What affects the performance of POD for the simulation of heat transfer through building component?

The capability of the proper orthogonal decomposition for the simulation of heat transfer in building components is investigated via three applications: linear heat transfer (not coupled to mass transfer), mildly non-linear heat transfer (coupled to air and moisture transfer (hygroscopic)) and highly non-linear heat transfer (coupled to moisture transfer (capillary)). It is shown that increasing non-linearity leads to an increasing number of required construction modes. To further investigate the reason for this degrading performance of POD, the singular values’ decay progress from the different training snapshots is addressed in this paper. The results confirm that a fast decay of the singular values implies a high interrelation of the snapshots and a better performance of the POD method.

Charge-Swapping Q-balls and Their Lifetimes

For scalar theories accommodating spherically symmetric Q-balls, there are also towers of quasi-stable composite Q-balls, called charge swapping Q-balls (CSQs). We investigate the properties, particularly the lifetimes, of these long-lived CSQs in 2+1D and 3+1D using numerical simulations with efficient second order absorbing boundary conditions. We find that the evolution of a CSQ typically consists of 4 distinct stages: initial relaxation, first plateau (CSQ stage), fast decay and second plateau (oscillon stage). We chart the lifetimes of CSQs for different parameters of the initial conditions and of the potential, and show the attractor behavior and other properties of the CSQs.

Spontaneous Formations of Dynamical Steady States in Polariton Condensates

We present a numerical analysis on dynamical steady states of polariton Bose–Einstein condensates (BECs) in an incoherent exciton reservoir driven by a ring-shaped optical pump. The balance between the loss and gain of polariton BEC induces a variety of steady states with different configurations, including approximate Gaussian distribution and topological defects, such as vortex–antivortex pairs, vortices with a winding number, and solitons. Besides, the system becomes unstable under fast decay rates and small pumping ring, where BECs can no longer exist in the long-time limit. We also confirm the soliton is dynamically stable in this system, with a steady polariton current induced by the repulsive polariton–polariton and polariton–exciton interactions.

Fast and slow decay solutions for supercritical fractional elliptic problems in exterior domains

We consider the fractional elliptic problem: where B1 is the unit ball in ℝ N , N ⩾ 3, s ∈ (0, 1) and p > (N + 2s)/(N − 2s). We prove that this problem has infinitely many solutions with slow decay O(|x|−2s/(p−1)) at infinity. In addition, for each s ∈ (0, 1) there exists P s > (N + 2s)/(N − 2s), for any (N + 2s)/(N − 2s) < p < P s , the above problem has a solution with fast decay O(|x|2s−N). This result is the extension of the work by Dávila, del Pino, Musso and Wei (2008, Calc. Var. Partial Differ. Equ. 32, no. 4, 453–480) to the fractional case.

Perovskite nanocrystal doped all-inorganic glass for X-ray scintillators

Perovskite nanocrystal doped all-inorganic glass shows good X-ray response and fast decay as well as excellent stability, resulting in good scintillator performance for various X-ray detection scenarios.

Reply to the ‘Comment on “Non-PGM electrocatalysts for PEM fuel cells: effect of fluorination on the activity and stability of a highly active NC_Ar + NH3 catalyst”’ by Xi Yin, Edward F. Holby and Piotr Zelenay, Energy Environ. Sci., 10.1039/D0EE02069A

The fast decay in PEM fuel cells of a highly active, high performance, but unstable Fe/N/C catalyst like our NC_Ar + NH3 follows a chemical, not an electrochemical, demetallation mechanism for its ORR active FeN4 sites in the catalyst micropores.

Broadband Visible Nonlinear Absorption and Ultrafast Dynamics of the Ti3C2 Nanosheet

The Ti3C2 nanosheet, as a new two-dimensional (2D) group, has been found to have attractive characteristics as material for electromagnetic shielding and energy storage. In this study, the nonlinear broadband absorption and ultrafast dynamics of the Ti3C2 nanosheet were investigated using nanosecond open-aperture Z-scan and transient absorption techniques. The mechanism of two-photon absorption (TPA) was revealed in the visible region (475–700 nm). At lower incident energies, nonlinear absorption could not happen. When the laser energy increased to 0.64 GW/cm2, electrons in the valence band could absorb two photons and jump to the conduction band, with TPA occurring, which meant that the sample exhibited reverse saturable absorption (RSA). In addition, when transient absorption was used to investigate the ultrafast carrier dynamics of the sample, it demonstrated that the relaxation contains a fast decay component and a slow one, which are obtained from electron–phonon and phonon–phonon interactions, respectively. Moreover, with the increasing pump fluence, the fast decay lifetime τ1 increased from 3.9 to 4.5 ps, and the slow one τ2 increased from 11.1 to 13.2 ps. These results show that the Ti3C2 nanosheet has potential applications in broadband optical limiters.