Volume Coefficient Research Articles

Lubrication and anti-wear behavior of duplex annealed nanodiamonds/PEO coating on Ti6Al4V: Functional mechanism of structural transformation

Titanium alloys have been widely used due to its low density, high strength and excellent corrosion resistance, but the poor tribological properties restrict its engineering application. Nanodiamond particles provide excellent lubrication and high wear resistance due to the unique physical-chemical properties, but the mismatched mechanical properties severely restrict the solid lubrication application of nanodiamond for titanium alloys. In this study, plasma electrolytic oxidation coatings were firstly prepared on Ti6Al4V substrates, and core-shell annealed nanodiamond particles obtained by high-temperature annealing at 1300 °C with nanodiamond core and graphitic outer shell were deposited on the PEO coatings. The plasma electrolytic oxidation-annealed nanodiamond coatings led to a 46.67 % and 96.13 % reduction of coefficient of friction and wear volume comparing to plasma electrolytic oxidation coatings. Annealed nanodiamond with unique core-shell structure can reduce the abrasion of friction pairs; and the friction-induced structural transformation of annealed nanodiamond particles in the top-layer tribofilm further enhanced the lubrication and wear-resistance. The proposed lubrication mechanism has implications for the development of novel nanomaterials with core-shell structure and duplex coating systems for engineering applications.

Deicing of Sessile Droplets Using Surface Acoustic Waves.

Deicing has significant relevance in various applications such as transportation, energy production, and telecommunication. The use of surface acoustic waves (SAWs) is an attractive option for deicing as it offers several advantages such as localized heating, in situ control, low power, and system integration for highly efficient deicing. Here, we report an understanding of the dynamics of deicing of microlitre volume water droplets (1 to 30 μL) exposed to low power (0.3 W) SAW actuation using an interdigitated electrode on a piezoelectric (LiNbO3) substrate. We study the time variation of the volume of liquid water from the onset of SAW actuation to complete deicing, which takes 2.5 to 35 s depending on the droplet volume. The deicing phenomenon is attributed to acoustothermal heating which is found to be greatly influenced by the loss of ice adhesion with the substrate and the acoustic streaming within the liquid water. Acoustothermal heating inside the droplet is characterized by the temperature distribution inside the droplet using infrared thermography, and acoustic streaming is observed using dye-based optical microscopy. A rapid enhancement in deicing is observed upon the detachment of ice from the substrate and the onset of acoustic streaming, marked by a sudden increase in the liquid water volume, droplet temperature, and heat transfer coefficient. The deicing time is found to increase linearly with droplet volume as observed from experiments and further verified using a theoretical model. Our study provides an improved understanding of the recently introduced SAW-based deicing technique that may open up the avenue for a suitable alternative to standard deicing protocols.

An investigation on the effects of geometrical parameters on the sensitivity of micro-disk and micro-ring plasmonic sensors

Geometrical parameters of coupled plasmonic resonators that consist of micro-disk and micro-ring structures have been investigated numerically, and changes in the Q factor, mode volume, and Purcell coefficient of the investigated structure have been calculated according to changes in geometrical variables. Optimal geometrical values for achieving plasmonic modes have been found using simulation results. Additionally, the performance of a single micro-disk, the single micro-ring, and two coupled micro-ring structures as a refractive index sensor has been compared and reported. It has also been shown that although the general shape of the figure of merit (FoM) graph is the same for all tested structures, the FoM of the disk resonator achieves lower values compared to ring and coupled resonators.

