Simulation of the Traweling Wave Burning Regime on Epithermal Neutrons

New results of two computer experiments on modeling of superthermal neutron-nuclear combustion of natural uranium for two different flux densities of external neutron source and duration of half a year each are presented. The simulation results demonstrate the dependence of the autowave combustion modes on the parameters of the external source.

Computational Fluid Dynamics Approach for Predicting Pipeline Response to Various Blast Scenarios: A Numerical Modeling Study

Recent industrial explosions globally have intensified the focus in mechanical engineering on designing infras-tructure systems and networks capable of withstanding blast loading.Initially centered on high-profile facilities such as embassies and petrochemical plants,this concern now extends to a wider array of infrastructures and facilities.Engineers and scholars increasingly prioritize structural safety against explosions,particularly to prevent disproportionate collapse and damage to nearby structures.Urbanization has further amplified the reliance on oil and gas pipelines,making them vital for urban life and prime targets for terrorist activities.Consequently,there is a growing imperative for computational engineering solutions to tackle blast loading on pipelines and mitigate associated risks to avert disasters.In this study,an empty pipe model was successfully validated under contact blast conditions using Abaqus software,a powerful tool in mechanical engineering for simulating blast effects on buried pipelines.Employing a Eulerian-Lagrangian computational fluid dynamics approach,the investigation extended to above-surface and below-surface blasts at standoff distances of 25 and 50 mm.Material descriptions in the numerical model relied on Abaqus’default mechanical models.Comparative analysis revealed varying pipe performance,with deformation decreasing as explosion-to-pipe distance increased.The explosion’s location relative to the pipe surface notably influenced deformation levels,a key finding highlighted in the study.Moreover,quantitative findings indicated varying ratios of plastic dissipation energy(PDE)for different blast scenarios compared to the contact blast(P0).Specifically,P1(25 mm subsurface blast)and P2(50 mm subsurface blast)showed approximately 24.07%and 14.77%of P0’s PDE,respectively,while P3(25 mm above-surface blast)and P4(50 mm above-surface blast)exhibited lower PDE values,accounting for about 18.08%and 9.67%of P0’s PDE,respectively.Utilising energy-absorbing materials such as thin coatings of ultra-high-strength concrete,metallic foams,carbon fiber-reinforced polymer wraps,and others on the pipeline to effectively mitigate blast damage is recommended.This research contributes to the advancement of mechanical engineering by providing insights and solutions crucial for enhancing the resilience and safety of underground pipelines in the face of blast events.

An estimate of the conversion rates of SO_2 to SO_4^(2-)- and NO_2 to HNO_(3+) NO_3^- for the evaluation air pollution in Beijing

The conversion rates of SO2 to SO42- and NO2 to HNO3+NO3- are estimated from the field-data obtained in Beijing in summer, 1988. The results show that the conversion rate of NO2 is about four times as much as that of SO2; The conversion rates have a diurnal variation in a day. On the average, the rate of SO2 is estimated to be 4.7% h-1 during the daytime and 3.4% h-1 during the nighttime. Similarly, the rate of NO2 is estimated to be 17.2% h-1 and 12% h-1 respectively.

Stochastic Simulation and Analysis of Geological Corrosion Defects in Dam Foundation

Uncertainty in geological structural modeling, especially geological corrosion(a kind of karst cave), is a bottleneck that restricts the development and application of geological computer modeling and effect estimation. To solve this issue, a stochastic modeling method based on the random field theory is proposed in comparison with the deterministic geometric modeling method. Then the constraint random field modeling method and the random field modeling method without constrained parameters are compared and analyzed. A case study shows that the novel stochastic simulation method is an effective tool to describe the distribution characteristics of corrosion parameters and reflect the updated geological prospecting information. The influence of geological corrosion on the dam behavior can also be better analyzed by using the stochastic simulation method. At the same time, the unconfined random field ignores the sample location information and may lead to higher variability. Therefore, the constraint random field modeling method can provide a useful reference for the numerical analysis under complex geological conditions.

