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  • Open Access
    Authors: 
    Fangong Kong; Shoujuan Wang; Weijue Gao; Pedram Fatehi;
    Publisher: Royal Society of Chemistry (RSC)
    Project: NSERC

    Kraft lignin (KL) produced in kraft pulping process has a low molecular weight and solubility, which limits its application in industry. For the first time, KL was polymerized with acrylic acid (AA) in an acidic aqueous suspension system to produce a water soluble lignin–AA polymer with a high molecular weight in this work. The polymerization reaction was carried out using K2S2O8 as an initiator, and the influence of reaction conditions on the carboxylate group content and molecular weight of resultant lignin polymers was systematically investigated. The mechanism of polymerization of KL and AA was discussed fundamentally. The resulting lignin–AA polymer was characterized by Fourier Transform Infrared spectrophotometry (FTIR), proton nuclear magnetic resonance (1H-NMR) and elemental analyses. The results showed that the phenolic hydroxyl group (Ph-OH) content of KL promoted the polymerization under an acidic environment. Under the conditions of 1.5 wt% of initiator, 3.5 of pH, 10.0 of AA/lignin molar ratio, 0.15 mol L−1 of lignin concentration, 3 h and 80 °C, the carboxylate group content and the molecular weight of the polymer were 7.37 mmol g−1 and 7.4 × 105 g mol−1, respectively. The lignin–AA polymer was water soluble at a 10 g L−1 concentration and a pH higher than 4.5. Furthermore, the flocculation performance of lignin–AA polymer in an aluminium oxide suspension was evaluated. Compared with polyAA, the lignin–AA polymer was a more efficient flocculant for aluminium oxide suspension, which shows its potential to be used as a green flocculant in industry.

  • Closed Access
    Authors: 
    Tingting Yu; Yishuai Xu; Yifan Liu; Puren Ouyang; M.M. Gupta; W.J. Zhang; W.J. Zhang;
    Publisher: IEEE

    This paper reports a work on developing a novel charge control circuit for control of the piezoelectric actuator to overcome its hysteresis nonlinearity when the actuator is driven at high voltage (as opposed to low voltage reported in literature). The charge control circuit also includes a balancing resistor. A test-bed for a piezoelectric actuator was established and an experiment was conducted. The result showed that the hysteresis nonlinearity of the piezoelectric actuator was reduced by 82% under the proposed charge control circuit. This charge control circuit can be used for control of piezoelectric inertia-friction actuator, in which the piezoelectric actuator is part of the whole actuator system.

  • Open Access
    Authors: 
    Marc Bohner; Gamal Baroud; Anke Bernstein; Nicola Döbelin; Laetitia Galea; Bernhard Hesse; Roman Heuberger; Sylvain Meille; Pascal Michel; Brigitte von Rechenberg; +2 more
    Publisher: Elsevier BV
    Country: France

    International audience; Although bone formation around and within implants has been intensively studied, the role of pores and pore geometry is still debated. Notwithstanding studies reporting the formation of bone and bone components within pores as small as a few micrometers ('micropores'), bone ingrowth is believed to only occur in pores larger than 100 mu m ('macropores'). A thorough analysis of 10 different porous beta-tricalcium phosphate cylinders (empty set: 8 mm; L: 13 mm) implanted for 2-24 weeks in an ovine model demonstrates ingrowth of mineralized tissue (MT) in pores as small as 1 mu m. This tissue contained calcium phosphate, collagen, and interconnected cells. It formed within the first 3-4 weeks of implantation, extended over several hundred micrometers within the ceramic, and contributed to the majority of the early MT formation (including bone) in the defect. The indentation stiffness of the MT-ceramic composite was significantly higher than that of bone and MT-free ceramic. The presented results substantiate the importance of micropores for optimal bone healing, particularly at early implantation times

  • Authors: 
    Jinli Zhang; Ning Nie; Yuanyuan Liu; Jiao Wang; Feng Yu; Junjie Gu; Wei Li;
    Publisher: American Chemical Society (ACS)

