Spreading Phase Research Articles

Surface wettability effects on droplet dynamics and heat transfer on heated stainless-steel foils

Abstract We report the dynamics and heat transfer characteristics of water droplets impacting on a thin stainless-steel foil maintained at different temperatures. The hydrophobic characteristics are imparted to the surface through polysiloxane coating and water droplets impact the uncoated and coated heated surfaces at different velocities. High-speed videography is utilized to capture the dynamics of the droplet upon impact, while the temperature field of the substrate, during the phenomenon, is simultaneously recorded using high-speed infrared thermography. Heat transfer to the droplet over different surfaces is determined through energy balance on the foil using the captured thermographs. The results reveal that the spreading phase and its duration are strong functions of droplet impact velocity, irrespective of the surface wettability, whereas surface wettability primarily affects the receding phase. The coated hydrophobic surfaces exhibited lower resistance to motion at the three-phase contact line, resulting in reduced spread ratios during the receding phase. It is noted that majority of heat transfer occurred during the initial spreading and receding phases, driven primarily by forced convection. The maximum heat fluxes were observed along the three-phase contact line, particularly at the onset of the receding phase. The coated surface demonstrated lower overall heat transfer rates compared to non-coated surfaces, with the difference increasing at higher surface temperatures. Additionally, an increase in surface temperature to 75°C enhanced the hydrophobicity of the coated surface, leading to prolonged receding phases and extended time to reach the sessile state.

Modeling the impacts of governmental and human responses on COVID-19 spread using statistical machine learning

ABSTRACT Understanding the impacts of governmental and human responses on the pandemic control is imperative for forecasting pandemic spread under various responsive scenarios and guiding localized interventions before pharmaceutical interventions are available. This study analyzed multiple data sets, including social media, mobility, policy evaluations, and COVID-19 infection reports, to delineate the interactions between governmental and human responses and COVID-19 spread in the United States in 2020 when vaccinations were unavailable. The contributions are (1) uncovering the spatiotemporal variations in governmental and human responses during COVID-19; (2) developing a statistical machine learning algorithm that incorporates spatiotemporal dependencies and temporal lag effects to model the relationships between governmental and human responses and the pandemic spread; (3) dissecting the impacts of human responses on the pandemic across space and time. Results reveal that the determinants of COVID-19 health impacts transitioned from human mobility during the initial outbreak phase to both human mobility and stay-at-home policies during the rapid spread phase, and ultimately to the compound of human mobility, stay-at-home policies and the public awareness in the full-blown phase. These findings furnish guidance for policymakers in implementing adaptive and phased strategies.

Binary collision dynamics of immiscible Newtonian and non-Newtonian fluid droplets

This experimental and theoretical study is devoted to the investigation of head-on collisions of two immiscible Newtonian and non-Newtonian droplets. The density of the two droplets is similar, and the viscosity of 0.3% carboxymethyl cellulose droplet is slightly larger than 10 cSt silicone oil. The sizes and relative velocity of the colliding droplets close to the point of impact are measured by means of image processing. The deformed states after the impact and their evolution with time are studied by experimental visualization and the energy evolution with time are discussed by numerical results. The accuracy of the two-dimensional axisymmetric three-phase flow computational model is validated. We study the effects of collisions of non-Newtonian droplets with Newtonian droplets and the subsequent retraction kinetics. Droplet “cannibalization” is commonly observed: after collision and spreading, the droplet retracts rapidly, resulting in a Newtonian droplet wrapping around a non-Newtonian droplet. We show the whole process of droplet collision captured by a high-speed camera and obtain the cloud and velocity vector maps of the droplets by numerical simulation. The droplet wrapping phenomenon is produced by different three-phase interfacial tensions and viscosities. We delineate the different phases of the collision process and discuss the dominant forces in each phase. We calculate the energy evolution of the spreading phase and use it to derive a predictive model for the dimensionless maximum spreading diameter and spreading time.

