Earticle

In the present study, the unsteady Hartmann flow with heat transfer of a viscous incompressible electrically conducting fluid under the influence of an exponentially decreasing pressure gradient is studied. The parallel plates are assumed to be porous and subjected to a uniform suction from above and injection from below while the fluid is acted upon by an external uniform magnetic field applied perpendicular to the plates. The equations of motion are solved analytically to yield the velocity distributions for both the fluid and dust particles. The energy equations for both the fluid and dust particles including the viscous and Joule dissipation terms, are solved numerically using finite differences to get the temperature distributions.

The unsteady Hartmann flow of an electrically conducting, viscous, incompressible fluid bounded by two parallel non-conducting porous plates is studied with heat transfer taking the Hall effect into consideration. An external uniform magnetic field and a uniform suction and injection are applied perpendicular to the plates while the fluid motion is subjected to an exponential decaying pressure gradient. The two plates are kept at different but constant temperatures while the Joule and viscous dissipations are included in the energy equation. The effect of the ion slip and the uniform suction and injection on both the velocity and temperature distributions is examined.

The unsteady Couette flow of an electrically conducting, V1SCOUS, incompressible fluid bounded by two parallel non-conducting porous plates is studied with heat transfer taking the Hall effect into consideration. An external uniform magnetic field and a uniform suction and injection are applied perpendicular to the plates while the fluid motion is subjected to an exponential decaying pressure gradient. The two plates are kept at different but constant temperatures while the Joule and viscous dissipations are included in the energy equation. The effect of the ion slip and the uniform suction and injection on both the velocity and temperature distributions is examined.

In the present study, the unsteady Couette flow with heat transfer of a dusty viscous incompressible electrically conducting fluid under the influence of an exponential decaying pressure gradient is studied without neglecting the Hall effect. The parallel plates are assumed to be porous and subjected to a uniform suction from above and injection from below while the fluid is acted upon by an external uniform magnetic field is applied perpendicular to the plates. The governing equations are solved numerically using finite differences to yield the velocity and temperature distributions for both the fluid and dust particles.

Aiming at the problem of the large error between the pressure gradient of multiphase flow predicted by the model presented in literature [12] (denoted by Liao model) and the experimental pressure gradient, this paper firstly compares the error between the Liao model and the experimental data, and builds a correlation model (denoted by CM model) between error of the Liao model and gas liquid ratio according to the close relations between the two. And then combining the CM model and the Liao model, a new predicting method of pressure gradient which is denoted by LCM model is built, and the algorithm is given. Finally, this paper gives the numerical experiment results for ninety groups of experimental data. The numerical results show that the average relative error of LCM model is about 3.3% and the one of Liao model is about 38%. Based on the known data with 30% water content and with 90% water content, this paper uses LCM model to calculate the pressure gradient under the case of 60% water content and compares the LCM gradient with the experimental pressure gradient under the same condition. The average relative error of LCM model is 10.44%, but the one of Liao model is 41.54%. The results shows that the LCM model proposed in this paper improves the predicting precision of pressure gradient for multiphase flowing in a certain range.

한외여과공정에서 압력구배를 주기적으로 변화시켜 막 표면의 용질층을 불안정화시켜 여과 flux의 총괄적 향상을 유도한 실험을 수행하였다. 일정압력에서의 여과 flux 감소현상을 Hernia 식을 사용하여 모사하였고, 또한 압력구배의 주기적 변화를 Fourer series로 표현하여 압력구배의 변화에 따른 flux 변화를 수학적으로 모사하였고 이 결과를 실제의 실험결과와 비교하여 보았다. 수학적 모사결과 압력변화의 형태, 진폭, 주기 등의 변화에 따른 평균 flux의 변화는 미미하였다. 하지만 실제실험결과 주기적으로 압력구배를 변화시킨 경우 약 11%의 향상을 관찰할 수 있었다. 이는 압력구배가 주기적으로 변하는 과정에서의 응질층의 압축이완속도가 다른 것에 기인하는 것으로 유추된다. 주기적 압력구배변화외에 feed pump interruption을 이용하여 평균총괄 flux를 약 32%까지 향상 시켰다. 역확산에 의한 용질층의 이완에는 일정한 시간이 필요함을 찾아내었고 interruption은 용질층이 형성되기 전부터 시작하는 것이 유리하다고 판단되었다. 본 실험을 위하여 한외여과의 자동제어 시스템을 설계제작하여 다양한 압력함수를 이용할 수 있었고, 공정운영 중 압력구매와 여과 flux를 실시간 모니터링 및 제어할 수 있었다. 자동제어 시스템을 통해 압력구매를 주기적으로 변화시켜 총괄 flux의 극대화를 도모하는 기법은 기존장치를 최소로 변경시키면서 한외여과성능을 극대화시킬 수 있는 방법으로 기대된다.

