Downstream Layer Research Articles

Mechanism of excavation-induced cracking of the protective layer of a rock bench in a large underground powerhouse under high tectonic stress

Excavation-induced unloading fractures in the rock mass can easily cause rock engineering structural failure under high stress. This research work investigated the unloading fracture characteristics of the protective layer of the rock bench in Shuangjiangkou underground powerhouse in detail, thereby revealing the unloading fracture mechanisms via numerical simulation and true triaxial unloading tests, and proposed an optimal method for protective layer excavation. The study found that unloading cracking failure in the rock mass is asymmetric in Shuangjiangkou underground powerhouse, with the fracturing degree of rock mass on the downstream protective layer being greater than that on the upstream side. The dip angle of the unloading fracture plane in the downstream protective layer increased with the aspect ratio (k) of the protective layer and gradually coincided with the diagonal of the protective layer. The stress concentration in the downstream protective layer was caused by the tectonic stress, the stress changed in the form of multistep loading σ1 and unloading σ3 during layered excavation. Tensile-shear unloading cracks were formed in the rock under the excavation stress path, becoming steeper and denser, and gradually parallel to σ1 as the unloading amount of σ3 increased. As k increases, the σ1 in the protective layer becomes steeper, causing the unloading fracture plane to steepen and eventually coincided with the diagonal of the protective layer. A formula for designing the protective layer width was proposed based on the relationship of the dip angle of the fracture plane with k. The findings lend themselves to implications to engineering geology in that engineers should consider the asymmetric failure characteristics of the tunnel caused by high tectonic stress, and formulate asymmetric excavation and support schemes during the construction process of rock benches or other similar structures.

Pressure-dependent fouling behavior during sterile filtration of mRNA-containing lipid nanoparticles.

The COVID-19 pandemic has generated growing interest in the development of mRNA-based vaccines and therapeutics. However, the size and properties of the lipid nanoparticles (LNPs) used to deliver the nucleic acids can lead to unique phenomena during manufacturing that are not typical of other biologics. The objective of this study was to develop a more fundamental understanding of the factors controlling the performance of sterile filtration of mRNA-LNPs. Experimental filtration studies were performed with a Moderna mRNA-LNP solution using a commercially available dual-layer polyethersulfone sterile filter, the Sartopore 2 XLG. Unexpectedly, increasing the transmembrane pressure (TMP) from 2 to 20 psi provided more than a twofold increase in filter capacity. Also surprisingly, the effective resistance of the fouled filter decreased with increasing TMP, in contrast to the pressure-independent behavior expected for an incompressible media and the increase in resistance typically seen for a compressible fouling deposit. The mRNA-LNPs appear to foul the dual-layer filter by blocking the pores in the downstream sterilizing-grade membrane layer, as demonstrated both by scanning electron microscopyand derivative analysis of filtration data collected for the two layers independently. These results provide important insights into the mechanisms governing the filtration of mRNA-LNP vaccines and therapeutics.

The exposome as the science of social-to-biological transitions.

The understanding of disease etiology and pathogenesis has radically changed as a consequence of the new challenges posed by climate change, environmental degradation and emerging infectious diseases. The awareness of the influence of distal causes (e.g. planetary changes at the roots of new pandemics), of the social environment and of early life exposures calls for innovative models of disease onset. Here we propose a scheme for the practice of epidemiology and toxicology that incorporates new recent advancements in both disciplines, under the general umbrella of the "exposome". The exposome approach to disease encompasses a lifecourse perspective from conception onwards, and the investigation of the role played by all exposures individuals undergo in their lives. These include social inequalities and psychosocial influences, in addition to chemical, biological and physical exposures. We stress the role played by social differences and inequalities in the course of life as an overarching factor that influences downstream layers (including behaviours). We show that the idea of "lifecourse exposome" is compatible with the current interpretation of Adverse Outcome Pathways in toxicology, and in fact we propose an extension of the concept towards "lifecourse Adverse Outcome Pathways". We propose to merge different research perspectives and promote an encounter between the sociological perspective of "biography" (using Pierre Bourdieu's conceptual framework) and biology, according to the idea of accumulated biological capital of individuals. We also propose to treat social capital (including inequalities) no longer as a confounding factor but as an overarching determinant, perhaps the most important of all because it is the one that influences all other exposures downstream. The importance of early exposures in a lifecourse perspective leads to policy implications, i.e. investing more in the various forms of capital (social, economic, cultural) in early life.