Geochronological assessment of the Arabian-Nubian Shield plutonic intrusions in the arc assemblages along the Qift-Quseir transect, Central Eastern Desert of Egypt

The ophiolitic mélange and granitic intrusions along the Qift‒Quseir transect in the Central Eastern Desert (CED) of Egypt are parts of the Egyptian Nubian Shield (ENS), which is the northern segment of the East African Orogeny (EAO). The Arabian-Nubian Shield (ANS) is the longest Neoproterozoic belt on Earth, and it was formed during the East and West Gondwanaland collisions within the framework of the EAO. The ANS basement rocks were developed during three distinct phases of magmatic activity: the island arc and syn-collisional phases, identifying a compressional tectonic regime, and a post-collisional phase that identifies changing the tectonic regime into an extensional type. The geochronological assessment of these magmatic activities is essential for understanding the regional geology and tectonic development of the ANS. In our study, we dated different rock units along the Qift‒Quseir transect and revealed ages ranging from the Late Tonian (820 ± 8 Ma) to the Late Ediacaran (563 ± 4 Ma). These ages were associated with three different magmatic pulses: (1) a seafloor spreading and island arc phase (ophiolite and related rocks), represented by sample QQ05, which was dated from 820 ± 8 Ma; (2) a syn-collisional phase, represented by samples QQ08 and QQ10, dated from 733 ± 10 Ma and 729 ± 10 Ma, respectively; and (3) a post-collisional phase, represented by all the other samples, dated from the Ediacaran at 603 ± 9 Ma to 563 ± 5 Ma. These results showed that the post-collisional phase was dominant, especially in terms of the alkali-feldspar granites, relative to ophiolitic rocks, and the syn-collisional granites in the CED. Initiation of the Dokhan Volcanic eruptions at 639 ± 2 Ma gave us the date of the compressional-to-extensional tectonic transition setting, and the post-collisional tensional regime was activated at 603 ± 9 Ma. Additionally, we identified evidence of local magmatic sources by dating 11 grains of Paleo-to Meso-Proterozoic xenocrysts with ages ranging from 1876 ± 18 to 1070 ± 13 Ma (i.e., components of the pre-Arabian-Nubian Shield).

Dry granular column collapse: Numerical simulations using the partially regularized [formula omitted]-model via stabilized finite elements and phase field formulation

We revisit the gravitational collapse of a 2D column of dry granular material surrounded by air, using a continuum mechanics approximation. By employing the Cahn-Hilliard phase-field equation as an interface capturing technique and by coupling it with the Cauchy equation, we numerically simulate this multiphase system, eliminating the need for any ad-hoc numerical adjustment to prevent the finger formation of light fluid between the material and the solid boundary due to the no-slip boundary condition. We implement the μ(I)-rheology in our stabilized Finite Element method, highlighting the presence of instabilities when using this constitutive law. Our study is characterized by three main goals. First, we address the instability issue by implementing the partially regularized formulation of the μ(I)-rheology proposed by Barker and Gray (2017). An important outcome is that using shock-capturing terms in the momentum equation can significantly smooth these oscillations by adding dissipation in the direction of the gradients. Second, we systematically study the fluid dynamics under realistic conditions. Our results accurately replicate the material dynamics during collapse, confirming three distinct stages: free-fall, spreading, and cessation. We identify two regions in the material during the spreading phase: a quasi-static zone with negligible velocities and deformations, and a flowing layer exhibiting high shear rates. These observations closely align with experimental data. Additionally, we examine the evolution of the yielded/unyielded regions based on the Drucker-Prager criterion, and we also explore an empirical criterion, based on a critical value of the velocity norm, that satisfactorily separates these regions. Finally, we perform an extensive parametric study covering a wide range of rheological parameters.

Life beyond Fritz: On the Detachment of Electrolytic Bubbles.