Characterization of structural, dynamic, optoelectronic, thermodynamic, mechanical and thermoelectric properties of AMgF3 (A = K or Ag) fluoro-perovskites compounds

Born effective charges Z(i),β α *, dielectric tensors ε α,β and the dynamic stability for AgMgF3 and KMgF3 compounds were treated based on the harmonic and quasi-harmonic theory implemented in phonopy code. The band gap for both compounds, and the effective masses of electrons and holes are calculated at different pressures using the TB-mBJ (GGA) approximation within the framework of the density functional theory. Furthermore, absorption coefficient, refractive index, extinction coefficient, reflectivity, and optical conductivity, for both compounds, were calculated. On the other hand, we studied the nature of atomic bonds by the topological distribution of the charge density as well as computing the effective charge of each atom based on the Quantum Theory of Atoms in Molecules (QTAIM) as implemented in Bader code, therefore the ionic type for bonds was explored. The mechanical stability was verified the elastic behavior at the equilibrium ground-state for both compounds. Thermal properties such as heat capacity at constant volume, entropy, Debye temperature, and thermal expansion coefficient are treated depending on the quasi-harmonic model. They are examined under both pressure and temperature influences. The thermoelectric properties of the compound AgMgF3 showed a high figure of merit (ZT) reached 0.75 at a temperature of 300 K in the case if it was grafted with a concentration of 1021 cm−3 of n-type.

Patient-specific three-dimensional dose distribution prediction via deep learning for prostate cancer therapy: Improvement with the structure loss

PurposeDeep learning (DL)-based dose distribution prediction can potentially reduce the cost of inverse planning process. We developed and introduced a structure-focused loss (Lstruct) for 3D dose prediction to improve prediction accuracy. This study investigated the influence of Lstruct on DL-based dose prediction for patients with prostate cancer. The proposed Lstruct, which is similar in concept to dose–volume histogram (DVH)-based optimization in clinical practice, has the potential to provide more interpretable and accurate DL-based optimization. MethodsThis study involved 104 patients who underwent prostate radiotherapy. We used 3D U-Net-based architecture to predict dose distributions from computed tomography and contours of the planning target volume and organs-at-risk. We trained two models using different loss functions: L2 loss and Lstruct. Predicted doses were compared in terms of dose–volume parameters and the Dice similarity coefficient of isodose volume. ResultsDVH analysis showed that the Lstruct model had smaller errors from the ground truth than the L2 model. The Lstruct model achieved more consistent dose distributions than the L2 model, with errors close to zero. The isodose Dice score of the Lstruct model was greater than that of the L2 model by >20% of the prescribed dose. ConclusionsWe developed Lstruct using labels of inputted contours for DL-based dose prediction for prostate radiotherapy. Lstruct can be generalized to any DL architecture, thereby enhancing the dose prediction accuracy.

Experimental Investigation of Tribological and Rheological Behaviour of Hybrid Nanolubricants for Applications in Internal Combustion Engines

In this study, the improvement in SAE 10W-40 engine oil tribological performance after the addition of magnesium oxide (MgO) nanoadditive and two different phosphonium-based ionic liquids (ILs) was investigated. Besides, the rheological behaviour of MgO-based nanolubricant and IL-based hybrid nanolubricants at the temperature range from 293.15 to 363.15 K was studied. The nanoparticle characterization was performed by means of transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The tribological properties, friction coefficients and wear parameters of the formulated oil modified with 0.01 wt% MgO and 1 wt% ILs compared with the neat 10W-40 oil were performed and analysed using a ball-on-three-pins tribometer and a 3D optical profilometer, respectively. Further analysis on the worn surface was shown by Raman spectroscopy and SEM images illustrating the formation of the protective IL and MgO tribo-films as hybrid additives. In friction tests with sliding steel-steel tribo-pairs, IL3-based hybrid nanolubricant decreased the coefficient of friction and wear volume by 7% and 59%, respectively, in comparison with the neat SAE 10W-40, hence better positive synergies were found for MgO and IL3 as hybrid additives. Interestingly, the thermophysical characterization by rheology also revealed that the nanoparticle and ionic liquids addition did not affect neither the viscosity response nor the Newtonian behaviour of the engine oil, adequately meeting the requirements for their use in internal combustion engines.Graphical

Slenderness coefficient and growth characteristics of Africa giant bamboo: Bambusa vulgaris Schrad. ex J.C. Wendl

