Interaction Mechanics Model for Rigid Driving Wheels of Planetary Rovers Moving on Sandy Terrain with Consideration of Multiple Physical Effects

Predicting wheel‐terrain interaction with semiempirical models is of substantial importance for developing planetary wheeled mobile robots (rovers). Primarily geared toward the design of manned terrestrial vehicles, conventional terramechanics models do not provide the sufficient fidelity required for application on autonomous planetary rovers. To develop a high‐fidelity interaction mechanics model, in this study the physical effects of wheel lug, slip sinkage, wheel dimension, and load are analyzed based on experimental results, including wheel sinkage, drawbar pull, normal force, and moment, which are measured on a single‐wheel test bed. The mechanism of lug‐terrain interaction is investigated systematically to clarify the principle of increasing shear stress, conditions of forming successive shearing among adjacent lugs, and the influence on shear displacement of soil. A mathematical model for predicting the concentrated forces and torque of rigid wheels with lugs for planetary rovers moving on sandy terrain is derived by integrating the improved models of normal and shearing stress distributions. In addition to the wheel parameters, terrain parameters, and motion state variables, wheel‐terrain interaction parameters, such as the linear varying sinkage exponent, the soil displacement radius, and load effect parameters, were proposed and explicitly included in the model. In the single‐wheel experiments, the slip ratio was increased approximately from 0.05 to 0.6, and the relative errors of the predicted results using the proposed model are less than 10% for all the wheels when compared with the experimental data. The proposed model has been used in the simulation of a four‐wheeled rover, and its effectiveness is evaluated by comparing the simulation results with experimental results.     

Accumulation rates,focusing factors,and chronologies from depth profiles of 210Pb and 137Cs in sediments of the Laurentian Great Lakes

Sediment cores from 41 sites were collected from the Laurentian Great Lakes during 2010–2014, sectioned into 0.5–2.0?cm intervals, and the activities of ²¹⁰Pb, ¹³⁷Cs, and ²²⁶Ra were measured in the upper 25 to 40?cm of the sediment column by gamma spectrometry. Sediment mass accumulation rates (dry mass) calculated from ²¹⁰Pb profiles range from 0.006?±?0.001 to 0.59?±?0.06?g?cm^?2?yr ^?1 and are similar to those reported in previous Great Lakes sediment studies. Sediment mass accumulation rates decreased with increasing water depth. ²¹⁰Pb-based models in cores exhibiting favorable characteristics (i.e., those having the highest unsupported-²¹⁰Pb activity at the sediment-water interface, exponential decrease of unsupported-²¹⁰Pb with increasing depth in sediment cores, and a clear peak in ¹³⁷Cs activity at some depth below the sediment-water interface) give calendar date profiles that are largely concordant with the maximum ¹³⁷Cs peak activity at 1963. Sediment focusing factors derived from unsupported-²¹⁰Pb inventories range from 0.09 to >5.34, and are well correlated with those derived from ¹³⁷Cs inventories that range from 0.07 to 4.04, demonstrating the ubiquitous occurrence of horizontal sediment transport processes within the lakes. This more recent survey provides a Great Lakes-wide chronological framework for comparing the depositional histories and inventories of a wide variety of persistent, bioaccumulative and toxic pollutants that have been measured in the same sediment cores. This information will be useful for resolving scientific and practical issues pertaining to the environmental quality and management of contaminated sediments in the Laurentian Great Lakes ecosystem.     

Temporal and spatial differences in deposition of organic matter and black carbon in Lake Michigan sediments over the period 1850–2010

Inorganic carbon (IC), total organic carbon (OC), and black carbon (BC) were analyzed in eight sediment cores obtained from deep water (>30 m) sediments in the Chippewa and south Chippewa basins, as well as Green Bay in Lake Michigan. These cores were segmented at high resolution and radio-dated to reconstruct a detailed history of deposition to the lake both spatially and temporally since ca. 1850 CE. To help interpret the depositional record, cores were also characterized for stable isotopes (¹³C and ¹⁵N), as well as particle size distribution, density, organic matter (OM), and other parameters. Fine (silt and clay) sediment particles contained OM of primarily lacustrine algal biomass origin. Sedimentation fluxes showed large increases in OM and OC fluxes through much of the lake during the onset of industrialization and the period of rapid industrialization to onset of Great Lakes environmental legislation. In contrast, fluxes and loading of BC increased dramatically in the southern basin until the 1930's, then decreased substantially after the 1940's. This observation was due largely to results from site M009 nearest the steel mills and industrial zones of Chicago and northern Indiana. Together, whole lake loadings of OM and BC provide evidence that changing industrial activity and legislation intended to curb air pollution in the Great Lakes region have had a fairly rapid and dramatic impact. In contrast, legislation intended to decrease eutrophication through reductions in nutrient loading to the lake have not had a similar impact on sedimentation of OM in the lake.     

