Adsorption mechanism of different coal ranks under variable temperature and pressure conditions

Variable temperature and pressure adsorption tests were conducted on four coal samples with different coal ranks, under simulated temperatures and pressures corresponding to coal reservoirs at different depths. The regularity of the variation in the amounts of adsorption by coals under variable temperature and pressure and 30 ℃ isothermal conditions are compared and the adsorption characteristics of coal under the composite effect of temperature and pressure were obtained. The adsorption test and data processing method of coal under variable temperature and pressure are presented and the effect of the mechanism of temperature and pressure on the adsorption capacity of coal has been studied. The research results are of significant importance in the investigation of coalbed methane storage mechanism and for the prediction of the amounts of coalbed methane at various depths.

The Effect of Variable Blank-Holder Forces on the Formability of Aluminum Alloy Sheets during Sheet Metal Forming

In this paper, the effect of variable Blank-holder forces (VBHF) on the strain path during sheet metal forming has been investigated by numerical simulation and experiments. The formability of select aluminum alloy sheet was evaluated by theory prediction of forming limit curve based on the M-K method. The effect of different VBHF on the formability was presented. In order to verify the predictions of strain path, experiments are being carried out using a recently-built multi-points variable blank-holder forces hydraulic press. The results show that large side BHF with small comer BHF during rectangular box deep drawing can improve the formability of the selected aluminum alloy

Experimental Analysis on the Variable Polarity Plasma Arc Pressure

Arc pressure is one of the key factors for variable polarity plasma arc（VPPA） and welding pool formation. In this paper, VPPA pressure is measured by pressure transducer and U-tube barometer methods, and advantages and disadvantages of the two methods are compared. The effects of welding parameters, including with straight polarity（SP） current, reverse polarity（RP） current, time ratio of SP to RP, plasma gas flow rate, on VPPA pressure are investigated by using an orthogonal design. The experimental results indicate that the influencing degree of the welding parameters are in the order of plasma gas flow rate, SP current, time ratio of SP to RP, RP current. These results are important to researches of VPPA welding process and its mechanism. The physics behavior of VPPA is taken into account when the above influence mechanisms are analyzed. Firstly, according to the mechanism of the cooling compression to the arc, the compression to VPPA is enhanced with the increase of plasma gas flow, so the VPPA pressure would increase obviously. Secondly, although the temperature of VPPA is as a function of the welding current, the radius of VPPA is also enhanced. So the effects of SP current on VPPA pressure are inferior to the effects of plasma gas flow. Thirdly, VPPA pressure increases as a function of time ratio of SP to RP because the frequency of welding current influences the arc pressure to the some degree; Finally, the RP intervals are farther less than the SP intervals, so the influence to the pressure is minimal.

On the Relationship between Climatic Variables and Pressure Systems over Saudi Arabia in the Winter Season

The synoptic circulation over Saudi Arabia is complicated and frequently governed by the effect of large-scale pressure systems. In this work, we used NCEP–NCAR global data to illustrate the relationship between climatic variables and the main pressure systems that affect the weather and climate of Saudi Arabia, and also to investigate the influence of these pressure systems on surface air temperature（SAT） and rainfall over the region in the winter season. It was found that there are two primary patterns of pressure that influence the weather and climate of Saudi Arabia. The first occurs in cases of a strengthening Subtropical High（Sub H）, a weakening Siberian High（Sib H）, a deepening of the Icelandic Low（Ice L）, or a weakening of the Sudanese Low（Sud L）. During this pattern, the Sub H combines with the Sib H and an obvious increase of sea level pressure（SLP） occurs over southern European, the Mediterranean, North Africa, and the Middle East. This belt of high pressure prevents interaction between midlatitude and extratropical systems, which leads to a decrease in the SAT,relative humidity（RH） and rainfall over Saudi Arabia. The second pattern occurs in association with a weakening of the Sub H, a strengthening of the Sib H, a weakening of the Ice L, or a deepening of the Sud L. The pattern arising in this case leads to an interaction between two different air masses： the first（cold moist） air mass is associated with the Mediterranean depression travelling from west to east, while the second（warm moist） air mass is associated with the northward oscillation of the Sud L and its inverted V-shape trough. The interaction between these two air masses increases the SAT, RH and the probability of rainfall over Saudi Arabia, especially over the northwest and northeast regions.