The tree slenderness coefficient (SC) has been widely used as an index of the resistance of trees to windthrow, and the slenderness coefficients of different tree species have been intensively studied. However, very little or no information is available for the slenderness coefficients of bamboo in many parts of the world including Nigeria. Here, we evaluated the slenderness coefficient of African giant bamboo (Bambusa vulgaris) in order to ascertain its level of resistance to windthrow and its suitability as a wind break. The study was undertaken in three states of south-western Nigeria (Osun, Oyo and Ondo states), with the diameter at breast height (DBH) and total height (TH) of the bamboo culms being measured. The volume, basal area and slenderness coefficient were evaluated and the relationship among the parameters and the slenderness coefficient was enumerated through correlation analysis. Regression analysis was undertaken to form models for the prediction of the slenderness coefficient for the study areas. The slenderness coefficients of bamboo culms were negatively correlated with diameter at breast height (DBH), volume and basal area but positively correlated with height for the three states. The graphical results indicated that bamboo has a slenderness coefficient below 70 and may not be at high-risk for windthrow, based on the model developed to predict slenderness coefficient values from (i) DBH and (ii) Height. The DBH function provided the best predictions and a Power model was found to have the best fit for prediction. We conclude that B. vulgaris has a low slenderness coefficient and it can be used as a wind break.

DESCRIPTIVE STUDY OF THE CAPACITY OF SIX HILLSIDE SOIL MANAGEMENT SYSTEMS IN THE CONTROL OF SURFACE RUNOFF

On tropical hillsides, torrential rains cause surface runoff that removes soil particles, nutrients and agro-inputs. This process limits soil fertility, agrosystem productivity and the rural economy. A descriptive study was conducted on a hillside in Los Tuxtlas, Veracruz, Mexico, to study water runoff and its runoff coefficients in four modalities of the “milpa intercropped with fruit trees” (MIAF) system, traditional and zero tillage, under rainfed conditions. The systems were established with a systematic design of treatments, without repetitions, between 2003 and 2011: 1) Milpa intercropped in chicozapote (Manilkara zapota), with sediment filter and minimum tillage (MIAF-CH-CF-LM); 2) Milpa intercropped with Persian lemon (Citrus x latifolia), with sediment filter and minimum tillage (MIAF-L-CF-LM); 3) Milpa intercropped in carambolo (Averrhoa carambola), with sediment filter and minimum tillage (MIAF-C-CF-LM); 4) Milpa intercropped in carambolo, without sediment filter and zero tillage (MIAF-C-SF-L0); 5) Zero tillage with crop residue distribution over the surface (Lo); and 6) Minimum tillage with crop residue burning and tracking (LM-QR). From August 2016 to February 2018, a 50 m2 runoff lot was installed in each system. Surface runoff was measured every 24 h; runoff sheet and runoff coefficient. The MIAF.system reduced surface runoff by 46.13 % with respect to that obtained in LM-QR. The MIAF systems with sediment filter and zero tillage without filter presented similar runoff and runoff coefficient values. The MIAF-CH-CF-LM system recorded the lowest runoff value among systems with tillage and filter. The L0 system showed the lowest volume and runoff coefficient.

(Na, Zr) and (Ca, Zr) Phosphate-Molybdates and Phosphate-Tungstates: I-Synthesis, Sintering and Characterization.

Submicron-grade powders of Na1-xZr2(PO4)3-x(XO4)x compounds (hereafter referred to as NZP) and Ca1-xZr2(PO4)3-x(XO4)x compounds (hereafter, CZP), X = Mo, W (0 ≤ x ≤ 0.5) were obtained by sol-gel synthesis. The compounds obtained were studied by X-ray diffraction phase analysis and electron microscopy. An increase in the W or Mo contents was shown to result in an increase in the unit cell volume of the NZP and CZP crystal lattices and in a decrease in the coherent scattering region sizes. Thermal expansion behavior at high temperatures of synthesized NZP and CZP compounds has been investigated. The dependencies of the parameters a and c on the heating temperature, as well as the temperature dependence of the crystal lattice unit cell volume V in the range from the room temperature up to 800 °C, were obtained. The dependencies of the average thermal expansion coefficient (αav) and of the volume coefficient (β) on the W and Mo contents in the compositions of NZP and CZP compounds were studied. Ceramics Na1-xZr2(PO4)3-x(XO4)x with relatively high density (more than 97.5%) were produced by spark plasma sintering (SPS). The increase in the W or Mo contents in the ceramics leads to an increase in the relative density of NZP and to a decrease of the optimum sintering temperature. The mean grain size in the NZP ceramics decreases with increasing W or Mo contents. The study of strength characteristics has revealed that the hardness of the NZP ceramics is greater than 5 GPa, and that the minimum fracture toughness factor was 1 MPa·m1/2.

