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Femto flow electrospray ionization (ESI) ranging from 240 fL/min to low pico flow (< 10 pL/min) was conducted and measured using submicron emitter tip and relay ESI configuration. Signature analyte ion intensities and profiles were obtained. Obtained flow rate and ionization current enabled size calculation for initial charged nanodroplet.

In this paper, allocation memory algorithms (i.e. First Fit, Next Fit and Best Fit) are redesigned to offload the tasks of end devices in multi-device multi-task D2D communication. The proposed algorithms offload each task to single device, which enhance the performance by 4x at their maximum performance. To enhance the performance, the next fit algorithm is redesigned to offload the task to multiple devices, which enhances the performance to 88x at its maximum performance. The proposed algorithms are evaluated for different cell scenarios (i.e. femto, pico, micro and macro cells). Simulation results demonstrates that utilizing computation offloading minimizes the latency.

A key issue in the optimal designing of a Stirling machine is to develop a precise thermodynamic numerical model that could predict the performances and provide means for further optimization. In this paper, a non-ideal second-order numerical model called modified simple analysis model has been presented for the Stirling cycle refrigerating machine. The model incorporates effects of shuttle heat loss to the expansion space and mass leakage to the crankcase in the differential equations of pressure change, rate of change of mass of gas in compression and expansion spaces, and mass flow rates across these working spaces. The model was simulated using MATLAB code for Beta configuration FEMTO 60 Stirling engine operating as a refrigerator and validated with an experiment. The validation of the numerical model with experimental work showed that the results of the simulation are consistent with the results of the experiment. Hence, the numerical model could be used to design a Stirling cycle refrigerating machine for moderate temperature applications with reasonable accuracy especially if optimization is performed further. The effects of incorporating shuttle heat loss in the differential equations on the temperature of working gas and the overall performance of the Stirling refrigerator have been analyzed. Lastly, parametric investigations have also been performed to evaluate the effect of operating parameters (temperature, pressure, and frequency) on the performances of the refrigerating machine. Better performance could be achieved at relatively lower frequency or higher pressure.

Refractive surgery is recognized as an effective method for myopia treatment, but it can induce night vision disturbances such as glare. We present an eye modeling method for the optical quality assessment in response to the structural changes in the eyes by femto-LASIK surgery. Customized eye models were built from the measurements of 134 right eyes pre- and post-operatively. Optical performance was evaluated using spot diagrams, point spread functions (PSFs), modulation transfer functions (MTFs), and chromatic aberrations at various fields (0°–30°), different pupil diameters (2–6 mm), and initial myopias (− 1.25 to − 10.5 D). Pupil size and initial myopia are the two major factors that affect visual performance of post-operative eyes. The results of spot diagrams, PSFs, and MTFs indicated that post-operative visual performance deteriorated as the visual field and pupil size increased, and it was significantly influenced by initial myopia. Post-operative chromatic aberrations were also affected by initial myopia. As pupil size increased, the post-operative longitudinal chromatic aberrations tended to decrease slightly, while the transverse chromatic aberrations remained similar. The use of eye modeling for refractive surgery assessment could possibly provide a more personalized surgical approach, could improve the prediction accuracy of refractive surgery outcomes, and promote the invention and development of better surgical methods.

In this article, a joint user pairing and secure resource allocation scheme for cognitive radio inspired nonorthogonal multiple access (CR-NOMA) femtocells in the presence of a jammer base station (JBS) is proposed. In the considered CR-NOMA-based femtocells, femto base stations (FBSs) serve their femto mobile station (FMS) by sharing the resource block (RB) with macromobile stations (MMSs), while the JBS in each femtocell secures the data rate of a weak user from the eavesdropping capability of the strong FMS. The strong FMS intercepts the data rate of the weak FMS using a successive interference cancellation technique to decode their own data as per the NOMA principle. The weak FMS protects its data from the strong eavesdroppers through the JBS. The JBS generates artificial noise to confuse the strong eavesdroppers. The problem of the joint user pairing and resource allocation is formulated as an optimization problem, whose main goal is to maximize the secure sum rate of the FMS while guaranteeing the secure data rate of the weak FMS and MMS. For RB allocation, CR at the FBS senses the best RB for its FMS using the Greedy approach. To optimize the power of the FBS and JBS, a successive convex approximation scheme with a low complexity is applied. Simulation results show that our proposed scheme provides an improvement in the secure sum rate of the FMS in comparison to the conventional NOMA and preexisting orthogonal multiple access schemes.