To improve the crossflow untrafiltration flux, we applied periodic oscillations in transmembrane pressure gradient in order to promote fluid turbulence by inducing repeated compression and relaxation of the cake/gel layer. The oscillatory forms used were square-, sine-, triangle-wave, and pumping interruption. The permeate flux profiles were mathematically simulated and compared with the experimental data. The result showed the periodic pumping interruption most effectively improved the overall flux by up to about 32%. Enough pumping off-time, at least on the order of tens of seconds, was needed to allow the solutes in the layer to diffuse back to the bulk phase. It was better to start the oscillations earlier before the layer was fully established. The square-wave oscillation yielded about 11% increase, which was particularly pronounced in the later part of the filtration. Either the amplitude or the period of the oscillations resulted little influence on flux.actate ester, and lactate ester produced in esterification reaction was distilled simultaneously with hydrolysis reaction into lactic acid. When the yields of lactic acid recovered by batch reactive distillations with various alcohols were compared, the yield of lactic acid was increased as the volatility of lactate ester was increased. In this batch reactive distillation, because the mixtures condensed in partial condensor were flown to reboiler through distillation column, the recovery yield of lactic acid was affected by operation temperature of partial condensor. Hydrolysis reaction into lactic acid in distillation column rarelyoccurred because of short retention time of lactate ester and water. Lactate ester was reacted into lactic acid in reboiler.

Background/Aims: In recent years, greater assessment accuracy after transjugular intrahepatic portosystemic shunt (TIPS) to ascertain prognosis has become important in decompensated cirrhosis due to portal hypertension. The aim of this study was to assess the ratio of the portal pressure gradient (PPG) pre-TIPS (pre-PPG) to albumin (PPA), which influence ascites formation in cirrhotic patients in the 6-months after TIPS placement, and is a metric introduced in our study. Methods: This was a retrospective cohort study of 58 patients with decompensated cirrhosis admitted to an academic hospital for the purpose of TIPS placement. We collected the following data: demographics, laboratory measures, and PPG during the TIPS procedure. Then we analyzed the association between the above data and ascites formation post- TIPS in cirrhosis patients. Results: Twenty-two patients with ascites and 28 without ascites were evaluated. Univariate and binary logistic regression analysis were adjusted for the following variables: to determine prognosis; Child-Pugh scores, lymphocyte count, platelet count, hemoglobin level, albumin level and pre-PPG or PPA. The outcome showed that PPA was better than pre-PPG and albumin for predicting ascites according to area under receiver operating characteristic curves and a statistical model that also showed PPA’s influence 6-months post-TIPS. Conclusions: The combined measurement of pre-PPG and albumin, defined as PPA, may provide a better way to predict post-TIPS ascites in decompensated cirrhosis, which underlines the need for a large clinical trial in the future.

Purpose: The present study aimed to investigate the role of hepatic venous pressure gradient (HVPG) for prediction of long-term mortality in patients with decompensated cirrhosis. Materials and Methods: Clinical data from 97 non-critically-ill cirrhotic patients with HVPG measurements were retrospectively and consecutively collected between 2009 and 2012. Patients were classified according to clinical stages and presence of ascites. The prognostic accuracy of HVPG for death, survival curves, and hazard ratios were analyzed. Results: During a median follow-up of 24 (interquartile range, 13?36) months, 22 patients (22.7%) died. The area under the receiveroperating characteristics curves of HVPG for predicting 1-year, 2-year, and overall mortality were 0.801, 0.737, and 0.687, respectively (all p<0.01). The best cut-off value of HVPG for predicting long-term overall mortality in all patients was 17 mm Hg. The mortality rates at 1 and 2 years were 8.9% and 19.2%, respectively: 1.9% and 11.9% with HVPG ≤17 mm Hg and 16.2% and 29.4% with HVPG >17 mm Hg, respectively (p=0.015). In the ascites group, the mortality rates at 1 and 2 years were 3.9% and 17.6% with HVPG ≤17 mm Hg and 17.5% and 35.2% with HVPG >17 mm Hg, respectively (p=0.044). Regarding the risk factors for mortality, both HVPG and model for end-stage liver disease were positively related with long-term mortality in all patients. Particularly,for the patients with ascites, both prothrombin time and HVPG were independent risk factors for predicting poor outcomes. Conclusion: HVPG is useful for predicting the long-term mortality in patients with decompensated cirrhosis, especially in the presence of ascites.

