SENSORNETS 2017 Abstracts

Area 1 - Energy and Environment
Full Papers
Area 2 - Intelligent Data Analysis and Processing
Full Papers
Area 3 - Security and Privacy in Sensor Networks
Full Papers Short Papers
Area 4 - Sensor Networks
Full Papers Short Papers
Area 5 - Sensor Networks Software, Architectures and Applications
Full Papers Short Papers

Area 1 - Energy and Environment

Full Papers
Paper Nr: 1
Title:

Estimating Spatial Averages of Environmental Parameters based on Mobile Crowdsensing
Authors:

Ioannis Koukoutsidis
Abstract: Mobile crowdsensing can facilitate environmental surveys by leveraging sensor-equipped mobile devices that carry out measurements covering a wide area in a short time, without bearing the costs of traditional field work. In this paper, we examine statistical methods to perform an accurate estimate of the mean value of an environmental parameter in a region, based on such measurements. The main focus is on estimates produced by considering the mobile device readings at a random instant in time. We compare stratified sampling with different stratification weights to sampling without stratification, as well as an appropriately modified version of systematic sampling. Our main result is that stratification with weights proportional to stratum areas can produce significantly smaller bias, and gets arbitrarily close to the true area average as the number of mobiles increases, for a moderate number of strata. The performance of the methods is evaluated for an application scenario where we estimate the mean area temperature in a linear region that exhibits the so-called Urban Heat Island effect, with mobile users moving in the region according to the Random Waypoint Model.
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Paper Nr: 15
Title:

Data Quality Issues in Environmental Sensing with Smartphones
Authors:

Tiago C. de Araújo, Lígia T. Silva and Adriano J. C. Moreira
Abstract: This paper presents the results of a study about the performance and, consequently, challenges of using smartphones as data gatherers in mobile sensing campaigns to environmental monitoring. It is shown that there are currently a very large number of devices technologically enabled for tech-sensing with minimal interference of the users. On other hand, the newest devices seem to broke the sensor diversity trend, therefore making the approach of environmental sensing in the ubiquitous computing scope using smartphones sensors a more difficult task. This paper also reports on an experiment, emulating different common scenarios, to evaluate if the performance of environmental sensor-rich smartphones readings obtained in daily situations are reliable enough to enable useful collaborative sensing. The results obtained are promising for temperature measurements only when the smartphone is not being handled because the typical use of the device pollutes the measurements due to heat transfer and other hardware aspects. Also, we have found indicators of data quality issues on humidity sensors embedded in smartphones. The reported study can be useful as initial information about the behaviour of smartphones inner sensors for future crowdsensing application developers.
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Paper Nr: 20
Title:

Occupancy Detection using Gas Sensors
Authors:

Andrzej Szczurek, Monika Maciejewska and Tomasz Pietrucha
Abstract: Room occupancy is an important variable in high performance building management. Presence of people is usually detected by dedicated sensing systems. The most popular ones exploit physical phenomena. Such sensing solutions include passive infrared motion detectors, magnetic reed switches, ultrasonic, microwave and audible sensors, video cameras and radio-frequency identification. However, in most cases either human movement is needed to succeed in detection or privacy issues are involved. In this work, we studied occupancy detection using chemical sensors. In this case, the basis for detecting human presence indoors is their influence of chemical composition of air. Movement of people is not needed to succeed and privacy of occupants is secured. The approach was reported effective when using carbon dioxide, which is one of major human metabolites. We focused on volatile organic compounds (VOCs). Their consideration is justified because numerous human effluents belong to this group. The analysis showed that VOCs’ sensors, such as semiconductor gas sensors, offer comparable occupancy detection accuracy (97.16 %) as nondispersive infrared sensor (NDIR) (97.36 %), which is considered as the benchmark. In view of our results, semiconductor gas sensors are interesting candidates for nodes of sensor nets dedicated to detection of human presence indoors. They are smaller, cheaper and consume less energy.
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Area 2 - Intelligent Data Analysis and Processing

Full Papers
Paper Nr: 6
Title:

Actual Consumption Estimation Algorithm for Occupancy Detection using Low Resolution Smart Meter Data
Authors:

Shunichi Hattori and Yasushi Shinohara
Abstract: This paper proposes an actual consumption estimation algorithm that achieves highly accurate occupancy detection using electricity consumption data derived from smart meters. In Japan, electricity consumption data on households will soon be available because smart meters, which enable electric power companies to monitor how much electric power people are using in each household, have been installed in all households. Occupancy detection is a major technique that leverages electricity consumption data and can be applied to various services such as ambient assisted living, sales promotions, and peak load shifting. However, it is difficult to conduct high-accuracy occupancy detection using electricity consumption data automatically derived from smart meters because of their low resolution: 30-min intervals and 100 Wh increments. An actual consumption estimation algorithm is therefore proposed to generate data that reflects the characteristics of a household’s state from low-resolution smart meter data. Occupancy detection is implemented using the estimated consumption data, which are generated by the proposed algorithm, and the results of experiments show that its performance is improved compared to the result obtained using raw smart meter data.
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Paper Nr: 18
Title:

Event Classification from Sensor Data using Spectral Analysis in Robotic Finishing Processes
Authors:

Bobby K. Pappachan, Tegoeh Tjahjowidodo and Tomi WIjaya
Abstract: Process monitoring using indirect methods leverages on the usage of sensors. Using sensors to acquire vital process related information also presents itself with the problem of big data management and analysis. Due to uncertainty in the frequency of events occurring, a higher sampling rate is often used in real-time monitoring applications to increase the chances of capturing and understanding all possible events related to the process. Advanced signal processing methods helps to further decipher meaningful information from the acquired data. In this research work, power spectrum density (PSD) of sensor data acquired at sampling rates between 40 kHz-51.2 kHz was calculated and the co-relation between PSD and completed number of cycles/passes is presented. Here, the progress in number of cycles/passes is the event this research work intends to classify and the algorithm used to compute PSD is Welchs estimate method. A comparison between Welchs estimate method and statistical methods is also discussed. A clear co-relation was observed using Welchs estimate to classify the number of cyceles/passes.
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Area 3 - Security and Privacy in Sensor Networks

Full Papers
Paper Nr: 9
Title:

Sensornet - A Key Predistribution Scheme for Distributed Sensors using Nets
Authors:

Deepak Kumar Dalai and Pinaki Sarkar
Abstract: Key management is an essential functionality for developing secure cryptosystems; particularly for implementations to low cost devices of a distributed sensor networks (DSN)–a prototype of Internet of Things (IoT). Low cost leads to constraints in various resources of constituent devices of a IoT (sensors of a DSN); thereby restricting implementations of computationally heavy public key cryptosystems. This leads to adaptation of the novel key predistribution trick in symmetric key platform to efficiently tackle the problem of key management for these resource starved networks. After a few initial proposals based on random graphs, most key predistribution schemes (KPS) use deterministic (combinatorial) approaches to assure essential design properties. Combinatorial designs like a (v;b; r;k)􀀀configuration which forms a μ(v;b; r;k)􀀀CID are effective schemes to design KPS (Lee and Stinson, 2005). A net in a vector space is a set of cosets of certain kind of subspaces called partial spread. A μ(v;b; r;k)􀀀CID can be formed from a net. In this paper, we propose a key predistribution scheme for DSN, named as sensornet, using net. Effectiveness of sensornet in term of crucial metrics in comparison to other prominent schemes has been theoretically established.
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Short Papers
Paper Nr: 8
Title:

Distributed Clone Detection in Mobile Sensor Networks
Authors:

Abu Sayed Chowdhury and Akshaye Dhawan
Abstract: In this paper, we present a clone detection technique for mobile wireless sensor networks. Since sensor nodes can be compromised and cloned by an adversary, it is desirable to have a distributed clone detection algorithm wherein the nodes in the network themselves identify cloned nodes. Most approaches in the literature have a deterministic set of witness nodes that check for the presence of cloned nodes for a given ID based by receiving claim messages that show two or more nodes with the same ID in different locations. We present a new approach to distributed clone detection called Distributed Detection using Prefix Matching (DDPM). Our approach is designed to work in a mobile sensor network and is based on using a random number and a hash function of the claiming nodes ID to generate a key. We then match the prefix of this key to sensor node IDs in the network to determine a set of inspector nodes that will detect clones for a given round. We demonstrate a 7-10% improvement in the number of witness nodes as a measure of security while also reducing the communication overhead.
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Area 4 - Sensor Networks

Full Papers
Paper Nr: 5
Title:

Discrete Strategy Game-theoretic Topology Control in Wireless Sensor Networks
Authors:

Evangelos D. Spyrou, Shusen Yang and Dimitrios K. Mitrakos
Abstract: One of the most significant problems in Wireless Sensor Network (WSN) deployment is the generation of topologies that maximize transmission reliability and guarantee network connectivity while also maximising the network’s lifetime. Transmission power settings have a large impact on the aforementioned factors. Increasing transmission power to provide coverage is the intuitive solution yet with it may come with lower packet reception and shorter network lifetime. However, decreasing the transmission power may result in the network being disconnected. To balance these trade-offs we propose a discrete strategy game-theoretic solution, which we call TopGame that aims to maximize the reliability between nodes while using the most appropriate level of transmission power that guarantees connectivity. In this paper, we provide the conditions for the convergence of our algorithm to a pure Nash equilibrium as well as experimental results. Here we show, using the Indriya WSN testbed, that TopGame is more energy-efficient and approaches a similar packet reception ratio with the current closest state of the art protocol ART.
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Paper Nr: 17
Title:

Performance Evaluation of Default Active Message Layer (AM) and TKN15.4 Protocol Stack in TinyOS 2.1.2
Authors:

Diego V. Queiroz, Ruan D. Gomes and Cesar Benavente-Peces
Abstract: Wireless Sensor Networks (WSN) have become a leading solution to monitor and control smart buildings, health, industrial environments, and so on. Sensor nodes in a WSN have resource constraints, presenting low processing power and, in some cases, restrictions in power consumption. The resource constraints forced the researchers to develop Operating Systems (OS) for low-power wireless devices, and one of the most important and in active use is the TinyOS. This paper presents an experimental study to evaluate the performance of TinyOS default Active Message (AM) layer protocol in comparison to the fully 802.15.4 compliant protocol stack TKN15.4 developed for TinyOS. The AS-XM1000 802.15.4 mote modules were used to compare both protocols. The results showed that TKN15.4 protocol is better in both energy consumption and packet reception rate.
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Paper Nr: 19
Title:

Comparison between Channel Hopping and Channel Adaptation for Industrial Wireless Sensor Networks
Authors:

Ruan D. Gomes, Marcelo S. Alencar, Diego V. Queiroz, Iguatemi E. Fonseca and Cesar Benavente-Peces
Abstract: One of the differences between the new standard IEEE 802.15.4e, in comparison to the previous IEEE 802.15.4 standard, is the use of multiple channels. The Time-Slotted Channel Hopping (TSCH) mode employs channel hopping, and the Deterministic and Synchronous Multi-channel Extension (DSME) mode employs channel hopping or channel adaptation, during the contention free periods. When using the channel adaptation as the channel diversity technique, a pair of nodes communicate using the same channel while the channel quality is good enough in terms of signal-to-noise ratio. Thus, it is necessary to evaluate the quality of the links, in order to proper use this mechanism. In this paper, three different approaches, based on the DSME protocol, were implemented and evaluated through a simulation study. The first one (CH-DSME) is based on a simple channel hopping mechanism, the second one (CA-DSME) employs channel adaptation, and the third one is a novel hybrid approach (H-DSME), that uses both channel hopping and channel adaptation. The H-DSME outperformed the other two approaches for the scenario in consideration, which shows that the use of channel adaptation is better than channel hopping for the transmission of unicast packets, when the quality of the links are monitored continuously. However, for packets transmitted in broadcast by the coordinator, the use of channel hopping is a good alternative to deal with the spatial variation in the quality of the channels.
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Paper Nr: 31
Title:

Distributed In-Network Processing of k-MaxRS in Wireless Sensor Networks
Authors:

Panitan Wonge-ammat, Muhammed Mas-ud Hussain, Goce Trajcevski, Besim Avci and Ashfaq Khokhar
Abstract: We address the problem of in-network processing of k-Maximizing Range Sum (k-MaxRS) queries in Wireless Sensor Networks (WSN). The traditional, Computational Geometry version of the MaxRS problem considers the setting in which, given a set of (possibly weighted) 2D points, the goal is to determine the optimal location for a given (axes-parallel) rectangle R to be placed so that the sum of the weights (or, a simple count) of the input points in R’s interior is maximized. In WSN, this corresponds to finding the location of region R such that the sum of the sensors’ readings inside R is maximized. The k-MaxRS problem deals with maximizing the overall sum over k such rectangular regions. Since centralized processing – i.e., transmitting the raw readings and subsequently determining the k-MaxRS in a dedicated sink – incur communication overheads, we devised an efficient distributed algorithm for in-network computation of k-MaxRS. Our experimental observations show that the novel algorithm provides significant energy/communication savings when compared to the centralized approach.
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Short Papers
Paper Nr: 4
Title:

Design and Evaluation of a High Throughput Seismic Sensor Network - Tools for Planning, Deployment and Assessment
Authors:

Marco Manso, Mourad Bezzeghoud and Bento Caldeira
Abstract: The rapid technological evolution in sensors, sensor platforms and networking is enabling the deployment of large sensor networks for "live" monitoring of seismic activity with high spatial resolution. In this regard, this paper describes our work in developing an online "High Throughput Seismic Sensor Network". We present the architecture and implementation comprising seismic sensors and servers (running data collection services) connected through internet-enabled technologies. We validate and assess the system, as well as identify bottlenecks, by means of experimentation. Based on the collected empirical data, we were able to identify methods and tools to support effective planning and implementation of sensor networks based on two main indicators: Sensor Network Transmission Rate (SNTR), which provides the overall network sensor data transmission throughput and thus an indication of the required network capacity; and CPU Sensor Network Performance Index (CSNPI), which provides an indication of a server capability to handle network sensor data. As we progress in our work to field deploy seismic sensor networks, we will continue to use these tools to plan and deploy future sensor networks, as well as assess improvements and modifications along the way.
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Paper Nr: 25
Title:

An Adaptive Acknowledgement On-demand Protocol for Wireless Sensor Networks
Authors:

Cung Lian Sang, Marc Hesse, Sebastian Zehe, Michael Adams, Timm Hörmann and Ulrich Rückert
Abstract: The concept of packet acknowledgement in wireless communication networks is crucial for reliable data transmission. However, reliability comes with the cost of an increased duty cycle of the network. This is due to the additional acknowledgement time for every single data packet sent. Therefore, energy consumption and latency of all sensor nodes is increased whilst the overall throughput in the network decreases. This paper contributes an adaptive acknowledgement on-demand protocol for wireless sensor networks with star network topology. The goal is to tackle the trade-off between energy efficiency and reliable data transmission. The proposed protocol is able to detect network congestion in real time by constantly monitoring the overall packet delivery ratio for each sensor node. In case the packet delivery ratio of any sensor nodes in the network is dropped significantly (e.g. due to environmental changes), the protocol switches automatically to a more reliable data transmission mode utilizing acknowledgements concerning the affected sensor nodes. Our proposed method is tested and evaluated based on a specific hardware implementation and the corresponding results are discussed in this paper.
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Paper Nr: 28
Title:

Virtualizing Closed-loop Sensor Networks: A Case Study
Authors:

Priyanka Dattatri Kedalagudde and Michael Zink
Abstract: Closed loop sensor networks are cyber-physical systems that establish a tightly coupled connection between computational elements and the control of physical elements. Existing closed-loop sensor networks are based on dedicated, ’stove-pipe’ architectures that prevent the sharing of these networks. This paper addresses the problem of sharing these networks through virtualization. We propose scheduling algorithms that manage requests from competing applications and evaluate their impact on system utilization as compared to a dedicated network. These algorithms are evaluated through trace-driven simulations. We aim to demonstrate that the proposed scheduling algorithms result in cost savings due to shared network infrastructure without unduly affecting application utility. In our evaluations, we observe only a 20% reduction in average utility via the DSES scheduling approach.
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Paper Nr: 37
Title:

A Lower Bound on the Number of Nodes with Multiple Slots in Wireless Sensor Networks with Multiple Sinks
Authors:

Sain Saginbekov, Arshad Jhumka and Yerzhan Mademikhanov
Abstract: Wireless Sensor Networks (WSNs) once deployed, are left unattended for extended periods of time. During this time, the network can experience a range of faulty scenarios. If a sink node fails, data gathered by sensor nodes may not be delivered to a destination. One way to increase the reliability of such WSNs is to deploy with more than one sink. In this paper, we formalise the problem of many-to-many data aggregation scheduling in WSNs with multiple sinks and establish a lower bound on the number of nodes with multiple slots.
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Area 5 - Sensor Networks Software, Architectures and Applications