We present an experimental study on detachment characteristics of hydrogen bubbles during electrolysis. Using a transparent (Pt or Ni) electrode enables us to directly observe the bubble contact line and bubble size. Based on these quantities we determine other parameters such as the contact angle and volume through solutions of the Young-Laplace equation. We observe bubbles without ("pinned bubbles") and with ("spreading bubbles") contact line spreading and find that the latter mode becomes more prevalent if the concentration of HClO4 is ≥0.1 M. The departure radius for spreading bubbles is found to drastically exceed the value predicted by the well-known formula of W. Fritz [Phys. Z. 1935, 36, 379-384] for this case. We show that this is related to the contact line hysteresis, which leads to pinning of the contact line after an initial spreading phase at the receding contact angle. The departure mode is then similar to a pinned bubble and occurs once the contact angle reaches the advancing contact angle of the surface. A prediction for the departure radius based on these findings is found to be consistent with the experimental data.

Formation and evolution of a protoplanetary disk: Combining observations, simulations, and cosmochemical constraints

The formation and evolution of protoplanetary disks remains elusive. We have numerous astronomical observations of young stellar objects of different ages with their envelopes and/or disks. Moreover in the last decade there has been tremendous progress in numerical simulations of star and disk formation. New simulations use realistic equations of state for the gas and treat the interaction of matter and the magnetic field with the full set of nonideal magnetohydrodynamic (MHD) equations. However, it is still not fully clear how a disk forms and whether it happens from inside-out or outside-in. Open questions remain regarding where material is accreted onto the disk and comes from, how dust evolves in disks, and the timescales of appearance of disk's structures. These unknowns limit our understanding of how planetesimals and planets form and evolve. We attempted to reconstruct the evolutionary history of the protosolar disk, guided by the large amount of cosmochemical constraints derived from the study of meteorites, while using astronomical observations and numerical simulations as a guide to pinpointing plausible scenarios. Our approach is highly interdisciplinary and we do not present new observations or simulations in this work. Instead, we combine, in an original manner, a large number of published results concerning young stellar objects observations, and numerical simulations, along with the chemical, isotopic and petrological nature of meteorites. We have achieved a plausible and coherent view of the evolution of the protosolar disk that is consistent with cosmochemical constraints and compatible with observations of other protoplanetary disks and sophisticated numerical simulations. The evidence that high-temperature condensates, namely, calcium-aluminum inclusions (CAIs) and amoeboid olivine aggregates (AOAs), formed near the protosun before being transported to the outer disk can be explained in two ways: there could have either been an early phase of vigorous radial spreading of the disk that occurred or fast transport of these condensates from the vicinity of the protosun toward large disk radii via the protostellar outflow. The assumption that the material accreted toward the end of the infall phase was isotopically distinct allows us to explain the observed dichotomy in nucleosynthetic isotopic anomalies of meteorites. It leads us toward intriguing predictions on the possible isotopic composition of refractory elements in comets. At a later time, when the infall of material waned, the disk started to evolve as an accretion disk. Initially, dust drifted inward, shrinking the radius of the dust component to $ 45$ au, probably about to about half of the width of the gas component. Next, structures must have emerged, producing a series of pressure maxima in the disk, which trapped the dust on Myr timescales. This allowed planetesimals to form at radically distinct times without significantly changing any of the isotopic properties. We also conclude that there was no late accretion of material onto the disk via streamers. The disk disappeared at about 5 My, as indicated by paleomagnetic data in meteorites. The evolution of the protosolar disk seems to have been quite typical in terms of size, lifetime, and dust behavior. This suggests that the peculiarities of the Solar System with respect to extrasolar planetary systems probably originate from the chaotic nature of planet formation and not from the properties of the parental disk itself.

