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An extension to the application area for discrete event simulation (DES) has been ongoing since the last decade and focused only on economic aspects to include ecologic sustainability. With this new focus, additional input parameters, such as electrical power consumption of machines, are needed. This paper aim at investigating how NC machine power consumption should be represented in simulation models of factories. The study includes data-sets from three different factories. One factory producing truck engine blocks, one producing brake disc parts for cars and one producing forklift components. The total number of data points analysed are more than 2,45,000, where of over 1,11,000 on busy state for 11 NC machines. The low variability between busy cycles indicates that statistical representations are not adding significant variability. Furthermore, results show that non-value-added activities cause a substantial amount of the total energy consumption, which can be reduced by optimising the production flow using dynamic simulations such as DES. [ABSTRACT FROM PUBLISHER]

In this study, we present a stochastic model to analyse a business plan that is based on offering energy-saving technologies as a service. In this arrangement, the total differential cost of replacing an existing technology with a more efficient one is financed from the future energy savings that are shared between a service provider that installs the more efficient technology and its customer. The model we present captures improvements in energy efficiencies and costs of technologies with time, variation in energy consumption, uncertainty in energy prices and useful life of a technology, and revenue from carbon offsets. By using an analytical model, we analyse the feasibility of this business model using expected cost and also value-at-risk criteria. We show that when the service provider selects the contract parameters in a right way, the business plan brings financial benefits. The customer also benefits financially from reduction in energy usage and replacement costs, and also from additional revenue obtained through selling carbon offsets. Furthermore, since this business plan is based on increasing energy efficiency, the proposed approach decreases energy consumption, and therefore carbon dioxide emissions. As a result, using an analytical model, we show that offering energy-saving technologies as a service is a win–win–win situation for the service provider, its customer and for the environment. [ABSTRACT FROM PUBLISHER]

Energy efficiency has become a primary goal to be pursued for sustainable logistics. In automated storage and retrieval systems this leads to revise the traditional control policies aimed at picking time minimisation and to pay more attention to rack configuration, which has been not a research concern from the time-based perspective. Proper models for energy calculation should be developed by introducing new factors neglected in time analysis, such as the weight of unit loads and the differentiation of shifts along the horizontal and vertical axis as regard energy requirements, due to different contribution of gravity, inertia and friction. In this study, a classification of racks based on system height is proposed in order to select the proper crane specifications needed to compute the torque to be overcome by motors to serve a given location within a rack. An overall optimisation model based on Constraint Programming hybridised with Large Neighborhood Search is developed, allowing the joint application of the best control policies for storage assignment and sequencing both for time and energy-based optimisation, as well as the introduction of multiple weight unit loads and energy recovery. Simulations analysis is performed in order to assess the impact of the rack shape on energy saving. Results show how, regardless the demand curve and the optimisation objective, the best performances in terms of energy efficiency are reached by the intermediate height rack shapes, while the lower ones outperform when considering travel time performance. [ABSTRACT FROM PUBLISHER]

The micro fluxgate sensors have shown high sensitivity for the magnetic beads detection. For portable magnetic biological detection, Co-based amorphous ribbons with high permeability and low saturation magnetic induction are chosen as core materials to lower the operation requirements of the fluxgate-based magnetic beads detection. The micro fluxgate sensors with single-layer core and bi-layer core are fabricated by Micro-Electro-Mechanical System technologies, which exhibit a power consumption of 10.88 mW and 24.48 mW, a sensitivity of 1644V/T and 1456V/T, and a noise of 1.66 nT/Hz1/2 @1Hz and 2.32 nT/H1/2 @1Hz, respectively. The Dynabeads with concentrations of 300 &#181g/ml in 10 µl are detected by the micro fluxgate-based sensing system based on static response, and the results show signal change ratio of 12.2% and 9.2% under the max signal difference at 215 µT and 480 µT of the bias magnetic field for two kinds of the sensors, respectively, which is near the saturation point of the sensors. The fluxgate-based bead detection system with Co-based ribbon core presents low demands for the bias magnetic field and power consumption. [ABSTRACT FROM AUTHOR]