Experimental Characterization of the Seismic Responses of Silt-Interlayered Stratified Sandy Tailings Slopes Using Centrifuge Shaking Table Tests

This study aims to characterize the seismic responses of silt-interlayered stratified sandy tailings slopes. In order to achieve this, a series of model tests were carried out in an advanced centrifuge shaking table. The experimental results demonstrate that sandy tailings slopes interlayered with silts are more prone to flow failure compared with homogeneous slopes. The failure process of a steep silt-interlayered sandy slope is further elaborated in detail, and two modes of tailings release have been identified. The initial loading cycles may only lead to localized deformation near the relatively shallow silty layer; however, there is continuous build-up of excess pore water pressure in deeper sandy tailings. With increasing the number of loading cycles, more sandy tailings start to spread laterally, and ejection of tailings may occur. After ejection, the excess pore pressure turns to dissipate, while the tailings near slope crest become liquefied and then flow toward the downstream direction layer by layer, leading to tailings release. This is the first mode of tailings release. Due to the continuous lateral spreading, the displaced tailings eventually arrive at the crest of the starter dam and then flow along its slope at the downstream side, leading to tailings release. This is the second mode of tailings release. Those unique and invaluable observations can be used to improve the seismic design of tailings impoundments and to validate associated numerical methods.

Reconstruction and analysis of a large-scale binary Ras-effector signaling network

BackgroundRas is a key cellular signaling hub that controls numerous cell fates via multiple downstream effector pathways. While pathways downstream of effectors such as Raf, PI3K and RalGDS are extensively described in the literature, how other effectors signal downstream of Ras is often still enigmatic.MethodsA comprehensive and unbiased Ras-effector network was reconstructed downstream of 43 effector proteins (converging onto 12 effector classes) using public pathway and protein–protein interaction (PPI) databases. The output is an oriented graph of pairwise interactions defining a 3-layer signaling network downstream of Ras. The 2290 proteins comprising the network were studied for their implication in signaling crosstalk and feedbacks, their subcellular localizations, and their cellular functions.ResultsThe final Ras-effector network consists of 2290 proteins that are connected via 19,080 binary PPIs, increasingly distributed across the downstream layers, with 441 PPIs in layer 1, 1660 in layer 2, and 16,979 in layer 3. We identified a high level of crosstalk among proteins of the 12 effector classes. A class-specific Ras sub-network was generated in CellDesigner (.xml file) and a functional enrichment analysis thereof shows that 58% of the processes have previously been associated to a respective effector pathway, with the remaining providing insights into novel and unexplored functions of specific effector pathways.ConclusionsOur large-scale and cell general Ras-effector network is a crucial steppingstone towards defining the network boundaries. It constitutes a ‘reference interactome’ and can be contextualized for specific conditions, e.g. different cell types or biopsy material obtained from cancer patients. Further, it can serve as a basis for elucidating systems properties, such as input–output relationships, crosstalk, and pathway redundancy.Graphical abstract3uuXA8noaAjvhTVsANJAr5Video .

Influence of position on the natural and forced convective heat transfer of a single heating sphere in a packed bed

Natural and forced convection experiments on a single heating sphere in a packed bed were performed by varying the axial and radial positions of the heating sphere. Based on the analogy between heat and mass transfer, mass transfer experiments were conducted using a copper electroplating system. The sphere diameter was varied from 0.004 to 0.010 m, which correspond to the Rad of 5.43 × 106–8.48 × 107. The Sc was 2,014. In the forced convection experiments, the range of superficial velocity was 0.01 to 0.58 m/s, which correspond the Red of 43–5,076. For natural convective flow, the influence of sphere position on the heat transfer of single heating sphere in the packed bed was not observed. However, for forced convective flow, the local heat transfer inside the bed was affected by the variation of the sphere position. The heat transfer increased at the downstream layer of bed due to the intensified turbulence level by the porous structure. The heat transfer near wall region was also enhanced due to the high local porosity. Based on the experimental results, we developed the correlation of local heat transfer for forced convection by adding the multiplier to the existing correlation.

