Electrochemical carbon dioxide reduction reaction(CO_(2)RR)provides a promising way to convert CO_(2)to chemicals.The multicarbon(C_(2+))products,especially ethylene,are of great interest due to their versatile indust...Electrochemical carbon dioxide reduction reaction(CO_(2)RR)provides a promising way to convert CO_(2)to chemicals.The multicarbon(C_(2+))products,especially ethylene,are of great interest due to their versatile industrial applications.However,selectively reducing CO_(2)to ethylene is still challenging as the additional energy required for the C–C coupling step results in large overpotential and many competing products.Nonetheless,mechanistic understanding of the key steps and preferred reaction pathways/conditions,as well as rational design of novel catalysts for ethylene production have been regarded as promising approaches to achieving the highly efficient and selective CO_(2)RR.In this review,we first illustrate the key steps for CO_(2)RR to ethylene(e.g.,CO_(2)adsorption/activation,formation of~*CO intermediate,C–C coupling step),offering mechanistic understanding of CO_(2)RR conversion to ethylene.Then the alternative reaction pathways and conditions for the formation of ethylene and competitive products(C_1 and other C_(2+)products)are investigated,guiding the further design and development of preferred conditions for ethylene generation.Engineering strategies of Cu-based catalysts for CO_(2)RR-ethylene are further summarized,and the correlations of reaction mechanism/pathways,engineering strategies and selectivity are elaborated.Finally,major challenges and perspectives in the research area of CO_(2)RR are proposed for future development and practical applications.展开更多
This paper presents a method for designing a class of countermeasures for DPA attacks based on attenuation of current variations. In this class of countermeasures, designers aim at decreasing the dynamic current varia...This paper presents a method for designing a class of countermeasures for DPA attacks based on attenuation of current variations. In this class of countermeasures, designers aim at decreasing the dynamic current variations to reduce the information that can be extracted from the current consumption of secure microsystems. The proposed method is based on a novel formula that calculates the number of current traces required for a successful DPA attack using the characteristics of the microsystem current signal and the external noise of the measurement setup. The different stages of the proposed method are illustrated through designing an example current flattening circuit. Meanwhile validity and applicability of the proposed formula is verified by comparing theoretical results with those obtained experimentally for the example circuit. The proposed formula not only estimates the required level of attenuation for a target level of robustness defined by design requirements, it also predicts the effectiveness of a countermeasure using simulation results therefore dramatically reducing the time to design of secure microsystems.展开更多
1.Introduction In recent years,there has been an intense research effort by the international community in the field of“artificial”electromagnetic materials,or“metamaterials.”Metamaterials are engineered structure...1.Introduction In recent years,there has been an intense research effort by the international community in the field of“artificial”electromagnetic materials,or“metamaterials.”Metamaterials are engineered structures that induce a tailored arrangement of magnetic and electric dipole moments when excited by an incident electromagnetic field.Under certain conditions,such as when the comprising unit cells are sub-wavelength,metamaterials can be homogenized and described in terms of macroscopic constitutive parameters such as permeability,permittivity,and refractive index.A summary of the early work on“artificial dielectrics”can be found in Ref.[1].In the over 20-year-old field of metamaterials,the desired macroscopic parameters correspond to extreme properties such as negative permittivity,negative permeability,and a negative refractive index.Perhaps the most recognized metamaterial is that which realizes a negative refractive index,originally demonstrated at microwaves and based on a unit cellmade out of a split-ring resonator and a wire[2].In the engineering community,a transmission-line approach was developed for implementing metamaterials with significant advantages,such as reduced transmission losses and wider operating bandwidths[3,4].展开更多
5G cellular infrastructures are supposed to provide higher data rate and lower latency along with the prospects of other various novel applications. But the signal strength seems to fluctuate unexpectedly due to doppl...5G cellular infrastructures are supposed to provide higher data rate and lower latency along with the prospects of other various novel applications. But the signal strength seems to fluctuate unexpectedly due to doppler shift resulting in negative impacts on downlink performance parameters over the network for high-speed users. One potential solution to overcome this problem can be the concentration of energy to a particular location using multiple antennas at the base station so that receiving power can be increased for the intended user while suppressing interferences from others. So, this paper has investigated the performance of beamforming with closed loop spatial multiplexing over a specific range of velocity of users. However, the simulation results also demonstrate that by scaling the number of transmitting antennas, beamforming can elevate average throughput, improve quality of service for cell edge users and ensure better spectral efficiency under any existing scheduler with no complexities involved in system designing. Moreover, through the estimations of the channel conditions obtained from the precoding matrix of closed loop spatial multiplexing, the strength of the transmitted signal can be amplified accordingly to improve mean throughput and minimize the bit error rate. Therefore, the proposed scheme of scaling transmitting antennas through CLSM along with beamforming seems to circumvent the repercussions of doppler shift on downlink (DL) performance of high velocity cellular users.展开更多
With the rapid developments of artificial intelligence(AI)and deep learning(DL)techniques,it is critical to ensure the security and robustness of the deployed algorithms.Recently,the security vulnerability of DL algor...With the rapid developments of artificial intelligence(AI)and deep learning(DL)techniques,it is critical to ensure the security and robustness of the deployed algorithms.Recently,the security vulnerability of DL algorithms to adversarial samples has been widely recognized.The fabricated samples can lead to various misbehaviors of the DL models while being perceived as benign by humans.Successful implementations of adversarial attacks in real physical-world scenarios further demonstrate their practicality.Hence,adversarial attack and defense techniques have attracted increasing attention from both machine learning and security communities and have become a hot research topic in recent years.In this paper,we first introduce the theoretical foundations,algorithms,and applications of adversarial attack techniques.We then describe a few research efforts on the defense techniques,which cover the broad frontier in the field.Several open problems and challenges are subsequently discussed,which we hope will provoke further research efforts in this critical area.展开更多