Background: The objective of this study was to verify the long-term effects of exercise on energy expenditure and body composition in individuals with spinal cord injury (SCI), as very little information is available on this population under free-living conditions. Methods: Free-living energy expenditure and body composition using doubly labeled water (DLW) was measured in 13 individuals with SCI, subdivided in 2 groups: (1) sedentary (SED; N = 7) and (2) regularly engaged in any exercise program, for at least 150 minwk"1 (EXE; N = 6). Results: The total daily energy expenditure (TDEE) was significantly higher in the EXE group (33 ± 4.5 kcal⋅kg-1day-1) if compared with SED group (27 ± 4.3 kcal⋅kg-1day-1). The percentage of body fat was significantly higher in SED group than in EXE group (38 ± 6% and 28 ± 9%). Conclusion: Our findings revealed that, despite the severity of SCI, the actual ACSM's guidelines for weight management for healthy adults exercise could significantly increase TDEE and BMR and improve body composition in individuals who regularly perform exercise. However, the EXE group still showed a high percentage of body fat, suggesting that a more specific approach might be considered (ie, increased intensity or volume, or combining with a diet program). [ABSTRACT FROM AUTHOR]

Manufacturing firms consume energy and natural resources in highly unsustainable manner and release large amounts of green house gases leading to many economic, environmental and social problems from climate change to local waste disposal. Consciousness about these issues has led to a new manufacturing paradigm of environmentally conscious manufacturing (ECM). However, there are various barriers to the implementation of ECM. A proper understanding and analysis of these barriers will allow the management of the company and government to prioritise their focus to mitigate root barriers for effective implementation of ECM. This paper aims at identifying the barriers to ECM, developing a model of these barriers using statistical analysis and testing the model using structural equation modelling technique. The results provide three types of barriers – internal, policy and economic. The results show that internal barriers are the root barriers and cause policy and economic barriers. It reflects that the barriers which are internal to the organisation should be mitigated first for effective implementation of ECM. [ABSTRACT FROM PUBLISHER]

Firms heavily emphasise reducing carbon footprint, an area warranting further improvement. This study examines carbon footprint within the context of production scheduling. Two multi-objective scheduling problems involving economic- and environmental-related criteria are studied: (1) a batch-processing machine scheduling problem to minimise the total weighted tardiness and carbon footprint simultaneously; (2) a triple-criteria scheduling problem involving of a hybrid flow shop consisting of a batch-processing machine followed by two parallel-processing machines, in which the shop attempts to minimise the total weighted tardiness, carbon footprint and peak power. Since the above problems are treated as a true multi-objective optimisation problem, decision-makers should select a solution among the trade-off solutions provided in the Pareto-optimal set. Therefore, the non-dominated sorting-based genetic algorithm II (NSGA-II) is implemented, which identifies the set of approximate efficient schedules to both multi-objective scheduling problems. Moreover, an adaptive multi-objective genetic algorithm (AMGA) is developed to generate the reference Pareto front, which validates the results that are obtained using NSGA-II. Results of this study demonstrate both the effectiveness of AMGA in converging to the true Pareto-optimal set and the efficiency of NSGA-II. [ABSTRACT FROM PUBLISHER]

In this paper, multi-layer Zn:SiO2/SiO2 structure is introduced to reduce the operation power consumption of resistive random access memory (RRAM) device by modifying the filament formation process. And the configuration of multi-layer Zn:SiO2/SiO2 structure is confirmed and demonstrated by auger electron spectrum. Material analysis together with conduction current fitting is applied to qualitatively evaluate the carrier conduction mechanism on both low resistance state and high resistance state. Finally, single layer and multilayer conduction models are proposed, respectively, to clarify the corresponding conduction characteristics of two types of RRAM devices. [ABSTRACT FROM AUTHOR]

In this paper, we presented a modified rectangular cymbal transducer used as the vibration energy harvesting device based on 0.71Pb(Mg1/3Nb2/3)O3–0.29PbTiO3 single crystal. The vibration modes of the device were analyzed and the electrical properties were studied systematically. Under a cyclic force of 0.55 N (peak value), a high peak voltage of 45.7 V and maximum power of 14 mW were measured at 500 Hz with a proof mass of 17.0 g. The power density of the transducer is more than three times as high as that of the Pb(ZrxTi1-x)O3 (PZT) ceramic cymbal transducer. The results demonstrate the potential of the device in energy harvesting applied to low-power portable electronics and wireless sensors. [ABSTRACT FROM AUTHOR]

