Effect of pH and calcium concentration on calcium diffusion in streptococcal model-plaque biofilms

Demineralization during a cariogenic episode is affected by storage and transport in dental plaque of ions released from enamel, and by the effect on both of plaque fluid pH and ion concentrations. To investigate this, 45Ca effusion from a condensed film of streptococci was measured at pH 7, 6 and 5, and 0-20 mmol/l calcium. Cells were loaded into effusion chambers and the appearance of 45Ca and [3H]-inulin in carrier-containing but initially tracer-free buffer was measured. Ratios of 45Ca and [3H]-inulin activity in the initial suspending solution and at equilibrium in the clearance solution, permitted calculation of extracellular volume and bound calcium. The rate of Ca appearance was proportional to the retarded diffusion coefficient (rDe), which was related to the effective diffusion coefficient (De) by: rDe = De/(1 + R) in which R is the ratio of bound to free Ca2+. The rate of Ca2+ effusion increased with calcium concentration, converging on a value of 2.8 x 10(-10) m2/sec. At low pH it reached convergence at a lower [Ca]. This demonstrates that calcium effusion is dependent on binding, so a high proportion of binding sites in plaque will reduce mineral loss in vivo. Loss of binding sites at low pH will increase mineral loss.     

Effect of Zn concentration on diffusion induced grain boundary migration in Cu -Zn system

Cu-Zn alloy system with three different compositions has been chosen to study the time, temperature and composition dependence of the Diffusion Induced Grain boundary Migration (DIGM) in the temperature range of 277–427°C. The grain boundary migration follows parabolic rate law as a function of time. The diffusivity, D_bα, was calculated from concentration-distance profile using growth rate, v. The activation energy for diffusion is found to be 101kJ/mol which is nearly half of the activation energy required for volume diffusion indicating that preferential grain boundary diffusion is more favorable than volume diffusion leading to grain boundary migration in Cu-Zn system.     

Multicomponent diffusion in the lung

Since breathing involves more than two gases, the physics of multicomponent diffusion is relevant to respiratory physiology. Fundamental principles and important studies in this area are reviewed, some pertain to equimolar diffusion, others to nonequimolar diffusion. As the lung is an open-system nonequimolar exchanger, emphasis is placed on the latter. A mathematical model that has been verified by both physical and biological experiments is presented. This model is used to study ternary diffusion in the alveolar spaces and to obtain effective diffusion coefficients. Based on the cumulative studies up to now, it may be concluded that Fick's law still holds when normal air is breathed under normal pressure and when tracer amounts of inert gases are added to normal air. Fick's law no longer holds when helium is used as a carrier gas or when breathing is under extreme hyperbaric conditions.     

Classification of concentration profiles in quaternary diffusion couples

Concentration profiles that can occur in quaternary diffusion couples have been classified into five types according to the number of extrema, the initial concentration differences, and the concentration gradient at the initial interface. The various profiles that are possible have zero, two or four extrema and are illustrated in this work by plotting appropriate error function solutions to the diffusion equation. The conditions under which the different types occur and the transitions between types, are given as well for quaternary systems. The only assumptions made are that the diffusivity is constant in the reaction zone and that the system is single phase.     

The affinity of human serum albumin for [3H]-digitoxin is dependent on albumin concentration

Binding of [3H]-digitoxin to human serum albumin and human serum was investigated in order to characterize the relationship between binding and albumin concentration. Binding was determined by equilibrium dialysis at 37 degrees, 24 hr was required to reach equilibrium. Volume shift and protein dilution were avoided by adding dextran 70 to the buffer compartment. [3H]-Digitoxin binding both to purified albumin and to normal serum was markedly pH-dependent, the bound/unbound ratio being highly significantly (P < 0.001) inversely correlated to pH in the range 6-8.5. When albumin concentration was increased within the physiological range, the ratio bound/unbound [3H]-digitoxin increased much less than expected from predictions using the law of mass action. Binding saturation experiments revealed that the equilibrium dissociation constant for [3H]-digitoxin was increased at higher albumin concentrations without any decrease in the number of binding sites per albumin molecule. In conclusion, the results strongly indicate that binding estimates in therapeutic monitoring of digitoxin in patients with elevated or reduced albumin concentration should not be based on the law of mass action but on empiric relationships between albumin concentration and binding.     

Homogenization of random concentration profiles by diffusion

A statistical analysis of the homogenization problem is given. The initial concentration profile is defined as a random function, nonperiodically oscillating around a constant value. The time evolution of the autocorrelation function that characterizes the concentration profile is investigated. Homogenization is shown to proceed less rapidly than for a sinusoidal concentration profile.     