Radial Permeability Measurements for Shale Using Variable Pressure Gradients

Shale gas is becoming an important component of the global energy supply, with permeability a critical controlling factor for long-term gas production. Obvious deviation may exist between helium permeability determined using small pressure gradient(SPG) methods and methane permeability obtained under actual field production with variable pressure gradients(VPG). In order to more accurately evaluate the matrix permeability of shale, a VPG method using real gas(rather than He) is established to render permeability measurements that are more representative of reservoir conditions and hence response. Dynamic methane production experiments were performed to measure permeability using the annular space in the shale cores. For each production stage, boundary pressure is maintained at a constant and the gas production with time is measured on the basis of volume change history in the measuring pump. A mathematical model explicitly accommodating gas desorption uses pseudo-pressure and pseudo-time to accommodate the effects of variations in pressuredependent PVT parameters. Analytical and semi-analytical solutions to the model are obtained and discussed. These provide a convenient approach to estimate radial permeability in the core by nonlinear fitting to match the semi-analytical solution with the recorded gas production data. Results indicate that the radial permeability of the shale determined using methane is in the range of 1×10-6– 1×10-5 mD and decreases with a decrease in average pore pressure. This is contrary to the observed change in permeability estimated using helium. Bedding geometry has a significant influence on shale permeability with permeability in parallel bedding orientation larger than that in perpendicular bedding orientation. The superiority of the VPG method is confirmed by comparing permeability test results obtained from both VPG and SPG methods. Although several assumptions are used, the results obtained from the VPG method with reservoir gas are much closer to reality and may be directly used for actual gas production evaluation and prediction, through accommodating realistic pressure dependent impacts.

Inner and outer pressure forming of nickel based super-alloy thin-walled part with variable diameter sections

A novel forming method of nickel based super-alloy thin-walled part with variable diameter sections was proposed by using inner and outer pressure with the visco-elasto-plastic pressure-carrying medium at room temperature,and the principle of the method was provided.Experiments and FE simulations were carried out to analyze the deformation characteristics for the part with larger variable diameter ratio(35%).The results show that visco-elasto-plastic pressure-carrying medium can meet the requirements of the room-temperature deformation condition for nickel based super-alloy sheet.The inner and outer pressure forming with the visco-elasto-plastic pressure-carrying medium can meet the requirements of dimensional accuracy for the thin-walled part with variable diameter sections.The thinning of wall-thickness is less than 4%.This method provides a new approach for near-net shape forming of nickel based super-alloy thin-walled parts with variable diameter sections.

Relationship between gestational body mass index,blood pressure variability,and postpartum depression in pregnant women with preeclampsia