Magnetic resonance imaging with perfusion and diffusion in assessment of intra-spinal lesions

BackgroundMRI is the imaging modality of choice in detecting and evaluating spinal lesions. However, advanced techniques as diffusion and perfusion studies can help more in differentiation between neoplastic and non-neoplastic lesions. Our study aimed to detect the role of diffusion and T2* perfusion weighted imaging in characterization of different spinal lesions by measuring the relative cerebral blood volume (rCBV) and apparent diffusion coefficient value (ADC) of all lesions, comparing perfusion of lesion in relation to normal cord and detection of diffusion pattern of each lesion by observing its signal intensity at diffusion images and ADC map.ResultsFifty patients were included in this study. Twenty-five patients were with non-neoplastic lesions and twenty-five patients were with neoplastic lesions. The cutoff value of rCBV was 1.2 in differentiation between neoplastic and non-neoplastic lesions with 92% sensitivity and 100% specificity. The cutoff value of ADC was 1 in differentiation between neoplastic and non-neoplastic lesions with 56% sensitivity and 80% specificity.ConclusionsDiffusion and perfusion weighted images help in differentiation between neoplastic and non-neoplastic spinal lesions.

Кластерні структури як організаційна основа здійснення стратегічної реорганізації підприємств

The article is concerned with studying topical issues of functioning of cluster structures in Ukraine, which are an important instrument for ensuring sustainable economic development of the country. The research is aimed at improving the methodological support of substantiation of the feasibility of forming and evaluating the efficiency of the results of functioning of cluster structures. The necessity of expanding the existing classification of cluster structures is substantiated and it is proposed to supplement the list of types of cluster structures with the following types in accordance with the purpose of functioning: discretionary, sales, service, income, profitable, costs, capital investment, venture, and investment. It is proposed to link individual indicators of efficiency of cluster activity with its type, defined in accordance with the purpose of functioning. For each type of cluster structures, it is advisable to use a separate set of indicators in accordance with their purpose and the developed list of types. For the operation of the discretionary cluster, it is necessary to calculate the coefficients of the level of performance of a certain list of works and compliance with the estimate of operating costs by elements. The basis for evaluating the performance of the «costs» cluster should be based on such indicators as the coefficient of compliance with the estimate of operating costs by elements, the total coefficient of operating costs for production and the cost efficiency ratio. The activities of the «sales» cluster should be assessed by indicators of the individual coefficient of sales volume, the coefficient of compliance with the standard of finished product balances in the warehouse, and the coefficient of transaction costs. For the cluster structures of service, it is necessary to determine the coefficients of compliance with the estimates of operating costs, services provided outside the enterprise, and the quality of service of its structural units. The results of the functioning of the income cluster structures are expressed in the sale of products of the i-th type, sales of products with the help of intermediaries, the coefficient of potential losses. For the profitable cluster structures, it is necessary to use such criteria as product profitability, total profitability of sales, compliance with operating cost estimates, profit growth rate. For the capital investment cluster structures, it is proposed to calculate the following criteria: coefficients of compliance with the estimate of operating costs, profitability of capital investments and their payback period for each investment project. For the venture cluster structures, it is advisable to calculate the level of risk, and for investment ones – indicators of economic efficiency of investment projects. The proposed types of cluster structures and the system of criterial indicators for evaluating their activities allow considering each cluster as an independent business entity that functions independently in accordance with its purpose, according to which individual strategies are developed, ensuring adaptability to changes in the external environment and creating real opportunities for self-development.