Unraveling the link between magma and deformation during slow seafloor spreading

Detachment faulting related to oceanic core complexes (OCCs) has been suggested to be a manifestation of slow seafloor spreading. Although numerical models suggest OCCs form under low magma supply, the specific interaction between magmatism and tectonic faulting remains elusive. This paper examines seismic observations detailing the spatiotemporal interactions between magmatism, high-angle faulting, and detachment faulting at a slow-spreading mid-ocean ridge in the West Philippine Basin. We identified a magma-rich spreading phase, indicated by a magmatic top basement and oceanic crust with shallow-penetrating high-angle normal faults. An axial valley reveals an along-strike transition from magmatically-dominated to highly tectonized oceanic crust over a distance of 70 km. Two older OCCs with concave-down fault geometries and a younger OCC with steep-dipping faulting suggest sequential detachments with the same polarity. Our findings suggest: (1) slow seafloor spreading alternates between high-angle faulting with a relatively high magma supply and detachment faulting with a limited magma supply; (2) sequential development of younger detachments in the footwall of its predecessor leads to an asymmetric split in the newly accreted crust; and (3) the life cycle of OCC ends with high-angle faults that overprint the detachment and act as magma pathways, sealing the OCC. Our study captures the dynamic interaction between high-angle and detachment faults and their concurrent and subsequent relationship to magmatic systems. This reveals that strain distribution along strike is critical to OCC formation, thus enriching our understanding beyond conventional considerations such as spreading rates and melt budgets at mid-ocean ridges.

Adhesion of pancreatic tumor cell clusters by desmosomal molecules enhances early liver metastases formation

Desmosomes are intercellular adhesion complexes providing mechanical coupling and tissue integrity. Previously, a correlation of desmosomal molecule expression with invasion and metastasis formation in several tumor entities was described together with a relevance for circulating tumor cell cluster formation. Here, we investigated the contribution of the desmosomal core adhesion molecule desmoglein-2 (DSG2) to the initial steps of liver metastasis formation by pancreatic cancer cells using a novel ex vivo liver perfusion mouse model. We applied the pancreatic ductal adenocarcinoma cell line AsPC-1 with and without a knockout (KO) of DSG2 and generated mouse lines with a hepatocyte-specific KO of the known interacting partners of DSG2 (DSG2 and desmocollin-2). Liver perfusion with DSG2 KO AsPC-1 cells led to smaller circulating cell clusters and a reduced number of cells adhering to murine livers compared to control cells. While this was independent of the expression levels of desmosomal adhesion molecules in hepatocytes, we show that increased cluster size of cancer cells, which correlates with stronger cell–cell adhesion and expression of desmosomal molecules, is a major factor contributing to the early phase of metastatic spreading. In conclusion, impaired desmosomal adhesion results in reduced circulating cell cluster size, which is relevant for seeding and attachment of metastatic cells to the liver.

Revealing the Relationship between Critical Inlet Velocity and a Double-Layer Oxide Film Combined with Low-Pressure Casting Technology

In the context of low-pressure casting, an excessive inlet velocity may result in the introduction of an oxide film and air into a liquid metal, leading to the formation of a two-layer film structure within the casting. Such defects can significantly degrade the mechanical properties of the castings. In order to optimize the advantages of low-pressure casting, an empirically designed equation for the inlet velocity was formulated and the concept of critical inlet velocity was further refined. A comprehensive numerical simulation was conducted to meticulously analyze the liquid metal spreading phase within the cavity. Subsequently, low-pressure casting experiments were carried out with actual castings of an A357 alloy, using two different entrance velocities—one critical and the other exceeding the critical entrance velocity. Tensile test specimens were extracted from the castings for the comparative evaluation of mechanical properties. It was observed that the average tensile strength of specimens cast at the critical inlet velocity exhibited a notable 16% enhancement. In contrast, specimens cast at velocities exceeding the critical inlet velocity manifested the presence of double oxide film defects. This evidence suggests that casting at a velocity faster than the critical inlet velocity leads to the formation of double oxide film defects, which in turn reduces the mechanical properties of the castings.