The Microchip Imaging Cytometer(MIC)is a class of integrated point-of-care detection systems based on the combination of optical microscopy and flow cytometry.MIC devices have the attributes of portability,cost-effect...The Microchip Imaging Cytometer(MIC)is a class of integrated point-of-care detection systems based on the combination of optical microscopy and flow cytometry.MIC devices have the attributes of portability,cost-effectiveness,and adaptability while providing quantitative measurements to meet the needs of laboratory testing in a variety of healthcare settings.Based on the use of microfluidic chips,MIC requires less sample and can complete sample preparation automatically.Therefore,they can provide quantitative testing results simply using a finger prick specimen.The decreased reagent consumption and reduced form factor also help improve the accessibility and affordability of healthcare services in remote and resource-limited settings.In this article,we review recent developments of the Microchip Imaging Cytometer from the following aspects:clinical applications,microfluidic chip integration,imaging optics,and image acquisition.Following,we provide an outlook of the field and remark on promising technologies that may enable significant progress in the near future.展开更多
The discovery of metal-nitrogen centers as the active sites for electrolysis has aroused significant interest in utilizing single-atom catalysts for nitrogen reduction reaction(NRR).Properly designed nanostructured ca...The discovery of metal-nitrogen centers as the active sites for electrolysis has aroused significant interest in utilizing single-atom catalysts for nitrogen reduction reaction(NRR).Properly designed nanostructured catalysts that strongly interact with nitrogen molecules(N_(2))can promote adsorption and activation,thereby resulting in efficient catalysts with high stability,activity,and selectivity.In this study,using density functional theory calculations,we selected monolayer black phosphorus(BP)as the substrate and screened a series of single-atom transition metals confined in tri-coordinated and tetra-coordinated active centers(without and with N dopants)to electro-catalyze NRR.As a result,we have identified two promising candidates(Hf_(1)-N_(1)P_(2)-1 and Tc_(1)-N_(4)),which exhibit not only low overpotentials of 0.56 and 0.49 V but also high thermodynamic and electrochemical stability,as well as good selectivity towards NRR over the competing hydrogen evolution reaction.We also demonstrate the ability of Hf_(1)-N_(1)P_(2)-1 and Tc_(1)-N_(4) to activate and hydrogenate N_(2) by donating electrons and regulating charge transfer.This study not only predicts new BP-based promising catalysts but also provides guidance for the rational design of high-performance NRR electrocatalysts under ambient conditions.展开更多
In response to thermal runaway(TR)of electric vehicles,recent attention has been focused on mitigation strategies such as efficient heat dredging in battery thermal management.Thermal management with particular focus ...In response to thermal runaway(TR)of electric vehicles,recent attention has been focused on mitigation strategies such as efficient heat dredging in battery thermal management.Thermal management with particular focus on battery cooling has been becoming increasingly significant.TR usually happened when an electric vehicle is unpowered and charged.In this state,traditional active battery cooling schemes are disabled,which can easily lead to dangerous incidents due to loss of cooling ability,and advanced passive cooling strategies are therefore gaining importance.Herein,we developed an enhanced thermal radiation material,consisting of~1μm thick multilayered nano-sheet graphene film coated upon the heat dissipation surface,thereby enhancing thermal radiation in the nanoscale.The surface was characterized on the nanoscale,and tested in a battery-cooling scenario.We found that the graphene-based coating's spectral emissivity is between 91% and 95% in the mid-infrared region,and thermal experiments consequently illustrated that graphene-based radiative cooling yielded up to15.1% temperature reduction when compared to the uncoated analogue.Using the novel graphene surface to augment a heat pipe,the temperature reduction can be further enlarged to 25.6%.The new material may contribute to transportation safety,global warming mitigation and carbon neutralization.展开更多
The essence of the peer-to-peer design philosophy is to design protocols for end hosts, or ＂peers＂, to work in collaboration to achieve a certain design objective, such as the sharing of a large file. From a theoret...The essence of the peer-to-peer design philosophy is to design protocols for end hosts, or ＂peers＂, to work in collaboration to achieve a certain design objective, such as the sharing of a large file. From a theoretical perspective, it has been recognized that the peer-to-peer design paradigm resembles gossip protocols, and with appropriate algorithmic design, it maximizes the network flow rates in multicast sessions. Over the past ten years, research on peer-to-peer computing and systems, a unique and intriguing category of distributed systems, has received a tremendous amount of research attention from academia and indus-try alike. Peer-to-peer computing eventually culminated in a number of successful commercial systems, showing the viability of their design philosophy in the Internet. The peer-to-peer design paradigm has pushed all design choices of innovative protocols to the edge of the Internet, and in most cases to end hosts themselves. It represents one of the best incarnation of the end-to-end argument, one of the frequently dis-puted design philosophies that guided the design of the Internet. Yet, research on peer-to-peer computing has recently receded from the spotlight, and suffered from a precipitous fall that was as dramatic as its me-teoric rise to the culmination of its popularity. This article presents a cursory glimpse of existing results over the past ten years in peer-to-peer computing, with a particular focus on understanding what has stimulated its rise in popularity, what has contributed to its commercial success, and eventually, what has led to its pre-cipitous fall in research attention. Our insights in this article may be beneficial when we develop our thoughts on the design paradigm of cloud computing.展开更多