BACKGROUND Pre-eclampsia has long been proven to be an independent risk factor for postpartum depression(PPD).Excessive increase in body mass index(BMI)during pregnancy is an important factor inducing pre-eclampsia.Increased blood pressure is the main symptom of patients with pre-eclampsia.However,whether there is a correlation between BMI and blood pressure variability during pregnancy and PPD occurrence in pregnant women with pre-eclampsia remains unclear.AIM To investigate the relationship between BMI,blood pressure variability,and PPD in pregnant women with pre-eclampsia.METHODS Using a cross-sectional survey research,201 pregnant women with pre-eclampsia who were treated and delivered in Suzhou Ninth People’s Hospital from May 2016 to June 2024 were selected as this study’s subjects.At 42 days after delivery,the subjects were re-examined in the hospital’s outpatient department.The Edinburgh Postnatal Depression Scale(EPDS)was used to evaluate whether PPD symptoms,divided the subjects into two groups:The PPD and non-PPD groups.We analyzed clinical data,changes in BMI during pregnancy,and blood pressure variability in the two groups.The Pearson method was used to test the correlation between BMI increase,blood pressure variability during pregnancy,and EPDS score in patients with pre-eclampsia.Logistic regression analysis was performed to explore whether increased BMI and blood pressure variability during pregnancy are influencing factors for PPD occurrence in patients with pre-eclampsia.RESULTS Of the 201 pre-eclamptic women who underwent an outpatient review 42 days after delivery,37 had PPD symptoms based on the EPDS scale evaluation,resulting in an incidence rate of 18.41%(37/201).The differences between the PPD and non-PPD groups in terms of age,educational level,place of residence,reproductive history,gestational age,mode of delivery,newborn gender,and newborn birth weight were not statistically significant(P>0.05).The gestational BMI increase,24-hour systolic blood pressure(SBP)variability,and 24-hour diastolic blood pressure(DBP)variability in the PPD group were significantly higher than those in the non-PPD group;the differences were statistically significant(P<0.001).Pearson correlation analysis showed that BMI increase,SBP variability,and DBP variability during pregnancy correlated positively with the EPDS score of pregnant women with pre-eclampsia(r=0.349,0.336,and 0.241;P<0.001).Logistic regression analysis showed that a high increase in BMI during pregnancy[odds ratio(OR)=4.614,95%confidence interval(CI):1.749-12.170,P=0.002],large variability in 24-hour SBP(OR=2.910,95%CI:1.322-6.404,P=0.008),and large variability in 24-hour DBP(OR=2.347,95%CI:1.138-4.831,P=0.021)were factors affecting PPD occurrence in patients with pre-eclampsia.CONCLUSION Increased BMI and blood pressure variability during pregnancy can increase the risk of PPD in patients with preeclampsia.Strengthening pregnancy guidance and controlling fluctuations in BMI and blood pressure variability during pregnancy within a reasonable range can help reduce the risk of PPD in patients with pre-eclampsia.

Modelling and Dynamic Characteristics for a Non-metal Pressurized Reservoir with Variable Volume

With the increasing demand to reduce emissions and save energy,hydraulic reservoirs require new architecture to optimize their weight,space,and volume.Conventional open reservoirs are large,heavy,and easily polluted,and threaten the operation of hydraulic systems.A closed reservoir provides the advantages of small volume and light weight,compared to open reservoirs.In this study,a non-metallic pressure reservoir with variable volume is designed and manufactured for closed-circuit hydraulic systems.The reservoir housing is made of rubber,and the Mooney-Rivlin model is chosen based on the rubber strain properties.The FEA simulation for the reservoir is performed using ANSYS Workbench to obtain the structural stiffness.The major contribution is the establishment of mathematical models for this reservoir,including the volume equation changing with height,flow equation,and force balance equation,to explore the output characteristics of this reservoir.Based on these results,simulation models were built to analyze the output characteristics of the reservoir.Moreover,the test rig of a conventional hydraulic system was transformed into a closed-circuit asymmetric hydraulic system for the reservoir,and preliminary verification experiments were conducted on it.The results demonstrate that the designed reservoir can absorb and discharge oil and supercharge pump inlet to benefit system operation.The changes in the volume and pressure with displacements under different volume ratios and frequencies were obtained,which verified the accuracy of the mathematical models.Owing to its lightweight design and small volume,the reservoir can replace conventional open reservoirs,and this lays a foundation for future theoretical research on this reservoir.

Forced vibration analysis of nano-composite rotating pressurized microbeam reinforced by CNTs based on MCST with temperature-variable material properties

In this study, free and forced vibration analysis of nano-composite rotating pressurized microbeam reinforced by carbon nanotubes （CNTs） under magnetic field based on modify couple stress theory （MCST） with temperature-variable material propertiesis presented. Also, the boundary conditions at two ends of nano-composite rotating pressurized microbeam reinforced by CNTs are considered as simply supported. The governing equations are obtained based on the Hamilton＇s principle and then computed these equations by using Navier＇s solution. The magnetic field is inserted in the thickness direction of the nano-composite microbeam. The effects of various parameters such as angular velocity, temperature changes, and pressure between of the inside and outside, the magnetic field, material length scale parameter, and volume fraction of nanocomposite microbeam on the natural frequency and response systemare studied. The results show that with increasing volume fraction of nano-composite microbeam, thickness, material length scale parameter, and magnetic fields, the natural frequency increases. The results of this research can be used for optimization of micro-structures and manufacturing sensors, displacement fluid, and drug delivery.

