Bottleneck For Transport Research Articles

Potential jumps at transport bottlenecks cause instability of nominally ionic solid electrolytes in electrochemical cells

Normal operations of electrochemical devices such as solid oxide fuel cells (SOFC), solid oxide electrolyzer cells (SOEC) and lithium ion batteries (LIB) sometimes fail because of unexpected formation of internal phases. These phases include oxygen bubbles at grain boundaries inside the zirconia electrolyte of SOEC, isolated Li metal islands inside the (garnet type) Li7La3Zr2O12 electrolyte of all-solid-state LIB, and similar Na metal islands inside the Na-beta-alumina and NASICON electrolytes of Na-S batteries. Remarkably, although the devices can operate in both polarities, the propensity for failure depends on the polarity. Here we explain these and other phenomena in nominally ionic solid electrolytes and mixed-conducting electrodes in simple thermodynamic and kinetic terms: the unexpected internal phases are caused by a large potential jump that is needed to push a constant ion or electron flow through its internal transport bottleneck. Definite rules for internal phase formation including its polarity dependence are formulated to help predict and mitigate it, which leads to microstructural instability, efficiency deterioration and breakdown.

Burundi

Economic impact. COVID-19 is having an adverse economic impact on Burundi. The pandemic is affecting Burundi through an evolving domestic outbreak and economic spillovers from the global and regional environment, including from the containment measures introduced in trading partners and neighboring countries. Economic growth projections for 2020 have been revised down by 5.3 percentage points to -3.2 percent in 2020. The pandemic has exacerbated pre-existing economic challenges and creates an external financing need of 4.7 percent of GDP in 2020 and 2021, mainly as a result of lower exports in line with lower foreign demand due to lower global growth and transportation bottlenecks from containment measures in other countries; elevated imports needs related in part to the planned fiscal spending aimed at responding to the pandemic; and reduced remittances inflows. The pandemic has also created a fiscal financing need of 6.9 percent of GDP, which will need to be met mainly from external sources.

A comprehensive study of charge transport in Au-contacted graphene on Ge/Si(001)

We investigate the electronic transport properties of Au-contacted graphene on Ge/Si(001). Kelvin probe force microscopy at room temperature with an additionally applied electric transport field is used to gain a comprehensive understanding of macroscopic transport measurements. In particular, we analyze the contact pads including the transition region, perform local transport measurements in pristine graphene/Germanium, and explore the role of the semiconducting Germanium substrate. We connect the results from these local scale measurements with the macroscopic performance of the device. We find that a graphene sheet on a 2 μm Ge film carries approximately 10% of the current flowing through the device. Moreover, we show that an electronic transition region forms directly adjacent to the contact pads. This transition region is characterized by a width of >100 μm and a strongly increased sheet resistance acting as the bottleneck for charge transport. Based on Rutherford backscattering of the contact pads, we suggest that the formation of this transition region is caused by diffusion.

TEN-T corridors – Stairway to heaven or highway to hell?

The European Union coordinates and co-finances supra-national transport infrastructure investments in the Trans-European Transport Network (TEN-T), which consists of road, rail, airport, and port infrastructure. To the best of our knowledge, we are the first to quantify the direct and indirect economic growth effects of newly created TEN-T core corridor roads in Eastern European countries. Both the panel data and the spatial analyses show that regional GDP growth at the NUTS3 level is between 0.5 and 2.0 percentage points higher, if a region has direct access to a newly built road. The analyses with a Durbin model (SDM) show that the new construction of a TEN-T core road also causes positive spillover effects on other regions that have direct access to the corridor network, as well as on regions that are not directly connected to the corridors. The results thus indicate that the TEN-T policy, which aims to alleviate transport bottlenecks, can increase cohesion between central and peripheral regions and consequently enhance regional welfare in Eastern Europe.