    An evolutionary composite of LiFePO4 with nitrogen and boron codoped carbon layers was prepared by processing hydrothermal-synthesized LiFePO4. This novel codoping method is successfully applied to LiFePO4 for commercial use, and it achieved excellent electrochemical performance. The electrochemical performance can be improved through single nitrogen doping (LiFePO4/C-N) or boron doping (LiFePO4/C-B). When modifying the LiFePO4/C-B with nitrogen (to synthesis LiFePO4/C-B+N) the undesired nonconducting N-B configurations (190.1 and 397.9 eV) are generated. This decreases the electronic conductivity from 2.56×10(-2) to 1.30×10(-2) S cm(-1) resulting in weak electrochemical performance. Nevertheless, using the opposite order to decorate LiFePO4/C-N with boron (to obtain LiFePO4/C-N+B) not only eliminates the nonconducting N-B impurity, but also promotes the conductive C-N (398.3, 400.3, and 401.1 eV) and C-B (189.5 eV) configurations-this markedly improves the electronic conductivity to 1.36×10(-1) S cm(-1). Meanwhile the positive doping strategy leads to synergistic electrochemical activity distinctly compared with single N- or B-doped materials (even much better than their sum capacity at 20 C). Moreover, due to the electron and hole-type carriers donated by nitrogen and boron atoms, the N+B codoped carbon coating tremendously enhances the electrochemical property: at the rate of 20 C, the codoped sample can elevate the discharge capacity of LFP/C from 101.1 mAh g(-1) to 121.6 mAh g(-1), and the codoped product based on commercial LiFePO4/C shows a discharge capacity of 78.4 mAh g(-1) rather than 48.1 mAh g(-1). Nevertheless, the B+N codoped sample decreases the discharge capacity of LFP/C from 101.1 mAh g(-1) to 95.4 mAh g(-1), while the commercial LFP/C changes from 48.1 mAh g(-1) to 40.6 mAh g(-1).

  • Open Access
    Authors: 
    Beth L. Volpov; Andrew J. Hoskins; Brian C. Battaile; Morgane Viviant; Kathryn E. Wheatley; Greg Marshall; Kyler Abernathy; John P. Y. Arnould;
    Publisher: Public Library of Science (PLoS)
    Country: France

    International audience; This study investigated prey captures in free-ranging adult female Australian fur seals (Arctocephalus pusillus doriferus) using head-mounted 3-axis accelerometers and animal-borne video cameras. Acceleration data was used to identify individual attempted prey captures (APC), and video data were used to independently verify APC and prey types. Results demonstrated that head-mounted accelerometers could detect individual APC but were unable to distinguish among prey types (fish, cephalopod, stingray) or between successful captures and unsuccessful capture attempts. Mean detection rate (true positive rate) on individual animals in the testing subset ranged from 67-100%, and mean detection on the testing subset averaged across 4 animals ranged from 82-97%. Mean False positive (FP) rate ranged from 15-67% individually in the testing subset, and 26-59% averaged across 4 animals. Surge and sway had significantly greater detection rates, but also conversely greater FP rates compared to heave. Video data also indicated that some head movements recorded by the accelerometers were unrelated to APC and that a peak in acceleration variance did not always equate to an individual prey item. The results of the present study indicate that head-mounted accelerometers provide a complementary tool for investigating foraging behaviour in pinnipeds, but that detection and FP correction factors need to be applied for reliable field application.

  • Open Access English
    Authors: 
    Logan, Clare V.; Murray, Jennie E.; Parry, David A.; Robertson, Andrea; Bellelli, Roberto; Tarnauskaitė, Žygimantė; Challis, Rachel; Cleal, Louise; Borel, Valerie; Fluteau, Adeline; +36 more
    Publisher: Elsevier
    Project: NIH | UT Southwestern Center fo... (4UL1TR001105-04), EC | GrowCELL (788093), EC | HUMGENSIZE (281847), WT | Causes and Consequences o... (210752)

    During genome replication, polymerase epsilon (Pol ε) acts as the major leading-strand DNA polymerase. Here we report the identification of biallelic mutations in POLE, encoding the Pol ε catalytic subunit POLE1, in 15 individuals from 12 families. Phenotypically, these individuals had clinical features closely resembling IMAGe syndrome (intrauterine growth restriction [IUGR], metaphyseal dysplasia, adrenal hypoplasia congenita, and genitourinary anomalies in males), a disorder previously associated with gain-of-function mutations in CDKN1C. POLE1-deficient individuals also exhibited distinctive facial features and variable immune dysfunction with evidence of lymphocyte deficiency. All subjects shared the same intronic variant (c.1686+32C>G) as part of a common haplotype, in combination with different loss-of-function variants in trans. The intronic variant alters splicing, and together the biallelic mutations lead to cellular deficiency of Pol ε and delayed S-phase progression. In summary, we establish POLE as a second gene in which mutations cause IMAGe syndrome. These findings add to a growing list of disorders due to mutations in DNA replication genes that manifest growth restriction alongside adrenal dysfunction and/or immunodeficiency, consolidating these as replisome phenotypes and highlighting a need for future studies to understand the tissue-specific development roles of the encoded proteins.

