Asymmetrical Tail Research Articles

Postcranial disparity of galeaspids and the evolution of swimming speeds in stem-gnathostomes.

Galeaspids are extinct jawless relatives of living jawed vertebrates whose contribution to understanding the evolutionary assembly of the gnathostome bodyplan has been limited by absence of postcranial remains. Here, we describe Foxaspis novemura gen. et sp. nov., based on complete articulated remains from a newly discovered Konservat-Lagerstätte in the Early Devonian (Pragian, ∼410 Ma) of Guangxi, South China. F. novemura had a broad, circular dorso-ventrally compressed headshield, slender trunk and strongly asymmetrical hypochordal tail fin comprised of nine ray-like scale-covered digitations. This tail morphology contrasts with the symmetrical hypochordal tail fin of Tujiaaspis vividus, evidencing disparity in galeaspid postcranial anatomy. Analysis of swimming speed reveals galeaspids as moderately fast swimmers, capable of achieving greater cruising swimming speeds than their more derived jawless and jawed relatives. Our analyses reject the hypothesis of a driven trend towards increasingly active food acquisition which has been invoked to characterize early vertebrate evolution.

Left-right asymmetry and attractor-like dynamics of dog’s tail wagging during dog-human interactions

SummaryTail wagging plays an important role in social interactions, e.g., dogs show asymmetrical tail wagging in response to different social stimuli. However, the effects of social cues on tail wagging and the intrinsic organization of wagging behavior remain largely unknown. Here, we developed a platform using a deep-learning-based motion-tracking technique to extract and analyze the movement trajectory of a dog’s tail tip during dog-human interactions. Individual dogs exhibited unique and stable wagging characteristics. We further found that tail wagging developed asymmetry toward the right side over three days of dog-human interactions, suggesting that it is a time-sensitive indicator of social familiarity. In addition, wagging appeared to follow an attractor-like dynamic process consisting of stable states and unstable, transitional states. Together, these results revealed sophisticated characteristics and organization of a dog’s tail-wagging behavior during interactions with humans, providing a useful paradigm for studying dogs’ social behaviors and the underlying neural mechanisms.

A new ichthyodectiform fish (Actinopterygii: Teleostei) from the Arlington Member (mid-Cenomanian) of the Upper Cretaceous Woodbine Formation in Texas, USA

Based on a nearly complete skeleton from the Arlington Member (mid-Cenomanian) of the Upper Cretaceous Woodbine Formation in Texas, USA, a new fossil fish, Bardackichthys carteri gen. et sp. nov. (Actinopterygii: Ichthyodectiformes), is described. Our phylogenetic analyses show the suborder Ichthyodectoidei (containing Amakusaichthys, Chirocentrites, Chiromystus, Cladocyclus, Cooyoo, Eubiodectes, Ghrisichthys, Gillicus, Heckelichthys, Ichthyodectes, Saurocephalus, Saurodon, Xiphactinus, Unamichthys, and Vallecillichthys) to be a cohesive, Cretaceous group of ichthyodectiforms that also includes B. carteri gen. et sp. nov. Furthermore, our study reveals a monophyletic assemblage within Ichthyodectoidei consisting of Bardackichthys gen. nov., Amakusaichthys, and Heckelichthys, where the clade is assigned to a new ichthyodectiform family, Bardackichthyidae fam. nov. With large eyes, stout body, anterodorsally directed mouth, and large asymmetrical tail, B. carteri gen. et sp. nov. was most likely a powerful swimmer capable of ambushing small pelagic fishes near the water surface in brackish environments.

Ontogeny of head and caudal fin shape of an apex marine predator: The tiger shark (Galeocerdo cuvier).

How morphology changes with size can have profound effects on the life history and ecology of an animal. For apex predators that can impact higher level ecosystem processes, such changes may have consequences for other species. Tiger sharks (Galeocerdo cuvier) are an apex predator in tropical seas, and, as adults, are highly migratory. However, little is known about ontogenetic changes in their body form, especially in relation to two aspects of shape that influence locomotion (caudal fin) and feeding (head shape). We captured digital images of the heads and caudal fins of live tiger sharks from Southern Florida and the Bahamas ranging in body size (hence age), and quantified shape of each using elliptical Fourier analysis. This revealed changes in the shape of the head and caudal fin of tiger sharks across ontogeny. Smaller juvenile tiger sharks show an asymmetrical tail with the dorsal (upper) lobe being substantially larger than the ventral (lower) lobe, and transition to more symmetrical tail in larger adults, although the upper lobe remains relatively larger in adults. The heads of juvenile tiger sharks are more conical, which transition to relatively broader heads over ontogeny. We interpret these changes as a result of two ecological transitions. First, adult tiger sharks can undertake extensive migrations and a more symmetrical tail could be more efficient for swimming longer distances, although we did not test this possibility. Second, adult tiger sharks expand their diet to consume larger and more diverse prey with age (turtles, mammals, and elasmobranchs), which requires substantially greater bite area and force to process. In contrast, juvenile tiger sharks consume smaller prey, such as fishes, crustaceans, and invertebrates. Our data reveal significant morphological shifts in an apex predator, which could have effects for other species that tiger sharks consume and interact with.

