Transition Of Regime Research Articles

Flat plate convection heat transfer enhancement via a square rib

Flow and convection heat transfer downstream of a square rib on a flat plate were experimentally investigated inside a closed loop wind tunnel. Heat transfer augmentation for the ribbed plate compared to the smooth plate (Nu/Nu0) was studied at Reynolds numbers, based on the rib’s height (H=1cm), of ReH=1.3×103, 2.6×103, 5×103 and 6.3×103. The ribbed plate presented an enhancement in heat transfer (Nu/Nu0>1) at all studied Reynolds numbers. A trend of decreasing enhancement with increasing ReH was observed, with the largest decrease in Nu/Nu0 occurring when ReH increased from 1.3×103 to 2.6×103. The remarkable enhancement in Nu at the lowest Reynolds number (ReH=1.3×103), compared to higher ReH, was presumably due to the transition of the boundary layer regime from laminar to turbulent. To investigate the effect of the rib on the flow over the surface, flow and turbulence structures were measured using an X-probe hot-wire anemometer. It appears that the turbulence generated by the rib (urms, vrms, uv‾) is the most influential factor on enhancing the heat transfer from the surface. Also, the normal velocity (V) created downstream of the rib seems to be somewhat effective in extracting heat from the surface, while the streamwise velocity (U) was blocked by the rib. The energy spectra of normal velocity fluctuations showed traces of vortex shedding from the rib’s edge at ReH=1.3×103.

Magnetoresistance effects associated with various electric conduction mechanisms in nanostructured [C/FeCo]n multilayers

An evolution of magnetoresistance (MR) mechanism with the film structure was discovered in nanostructured [C/FeCo]n thin films fabricated by magnetron sputtering. The discontinuous multilayer nanogranular structure was confirmed by microstructure characterization. As the layer number n increased, the MR value of the film changed from positive to negative. The fitting curves of lnR−T−1/2 and lnR−T−1/4 show that there is a transition of the conduction regime in the temperature range of 2–300K. The significant different MR effects at various conduction regimes indicated that the type of transport regime plays an important role in MR origin.

“All Hands on Deck”: The Paris Agreement and Nonstate Climate Action

The 2015 Paris Climate summit consolidated the transition of the climate regime from a “regulatory” to a “catalytic and facilitative” model. A key component of this shift was the intergovernmental regime’s embrace of climate action by sub- and nonstate actors. Although a groundswell of transnational climate action has been growing over time, the Paris Agreement seeks to bring this phenomenon into the heart of the new climate regime. This forum article describes that transition and considers its implications.

Bubble breakup in a microfluidic T-junction

We conduct a computational fluid dynamics simulation to investigate the behaviors of bubble breakup in a microfluidic T-junction using volume-of-fluid method to represent the interface. The evolution of bubble morphology and the distributions of velocity and pressure in flow field are analyzed, and the effect of width ratio between main channel and branch on the bubble morphology are evaluated. The results indicate that, the “tunnel” breakup, obstructed breakup, combined breakup and non-breakup are observed during the bubble flows through the T-junctions under different condition. The whole bubble breakup process undergoes the extension, squeeze and pinch-off stages, while the non-breakup process experiences extension and pushing stages. We find that, in the squeeze stage, a local vortex flow forms at the front edge of the bubble for the “tunnel” breakup while the velocity inside the bubble is of a parabolic distribution for the obstructed breakup. Irrespective of non-breakup regimes, there is a sudden pressure drop occurring at the gas–liquid interface of the bubble in the squeeze stage, and the pressure drop at the front interface is far larger than that at the depression region. The transition of the bubble breakup regime through the T-junction occurs with an increase in width ratio of main channel to the branch, which sequentially experiences the non-breakup regime, “tunnel” breakup regime and obstructed breakup regime. The flow regime diagrams are plotted with a power-law correlation to distinguish the bubble/droplet breakup and non-breakup regimes, which also characterize the difference between bubble and droplet breakup through a T-junction.

