scholarly journals Operation of the alula as an indicator of gear change in hoverflies

2011 ◽  
Vol 9 (71) ◽  
pp. 1194-1207 ◽  
Author(s):  
Simon M. Walker ◽  
Adrian L. R. Thomas ◽  
Graham K. Taylor
Keyword(s):  
High Speed ◽  
Aerodynamic Force ◽  
Angular Acceleration ◽  
The State ◽  
The Body ◽  
Kinematic Parameters ◽  
Wing Kinematics ◽  
Change Mechanism ◽  
The Third ◽  
Gear Change

The alula is a hinged flap found at the base of the wings of most brachyceran Diptera. The alula accounts for up to 10 per cent of the total wing area in hoverflies (Syrphidae), and its hinged arrangement allows the wings to be swept back over the thorax and abdomen at rest. The alula is actuated via the third axillary sclerite, which is a component of the wing hinge that is involved in wing retraction and control. The third axillary sclerite has also been implicated in the gear change mechanism of flies. This mechanism allows rapid switching between different modes of wing kinematics, by imposing or removing contact with a mechanical stop limiting movement of the wing during the lower half of the downstroke. The alula operates in two distinct states during flight—flipped or flat—and we hypothesize that its state indicates switching between different flight modes. We used high-speed digital video of free-flying hoverflies ( Eristalis tenax and Eristalis pertinax ) to investigate whether flipping of the alula was associated with changes in wing and body kinematics. We found that alula state was associated with different distributions of multiple wing kinematic parameters, including stroke amplitude, stroke deviation angle, downstroke angle of incidence and timing of supination. Changes in all of these parameters have previously been linked to gear change in flies. Symmetric flipping of the alulae was associated with changes in the symmetric linear acceleration of the body, while asymmetric flipping of the alulae was associated with asymmetric angular acceleration of the body. We conclude that the wings produce less aerodynamic force when the alula is flipped, largely as a result of the accompanying changes in wing kinematics. The alula changes state at mid-downstroke, which is the point at which the gear change mechanism is known to come into effect. This transition is accompanied by changes in the other wing kinematic parameters. We therefore find that the state of the alula is linked to the same parameters as are affected by the gear change mechanism. We conclude that the state of the alula does indeed indicate the operation of different flight modes in Eristalis , and infer that a likely mechanism for these changes in flight mode is the gear change mechanism.

Vortex Formation in the Tethered Flight of the Peacock Butterfly Inachis io L. (Lepidoptera, Nymphalidae) and some Aspects of Insect Flight Evolution

1991 ◽  
Vol 161 (1) ◽  
pp. 77-95 ◽  
Author(s):  
A. K. BRODSKY
Keyword(s):  
High Speed ◽  
Insect Flight ◽  
Aerodynamic Force ◽  
Vortex Formation ◽  
Flow Distribution ◽  
The Body ◽  
Body Axis ◽  
Vortex Rings ◽  
Lower Amplitude ◽  
Inachis Io

High-speed filming has been used to investigate the performance of the peacock butterfly Inachis io while flying in a wind-tunnel. The wake of the butterfly in ‘feeding’ flight is a system of discrete pairs of vortex rings: in each pair the vortex rings are coupled at right angles. The flow distribution around the butterfly and the dynamics of the vortex rings suggest that useful force is produced continuously throughout the wingbeat. The butterfly's flapping flight can be divided into three successive stages: during the downstroke, force generation can be explained by quasi-steady aerofoil action; during the upstroke and supination, by unsteady aerofoil action; and during pronation, by a jet mechanism. The study of airflow around the peacock butterfly throws light on the evolutionary changes in the pattern of interaction between insect wings and the air. At the first stage of the evolution of insect flight, documented in a subimago of the mayfly Heptagenia sulphurea and some other primitive insects, flapping wings generate a system of coupled vortex rings; the aerodynamic force, being perpendicular to the stroke plane, coincides with the direction of the longitudinal body axis. At the second stage, this force is directed forwards and upwards relative to the body axis; the vortex wake is the same as that at the first stage. From this point, two paths of evolution are possible. The first leads to the vortex pattern recorded in the peacock butterfly. The second is typically found in higher orders, where the narrow and relatively short wings flap with lower amplitude and higher frequency, leaving in their wake two chains of uncoupled small vortex rings.

