The use of a diffuser in hydrokinetic turbines can improve the power coefficient. However, the risk of cavitation in the rotor blades increases. Studies suggest that backward-curved blades can reduce ...the axial load on the rotor and therefore prevent cavitation. Therefore, this work develops an optimization procedure applied to backward-curved blades in hydrokinetic turbines with diffusers based on the Blade Element Momentum Theory. The main contribution is to consider both the sweep effect and the presence of a diffuser in the optimization in an innovative way. We use a radial transformation function that adjusts the radial position considering the curvature of the blade during optimization under the effect of the diffuser. The results showed that the increase in blade curvature resulted in greater chord distributions and twist angles, especially at the blade tips. The Prandtl’s loss factor was not sensitive to sweep, but the linked circulation increased at the blade tips, suggesting an increased risk of cavitation. Depending on the sweep angle, the optimized blades were able to mitigate or avoid cavitation. In particular, a sweep angle of 30∘ eliminated cavitation. This study indicated that the proposed optimization can effectively prevent cavitation, showing satisfactory results.
Martian dunes are sculpted by meter‐scale bed forms, which have been interpreted as wind ripples based on orbital data. Because aeolian ripples tend to orient and migrate transversely to the last ...sand‐moving wind, they have been widely used as wind vanes on Earth and Mars. In this report we show that Martian large ripples are dynamically different from Earth's ripples. By remotely monitoring their evolution within the Mars Science Laboratory landing site, we show that these bed forms evolve longitudinally with minimal lateral migration in a time‐span of ~ six terrestrial years. Our observations suggest that the large Martian ripples can record more than one wind direction and that in certain cases they are more similar to linear dunes from a dynamic point of view. Consequently, the assumption of the transverse nature of the large Martian ripples must be used with caution when using these features to derive wind directions.
Key Points
Martian large ripples dynamics are more similar to longitudinal dunes than impact ripples
First evidence for longitudinal large ripple migration on Mars
Martian large ripples consistently migrate in Gale Crater
In this report we show evidence of widespread ripple migration over the stoss side of dark barchan dunes in Nili Patera on Mars. The measured average migration of ∼1.7 meters in less than 4 ...terrestrial months clearly indicates that active sand saltation is occurring in the study area. In addition, we document widespread changes in the dune base‐ground surface contact and in the slip face structures, showing that not only the ripples, but the whole dunes are actually migrating in the present‐day atmospheric setting. These results provide unequivocal evidence of recent aeolian activity and suggest that other dunes and ripples on Mars may also be active.
Peptidase inhibitors in tick physiology PARIZI, L. F.; ALI, A.; TIRLONI, L. ...
Medical and veterinary entomology,
June 2018, Letnik:
32, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Peptidase inhibitors regulate a wide range of physiological processes involved in the interaction between hematophagous parasites and their hosts, including tissue remodeling, the immune response and ...blood coagulation. In tick physiology, peptidase inhibitors have a crucial role in adaptation to improve parasitism mechanisms, facilitating blood feeding by interfering with defense‐related host peptidases. Recently, a larger number of studies on this topic led to the description of several new tick inhibitors displaying interesting novel features, for example a role in pathogen transmission to the host. A comprehensive review discussing these emerging concepts can therefore shed light on peptidase inhibitor functions, their relevance to tick physiology and their potential applications. Here, we summarize and examine the general characteristics, functional diversity and action of tick peptidase inhibitors with known physiological roles in the tick−host−pathogen interaction.
Peptidase inhibitors regulate a wide range of physiological processes.
Peptidase inhibitors improve parasitism mechanisms.
Tick peptidase inhibitors have physiological role in tick-host-pathogen interaction.