Three-dimensional flow instability of natural convection induced by variation in radius of inner circular cylinder inside cubic enclosure

Three-dimensional numerical simulations were conducted for the natural convection phenomena around a hot inner circular cylinder positioned in a cold cubic enclosure in the Rayleigh number range of 103⩽Ra⩽106 at the Prandtl number of Pr=0.7. The immersed boundary method (IBM) was used to capture the virtual wall boundary of the inner cylinder, based on the finite volume method (FVM). In this study, the transition of the flow regime from the steady state to the unsteady state and consequent three-dimensionality in the system induced by the increase in the flow instability were investigated. Detailed three-dimensional vortical structures of the convection cells at a relatively high Rayleigh number of Ra=106 were analyzed using the visualization technique, and the heat transfer characteristics in the system resulting from the change in the vortical structures were addressed.

Foam drainage in the presence of solid particles.

We conducted forced drainage experiments to study the liquid flow within the foams stabilized by a cationic surfactant (CTAB) in the presence of partially hydrophobic silica particles. The results show that the presence of solid particles, even when present in small amounts (0.0932 g L(-1) foam), can significantly decrease the foam permeability. The scaling behaviour (power law) between the drainage velocity and the imposed flow rate indicates that the presence of solid particles in the foams triggers a transition of the foam drainage regime from a node-dominated regime to a Plateau border-dominated regime. We applied two foam drainage equations for aqueous foams to simulate the experimental data and interpret the transition. The simulation results show that the presence of solid particles in the foams increases the rigidity of the interfaces and the viscous losses in the channels (the Plateau borders) of the foams, and decreases the foam permeability. We also generalize the theory for the effects of unattached hydrophilic particles on foam drainage by considering the effects of hydrophobicity and concentration of solid particles on the confinement of foam networks. This study explores liquid drainage in three-phase foams and is relevant to the field of hydrophobic particle separation by froth flotation, in which the wash water is commonly applied to the froth layer to improve the product grade.

Optimising time-series experimental design for modelling of circadian rhythms: the value of transient data

Abstract: Circadian clocks consist of complex networks that coordinate the daily cycle of most organisms. In light/dark cycles, the clock is synchronized (or entrained) by the environment, which corresponds to a constant rephasing of the oscillations and leads to a steady state regime. Some circadian clocks are endogenous oscillators with rhythms of about 24-hours that persist in constant light or constant darkness. This operating mechanism with and without entrainment provides flexibility and robustness to the clock against perturbations. Most of the clock-oriented experiments are performed under constant photoperiodic regime, overlooking the transitory regime that takes place between light/dark cycles and constant light or darkness. This paper provides a comparative analysis of the informative potential of the transient time-series data with the other regimes for clock modelling. Realistic data were simulated from 2 experimentally validated plant circadian clock models and sliced into several time windows. These windows represent the different regimes that take place before, meanwhile and after the switch to constant light. Then, a network inference tool was used over each window and its capability of retrieving the ground-truth of the network was compared for each window. The results suggest that including the transient data to the network inference technique significally improves its performance.

Studies Regarding the Evolution of Pollutant Emissions Related to Certain Transitory Condition of an Internal Combustion Engine Using Mobile Measuring Systems

The internal combustion engine that equips a vehicle is a complex assembly of mechanical parts and electronics that controls almost every system. The electronic part of the vehicle gives the opportunity to observe and control what happens with the engine during function. The present paper follows the evolution of the pollutant emissions in relation with some transitory regimes of the car.

Amplitude and frequency variations of oscillation modes in the pulsating DB white dwarf star KIC 08626021