The Hydraulic Mechanism of the Predatory Strike in Dragonfly Larvae

1980 ◽  
Vol 88 (1) ◽  
pp. 1-20 ◽  
Author(s):  
YOSHITAKA TANAKA ◽  
MITUHIKO HISADA
Keyword(s):  
High Speed ◽  
Late Phase ◽  
Angular Acceleration ◽  
The Body ◽  
Extensor Muscles ◽  
Flexor Muscles ◽  
Electrophysiological Measurements ◽  
Hydraulic Mechanism ◽  
Great Acceleration ◽  
Internal Body

1. Aeschna larvae catch prey with a fast-moving elongated labium. The mechanism of this movement was analysed by high-speed cinematographs and by hydrostatic and electrophysiological measurements. 2. The strike movement consists of an initial, mid and late phase. The angular acceleration of the joints of the labium is 2·6 × 105 and 7·8 × 105 deg·s−2 during the initial and mid phase respectively. The torque necessary for the acceleration was calculated to be 1·3 × 10−5 and 4·0 × 10−5 N.m for the initial and mid-phases respectively. 3. The relation between the pressure applied to the labium and the extension torque at the joints has been established. No torque develops about the postmentum-prementum joint as long as the click of the flexed labium is engaged. 4. The power production of the extensor muscles is less than the power output of the mid phase. The power for the mid phase is derived from the internal body pressure developed by the contraction of the abdominal dorsoventral muscles. The required pressure for the mid phase is about 60 cmH2O if the resistance is neglected and 80 cmH2O when the resistance is considered. 5. Abdominal dorso-ventral muscles contract 110–500 ms before the onset of the strike and the body pressure of the animal increases to a peak of 40–120 cmH2O at the onset of the strike. 6. The geometry of the labial joints gives the primary flexor muscles of the labium a large mechanical advantage over the extensor muscles in the fully flexed labium, and allows the extensor muscles to contract almost isometrically. 7. The extensor muscles and the primary flexor muscles co-contract for 75–100 ms before the strike. The strike movement begins when the flexor muscles relax. The stored energy in the extensor system is released suddenly and disengages the click producing the initial phase. Once the click is disengaged the internal pressure produces the large torque to move the labium with great acceleration during the mid phase.

Effects of stretch receptor ablation on the optomotor control of lift in the hawkmothManduca sexta

2001 ◽  
Vol 204 (21) ◽  
pp. 3683-3691 ◽  
Author(s):  
Mark A. Frye
Keyword(s):  
Action Potentials ◽  
High Speed ◽  
Visual Cues ◽  
Aerodynamic Force ◽  
Video Recording ◽  
Force Production ◽  
Stretch Receptor ◽  
Flight Behavior ◽  
Wing Kinematics ◽  
Control Flight

SUMMARYIn insects, fast sensory feedback from specialized mechanoreceptors is integrated with guidance cues descending from the visual system to control flight behavior. A proprioceptive sensory organ found in both locusts and moths, the wing hinge stretch receptor, has been extensively studied in locusts for its powerful influence on the activity of flight muscle motoneurons and interneurons. The stretch receptor fires a high-frequency burst of action potentials near the top of each wingstroke and encodes kinematic variables such as amplitude and timing. Here, I describe the effects of stretch receptor ablation on the visual control of lift during flight in the hawkmoth Manduca sexta. Using a combination of extracellular muscle recordings, force and position measurements and high-speed video recording, I tracked power muscle activity, net vertical flight force (lift), abdomen deflection and wing kinematics in response to image motions of varying velocity during tethered flight in a wind tunnel. As a result of bilateral ablation of the wing hinge stretch receptors, visually evoked lift decreased to nearly one-third of that exhibited by intact animals. The phase and frequency of indirect power muscle action potentials and the patterns of abdominal deflection were unaffected; however, wingstroke amplitude was clearly reduced after ablation. Collectively, these results suggest that stretch receptor feedback is integrated with descending visual cues to control wing kinematics and the resultant aerodynamic force production during flight.

scholarly journals Deformable wing kinematics in free-flying hoverflies

2009 ◽  
Vol 7 (42) ◽  
pp. 131-142 ◽  
Author(s):  
Simon M. Walker ◽  
Adrian L. R. Thomas ◽  
Graham K. Taylor
Keyword(s):  
High Speed ◽  
Control Device ◽  
Angle Of Incidence ◽  
Recoil Effect ◽  
Substantial Variation ◽  
Kinematic Parameters ◽  
Wing Kinematics ◽  
Video Cameras ◽  
Flow Control Device ◽  
Modelling Studies