The understanding of materials requires access to the dynamics over many orders of magnitude in time; however, single analytical techniques are restricted in their respective time ranges. Assuming a functional relationship between time and temperature is one viable tool to overcome these limits. Despite its frequent usage, a breakdown of this assertion at the glass-transition temperature is common. Here, we take advantage of time- and length-scale information in neutron spectroscopy to show that the separation of different processes is the minimum requirement toward a more universal picture at, and even below, the glass transition for our systems. This is illustrated by constructing the full proton mean-square displacement for three bottlebrush polymers from femto- to nanoseconds, with simultaneous information on the partial contributions from segmental relaxation, methyl group rotation, and vibrations. The information can be used for a better analysis of results from numerous techniques and samples, improving the overall understanding of materials properties.

Electromagnetically induced gratings (EMIGs) of atomic populations are formed in the resonant media at the interference of two or more overlapping monochromatic beams. They are of great interest in the view of the possibility of numerous applications in optics and spectroscopy. The significant progress has been achieved recently in the generation of ultrashort femto- and attosecond pulses. Such ultrashort pulses cannot provide an interference pattern because the region of their overlapping is very small and insufficient to form even few interference fringes. However, when the pulse duration is shorter than the relaxation times in the medium in the presence of a coherent interaction with the medium, they can rapidly change of the population of atomic levels owing to carrier-wave Rabi flopping. In this case, population gratings can be formed without the instantaneous overlapping of ultrashort light pulses in the medium. The latest results on the production and control of EMIGs received by means of a sequence of single- and subcycle light pulses have been reviewed. It has been shown that the unipolar subcycle pulses can be used to control more efficiently the EMIGs compared to multipolar multicycle pulses. Various applications of these gratings have been discussed in the ultrafast optics and for the holographic recording.

Purpose of the study to carry out a comparative analysis of the state of the zonular fibers before and after surgery on UBM between femtolaser assisted and classical ultrasound cataract removal. Material and methods. 19 patients (38 eyes) with age-related cataracts. 22 eyes were with pseudo-exfoliative syndrome. All patients were examined with grade 1 lens subluxation. The first group of 19 eyes underwent cataract femto-phacoemulsification. The second group included 19 eyes without using a femtolaser. The state of the fibers was determined on the UBM on the fifth day after the operation at the end of antibiotic therapy. Results. The data showed the presence of a statistically significant difference between the group with femto-assistance and the group without it. In the first group, UBM analysis showed that the state of the zonular fibers remained in the same state in 16 of 19 eyes. In the second group, 11 of 19 eyes required ring implantation with suturing to the sclera and 3 required IOL implantation with seamless fixation to the sclera and vitrectomy. Conclusions. The appropriate path to surgery depends on the most accurate objective assessment of the condition of the lens ligaments, since the position of the IOL is one of the main factors for a good result expected by the patient after surgery. Reducing the «trauma» of the eye with lens surgery has been a key success factor and femtolaser guidance provides valuable assistance in obtaining it. Key words: lens subluxation, femtosecond laser, UBM.

Recently discovered extraordinary optical nonlinearities in epsilon-near-zero (ENZ) materials open a new realm of ultra-energy-efficient, all-optical switching devices for future optical communication and computation. In this paper, we propose a sub-micron, sub-pico-second, femto-joule level all-optical switch (AOS) using hybrid plasmonic-silicon waveguides driven by high mobility transparent conductive oxides (HMTCOs) such as cadmium oxide. Our analysis indicates that the ENZ-induced nonlinear optical effect is greatly enhanced by the high free carrier mobility in the telecom wavelength region. We propose an electrically tunable AOS device which is precisely biased at the ENZ condition, or the high-loss “OFF” state. Then the AOS device can be switched to the “ON” state with an unprecedented modulation strength of 15.9 dB/μm and a rapid switching time of 230 fs at the cost of an ultralow switching energy of 13.5 fJ. By defining a comprehensive metric using the product of device size, switching energy and switching time, the proposed ENZ-enabled device shows superior performance than any existing on-chip AOS device. We envision that such HMTCO-driven AOS device can be integrated with silicon photonic integrated circuits to realize on-chip optical signal processing and computation with ultra-low energy and ultra-high bandwidth.