Physiological response to firefighting activities of various work cycles using extended duration and prototype SCBA

Firefighters’ self-contained breathing apparatus (SCBA) protects the respiratory system during firefighting but increases the physiological burden. Extended duration SCBA (>30 min) have increased air supply, potentially increasing the duration of firefighting work cycles. To examine the effects of SCBA configuration and work cycle (length and rest), 30 firefighters completed seven trials using different SCBA and one or two bouts of simulated firefighting following work cycles common in the United States. Heart rate, core temperature, oxygen consumption, work output and self-reported perceptions were recorded during all activities. Varying SCBA resulted in few differences in these parameters. However, during a second bout, work output significantly declined while heart rates and core temperatures were elevated relative to a single bout. Thirty seven per cent of the subjects were unable to complete the second bout in at least one of the two-bout conditions. These firefighters had lower fitness and higher body mass than those who completed all assigned tasks.

Practitioner Summary: The effects of extended duration SCBA and work/rest cycles on physiological parameters and work output have not been examined. Cylinder size had minimal effects, but extended work cycles with no rest resulted in increased physiological strain and decreased work output. This effect was more pronounced in firefighters with lower fitness.     

MIMO PID tuning via iterated LMI restriction

We formulate multi‐input multi‐output proportional integral derivative controller design as an optimization problem that involves nonconvex quadratic matrix inequalities. We propose a simple method that replaces the nonconvex matrix inequalities with a linear matrix inequality restriction, and iterates to convergence. This method can be interpreted as a matrix extension of the convex–concave procedure, or as a particular majorization–minimization method. Convergence to a local minimum can be guaranteed. While we do not know that the resulting controller is globally optimal, the method works well in practice, and provides a simple automated method for tuning multi‐input multi‐output proportional integral derivative controllers. The method is readily extended in many ways, for example, to the design of more complex, structured controllers. Copyright © 2015 John Wiley & Sons, Ltd.     

Corrosion of Sic Materials in N2–H2–CO Gaseous Environments: I, Thermodynamics and Kinetics of Reactions

Two sintered SiC materials and a siliconized SiC materials were exposed to two gas compositions in the N₂–H₂–CO system at 1000°–1350°C, 133 Pa and 98.7 kPa for 8–1000 h. The two gases were a nitrogen-based gas which contained 98.2% N₂, 1.2% H₂, and 0.6% CO; and an endothermic gas which contained 37.8% N₂, 41.1% H₂, and 21.1% CO by volume. Thermodynamics of reactions were modeled using the program SOLGASMIX. Kinetic studies were based on weight change measurements obtained from vacuum TGA and long-term tube–furnace experiments. In the case of a siliconized SiC, reactions were complex, owing to its two phase composition and to the presence of impurities. Under many conditions, silicon was rapidly etched from the surface of the siliconized SiC during a short initial period due to the formation of SiO and carbon or SiO and β-SiC. In the case of sintered mateials (and the siliconized material during the later stages of corrosion), etching of SiC was observed under many of the conditions studied, due to the apparent formation of SiO, HCN, and/or carbon. Corrosion in an endothermic gas was typically more severe than in a nitrogen-based gas, due to its higher Pco .     

Synthesis,characterization and polymerization of waxy monomers

Waxy monomers and crosslinkers, respectively, were synthesized from commercially available waxes by esterification with 2-hydroxyethyl methacrylate, glycerol dimethacrylate, or glycidyl methacrylate or by functionalization with 2-isocyanatoethyl methacrylate. The resulting opaque methacrylates with melting points between 45 and 80°C were polymerized in bulk and in toluene solution in presence of free radical initiators. The obtained polymers were characterized by a broad molecular weight distribution. Opposite to the bulk polymerization, the double bond conversion in solution polymerization is nearly quantitative. The observed volume shrinkage during polymerization is very low due to the high molecular weight of the monomers. Polymerizates containing crosslinking comonomers exhibit improved mechanical stability.     

Influence of pressure and crystallization rate on the surface microhardness of high-density polyethylene

The indentation microhardnessMH of high-density polyethylene crystallized at different pressuresp and crystallization rates _c has been investigated. The results confirm thatMH is an increasing function of lamellar thickness and therefore of density. The rate of increase depends on the crystallization conditionsp and _c. Crystallization at high pressure leads toMH values considerably higher than those of samples prepared under atmospheric pressure. The results are discussed in terms of compressed amorphous regions contributing to an elastic release after removal of the indenter. For samples crystallized under different pressures the hardness value turns out to be nearly independent of the elastic modulusE. For samples crystallized at different rates _c there is a steady decrease of microhardness with increasing _c (decrease of lamellar thickness) but no simple relationship withE. With higher rates _c the appearance of strained tie molecules provokes a rapid increase ofE whileMH decreases further because the crystals become smaller.     