In this paper we analyze the system proposed by Trupke et al. [J. Appl. Phys. 92, 1668 (2002)] to increase solar cell efficiency. The system consists of adding to the solar cell a so-called down-converter, which is a device able to convert the high-energy incident photons into photons of lower energy. The contribution consists of taking account (i) the nonradiative recombination in both solar cell and converter, (ii) the refractive index of solar cell and converter materials, and (iii) the solar radiation concentration. Two configurations are studied: the cell and rear converter (C-RC) and front converter and cell (FC-C). The main conclusions of this work are as follow. (1) For ideal down-converters, with radiative recombination only, the solar energy conversion efficiency may be, or may not be, increased by adding a front (or a rear) down-converter to the cell, depending on the value of the solar cell refractive index. (2) More realistic systems, where nonradiative recombinations exist inside the converter, are also considered. The efficiency of the FC-C system is generally less than the efficiency of a single cell. C-RC systems perform better than the cell operating alone for some values of the refractive indices. (3) C-RC systems perform generally better than FC-C systems whatever the values of the refractive indices and the concentration ratio. [ABSTRACT FROM AUTHOR]

Abstract Applications for sizing Photovoltaic (PV) self-consumption systems have been studied over recent years in order to achieve either an optimization of the cost of energy, the investment cost or any economic profitability criteria. However, PV self-consumption systems at the residential or small business level can be designed with the aims of reducing the electricity consumption from the conventional local grid and achieving competitiveness with grid electricity prices. These criteria will provide not only greater environmental benefits, security and independence of the grid but it will make the cost of PV self-consumption electricity competitive with electricity prices from the power grid. In this sense, this paper proposes a method to size the generator for a PV self-consumption system based on cost-competitiveness, maximizing direct self-consumption. The method will be applied for three different households located in the south of Spain using the household daily consumption and generation profiles for a single year. However, the method here illustrated can be applied to other countries. The results obtained suggest that residential direct PV self-consumption systems with an annual global irradiation at the optimal tilt angle higher than 1000 kWh/(m2·year) may be a feasible investment to future owners of these systems. Highlights • A method to size PV generators based on the cost of PV self-consumed electricity has been developed. • The method is based on cost–competitiveness, maximizing direct self-consumption. • Real household load data have been used to illustrate the method. • In Spain PV self-consumption may be cost-competitive for irradiation >1000 kWh/(m2 y). • The method can be also used when considering batteries and Demand side Management. [ABSTRACT FROM AUTHOR]

Continuous-display, electricity-use monitors provide more comprehensive electricity cost information than previously considered initiatives. This study analyzes the effect of monitor-provided information on consumers' monthly peak period, off-peak period, and total electricity consumption using an ANCOVA framework. Results indicate that monitoring did not induce conservation but did significantly contribute to shifting electricity use from peak to off-peak periods. [ABSTRACT FROM AUTHOR]

We explored a novel doubly labelled water (DLW) method based on breath water (BW-DLW) in mice to determine whole body CO2 production and energy expenditure noninvasively. The BW-DLW method was compared to the DLW based on blood plasma. Mice (n = 11, 43.5 ± 4.6 g body mass (BM)) were administered orally a single bolus of doubly labelled water (1.2 g H218O kg BM−1 and 0.4 g 2H2O kg BM−1, 99 atom% (AP) 18O or 2H). To sample breath water, the mice were placed into a respiration vessel. The exhaled water vapour was condensed in a cold-trap. The isotope enrichments of breath water were compared with plasma samples. The 2H/1H and 18O/16O isotope ratios were measured by means of isotope ratio mass spectrometry. The CO2 production (RCO2) was calculated from the 2H and 18O enrichments in breath water and plasma over 5 days. The isotope enrichments of breath water vs. plasma were correlated (R2 = 0.89 for 2H and 0.95 for 18O) linearly. The RCO2 determined based on breath water and plasma was not different (113.2 ± 12.7 vs. 111.4 ± 11.0 mmol d-1), respectively. In conclusion, the novel BW-DLW method is appropriate to obtain reliable estimates of RCO2 avoiding blood sampling. [ABSTRACT FROM AUTHOR]

