Equal Densities Research Articles

Combining Micro and Macro Relative Density: An Experimental and Computational Study on Hierarchical Porous 3D‐Printed Polylactic Acid Structures

Polymer foams and cellular solids have gained significant interest due to their enhanced properties. This study introduces a novel approach by employing foamed fused filament fabrication printing of cellular solids. A composite polylactic acid filament containing chemical blowing agents is used to create structures with varying micro relative density, which is examined through scanning electron microscopy and tensile testing, with comparisons made to a Mori Tanaka analytical model and representative volume elements investigation. Two different types of cellular solid structures, specifically body‐centered cubic and Gyroid triple periodic minimal surface structures, have been created with different thicknesses and printed at various temperatures. This is done to attain a range of micro‐ and macroporosity, leading to samples with equal total relative densities. Compression tests, coupled with finite element analysis, provide insights into the influence of each type of porosity. The fabricated specimens exhibit compressive strengths ranging from 1.07 to 79.14 MPa and elastic moduli ranging from 0.064 to 3.35 GPa. The findings suggest that porous structures relying on macroporosity exhibit higher compressive strength, while those relying on microporosity demonstrate more appealing energy absorption properties, particularly under stresses approaching the plateau region.

Thermal comfort and mechanical analysis of vigorous diamond and diaper weaves; warp, weft and balanced float fabrics with equal thread densities

Diamond (pointed twill) and diaper (herringbone twill) woven assemblies are considered ideal for applications where thermal insulation, heat retention, wrinkle resistance, strength, softness, and breathability attributes are crucial. Limited research has been found on the optimization of thermal comfort and mechanical performance of warp face, weft face and balanced float diaper and diamond woven assemblies. In this work six different woven assemblies have been engineered using cotton (cellulosic yarn) on a dobby machine, having warp face (4/2) weft face (2/4) and balanced float (3/3) based diamond and diaper weave designs with equal number of thread densities. Thermal comfort (dry fluid transmission, thermal resistance, stiffness, and overall wet fluid management capability) and mechanical (tensile, puncture and tear strength) tests were performed for developed woven fabrics. The results of diamond warp face sample showed the highest dry fluid transmission and volume porosity. Diamond weft face specimens showed the highest thermal conductivity behavior and diaper weft face exhibited the highest overall wet fluid management capability behavior. Stiffness was the highest in diamond balanced float. Diamond warp faced fabric showed the highest tearing durability and diaper weft face showed the highest tensile resilience in mechanical performance attributes.

Differential cholinergic innervation of lemniscal versus non-lemniscal regions of the inferior colliculus

The inferior colliculus (IC), a midbrain hub for integration of auditory information, receives dense cholinergic input that could modulate nearly all aspects of hearing. A key step in understanding cholinergic modulation is to identify the source(s) and termination patterns of cholinergic input. These issues have not been addressed for the IC in mice, an increasingly important model for study of hearing. We examined cholinergic inputs to the IC in adult male and female mice. We used retrograde tracing and immunochemistry to identify three sources of cholinergic innervation of the mouse IC: the pedunculopontine tegmental nucleus (PPT), the laterodorsal tegmental nucleus (LDT) and the lateral paragigantocellular nucleus (LPGi). We then used Cre-dependent labeling of cholinergic neurons in normal-hearing ChAT-Cre mice to selectively label the cholinergic projections to the IC from each of the cholinergic sources. Labeling of cholinergic projections from the PPT and LDT revealed cholinergic axons and boutons terminating throughout the IC, with the ipsilateral projection being denser. Electron microscopic examination showed that these cholinergic axons can form traditional synaptic junctions with IC neurons. In separate experiments, selective labeling of cholinergic projections from the LPGi revealed bilateral projections to the IC. The LPGi axons exhibited relatively equal densities on ipsilateral and contralateral sides, but on both sides the terminations were largely restricted to the non-lemniscal regions of the IC (i.e., the dorsal cortex, lateral cortex and intercollicular tegmentum). We conclude first that cholinergic axons can form traditional synapses in the IC. In addition, lemniscal and non-lemniscal regions of the IC receive different patterns of cholinergic innervation. The lemniscal IC (IC central nucleus) is innervated by cholinergic neurons in the PPT and the LDT whereas the non-lemniscal “shell” areas of the IC are innervated by the PPT and LDT and by cholinergic neurons in the LPGi. Data AvailabilityData will be made available on request.

