Temperature Loading Research Articles

A Study on Effect of Sintering Temperature and Compaction Load on Mechanical Properties of Aluminium-Magnesium Alloy by Powder Metallurgy

The presented study is intended to investigate the mechanical properties of an aluminium-magnesium alloy (Al-Mg) produced by powder metallurgy process and sintered at different temperatures. The investigation involves aluniminum is alloyed with different weight percentages of magnesium powder (0%, 2%, 4%, and 6%), which were compacted under 260 KN and 300 KN pressure using a compaction die in the room temperature. The compacted green samples were then sintered at two different temperatures, 540°C and 580°C. Sintered specimens of Al-Mg alloys are tested for mechanical properties like hardness, density, wear resistance and Microstructure. The investigation shows that there is an increase in hardness by 36% for specimens compacted at 300kN load and sintered at 580°C. Major Findings: Overall, the results highlight the potential for tailoring the mechanical properties of Al-Mg alloys through careful control of compaction pressure and sintering temperature. This knowledge could be valuable in optimizing the fabrication process for various industrial applications where enhanced mechanical performance is desired.

Study of hygrothermal environment impact on the vibration behavior of thick nanocomposite beams reinforced with multilayer Graphene Nanoplatelet

This paper aims to investigate the free vibration of a multilayer piezo-electric beam strengthened with functionally graded graphene platelets (FG-GPLRC) and subjected to a consistent increase in temperature and humid external loads. Graphene platelets (GPLs) are supposed to be dispersed either uniformly or layerwise form in the polymeric matrix, with a variety of patterns configurations taken into consideration. The rule of mixing is employed to evaluate Poisson's ratio and mass density features. In order to estimate the efficient Young's modulus, the modifier Halpin-Tsai model has been employed. The whole system of governing equations for motion were achieved by exploiting Hamilton’s concept based on Timoshenko beam theory (TBT). After that, these equations were solved using the Navier analytical solution-based Fourier series with high accuracy. Next, to examine the effects of several elements, including graphene weight percentage and their distribution shape, length by thickness ratio, externally provided thermal-humidity fields, on the dynamic of nanocomposite reinforced beams.

Multicomponent Synthesis of Structurally Diverse Spiroheterocycles using Bio-organic Catalyst in Aqueous Medium

Background: MCRs are one of the most significant tools in the synthesis of organic compounds. MCR is a rapid chemical technique that uses three or more reactants to produce products that sustain all structural and substructural properties of the initial components. MCRs are useful in all fields of synthetic chemistry because of their rapid rate of reaction, simple procedure and excellent yields. We reported an efficient and environmentally friendly domino approach for the synthesis of spiroheterocycles spiro annulated with indeno[1,2-b]quinoline. Method: The spiroheterocycles with privileged heterocyclic substructures have been synthesized using taurine (2-aminoethanesulfonic acid) as a green, sustainable, bio-organic and recyclable catalyst in a three-component reaction of isatins, 1,3-diketones, and 1-napthylamine in aqueous media. The present synthetic method is probably the first report to synthesize spiroheterocycles, spiroannulated with indeno[1,2-b]quinoline. Furthermore, the approach is valuable because of the excellent yield that results from the reaction in 15-20 min. Result: The optimization of reaction conditions is an important case of efficient synthesis. The solvent, temperature, time and catalyst loading were all examined. The reusability of the catalyst was also investigated experimentally. The used catalyst taurine has a high activity as well as good reusability. The present synthetic protocol will be extended to synthesise a library of hybrid compounds. The present synthetic approach is cost-effective, and time-efficient with an easy-workup methodology that gives outstanding yields (80–95%) in 15–20 min. Conclusion: Taurine-catalyzed multicomponent reaction is a novel and efficient method for the synthesis of spiroannulated indeno[1,2-b]quinolines. The high catalytic activity of taurine as a catalyst with water as a green solvent makes the process environmentally friendly. The special features of the synthetic protocol include synthetic efficiency, operational simplicity, and reusability of the catalyst and it is expected to make significant contributions not only to drug discovery studies but also to pharmaceutical and therapeutic chemistry in view of introducing molecular diversity in the synthesized molecules.

