scholarly journals Numerical study of the propulsive performance of two-dimensional pitching foils at very high frequencies: scaling laws and turbulence effects

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Enrique Sanmiguel-Rojas ◽  
Ramon Fernandez-Feria
Keyword(s):  
Numerical Simulations ◽  
Scaling Laws ◽  
Theoretical Models ◽  
Linear Potential ◽  
Propulsive Efficiency ◽  
Content Type ◽  
High Frequencies ◽  
Linear Potential Theory ◽  
Very High Frequencies ◽  
Very High

Purpose This paper aims to analyze the propulsive performance of small-amplitude pitching foils at very high frequencies with double objectives: to find out scaling laws for the time-averaged thrust and propulsive efficiency at very high frequencies; and to characterize the Strouhal number above which the effect of turbulence on the mean values cannot be neglected. Design/methodology/approach The thrust force and propulsive efficiency of a pitching NACA0012 foil at high reduced frequencies (k) and a Reynolds number Re = 16 000 are analyzed using accurate numerical simulations, both assuming laminar flow and using a transition turbulence model. The time-averaged results are validated with available experimental data for k up to about 12 (Strouhal number, St, up to 0.6). This study also compares the present numerical results with the predictions of theoretical models and existing numerical results. For a foil pitching about its quarter chord with amplitude α0 = 8o, the reduced frequency is varied here up to k = 30 (St up to 2), much higher than in any previous numerical or experimental work. Findings For this pitch amplitude, turbulence effects are found negligible for St ≲ 0.8, and affecting less than 10% to the time-averaged thrust coefficient CT¯ for larger St Linear potential theory fails for very large k, even for the small pitch amplitude considered, particularly for the power coefficient, and therefore for the propulsive efficiency. It is found that CT¯ ∼ St2 for large St, in agreement with recent models, and the propulsive efficiency decays as 1/k, in disagreement with the linear potential theory. Originality/value Pitching foils are increasingly studied as efficient propellers and energy harvesting devices. Their performance at very high reduced frequencies has not been sufficiently analyzed before. The authors provide accurate numerical simulations to discern when turbulence is relevant for the computation of the time-averaged thrust and efficiency and how their scaling with the reduced frequency is affected in relation to the laminar-flow predictions. This is relevant because some small-amplitude theoretical models predict high propulsive efficiency of pitching foils at very high frequencies over certain ranges of the structural parameters, and only very accurate numerical simulations may decide on these predictions.

An ammeter for very high frequencies

1930 ◽  
Vol 68 (401) ◽  
pp. 556-559
Author(s):  
C.L. Fortescue ◽  
L.A. Moxon
Keyword(s):  
High Frequencies ◽  
Very High Frequencies ◽  
Very High

scholarly journals Idiotypic analysis of potential and available repertoires in the arsonate system.

1984 ◽  
Vol 160 (1) ◽  
pp. 1-11 ◽  
Author(s):  
M Slaoui ◽  
O Leo ◽  
J Marvel ◽  
M Moser ◽  
J Hiernaux ◽  
...  
Keyword(s):  
Monoclonal Antibody ◽  
B Cells ◽  
Keyhole Limpet Hemocyanin ◽  
High Frequencies ◽  
Specific Subset ◽  
A Minor ◽  
Very High Frequencies ◽  
Very High ◽  
Limiting Dilution

We have shown that, by suitable idiotypic manipulation, BALB/c mice can express the major cross-reactive idiotype (CRI) of A/J mice in response to azophenylarsonate (Ars). In order to know if the CRIA idiotype is present in the potential repertoire of BALB/c before any intentional selection, we used polyclonal activation in vitro and limiting dilution analysis. The readout was done with two monoclonal anti-CRIA antibodies that recognize distinct idiotopes on a CRIA+ A/J germline-encoded monoclonal antibody. We studied the frequency of CRIA+ lipopolysaccharide (LPS)-reactive cells in the spleens of nonimmune and immune A/J mice and in the spleens of naive and manipulated (i.e., producing CRIA+ antibodies) BALB/c mice. A/J and BALB/c naive individuals presented very high frequencies of Ars-specific B cells while the frequency of CRIA+ B cells was only a minor subset (0.5%) of the total Ars-specific subset in the two strains. When A/J mice were immunized with Ars-keyhole limpet hemocyanin, a clear preferential expansion of the CRIA+ minor subset of A/J mice was observed (100x). No such enhancement was observed in BALB/c mice similarly treated. Manipulated BALB/c mice presented a higher frequency of CRIA+ anti-Ars B cells than naive or antigen-immunized BALB/c individuals.

