Damp Sand Research Articles

Controls on reservoir compartmentalization of an Upper Permian tight gas field in Germany and links to a modern analogue in the Western US

This study focuses on the reservoir characteristics of a Permian tight gas field in the Southern Permian Basin, Eastern Frisia, Germany. To improve the understanding of the reservoir, 3D seismic, wireline and core data were compared with a reservoir analogue in the Panamint Valley, United States. Depositional environments of the Permian Upper Rotliegend II include perennial saline lakes, coastal parallel sand belts comprising wet, damp and dry sand flats and aeolian dunes with interdune deposits. Polygonal patterns at different scales were observed on seismic horizon slices in the reservoir intervals and the overlying Zechstein. Outlines of superordinate polygons coincide with interpreted faults. Similar polygonal networks were identified on modern dry lakes in the western United States. The kilometre-long, up to 1.20 m deep open fissures in the Panamint Valley are interpreted to originate from the combined effects of synaeresis and tectonics. Subsequently, the fissures were filled with aeolian sediment. Vegetation growth confined to the lineaments indicates enhanced fluid circulation. Such fissures systems may serve as weakness zones and fault grain and impact reservoir quality in terms of hydraulic connectivity of reservoir compartments. For the Rotliegend reservoirs, original porosities and permeabilities of these zones were reduced to a minimum by enhanced cementation along the fluid migration pathways. Permeability barriers and reservoir compartmentalization, which can be clearly depicted on seismic attribute volumes, are a potential result of this development.

Penetrometry of granular and moist planetary surface materials: Application to the Huygens landing site on Titan

The Huygens probe landed on the then unknown surface of Titan in January 2005. A small, protruding penetrometer, part of the Surface Science Package (SSP), was pushed into the surface material measuring the mechanical resistance of the ground as the probe impacted the landing site. We present laboratory penetrometry into room temperature surface analogue materials using a replica penetrometer to investigate further the nature of Titan’s surface and examine the sensor’s capabilities. The results are then compared to the flight instrument’s signature and suggest the Titan surface substrate material consists of sand-sized particles with a mean grain size ∼2 mm. A possible thin 7 mm coating with mechanical properties similar to terrestrial snow may overlie this substrate, although due to the limited data we are unable to detect any further layering or grading within the near-surface material. The unusual weakening with depth of the signature returned from Titan has, to date, only been reproduced using a damp sand target that becomes progressively wetter with depth, and supports the suggestion that the surface may consist of a damp and cohesive material with interstitial liquid contained between its grains. Comparison with terrestrial analogues highlights the unusual nature of the landing site material.

Short‐ and long‐term consequences of thermal variation in the larval environment of anurans

1. To survive adverse or unpredictable conditions in the ontogenetic environment, many organisms retain a level of phenotypic plasticity that allows them to meet the challenges of rapidly changing conditions. Larval anurans are widely known for their ability to modify behaviour, morphology and physiological processes during development, making them an ideal model system for studies of environmental effects on phenotypic traits. Although temperature is one of the most important factors influencing the growth, development and metamorphic condition of larval anurans, many studies have failed to include ecologically relevant thermal fluctuations among their treatments. 2. We compared the growth and age at metamorphosis of striped marsh frogs Limnodynastes peronii raised in a diurnally fluctuating thermal regime and a stable regime of the same mean temperature. We then assessed the long-term effects of the larval environment on the morphology and performance of post-metamorphic frogs. 3. Larval L. peronii from the fluctuating treatment were significantly longer throughout development and metamorphosed about 5 days earlier. Frogs from the fluctuating group metamorphosed at a smaller mass and in poorer condition compared with the stable group, and had proportionally shorter legs. 4. Frogs from the fluctuating group showed greater jumping performance at metamorphosis and less degradation in performance during a 10-week dormancy. Treatment differences in performance could not be explained by whole-animal morphological variation, suggesting improved contractile properties of the muscles in the fluctuating group.

