Current Stress Research Articles

Revealing enhanced dilution effect of conjugated polymers in partially miscible blends

AbstractRecent experiments have shown that hole traps could be suppressed in polymer light‐emitting diodes under current stress by diluting the light‐emitting conjugated polymers within an “inert” large‐bandgap host material. However, it is unclear why there is an enhanced dilution effect in partially miscible blends rather than fully miscible blends, as intuition would suggest that better miscibility leads to better dilution. In this work, we propose a cascade analysis by combining multiple fluorescence microscopic techniques and all‐atom molecular dynamics simulations to study the solid‐to‐solid dilution of poly[2‐methoxy‐5‐(2‐ethylhexyloxy)‐1,4‐phenylenevinylene] (MEH‐PPV) in MEH‐PPV/polystyrene (PS) blends and MEH‐PPV/poly(vinylcarbazole) (PVK) blends. By varying the molecular weights of PS and PVK, we can regulate their miscibility with MEH‐PPV. The results corroborate that the dilution effect is enhanced in partially miscible blends rather than fully miscible ones. This is because, in partially miscible blends undergoing phase separation, the concentration of MEH‐PPV is notably decreased in the phase occupying the majority of the volume, leading to an overall greater dilution effect than in fully miscible blends. Moreover, MEH‐PPV could adopt the more extended conformation in the fully miscible blend, causing a shorter intermolecular distance to further undermine the dilution effect. These findings explain the seemingly counterintuitive more effective dilution effect observed in the recently reported partially miscible blends and provide guidance for further enhancing the performance of future generations of polymer light‐emitting diodes.

Computational study of pulse current and thermal stress on thermoelectric cooler

The thermal performance of a Peltier thermoelectric cooler (TEC) can be enhanced by multi-staging, modifying the geometry of the thermoelement, and using new material with improved thermoelectric properties. This study utilizes COMSOL multiphysics to simulate thermomechanical analyses of various geometries of thermoelectric coolers under pulse current conditions. This investigation explores the influence of pulse current parameters, such as pulse width, pulse ratio, and hot-side convective heat transfer coefficient, on a thermoelectric cooler with different leg geometries. Additionally, the impact of the TEC cold-side temperature, hot-side temperature, and thermal stress on both sides is discussed. The results indicate that TEC leg shapes, such as pin and trapezoid, exhibit the minimum cold-side temperature. Increasing the pulse ratio leads to a decrease in the cold-side temperature and an increase in the hot-side temperature. A notable improvement in the cold-side temperature is also observed with higher pulse ratios, with the pin geometry achieving a minimum cold-side temperature of 276 K. Furthermore, the cooling load affects the temperature on both sides of the TEC. These findings provide valuable insights for optimizing thermoelectric coolers for electronic cooling applications using pulse current methods.

A novel high step‐up, low switching voltage stress DC‐DC converter using leakage inductance for resonant boosting

AbstractA DC‐DC converter with high boost and low switching voltage stress is proposed by combining switched capacitor (SC) and coupled inductor (CL) techniques based on a conventional boost circuit. The design methodology of this converter includes substituting SC for a single switch in the boost converter, combining CL, and integrating a resonant boost circuit for absorbing leakage inductance. The improved power switch topology in this design has lower voltage stress, lower diode current stress, fewer total components, and common ground than other conventional DC‐DC converters. The operating modes and steady state analysis of the converter are provided in terms of leakage inductance utilization, with component stress derivation and theoretical efficiency analysis. In addition, comparisons with other dc‐dc converters are made. Subsequently, experiments were conducted on a 200 W DC‐DC converter prototype to verify the reliability of the converter.

Efficient power conversion with four switch soft-switching boost integrated half-bridge dual-output series resonant converter

Soft switching reduces voltage and current stress during transitions, smoothing and quieting operations and reducing electromagnetic interference while also increasing efficiency and equipment lifespan. Circuit design, component selection, and switching frequency optimization affect power electronics soft switching. This paper proposes boost integrated half-bridge dual-output series resonant (BIHBDOSR) converter, a novel converter design and control method to increase series resonant converter performance by reducing storage element size, switch count, and switching losses. This methodology relies on soft-switching technologies like zero-voltage switching (ZVS) and zero-current switching (ZCS). These methods use class-D, class-E, series, parallel, and series–parallel resonant converter circuits to increase efficiency and minimize component stress. The proposed converter is ideal for constant voltage, constant power, and current-controlled loads with the output voltage being regulated by a closed-loop PI controller. The output voltages for two loads in the simulation depart from reference values. V01 changes from 14 to 20 V and V02 from 18 to 15 V at 300 ms owing to switching variances. The proposed converter utilizes gate driver circuits, resonant tank circuit, current sensor, FPGA board for closed-loop control, and current sensor for stability, ensuring converter stability. The proposed converter closed-loop control method modifies PWM signals to regulate both loads independently and ensure steady output voltage. Additionally, to validate the effectiveness of proposed converter, a 50-W driver circuit is designed, delivering two independent outputs of 20 W and 30 W. Frequency modulation (FM) and duty cycle control methods are employed to obtain the desired outputs.

