Analog Part Research Articles

The development of the computer-aided design system for production processes of component part machining for single-piece production and repair conditions

The given article provides material on the development of the CADS applied for production processes of component part machining for single-piece production and repair conditions. The article describes technique used to organize a data fl ow and hose methods of machining which cannot be applied under these conditions of machining. This research uses graph theory. The article describes the developed algorithm for machining planning of details. A mathematical model of transitions in the technological process for the processing of parts has been obtained.The developed design CADS reduces the number of errors in the development of production processes. The article describes database for machining planning. In order to form input data, knowledge of production processes of analogous machine parts or products production is not required. Thus developed models of system determines of machine-part production stages. This system gives schemes of its basing, a set of bases and an order of their preparation and forming of schemes of technological dimensional chains. This system counts and recounts interoperational dimensions. Developed models and system allows to increase amount of output information to the level of operational fl ow charts. The designed system gives the chance of its use in modern multiproduct. This system is universal, multifunctional.

Study of Power Consumption of Timepix3 Detector

The Timepix3 readout chip—the latest member of the Medipix family of hybrid pixel detectors—brought several new functionalities in comparison with the older Timepix, i.e. a high hit-rate, a time granularity of 1.5625 ns, a data-driven readout scheme (with a per pixel dead time of approximately 475 ns), and the capability of measuring Time-over-Threshold (ToT) and Time-of-Arrival (ToA) in each pixel at the same time. However, the high power consumption of the Timepix3 in the standard setting prevents its use in applications with limited power budget. Moreover, the high power consumption poses the risk of overheating the sensor so that proper cooling is crucial. The presented work investigates the effect of different settings in the analogue and a digital part of the Timepix3 detector on its power consumption. Measurements were performed with the Timepix3 chipboard. The firmware of the Katherine readout was modified so that the user can monitor the power consumptions of analogue and digital part “on-line” (directly in the control software). In standard settings, a power consumption of approximately 1.3 W was found. By changes of internal DACs, the consumption could be reduced to 650 mW. Further reduction was achieved by the change of the clock management in the digital part of the Timepix3. In result, a power consumption of 216 mA could be achieved. In these low power settings, the ToA clock was reduced to 10 MHz and thus the time binning was 100 ns. The energy resolution was not affected significantly. The pixel dead time is also negatively affected when the matrix clock is reduced. In the case of 10 MHz, the minimal per pixel dead time is 1.9 μs.

Hybrid Precoding for Beamspace MIMO Systems With Sub-Connected Switches: A Machine Learning Approach

By employing lens antenna arrays, the number of radio frequency (RF) chains in millimeter-wave (mmWave) communications can be significantly reduced. However, most existing studies consider the phase shifters (PSs) as the main components of the analog beamformer, which may result in a significant loss of energy efficiency (EE). In this paper, we propose a switch selecting network to solve this issue, where the analog part of the beamspace MIMO system is realized by a sub-connected switch selecting network rather than the PS network. Based on the proposed architecture and inspired by the cross-entropy (CE) optimization developed in machine learning, an optimal hybrid cross-entropy (HCE)-based hybrid precoding scheme is designed to maximize the achievable sum rate, where the probability distribution of the hybrid precoder is updated by minimizing CE with unadjusted probabilities and smoothing constant. Simulation results show that the proposed HCE-based hybrid precoding can not only effectively achieve the satisfied sum-rate, but also outperform the PSs schemes concerning energy efficiency.

Dimension-Deficient Channel Estimation of Hybrid Beamforming Based on Compressive Sensing

Due to high hardware costs for digital beamforming, hybrid beamforming (HBF) is widely employed in millimeter-wave (mmWave) communications systems. However, the number of radio frequency chains in the analog part of HBF is far less than that of antennas, which causes a serious dimension-deficient problem. In order to overcome this problem, this paper proposes a compressive sensing algorithm using an adaptive overcomplete dictionary to estimate the sparse channel in the HBF-based mmWave system. The algorithm adaptively generates the dictionary by using the received signal to accurately reconstruct the mmWave channel. The simulation results are presented to demonstrate that the proposed algorithm outperforms its traditional counterparts in terms of the normalized mean square error and the spectral efficiency.