VARIATIONS IN THE MORPHOLOGY OF EMU (DROMAIUS NOVAEHOLLANDIAE) TRACKS REFLECTING DIFFERENCES IN WALKING PATTERN AND SUBSTRATE CONSISTENCY: ICHNOTAXONOMIC IMPLICATIONS

Abstract: Fossil footprints appear in a variety of preservational states, each revealing a different morphology that can give rise to misidentification and misinterpretations. Comparative ichnological work was conducted using living emus (Dromaius novaehollandiae). It was clearly demonstrated that the morphological variation that occurred in footprints of the same animal, walking in the same manner, was caused by variation in substrate consistency. Dry sand substrates are unlikely to preserve any anatomical details of the foot, whereas damp sand or mud of firm consistency preserves a high level of anatomical detail. The finest anatomical details, such as skin impressions, are only preserved in firm mud or clay. In semi‐fluid to fluid mud the track walls collapse, destroying the shape of the footprint. Increased speed of progression affects the shape of the footprint dramatically as the distal ends of the digits become more deeply impressed in the substrate during acceleration. Plantigrade stance adopted by the emu while feeding produces highly elongated footprints. Applying these observations to the study of fossil footprints demonstrates that great care should be paid to the original sedimentary conditions at the time of track making, as well as to the stance and gait of the trackmaker.

Cracks and fins in sulfate sand: Evidence for recent mineral-atmospheric water cycling in Meridiani Planum outcrops?

Research Article| April 01, 2006 Cracks and fins in sulfate sand: Evidence for recent mineral-atmospheric water cycling in Meridiani Planum outcrops? Gregory V. Chavdarian; Gregory V. Chavdarian 1Geology Department, University of California–Davis, Davis, California 95616, USA Search for other works by this author on: GSW Google Scholar Dawn Y. Sumner Dawn Y. Sumner 1Geology Department, University of California–Davis, Davis, California 95616, USA Search for other works by this author on: GSW Google Scholar Geology (2006) 34 (4): 229–232. https://doi.org/10.1130/G22101.1 Article history received: 08 Aug 2005 rev-recd: 20 Nov 2005 accepted: 22 Nov 2005 first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Gregory V. Chavdarian, Dawn Y. Sumner; Cracks and fins in sulfate sand: Evidence for recent mineral-atmospheric water cycling in Meridiani Planum outcrops?. Geology 2006;; 34 (4): 229–232. doi: https://doi.org/10.1130/G22101.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Gypsum dunes at White Sands National Monument, New Mexico, provide an excellent analog to sulfate-rich eolian outcrops on Meridiani Planum, Mars, as characterized by the Rover Opportunity. Numerous outcrops imaged by Opportunity contain polygonal cracks that crosscut bedding and extend across most surfaces of boulders. Some of these cracks are associated with millimeter-thick platy fins that protrude as much as a few centimeters above outcrops. Similar cracks crosscut bedding at White Sands on erosional stoss slopes and in pedestals of cemented dune sand. The cracks at White Sands form in response to cementation of damp gypsum sand followed by contraction due to dehydration. During warm seasons, cracked sand is dry and cracks rarely grow, although some may form after rainstorms. Two types of fins form along cracks and differentially eroded laminae. White fins represent subsurface differential cementation along cracks followed by differential erosion. Tan fins form due to cementation of crack edges and laminae on exposed dune surfaces. Wind-blown sediment adheres to damp tan fins. Similar processes may be important for crack and fin formation in Meridiani Planum outcrops, implying recent water cycling between sulfate outcrops and the Martian atmosphere. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

The HYDAD-D antipersonnel landmine detector

HYDAD (HYdrogen Density Anomaly Detection) systems have been developed to detect small (>200 g) antipersonnel landmines (APM) of plastic construction. The HYDAD-D detector is based on the earlier HYDAD designs HYDAD-H and HYDAD-VM. It consists of a neutron source and two identical slow neutron detectors. The difference between the responses of the two detectors is monitored as a function of position in the minefield and APM detection is based on an analysis of this difference. Laboratory tests and Monte Carlo simulations demonstrate that HYDAD-D is capable of detecting the IAEA standard dummy landmine DLM2 at burial depths up to 23 cm in dry sand and at burial depths up to 7 cm in damp sand containing 12% (by mass) water.