Einflu? der Geschwindigkeit des Einfrierens von Rindfleisch prae rigor auf Muskelstoffwechsel und Wasserbindungsverm?gen

Summary The high water-holding capacity (WHC) of prerigor beef, which is of advantage for the production of bruehwurst (frankfurter and bologna type sausages), can be preserved by mincing and rapid freezing without or with added salt. For the elucidation of the optimum conditions for freezing, pieces of beef, minced beef, and minced and salted (2% NaCI) beef were frozen 30–60 min after slaughter at various temperatures between -6°C and -70°C. The influence of freezing rate on muscle metabolism and on WHC of raw and heated muscle homogenates containing 2% NaCl was studied.With decreasing velocity of freezing the turnover of adenosine triphosphate and the rate of pH drop increases. In minced meat, ATP breakdown and glycolysis occur faster than in the intact tissue. Addition of salt retards glycolysis but accelerates the decrease of ATP concentration.If prerigor beef, frozen without added NaCl, is homogenized with 50% water and NaCl to a final concentration of 2%, the high WHC of the slaughter-fresh tissue is maintained as long as during the process of cooling and freezing the ATP concentration and pH are not reached at whichrigor mortis occurs: this is the case at freezing rates down to 0.05 °C/min in the critical temperature range between +10° and -1°C. At a freezing rate of 0.02 °C/min, however, at which rigor mortis occurs before freezing, the WHC of the homogenate prepared from this material is strongly lowered. With prerigor beef, minced and salted before freezing, homogenates with high WHC are always obtained no matter at which rate the material was frozen.Zusammenfassung Da schlachtwarmes Rindfleisch (Muskel vor Eintritt desRigor mortis), das dank seines hohen Wasserbindungsvermögens für die Brühwurstherstellung hervorragend geeignet ist, oft nicht sofort verarbeitet werden kann, bietet sich zur Aufrechterhaltung der guten Verarbeitungsqualität Zerkleinern unmittelbar nach der Schlachtung und rasches Einfrieren mit oder ohne Kochsalzzusatz an. Um die optimalen Einfrierbedingungen zu ermitteln, werden Stückfleisch, zerkleinertes Fleisch und zerkleinertes und gesalzenes (2% NaCI) Fleisch (Nackenmuskeln) 30 bis 60 min nach dem Schlachten bei Einfriertemperaturen zwischen -6° and - 70°C eingefroren und der Einfluß der Gefriergeschwindigkeit auf den Muskelstoffwechsel und auf das WBV von rohen und erhitzten Muskelhomogenaten (2% NaCI) untersucht. Mit abnehmender Einfriergeschwindigkeit nehmen der Umsatz von Adenosintriphosphat (ATP) and die Geschwindigkeit des pH-Abfalls im Gewebe zu. Im zerkleinerten Fleisch gehen ATP-Abbau and Glykolyse rascher vonstatten als im intakten Gewebe. Zusatz von NaCl verlangsamt die Glykolyse and beschleunigt die Abnahme der ATP-Konzentration.Homogenisiert manprae rigor ohne NaCI-Zusatz eingefrorenes Fleisch mit 50% Wasser unter NaCI-Zugabe (2% NaCl im Homogenat), so bleibt das hohe WBV des schlachtfrischen Materials erhalten, solange nicht während des Kühl- und Gefrierprozesses eine ATP-Konzentration und ein pH-Wert erreicht werden, bei welchenRigor mortis eintritt; dies ist his zu Gefriergeschwindigkeiten von 0,05°C/min im kritischen Temperaturbereich zwischen +10 °C and -1 °C der Fall. Bei einer Geschwindigkeit von 0,02 °C/min jedoch, bei welcher derRigor vor Gefrieren eintritt, kommt es zu einer starken Abnahme des WBV der Homogenate. Wird hingegen das schlachtwarme Fleisch vor dem Einfreiren zerkleinert und gezalzen, dann weisen die aus diesem material Hergestellten Homogenate (2% NaCl) unabhängig von der Einfriergeschwindigkeit stet hohes WBV auf.

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Gefördert von der AIF über den Forschungskreis der Ernährungsindustrie e. V., Hannover

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Fran K. Fischer and Herrn R. Egginger danken wir für ausgezeichnete technische Mitarbeit.