Eng | Encyclopedia MDPI

Summary

Eng (ISSN 2673-4117) is an international, peer-reviewed open access journal which publishes original papers, critical reviews, rapid communications, technical notes, and discussions on all areas of engineering. Eng's aim is to encourage scientists to publish their experimental and theoretical research relating to engineering science and technology in as much detail as possible. There is no restriction on the maximum length of the papers. Launched in 2020, Eng was indexed in Scopus in 2023. The journal was subsequently included in the Emerging Sources Citation Index (ESCI, Web of Science) in March 2024 and Ei Compendex in April 2025. It holds a 2025 Impact Factor of 3.5 and is ranked JCR Q1 in the “ENGINEERING, MULTIDISCIPLINARY” category. Its 2025 CiteScore is 4.1, and it currently ranks Q2 in Scopus’ “Engineering (miscellaneous)” category.

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Topic Review

Nuclear Magnetic Resonance

Nuclear magnetic resonance (NMR) is a quantum-mechanical phenomenon in which atomic nuclei possessing a non-zero magnetic moment absorb and re-emit electromagnetic energy when placed in a static magnetic field and irradiated by resonant radiofrequency radiation [1]. In a static field B0, spin-active nuclei precess at the Larmor frequency, which is proportional to B0 and the magnetogyric ratio; the ensemble magnetization then relaxes back toward equilibrium through longitudinal (T1) and transverse (T2) processes described by the Bloch equations [2]. Because the resonant frequency depends on the local electronic environment, the resonance position of a nucleus carries information about its chemical bonding and neighborhood, forming the basis of NMR spectroscopy [3]. The term also covers magnetic resonance imaging, in which spatial gradients encode the resonant signal to produce tomographic images of internal structures [4]. NMR is distinguished from other magnetic resonances by the involvement of nuclear spin rather than electron spin, and from absorption spectroscopy by the use of radiofrequency excitation and phase-sensitive detection [5].

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17 Sep 2026

Topic Review

Voltage Source Converter

A voltage source converter (VSC) is a power-electronic converter that uses a DC voltage source as its energy-storage element and synthesizes an AC voltage waveform by switching the DC voltage onto the AC terminals through controlled semiconductor devices [1]. The DC side is characterized by a relatively stiff voltage, typically maintained by a capacitor, while the AC-side current is controlled by modulating the magnitude and phase of the synthesized AC voltage relative to the AC system voltage [2]. VSCs are implemented using self-commutated devices such as insulated-gate bipolar transistors, gate-turn-off thyristors, or integrated gate-commutated transistors, which permit independent control of active and reactive power exchange with the AC system [3]. The AC output is generally pulse-width-modulated, with passive filters used to attenuate switching harmonics [2]. A VSC is distinguished from a current source converter (CSC), which uses a stiff DC current source and a series inductor on the DC side, by the nature of its DC-side energy storage and by the quantity that is held constant on the DC side [1].

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17 Sep 2026

Topic Review

Ultra‑High‑Performance Concrete

Ultra-high-performance concrete (UHPC) is a class of cementitious composite characterized by exceptionally high compressive strength, typically exceeding 120 MPa, together with enhanced durability relative to conventional concrete [1]. UHPC is formulated through a densely packed particle matrix consisting of Portland cement, silica fume, fine sand, quartz powder, and high-range water-reducing admixtures, with a water-to-binder ratio generally below 0.25 and no coarse aggregate in most formulations [2]. Steel or synthetic fibers are commonly incorporated at volume fractions of 1–3% to impart tensile ductility and strain-hardening behavior after cracking [3]. The material exhibits low porosity and permeability owing to optimized particle packing and the pozzolanic reaction of silica fume, which confers high resistance to chloride-ion penetration, freeze–thaw cycles, abrasion, and chemical attack [4]. UHPC is distinguished from high-performance concrete not only by its compressive-strength threshold (typically 120–200 MPa) but also by its fracture energy, post-cracking tensile capacity, and dimensional stability under exposure [5].

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17 Sep 2026

Topic Review

Total Harmonic Distortion

Total harmonic distortion (THD) is a power-quality metric that quantifies the harmonic content present in an electrical voltage or current waveform relative to its fundamental component [1]. For a periodic waveform, THD is defined as the ratio of the root-sum-square of the amplitudes of all harmonic components—excluding the fundamental—to the amplitude of the fundamental component, usually expressed as a percentage [2]. The harmonics considered are integer multiples of the fundamental power frequency and arise from nonlinear loads and power-electronic converters [3]. THD may be evaluated for voltage (THD_V) or current (THD_I); a higher THD indicates a waveform that deviates more strongly from a pure sinusoid [2]. THD is distinct from total demand distortion (TDD), which normalizes harmonic current to the maximum demand current rather than to the fundamental [1]. Limits on harmonic distortion at the point of common coupling are established in power-quality standards, and THD serves as the primary figure of merit for waveform quality in such assessments [3].

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17 Sep 2026

Topic Review

Printed Circuit Board

A printed circuit board (PCB) is a rigid or flexible insulating substrate onto which conductive pathways, pads, and other features are patterned in order to mechanically support and electrically interconnect electronic components [1]. The conductive patterns are typically formed from copper laminated to the substrate and etched or plated to define traces, with plated-through holes or vias connecting conductive layers in multilayer constructions [2]. Components are mounted onto the board by soldering to pads that are themselves integrated into the patterned copper layer [1]. The substrate materials are commonly glass-reinforced epoxy laminates, polyimide, or other dielectric materials selected for mechanical rigidity, thermal stability, and electrical insulation [2]. A PCB is distinguished from a bare printed wiring board by the inclusion of patterned conductive features that form a defined circuit, and from a backplane by the integration of active and passive components as well as interconnects [3]. Design and manufacturing requirements for PCBs—including conductor width, spacing, dielectric thickness, and via geometry—are standardized in industry specifications [3].