Governments all over the world are tending to accelerate the process of replacing fossil based energies with renewable energy sources through developing incentive or punitive policies. In Iran, various incentive and punitive guidelines are regulated to persuade governmental and nongovernmental organizations to use renewable energy resources. In this paper, optimal planning and sizing of distributed renewable energy resources for governmental organizations in Iran, under persuasive policies, is proposed. This design includes a techno-economic analysis on the basis of total Net Present Cost (NPC) to obtain the optimal configuration of the hybrid energy system for governmental institutes among all possible combinations of distributed diesel generators (consisting of internal combustion engines with diesel fuel) as well as renewable energy resources such as wind energy conversion systems and solar photovoltaics. In order to evaluate the economic and technical aspects of the persuasive policies for governmental institutes in Iran, an optimal hybrid energy system is designed to provide for the energy consumption of the University of Bojnord. The proposed hybrid energy system consists of 100 kW photovoltaic panels, 20 kW wind turbines, a 10 kW diesel generator, and 10 one kW h batteries. The total NPC of the system is estimated to be 1.04 $M. In addition, a sensitivity analysis is carried out to investigate the impact of economic indicators on the design. The results show that the University of Bojnord would benefit from investing in the proposed design after six years. [ABSTRACT FROM AUTHOR]

Polygeneration is a promising technology for enhancing the performance of traditional centralized district heating and cooling (DHC) systems since it enables the use of renewable energy sources and provides flexibility in supplying a range of value-added products. The main objective of this study is to evaluate how a reduction in heating, cooling and electricity loads would impact on the performance of a polygeneration DHC system based on waste gasification from thermodynamic, exergy, economic and environmental perspectives. To this end, system models considering hourly performance for a typical year of operation were established with either refuse derived fuel (RDF) or municipal solid waste (MSW) as feedstocks. The study reveals that with a decrease in heating, cooling and electricity loads the system, using RDF or MSW as the main fuel, is still capable of delivering energy services, but with reduced amounts of value-added products and less favourable overall system performance. For example, with RDF as the main fuel, when char, syngas, synthetic natural gas and hydrogen are produced with the gas turbine operating at 25% of its nominal value, with no heating and cooling supplies, the system thermodynamic efficiency is only 3.9%, as compared with 31.5% for the maximal heating, cooling and electricity supplies for the same group of value-added products. Nevertheless, under these conditions the system operation is still feasible and economically viable; specifically, annual revenues and discounted net cash flows are 6.4 and 11.1 mln USD, respectively. [ABSTRACT FROM AUTHOR]

Clustering, as an essential part in an hierarchy protocol that can prolong the network lifetime, is influenced by the cluster head selection and clustering scheme. A new clustering algorithm called clustering by fast search and finding of density peaks (CFSFDP) based on local density and distance is implementable and efficient. In this paper, we combine this clustering algorithm with a hierarchy protocol in wireless sensor networks (WSNs). However, energy consumption in each round is unbalanced only considering these two variables during the clustering phase, which leads to the early death of the first node. In order to solve this problem, we take residual energy into consideration in our improved CFSFDP-E (energy) algorithm so as to ultimately balance the energy consumption of the network. We analyze different forms of energy and choose a dynamic threshold for each round in the CFSFDP-E algorithm. Simulation results demonstrate that the proposed approach can not only postpone the death of the first node by almost 50% compared to LEACH, but that it also outperforms several related protocols with respect to energy efficiency. [ABSTRACT FROM AUTHOR]

At present, the domotization of homes and public buildings is becoming increasingly popular. Domotization is most commonly applied to the field of energy management, since it gives the possibility of managing the consumption of the devices connected to the electric network, the way in which the users interact with these devices, as well as other external factors that influence consumption. In buildings, Heating, Ventilation and Air Conditioning (HVAC) systems have the highest consumption rates. The systems proposed so far have not succeeded in optimizing the energy consumption associated with a HVAC system because they do not monitor all the variables involved in electricity consumption. For this reason, this article presents an agent approach that benefits from the advantages provided by a Multi-Agent architecture (MAS) deployed in a Cloud environment with a wireless sensor network (WSN) in order to achieve energy savings. The agents of the MAS learn social behavior thanks to the collection of data and the use of an artificial neural network (ANN). The proposed system has been assessed in an office building achieving an average energy savings of 41% in the experimental group offices. [ABSTRACT FROM AUTHOR]