Research on early identification of burning status in a fire area in Xinjiang based on data-driven

The early combustion stage in coalfield fire areas (CFA) is the initial phase of coal fire development and spread, making the effective identification of the combustion state crucial. To effectively identify the early combustion state of CFA, this study investigates the CFA in Xinjiang, China. Based on the abnormal characteristics of shallow soil and surface space, a data-driven evaluation method for identifying early combustion states of CFA is proposed. Construct a soil-gas dual-layer early combustion state assessment model of CFA. The evaluation model was applied and validated in the coal fire areas of Xinjiang, China.The results show that there are obvious differences in the spatial distribution of auto-ignition gas, temperature, humidity, surface vegetation coverage and other indicators in the shallow soil and surface space of the coal fire area. The early combustion states of coal fires in areas A, B, and C in the survey area are all in the combustion stage, the combustion state in area D is in the oxidation stage. The accuracy of the evaluation method is bidirectionally verified by the radon measurement method and the infrared thermal imaging detection method. It provides a theoretical basis for controlling the development and spread of coalfield fire areas.

The structure and evolution of relativistic jetted blast waves

ABSTRACT We study, analytically and numerically, the structure and evolution of relativistic jetted blast waves that propagate in uniform media, such as those that generate afterglows of gamma-ray bursts. Similar to previous studies, we find that the evolution can be divided into two parts: (i) a pre-spreading phase, in which the jet core angle is roughly constant, θc,0, and the shock Lorentz factor along the axis, Γa, evolves as a part of the Blandford–Mckee solution, and (ii) a spreading phase, in which Γa drops exponentially with the radius and the core angle, θc, grows rapidly. Nevertheless, the jet remains collimated during the relativistic phase, where $\theta _\mathrm{ c}(\Gamma _\mathrm{ a}\beta _\mathrm{ a}=1)\simeq 0.4\theta _{\mathrm{ c},0}^{1/3}$. The transition between the phases occurs when $\Gamma _\mathrm{ a}\simeq 0.2\theta _{\mathrm{ c},0}^{-1}$. We find that the “wings” of jets with initial “narrow” structure ($\frac{\mathrm{ d} \log \, E_{\mathrm{ iso}}}{\mathrm{ d}\log \, \theta }\lt -3$ outside of the core, where Eiso is isotropic equivalent energy), start evolving during the pre-spreading phase. By the spreading phase these jets evolve to a self-similar profile, which is independent of the initial structure, where in the wings Γ(θ)∝θ−1.5 and Eiso(θ)∝θ−2.6. Jets with initial “wide” structure roughly keep their initial profile during their entire evolution. We provide analytic description of the jet lateral profile evolution for a range of initial structures, as well as the evolution of Γa and θc. For off-axis GRBs, we present a relation between the initial jet structure and the light curve rising phase. Applying our model to GW170817, we find that initially the jet had $\theta _{\mathrm{ c},0}=0.4-4.5~\deg$ and wings consistent with Eiso∝θ−3 − θ−4.

Heat transport during drop impact onto a heated wall covered with an electrospun nanofiber mat: The influence of wall superheat, impact velocity, and mat thickness

Nanofiber surface coating is a promising method for the enhancement of heat transfer during spray cooling. In the present work, the drop dynamics as well as local and overall heat transfer during single drop impact onto a heated wall covered with a polyacrylonitrile (PAN) nanofiber mat are investigated to obtain insight into the mechanisms governing the heat transport enhancement. The influence of wall superheat, drop impact velocity, and mat thickness on the hydrodynamics and heat transfer from the heated wall to the fluid is studied. The experiments were conducted inside a temperature-controlled test cell with a pure vapor atmosphere maintained with refrigerant FC−72 (perfluorohexane). The temperature field at the solid–fluid interface was observed with a high-speed infrared camera, and the heat flux field was derived by solving a three-dimensional transient heat conduction equation within the substrate. The presence of the nanofiber mat on the heater surface suppresses the drop receding phase due to the pinning of the contact line at the end of the spreading phase. Two different heat transfer scenarios are observed depending on the wall superheat and drop impact velocity: scenario (I), in which the liquid drop completely penetrated through the porous nanofiber mat and made contact with the heater surface; and scenario (II) in which the vapor produced inside the pores of the nanofiber mat prevented the liquid drop from touching the heater surface. In scenario (I), an up 450% heat flow enhancement during the sessile drop evaporation stage has been observed. In scenario (II), a 80% heat flow enhancement at this stage has been registered.