Here, we present a detailed analysis of the deforming wing kinematics of free-flying hoverflies ( Eristalis tenax , Linnaeus) during hovering flight. We used four high-speed digital video cameras to reconstruct the motion of approximately 22 points on each wing using photogrammetric techniques. While the root-flapping motion of the wing is similar in both the downstroke and upstroke, and is well modelled as a simple harmonic motion, other wing kinematic parameters show substantial variation between the downstroke and upstroke. Whereas the magnitude of the angle of incidence varies considerably within and between different hoverflies, the twist distribution along the wing is highly stereotyped. The angle of incidence and camber both show a recoil effect as they change abruptly at stroke reversal. Pronation occurs consistently after stroke reversal, which is perhaps surprising, because this has been found to reduce lift production in modelling studies. We find that the alula, a hinged flap near the base of the wing, operates in two discrete states: either in plane with the wing, or flipped approximately normal to it. We hypothesize that the alula may be acting as a flow-control device.

scholarly journals FORMING OF ECONOMIC-AND-USEFUL TRAITS OF COWS IN DEPEND OF ORIGIN BY FATHER

2017 ◽  
Vol 54 ◽  
pp. 50-58
Author(s):  
G. D. Ilyashenko
Keyword(s):  
Dairy Cows ◽  
The State ◽  
The Body ◽  
Reproductive Capacity ◽  
Linear Classification ◽  
Milk Productivity ◽  
The Third ◽  
Breed Type ◽  
The Difference ◽  
Selection Of

The increase in the productivity of dairy cows significantly depends on the qualitative selection, evaluation and intensive use of procreator bulls with breeding value both for milk production and exteriors. The proper selection of bull for reproduction the herd is an important and responsible measure as the heredity of the procreators in the genetic improvement of breeds is extremely high, especially at the present stage of breeding. The aim of the research was to determine the level of influence of father's origin on dairy productivity, exterior and reproductive capacity of Ukrainian Red dairy cows in the conditions of the Central region. Materials and methods. The research was carried out on the basis of zootechnical records in a herd breeding plant for the breeding of the Ukrainian Red dairy breeds of cattle of the State Enterprise of Experimental Household «Elitne» of the Kirovograd SAES NAAS. The analysis involves the materials of the formed electronic database on indicators of milk productivity, reproductive capacity and structure of the body of cows for the year 2015. Estimation of the exterior type of cows was conducted using the linear classification method at the age of 2–4 months after calving in two systems - 9-ball, with a linear description of 18 articles of the exterior and 100-point classification system, taking into account four sets of breeding grounds, which characterize: the severity of the dairy type, the development of the body, the state of the limbs and the morphological qualities of the udder. In the exterior, the half-sisters groups of 6 bulls with a population of 28 to 118 cows were compared. The force of origin's influence on the father was calculated by one-factor dispersion analysis. The calculations were carried out using the methods of mathematical statistics using the software package "STATISTICA-6.1". Results of the research. By comparison of group average, a significant level of differentiation of the bulls in the herd of the breeder is determined by the characteristics of their daughters. By the age of the first calving, the difference between the best and worst half-sistesr groups reached 283 ± 148,9 days or 36,5 %, with a reproduction rate of 0,181 ± 0,180 or 21,0%, for the livelihood of 305 days of first lactation – 2890 ± 959 kg оr 78,3% (P < 0,01), the second one was 2112 ± 926 kg or 40,9% (P < 0,05), the third group was 113 ± 521 kg or 18,4% (P < 0,05). In terms of the content of fat in milk, the intergroup difference was 0,38 ± 0,294% (td = 1,29) for the first, 0.64 ± 0,155% (td = 1,62) for the second and 0,44 ± 0,311% (td = 2,03) – for the third lactation, for protein content – the difference was insignificant. Among the daughters of the studied protectors, the highest tastes for the first lactation were characterized by daughters of Tsvitka 435, Roman Reda 86883, Diplomat 401497. For the second and third Rainer 23685, Tsvitka 435, Hens Reda 398624, below all lactations of the Vendian 67955 and Cup 405. Noticed, Cvitok 435, holsteinized bull of intrarenal type of Ukrainian Red dairy breed, for the dignity of its daughters, exceeded all Holstein breeders, used in the herd. Summarized, according to the results of the classification of the four complexes exterior signs, the assessment shows the level of expression of the exterior type and suggests that it is best at the daughters of Bensons Hens Red 398624, Jorin 114414759 and Tsvitka 435. Reduce the gap between the actual estimate and the maximum possible, which is respectively 5,5, 5,7 and 6,2 points, possibly due to the quality control of the stock herd by the exteriors in the herds with the selection of procreator-bulls, estimated by the type of daughters. Conclusions. The study of milk productivity and reproductive ability of cows definited the level of differentiation between the groups of half sisters by father. The difference between the groups on separate grounds is 78,3%. At the same time, cows of the Holstein and Holstinizovany In-breed Type (HRD) of Ukrainian Red dairy breeds have a marked advantage over milk yield. The worst manifestation of the features – in animals of the bulls of Angler and Rich-Milkfat In-breed Type (FRD) of Ukrainian Red dairy breeds. Using of linear classification allowed to differentiate sufficiently the bull-producers by the exterior characteristics of the structure of the body and the mummies of their daughters. The high variability of descriptive articles indicates the need for their improvement in a part of the animals of the study population. The influence of the genetic factor of the father's origin on the variability of the considered characteristics ranged from 12 to 36%.

