Attenuation model of tunnel blast vibration velocity based on the influence of free surface

In tunnel blasting excavation, it is important to clarify the attenuation law of blast wave propagation and predict the blast vibration velocity effectively to ensure safe tunnel construction and protection design. The effects of the free surface area its quantity on the blast vibration velocity are considered, and free surface parameters are introduced to improve the existing blast vibration velocity prediction formula. Based on the Tianhuan railway Daqianshiling tunnel project, field blast vibration monitoring tests are performed to determine changes in the peak blasting vibration velocity based on the blast distance and free surface area. LS-DYNA is used to establish tunnel blasting excavation models under three operating conditions; subsequently, the attenuation law of blast vibration velocity and changes in the vibration response spectrum are analysed. Results show that the free surface area and number of free surfaces enable the blast vibration velocity to be predicted under various operating conditions: a smaller free surface area results in a narrower frequency band range, whereas more free surfaces result in a narrower frequency band range. The improved blast vibration velocity prediction formula is validated using field and numerical test data. It is indicated that the improved formula is applicable to various tunnelling conditions.

SIZING AND EXPERIMENTAL STUDY OF A SOLAR STILL FOR THE PRODUCTIVITY OF WATER DESALINATION IN SOUTH-WEST OF ALGERIA – BECHAR: التصميم والدراسة التجريبية لجهاز التقطير الشمسي لإنتاجية تحلية المياه في جنوب غرب الجزائر – بشار

Algeria, like many countries belonging mostly to the Third World, has considerable water resources saline (salt content ranging between 1500 and 2000 ppm, exceeding the required standards for drinking water and therefore unfit for consumption). We must therefore think of making use these huge reserves interested in desalination techniques. The stain majored is therefore to achieve a distiller solar plan which meets these needs in drinking water. The absorber surface of the modified solar still is coated with black enamel paint and covered with copper chips. The evaporation rate of the water in the solar still is directly proportional to the exposure area of the water. Thus the productivity of the solar still increases with the free surface area of the water in the basin. The distillate yield was found to have improved considerably, especially when the water depth was high. The study also indicated some design features that would further enhance the improvement in output due to the modification made, the evaporation rate is proportional to the temperature of the free surface area of the water only. A general model based on heat transfer balances in each component of the system was developed to predict the mass of freshwater. The efficiency of this still was about 65% and can produce about 5.13 l/m2 per day, experimental studies and the outcomes are discussed in the article. We propose a new design of the cascading solar desalination still with obstacles and preheating of inlet water.

Study of the geometric and mechanical features of nanoparticles of various nature by atomic force microscopy in PeakForce QNM mode

Objective: to identify the difference of the numerical values of parameters characterizing the geometric and mechanical (adhesive) properties of inorganic nanosized particles and nanosized particles of biological origin by atomic force microscopy using the mode of the mapping of surface features at nanosized resolution.Material and methods. Exosomes isolated from the blood of Af mice by the method of sequential ultracentrifugation were used as bionanoparticles. Silver nanoparticles were used as inorganic nanoparticles. The nanoparticles were scanned in air with the help of the BioScope Resolve (Bruker) atomic force microscope in the PeakForce QNM in Air mode with the recording of the maps of adhesion forces and imaging of the topography of the studied surfaces.Results. The silver nanoparticles and exosomes had similar but statistically different diameters (45.59 ± 1.04 nm and 41.25 ± 0.91 nm, р < 0.001 t-test). Nevertheless, the silver nanoparticles were characterized by higher values of both height and free surface area in comparison with the corresponding values of the exosome parameters. This leads to a higher value of the spreading ration for exosomes (the average ratio of diameter to height (d/h) was 11.78 for exosomes and 6.67 for nanoparticles (p < 0.001, Mann-Whitney U test) due to greater adhesion properties of the exosome membranes compared to the silver nanoparticles and a lower value of the ratio of the particle volume to its surface area. Averaged over the nanoscale areas of the nanoparticle surface, the adhesion forces of exosomes were higher (3.2 ± 0.57 nN) compared to those of silver nanoparticles (2.2 ± 0.03 nN, p < 0.05, Mann-Whitney U test).Conclusion. The differences in the parameters of the geometric (diameter, height, free surface area) and mechanical properties (adhesion forces) of the silver nanoparticles and exosomes have been revealed, which allows identifying and differentiating of these nanoparticles by the methods of atomic force microscopy during the study of complex biological fluids with possible content of both the types of nanoparticles.

