Research on rheological behavior of fresh concrete single-cylinder pumping based on SPH-DEM.

In contrast to traditional approaches to simulating fresh concrete, the model applied here allows issues such as liquid phase and the motion of sub-scale particles to be considered. The rheological behavior of fresh concrete materials was investigated, and the slump test and pumping process of fresh concrete were simulated by combining the smooth particle hydrodynamics coupled with discrete element method. Based on Bi-viscosity model and Bingham model, linear and nonlinear fitting of rheometer data and the derivation equations were educing. Bi-viscosity model and the Bingham model were compared in slump test. The results show that the Bi-viscosity model is more accurate in simulation, and the error percentage is less than 10%. The Bi-viscosity model was used to simulate and predict the results of slump experiment, and the influence of rheological parameters on the slump velocity and shape was obtained. The simulation analysis model of concrete single-cylinder pumping is established, and the experimental and simulation analysis models are compared. The results show that the SPH-DEM pumping pressure prediction is very close to the experimental results.

Simulation Analysis of Concrete Pumping Based on Smooth Particle Hydrodynamics and Discrete Elements Method Coupling.

With an increase of suction efficiency of fresh concrete pumping in confined spaces, the laminar flow state will be damaged by the return flow caused by distribution value direction changes and concrete gravity. This is a fact, but one which is rarely studied. In this work, the flow state, flow velocity, and suction efficiency of fresh concrete pumping are simulated using the coupled smooth particle hydrodynamics and Discrete Elements Method (SPH-DEM). The rheological parameters and Herschel-Bulkley-Papanastasiou (HBP) rheological model are adopted to simulate fresh concrete in the numerical simulation model. The study reveals that the error between the slump experimental result and that obtained by the HBP model is negligible. A model is therefore established for numerical simulations of the suction efficiency of fresh concrete pumping. An experimental concrete pumping platform is built, and the pressure and efficiency data during pumping are collected. A comparison of the numerical simulation with experimental results shows that the error is less than 10%.

[Effect of dexmedetomidine pretreatment on hypoxia/reoxygenation-induced injury in human umbilical vein endothelial cells and the possible mechanism].

OBJECTIVE: To investigate the effect of dexmedetomidine pretreatment on hypoxia/reoxygenation-induced injury in human umbilical vein endothelial cells and the possible mechanism. METHODS: Cultured human umbilical vein endothelial cell-12 (HUVEC-12) were randomly divided into four groups(n = 24): group control (C), group dexmedetomidine (D), group hypoxia/reoxygenation (H/R), group hypoxia/reoxygenation plus dexmedetomidine (H/R+D). In groups D and H/R+D, Dexmedetomidine 50 µmol/L was added to the culture medium and the cells were incubated for 2 h. Then groups C and D were exposed to regular incubator and incubated for 12 h, groups H/R and H/R+D were incubated in an anaerobic chamber for 6 h and then returned to a regular incubator and incubated for 6 h. Cell growth conditions were observed under inverted microscope, the cell viability and apoptosis were measured by methyl thiazolyl tetrazolium (MTT) assay and flow cytometry respectively. Reverse transcriptase polymerase chain reaction (RT-PCR) was used to detect the expression of CHOP mRNA. Western blotting was used to detect the expression of CHOP and cleaved caspase-3 protein. RESULTS: Compared with group C, the cell survival rate was significantly decreased, the expression of CHOP mRNA and CHOP protein, cleaved caspase-3 protein were up-regulated, the apoptotic rate was significantly increased in group H/R and group H/R+D (P < 0.05),No significant difference was found in group D (P > 0.05);compared with group H/R, the cell survival rate was significantly increased, the expression of CHOP mRNA and CHOP protein, cleaved caspase-3 protein were down-regulated, the apoptotic rate was decreased significantly in the group H/R+D (P < 0.05). CONCLUSIONS: Dexmedetomidine pretreatment can effectively attenuate hypoxia/reoxygenation-induced apoptosis to human umbilical vein endothelial cell-12. The mechanism maybe related with down-regulating the expression of CHOP.

[The analgesic effect of plexus anesthesia with buprenorphine in patients].

