Low Power Levels Research Articles

Effective Stakeholder Management for Inclusive Post-Flood Management: Sri Lanka as a Case Study

This study aimed to examine post-flood management, with a particular focus on enhancing the inclusivity of marginalised communities through stakeholder analysis. This study was based on an interpretivist mixed method approach, under which 30 semi-structured stakeholder interviews were conducted. Interest versus power versus actual engagement matrix, social network analysis, and thematic analysis techniques were employed under the stakeholder analysis tool to analyse the collected data. The findings highlight the lack of clearly defined responsibilities among key stakeholders. Marginalised communities and community-based organisations have a high level of interests but a low level of power in decision making, resulting in weak engagement and the exclusion of their perceptions. This lack of collaboration and coordination among stakeholders has made marginalised communities more vulnerable in post-flood situations, as their interests are not defended. The findings emphasise the importance of conducting stakeholder analysis in the decision-making process to enhance stakeholder engagement and interaction, as well as promote inclusivity of marginalised communities in the post-flood recovery efforts of the government. Finally, this study recommends developing strategies to improve collaboration among stakeholders, fostering inclusiveness and customising these strategies according to the different types of stakeholders identified through stakeholder analysis.

Design of Low Noise Low Power Instrumentation Amplifier for Biomedical Applications

Advancements in integrated circuit (IC) technology and circuit design are enabling devices to replace complex biological applications. Despite this progress, achieving necessary functionality at low power levels is crucial for fully integrated systems. Biomedical devices like pacemakers, which require ongoing battery charging, operate at nanowatt power levels over several years. To ensure long-term pacemaker survival, an Analog Front End (AFE) with low to moderate power consumption and high precision is essential. The front-end Instrumentation Amplifier (INA) is vital for signal acquisition, significantly improving the effectiveness of ECG signal collection systems.The primary aim of this research is to develop an integrated ECG instrumentation amplifier (INA) that can deliver top-notch performance while keeping noise and power consumption to a minimum. This amplifier will enable seamless monitoring of the ECG signal without interruptions. Using an AC connected Common Mode Feedback system [1]. in conjunction with an Operational Trans-conductance Amplifier (OTA) that uses a Chopper stabilization technique, the study's band pass filtering response within the ECG signal frequency range of 0-100Hz is obtained as anticipated. CMOS 45 nm technology is used throughout the entire process using Mentor Graphics EDA Tools

Ultra-low power, high-data rate, fully on-chip radio frequency on-off keying receiver for internet-of-things applications

Despite the enormous potential of energy-efficient receivers for wireless sensor networks, the large power consumption or limited data rate support impedes its extensive applications. Here, we present an energy-efficient, ultra-low power, higher data rate supporting, completely on-chip radio-frequency receiver frontend for on-off keying modulated signals in the 2.4 GHz industrial, scientific, and medical band. This compact-sized receiver is achieved by implementing temperature-resilient oscillator, pseudo-differential mixer, and a wideband detector while avoiding bulky external components such as bulk-acoustic wave resonators, crystal oscillators. Measurement results demonstrate that the proposed on-off keying receiver can decode low power level radio-frequency signals up to 5 Mbps data rate while consuming only 178 µW power. This work also demonstrates support for lower data rates at reduced power. Since the proposed receiver operates in different power modes, it can be integrated in diverse applications including internet-of-things devices and continuously monitoring biomedical/wearable implants.

Unveiling Acoustic Cavitation Characterization in Opaque Chambers through a Low-Cost Piezoelectric Sensor Approach

This study investigates the characterization of acoustic cavitation in a water-filled, opaque chamber induced by ultrasonic waves at 20 kHz. It examines the effect of different acoustic radiator geometries on cavitation generation across varying electrical power levels. A cost-effective piezoelectric sensor, precisely positioned, quantifies cavitation under assorted power settings. Two acoustic radiator shape configurations, one with holes and another solid, were examined. The piezoelectric sensor demonstrated efficacy, corroborating with existing literature, in measuring acoustic cavitation. This was achieved through the Fast Fourier Transform (FFT) analysis of voltage data, specifically targeting sub-harmonic patterns, thereby providing a robust method for cavitation detection. Results demonstrate that perforated geometries enhance cavitation intensity at lower power levels, while solid shapes predominantly affect cavitation axially, exhibiting decreased activity at minimal power. The findings recommend using two different shape geometries on the acoustic radiator for efficient cavitation detection, highlighting intense cavitation on radial walls and cavitation generation on the bottom. Due to the stochastic nature of cavitation, averaging data is critical. The spatial limitation of the sensor necessitates prioritizing specific areas over complete coverage, with multiple sensors recommended for comprehensive cavitation pattern analysis.

