Mathematical model for nitrogen control in oxygen steelmaking

A mathematical model was developed to quantify the effects of different operational parameters on the nitrogen content of steel produced during oxygen steelmaking. The model predicts nitrogen removal by the CO produced during decarburization and how the final nitrogen content is affected by different process variables. These variables include the type of coolants used (scrap, direct reduced iron (DRI), etc.), the sulfur content of the metal, combined gas blowing practices, and the nitrogen content in the hot metal, scrap and oxygen blown. The model is a mixed control model that incorporates mass transfer and chemical kinetics. It requires a single parameter that reflects the surface area and mass-transfer coefficient that is determined from the rate of decarburization. The model also computes the rate of decarburization and the change in surface active elements, such as sulfur and oxygen, that affect the rate of the nitrogen reaction. Nitrogenization of steel in the converter is also predicted with the model. The computed results are in good agreement with plant data and observations.     

Mathematical model for post combustion in smelting reduction

Post combustion in the top space of iron bath smelting reduction furnaces is analysed with three-dimensional mathematical modelling. Momentum transport and continuity equations in combination with a k-? model of turbulence are numerically solved for the gas flow field. Combustion reactions are modelled by a set of transport equations based on the SCRS combustion model and its extension to the k-?-g model. A two-stage combustion scheme is formulated to include carbon transfer and combustion. Heat transfer to bath and droplets is approximated including radiation. Computation results for rectangular reactors are presented with velocity patterns and combustion fields. The complex shapes of post combustion flames are demonstrated. Process parameters are varied to study their influence on combustion and heat transfer to the bath. Effects of the injection geometry are illustrated.     

Mathematical model for burden distribution in blast furnace

Burden distribution in a blast furnace is vital to its smooth running. However, it is difficult to directly measure the burden distribution for an operating blast furnace. Therefore, mathematical models have been applied to guide the charging process to achieve the desired burden distribution. The accuracies of such models depend on the prediction of falling curve, stockline profile formation, and burden descent mode. In this study, a new stockline profile formation model is proposed in which new equations have been developed for the inner and outer repose angle by considering the influence of the burden flow's vertical and horizontal velocity at the apex of the stockline profile. Validation of this new stockline profile formation model is provided through comparison between calculated results and experimental data for stockline profile. A stepped burden descending strategy, in which the burden would descend through a specified distance after each ring charging process, is proposed corresponding to the successive charging process. The influence of the burden descending strategy on the falling point, the final burden profile and radial depth ratio of ore to coke is also analysed. The result shows that the burden descending strategy greatly affects the final burden distribution, especially in the peripheral region.     

Gene therapy for infectious diseases: the AIDS model

Genetic manipulation of somatic cells may be of therapeutic value in a variety of infectious diseases, particularly in human immunodeficiency virus (HIV) infection. Stable insertion of custom-designed 'resistance genes' into cells susceptible to HIV could reduce the viral burden in infected individuals and potentially retard the characteristic progressive immune dysfunction. Alternatively, ectopic expression of genes that encode viral antigens might induce potent antiviral immune responses and form the basis for novel prophylactic and therapeutic vaccines. While laboratory studies have proved that the approach works in principle, preclinical and clinical studies will be necessary to evaluate the therapeutic benefit of such gene-based therapies.     

The parameters of the immune function in the evolution of HIV-1 infection in institutionalized children in Romania