In transfusion medicine,there has been a decades-long debate about whether the age of stored red blood cells(RBCs)is a factor in transfusion efficacy.Existing clinical studies investigating whether older RBCs cause wo...In transfusion medicine,there has been a decades-long debate about whether the age of stored red blood cells(RBCs)is a factor in transfusion efficacy.Existing clinical studies investigating whether older RBCs cause worse clinical outcomes have provided conflicting information:some have shown that older blood is less effective,while others have shown no such difference.The controversial results could have been biased by the vastly different conditions of the patients involved in the clinical studies;however,another source of inconsistency is a lack of understanding of how well and quickly stored RBCs can recover their key parameters,such as stiffness and ATP concentration,after transfusion.In this work,we quantitatively studied the stiffness and ATP recovery of stored RBCs in 37℃ human serum.The results showed that in 37℃ human serum,stored RBCs are able to recover their stiffness and ATP concentration to varying extents depending on how long they have been stored.Fresher RBCs(1–3 weeks old)were found to have a significantly higher capacity for stiffness and ATP recovery in human serum than older RBCs(4–6 weeks old).For instance,for 1-week-old RBCs,although the shear modulus before recovery was 1.6 times that of fresh RBCs,97%of the cells recovered in human serum to have 1.1 times the shear modulus of fresh RBCs,and the ATP concentration of 1-week-old RBCs after recovery showed no difference from that of fresh RBCs.However,for 6-week-old RBCs,only~70%of the RBCs showed stiffness recovery in human serum;their shear modulus after recovery was still 2.1 times that of fresh RBCs;and their ATP concentration after recovery was 25%lower than that of fresh RBCs.Our experiments also revealed that the processes of stiffness recovery and ATP recovery took place on the scale of tens of minutes.We hope that this study will trigger the next steps of comprehensively characterizing the recovery behaviors of stored RBCs(e.g.,recovery of normal 2,3-DPG[2,3-Diphosphoglycerate]and SNO[S-nitrosation]levels)and quantifying the in vivo recovery of stored RBCs in transfusion medicine.展开更多
In the context of edge computing environments in general and the metaverse in particular,federated learning(FL)has emerged as a distributed machine learning paradigm that allows multiple users to collaborate on traini...In the context of edge computing environments in general and the metaverse in particular,federated learning(FL)has emerged as a distributed machine learning paradigm that allows multiple users to collaborate on training a shared machine learning model locally,eliminating the need for uploading raw data to a central server.It is perhaps the only training paradigm that preserves the privacy of user data,which is essential for computing environments as personal as the metaverse.However,the original FL architecture proposed is not scalable to a large number of user devices in the metaverse community.To mitigate this problem,hierarchical federated learning(HFL)has been introduced as a general distributed learning paradigm,inspiring a number of research works.In this paper,we present several types of HFL architectures,with a special focus on the three-layer client-edge-cloud HFL architecture,which is most pertinent to the metaverse due to its delay-sensitive nature.We also examine works that take advantage of the natural layered organization of three-layer client-edge-cloud HFL to tackle some of the most challenging problems in FL within the metaverse.Finally,we outline some future research directions of HFL in the metaverse.展开更多
In the originally published version of this article1,references 83-92 were inadvertently included in the reference list due to a glitch in the LaTeX template used.These references have been removed from the corrected ...In the originally published version of this article1,references 83-92 were inadvertently included in the reference list due to a glitch in the LaTeX template used.These references have been removed from the corrected version of the article.展开更多
The index of refraction plays a decisive role in the design and classification of optical materials and devices;therefore,its proper and accurate determination is essential.In most refractive index(RI)sensing schemes,...The index of refraction plays a decisive role in the design and classification of optical materials and devices;therefore,its proper and accurate determination is essential.In most refractive index(RI)sensing schemes,however,there is a trade-off between providing high-resolution measurements and covering a wide range of RIs.We propose and experimentally demonstrate a novel mechanism for sensing the index of refraction of a medium by utilizing the orbital angular momentum(OAM)of structured light.Using a superposition of co-propagating monochromatic higher-order Bessel beams with equally spaced longitudinal wavenumbers,in a comb-like setting,we generate non-diffracting rotating light structures in which the orientation of the beam’s intensity profile is sensitive to the RI of the medium(here,a fluid).In principle,the sensitivity of this scheme can exceed~2700°/RI unit(RIU)with a resolution of~105 RIU.Furthermore,we show how the unbounded degrees of freedom associated with OAM can be deployed to offer a wide dynamic range by generating structured light that evolves into different patterns based on the change in RI.The rotating light structures are generated by a programmable spatial light modulator.This provides dynamic control over the sensitivity,which can be tuned to perform coarse or fine measurements of the RI in real time.This,in turn,allows high sensitivity and resolution to be achieved simultaneously over a very wide dynamic range,which is a typical tradeoff in all RI sensing schemes.We thus envision that this method will open new directions in refractometry and remote sensing.展开更多
The higher risk of vaso-occlusion events and sudden death for sickle-cell trait(SCT)athletes has been speculatively ascribed to SCT red blood cell(RBC)stiffening during strenuous exercise.However,the microenvironmenta...The higher risk of vaso-occlusion events and sudden death for sickle-cell trait(SCT)athletes has been speculatively ascribed to SCT red blood cell(RBC)stiffening during strenuous exercise.However,the microenvironmental changes that could induce the stiffening of SCT RBCs are unknown.To address this question,we measured the mechanical properties of and changes in SCT RBCs under deoxygenated and acidic environments,which are two typical conditions present in the circulation of athletes undertaking strenuous exercise.The results reveal that SCT RBCs are inherently stiffer than RBCs from non-SCT healthy subjects,and a lower pH further stiffens the SCT cells.Furthermore,at both normal and low pH levels,deoxygenation was found to not be the cause of the stiffness of SCT RBCs.This study confirms that the stiffening of SCT RBCs occurs at a low pH and implies that SCT RBC stiffening could be responsible for vaso-occlusion in SCT athletes during strenuous exercise.展开更多
Machine learning models of material properties accelerate materials discovery,reproducing density functional theory calculated results at a fraction of the cost1–6.To bridge the gap between theory and experiments,mac...Machine learning models of material properties accelerate materials discovery,reproducing density functional theory calculated results at a fraction of the cost1–6.To bridge the gap between theory and experiments,machine learning predictions need to be distilled in the form of interpretable chemical rules that can be used by experimentalists.Here we develop a framework to address this gap by combining evolutionary algorithm-powered search with machine-learning surrogate models.We then couple the search results with supervised learning and statistical testing.This strategy enables the efficient search of a materials space while providing interpretable design rules.We demonstrate its effectiveness by developing rules for the design of direct bandgap materials,stable UV emitters,and IR perovskite emitters.Finally,we conclusively show how DARWIN-generated rules are statistically more robust and applicable to a wide range of applications including the design of UV halide perovskites.展开更多