Gain scheduled internal model control based on the dynamic sliding mode method for the water level of nuclear steam generators

Abstract The Steam Generator (SG) is a crucial component of a nuclear power plant. Proper water level control in a nuclear steam generator is of great importance to ensure a sufficient cooling source for the nuclear reactor and to prevent damage to turbine blades. The water level control problem of steam generators has been a leading cause of unexpected shutdowns in nuclear power plants, which must be addressed for plant safety and availability. The control problem is challenging, particularly at low power levels due to shrink and swell phenomena and flow measurement errors. Furthermore, the dynamics of the steam generator vary as the power level changes. Therefore, there is a need to enhance the water level control system of the SG. In this paper, a Gain Scheduled Internal Model Control (IMC) based on the Dynamic Sliding Mode (DSMC) method is developed for the level control problem. The proposed method exhibits the desired dynamic properties throughout the entire output tracking process, independent of perturbations. Simulation results are presented to demonstrate the effectiveness of the proposed controller in terms of performance, robustness, and stability. The simulation results confirm the improvement in transient response achieved by using the proposed controller.

Numerical investigation and optimisation of solid–solid phase change material composite-based plate-fin heat sink for thermal management of electronic package

Phase Change Material based Thermal Management Systems show promise in electronic packaging systems for safe operation, acting as a thermal storage element to prevent sudden temperature surges, enhancing operational time and mitigating electronic system failures. Therefore, the meticulous design of a solid–solid phase change material (SSPCM) based heat sink with fins is imperative for effective electronic thermal management by improving its safe operational time. This study performs a numerical analysis of two-dimensional transient heat transfer for the SSPCM-based plate-fin heat sink using the modified enthalpy porosity method, where the plate fins serve as Thermal Conductivity Enhancers (TCEs). Neopentyl glycol with 6% (w/w) Copper oxide nanoparticle is used as the SSPCM composite. Enhancement ratio based on safe operational time at different power levels (2–6 W) with different percentages of TCE and fin count recorded variation from 1.32 to 13.7. The TCE integration is more effective at higher power levels. The optimisation of SSPCM-based heat sink design for maximum safe operational time is accomplished through Response Surface Methodology. The significance of the TCE fraction, number of fins, heat generation rate, and interaction effects over the safe operational time are observed. The correlation for safe operational time as a function of TCE volume fraction, fin count and heat generation rate is developed. TCE volume fraction possesses the highest influencing factor over safe operational time at lower and higher power levels compared to fin count. At 2 W and 6 W, a maximum change in safe operational time is observed from 72.7% at 2 W to 83.45% at 6 W. The heat sink with 0.262 volume fraction of TCE and 11 fins is the optimised design that can provide the desirable safe operational time for the tested range of power levels.

Impact of microwave heating on product safety and quality in meatballs

The effects of microwave heating at different processing time and power levels (360 W, 600 W and 900 W) on Salmonella Typhimurium, Escherichia coli O157:H7, Listeria monocytogenes and Staphylococcus aureus in Turkish type meatballs were evaluated. Besides, the changes in the textural and sensorial properties of meatballs were determined to reveal the cooking time and temperatures that would make the product safety without affecting the consumer preferences. In this direction, the experimentally contaminated meatballs were subjected to microwave heating at low, medium and high power levels for different processing times and analysed for the survival of the relevant pathogenic bacteria. The total aerobic bacteria count in meatballs could be reduced approximately 3–4 log CFU/g by medium and high microwave powers, whereas 5–7 log CFU/g inhibition was obtained in meatballs inoculated with pathogens. The increase in power level together with the increasing process time resulted in a decrease in the counts of bacteria and an undesirable effect on the textural and sensorial qualities of meatballs. Microwave heating at medium and high power levels as from 3 min, caused excessive drying and blackening of the product, making it difficult to consume due to crust formation. Consequently, to achieve optimal acceptability of the product by consumers, meatballs should be heated with a microwave power of 600 W and 900 W for 3 min.