Elastic-plastic conductor damage evaluation at over 0.4% strain using a high-stress REBCO coil

Recent reports on screening current stress simulations of high-field REBCO magnets frequently present peak stresses over 1 GPa. However, this result is probably an unrealistic artifact of purely elastic calculations, considering the macroscopic yield and fracture stresses of approximately 900 MPa and less than 1.1 GPa for Hastelloy substrate-coated conductors. Here, we evaluate elastic-plastic conductor damage at over 0.4% strain using a high-stress REBCO coil exposed to a high field to explore this elastic-plastic regime. The coil was located off-center in a low-temperature superconductor magnet so as to induce a significant screening current in the enhanced radial field. Voltage taps, a Hall sensor, and two strain gauges were used for the instrumentation. We obtained strains exceeding 0.4% near the outward edge during the coil current charge from 350 A to 390 A, where the coil was exposed to external axial and radial magnetic fields of 13 T and 0.5 T. Post mortem results showed wavy plastic deformation, electrical damage, and REBCO defects. An elastic-plastic simulation reproduced the measured strains and predicted that ∼1 GPa stress is sufficient to induce ∼0.9% strain, thus validating our initial concerns with purely elastic models. This paper provides our experimental and simulation results.

Structural Performance and Stress Contour Analysis of Multi Utility Tunnels Using LISA V.8 Finite Element Analysis

The growing complexity of urban infrastructure necessitates efficient management of utilities like electricity, water, and telecommunications. Multi Utility Tunnels (MUTs) provide a consolidated approach to housing these utilities, reducing surface disruption and enhancing maintenance efficiency. This study assesses the structural performance and stress distribution within MUTs using Finite Element Analysis (FEA) through LISA FEA V.8 software. The analysis involved detailed geometric modeling of the MUT, considering initial conditions and potential subsidence. Material properties for steel, concrete, wood, backfill soil, and the top surface layer were defined, focusing on their Young's modulus, density, and Poisson's ratio. The MUT was subjected to a uniform line pressure of 86.49 kN/m, representing vehicular traffic and pedestrian loads. Results showed that the applied stresses and observed deflections were within safe limits, with a tensile strength of 3.4 MPa and current stress at 3046 kN/m², indicating no risk of cracking. The observed deflection of 3.9 mm was significantly below the allowable limit of 10 mm, affirming structural stability. The reinforcing steel also exhibited stress levels well within its allowable limit, demonstrating the design's adequacy and ensuring the structure's safety and efficiency under the specified load conditions

In-situ stress field simulation and fracture distribution prediction of middle lower Ordovician in Zone B of Tahe Oilfield, Tarim Basin

This study constructed a heterogeneous rock mechanics model through well seismic joint inversion, set up a dual cycle statement to optimize the application of boundary loads, and obtained the current stress field distribution in Zone B. At the same time, we preferred the rock fracture criterion, carried out the quantitative characterization of different natures of fractures, and used the integrated fracture development rate to portray the integrated fracture development situation. Finally, the horizontal stress difference, stress heterogeneity coefficient, and comprehensive fracture rate were proposed to define the development index of fractured reservoirs. The results show that (1) the maximum horizontal principal stress is 102–144 MPa, and the minimum horizontal principal stress is 85–125 MPa; (2) the development rate of tension fractures is 0.03–0.23, the development rate of shear fractures is 0.15–0.54, and the integrated fracture development rate is 0.28–0.79; (3) the development index of fracture-type reservoirs is >2.3, Class I; 1.8–2.3, Class II; When it is lower than 1.8, Grade III. This article attempts to apply the stress field simulation results to the quantitative prediction of reservoir fractures, adding new ideas for the practical application of stress field results.

Ripple current control for single phase-shift dual active bridge converters

Nowadays, the need for isolated bidirectional DC/DC converters is growing. In these types of equipment, the dual active bridge topology is widespread, where mostly the trans- former leakage inductance value determines its dynamic behavior. Voltage imbalance between the primary and secondary side results in unwanted excessive transformer peak current if the leakage in- ductance is low, thus limiting the load transient response of the converter. In this paper, a ripple current control method is pre- sented, which reduces the transformer peak current to its minimal level, furthermore, allows the magnetizing current components to be distributed between the primary and secondary sides in an ar- bitrary proportion. The proposed control was tested in HIL sim- ulation and on a real 360kW dual active bridge converter. Based on the results the current stress on semiconductors and DC capac- itors were reduced while the utilization and the efficiency of the converter were increased.