Aims. We use the Kepler data accumulated on the pulsating DB white dwarf KIC 08626021 to explore in detail the stability of its oscillation modes, searching in particular for evidences of nonlinear behaviors. Methods. We analyse nearly two years of uninterrupted short cadence data, concentrating in particular on identified triplets due to stellar rotation that show intriguing behaviors during the course of the observations. Results. We find clear signatures of nonlinear effects attributed to resonant mode coupling mechanisms. We find that a triplet at 4310 {\mu}Hz and this doublet at 3681 {\mu}Hz (most likely the two visible components of an incomplete triplet) have clear periodic frequency and amplitude modulations typical of the so-called intermediate regime of the resonance, with time scales consistent with theoretical expectations. Another triplet at 5073 {\mu}Hz is likely in a narrow transitory regime in which the amplitudes are modulated while the frequencies are locked. Using nonadiabatic pulsation calculations based on a model representative of KIC 08626021 to evaluate the linear growth rates of the modes in the triplets, we also provide quantitative information that could be useful for future comparisons with numerical solutions of the amplitude equations. Conclusions. The identified modulations are the first clear-cut signatures of nonlinear resonant couplings occurring in white dwarf stars. These should resonate as a warning to projects aiming at measuring the evolutionary cooling rate of KIC 08626021, and of white dwarf stars in general. Nonlinear modulations of the frequencies can potentially jeopardize any attempt to measure reliably such rates, unless they could be corrected beforehand. These results should motivate further theoretical work to develop nonlinear stellar pulsation theory.

Sustainable urban transformation and sustainability transitions; conceptual framework and case study

The objective of urban sustainability requires sustainable urban transformation (SUT), which is closely related to urban sustainability transitions. This paper contributes to the knowledge and discussion on these fields in two ways. First, it defines SUT as a subset of urban sustainability transitions, consisting of 1) sustainable places and their management and usage, 2) the sustainability transition of the urban development regime and 3) sustainability transitions in related societal sectors. Normative societal goals for both the urban development regime and sustainable urban areas are incorporated in this definition. Second, it describes transition patterns in the complex transformation process of the Rijnhaven area (Rotterdam, The Netherlands), and relates the process to transition literature.

Influence of Non-Stationary Thermal Field on the Hardness of Welded Samples

The ends of the welding beads are the site of certain non-conformities due to the transitory regime used for welding. In these start and end areas of the welding beads, the thermal field is propagated in non-stationary regime, as opposed to the portions from the middle of the welding bead where the heat is propagated in quasistationary regime.This paper proposes to present the influence of non-stationary thermal field from the welding ends on the hardness values performed in such critical areas, by comparing these values with the values of hardness performed on the middle portions of welding beads. A similarity comparison is made with the situation of the welding works performed within the reconditioning process by welding, when the welding works are of short length executed with multiple rows, were the thermal field is also propagated in non-stationary regime.

Geology and geochemistry of the Triassic Wenquan Mo deposit and Mo-mineralized granite in the Western Qinling Orogen, China

The recently-discovered Wenquan porphyry Mo deposit hosted in the Wenquan granite of the West Qinling Orogen has been recognized as a product of the Indosinian metallogenesis. Three generations of mineral assemblage for the deposit are identified as follows: (1) quartz–biotite–K-feldspar; (2) quartz–sulfide and (3) sulfide–calcite. Geochemical study shows that the mafic microgranular enclaves (MMEs) in the ore-bearing Wenquan granite have lower SiO2, and higher Mg# and Nb/Ta ratios than the host granite itself. Different from the granite which have zircon εHf(t) values of −3.6–3.0 and TDM2 of 1234–890Ma, the MMEs are characterized by the εHf(t) values of −10.1–10.8 and TDM1 of 865–441Ma. This can be interpreted to indicate a mixture origin of the Meso- and Neoproterozoic crust-derived component and Neoproterozoic SCLM-derived materials for the formation of the Wenquan granite, which played an essential role in the Mo mineralization. Comparative Pb isotopic data between ores and K-feldspar suggest that the Wenquan granitic magma originated from the middle-lower crust of the South China Block and the ore-forming materials were incorporated by hydrothermal fluid differentiated from the Triassic magmatic system, with minor contribution of sedimentary rocks. The δ34S values of 5.0–11.7‰ with a pronounced mode at 5.0 to 6.1‰ for the ores probably represent the sulfur incorporation of a typical magmatic hydrothermal fluid contaminated by heavy sulfur of Devonian sediments. The granite yielded the zircon U–Pb ages of 218±2.4Ma and 221±1.3Ma, as the same as the ages of 217±2.0Ma and 218±2.5Ma obtained for the MMEs. These ages are indistinguishable with the molybdenite Re–Os isochron age of 219±5.2Ma which is the timing for the Mo mineralization. Tectonically, the magmatic mixture processes of the Wenquan granite and the Mo mineralization to form the Wenquan Mo deposit contemporaneously occurred during the transition of tectonic regime from syn- to post-collision orogeny in the Qinling Orogen in the Late Triassic.

