We develop a three dimensional compartmental model to investigate the impact of media coverage to the spread and control of infectious diseases (such as SARS) in a given region/area. Stability analysis of the model shows that the disease-free equilibrium is globally-asymptotically stable if a certain threshold quantity, the basic reproduction number (R 0), is less than unity. On the other hand, if R 0 > 1, it is shown that a unique endemic equilibrium appears and a Hopf bifurcation can occur which causes oscillatory phenomena. The model may have up to three positive equilibria. Numerical simulations suggest that when R 0 > 1 and the media impact is stronger enough, the model exhibits multiple positive equilibria which poses challenge to the prediction and control of the outbreaks of infectious diseases.

No abstract

Low utilization of active metallic sodium (Na) and uncontrollable growth of Na dendrites remain significant challenges for high-performance Na metal batteries, which are limited to inefficient Na utilization (<1%) and shallow cycling conditions (0.25–1.0 mAh cm–2). In this work, a kind of Na metal anode with record-high utilization and long-term cycling stability is reported, using carbon-substrate-supported nitrogen-anchored zinc (Zn) single atoms as a current collector. Single Zn atom sites which serve as a strong “magnet” for Na ions, can guide the metallic Na uniform nucleation and free from dendrite-induced short circuit. The nucleation overpotential of our strategy is essentially zero, where most of the reported modified substrates were greatly exceed 20 mV. Specifically, the Na anodes exhibit a high Na stripping/plating Coulombic efficiency with 99.8% over 350 cycles and a stable voltage response with small voltage hysteresis after cycling 1000 h. The full cell exhibits high Na utilization up to 100% and superior long-term cycling stability for more than 1000 cycles with excellent capacity retention. In terms of lifetime and Na utilization, the Na metal anodes based on our strategy significantly outperforms the reported state-of-the-art Na metal anodes. Moreover, this affords new insights into the controllable Na nucleation behavior and high Na utilization and sheds fresh light on atomic level design of an electrode for Na metal anodes.

PADB was a highly efficient cationic flocculant, which was synthesized through the copolymerization of acrylamide (AM), acryloyloxyethyl trimethyl ammonium chloride (DAC), and butylacrylate (BA) with ultraviolet initiation by micellar polymerization technology. The PADB was the terpolymer of AM, DAC, and BA. In order to observe this flocculant's structural characteristics, nuclear magnetic resonance hydrogen spectroscopy ( 1 H NMR), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and thermal gravimetric analysis (TGA) were used. The most important study was to analyze its physicochemical parameters during dewatering of activated sludge. These tested parameters included residual turbidity of supernatant, dry solid content (DS), extracellular polymeric substances (EPS), specific resistance to filtration (SRF), ζ-potential, floc size, and settling rate. Results demonstrated that the PADB have a superiority over both poly(acrylamide-acryloyloxyethyl trimethyl ammonium chloride) (PAD) and commercially available cationic polyacrylamide (CPAM). However, it was dependent on pH and dosage. A favorable pH was in the neutral range while the appropriate dosage (20 mg·L −1 -60 mg·L −1 ) was crucial to the conditioning process. For the PADB at40 mg·L −1 and pH at 7, the residual turbidity of supernatant, DS, SRF, and settling rate could reach 5.5 NTU, 32.2%, 5.51 × 10 12 m·kg −1 , and 3.318 cm·min −1 , respectively. During the sludge flocculation process, the charge neutralization mechanism and bridging flocculation played an important role in floc's formation and settlement.

No abstract

Two cationic polyacrylamides, PAA and PAD, were synthesized for sludge dewatering. The advanced instruments such as 1 H NMR, FTIR, and SEM were used to characterize the two copolymers. Their hydrophobic association properties in water were investigated by viscosimetry as well as the dewatering performance studied by the sludge dewatering experiment. The results showed that the optimum conditions for preparation of PAA were that the initiator concentration, urea concentration, molar ratio of AODBAC to AM, and irradiation time were 0.3‰, 1.0%, 10:90, and 60 min, respectively. Also, it was found that PAA had a stronger hydrophobic interaction with a lower intrinsic viscosity and longer dissolution time as well as a better dewatering performance. Furthermore, the charge neutralization and bridging effects were found to contribute much to the sludge dewatering by PAA in which the dewatering performance was able to be enhanced further by the hydrophobic interaction.