Synthesis and Unique Behaviors of High-Purity HEA Nanoparticles Using Femtosecond Laser Ablation.

High-entropy alloys (HEAs) are a class of metal alloys consisting of four or more molar equal or near-equal elements. HEA nanomaterials have garnered significant interest due to their wide range of applications, such as electrocatalysis, welding, and brazing. Their unique multi-principle high-entropy effect allows for the tailoring of the alloy composition to facilitate specific electrochemical reactions. This study focuses on the synthesis of high-purity HEA nanoparticles using the method of femtosecond laser ablation synthesis in liquid. The use of ultrashort energy pulses in femtosecond lasers enables uniform ablation of materials at significantly lower power levels compared to longer pulse or continuous pulse lasers. We investigate how various femtosecond laser parameters affect the morphology, phase, and other characteristics of the synthesized nanoparticles. An innovative aspect of our solution is its ability to rapidly generate multi-component nanoparticles with a high fidelity as the input multi-component target material at a significant yielding rate. Our research thus focuses on a novel synthesis of high-entropy alloying CuCoMn1.75NiFe0.25 nanoparticles. We explore the characterization and unique properties of the nanoparticles and consider their electrocatalytic applications, including high power density aluminum air batteries, as well as their efficacy in the oxygen reduction reaction (ORR). Additionally, we report a unique nanowire fabrication phenomenon achieved through nanojoining. The findings from this study shed light on the potential of femtosecond laser ablation synthesis in liquid (FLASiL) as a promising technique for producing high-purity HEA nanoparticles.

INVOLVEMENT OF DIFFERENT STAKEHOLDER GROUPS IN ENSURING CHILDREN’S DENTAL PUBLIC HEALTH: ANALYSIS AND PERSPECTIVES

Introduction: Strengthening the dental public health (DPH) of the pediatric population requires prioritizing development with the identification of key stakeholders and their leading functions.
 The aim. To analyze the current state and identify prospects for intra-industry and inter-sectoral cooperation in the process of strengthening the dental public health of the child population to justify ways of optimization.
 Materials and methods. A cross-sectional study using expert assessments involving 15 highly competent experts (competence level above 0.85) was conducted through a specially designed program. Bibliosemantic and sociological methods were employed. Expert assessments and stakeholder mapping were performed, visualizing the «authority-interest» relationship of different interested groups on a two-dimensional model. The results were analyzed using standard statistical methods with the application of Jupyter Notebook (https://jupyter.org/install). Intra-class correlation coefficients were used to assess the agreement of expert opinions. A significance level of p<0.05 was considered critical in testing all statistical hypotheses.
 Results. The graphical analysis allowed for the identification of stakeholders and determination of their roles in the DPH system. Groups with high and low levels of power and interest were identified. The agreement among experts regarding the determination of power and interest was respectively ICC=0.76 (95% CI 0.56 – 0.91) and ICC=0.79 (95% CI 0.59 – 0.92). The necessity of targeted efforts with each group, considering their capabilities and limitations, was emphasized. Key stakeholders included families, communities, family physicians, public health institutions, pediatric dentists, and others. Primary functions aimed at strengthening children’s dental health were attributed to influencing determinants of dental health, intersectoral collaboration and support for relevant initiatives at the local level are essential.
 Conclusions. The importance of developing and implementing programs aimed at improving the dental health of the child population has been established. Emphasis is placed on the significance of collaboration among various stakeholders in supporting a strategic approach to managing DPH.

Construction of irregular and high-density microtexture on ultra-thin 304 austenitic stainless steel strip via laser surface treatment to improve steel/epoxy resin adhesive bonding properties

Ultra-thin steel strip can be used in composite materials to create high-performance and low-deadweight components for the aerospace industry. The present study used a laser to create surface microtextures on 304 austenitic ultra-thin stainless steel (SS) strips to improve their adhesion to epoxy resin. Modification was conducted at various laser power levels, resulting in ring-like textures of various qualities. The strips were bonded to epoxy resin at single-lap joints, which were then strength-tested. The bonding mechanisms were investigated via analyses of microstructure, surface chemical composition and interfacial failure modes. The laser power level affected the density and distinctiveness of the ring-like structures. The optimal level of 40 W produced a bond with a shear strength of 14.43 MPa. Bonding is enhanced by the interlocking effect of the texture, improved wettability between the steel and epoxy resin, and –C–O=C polar bonds. Lower and higher power levels provided weaker textures. In summary, irregular laser surface treatment can optimize the shear strength of SS–epoxy-resin joints, allowing the fabrication of stronger componentry.