Due to overshadow and channel fading, many mobile users are unable to receive the signal transmitted from satellite directly. Hence, some relay stations should be set to help this type of users to receive signals reliably. In this paper, we present a novel cognitive hybrid satellite-terrestrial model, where two cognitive relays forward their received signal for a mobile user successively. Furthermore, we address its achievable rate maximization. We first convert the co-channel interference threshold into transmit power constraints, and then formulate the maximization of the achievable rate as an optimization problem. Based on Karush–Kuhn–Tucker conditions, the optimization problem is decomposed into four cases, each of which is solved in closed form. Simulation study with different system settings is presented, and the efficiency of the proposed power allocation scheme is shown. [ABSTRACT FROM PUBLISHER]

Building energy consumption makes up 40% of the total energy consumption in the United States. Given that energy consumption in buildings is influenced by aspects of urban form such as density and floor-area-ratios (FAR), understanding the distribution of energy intensities is critical for city planners. This paper presents a novel technique for estimating commercial building energy consumption from a small number of building features by training machine learning models on national data from the Commercial Buildings Energy Consumption Survey (CBECS). Our results show that gradient boosting regression models perform the best at predicting commercial building energy consumption, and can make predictions that are on average within a factor of 2 from the true energy consumption values (with an r 2 score of 0.82). We validate our models using the New York City Local Law 84 energy consumption dataset, then apply them to the city of Atlanta to create aggregate energy consumption estimates. In general, the models developed only depend on five commonly accessible building and climate features, and can therefore be applied to diverse metropolitan areas in the United States and to other countries through replication of our methodology. [ABSTRACT FROM AUTHOR]

In the UK, buildings contribute about one third of the energy-related greenhouse gas emissions. Space heating and cooling systems are among the biggest energy consumers in buildings. This research aims to develop a novel Building Energy Management System (BEMS) to reduce the energy consumption of the heating, ventilation and air-conditioning (HVAC) system while fulfilling each occupant’ thermal comfort requirement. This paper presents a newly developed novel method, Epistemic-Deontic-Axiologic (EDA) Agent-based solution to support the Energy Management System meeting the dual targets of occupant thermal comfort and energy efficiency. The multi-agent solutions are applied to the BEMS. The problem decomposition method is used to define the architecture of the system. The Epistemic-Deontic-Axiologic (EDA) agent model is applied to develop the rational local and personal agents inside the system. These EDA-based agents select their optimal action plan by considering the occupants’ thermal sensations, their behavioural adaptations and the energy consumption of the HVAC system. The Newly-developed personal thermal sensation models and group-of-people-based thermal sensation models generated by support vector machine (SVM) based algorithms are applied to evaluate the occupants’ thermal sensations. These models are developed from the data collected in a real built environment. Simulation results prove that the newly-developed BEMS can help the HVAC system reduce the energy consumption by up to 10% while fulfilling the occupants’ thermal comfort requirements. [ABSTRACT FROM AUTHOR]

Since use of directional antennas in mobile ad hoc networks gaining popularity day by day because of its properties. Although MAC protocol using directional antenna enhances the network performance as it increases spatial reuse and minimizes energy consumption, in comparison of MAC protocols using omnidirectional antennas. But directional MAC protocol still have some well known problem, namely hidden terminal, exposed terminal problem, and deafness. Therefore, in this paper we proposed a MAC protocol that will attempt to minimize these problems without degrading network performance. Simulation results show that the performance of proposed work is better as compared to existing protocols. [ABSTRACT FROM AUTHOR]