Quest for the golden ratio universality class.

Using mode-coupling theory, the conditions for all allowed dynamical universality classes for the conserved modes in one-dimensional driven systems are presented in closed form as a function of the stationary currents and their derivatives. With an eye on the search for the golden ratio universality class, the existence of some families of microscopic models is ruled out a priori by using an Onsager-type macroscopic current symmetry. In particular, if the currents are symmetric or antisymmetric under the interchange of the conserved densities, then at equal mean densities the golden modes can only appear in the antisymmetric case and if the conserved quantities are correlated, but not in the symmetric case where at equal densities one mode is always diffusive and the second may be either Kardar-Parisi-Zhang (KPZ), modified KPZ, 3/2-Lévy, or also diffusive. We also show that the predictions of mode-coupling theory for a noisy chain of harmonic oscillators are exact.

The challenge of assessing multiple stressors in freshwater ecosystems: nonintuitive interactions between pesticide exposure and larval crowding

It is widely recognized that populations of freshwater aquatic organisms are faced with a myriad of co-occurring stressors. These likely include manufactured chemicals, stressors due to climate change, habitat alterations, water quality parameters, etc. Importantly, these stressors are superimposed over “natural” stressors such as density of conspecifics. Density effects, in particular, are important and can result from resource competition or crowding; here we define crowding as high density but without resource limitation. Crowding has received less research attention despite its potential ecological importance and frequency of occurrence. In larval mosquitoes, for example, both physical and chemical components are important effects of crowding, which result in increased mortality, prolonged development, and reduced size. The objective of this research was to determine how different crowding conditions would affect subsequent insecticide sensitivity using the yellow-fever mosquito, Aedes aegypti. We hypothesized that stress due to crowding in the larval stage would increase insecticide sensitivity. Results showed that when larvae were reared at various crowding densities (without resource competition) but later exposed to a contact insecticide (permethrin) at equal densities they exhibited similar sensitivity. However, when larvae were reared at equal densities but exposed at various crowding densities there appeared to be a protective effect of crowding, as more densely crowded larvae were significantly less sensitive to the insecticide. Possible mechanisms for this protective effect were investigated. Induced detoxification enzymes do not appear to be a factor, but density-modified larval exposure is likely a mechanism. This research provides important insights into how mosquitoes may respond to control efforts as well as providing empirical recommendations on designing laboratory toxicity tests to better reflect ecological conditions in natural mosquito populations.

Molecular mechanisms and energetics of lipid droplet formation and directional budding.

The formation and budding of lipid droplets (LDs) are known to be governed by the LD size and by membrane tensions in the endoplasmic reticulum (ER) bilayer and LD-monolayers. Using coarse-grained simulations of an LD model, we first show that ER-embedded LDs of different sizes can form through a continuous transition from wide LD lenses to spherical LDs at a fixed LD size. The ER tendency to relax its bilayer modulates the transition via a subtle interplay between the ER and LD lipid densities. By calculating the energetic landscape of the LD transition, we demonstrate that this size-independent transition is regulated by the mechanical force balance of ER and LD-tensions, independent from membrane bending and line tension whose energetic contributions are negligible according to our calculations. Our findings explain experimental observation of stable LDs of various shapes. We then propose a novel mechanism for directional LD budding where the required membrane asymmetry is provided by the exchange of lipids between the LD-monolayers. Remarkably, we demonstrate that this budding process is energetically neutral. Consequently, LD budding can proceed by a modest energy input from proteins or other driving agents. We obtain equal lipid densities and membrane tensions in LD-monolayers throughout budding. Our findings indicate that unlike LD formation, LD budding by inter-monolayer lipid exchange is a tension-independent process.

