Expulsion Of Water Research Articles

Salinity effect on the liquid limit of soils

Previous studies stated that, with increasing salinity, the decreased liquid limit for expansive soils was attributed to the shrinkage of diffuse double layer, while the increased liquid limit for non-expansive soils was explained by the growing particle flocculation. These two mechanisms seem to be controversial and it is difficult to understand how an increasing salinity can promote soil flocculation. This study aims at clarifying the mechanism controlling liquid limit by conducting cone penetration test, sedimentation and rheological tests on MX80 Na-bentonite and silty soil. Results showed that the liquid limit and yield stress of MX80 increased then decreased with increasing salinity, while they increased slightly for the silty soil. In sedimentation test, faster settling rate and smaller sediment volume were identified for MX80 and silt suspensions in NaCl solution, evidencing the shrinkage of diffuse double layer and the formation of denser aggregated structure. This suggested that the change of liquid limit is the result of two mechanisms in competition, which depend on the compression rate of diffuse double layer: (1) the water storage in nano-fissures which correspond to the nanoscale spaces among interlayers of clay particles resulting from the slight shrinkage of diffuse double layer, and (2) the water expulsion into larger pores with significant shrinkage of diffuse double layer. For the MX80 at low salinity and for the silt soil, the first mechanism prevailed and the increasing liquid limit was attributed to the requirement of more water to fill the nano-fissures. In contrast, for MX80 at high salinity, the second mechanism prevailed—the diffuse double layer was compressed significantly, changing the double-layer water to free water and giving rise to the decrease in liquid limit.

A Miniature pH Probe Using Functional Microfiber Bragg Grating

Operando and precisely probing aqueous pH is fundamentally demanded, both in chemical and biological areas. Conventional pH probes, subjected to the larger size, are probably unfit for application in some extreme scenarios, such as a trace amount of samples. In this paper, we have further developed the pH sensor that leverages the microfiber Bragg grating with an ultra-compact size down to an order of magnitude of 10−14 m3. Using the electrostatic self-assembly layer-by-layer technique, the functional film consisting of sodium alginate, which harnesses a pH-dependent hygroscopicity, is immobilized on the fiber surface. Consequently, the alteration of aqueous pH could be quantitatively indicated by the wavelength shift of the grating resonance via the refractive index variation of the sensing film due to the water absorption or expulsion. The grating reflections involving fundamental mode and higher order mode exhibit the sensitivities of −72 pm/pH and −265 pm/pH, respectively. In addition, temperature compensation can be facilitated by the recording of the two reflections simultaneously. Furthermore, the modeling and simulation results predict the pivotal parameters of the configuration in sensitivity enhancement. The proposed proof-of-concept enriches the toolbox of pH sensor for catering to the need of detection in some extremely small spaces—for example, the living cells or the bio-tissues.

Microstructure Investigation of Oil-Bearing Rhyolites: A Case Study from the Hailar Basin, NE China

Understanding the microstructure of rhyolites may greatly promote exploration efforts on rhyolitic hydrocarbon reservoirs; however, related studies are sparse. In this contribution, the microstructure and related porosity of oil-bearing rhyolitic lavas from the Hailar Basin (NE China) were investigated using a combination of optical microscopy, fluorescence image analysis, and scanning electron microscopy. The direct visual and quantitative analyses show that the rhyolites are heterogeneous and porous rocks and have complex microstructures. Phenocryst-rich rhyolitic lava, perlitic lava, and spherulitic rhyolite may be favorable targets for rhyolitic hydrocarbon exploration. For the phenocryst-rich rhyolitic lavas, embayment pores, cleavages, cavitational and shear fractures, and intracrystalline sieve pores are commonly observed in the phenocrysts; while flow-parallel laminar and micropores are ubiquitous in the groundmass. Perlitic lavas are characterized by the occurrence of numerous perlitic fractures which can also be produced in the glassy groundmass of other lavas. Spherulitic rhyolites mainly consist of small-sized (<1 mm) clustered or large-sized (>1 mm) isolated spherulites. Clustered spherulites are characterized by the development of interspherulite pores. Isolated spherulites contain numerous radiating micropores. Both types of spherulites may have water expulsion pores formed in the spherulite–glass border. The formation of the microstructure and related porosity of rhyolites is controlled by pre-, syn- (e.g., deuteric crystal dissolution, cavitation, ductile–brittle deformation, and high-T devitrification), and post-volcanic (e.g., hydration and low-T devitrification) processes. Although pores with diameters > 50 μm are often observed, small pores dominate in pore-size distribution. Small (<15 μm) and large (>300 μm) pores give the most volumetric contribution in most cases. Medium-sized pores with diameters ranging from ~150–300 μm are the least developed and contribute the least to the total volume. The results of this paper can be beneficial to further the understanding of the microstructure and pore system of rhyolites and may be applied to rhyolitic lava hydrocarbon reservoirs elsewhere.

