Analysis of densification mechanisms of dry granulated materials

International audienceDry granulation by roll compaction is a continuum manufacturing process to produce granules with improved flowability which can further be easily used in tableting process. However, the granules are non-homogeneous in density and have non-spherical shapes which impact their densification behaviour during die-compaction. The aim of this study was to investigate both the densification mechanism and the failure strength of granules of microcrystalline cellulose (MCC) and mannitol using Cooper-Eaton and Adams models. For both materials, the Cooper-Eaton approach led to the quantification of fractional volume compaction by particle rearrangement and by plastic deformation respectively to explain the difference in densification behaviour of raw material and granules. Moreover, the model showed its ability to capture the effect of granule density and granule sizes and to differentiate the densification mechanisms of MCC as a plastic material and mannitol as a brittle material. The Adams model was used to compute the failure strength of single granule from in-die compression data. The obtained results of the granules were in the range [0.6–1.43  MPa]. However, regarding the effect of granule density, the model showed mixed results indicating that the model is not representative of the studied granules which are not spherical and have a relatively wide range of sizes, nevertheless, the model was derived for near spherical particles with a narrow size distribution

Spectral gaps in a double-periodic perforated Neumann waveguide

We examine the band-gap structure of the spectrum of the Neumann problem for the Laplace operator in a strip with periodic dense transversal perforation by identical holes of a small diameter ε>0. The periodicity cell itself contains a string of holes at a distance O(ε) between them. Under assumptions on the symmetry of the holes, we derive and justify asymptotic formulas for the endpoints of the spectral bands in the low-frequency range of the spectrum as ε→0. We demonstrate that, for ε small enough, some spectral gaps are open. The position and size of the opened gaps depend on the strip width, the perforation period, and certain integral characteristics of the holes. The asymptotic behavior of the dispersion curves near the band edges is described by means of a 'fast Floquet variable' and involves boundary layers in the vicinity of the perforation string of holes. The dependence on the Floquet parameter of the model problem in the periodicity cell requires a serious modification of the standard justification scheme in homogenization of spectral problems. Some open questions and possible generalizations are listed.The work has been partially supported by MICINN through PGC2018-098178-B-I00, PID2020-114703GB-I00 and Severo Ochoa Programme for Centres of Excellence in R&D (CEX2019-000904-S)

On correctors for spectral problems in the homogenization of Robin boundary conditions with very large parameters

We obtain estimates for convergence rates of the eigenelements (λ", u") for the Laplace operator in a domain ⊂ R3 periodically perforated along a plane γ = ∩ {x1 = 0}. The boundary conditions are of the Dirichlet type on ∂ and of the Robin type, involving a large parameter O(ε− ), on the boundary of the cavities. The small parameter ε denotes the period while the size of each cavity is O(ε ). Here we consider the most significant case where α = κ = 2

Performance and carcass characteristics of steers fed with two levels of metabolizable energy intake during summer and winter season

Climate change is producing an increase on extreme weather events around the world such as flooding, drought and extreme ambient temperatures impacting animal production and animal welfare. At present, there is a lack of studies addressing the effects of climatic conditions associated with energy intake in finishing cattle in South American feed yards. Therefore, two experiments were conducted to assess the effects of environmental variables and level of metabolizable energy intake above maintenance requirements (MEI) on performance and carcass quality of steers. In each experiment (winter and summer), steers were fed with 1.85 or 2.72 times of their requirements of metabolizable energy of maintenance. A total of 24 crossbred steers per experiment were used and located in four pens (26.25 m2/head) equipped with a Calan Broadbent Feeding System. Animals were fed with the same diet within each season, varying the amount offered to adjust the MEI treatments. Mud depth, mud scores, tympanic temperature (TT), environmental variables, average daily gain, respiration rates and carcass characteristics plus three thermal comfort indices were collected. Data analysis considered a factorial arrangement (Season and MEI). In addition, a repeated measures analysis was performed for TT and respiration rate. Mean values of ambient temperature, solar radiation and comfort thermal indices were greater in the summer experiment as expected (P\u3c 0.005). The mean values of TT were higher in steers fed with higher MEI and also in the summer season. The average daily gain was greater during summer v. winter (1.10 ± 0.11 v. 0.36 ± 0.06) kg/day, also when steers were fed 2.72 v. 1.85 MEI level (0.89 ± 0.12 v. 0.57 ± 0.10) kg/day. In summer, respiration rate increased in 41.2% in the afternoon. In winter, muddy conditions increased with time of feeding, whereas wind speed and rainfall had significant effects on TT and average daily gain. We conclude that MEI and environmental variables have direct effects on the physiology and performance of steers, including TT and average daily gain, particularly during the winter. In addition, carcass characteristics were affected by season but not by the level of MEI. Finally, due to the high variability of data as well as the small number of animals assessed in these experiments, more studies on carcass characteristics under similar conditions are required

Application of crop-based irrigation operations to Chasma Right Bank Canal

Crop-based irrigation / Irrigation operation / Irrigation programs / Irrigation canals / Distributary canals / Water requirements / Drainage / Water allocation / Water delivery / Irrigation scheduling / Pakistan / Chasma Right Bank Canal

Relación de los niveles de testosterona sérica y el tamaño testicular en alpacas según grupo etario y mes del año en Tacna, Perú

El objetivo del presente estudio fue evaluar la relación del tamaño testicular con los niveles de testosterona sérica en alpacas según la edad y mes del año. Se trabajó con ocho machos (4 jóvenes y 4 adultos). Las mediciones del tamaño testicular se realizaron con una regla Vernier y la determinación de los niveles de testosterona en suero se realizó mediante una prueba de quimioluminiscencia. Los adultos presentaron mayor tamaño testicular en los meses de abril, octubre, noviembre y en jóvenes en abril y noviembre. Así mismo, se encontró una diferencia significativa (t=3.17; p=0.009) entre adultos (8.41 cm2) y jóvenes (6.57 cm2). Con relación al nivel de testosterona, tanto en adultos y jóvenes, los niveles más altos fueron en el mes de abril. La comparación entre jóvenes y adultos no presentó diferencias significativas (t=0.23; p=0.81).  Además, la concentración de testosterona no presentó una relación significativa con el largo (r = 0.41), ancho (r = 0.21) y área testicular (r = 0.32)