Physical Properties of the Young Asteroid Pair 2010 UM26 and 2010 RN221

The main belt asteroids 458271 (2010 UM26) and 2010 RN221 share almost identical orbital elements, and currently appear as comoving objects ∼30″ apart in the plane of the sky. They are products of the breakup of a parent object, or the splitting of a binary, with a separation age measured in decades rather than thousands or millions of years as for most other asteroid pairs. The nature of the precursor body and the details of the breakup and separation of the components are unknown. We obtained deep, high-resolution imaging using the Hubble Space Telescope to characterize the pair and to search for material in addition to the main components that might have been released upon breakup. The primary and secondary have absolute magnitudes H = 17.98 and 19.69, respectively, and effective diameters 760 and 350 m (assuming geometric albedo 0.20). The secondary/primary mass ratio is 0.1, assuming equal densities. Time-series photometry shows that the primary rotates with period ∼5.9 hr and has a small photometric range (0.15 mag), while the period of the secondary is undetermined (but ≳20 hr) and its lightcurve range is at least 1 mag. The primary rotation period and component mass ratio are consistent with a simple model for the breakup of a rotationally unstable precursor. However, unlike other observationally supported instances of asteroid breakup, neither macroscopic fragments nor unresolved material are found remaining in the vicinity of this asteroid pair. We suggest that the pair is a recently dissociated binary, itself formed earlier by rotational instability of 2010 UM26.

Plasma functionalization mechanism to modify isocyanate groups on multiwalled carbon nanotubes

This article reports a possible functionalization mechanism of isocyanate (NCO) groups on multiwalled carbon nanotubes (CNTs) with low-temperature plasma. The mechanism was clarified according to the analysis with two plasmas generated with the gas mixture of (1) nitrogen and carbon dioxide and (2) nitrogen and oxygen. We analyzed the mechanism through optical emission spectroscopy from these plasmas and the NCO functionalization ratio measured with the fluorescent method after plasma exposure over CNTs. The optical emission gave us information on the quantitative analysis of the gas species of atomic nitrogen (N), atomic oxygen (O), and carbon monoxide (CO) and the qualitative analysis of carbon nitride (CN) species in the plasma. Compared with our results from the gas species in the plasma and the NCO functionalization ratio on CNTs, CO and CN species in the gas phase in plasma are less likely to contribute to forming NCO groups on CNTs. Rather, the equal densities of atomic nitrogen and oxygen species in the plasma could be effective in forming NCO groups on the CNT surface: the NCO groups should form by N, O, and carbon (C) species on the CNT surface. The groups likely build up gradually by N, O, and C individually reaching a CNT surface, or the NCO radicals form in the gas phase and then attach to the CNT surface.

Transport conditions in the planktonic phase for seahorses Hippocampus reidi Ginsburg, 1933 (Teleostei: Syngnathidae)

Thousands of seahorses are traded every year as marine ornamental species. Although packing methods for live adult seahorses have already been addressed, there is no information on the transportation of juvenile seahorses. Thus, this study aimed to evaluate the possibility of packing and transportation for newly-birthed seahorses. Three batches of newborn long-snout seahorses Hippocampus reidi were transported in three independent events from Ubatuba, north coast of São Paulo, to the city of São Paulo, covering 248 km in each trip, with an average duration of 3.5 h. A mean of 350 offspring of one day old was distributed in 1 L containers with round borders at equal densities, provided with constant aeration by portable pumps. Aeration was kept so that large bubbles would create an ascending flow keeping juveniles in suspension throughout transportation. Values of survival achieved in this study, even after 10 days post-transportation, were surprisingly high, reaching over 70%. No significant shift in water temperature, pH, or salinity was observed for any transportation events. For oxygen levels, although portable pumps were used, a drop of around 15% in DO level was recorded. In view of the trending ornamental fish market, considering the limited swimming capacity of newly born seahorses and that a great number of marine fish undergo a planktonic phase, this study provides important directions to a better understanding on seahorse transportation and yet, directions for the design of new transport methodology for an efficient shipping protocol for other species.