Design optimization of continuous fiber composites with thermo-mechanical coupling and load uncertainties

This paper introduces a theoretical framework for the design optimization of continuous fiber composites reinforced with continuous fiber trajectories subject to thermo-mechanical coupling and load uncertainties. Different uniform temperature variations are applied in the structure to investigate the influence of ambient temperature change on the structural performance. To consider the external load uncertainties, a robust design optimization model is proposed where the loads are modeled as hybrid variables, namely magnitudes as random variables and directions as interval variables, with the robust objective determined through a hybrid orthogonal polynomial expansion method. Furthermore, we use a level-set function to represent the structural boundary, with its evolution driven by shape derivatives calculated based on uncertainty analysis. The continuous fiber paths are subsequently determined by the level-set isoline extracted from the structural boundary, which in turn influences the structural mechanical performance due to the material anisotropy of composites. The continuity of continuous fiber and the equal space between adjacent trajectories largely ensure the additive manufacturability of the composites. Three numerical examples are presented to demonstrate the effectiveness of the developed framework. The results show that the ambient temperature variations and load uncertainties largely impact the optimized topology and fiber infill patterns of composites, thus are important to be considered in the design stage. Moreover, the optimized structure can have a 5-fold stiffness per unit mass compared with the initial design thus largely increasing the material efficiency in carrying external uncertain loads.

Comparison of cost and performance between traditional and green processes for producing bimetallic carbide based oxygen reduction electrocatalysts

Chemical (ion exchange resin) and biomass (water hyacinth leaves) as carbon precursors are adopted to prepare two kinds of bimetallic carbide (Fe2MoC)-based catalytic materials. It is found that, compared with the material that use ion-exchange resin as carbon precursor (N-Fe2MoC-RG), the material that use water hyacinth as carbon precursor (N-Fe2MoC-WHG) has more advantages in cost, environment protection, synthesis simplicity, and catalytic activity for oxygen reduction reaction (ORR). Therein, the N-Fe2MoC-WHG as a cathode catalyst displays a half-wave potential of 0.905 V (vs. RHE) for catalyzing ORR in alkaline media, and gets a high peak power density of 1.52 W cm-2 in alkaline electrolyte membrane fuel cell; moreover, the N-Fe2MoC-WHG displays higher power-density retention or growth rate at lower relative humidity, higher back pressure, higher working temperature and higher catalyst loading, compared with the N-Fe2MoC-RG. The N-Fe2MoC-WHG is one of the most active precious metal-free catalysts reported so far, and its stability is very excellent.

Catalysts screening on production of syngas over novel cobalt-based catalysts supported with dolomite: effect of calcination temperature and Co loading

Catalysts screening on production of syngas over novel cobalt-based catalysts supported with dolomite: effect of calcination temperature and Co loading

Land use and runoff effects on tidal creek ecosystem metabolism

Tidal creeks connect coastal lands and estuaries and are important conduits of watershed runoff and pollutants. With expanding urban development in many coastal areas, increased stormwater runoff to tidal creeks has the potential to increase nutrient loading, shift salinity regimes, and change ecosystem functions. To better understand these linkages, we measured dissolved oxygen (DO), water levels, salinity, and temperature for over 1 yr at 6 tidal creeks in Alabama and western Florida, USA. We coupled these measures with watershed-model (Soil and Water Assessment Tool) estimates of nutrient (NO3-, NH4+, and mineralized P) loading, flow, and other available watershed data. We estimated gross primary productivity, ecosystem respiration (ER), and net ecosystem metabolism (NEM) and found that all creeks were heterotrophic throughout the study period and frequently experienced periods of low DO. Our results did not identify a direct relation between urban land use and metabolism measures. Stepwise regression models showed that temperature, salinity fluctuations, and nitrogen loading were associated with seasonal measures of ER and NEM, which may be related to agricultural land use in some watersheds. We also noted that severe declines in DO related to ER occurred in most creeks following rainfall events associated with tropical cyclones. While this study indicates that low- to moderate-density residential development in this region may not readily elicit a response in ecosystem metabolism, runoff factors associated with land use change and excessive precipitation were related to metabolism. Further research is needed to understand how these stressors may interact to influence tidal creeks and the larger estuary.

