Characterizing the Conductivity and Enhancing the Piezoresistivity of Carbon Nanotube-Polymeric Thin Films.

The concept of lightweight design is widely employed for designing and constructing aerospace structures that can sustain extreme loads while also being fuel-efficient. Popular lightweight materials such as aluminum alloy and fiber-reinforced polymers (FRPs) possess outstanding mechanical properties, but their structural integrity requires constant assessment to ensure structural safety. Next-generation structural health monitoring systems for aerospace structures should be lightweight and integrated with the structure itself. In this study, a multi-walled carbon nanotube (MWCNT)-based polymer paint was developed to detect distributed damage in lightweight structures. The thin film's electromechanical properties were characterized via cyclic loading tests. Moreover, the thin film's bulk conductivity was characterized by finite element modeling

Falling chains

The one-dimensional fall of a folded chain with one end suspended from a rigid support and a chain falling from a resting heap on a table is studied. Because their Lagrangians contain no explicit time dependence, the falling chains are conservative systems. Their equations of motion are shown to contain a term that enforces energy conservation when masses are transferred between subchains. We show that Cayley's 1857 energy nonconserving solution for a chain falling from a resting heap is incorrect because it neglects the energy gained when a transferred link leaves a subchain. The maximum chain tension measured by Calkin and March for the falling folded chain is given a simple if rough interpretation. Other aspects of this falling folded chain are briefly discussed.Comment: 9 pages, 1 figure; the Abstract has been shortened, three paragraphs have been re-written for greater clarity, and textual improvements have been made throughout the paper; to be published by the Am. J. Physic

A Unification of Models of Tethered Satellites

In this paper, different conservative models of tethered satellites are related mathematically, and it is established in what limit they may provide useful insight into the underlying dynamics. An infinite dimensional model is linked to a finite dimensional model, the slack-spring model, through a conjecture on the singular perturbation of tether thickness. The slack-spring model is then naturally related to a billiard model in the limit of an inextensible spring. Next, the motion of a dumbbell model, which is lowest in the hierarchy of models, is identified within the motion of the billiard model through a theorem on the existence of invariant curves by exploiting Moser's twist map theorem. Finally, numerical computations provide insight into the dynamics of the billiard model

Rotating strings

Analytical expressions are provided for the configurations of an inextensible, flexible, twistable inertial string rotating rigidly about a fixed axis. Solutions with trivial radial dependence are helices of arbitrary radius and pitch. Non-helical solutions are governed by a cubic equation whose roots delimit permissible values of the squared radial coordinate. Only curves coplanar with the axis of rotation make contact with it.Comment: added to discussion and made small revisions to tex

Diatom community structure in relation to physico-chemical factors in a tropical soda Lake Shala and inflowing hot-springs, Ethiopia

Diatoms are highly diverse and versatile, with members growing under different environmental conditions including extreme environments. Although diatom communities in some extreme environments have been investigated recently, little is known about their community structure within the hot springs of soda lakes in Ethiopia. The study aimed to assess the diversity and distribution of diatoms from Lake Shala and inflowing hot springs in relation to physico-chemical variables. Water and diatom samples were collected from Lake Shala and three inflowing hotsprings. The mean pH, temperature, EC, salinity, TDS, DO, NO3-+NO2-, NH3+NH4+, SRP, TP and SiO2 were significantly different among the stations. The significant variations in these factors could be attributed to their heterogeneous geological characteristic and the hydrology of the study area.  A total of 45 diatom taxa were identified, with the highest species observed in Shala Hora Mid Hotspring sites (37) and the lowest in Shala Gike Hotspring (29). Diatom community structure was also examined and it was found that the diatom community of Lake Shala and inflowing hotsprings are highly influenced by environmental water conditions. Characteristic taxa including Anomoeoneis sphaerophora, Nitzschia spp., Rhomboids gibberula, R. gibba, R. acuminata, R. operculata, Navicula spp. and Frustulia rhomboids, showed a wide tolerance to pH, salinity, EC, TDS, temperature, nitrogen and phosphate. RDA analysis found a number of discriminating taxa and salinity, conductivity, pH, DO SRP and temperature were key factors that accounted for a significant variation in the diatom community structure

Solving the paradox of the folded falling chain by considering horizontal kinetic energy and link geometry

A folded chain, with one end fixed at the ceiling and the other end released from the same elevation, is commonly modeled as an energy-conserving system in one-dimension. However, the analytical paradigms in previous literature is unsatisfying: The theoretical prediction of the tension at the fixed end becomes infinitely large when the free end reaches the bottom, contradicting to the experimental observations. Furthermore, the dependence of the total falling time on the link number demonstrated in numerical simulations is still unexplained. Here, considering the horizontal kinetic energy and the geometry of each link, we derived analytical solutions of the maximal tension as well as the total falling time, in agreement with simulation results and experimental data reported in previous studies. This theoretical perspective shows a simple representation of the complicated two-dimensional falling chain system and, in particular, specifies the signature of the chain properties.Comment: 13 pages, 4 figure

The motion of the freely falling chain tip

The dynamics of the tip of the falling chain is analyzed. Results of laboratory experiments are presented and compared with results of numerical simulations. Time dependences of the velocity and the acceleration of the chain tip for a number of different initial conformations of the chain are determined. A simple analytical model of the system is also considered.Comment: 29 pages, 13 figure