Examining the Impact of Distance Between VSL Road Signs on Vehicle Speed Variance

Variable speed limit (VSL) is an intelligent transportation system (ITS) solution for traffic management. The speed limits can be changed dynamically to adapt to traffic conditions such as visibility and traffic volume, curvature, and grip coefficient of the road surface. The VSL traffic sign location problem and attempts to solve it using computer simulation are presented in this paper. Experiments on a selected road segment, carried out using the traffic simulator, have shown that the proposed method allows the driver’s habits to be taken into account so that the location of road signs can be optimized. The observable effect was a reduction in vehicle speeds and speed variance on critical road segments, translating directly into increased safety and harmonized traffic.

Plasma Circulating Cell-free DNA in Advanced Hepatocellular Carcinoma Patients Treated With Radiation Therapy.

Although radiation therapy (RT) is an effective and safe treatment when administered locally for various stages of hepatocellular carcinoma (HCC), adequate biomarkers that are predictive of therapeutic efficacy have not been identified. We evaluated the clinical utility of circulating cell-free DNA (cfDNA) to predict treatment response of patients with HCC treated with RT. We prospectively recruited 37 patients diagnosed with HCC between March 2019 and May 2020. All patients were treated with RT as salvage therapy. Whole peripheral blood was collected twice, one before RT (baseline; V1) and another aliquot one week after the end of RT (V2). We determined whether cfDNA genomic copy number variations (CNVs) could predict treatment outcome. An I-score was calculated from the plasma cfDNA that reflected CNVs of cfDNA, which is evidence of genomic instability. The I-score at V1 exhibited a strong correlation with the planning target volume (PTV) (coefficient=0.65) and was a predictive marker for progression-free survival (PFS). In particular, a mean I-score value at V1 of ≥6.3 had a significant positive correlation with PFS (p=0.017). Compared with patients who had a complete response (CR) following RT, non-CR patients had a higher mean I-score value at V2 ≥6.2 (p=0.034). Furthermore, I-score values at V1 and V2 and the delta I-score ratio were significantly associated with a pre-RT alpha-fetoprotein level ≥200 among non-CR patients. I-score values calculated from plasma cfDNA represent a potential biomarker for predicting treatment outcomes in patients with advanced HCC receiving RT.

Development of retinal structure in perinatally HIV-infected children and adolescents: A longitudinal and cross-sectional assessment.

In perinatally HIV-infected (PHIV) children, cross-sectional studies reported on subtle structural retinal differences and found associations between the retina and structural brain changes. Our objective is to investigate whether neuroretinal development in PHIV children is similar to the development in healthy matched controls and to explore associations with the brain structure. We measured RT using optical coherence tomography (OCT) on two occasions in 21 PHIV children or adolescents and 23 matched controls-all with good visual acuity-with a mean interval of 4.6 years (SD 0.3). We also included 22 participants (11 PHIV children and 11 controls) together with the follow-up group for a cross-sectional assessment using a different OCT device. Magnetic resonance imaging (MRI) was used to assess the white matter microstructure. We used linear (mixed) models to assess changes in RT and its determinants (over time), adjusting for age and sex. The development of the retina was similar between the PHIV adolescents and controls. In our cohort, we found that changes in the peripapillary RNFL was significantly associated with changes in WM microstructural makers: fractional anisotropy (coefficient = 0.030, p = 0.022) and radial diffusivity (coefficient = -0.568, p = 0.025). We found comparable RT between groups. A thinner pRNFL was associated with lower WM volume (coefficient = 0.117, p = 0.030). PHIV children or adolescents appear to have a similar development of the retinal structure. In our cohort, the associations between RT and MRI biomarkers underscore the relation between retina and brain.

Effects of pressure and temperature on topological electronic materials X2Y3 (X = As, Sb, Bi; Y = Se, Te) using first-principles.

