The role of the fish otolith mass asymmetry in acoustic functionality is studied. The saccular, lagenar and utricular otoliths are weighted in two species of the Black Sea rays, 15 species of the ...Black Sea teleost fish and guppy fish. The dimensionless otolith mass asymmetry
χ is calculated as ratio of the difference between masses of the right and left paired otoliths to average otolith mass.
In the most fish studied the otolith mass asymmetry is within the range of −0.2
<
χ
<
+
0.2 (<20%). We do not find specific fish species with extremely large or extremely small otolith asymmetry. The large otoliths do not belong solely to any particular side, left or right. The heavier otoliths of different otolithic organs can be located in different labyrinths. No relationship has been found between the magnitude of the otolith mass asymmetry and the length (mass, age) of the animal. The suggested fluctuation model of the otolith growth can interpret these results. The model supposes that the otolith growth rate varies slightly hither and thither during lifetime of the individual fish. Therefore, the sign of the relative otolith mass asymmetry can change several times in the process of the individual fish growth but within the range outlined above.
Mathematical modeling shows that acoustic functionality (sensitivity, temporal processing, sound localization) of the fish can be disturbed by the otolith mass asymmetry. But this is valid only for the fish with largest otolith masses, characteristic of the bottom and littoral fish, and with highest otolith asymmetry. For most fish the values of otolith mass asymmetry is well below critical values. Thus, the most fish get around the troubles related to the otolith mass asymmetry. We suggest that a specific physicochemical mechanism of the paired otolith growth that maintains the otolith mass asymmetry at the lowest possible level should exist. However, the principle and details of this mechanism are still far from being understood.
The masses and the area sizes of the otoliths for the utriculus, sacculus and lagena of 15 species of the Black Sea fish are analyzed. Morphometrical otolith regularities are derived and their ...functional and ecomorphological explanations are suggested. The otolith regularities are summarized in four otolith rules: (1) the masses of the otoliths gradually increase with the fish growth. (2) The mass ratio of the sacculus and utriculus or the sacculus and lagena otoliths does not change with the fish growth. (3) The ratio between the otolith area
s and the otolith mass
m is described by the exponential equation
s=
αm
2/3. (4) The ratio between the otolith and macula sizes does not change with fish growth. Mathematical modeling of the otolith displacement responses to the acoustic and the instant force stimuli is performed. Based on the modeling the functional and ecomorphological explanations of the otolith regularities are suggested: (1) the greater the otolith mass, the higher the acoustic sensitivity at low frequencies and the sharper the frequency–response curve at its maximum. (2) The separation between maxima of the frequency–response curves for the saccular and lagenar otoliths remains virtually constant with the fish growth. (3) The bottom and littoral fish have better auditory capabilities than the pelagic fish. (4) The sensitivity to vestibular stimuli for greater otoliths is higher but the response is slower. The corresponding acceleration resolution for greater otoliths is higher and the range of accelerations in which the otolith organ can operate is narrower. (5) The relative vestibular sensitivities of the utriculus, sacculus and lagena otolith organs remain constant with fish growth. (6) The otolith organs of the bottom and littoral fish are tuned to different accelerations and possess different functional properties. The otolith organs of pelagic fish are adapted to a limited range of accelerations and are less sensitive to low accelerations as compared to the bottom and littoral fish.
Mathematical modeling suggests that relatively large values of otolith mass asymmetry in fishes can alter acoustic functionality and may be responsible for abnormal fish behavior when subjected to ...weightlessness during parabolic or space flight D.V. Lychakov, Y.T. Rebane, Otolith mass asymmetry in 18 species of fish and pigeon, J. Grav. Physiol. 11 (3) (2004) 17–34; D.V. Lychakov, Y.T. Rebane, Fish otolith mass asymmetry: morphometry and influence on acoustic functionality, Hear. Res. 201 (2005) 55–69. The results of morphometric studies of otolith mass asymmetry suppose that the absolute value and the sign of the otolith mass asymmetry can change many times during the growth of individual fish within the range ±20% D.V. Lychakov, Y.T. Rebane, Otolith mass asymmetry in 18 species of fish and pigeon, J. Grav. Physiol. 11 (3) (2004) 17–34; D.V. Lychakov, Y.T. Rebane, Fish otolith mass asymmetry: morphometry and influence on acoustic functionality, Hear. Res. 201 (2005) 55–69. This implies that the adverse effects of otolith asymmetry on acoustic and vestibular functionality could change during the lifetime of an individual fish. The aims of the present article were to examine the nature of otolith mass asymmetry fluctuation and to quantify otolith mass asymmetry in a large number of teleost fishes to verify our previous measurements.
A dimensionless measure of otolith mass asymmetry,
χ, was calculated as the difference between the masses of the right and left paired otoliths divided by average otolith mass. Saccular otolith mass asymmetry was studied in 59 Mediterranean teleost species (395 otolith pairs), 14 Black Sea teleost species (42 otolith pairs), red drum (196 otolith pairs) and guppy (30 otolith pairs). Utricular otolith mass asymmetry was studied in carp (103 otolith pairs) and goldfish (45 otolith pairs). In accordance with our previous results the value of
χ did not depend on fish size (length or mass), systematic or ecological position of the fish, or otolith growth rate. In the great majority of the fishes studied, the saccular otolith
χ was small ∣
χ∣
<
0.05 (or <5%). Mathematical modeling indicates that values of
χ vary among individual fish, but that the value is probably stable during a fish’s lifetime.