The Time-Dependent Lead-Lag Relationship Between WTI and Brent Crude Oil Spot Markets

Based on daily returns, we comprehensively characterize the lead-lag relationship between Brent and WTI crude oil spot markets from 1987 to 2017 with the non-parametric symmetric thermal optimal path (TOPS) method. The empirical results indicate that WTI spot price leads Brent spot price slightly, which provides support to the price leadership of WTI over Brent. However, the lead-lag relationship is volatile and sensitive to extreme events like geopolitical conflict and policy shift. Due to the concerns about future oil supply triggered by the two Gulf wars, both WTI and Brent experienced extreme uncertainty and co-moved closely during wartime. Notably, the TOPS method captures the structural break in the WTI-Brent price spread in 2011 which is influenced by the U.S. oil export ban and transportation bottleneck. After the lift of the ban, the two benchmark prices have reconnected. The lead-lag signals basically coincide with major influential changes in the oil markets, which suggests that the TOPS method provides a viable approach to reflecting the impact of extreme events on the crude oil prices motion.

Sharply Increased Current in Asymmetrically Aligned Polycrystalline Polymer Transistors With Sub-Domain-Size Channels

Shortening channels to the feature length of polymer domains is important to understand the charge transport in semiconducting polymers from macroscopic to microscopic scales. In this work, we fabricated polymer transistors with sub-domain-size channels by electron-beam lithography and asymmetrically aligned domains by off-center spin coating, in which a dry self-patterning method with hexagonal boron nitride was developed to eliminate parasitic leakage. The current sharply increased by 60 times when the channel length was shortened from 200 to 80 nm. The device with an 80 nm-long channel in the direction parallel to the aligned polymer domains delivered a saturation current 160 times higher than that of the orthogonal counterpart. These results and a velocity calculation suggested that the bottleneck of charge transport in electronic devices is domain boundaries. These results highlight the importance of high-efficiency intra-domain charge transport and also the inter-domain limitation. Our findings will contribute to further polymer optimization to improve the performance of polymer devices.

Chalcogen-Assisted Enhanced Atomic Orbital Interaction at TMD–Metal Interface and Sulfur Passivation for Overall Performance Boost of 2-D TMD FETs

Metal-semiconductor interface is a bottleneck for efficient transport of charge carriers through Transition Metal Dichalcogenide (TMD) based field-effect transistors (FETs). Injection of charge carriers across such interfaces is mostly limited by Schottky barrier at the contacts which must be reduced to achieve highly efficient contacts for carrier injection into the channel. Here we introduce a universal approach involving dry chemistry to enhance atomic orbital interaction between various TMDs (MoS2, WS2, MoSe2 and WSe2) & metal contacts has been experimentally demonstrated. Quantum chemistry between TMDs, Chalcogens and metals has been explored using detailed atomistic (DFT & NEGF) simulations, which is then verified using Raman, PL and XPS investigations. Atomistic investigations revealed lower contact resistance due to enhanced orbital interaction and unique physics of charge sharing between constituent atoms in TMDs with introduced Chalcogen atoms which is subsequently validated through experiments. Besides contact engineering, which lowered contact resistance by 72, 86, 1.8, 13 times in MoS2, WS2, MoSe2 and WSe2 respectively, a novel approach to cure / passivate dangling bonds present at the 2D TMD channel surface has been demonstrated. While the contact engineering improved the ON-state performance (ION, gm, mobility and RON) of 2D TMD FETs by orders of magnitude, Chalcogen based channel passivation was found to improve gate control (IOFF, SS, & VTH) significantly. This resulted in an overall performance boost. The engineered TMD FETs were shown to have performance on par with best reported till date.