Wake Shape and Height Profile Measurements in a Concave Open Channel Flow regarding the Target in DONES

Wakes appearing downstream of disturbances on the surface of a water flow in a concave open channel were examined experimentally. The investigated channel geometry was similar to the liquid lithium target in DONES (Demonstration fusion power plant Oriented NEutron Source). The objective of the measurements was to analyze the effect of a disturbance on the downstream layer thickness. For measuring the height profiles in the channel, an optical measurement system based on laser triangulation was developed. It was shown that the wake of the undisturbed flow emerged from the nozzle corner, which was in accordance with analytical solutions. For sufficiently large disturbances at the nozzle edge, the height profiles located downstream showed symmetrical minima and maxima on both sides of the disturbance. The wake depth strongly depended on the diameter and penetration depth of the disturbance, as well as the circumferential position in the channel, which yields to a critical wake depth of one millimeter for the lithium target in DONES.

Triglobal infinite-wing shock-buffet study

This article uses triglobal stability analysis to address the question of shock-buffet unsteadiness, and associated modal dominance, on infinite wings at high Reynolds number, expanding upon recent biglobal work, aspiring to elucidate the flow phenomenon's origin and characteristics. Infinite wings are modelled by extruding an aerofoil to finite aspect ratios and imposing a periodic boundary condition without assumptions on spanwise homogeneity. Two distinct steady base flows, spanwise uniform and non-uniform, are analysed herein on straight and swept wings. Stability analysis of straight-wing uniform flow identifies both the oscillatory aerofoil mode, linked to the chordwise shock motion synchronised with a pulsation of its downstream shear layer, and several monotone (non-oscillatory), spatially periodic shock-distortion modes. Those monotone modes become outboard travelling on the swept wing with their respective frequencies and phase speeds correlated with the sweep angle. In the limiting case of very small wavenumbers approaching zero, the effect of sweep creates branches of outboard and inboard travelling modes. Overall, triglobal results for such quasi-three-dimensional base flows agree with previous biglobal studies. On the contrary, cellular patterns form in proper three-dimensional base flow on straight wings, and we present the first triglobal study of such an equilibrium solution to the governing equations. Spanwise-irregular modes are found to be sensitive to the chosen aspect ratio. Nonlinear time-marching simulations reveal the flow evolution and distinct events to confirm the insights gained through dominant modes from routine triglobal stability analysis.

Opsin Expression Varies with Reproductive State in the Cichlid Fish Astatotilapia burtoni.

Animals use visual communication to convey crucial information about their identity, reproductive status, and sex. Plasticity in the auditory and olfactory systems has been well-documented, however, fewer studies have tested for plasticity in the visual system, a surprising detail since courtship and mate choice are largely dependent on visual signals across taxa. We previously found reproductive state-dependent plasticity in the eye of the highly social cichlid fish Astatotilapia burtoni. Male A. burtoni increase their courtship, including multicomponent visual displays, when around ovulated females, and ovulated females are more responsive to male visual courtship displays than non-ovulated females. Based on this, we hypothesized that ovulation status impacts visual capabilities in A. burtoni females. Using electroretinograms, we found that ovulated females had greater visual sensitivity at wavelengths corresponding to male courtship coloration compared with non-reproductively-receptive females. In addition, ovulated females had higher neural activation in the retina and higher mRNA expression levels of neuromodulatory receptors (e.g., sex-steroids; gonadotropins) in the eye than non-ovulated females. Here, we add to this body of work by testing the hypothesis that cone opsin expression changes with female reproductive state. Ovulated females had higher expression of short wavelength sensitive opsins (sws1, sws2a, sws2b) compared with mouthbrooding females. Further, expression of sws2a, the most abundant opsin in the A. burtoni eye, positively correlated with levels of circulating 11-ketotestosterone and estradiol and estrogen, androgen, and gonadotropin system receptor expression in the eye in females. These data indicate that reproductive state-dependent plasticity also occurs at the level of photoreceptors, not just through modulation of visual signals at downstream retinal layers. Collectively, these data provide crucial evidence linking endocrine modulation of visual plasticity to mate choice behaviors in females.