OBJECTIVE: To study the anesthetic effect of brachial plexus block by adding buprenorphine in local anesthetics and patients with intramuscular injection, and observe the anesthesia effects, the anesthesia maintenance time, postoperative analgesia effects. METHODS: 60 cases of upper limb to line, hand surgery patients from Sep. 2009 to Dec. 2009 in Tianjin Hospital were randomly divided into 3 groups. A (local anesthetics without buprenorphine, n = 20); B group (plus 2 µg/kg buprenorphine in local anesthetics, n = 20); C group (intramuscular injection 2 µg/kg buprenorphine before anesthesia, n = 20). With B/BRAMN-STIMMPLEX-DIG nerve stimulator guided positioning of brachial plexus block of axillary line. 3 groups of patients recorded (1) the onset time of narcotic; (2) the duration of anesthesia; (3) the surgery time; (4) the pain score of postoperative 4, 8, 12, 24, 36, 48, 72 h; (5) the incidence of nausea and vomiting; (6) observed other side effects. RESULTS: the patients' age, weight, sex, operation time of the 3 groups had no significant difference between the comparison (P > 0.05); anesthesia onset time between the 3 groups showed no significant difference (P > 0.05). Duration of anesthesia: A, C group was significantly shorter than the B group (P < 0.01); pain score at 4 h, A and B, C no significant difference between groups (P > 0.05); 8, 12, 24 h, when group A was significantly higher than the B, C group (P < 0.01), 36, 48, 72 h when the A group and B, C no significant difference between groups (P > 0.05); the incidence of nausea A group 10%, B group 20%, C group 20%. Vomiting, the incidence of A, B group was 0, C group 30%. CONCLUSION: Buprenorphine adding local anesthetics in brachial plexus block or intramuscular injection buprenorphine before a block can be to achieve a satisfactory effect of postoperative analgesia, buprenorphine adding local anesthetics in brachial plexus block Narcotic maintenance of anesthesia time can be extended and have a significant effect and fewer adverse reactions.

[Effects of naloxone on the expression of stem cell factor and C-kit receptor in combined oxygen-glucose deprivation of primary cultured human embryonic neuron in vitro].

OBJECTIVE: To explore the effects of naloxone on the expression of c-kit receptor (c-kit R) and its ligand stem cell factor (SCF) in human embryo neuronal hypoxic injury. METHODS: Serum-free cerebral cortical cultures prepared from embryonic human brains were deprived of both oxygen and glucose which would set up an environment more likely with that of in vivo ischemic injury. Neurons in 24-well culture plates were randomly divided into four groups: control group, hypoxia group, naloxone 0.5 microg/ml group and naloxone 10 microg/ml group. MTT assay and biological analysis were performed to study the cell death and the changes of extracellular concentrations of lactate dehydrogenase (LDH) after combined oxygen-glucose deprivation. Neurons in 25 ml culture flasks were also randomly allocated into four groups as previously described. Intracellular total RNA were extracted at different time points: pre-hypoxia, immediately after hypoxia, and 3, 6, 12, and 24 hours after reoxygenation. The changes of SCF/c-kit R mRNA expression in hypoxic neurons treated with different concentrations of naloxone pre and post oxygen-glucose deprivation were determined with RT-PCR. RESULTS: The cell vitality detected by MTT assay decreased significantly in hypoxia group and naloxone 0.5 microg/ml group when compared with control group (P<0.01), while no significant difference was found between naloxone 0.5 microg/ml group and hypoxia group or between naloxone 10 microg/ml group and control group. Extracellular concentration of LDH significantly increased in hypoxia group (P<0.05), while no difference was found between naloxone 0.5 microg/ml group and control group, between naloxone 0.5 microg/ml and hypoxia group, or between naloxone 10 microg/ml and control group (all P>0.05). Immediately after oxygen-glucose deprivation, the expression of SCF/c-kit R mRNA increased significantly (P<0.01). Among those the expression of SCF presented a distribution of double-peak value within 24 hours. After treated with different concentrations of naloxone, the peak value of each group were delayed to appear and went down with the increasing of naloxone concentration. The peak values in all treated groups were significantly different from that in control group (P<0.01). CONCLUSIONS: The expression of SCF/c-kit R mRNA increases at the early stage after combined oxygen-glucose deprivation. Naloxone 0.5 microg/ml can attenuate cell injuries and regulate the expression of SCF/c-kit R. Naloxone may protect neurons by modulating the expressions of some cytokines.