A Coupled Inductor-Based High Step-Down/ Step-Up DC-DC Nonisolated Bidirectional Converter With Reduced Ripple in Current and Voltage Stress

A Coupled Inductor-Based High Step-Down/ Step-Up DC-DC Nonisolated Bidirectional Converter With Reduced Ripple in Current and Voltage Stress

Parallel Capacitive-Link Universal Converters With Low Current Stress and High Efficiency

Parallel Capacitive-Link Universal Converters With Low Current Stress and High Efficiency

A composite control method of PWM and phase shift for a three-level DC-DC converter

Abstract This research introduces a control strategy for the Three Level Active Half Bridge (TL-DAHB) DC-DC converter that integrates PWM combined with phase-shift control. This composite control method precisely regulates the output voltage by adjusting the phase-shift duty cycle between the input and output sides. Additionally, the application of the PWM control loop optimizes the duty cycle of the switches, effectively reducing the current stress on the converter during operation, improving transmission efficiency, and decreasing conduction losses of the switches. These enhancements boost the overall performance and the reliability of the converter. With its excellent voltage regulation capabilities and safety features, this converter is an ideal choice in the field of power conversion, especially in applications that demand high levels of stability and safety.

Effect of βSn grain orientations on the electromigration-induced evolution of voids in SAC305 BGA solder joints

The electromigration (EM) failure of solder joints is closely related to the development of voids during EM. In this paper, an integrated approach combining experimentation and finite element simulation was employed to reveal the evolution of voids in solder joints under current stress. The results indicate that the quantity and volume of voids near the cathode consistently increase, while those close to the anode decrease. These asymmetric evolutions of voids are mainly due to the Sn flux, which is controlled by both current density and βSn grain orientation. The magnitude of Sn flux increases with higher current densities and larger angles γ between the c-axis of βSn and the current direction. The direction of Sn flux is more significantly influenced by the current direction rather than the βSn orientation, due to the weak anisotropic self-diffusion of Sn. Voids near the anode tend to shrink while those close to the cathode expand, parallel to the substrate, due to higher Sn flux distributions at the waists of voids, where current crowding is seen. Void splitting related to rapid Cu diffusion has been observed, leading to an abnormal increase in the number of voids near the cathode. This study enhances the understanding of the electromigration failure mechanisms involving void evolution in solder joints.

A Systematic Review on Advances in Management of Oxidative Stress-Associated Cardiovascular Diseases.

Oxidative stress plays a significant role in the pathogenesis of cardiovascular diseases, such as myocardial ischemia/reperfusion injury, atherosclerosis, heart failure, and hypertension. This systematic review aims to integrate most relevant studies on oxidative stress management in cardiovascular diseases. We searched relevant literatures in the PubMed database using specific keywords. We put emphasis on those manuscripts that were published more recently and in higher impact journals. We reviewed a total of 200 articles. We examined current oxidative stress managements in cardiovascular diseases, including supplements like resveratrol, vitamins C and E, omega-3 fatty acids, flavonoids, and coenzyme-10, which have shown antioxidative properties and potential cardiovascular benefits. In addition, we reviewed the pharmacological treatments including newly discovered antioxidants and nanoparticles that show potential effects in targeting the specific oxidative stress pathways. Lastly, we examined biomarkers, such as soluble transferrin receptor, transthyretin, and cystatin C in evaluating antioxidant status and identifying cardiovascular risk. By addressing oxidative stress management and mechanisms, this paper emphasizes the importance of maintaining the balance between oxidants and antioxidants in the progression of cardiovascular diseases. This review paper is registered with the International Platform of Registered Systematic Review and Meta-analysis Protocols (INPLASY), registration # INPLASY202470064.

Power factor preregulation in power supplies using modified single stage non-isolated interleaved Sepic converter with minimal part count

This paper pontificates on design and realization of low-cost single phase single stage modified interleaved Sepic (MILS) converter for power supplies. On contrary to the classical Sepic power converters, the introduced active power factor correction (APFC) converter involves simple idea of paralleling that enables low input and output ripples with minimal device count. The interleaving conceptualization also lessens current stresses and static losses. Also, this modified power processing converter reveals natural power factor correction (PFC) and zero current switching (ZCS) features by discontinuous conduction mode (DCM) operation. Furthermore, the practical corroboration of the proposed converter is built and tested for 250 W hardware model to affirm benefits with 92 % efficiency and their relevant outcomes are reported in this scope. Finally, the power quality (PQ) attributes like, input power factor (PF), total harmonic distortion (THD) over input current under stable and transient cases are disclosed to prove bettered PQ limits at the AC mains as prescribed by various IEEE-519 and IEC 61,000–3-2 standards.