Enzyme activities of rumen particles and feed samples incubatedin situwith differing types of cloth

Three ruminally cannulated non-lactating dairy cows were used to investigate the effects of six different bag cloth types with pore size (μm): free surface area (%) ratios of 200: 45, 41: 33, 16: 5, 10: 2, 6: 5 and 1: 2 respectively on the disappearance of grass silage DM and neutral-detergent fibre (NDF), and on particle-associated carboxymethylcellulase (EC3.2.1.4; CMCase) and xylanase (EC3.2.1.8) activties extracted from feed residues. Another objective was to compare microbial activity inside the bags and in rumen ingesta. Rumen incubation periods were 3, 6, 12, 24, 48 and 96 h. DM and NDF disappearance and particle-associated enzyme activities were greatly reduced with the smaller pore size and/or open surface area. Re-analysing some of the data as a 2 x 2 factorial (pore size x free surface area) indicated that, generally, free surface area rather than pore size affected the disappearance of feed components and particle-associated enzyme activities. Enzyme activities were highly correlated with NDF disappearance at 6–48 h of incubation. Cumulative area under CMCase and xylanase activity curves explained 0·79 and 0·88 of the variation in NDF disappearance when different cloth type and 6–48 h incubation data were combined. Weighted mean enzyme activities inside the bags were less than 0·35 those in rumen ingesta. The highest activity values inside the bags (24 or 48 h) were less than 0·50 those found in rumen ingesta. The lower microbial activity inside the bags explains the slower rates of NDF digestion reported within situtechniques than with rumen evacuation techniques. The general assumption of similar microbial activity inside the bags and in rumen ingesta is not justified by the present results, and caution must be taken in interpretingin situresults quantitatively for feed evaluation systems.

Changes in microstructure of snow under large deformations

A set of microstructural variables is selected to characterize the behavior of snow. Corresponding mathematical relations from quantitative stereology theory are presented along with relations and techniques required for numerical evaluation. An experimental investigation is carried out to determine changes in these variables for snow subjected to large compressive deformations. The micro-structural variables studied included coordination number, grain-size, bond radius, neck length, pore-size, free surface area and grains/unit volume. Measurements at several stages of deformation are used to evaluate the changes in the microstructure as functions of deformation. Microstructure measurements of six snow samples subjected to confined compression tests are presented for pre-compressed and compressed states, corresponding to final stresses of 0.387, 0.77 and 1.55 MPa. Grain-size and bond radius were found to go through finite changes during compression, although the variation of bond radius was more complicated in nature. The coordination number and number of bonds/unit volume were found to go through large changes during compression, while specific free surface area was found to increase by 100% due to grain- and bond-fracture processes. No discernible patterns of change in neck length could be found in the experiments. A close relationship between some of the microstructural variables and the stress response of the material was observed. These results serve to contribute to the presently available data and understanding of the microstructural behavior of snow.

Changes in microstructure of snow under large deformations

A set of microstructural variables is selected to characterize the behavior of snow. Corresponding mathematical relations from quantitative stereology theory are presented along with relations and techniques required for numerical evaluation. An experimental investigation is carried out to determine changes in these variables for snow subjected to large compressive deformations. The micro-structural variables studied included coordination number, grain-size, bond radius, neck length, pore-size, free surface area and grains/unit volume. Measurements at several stages of deformation are used to evaluate the changes in the microstructure as functions of deformation. Microstructure measurements of six snow samples subjected to confined compression tests are presented for pre-compressed and compressed states, corresponding to final stresses of 0.387, 0.77 and 1.55 MPa. Grain-size and bond radius were found to go through finite changes during compression, although the variation of bond radius was more complicated in nature. The coordination number and number of bonds/unit volume were found to go through large changes during compression, while specific free surface area was found to increase by 100% due to grain- and bond-fracture processes. No discernible patterns of change in neck length could be found in the experiments. A close relationship between some of the microstructural variables and the stress response of the material was observed. These results serve to contribute to the presently available data and understanding of the microstructural behavior of snow.