Respiratory monitoring system using Bluetooth Low Energy

The paper presents a system for monitoring respiratory frequency and strength using a BLE transmitter in non-connectable advertising mode and a variable impedance sensor operating in a relaxation oscillator circuit. The presented solution is characterized by low energy consumption. Both the measurement system and teletransmission system operate at 2.2 V power supply. By using a micropower operational amplifier, the analogue part of the system consumes 240–300 μW. Unipolar power supply and configuration of the relaxation oscillator enable to create a pseudobinary signal with the frequency f < 10 kHz. The relaxation oscillator is connected to the microcontroller binary input without having to convert the signal. By using a System On Chip (SoC) with CPU ARM Cortex to control the radio and perform measurements of the pseudobinary signal, the design was simplified and its dimensions were reduced. The operation of the analogue part of the system was compared with a commercial sensor. In addition, the ability of the system to reproduce the breath cycle signal on the BLE side was verified. Differences between the duration of individual cycles turned out to be statistically insignificant, both in the case of normal (p = 0.6889) and fast (p = 0.3226) breathing.

Faults Detection in Active Analog Bandpass Filter Using OBIST Method

The main objective of this paper is to explain the principal of different analog circuit testing methods to examine the difficulties present in the analog circuit testing i.e. to test the analog parts in a mixed signal circuit. In this paper all possible catastrophic and parametric faults present in the analog bandpass filter are tested by OBIST method which does not requires test vector generator which reduces the test development. Bandpass filter is examined for all possible fault detection and verifying that OBIST approach can improve the overall percentage of fault detection.

SEISAR-5 Portable Seismic Recorder with Low Energy Consumption for Autonomous Operation in Harsh Climatic Conditions

An autonomous three-channel digital recorder developed at the Schmidt Institute of Physics of the Earth, of Russian Academy of Sciences is considered. The recorder was designed to meet the requirements of particularly difficult climatic conditions, minimum energy consumption, and ease of maintenance. Special attention is devoted to the reliability of data storage in case of sudden power loss, for which a new file-free recording format was developed. For each second of data recording, the system assigns a service line consisting of the exact time, the station code, and the station’s coordinates. This prevents loss of data when reading. When power is restored, the recorder automatically switches to the operating mode and continues the interrupted recording. The power supply for the analog part of the recorder is galvanically decoupled from the power supply of the digital part and carefully smoothed by special linear stabilizers and filters. To exclude the penetration of pulsations from the digital to the analog part by the common (grounded) wire, the control interface of the ADC is separated from the microcontroller by digital galvanic isolation circuits. Recorded data is recovered from the instrument by replacing the memory card, which takes just a few seconds. The control functions are also minimized, since the recorder has only two control buttons. The ease of maintenance allows quick installation of a large number of seismic stations with a small number of staff. The most important feature of the recorder is significantly reduced power consumption (less than 0.7 A h per day at a supply voltage of 12 V). This is five to six times lower than that of domestic and foreign counterparts and allows the recorder to operate on a single set of dry manganese–air batteries with a capacity of 150 A h and a weight of 4 kg for more than 6 months. As a component of seismic monitoring systems and in conducting epicentral measurements, these recorders are used in all climate zones of the Northern Hemisphere, from Serbia to Sakhalin and from Yakutia to Bangladesh; they have proved reliable and low-maintenance devices.

Development of a System for Measuring and Recording Ion Currents for an MI-1201IG Mass Spectrometer

In the complex modernization of an MI-1201IG isotope mass spectrometer, a new system for measuring and recording ion currents was developed, including an electrometric amplifier based on a high-resistivity (1 TΩ) feedback resistor and a special chip located in the electrometer head. A recording circuit based on a high-precision analog-to-digital converter was included in the new unit for controlling the separating magnetic field and measuring the ion current. In designing the system circuit, the task was not only to increase the sensitivity and expand the dynamic range when measuring the intensity of peaks in mass spectra but also to decrease the time constant of the analog part of the measuring system for the undistorted transfer of the ion current distribution form to the input of the analog-to-digital converter in a dynamic mode. A shielding system was designed that distributes the electric field gradient on the surface of a high-resistivity feedback resistor, which made it possible to compensate its distributed capacitance and decrease the time constant of the electrometric amplifier to 0.2 s. To compensate for the distortion of the shape of the ion current pulses, caused by the in-to-out stray capacitance of the electrometer’s amplifier chip, a special circuit was developed. This results in that the end-to-end frequency response of the new system for measuring and detecting ion currents is determined only by the upper cut-off frequency of the low-pass filters of 10 Hz. The high-speed measuring system made it possible to improve the mass-spectrometric resolution and mass accuracy and to increase full-spectrum scan rate. The working range of the new system for measuring and recording ion currents is 1 × 10–15 to 3 × 10–12 A. The measured equivalent root-mean-square input noise is 0.86 fA at the sampling frequency of 10 Hz and the integration time of 1 s and 0.14 fA at the integration time of 10 s.