CoEdge: Exploiting the Edge-Cloud Collaboration for Faster Deep Learning

Recently a great number of ubiquitous Internet-of-Things (IoT) devices have been connecting to the Internet. With the massive amount of IoT data, the cloud-based intelligent applications have sprang up to support accurate monitoring and decision-making. In practice, however, the intrinsic transport bottleneck of the Internet severely handicaps the real-time performance of the cloud-based intelligence depending on IoT data. In the past few years, researchers have paid attention to the computing paradigm of edge-cloud collaboration; they offload the computing tasks from the cloud to the edge environment, in order to avoid transmitting much data through the Internet to the cloud. To present, it is still an open issue to effectively allocate the deep learning task (i.e., deep neural network computation) over the edge-cloud system to shorten the response time of application. In this paper, we propose the latency-minimum allocation (LMA) problem, aimed at allocating the deep neural network (DNN) layers over the edge-cloud environment while the total latency of processing this DNN can be minimized. First, we formalize the LMA problem in general form, prove its NP-hardness, and present an insightful characteristic of feasible DNN layer allocations. Second, we design an approximate algorithm, called CoEdge, which can handle the LMA problem in polynomial time. By exploiting the communication and computation resources of the edge, CoEdge greedily selects the beneficial edge nodes and allocates the DNN layers to the selected nodes by a recursion-based policy. Finally, we conduct extensive simulation experiments with realistic setups, and the experimental results show the efficacy of CoEdge in reducing the deep learning latency compared to two state-of-the-art schemes.

Proton Redox and Transport in MXene-Confined Water.

The redox reaction of intercalated protons is key to the pseudocapacitance of MXenes (two-dimensional (2D) carbides and nitrides) in H2SO4. However, an atomistic understanding of proton redox and transfer in water confined between MXene layers is still lacking. Here, we use first-principles molecular dynamics (FPMD) simulations to reveal the proton-transfer mechanism in MXene-confined water layers of different thicknesses by using O-terminated Ti3C2 as a prototypical MXene. We found that the proton redox process takes place reversibly between surface -O sites and interfacial water molecules, intermitted by the more frequent in-water proton-transfer events. The surface redox rate is much higher in the highly confined one-layer water than in the two or three layers of water. Proton mobility increases with the water-layer number and already approaches the bulk value in the three-layer water. The proton transfer still follows the Eigen-Zundel-Eigen mechanism in the 2D-like confined water (regardless of the thickness) as in the 3D bulk water via the special pair dance. Our model in the case of two layers of water is in excellent agreement with the experimental interlayer spacing after charging the Ti3C2O2 electrode in H2SO4. Our finding from FPMD of fast surface redox and in-water transfer for the intercalated protons implies that other processes such as the intercalating step are likely the bottleneck for the ionic transport.

S-Shaped Current–Voltage Characteristics in Solar Cells: A Review

S-shaped current–voltage ( I – V ) characteristics are a frequently occurring hurdle in the development of new solar cell material combinations and device architectures. Their presence points to the existence of a charge transport bottleneck that needs to be removed in order to unlock high fill factors and power conversion efficiencies. In this review, examples of studies in which s-shaped I – V curves have appeared are presented, and the cause and mitigation are discussed. Different solar cell material systems are often treated by separate communities, thereby, also the physics of s-shaped I – V curves have been treated separately. This review covers the main solar cell technologies—silicon, thin film, organic, hybrid—with the aim to provide an overarching picture of the common mechanisms and universal guidelines for mitigation of s-shaped I – V characteristics in emerging solar cell technologies. Except for a few studies on organic solar cells, s-shaped I – V curves are reported to result from charge transport barriers at one of the (selective) contact layers that can be overcome by interface engineering and doping.

Halide Perovskite High-k Field Effect Transistors with Dynamically Reconfigurable Ambipolarity

Despite the remarkable optoelectronic properties of halide perovskites, achieving reproducible field effect transistor (FET) action in polycrystalline films at room temperature has been challenging and represents a fundamental bottleneck for understanding electronic charge transport in these materials. In this work, we report halide perovskite-based FET operation at room temperature with negligible hysteresis. Extensive measurements and device modeling reveal that incorporating high-k dielectrics enables modulation of the channel conductance. Furthermore, continuous bias cycling or resting allows dynamical reconfiguration of the FETs between p-type behavior and ambipolar FET with balanced electron and hole transport and an ON/OFF ratio up to 104 and negligible degradation in transport characteristics over 100 cycles. These results elucidate the path for achieving gate modulation in perovskite thin films and provide a platform to understand the interplay between the perovskite structure and external stimuli such as photons, fields, and functional substrates, which will lead to novel and emergent properties.

