Buffer Space Research Articles

The influence of air gaps on buffer temperature within an engineered barrier system

High-level radioactive waste produced by nuclear power plants are disposed subterraneously utilizing an engineered barrier system (EBS). A gap inevitably exists between the disposal canisters and buffer materials, which may have a negative effect on the thermal transfer and water-blocking efficiency of the system. As few previous experimental works have quantified this effect, this study aimed to create an experimental model for investigating differences in the temperature changes of bentonite buffer in the presence and absence of air gaps between it and a surrounding stainless steel cell. Three test scenarios comprised an empty cell and cells partially or completely filled with bentonite. The temperature was measured inside the buffers and on the inner surface of their surrounding cells, which were artificially heated. The time required for the entire system to reach 100 °C was approximately 40% faster with no gap between the inner cell surface and the bentonite. This suggests that rock–buffer spaces should be filled in practice to ensure the rapid dissipation of heat from the buffer materials to their surroundings. However, it can be advantageous to retain buffer–canister gaps to lower the peak buffer temperature.

Thermal environment optimisations of cave dwellings for the elderly in heating season among cold regions of China

In the vast developing world represented by China, the unsatisfactory thermal and humidity conditions among rural built environments are extremely harmful to the elderly-health in cold regions. The cave-dwellings maintain competent thermal stability, while with current refurbishment still cannot meet their relatively demanding thermal comfort needs. In fact, few studies have highlighted the optimisation effect of passive designs engaging various buffer spaces. Through experimental field measurements of representative cave dwelling and numerical simulations based on the DesignBuilder tool for the corresponding retrofit prototypes, this study investigated in detail the hidden correlations between key buffer space design variables (sunroom, under-eave gray space, courtyard, etc.) and the resulting indoor thermal and humidity performances for the elderly. The results of the study showed that:1) The average winter room temperatures of both heated (11.2 ± 1.5 °C) and unheated (6.4 ± 2.7 °C) rooms in traditional cave-dwellings fail to meet the recommended standard by World Health Organization (18 °C) and the Chinese national standard (16 °C–24 °C). 2) For living track temperature steps reduction, the southern sunroom has obvious impact (mostly <10 °C), while enclosed courtyards with glass-top can even enhance such performance (mostly <5 °C). 3) For boosting indoor temperatures in winter, sunroom with enclosed courtyard are most effective in unheated and heated conditions. As the first systematic work to reveal the thermal-enhancing effectiveness of the south-facing buffer space for cave-dwellings in cold climates, the research findings can assist optimizing-retrofitting for cave-dwellings among similar climatic regions globally.

Detection of Cache Pollution Attack Based on Ensemble Learning in ICN-Based VANET

Content Centric Network (CCN) can be extended to efficiently and reliably support content delivery and solve the network performance degradation caused by dynamic topology and intermittent connectivity of Vehicle Ad hoc NETwork (VANET). However, the in-network caching mechanism of Vehicular Content Centric Network (VCCN) is vulnerable against Cache Pollution Attack (CPA), where attackers aim to fill the buffer space with non-popular contents by releasing fake requests. Unavoidably, the cache hit ratio of content requests from legal users is degraded and the content retrieval latency is increased under CPA. Hence, it is critical to detect and mitigate CPA. The current solutions for static CCN cannot be directly applied into dynamic VCCN. In this paper, we propose a detection scheme based on hybrid heterogeneous multi-classifier ensemble learning, where CPA is determined by the cooperation of multiple vehicles. In our scheme, each vehicle can build or join a cluster whose head possesses more common moving attributes of position, speed and direction with other members. Besides, the cluster head as a base learner is responsible for training its own classifier by making some relevant statistics on requests and hit ratio. Specifically, the problem of ensemble classifier making from the individual classifiers is formulated as a linear optimization problem, with the goal of minimizing the false ratio of detecting CPA. The generalization ability of ensemble learning can make very accurate predictions on CPA. By comparison, our detection scheme outperforms the existing schemes in terms of detection ratio, hit ratio, retrieval delay. Besides, simulations have proved that the overfitting problem of adopting a singe base learning algorithm can be alleviated in our scheme.