Although the compact endless cast and rolling mill (CEM) is a promising candidate as a next-generation energy-saving steel process, due to its short history, the formability of the steel sheet produced by the CEM process are not known yet. Herein, drawability and stretchability of low-carbon steel sheets produced by the CEM process are investigated and compared with those of conventional hot-rolled low-carbon steel sheets, to estimate its applicability to industrial parts. Finite element analyses using the Gurson-Tvergaard-Needleman damage model were conducted and compared with the experimental results. Homogeneous microstructure and relatively strong textures of {111}||ND γ-fibers and 〈110〉||RD α-fibers were developed in the CEM-processed steel in comparison with the conventional hot-rolled specimen. The drawn cup of the CEM specimen showed weak earing phenomena, while having higher limiting drawing ratios (2.0 and 1.95 in the experimental and numerical simulation, respectively). Furthermore, a difference in limit dome height between the two specimens is negligible. Therefore, it is confirmed that CEM-processed steels have comparable properties of strength and formability, provide an effective manufacturing process, and exhibit good potential as a next-generation energy-saving process. [ABSTRACT FROM AUTHOR]

This study aims at examining the causal relationship between energy consumption, natural resources, environmental pollution (i.e., CO2 emissions) and climate change (i.e., Greenhouse gas emissions - GHG) in the context of Pakistan, over the period of 1975-2012. The study applied bivariate cointegration and Granger causality technique for robust inferences. The results show that energy demand increases gas rents, natural resource rents, and oil rents while it exhausts the natural resources. Natural resources further affected by air pollution and climate change in a country. The results of Granger causality indicate that there is a bidirectional causality between (i) energy consumption and net forest depletion, (ii) energy demand and oil rent, (iii) forest rents and CO2 emissions, (iv) natural resource depletion and GHG emissions, and (v) net forest depletion and GHG emissions, while, there is a unidirectional causality running from CO2 emissions to oil rents, from net forest depletion to CO2 emissions, and from GHG emissions to forest rent, mineral rent, natural gas rent, and oil rent in a country. Finally, the study confirmed the 'neutrality hypothesis' between coal rent, natural resource rent, and GHG emissions in Pakistan. © 2016 American Institute of Chemical Engineers Environ Prog, 36: 638-648, 2017 [ABSTRACT FROM AUTHOR]

With a large nationwide retailer, we run a natural field experiment to measure the effects of energy use information disclosure, customer rebates, and sales agent incentives on demand for energy-efficient durable goods. Although a combination of large rebates plus sales incentives substantially increases market share, information and sales incentives alone each have zero statistical effect and explain at most a small fraction of the low baseline market share. Sales agents strategically comply only partially with the experiment, targeting information to more interested consumers but not discussing energy efficiency with the disinterested majority. These results suggest that seller-provided information is not a major barrier to energy-efficiency investments at current prices in this context. Data, as supplemental material, are available at . This paper was accepted by John List, behavioral economics. [ABSTRACT FROM AUTHOR]

Any machine or manufacturing process designed by engineers is not as excellent as alive organisms or processes carried out in natural surroundings, which have been designed by The NATURE in evolution process. Because of this fact in many areas in order to develop machines, tooling or manufacturing processes engineers are looking for inspirations at plants or animals behaviour, structure or living processes. In the paper the examples of bioinspration in aspect of energy production and consumption are presented. [ABSTRACT FROM AUTHOR]

Many municipal wastewater treatment plants are retrofitted with membrane filtration that replaces secondary clarification. Such a solution saves space and improves overall treatment efficiency but at the cost of increased energy consumption and reduced potential for energy recovery from sewage sludge. Thus, the plant takes a step back from reaching energy self-sufficiency. In the presented case study, two alternative upgrade options were simulated for a medium-size municipal wastewater treatment plant in Poland: the first one assumed optimization of the existing bioreactor, and the other – installation of microfiltration membrane units inside the bioreactor. In both cases, anaerobic digestion of waste sludge with biogas utilization is planned. The results have shown that while under both upgrade options, the plant's capacity can be effectively increased by approximately 50%, their effects on the plant's energy balance will be very different. Although the installation of membrane modules accompanied by the construction of anaerobic digestion tanks improves the plant's energy balance, it will remain negative. The option of optimizing the existing biological treatment system produces a positive energy balance with more energy produced from biogas than consumed. Thus, the plant is able to approach energy self-sufficiency. It has been concluded that retrofitting the plants with membrane filtration is not always the best option from the energy balance point of view and it should be preceded with a detailed analysis on a case-by-case basis. [ABSTRACT FROM PUBLISHER]