Thermal history of the Acoculco geothermal system, eastern Mexico: Insights from numerical modeling and radiocarbon dating

Acoculco is a geothermal prospective area hosted by a volcanic caldera complex in the eastern Trans-Mexican Volcanic Belt. Surface manifestations are scarce and consist of gas discharges (CO2-rich) and acid-sulfate springs of low temperature, whereas hydrothermal explosive activity is profusely manifested by meter-scale craters and mounds of hydrothermal debris and breccias. Silicic alteration extends for several square kilometers around the zone with gas manifestations and explosive features, affecting surficial volcanic rocks, primarily tuffs and breccias. In the subsurface, an argillic alteration zone (ammonium illite) extends down to a depth of ∼600m, and underneath it a propylitic zone (epidote–calcite–chlorite) occurs down to ∼1000m.Thermal logs from an exploratory borehole (EAC-1, drilled in 1995 down to 1810m) showed a conductive heat transfer regime under high geothermal gradient (∼140°C/1000m). In contrast, the thermal profile established from temperatures of homogenization of fluid inclusions—measured on core samples from the same drill hole—suggests that convection occurred in the past through the upper ~1400m of the geothermal system. A drop in permeability due to the precipitation of alteration minerals would have triggered the cessation of the convective heat transfer regime to give place to a conductive one. With the purpose of determining when the transition of heat transfer regime occurred, we developed a 1D model that simulates the time-depth distribution of temperature. According to our numerical simulations, this transition happened ca. 7000years ago; this date is very recent compared to the lifespan of the geothermal system. In addition, radiocarbon chronology indicates that the hydrothermal explosive activity postdates the end of the convective heat transfer regime, having dated at least three explosive events, at 4867–5295, 1049–1417 and 543–709y cal. BP. Therefore, hydrothermal explosions arise from the self-sealing of the Acoculco geothermal system, involving a natural hazard that could affect future geothermal-power infrastructure.

Wear Behavior of Cooling Slope Rheocast A356 Al Alloy

In the present study, the dry sliding wear behavior of rheocast A356 Al alloys, cast using a cooling slope, as well as gravity cast A356 Al alloy have been investigated at a low sliding speed of 1 ms−1, against a hardened EN 31 disk at different loads. The wear mechanism involves microcutting–abrasion and adhesion at lower load for all of the alloys studied in the present work. On the other hand, at higher load, mainly adhesive wear along with oxide formation is observed for gravity cast A356 Al alloy and rheocast A356 Al alloy, cast using a 45° slope angle. Unlike other alloys, 60° slope rheocast A356 Al alloy is found to undergo mainly abrasive wear at higher load. Accordingly, the rheocast sample, cast using a 60° cooling slope, exhibits a remarkably lower wear rate at higher load compared to gravity cast and 45° slope rheocast samples. This is attributed to the dominance of abrasive wear at higher load in the case of rheocast A356 Al alloy cast using a 60° slope. The presence of finer and more spherical primary Al grain morphology is found to resist adhesive wear in case of 60° cooling slope processed rheocast alloy and thereby delay the transition of the wear regime from normal wear to severe wear.

Modeling of Fast Reaction Mechanisms for Biomass Conversion Processes

ABSTRACTThe article presents the results obtained through an advanced modeling of fast developing processes, such as oxidation reactions applied to biomass products, which are useful to quantify the evolution of the reactants and the reaction products throughout the entire process. The model enables the real time observation of the process, starting with process initiation, run, and burnout, providing useful information for transitory regimes when the experimental measurements and continuous observation are very difficult due to sampling and analyzing equipment limitation. The modeling tool used within this study is based on bond graph methodology, which is an alternative to classic modeling methods. This tool integrates advanced chemical dynamics information (reaction kinetics, formation enthalpy, mass, and energy balance) delivering results for fast reacting chemical systems. The results present the evolution of reaction products concentration during the reaction start-up according to the time period imposed by the user. The article highlights the importance of accurate modeling of transitory regimes of the processes when the concentration of the pollutants emissions is at the highest peak, providing information for processes control and optimization.