Hollow Porous CoO@Reduced Graphene Oxide Self-Supporting Flexible Membrane for High Performance Lithium-Ion Storage.

We report an environment-friendly preparation method of rGO-based flexible self-supporting membrane electrodes, combining Co-MOF with graphene oxide and quickly preparing a hollow CoO@rGO flexible self-supporting membrane composite with a porous structure. This unique hollow porous structure can shorten the ion transport path and provide more active sites for lithium ions. The high conductivity of reduced graphene oxide further facilitates the rapid charge transfer and provides sufficient buffer space for the hollow Co-MOF nanocubes during the charging process. We evaluated its electrochemical performance in a coin cell, which showed good rate capability and cycling stability. The CoO@rGO flexible electrode maintains a high specific capacity of 1103 mAh g-1 after 600 cycles at 1.0 A g-1. The high capacity of prepared material is attributed to the synergistic effect of the hollow porous structure and the 3D reduced graphene oxide network. This would be considered a promising new strategy for synthesizing hollow porous-structured rGO-based self-supported flexible electrodes.

Effect of annular ribs in heat exchanger tubes on the performance of phase‐change regenerative heat exchangers

AbstractOptimizing the efficiency of conventional heat exchangers is critical for improving the performance of various processes. This study proposed increasing the heat dissipation buffer space of heat exchangers by filling the gap between the heat exchanger and the shell with phase‐change materials for optimizing phase‐change heat exchangers. Comparative simulation analyses were performed by investigating the difference between the internal and external diameters of the inner ring ribs of the heat exchanger, the flow rate of the cooling liquid, the spacing distance, and the number of the inner ring ribs as independent variables. The results revealed that the heat transfer efficiency of heat exchangers can be improved by adding the inner ring rib structure to the heat exchange copper tube. The difference between the inner and outer diameters of the inner ring rib considerably influences heat dissipation. Furthermore, a sensitivity coefficient of 0.2457 can be obtained. The distance and number of inner ring ribs and the flow rate of cooling liquid exhibit certain effects on the heat transfer efficiency of the heat exchanger. The sensitivity coefficients were 0.1477 and 0.0935. The heat dissipation efficiency of the coil heat exchanger was improved by 3.8% by adding inner ring ribs in the coil heat exchanger channel.

Core-shell structured Si@Cu nanoparticles segregated in graphene-carbon nanotube networks enable high reversible capacity and rate capability of anode for lithium-ion batteries

The volume expansion of Si electrodes and the poor conductivity of Si as well as the repeated rupture of solid electrolyte interface (SEI) lead to the rapid capacity decay of Si-based anode Li-ion batteries. The rational design of anode materials for the above problems is considered an effective solution. In this work, core-shell structured Si@Cu nanoparticles segregated in graphene-carbon nanotube networks (Si@Cu/CNT/rGO) is constructed by one-step hybrid and reduction self-assembly strategy. First, metallic copper was coated on silicon nanoparticles to improve the reaction kinetics of the cell during operation. The flexible reduced graphene oxide and rigid carbon nanotube are designed as a network structure for increasing the electrical conductivity and mechanical strength of the electrode material. This design not only provides sufficient buffering space for the volume change during cell operation, but also improves the electron migration effect of the composite Si@Cu/CNT/rGO. Thanks to this design, the composite electrode maintains a high lithium storage capacity of 1915.5 mAh/g (130 cycles) and 1486.7 mAh/g (200 cycles) after charging and discharging at 100 mA g−1 and 1000 mA g−1, respectively.