Development of detailed action plans in the event of a sodium hydride spill/fire

AbstractThe Center for Chemical Process Safety (CCPS) has developed a process for managing chemical reactivity hazards, such as water‐reactive/pyrophoric sodium hydride. This coupled with a recent fire while handling sodium hydride, at a pharmaceutical production facility, revealed gaps in the handling and emergency response process as well as in the emergency response materials used for spills of sodium hydride. A detailed action plan (DAP) was developed for personnel handling sodium hydride, as well as emergency first responders. The DAP identified actions in the event of a spill or fire for material handlers, emergency first responders, and the subsequent safe disposition of the contained material. Development of the DAP for sodium hydride required in‐house testing of various fire‐extinguishing agents and the benchmarking of best practices within the pharmaceutical and chemical industries. The optimum method or template chosen to develop the DAP was adaptable to conditions both in warehouses and in production buildings. Laboratory testing followed by field testing with up to 0.5 kg of sodium hydride identified damp sand in combination with liquid nitrogen as the superior agents to smother, contain, and permit transport to a suitable disposition area for destruction of unreacted sodium hydride. The template and method used to create the sodium hydride DAP may have applications for other water‐reactive/pyrophoric reagents.The use of wet sand with liquid nitrogen as a smothering agent promises to be a unique and potentially breakthrough method for smothering and transporting spilled water‐reactive/pyrophoric reagents. Additional testing is planned for other water‐reactive/pyrophoric reagents to assess the use of these emergency response materials and to develop additional DAPs. © 2005 American Institute of Chemical Engineers Process Saf Prog

Detection of tree roots and determination of root diameters by ground penetrating radar under optimal conditions.

A tree's root system accounts for between 10 and 65% of its total biomass, yet our understanding of the factors that cause this proportion to vary is limited because of the difficulty encountered when studying tree root systems. There is a need to develop new sampling and measuring techniques for tree root systems. Ground penetrating radar (GPR) offers the potential for direct nondestructive measurements of tree root biomass and root distributions to be made. We tested the ability of GPR, with 500 MHz, 800 MHz and 1 GHz antennas, to detect tree roots and determine root size by burying roots in a 32 m3 pit containing damp sand. Within this test bed, tree roots were buried in two configurations: (1) roots of various diameters (1-10 cm) were buried at a single depth (50 cm); and (2) roots of similar diameter (about 5 cm) were buried at various depths (15-155 cm). Radar antennas were drawn along transects perpendicular to the buried roots. Radar profile normalization, filtration and migration were undertaken based on standard algorithms. All antennas produced characteristic reflection hyperbolas on the radar profiles allowing visual identification of most root locations. The 800 MHz antenna resulted in the clearest radar profiles. An unsupervised, maximum-convexity migration algorithm was used to focus information contained in the hyperbolas back to a point. This resulted in a significant gain in clarity with roots appearing as discrete shapes, thereby reducing confusion due to overlapping of hyperbolas when many roots are detected. More importantly, parameters extracted from the resultant waveform through the center of a root correlated well with root diameter for the 500 MHz antenna, but not for the other two antennas. A multiple regression model based on the extracted parameters was calibrated on half of the data (R2 = 0.89) and produced good predictions when tested on the remaining data. Root diameters were predicted with a root mean squared error of 0.6 cm, allowing detection and quantification of roots as small as 1 cm in diameter. An advantage of this processing technique is that it produces results independently of signal strength. These waveform parameters represent a major advance in the processing of GPR profiles for estimating root diameters. We conclude that enhanced data analysis routines combined with improvements in GPR hardware design could make GPR a valuable tool for studying tree root systems.

A taxonomic review of some British coastal species of the Bryum bicolor complex, with a description of Bryum dyffrynense sp. nov.

Bryum dyffrynense sp. nov. is described from coastal sites in England and Wales. It is a rare moss species that grows as a colonist on damp sand, often closely associated with other rare Bryum including the threatened B. warneum. The other British coastal species of the B. bicolor complex with large bulbils are reviewed. The European nominal taxa B. versicolor, B.excurrens and B. dunense intergrade so they are regarded as conspecific. Since plants of B. dunense type intergrade with B. bicolor it appears best to regard these also as conspecific. Studies by Ochi have shown that the oldest name for this broadly defined species is B. dichotomum Hedw., based on a type from New Zealand.

SEASONAL VARIATION IN NESTING BEHAVIOR OF OXYBELUS BIPUNCTATUS (HYMENOPTERA: SPHECIDAE)

Abstract The nesting behavior of >300 females of Oxybelus bipunctatus was studied for 15 straight weeks in a sandpit in central New York during late spring-summer 1985. Cool and rainy weather in late spring induced moldy conditions in the cells that caused much larval mortality. Successive generations of wasps emerged in the field and laboratory every four to six weeks. Cells were always excavated in moderately damp sand. Cell depth varied inversely with soil moisture as tied to the amount of rainfall. Female cocoons were larger and heavier than male cocoons, but they did not occupy deeper or shallower cells. One-celled nests were predominant in this species. The number of prey per cell was rather uniform throughout the nesting season despite much variation in the prey fly families. Individual and aggregate prey weight per cell decreased slightly through the summer. Male Cyclorrapha were preyed upon more than any other taxon.