A dimensionless measure of otolith mass asymmetry, χ, was calculated as the difference between the masses of the right and left paired otoliths divided by average otolith mass. Saccular otolith mass ...asymmetry was studied in eight flatfish species (110 otolith pairs) and compared with data from a previously published study on roundfishes. As in the case of symmetrical fishes, the absolute value of χin flatfishes does not depend on fish length and otolith growth rate, although otolith mass and the absolute value of otolith mass difference are correlated with fish length. The values of χwere between −0·2 and +0·2 in 96·4% of flatfishes studied. The mean ±s.e. value of χin flatfishes was significantly larger than in standard bilaterally symmetrical marine fishes (‘roundfishes’), respectively 0·070 ± 0·006 and 0·040 ± 0·006. The most prominent distinction is the existence of downside prevalence of saccular otolith mass in flatfishes, which contrasts with no right–left prevalence in roundfishes found in a previous study. In the right‐eyed flatfishes (Soleidae), the left saccular otoliths are heavier than the right otoliths. In the left‐eyed flatfishes (Bothidae and Citharidae), the right saccular otoliths are heavier than the left otoliths. Not all flatfishes, however, fit in this design: 11·8% of flatfishes studied had the heavier saccular otoliths in the upside labyrinth and 5·4% of flatfishes had no otolith mass asymmetry (within the accuracy of the analysis). At the same time, the more mobile flatfishes (bothids and citharids) have more symmetrical and, hence, more precisely organized saccular otolith organs than the bottom‐associated flatfishes (soleids). It is possible to assume that the value of the otolith asymmetry is not only correlated with flatfish placement in a particular family, or position of eyes, but also may correlate with general aspects of their ecology. Mathematical modelling indicated that for most flatfishes one‐side saccular prevalence had no substantial significance for sound processing. On the other hand, calculations showed that 49% of flatfishes (but only 14·5% of roundfishes) have |χ| which exceed the critical level and, in principle, could sense the difference between the static displacement of the large and small paired otoliths. At that, the number of the soleids that could sense this difference is greater than the number of the bothids and citharids, 84 and 27%, respectively.
The phenomenon of the emission efficiency droop of InGaN/GaN quantum wells (QWs) in light-emitting diode
p
-
n
structures is studied. The influence exerted by two basic processes on the emission ...efficiency is considered: tunnel injection into a QW and incomplete lateral carrier localization in compositional fluctuations of the band-gap width in InGaN. The sharp efficiency peak at low currents and the rapid efficiency droop with increasing current are due to tunneling leakage currents along extended defects, which appear as a result of a local increase in the electron hopping conductivity via the depletion
n
region and a corresponding local decrease in the height of the injection
p
barrier. A less sharp efficiency peak and a weak, nearly linear, decrease in efficiency with increasing current are caused by incomplete lateral carrier localization in the QW due to slowing-down of the carrier energy-relaxation rate and to the nonradiative recombination of mobile carriers.
We suggest a system of two wells connected with Charge Asymmetric Resonance Tunneling (CART) as a basic element of light emitting diode (LED) structure for semiconductors with different masses of ...electrons and holes. The system consists of an emitter of electrons, an emitter of holes and an active layer. The hole emitter is coupled with the active in such a way that holes can be freely supplied into the active layer without a barrier. The electron emitter is coupled to the active layer via a barrier. The barrier design uses the charge asymmetric resonance tunneling phenomenon which allows to make the barrier transparent for electrons and blocking for holes. Advantages of this design are: the increased capture efficiency of the electrons into the active layer due to direct resonance tunneling of the electrons from the electron emitter on bound electron level in the active quantum well, the suppression of electron leakage into the hole emitter, the elimination of the parasitic light generated outside the active layer, and the electron emitter acts also as a good current spreading layer. First results of experimental investigation and theoretical modeling of the CART LED devices are reported.
A model of the exciton bound to stacking faults (SF) in GaN is suggested. It is shown that SFs are potential wells (depth ≈︂120 meV and width ≈︂10 Å) for electrons and potential barriers (height ≈︂60 ...meV and width ≈︂10 Å) for holes. The binding energy of excitons at SF found from variational calculation is 45 meV. The 364 nm line in GaN photoluminescence at 4 K is attributed to excitons bound to SFs.
Topological interaction of shallow impurities with dislocations is studied. This problem is related with the violation of the topological structure of the crystal lattice by dislocations. The ...interaction results in a topological gauge field that is confined inside the dislocation cores but influences the shallow impurity states in vicinity of the dislocations via an Aharonov‐Bohm effect‐like way. It is found that this effect reduces the binding energies of shallow centers localized at unsplit dislocations. For split dislocations, the interaction of shallow‐level centers with the stacking faults existing between partials is important and is taken into account on the base of the δ‐potential quantum well model of the stacking faults.
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