International audience; As the progress towards 5G wireless networks, energy efficiency (EE) has become one of the critical design criteria for future wireless communications. In this regard, the joint transmission coordinated multipoint (JT-CoMP) technique is considered as a promising technology to save energy by mitigating intercell interference and improving spectral efficiency. However, additional power for data sharing and resource information is consumed by this technology. To evaluate the EE in dense femtocell networks with joint transmission CoMP approach and capture the significant factors involved in the energy consumption process, representative and accurate models are needed. In this paper, while applying a realistic power consumption model, we develop a tractable model in a JT-CoMP downlink transmission network based on spatial fluid modeling, which reduces the analysis complexity. Moreover, the proposed model’s effectiveness and accuracy are shown by comparing the obtained results to those of Monte Carlo simulations. Afterward, our simulation outcomes point out that EE is mainly highest in free space than urban areas, and can be improved with the increase of cooperative BSs number for a constant backhauling power cost. Moreover, in the case of a variable backhauling power cost, JT-CoMP becomes beneficial when the SINR threshold is 3dB.

Benzo and Naphthopyrans (chromenes) have been extensively studied since the discovery of photochromic reaction of 2 H -1-benzopyrans in 1966 by Becker and Michl. Researchers have investigated chromenes for their use in sunglass lenses and also other potential applications such as optical memories and optical switches. Femto/picosecond and nano/microsecond experiments were released on two 6,6 a -dihydrochromeno(3,4- b )chromene derivatives. After disappearance of the singlet state S 1 formed from each compound, photoproducts with short lifetime (2.2 to 21 ?s) obtained were attributed to the open forms. Keywords : 6,6 a -dihydrochromeno(3,4- b )chromene, photochromic, nano/microsecond domain, femto/picosecond domain, wavelength, lifetime.

The paper is motivated by the urgent need, imposed by the COVID-19 pandemic, for trustworthy access to secure communication systems with the highest achievable availability and minimum latency. In this regard, we focus on an ultra-dense wireless network consisting of Femto Access Points (FAPs) and Unmanned Aerial Vehicles (UAVs), known as caching nodes, where there are more than one possible caching node to handle user's request. To efficiently cope with the dynamic topology of wireless networks and time-varying behavior of ground users, our focus is to develop an efficient connection scheduling framework, where ground users are autonomously trained to determine the optimal caching node, i.e., UAV or FAP. Our aim is to minimize users' access delay by maintaining a trade-off between the energy consumption of UAVs and the occurrence of handovers. To achieve these objectives, we formulate a multi-objective optimization problem and propose the Convolutional Neural Network (CNN) and Q-Network-based Connection Scheduling (CQN-CS) framework. More specifically, to solve the constructed multi-objective connection scheduling problem, a deep Q-Network model is developed as an efficient Reinforcement Learning (RL) approach to train ground users to handle their requests in an optimal and trustworthy fashion within the coupled UAV-based femtocaching network. The effectiveness of the proposed CQN-CS framework is evaluated in terms of the cache-hit ratio, user's access delay, energy consumption of UAVs, handover, lifetime of the network, and cumulative rewards. Based on the simulation results, the proposed CQN-CS framework illustrates significant performance improvements in companion to Q-learning and Deep Q-Network (DQN) schemes across all the aforementioned aspects.

Though efforts to improve the temporal resolution of transmission electron microscopes (TEMs) have waxed and waned for decades, with relatively recent advances routinely reaching sub-picosecond scales, fundamental and practical challenges have hindered the advance of combined Å-fs-meV resolutions, particularly for core-loss spectroscopy and real-space imaging. This is due in no small part to the complexity of the approach required to access timescales upon which electrons, atoms, molecules, and materials first begin to respond and transform - attoseconds to picoseconds. Here we present part of a larger effort devoted to systematically mapping the instrument parameter space of a TEM modified to reach ultrafast timescales. With General Particle Tracer, we studied the statistical temporal distributions of single-electron packets as a function of various fs pulsed-laser parameters and electron-gun configurations and fields for the exact architecture and dimensions of a Thermo Fisher Tecnai Femto ultrafast electron microscope. We focused on easily-adjustable parameters, such as laser pulse duration, laser spot size, photon energy, Wehnelt aperture diameter, and photocathode size. In addition to establishing trends and dispersion behaviors, we identify regimes within which packet duration can be 100s of fs and approach the 300 fs laser limit employed here. Overall, the results provide a detailed picture of the temporal behavior of single-electron packets in the Tecnai Femto gun region, forming the initial contribution of a larger effort.