Improved finite difference method for pressure distribution of aerostatic bearing

An improved finite difference method （FDM）is described to solve existing problems such as low efficiency and poor convergence performance in the traditional method adopted to derive the pressure distribution of aerostatic bearings. A detailed theoretical analysis of the pressure distribution of the orifice-compensated aerostatic journal bearing is presented. The nonlinear dimensionless Reynolds equation of the aerostatic journal bearing is solved by the finite difference method. Based on the principle of flow equilibrium, a new iterative algorithm named the variable step size successive approximation method is presented to adjust the pressure at the orifice in the iterative process and enhance the efficiency and convergence performance of the algorithm. A general program is developed to analyze the pressure distribution of the aerostatic journal bearing by Matlab tool. The results show that the improved finite difference method is highly effective, reliable, stable, and convergent. Even when very thin gas film thicknesses （less than 2 Win）are considered, the improved calculation method still yields a result and converges fast.

Significance of blood pressure variability in patients with sepsis

BACKGROUND: This study was undertaken to observe the characteristics of blood pressure variability(BPV) and sepsis and to investigate changes in blood pressure and its value on the severity of illness in patients with sepsis.METHODS: Blood parameters, APACHE II score, and 24-hour ambulatory BP were analyzed in 89 patients with sepsis.RESULTS: In patients with APACHE II score>19, the values of systolic blood pressure(SBPV), diasystolic blood pressure(DBPV), non-dipper percentage, cortisol(COR), lactate(LAC), platelet count(PLT) and glucose(GLU) were significantly higher than in those with APACHE II score ≤19(P<0.05), whereas the values of procalcitonin(PCT), white blood cell(WBC), creatinine(Cr), PaO2, C-reactive protein(CRP), adrenocorticotropic hormone(ACTH) and tumor necrosis factor α(TNF-α) were not statistically significant(P>0.05). Correlation analysis showed that APACHE II scores correlated significantly with SBPV and DBPV(P<0.01, r=0.732 and P<0.01, r=0.762). SBPV and DBPV were correlated with COR(P=0.018 and r=0.318; P=0.008 and r=0.353 respectively). However, SBPV and DBPV were not correlated with TNF-α, IL-10, and PCT(P>0.05). Logistic regression analysis of SBPV, DBPV, APACHE II score, and LAC was used to predict prognosis in terms of survival and non-survival rates. Receiver operating characteristics curve(ROC) showed that DBPV was a better predictor of survival rate with an AUC value of 0.890. However, AUC of SBPV, APACHE II score, and LAC was 0.746, 0.831 and 0.915, respectively.CONCLUSIONS: The values of SBPV, DBPV and non-dipper percentage are higher in patients with sepsis. DBPV and SBPV can be used to predict the survival rate of patients with sepsis.

Characteristics of arc in variable polarity plasma arc welding of aluminum alloy

A double invert variable polarity plasma arc （VPPA） power source based on 16-bit MCU applied for aluminum alloys was developed. Mechanics, electrical and the produced heat mechanism of VPPAW arc were tested and analyzed. Results indicate that during the VPPA welding procedure of aluminum alloy, the arc of electrode negative （EN） has more effect on force, whereas the arc of electrode positive （ EP ） has more effect on heat. It should be noted that keeping the balance of the force and heat is the critical element of VPPAW. This power source had been successfully used to weld aluminum alloy with a 15 mm thickness in vertical welding. The conclusions are applicable to the variable polarity plasma arc welding technique used in the aerospace industry.