OBJECTIVE: To describe the evolution of HIV-1 + horizontal infected children nursed in closed community. METHOD: The biological status of 26 HIV-1 + children nursed in Ia?i Orphanage was assessed in dynamic during April. 1993-Feb. 1994. The income age ranged among 1 month-3 years. RESULTS: The following progressive stages could be drawn accordingly to the biological status parameters dynamic: stage 1 ("oligosymptomatic"), stage 2 ("multiform, medium or severe symptomatology"), and stage 3 ("severe immunodepression, with predominant infectious symptomatology, waves evolution"). These stages could not be assimilated to the currently CDC or WHO classifications. The following thresholds of the immunologically parameters separate the stages 1 and 2, and respective stages 2 and 3: CD4% lymphocytes (27% respective 20%); absolute CD4+ lymphocytes (1150/microliter respective 700 + 750/microliter), CD4/CD8 ratio (0.75 respective 0.45), beta 2-microglobulin (1.5 mg/1000 respective 2.5 mg/ 1000). Lymphocytes lacking the markers CD4, CD8, CD19, CD3, ranging between 15 + 20% were also detected by flow-cytometry; these cells could be attributed to the immature subpopulations (typically for dystrophy) or to down-regulation of membrane expression of some markers. Also, a dichotomy in the distribution of the CD2/CD3 surface markers was recorded in the case of lymphocytes. CONCLUSIONS: Immunological features demarcate this epidemiological group versus the current described models for the HIV-1 + child.     

A model for evolution and extinction

We present a model for evolution and extinction in large ecosystems. The model incorporates the effects of interactions between species and the influences of abiotic environmental factors. We study the properties of the model by approximate analytic solution and also by numerical simulation, and use it to make predictions about the distribution of extinctions and species lifetimes that we would expect to see in real ecosystems. It should be possible to test these predictions against the fossil record. The model indicates that a possible mechanism for mass extinction is the coincidence of a large coevolutionary avalanche in the ecosystem with a severe environmental disturbance.     

转炉冶炼脱磷过程数学模型

在对复吹转炉脱磷过程的机理分析的基础上,应用冶金热力学、动力学、传输原理和反应工程学理论,建立了转炉冶炼脱磷过程数学模型,确定了模型的有关参数.模型的     

汽车钢淬透性数学模型建立

在测定 2 0CrMnTi、4 0MnBH、2 0MnVBH钢淬透性及试样的化学成分基础之上 ,利用计算机采用逐步回归分析方法进行了回归运算 ,得到淬透性与化学成分的关系———回归方程 ,根据回归方程求出了不同窄淬透带规格所对应控制的化学成分范围     

The evolution of adjustment issues in HIV/AIDS

The issues of emotional adjustment to AIDS have been inextricably linked to medical advances in fundamental knowledge about the human immunodeficiency virus and its potential therapies. In 1987 patients were struggling with the advantages and disadvantages "to do or not to do AZT (zidovudine)," whereas the choices imposed by combination therapies and the protease inhibitors in 1997 are fundamentally different and are occurring in an evolving context created by a number of striking medical advances, expanding populations, the availability of environmental support, and changing public sentiments. As the psychiatric treatment of HIV-positive individuals shifts increasingly from "AIDS specialists" to the wider therapeutic community, it is important that the therapist who has had relatively little experience with this population not assume that contemporary issues and concerns of the seropositive patient, or the patient with AIDS, are essentially those discussed widely in the earlier years of the epidemic. Patients living with this virus for a number of years have traveled a long and arduous journey and will experience more empathy from a therapist who has some knowledge of that path. Awareness of the evolution of emotional adjustment, counseling, and ethical issues of AIDS should amplify the general fund of knowledge required for good clinical management of the person living with AIDS.     

Mathematical model of oxygen transport in the cerebral cortex

To estimate the magnitude of hyperemia necessary to support oxidative metabolism in the cerebral cortex during functional activation, a mathematical model of O2 transport from capillary to tissue was developed. Radial and axial gradients of O2 pressure in tissue surrounding a single capillary were calculated at normal and increased cerebral metabolic rates for O2. Cone-shaped tissue geometry and nonlinear oxyhemoglobin dissociation were assumed. Local O2 consumption was assumed to be supported with local tissue pO2 greater than 1 mmHg. The distribution of tissue pO2 was also calculated during moderate hypoxemia (paO2=42 mmHg), using experimental values of red blood cell velocity measured in individual capillaries of the rat cerebral cortex using intravital video-microscopy. The model predicted that moderate increases (相似文献   