Sensitivity analysis of ship traffic in restricted two-way waterways considering the impact of LNG carriers

The restricted waterway is usually regarded as the bottleneck of port transportation. Many factors influence the overall efficiency and safety of the waterways. In this paper, an attempt is undertaken to investigate how the parameters related to LNG carriers, general ships, waterway dimensions and weather conditions affect the navigation risk and efficiency of restricted two-way waterways. Three indices including one efficiency and two risk indicators are adopted as the objective functions. To determine the correlations between the input and output factors, a traffic simulation model is constructed, which synthesizes the navigational rules, the impact of LNG carriers, the interactions among ships, the arrival characteristics of ships, among others. Subsequently, an Elementary Effect method based iterative procedure is developed to identify the influential and non-influential factors. Numerous experiments are performed by integrating the simulation model with the iterative procedure. The results reveal that the ships' arrival rate, mean and variance of ship speed and channel length are the most influential factors. LNG carriers’ speed and arrival rate have remarkable nonlinearities and/or interactions with other factors. These findings are valuable for the guidance of improving the efficiency and safety strategies implemented in restricted waterways.

(Invited) Engineered Particle-Particle Contacts for Improved Thermal Interface Materials

I present my group’s ongoing work to use liquid metal to overcome thermal transport bottlenecks in polymer composites. The central premise behind this effort is that liquid metal-coated particle inclusions will have enlarged particle-particle contact regions relative to the point-like contacts between non-coated particle inclusions. In effect, the LM functions as a thermally conductive “solder” between particles. Polymer composites play an important role for thermal interface materials (TIMs). TIMs improve thermal transport by filling micro air gaps between the rough surfaces of adjacent components (e.g., between a computer chip and heat spreader). These applications require mechanically compliant materials such as polymers that unfortunately also suffer from low thermal conductivity. Consequently high thermal conductivity solid particles are typically added to the polymer to boost thermal transport. Despite these efforts, TIM conductivities still usually fall below 2 W m-1 K-1because the small point-like contacts between solid filler particles lead to large thermal contact resistances that bottleneck thermal transport. I first present our work on polymer composites with nickel-based particle inclusions. We explore bare nickel particles, nickel particles coated with silver, and nickel particles coated with liquid metal. These coatings impart mechanical compliance to the surface of the hard nickel particles and lead to a 3-fold increase in thermal conductivity of the polymer composite. These studies also reveal that a nanometer-scale native oxide coating on the liquid metal impedes thermal transport. In order to improve thermal transport for liquid-metal coated particles, we next focus on methods to physically break the native oxide. Rupturing this thin oxide allows liquid metal to flow and yields improved contact between particles. To address this challenge, we conduct a series of thermal-mechanical studies on liquid metal droplets. In order to focus on the key physics, we create beds of liquid metal droplets with their native oxides intact (i.e. no polymer matrix and no solid particle core). We then study thermal transport as a function of applied mechanical pressure. We observe an enhancement in thermal transport that accompanies the rupture of the native oxide. We also find that the oxide rupture follows theoretical predictions for failure of thin-walled pressure vessels. Lastly, we chemically modify the native oxide shell to reduces its strength, promote oxide rupture, and improve thermal transport.

Effects of phloem on canopy dieback, tested with manipulations and a canker pathogen in the Corylus avellana/Anisogramma anomala host/pathogen system.