Risk analysis and resilience assessment of China's oil imports after the Ukraine Crisis：A network-based dynamics model

Global oil trade integration while creating a platform for risk spread. This study established a two-stage model for risk spread and recovery, simulating the cascading impact of oil supply shortage risks. On this basis, an assessment of the resilience of China's oil imports is conducted. The results indicate that, during the risk spread phase, countries causing a significant negative impact on China's oil imports may not necessarily be China's primary import sources. The proportion of indirect losses in Chinese oil imports due to Canadian oil supply shortages accounted for more than 70 % of the total losses. The United States, Singapore, Australia, the United Kingdom, and Brazil repeatedly act as intermediaries in risk spread. For the recovery phase, swiftly restoration of China's initial imports needs to establish new trade relationships with other non-traditional partners through competition. The top three countries in terms of accumulated new trade relationships are Korea (21), Turkmenistan (13), and Mexico (4). Regarding resilience, when the risk originates from Saudi Arabia, China demonstrates the weakest risk resistance, followed by Russia and Iran. The results not only serve as an early warning for China on regional oil supply risks but also provide policy directions for securing oil stable supply.

Similarity solutions in elastohydrodynamic bouncing

We investigate theoretically and numerically the impact of an elastic sphere on a rigid wall in a viscous fluid. Our focus is on the dynamics of the contact, employing the soft lubrication model in which the sphere is separated from the wall by a thin liquid film. In the limit of large sphere inertia, the sphere bounces and the dynamics is close to the Hertz theory. Remarkably, the film thickness separating the sphere from the wall exhibits non-trivial self-similar properties that vary during the spreading and retraction phases. Leveraging these self-similar properties, we establish the energy budget and predict the coefficient of restitution for the sphere. The general framework derived here opens many perspectives to study the lubrication film in impact problems.

Effect of different chemical conversion coatings on the tribological performance of cylindrical thrust roller bearings under conditions of dry friction and solid lubrication

The chemical conversion coating technology, as a surface technique, can effectively reduce surface wear. In this study, the chemical conversion coating technique was implemented to acquire three distinct coating variations on the surface of cylindrical thrust roller bearings (CTRBs). Nanoindentation tests were conducted to analyze the mechanical features of the coatings, specifically targeting the elastic modulus and nanohardness. To evaluate the surface properties of the coatings, a 3D profilometer was employed. Moreover, the tribological behavior of the CTRBs, subsequent to the application of the coatings, was examined under conditions of dry friction and solid lubrication using a vertical friction and wear testing apparatus. A theoretical framework was established to elucidate the initial phase of transfer film spreading and determine the friction coefficient (COF). The impact of mechanical properties, surface characterization, and crystal structure of the coatings on the tribological performance, both under dry friction and polytetrafluoroethylene (PTFE) solid lubrication conditions, was thoroughly investigated. The findings revealed that, when subjected to dry friction, the dominant factor influencing the tribological performance of the coatings was surface roughness. The addition of solid lubricants can effectively improve the friction performance, resulting in a maximum reduction in bearing wear of 83.9 % and a minimum reduction of 13.0 %. By analyzing the worn surfaces and bearing vibration signals, the influence of coating characterization on the wear and anti-friction performance of solid lubricants is discussed.