scholarly journals INFLAMMATORY-DESTRUCTIVE PROCESS IN PERIODONTIUM WHILE MODELLING HYPО- AND HYPERREACTIVITY OF THE ORGANISM

2021 ◽  
pp. 54-58
Author(s):  
Yu.Yu. Yarov
Keyword(s):  
Inflammatory Reaction ◽  
Clinical Course ◽  
The State ◽  
The Body ◽  
Periodontal Tissues ◽  
The Third ◽  
Pi Index ◽  
Destructive Process ◽  
Mechanisms Of Development ◽  
Purebred Dogs

The issues of clarifying the key mechanisms of development and course of generalized periodontitis in different conditions of reactivity of the organism remain relevant. The aim of the research is study of the peculiarities of course of the inflammatory-destructive process in the periodontium according to the dynamics of clinical and paraclinical indicators depending on the state of reactivity of the body in the conditions of modeling hyper- and hyporeaction. Materials and methods. The experiments were performed on 24 adult not purebred dogs weighing 8-12 kg. The animals were divided into three equal groups. In the first group, drugs that disrupt the reactivity of the organism were not used (normoreactivity of the organism). In the second group drugs simulated the state of hyperreactivity, and in the third they provoked the condition of the hyporeactivity of the organism. The condition of periodontal tissues was assessed initially, on the 14th and 28th day of observation of clinical and paraclinical parameters (creviculars liquor, PMA indices, PI Russell, GI Fedorov-Volodkina, Kulazhenko's test). Results. On the 14th day of modelling the states of hyper- and hyporeactivity of the organism a number of differences in the nature of inflammation in periodontal tissues were revealed in animals of different groups. Control of the amount of creviculars liquor increased in 1,1 times, PMA indices, PI Russell, GI Fedorov-Volodkina, Kulazhenko's test, respectively, in 1,12; 1,19; 1,33 and 1,29 times (p <0,05). On the 28th day of the experiment, significant differences in the intensity of the destructive process in animals with unchanged and changed reactivity of the organism attracted attention. Thus, in cases of normoreactivity the depth of periodontal pockets reached 3 mm, the mobility of the teeth was I degree, with the changed - the depth of periodontal pockets was 5-6 mm, the mobility of the teeth was II-III degree. The amount of creviculars liquor, reflecting the intensity of the inflammatory reaction, increased compared with the 14th day, 1,3 times (p <0,05); PMA index, which characterizes the prevalence of gingivitis, and the Kulazhenko test probably did not change (p> 0,05); Russell's PI index, which indicates a pronounced intensity of inflammatory-destructive periodontal lesions, increased 2,05 times (р <0,05). Conclusions. Thus, in cases of normoreactivity of organism the inflammatory-destructive process in periodontium has moderate nature; when modelling the hyper- and hyporeactivity of the organism it acquires the character of “rapidly progressing periodontitis”. Therefore, it is necessary to continue studying the question of explaining the mechanism of different clinical course of the inflammatory-destructive process with changed and unchanged reactivity of the organism.

scholarly journals Deformable wing kinematics in the desert locust: how and why do camber, twist and topography vary through the stroke?