In this paper, we study energy-efficient power allocation in distributed antenna systems (DASs). Unlike previous works that assumed perfect channel-state information (CSI) at the transmitter, we investigate a more practical case, where only the slowly varying large-scale CSI is known, to reduce the system overhead for CSI acquisition. Under a generalized DAS model, the power allocation problem for energy-efficiency (EE) maximization is formulated as a nonconvex fractional programming problem. Using the random matrix theory, the nonlinear fractional programming theory, and the saddle-point theory, we propose an iterative algorithm that achieves the global optimal solution. We also show that deploying the antennas in a distributed manner may enlarge the region where the optimal EE and the optimal spectral efficiency (SE) can be simultaneously achieved. Accordingly, we suggest the DAS-like way to densify the future 5G and beyond cellular networks to achieve EE and SE simultaneously. [ABSTRACT FROM PUBLISHER]

In this paper, the energy efficiency (EE) of multihop relaying over Nakagami- $m$ fading channels is investigated. The “consumption factor” (CF), which is adopted as a metric to evaluate the EE, is derived for both amplify-and-forward and decode-and-forward relaying strategies. Then, based on the obtained expressions, we propose a power-allocation (PA) strategy maximizing the CF. In addition, a suboptimal low-complexity PA algorithm is proposed and analyzed, and the obtained PA scheme is compared in terms of EE with other PA schemes from the literature. Analytical and simulation results confirm the accuracy of our derivations and assess the performance gains of the proposed approach. [ABSTRACT FROM PUBLISHER]

The base station (BS) density configuration is a crucial factor in improving energy efficiency (EE) in cellular networks, particularly when the sleeping strategy is used to reduce energy consumption. In this paper, the optimization of BS density for enhancing EE through traffic-aware sleeping strategies in both one- and two-tier cellular networks is researched, where the BS location is modeled as a Poisson point process. In the one-tier scenario, the EE optimization objective function is proved to be quasi-concave, and the optimal BS density solution is derived, where the maximum achievable EE is demonstrated to be independent of user density. In the two-tier scenario, both the activation probability of BSs and the coverage probability are analyzed, where the EE optimization objective function is proved to be not necessarily quasi-concave. To handle this nonconvex issue, an equivalent optimization problem that jointly optimizes the ratio and weighted sum of BS densities is proposed and solved by a dynamic gradient iterative algorithm. Meanwhile, a data fitting method is utilized to quantitatively analyze EE performances, in which the relationship between the optimal BS density and the user density is approximately linear when the user density is sufficiently high. Simulation results verify the relevant derivations and reflect that the sleeping strategy can not only save energy but improve the quality of radio links as well. [ABSTRACT FROM PUBLISHER]

In this paper, using stochastic geometry, we investigate the average energy efficiency (AEE) of the user terminal (UT) in the uplink of a two-tier heterogeneous network, where the two tiers are operated on separate carrier frequencies. In such a deployment, a typical UT must periodically perform the interfrequency small-cell discovery (ISCD) process to discover small cells in its neighborhood and benefit from the high data rate and traffic offloading opportunity that small cells present. We assume that the base stations of each tier and UTs are randomly located, and we derive the average ergodic rate and UT power consumption, which are later used for our AEE evaluation. The AEE incorporates the percentage of time that a typical UT missed small-cell offloading opportunity as a result of the periodicity of the ISCD process. The additional power consumed by the UT due to the ISCD measurement is also included. Moreover, we derive the optimal ISCD periodicity based on the UT's average energy consumption (AEC) and AEE. Our results reveal that ISCD periodicity must be selected with the objective of either minimizing the UT's AEC or maximizing the UT's AEE. [ABSTRACT FROM PUBLISHER]