Focusing incident power into an area of high concentration is of significant interest for various applications.In optics,this has been traditionally achieved with lenses where a higher curvature and lens permittivity ...Focusing incident power into an area of high concentration is of significant interest for various applications.In optics,this has been traditionally achieved with lenses where a higher curvature and lens permittivity typically result in shorter focal distances(low f/D).In this work,we present designs and techniques for collecting,refracting and guiding incident light into an area of high power concentration(a hot spot)at extremely short distances.Specifically,a flat low-profile focusing mechanism is presented using a hetero-junction of anisotropic metamaterials(MTMs).The hetero-junction is formed from two cleaved finite slabs of low(near zero)permittivity anisotropic MTMs with rotated optical axes.The MTMs have near zero longitudinal permittivity while matched in the transverse direction.Such MTMs are shown to provide a unique ability to bend the transverse magnetic or p-polarized light away from the normal and along the interface,contrary to conventional dielectrics,and with minimal reflections;hence allowing for a low profile design.Realizations in the optical regime are presented using periodic bilayers of metal and dielectric.The proposed hetero-junction focusing device concentrates the normally incident plane wave and/or beam into a corresponding focal region similar to a lens via multiple refractions.The hetero-junction is capable of creating a hot spot very close to the device,much closer than dielectric lenses and it significantly outperforms the size requirements of thick high curvature lenses with low f/D ratios.The proposed designs can find applications in various scenarios including solar and thermo photovoltaics,photodetectors,concentrated photovoltaics,non-imaging optics,micro-and nano-Fresnel lenses.展开更多
Software-Defined Networking （SDN） has emerged as a promising direction for next-generation network design. Due to its clean-slate and highly flexible design, it is believed to be the foundational principle for desig...Software-Defined Networking （SDN） has emerged as a promising direction for next-generation network design. Due to its clean-slate and highly flexible design, it is believed to be the foundational principle for designing network architectures and improving their flexibility, resilience, reliability, and security. As the technology matures, research in both industry and academia has designed a considerable number of tools to scale software-defined networks, in preparation for the wide deployment in wide-area networks. In this paper, we survey the mechanisms that can be used to address the scalability issues in software-defined wide-area networks. Starting from a successful distributed system, the Domain Name System, we discuss the essential elements to make a large scale network infrastructure scalable. Then, the existing technologies proposed in the literature are reviewed in three categories： scaling out/up the data plane and scaling the control plane. We conclude with possible research directions towards scaling software-defined wide-area networks.展开更多
In transfusion medicine,the deformability of stored red blood cells(RBCs)changes during storage in blood banks.Compromised RBC deformability can reduce the transfusion efficiency or intensify transfusion complications...In transfusion medicine,the deformability of stored red blood cells(RBCs)changes during storage in blood banks.Compromised RBC deformability can reduce the transfusion efficiency or intensify transfusion complications,such as sepsis.This paper reports the microfluidic mechanical measurement of stored RBCs under the physiological deformation mode(that is,folding).Instead of using phenomenological metrics of deformation or elongation indices(DI or EI),the effective stiffness of RBCs,a flow velocityindependent parameter,is defined and used for the first time to evaluate the mechanical degradation of RBCs during storage.Fresh RBCs and RBCs stored up to 6 weeks(42 days)in the blood bank were measured,revealing that the effective stiffness of RBCs increases over the storage process.RBCs stored for 1 week started to show significantly higher stiffness than fresh RBCs,and stored RBC stiffness degraded faster during the last 3 weeks than during the first 3 weeks.Furthermore,the results indicate that the time points of the effective stiffness increase coincide well with the degradation patterns of S-nitrosothiols(SNO)and adenosine triphosphate(ATP)in RBC storage lesions.展开更多
Emerging heart-on-a-chip platforms are promising approaches to establish cardiac cell/tissue models in vitro for research on cardiac physiology,disease modeling and drug cardiotoxicity as well as for therapeutic disco...Emerging heart-on-a-chip platforms are promising approaches to establish cardiac cell/tissue models in vitro for research on cardiac physiology,disease modeling and drug cardiotoxicity as well as for therapeutic discovery.Challenges still exist in obtaining the complete capability of in situ sensing to fully evaluate the complex functional properties of cardiac cell/tissue models.Changes to contractile strength(contractility)and beating regularity(rhythm)are particularly important to generate accurate,predictive models.Developing new platforms and technologies to assess the contractile functions of in vitro cardiac models is essential to provide information on cell/tissue physiologies,drug-induced inotropic responses,and the mechanisms of cardiac diseases.In this review,we discuss recent advances in biosensing platforms for the measurement of contractile functions of in vitro cardiac models,including single cardiomyocytes,2D monolayers of cardiomyocytes,and 3D cardiac tissues.The characteristics and performance of current platforms are reviewed in terms of sensing principles,measured parameters,performance,cell sources,cell/tissue model configurations,advantages,and limitations.In addition,we highlight applications of these platforms and relevant discoveries in fundamental investigations,drug testing,and disease modeling.Furthermore,challenges and future outlooks of heart-on-a-chip platforms for in vitro measurement of cardiac functional properties are discussed.展开更多
In order to handle undesirable failures of a multicopter,which occurs in either the pre-flight process or the in-flight process,a failsafe mechanism design method based on supervisory control theory(SCT)is proposed fo...In order to handle undesirable failures of a multicopter,which occurs in either the pre-flight process or the in-flight process,a failsafe mechanism design method based on supervisory control theory(SCT)is proposed for the semi-autonomous control mode.The failsafe mechanism is a control logic that guides what subsequent actions the multicopter should take,by taking account of real-time information from guidance,attitude control,diagnosis and other low-level subsystems.In order to design a failsafe mechanism for the multicopters,safety issues of the multicopters are introduced.Then,user requirements including functional requirements and safety requirements are textually described,where functional requirements guide the modelling of a general multicopter plant,and safety requirements cover the failsafe measures dealing with the presented safety issues.Based on these requirements,several multicopter modes and events are defined.On this basis,the multicopter plant and control specifications are modelled by automata.Then,a supervisor is synthesized by using SCT.In addition,the authors present three examples to demonstrate the potential conflicting phenomena due to the inappropriate design of control specifications.Finally,based on the obtained supervisor,an implementation method suitable for multicopters is presented,in which the supervisor is transformed into decision-making codes.展开更多