  • Closed Access
    Authors: 
    Duan Li; Christopher Wayne Schmidt;
    Publisher: Elsevier BV

    A smooth cost distribution can be a desirable feature in optimal control design when concerning even distribution of control energy and uniform resource allocation. This consideration is formulated in this paper for discrete-time linear systems where a square cost-variation term is attached to a primal quadratic performance index in an additive form. An analytical control law is obtained for the resulting non-linear-quadratic and nonseparable optimal control problem using a multilevel solution scheme. Investigating the trade-off between minimizing the primal quadratic performance index and minimizing the square cost-variation term offers some useful insights into multiobjective design of control systems.

  • Publication . Part of book or chapter of book . 2000
    Authors: 
    Jerzy Urbanowicz; Kenneth S. Williams;
    Publisher: Springer Netherlands

    Our purpose in this chapter is to investigate divisibility properties of the values of L-functions attached to quadratic characters at integers, for example, class numbers and the orders of K 2-groups of the integers of quadratic fields. Making use of 2-adic L-functions we extend the linear congruence relations considered in the previous chapters. Extensions of this type have been considered in [Gras, 1989], [Uehara, 1990], [Urbanowicz and Wojcik, 1995/1996] and [Wojcik, 1998]. This chapter will focus on the results given in the latter three papers. We begin with some notation and basic properties of p-adic numbers and functions, especially p-adic L-functions.

  • Publication . Other literature type . Article . 2021
    Open Access
    Authors: 
    Shengnan Ke; Jun Gong; Songnian Li; Qing Zhu; Xintao Liu; Yeting Zhang;
    Publisher: Ryerson University Library and Archives

    In recent years, there has been tremendous growth in the field of indoor and outdoor positioning sensors continuously producing huge volumes of trajectory data that has been used in many fields such as location-based services or location intelligence. Trajectory data is massively increased and semantically complicated, which poses a great challenge on spatio-temporal data indexing. This paper proposes a spatio-temporal data indexing method, named HBSTR-tree, which is a hybrid index structure comprising spatio-temporal R-tree, B*-tree and Hash table. To improve the index generation efficiency, rather than directly inserting trajectory points, we group consecutive trajectory points as nodes according to their spatio-temporal semantics and then insert them into spatio-temporal R-tree as leaf nodes. Hash table is used to manage the latest leaf nodes to reduce the frequency of insertion. A new spatio-temporal interval criterion and a new node-choosing sub-algorithm are also proposed to optimize spatio-temporal R-tree structures. In addition, a B*-tree sub-index of leaf nodes is built to query the trajectories of targeted objects efficiently. Furthermore, a database storage scheme based on a NoSQL-type DBMS is also proposed for the purpose of cloud storage. Experimental results prove that HBSTR-tree outperforms TB*-tree in some aspects such as generation efficiency, query performance and query type.

  • Open Access English
    Authors: 
    Nan Zhao; Fen Cheng; F. Richard Yu; Jie Tang; Yunfei Chen; Guan Gui; Hikmet Sari;
    Publisher: IEEE
    Country: United Kingdom

    Unmanned aerial vehicles (UAVs) can help smallcell base stations (SBSs) offload traffic via wireless backhaul to improve coverage and increase rate. However, the capacity of backhaul is limited. In this paper, UAV assisted secure transmission for scalable videos in hyper-dense networks via caching is studied. In the proposed scheme, UAVs can act as SBSs to provide videos to mobile users in some small cells. To reduce the pressure of wireless backhaul, UAVs and SBSs are both equipped with caches to store videos at off-peak time. To facilitate UAVs, a single antenna is equipped at each UAV and thus, only the precoding matrices of SBSs should be cooperatively designed to manage interference by exploiting the principle of interference alignment. On the other hand, the SBSs replaced by UAVs will be idle. Thus, in order to guarantee secure transmission, the idle SBSs can be further exploited to generate jamming signal to disrupt eavesdropping. The jamming signal is zero-forced at the legitimate users through the precoding of the idle SBSs, without affecting the legitimate transmission. The feasibility conditions of the proposed scheme are derived, and the secrecy performance is analyzed. Finally, simulation results are presented to verify the effectiveness of the proposed scheme.\ud

search
Include:
The following results are related to Canada. Are you interested to view more results? Visit OpenAIRE - Explore.
163,264 Research products, page 1 of 16,327
  • Open Access
    Authors: 
    Fangong Kong; Shoujuan Wang; Weijue Gao; Pedram Fatehi;
    Publisher: Royal Society of Chemistry (RSC)
    Project: NSERC