Visit-to-visit Systolic Blood Pressure Variability and Stroke Risk: A Systematic Review and Meta-analysis

Visit-to-visit variability in systolic blood pressure(SBP)may have an important additional role in increasing the risk of vascular complications,including stroke.We conducted a meta-analysis to assess the relationship between visit-to-visit SBP variability(SBPV)and stroke risk.PubMed,EMBASE,and the Cochrane library databases were searched for cohort studies with data on visit-to-visit SBPV and stroke risk.Studies that reported adjusted relative risks(RRs)with 95%Cis of stroke associated with SBPV were included.Fourteen cohort studies met the inclusion criteria and were included in our meta-analysis.After adjustment for age,sex,and existing vascular risk factors,the analysis showed that the risk of stroke in patients with SBPV was significantly increased compared with patients with a small baseline SBPV[SD(RR=1.20,95%CI=(1.07-1.35),P=0.0005),CV(RR=1.12,95%CI=(1.00-1.26),P=0.008)].In addition,follow-up variations of more than 5 years were associated with a higher risk of stroke than those of less than 5 years[RR=1.08,95%CI=(1.04-1.11)].Visit-to-visit SBPV was associated with an increased risk of stroke,especially in terms of the time of variation.Taken together,SBPV data may be useful as a preventative diagnostic method in the management of stroke.

An efficient algorithm to compute transient pressure responses of slanted wells with arbitrary inclination in reservoirs

Compared with vertical and horizontal wells, the solution and computation of transient pressure responses of slanted wells are more complex. Vertical and horizontal wells are both simplified cases of slanted wells at particular inclination, so the model for slanted wells is more general and more complex than other models for vertical and horizontal wells. Many authors have studied unsteady-state flow of fluids in slanted wells and various solutions have been proposed. However, until now, few of the published results pertain to the computational efficiency. Whether in the time domain or in the Laplace domain, the computation of integration of complex functions is necessary in obtaining pressure responses of slanted wells, while the computation of the integration is complex and time-consuming. To obtain a perfect type curve the computation time is unacceptable even with an aid of high-speed computers. The purpose of this paper is to present an efficient algorithm to compute transient pressure distributions caused by slanted wells in reservoirs. Based on rigorous derivation, the transient pressure solution for slanted wells of any inclination angle is presented. Assuming an infinite-conductivity wellbore, the location of the equivalent-pressure point is determined. More importantly, according to the characteristics of the integrand in a transient pressure solution for slanted wells, the whole integral interval is partitioned into several small integral intervals, and then the method of variable substitution and the variable step-size piecewise numerical integration are employed. The amount of computation is significantly reduced and the computational efficiency is greatly improved. The algorithm proposed in this paper thoroughly solved the difficulty in the efficient and high-speed computation of transient pressure distribution of slanted wells with any inclination angle.

Stress analytical solution for plane problem of a double-layered thick-walled cylinder subjected to a type of non-uniform distributed pressure

The stress state around circular openings,such as boreholes,shafts,and tunnels,is usually needed to be evaluated.Solutions for stresses,strains and ultimate bearing capacities of pressurized hollow cylinder are common cases.Stress analytical method for plane problem of a double-layered thick-walled cylinder subjected to a type of non-uniform pressure on the outer surface and uniform radial pressure on the inner surface is given.The power series method of complex function is used.The stress analytical solution is obtained with the assumption that two layers of a cylinder are fully contacted.The distributions of normal and tangential contact stress along the interface,tangential stress on the inner boundary and stresses in the radial direction at θ=0°,45° and 90°,are obtained.An example indicates that,when the elastic modulus of the inner layer of a double-layered thick-walled cylinder is smaller than that of the outer layer,the tangential stress is smaller than that in the corresponding point for a traditional cylinder composed of homogeneous materials.In that way,stress concentration at the inner surface can be alleviated and the stress distribution is more uniform.This is a capable way to enhance the elastic ultimate bearing capacity of thick-walled cylinder.

An efficient FEM for pressure analysis of oil film in a piston pump

The paper concerns numerical analysis of pressure distribution of an oil film on the valve plate in the variable height gap of an axial piston pump. The analysis employs the finite element method. For determination of oil pressure variations in the gap, the Reynolds equation, commonly applied in the theory of lubrication, is applied. The equation is solved numerically with the use of self-developed program based on the finite element method. In order to obtain high accuracy of the results, an adaptive mesh refinement based on residual estimations of solution errors is applied. The calculation results are represented as dependent on the geometric and working parameters of the pump.