A Load-Adaptive Driving Method for a Quasi-Continuous-Wave Laser Diode.

A quasi-continuous-wave (QCW) laser diode (LD) driver is commonly used to drive diode bars and stacks designed specifically for QCW operations in solid-state lasers. Such drivers are optimized to deliver peak current and voltage pulses to LDs while maintaining low average power levels. As a result, they are widely used in laser processing devices and laser instruments. Traditional high-energy QCW LD drivers primarily use capacitors as energy storage components and pulsed constant-current sources with op-amps and power metal-oxide-semiconductor field-effect transistors (MOSFETs) as their core circuits for generating repeated constant-current pulses. The drawback of this type of driver is that the driver's output voltage needs to be manually adjusted according to the operating voltage of the load before use to maximize driver efficiency while providing a sufficient current. Another drawback is its inability to automatically adjust the output voltage to maintain high efficiency when the load changes during the driver operation. Drastic changes in the load can cause the driver to fail to function properly in extreme cases. Based on the above traditional circuit structure, this study designed a stability compensation circuit and realized a QCW LD driver for driving a GS20 diode stack with a maximum repetition rate of 100 Hz, a constant current of approximately 300 A, a load voltage of approximately 10 V, and a pulse width of approximately 300 μs. In particular, a high-efficiency, load-adaptive driving method was used with the MOSFETs in the critical saturation region (i.e., between the linear and saturated regions), controlling its power loss effectively while achieving maximum output current of the driver. The experiments demonstrated that the driver efficiency could be maintained at more than 80% when the load current varied from 50 to 300 A.

로봇 셰프 의인화와 심리적 파워가 소비자의 맛에 대한 판단에 미치는 영향

The goal of the study is to examine the impact of the anthropomorphism of a robot chef and consumers' psychological power levels on consumers’ taste expectations in a restaurant setting. As robot chefs becomes popular in the dining industry, consumers may rely on the robot's appearance as an extrinsic cue to judge food quality. Anthropomorphism tends to be higher among consumers with low psychological power levels, driven by a desire to compensate for power deficiency through non-human entities. Conversely, high-power consumers exhibit lower intention to rely on anthropomorphism. Two lab experiments are conducted to test the hypotheses. The results reveal that psychological power moderates the influence of anthropomorphism on taste expectations. Low-power consumers expect more flexible and tastier food from an anthropomorphized robot chef. However, this effect is diminished for high-power consumers. These findings provide practical insights into the interplay between psychological power, anthropomorphism, and taste expectations in the context of robot chefs in the dining industry.

Neutronic design of small modular long­life pressurized water reactor using thorium carbide fuel at a power level of 300–500 MWth

This study presents the neutronic design of a small modular long­life Pressurized Water Reactor (PWR) using thorium carbide fuel with 233U fissile material. The target optimization for this study is a reactor designed to operate for 20 years, with excess reacti­vity throughout the reactor operational cycle consistently below 1.00 % dk/k. The analysis involves dividing the reactor core into three fuel regions with 233U enrichment levels ranging from 3 % to 8 %, with a 1 % difference for each fuel region. To achieve optimum conditions, 231Pa was randomly added to the fuel. The fuel volume fraction in this design varied from 30 % to 65 %, with a 5 % incremental variation. Power level variations are also studied within the 300–500 MWth with increments of 50 MWth. Calculations were performed using the Standard Reactor Analysis Code (SRAC) program with the PIJ and CITATION modules for cell and core calculations utilizing JENDL­4.0 nuclide data. Neutronic calculations indicate that the fuel with a 60 % volume fraction achieves optimum conditions at a power level of 300 MWth. The best performance was observed with a fuel volume fraction of 65 %, reaching optimum conditions across power levels ranging from 300 to 500 MWth. For the fuel with the best performance, the power density distributions for low and high power levels follow the same pattern radially and axially. The power peaking factor (PPF) for all fuel configurations approaching the optimum conditions remains below two, a safe limit for the PWR. Other neutronic safety parameters, such as the Doppler coefficient and void fraction coefficient, also stay within the safe limits for the PWR, with both values remaining negative throughout the reactor operational cycle