基金financially supported via Australian Research Council(FT180100705)the support by the National Natural Science Foundation of China(22209103)+3 种基金the support from UTS Chancellor's Research Fellowshipsthe support from Open Project of State Key Laboratory of Advanced Special Steel,the Shanghai Key Laboratory of Advanced Ferrometallurgy,Shanghai University(SKLASS 2021-**)Joint International Laboratory on Environmental and Energy Frontier MaterialsInnovation Research Team of High-Level Local Universities in Shanghai。
文摘Electrochemical carbon dioxide reduction reaction(CO_(2)RR)provides a promising way to convert CO_(2)to chemicals.The multicarbon(C_(2+))products,especially ethylene,are of great interest due to their versatile industrial applications.However,selectively reducing CO_(2)to ethylene is still challenging as the additional energy required for the C–C coupling step results in large overpotential and many competing products.Nonetheless,mechanistic understanding of the key steps and preferred reaction pathways/conditions,as well as rational design of novel catalysts for ethylene production have been regarded as promising approaches to achieving the highly efficient and selective CO_(2)RR.In this review,we first illustrate the key steps for CO_(2)RR to ethylene(e.g.,CO_(2)adsorption/activation,formation of~*CO intermediate,C–C coupling step),offering mechanistic understanding of CO_(2)RR conversion to ethylene.Then the alternative reaction pathways and conditions for the formation of ethylene and competitive products(C_1 and other C_(2+)products)are investigated,guiding the further design and development of preferred conditions for ethylene generation.Engineering strategies of Cu-based catalysts for CO_(2)RR-ethylene are further summarized,and the correlations of reaction mechanism/pathways,engineering strategies and selectivity are elaborated.Finally,major challenges and perspectives in the research area of CO_(2)RR are proposed for future development and practical applications.
文摘This paper presents a method for designing a class of countermeasures for DPA attacks based on attenuation of current variations. In this class of countermeasures, designers aim at decreasing the dynamic current variations to reduce the information that can be extracted from the current consumption of secure microsystems. The proposed method is based on a novel formula that calculates the number of current traces required for a successful DPA attack using the characteristics of the microsystem current signal and the external noise of the measurement setup. The different stages of the proposed method are illustrated through designing an example current flattening circuit. Meanwhile validity and applicability of the proposed formula is verified by comparing theoretical results with those obtained experimentally for the example circuit. The proposed formula not only estimates the required level of attenuation for a target level of robustness defined by design requirements, it also predicts the effectiveness of a countermeasure using simulation results therefore dramatically reducing the time to design of secure microsystems.
文摘1.Introduction In recent years,there has been an intense research effort by the international community in the field of“artificial”electromagnetic materials,or“metamaterials.”Metamaterials are engineered structures that induce a tailored arrangement of magnetic and electric dipole moments when excited by an incident electromagnetic field.Under certain conditions,such as when the comprising unit cells are sub-wavelength,metamaterials can be homogenized and described in terms of macroscopic constitutive parameters such as permeability,permittivity,and refractive index.A summary of the early work on“artificial dielectrics”can be found in Ref.[1].In the over 20-year-old field of metamaterials,the desired macroscopic parameters correspond to extreme properties such as negative permittivity,negative permeability,and a negative refractive index.Perhaps the most recognized metamaterial is that which realizes a negative refractive index,originally demonstrated at microwaves and based on a unit cellmade out of a split-ring resonator and a wire[2].In the engineering community,a transmission-line approach was developed for implementing metamaterials with significant advantages,such as reduced transmission losses and wider operating bandwidths[3,4].
文摘5G cellular infrastructures are supposed to provide higher data rate and lower latency along with the prospects of other various novel applications. But the signal strength seems to fluctuate unexpectedly due to doppler shift resulting in negative impacts on downlink performance parameters over the network for high-speed users. One potential solution to overcome this problem can be the concentration of energy to a particular location using multiple antennas at the base station so that receiving power can be increased for the intended user while suppressing interferences from others. So, this paper has investigated the performance of beamforming with closed loop spatial multiplexing over a specific range of velocity of users. However, the simulation results also demonstrate that by scaling the number of transmitting antennas, beamforming can elevate average throughput, improve quality of service for cell edge users and ensure better spectral efficiency under any existing scheduler with no complexities involved in system designing. Moreover, through the estimations of the channel conditions obtained from the precoding matrix of closed loop spatial multiplexing, the strength of the transmitted signal can be amplified accordingly to improve mean throughput and minimize the bit error rate. Therefore, the proposed scheme of scaling transmitting antennas through CLSM along with beamforming seems to circumvent the repercussions of doppler shift on downlink (DL) performance of high velocity cellular users.
基金Ant Financial,Zhejiang University Financial Technology Research Center.
文摘With the rapid developments of artificial intelligence(AI)and deep learning(DL)techniques,it is critical to ensure the security and robustness of the deployed algorithms.Recently,the security vulnerability of DL algorithms to adversarial samples has been widely recognized.The fabricated samples can lead to various misbehaviors of the DL models while being perceived as benign by humans.Successful implementations of adversarial attacks in real physical-world scenarios further demonstrate their practicality.Hence,adversarial attack and defense techniques have attracted increasing attention from both machine learning and security communities and have become a hot research topic in recent years.In this paper,we first introduce the theoretical foundations,algorithms,and applications of adversarial attack techniques.We then describe a few research efforts on the defense techniques,which cover the broad frontier in the field.Several open problems and challenges are subsequently discussed,which we hope will provoke further research efforts in this critical area.
