Recent developments in high-performance Nafion membranes for hydrogen fuel cells applications

As a promising alternative to petroleum fossil energy,polymer electrolyte membrane fuel cell has drawn considerable attention due to its low pollution emission,high energy density,portability,and long operation times.Proton exchange membrane(PEM)like Nafion plays an essential role as the core of fuel cell.A good PEM must have satisfactory performance such as high proton conductivity,excellent mechanical strength,electrochemical stability,and suitable for making membrane electrode assemblies(MEA).However,performance degradation and high permeability remain the main shortcomings of Nafion.Therefore,the development of a new PEM with better performance in some special conditions is greatly desired.In this review,we aim to summarize the latest achievements in improving the Nafion performance that works well under elevated temperature or methanol-fueled systems.The methods described in this article can be divided into some categories,utilizing hydrophilic inorganic material,metal-organic frameworks,nanocomposites,and ionic liquids.In addition,the mechanism of proton conduction in Nafion membranes is discussed.These composite membranes exhibit some desirable characteristics,but the development is still at an early stage.In the future,revolutionary approaches are needed to accelerate the application of fuel cells and promote the renewal of energy structure.

Hydrodynamic coefficients of a simplified floating system of gravity cage in waves

Numerical simulation and experimental tests were carried out to examine the hydrodynamic behaviors of a double-column floating system of gravity cage under wave conditions. A floating system of gravity cage can be treated as a small-sized floating structure when compared with the wavelengths. The main problem in calculating the wave loads on the small-sized floating structure is to obtain the reasonable force coefficients, which may differ from a submerged structure. In this paper, the floating system of gravity cage is simplified to a 2D problem, where the floating system is set symmetrically under wave conditions. The motion equations were deduced under wave conditions and a specific method was proposed to resolve the problem of wave forces acting on a small-sized floating system of gravity cage at water surface. Results of the numerical method were compared with those from model tests and the hydrodynamic coefficients Cn and Cτ were studied. It is found that Cn ranges from 0.6 to 1.0 while Cτ is between 0.4 and 0.6 in this study. The results are useful for research on the hydrodynamic behavior of the deep-water gravity sea cages.

Comparison of different methods of intestinal obstruction in a rat model

AIM:To investigate different methods of creating incomplete intestinal obstruction in a rat model and to compare their electrophysiologic,morphologic and histologic characteristics. METHODS:Rat ileum was partially obstructed by the respective application of:braided silk(penetrated the mesentery and surrounded intestine);half ligation (penetrated directly and ligated 1/2 cross-section of the intestine);wide pipe(6 mm in width,surrounded the intestine);narrow pipe(2 mm in width,surrounded the intestine).A control was also included(no obstruction). Various behavioral and electrophysiologic variables, as well as morphologic and immunohistochemical observations were recorded by blinded investigators at different time points(12,24,48,72 h),including daily general condition,ileal wet weight and circumference, macromorphous and micromorphous intestine,bowel movement capability in vivo and in vitro,slow wave and neural electrical activity,and the number of c-Kit positive interstitial cells of Cajal(ICC). RESULTS:Despite being of a similar general condition, these methods resulted in different levels of obstruction in each group compared with the control at different time points(12,24,48,72 h).However,these fields of the wide pipe rat showed significantly differences when compared with the other three obstructed groups at 12 to 72 h,including macroscopic and histological presentation,intestinal transit ratio and contractility,circumference and wet weight,amplitude and frequency of nerve electrical discharge and slow wave,and ICC numbers(all P<0.01). CONCLUSION:The wide pipe rat method is significantly more reliable and stable than the other methods of obstruction,demonstrating that use of the wide pipe method can be a useful model of incomplete intestinal obstruction.

The commutant and similarity invariant of analytic Toeplitz operators on Bergman space

The famous von Neumann-Wold Theorem tells us that each analytic Toeplitz operator with n + 1-Blaschke factors is unitary to n + 1 copies of the unilateral shift on the Hardy space. It is obvious that the von Neumann-Wold Theorem does not hold in the Bergman space. In this paper, using the basis constructed by Michael and Zhu on the Bergman space we prove that each analytic Toeplitz operator Mb(z) is similar to n + 1 copies of the Bergman shift if and only if B(z) is an n + 1-Blaschke product. Prom the above theorem, we characterize the similarity invariant of some analytic Toeplitz operators by using K0-group term.