A Genetically Marked I Element in Drosophila melanogaster Can Be Mobilized When ORF2 Is Provided in trans

Genetics ◽  
1998 ◽  
Vol 148 (1) ◽  
pp. 267-275
Author(s):  
Isabelle Busseau ◽  
Sophie Malinsky ◽  
Maria Balakireva ◽  
Marie-Christine Chaboissier ◽  
Danielle Teninges ◽  
...  
Keyword(s):  
Drosophila Melanogaster ◽  
Heat Shock ◽  
Reverse Transcriptase ◽  
Germ Line ◽  
Ltr Retrotransposons ◽  
Low Frequencies ◽  
High Frequencies ◽  
In Trans ◽  
Very High Frequencies ◽  
Very High

Abstract I factors in Drosophila melanogaster are non-LTR retrotransposons similar to mammalian LINEs. They transpose at very high frequencies in the germ line of SF females resulting from crosses between reactive females, devoid of active I factors, and inducer males, containing active I factors. The vermilion marked IviP2 element was designed to allow easy phenotypical screening for retrotransposition events. It is deleted in ORF2 and therefore cannot produce reverse transcriptase. IviP2 can be mobilized at very low frequencies by actively transposing I factors in the germ line of SF females. This paper shows that IviP2 can be mobilized more efficiently in the germ line of strongly reactive females in the absence of active I factors, when it is trans-complemented by the product of ORF2 synthesized from the hsp70 heat-shock promoter. This represents a promising step toward the use of marked I elements to study retrotransposition and as tools for mutagenesis.

scholarly journals Field Measurements of Dielectric Absorption in Antarctic Ice and Snow at Very High Frequencies

1968 ◽  
Vol 7 (49) ◽  
pp. 89-94 ◽  
Author(s):  
M. E. R. Walford
Keyword(s):  
Impurity Content ◽  
Field Measurements ◽  
Relaxation Mechanism ◽  
Absorption Bands ◽  
High Frequencies ◽  
Dielectric Absorption ◽  
Antarctic Snow ◽  
Radio Frequencies ◽  
Very High Frequencies ◽  
Very High

AbstractField measurements are presented of dielectric absorption in Antarctic snow and ice at frequencies of a few hundred megahertz. They are compared with measurements by other authors at very high frequencies. The dielectric absorption in ice at these frequencies is accounted for in terms of absorption bands both at radio frequencies and in the infrared. Bands at radio frequencies are caused by a relaxation mechanism which depends upon the temperature and the impurity content of the ice. These two factors are therefore included in an account of the dielectric absorption in ice at very high frequencies.

scholarly journals Ephemeral states in protein folding under force captured with a magnetic tweezers design

2019 ◽  
Vol 116 (16) ◽  
pp. 7873-7878 ◽  
Author(s):  
Rafael Tapia-Rojo ◽  
Edward C. Eckels ◽  
Julio M. Fernández
Keyword(s):  
Magnetic Field ◽  
Molten Globule ◽  
Magnetic Tweezers ◽  
Protein L ◽  
High Frequencies ◽  
Electric Signals ◽  
Very High Frequencies ◽  
The Magnetic Field ◽  
Very High ◽  
Unique Capability

Magnetic tape heads are ubiquitously used to read and record on magnetic tapes in technologies as diverse as old VHS tapes, modern hard-drive disks, or magnetic bands on credit cards. Their design highlights the ability to convert electric signals into fluctuations of the magnetic field at very high frequencies, which is essential for the high-density storage demanded nowadays. Here, we twist this conventional use of tape heads to implement one in a magnetic tweezers design, which offers the unique capability of changing the force with a bandwidth of ∼10 kHz. We calibrate our instrument by developing an analytical expression that predicts the magnetic force acting on a superparamagnetic bead based on the Karlqvist approximation of the magnetic field created by a tape head. This theory is validated by measuring the force dependence of protein L unfolding/folding step sizes and the folding properties of the R3 talin domain. We demonstrate the potential of our instrument by carrying out millisecond-long quenches to capture the formation of the ephemeral molten globule state in protein L, which has never been observed before. Our instrument provides the capability of interrogating individual molecules under fast-changing forces with a control and resolution below a fraction of a piconewton, opening a range of force spectroscopy protocols to study protein dynamics under force.

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