An Analysis of Microbial Contamination in Military Aviation Fuel Systems

Military aviation fuel systems can be an ideal environment for microorganisms. Microbial growth in hydrocarbon fuel systems arises because of the impracticality of keeping fuel tanks sterile and the inevitable presence of water from condensation. Microbial contaminants in aviation fuel systems are a concern because of their potential to degrade the fuel, accelerate tank corrosion, and threaten flight safety. This research addresses the concern of using more environmentally friendly Fuel System Icing Inhibitors (FSII), which are also biocidal. Are significant levels of microorganisms growing in military aviation fuel systems, and if so, are there any common variables? Forty aviation fuel samples were collected from fuel storage tanks (including flexible expeditionary fuel bladders), refueling trucks, and aircraft from 12 U,S, military bases. Samples were analyzed using peak naming and pattern recognition algorithms of sample extracts processed on a gas chromatograph. Significant levels of microorganisms were found in military aviation fuel systems 90% (36 of 40) of fuel samples produced microbial growth. Over 40% of the serial dilutions that produced microbial growth were characterized as moderately or heavily contaminated samples. The microorganisms isolated were overwhelmingly Gram negative, anaerobic, bacilli with populations varying by orders of magnitude

Boundedness and convergence to zero of solutions of a forced second-order nonlinear differential equation

AbstractSufficient conditions for continuability, boundedness, and convergence to zero of solutions of (a(t)x′)′ + h(t, x, x′) + q(t) f(x) g(x′) = e(t, x, x′) are given

On the positive solutions of a higher order functional differential equation with a discontinuity

The n-th order nonlinear functional differential equation [r(t)x(n−υ)(t)](υ)=f(t,x(g(t)))is considered; necessary and sufficient conditions are given for this equation to have: (i) a positive bounded solution x(t)→B>0 as t→∞; and (ii) all positive bounded solutions converging to 0 as t→∞. Other results on the asymptotic behavior of solutions are also given. The conditions imposed are such that the equation with a discontinuity [r(t)x(n−υ)(t)](υ)=q(t)x−λ,   λ>0is included as a special case

Positive Solutions for a Singular Fourth Order Nonlocal Boundary Value Problem

Positive solutions are obtained for the fourth order nonlocal boundary value problem, u(4)=f(x,u), 0 \u3c x \u3c 1, u(0) = u\u27\u27(0) = u\u27(1) = u\u27\u27(1) - u\u27\u27(2/3)=0, where f(x,u) is singular at x = 0, x=1, y=0, and may be singular at y=∞. The solutions are shown to exist at fixed points for an operator that is decreasing with respect to a cone

Classification of nonoscillatory solutions of higher order neutral type difference equations

summary:The authors consider the difference equation $$\Delta ^{m} [y_{n} - p_{n} y_{n - k}] + \delta q_{n} y_{\sigma (n + m - 1)} = 0 \qquad \mathrm {(\ast )}$$ where $m \ge 2$, $\delta = \pm 1$, $k \in N_0 = \lbrace 0,1, 2, \dots \rbrace$, $\Delta y_{n} = y_{n + 1} - y_{n}$, $q_{n} > 0$, and $\lbrace \sigma (n)\rbrace$ is a sequence of integers with $\sigma (n) \le n$ and $\lim _{n \rightarrow \infty } \sigma (n) = \infty$. They obtain results on the classification of the set of nonoscillatory solutions of ($\ast$) and use a fixed point method to show the existence of solutions having certain types of asymptotic behavior. Examples illustrating the results are included

The existence of solutions for -Laplacian boundary value problems at resonance on the half-line

The concept of collective efficacy, defined as the combination of mutual trust and willingness to act for the common good, has received widespread attention in the field of criminology. Collective efficacy is linked to, among other outcomes, violent crime, disorder, and fear of crime. The concept has been applied to geographical units ranging from below one hundred up to several thousand residents on average. In this paper key informant- and focus group interview transcripts from four Swedish neighborhoods are examined to explore whether different sizes of geographical units of analysis are equally important for collective efficacy. The four studied neighborhoods are divided into micro-neighborhoods (N=12) and micro-places (N=59) for analysis. The results show that neighborhoods appear to be too large to capture the social mechanism of collective efficacy which rather takes place at smaller units of geography. The findings are compared to survey responses on collective efficacy (N=597) which yield an indication in the same direction through comparison of ICC-values and AIC model fit employing unconditional two-level models in HLM 6