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17 Sep 2026

Topic Review

Pavement Condition Index

The Pavement Condition Index (PCI) is a numerical rating on a 0–100 scale that expresses the surface condition of a pavement section, where 100 denotes a pavement in perfect condition and 0 denotes a failed pavement [1]. The PCI is derived from a standardized visual survey in which trained inspectors identify visible surface distresses, classify each by severity level (low, medium, high), and measure its quantity over defined sample units [2]. Deduct-value curves convert the distress inventory into weighted deductions, which are then combined by an optimized combination procedure — originally developed for the U.S. Army Corps of Engineers — to yield a single PCI value for each sample unit and, by aggregation, for the section or network [1][3]. The PCI is an indirect measure of structural integrity and functional surface condition; it is not a direct measure of structural capacity, skid resistance, or ride roughness [2]. The method applies to both asphalt concrete and Portland cement concrete pavements, each with its own distress catalog, and is standardized in ASTM D6433. It is distinguished from profile-based indices such as the International Roughness Index by being distress-based rather than measurement-based.

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17 Sep 2026

Topic Review

Solar Power Plants

A solar power plant is a centralized, grid-connected installation that converts solar radiation into electrical energy, either by photovoltaic (PV) modules exploiting the photovoltaic effect in semiconductor cells or by concentrated solar thermal (CSP) collectors that concentrate sunlight to heat a working fluid driving a thermodynamic cycle [1]. In a PV-based plant, many modules are grouped into strings and arrays, and their direct-current output is collected and inverted to alternating current; in a CSP plant, heliostats or parabolic troughs focus radiation onto a receiver that supplies steam or thermal oil to a power block [2]. The plant integrates tracking or fixed mounting, DC collection, power-conversion equipment, step-up transformers, and a dedicated point of interconnection, and is rated by its installed capacity in megawatts [3]. It is distinguished from distributed rooftop PV by its centralized scale, dedicated land or structure, and connection to the transmission or distribution system rather than the on-site load of a single dwelling [4].

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16 Sep 2026

Topic Review

Global Navigation Satellite Systems

Global Navigation Satellite Systems (GNSS) is the generic term for the satellite-based radio positioning, navigation, and timing systems that provide autonomous geospatial positioning and time references on a global or regional basis [1]. A GNSS constellation comprises a space segment of satellites in precisely modeled orbits that continuously transmit ranging signals carrying navigation data formatted according to standardized interface specifications [2], a control segment of ground stations that tracks the satellites, uploads ephemerides and clock corrections, and maintains the constellation, and a user segment of receivers that measure pseudorange and carrier-phase observables to derive position, velocity, and time [1]. Position is determined by trilateration: a receiver measures the travel time of signals from at least four satellites, converting geometric range into three-dimensional coordinates and a common clock offset through solution of the ranging equations [1]. GNSS includes fully global systems such as the United States GPS, Russian GLONASS, European Galileo, and Chinese BeiDou, as well as regional augmentation systems, and is distinguished from terrestrial navigation aids by its space-borne transmitters and global coverage [3].

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16 Sep 2026

Topic Review

Extended Kalman Filter

The extended Kalman filter (EKF) is a recursive Bayesian state-estimation algorithm that extends the linear Kalman filter to systems governed by nonlinear state-transition or measurement functions [1]. Like the linear Kalman filter, the EKF operates in two alternating steps: a time update that propagates the state estimate and its associated error covariance forward through the nonlinear process model, and a measurement update that corrects the prediction using an available observation [2]. The nonlinear functions are linearized about the current state estimate by a first-order Taylor expansion, with the Jacobian matrices of the process and observation functions evaluated at the current estimate replacing the constant state-transition and observation matrices of the linear filter [1]. The EKF assumes additive Gaussian process and measurement noise and Gaussian initial uncertainty, and it propagates only the first two moments—mean and covariance—of the state distribution [3]. Because the linearization is performed around the current estimate rather than a fixed trajectory, the EKF is a nonlinear filter in which the gain and covariance depend on the actual measurements received [2]. It is distinguished from the linear Kalman filter by its handling of nonlinearity, and from second-order or sigma-point filters by its first-order Taylor approximation [4].

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16 Sep 2026

Topic Review

Signal to Noise Ratio

Signal-to-noise ratio (SNR) is a dimensionless measure that quantifies the ratio of the power of a desired signal to the power of background noise in a communication or measurement system. Expressed in decibels (dB), SNR is calculated as ten times the base-10 logarithm of the signal power divided by the noise power, or equivalently as twenty times the logarithm of the amplitude ratio when signal and noise are measured across the same impedance [1]. A positive SNR indicates that the signal power exceeds the noise power, while a negative SNR indicates that noise dominates [2]. SNR serves as a fundamental metric for assessing system fidelity, receiver sensitivity, and the reliability of data transmission across analog and digital communication channels [3]. In digital communications, SNR is directly related to bit error rate through modulation-specific relationships, where higher SNR values correspond to lower error probabilities [4]. The measure is applied across electrical engineering, acoustics, imaging, and spectroscopy, although the precise definition of signal and noise power may vary by domain [5].

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16 Sep 2026

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