Background/Aims: Both hepatic venous pressure gradient (HVPG) and liver stiffness (LS) are useful tools for predicting mortality in patients with cirrhosis. We investigated the combined effect of HVPG and LS on long-term mortality in patients with cirrhosis. Methods: We retrospectively collected data from 103 patients with cirrhosis, whose HVPG and LS were measured between November 2009 and September 2013. The patients were divided into four groups according to the results of the HVPG and LS measurements. Long-term mortality and the risk factors for mortality were analyzed. Results: Of the 103 patients, 35 were in group 1 (low HVPG and low LS), 16 in group 2 (high HVPG and low LS), 24 in group 3 (low HVPG and high LS), and 28 in group 4 (high HVPG and high LS). Over a median follow-up of 47.3 months, 18 patients died. The mortality rate of patients in group 4 was significantly higher than in the other three groups (vs. group 1, p = 0.005; vs. group 2, p = 0.049; vs. group 3, p = 0.004), but there were no significant differences in survival between groups 1, 2, and 3. In multivariable analyses, both HVPG and LS were identified as independent risk factors for mortality (hazard ratio [HR], 1.127, p = 0.018; and HR, 1.062, p = 0.009, respectively). Conclusions: In patients with cirrhosis, those with concurrent elevation of HVPG and LS had the highest long-term mortality rates. However, when either HVPG or LS alone was elevated, mortality did not increase significantly.

Background/Aims: Transient elastography (TE) has been proposed as a promising noninvasive alternative to hepatic venous pressure gradient (HVPG) for detecting portal hypertension (PH). However, previous studies have yielded conflicting results. We gathered evidence from literature on the clinical usefulness of TE versus HVPG for assessing PH. Methods: We conducted a systematic review by searching databases for relevant literature evaluating the clinical usefulness of non-invasive TE for assessing PH in patients with cirrhosis. A literature search in Ovid Medline, EMBASE and the Cochrane Library was performed for all studies published prior to December 30, 2015. Results: Eight studies (1,356 patients) met our inclusion criteria. For the detection of PH (HVPG ≥6 mmHg), the summary sensitivity and specificity were 0.88 (95% confidence interval [CI] 0.86-0.90) and 0.74 (95% CI 0.67-0.81), respectively. Regarding clinically significant PH (HVPG ≥10 mmHg), the summary sensitivity and specificity were 0.85 (95% CI 0.63-0.97) and 0.71 (95% CI 0.50-0.93), respectively. The overall correlation estimate of TE and HVPG was large (0.75, 95% CI: 0.65; 0.82, P<0.0001). Conclusions: TE showed high accuracy and correlation for detecting the severity of PH. Therefore, TE shows promise as a reliable and non-invasive procedure for the evaluation of PH that should be integrated into clinical practice.

Background/Aims: Variceal hemorrhage is one of the major complications of cirrhosis and is associated with significant mortality and morbidity. The development of gastroesophageal varices and variceal hemorrhage is the most direct consequence of portal hypertension. Correlations between the hepatic venous pressure gradient (HVPG) and first variceal hemorrhage were examined. Methods: Patients with cirrhosis who underwent HVPG measurement between July 2009 and September 2010 were enrolled (n=535). All patients underwent esophagogastroduodenoscopy to enable the evaluation of gastroesophageal varices. Results: The HVPG for all patients was 16.46±7.05 mmHg (mean±SD), and was significantly higher among those with first variceal hemorrhage than in those without it. The HVPG was significantly correlated with both Child-Turcotte-Pugh (r=0.488, P<0.001) and Model for End-stage Liver Disease (r=0.478, P<0.001) scores. An HVPG value of 11 mmHg was predictive of first variceal hemorrhage with a sensitivity of 92.4% and a specificity of 27.7%. Conclusions: The HVPG was higher in patients with first variceal hemorrhage than in those without it. (Clin Mol Hepatol 2012;18:391-396)

The carbon brake discs were manufactured by densification the carbon fiber preform using PG-CVI technology with Propene as a carbon precursor gas and Nitrogen as a carrier gas. The densities of carbon brake discs were tested at different densification time. The results indicate that the densification rate is more rapid before 100 hrs than after 200 hrs. The CTscanning image and the SEM technology were used to observe the inner subtle structure. CT-images show the density distribution in the carbon brake disc clearly. The carbon brake disk made by PG-CVI is not very uniform. There is a density gradient in the bulk. The high-density part in the carbon brake is really located in the friction surface, especially in the part of inner circle. This density distribution is most suitable for the stator disc.