Convective Heat Transfer Characteristics of Single Phase Liquid in Multiport Minichannel Tube: Experiment and CFD Simulation

This study demonstrated the single phase boiling heat transfer of water in horizontal multiport minichannels. The experimental data were observed in aluminum tube of 7.9 x 2.5mm (width x high) with 7 rectangular channels and the length of 500mm, the Reynolds number of 1400 – 4200, and heat fluxes of 3 – 6 kWm-2. The effects of mass fluxes and heat fluxes on heat transfer coefficient were analyzed. The transition of flow regime was observed at the Reynolds number of 3000. Finally, the CFD simulation was also set up and compared with the experimental data. The results showed that the CFD simulation was in well agreement with the experimental ones.

Impact of film thickness and temperature on the dielectric breakdown behavior of sputtered aluminum nitride thin films

In micromachined devices, piezoelectric aluminum nitride (AlN) thin films are commonly used as functional material for sensing and actuating purposes. Additionally, AlN features a high chemical and thermal stability, making it also a good choice for passivation purposes for microelectronic devices. With those aspects and current trends towards minimization in mind, the dielectric reliability of ultra-thin AlN films is of utmost importance for the realization of advanced device concepts.In this study, we present a systematic analysis of the transversal dielectric strength of sputtered AlN thin films of varying film thickness (i.e. 70nm to 400nm) up to 300°C. Using a time-zero approach, the dielectric strength is measured by applying a voltage ramp to stress the film up to the point of breakdown. The results are subsequently analyzed using the Weibull approach.For temperatures T>180°C, the characteristic breakdown field Eb,0 follows the relationship Eb,0∼T2, while showing a weak temperature dependence below, thus indicating a transitory regime between thermally induced breakdown at higher T and electrically induced breakdown at lower T. It is shown, that the characteristic breakdown field increases at lower film thickness which is in good correlation with a corresponding decrease in leakage current.

Geochronology and geochemistry of tuff beds from the Shicaohe Formation of Shennongjia Group and tectonic evolution in the northern Yangtze Block, South China

Meso- to Neoproterozoic magmatic events are widespread in the Yangtze Block. The geochronology and tectonic significance of the Shennongjia Group in the Yangtze Block are still highly controversial. An integrated geochronology and geochemistry approach provides new insights into the geochronological framework, tectonic setting, magmatic events, and basin evolution of the northern Yangtze Block. Our new precise sensitive high-resolution ion microprobe U–Pb data indicate a deposition age of 1180 ± 15 Ma for the Shicaohe Formation subalkaline basaltic tuff that is geochemically similar to modern intracontinental rift volcanic rocks. The integration of available geochemical data together with our new U–Pb ages indicates the Shicaohe Formation subalkaline basaltic tuff formed ca. 1180 in a continental rift-related setting on a passive continental margin. The Shennongjia Group is topped by the Zhengjiaya Formation volcanic sequence, indicating arc-related igneous events at 1103 Ma. The transition of the late Mesoproterozoic tectonic regime from intracontinental extension to convergence occurred between ca. 1180 and 1103 Ma in the northern Yangtze Block. Tectonic evolution in the Neoproterozoic led to accretion along the northern margin of the Yangtze Block. These results provide geochronological evidence, which is of utmost importance for reconfiguration of the chronostratigraphic framework and for promoting research on Mesoproterozoic strata in China, thereby increasing understanding of magmatic events and basin evolutionary history in the northern Yangtze Block.