Complexation-induced resolution enhancement of 3D-printed hydrogel constructs

Three-dimensional (3D) hydrogel printing enables production of volumetric architectures containing desired structures using programmed automation processes. Our study reports a unique method of resolution enhancement purely relying on post-printing treatment of hydrogel constructs. By immersing a 3D-printed patterned hydrogel consisting of a hydrophilic polyionic polymer network in a solution of polyions of the opposite net charge, shrinking can rapidly occur resulting in various degrees of reduced dimensions comparing to the original pattern. This phenomenon, caused by complex coacervation and water expulsion, enables us to reduce linear dimensions of printed constructs while maintaining cytocompatible conditions in a cell type-dependent manner. We anticipate our shrinking printing technology to find widespread applications in promoting the current 3D printing capacities for generating higher-resolution hydrogel-based structures without necessarily having to involve complex hardware upgrades or other printing parameter alterations.

Tree species identification via 1H NMR fingerprinting of supercritical carbon dioxide wood extractives

Six tree species were examined using 1H NMR spectroscopy of sap extracted by supercritical CO2. A metabolomic approach was developed to evaluate the sap extracted from sapwood of Norway spruce (Picea abies), Sitka spruce (Picea sitchensis), radiata pine (Pinus radiata), macrocarpa (Cupressus macrocarpa), and two Eucalyptus species—shining gum and mountain ash (Eucalyptus nitens and Eucalyptus regnans. The sap extraction patterns in the different species were visualised using 1H magnetic resonance imaging. In softwoods with distinct annual rings, water was first removed from the latewood bands, and then gradually from the earlywood bands. In the case of the hardwood species an almost random water redistribution, rather than water expulsion, was observed. Analysis of the principal component analysis loading plots showed that the significant differences in the sap between each species were due to the carbohydrate region. Key discriminators were identified as pinitol, sucrose, glucose, and fructose.

Opto-chemo-mechanical transduction in photoresponsive gels elicits switchable self-trapped beams with remote interactions

Next-generation photonics envisions circuitry-free, rapidly reconfigurable systems powered by solitonic beams of self-trapped light and their particlelike interactions. Progress, however, has been limited by the need for reversibly responsive materials that host such nonlinear optical waves. We find that repeatedly switchable self-trapped visible laser beams, which exhibit strong pairwise interactions, can be generated in a photoresponsive hydrogel. Through comprehensive experiments and simulations, we show that the unique nonlinear conditions arise when photoisomerization of spiropyran substituents in pH-responsive poly(acrylamide-co-acrylic acid) hydrogel transduces optical energy into mechanical deformation of the 3D cross-linked hydrogel matrix. A Gaussian beam self-traps when localized isomerization-induced contraction of the hydrogel and expulsion of water generates a transient waveguide, which entraps the optical field and suppresses divergence. The waveguide is erased and reformed within seconds when the optical field is sequentially removed and reintroduced, allowing the self-trapped beam to be rapidly and repeatedly switched on and off at remarkably low powers in the milliwatt regime. Furthermore, this opto-chemo-mechanical transduction of energy mediated by the 3D cross-linked hydrogel network facilitates pairwise interactions between self-trapped beams both in the short range where there is significant overlap of their optical fields, and even in the long range--over separation distances of up to 10 times the beam width--where such overlap is negligible.