Effect of hematocrit and albumin concentration on hepatic clearance of tacrolimus (FK506) during rabbit liver perfusion

Tacrolimus is an immunosuppressive agent used for organ transplantation. Studies were performed to examine the influence of different perfusate hematocrits and albumin concentrations on hepatic extraction of tacrolimus. In vitro binding, efflux and influx between red blood cells (RBCs) and buffer or plasma, and rabbit liver perfusion with use of human erythrocytes were studied. In the range of hematocrits from 0.05 to 0.4, plasma concentrations of tacrolimus were not affected by increased albumin content. Increased hematocrit caused decreases in whole blood:plasma (buffer) concentration ratios. The binding capacity of drug with RBCs was independent of hematocrit, with a value of 440 ng/ml of RBCs; the binding affinity was 0.876 ng/ml using plasma or buffer. Diffusion of tacrolimus from RBCs to buffer was rapid with a clearance of 0.940 ml/min, and equilibration was achieved within 2 min. Diffusion in the opposite direction (buffer-RBCs) was slower with a clearance of 0.576 ml/min. In such diffusion studies, plasma produced a greater difference between efflux (1.70 ml/min) and influx (0.276 ml/min) clearances. During liver perfusion, the major factor regulating elimination of tacrolimus was hematocrit. Both well-stirred and parallel-tube models reflected a low extraction ratio drug with values of 0.15 and 0.17 for the 0.05 and 0.2 hematocrits. Intrinsic clearances were 8.43 and 17.44 ml/min for the well-stirred and parallel-tube models. Albumin had a negligible influence on liver extraction of drug. A model-building process of characterizing nonlinear RBC binding, RBC diffusion rates, and liver perfusion parameters allows the complexities of tacrolimus hepatic clearance to be dissected and shows that strong RBC binding can be artificially perceived as causing a high clearance of the drug.     

碳化对混凝土中氯离子扩散的影响

混凝土与静浆快速碳化0,14,28d后浸泡到3.5%NaCl溶液中650d,测试了混凝土不同深度的自由氯离子、总氯离子含量,计算出混凝土的表观氯离子扩散系数和氯离子结合能力;采用压汞法测试了不同腐蚀制度下静浆表层的孔结构,利用DSC分析了静浆的腐蚀产物.结果表明:混凝土碳化后浸泡到腐蚀溶液中,增加了混凝土中的氯离子含量,提高了混凝土表观氯离子扩散系数,降低了混凝土对氯离子的结合能力;且随碳化时间的增加,变化幅度变大.快速碳化粗化了混凝土的孔结构,其大于30nm的毛细孔数量增加了11%,最可几孔径增加了17nm;降低了混凝土中Friedel'S生成量,以及混凝土对氯离子的化学结合能力.     

Effect of surface diffusion on creep fracture

The effect of surface diffusion on the growth of intergranular cavities under creep conditions is investigated considering its influence on the shape of the cavities. First, general equations relating the rate of cavity growth and the applied stress are given for the case of isolated cavities and an array of interacting cavities. The conditions for cavities to grow in an equilibrium and crack-like forms, respectively, are established. The transition from equilibrium to crack-like forms is discussed and an estimate for the lower and upper limit of the rate of cavity growth during this transition suggested. Expressions for the growth rates of crack-like cavities which grow independently of each other as well as those in an array of interacting cavities are then derived. Several different regimes in which stress dependence of the rate of cavity growth vary are found. Conditions under which these regimes can occur are discussed. A comparison of the theory with several recent experimental studies is made and an excellent agreement between the theory and experiment is obtained assuming that different regimes of cavitation occur in different materials and at different stress levels in the same material. T. Takasugi is on leave from The Institute for Iron Steel and Other Metals, Tohoku University, Sendai, Japan.     

The concentration dependence of the hemoglobin mutual diffusion coefficient

1. The mechanism of potassium transport across human distal colon was investigated in twenty-two individuals without evidence of bowel disease, by using a dialysis method in conjunction with measurements of the transepithelial potential difference (p.d.). 2. Whether potassium was absorbed or secreted depended on its initial concentration in the lumen. The potassium net flux was approximately zero when the luminal potassium concentration was between 30 and 50 mmol/l. 3. Potassium secretion rate was little affected by sodium absorption rate, or by the luminal sodium concentration or by the osmolality of the luminal solution. 4. Potassium secretion rate was increased by partial substitution of other cations for sodium, in the descending order Li greater than NH4 greater than Rb greater than Na. Potassium concentration increased on average to over 80 mmol/l when lithium was in the lumen. 5. The observed transepithelial p.d. was inadequate to account for the intraluminal potassium concentrations attained, the discrepancy being most marked when ammonium or lithium was in the lumen. It is suggested that some potassium is secreted by the epithelial cells and this component of the total potassium flux into the lumen is increased when rubidium, ammonium or lithium is substituted for sodium.     