Study of vibration modes and strain distribution of a flow energy harvester in the wake region of different bluff bodies

This paper aims to analyze mode shapes and corresponding strain distribution in a two-dimensional plane structure exhibiting flow-induced vibration in the wake field of four different upstream bluff bodies such as cylinder, square, triangle, and D-shape. This research is important from the point of view of flow-induced piezoelectric energy harvesting; wherein, induced strain in the structure is directly related to the amount of energy generated. Mainly, all investigations are carried out at low Reynolds number ( Re = 200); however, to widen the scope of the work, other Reynolds numbers are also considered ( Re = 300, 500, and 750 ). The results obtained indicated that the plane structure vibrates in different mode shapes under different wake fields. The square section dominantly gives rise to the fundamental mode vibration, whereas, cylinder, D-shape, and triangular bluff body induce vibration in a mix of fundamental and higher bending modes. Analysis of the corresponding flow regime shows that the position of reattachment point of the downstream shear layer plays an important role in the realization of different vibration modes. The strain distribution under different cases revealed that the wake of a cylindrical bluff body produces highest peak strain, and D-shape bluff body results in highest cumulative strain. From the aspect of energy harvesting, a quantitative comparison of strain-induced and per second charge generation have indicated that for an equivalent flow condition, the D-shape will produce higher energy per unit time than the cases of a square, cylinder, and triangular cross-sections.

Ignition, Propagation, and Stabilization of a Premixed Jet Flame from a Bluff-Body Burner

The warm-up and ignition together in real combustors is a complicated process that may involve either forced spark ignition (SI) or unforced autoignition (AI) or both (SI and AI). This numerical study is to systematically investigate both SI and AI processes of a premixed bluff-body (BB) flame in the coflow of exhaust gas, respectively, at two constant temperatures (300 K, 1500 K) and a rising temperature (300–1500 K). The high-temperature sparking (2500 K) is applied in the recirculation zone (RZ) behind a BB to mimic the actual SI. With this sparking, SI kernel appears immediately downstream of the BB, forming a traditional flame. Moreover, under high-temperature (>minimal self-ignition value) hot coflow, AI occurs in the downstream mixing layer and evolves into an AI flame. Later, the AI-generated flame joins up with the upstream BB flame. Such ignition processes are observed in all the 2500 K sparking cases under the heated-up coflow (with different heating times) or constant-temperature coflow, though AI kernels appear later and develop more slowly in the former. Further analyses show that both traditional BB flame and lift-off AI-generated flame coexist in the final state, which are connected by a thin neck zone around the RZ end. Furthermore, both low temperature (1500 K) sparking and nonsparking cases are investigated. It is found that the low-temperature SI fails with only CH₂O and CO generations and no OH and ignition kernels are produced, while AI still occurs in the downstream mixing layer. Additionally, in all the 1500 K sparking and nonsparking cases, AI kernels firstly arise in the mixing layer and then propagate into the central area, finally forming an invisible lifted “flame” in the regime of MILD combustion (MC).

Clogging Model for Coarse and Fine Filtering Cloths of Filtering Cylindrical Elements, Preventing Sedimentation of Mechanical Impurities in Their Gap

In this paper we propose a method for preventing sedimentation of solid particles in the lower part of the gap between filtering cylindrical elements of coarse and fine purification by increasing the size of the meshes and total thickness of the first downstream gas flow layers of the fine filtering element in excess of the maximum diameter of solid particles. Experimental corroboration for the proposed method showed absence of solid particles’ sedimentation in the lower part of the gap between filtering cylindrical elements of coarse and fine purification and clogging of their meshes. As a result of the experiments, we found that the maximum sedimentation of mechanical impurities inside the first screens of the fine filtering cloth is achieved when their meshes’ size and screens’ thickness are, respectively, equal to three and two and a half maximum diameters of a solid particle. We developed a mathematical model that describes the clogging dynamics of filtering elements, where pressure losses in the first section with constant mesh sizes of all screens and in the second section with a sequential decrease in mesh sizes have different clogging rates and therefore are calculated separately from each other. The clogging process at each section of the multilayer filter cloth is represented as a successive decrease in the effective screening area of the screen meshes. The mathematical model makes it possible to prevent the sedimentation of mechanical impurities in the gap between gas filter elements of coarse and fine purification and allows to analytically determine the clogging degree at any time of operation, depending on the pressure losses’ values.