Posttraumatic Stress Disorder Among Adults in Communities With Mass Violence Incidents

Mass violence incidents (MVIs) are prevalent in the US and can have profound and long-lasting psychological consequences on direct survivors, but their outcomes among the broader communities where the MVI occurred are unknown. To investigate the prevalence of and factors associated with past-year and current posttraumatic stress disorder (PTSD) among adults in communities that experienced an MVI. This cross-sectional survey was completed between February and September 2020 with a household probability sample of adults from 6 communities that had experienced an MVI between 2015 and 2019: Dayton, Ohio; El Paso, Texas; Parkland, Florida; Pittsburgh, Pennsylvania; San Bernadino, California; and Virginia Beach, Virginia. Address-based sampling was used to identify randomly selected households, mail invitations, and select 1 adult per household to complete a self-administered paper or online survey. Data analysis was performed from September to November 2023. The primary outcome was presumptive diagnostic-level past-year PTSD and current (past month) PTSD determined using American Psychiatric Association Diagnostic and Statistical Manual of Mental Disorders (Fifth Edition) (DSM-5) PTSD criteria. A total of 6867 adults aged 18 years or older accessed the website with a description of the study and consent materials. Of these, 5991 (87.2%) agreed to participate and completed the survey, 343 (6.3%) partially completed the survey, and 443 (6.5%) did not meet eligibility criteria or refused to participate. Most of the 5991 respondents were female (3825 individuals [53.5%]) and had a mean (SD) age of 45.56 (17.58) years. A total of 1261 of 5931 individuals (21.0%) reported high exposure to the MVI (either they or a close friend and/or family member was on site during the shooting). Nearly one-quarter (23.7%; 1417 of 5977 participants reporting PTSD) met presumptive DSM-5 diagnostic criteria for past-year PTSD, with 8.9% (530 participants) meeting the criteria for current PTSD. Regression analyses found that being female (odds ratio, 2.32; 95% CI, 2.01-2.68) and having a history of both physical or sexual assault and other potentially traumatic events (odds ratio, 9.68; 95% CI, 7.48-12.52) were associated with the greatest risk of past-year PTSD. In this survey study of 5991 participants, presumptive PTSD was quite prevalent long after the MVI among adults in communities that have experienced an MVI, suggesting that MVIs have persistent and pervasive public health impacts on communities, particularly among those with prior exposure to physical or sexual assault and other potentially traumatic events. Focusing exclusively on direct exposure to MVIs is not sufficient. Incorporating these findings into screening should improve efforts to identify the individuals most in need of prevention or mental health service after MVIs.

An online supportive music and imagery intervention to promote ICU nurses’ stress management: Preliminary study

Nurses in intensive care units are subjected to high levels of work-related stress and must cope with psychological distress. This preliminary study explored the effects of an online supportive music and imagery intervention on these nurses’ perceived stress, psychological distress, and sleep quality. A prospective pre–post design was employed to investigate the effectiveness of online supportive music and imagery interventions. The intervention comprised five weekly sessions, each lasting 50–60 min, which included verbal interactions and listening to music, and were facilitated by trained music therapists. Perceived stress and psychological distress were measured before and after the five-week program to investigate its effectiveness, and the current stress level and emotional state were measured before and after each session to explore changes over the intervention period. Sleep quality was measured weekly. In total, 29 participants completed the program. The results showed a significant decrease in perceived stress (d = 0.45, p = .045) and psychological distress (d = 0.53, p = .045) after the intervention. Regarding changes over the intervention period, the findings demonstrated a significant main effect of the number of sessions on perceived stress (p = 0.001), energy (p = 0.001), and tension (p = 0.023), whereas the effects on perceived valence and scores on the Korean version of the Insomnia Severity Index were not significant. Moreover, a significant post-session main effect was observed for all perceived stress and emotion ratings (p < 0.001). Online supportive music and imagery interventions may help reduce stress levels and enhance positive emotional states among nurses in intensive care units. Integrating self-work into supportive music imagery interventions may increase adherence to the intervention and extend its effect.

What is in a name: Taxonomy of speech sound disorders from a cross-linguistic perspective.