基金Natural Sciences and Engineering Research Council of Canada (NSERC)Ontario Research Fund (ORF)the India-Canada Centre for Innovative Multidisciplinary Partnerships to Accelerate Community Transformation and Sustainability (IC-IM-PACTS)
文摘The Microchip Imaging Cytometer(MIC)is a class of integrated point-of-care detection systems based on the combination of optical microscopy and flow cytometry.MIC devices have the attributes of portability,cost-effectiveness,and adaptability while providing quantitative measurements to meet the needs of laboratory testing in a variety of healthcare settings.Based on the use of microfluidic chips,MIC requires less sample and can complete sample preparation automatically.Therefore,they can provide quantitative testing results simply using a finger prick specimen.The decreased reagent consumption and reduced form factor also help improve the accessibility and affordability of healthcare services in remote and resource-limited settings.In this article,we review recent developments of the Microchip Imaging Cytometer from the following aspects:clinical applications,microfluidic chip integration,imaging optics,and image acquisition.Following,we provide an outlook of the field and remark on promising technologies that may enable significant progress in the near future.
基金support from the National Natural Science Foundation of China(No.11404230)the Foundation of Science and Technology Bureau of Sichuan Province(No.2013JY0085).
文摘The discovery of metal-nitrogen centers as the active sites for electrolysis has aroused significant interest in utilizing single-atom catalysts for nitrogen reduction reaction(NRR).Properly designed nanostructured catalysts that strongly interact with nitrogen molecules(N_(2))can promote adsorption and activation,thereby resulting in efficient catalysts with high stability,activity,and selectivity.In this study,using density functional theory calculations,we selected monolayer black phosphorus(BP)as the substrate and screened a series of single-atom transition metals confined in tri-coordinated and tetra-coordinated active centers(without and with N dopants)to electro-catalyze NRR.As a result,we have identified two promising candidates(Hf_(1)-N_(1)P_(2)-1 and Tc_(1)-N_(4)),which exhibit not only low overpotentials of 0.56 and 0.49 V but also high thermodynamic and electrochemical stability,as well as good selectivity towards NRR over the competing hydrogen evolution reaction.We also demonstrate the ability of Hf_(1)-N_(1)P_(2)-1 and Tc_(1)-N_(4) to activate and hydrogenate N_(2) by donating electrons and regulating charge transfer.This study not only predicts new BP-based promising catalysts but also provides guidance for the rational design of high-performance NRR electrocatalysts under ambient conditions.
基金supported by the National Natural Science Foundation of China(no.52106114)Beijing Natural Science Foundation(no.3234061)Hong Kong Scholars Program(no.XJ2022027)。
文摘In response to thermal runaway(TR)of electric vehicles,recent attention has been focused on mitigation strategies such as efficient heat dredging in battery thermal management.Thermal management with particular focus on battery cooling has been becoming increasingly significant.TR usually happened when an electric vehicle is unpowered and charged.In this state,traditional active battery cooling schemes are disabled,which can easily lead to dangerous incidents due to loss of cooling ability,and advanced passive cooling strategies are therefore gaining importance.Herein,we developed an enhanced thermal radiation material,consisting of~1μm thick multilayered nano-sheet graphene film coated upon the heat dissipation surface,thereby enhancing thermal radiation in the nanoscale.The surface was characterized on the nanoscale,and tested in a battery-cooling scenario.We found that the graphene-based coating's spectral emissivity is between 91% and 95% in the mid-infrared region,and thermal experiments consequently illustrated that graphene-based radiative cooling yielded up to15.1% temperature reduction when compared to the uncoated analogue.Using the novel graphene surface to augment a heat pipe,the temperature reduction can be further enlarged to 25.6%.The new material may contribute to transportation safety,global warming mitigation and carbon neutralization.
文摘The essence of the peer-to-peer design philosophy is to design protocols for end hosts, or ＂peers＂, to work in collaboration to achieve a certain design objective, such as the sharing of a large file. From a theoretical perspective, it has been recognized that the peer-to-peer design paradigm resembles gossip protocols, and with appropriate algorithmic design, it maximizes the network flow rates in multicast sessions. Over the past ten years, research on peer-to-peer computing and systems, a unique and intriguing category of distributed systems, has received a tremendous amount of research attention from academia and indus-try alike. Peer-to-peer computing eventually culminated in a number of successful commercial systems, showing the viability of their design philosophy in the Internet. The peer-to-peer design paradigm has pushed all design choices of innovative protocols to the edge of the Internet, and in most cases to end hosts themselves. It represents one of the best incarnation of the end-to-end argument, one of the frequently dis-puted design philosophies that guided the design of the Internet. Yet, research on peer-to-peer computing has recently receded from the spotlight, and suffered from a precipitous fall that was as dramatic as its me-teoric rise to the culmination of its popularity. This article presents a cursory glimpse of existing results over the past ten years in peer-to-peer computing, with a particular focus on understanding what has stimulated its rise in popularity, what has contributed to its commercial success, and eventually, what has led to its pre-cipitous fall in research attention. Our insights in this article may be beneficial when we develop our thoughts on the design paradigm of cloud computing.
基金The authors acknowledge financial support from the Natural Sciences and Engineering Research Council of Canada(NSERC)the Canada Research Chairs Program,and the Ontario Research Funds–Research Excellence Program.
文摘In transfusion medicine,there has been a decades-long debate about whether the age of stored red blood cells(RBCs)is a factor in transfusion efficacy.Existing clinical studies investigating whether older RBCs cause worse clinical outcomes have provided conflicting information:some have shown that older blood is less effective,while others have shown no such difference.The controversial results could have been biased by the vastly different conditions of the patients involved in the clinical studies;however,another source of inconsistency is a lack of understanding of how well and quickly stored RBCs can recover their key parameters,such as stiffness and ATP concentration,after transfusion.In this work,we quantitatively studied the stiffness and ATP recovery of stored RBCs in 37℃ human serum.The results showed that in 37℃ human serum,stored RBCs are able to recover their stiffness and ATP concentration to varying extents depending on how long they have been stored.Fresher RBCs(1–3 weeks old)were found to have a significantly higher capacity for stiffness and ATP recovery in human serum than older RBCs(4–6 weeks old).For instance,for 1-week-old RBCs,although the shear modulus before recovery was 1.6 times that of fresh RBCs,97%of the cells recovered in human serum to have 1.1 times the shear modulus of fresh RBCs,and the ATP concentration of 1-week-old RBCs after recovery showed no difference from that of fresh RBCs.However,for 6-week-old RBCs,only~70%of the RBCs showed stiffness recovery in human serum;their shear modulus after recovery was still 2.1 times that of fresh RBCs;and their ATP concentration after recovery was 25%lower than that of fresh RBCs.Our experiments also revealed that the processes of stiffness recovery and ATP recovery took place on the scale of tens of minutes.We hope that this study will trigger the next steps of comprehensively characterizing the recovery behaviors of stored RBCs(e.g.,recovery of normal 2,3-DPG[2,3-Diphosphoglycerate]and SNO[S-nitrosation]levels)and quantifying the in vivo recovery of stored RBCs in transfusion medicine.