Efficient on board storage and retrieval of fast maneuver profiles for space applications

Attitude guidance is a concept for implementing performance enhancing rotational maneuvers that uses a conventional closed-loop attitude control system to track an optimized maneuver trajectory. Minimum-time attitude guidance is presently being used for executing fast occultation avoidance maneuvers on NASA’s Lunar Reconnaissance Orbiter (LRO). A challenge in operationalizing the idea is related to the limited size of the spacecraft’s command buffer, which was not designed with maneuver tracking in mind. In this paper, we propose an interpolating pre-filter built on B-splines that can be used on board to process downsampled maneuver commands (to save buffer space) and provide attitude control inputs at the servo-rate. The approach is validated using a high-fidelity simulation of the LRO developed at NASA’s Goddard Space Flight Center.

Graphene Oxide-Wrapped Co3O4/NiO Micron Flowers as an Anode of Lithium-Ion Batteries with Enhanced Rate Performance and Cycling Stability.

A graphene oxide-wrapped Co3O4/NiO (denoted as CNO/GO) micron flower is successfully synthesized by a rapid solvothermal method, which is formed through interpenetrating nanosheets. Nanosheets with a large specific surface area expose a large number of active sites for an electrochemical reaction. Moreover, abundant pores formed during the interpenetration of nanosheets are instrumental in providing enough buffer space to relieve the large volume expansion from the repeated lithium insertion/delithiation processes, and the tightly wrapped GO can effectively sustain the stability of the CNO micron flower structure during the long-term cycle processes. The reversible specific capacity as high as 602.9 mA h g-1 is maintained after 800 cycles at 5000 mA g-1. In addition, GO with good conductivity can greatly enhance the conductivity of CNO micron flowers, accelerate the transfer of electrons, and then achieve a high rate performance (the reversible specific capacity is 570.2 mA h g-1 at 10 000 mA g-1). This work provides a viable method for synthesizing the CNO micron flowers as a promising high-performance transition metal oxide anode for lithium-ion batteries.

Minimizing running buffers for tabletop object rearrangement: Complexity, fast algorithms, and applications

For rearranging objects on tabletops with overhand grasps, temporarily relocating objects to some buffer space may be necessary. This raises the natural question of how many simultaneous storage spaces, or “running buffers,” are required so that certain classes of tabletop rearrangement problems are feasible. In this work, we examine the problem for both labeled and unlabeled settings. On the structural side, we observe that finding the minimum number of running buffers (MRB) can be carried out on a dependency graph abstracted from a problem instance and show that computing MRB is NP-hard. We then prove that under both labeled and unlabeled settings, even for uniform cylindrical objects, the number of required running buffers may grow unbounded as the number of objects to be rearranged increases. We further show that the bound for the unlabeled case is tight. On the algorithmic side, we develop effective exact algorithms for finding MRB for both labeled and unlabeled tabletop rearrangement problems, scalable to over a hundred objects under very high object density. More importantly, our algorithms also compute a sequence witnessing the computed MRB that can be used for solving object rearrangement tasks. Employing these algorithms, empirical evaluations reveal that random labeled and unlabeled instances, which more closely mimic real-world setups generally have fairly small MRBs. Using real robot experiments, we demonstrate that the running buffer abstraction leads to state-of-the-art solutions for the in-place rearrangement of many objects in a tight, bounded workspace.

Application of an Architect-Friendly Digital Design Approach to the Wind Environment of Campus Dormitory Buildings

Good natural ventilation can improve the comfort of campus dormitories and effectively avoid pollution caused by particle accumulation. Parametric design can effectively address the feedback and connection between building performance analysis and design. This study employs an architect-friendly digital design method based on the Rhino/Grasshopper parametric platform. It takes campus dormitories in the cold region as a case, using parameterized digital tools, such as the Butterfly plugin to simulate wind performance under three influencing factors: building layout, opening position, and building façade (shape and spoiler). Finally, the optimal design that can simultaneously meet the local winter and summer wind environment requirements is selected and validated. In addition, the reasonable design of external balconies and bathrooms in a dormitory can form buffer spaces to achieve effective wind shelter and insulation effects in cold regions. This article describes how to use digital tools to quickly and easily optimize the design of building forms based on wind simulations to promote campus sustainability.