Digital compensation of the sideband-rejection ratio in a fully analog 2SB sub-millimeter receiver

Context. In observational radio astronomy, sideband-separating receivers are preferred, particularly under high atmospheric noise, which is usually the case in the sub-millimeter range. However, obtaining a good rejection ratio between the two sidebands is difficult since, unavoidably, imbalances in the different analog components appear. Aims. We describe a method to correct these imbalances without making any change in the analog part of the sideband-separating receiver, specifically, keeping the intermediate-frequency (IF) hybrid in place. This opens the possibility of implementing the method in any existing receiver. Methods. (i) We have built hardware to demonstrate the validity of the method and tested it on a fully analog receiver operating between 600 and 720 GHz. (ii) We have tested the stability of calibration and performance versus time and after full resets of the receiver. (iii) We have performed an error analysis to compare the digital compensation in two configurations of analog receivers, with and without intermediate-frequency hybrid. Results. (i) An average compensated sideband-rejection ratio of 46 dB is obtained. (ii) Degradation of the compensated sideband rejection ratio on time and after several resets of the receiver is minimal. (iii) A receiver with an IF hybrid is more robust to systematic errors. Moreover, we have shown that the intrinsic random errors in calibration have the same impact for configuration without IF hybrid and for a configuration with IF hybrid with analog rejection ratio better than 10 dB. Conclusions. We demonstrate that compensated rejection ratios above 40 dB are obtained even in the presence of high analog rejection. Further, we demonstrate that the method is robust allowing its use under normal operational conditions at any telescope. We also demonstrate that a full analog receiver is more robust against systematic errors. Finally, the error bars associated with the compensated rejection ratio are almost independent of whether IF hybrid is present or not.

A Unifying Design of Hybrid Beamforming Architectures Employing Phase Shifters or Switches

Hybrid beamforming (BF) architectures employing phase shifters or switches reduce the number of required radio frequency chains and the power consumption of base stations that employ a large number of antennas. Due to the inherent tradeoff between the number of radio frequency chains, the complexity of the employed analog and digital BF algorithms and the achieved spectral and energy efficiency, designing hybrid BF architectures is a complex task. To deal with this complexity, we propose a unifying design that is applicable to architectures employing either phase shifters or switches. In our design, the analog part of the hybrid BF architecture maximizes the capacity of the equivalent channel, while the digital part is updated using the well-known block diagonalization approach. We then employ the proposed joint analog-digital beamforming algorithm on four recently proposed hybrid architectures and compare their performance in terms of spectral and energy efficiency, and find that the proposed analog-digital BF algorithm outperforms previously proposed schemes. We also find that phase shifter-based architectures achieve high spectral efficiency, whereas switching-based architectures can boost energy efficiency with increasing number of base station antennas.

An Electrooptic Chaotic System Based on a Hybrid Feedback Loop

An electrooptic chaos source is proposed based on phase-modulation-to-intensity-modulation conversion theory and an analog–digital hybrid time-delay feedback loop. The analog part takes the digital binary sequences from shift registers as input and converts them into an analog noise-like signal, from which new bits are determined. The dynamical characteristic of the generated waveform is studied in detail by means of spectrum analysis, periodicity analysis, correlation performance, and complexity analysis. Moreover, the evolution between chaos and stochastic noise is observed and measured by adopting the complexity–entropy curves when a random perturbation is introduced. Such a perturbation can help with recovering chaotic dynamics from degradation. Based on this chaotic source, a secure and robust synchronization scheme that can exactly reproduce the signal is put forward. The effect of parameters’ mismatch and noise level on the synchronization quality is also investigated. The scheme has the potential to be applied in various applications when a robust random source is needed.