Petrogenesis of the early Paleozoic low-Mg and high-Mg adakitic rocks in the North Qilian orogenic belt, NW China: Implications for transition from crustal thickening to extension thinning

The petrogenesis and geodynamic implications of the early Paleozoic adakitic rocks in the North Qilian orogenic belt remain topics of debate. In this study, petrology, zircon U–Pb age and Lu–Hf isotopic composition, whole-rock geochemistry and Sr–Nd isotopes were carried on both low-Mg and high-Mg adakitic rocks from the North Qilian orogenic belt. These results will provide significant constraints on the evolution of the North Qilian orogenic belt. In general, the low-Mg adakitic granites mainly consist of plagioclase (50–55%), alkali feldspar (20–25%), quartz (20–25%) and biotite (5%). In contrast, the high-Mg adakitic granodiorites are generally composed of alkali feldspar (30–35%), plagioclase (30–45%), quartz (20–25%) and amphibole (∼10%). The low-Mg adakitic granitoids (446–457Ma) are characterized by high SiO2 (69–72wt.%), low Mg# (39–42) and low Cr and Ni contents. However, the high-Mg adakitic granitoids (430–431Ma) have relatively lower SiO2 (65–66wt.%), higher Mg# (50–59) and higher Cr and Ni contents. The low-Mg adakitic rocks have high initial 87Sr/86Sr ratios (0.7068–0.7080), negative εNd(t) (−2.3 to −3.3) and εHf(t) values (−6.8 to 1.9) with old zircon Hf model ages (1.2–1.6Ga). However, the high-Mg adakitic rocks show lower initial 87Sr/86Sr ratios (0.7044–0.7066), higher εNd(t) (−1.8 to 3.0) and positive εHf(t) values (2.3–7.7) with younger zircon Hf model ages (0.9–1.1Ga). These results suggest that the low-Mg rocks were generated by partial melting of thickened crust, whereas the high-Mg rocks were derived from anatexis of delaminated lower crust, which subsequently interacted with mantle magma upon ascent. The data obtained in this study provide significant information about the geological and tectonic processes after the closure of the Qilian Ocean. The continent–continent collision and thickening probably occurred during 440–467Ma with formation of low-Mg adakitic rocks; and the transition of the tectonic regime from compression to extension probably occurred at ∼430Ma with formation of high-Mg adakitic rocks.

40Ar–39Ar age constraint on deformation and brittle–ductile transition of the Main Central Thrust and the South Tibetan Detachment zone from Dhauliganga valley, Garhwal Himalaya, India

40Ar–39Ar data from two sets of mylonitic two-mica granites present in the Main Central Thrust (MCT) and one leucogranite from the South Tibetan Detachment (STD) of Dhauliganga valley, Garhwal Himalaya are presented. The MCT and the STD bound the High Himalayan Crystallines (HHC) and are believed to facilitate its extrusion. Field evidence of ductile deformation in the form of tight isoclinal folding and brittle deformation in the form of back thrusts and transverse fractures are observed. The STD zone shows evidence of pervasive migration of leucogranitic melt through north dipping extensional shear zones. The ∼19.5Ma old Malari Leucogranite, present adjacent to the STD zone, experienced ductile and brittle deformation related to the tectonics of the STD. Muscovite analysis from the Malari leucogranite gives a cooling age of ∼15.2Ma suggesting that ductile deformation in the STD zone may have ceased by ∼15Ma. 40Ar–39Ar chronology of biotite from two mylonitic granites of the MCT yields cooling ages of 10.8Ma and 9.7Ma, which we correlate with activity of the MCT at ∼10Ma that caused rapid exhumation of the HHC. 40Ar–39Ar ages of 6.4Ma and 6.2Ma from white mica represent newly crystallized white mica post-dating biotite cooling and indicate late stage deformation. It is inferred that, as the HHC wedge started to exhume and erode rapidly along the MCT zone at ∼10Ma, the taper angle of the Himalayan wedge decreased to a ‘sub-critical’ stage. To regain the critical taper angle, the wedge underwent internal deformation in the form of back thrusts and duplex structures. Comparison of our data with earlier results from other sections of the MCT helps us envisage that the ∼6Ma white mica ages can be correlated with this internal deformation event and also with the transition of deformation regime in the MCT zone from ductile to brittle.