High cycling stability anode of interlayer silicon film with carbon buffer layer on 3D collector

The application scope of silicon-based anode is limited by its poor electrical conductivity and massive volume expansion. Herein, we propose a method to modify electrochemical performance of silicon-based anode with 3D collector and carbon buffer layer by magnetron sputtering. With foam Ni as collector, at a current density of 1 A/g, the first reversible specific capacity reached 1973 mAh/g, and the specific capacity after 100 cycles was1700 mAh/g. With carbon cloth as collector, the first reversible specific capacity was 1543 mAh/g, and the specific capacity after 100 cycles was 1337 mAh/g. The 3D collector was used to buffer the internal stress caused by the bulk effect of silicon. The carbon buffer layer not only improved the material conductivity but also avoided the repeated growth of SEI film, thus providing more buffer space for silicon. This work provides a new promising solution to silicon-based lithium-ion batteries.

Deep Reinforcement Learning for Joint Trajectory Planning, Transmission Scheduling, and Access Control in UAV-Assisted Wireless Sensor Networks.

Unmanned aerial vehicles (UAVs) can be used to relay sensing information and computational workloads from ground users (GUs) to a remote base station (RBS) for further processing. In this paper, we employ multiple UAVs to assist with the collection of sensing information in a terrestrial wireless sensor network. All of the information collected by the UAVs can be forwarded to the RBS. We aim to improve the energy efficiency for sensing-data collection and transmission by optimizing UAV trajectory, scheduling, and access-control strategies. Considering a time-slotted frame structure, UAV flight, sensing, and information-forwarding sub-slots are confined to each time slot. This motivates the trade-off study between UAV access-control and trajectory planning. More sensing data in one time slot will take up more UAV buffer space and require a longer transmission time for information forwarding. We solve this problem by a multi-agent deep reinforcement learning approach that takes into consideration a dynamic network environment with uncertain information about the GU spatial distribution and traffic demands. We further devise a hierarchical learning framework with reduced action and state spaces to improve the learning efficiency by exploiting the distributed structure of the UAV-assisted wireless sensor network. Simulation results show that UAV trajectory planning with access control can significantly improve UAV energy efficiency. The hierarchical learning method is more stable in learning and can also achieve higher sensing performance.

Carbon coating hollow NiS nanoparticles anchored on Ti3C2 nanosheet as high-performance anode for lithium-ion batteries

Exploring novel electrode materials is the key to developing attractive lithium-ion batteries (LIBs). Hence, we successfully synthesized NiS@C/Ti3C2 by in situ growth-sulfuration-pyrolysis strategies. As LIBs anode, its initial discharge capacity of NiS@C/Ti3C2 was 1509 mAh g−1 and its discharge capacity was 301.2 mAh g−1 at 1 A g−1. Most importantly, when the current density recovered to 0.03 A g−1 continuing 20 cycles and maintained excellent capacity of 864.6 mAh g−1. Notably, its capacity was 649.9 mAh g−1 after 700 cycles at 0.5 A g−1. Such extraordinary performances are mainly attributed to (1) carbon matrix can improve conductivity of composite material, effectively buffer volume expansion of material during cycles process, and prevent structure collapse. (2) the hollow structure produced by sulfuration, porous carbon matrix and the gaps among Ti3C2 nanosheets are conducive to the penetration of electrolytes. They provide abundant buffer space for volume expansion during Li+ embedding/stripping process, which effectively alleviates structure collapse and electrode crushing. (3) Ti3C2 nanosheets as high-conductive 2D substrate not only offer fast diffusion channels but also alleviate structure collapse of NiS@C. More importantly, this unique structure can alleviate restacking of Ti3C2 and provide affluent active sites, thus endowing material with improved electrical conductivity. Our work provides insightful insights into the design of transition metal sulfides (TMSs) anchored at Ti3C2 nanosheets as LIBs anode.