We systematically study the thermal and topological properties of X2Y3 (X = As, Sb, Bi; Y = Se, Te) and the effects of pressure and temperature on their electronic properties using first-principles. We find that the external pressure-induced electronic topological transition occurs at about 5 GPa for Bi2Se3, and the type of band gap tends to become indirect with the increase of pressure. We also investigate the lattice expansion with temperature in quasi-harmonic approximation and further explore the effect of temperature on the volume, band gap, and volumetric thermal expansion coefficient of the studied selenides and tellurides. Finally, we calculate the evolution of the Wannier charge center of X2Y3 to determine their topological invariants, and theoretically suggest that Bi2Se3 changes from a topological to an ordinary insulator when the pressure decreases to -8 GPa; As2Se3 is found to be an ordinary insulator, while all other four compounds are always strong topological insulators at any pressure or temperature.

Significantly Affected Lubrication Behavior of Silicone Oil Lubricated Si3N4/Glass Contact after Cleaning with Different Solvents

Conventional methyl silicone oils have poor lubricating properties in boundary lubrication regions, particularly for ceramic/oxide point contact lubrication. In this study, the residues of various organic solvents on the surfaces of Si3N4 spheres/glass disks were used to determine their effect on the lubricating properties of silicone oil 200. The minute ethanol residues significantly enhanced the antifriction and antiwear properties of silicone oil. Compared to the blank sample, the coefficient of friction (COF) and wear volume of silicone oil 200 with the residual ethanol friction pair were reduced by >40% and >98%, respectively. Being immiscible with silicone oil, the minute ethanol residues also removed impurities from the glass surface and maintained a clean interface, thus effectively blocking direct interactions between the friction pair interfaces. In addition, the residual ethanol reduced the atomic force microscope probe-to-glass surface adhesive force in the silicone oil 200 environment, thus allowing it to maintain low COF and wear rates over a broader range of speeds, loads, and times. In contrast to previous work, this study is the first to effectively regulate the lubrication properties of silicone oil using a residual organic solvent. The findings further verified that the adsorption of vapor molecules can significantly alter the surface forces between interfaces. Thus, adjusting the adhesion force through trace amounts of organic solvent residues may provide novel research inputs, thereby guiding the expansion and scope of silicone oil lubrication applications.

Significance of Prolapse Reduction in Measurement of Postvoid Residual Urine Volume in Pelvic Organ Prolapse Patients: A Prospective Study

Background: This study compared postvoid residual (PVR) urine volume by ultrasonography in pelvic organ prolapse (POP) patients before and after prolapse reduction to evaluate the need for prolapse reduction in accurately assessing PVR in women with POP. Methods: This was a prospective study including 128 patients. Both standard methods for measuring PVR urine volume, urethral catheterization, and portable abdominal ultrasound machines were used. An examination was performed by one urogynecologist within five minutes after the patients self-voided. The patients were divided into two groups according to pelvic organ prolapse quantification (POP-Q) stage, early prolapse stage, and advanced prolapse stage, and comparative analysis was performed. Results: Before prolapse reduction, the Pearson correlation coefficient of PVR urine volume measured by ultrasonography and PVR urine volume measured through urethral catheterization was 0.708 in the early prolapse stage and 0.949 in the advanced prolapse stage. After prolapse reduction, the Pearson correlation coefficient of PVR urine volume measured by ultrasonography and PVR urine volume measured through urethral catheterization was 0.895 in the early prolapse stage and 0.982 in the advanced prolapse stage. Conclusions: These study results showed that prolapse reduction when measuring PVR urine volume by ultrasonography in POP patients is acceptable and essential for enhancing accurate patient assessment.