Banco de dados em software livre: uma solução para acesso e recuperação do patrimônio documental

Este trabalho apresenta um estudo sobre a criação de um banco de dados em software livre como solução para acesso e recuperação da informação do programa Pacto Nacional pela Alfabetização na Idade Certa, especificamente a documentação produzida e recebida que está sob custódia da coordenação geral do Pacto pela Universidade Federal de Santa Maria. Para a construção do banco de dados, utilizou-se o software livre BASE disponível tanto na suíte de software Libre Office, quanto no Open Office. O diagnóstico foi realizado por meio da observação direta da situação do acervo analógico e de parte do acervo digital, pois os documentos digitais estavam dispersos e muitos foram perdidos. Para os documentos em suporte papel, foi necessário criar representantes digitais para acessá-los no banco de dados, visando a facilitar o acesso e a recuperação da informação aos usuários. A digitalização foi feita de acordo com as recomendações do Conselho Nacional de Arquivos e com adoção de um vocabulário controlado para nomeação dos arquivos digitais. Foi aplicado um formulário online para o levantamento das necessidades informacionais dos usuários visando a construir um banco de dados que suprisse as suas necessidades informacionais. A partir dos resultados obtidos, foi possível construir um banco de dados em software livre, que reuniu, em um único local, a maior parte dos documentos, relatórios e apresentações elaboradas para as capacitações dos professores alfabetizadores integrantes do Pacto.

The Scale of instantaneous wellbeing: validity in a population with major neurocognitive disorders.

The quality of life (QoL) of people with a neurodegenerative pathology is a major issue in the absence of curative treatment. However, validated tools, suitable for patients with major neurocognitive disorders at a severe stage are rare and time-consuming in routine. The aim of this study is to analyze the validity of convergence and the reliability over time of a visual analog scale of well-being named EVIBE (Échelle d'évaluation instantanée de bien-être). The correlation between the EVIBE and another quality of life scale, the Qol-Ad was studied. The correlation with other scales expected to vary with QoL was also studied with the EQ-5D for the measurement of the state of health felt and the NPI-ES for the measurement of behavioral disorders. The EVIBE was administered twice, a few minutes apart, to measure its reliability over time. One hundred and thirty-five patients with Alzheimer's disease or a related disorder were recruited. The results indicated a significant correlation with Qol-AD (r=0.54, p< 0.001). The correlation remained significant when the Mini mental state examination was less than 10 (r=0.39, p=0.05). Correlations between EVIBE and EQ-5D and NPI-ES indicated more mixed results with significant correlation only for the analog part of the EQ-5D (r=0.34, p=0.007). The comparison between the two EVIBEs a few minutes apart showed a satisfactory agreement (r=0.52, p> 0.001). This study shows that EVIBE present a good convergence validity and a good reliability over time to measure the QoL of patients with neurodegenerative pathology even at severe stages of the disease. The scale allows a direct and rapid assessment of the QoL of patients in routine.

Subchannel Allocation and Hybrid Precoding in Millimeter-Wave OFDMA Systems

Constrained by the number of transmitted data streams, this paper proposes sub-carrier allocation (SA) and hybrid precoding (HP) designs for sum-rate maximization in mm-wave OFDMA systems. The optimization is first formulated as a computation sparsity-constrained HP design problem, which is non-convex and challenging to solve. Two two-stage solution approaches are proposed. In the first approach, a fully digital precoder (FDP) is optimized considering the computation sparsity constraint in the first stage. In the second approach, the sparsity constraint is only imposed in the second stage. To find the FDP, we employ the minimization of the weighted mean-squared error and the $\ell 1$ -reweighted methods to tackle the non-convex objective function and sparsity constraints, respectively. In the second stage of each approach, we exploit an alternating weighted mean-squared error minimization algorithm to reconstruct HP’s based on the FDP found in the first stage. Two novel analog precoding designs, namely semi-definite-relaxation-based and projected-gradient-descent-based, are then proposed to optimize the analog part of the obtained HP’s. We also study the impacts of various system parameters on the system sum-rate and provide resource provisioning insights for HP systems. Numerical results show the superior performances of the proposed designs over joint SA and HP benchmark algorithms.