Full Papers
Paper Nr: 32
Title:

Modified RSSI Fingerprinting Algorithm with Reliability Factor for Wi-Fi based Indoor Navigation System
Authors:

Rishabh Chauhan, Hong Wang, Ahmad Javaid and Mansoor Alam
Abstract: Asset localization and navigation in a designated area is an important field of research today. For outdoor navigation, there are techniques like Global Navigation Satellite System (GNSS) which have proven their efficiency time and again. Unfortunately, these techniques do not work efficiently in an indoor environment due to various reasons. An indoor navigation system is required to locate assets like patients, industrial mobile equipment and victims to be rescued inside hospitals, industries, hazardous buildings respectively. This paper briefly explains our indoor localization technique and experimental evaluation of the modified Received Signal Strength Indicator (RSSI) fingerprinting algorithm using Reliability factor which is a relatively more efficient algorithm than the Traditional RSSI fingerprinting algorithm and K-Weighted Nearest Neighbor(KWNN) algorithm with Gaussian filter. The drawback of the Traditional approach and KWNN with Gaussian filter is that the data processed is not very reliable since the Wi-Fi signals are adversely affected by multipath reflection, absorption, stray signal etc. The modified technique generates a Reliability factor which ranks data w.r.t accuracy of data, from which the final location estimation is done. We used an android phone, an Arduino microcontroller and various Wi-Fi Access Points (AP) already available in a building and Android Studio, Arduino IDE and Mobizen mirroring software.
Short Papers
Paper Nr: 10
Title:

Cost-efficient Localisation System for Agricultural Use Cases
Authors:

Gábor Paller, Sébastien Aubin, Gábor Élő and Olivier Camp
Abstract: Connected agricultural applications often depend on exact localisation solutions. Often the term “precision agriculture” implies a technology that identifies the location of the livestock, crop, field of agricultural machinery with more or less of precision. While precision requirements vary, the localisation often has to be quite precise like sub-meter or even decimeter precision. Dual-band GPS solutions are able to satisfy these high-precision requirements but these equipments are quite costly and their purchase is often regulated. This paper presents two agricultural use cases and the combination of low-cost GPS and short-range localisation systems that are able to satisfy high-precision requirements for fraction of the costs of dual-band GPS.
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Paper Nr: 13
Title:

A Concept for an Ultra-low Power Sensor Network - Detecting and Monitoring Disaster Events in Underground Metro Systems
Authors:

Jonah Vincke, Scott Kempf, Niklas Schnelle, Clemens Horch and Frank Schäfer
Abstract: In this paper, the concept for an ultra-low power wireless sensor network (WSN) for underground tunnel systems is presented highlighting the chosen sensors. Its objectives are the detection of emergency events either from natural disasters, such as flooding, or from terrorist attacks. Earlier works have demonstrated that the power consumption for the communication can be reduced such that the data acquisition (i.e. sensor subsystem) becomes the most significant energy consumer. By using ultra-low power components for the smoke detector, a hydrostatic pressure sensor for water ingress detection and a passive acoustic emission sensor for explosion detection, all considered threats are covered while the energy consumption can be kept very low in relation to the data acquisition. The total average consumption for operating the sensor sub-system is calculated to be less than 35.9 μW.
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Paper Nr: 14
Title:

Optimization Techniques for Routing Design Problems over Wireless Sensor Networks: A Short Tutorial
Authors:

Ahmed Ibrahim and Attahiru Alfa
Abstract: This paper is intended to serve as an overview of, and mostly a short tutorial to illustrate, the optimization techniques used in several different key design problems that have been considered in the literature of routing over wireless sensor networks. For each routing design problem, a key paper that implements optimization techniques is selected, and for each we present the formulation techniques and the solution methods implemented. We observed that good formulation is the key to fully exploiting the features of the techniques. Hence we focus on presenting the formulation techniques, to facilitate the use of “on the shelf” efficient algorithms in the operations research literature. This we believe will help researchers in better understanding the issues and how to improve further on solution techniques.
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Paper Nr: 16
Title:

Experimental Synthesis of Routing Protocols and Synthetic Mobility Modeling for MANET
Authors:

Nisrine Ibadah, Khalid Minaoui, Mohammed Rziza and Mohammed Oumsis
Abstract: Many performance analyses are already done with a lot of flaws. But, they do not look to all influenced constraints. In this study, we aim to summarize several parameters into 90 different scenarios with an average of 1350 simulated files. That shows results of three performance metrics combined with five mobile ad hoc routing protocols under three synthetic mobility models. All these parameters are applied to two dissimilar simulation areas. Basing on one exhaustive analysis with all these details like this paper; leads to well understand the accurate behaviors of routing protocols and mobility models used. By displaying the ability of every routing protocol to deal with some topology changes, as well as to ensure network performances.
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Paper Nr: 27
Title:

homeSound: A High Performance Platform for Massive Data Acquisition and Processing in Ambient Assisted Living Environments
Authors:

Marcos Hervás, Rosa Ma Alsina-Pagès and Joan Navarro
Abstract: Human life expectancy has steadily grown over the last century, which has driven governments and institutions to increase the efforts on caring about the eldest segment of the population. The first answer to that increasing need was the building of hospitals and retirement homes, but these facilities have been rapidly overfilled and their associated maintenance costs are becoming far prohibitive. Therefore, modern trends attempt to take advantage of latest advances in technology and communications to remotely monitor those people with special needs at their own home, increasing their life quality and with much less impact on their social lives. Nonetheless, this approach still requires a considerable amount of qualified medical personnel to track every patient at any time. The purpose of this paper is to present an acoustic event detection platform for assisted living that tracks patients status by automatically identifying and analyzing the acoustic events happening in a house. Specifically, we have taken benefit of the amazing capabilities of a Jetson TK1, with its NVIDIA Graphical Processing Unit, to collect the data in the house and process it to identify a closed number of events, which could led doctors or care assistants in real-time by tracking the patient at home. This is a proof of concept conducted with data of only one acoustic sensor, but in the future we have planned to extract information of the sensor network placed in several places in the house.
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Paper Nr: 34
Title:

Impact of Time Slot Adjustment on a Multi-hop and Multi-channel Solution for Dynamic WSN Topologies
Authors:

Honoré Bizagwira, Joël Toussaint and Michel Misson
Abstract: Ensure data delivery and extend the network lifetime are challenges that must be addressed when it comes to deploy a WSN in outdoor harsh environment where it operates over unstable links. The instability of radio links may induce a connectivity that is time-varying even when nodes are not moving. For these dynamic topologies, resources allocated to the nodes must be adjusted to the local traffic conditions. Amongst the proposed solutions, schedule-based protocols achieve an energy efficiency as they allow nodes to sleep during their inactive periods. As the channel conditions are time-varying, and paths followed by the packets are changing, inducing an instability in the distribution of the traffic load over the network. This paper is dealing with the mastering of the size of the reception time slot of the next hop node. Our solution dynamically takes in consideration the local traffic load to resize the time slots. This adaptive solution is compared with the fixed-length window scheme, it obviously improves the performance of the WSN in terms of cycle length, idle listening and collision reduction, and achieves suitable data delivery ratio.
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Paper Nr: 38
Title:

Synthesis of Pd@ZnO Core-shell Nanoparticles with Different Size and Their Gas Sensing Properties
Authors:

Yeon-Tae Yu, Sanjit Manohar Majhi, Gautam K. Naik and Ho-Geum Song
Abstract: Two different sizes of Pd@ZnO core-shell nanoparticles (NPs) have been prepared by using two different sizes of Pd NPs (15 and 50 nm) as metal cores and applied for acetaldehyde gas sensing. Transmission electron microscopy images revealed that the overall size of two sensing materials such as Pd15@ZnO and Pd50@ZnO core-shell NPs are 80-100 nm and 100-120 nm, respectively. Xray-diffraction pattern revealed that the oxidation of Pd metal core was started from 300°C. The spherical shape and size are maintained after the Pd@ZnO core-shell NPs was calcined at 500°C for 2 h. PdO15@ZnO core-shell NPs showed higher response to acetaldehyde. The maximum response of PdO15@ZnO core-shell NPs to 100 ppm of acetaldehyde at 350 °C was 75, whereas the maximum response of PdO50@ZnO core-shell NPs to 100 ppm of acetaldehyde was 28 as compared to the pure ZnO NPs (Rs=18). The high response of PdO15@ZnO coreshell NPs than PdO50@ZnO core-shell NPs is due to the smaller size of PdO core, which has more catalytic activity than 50 nm sized PdO core.
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