In response to the call for papers under the theme "What is in a name" proposed by the Scientific Child Speech Committee of the International Association of Communication Sciences and Disorders (IALP), the current paper discusses taxonomy and its relation to speech sound disorders (SSD) from a cross-linguistic perspective. This paper starts with a brief description of specific SSD frameworks and nomenclature. The authors draw from international theoretical and clinical research which underscore the importance of taxonomy systems in SSD. The current papers stresses the importance of the contribution to differential diagnosis and prognosis of children with protracted speech profiles on the bases of taxonomy profiles and systems for SSD. The advantages and shortcomings of taxonomy in SSD are also discussed from a cross-linguistic context. The language of focus includes the Greek dialectal variation of Cypriot-Greek. The paper adds to the importance of taxonomy and SSD subsystems which allow differential diagnosis of SSD and the implementation of appropriate intervention methods. What is already known on this subject The use of various taxonomy systems regarding SSD are widely available for English-speaking populations. Such systems in the cross-linguistic framework remain underexplored. What this paper adds to existing knowledge The paper underscores the need for the development, adaptation and use of taxonomy systems that will add to the existing databases and taxonomy subsystems used in English What are the potential or actual clinical implications of this work? Potential clinical implications include the development and implementation of taxonomy systems in profile SSD productions in children.

Officer gunpoint during police stops: Repercussions for youth mental health and perceived safety.

Youth-police contact is increasingly acknowledged as a stressor and a racialized adverse childhood experience that can undermine youths' mental health. The present study investigates a particularly distressing feature of youths' direct and witnessed in-person police stops-officer gunpoint (i.e., officers drawing of firearms and pointing them at youth, their peers, or other community members). We examine patterns of youths' officer gunpoint exposure and associations with youth mental health and safety perceptions. Data come from the Survey of Police-Adolescent Contact Experiences (SPACE), a cross-sectional survey of a community-based sample of Black youth ages 12-21 in Baltimore City, Maryland (n = 335), administered from August 2022 to July 2023. Findings indicate that ~33% of youth reporting in-person police stops had been exposed to officer gunpoint during stops. Officer gunpoint was significantly and positively associated with being male, unemployed, having an incarcerated parent, living in a neighborhood with greater disorder, and having been directly stopped by police, in addition to youth delinquency and impulsivity. Net of covariates, experiencing officer gunpoint was associated with a significantly higher rate of youth emotional distress during stops. Significant associations between officer gunpoint and youths' current police violence stress, police avoidance, and diminished safety perceptions also emerged and were largely explained by youths' heightened emotional distress at the time of police stops. Trauma-informed approaches are needed to mitigate the mental health harms of youth experiencing officer gunpoint.

Experimental study on strengthening the magneto-mechanical coupling effect of X80 steel by weak magnetic excitation

Abstract Current magnetic stress detection techniques are significantly impacted by external noise signals. The magnetic stress detection technology under excitation magnetic fields is proposed to weaken the external noise signals on the detection results. In this study, the uniaxial tensile magnetic signal testing system with the excitation magnetic field was built. The enhancement of the weak magnetic excitation on magnetic signals has been quantitatively analyzed and the concept of optimal weak excitation magnetic field has been proposed. The response law between triaxial magnetic induction intensity and stress under the excitation magnetic field is determined. The results indicate that the weak excitation magnetic field significantly enhances the magnetic induction signal intensity, more importantly, the linearity of the magnetic signal and stress response is also enhanced. Furthermore, the optimal excitation magnetic field under uniaxial stress states is 600 A/m, and the corresponding stress-magnetic change rate is 0.002 Oe/MPa. This study provides a theoretical basis for the long-distance detection of pipelines under weak magnetic excitation. The long-distance magnetic stress detection results of pipelines will become more accurate with the weak magnetic excitation which has a good engineering significance.&amp;#xD;

A single-bridge interleaved three-level LLC resonant converter with current sharing capability for fuel cell system

This paper propose a wide gain single-bridge interleaved three-level LLC resonant converter with current sharing capability. This novel converter offers numerous advantages, including low cost, low current ripple, reduced voltage and current stress, widely gain range, high efficiency, good current sharing capability and versatile application scalability. Utilizing the three-level inverter + full-wave rectifier LLC converter as a representative case, the paper conducts an in-depth analysis and research on the proposed method. Finality, a 600 W experimental prototype was constructed and tested. Experimental results reveal that the proposed converter exhibits lower current ripple and a broader gain range. Moreover, the converter shows good current sharing capability (with a resonant element tolerance of 10%, the current error between the two phases does not exceed 12%) and high efficiency (peaking at 95.8%).