2008 ◽  
Vol 6 (38) ◽  
pp. 735-747 ◽  
Author(s):  
Simon M. Walker ◽  
Adrian L. R. Thomas ◽  
Graham K. Taylor
Keyword(s):  
Flight Control ◽  
High Speed ◽  
Schistocerca Gregaria ◽  
Aerodynamic Force ◽  
Angle Of Attack ◽  
Force Production ◽  
Linear Increase ◽  
Trailing Edge ◽  
Wing Kinematics ◽  
Drag Ratio

Here, we present a detailed analysis of the wing kinematics and wing deformations of desert locusts ( Schistocerca gregaria , Forskål) flying tethered in a wind tunnel. We filmed them using four high-speed digital video cameras, and used photogrammetry to reconstruct the motion of more than 100 identified points. Whereas the hindwing motions were highly stereotyped, the forewing motions showed considerable variation, consistent with a role in flight control. Both wings were positively cambered on the downstroke. The hindwing was cambered through an ‘umbrella effect’ whereby the trailing edge tension compressed the radial veins during the downstroke. Hindwing camber was reversed on the upstroke as the wing fan corrugated, reducing the projected area by 30 per cent, and releasing the tension in the trailing edge. Both the wings were strongly twisted from the root to the tip. The linear decrease in incidence along the hindwing on the downstroke precisely counteracts the linear increase in the angle of attack that would otherwise occur in root flapping for an untwisted wing. The consequent near-constant angle of attack is reminiscent of the optimum for a propeller of constant aerofoil section, wherein a linear twist distribution allows each section to operate at the unique angle of attack maximizing the lift to drag ratio. This implies tuning of the structural, morphological and kinematic parameters of the hindwing for efficient aerodynamic force production.

Swimming of the pea crab (Pinnotheres pisum)

2014 ◽  
Vol 64 (3) ◽  
pp. 239-260
Author(s):  
Corstiaen P.C. Versteegh ◽  
Mees Muller
Keyword(s):  
Particle Tracking ◽  
High Speed ◽  
Particle Tracking Velocimetry ◽  
Video Recording ◽  
Aquatic Organisms ◽  
The Body ◽  
Forward Movement ◽  
High Speed Video ◽  
The Third ◽  
Pea Crab

Aquatic organisms have to deal with different hydrodynamic regimes, depending on their size and speed during locomotion. The pea crab swims by beating the third and fourth pereiopod on opposite sides as pairs. Using particle tracking velocimetry and high-speed video recording, we quantify the kinematics and vortices in the wake of the pea crab. Where the proximal parts of the pereiopods beat in antiphase, their distal parts show an overlapping beat period. By using four instead of two limbs for propulsion, an uninterrupted forward movement is established, reducing the influence of the acceleration reaction. Before body speed is maximal, force generation of the pereiopods seems most active when passing an orthogonal position with the body.

scholarly journals The correlation between wing kinematics and steering muscle activity in the blowfly Calliphora vicina

2001 ◽  
Vol 204 (24) ◽  
pp. 4213-4226
Author(s):  
Claire N. Balint ◽  
Michael H. Dickinson
Keyword(s):  
Muscle Activity ◽  
High Speed ◽  
The Body ◽  
Calliphora Vicina ◽  
Strongly Correlated ◽  
Motor Patterns ◽  
Wing Kinematics ◽  
Wing Motion ◽  
The Relationship ◽  
Electromyographic Signals

SUMMARY Determining how the motor patterns of the nervous system are converted into the mechanical and behavioral output of the body is a central goal in the study of locomotion. In the case of dipteran flight, a population of small steering muscles controls many of the subtle changes in wing kinematics that allow flies to maneuver rapidly. We filmed the wing motion of tethered Calliphora vicina at high speed and simultaneously recorded multi-channel electromyographic signals from some of the prominent steering muscles in order to correlate kinematics with muscle activity. Using this analysis, we found that the timing of each spike in the basalare muscles was strongly correlated with changes in the deviation of the stroke plane during the downstroke. The relationship was non-linear such that the magnitude of the kinematic response to each muscle spike decreased with increasing levels of stroke deviation. This result suggests that downstroke deviation is controlled in part via the mechanical summation of basalare activity. We also found that interactions among the basalares and muscles III2–III4 determine the maximum forward amplitude of the wingstroke. In addition, activity in muscle I1 appears to participate in a wingbeat gearing mechanism, as previously proposed. Using these results, we have been able to correlate changes in wing kinematics with alteration in the spike rate, firing phase and combinatorial activity of identified steering muscles.