Negative Thermal Expansion of Undulating Coordination Layers through Interlayer Interaction

The negative thermal expansion (NTE) of solid-state materials is of significance in various fields, but a very rare phenomenon. In this study, we carried out a meta-analysis for the anisotropic thermal expansion behavior of fifteen two-dimensional coordination polymers [M(salen)]2[M'(CN)4(solvent)] (M = Mn, Fe; M' = MnN, ReN, Pt, Pt(I2)x; x = 0.18, 0.45, 0.85, 1.0; solvent = H2O, MeOH, MeCN) with a newly synthesized [Fe(salen)]2[MnN(CN)4(MeCN)]. Consequently, we successfully demonstrate the unusual NTE of the undulating coordination layers by an expansion deformation of the layers via strong interlayer interaction within the layer stacking. Notably, the layer volume of [Mn(salen)]2[ReN(CN)4] with its powder form decreases with a large NTE coefficient, αlayer-volume = -27 × 10-6 K-1 (100-500 K). This is a significantly large value despite the increase in layer thickness along the layer contraction based on the anisotropic transformation of undulating layers. Conversely, the analysis demonstrates that the chemical modification of the layers to enhance intralayer interaction rather than interlayer interaction switches a direction of the layer anisotropy, yielding positive thermal expansion materials with the coefficient of the layer volume reaching +92 × 10-6 K-1.

Gas desorption and diffusion characteristics in different rank coals under different pressure-drop conditions

To compare gas desorption and diffusion characteristics under different pressure-drop conditions, different rank coals were collected to conduct desorption and diffusion experiments under the direct pressure-drop condition (DPDC) and the progressive pressure-drop condition (PPDC). Moreover, mercury injection capillary pressure (MICP) analysis was performed to determine pore structure characteristics. When the pressure-drop condition is changed from DPDC to PPDC, the initial desorption rate decreases, while the desorption volume and diffusion coefficient increase, suggesting the damage on desorption capacity and diffusion capacity resulted from DPDC. The maximum changes of these three parameters occur in the medium-volatile bituminous coal, which decrease from 0.255 to 0.063 cm3/(g·min), increase from 2.96 to 18.82 cm3/g and increase from 0.4732 × 10−10 to 3.8239 × 10−10 cm2/s, respectively. Micropores and transition pores predominate in all samples. With increasing coal rank, the pore volume generally shows a decreasing trend, whereas the fractal dimension shows an increasing trend. The difference in diffusion coefficient between DPDC and PPDC of different rank coals is predominated by micropores, which arises from the various diffusion regimes at different pressure ranges in micropores. Specifically, the rapid pressure-drop rate in DPDC causes the atmospheric pressure condition, and Knudsen diffusion and Transitional diffusion play dominant roles in micropores, resulting in the lower diffusion coefficient. The difference in desorption volume between DPDC and PPDC of different rank coals is predominated by transition pores, which results from the water block effect in transition pores. In DPDC, large bubbles easily form in transition pore throats and show large deformation when they pass through transition pore throats, which increases capillary resistance and intensifies the water block effect. However, in PPDC, the size of gas bubbles in the same transition pore throats is smaller than that in DPDC, which weakens the water block effect and enhances desorption capacity. This research can provide strategies for optimizing the pressure-drop rate during CBM production. PPDC is more suitable for CBM exploration. The drainage intensity should be reduced, or secondary reformation measures should be taken to reduce the proportions of micropores and transition pores in DPDC to reduce the damage of desorption capacity and diffusion capacity.

Dry Sliding Wear Features of an Al-20Sn-5Zn Alloy Affected by Microstructural Length Scales

Al-Sn-Zn alloys are attractive options for use as wear-resistant materials. While Sn promotes self-lubricating characteristics, Zn strengthens the Al-rich matrix. Conventionally, the manufacturing of these alloys involves casting. However, there is still a paucity of studies that associate the solidification microstructure with the wear resistance of these alloys. Inspired by such considerations, this work aims at investigating the wear behavior of an Al-20Sn-5Zn [wt.%] alloy produced by a directional solidification technique. A set of samples with different microstructure length scales was subjected to ball cratering tests using a normal contact load of 0.25 N and six test times. The results show that the dependence of the wear behavior on the microstructure length scale becomes more expressive for longer sliding distances. It was found that coarser microstructures provide an improved wear resistance. In view of that, a possible spectrum of specific wear rates was determined as a function of the sliding distance, considering different microstructure length scales. Finally, experimental equations are proposed to represent a possible range of wear volume and wear coefficient according to the dendrite arm spacings.