Construction of tunable ZnCoOx/C-PANI electrode materials for high-performance supercapacitors

Polyaniline (PANI) has been widely studied because of its unique physicochemical properties, but its practical significance in supercapacitors is seriously affected by its structural collapse during charging and discharging. We have successfully synthesized transition metal oxide/carbon-polyaniline composite electrode materials by in situ growth of polyaniline using the electrodeposition method with a metal-organic skeleton as a sacrificial template. This method not only can obtain high capacitance materials but also carbon materials provide buffer space during long-term charge/discharge to improve the overall stability. ZnCoOx/C-PANI-3 has a smaller charge transfer resistance and solution resistance compared to other materials, indicating that the interfacial coupling between PANI and ZnCoOx/C shortens the ion transport path between electrolyte and electrode surface, which is beneficial for rapid ion transfer and thus enhances its electrochemical performance. ZnCoOx/C-PANI-3 as an electrode material in the three-electrode system, has remarkable specific capacitance (1055 F.g−1 at a current density of 1 A.g−1) and good cycling stability (85.7% capacitance retention after 10,000 cycles of charge and discharge at high current density). Similarly, the asymmetric supercapacitor (ZnCoOx/C-PANI-3//AC) assembled with ZnCoOx/C-PANI-3 as the positive electrode material and activated carbon as the negative electrode material has a maximum energy density of 42.77 Wh.kg−1 at a power density of 705 W.kg−1 and a remarkable cycle life with a capacitance retention rate of 80% after 5000 cycles. This research opens up new avenues for studying polyaniline/MOF derivatives (transition metal oxide-carbon) composites.

Buffer spaces in healthcare facilities: strategies for managing and designing strategic areas

Buffer spaces in healthcare facilities: strategies for managing and designing strategic areas

Rational design of Co3S4-CoN@N-doped carbon hollow spheres with polar S-Co-N bond as bifunctional host materials for lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries have drawn much research attention as a contender for next-generation energy conversion systems because of their high capacity density and abundant raw materials. The large volume expansion and the insulating nature of sulfur and polysulfide shuttling issues limit future Li-S battery development. Herein, MOF-derived CoN nanoparticles embedded in an N-doped carbon layer are successfully constructed on the surface of the Co3S4 hollow sphere to form the Co3S4-CoN@NC heterostructure with strong S-Co-N bonds, which act as bifunctional host materials for Li-S batteries and show excellent adsorption and high-efficiency catalysis for lithium polysulfide (LiPSs). The hollow structure pre-stores a buffer space for the volume change of the electrode, limiting polysulfide dissolution. Furthermore, the carbon layer can improve the material's overall structural strength and electrical conductivity. Co3S4-CoN heterostructure with strong S-Co-N bonds can adsorb and accelerate the catalytic conversion of LiPSs. Co3S4-CoN@NC exhibits a high initial specific capacity of 1542.0 mAh g−1 at 0.1 C and a stable capacity of 872.6 mAh g−1 at 0.5 C after 100 cycles with a high Coulombic efficiency of nearly 100 %.