scholarly journals Kirjandus kui vastupanu Nõukogude Eestis Teise maailmasõja järgsel perioodil

2019 ◽  
Author(s):  
Tiit Hennoste
Keyword(s):  
Literary Criticism ◽  
Communist Party ◽  
Zen Buddhism ◽  
Socialist Realism ◽  
The State ◽  
The Body ◽  
Political Freedom ◽  
World War ◽  
The Third ◽  
Soviet Ideology

Abstract: Literature as resistance in Soviet Estonia in the post-World War II period The theme of this article is the resistance that took place in Soviet Estonian literature, literary criticism and literary studies in the post-Second World War period. The article accentuates that different modes and objectives of resistance were central in different periods. Literary resistance is divided into four groups according to the nature of the pressure and the aims of resistance: first, ideological resistance to Soviet ideology in the name of literature that is free of ideology, or in the name of some other ideology; second, national resistance in the name of the unity of the people and preservation of identity; third, aesthetic resistance to the official literary doctrine; and fourth, resistance in the name of general or personal freedom and authenticity. Writers and literary scholars used different modes of resistance. These were so-called writing for the desk drawer, silence within a text, the use of ‘secret codes’, self-publication, the selection of themes or modes of writing that were not favoured by the regime and were apolitical and nonideological, and the use of neutral words and concepts instead of concepts and words bearing Soviet ideology. Totalitarian control of literature by way of decisions and direct instructions from the Communist Party characterised the Stalinist period (until 1956). All literature had to adhere to the doctrine of socialist realism. Practically the only form of resistance in this period was to keep silent. Some authors remained completely silent, some worked on translations, some wrote for their desk drawer for themselves and presented texts for publication that adhered to the officially sanctioned model. Keeping silent can also be interpreted as resistance in the name of aesthetic authenticity. The subsequent period that lasted until the 1970s is characterised by an increase in liberty in society, including literature. The body of norms of socialist realism was relaxed. Literary activities were controlled by writers’ organisations according to the guidelines provided by the Communist Party. Different aesthetic and ideological camps of writers emerged and competed with one another. The era of keeping silent and writing for one’s desk drawer ended. Public resistance, which was united by the question of relating to literature that preceded the Soviet era, was at the centre of this period. The fight for aesthetic freedom and literature that was free of ideology carried on throughout this period and was finally won by 1968–69. By that time, socialist realism had essentially ended in Estonian literature. In place of it, avant-gardism, modernism and broader realism prevailed. In place of Marxism-Leninism, non-Marxist ways of thinking had become important: first and foremost existentialism, but also Buddhism, Zen Buddhism, Taoism and classical psychoanalysis. Secondly, resistance was put up in the name of Estonian national unity and national memory. This was resistance in the name of authors who had been banished from the history of literature and of bringing back the pre-war metalanguage. This was concerned with modern writers (symbolists, decadents, impressionists, expressionists) in Estonian literature from the early 20th century. Generally speaking, this struggle was successful. The third struggle was waged in the name of creative freedom and the writer’s inner authenticity. Here political freedom and independence in general intertwined as ideals, with the Soviet system and any kind of system as the enemy that oppresses human freedom and independence: institutions and the state, machines and rationality, conformism and the middle-class way of life. The third period of resistance began at the start of the 1970s and continued until perestroika. The so-called tightening of the screws took place throughout the state during this period and Russification was adopted as a new orientation starting in the mid-1970s. On the other hand, a socialist consumer society took shape in Estonia, characterised by Communist Party membership for the sake of one’s career and openly double morality. Ideological censorship in literature was intensified, along with the partial steering of literature by way of Party documents. Such new conditions brought new variants of resistance to the fore. Nationalist resistance and resistance to Russification came to the fore in the 1970s and 1980s. Open struggle receded into the background. Covert resistance, primarily within individual texts, which had previously been insignificant, became central. This resistance used joint secret codes common to writers and readers (allusions, irony, parodies, and other such devices). The struggle continued in the name of a neutral metalanguage that is not ideologised. Resistance criticism, so to speak, took shape: keeping silent about negative assessments that could potentially have provided the basis for political accusations, and keeping silent about secret codes in texts that the authorities did not have to know about. The struggle for words and concepts without ideological connotations at the level of phenomena that were ideologically important for the Soviet regime was a continuing theme: the Republic of Estonia, the blue, black and white colour combination, expatriates, deportation, and other such concepts.

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