Bio-inspired design of ice-retardant devices based on benthic marine invertebrates: the effect of surface texture

Growth of ice on surfaces poses a challenge for both organisms and for devices that come into contact with liquids below the freezing point. Resistance of some organisms to ice formation and growth, either in subtidal environments (e.g. Antarctic anchor ice), or in environments with moisture and cold air (e.g. plants, intertidal) begs examination of how this is accomplished. Several factors may be important in promoting or mitigating ice formation. As a start, here we examine the effect of surface texture alone. We tested four candidate surfaces, inspired by hard-shelled marine invertebrates and constructed using a three-dimensional printing process. We screened biological and artifical samples for ice formation and accretion in submerged conditions using previous methods, and developed a new test to examine ice formation from surface droplets as might be encountered in environments with moist, cold air. It appears surface texture plays only a small role in delaying the onset of ice formation: a stripe feature (corresponding to patterning found on valves of blue mussels, Crassostrea gigas, or on the spines of the Antarctic sea urchin, Sterechinus neumayeri) slowed ice formation an average of 25% compared to a grid feature (corresponding to patterning found on sub-polar butterclams, Saxidomas). The geometric dimensions of the features have only a small (~6%) effect on ice formation. Surface texture affects ice formation, but does not explain by itself the large variation in ice formation and species-specific ice resistance observed in other work. This suggests future examination of other factors, such as material elastic properties and coatings, and their interaction with surface pattern

Methods for identifying cancellous bone specimen location and size for the Reduced Platen Compression Test

Due to the character of the original source materials and the nature of batch digitization, quality control issues may be present in this document. Please report any quality issues you encounter to [email protected], referencing the URI of the item.Includes bibliographical references (leaf 22).The skeleton functions as a vital part of our everyday existence and acts as a framework for the body to provide movement, resist the forces of gravity, and protect vital organs. Skeletal research studies the effect of disease, lifestyle, and stimuli on the skeleton and its ability to perform these everyday functions. The current state of bone testing is focused on understanding the mechanical properties of bone through use of traditional mechanical testing procedures such as three point bending, torsion, and compression testing. The traditional method of compression testing involves compressing a bone specimen between two parallel platens to failure or until a desired displacement is obtained. This method is useful for studying the properties of the entire bone sample. Bone can be categorized into two major types: cortical bone and cancellous bone. Current compression testing techniques do not allow the properties of cancellous bone to be determined. The Reduced Platen Compression Test attempts to improve the traditional compression test to allow cancellous bone to be tested while the outer cortical shell remains on the specimen by using smaller diameter platens to compress only the inner cancellous area of the specimen. The RPC is relatively new and several questions still remain as to the correct method for identifying the location and size of the test specimen. Rat femurs used in preliminary RPC Testing were analyzed to determine the best method for locating and sizing the test specimen. X-rays of approximately 120 rat femurs were studied to see if a standard location and size could be defined for the RPC test specimen. The results indicate that the rat femur develops too inconsistently for a standard length or percentage of the overall length to be used to define the location. The best method for locating the specimen is to identify the location of the distal end of the epiphyseal growth plate and take the specimen just below that location. The results also indicate that the best method for defining the specimen thickness is to average the largest and smallest overall bone lengths in the test group and use a reference thickness of 2 millimeters as a percentage of this average length. This percentage of the overall average length then defines the specimen thickness for each individual bone

Variations on a demonic theme: Szilard's other engines.

Szilard's now-famous single-molecule engine was only the first of three constructions he introduced in 1929 to resolve several challenges arising from Maxwell's demon paradox. Given that it has been thoroughly analyzed, we analyze Szilard's remaining two demon models. We show that the second one, though a markedly different implementation employing a population of distinct molecular species and semipermeable membranes, is informationally and thermodynamically equivalent to an ideal gas of the single-molecule engines. One concludes that (i) it reduces to a chaotic dynamical system-called the Szilard Map, a composite of three piecewise linear maps and associated thermodynamic transformations that implement measurement, control, and erasure; (ii) its transitory functioning as an engine that converts disorganized heat energy to work is governed by the Kolmogorov-Sinai entropy rate; (iii) the demon's minimum necessary "intelligence" for optimal functioning is given by the engine's statistical complexity; and (iv) its functioning saturates thermodynamic bounds and so it is a minimal, optimal implementation. We show that Szilard's third construction is rather different and addresses the fundamental issue raised by the first two: the link between entropy production and the measurement task required to implement either of his engines. The analysis gives insight into designing and implementing novel nanoscale information engines by investigating the relationships between the demon's memory, the nature of the "working fluid," and the thermodynamic costs of erasure and measurement