Post-liquefaction pore pressure dissipation in sand under cyclic stress triaxial testing

Soil liquefaction has conventionally been studied as a pure undrained condition subject to cyclic shearing in the laboratory. However, in the field, ground settlement and expulsion of pore water in the form of sand boils are frequently observed, which conventional triaxial and simple shear apparatus are unable to replicate. In this study, a novel insight of coupled pore pressure generation and dissipation in liquefiable clean sand is discussed with the use of a modified cyclic triaxial testing set-up. Stress-controlled cyclic triaxial tests with controlled pore water drainage far lower than the soil's permeability were carried out to investigate ‘near-perfect undrained’ conditions, which are more representative of field conditions. Comparison of results from three sets of stress-controlled cyclic triaxial testing were carried out: (a) conventional shearing under an undrained condition; (b) shearing under controlled drainage; and (c) undrained shearing until liquefaction, and thereafter continual shearing under controlled drainage. The critical cyclic shear stress ratio where excess pore pressure dissipation dominates excess pore pressure generation is identified from the coupled cyclic shear loading and pore water drainage tests. In addition, this study also noted a critical void ratio where the soil is no longer susceptible to liquefaction even under considerable shearing amplitudes. These findings may offer guidance on the tolerable cyclic shear stress and minimum degree of densification to avoid occurrence of soil liquefaction in the field.

Multiaxial movements at the minke whale temporomandibular joint.

Mandibular mobility accompanying gape change in Northern and Antarctic minke whales was investigated by manipulating jaws of carcasses, recording jaw movements via digital instruments (inclinometers, accelerometers, and goniometers), and examining osteological and soft tissue movements via computed tomography (CT)-scans. We investigated longitudinal (α) rotation of the mandible and mediolateral displacement at the symphysis (Ω1 ) and temporomandibular joint (Ω2 ) as the mouth opened (Δ). Results indicated three phases of jaw opening. In the first phase, as gape increased from zero to 8°, there was slight (<1°) α and Ω rotation. As gape increased between 20 and 30°, the mandibles rotated slightly laterally (Mean 3°), the posterior condyles were slightly medially displaced (Mean 4°), and the anterior ends at the symphysis were laterally displaced (Mean 3°). In the third phase of jaw opening, from 30° to full (≥90°) gape, these motions reversed: mandibles rotated medially (Mean 29°), condyles were laterally displaced (Mean 14°), and symphyseal ends were medially displaced (Mean 1°). Movements were observed during jaw manipulation and analyzed with CT-images that confirmed quantitative inclinometer/accelerometer data, including the unstable intermediate (Phase 2) position. Together these shifting movements maintain a constant distance for adductor muscles stretched between the skull's temporal fossa and mandible's coronoid process. Mandibular rotation enlarges the buccal cavity's volume as much as 36%, likely to improve prey capture in rorqual lunge feeding; it may strengthen and stabilize jaw opening or closure, perhaps via a simple locking or unlocking mechanism. Rotated lips may brace baleen racks during filtration. Mandibular movements may serve a proprioceptive mechanosensory function, perhaps via the symphyseal organ, to guide prey engulfment and water expulsion for filtration.

Effect of supercritical CO2 treatment and kiln drying on collapse in Eucalyptus nitens wood

Collapse-prone timbers such as species of Eucalyptus are poorly utilised due to low conversion rates that necessitate long pre-drying times. A supercritical CO2 lumen water expulsion pre-treatment prior to kiln drying is proposed to bypass lengthy pre-drying. After drying (air, kiln or oven drying), shrinkage, collapse, washboard depression and checking of Eucalyptus nitens were determined using image analysis of 0.8 mm thick wafers and 5 mm thick biscuits. Lumen water expulsion-kiln drying reduced collapse by 75% and washboard depression by 71%, compared to drying from green. As water is removed from the water conductive tissue (vessels, rays, and fibre-tracheids) by lumen water expulsion, the water column is broken throughout the specimen, thereby disrupting the development of meniscus-induced water tension as subsequent drying occurs. Remaining water is proposed to reside in the non-water-conductive fibre tissue. If the process can be applied on large scale to Eucalyptus nitens, there is the opportunity for higher conversion rates to increase the commercial viability of solid wood products.

Long-term frost weathering rates of limestone beach clasts, Fårö Island, Central Baltic Sea

ABSTRACTThe known post-glacial isostatic land rise rates at Fårö Island, Central Baltic Sea, allowed for the reliable estimation of frost weathering rates of limestone clasts along five beach profiles. Weathering rates measured by clast dimension change were quantified over periods ranging between 640 and 2090 years. While the deposited beach materials at each profile have varying lithostratigraphic compositions these attributes appear to have no direct influence on the long-term comminution rates. Mean clast size of initially deposited beach materials is suggested to be primarily a function of local wave energy and sourced from local rock platforms. Field observations, climate data and literature point to the beach materials in the upper 10–20 cm being fractured under an active diurnal to short-term frost environment that has persisted over the past 1000–2000 years. Pore water freezing by 9% volumetric expansion and the development of pore water expulsion and hydrofracture is suggested to increase pore volume and pore interconnectedness over time and facilitate ice segregation growth. Observed modes of clast fracture, bursting, flaking and granular disaggregation suggest different frost weathering mechanisms to operate on different limestone lithologies. Long term rates of break down appear however not differentiated by limestone composition.