文摘In the context of edge computing environments in general and the metaverse in particular,federated learning(FL)has emerged as a distributed machine learning paradigm that allows multiple users to collaborate on training a shared machine learning model locally,eliminating the need for uploading raw data to a central server.It is perhaps the only training paradigm that preserves the privacy of user data,which is essential for computing environments as personal as the metaverse.However,the original FL architecture proposed is not scalable to a large number of user devices in the metaverse community.To mitigate this problem,hierarchical federated learning(HFL)has been introduced as a general distributed learning paradigm,inspiring a number of research works.In this paper,we present several types of HFL architectures,with a special focus on the three-layer client-edge-cloud HFL architecture,which is most pertinent to the metaverse due to its delay-sensitive nature.We also examine works that take advantage of the natural layered organization of three-layer client-edge-cloud HFL to tackle some of the most challenging problems in FL within the metaverse.Finally,we outline some future research directions of HFL in the metaverse.
文摘In the originally published version of this article1,references 83-92 were inadvertently included in the reference list due to a glitch in the LaTeX template used.These references have been removed from the corrected version of the article.
基金the support from the Natural Sciences and Engineering Research Council in Canada,the Ontario Graduate Scholarship,FAPESP(Grant No.2015/26444-8)CNPq(Grant No.304718/2016-5).
文摘The index of refraction plays a decisive role in the design and classification of optical materials and devices;therefore,its proper and accurate determination is essential.In most refractive index(RI)sensing schemes,however,there is a trade-off between providing high-resolution measurements and covering a wide range of RIs.We propose and experimentally demonstrate a novel mechanism for sensing the index of refraction of a medium by utilizing the orbital angular momentum(OAM)of structured light.Using a superposition of co-propagating monochromatic higher-order Bessel beams with equally spaced longitudinal wavenumbers,in a comb-like setting,we generate non-diffracting rotating light structures in which the orientation of the beam’s intensity profile is sensitive to the RI of the medium(here,a fluid).In principle,the sensitivity of this scheme can exceed~2700°/RI unit(RIU)with a resolution of~105 RIU.Furthermore,we show how the unbounded degrees of freedom associated with OAM can be deployed to offer a wide dynamic range by generating structured light that evolves into different patterns based on the change in RI.The rotating light structures are generated by a programmable spatial light modulator.This provides dynamic control over the sensitivity,which can be tuned to perform coarse or fine measurements of the RI in real time.This,in turn,allows high sensitivity and resolution to be achieved simultaneously over a very wide dynamic range,which is a typical tradeoff in all RI sensing schemes.We thus envision that this method will open new directions in refractometry and remote sensing.
基金Financial support from the Natural Sciences and Engineering Research Council of Canada(NSERC)through a Steacie Fellowship,from Grand Challenges of Canada,and from the Canada Research Chairs Program is acknowledged.
文摘The higher risk of vaso-occlusion events and sudden death for sickle-cell trait(SCT)athletes has been speculatively ascribed to SCT red blood cell(RBC)stiffening during strenuous exercise.However,the microenvironmental changes that could induce the stiffening of SCT RBCs are unknown.To address this question,we measured the mechanical properties of and changes in SCT RBCs under deoxygenated and acidic environments,which are two typical conditions present in the circulation of athletes undertaking strenuous exercise.The results reveal that SCT RBCs are inherently stiffer than RBCs from non-SCT healthy subjects,and a lower pH further stiffens the SCT cells.Furthermore,at both normal and low pH levels,deoxygenation was found to not be the cause of the stiffness of SCT RBCs.This study confirms that the stiffening of SCT RBCs occurs at a low pH and implies that SCT RBC stiffening could be responsible for vaso-occlusion in SCT athletes during strenuous exercise.
基金This work was supported financially by the US Research Center,A Division of Sony Corporation of America(2018 Sony Research Award Program Ref#2019-0669)the Natural Sciences and Engineering Research Council(NSERC)of Canada.Authors thank Prof.M.Saidaminov from the University of Victoria for fruitful discussions.Computations were performed on the SOSCIP Consortium’s Niagara and MIST computing platforms.SOSCIP is funded by the Federal Economic Development Agency of Southern Ontario,the Province of Ontario,IBM Canada Ltd.,Ontario Centres of Excellence,MITACS,and 15 Ontario academic member institutions.Machine learning models were trained using GPU resources of Northwestern’s QUEST computing cluster.
文摘Machine learning models of material properties accelerate materials discovery,reproducing density functional theory calculated results at a fraction of the cost1–6.To bridge the gap between theory and experiments,machine learning predictions need to be distilled in the form of interpretable chemical rules that can be used by experimentalists.Here we develop a framework to address this gap by combining evolutionary algorithm-powered search with machine-learning surrogate models.We then couple the search results with supervised learning and statistical testing.This strategy enables the efficient search of a materials space while providing interpretable design rules.We demonstrate its effectiveness by developing rules for the design of direct bandgap materials,stable UV emitters,and IR perovskite emitters.Finally,we conclusively show how DARWIN-generated rules are statistically more robust and applicable to a wide range of applications including the design of UV halide perovskites.
基金This work was supported by the Natural Sciences and Engineering Research Council of Canada and by Defence Research and Development Canada.