Coalescence of liquid marbles on oil-infused surface

While droplets typically merge instantly in an air medium, alterations to the outer medium can complicate the coalescence process. This study investigates droplet coalescence dynamics when encapsulated by a uniform liquid–solid composite shell, aiming to understand its implications for mechanical stability and merging behavior. The uniform shell around a sessile droplet is produced by using liquid marble on oil-infused surfaces (LMOI). The coalescence dynamics was studied under two different conditions: droplet with LMOI and LMOI with LMOI. In contrast to merging of bare droplets, coalescence involving at least one LMOI reveals a three-step process, including spreading, depletion, and eventual merging phases. Higher oil viscosity influences the merging process, with increased viscosity leading to delayed merging with longer spreading and depletion phases. LMOI exhibits significant resistance to merging with another LMOI, necessitating external triggers like pressure or electric fields for coalescence. These findings provide insights into designing microreactor systems based on LMOI, contributing to the comprehension of their dynamics and functionalities.

Refining the final phase of the seafloor spreading process in the West Philippine Basin through the recalibration of magnetic isochrones

The evolution of the West Philippine Basin (WPB), the largest back-arc basin in the northwestern Pacific margin, remains unclear, mainly due to the lack of accurate magnetic chronological constraints. We integrate a newly acquired shipborne magnetic grid and EMAG2 data to investigate the final phase of seafloor spreading and post-spreading magma-poor extension in the WPB during the Eocene and Oligocene. An ∼800 km-long transect located in the eastern part of the WPB was modeled to recalibrate the magnetic isochrones. The results show that the seafloor spreading direction of the WPB rotated counterclockwise from ∼NE–SW to ∼NNE–SSW at ∼44 Ma (Isochrone C20r) and from ∼NNE–SSW to ∼N–S at ∼39 Ma (Isochrone C18n.1n). After the latter rotation, the spreading became unstable, decreased significantly, fluctuated, and finally ceased at ∼33 Ma (Isochrone C13n). The post-spreading magma-poor extension along the Central Basin Rift (CBR) driven by the initial opening of the Parece Vela Basin (PVB) began ∼4 Myr after the cessation of spreading. In the area east of ∼132°E, the CBR inherited the fossil spreading center, but to the west, it manifests a newly formed rift valley intersecting the segmented fossil spreading center. The destabilization of the spreading process in the marginal basin during its extinction phase was predominantly controlled by the dynamic process and stress field imposed by the adjacent plate boundaries.

Evolution is more repeatable in the introduction than range expansion phase of colonization.

How repeatable is evolution at genomic and phenotypic scales? We studied the repeatability of evolution during 8 generations of colonization using replicated microcosm experiments with the red flour beetle, Tribolium castaneum. Based on the patterns of shared allele frequency changes that occurred in populations from the same generation or experimental location, we found adaptive evolution to be more repeatable in the introduction and establishment phases of colonization than in the spread phase, when populations expand their range. Lastly, by studying changes in allele frequencies at conserved loci, we found evidence for the theoretical prediction that range expansion reduces the efficiency of selection to purge deleterious alleles. Overall, our results increase our understanding of adaptive evolution during colonization, demonstrating that evolution can be highly repeatable while also showing that stochasticity still plays an important role.

Prediction and evolution of core-shell morphology and their effect on mechanical properties of PP blends

The prediction of phase morphology is highly valuable in designing and regulating the properties of multiphase composites, particularly polymer blends. In this study, we prepared two types of ternary blends, PP/HDPE/EPR and PP/HDPE/EPDM composites and compared and analyzed the predicted and observed phase morphology of blends with different elastomers. Using Palierne and Bousmina equations, we calculated the interfacial tensions between two components in PP blends and then predicted the relationship between the spreading coefficient, interfacial tension, and phase morphology according to the spreading coefficient theory. Based on our findings, it was observed that the core-shell structure of EPR and EPDM rubber phase encapsulated HDPE core tends to form in PP ternary blends, which aligns with our experimental results. Additionally, SEM morphology observation results revealed a less number of dispersed phases in PP/HDPE/EPR composites with the same composition ratio. It was observed that the shell had a greater thickness due to the difficulty in dispersing EPR with higher viscosity. Mechanical tests indicated that composites with thin-shell and small-core dispersed phases had better toughness. These composites also displayed less yield strength loss under the same impact conditions compared to those with single rubber phases.