The remaining useful life (RUL) prediction plays a pivotal role in the predictive maintenance of industrial manufacturing systems. However, one major problem with the existing RUL estimation algorithms is the assumption of a single health degradation trend for different machine health stages. To improve the RUL prediction accuracy with various degradation trends, this article proposes an algorithm dubbed degradation-aware long short-term memory (LSTM) autoencoder (AE) (DELTA). First, the Hilbert transform is adopted to evaluate the degradation stage and factor with the real-time sensory signal. Second, we adopt LSTM AE to predict RUL based on multisensor time-series data and the degradation factor. Distinct from the existing studies, the proposed framework is able to dynamically model the degradation factor and explore latent variables to improve RUL prediction accuracy. The performance of DELTA is evaluated with the open-source FEMTO bearing data set. Compared with the existing algorithms, DELTA achieves appreciable improvements in the RUL prediction accuracy.

Active femto- and nano-objects can determine the composition, structure, and behavior of the solar and interstellar winds (flows of various particles) near the Sun, the Earth, and in interstellar space (near the heliopause). Using the anisotropic model, parameters are estimated that are consistent with experimental data from the Planck space observatory, the UTR-2 and URAN-2 radio telescopes, the Parker solar probe, and the Voyager 1 and Voyager 2 probes.

In the rapid development of wireless communications, femtocells provide tremendous improvement in coverage and quality of service for users. Macro-femto based networks are envisioned to be the de-f...

This review offers the reader some of the achievements of modern optical metrology. Over the past decades, it has become possible to make a leap in the basic approaches of metrology from the nano to the femto, approaching the pico level of measurements. Control of nano (micro) particle motion by an optical field and their use for testing complex optical fields; ultra-precise determination of the optical parameters of both solid and liquid and gas-like substances by optical methods; the tiny metrology of the phase shift of orthogonally polarized beams and the determination of their degree of mutual coherence, by interference methods and many other, are proposed for consideration in this paper. Optical metrology, which is provided by three-dimensional polarization distributions of optical fields, where structured light plays a special role; by using femtosecond lasers, and much more, demonstrates the prospects of optical methods in modern measuring systems.

For macro-femto network, intratier and cross-tier interference (CI) must be canceled to achieve the quality of service, better indoor coverage, and higher data rates. Moreover, for better wireless local area network (WLAN) and mobile communication services while ensuring WLAN security, appropriate temperature in modern buildings with reduced energy cost is also required. To address these issues, RadioClear (RC) film can be pasted on an ordinary glass and installed in different sections to cancel the intratier interference between the femto network as well as CI between the femto and macro network. Moreover, this technique can also ensure enhanced WLAN security and thermal insulation in modern buildings. For WLAN transmission, a fractal dual bandpass frequency selective surface (FSS) designed in the RC sheet can be used to improve the WLAN communication in a situation where two or more than two rooms are served through a single WLAN router. Theoretical results are presented which are further verified through the experimental results.

Recent developments and advancements in wireless networks have brought about new challenges including the backhaul bottleneck and content download latency. The paper focuses on an enterprise wireless network consisting of various candidate caching nodes to serve users’ requests such as Femto Access Points (FAPs) and Mobile Users (MUs), supported by Device-to-Device (D2D) communications. Due to the fact that user's mobility is one of the inherent features of massive wireless networks, where FAPs operate in an open access mode, the small transmission range of FAPs leads to triggering frequent handovers. Taking the above challenges into account, we propose a novel Mobility-Aware Femtocaching scheme based on Handover (MAFH). To implement a real wireless network, a random walk model as the mobility pattern of users is utilized within the proposed scheme. In this regard, the best caching node is selected by considering the Received Signal Strength Indicator (RSSI) value and the velocity of users as decision criteria to extend the time interval between two consecutive handovers and increase the battery life of devices. The effectiveness of the proposed MAFH algorithm is evaluated in terms of the cache hit ratio, transferred byte volume, connecting time, content delivery time, the number of handovers, and the energy consumption of clients. Based on the simulation results, the proposed MAFH framework illustrates significant performance improvements in companion to its counterparts across all the aforementioned aspects.