Energy efficiency have always been a priority while designing wireless sensor networks. Introduction of mobile agent technology in wireless sensor networks for collaborative signal and information processing has provided the new scope for efficient processing and aggregation of data. Mobile agent based distributed computing paradigm offers numerous benefits over the existing and commonly used client/server computing paradigm in wireless sensor networks. Mobile agent performs the task of data processing and data aggregation at the node level rather than at the sink, thus, eliminating the redundant network overhead. One of the most important issues in mobile agent based paradigm is planning of an itinerary for agent traversal. In this paper, we have proposed a dynamic mobile agent based data aggregation approach that takes into consideration energy efficiency, network lifetime, end to end delay and aggregation ration while making the decision for migration of agent in multihop sensor network. As our approach focuses on finding the most informative route by traversing comparatively less number of nodes consequently mobile agent takes less time to return to processing element, thus, exhibiting lower delay. [ABSTRACT FROM AUTHOR]

Secure communication is an important task for wireless sensor networks (WSNs). Signcryption is a good choice to guarantee the security of resource-constrained WSNs since it simultaneously achieves confidentiality, authentication, integrity and non-repudiation at a low cost. In this paper, we propose a heterogeneous signcryption scheme for secure communication from the WSNs to an Internet server. In our scheme, the WSNs belong to the certificateless cryptosystem (CLC) and the server belongs to the public key infrastructure (PKI). The CLC has neither key escrow problem nor public key certificates and is very suitable for the WSNs. The PKI is also suitable for the server since the PKI technique has been widely adopted in the Internet security. We prove that our scheme has the existential unforgeability against adaptive chosen message attack under q-strong Diffie-Hellman and modified inverse computational Diffie-Hellman problems and indistinguishability against adaptive chosen ciphertext attack under bilinear Diffie-Hellman inversion problem in the random oracle model. As compared with the existing three certificateless signcryption schemes (i.e., YL, BF and WC), our scheme respectively costs a 28.4, 58.3, and 68.2 % less in computational time and a 26.9, 56.6, and 67.3 % saving in energy consumption (the length of transmitted message is 100 bits). [ABSTRACT FROM AUTHOR]

Mitigation of thermal stress and adverse indoor climatic conditions is important to older low-income populations whose age, health, and economic circumstances make them vulnerable to indoor environmental conditions. This research examines whether energy retrofits in affordable housing for older adults can also improve indoor climatic (i.e., temperature, humidity, air infiltration) conditions and whether such improvements correspond with improved health and comfort of residents. An apartment complex for low-income older adults in Phoenix was the study site. In 2010, renovations were undertaken to make it more energy efficient and to replace interior cabinetry, flooring, and paint with materials that had low or no volatile organic compounds ( VOCs). Fifty-seven residents from 53 apartment units participated in both baseline (pre-renovation) and 1 year post-renovation data collection trials. Environmental measures included temperature, relative humidity, and air infiltration. Health measures included general health, emotional distress, and sleep. Four questions addressed residents' perceptions of temperature quality. Results demonstrated a 19% reduction in energy consumption following the retrofit. In addition, fixed effects statistical models of the panel data showed significant stabilization of unit temperature from pre-retrofit to 1 year post-retrofit. Reductions in an apartment's temperature extremes of 27.2°C (81°F) and above also corresponded with improvement in occupant's reported health over the same time period, although not with occupant's perceptions of thermal comfort. [ABSTRACT FROM AUTHOR]

Multicast delivery in wireless multi-hop networks has become the popular research topic and holds the important applications such as sensor and tactical networks. However, how to minimize multicast energy consumption and prolong the lifetime of multicast connection in wireless multi-hop networks with limited energy is a challenge at present. This paper presents a new approach to solve this problem by considering the cognitive ability of nodes. Above all, we exploit the directional reception antennas to propose a directional reception two-step reconstruction routing scheme to set up multicast tree for wireless multi-hop networks. Different from previous methods, we grant the cognitive ability to each node so that they can obtain the minimum transmission power by sensing, learning, acting, and deciding. We propose two algorithms to find the minimum transmission power of all the nodes in the multicast tree built above. And a global optimal multicast delivery algorithm with the minimum energy consumption is proposed to implement effective multicast communication for wireless multi-hop networks with energy limited. Numerical experiments show that the proposed approach can significantly improve the multicast performance of wireless multi-hop networks with energy limited such as the lifetime of multicast connection and transmission power. [ABSTRACT FROM AUTHOR]