A Multi-Scale Thermal-Mechanical Numerical Method for Mini-Channel Heat Exchanger Subjected to Fluid Pressure Loads

Abstract This study proposes a novel multi-scale numerical method for thermal-mechanical analysis of mini-channel heat exchangers (MCHEs) under internal fluid pressure and temperature loads. The method comprises a macro-scale model for global analysis and a meso-scale model for detailed submodel analysis, specifically focusing on the internal fluid pressure effects within the MCHEs. The macroscopic model divides the MCHE into cover plate and homogenized regions subjected to pressure and temperature loads. To incorporate internal pressures into the homogenized MCHE model, mathematical equations are formulated to convert internal fluid pressures into equivalent strain loads. Additionally, a novel equivalent thermal expansion method is introduced, integrating internal fluid pressure loads by prescribing equivalent thermal expansion coefficients alongside spatially-varying nodal temperature fields within the MCHE. The meso-scale models with detailed channel patterns are assigned to specific portions of the homogenized region. The integration of the mesoscale model into the macroscopic framework is achieved through the application of the submodel method. Comparisons between the equivalent and actual MCHE models show that the proposed equivalent method can provide accurate predictions for thermal-mechanical deformations and stresses, and significantly reduce the computational expenses.

The Intermediate Barrier Performance of Electroless Co-W-B / Ni-P Stacked Deposits Between Cu and Solder Joint

Nickel (Ni) is one of the most common surface finishing materials for solder joint and wire bonding because it can behave as the diffusion barrier for Copper (Cu) and bring excellent reliability. Electroless Ni plating has many advantages such as high productivity, good thickness uniformity, and the deposition ability for isolated patterns of printed circuit boards without supplying electrolytic power. Electroless Ni plating is widely used as the jointing material for Tin (Sn) or Sn alloy solder in printed circuit boards, lead frames, and so on. The amorphous deposits of electroless Nickel-Phosphorus (Ni-P) generate the intermetallic compounds (IMC) with solder after the reflow and the remaining Ni behaves as the barrier between Cu and solder. In this time, the P amount of Ni-P deposits generally have the impact to the growth of IMC. Electroless Ni-P with high P (high P Ni) such as 10-12 wt% has been selected to achieve both corrosion resistance and solder joint reliability. Because the growth of Sn-Ni IMC between high P Ni is faster than deposits with lower P, the target thickness of high P Ni has been set to approximately 10 µm to sustain the Ni-P layer as the barrier layer between Cu and solder during reflow. However, if the Ni-Sn IMC is repeatedly formed and dissolved by the diffusion after solder jointing, the Ni-P layer reduces and finally disappears. As a result, an additional barrier layer is desirable for higher reliability. In this study, we investigated adding electroless Cobalt-Tungsten-Boron (Co-W-B) as a new intermediate barrier between Cu and solder jointing. We evaluated the bonding strength and IMC analysis after mounting Sn-Cu-Ni-P type solder on Cu/Co-W-B/Ni-P by using different reflow profiles. Results showed that Co-W-B 0.1-0.2 µm/Ni-P 1-2 µm stacked deposits had excellent bonding strength even though the Ni-P thickness is thinner such as 1 µm. After mounting solder, a P-rich layer was generated on the Co-W-B layer in cross-sectional Transmission Electron Microscope (TEM) observation. Scanning Transmission Electron Microscope (STEM) –Energy Dispersive X-ray Spectroscopy (EDS, STEMEDS) analysis showed the P-rich layer and Co-W-B layer prevented diffusion between solder and Cu. Furthermore, even if after the thermal loading of high temperature, the bonding strength was excellent. Additionally, the cross-section analysis of STEM-EDS revealed that a thin layer composed of Ni, Co and P was formed between Co-W-B and the P-rich layer. This thin layer also might behave as the barrier for solder. In conclusion, Co-W-B / Ni-P stacked deposits exhibited excellent reliability as the additional intermediate barrier layer between Cu and solder.