Power exhaust by core radiation at COMPASS tokamak

Substantial power dissipation in the edge plasma is required for the safe operation of ITER and next-step fusion reactors, otherwise unmitigated heat fluxes at the divertor plasma-facing components (PFCs) would easily exceed their material limits. Traditionally, such heat flux mitigation is linked to the regime of detachment, which is characterised by a significant pressure gradient between upstream and downstream scrape-off layer (SOL). However, the physics phenomena responsible for power dissipation and pressure loss are distinctly different, especially when the power dissipation is achieved by impurity seeding. In principle, it is possible to achieve substantial mitigation of the heat fluxes while maintaining conservation of the pressure along the open field lines in the SOL. This regime can be accessed by injection of medium- or high-Z impurities, which mostly radiate inside the last closed flux surface. The critical question related to such an approach is the effect on confinement and perspective fusion power generation in future thermonuclear reactors. In this work, we report on experiments at COMPASS tokamak, where neon and argon impurities were injected in ohmic or NBI-heated low confinement plasmas. With appropriate seeding waveform, stable scenarios were achieved, avoiding the radiative collapse of plasmas. Significant reduction of heat fluxes at the outer target was observed, with heat flux pattern similar to the one previously achieved by nitrogen seeding. The reduction of downstream pressure was, however, accompanied by an equal reduction of upstream pressure, indicating that the power dissipation occurred inside the separatrix. Indeed, the impurity cooling is causing a significant drop of edge temperature; however, the effect in the plasma centre is much less pronounced.

Ernie: Scalable Load-Balanced Multicast Source Routing for Cloud Data Centers

Nowadays, most applications hosted on public cloud data centers (DCs) disseminate data from a single source to a group of receivers for service deployment, data replication, software upgrade, etc. For such one-to-many data communication paradigm, multicast routing is the natural choice as it reduces network traffic and improves application throughput. Unfortunately, recent approaches adopting IP multicast routing suffer from scalability and load balancing issues, and do not scale well with the number of supported multicast groups when used for cloud DC networks. Furthermore, IP multicast does not exploit the topological properties of DCs, such as the presence of multiple parallel paths between end hosts. Despite the recent efforts aimed at addressing these challenges, there is still a need for multicast routing protocol designs that are both scalable and load-balancing aware. This paper proposes Ernie, a scalable load-balanced multicast source routing for large-scale DCs. At its heart, Ernie further exploits DC network structural properties and switch programmability capabilities to encode and organize multicast group information inside packets in a way that minimizes downstream header sizes significantly, thereby reducing overall network traffic. Additionally, Ernie introduces an efficient load balancing strategy, where multicast traffic is adequately distributed at downstream layers. To study the effectiveness of Ernie, we extensively evaluate Ernie’s scalability behavior (i.e., switch memory, packet size overheads, and CPU overheads), and load balancing ability through a mix of simulation and analysis of its performances. For example, experiments of large-scale DCs with 27k+ servers show that Ernie requires a downstream header sizes that are 10× smaller than those needed under state-of-the-art schemes while keeping end-host overheads at low levels. Our simulation results also indicate that at highly congested links, Ernie can achieve a better multicast load balancing than other existing schemes.

A Layer 3→5 Circuit in Auditory Cortex That Contributes to Pre-pulse Inhibition of the Acoustic Startle Response.