The goal is to develop a combined technique for preliminary YAG laser fragmentation and Femto laser exposure on a CATALYS device and to evaluate its role in reducing the time and energy parameters of a surgery of high-density cataract. Material and methods. The study included 118 patients (118 eyes) with age-related cataracts of the 3rd and 4th degrees of lens nucleus density. In the main group, before phacoemulsification (PE) with a Femto laser support and IOL implantation, preliminary YAG laser phacofragmentation of the lens nucleus was performed. In the first control group, PE was performed with Femto laser support and IOL implantation. In the second control group PE with IOL implantation. Results. A 35% decrease in the energy of the Femto laser action at a 3rd degree of lens nucleus density was achieved, and 40% at the 4th degree, in comparison with the PE with the Femto laser support without preliminary YAG laser phacofragmentation, a 38% decrease in the cumulative ultrasound energy at 3rd degree of the lens nucleus density, and 42% at 4th degree compared with isolated ultrasonic cataract phacoemulsification. Conclusion. The proposed modification of the technique of combined YAG laser and Femto laser exposure allows achieving during cataract surgery a complete fragmentation of the lens nucleus of a high degree of density, helps minimizing the risk of complications and reaching quick postoperative rehabilitation of patients.

The emerging fifth generation (5G) and beyond radio access networks are expected to be extremely dense and heterogeneous as compared to the current networks, involving a large number of different classes of base stations (BSs), namely macro, micro, femto and pico BSs. Among several performance requirements 5G and beyond systems aim to achieve, energy efficiency is one of the crucial requirements. In order to achieve energy-efficient design in dense heterogeneous 5G networks, various approaches in terms of resource allocation, off-loading techniques, hardware solutions and energy harvesting are being considered. In this regard, this paper develops an energy usage optimization framework in a cellular heterogeneous network (HetNet) consisting of a central macro-BS and a number of micro-BSs, equipped with renewable energy sources (RESs) such as solar panels and wind turbines. The proposed framework incorporates an energy cooperation mechanism along with a sleep mechanism (BS ON/OFF switching), in which the BSs having lean traffic are put into a sleep mode and their traffic load gets shared by the central BS. The surplus harvested energy from RESs of the sleeping BSs can then be sold back to the grid. An optimization problem for maximizing the utilization of RES and minimizing the usage of the traditional sources, such as utility and generator, is formulated and this mixed integer non-linear programming problem is solved through an interior point method. The presented results for various HetNet sizes demonstrate the significant savings in the energy cost with the proposed RES-enabled HetNet sleep mechanism model over the conventional approaches.

In this paper, we propose, an energy-efficient resource allocation scheme for simultaneous wireless information and power transfer (SWIPT)-Non-orthogonal multiple access (NOMA) based femtocell users with imperfect channel state information. SWIPT enhances the transmission power of Femto users and NOMA improves the spectral efficiency. Therefore, SWIPT and NOMA at Femto base station are integrated to improve the energy efficiency and spectral efficiency of femtocells. The formulated resource allocation problem is divided into subchannel allocation and power control. The preference list of Femto users and macro users is developed on the basis of their energy harvested from the Femto base station and macro base station, respectively. Then, to optimize the power of a Femto base station, a successive convex approximation low complexity technique at each Femto base station is used. Also, Dinkelbach method is used to convert the non-liner fractional problem into a subtractive problem and Lagrangian duality is used for power computation of Femto base station. Finally, the simulation results demonstrate that our proposed scheme provides 0.2% and 31.25% higher energy-efficiency in comparison to the existing EH-NOMA and EH-OFDMA schemes.

The ever-increasing demand for media streaming together with limited backhaul capacity renders developing efficient file-delivery methods imperative. One such method is femto-caching, which, despite its great potential, imposes several challenges such as efficient resource management. We study a resource allocation problem for joint caching and transmission in small cell networks, where the system operates in two consecutive phases: (i) cache placement, and (ii) joint file- and transmit power selection followed by broadcasting. We define the utility of every small base station in terms of the number of successful reconstructions per unit of transmission power. We then formulate the problem as to select a file from the cache together with a transmission power level for every broadcast round so that the accumulated utility over the horizon is maximized. The former problem boils down to a stochastic knapsack problem, and we cast the latter as a multi-armed bandit problem. We develop a solution to each problem and provide theoretical and numerical evaluations. In contrast to the state-of-the-art research, the proposed approach is especially suitable for networks with time-variant statistical properties. Moreover, it is applicable and operates well even when no initial information about the statistical characteristics of the random parameters such as file popularity and channel quality is available.