MnS夹杂对钢中氢扩散行为的影响

通过实验和有限元计算研究了MnS夹杂对钢中氢扩散行为的影响.结果表明:当MnS夹杂长度取向与氢渗透方向平行时,氢在钢中的表观扩散系数随MnS含量的增加而增加;当MnS夹杂长度取向与氢渗透方向垂直时,氢在钢中的表观扩散系数随MnS含量的增加而降低.对于具有扩散通道效应和陷阱效应的第二相,它对氢扩散的影响取决于扩散通道效应和陷阱效应的强弱以及第二相的形状、数量和取向.     

An analysis of concentration profiles for fluxes,diffusion depths,and zero-flux planes in multicomponent diffusion

Concentration profiles developed during isothermal, multicomponent diffusion for a single-phase, solid-solid diffusion couple are expressed on the basis of a relative concentration variable for each component and analyzed for the determination of interdiffusion fluxes. The individual concentration profiles intersect at a common cross-over composition where the relative concentrations of all components are identical. New relations are developed for describing internal consistency among the concentration profiles of the various components. A link is made between the cross-over composition and the depths of the diffusion zone on either side of the Matano plane for a diffusion couple. The cross-over composition is interpreted as the average relative concentration of each component over the diffusion zone. The identification of a zero-flux plane from concentration profiles is also described. The analysis offers several advantages in presenting as well as checking the self-consistency of results as illustrated with a single phase Cu-Ni-Zn diffusion couple annealed at 775 °C.     

Effect of parenteral and enteral nutrition on hepatic albumin synthesis in rats

It is well known that surgery significantly decreases immune responses. Laparoscopic cholecystectomy (LC) is a "miniinvasive" surgical procedure; and on the basis of this consideration we have investigated if and how the immune response is modified in patients after laparoscopic cholecystectomy compared to patients who underwent open cholecystectomy. Immune activity [neutrophils, total lymphocytes count, lymphocytes subpopulations, human leukocyte antigen-DR (HLA-DR)] was evaluated in 53 patients 1 day before surgery and respectively, 1, 3, and 6 days after surgery; 26 patients underwent "open" cholecystectomy and 27 LC. A day after surgery, patients with open cholecystectomy showed a significant increase (p < 0.05) in plasma neutrophils, while they were almost unchanged in LC patients. Monocyte antigen HLA-DR was reduced in patients with "open" cholecystectomy. We recorded two cases (7.6%) of respiratory tract infection in the "open" group. In conclusion, LC strongly reduces postoperative (p.o.) pain and hospitalization, and it promotes earlier recovery and return to normal activity, avoiding p.o. immunosuppression, mostly due to conservation of HLA-DR activity, with less p.o. morbidity compared to that seen with open surgery.     

Correlation between serum-ascites albumin concentration gradient and endoscopic parameters of portal hypertension

OBJECTIVE: We sought to determine the correlation between the level of serum-ascites albumin concentration gradient (SAAG) and the complications of portal hypertension (PHTN), manifested by the presence and grade of esophageal varices (EV). METHODS: Our study included 31 patients with ascites, demonstrated by ultrasonography, who had measurement of the SAAG. All had upper gastrointestinal endoscopy with assessment of the presence and size of EV. High SAAG was considered to be present when the SAAG was > or = 1.1 g/dl and Low SAAG when it measured < 1.1 g/dl. RESULTS: We found that 25 of 31 (80.6%) patients had High SAAG and six of 31 (19.4%) had Low SAAG. Esophageal varices were present in 17 of 25 (68%) patients with High SAAG and in none of six (0%) patients with Low SAAG (p = 0.028). In patients with alcoholic liver disease (ALD), 14 of 14 (100%) had EV. Otherwise, in patients with nonALD, only three of 11 (27.3%) had EV (p < 0.05). The presence of EV was associated with the Child-Pugh Score (p = 0.039). Among patients with High SAAG, EV were present in four of 10 (40%) with SAAG values of 1.10-1.49 g/dl; in four of 6 (66.7%) with SAAG values of 1.50-1.99 g/dl; and in nine of nine (100%) with SAAG values of > or =2.0 g/dl (p = 0.049). The size of the EV had no association with the level of SAAG in patients with High SAAG (p = 0.788), with a Pearson correlation coefficient of R = 0.54 (p = 0.005). Using the Receiver-Operating-Characteristic Curve a SAAG value of > or =1.435 +/- 0.015 g/dl was an accurate indicator of the presence of EV (cutoff point for the higher predictive value: positive = 87.5% and negative = 66.7%). CONCLUSIONS: In patients with ascites the presence of EV is associated only with patients with High SAAG. The presence of EV in patients with ascites and High SAAG is directly related to the degree of SAAG. The size of the EV in patients with ascites and High SAAG is not associated with the degree of SAAG. A SAAG value of > or =1.435 +/- 0.015 g/dl is a useful means to predict the presence of EV in patients with ascites. Finally, in patients with ascites, EV were more prevalent in those with ALD.