While connectivity within sensory cortical circuits has been studied extensively, how these connections contribute to perception and behavior is not well understood. Here we tested the role of a circuit between layers 3 and 5 of auditory cortex in sound detection. We measured sound detection using a common variant of pre-pulse inhibition of the acoustic startle response, in which a silent gap in background noise acts as a cue that attenuates startle. We used the Nr5a-Cre driver line, which we found drove expression in the auditory cortex restricted predominantly to layer 3. Photoactivation of these cells evoked short-latency, highly reliable spiking in downstream layer 5 neurons, and attenuated startle responses similarly to gaps in noise. Photosuppression of these cells did not affect behavioral gap detection. Our data provide the first demonstration that direct activation of auditory cortical neurons is sufficient to attenuate the acoustic startle response, similar to the detection of a sound.

Control pathway for an advanced divertor on ITER

Abstract This paper presents the development of a coupled shape and divertor controller for ITER with capabilities to control the flux expansion and an advanced divertor configuration, the x-divertor (XD), in which a secondary x-point is placed in the downstream scrape-off layer. Due to the high-performance nature of ITER and its relatively few shaping coils, satisfying constraints on the coil currents, power supplies, and plasma shape is a challenge for this configuration. To meet these constraints the controller uses the constrained linear quadratic regulator (CLQR) framework [1] , a variant of model predictive control (MPC). Previous work [2] has shown the existence of XD equilibria on ITER and in this study, we identify a control pathway for achieving the “pure” XD where the secondary x-point is placed at the outer strike point, representing a maximally flux-expanding scenario. Constraints are observed throughout the transition. One limitation is that at high flux expansion, the shallow angle of incidence of the magnetic field on the divertor results in a reduced plasma wetted area via tile shadowing. On the other hand, the high flux expansion and flaring characteristic of the XD facilitate enhanced detachment, which could negate the shadowing effect to some degree. In this case it would be desirable to operate as close to the flux expansion limit as possible. To this end we also demonstrate the controller's ability to track a trajectory for the flux expansion near the accepted angle of incidence limit.

Wake events during early three-dimensional transition of a circular cylinder placed in shear flow

Three-dimensional (3D) direct numerical simulations are carried out for shear flows past a circular cylinder in the early 2D (two-dimensional)–3D transition regime. The effect of incoming shear is buried in a source term employing a velocity transformation. Wake transition events are inspected for both planar and span-wise shear flows. Parallel, time-mean-symmetric shedding for planar shear and oblique vortex shedding for span-wise shear are observed with a near wake roll-up vortical structure. Vortex splits and dislocations are found without any order in time for moderate shear, while they give way to visibly higher levels of instabilities at higher shear rates. Mode “B” instabilities are noted for planar shear, while opposite streamwise vortices align in parallel horizontal layers for span-wise shear. Local Strouhal frequency (Stz) drops inside a span-wise cell for span-wise shear with finite jumps across cell boundaries. Wavelet multiresolution analysis indicates a strong flushing effect, triggered by vortex dislocations, which gives rise to a new frequency event. The dominant span-wise mode indicates periodic forcing of mode “A” instabilities at a rate close to the inverse of local Strouhal number. In contrast, the streamwise velocity modes result in a global span-wise similarity. Intrinsic secondary instabilities play a vital role in span-wise shear cases. The addition of planar shear makes the downstream defect layer nearly span-wise-invariant. However, the velocity defect is entirely controlled by the span-wise shear. The momentum thickness exhibits streamwise growth, similar to the Blasius profile. The shape factor of such profiles indicates a delay in laminar–turbulent transition for span-wise shear.

Enhanced nano-aerosol loading performance of multilayer PVDF nanofiber electret filters