Feasibility of successive hydrogen and methane production: Effects of temperature and organic loads on energy potential and microbial dynamics

This study aims to assess the co-digestion of Cassava Wastewater (CW) and glycerol in a two-stage process using fluidized bed reactors (AFBR), verifying the effect of organic loading rate (OLR) and temperature (mesophilic [SMR] and thermophilic [STR]) in sequential reactors on CH4 production. The OLR ranged from 1.2 to 15 g COD.L−1.d−1 and the hydraulic retention time (HRT) was set at 20 h. The mesophilic sequential reactor (MSR) (average temperature of 30 °C) showed greater tolerance to high OLR and its best MPR was 101.12 mL of CH4.d−1.L−1 h−1, obtained at a OLR of 15 g COD.L−1.d−1). The maximum yield was 341.10 mL of CH4.g−1CODcons, found at the OLR of 1.2 g COD.L−1.d−1. The sequential thermophilic reactor (STR) showed the maximum yield and MPR of 333.03 mL of CH4.g−1CODcons (1.2 g COD.L−1.d−1) and 58.84 mL of CH4.d− 1.L−1 h−1 (12 g COD.L−1.d−1), respectively. Through the massive sequencing analysis of the 16S rRNA gene, it was possible to observe a greater diversity of microorganisms in the TSR than in the MSR. A predominance of acetoclastic microorganisms was observed, with the genera Methanobacterium, Methanosarcina and Methanobrevibacter being the most abundant in both reactors. The two-stage system composed of mesophilic acidogenic reactor + MSR was more suitable for the co-digestion of CW and glycerol than the acidogenic reactor + TSR. These results support the notion of standard operating conditions at the industrial plant, where the cassava processing process is carried out at room temperature (25–30 °C).

A Quasi Time-Domain Method for Fatigue Analysis of Reactor Pressure Vessels in Floating Nuclear Power Plants in Marine Environments

The reactor pressure vessel (RPV) in onshore nuclear power plants is typically analysed for fatigue life by considering the temperature, internal pressure, and seismic effects using a simplified time-domain fatigue analysis. In contrast, the frequency-domain fatigue analysis method is commonly employed to assess the fatigue life of ship structures. The RPV of a floating nuclear power plant (FNPP) is subjected to a combination of temperature, internal pressure, and wave loads in the marine environment. Consequently, it is essential to effectively integrate the frequency-domain fatigue analysis method used for hull structures with the time-domain fatigue analysis method for RPVs in FNPPs or, alternatively, to develop a suitable method that effectively accounts for the temperature, internal pressure, and wave loads. In this study, a quasi-time-domain method is proposed for the fatigue analysis of RPVs in FNPPs. In this method, secondary components of marine environmental loads are filtered out using principal component analysis. Subsequently, the stress spectrum induced by waves is transformed into a stress time history. Fatigue stress under the combined influence of temperature, internal pressure, and wave loads is then obtained through a stress component superposition method. Finally, the accuracy of the quasi-time-domain method was validated through three numerical examples. The results indicate that the calculated values obtained by the quasi-time-domain method are slightly higher than those obtained by the traditional time-domain method, with a maximum deviation of no more than 24%. Additionally, the computation time of the quasi-time-domain method is reduced by 98.67% compared to the traditional time-domain method.