Temperature Effects on Egg Survival and Hatching during the Extended Incubation Period of California Grunion, Leuresthes tenuis

The California grunion Leuresthes tenuis, a teleost fish (Atherinopsidae), spawns terrestrially by burying its eggs in damp sand on beaches following semilunar spring tides. The eggs incubate above the water line and are ready to hatch after approximately 10 days at 18 C. However, grunion eggs do not hatch, even when developmentally ready, until returned to water and mechanically stimulated by wave action. In nature, the environmental trigger occurs on subsequent semilunar tides, when waves reach as high on the shore as the eggs were buried during spawning. If waves do not reach the eggs after one semilunar tidal cycle, the eggs survive by extending incubation and delaying hatching until the trigger occurs. This may take up to several additional weeks. Temperature affects the time to hatching readiness in California grunion eggs; this interval is shorter at warmer temperatures than at cooler ones. We incubated grunion eggs at three relevant temperatures: 15, 20, and 25 C. Viability of embryos was ascertained by microscopic examination, and hatching was attempted daily for eggs from each temperature, until no eggs hatched. The ability to extend incubation and delay hatching decreased with increasing incubation temperature. At the coolest temperature, eggs survived longer but were not able to hatch at the time of the first semilunar spring tide series. Hatching success and the duration of extended incubation are also influenced by temperature. Eggs incubated at 15 C always had lower hatching success than eggs incubated at the two higher temperatures. Eggs incubated at 20 C had a significantly greater chance of surviving and hatching during the three subsequent semilunar tides than eggs at 15 or 25 C. Eggs incubated at higher temperatures matured more quickly but had a shorter total period of viability. Temperature affects the duration of extended incubation for grunion eggs, and influences their hatching success, yet a majority of the eggs can mature and hatch successfully at each of the three temperatures. A broad temperature tolerance, plasticity in incubation duration, and environmentally triggered hatching allow the grunion fish to spawn terrestrially over a long season in a variable coastal ecosystem.

A dinosaur ichnocoenosis from the middle jurassic of Yorkshire, UK

An assemblage of dinosaur tracks from the undersurface of a sandstone bed in the Saltwick Formation (Middle Jurassic) of Yorkshire shows a range of morphological types, preservational variants and behavioral styles. The tracks are combinations of transmitted prints and underprints and include three distinct trackways. One trackway was made by an animal walking on exposed damp sand, another was left by an animal swimming diagonally across a current and being swept down current, while the third may have been made by an animal either running or pushing off with its feet as it drifted down current. Environmental conditions that existed during the formation of the trackways varied between crevasse splay floods and exposed damp sand. The morphology of the swimming tracks is sufficiently distinctive to warrant the erection of a new ichnogenus and ichnospecies—Characichnos tridactylus. Previously described material from Kansas, Wyoming and New Mexico can be attributed to this new ichnogenus, while specimens from Germany and Utah are only provisionally referred to it. This indicates a known range from Triassic to Cretaceous.

LARVAL DEVELOPMENT OF THE LAND HERMIT CRAB COENOBITA COMPRESSUS H. MILNE EDWARDS REARED IN THE LABORATORY

Abstract The complete larval development of the land hermit crab Coenobita compressus is described from specimens reared in the laboratory at 26°C. Eighty-eight percent passed through five zoeal stages and 12% passed through four zoeal stages before metamorphosing 21–33 days after hatching. Megalopae left their water dishes as soon as seven days after metamorphosis, buried themselves in damp sand approximately 29 days after metamorphosis, and emerged as young crabs 1–5 days later. Coenobita compressus zoeae can be distinguished from the other seven described coenobitids by the setation of the maxillule and antenna, whereas the megalopa can be distinguished by the segmentation of the second and third maxillipeds. Characters are also given to distinguish C. compressus zoeae from those of sympatric marine hermit crab zoeae.

The energetics of burrow excavation by the inland robust scorpion, Urodacus yaschenkoi (Birula, 1903)

The inland robust scorpion, Urodacus yaschenkoi (Urodacinae, Scorpionidae), is a large (~3 g) semifossorial scorpion that is widespread in arid regions of Australia. It constructs spiralling burrows up to 1 m deep in sandy soils. This study determined the net cost of transport (NCOT) by burrowing, which represents the energy used in horizontally burrowing a given distance, excluding maintenance metabolism. A mathematical model generally applicable to semi-fossorial species was developed and used to estimate the total cost of burrow construction. The model incorporates (1) horizontal NCOT, (2) the cost of moving spoil and the animal’s mass along the length of the tunnel, and (3) the cost of working against gravity to raise spoil and the animal’s mass to the surface. The total cost of burrow excavation to a depth of 47 cm was estimated to be 350–530 J. This represents approximately 2% of an adult scorpion’s yearly energy turnover. Interspecific allometric comparisons of published NCOT data from phylogenetically diverse burrowers (with body masses spanning over two orders of magnitude) showed that burrowing method and substrate are important determinants of NCOT. Specifically, the cost of constructing an open tunnel through damp or dry sand is higher than the cost of moving through wet sand or mud without forming a tunnel.

