Linear power flow models are widely used in power systems to simplify the nonlinear power flow equations. The DC power flow model is one of the representatives. There are many other linear power flow ...models that improve the DC power flow model with the inclusion of <inline-formula><tex-math notation="LaTeX">\boldsymbol{Q}</tex-math></inline-formula> and <inline-formula><tex-math notation="LaTeX">\boldsymbol{v}</tex-math></inline-formula>. However, existing linear models are derived based on empirical mathematical approximation without a general methodology guidance. In this paper, we found that the fundamental difference among different linear power flow models lies in the formulation of "independent variables." Based on this finding, a general formulation of linear power flow models is proposed. The linearization error is theoretically analyzed. In particular, the case when <inline-formula><tex-math notation="LaTeX">\boldsymbol{ \theta }</tex-math></inline-formula> and <inline-formula><tex-math notation="LaTeX">\boldsymbol{v^{\scriptscriptstyle k}}</tex-math></inline-formula> are regarded as independent variables is thoroughly investigated. Method for finding the linear power flow with the minimum error is presented. The formulation of the independent variables associated with the minimum linearization error is determined by the distribution of state variables <inline-formula><tex-math notation="LaTeX">\boldsymbol{v}</tex-math></inline-formula> and <inline-formula><tex-math notation="LaTeX">\boldsymbol{\theta }</tex-math></inline-formula>. It is shown that the linearization error when <inline-formula><tex-math notation="LaTeX">\boldsymbol{v^{\scriptscriptstyle 2}}</tex-math></inline-formula> is regarded as an independent variable is normally smaller than that for <inline-formula><tex-math notation="LaTeX">\boldsymbol{v}</tex-math></inline-formula> because of the special properties of the distribution of <inline-formula><tex-math notation="LaTeX">\boldsymbol{v}</tex-math></inline-formula> in power grids.
The surge of patients in the pandemic of COVID‐19 caused by the novel coronavirus SARS‐CoV‐2 may overwhelm the medical systems of many countries. Mask‐wearing and handwashing can slow the spread of ...the virus, but currently, masks are in shortage in many countries, and timely handwashing is often impossible. In this study, the efficacy of three types of masks and instant hand wiping was evaluated using the avian influenza virus to mock the coronavirus. Virus quantification was performed using real‐time reverse transcription‐polymerase chain reaction. Previous studies on mask‐wearing were reviewed. The results showed that instant hand wiping using a wet towel soaked in water containing 1.00% soap powder, 0.05% active chlorine, or 0.25% active chlorine from sodium hypochlorite removed 98.36%, 96.62%, and 99.98% of the virus from hands, respectively. N95 masks, medical masks, and homemade masks made of four‐layer kitchen paper and one‐layer cloth could block 99.98%, 97.14%, and 95.15% of the virus in aerosols. Medical mask‐wearing which was supported by many studies was opposed by other studies possibly due to erroneous judgment. With these data, we propose the approach of mask‐wearing plus instant hand hygiene (MIH) to slow the exponential spread of the virus. This MIH approach has been supported by the experiences of seven countries in fighting against COVID‐19. Collectively, a simple approach to slow the exponential spread of SARS‐CoV‐2 was proposed with the support of experiments, literature review, and control experiences.
We test the anisotropy in the Finslerian cosmological model with the X-ray and ultraviolet (UV) fluxes of quasars. The 2015 and 2020 compilations of quasars are used in the cosmological constraints. ...We find that the dipole direction given by the 2015 quasar compilation is not far away from the one provided by the Pantheon sample and the angular differences are around
30
∘
. The Pantheon sample is combined with quasars as the “standardized candles” to test the cosmic anisotropy. The results from two combined datasets are consistent. They show that the dipole anisotropy is weak in the Finslerian cosmological model. We investigate the Hubble constant
H
0
in the Finslerian cosmological model. Though the central value of
H
0
from the combination of six gravitationally lensed quasars, Pantheon sample, and 2020 quasar compilation decreases a little bit, it is consistent with the result from six gravitationally lensed quasars within statistical uncertainties.
We test the cosmic anisotropy in the dipole-modulated
Λ
CDM model and Finslerian cosmological model with the recently-released quasar sample. Based on the redshift tomographic method, the quasar ...sample is divided into two subsets
z
≤
z
cut
and
z
>
z
cut
by different cutting redshifts. The dipole amplitudes of the two cosmological models from the subsets
z
≤
z
cut
are very weak. We find that quasars at a higher redshift range may provide more detailed information about the dipole amplitude
A
D
. The dipole directions of each cosmological model from the subsets
z
≤
1.1
and
z
>
1.1
are deviated by
1
σ
level. The Pantheon sample is combined with the two subsets. The dipole amplitude from the two combined datasets is also very weak. In the dipole-modulated
Λ
CDM model, the dipole direction from the combined dataset quasar at
z
≤
1.1
and Pantheon sample is far away from the one given by the Pantheon sample. In the Finslerian cosmological model, the dipole directions from the two combined datasets are close to the one in the Pantheon sample.
We revisit motility-induced phase separation in two models of active particles interacting by pairwise repulsion and uncover new qualitative features: the resulting dense phase contains gas bubbles ...distributed algebraically up to a typically extremely large cutoff scale. At large enough system size and/or global density, all the gas may be contained inside the bubbles, at which point the system is microphase separated with a finite cutoff bubble scale. We further observe that the ordering is clearly anomalous, with different dynamics for the coarsening of the dense phase and of the gas bubbles. This self-organized critical phenomenology is reproduced by a "reduced bubble model" that implements the basic idea of reverse Ostwald ripening put forward in Tjhung et al. Phys. Rev. X 8, 031080 (2018).