Squids use multiple escape jet patterns throughout ontogeny.

ABSTRACTThroughout their lives, squids are both predators and prey for a multitude of animals, many of which are at the top of ocean food webs, making them an integral component of the trophic structure of marine ecosystems. The escape jet, which is produced by the rapid expulsion of water from the mantle cavity through a funnel, is central to a cephalopod's ability to avoid predation throughout its life. Although squid undergo morphological and behavioral changes and experience remarkably different Reynolds number regimes throughout their development, little is known about the dynamics and propulsive efficiency of escape jets throughout ontogeny. We examine the hydrodynamics and kinematics of escape jets in squid throughout ontogeny using 2D/3D velocimetry and high-speed videography. All life stages of squid produced two escape jet patterns: (1) ‘escape jet I’ characterized by short rapid pulses resulting in vortex ring formation and (2) ‘escape jet II’ characterized by long high-volume jets, often with a leading-edge vortex ring. Paralarvae exhibited higher propulsive efficiency than adult squid during escape jet ejection, and propulsive efficiency was higher for escape jet I than escape jet II in juveniles and adults. These results indicate that although squid undergo major ecological transitions and morphology changes from paralarvae to adults, all life stages demonstrate flexibility in escape jet responses and produce escape jets of surprisingly high propulsive efficiency.This article has an associated First Person interview with the first author of the paper.

Volumetric and ultraacoustic properties of sodium salts of ibuprofen/diclofenac drugs in aqueous and aqueous-β-cyclodextrin solution

Present paper reports the study of inclusion complex formation between two non-steroidal anti-inflammatory drugs namely sodium ibuprofen and diclofenac sodium in water and aqueous-β-cyclodextrin solutions through thermodynamic properties like the standard partial molar volumes and the standard partial molar compressibility at 303.15, 308.15 and 313.15 K and at atmospheric pressure. For this, the densities and ultrasonic velocities of ternary sodium ibuprofen/diclofenac-β-cyclodextrin-water mixtures were measured and used for the calculation of apparent molar volume (V2,ϕ) and apparent molar compressibility (κs,2,ϕ). The concentration dependence of apparent properties has been fitted to standard relations and corresponding the standard partial molar volume (V2o) and the standard partial molar compressibility (κs,2o) and respective solute-solute interaction parameters Sv and Sk were graphically determined. The standard transfer volumes (ΔtrV2o) and standard transfer compressibility (Δtrκs,2o) were also computed and these properties have been interpreted in terms of drug hydration, inclusion complex formation, and different interactions involved. The sign of Sv and Sk revealed the weakening of solute–solute interactions in presence of cosolute β-cyclodextrin. Solubilization of hydrophobic parts, expulsion of water from hydrophobic cavity of β-cyclodextrin and inclusion complex formation of these drugs with β-cyclodextrin has been confirmed from partial molar volume and transfer properties.

Molybdenum contents of sulfides in ancient glacial diamictites: Implications for molybdenum delivery to the oceans prior to the Great Oxidation Event