A Framework on Hybrid MIMO Transceiver Design Based on Matrix-Monotonic Optimization

Hybrid transceiver can strike a balance between complexity and performance of multiple-input multiple-output (MIMO) systems. In this paper, we develop a unified framework on hybrid MIMO transceiver design using matrix-monotonic optimization. The proposed framework addresses general hybrid transceiver design, rather than just limiting to certain high frequency bands, such as millimeter wave (mmWave) or terahertz bands or relying on the sparsity of some specific wireless channels. In the proposed framework, analog and digital parts of a transceiver, either linear or nonlinear, are jointly optimized. Based on matrix-monotonic optimization, we demonstrate that the combination of the optimal analog precoders and processors are equivalent to eigenchannel selection for various optimal hybrid MIMO transceivers. From the optimal structure, several effective algorithms are derived to compute the analog transceivers under unit modulus constraints. Furthermore, in order to reduce computation complexity, a simple random algorithm is introduced for analog transceiver optimization. Once the analog part of a transceiver is determined, the closed-form digital part can be obtained. Numerical results verify the advantages of the proposed design.

50 Gb/s short-reach interconnects with DSP-free direct-detection enabled by CAPS codes.

We experimentally demonstrate 50 Gb/s transmission below an uncorrected bit error rate (BER) of 10-3 in the C band over a transmission reach that extends from 0 to 20 km using combined amplitude and phase shift (CAPS) codes. The CAPS signal, which is not required to be specifically dispersion compensated for each reach within the 20 km operating range, is amenable for simple direct detection using a single photodetector without any subsequent digital signal processing (DSP). Hence, the presented solution constitutes a potentially attractive low cost solution for mobile Xhaul applications employing single mode fiber interconnects with reaches extending to 20 km. Furthermore, the CAPS signaling is compared to other modulation schemes all delivering 50 Gb/s and is found to outperform on-off-keying (OOK), 4-level pulse amplitude modulation (PAM4) and dispersion precompensated OOK in terms of dispersion tolerance. At a lower reach of 10 km, the maximum bit rate that can be achieved using CAPS coding at a BER below 10-3 is found to increase to 67 Gb/s. In addition, using the same testbed, we experimentally tested the IQ duobinary modulation format, which is an alternative format that approximates the CAPS transmitted waveforms in order to omit the need for a power consuming digital-to-analog converter (DAC) to generate the transmitted waveforms at the expense of slightly worse dispersion tolerance. Though the IQ duobinary format can be in principle generated using a simple DAC-less analog transmitter, our proof-of-concept experiment used a DAC to emulate the analog transmitter by generating the corresponding transmitted waveforms due to unavailability of all required analog parts. The IQ duobinary format was found experimentally to enable 50 Gb/s over a reach of ~17 km; that is slightly less than a CAPS signal at the same bit rate. Finally, we verified the excellent performance of the CAPS signaling in an ASE-limited regime where the CAPS signal achieved very low OSNR penalty after 10 km relative to OOK in back-to-back.

The development of microprocessor measuring system for the inclination angles of an object relative to the horizon plane

The need to measure the angles of inclination is essential for many branches of technology and industry. At the current Ukrainian market of devices there are no domestic accelerometer devices for measuring roll and pitch angles (DMRPA),which would meet the following requirements: the mean square error less than one angular minute in the range of angles ± 10 °, the operating temperature range -40 ... + 70 ° С, output information in a digital code with a discreteness of 1 angular second. Such DMRPAs are needed to control the position of radars and antennas, horizontals of platforms and vehicles.The developed microprocessor system for measuring the inclination angles of an object relative to the horizon plane (MSMIA) provides measurements of the roll and pitch angles in accordance with the above requirements. Issuance of output digital data for consumer is carried out on the interface RS-422.The MSMIA's metal rectangular case consists of a bottom base plate having three legs for attachment to the object base surface and a casing. On the base plate two accelerometer sensors (AS) – primary accelerators transducer, with mutually perpendicular measuring axes, are installed. Digital temperature transducers are installed near them. The analogue parts of the device electronic circuit board contain the electronics for the transformation of the pendulum sensitive elements displacement into the voltage, and electronics of the feedback regulators, the current from which goes to the coil of the reverse compensating converter. This current is proportional to the projection of gravity accelerating on the sensitivity axis of the AS, and is converted into a voltage across the precision resistor. The microcontroller located on the board includes two high precision analogue-digital converters, converting signals from these resistors into digital codes, proportional to measured acceleration. The microcontroller software performs algorithmic compensation for the measurement errors of the acceleration and the calculation of the roll and pitch angles. During the experimental tests, it has been confirmed that for various combinations of temperatures with range - 40 ... + 70 ° С and angles of inclination in the range of ± 10 °, the mean square error is not more than one angular minute, which is unique for the devices presented on the modern domestic market.Consequently, this development will allow Ukraine to establish the production of high-precision MSMIAs to meet the needs of domestic new technical manufacturers. Further research can be directed to the study of long-term instability of the MSMIA's parameters, the reduction of the mean-square error due to the installation of additional temperature sensors and the improvement of temperature errors compensation.