A virtual model of the retina based on histological data as a tool for evaluation of the visual fields

Background:To settle the fundamentals of a numerical procedure that relates retinal ganglion-cell density and threshold sensitivity in the visual field.The sensitivity of a generated retina and visual pathways to virtual stimuli are simulated,and the conditions required to reproduce glaucoma-type defects both in the optic-nerve head(ONH)and visual fields are explored.Methods:A definition of selected structural elements of the optic pathways is a requisite to a translation of clinical knowledge to computer programs for visual field exploration.The program is able to generate a database of normalized visual fields.The relationship between the number of extant receptive fields and threshold sensitivity is plotted for background sensitivity and corresponding automated perimetry.A solution in two planes to the 3D distribution of axons in the ONH is proposed.Visual fields with induced damage in the optic disc are comparable in pattern and quantity to glaucomatous records.Results:The two-level simulation of the ONH facilitates the analysis of optic-cup/retinal defects.We can generate the virtual optic pathways tailored to the age and morphology of the patient’s eye,and it is possible to reproduce glaucomatous damage by“reverse engineering”engineering.The virtual cortical model renders a quantitative relationship between visual defect and neural damage.Conclusions:A two-level computing of the retina/optic nerve facilitates the analysis of neuroretinal defects and can be incorporated to automatic perimeters to facilitate visual field analysis.

Optimum Kinetic Parameters of Mefenamic Acid Crystallization by PBM

Mefenamic acid (MA) is a high-dose, anti-inflammatory, analgesic agent that is widely prescribed for pain related to menstrual disorders. It has some negative properties, such as a high hydrophobicity with a propensity to stick to surfaces, and possess great problems during granulation and tableting. Crystallization kinetics was investigated for mefenamic acid. Availability of data on the kinetics of crystal growth is very important for the development and operation of industrial crystallisation processes. The experiments for the measurement of crystal growth kinetics were carried out using the desupersaturation curve technique based on the measurement of the solution concentration versus time in a seeded isothermal batch experiment. To predict the optimum parameters (b, kb, g, kg) for the nucleation and growth kinetics from the desupersaturation curve obtained, the Population Balance Modelling was used and solved by the method of moments. The initial values for the optimisation problem were estimated by using the approach developed by Garside et al. (1982) [1].

Valence electron structure and hydrogen storage property of LaNi_-4Co

In the present study, two models of atom occupation in LaNi4Co were put forward and corresponding valence electron structures （VESs） of these two models were investigated according to empirical electron theory （EET） of solids and molecules. Results demonstrate that the VES-concerned hardness factor （FH） of LaNi4Co is lower than that of LaNi5, so LaNi4Co has lower hardness, higher plasticity and improved anti-pulverization ability. In the mean time, the difference of the equilibrium hydrogen pressure between LaNiaCo and LaNi5 was analyzed in the electronic level. The analysis shows that the strength of the weakest bond net in octahedron lattice interstices of LaNi4Co is much lower than that in LaNis; consequently, LaNi4Co＇s bond net easily deforms to accommodate hydrogen so that LaNi4Co has lower equilibrium hydrogen pressure in comparison with LaNis. The results can provide some theory guide on the design of hydrogen storage alloys.

Multicompartment Micelles From π-Shaped ABC Block Copolymers

Dissipative particle dynamics simulations were performed on the morphology and structure of multicompartmerit micelles formed from n-shaped ABC block copolymers in water. The influences of chain architectures were studied in a systematic way, and a rich variety of morphologies were observed, such as spherical, wormlike, X-shaped, Y-shaped, ribbon-like, layered rod-like, layered disk-like, as well as network morphologies. The simulations show that the distance between the two grafts plays an important role in control of the morphology. Since n-shaped ABC block copolymers can be reduced to linear ABC and star ABC block copolymers, they are good model copolymers for studying the self-assembly of complex block copolymers into micelles. The knowledge obtained in this work as well as the new morphologies identified provide useful information for future rational design and synthesis of novel multicompartment micelles.