Starting of small turbines is significantly affected by friction resistance of drivetrains. When the effect of drivetrain is not considered in small turbine design, the rotor starting may be ...overestimated, becoming resistance assessment of small turbines relevant in the literature. The present work develops a novel modeling to estimate starting of small wind turbines using an extension of the generalized Maxwell-slip (GMS) friction model. The friction torque of a small wind turbine is analyzed and compared with experimental data available in the literature. Static and dynamic torques are evaluated through the use of the extended GMS, in which a procedure to estimate the aerodynamic starting torque of the turbine is performed. The results show that the proposed approach is a generalization of Stribeck model applicable to both regimes unsteady and steady-state, demonstrating good agreement with measurements from the literature. For a constant wind velocity, the aerodynamic torque for a stationary blade always decreases along the time, and only lift force and chord distribution can generate aerodynamic torque at starting. However, it is interesting whether the wind velocity is variant, starting from zero to a constant value, this variation increases the aerodynamic torque a little soon after starting. The estimated powertrain axial load and torque are close to the measurements with maximum errors of 9.4 and 6.7%, respectively, demonstrating the good behavior of GMS for starting of small turbines.
We present evidence of widespread aeolian activity in the Arabia Terra/Meridiani region (Mars), where different kinds of aeolian modifications have been detected and classified. Passing from the ...regional to the local scale, we describe one particular dune field in Meridiani Planum, where two ripple populations are distinguished by means of different migration rates. Moreover, a consistent change in the ripple pattern is accompanied by significant dune advancement (between 0.4–1 meter in one Martian year) that is locally triggered by large avalanche features. This suggests that dune advancement may be common throughout the Martian tropics.
Key Points
Active sand saltation is common on the Martian surface
Dune advancement and sand movement not related to CO2 frost sublimation
Different ripple populations are distinguished by means of different migration rates
Wind‐formed features are abundant in Oxia Planum (Mars), the landing site of the 2022 ExoMars mission, which shows geological evidence for a past wet environment. Studies of aeolian bedforms at the ...landing site were focused on assessing the risk for rover trafficability, however their potential in recording climatic fluctuations has not been explored. Here we show that the landing site experienced multiple climatic changes in the Amazonian, which are recorded by an intriguing set of ridges that we interpret as Periodic Bedrock Ridges (PBRs). Clues for a PBR origin result from ridge regularity, defect terminations, and the presence of preserved megaripples detaching from the PBRs. PBR orientation differs from superimposed transverse aeolian ridges pointing toward a major change in wind regime. Our results provide constrains on PBR formation mechanisms and offer indications on paleo winds that will be crucial for understanding the landing site geology.
Plain Language Summary
Oxia Planum on Mars is the landing site for the ExoMars 2022 mission. The region likely hosted a standing body of water, but the effect of the wind was also important in shaping the landscape. In this study, we first describe a set of linear ridges that, in our interpretation, were sculpted by the wind in a more recent past. We also show that the wind that formed the ridges (Periodic Bedrock Ridges) was blowing from a different direction than the ones that formed younger ripples on top, suggesting a complex geological history of wind erosion and deposition that will be further investigated during the ExoMars mission.
Key Points
We present the first evidence for a periodic bedrock ridge (PBRs) pattern from the ExoMars 2022 landing site
Formative paleowind directions are extrapolated from PBRs and transverse aeolian ridges
Evidence for an Amazonian change in the wind regime are provided
This work explores the dynamics of hydrogen bond networks in cellulose through inelastic neutron scattering (INS) and periodic CASTEP calculations. Estimated spectra were based on the crystal ...structure of cellulose Iα and Iβ and replicate the INS spectrum of cellulose samples with remarkable similarity, allowing a reliable assignment of INS bands to vibrational modes of cellulose. Comparison of cellulose samples from varied sources, from bacterial to kraft pulp, allows the identification of characteristic INS bands, arising from C2-OH torsional motions, which easily identify which allomorphIα or Iβis prevalent. A high crystallinity index is revealed by the presence of well-defined INS bands associated with highly cooperative CH bending modes along the chain. Hydrating kraft cellulose samples clearly affects those INS bands related with the hydroxymethyl group, identified as the preferred binding site for water molecules. At high humidity content level, a significant proportion of the water molecules is aggregated in clusters within the amorphous cellulose domains. The formation of ice microcrystals leads to a partial disruption of the hydrogen-bond network, as can be concluded from the observed red-shift of the torsional OH vibrational modes. The full assignment and interpretation of cellulose’s INS spectra herein provided is a sound basis for future use of INS spectroscopy in the characterization of functionalized cellulose fibers and composite materials.
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