Hierarchical Cross-Domain Satellite Resource Management: An Intelligent Collaboration Perspective

The expansion of satellite applications induces the formation of the multi-domain satellite system (MDSS) containing multiple domains with specific applications such as earth resource remote sensing and the Internet of remote things. Resource management is pivotal in enhancing the scheduling capability of the MDSS. However, this is challenging since the dynamic buffer space and communication opportunity, as well as the uncertain data traffic, exacerbate the difficulty of matching satellite resources with data traffic. Moreover, the coexistence of resource competition and collaboration across domains aggravates the dilemma of cross-domain collaboration. In this paper, we propose a hierarchical cross-domain collaborative resource management framework that can flexibly allocate the mission data through local intra-domain and global cross-domain scheduling. Then, to match the uncertain demands of missions with dynamic and limited resources, we propose a multi-agent reinforcement learning-based resource management method to guide collaboration for multi-satellite data carry-forward in a domain. Further, considering resource competition and collaboration in MDSS, we propose a domain-satellite nested matching game data scheduling algorithm to achieve pair-wise stable collaboration of cross-domain satellites. The simulation results indicate that the proposed algorithm improves the amount of offloaded data by 64.4% and 12.7% compared to the non-collaborative and the non-cross-domain schemes, respectively.

An innovative destressing technology and key parameters determination in both sides of a deep roadway

The general or single supporting theory and technology of the shallow surrounding rock of the roadway are not suitable for solving the problem of continuous large deformation of the both sides under the continuous migration of coal mass in the deep domain of the roadway side. Furthermore, the general destressing technology of dense drilling in the roadway destroys the shallow anchorage domain while releasing the stress. Therefore, this study proposes the “shallow supporting and deep destressing” synergism technology. This technology provides puissant supporting in the shallow domain of roadway sides, and at the same time, large destressing holes are excavated at the coal mass migration channel in deep stress peak domain far from the anchorage domain, conducting destressing regulation of roadway sides. This technology can shift stress peak domain of the roadway side to solid coal side of destressing hole without destroying the shallow anchorage domain, and at the same time, provide a buffer space for that coal mass in the deep domain of the roadway side continuously migrates to the anchorage surrounding rock, creating a beneficial stress circumstances for the roadway stability. The “shallow supporting and deep destressing” synergism technology can solve the contradiction between the shallow surrounding rock supporting and the continuous migration of coal mass in deep domain. The field application results show that the innovative destressing technology can effectively solve the problem of surrounding rock control in deep roadway.

The construction of scale-like Fe7S8/C composite nanotubes and their electrochemical properties

Iron sulfides is promising anode material for lithium-ion battery. However, the shortcomings of low electronic conductivity and severe volume expansion effect, restrict their electrochemical performance. Herein, we report an in situ growth strategy for fabricating scale-like Fe7S8/C composite nanotubes. The hierarchical structure of scale-like Fe7S8/C composite nanotubes combine the structural advantages of sheet structure and tubular structure. As lithium-ion battery anodes, the prepared scale-like Fe7S8/C composite nanotubes deliver superior reversible capacity of 688 ​mA ​h ​g−1 even after 500 cycles at a current density of 1 ​A ​g−1. These outstanding electrochemical performances can be attributed to the synthetic effects of the structure. The sheet structure can provide large active area and abundant Li-ion storage sites, and the tubular structure can provide buffer space for the volume expansion effect. Moreover, the combination with carbon improves the electrical conductivity of the material effectively. Therefore, the results show that the scale-like Fe7S8/C composite nanotubes are excellent electrode materials.

A Study on the Influencing Factors of Children-friendly Walking Space Perception in Elementary Schools

In this paper, based on the concept of child-friendly primary school students aged 7-12 years and their parents as the object, selected five typical primary schools in Shenyang as research cases, conducted social questionnaires and interviews, combined with the existing space problems and children's needs characteristics of the primary school walkable space are divided into children safe evacuation section and activity-friendly section. The SP method was used to obtain the perceptual preferences of children and parents in two virtual learning space segments, and the influencing factors of their perceptual preferences were explored. The results showed that green vision rate, buffer space type, and walking space width were the key factors affecting children's sense of security in the safe evacuation area, and green vision rate had no significant effect on parents' preference choice. In the child-friendly section, color vision, building line rate, building transparency along the street floor, and play space Settings have positive effects on children's comfort, while the interface aspect ratio has no obvious effect on children's comfort.