Biomechanics of Speed Skating
Christopher L. Vaughan in Biomechanics of Sport, 2020
It is a well-known fact that optimal performances (personal, national, or world records) are often established during weather conditions which are not regarded as “optimal”. Even during unstable weather, many good performances are sometimes possible. The opposite is also true. At seemingly optimal conditions (sun, temperature around or just below zero, low humidity, no wind) everyone expects records during national or international competitions, but the times can often be disappointing. Although in particular, the reporters and also the coaches are apt to doubt the expertise of the local ice maker, it is likely that one of the most important factors is often overlooked; the pressure of the air. As shown in Equation 18, the power losses to air friction are dependent on the density of the air. This density is not only dependent on altitude, but also on local air pressure. Since pressure variations between 980 and 1040 millibars at sea level are normal in many countries, these variations can explain the differences in the times. If all other factors remain constant, the model predictions that skaters can skate almost 1 sec per lap faster at 980 millibars than at 1040 millibars,60 are correct. This is of course a large difference, which explains why an area with very high pressure and beautiful weather is not optimal with respect to personal times in speed skating. Good times may be expected in indoor 400 m rinks with miserable weather conditions outside.
Solid State Testing of Inhaled Formulations
Anthony J. Hickey, Sandro R.P. da Rocha in Pharmaceutical Inhalation Aerosol Technology, 2019
Density equals mass divided by volume. However, there are several types of densities with regards to solids, depending on what volume is included in the measurement. True density of a compound is the mass divided by the volume of the atomic or molecular unit cell in a crystal, without voids. It can be derived from X-ray diffraction data on the composition and volume of a unit cell (British Pharmacopoeia 2017, European Pharmacopoeia 2017). Pycnometric density is obtained by measuring the volume occupied by a powder in a gas displacement pycnometer (British Pharmacopoeia 2017, European Pharmacopoeia 2017, United States Pharmacopeia 40-National Formulary 35 2017). There are two chambers in the gas pycnometer, namely, a calibrated test chamber with volume Vc and an expansion chamber with volume Vr. They are connected by a valve in between. A known mass of powder is first put into the test chamber. After closing the pycnometer and with the valve open between the two chambers, the reference pressure (Pr) is recorded. That valve is then closed and the test chamber is filled with a gas to an initial pressure Pi. Helium is usually used because it can fill small pores due to its high diffusivity. Then the valve between the two chambers is opened and the final pressure within the two connected chambers becomes Pf. The volume occupied by the sample (Vsample) can be calculated as below (British Pharmacopoeia 2017, European Pharmacopoeia 2017, United States Pharmacopeia 40-National Formulary 35 2017):
Physics
Peter R Hoskins, Kevin Martin, Abigail Thrush in Diagnostic Ultrasound, 2019
The material properties which determine the speed of sound are density and stiffness. Density is a measure of the weight of a standard volume of material. For example, bone has a higher density than water; a 1 cm cube of bone weighs almost twice as much as a 1 cm cube of water. Density is normally given the symbol ρ (rho) and is measured in units of kilograms per cubic metre (kg m−3). Bone has a density of 1850 kg m−3; water has a density of 1000 kg m−3, which is the same as 1 gram per cubic centimetre.
Spray freeze-drying for inhalation application: process and formulation variables
Published in Pharmaceutical Development and Technology, 2022
Mostafa Rostamnezhad, Hossein Jafari, Farzad Moradikhah, Sara Bahrainian, Homa Faghihi, Reza Khalvati, Reza Bafkary, Alireza Vatanara
Basically, the drying gas is only an inert heat transfer media in this method and has no role in mass transfer. It can be proven that the mass of required gas for the process is reduced by the same ratio as the system pressure (when pressure is reduced by 10 times). A decrease in pressure causes a lower density of the gas. Therefore, the reduction in the inertial tensile forces on the particles would be caused by the lower density at the more downward pressure. The low pressure is advantageous due to the two following items: reducing the required gas mass and preventing particle agglomeration (Anandharamakrishnan et al. 2010). It must be noted that elutriation is a major problem because viscous forces do not reduce until very low pressures are obtained. The SFD in a fluidized bed at usual and low pressure was compared by Leuenberger et al. (2006). They chose three pressure values: 150, 300, and 1000 mbar. Operating at pressures lower than atmospheric pressure achieved a threefold reduction in drying time. The capacity of air to uptake water negatively correlated with the water capacity at the atmospheric pressure since the total pressure is much more than the partial pressure of water in the ice phase even at the decreased pressures. The density of the air and the total pressure are two corresponding values, and consequently, the drying air velocity could not drop off. Hence, at the lower pressures, the fluidization air velocity could be set at 1.5–2 times higher, and a drying time shorter than about 200 min can be achieved. A schematic of the sub-atmospheric fluidized bed FD is shown in Figure 9.
Assessment of the effect of polymers combination and effervescent component on the drug release of swellable gastro-floating tablet formulation through compartmental modeling-based approach
Published in Drug Development and Industrial Pharmacy, 2020
Syaiful Choiri, T. N. Saifullah Sulaiman, Abdul Rohman
According to the linear mixture model, HPMC (coefficient of regression (CR) in logarithmic transformation of +2.88) had greater contribution on increasing the FLT than IPC (CR of +2.29). The effervescent components (CR of +1.84) had the lowest contribution on FLT. The significant interaction was observed between polymers and effervescent components, namely HPMC-effervescent components (CR of −4.25) and IPC-effervescent components (CR −3.60) (p < 0.05). Although, interaction of both polymers did not significantly influence FLT (p > 0.05). IPC had better effect on floating behavior than HPMC due to native density of polymer. Not only the density, but also the gas formed by effervescent reaction when introduced into medium contributed to the floating behavior [36]. The density profile of swellable gastro-floating tablet is presented in Figure S1 (Supplementary Material). It proved that the FLT was strongly affected by formation of effervescent gas. The density of all tablets below the threshold (dashed red-line, 1.027 g/mL) promoted that the tablet was naturally buoyant. The density of tablets was reduced exponentially with time. In addition, it maintained the tablet floating on the surface of medium.
Application of scCO2 technology for preparing CoQ10 solid dispersion and SFC-MS/MS for analyzing in vivo bioavailability
Published in Drug Development and Industrial Pharmacy, 2018
Rujie Yang, Yingchao Li, Jing Li, Cuiru Liu, Ping Du, Tianhong Zhang
The 90 min dissolution results of CoQ10-SD under various reaction pressure, temperature, and reaction time are displayed in Figure 2(b–d). The results indicated that the dissolution rate was enhanced as the increasing of pressure and temperature. For the reaction time, the drug dissolution of 1 h was higher than that of 0.5 h, and was close to that of 2 h. However, the dissolution of 25 MPa was similar to 20 MPa and the temperature of 45 °C was higher than 35 and 40 °C. The pressure and temperature can affect the diffusivity and viscosity of supercritical carbon dioxide. The supercritical temperature of carbon dioxide is 304 K, and the supercritical pressure is 7.4 MPa. When the pressure and temperature reach up to the critical points, the scCO2 has density similar to a liquid, allowing the molecules to move freely and collide with the drug particles more frequently. With increasing pressure, the density increases at constant temperature, and with increasing temperature, the density decreases at fixed pressure [35]. The higher density allows carbon dioxide molecules to penetrate into the drug particles [36]. However, the temperature of 45 °C was the best choice in our study possibly because 45 °C was the most close to the melting point of CoQ10 (49 °C). Therefore, 20 MPa, 45 °C, and 1 h were chosen for the optimized reaction conditions. The design of the optimized formulation is listed in Table 2.
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