    Kraft lignin (KL) produced in kraft pulping process has a low molecular weight and solubility, which limits its application in industry. For the first time, KL was polymerized with acrylic acid (AA) in an acidic aqueous suspension system to produce a water soluble lignin–AA polymer with a high molecular weight in this work. The polymerization reaction was carried out using K2S2O8 as an initiator, and the influence of reaction conditions on the carboxylate group content and molecular weight of resultant lignin polymers was systematically investigated. The mechanism of polymerization of KL and AA was discussed fundamentally. The resulting lignin–AA polymer was characterized by Fourier Transform Infrared spectrophotometry (FTIR), proton nuclear magnetic resonance (1H-NMR) and elemental analyses. The results showed that the phenolic hydroxyl group (Ph-OH) content of KL promoted the polymerization under an acidic environment. Under the conditions of 1.5 wt% of initiator, 3.5 of pH, 10.0 of AA/lignin molar ratio, 0.15 mol L−1 of lignin concentration, 3 h and 80 °C, the carboxylate group content and the molecular weight of the polymer were 7.37 mmol g−1 and 7.4 × 105 g mol−1, respectively. The lignin–AA polymer was water soluble at a 10 g L−1 concentration and a pH higher than 4.5. Furthermore, the flocculation performance of lignin–AA polymer in an aluminium oxide suspension was evaluated. Compared with polyAA, the lignin–AA polymer was a more efficient flocculant for aluminium oxide suspension, which shows its potential to be used as a green flocculant in industry.

  • Closed Access
    Authors: 
    Tingting Yu; Yishuai Xu; Yifan Liu; Puren Ouyang; M.M. Gupta; W.J. Zhang; W.J. Zhang;
    Publisher: IEEE

    This paper reports a work on developing a novel charge control circuit for control of the piezoelectric actuator to overcome its hysteresis nonlinearity when the actuator is driven at high voltage (as opposed to low voltage reported in literature). The charge control circuit also includes a balancing resistor. A test-bed for a piezoelectric actuator was established and an experiment was conducted. The result showed that the hysteresis nonlinearity of the piezoelectric actuator was reduced by 82% under the proposed charge control circuit. This charge control circuit can be used for control of piezoelectric inertia-friction actuator, in which the piezoelectric actuator is part of the whole actuator system.

  • Open Access
    Authors: 
    Marc Bohner; Gamal Baroud; Anke Bernstein; Nicola Döbelin; Laetitia Galea; Bernhard Hesse; Roman Heuberger; Sylvain Meille; Pascal Michel; Brigitte von Rechenberg; +2 more
    Publisher: Elsevier BV
    Country: France

    International audience; Although bone formation around and within implants has been intensively studied, the role of pores and pore geometry is still debated. Notwithstanding studies reporting the formation of bone and bone components within pores as small as a few micrometers ('micropores'), bone ingrowth is believed to only occur in pores larger than 100 mu m ('macropores'). A thorough analysis of 10 different porous beta-tricalcium phosphate cylinders (empty set: 8 mm; L: 13 mm) implanted for 2-24 weeks in an ovine model demonstrates ingrowth of mineralized tissue (MT) in pores as small as 1 mu m. This tissue contained calcium phosphate, collagen, and interconnected cells. It formed within the first 3-4 weeks of implantation, extended over several hundred micrometers within the ceramic, and contributed to the majority of the early MT formation (including bone) in the defect. The indentation stiffness of the MT-ceramic composite was significantly higher than that of bone and MT-free ceramic. The presented results substantiate the importance of micropores for optimal bone healing, particularly at early implantation times

  • Authors: 
    Jinli Zhang; Ning Nie; Yuanyuan Liu; Jiao Wang; Feng Yu; Junjie Gu; Wei Li;
    Publisher: American Chemical Society (ACS)