Gigahertz Sub-Landauer Momentum Computing

We introduce a fast and highly-efficient physically-realizable bit swap. Employing readily available and scalable Josephson junction microtechnology, the design implements the recently introduced paradigm of momentum computing. Its nanosecond speeds and sub-Landauer thermodynamic efficiency arise from dynamically storing memory in momentum degrees of freedom. As such, during the swap, the microstate distribution is never near equilibrium and the memory-state dynamics fall far outside of stochastic thermodynamics that assumes detailed-balanced Markovian dynamics. The device implements a bit-swap operation -- a fundamental operation necessary to build reversible universal computing. Extensive, physically-calibrated simulations demonstrate that device performance is robust and that momentum computing can support thermodynamically-efficient, high-speed, large-scale general-purpose computing that circumvents Landauer's bound.Comment: 18 pages, 11 figures, 5 appendices; http://csc.ucdavis.edu/~cmg/compmech/pubs/gslmc.ht

Freshwater Community Responses to Mixtures of Agricultural Pesticides: Synergistic Effects of Atrazine and Bifenthrin

This study was an investigation of the effects of the herbicide atrazine and the insecticide bifenthrin on lake communities. The study was conducted in two phases: in phase one, we examined the effects of environmentally realistic levels of atrazine and bifenthrin, based on published data of concentrations measured in fresh waters; in phase two, the impacts of higher levels of atrazine and bifenthrin were investigated, based on concentrations used in previous studies. The factorial designed experiment included three levels of bifenthrin (0, 1/39, and 1/287 ngL in phase one and 0, 1/125, and 1/3150 ngL in phase two) cross-classified with three levels of atrazine (0, 1/15, and 1/153 ugL in phase one and 0, 1/385, and 1/2167 ugL in phase two), with duplicate replication of each treatment combination. Pesticides were added to 5,500 L fiberglass tanks containing natural plankton assemblages and bluegill. Tanks were sampled 7 and 14 d following the first pesticide treatment and 7 d after the second pesticide addition. In phase one of the study, atrazine significantly reduced chlorophyll concentrations and turbidity on day 7 Wand had no significant impact on primary productivity or algal cell densities. Atrazine also had a significant negative effect on copepod nauplii and rotifers (days 7 and 14) and on Bosmina and particulate phosphorus in the 20-200 um size fraction (day 14). Bifenthrin significantly reduced Bosmina (days 7 and 14), cyclopoid copepodids (days 7 and 14), and copepod nauplii (day 14), however bifenthrin increased rotifers at day 7. Bifenthrin addition also increased colonial green algae and decreased particulate phosphorus in the 20-200 um size fraction on day 7 and decreased turbidity and particulate phosphorus in the >200 um size fraction on days 7 and 14. Only one fish mortality (in the high bifenthrin, no atrazine treatment combination) occurred during phase one of the study. Significant interaction effects were found only for Bosmina (day 14), rotifers (day 7), and turbidity (days 7 and 14), indicating that at the concentrations used in phase one of this study, these agricultural pesticides did not act synergistically. In phase two, higher levels of atrazine resulted in significant reductions in primary productivity, chlorophyll, green colonies, Bosmina, rotifers, and particulate phosphorus (>200 um and 20-200 um) on day 7. Bifenthrin had a negative impact on Bosmina, copepod nauplii, rotifers, primary productivity, chlorophyll, green colonies, and all particulate phosphorus fractions. In addition, 33% bluegill mortality was observed in treatment combinations with an average maximum concentration of 1/3150 ngL bifenthrin. The interaction effects found indicated that when either compound was introduced at ecologically realistic levels, its effects were essentially masked if the other toxicant was present at high concentrations

Observation of thermal acoustic modes of a droplet coupled to an optomechanical sensor

The bulk acoustic modes of liquid droplets, well understood from a theoretical perspective, have rarely been observed experimentally. Here, we report the direct observation of acoustic vibrational modes in a picoliter-scale droplet, extending up to ~ 40 MHz. This was achieved by coupling the droplet to an ultra-sensitive optomechanical sensor, which operates in a thermal-noise limited regime and with a substantial contribution from acoustic noise in the ambient medium. The droplet vibrational modes manifest as Fano resonances in the thermal noise spectrum of the sensor. This is amongst the few reported observations of droplet acoustic modes, and of Fano interactions in a coupled mechanical oscillator system driven only by thermal Brownian motion.Comment: 11 pages, 3 figure

The Thermodynamic Uncertainty Theorem

Thermodynamic uncertainty relations (TURs) express a fundamental tradeoff between the precision (inverse scaled variance) of any thermodynamic current by functionals of the average entropy production. Relying on purely variational arguments, we significantly extend these inequalities by incorporating and analyzing the impact of higher statistical cumulants of entropy production within a general framework of time-symmetrically controlled computation. This allows us to derive an exact expression for the current that achieves the minimum scaled variance, for which the TUR bound tightens to an equality that we name Thermodynamic Uncertainty Theorem (TUT). Importantly, both the minimum scaled variance current and the TUT are functionals of the stochastic entropy production, thus retaining the impact of its higher moments. In particular, our results show that, beyond the average, the entropy production distribution's higher moments have a significant effect on any current's precision. This is made explicit via a thorough numerical analysis of swap and reset computations that quantitatively compares the TUT against previous generalized TURs. Our results demonstrate how to interpolate between previously-established bounds and how to identify the most relevant TUR bounds in different nonequilibrium regimes