Canker pathogens cause necrosis of the phloem, but in many host/pathogen systems, they also cause canopy dieback, which implicates xylem, not phloem dysfunction. We hypothesize that this dieback distal to the canker is caused by water stress resulting from the lack of a phloem-to-xylem connection, which in a healthy plant would allow delivery of nonstructural carbohydrates (NSCs) and water inward to aid in xylem embolism refilling. We tested several components of this hypothesis in the host/pathogen system Corylus avellana L./Anisogramma anomala (Peck) E. Müll (Eastern filbert blight). Cankers were non-girdling and usually ≥0.1m long. As expected, healthy controls had higher specific conductivity (Ks) than diseased stems, but unexpectedly, had similar moisture content (m.c.), showing that the lower Ks did not result from more embolisms in the diseased stems. Moreover, manipulations that removed cambium and phloem to simulate a canker, or that shaded stems to lower NSCs, did not result in lower Ks or m.c. than controls. The outer millimeter of xylem adjacent to a canker had infrequent tyloses and/or fungal hyphae in many but not all samples, and dye studies showed little xylem water transport in that region, but the incidence of these blockages was insufficient to cause the observed 19% decrease in Ks. Healthy stems had higher m.c. than diseased stems above the canker (or analogous) location and were longer for the same leaf weight, suggestive of water stress in the upper portion of diseased stems. These results suggest that dieback distal to cankers in this system results from the bottleneck in water transport in the region adjacent to a canker, but did not find evidence to support the requirement of a phloem-to-xylem connection for continued water transport.

Fault‐tolerant data transport backbone for 3D wireless sensor networks

AbstractExisting approaches for clustering wireless sensor networks by using relay nodes (RNs) suffer from two major problems: impracticability for realistic scenarios and lack of fault tolerance. The first problem is due to the assumption of a two‐dimensional Region of Interest (RoI). The second problem stems from the fact that these approaches do not address the construction of disjoint routing paths, where multiple routing paths have common intermediate RNs, which create a bottleneck for the data transport and points of failure. In this paper, we tackle these two problems by proposing a new RNs deployment approach based on more realistic assumptions. Indeed, a more realistic communication model is considered, which takes into account the impact of the RoI topography on wireless communications. Additionally, a practical position constraint is adopted, where the RNs are placed only on the RoI crest points, to minimize the topography impact on the wireless communications. By relying on an efficient algorithm that constructs from a connected graph many Steiner trees, covering the same subset of vertices, the proposed RNs deployment approach selects the appropriate positions of the RNs and ensures a reliable data transport from the sensor nodes to the collector node, according to a two‐tier topology while satisfying other secondary objectives related to the cost and the quality of the communication links. The simulation results demonstrate the feasibility of the proposed approach and its ability to minimize cost and improve communication links quality.

Single cell and single molecule resolution of herpesvirus genome transport, condensation state and transcriptional output

Events controlling herpesvirus nuclear genome uncoating, nuclear transport, and the onset of transcription remain poorly understood. We have now developed procedures to examine these processes within individual cells and at the single molecule level for both the genome and the transcripts produced from it. We have combined two novel techniques of, firstly, bioorthogonal chemistry to visualise genomes which incorporate an alkyne-nucleoside analogue (ethynyl deoxycytidine, EdC) and secondly, single molecule RNA in-situ hybridisation (smFISH) which allows detection of individual mRNA transcripts. Using these techniques simultaneously, we can now qualitatively and quantitatively analyse individual transcript abundances and their intracellular localisation, in relation to the genome itself at single molecule resolution during the progression of infection. Moreover, we are able to examine these parameters when a single genome infects a cell. We have examined the transcripts of the immediate-early mRNA for ICP0, and features revealed from this work include; transcriptional ‘bursting’ with clustered transcripts around individual genomes; mean mRNA transcript number, variance, and intracellular localisation produced from a single genome; the progressive abundant ICP0 transcription occurring selectively from replicated genomes; an increasing bottleneck in cytoplasmic transport of transcripts emanating from replicated genomes; and increased transcription bursts from virtually every uncoated genome when protein synthesis is suppressed. Further, by multiplexing probes, we can simultaneously analyse distinct transcription outputs from different genes of the same or classes, and genomes, in the same individual cell. Our results reveal completely new perspectives on the very early events of genome presentation and transcription from those genomes.