Functional diversity and identity influence the self‐thinning process in young forest communities

AbstractThere is increasing evidence that the strength of tree diversity effects on productivity varies considerably over the course of forest development. Evidence points to canopy closure and the subsequent self‐thinning as key phases of forest development during which positive diversity effects emerge. A number of studies have shown that self‐thinning can differ among species, and also in mixtures compared with monocultures. Yet, how diversity influences the process of canopy closure and self‐thinning remains poorly understood.In this study, using 11 years of growth and mortality records from a large diversity experiment, we fitted self‐thinning trajectories for 37 tree communities with equal initial densities and explored whether and how functional diversity and identity may affect these trajectories. We then examined whether the diversity effects on self‐thinning were influenced by differences in growth or in mortality.We found that tree communities' functional diversity and identity strongly influence the self‐thinning process. First, we observed that tree communities dominated by early successional species, and slow‐growing evergreens begin self‐thinning at a larger mean tree size. Second, we found that mixing species with contrasting resource‐use strategies, and the dominance of deciduous, fast‐growing species, reduce tree mortality rate in relation to mean tree size during self‐thinning (i.e. shallower self‐thinning slope). The lower rates of self‐thinning in these functionally diverse communities seem to be explained by both an increase in tree growth and a reduction in density‐related mortality simultaneously over time.Synthesis. Overall, this study highlights that increasing tree diversity has the potential to enhance forest productivity in the long term through a better performance during the self‐thinning process when competition for resources is most intense.

Long‐term cover crop effects on biomass, soil nitrate, soil water, and wheat

AbstractCover crops during summer fallow have been rarely researched in the semiarid northern Great Plains. This study was conducted during 2012–2019 at four Montana locations and included four functional groups (Brassica family, fibrous‐rooted crops, legumes, and tap‐rooted crops). Eleven treatments included sole functional groups, a Full Mix, the Full Mix minus each functional group, pea, and chemical fallow. Wheat (Triticum aestivum L.) was grown after each cover crop year with three nitrogen (N) fertilizer rates. Cover crops were terminated with herbicide at first flower stage of pea (Pisum sativum L.) 57 to 66 days after planting. Shoot biomass averaged 2.0 Mg ha−1 over eight site‐years representative of dryland farming in Montana. Using equal overall plant densities, treatments with six species averaged 13% greater biomass than two species. Measured at termination to a 0.9‐m depth, Fallow held greater soil water than cover crop treatments, with Fallow averaging 57 mm greater than the Full Mix. Soil nitrate averaged 49 kg N ha−1 greater after Fallow than the Full Mix; the Legume treatment averaged 26 kg N ha−1 greater than the Minus Legume treatment. Wheat yield on Fallow averaged 0.85 Mg ha−1 greater than the Full Mix in 5 of 10 site‐years, mainly at the driest site‐years. The Legume treatment elevated wheat protein over the Minus Legume treatment by an average of 15 g kg−1. Cover crops grown during summer fallow reduced soil nitrate‐N, soil water, and wheat yields compared with chemical fallow, especially in the major wheat growing region of north central Montana.