The optimization techniques are explored in the direction of arrival (DOA) estimation based on single acoustic pressure gradient vector sensor (APGVS). By analyzing the working principle and measurement errors of the APGVS, acoustic intensity approaches (AI) and the minimum variance distortionless response beamforming approach based on single APGVS (VMVDR) are deduced. The radius to wavelength ratio of the APGVS must be not bigger than 0.1 in the actual application, otherwise its DOA estimation performance will degrade significantly. To improve the robustness and estimation performance of the DOA estimation approaches based on single APGVS, two modified processing approaches based on single APGVS are presented. Simulation and lake trial results indicate that the performance of the modified approaches based on single APGVS are better than AI and VMVDR approaches based on single APGVS when the radius to wavelength ratio is not bigger than 0.1, and the two modified DOA estimation methods have excellent estimation performance when the radius to wavelength ratio is bigger than 0.1.

Background/Aims: The hepatic venous pressure gradient (HVPG) reflects portal hypertension, but its measurement is invasive. Transient elastography (TE) is a noninvasive method for evaluating liver stiffness (LS). We investigated the correlation between the value of LS, LS to platelet ratio (LPR), LS-spleen diameter-to-platelet ratio score (LSPS) and HVPG according to the etiology of cirrhosis, especially focused on alcoholic cirrhosis. Methods: Between January 2008 and March 2017, 556 patients who underwent HVPG and TE were consecutively enrolled. We evaluated LS, LPR, and LSPS according to the etiology of cirrhosis and analyzed their correlations with HVPG. Results: The LS value was higher in patients with alcoholic cirrhosis than viral cirrhosis based on the HVPG (43.5 vs. 32.0 kPa, P<0.001). There were no significant differences in the LPR or LSPS between alcoholic and viral cirrhosis groups, and the areas under the curves for the LPR and LSPS in subgroups according to HVPG levels were not superior to that for LS. In alcoholic cirrhosis, the LS cutoff value for predicting an HVPG ≥10 mmHg was 32.2 kPa with positive predictive value (PPV) of 94.5% and 36.6 kPa for HVPG ≥12 mmHg with PPV of 91.0%. Conclusions: The LS cutoff value should be determined separately for patients with alcoholic and viral cirrhosis. In alcoholic cirrhosis, the LS cutoff values were 32.2 and 36.6 kPa for predicting an HVPG ≥10 and ≥12 mmHg, respectively. However, there were no significant differences in the LPR or LSPS between alcoholic and viral cirrhosis groups.

A mathematical model of the pressure gradient of supercritical CO2 in a vertical tobacco bed was developed in this study. In particular, the compaction of the tobacco as a function of temperature and CO2 flow is included in the model. Downflow of CO2 (low condition is described. At velocities in excess of 0.6 cm/sec at 7$0^{\circ}C$, there is a large increase in pressure gradient for beds deeper than about 0.5 m. The proposed model offers a better understanding of operating the process using supercritical CO2.

background: The prognosis after an aortic valve replacment can be affected significantly by the transprosthetic pressure gradient which is determined mainly by the size of the patients body and the prosthesis used. We analyzed the hemodynamic feature of two relatively new prosthese the ATS and the evensized Medtronic-Hall(M-H) valves by measuring the transprosthetic pressure gradient in the cases where small sizes (23mm or smaller) were used. Material and method: There were 94 patients who received whom aortic valve replacement with prosthesis smaller than 23 mm from October 1994 to June 1998. In these patients the transprosthetic pressure gradient clalculated from the pressure half time during postoperative Dopper echocardiographic examination was compared between the prostheses of different sizes. The body surface area of each patient was also taken into consideration. result: The mean pressure gradient and body surface area in each group were 21.7$\pm$10.2 mmHg and 1.52$\pm$0.14m2 in ATS 19mm 11.4$\pm$6.5 mmHg and 1,57$\pm$0.20m2 in M-H 20mm 15.2$\pm$6.3 mmHg and 1.54$\pm$0.13m2 in ATS 21mm 9.3$\pm$2.5 mmHg and 1.63 $\pm$0.14m2 in M-H 22 mm and 12.9$\pm$5.3 mmHg and 1.69$\pm$0.13m2 in ATS 23mm. Conclusion: The 19mm ATS prosthesis showed significant trasprosthetic pressure gradient which is similar to the values previously reported with other bileaflet prosthesesm Close follow-up was needed in terms of exercise capacity and change in left ventiricular geometry. In patients with small aortic valve annulus the 20mm M-H valve is recomendable as an alternative to 19mm bileaflet valves because it has less pressure gradient with similar outer diameter.