In order to determine whether sulfides are major reservoirs for Mo in the upper continental crust (UCC), we determined the composition and mode of occurrence of sulfides and evaluated their contribution to the molybdenum budget in twelve glacial diamictites with ages ranging from 2900 to 300 Ma. The diamictites provide a snapshot of UCC mineralogy and composition at the time of their deposition and show systematic depletion in bulk rock Mo concentrations after the Great Oxidation Event (GOE), reflecting the effects of oxidative weathering in their provenance (Gaschnig et al., 2014; Li et al., 2016). Sulfides are generally confined to Archean and Paleoproterozoic diamictites, although they also have been found in one Phanerozoic sample with an ancient provenance. We classify the sulfides based on their compositions and morphologies. Detrital sulfides are generally rounded, may be a single mineral, or an assemblage of minerals, and show a very wide range in mineralogy, including a single molybdenite grain. Sedimentary sulfides are pyrites, generally with framboidal-like textures. Pyrites also include non-framboidal textured authigenic pyrites. Epigenetic sulfides consist of irregular pyrrhotite aggregates (sometimes pyrrhotite intergrown with chalcopyrite and cobaltite), late-stage euhedral pyrites and pyrite aggregates in veins. High Mo concentrations (up to ∼230 ppm) are found in some sedimentary framboidal-like pyrites from the Mesoarchean Coronation and Paleoproterozoic Makganyene Formations, epigenetic pyrrhotite aggregates and chalcopyrite in the Ramsay Lake diamictite, and in detrital sulfides in Timeball Hill diamictites that may have originated from hydrothermal fluids in the sedimentary basins. Other detrital sulfides have widely variable Mo concentrations (0.5–36 ppm). Mass balance calculations show that sulfides can account for only <8% of the whole rock Mo contents in all glacial diamictites except for the Makganyene Formation, and thus sulfides (including molybdenite) are unlikely to be a significant host of Mo within the UCC before the GOE. In the Makganyene diamictites, ∼37% of whole rock Mo is contained within sulfides, which are predominantly framboidal-like pyrites interpreted to have grown in the matrix at the time of deposition. In these, the Mo contents correlate with the size of the microcrystals: smaller-sized crystals contain significantly higher concentrations than larger-sized crystals, suggesting that rapid nucleation and growth of framboidal pyrites leads to incorporation of large amounts of Mo available in the pore water or Mo expulsion during recrystallization. The presence of Mo in sedimentary pyrites from a pre-GOE deposit – the 2900 Ma Coronation Formation – points to the availability of Mo and S in pre-GOE seawater (and associated pore fluids), and is consistent with previously reported evidence for isolated pulses of atmospheric oxygen and oxidative continental weathering prior to the GOE. However, the lack of significant whole rock Mo depletion in pre-GOE diamictites limits the amount of Mo released from the continents prior to the GOE.

Consolidation behaviour of double-porosity clay using flexible wall permeameter

Restoration of a site that has previously been prepared using dredged clay is a serious geotechnical challenge. Much of these clays exists as lumps suspended in slurry. These double-porosity soils consolidate due to the expulsion of water from the voids within each lump and the voids between the lumps. Due to this complex nature, the conventional theory of consolidation is not applicable to them. This study discusses the laboratory consolidation test results of double porosity samples. The tests were conducted on 10–30 mm clay lumps. The size, initial packing and the stiffness of the lumps were the variables. At low confining pressure the 30 mm lumpy samples experienced a significantly higher deformation than the 10 mm lumpy samples. In all the tests, the lumps and slurry merged to close the inter-lump voids as confining pressure neared or reached the pre-consolidation lump pressure. This paper also discusses the use of a simple constitutive relationship to model the behaviour of double-porosity fill. It uses the structured clay framework to describe the volumetric strain in the double-porosity samples by using two parameters, in addition to those required in the critical state soil mechanics. A parametric study demonstrated the capabilities of this model.

Tectonic evolution of Juventae Chasma, Mars, and the deformational and depositional structural attributes of the four major light-toned rock exposures therein

Juventae Chasma, a canyon peripheral to the Valles Marineris trough system, is the product of a unique merger of a Martian chaotic terrain depression and an extensional (tectonic) chasm. The chaotic terrain portion is set along a NNE-SSW axis, while a linear trough (the chasm component) is present along a WNW-ESE axis. Within the chasm are four discrete bodies of layered, light-toned rocks of sedimentary origin, Features A–D. The chaotic terrain component formed during the Early Hesperian as a result of expulsion of liquid water along pre-existing planes of weaknesses resulting from a WNW-ENE compression. The chasm component formed in response to NE-SW extension during the Middle to Late Amazonian. The light-toned Features A–D are layered at <2 m scale. A dark-toned material, previously interpreted as interstratified with the light-toned layers, is a secondary accumulation deposited after the light-toned rocks were lithified and exposed at the Martian surface. The bedding configurations within Features A, C, and D indicate eolian sand deposition; whereas a lacustrine or low-energy eolian origin is more fitting for Feature B. Features A–D also record Early Hesperian compressional events in the form of joints. Bedding joints, formed in response to release of an overburden, are also found. In addition, closed, elliptical outcrop patterns of inward dipping layers are also identified; these are either folds (structural basins) or erosional surfaces cutting three-dimensional eolian cross-beds.

