413 research outputs found
Increased power generation in supercapacitive microbial fuel cell stack using Fe-N-C cathode catalyst
The anode and cathode electrodes of a microbial fuel cell (MFC) stack, composed of 28 single MFCs, were used as
the negative and positive electrodes, respectively of an internal self-charged supercapacitor. Particularly, carbon
veil was used as the negative electrode and activated carbon with a Fe-based catalyst as the positive electrode.
The red-ox reactions on the anode and cathode, self-charged these electrodes creating an internal electrochemical
double layer capacitor. Galvanostatic discharges were performed at different current and time pulses.
Supercapacitive-MFC (SC-MFC) was also tested at four different solution conductivities. SC-MFC had an
equivalent series resistance (ESR) decreasing from 6.00 Ω to 3.42 Ω in four solutions with conductivity between
2.5 mScm−1 and 40 mScm−1. The ohmic resistance of the positive electrode corresponded to 75–80% of the
overall ESR. The highest performance was achieved with a solution conductivity of 40 mS cm−1 and this was due
to the positive electrode potential enhancement for the utilization of Fe-based catalysts. Maximum power was
36.9mW (36.9Wm−3) that decreased with increasing pulse time. SC-MFC was subjected to 4520 cycles (8 days)
with a pulse time of 5 s (ipulse 55 mA) and a self-recharging time of 150 s showing robust reproducibility
Wave packet evolution approach to ionization of hydrogen molecular ion by fast electrons
The multiply differential cross section of the ionization of hydrogen
molecular ion by fast electron impact is calculated by a direct approach, which
involves the reduction of the initial 6D Schr\"{o}dinger equation to a 3D
evolution problem followed by the modeling of the wave packet dynamics. This
approach avoids the use of stationary Coulomb two-centre functions of the
continuous spectrum of the ejected electron which demands cumbersome
calculations. The results obtained, after verification of the procedure in the
case atomic hydrogen, reveal interesting mechanisms in the case of small
scattering angles.Comment: 7 pages, 8 Postscript figure
Group classification of heat conductivity equations with a nonlinear source
We suggest a systematic procedure for classifying partial differential
equations invariant with respect to low dimensional Lie algebras. This
procedure is a proper synthesis of the infinitesimal Lie's method, technique of
equivalence transformations and theory of classification of abstract low
dimensional Lie algebras. As an application, we consider the problem of
classifying heat conductivity equations in one variable with nonlinear
convection and source terms. We have derived a complete classification of
nonlinear equations of this type admitting nontrivial symmetry. It is shown
that there are three, seven, twenty eight and twelve inequivalent classes of
partial differential equations of the considered type that are invariant under
the one-, two-, three- and four-dimensional Lie algebras, correspondingly.
Furthermore, we prove that any partial differential equation belonging to the
class under study and admitting symmetry group of the dimension higher than
four is locally equivalent to a linear equation. This classification is
compared to existing group classifications of nonlinear heat conductivity
equations and one of the conclusions is that all of them can be obtained within
the framework of our approach. Furthermore, a number of new invariant equations
are constructed which have rich symmetry properties and, therefore, may be used
for mathematical modeling of, say, nonlinear heat transfer processes.Comment: LaTeX, 51 page
Superposition in nonlinear wave and evolution equations
Real and bounded elliptic solutions suitable for applying the Khare-Sukhatme
superposition procedure are presented and used to generate superposition
solutions of the generalized modified Kadomtsev-Petviashvili equation (gmKPE)
and the nonlinear cubic-quintic Schroedinger equation (NLCQSE).Comment: submitted to International Journal of Theoretical Physics, 23 pages,
2 figures, style change
New conditional symmetries and exact solutions of nonlinear reaction-diffusion-convection equations. II
In the first part of this paper math-ph/0612078, a complete description of
Q-conditional symmetries for two classes of reaction-diffusion-convection
equations with power diffusivities is derived. It was shown that all the known
results for reaction-diffusion equations with power diffusivities follow as
particular cases from those obtained in math-ph/0612078 but not vise versa. In
the second part the symmetries obtained in are successfully applied for
constructing exact solutions of the relevant equations. In the particular case,
new exact solutions of nonlinear reaction-diffusion-convection (RDC) equations
arising in application and their natural generalizations are found
Bacterial formate dehydrogenase. Increasing the enzyme thermal stability by hydrophobization of alpha-helices
AbstractNAD+-dependent formate dehydrogenase (EC 1.2.1.2, FDH) from methylotrophic bacterium Pseudomonas sp.101 exhibits the highest stability among the similar type enzymes studied. To obtain further increase in the thermal stability of FDH we used one of general approaches based on hydrophobization of protein α-helices. Five serine residues in positions 131, 160, 168, 184 and 228 were selected for mutagenesis on the basis of (i) comparative studies of nine FDH amino acid sequences from different sources and (ii) with the analysis of the ternary structure of the enzyme from Pseudomonas sp.101. Residues Ser-131 and Ser-160 were replaced by Ala, Val and Leu. Residues Ser-168, Ser-184 and Ser-228 were changed into Ala. Only Ser/Ala mutations in positions 131, 160, 184 and 228 resulted in an increase of the FDH stability. Mutant S168A was 1.7 times less stable than the wild-type FDH. Double mutants S(131,160)A and S(184,228)A and the four-point mutant S(131,160,184,228)A were also prepared and studied. All FDH mutants with a positive stabilization effect had the same kinetic parameters as wild-type enzyme. Depending on the position of the replaced residue, the single point mutation Ser/Ala increased the FDH stability by 5–24%. Combination of mutations shows near additive effect of each mutation to the total FDH stabilization. Four-point mutant S(131,160,184,228)A FDH had 1.5 times higher thermal stability compared to the wild-type enzyme
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