Seismic/electromagnetic system for landmine detection

A system has been designed for the detection of buried landmines. The system uses a stationary seismic source in conjunction with a movable displacement sensor that is based on an 8 GHz CW radar. The sensor measures the surface displacement by analog demodulation of the radar signal, which is reflected from the soil surface and modulated by the surface motion. The sensor is not in direct contact with the soil surface and is, therefore, capable of interrogating surface motion immediately above a buried mine. This configuration provides the dual advantage of removing half the seismic propagation path that would be encountered with a classical pulsed echo technique and detecting localized fields that would not propagate to a remote receiver. The system has been used in the laboratory to image inert antipersonnel mines and simulated antitank mines buried in damp compacted sand. Signal processing in the wave number domain provides significant improvement in the contrast between mine-related and background motion. The simplest detection cue for antipersonnel mines was found to be low-frequency resonances of their trigger mechanisms. These responded to seismic excitations with substantial local displacement. The resonances made these mines easily discernable from buried clutter such as rocks and sticks. [Work supported by ARO.]

Patterns of feeding behaviour in adult male riodinid butterflies and their relationship to morphology and ecology

Abstract Adult butterflies are known to visit a wide variety of food substrates, but, with the exception of flower visitation, little is known about what substances are being sought or what determines substrate choice. This is especially true for the Riodinidae, a large family ( c. 1300 spp.) of almost exclusively Neotropical butterflies. We present adult male feeding records for 124 species in 41 genera of Riodinidae (out of a total of 441 species in 85 genera collected in the study), based on ten months sampling in Ecuador. Records of food substrates visited in this study include flowers, damp sand or mud («puddling») and rotting carrion. Rotting carrion placed in traps was the most frequently recorded food source in terms of numbers of individuals and taxa, attracting 89 species from 32 genera. A correlation is found between food substrate choice and morphology, specifically wing area to thoracic volume ratio (WA:TV ratio). Our data suggest the possible existence of two adaptive syndromes whose species have significantly different mean WA:TV ratios and differing suites of accompanying ecological traits, with lower ratios being significantly correlated with species that were recorded feeding. Among species recorded feeding, carrion feeders and puddlers have significantly lower mean WA:TV ratios than flower nectarers, and carrion feeders have a lower mean WA:TV ratio than species not recorded on this food source, a correlation that is significant across all tribes and within some tribes (Riodinini and Saratoni). We reanalyse previously published data on flight and morphology for species in other butterfly and moth families and show that the ratio of wing area to thoracic mass is significantly negatively correlated with flight speed and oxygen consumption (a direct indicator of metabolic rate). We suggest that adult male riodinids may puddle and feed at rotting carrion to supplement nutrient stores from larval feeding, not only to increase reproductive success, but also to provide the necessary nutrients to maintain high metabolic rates during rapid flight.

Patterns of feeding behaviour in adult male riodinid butterflies and their relationship to morphology and ecology

Adult butterflies are known to visit a wide variety of food substrates, but, with the exception of flower visitation, little is known about what substances are being sought or what determines substrate choice. This is especially true for the Riodinidae, a large family (c. 1300 spp.) of almost exclusively Neotropical butterflies. We present adult male feeding records for 124 species in 41 genera of Riodinidae (out of a total of 441 species in 85 genera collected in the study), based on ten months sampling in Ecuador. Records of food substrates visited in this study include flowers, damp sand or mud («puddling») and rotting carrion. Rotting carrion placed in traps was the most frequently recorded food source in terms of numbers of individuals and taxa, attracting 89 species from 32 genera. A correlation is found between food substrate choice and morphology, specifically wing area to thoracic volume ratio (WA:TV ratio). Our data suggest the possible existence of two adaptive syndromes whose species have significantly different mean WA:TV ratios and differing suites of accompanying ecological traits, with lower ratios being significantly correlated with species that were recorded feeding. Among species recorded feeding, carrion feeders and puddlers have significantly lower mean WA:TV ratios than flower nectarers, and carrion feeders have a lower mean WA:TV ratio than species not recorded on this food source, a correlation that is significant across all tribes and within some tribes (Riodinini and Saratoni). We reanalyse previously published data on flight and morphology for species in other butterfly and moth families and show that the ratio of wing area to thoracic mass is significantly negatively correlated with flight speed and oxygen consumption (a direct indicator of metabolic rate). We suggest that adult male riodinids may puddle and feed at rotting carrion to supplement nutrient stores from larval feeding, not only to increase reproductive success, but also to provide the necessary nutrients to maintain high metabolic rates during rapid flight.