A new FEM-based approach on the modeling of stress-induced velocity shift of piezoelectric surface acoustic wave resonators

A novel methodology is introduced for the computation of stress-induced surface acoustic wave velocity shifts in piezoelectric resonators including quartz, lithium niobate and langasite resonators. The numerical framework has been verified through a comparative analysis of experimental and Finite Element Method (FEM) results for quartz resonators. This approach introduces the combined capabilities of COMSOL Multiphysics and MATLAB, facilitated by LiveLink, to systematically calculate all parameters contributing to the perturbation integral. The findings have a better accuracy using the LiveLink methodology in this study compared to prior approaches that rely on average stress and strain calculations in the central point of the resonator. Moreover, the utilization of LiveLink not only enhances accuracy but also establishes MATLAB as a fundamental software platform for interfacing with COMSOL Multiphysics. The proposed approach in this paper can extend to complex strain sensors or investigations into the influence of temperature and imbalanced loading effects in future research endeavors. Furthermore, the LiveLink approach introduced herein can be extended to optimize crystal orientation and identify premium wave directions, thereby contributing to the enhanced design of Surface Acoustic Wave (SAW) resonators. This innovative methodology is used to advance the understanding and application of stress-induced velocity shifts in SAW devices, presenting future developments in sensor technologies and resonator designs. © 2024 Elsevier Science. All rights reserved.

Model Test on Thermomechanical Behavior of Deeply Buried Pipe Energy Pile Under Different Temperature Loads and Mechanical Loads

Deeply buried pipe energy pile (DBP-EP) offers the capability to harness geothermal energy from significantly deeper subterranean layers than those available inside buried pipe energy pile (IBP-EP). Despite its potential, there is a notable scarcity of research on the thermomechanical behavior of DBP-EP. This study meticulously observed the thermal variations in the soil surrounding the DBP-EP, the mechanical response of the pile itself, the earth pressure at the pile toe, and the displacement occurring at the pile’s top during the heating phase across various operational conditions. The findings show that for every 1 °C increase in inlet temperature, the temperature difference between the inlet and outlet increases by about 0.27 °C. The method of load application at the pile top during heating markedly influences the frictional resistance along the pile’s sides. Furthermore, When the pile top load rises from 0.26 kN to 0.78 kN, the observed vertical load at the pile foot decreases by 2.2–8.51%. This indicates that the increase in the pile top load reduces the downdrag effect on the sandy soil near the pile toe. This reduction subsequently diminishes the impact of vertical loads on the pile toe. Notably, after continuous operation for 8 h, the rate of increase in pile top displacement for DBP-EP shows a decline. Additionally, for every 1 °C rise in the inlet water temperature, the final displacement at the pile top diminishes by approximately 0.03‰D. This research endeavors to furnish a robust theoretical foundation for the structural design and practical engineering applications for DBP-EP.

Performance and mechanism of the biochar-supported Ni0/Co0/MnO composite catalyst for peroxymonosulfate activation to degrade iopamidol

A biochar-supported Ni0/Co0/MnO composite catalyst was prepared from the cathode material (CM) of spent ternary 523 lithium-ion batteries (LIBs) and buckwheat hulls. The effect of pyrolysis temperature (x) and different loading ratios (y) of xBCyCM on the activation of peroxymonosulfate (PMS) was investigated. The results showed that the loading of Ni0/Co0/MnO on the biochar (BC) enhanced the IPM degradation and effectively reduced metal ions’ leaching. The 850BC10CM/PMS system degraded iopamidol (IPM) within the wide pH range of 5.0–10.0. The pseudo-first reaction rate constant kobs was 0.0944 min−1 during 25 min under optimal conditions (catalyst dose of 0.1 g·L−1, 0.5 mM of PMS, and an initial pH value of 10.0), while the leaching concentrations of Ni, Co, and Mn were 0.089, 0.035, and 0.067 mg·L−1, respectively. Furthermore, the 850BC10CM degraded IPM by radicals (·OH, SO4•−, and ·O2-) and non-radical pathways (1O2 and an electron transfer). As the pH value increased from 7.0 to 10.0, the fluorescence analysis and quenching experiments revealed a decrease in the effects of SO4•− and ·OH, while the effect of 1O2 was enhanced. The 850BC10CM could still achieve a removal rate of 86.6 % for IPM after four cycles. Based on the liquid chromatography-mass spectrometry (LC-MS) results of degradation intermediates, five possible degradation pathways were proposed. The 850BC10CM inhibited the formation of the iodoform CHI3. In short, the 850BC10CM, which was prepared by using a green, sustainable development of waste utilization, exhibited a safe and effective performance for the removal of emerging IPM pollutants.