Energy balances for the collision of gravity currents of equal strengths

Collision of two counterflowing gravity currents of equal densities and heights was investigated by means of three-dimensional high-resolution simulations with the goal of understanding the flow structures and energetics in the collision region in more detail. The lifetime of collision is approximately $3 \tilde {H}/\tilde {u}_f$ , where $\tilde {H}$ is the depth of heavy and ambient fluids, and $\tilde {u}_f$ is the front velocity of the approaching gravity currents, and the lifetime of collision can be divided into three phases. During Phase I, $-0.2 \leqslant (\tilde {t}-\tilde {t}_c) \tilde {u}_f/\tilde {H} \leqslant 0.5$ , where $\tilde {t}$ is the time, and $\tilde {t}_c$ is the time instance at which the two colliding gravity currents have fully osculated, geometric distortions of the gravity current fronts result in stretching of pre-existing vorticity in the wall-normal direction inside the fronts, and an array of vertical vortices extending throughout the updraught fluid column develop along the interface separating the two colliding gravity currents. The array of vertical vortices is responsible for the mixing between the heavy fluids of the two colliding gravity currents and for the production of turbulent kinetic energy in the collision region. The presence of the top boundary deflects the updraughts into the horizontal direction, and a number of horizontal streamwise vortices are generated close to the top boundary. During Phase II, $0.5 \leqslant (\tilde {t}-\tilde {t}_c) \tilde {u}_f/\tilde {H} \leqslant 1.2$ , the horizontal streamwise vortices close to the top boundary induce turbulent buoyancy flux and break up into smaller structures. While the production of turbulent kinetic energy weakens, the rate of transfer of energy to turbulent flow due to turbulent buoyancy flux reaches its maximum and becomes the primary supply in the turbulent kinetic energy in Phase II. During Phase III, $1.2 \leqslant (\tilde {t}-\tilde {t}_c) \tilde {u}_f/\tilde {H} \leqslant 2.8$ , the collided fluid slumps away from the collision region, while the production of turbulent kinetic energy, turbulent buoyancy flux and dissipation of energy attenuate. From the point of view of energetics, the production of turbulent kinetic energy and turbulent buoyancy flux transfers energy away from the mean flow to the turbulent flow during the collision. Our study complements previous experimental investigations on the collision of gravity currents in that the flow structures, spatial distribution and temporal evolution of the mean flow and turbulent flow characteristics in the collision region are presented clearly. It is our understanding that such complete information on the energy budgets in the collision region can be difficult to attain in laboratory experiments.

Momentum transfer from the DART mission kinetic impact on asteroid Dimorphos

The NASA Double Asteroid Redirection Test (DART) mission performed a kinetic impact on asteroid Dimorphos, the satellite of the binary asteroid (65803) Didymos, at 23:14 UTC on 26 September 2022 as a planetary defence test1. DART was the first hypervelocity impact experiment on an asteroid at size and velocity scales relevant to planetary defence, intended to validate kinetic impact as a means of asteroid deflection. Here we report a determination of the momentum transferred to an asteroid by kinetic impact. On the basis of the change in the binary orbit period2, we find an instantaneous reduction in Dimorphos’s along-track orbital velocity component of 2.70 ± 0.10 mm s−1, indicating enhanced momentum transfer due to recoil from ejecta streams produced by the impact3,4. For a Dimorphos bulk density range of 1,500 to 3,300 kg m−3, we find that the expected value of the momentum enhancement factor, β, ranges between 2.2 and 4.9, depending on the mass of Dimorphos. If Dimorphos and Didymos are assumed to have equal densities of 2,400 kg m−3, {beta =3.61}_{-0.25}^{+0.19}(1sigma ). These β values indicate that substantially more momentum was transferred to Dimorphos from the escaping impact ejecta than was incident with DART. Therefore, the DART kinetic impact was highly effective in deflecting the asteroid Dimorphos.

Estimates of large whale abundance in West Greenland waters from an aerial survey in 2005

An aerial line transect and cue counting survey of large whales in West Greenland was conducted in August and September 2005. The survey covered the area between Cape Farewell and Disko Island on the West Greenland coast out to the 200m depth contour. The surveyed area covered 163,574km2 and a total of 246 sightings of 9 cetacean species were obtained. Abundance estimates were developed for humpback whales, Megaptera novaeangliae (21 sightings), fin whales, Balaenoptera physalus (78 sightings) and common minke whales, B. acutorostrata (42 sightings). The mean group size of humpback whales was 3.30 but groups as large as 95 animals were seen off effort. The mean group size of fin whales was 2.96 with groups as large as 50 seen. Common minke whale group size was 1.1 with only one sighting of a group of two whales. Humpback whales were found both in offshore and coastal areas of West Greenland with the exception of Store Hellefiske Bank and the Cape Farewell offshore area. The line transect abundance estimate of humpback whales was 1,218 (CV=0.56), uncorrected for submerged whales (availability bias) and whales that were available to be seen but were missed by the observers (perception bias). Fin whales were observed in all areas of the survey and the uncorrected line transect estimate was 1,660 (CV=0.38). When corrected for perception bias the estimates increases to 3,234 fin whales (CV=0.44). Common minke whales were found in almost equal densities in all strata except for the Cape Farewell offshore area, where none were seen. The cue-counting abundance estimate of common minke whales was 4,856 (CV=0.49) for West Greenland using a cue rate of 46.3 cues per hour (CV=0.11). If the estimate is corrected for perception bias the common minke whale abundance is estimated to be 10,792 whales (CV=0.59). Low coverage was attained in the northern area of West Greenland and this should cause an especially large negative bias for the estimates of fin whale and humpback whale abundance because this area is believed to have particularly large densities of these whales.