Linearized power flow models are of great interest in power system studies such as contingency analyses and reliability assessments, especially for large-scale systems. One of the most popular ...models-the classical DC power flow model-is widely used and praised for its state independence, robustness, and computational efficiency. Despite its advantages, however, the DC power flow model fails to consider reactive power or bus voltage magnitude. This paper closes this gap by proposing a decoupled linearized power flow (DLPF) model with respect to voltage magnitude and phase angle. The model is state independent but is distinguished by its high accuracy in voltage magnitude. Moreover, this paper presents an in-depth analysis of the DLPF model with the purpose of accelerating its computation speed, leading to the fast DLPF (FDLPF) model. The approximation that is applied to obtain the FDLPF model from the DLPF model is justified by a theoretical derivation and numerical tests. The proposed methods are provably accurate and robust for several cases, including radial distribution systems, meshed large-scale transmission systems and ill-conditioned systems. Finally, expressions for sensitivity with regard to MW flow and bus voltage are provided as a potential application.
Collective oscillatory behaviour is ubiquitous in nature, having a vital role in many biological processes from embryogenesis and organ development to pace-making in neuron networks. Elucidating the ...mechanisms that give rise to synchronization is essential to the understanding of biological self-organization. Collective oscillations in biological multicellular systems often arise from long-range coupling mediated by diffusive chemicals, by electrochemical mechanisms, or by biomechanical interaction between cells and their physical environment. In these examples, the phase of some oscillatory intracellular degree of freedom is synchronized. Here, in contrast, we report the discovery of a weak synchronization mechanism that does not require long-range coupling or inherent oscillation of individual cells. We find that millions of motile cells in dense bacterial suspensions can self-organize into highly robust collective oscillatory motion, while individual cells move in an erratic manner, without obvious periodic motion but with frequent, abrupt and random directional changes. So erratic are individual trajectories that uncovering the collective oscillations of our micrometre-sized cells requires individual velocities to be averaged over tens or hundreds of micrometres. On such large scales, the oscillations appear to be in phase and the mean position of cells typically describes a regular elliptic trajectory. We found that the phase of the oscillations is organized into a centimetre-scale travelling wave. We present a model of noisy self-propelled particles with strictly local interactions that accounts faithfully for our observations, suggesting that self-organized collective oscillatory motion results from spontaneous chiral and rotational symmetry breaking. These findings reveal a previously unseen type of long-range order in active matter systems (those in which energy is spent locally to produce non-random motion). This mechanism of collective oscillation may inspire new strategies to control the self-organization of active matter and swarming robots.
It is often said that pnictogen‐bonding catalysis, and σ‐hole catalysis in general, would not work in aqueous systems because the solvent would interfere as an overcompetitive pnictogen‐bond ...acceptor. In this study, we show that the transfer of pnictogen‐bonding catalysis from hydrophobic solvents to aqueous systems is possible by replacing only hydrophobic with hydrophilic substrates, without changing catalyst or reaction. This differs from conventional covalent Lewis acid catalysts, which are instantaneously destroyed by ligand exchange. With their water‐proof substituents in place of exchangeable ligands, pnictogen‐bonding catalysts, the supramolecular counterpart of Lewis acid catalysts, are evinced to catalyze transfer hydrogenation of quinolines in neutral aqueous systems. To secure these results, we introduce a water‐soluble fluorogenic substrate that releases a coumarin upon the reduction of quinolines instead of activated quinolidiniums, and stiborane catalysts with deepened σ holes. They demonstrate that pnictogen‐bonding catalysts can operate in higher‐order architectures for supramolecular systems catalysis under biologically relevant conditions, and provide an operational assay for high‐throughput catalyst screening by fluorescence imaging, in situ under relevant aqueous conditions.
The enantioselective aza‐Diels–Alder reaction is efficient for constructing chiral tetrahydropyridines, but the catalytic asymmetric aza‐Diels–Alder reaction of ketimines with unactivated dienes is ...still a challenging topic. Herein, guided by computational screening, a highly enantioselective aza‐Diels–Alder reaction of 2‐aryl‐3H‐indol‐3‐ones with unactivated dienes was realized by using a B(C6F5)3/chiral phosphoric acid catalyst system under mild conditions. The reaction has a broad scope with respect to both aza‐Diels–Alder reaction partners and hence offers rapid access to an array of tetrahydropyridine derivatives with pretty outcomes (up to 99 % yield, >20:1 dr and 98:2 er). The reaction is very efficient: lowering catalyst loadings for the model reaction to 0.1 mol %, enantioselectivity is still maintained. The synthetic utility was confirmed by transformations of the products. DFT calculations provide convincing evidence for the interpretation of stereoselection.
Guided by computational screening, a highly enantioselective aza‐Diels–Alder reaction of 2‐aryl‐3H‐indol‐3‐ones with unactivated dienes was realized by using a B(C6F5)3/chiral phosphoric acid catalyst system under mild conditions. The reaction has a broad scope with respect to both aza‐Diels–Alder reaction partners and offers rapid access to an array of tetrahydropyridine derivatives (up to 99 % yield, >20:1 dr and 98:2 er).
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