In this study, a cationic block structure with a strong neutralizing ability was formed through template polymerization. Acryloxyethyltrimethyl ammonium chloride (DAC) and acrylamide (AM) were used as monomers, and the ionic homopolymer sodium polyacrylate (NaPAA) was used as the template. The product containing NaPAA after template polymerization is denoted as NTP, whereas the copolymer obtained after removing the NaPAA is denoted as TP. The common polymer (denoted SP) of AM and DAC was copolymerized through solution polymerization. TP and SP were characterized and compared by Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), 1 H nuclear magnetic resonance ( 1 H NMR) spectroscopy, and thermogravimetric analysis (TGA). The results of 1 H NMR spectroscopy and TGA showed that a cationic block structure was formed in TP. The mechanism of the cationic block polymer used in water treatment was extensively studied through a jar test in which turbidity, zeta potential, and average floc size were used to evaluate the flocculation performance. The results further supported the cationic block structure of TP. TP, with a different structure than SP, resulting in a stronger neutralization ability, showed a better performance in flocculating kaolin suspensions. The dominant mechanisms for TP flocculation behavior at pH 5, 7, and 9 might be patching, charge neutralization, and bridging adsorption. The flocculation performance of NTP was not acceptable, whereas acidic NTP at pH < 2 showed a flocculation effect similar to that of TP.

the capacity of batteries; 3) large volume changes during circulation process can tend to bring about the fragmentation of solid electrolyte interphase (SEI), exposing the fresh lithium metal inside that the electrolyte will continue to react with lithium metal to consume the electrolyte and the growth of dendrite cannot be effectively inhibited (Figure 1). [3-6] Several ways have been put forward to solve these problems, [7-9] but the proposed methods to improve the performance of LMBs still face several influence factors: 1) the solvation sheath of Li + in liquid electrolyte and the ion conductivity in both gel and solid electrolyte; 2) the formation and components of solid electrolyte interfaces (SEI); (3) the deposition behavior of Li + on the surface of anode. A detailed microscopic understanding of island growth mechanism is required to successful solve these problems. Recently, some advanced characterization methods (scanning electron microscope, cryo-transmission electron microscope and lots of in situ characterization technology such as in situ X-ray diffraction, in situ fourier transform infrared spectroscopy, in situ UV absorption spectroscopy [10-12]) and advanced electrochemical measurement (cyclic voltammetry, impedance test, magnification test, exchange current density, and polarization test [13-16]) have been employed to figure out the dynamic behavior of different models. However, these characterizations and measurements are only focused on the description of test results in the level of phenomenon, lack of rational explanation. Many applications still need physical theoretical analysis to comprehend their kinetics mechanism, where molecular dynamics simulation can be used to strengthen the insights into the mechanism investigation of LMBs. [17] With the development of computational simulation technique such as Density Functional Theory (DFT) and Finite element simulation, molecular dynamics (MD) is one of the most frequently-used computational simulations in many fields. It is a science of simulating the motions of particles in system which combines with physics, mathematics and chemistry. Therefore, it can help researchers understand properties of assemblies of molecules by calculating the forces under different interaction potentials. Generally speaking, MD simulate can be divided into classic molecular dynamics (CMD) under Newtonian equation, reactive molecular dynamics (RMD) under reaction force field, ab initio molecular dynamics (AIMD) under Schrodinger The Li metal battery is attracting more and more attention in the field of electric vehicles because of its high theoretical capacity and low electrochemical potential. But its inherent disadvantages including uncontrolled lithium dendrites, high chemical activity, and large volume changes hold back the large-scale application of stable Li metal anodes. Recently, various computational studies have been used to facilitate the rationalization of experimental observed phenomenon. In this review, the progress of molecular dynamics simulations i...