Insight into the “synergistic-relaxation effects” in amorphous polymer: Thermodynamic modeling, multiphysics simulation and application in 4D printing

Structure and stress relaxation in shape memory polymers (SMPs), which show the time-dependent response to temperature and mechanical loading, respectively, are usually thought to be the primary mechanisms of shape memory effects (SMEs). However, the synergistic effect of structure and stress relaxation has not been well investigated. What's more, convenient and economic manufacturing and structural customization of SMPs can be easily achieved by four-dimensional (4D) printing technology. Thus, in this paper, we comprehensively analyze the working mechanisms of synergistic-relaxation effects in both traditional and 4D-printed SMPs using theoretical calculations and experimental confirmation. Specifically, the calculations are based on the thermo-mechanical and electro-thermo-mechanical models, and multiple sets of experimental data are used to verify the model results. The model results agree well with the experimental data and demonstrate that synergistic-relaxation mechanisms play an important role in thermo-mechanical behaviors.

Wear Calculation for a Shaft Lip Seal under Randomly Changing Temperature and Load

A stochastic model of the wear process of a shaft lip seal that takes into account random changes in the temperature and external load was described. The results of a numerical analysis of the process of seal wear in relation to the conditions of operation in open space at near-Earth orbital stations are presented. The importance of taking into account random changes in temperature and external load for predicting the seal durability was evaluated.

Effect of stabilizers on the detection of swine influenza A virus (swIAV) in spiked oral fluids over time

BackgroundAggregated samples such as oral fluids (OFs) display an animal friendly and time and cost-efficient sample type for swine Influenza A virus (swIAV) monitoring. However, further molecular and biological characterization of swIAV is of particular significance. The reportedly inferior suitability of aggregated samples for subtyping of swIAV presents a major drawback compared to nasal swabs, still considered the most appropriate sample type for this purpose (Garrido-Mantilla et al. BMC Vet Res 15(1):61, 2019). In addition, the viral load in the original sample, storage conditions and characteristics of different swIAV strains might further compromise the eligibility of aggregated samples for molecular detection and subtyping. Therefore, the present study aimed to evaluate the suitability of stabilizing media to minimize the degradation of viral RNA and thus increase the detection and subtyping rate of swIAV by RT-qPCR in spiked OFs under different conditions (virus strain, storage temperature and viral load in the original sample) over a time span of 14 days.ResultsThe use of stabilizing media in spiked OFs resulted in a significant higher probability to detect swIAV RNA compared to OFs without stabilizers (OR = 46.1, p < 0.001). In addition, swIAV degradation over time was significantly reduced in samples suspended with stabilizer (OR = 5.80, p < 0.001), in samples stored at 4 °C (OR = 2.53, p < 0.001) and in samples spiked with the avian derived H1N2 subtype (OR = 2.26, p < 0.01). No significant differences in swIAV RNA detection and degradation of swIAV RNA in spiked OFs over time were observed between the three different stabilizing media.ConclusionAddition of stabilizers and storage of samples under cooled conditions significantly improved detection and subtyping of swIAV in spiked OFs.