The Effect of Baroreflex Function on Blood Pressure Variability

Objective: The aim of this study was to assess the relationship of blood pressure variability (BPV) and heart rate variability (HRV) to investigate the effect of baroreflex function on blood pressure variability. Methods: This study consisted of 111 subjects, including 32 normotensives and 79 hypertensives. All the subjects were given two concurrent tests: 24-hour Holter ECG and ambulatory blood pressure monitoring. According to standard deviation of normal-to-normal sinus RR intervals (SDNN) derived from the Holter ECG, the hypertensives were divided into two groups: an HRV normal group with SDNN > 100 ms and an HRV abnormal group with

Pressure pulsation in stages of electric submersible pump at shut-off under various speeds

Electric submersible pumps were widely used in agricultural fields,petroleum and various other industries. The pressure pulsation caused fatigue failure due to vibration in electric submersible pump and affects the life and performance of its system. The objective of this study was to experimentally investigate the characteristics of pressure pulsation which were generated at various stages of a multistage electric submersible pump during closed valve operation at different speeds. An electric submersible pump with five stages was selected for conducting experiments. A variable frequency drive( VFD)was used to operate the electric submersible pump at five different speed settings from 40 to 60 Hz. Piezoresistive pressure transducers were mounted at each stage of the electric submersible pump to capture the unsteady pressure signals. At each speed setting,the electric submersible pump was operated at the shut-off condition and the signals of unsteady pressure from all the five stages were captured. A fast fourier transformation( FFT) was carried out on the pressure signals to convert into frequency domain.From the spectra of pressure pulsation signals,the characteristics of pressure pulsation are obtained for each stage and for various speed settings which were then used to understand its variation with speed and stages.

Visit-to-Visit Blood Pressure Variability Are Associated with an Imbalance between Sympathetic and Parasympathetic Tone in Hypertensive Patients

Greater fluctuations in office blood pressure increase the risk of stroke and blood pressure volatility is an important risk factor for cardiovascular events. Effects of sympathetic and parasympathetic nerve on blood pressure regulation are well known, however, those on visit-to visit variation remains unclear. Aim of this study is to clarify the contribution of sympathetic and parasympathetic balance on blood pressure fluctuation. Methods: We enrolled 23 outpatients with essential hypertension. We measured blood pressure, and pulse rate at clinic 14 times in a row and calculated coefficient of variance (CV) as visit-to-visit variability. The velocity of pupil contraction, miosis (VC) and dilation, mydriasis (VD) was determined from pupillary function test. Results: Systolic blood pressure and diastolic blood pressure were not significantly correlated with VC, VD and VD/VC. Heart rate was not correlated with VC and VD, but significantly correlated with VD/VC. CV of systolic blood pressure, diastolic blood pressure and heart rate were not significantly correlated with VC or VD. Ratio of VD to VC significantly negative correlated with CV of blood pressure, diastolic blood pressure, and heart. Value of VD was significantly correlated with value of VC. Conclusion: Visit-to-visit variability of blood pressure and heart rate is not related with sympathetic or parasympathetic tone independently but augmented by the impaired sympathetic and parasympathetic balance.

Correlation of Inferior Vena Cava Respiratory Variability Index with Central Venous Pressure and Hemodynamic Parameters in Ventilated Pigs with Septic Shock

Septic shock is a common critical condition, for which effective early fluid resuscitation is the therapeutic focus. According to the 2008 international guidelines for management of severe sepsis and septic shock, resuscitation should achieve a central venous pressure （CVP） of 8-12 mmHg within the first 6 h. However, it is still uncertain about the sensitivity and specificity of CVP in reflecting the cardiac preload. Ultrasonography is a simple, rapid, non-invasive, and repeatable method for the measurement of sensitivity and specificity of CVP and has thus gradually attracted the increasing attention of physicians. It was reported that ultrasonography can show the inferior vena cava diameter, respiratory variability index, and blood volume in patients with sepsis or heart failure.