Different kinds of low transmit power, flexible cell extension and hyper dense base stations (BSs) overlaying on the well established macro cells, forming the hyper-dense multilayer heterogeneous wireless cell networks (HetNets), where the BSs in each tier are characterized by the differences in BSs transmit power, path loss exponent, tier-biasing factor and BSs spatial density, is the promising technology for 5th generation mobile networks and to support hot spots and cell edge coverage. The HetNets downlink rate modeling is one of the key and challenge problems for the random deployment characteristics of BSs in lower layer. In this paper, a three tier HetNets, which includes macro tier, Pico tier and Femto tier, is first modeled with the spatial point process in stochastic geometry theory; then, considering the BSs low transmit power, flexible cell extension and hyper BSs spatial density, a tractable downlink rate model based on the nearest distance and bias accepted factor is proposed, which adopt stochastic geometry theory and is easy to compute; last, the proposed downlink rate model is validated by numerical examples to confirm that the flexible cell extension BSs deployment in complex high traffic area with different path loss exponent is an effective scheme to improve quality of service.

Detecting matter at a single-molecule level is the ultimate target in many branches of study. Nanosensors based on plasmonics have garnered significant interest owing to their ultrahigh sensitivity even at single-molecule level. However, currently, plasmonic-enhanced nanosensors have not achieved excellent performances in practical applications and their detection at femtomolar or attomolar concentrations remains highly challenging. Here we show a plasmonic sensing strategy, called buoyant plasmonic-particulate-based few-to-single particle-nanosensors. Large-sized floating particles combined with a slippery surface may prevent the coffee-ring effect and enhance the spatial enrichment capability of the analyte in plasmonic sensitive sites via the aggregation and lifting effect. Dimer and single particle-nanosensors demonstrate an enhanced surface-enhanced Raman spectroscopy (SERS) and a high fluorescence sensitivity with an enrichment factor up to an order of ∼104 and the limit of detection of CV molecules down to femto- or attomolar levels. The current buoyant particulate strategy can be exploited in a wide range of plasmonic enhanced sensing applications for a cost-effective, simple, fast, flexible, and portable detection., Plasmonic-enhanced nanosensors are limited in practical applications, as it remains challenging to detect molecules at low concentrations. Here, the authors introduce a buoyant particulate strategy in order to enrich analytes in the plasmonic hot spots.

This paper presents the development and integration of a power control algorithm into the User Association Algorithm with Optimal Bandwidth Allocation (UAAOBA) to form a Hybrid Algorithm for User Association and Resource Allocation (HAUARA). The power control algorithm updates the transmit power of the Base Stations (BSs) towards a minimum transmit power that satisfies the minimum data rate requirement (1 Gbps) of the User Equipment UEs. The power update is achieved using the Newton Rhapson’s method and it adapts the transmit powers of the BSs to the number of their connected UEs. The developed HAUARA provides an optimal solution for user associations, bandwidth allocation, and transmit powers to UEs concurrently. This maximizes the network energy efficiency by coordinating the load fairness of the network while guaranteeing the quality of service requirement of the UEs. The network energy efficiency performance of the developed HAUARA is compared with that of the UAAOBA. The results show that the developed algorithm has network energy efficiency improvement of 12.36%, 10.58%, and 13.44% with respect to UAAOBA for increase number of macro BS antennas, pico BSs, and femto BSs, respectively. Also, the network load balancing performance of the developed HAUARA is compared with that of the UAAOBA. The results show that the developed algorithm has network load balancing improvement of 12.62%, 10.04%, and 10.34% with respect to UAAOBA for increase number of macro BS antennas, pico BSs, and femto BSs, respectively. This implies that the developed algorithm outperforms the UAAOBA in terms of network energy efficiency and load balancing.

We report a significant improvement in the operational stability and photosensitivity of an interdigitated photodetector using a hybrid sensing material based on a reduced graphene oxide gel (femto...