Impact of thermal transport parameters on the operating temperature of organic light emitting diodes

Excess heat in organic light emitting diodes (OLEDs) that is produced during their operation may accelerate their degradation and may cause an inhomogeneous brightness distribution, in particular in large area OLEDs. Assessing the quantitative impact of heat excess is difficult, because all decisive processes related to charge transport and emission via charge recombination are thermally activated. For example, electric currents that are elevated due to larger temperatures cause additional Joule heating and, hence, increase the device temperature even further. Here, we establish how parameters responsible for heat transport, i.e., the thermal conductivity of the organic layers and the heat transfer coefficient between the device surface and the environment, govern the temperature inside the OLED. Relying on three-dimensional drift-diffusion simulations that self-consistently couple thermally-activated charge transport and heat transport, we establish that the thermal conductivity of organic layers is not a bottleneck for heat transport, because the encountered layer thicknesses in realistic device geometries prevent heat accumulation. The heat transfer to the ambient environment is the key parameter to dissipate excess heat from the device. Intentionally elevated operating temperatures, which may improve the OLEDs’ electric performance, are not necessarily beneficial, as any increase in operating temperature reduces the device stability. The thermal effects, being decisive for the OLED temperature, occur in device layers beyond the electrically active region. We propose analytical expressions that relate the temperature in the device for a given point of operation to the heat transfer to the environment and the substrate.

Research on the Issues of Resource Allocation Efficiency of Multimodal Transport in Yangtze River Economic Zone

Yangtze River Economic Zone shoulder strategic missions of regional economic development as well as eco-civilization improvement. There for its multi-modal transportation system should be stressed in terms of high efficiency operation. High lighted by the first theorem of welfare economics, the paper works out the technical model of efficient allocation of multimodal transport resources in the Yangtze River Economic Zone by applying the transportation optimization method. As the findings of the paper, there are al least 6 categories of the resolutions in improving the transport efficiency, namely reducing the institution cost, improving the transportation demand, reducing the freight rate, shortening the transfer time, shortening the transit time, breaking the bottleneck of transportation between the two dams. The results of the research are respected to reduce the negative impact of the unfavorable shipping conditions as well as the blocks of river dams on the smooth operation of multimodal transport turnover in the region.

A Data-driven Approach to Estimate the Probability of Pedestrian Flow Congestion at Transportation Bottlenecks

In public gathering places, pedestrian flow congestion may happen in transportation bottlenecks. Limitations exist in the conventional judgment of congestion by considering the crowd density or the walking speed merely. In this paper, a data-driven mathematical approach based on Kernel Density Estimation (KDE) to analyze the probability of pedestrian flow congestion is proposed, which comprehensively considers the walking speed, the crowd density and the flow rate when pedestrians walk towards possible bottlenecks. With the case study of Nanjing metro station during rush hours, the advantages of non-parametric KDE compared with traditional parametric normal distribution estimation are analyzed and the optimal bandwidth for KDE is also discussed. The case study shows that the proposed method can obtain a more reliable quantitative assessment of congestion risk, as it overcomes the limitation of parametric estimation that relies on experience, and also avoids biased assessment of congestion that merely concerns single parameter of pedestrian flow. Finally, an assessment framework for dynamic congestion risk at bottlenecks is suggested. With this framework, the change of congestion situations of a monitored region can be mastered through data-driven approach, and thus the transformation of normal flowing to congestion of the crowd can be quantified through probabilistic analysis.

Market Power and Spatial Arbitrage between Interconnected Gas Hubs

This paper examines the performance of the spatial arbitrages carried out between two regional markets for wholesale natural gas linked by a pipeline system. We develop a new empirical methodology to (i) detect if these markets are integrated, i.e., if all the spatial arbitrage opportunities between the two markets are being exploited, and (ii) decompose the observed spatial price differences into factors such as transportation costs, transportation bottlenecks, and the oligopolistic behavior of the arbitrageurs. Our framework incorporates a new test for the presence of market power and it is thus able to distinguish between physical and strategic behavior constraints on marginal cost pricing. We use the case of the "Intercon-nector" pipeline linking Belgium and the UK as an application. Our empirical findings show that all the arbitrage opportunities between the two zones are being exploited but confirm the presence of market power.