Collective Transformation of Water between Hyperactive Antifreeze Proteins: RiAFPs

We demonstrate, by molecular dynamics simulations, that water confined between a pair of insect hyperactive antifreeze proteins from the longhorn beetle Rhagium inquisitor is discontinuously expelled as the two proteins approach each other at a certain distance. The extensive striped hydrophobic–hydrophilic pattern on the surface, comprising arrays of threonine residues, enables water to form three independent ice channels through the assistance of hydroxyl groups, even at 300 K. The transformation is reminiscent of a freezing–melting transition rather than a drying transition and governs the stable protein–protein separation in the evaluation of the potential of mean force. The collectivity of water penetration or expulsion and the hysteresis in the time scale of ten nanoseconds predict a potential first-order phase transition at the limit of infinite size and provide a new framework for the water-mediated interaction between solutes.

Effects of Controlled Relative Humidity Storage on Moisture Sorption and Amylopectin Retrogradation in Gelatinized Starch Lyophiles.

Water plays a significant role in the gelatinization and retrogradation (crystallization) of starch. Amylopectin crystalline regions can adopt several hydrated polymorphic forms; however, reports differ on the migration of water during retrogradation. The objectives of this study were to determine the moisture sorption patterns of gelatinized starch lyophiles during retrogradation in controlled relative humidity (RH) environments and document the amylopectin polymorph(s) formed. Starches from different botanical sources containing A-type and B-type amylopectin polymorphs were studied. Suspensions of starch were heated and then frozen and freeze-dried to make primarily amorphous matrices. Moisture sorption profiles of the dried samples were collected from 5% RH to 95% RH at 25 °C. To capture the retrogradation event, sample masses were also monitored at constant RHs over time (95%, 92.5%, and 90% RH). Powder X-ray diffraction was used to document the physical state of the samples, including the amylopectin polymorph formed upon retrogradation, and differential scanning calorimetry was used to determine glass transition temperatures (Tg s). In all lyophiles, water was first absorbed (mass gain), and if a critical water content was reached (at ≥92.5%RH), sample Tg s dropped below room temperature and concurrent retrogradation and water expulsion (mass loss) occurred, regardless of starch botanical source and whether A- or B-type polymorphs were formed. Overall, retrogradation and water expulsion increased as storage RH increased. These results offer further knowledge into the role of water in amylopectin retrogradation and the relationship among starch type, environmental RH, moisture sorption prior to retrogradation, and water redistribution during retrogradation. PRACTICAL APPLICATION: Starch gelatinization and retrogradation require molecular mobility, which is facilitated by water. Limited retrogradation occurred in lyophiles in the glassy state (90% RH, 25 °C), but increasing the storage RH (to ≥92.5% RH) resulted in increasing amylopectin retrogradation (note: many baked products have water activities in this range). Regardless of starch type (botanical source and amylose content), when the storage RH was high enough, the starch lyophiles first absorbed water, which depressed the Tg below the storage temperature, and then exhibited concomitant retrogradation and water expulsion. The water expelled during amylopectin retrogradation was not (fully) retained in the amorphous starch fraction, which is why samples lost weight. Water leaving the starch matrix during retrogradation could pose challenges for quality, texture, and shelf-life of starch-based products.

Water vapor absorption allows for volume expansion during molting in Armadillidiumvulgare and Porcelliodilatatus (Crustacea, Isopoda, Oniscidea).