With the ubiquitous demand for wireless communications, researchers have studied heterogeneous networks (HetNets) for years. Often the HetNets include a macrocell base station (MBS), several sets of macrocell users (MUs), a large number of femtocell base stations (FBSs), and femtocell users (secondary users), where the femtocells help the macrocell system relay the uplink or downlink traffic between the MUs and the MBS. In this article, we propose a novel joint information and energy cooperation method, with the aim of enhancing the spectrum and energy efficiency (EE) for cognitive HetNets. Specifically, the MUs and the femtocells harvest wireless energy from the radio frequency signal transmitted by MBS. By using the harvested energy, femtocells obtain the transmission opportunity to forward the signals of their serving users. We theoretically derive the theoretical expressions of the outage probabilities of the primary link as well as the secondary link. Then, we focus on investigating how to maximize EE by jointly considering time allocation and power control. Furthermore, we formulate the EE maximization problem, which contains the fractional form objective function and the linear inequality constraints and hence is nonconvex. To resolve this, we integrate the Dinkelbach method with convex optimization to derive the tractable and optimal solution. The numerical results demonstrate the simulations well match our theoretical analysis. Moreover, the results validate the feasibility of the proposed method for high-quality transmission without incurring extra energy consumption.

In millimeter wave (mmW) dense femto-networks, major challenges are overcoming the performance loss imposed by the channel and managing the co-channel interference. The former is due to the mmW susceptibility to pathloss and shadowing and the latter is due to density of the network. We cope with both challenges by a clustering method designed for mmW environment. In our approach, the femto access points (FAP) and femto users (FU) are clustered based on having the most line of sight connectivity. We modify this binary optimization problem into a continuous problem using deductive penalty functions and solve it by difference of two convex functions (D.C.) programming. Our clustering algorithm achieves higher data rate compared to the foremost clustering method. We also propose a technique to assign FUs to FAPs in each cluster which has near-optimal performance and polynomial time complexity. We solve mixed integer nonlinear programming of power and sub-channel allocation by D.C. programming. Instead of using the deductive penalty terms in D.C. programming, we penalize the objective function in a multiplicative manner. Thus, the penalty term depends on both constraint violation and objective function. Our scheme achieves around 10% higher data rate compared to the method using deductive penalty terms.

The proliferation of smart IoT/mobile devices has ignited the development of new applications that not only require additional compute resources but add new constraints of privacy and low latency. This trend has motivated the recent edge/fog computing paradigm, which introduces a middle tier of rich resources between cloud and IoT/mobile devices. In this article, we argue for the overlooked compute opportunity that lies beyond the traditional edge/fog paradigms, which we refer to as FemtoClouds. Femto- Clouds represent pools of beyond edge idle IoT devices that have computational capacity competitive with traditional data centers and potentially are available at lower costs. With proper enabling technologies and addressing their challenges, FemtoClouds can be leveraged as a complementary platform to the current computational options spectrum.

In the fractional frequency reuse (FFR) system, the bandwidth is partitioned into orthogonal subbands such that users in the cell-center region use the subbands of a frequency reuse factor (FR factor) equal to 1, whereas users in the cell-edge region exploit the subbands of an FR factor larger than 1. The distance threshold, which is used to distinguish the cell-edge region from the cell-center region, is an important factor in FFR system performance. In this paper, we study the optimal distance threshold to maximize system throughput in the downlink cellular networks, including aerial base stations. Subject to the constraint that a given target outage probability is satisfied, the optimal distance threshold is analyzed as a function of the cell size. It is proven that when the sizes of all cells in the network are scaled at the same rate, the optimal distance threshold normalized by the cell size is nondecreasing in the cell size. The analytical results in this paper provide a system design guideline for initial planning of FFR cellular networks of different sizes, including macro, pico, and femto systems. In particular, for size-scalable aerial networks comprising base stations in the sky, such as balloons or unmanned aerial vehicles, our analysis offers insight into the design of the distance threshold with regard to the cell size.

Capacitance detection is a universal transduction mechanism used in a wide variety of sensors and applications. It requires an electronic front-end converting the capacitance variation into another more convenient physical variable, ultimately determining the performance of the whole sensor. In this paper we present a comprehensive review of the different signal conditioning front-end topologies targeted in particular at sub-femtofarad resolution. Main design equations and analysis of the limits due to noise are reported in order to provide the designer with guidelines for choosing the most suitable topology according to the main design specifications, namely energy consumption, area occupation, measuring time and resolution. A data-driven comparison of the different solutions in literature is also carried out revealing that resolution, measuring time, area occupation and energy/conversion lower than 100 aF, 1 ms 0.1 mm2, and 100 pJ/conv. can be obtained by capacitance to digital topologies, which therefore allow to get the best compromise among all design specifications.