Design optimization of noise reduction for labyrinth control valve in secondary circuit flow regulation system

The labyrinth control valve has been widely used in the secondary circuit flow regulation system of nuclear power field for good pressure reduction and cavitation suppression characteristics. The design of the labyrinth channel is a key to realizing pressure regulation and cavitation suppression for the labyrinth control valve. However, an unreasonable labyrinth flow channel design will be challenging to meet the requirements and aggravate the noise problem under severe operating conditions. This paper proposes a hybrid labyrinth flow channel structure (HLS) that combines the traditional labyrinth flow channel (TLS) and orifice plate structure. The cavitation volume and maximum flow velocity are used as evaluation parameters of the labyrinth flow channel noise. The flow characteristics analysis show that compared with the TLS, the HLS can reduce flow velocity, decrease cavitation volume, improve transmission loss, and lower sound power levels. In addition, the influence between the HLS structural parameters and the noise evaluation parameters is clarified by correlation coefficient analysis. A low noise HLS based on the adaptive NSGA-II algorithm is established. The experimental results indicate that the optimized HLS reduces air noise by 4.21 dB(A) compared to the TLS. The optimized HLS can effectively reduce noise, and help the design of low noise labyrinth flow channels for nuclear power field.

Analysis and Design of Independent DC Bus Structure Multiport Power Electronic Transformer Based on Maximum Power Transmission Capability of Low-Voltage DC Ports

Owing to the diverse connection configurations of dual active bridge converters, a multiplicity of low-voltage DC port structures are anticipated to emerge in the independent DC bus structure multiport power electronic transformer (IDBS-MPET). An inadequate low-voltage DC port structure exacerbates the power imbalance in IDBS-MPET, presenting a risk of overmodulation even when transmitting relatively low levels of power. To overcome this limitation, a design scheme of IDBS-MPET topology based on the maximum power transmission capability of the low-voltage DC ports is proposed in this paper. Three topology design rules are derived from the maximum power transmission capability results of more than 80 typical IDBS-MPET topologies. The symmetrical triple cross-phase connection structure, the symmetrical double cross-phase connection structure and the single-phase connection structure are sequentially identified as the three most optimal structures of low-voltage DC ports. By employing the proposed design methodology, each low-voltage DC port achieves its maximum power transfer capability relative to other configurations. The effectiveness of the proposed design scheme is validated by an optimal designed IDBS-MPET topology with six low-voltage DC ports.

Advancements in VLSI low-power design: Strategies and optimization techniques

As production technology advances, integrated circuits are increasing in size, leading to a corresponding rise in power consumption if not properly optimized. Consequently, the optimization of integrated circuit power consumption has gained paramount significance. This paper provides an overview of the theoretical and research developments in Very Large Scale Integration (VLSI) low-power design. Initially, the paper delves into the components of VLSI power consumption, elucidating the origins of various power consumption types and the factors influencing their magnitude. Subsequently, existing power reduction technologies are examined, including transistor-level optimization, gate-level optimization, and system-level power optimization. The principles, applicable power consumption types, as well as their respective advantages and drawbacks are analysed. The paper also introduces methods for evaluating VLSI power consumption and summarizes the characteristics, advantages, and disadvantages of high-level power estimation and low-level power estimation. Ultimately, it underscores the importance of considering multiple power optimization strategies during VLSI design and discusses research approaches for achieving low power consumption. This comprehensive exploration contributes to the enhancement and optimization of VLSI design efforts.

Design and optimization of broadband CPW rectenna for RF energy harvesting

ABSTRACT Wireless sensor networks (WSNs) are widely used in a variety of sectors, including the surveillance, healthcare, and military, and so on. The high cost and short lifespan of wireless sensor networks prohibit emerging and low-income nations for using their benefits. This article proposes a compact, low cost, and broadband coplanar waveguide rectenna with a simple novel ground plane operate in band range of 4.8–5.5 GHz (700 MHz) for an effective solution to radio frequency (RF) energy harvesting applications in WSNs. A parametric study of distinct antennas is also conducted to strengthen the attributes of the proposed antenna. The defected ground structure created on the co-plane offers 105° measured half power beamwidth (HPBW) in the H-plane for wide angular coverage. As a result, design alignment does not need to be extremely perfect in order to make conversion efficiency constant. The rectifying circuit is made compact by using a two-stub impedance matching network. At load resistance of 1k Ω, the power conversion efficiency of the proposed rectenna for a low input power level of −10 dBm is 27.2% (simulated) and 20.1% (measured) while its maximum value is 52.5% (simulated) and 50.1% (measured) for input power level of 10 dBm.