An Ultra-Low-Power RFID/NFC Frontend IC Using 0.18 μm CMOS Technology for Passive Tag Applications.

Battery-less passive sensor tags based on RFID or NFC technology have achieved much popularity in recent times. Passive tags are widely used for various applications like inventory control or in biotelemetry. In this paper, we present a new RFID/NFC frontend IC (integrated circuit) for 13.56 MHz passive tag applications. The design of the frontend IC is compatible with the standard ISO 15693/NFC 5. The paper discusses the analog design part in details with a brief overview of the digital interface and some of the critical measured parameters. A novel approach is adopted for the demodulator design, to demodulate the 10% ASK (amplitude shift keying) signal. The demodulator circuit consists of a comparator designed with a preset offset voltage. The comparator circuit design is discussed in detail. The power consumption of the bandgap reference circuit is used as the load for the envelope detection of the ASK modulated signal. The sub-threshold operation and low-supply-voltage are used extensively in the analog design—to keep the power consumption low. The IC was fabricated using 0.18 m CMOS technology in a die area of 1.5 mm × 1.5 mm and an effective area of 0.7 . The minimum supply voltage desired is 1.2 V, for which the total power consumption is 107 W. The analog part of the design consumes only 36 W, which is low in comparison to other contemporary passive tags ICs. Eventually, a passive tag is developed using the frontend IC, a microcontroller, a temperature and a pressure sensor. A smart NFC device is used to readout the sensor data from the tag employing an Android-based application software. The measurement results demonstrate the full passive operational capability. The IC is suitable for low-power and low-cost industrial or biomedical battery-less sensor applications. A figure-of-merit (FOM) is proposed in this paper which is taken as a reference for comparison with other related state-of-the-art researches.

Hybrid Analog–Digital Transmit Beamforming for Spectrum Sharing Backhaul Networks

This paper deals with the problem of analog–digital transmit beamforming under spectrum sharing constraints for backhaul systems. In contrast to fully digital designs, where the spatial processing is done at baseband unit with all the flexible computational resources of digital processors, analog–digital beamforming schemes require that certain processing is done through analog components, such as phase-shifters or switches. These analog components do not have the same processing flexibility as the digital processor, but on the other hand, they can substantially reduce the cost and complexity of the beamforming solution. This paper presents the joint optimization of the analog and digital parts, which results in a nonconvex, NP-hard, and coupled problem. In order to solve it, an alternating optimization with a penalized convex–concave method is proposed. According to the simulation results, this novel iterative procedure is able to find a solution that behaves close to the fully digital beamforming upper bound scheme.

Compact high-sensitivity potentiometer for detection of low ion concentrations in liquids.

The compact potentiometer, based on an electronic circuit protected from electrostatic and electromagnetic interference, was developed for the measurement of low ion concentrations in liquids. The electronic circuit of the potentiometer, consisting of analogous and digital parts, enables the measurement of fA currents. This makes it possible to perform reliable measurements of ion concentrations in liquids that are as small as 10-8-10-7M. The instrument was tested using electrodes that were selective for tetraphenylphosphonium (TPP+) ions. It was demonstrated that the characteristic response time of the potentiometer electronic circuit to changes in the concentration of these ions in a liquid was in the order of 10 s. An investigation of TPP+ absorption by baker yeast has shown that this device can be successfully used for long term (several hours) measurements with zero signal drift, which was about 1 μV/s. Finally, due to the small dimensions of the electronic circuit (7.5 × 2 × 1.5 cm), this potentiometer can be easily installed at a large apparatus in the laboratory condition (≈25 °C), such as high pulsed electrical generators of magnetic fields that are used in electroporation studies of biological cells.