Aggregation Properties of Triton X-100 in a Mixture of Ordinary and Heavy Water

The dynamic and aggregation properties of Triton X-100 in a mixture of ordinary and heavy water in a wide temperature range from room temperature to the cloud point and above were studied. The ratio of ordinary and heavy water was calculated in such a way as to ensure equal densities of Triton X-100 and the water mixture. This made it possible to exclude the effects of sedimentation and study the evolution of Triton X-100 micelles and aggregates, without complication by the effects of spatial phase separation above the cloud point. Self-diffusion coefficients of Triton X-100 molecules were measured by NMR, and the effective hydrodynamic radii of micelles and aggregates were calculated using the Stokes–Einstein relation. The anomalous temperature behavior of the diffusion coefficient of Triton X-100 molecules is explained by changes in the sizes of diffusing objects during their evolution from micelles to dehydrated aggregates below the cloud point and by changes in the sizes of aggregates above the cloud point. The results of the NMR studies are confirmed by data obtained by dynamic light scattering.

Initial stages of gravity-driven flow of two fluids of equal depth

Short-time behavior of gravity-driven free surface flow of two fluids of equal depth and different densities is studied. Initially, the fluids are at rest and separated with a vertical rigid plate of negligible thickness. Then, the plate disappears suddenly and a gravity-driven flow of the fluids starts. The flow in an early stage is described by the potential theory. The initial flow in the leading order is described by a linear problem, which is solved by the Fourier series method. The motions of the interface between the fluids and their free surfaces are investigated. The singular behaviors of the velocity field at the bottom point, where the interface meets the rigid bottom, and the top point, where the interface meets both free surfaces, are analyzed in detail. The flow velocity is shown to be log-singular at the bottom point. The leading-order inner asymptotic solution is constructed in a small vicinity of this point. It is shown that the flow close to the bottom point is self-similar. The motion of the interface is independent of any parameters, including the density ratio, of the problem in specially stretched variables. In the limiting case of negligible density of one of the fluids, the results of the classical dam break problem are recovered. The Lagrangian representation is employed to capture the behavior of the interface and the free surfaces at the top, where the fluid interface meets the free surfaces. The shapes of the free surfaces and the interface in the leading order computed by using the Lagrangian variables show a jump discontinuity of the free surface near the top point where the free surfaces and the interface meet. Inner region formulation is derived near the top point.

Effect of Cellulosic Material and Weave Design on Comfort Performance of Woven Fabrics

ABSTRACT Availability, simplicity of processing, biodegradability, sustainability, and compatibility with human skin in terms of moisture management and temperature regulation, cellulosic fibers are preferred for clothing. In this study four (04) different cellulosic yarns (cotton, bamboo, viscose, and tencel) and two weave designs (1/1 plain and 2/2 warp rib) were used to develop eight (08) woven fabrics with equal thread densities, and their volume porosity %, air permeability, thermal resistance, water vapor permeability index, and moisture management properties were compared. The results showed that tencel fabrics showed the highest water vapor permeability index and overall moisture management capability (OMMC) values, whereas cotton fabrics had the highest values of volume porosity %, air permeability, and thermal resistance. Furthermore, the 2/2 warp rib weave design showed higher values of volume porosity %, air permeability, and thermal resistance in comparison with 1/1 plain woven fabrics, while the water vapor permeability index and OMMC values were higher in 1/1 plain woven fabrics. Moreover, the statistical significance of both factors (cellulose material and weave design) on different results was also analyzed.