A developmental model for risk avoidance in adolescents confronting AIDS

Epidemiologic studies indicate that HIV infection is on the rise within the adolescent population. Much of this increase has been attributed to the teenager's developmental proclivity for risk-taking behavior. Intervention programs designed to curtail high-risk behaviour among adolescents have focused primarily on educational methods alerting teenagers to modes of disease transmission. Among these programs, demonstration and role-playing techniques have shown promise, but have not significantly modified behavior patterns. In contrast, a new developmental technique known as previewing advocates the use of representation and enactment to promote risk deterrence. Previewing may serve as a productive alternative to traditional interventions, since it directly addresses the adolescent's cognitive limitations with regard to the prediction of behavioral outcomes. This paper recommends a prevention model using previewing that is designed to lower the incidence of AIDS transmission among adolescents.     

Mathematical model for on-line heat treatment of steel bars

A mathematical model to predict steel bar thermal behaviour during continuous quenching after the finishing mill has been developed. The model includes process variables, such as finishing rolling speed, finishing temperature, rod size and chemical composition, water flowrate and mechanical design of the cooling device. It was found that empirical correlations for the heat-transfer coefficient belonging to water spray systems are suitable to simulate fast cooling employing submerged water-cooling tubes. Martensite depth is strongly influenced by the bar diameter and water velocity inside the submerged tube. Mist spray systems are not as effective as submerged tubes for cooling steel bars, although, the initial cooling rates are higher. The % volume of martensite is a direct function of the self-tempering temperature, and independent of the fast cooling device.     

A model for microstructure evolution in adiabatic shear bands

A mechanical subgrain rotation model is proposed to account for the recrystallized grains which have been observed to form in adiabatic shear bands in a number of materials. The model is based on a “bicrystal” approach using crystal plasticity theory to predict the evolution of subgrain misorientations. These mechanically induced rotations are shown to occur at the high strain rate associated with adiabatic shear band formation. Recrystallized grain formation is proposed to occur by the formation and mechanical rotation of subgrains during deformation, coupled with boundary refinement via diffusion during shear band cooling. This model is referred to as progressive subgrain misorientation recrystallization and appears to account for shear band microstructures in a variety of metals.     

Mathematical model of bilirubin transport

The mathematical model of the bilirubin transport through liver is suggested. The model is sufficiently reflects the peculiarities of the bilirubin behavior under the different physiological conditions. The model is described by the system of difference-differential equations. The coefficients of the intensity of bilirubin transfer in normal liver are calculated.     

Mathematical model for computer simulation and control of steelmaking

A dynamic model for computer simulation and control of steelmaking has been developed. It is essentially based on multicomponent mixed transport control theory with the incorporation of energy balance calculations. The model is applicable to both steelmaking in electric furnaces as well as in oxygen steelmaking converters. The adjustable parameters of the model for simulation of oxygen steelmaking are gas evolution rate (G_co). oxygen flux factor (F_o) and emulsification factor (EM). These simulation parameters, when combined with on-line measurement of off-gas composition and temperature, enable complete dynamic control of the process. The model developed is applied, as an example, to an industrially produced heat in a top blown oxygen steelmaking converter and the results of simulation are discussed.     

板坯结晶器水模型内气泡运动行为的数学模拟

建立了吹氩板坯结晶器水模型内气泡运动行为的数学模型.以水模型实验获得的整个结晶器内各气泡尺寸和数量浓度为气泡的初始条件,对不同尺寸气泡的运动行为进行数值模拟.结果表明:当水流量为2.54 m3/h,气流量为0.037m3/h,水口浸入深度为78 mm时,气泡都分布在上回流区,没有卷入下回流区.较大的气泡在水口附近上浮,较小的气泡在距离水口较远的区域上浮.这和实验结果相吻合.