Die Schildblättrigkeit krautiger Angiospermen-Sippen in ihrer Beziehung zu Standort und Verbreitung )

Summary This study is an attempt to analyse the leaf peltation principally amongst herbaceous plants in its relation to natural habitat anddistribution, and concurrently to investigate their connection with certain growth forms and family groupings. The results confirm that in herbaceous plants peltation occurs predominantly amongst perennials with adventitious roots, that is to say amongst growth forms possessing rhizomes, creeping shoots, bulbs, tubers and stolons with stem tubers. Peltation was only marginally established amongst the phylogenetically young annuals which prefer dry growing conditions. Oceanity has a clear influence upon the distribution of peltate taxa. The majority of peltate perennials are associated with the OZ 1–3 degrees of oceanity. In subtropical, meridional and temperate steppes, deserts, and semi-deserts, peltation declines dramatically. The influence of zonality upon the distribution of peltate taxa is limited. In subtropical, meridional and temperate areas of N. America (including Central America) and East Asia, the proportion of peltate genera within the total genera stock of one region is relatively constant. This proportion declines in the boreal zone and peltate taxa are absent in the arctic zone. Almost all peltate perennials colonise wet, damp or humid locations, or sites with variable wetness and humidity. They favour lakes, ponds, swamps, moors, meadows, damp sand, stream and riverbanks, woods and damp shaded or half-shaded rocks. The ascidiate groups of plants resemble peltate species in their preference for wet, damp and humid habitats. Their leaf type is also related to the peltate one. The more or less frequent appearence of peltate taxa within the taxonomic sphere of the ascidiate families (Nepenthaceae, Sarraceniaceae) and genera ( Utricularia, Genlisea ) may indicate familial relationships. This should be borne in mind in phylogenetic studies of carnivors. Questions relating to the evolution of some succulent peltate plant groups are also discussed.

Variations in salamander trackways resulting from substrate differences

As part of a study of vertebrate trackways in the cross-stratified Coconino Sandstone (Permian) of northern Arizona, trackways made by living salamanders under different substrate conditions were compared. The sample of 230 trackways of the western newt,Taricha torosa,included ten combinations of the following substrate characteristics: 1) sediment: muddy or of fine sand; 2) attitude: level or sloped (25 degrees); 3) moisture content: dry, damp, wet, or submerged.Trackways in wet mud produced the most accurate representation of the number of toes per foot and the arrangement of toes. All other conditions studied yielded a reduced average number of toes per foot, and a large sample was needed before the data had the potential to indicate the true structure of the trackmaker's feet. Trackways made on sloped, submerged mud or sand, sloped, dry sand, and sloped, damp sand rarely included the full complement of toes. The positions and orientations of the toe marks were distorted if the animals were walking underwater or on sloped, damp sand. Trackways on the slopes of cross-stratified deposits make reliable identification of the trackmaking animals exceptionally difficult.

Technical approach to characterization of perceived comfort of walking surfaces

Abstract The purpose of this study was to develop laboratory and field test methods to simulate the motions and system responses when an individual walks on a synthetic surface such as carpet. The heel-strike was simulated by the impact of a Clegg tester, a free-falling 2.27-kg missile, instrumented to record peak deceleration (g max ). Comparisons were made between indentations by the Clegg tester, dropped from different heights, and heel imprints in damp sand, collected with the aid of five test subjects under controlled conditions. A single Clegg drop height, 178 mm, was found to be a good compromise for the heel-strike simulation. Impact tests from this height and three other mechanical tests were performed on four carpet/cushion systems, which were also evaluated subjectively by a panel of pedestrians. Generally speaking, perceived comfort in walking over the test surfaces increased with decreasing g max values and with increasing ball rebound, a standard test for surface elaticity. Other tests of mechanical properties, performed at slower rates of loading, related less well to the comfort ratings of the carpets.