Effect of Geometric Parameters of High-Speed Helical Gears on Friction Flash Temperature and Scuffing Load Capacity in Electric Vehicles

High-speed reducers in electric vehicles, characterized by high rotation speeds, heavy loads, large helix angles, and high contact ratios, are prone to tooth surface scuffing due to high sliding speeds. This scuffing is caused by adhesion wear from excessive instantaneous friction flash temperatures. The prevailing approach to gear scuffing analysis relies on the standard formula method, which is a relatively rudimentary technique. This method lacks the precision required to accurately assess the intricate distribution of tooth surface flash temperature (TSFT), limiting its efficacy in targeted tooth optimization. This study introduces an enhanced semi-analytical method to calculate TSFT and analyzes its variation under different conditions: increased tooth number and reduced module, altered pressure angle, and varied helix angle. The aim is to understand how these geometric parameters affect TSFT and the scuffing load capacity of high-speed reducer gears. This study calculates load distribution and TSFT under peak operating conditions and shows that increasing the tooth number, pressure angle, and helix angle can reduce maximum TSFT by more than 30%, improving scuffing safety and load capacity. However, these improvements must consider the gear’s allowable bending safety factor and bearing service life. The research concludes that optimizing these geometric parameters can significantly enhance the scuffing load capacity of gearsets.

Indoor air bacterial quality and associated factors in prison inmate cells of East Hararghe Zone and Harari Regional State, Eastern Ethiopia.

Bacterial indoor air load refers to the level of bacteria within and around dwellings and other structures. Pathogens, bacterial cell fragments, and bacterial organisms' byproducts can all pose major issues indoors, especially in prison inmate cells. However, there is lack of data on bacterial load and contributing factors in the East Hararghe zone and Harari regional state. The lack of studies on microbiological indoor air quality in prisons with contributing factors will therefore be filled by this investigation. The study aimed to assess bacterial indoor air load and contributing factors in prison inmate cells from October 1 to October 30, 2020. An institutional cross-sectional study was employed. All of the prisons in the East Hararghe zone and the Harari regional state served as the study's and source population. 62 prison cells were used in the investigation. Samples were obtained using the passively settling plate technique. The data were evaluated through the use of SPSS statistical software, Excel, and the statistical procedures of ANOVA, correlation, and chi-square test. The maximum and minimum bacterial loads, were recorded at 8:00 am (3027 CFU/m3) and 2:00 pm (1048 (CFU/m3) respectively. The correlation between the temperature and bacterial load was strongly positive (r = 0.680, p = 0.047), and the correlation of the moisture content and bacterial load was strongly negative (r = -0.671, p = 0.039). The levels of bacteria were higher than the guideline (2000 CFU/m3). While the relative humidity of indoor air was negatively correlated with bacterial load, temperature and bacterial load were significantly positively correlated. Harari regional state and East Hararghe zone prison commissions should be alarmed to alleviate these problems. The building standards need to be completely updated to the latest standards.

Tunable impact resistant materials: Synergistic enhancement of paraffin/MRP/re-entrant structures

In the realm of safety protection, there is a critical demand for materials capable of superior energy absorption and adaptability across diverse application scenarios. Here, this study presents integrated two-phase negative Poisson’s ratio (NPR) composites with adjustable mechanical properties sensitive to magnetic field, temperature and impact load. It is achieved by substituting the vacancy of re-entrant structures (frame phase) with soft paraffin/magnetorheological plastomer (MRP) fillers (matrix phase). The paraffin/MRP exhibits temperature-sensitive properties, enhanced magnetorheological (MR) effect (up to 4178%) and shear thickening (ST) effect (up to 2365%). Through quasi-static compression and dynamic impact tests, the composites demonstrate remarkable adaptability in impact resistance. Specifically, the first peak force exhibits responsiveness to changes in magnetic flux density, temperature, and impact velocity, with respective variations of 80.6%, 68.2%, and 30.3%. The design strategy paves the way for tunable impact resistant materials with potential for extreme environment buffering applications.