    An evolutionary composite of LiFePO4 with nitrogen and boron codoped carbon layers was prepared by processing hydrothermal-synthesized LiFePO4. This novel codoping method is successfully applied to LiFePO4 for commercial use, and it achieved excellent electrochemical performance. The electrochemical performance can be improved through single nitrogen doping (LiFePO4/C-N) or boron doping (LiFePO4/C-B). When modifying the LiFePO4/C-B with nitrogen (to synthesis LiFePO4/C-B+N) the undesired nonconducting N-B configurations (190.1 and 397.9 eV) are generated. This decreases the electronic conductivity from 2.56×10(-2) to 1.30×10(-2) S cm(-1) resulting in weak electrochemical performance. Nevertheless, using the opposite order to decorate LiFePO4/C-N with boron (to obtain LiFePO4/C-N+B) not only eliminates the nonconducting N-B impurity, but also promotes the conductive C-N (398.3, 400.3, and 401.1 eV) and C-B (189.5 eV) configurations-this markedly improves the electronic conductivity to 1.36×10(-1) S cm(-1). Meanwhile the positive doping strategy leads to synergistic electrochemical activity distinctly compared with single N- or B-doped materials (even much better than their sum capacity at 20 C). Moreover, due to the electron and hole-type carriers donated by nitrogen and boron atoms, the N+B codoped carbon coating tremendously enhances the electrochemical property: at the rate of 20 C, the codoped sample can elevate the discharge capacity of LFP/C from 101.1 mAh g(-1) to 121.6 mAh g(-1), and the codoped product based on commercial LiFePO4/C shows a discharge capacity of 78.4 mAh g(-1) rather than 48.1 mAh g(-1). Nevertheless, the B+N codoped sample decreases the discharge capacity of LFP/C from 101.1 mAh g(-1) to 95.4 mAh g(-1), while the commercial LFP/C changes from 48.1 mAh g(-1) to 40.6 mAh g(-1).

  • Open Access
    Authors: 
    Beth L. Volpov; Andrew J. Hoskins; Brian C. Battaile; Morgane Viviant; Kathryn E. Wheatley; Greg Marshall; Kyler Abernathy; John P. Y. Arnould;
    Publisher: Public Library of Science (PLoS)
    Country: France

    International audience; This study investigated prey captures in free-ranging adult female Australian fur seals (Arctocephalus pusillus doriferus) using head-mounted 3-axis accelerometers and animal-borne video cameras. Acceleration data was used to identify individual attempted prey captures (APC), and video data were used to independently verify APC and prey types. Results demonstrated that head-mounted accelerometers could detect individual APC but were unable to distinguish among prey types (fish, cephalopod, stingray) or between successful captures and unsuccessful capture attempts. Mean detection rate (true positive rate) on individual animals in the testing subset ranged from 67-100%, and mean detection on the testing subset averaged across 4 animals ranged from 82-97%. Mean False positive (FP) rate ranged from 15-67% individually in the testing subset, and 26-59% averaged across 4 animals. Surge and sway had significantly greater detection rates, but also conversely greater FP rates compared to heave. Video data also indicated that some head movements recorded by the accelerometers were unrelated to APC and that a peak in acceleration variance did not always equate to an individual prey item. The results of the present study indicate that head-mounted accelerometers provide a complementary tool for investigating foraging behaviour in pinnipeds, but that detection and FP correction factors need to be applied for reliable field application.

  • Open Access English
    Authors: 
    Logan, Clare V.; Murray, Jennie E.; Parry, David A.; Robertson, Andrea; Bellelli, Roberto; Tarnauskaitė, Žygimantė; Challis, Rachel; Cleal, Louise; Borel, Valerie; Fluteau, Adeline; +36 more
    Publisher: Elsevier
    Project: NIH | UT Southwestern Center fo... (4UL1TR001105-04), EC | GrowCELL (788093), EC | HUMGENSIZE (281847), WT | Causes and Consequences o... (210752)

    During genome replication, polymerase epsilon (Pol ε) acts as the major leading-strand DNA polymerase. Here we report the identification of biallelic mutations in POLE, encoding the Pol ε catalytic subunit POLE1, in 15 individuals from 12 families. Phenotypically, these individuals had clinical features closely resembling IMAGe syndrome (intrauterine growth restriction [IUGR], metaphyseal dysplasia, adrenal hypoplasia congenita, and genitourinary anomalies in males), a disorder previously associated with gain-of-function mutations in CDKN1C. POLE1-deficient individuals also exhibited distinctive facial features and variable immune dysfunction with evidence of lymphocyte deficiency. All subjects shared the same intronic variant (c.1686+32C>G) as part of a common haplotype, in combination with different loss-of-function variants in trans. The intronic variant alters splicing, and together the biallelic mutations lead to cellular deficiency of Pol ε and delayed S-phase progression. In summary, we establish POLE as a second gene in which mutations cause IMAGe syndrome. These findings add to a growing list of disorders due to mutations in DNA replication genes that manifest growth restriction alongside adrenal dysfunction and/or immunodeficiency, consolidating these as replisome phenotypes and highlighting a need for future studies to understand the tissue-specific development roles of the encoded proteins.