文摘Focusing incident power into an area of high concentration is of significant interest for various applications.In optics,this has been traditionally achieved with lenses where a higher curvature and lens permittivity typically result in shorter focal distances(low f/D).In this work,we present designs and techniques for collecting,refracting and guiding incident light into an area of high power concentration(a hot spot)at extremely short distances.Specifically,a flat low-profile focusing mechanism is presented using a hetero-junction of anisotropic metamaterials(MTMs).The hetero-junction is formed from two cleaved finite slabs of low(near zero)permittivity anisotropic MTMs with rotated optical axes.The MTMs have near zero longitudinal permittivity while matched in the transverse direction.Such MTMs are shown to provide a unique ability to bend the transverse magnetic or p-polarized light away from the normal and along the interface,contrary to conventional dielectrics,and with minimal reflections;hence allowing for a low profile design.Realizations in the optical regime are presented using periodic bilayers of metal and dielectric.The proposed hetero-junction focusing device concentrates the normally incident plane wave and/or beam into a corresponding focal region similar to a lens via multiple refractions.The hetero-junction is capable of creating a hot spot very close to the device,much closer than dielectric lenses and it significantly outperforms the size requirements of thick high curvature lenses with low f/D ratios.The proposed designs can find applications in various scenarios including solar and thermo photovoltaics,photodetectors,concentrated photovoltaics,non-imaging optics,micro-and nano-Fresnel lenses.
文摘Software-Defined Networking （SDN） has emerged as a promising direction for next-generation network design. Due to its clean-slate and highly flexible design, it is believed to be the foundational principle for designing network architectures and improving their flexibility, resilience, reliability, and security. As the technology matures, research in both industry and academia has designed a considerable number of tools to scale software-defined networks, in preparation for the wide deployment in wide-area networks. In this paper, we survey the mechanisms that can be used to address the scalability issues in software-defined wide-area networks. Starting from a successful distributed system, the Domain Name System, we discuss the essential elements to make a large scale network infrastructure scalable. Then, the existing technologies proposed in the literature are reviewed in three categories： scaling out/up the data plane and scaling the control plane. We conclude with possible research directions towards scaling software-defined wide-area networks.
基金financial support from the Natural Sciences and Engineering Research Council of Canada via an NSERC Steacie Memorial Fellowship and the Canada Research Chairs program.
文摘In transfusion medicine,the deformability of stored red blood cells(RBCs)changes during storage in blood banks.Compromised RBC deformability can reduce the transfusion efficiency or intensify transfusion complications,such as sepsis.This paper reports the microfluidic mechanical measurement of stored RBCs under the physiological deformation mode(that is,folding).Instead of using phenomenological metrics of deformation or elongation indices(DI or EI),the effective stiffness of RBCs,a flow velocityindependent parameter,is defined and used for the first time to evaluate the mechanical degradation of RBCs during storage.Fresh RBCs and RBCs stored up to 6 weeks(42 days)in the blood bank were measured,revealing that the effective stiffness of RBCs increases over the storage process.RBCs stored for 1 week started to show significantly higher stiffness than fresh RBCs,and stored RBC stiffness degraded faster during the last 3 weeks than during the first 3 weeks.Furthermore,the results indicate that the time points of the effective stiffness increase coincide well with the degradation patterns of S-nitrosothiols(SNO)and adenosine triphosphate(ATP)in RBC storage lesions.
基金The authors acknowledge the Canadian Institutes of Health Research(CIHR)and the Natural Sciences and Engineering Research Council of Canada(NSERC)for financial support through a Collaborative Health Research Projects(CHRP)grant.W.K.D.acknowledges the Ted Rogers Centre for Heart Research Education Fund for a fellowshipN.L.acknowledges the National Natural Science Foundation of China(NSFC)for financial support under Grant 61933008。
文摘Emerging heart-on-a-chip platforms are promising approaches to establish cardiac cell/tissue models in vitro for research on cardiac physiology,disease modeling and drug cardiotoxicity as well as for therapeutic discovery.Challenges still exist in obtaining the complete capability of in situ sensing to fully evaluate the complex functional properties of cardiac cell/tissue models.Changes to contractile strength(contractility)and beating regularity(rhythm)are particularly important to generate accurate,predictive models.Developing new platforms and technologies to assess the contractile functions of in vitro cardiac models is essential to provide information on cell/tissue physiologies,drug-induced inotropic responses,and the mechanisms of cardiac diseases.In this review,we discuss recent advances in biosensing platforms for the measurement of contractile functions of in vitro cardiac models,including single cardiomyocytes,2D monolayers of cardiomyocytes,and 3D cardiac tissues.The characteristics and performance of current platforms are reviewed in terms of sensing principles,measured parameters,performance,cell sources,cell/tissue model configurations,advantages,and limitations.In addition,we highlight applications of these platforms and relevant discoveries in fundamental investigations,drug testing,and disease modeling.Furthermore,challenges and future outlooks of heart-on-a-chip platforms for in vitro measurement of cardiac functional properties are discussed.
基金This work was partially supported by the National Natural Science Foundation of China(61973015,61903008)the Beijing Natural Science Foundation(4194074)the Natural Sciences and Engineering Research Council(NSERC)of Canada(Grant#DG_480599).
文摘In order to handle undesirable failures of a multicopter,which occurs in either the pre-flight process or the in-flight process,a failsafe mechanism design method based on supervisory control theory(SCT)is proposed for the semi-autonomous control mode.The failsafe mechanism is a control logic that guides what subsequent actions the multicopter should take,by taking account of real-time information from guidance,attitude control,diagnosis and other low-level subsystems.In order to design a failsafe mechanism for the multicopters,safety issues of the multicopters are introduced.Then,user requirements including functional requirements and safety requirements are textually described,where functional requirements guide the modelling of a general multicopter plant,and safety requirements cover the failsafe measures dealing with the presented safety issues.Based on these requirements,several multicopter modes and events are defined.On this basis,the multicopter plant and control specifications are modelled by automata.Then,a supervisor is synthesized by using SCT.In addition,the authors present three examples to demonstrate the potential conflicting phenomena due to the inappropriate design of control specifications.Finally,based on the obtained supervisor,an implementation method suitable for multicopters is presented,in which the supervisor is transformed into decision-making codes.