Arthropods require periodic molting in order to grow which presents a number of challenges to terrestrial taxa. Following ecdysis, the pliant new cuticle is susceptible to buckling under gravity and requires elevated hydrostatic pressure for support. Terrestrial species also require a mechanism of volume expansion and stretching of the integument prior to sclerotization, a need that is readily met in aquatic arthropods by drinking. Options for land arthropods include drinking of dew, swallowing of air, or using muscular contractions to inflate air sacs in tracheate taxa. In this study we tested the hypothesis that crinochete terrestrial isopods (Isopoda: Oniscidea: Crinocheta) exploit their capacity for active water vapor absorption (WVA) to increase volume during molting. Two crinochete species, Armadillidiumvulgare and Porcelliodilatatus, were studied and compared with the non-absorbing species Ligidiumlapetum (Oniscidea: Ligiamorpha). Pre-molting animals were identified by sternal CaCO3 deposits and exposed to 100% or 97% relative humidity (RH). Mass-changes were monitored by daily weighing and the timing of the posterior and anterior ecdyses was used to categorize time (days premolt and days post-molt) over the molt cycle. In each treatment RH, A.vulgare and P.dilatatus showed a progressive mass increase from 5 days premolt until the posterior or anterior ecdysis, followed abruptly by period of mass-loss lasting 3–4 days post-molt. The fact that the initial mass-gain is seen in 97 % RH, a humidity below the water activity of the hemolymph, confirms the role of WVA. Similarly, since the post-molt mass-loss is seen in 100 % RH, this must be due to active expulsion of water, possibly via maxillary urine. Concurrent changes in hemolymph osmolality were monitored in a separate batch of A.vulgare and show sustained osmolality during premolt and an abrupt decrease between the anterior and posterior ecdysis. These patterns indicate a mobilization of sequestered electrolytes during premolt, and a loss of electrolytes during the post-molt mass-loss, amounting to approximately 8.6 % of total hemolymph solutes. WVA, in conjunction with pulses of elevated hemolymph pressure, provides an efficient mechanism of pre-molt volume expansion prior to and during the biphasic molt in these species. Premolt Ligidiumlapetum exposed to same treatments failed to molt successfully and no premolt animals survived to day 3 (72 h) even in 100 % RH. The apparent dependence of this species on liquid water for successful molting could explain its obligatory association with riparian fringe habitats.

Why Does RNA Collapse? The Importance of Water in a Simulation Study of Helix-Junction-Helix Systems.

Using computer simulations, we consider the balance of thermodynamic forces that collapse RNA. A model helix-junction-helix (HJH) construct is used to investigate the transition from an extended to a collapsed conformation. Conventional Molecular Dynamics and Milestoning Simulations are used to study the free energy profile of the process for two ion concentrations. We illustrate that HJH folds to a collapsed state with two types of counterions (Mg2+ and K+). By dissecting the free energy landscape into energetic and entropic contributions, we illustrate that the electrostatic forces between the RNA and the mobile ions do not drive the RNA to a collapsed state. Instead, entropy gains from water expulsion near the neighborhood of the RNA provide the stabilization free energy that tilt HJH into more compact structures. Further simulations of a three-helix hammerhead ribozyme show a similar behavior and support the idea of collapse due to increased gain in water entropy.

Characterization of Simultaneous Pressure Waves as Biomarkers for Colonic Motility Assessed by High-Resolution Colonic Manometry.

Simultaneous pressure waves (SPWs) in manometry recordings of the human colon have been associated with gas expulsion. Our hypothesis was that the SPW might be a critical component of most colonic motor functions, and hence might act as a biomarker for healthy colon motility. To that end, we performed high-resolution colonic manometry (HRCM), for the first time using an 84-sensor (1 cm spaced) water-perfused catheter, in 17 healthy volunteers. Intraluminal pressure patterns were recorded during baseline, proximal and rectal balloon distention, after a meal and following proximal and rectal luminal bisacodyl administration. Quantification was performed using software, based on Image J, developed during this study. Gas expulsion was always associated with SPWs, furthermore, SPWs were associated with water or balloon expulsion. SPWs were prominently emerging at the termination of proximal high amplitude propagating pressure waves (HAPWs); we termed this motor pattern HAPW-SPWs; hence, SPWs were often not a pan-colonic event. SPWs and HAPW-SPWs were observed at baseline with SPW amplitudes of 12.0 ± 8.5 mmHg and 20.2 ± 7.2 mmHg respectively. The SPW occurrence and amplitude significantly increased in response to meal, balloon distention and luminal bisacodyl, associated with 50.3% anal sphincter relaxation at baseline, which significantly increased to 59.0% after a meal, and 69.1% after bisacodyl. Often, full relaxation was achieved. The SPWs associated with gas expulsion had a significantly higher amplitude compared to SPWs without gas expulsion. SPWs could be seen to consist of clusters of high frequency pressure waves, likely associated with a cluster of fast propagating, circular muscle contractions. SPWs were occasionally observed in a highly rhythmic pattern at 1.8 ± 1.2 cycles/min. Unlike HAPWs, the SPWs did not obliterate haustral boundaries thereby explaining how gas can be expelled while solid content can remain restrained by the haustral boundaries. In conclusion, the SPW may become a biomarker for normal gas transit, the gastrocolonic reflex and extrinsic neural reflexes. The SPW assessment reveals coordination of activities in the colon, rectum and anal sphincters. SPWs may become of diagnostic value in patients with colonic dysmotility.