Aerosol loading behavior of PVDF nanofiber electret filters using neutrally charged nano- and submicron aerosols was investigated experimentally for the first time. The loading behavior include variations of filtration efficiency and pressure drop and distribution of deposited aerosols in the filters all having the same fiber basis weight (3.060 gsm). Through the filtration efficiency variations of uncharged/charged, single-/multi-layer filters with aerosol loading, it was observed that mechanical PVDF filters had continuously increasing filtration efficiency, while PVDF electret filters had initially decreasing and subsequently increasing filtration efficiency until reaching 100% due to diminishing electrostatic effect and enhancing mechanical effect.By combining the pressure drop evolution of different filters during aerosol loading and detailed SEM images of the loaded filters, we have demonstrated that multilayer PVDF filters, especially the electret ones, could significantly slow down the pace of filter clogging (skin effect) and increase significantly the aerosol holding capacity during depth filtration. Generally, the multilayer nanofiber filters received the most aerosol deposit during depth filtration, whereas the single-layer nanofiber filters with the same basis weight of fibers received the most deposit during cake filtration. The multilayer nanofiber filters had approximately 70% aerosol deposit in the filter during depth filtration fully utilizing the full filter thickness, especially for the electret filters that had charged fibers, and only 30% deposit in the cake. On the contrary, the single-layer uncharged/charged nanofiber filters were exactly the reverse due to persistency of the skin effect with only 30% deposit in the filter mostly located in the upstream layer, yet 70% deposit in the cake. During depth filtration, the pressure drop per added mass deposit for the multilayer electret filter was very low at 11 Pa gsm−1, which was at least twice below any other nanofiber filters. This was all attributed to the uniform capture of aerosols by electrostatic effect across the entire filter depth from the upstream to downstream layers of the multilayer electret filter. The above conclusion was confirmed by the detailed SEM images taken across the different filter layers for the multilayer filter configuration. The 4-layer electret nanofiber filter with a 3.060-gsm basis weight has 4 times more aerosol holding capacity than the single uncharged/charged nanofiber filter with the same fiber basis weight in depth filtration. Based on the standpoint of highest efficiency and capacity with maximum pressure drop 800 Pa imposed on the filtration operation, the 4-layer nanofiber electret was the best among all 4 filters. It had 52% more aerosol holding capacity than the single layer uncharged nanofiber filter and 38% more capacity than the charged single-layer and the uncharged multilayer nanofiber filters. The multilayer PVDF electret filters have excellent filtration performance for long-term aerosol filtration and also great potential applications in the fields of personal health care and environmental protection.

Effects of passenger blockage on smoke flow properties in longitudinally ventilated tunnel fires

SummaryThis paper investigates the effects of passenger blockage on smoke flow properties in longitudinally ventilated tunnel fires. A series of numerical simulations were conducted in a 1/5 small‐scale tunnel with the different heat release rates (50‐100 kW), longitudinal ventilation velocities (0.5‐1 m/s), passenger blockage lengths (2‐6 m), and ratios (0.17‐0.267). The typical smoke flow properties in different tunnel fire scenarios are analyzed, and the results show that under the same heat release rate and longitudinal ventilation velocity, the smoke back‐layering length, maximum smoke temperature, and downstream smoke layer height decrease with increasing passenger blockage length or ratio. The Li correlations can well predict the smoke back‐layering length and maximum smoke temperature in tunnel fire scenarios without the passenger blockage. When the passenger blockage exists, the modified local ventilation velocity that takes the blockage length and ratio into account has been proposed to correct the Li correlations. The smoke back‐layering length and maximum smoke temperature with the different blockage lengths and ratios can be predicted by the modified correlations, which are shown to well reproduce the simulation results.

Bi-global stability analysis in curvilinear coordinates

A method is developed to solve biglobal stability functions in curvilinear systems which avoids reshaping of the airfoil or remapping the disturbance flow fields. As well, the biglobal stability functions for calculation in a curvilinear system are derived. The instability features of the flow over a NACA (National Advisory Committee for Aeronautics) 0025 airfoil at two different angles of attack, corresponding to a flow with a separation bubble and a fully separated flow, are investigated at a chord-based Reynolds number of 100 000. The most unstable mode was found to be related to the wake instability, with a dimensionless frequency close to one. For the flow with a separation bubble, there is an instability plateau in the dimensionless frequency ranging from 2 to 5.5. After the plateau and for an increasing dimensionless frequency, the growth rate of the most unstable mode decreases. For a fully separated flow, the plateau is narrower than that for the flow with a separation bubble. After the plateau, with an increased dimensionless frequency, the growth rate of the most unstable mode decreases and then increases once again. The growth rate of the upstream shear layer instability was found to be larger than that of the downstream shear layer instability.