable within 21 days of incubation. Based on these properties, a vessel-on-a-chip was established by seeding human umbilical vein endothelial cells (HUVECs) onto the microchannel surfaces inside the microfluidic chip. Under 6 days of perfusion culture with a physiologically relevant shear stress of 5 dyne per cm
2
, the HUVECs in the chip show responsivity to fluid shear stress and express higher endothelial functions than the corresponding static culture. Therefore, non-swelling hydrogel-based microfluidic chips could potentially be applicable for cell/tissue-related applications, performing much better than conventional PDMS or existing hydrogel based microfluidic chips.
We use a non-swelling hydrogel to construct microfluidic chips and show that they could potentially be applicable for cell/tissue-related applications, performing much better than conventional PDMS or existing hydrogel based microfluidic chips.
•Spin-dependent tunnelling in 13 nm magnetite nanoparticles made by coprecipitation.•Nanoparticle electrostatic charging effect dominates the carrier transport.•Spin-disorder in the nanoparticle ...shell region.•High field magnetization 81% of the bulk value.•Evidence of the Verwey transition in the magnetic data.
Fe3O4 nanoparticles have been made by a co-precipitation method with an average size of 13 nm. Raman measurements show that there is also a small fraction of maghemite that is not seen in the XRD data. The saturation magnetization is high for this preparation method and the coercive field is low at 300 K. The high field magnetic moment cannot be fitted to a Bloch temperature dependence over the full temperature range, which is likely due to the effect of the Verwey transition at 120 K. Pressed powders shows a magnetoresistance of up to −6.5% at 8 T and 300 K. The magnetoresistance can be fitted to a model where there is a spin-dependent tunnelling between nanoparticles with a spin-disordered shell. The temperature dependence of the resistivity can be attributed to nanoparticle electrostatic charging effects.
Four new tetradentate Schiff-base ligands were prepared in situ from the 1 : 2 condensation of 1,3-diaminopropane and either 2-thiazolecarboxaldehyde (L2thiazole), 4-thiazolecarboxaldehyde ...(L4thiazole), 4-oxazolecarboxaldehyde (L4oxazole), or 5-bromopyridine-2-aldehyde (L5Br-pyridine), and complexed with Fe(NCS)2(pyridine)4 to give four monometallic FeII complexes, Fe(Lheterocycle)(NCS)2. Structural characterisation shows the expected octahedral FeII centres in all cases, with Lheterocycle occupying the equatorial plane and the two thiocyanate ligands trans to each other, resulting in an N6 coordination sphere. Solid state magnetic measurements showed that the two complexes with the thiazole-based ligands exhibit the beginning of a spin transition above 300 K, with T1/2 = 350 K for Fe(L4thiazole)(NCS)2 and 400 K for Fe(L2thiazole)(NCS)2, whereas the 4-oxazole-based ligand gives Fe(L4oxazole)(NCS)2 which remains high spin at all measured temperatures (50–400 K). Interestingly, Fe(L5Br-pyridine)(NCS)2 crystallised as two solvent-free polymorphs: magnetic measurements on samples with both polymorphs present showed a two step SCO with an abrupt transition at T1/2 = 245 K assigned to the transition in polymorph A (as this was also seen in a sample of pure polymorph A), and a gradual transition at T1/2 = 304 K assigned to polymorph B. These findings show that the order of increasing ligand field strength for these heterocycles is 4-oxazole ≪ 5Br-pyridine < 4-thiazole < 2-thiazole.
Liver is fed by nutrition via diffusion across the vascular wall from blood flow. However, hepatocytes in liver models are directly exposed to the perfusion culture medium, where the shear stress ...reduces the cell viability and liver‐specific functions. By mimicking the mass transfer and structural features of hepatic lobule, we designed a microfluidic liver‐on‐a‐chip based on the di‐acrylated pluronic F127 hydrogel. In the hydrogel chip, hepatocellular carcinoma HepG2 and human hepatic stellate cell LX‐2 were statically cultured inside the microwells on the outer channel. These hepatic cells were fed by the diffused medium from the adjacent but separated inner channel with endothelial cell monolayers, which was perfused by the medium with physiologically relevant shear stress. As found, the hepatic cells in the liver‐on‐a‐chip rapidly formed spheroids within 1‐day incubation and expressed about one to two‐fold higher viability/liver‐specific functions than the corresponding static culture for at least 8 days. Moreover, the presence of endothelial cells also contributed to the expression of liver‐specific functions in the liver‐on‐a‐chip. Therefore, the proposed liver‐on‐a‐chip provides a new concept for construction of 3D liver models in vitro, and shows the potential value for a variety of applications including bio‐artificial livers and drug toxicity screening.
By mimicking the mass transfer and structural features of hepatic lobule, the authors designed a microfluidic liver‐on‐a‐chip based on the di‐acrylated Pluronic F127 hydrogel. In the hydrogel chip, hepatic cells formed spheroids inside the microwells on the outer channel without perfusion. These hepatic spheroids were fed by the diffused medium from the adjacent but separated inner channel with endothelial cell monolayers, which was perfused by the medium with physiologically relevant shear stress.
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