  • Closed Access
    Authors: 
    Duan Li; Christopher Wayne Schmidt;
    Publisher: Elsevier BV

    A smooth cost distribution can be a desirable feature in optimal control design when concerning even distribution of control energy and uniform resource allocation. This consideration is formulated in this paper for discrete-time linear systems where a square cost-variation term is attached to a primal quadratic performance index in an additive form. An analytical control law is obtained for the resulting non-linear-quadratic and nonseparable optimal control problem using a multilevel solution scheme. Investigating the trade-off between minimizing the primal quadratic performance index and minimizing the square cost-variation term offers some useful insights into multiobjective design of control systems.

  • Publication . Part of book or chapter of book . 2000
    Authors: 
    Jerzy Urbanowicz; Kenneth S. Williams;
    Publisher: Springer Netherlands

    Our purpose in this chapter is to investigate divisibility properties of the values of L-functions attached to quadratic characters at integers, for example, class numbers and the orders of K 2-groups of the integers of quadratic fields. Making use of 2-adic L-functions we extend the linear congruence relations considered in the previous chapters. Extensions of this type have been considered in [Gras, 1989], [Uehara, 1990], [Urbanowicz and Wojcik, 1995/1996] and [Wojcik, 1998]. This chapter will focus on the results given in the latter three papers. We begin with some notation and basic properties of p-adic numbers and functions, especially p-adic L-functions.

  • Publication . Other literature type . Article . 2021
    Open Access
    Authors: 
    Shengnan Ke; Jun Gong; Songnian Li; Qing Zhu; Xintao Liu; Yeting Zhang;
    Publisher: Ryerson University Library and Archives

    In recent years, there has been tremendous growth in the field of indoor and outdoor positioning sensors continuously producing huge volumes of trajectory data that has been used in many fields such as location-based services or location intelligence. Trajectory data is massively increased and semantically complicated, which poses a great challenge on spatio-temporal data indexing. This paper proposes a spatio-temporal data indexing method, named HBSTR-tree, which is a hybrid index structure comprising spatio-temporal R-tree, B*-tree and Hash table. To improve the index generation efficiency, rather than directly inserting trajectory points, we group consecutive trajectory points as nodes according to their spatio-temporal semantics and then insert them into spatio-temporal R-tree as leaf nodes. Hash table is used to manage the latest leaf nodes to reduce the frequency of insertion. A new spatio-temporal interval criterion and a new node-choosing sub-algorithm are also proposed to optimize spatio-temporal R-tree structures. In addition, a B*-tree sub-index of leaf nodes is built to query the trajectories of targeted objects efficiently. Furthermore, a database storage scheme based on a NoSQL-type DBMS is also proposed for the purpose of cloud storage. Experimental results prove that HBSTR-tree outperforms TB*-tree in some aspects such as generation efficiency, query performance and query type.

  • Open Access English
    Authors: 
    Nan Zhao; Fen Cheng; F. Richard Yu; Jie Tang; Yunfei Chen; Guan Gui; Hikmet Sari;
    Publisher: IEEE
    Country: United Kingdom

    Unmanned aerial vehicles (UAVs) can help smallcell base stations (SBSs) offload traffic via wireless backhaul to improve coverage and increase rate. However, the capacity of backhaul is limited. In this paper, UAV assisted secure transmission for scalable videos in hyper-dense networks via caching is studied. In the proposed scheme, UAVs can act as SBSs to provide videos to mobile users in some small cells. To reduce the pressure of wireless backhaul, UAVs and SBSs are both equipped with caches to store videos at off-peak time. To facilitate UAVs, a single antenna is equipped at each UAV and thus, only the precoding matrices of SBSs should be cooperatively designed to manage interference by exploiting the principle of interference alignment. On the other hand, the SBSs replaced by UAVs will be idle. Thus, in order to guarantee secure transmission, the idle SBSs can be further exploited to generate jamming signal to disrupt eavesdropping. The jamming signal is zero-forced at the legitimate users through the precoding of the idle SBSs, without affecting the legitimate transmission. The feasibility conditions of the proposed scheme are derived, and the secrecy performance is analyzed. Finally, simulation results are presented to verify the effectiveness of the proposed scheme.\ud