Dynamics of a clamped drop under translational vibrations

The free and forced translational oscillations of an ideal liquid drop have been investigated. The drop was placed in a large-sized vessel filled with a liquid of different density. In equilibrium, the drop has the shape of a circular cylinder, and it is sandwiched between the lid and bottom of the vessel. The contact line-speed at the end plates is proportional to the deviation of the contact angle from its equilibrium value (the angle is formed by the corresponding plate and the undeformed cylindrical surface of the drop). The proportionality coefficient (the wetting or Hocking parameter) is different for each surface; it characterizes the force of interaction between the contact line and the solid surface, which leads to energy dissipation during its movement. This makes it possible to use the velocity potential to describe motion in the presence of a deformed interface between inviscid fluids. It is shown that the fundamental frequency of the translational mode of natural oscillations may not vanish in contrast to the case of equal wetting parameters. The energy dissipation is determined by the total contribution of these parameters, which makes it possible to vary the motion of the contact line over a wide range. The oscillation amplitude is proportional to the density difference of the liquids, i.e., at equal densities, the system moves as a whole. It has been found that both integer and non-integer harmonics of shape oscillations are excited due to different wetting parameters. The external vibrational force excites only even harmonics and, with identical surfaces, only they are present in the oscillation spectrum.

Influence of surfactant on foam generation and stabilization in cement slurry

Modern civil engineering and industrial buildings use foamed cement because of its low heat conductivity and light weight.Despite their high performance, foamed cement products manufactured solely from cement might be prohibitively expensive for commercial entities. Thus, chemically foaming cement is important. This paper compiles and reviewsthe foamed cement preparation, mostly used physical and chemical foaming processes. Physical foaming creates foamed cement by mixing foam into a slurry. Physical foaming methods are inefficient and energy-intensive. Chemical foaming involves adding a foaming ingredient to cement slurry. Foaming agents like surfactants react to create bubbles that expand the slurry. Surfactants in the liquid solution promote a bubble by spontaneously cicatrizing holes caused by external perturbations. These chemicals stabilize foams and bubbles for minutes to hours. Oil and gas well cementing uses Self-generated nitrogen foam cement (SNFC) with a high-efficiency foam stabilizer. Three surfactants produced cement pastes with and without MWCNT. A viscosity-modifying agent (VMA) in an aqueous cement paste dispersion can change its rheology. Sodium dodecyl sulfate (SDS) and CaCl2 increase nanosilica (NS) fluidity for pumping cement-based grout. FSCGM is used for coal mine infill grouting. Foamed sulfoaluminate cement-based grouting material (FSCGM) makes firefighting CO2 foam. Cement-hollow glass microballoon syntactic foams have greater compressive strength than neat cement at equal densities. Polydentatephosphonate-modified polymers and ester-type polycarboxylate superplasticizers create many cement mortar bubbles (PCE-1). Calcium ions stabilize polymer bubbles. Aqueous epoxy resin is added to cement slurries to reduce plastic viscosity and boost heat conductivity to make high-porosity cement foams (HPCF). Foamed cement bubble stability is highest at particle wetting angle π/2. SDS in silica suspension adjusts this angle. Ti-extraction blast furnace slag (TEBFS) foam with 20–40% sulfoaluminate cement (SAC) makes foamed cement.

Coulomb drag between two graphene layers at different temperatures

We theoretically study the Coulomb drag in graphene when there is a temperature difference between the layers. Within the degenerate limit for equal layer densities, we find that this can lead to significant deviations from the usual quadratic temperature dependence of the drag resistivity. The exact behavior depends strongly on the phase space available for intraband scattering, and is not symmetrical when the temperatures of the layers are interchanged. In particular, when one layer is at a much higher temperature $T$ than the other, the drag resistivity behaves as $\rho_D\sim T/d^5$, where $d$ is the interlayer separation. The magnitude of the drag in this limit is always larger when the active layer is at the higher temperature.