On Weighted Sum Rate of Multi-User Photon-Counting Multiple-Input Multiple-Output Visible Light Communication Systems under Poisson Shot Noise

Photon counting has been proven to possess excellent signal detection capabilities at low power levels and has extensive potential applications in sixth-generation (6G) communications. However, the inherent dependency between the signal and noise complicates system analysis, and optimizing achievable rates in photon-counting visible light communication (VLC) systems remains unresolved. This paper introduces a new method aimed at minimizing multi-user interference (MUI) through a zero-forcing (ZF) scheme and maximizing the weighted sum rate of the proposed downlink multi-user photon-counting multiple-input multiple-output (MU-PhC-MIMO) VLC system by solving an optimization problem. The key point lies in our utilization of the ZF approach to derive a reasonable asymptotic approximation expression for the weighted sum rate. Subsequently, we use variable substitution and methods like successive convex approximation (SCA) to iteratively convexify the non-convex optimization problem and maximize the weighted sum rate under the ZF form. Compared to other algorithms, this approach can save 2.5 dB of transmission power to achieve the same system-weighted sum rate and significantly outperforms the repetition coding scheme at sufficient transmission power.

Water level control of nuclear steam generators using intelligent hierarchical autonomous controller

The challenge of water level control in steam generators, particularly at low power levels, has always been a critical aspect of nuclear power plant operation. To address this issue, this paper introduces an IHA controller. This controller employs a CPI controller as the primary controller for direct water level control, coupled with an agent-based controller optimized through a DRL algorithm. The agent dynamically optimizes the parameters of the CPI controller in real-time based on the system’s state, resulting in improved control performance. Firstly, a new observer information is obtained to get the accurate state of the system, and a new reward function is constructed to evaluate the status of the system and guide the agent’s learning process. Secondly, a deep ResNet with good generalization performance is used as the approximator of action value function and policy function. Then, the DDPG algorithm is used to train the agent-based controller, and an advanced controller with good performance is obtained after training. Finally, the popular UTSG model is used to verify the effectiveness of the algorithm. The results demonstrate that the proposed method achieves rise times of 73.9 s, 13.6 s, and 16.4 s at low, medium, and high power levels, respectively. Particularly, at low power levels, the IHA controller can restore the water level to its normal state within 200 s. These performances surpass those of the comparative methods, indicating that the proposed method excels not only in water level tracking but also in anti-interference capabilities. In essence, the IHA controller can autonomously learn the control strategy and reduce its reliance on the expert system, achieving true autonomous control and delivering excellent control performance.

A novel method for supersonic plasma measurement using a double-jacketed enthalpy probe

A novel method to characterize a supersonic plasma jet using a double-jacketed enthalpy probe is presented and applied to Ar supersonic plasma jets generated by a plasma torch operated at an input power level of 5.7 kW and a chamber pressure of 2.3 kPa. The basis of this method is to measure total stagnation pressure, total enthalpy, and static pressure at the backside of a shock wave formed in front of the probe with a single insertion of the probe. Once these three variables are known, normal shock relations before and after the shock wave can disclose information on static pressures, Mach numbers, temperatures, and velocities of the supersonic plasma jet under a calorically perfect gas assumption. For example, measurement experiments carried out with the proposed probe revealed that static pressure of Ar supersonic plasma jet oscillated around the chamber pressure of 2.3 kPa in a range of 1–5 kPa along the jet axis, clearly showing an aerodynamic non-equilibrium. Corresponding to the behaviors of static pressures, Mach numbers also oscillated in the range of 1.1–3.5 along the jet axis. In addition, oscillation patterns of static pressures and Mach numbers agreed well with those of compression and expansion wave zones observed in the photograph of an over-expanded Ar supersonic plasma jet. Although relatively large errors were accompanied due to a low input power level, plasma temperatures and velocities were measured to be decreasing and increasing, respectively, in the expansion wave zone while opposite behaviors were observed in the compression wave zone.