Dynamic changes in the sperm quality of Mytilus galloprovincialis under continuous thermal stress.

Global warming is an increasingly serious problem underlying ecological change in marine flora and fauna. Mytilus galloprovincialis is an intertidal species that colonizes coasts in moderate and warm climates, and can thus withstand extreme climatic conditions; however, it successfully reproduces only within a certain temperature range. The effects of prolonged exposure to 28 °C, a temperature unsuitable for breeding activity, on sperm quality were evaluated in this study. Such heat stress induced the following: a significant reduction in concentration; a biphasic pattern of motility and mitochondrial membrane potential that first increased, and then collapsed; a decrease in the intracellular calcium concentration; a rapid increase in lipid peroxidation that was normalized after the third week of heat stress; an increase in DNA fragmentation after the third week of heat stress; and atypical morphology (i.e., sperm with a globular head, asymmetrical tail, and acrosome loss). Currently, these elevated-temperature conditions are achieved along the Mediterranean coast during the late summer, when the reproductive activity of M. galloprovincialis is suspended after massive spawning in the spring. The increasing global temperature, however, may shift their breeding season, thus significantly impacting marine ecosystems and mussel production.

Anatomy and Evolution of Heterocercal Tail in Lamniform Sharks

Lamniformes is a small shark group consisting of 15 extant species with remarkably diverse lifestyles and a wide range in heterocercal tail morphology. The caudal fin morphology must be related to their lifestyle because the tail is a main locomotive structure in sharks, but such relationships have remained largely uninvestigated. Here, the morphology-lifestyle relationship in lamniforms is examined through phylogenetic mapping. This study suggests that, within Lamniformes, caudal fins with a more horizontally directed curvature of the vertebral column are plesiomorphic, whereas those with a large dorsally directed curvature of the vertebral column are apomorphic. It also shows that caudal fins with posteriorly directed hypochordal rays are plesiomorphic, and that those with ventrally directed hypochordal rays are apomorphic within Lamniformes. Four basic caudal fin types are recognized in lamniforms on the basis of these skeletal variables in which one corollary is that the evolution of external morphology of caudal fin does not necessarily correspond to the evolution of its skeletal anatomy. This study also demonstrates that specific lifestyles seen in different lamniforms are indeed correlative with different caudal fin types in which a less asymmetrical heterocercal tail is a derived feature in lamniforms that evolved for fast swimming to capture fast swimming prey.

Volumetric imaging of shark tail hydrodynamics reveals a three-dimensional dual-ring vortex wake structure

Understanding how moving organisms generate locomotor forces is fundamental to the analysis of aerodynamic and hydrodynamic flow patterns that are generated during body and appendage oscillation. In the past, this has been accomplished using two-dimensional planar techniques that require reconstruction of three-dimensional flow patterns. We have applied a new, fully three-dimensional, volumetric imaging technique that allows instantaneous capture of wake flow patterns, to a classic problem in functional vertebrate biology: the function of the asymmetrical (heterocercal) tail of swimming sharks to capture the vorticity field within the volume swept by the tail. These data were used to test a previous three-dimensional reconstruction of the shark vortex wake estimated from two-dimensional flow analyses, and show that the volumetric approach reveals a different vortex wake not previously reconstructed from two-dimensional slices. The hydrodynamic wake consists of one set of dual-linked vortex rings produced per half tail beat. In addition, we use a simple passive shark-tail model under robotic control to show that the three-dimensional wake flows of the robotic tail differ from the active tail motion of a live shark, suggesting that active control of kinematics and tail stiffness plays a substantial role in the production of wake vortical patterns.

Behavioural responses of dogs to asymmetrical tail wagging of a robotic dog replica

Recent evidence suggests that bilateral asymmetry in the amplitude of tail wagging of domestic dogs (Canis familiaris) is associated with approach (right wag) versus withdrawal (left wag) motivation and may be the by-product of hemispheric dominance. We consider whether such asymmetry in motion of the tail, a crucial appendage in intra-specific communication in all canids, provides visual information to a conspecific leading to differential behaviour. To evaluate this, we experimentally investigated the approach behaviour of free-ranging dogs to the asymmetric tail wagging of a life-size robotic dog replica. Our data, involving 452 separate interactions, showed a significantly greater proportion of dogs approaching the model continuously without stopping when the tail wagged to the left, compared with a right wag, which was more likely to yield stops. While the results indicate that laterality of a wagging tail provides behavioural information to conspecifics, the responses are not readily integrated into the predicted behaviour based on hemispheric dominance.

On the tail ofErrivaspisand the condition of the caudal fin in heterostracans

AbstractArticulated caudal fins of heterostracans are preserved in very rare cases. Their morphology and internal structure are completely unknown for the majority of species. One of the few preserved caudal fins belongs to the Early Devonian pteraspididErrivaspis waynensisfrom the Welsh Borderland, UK. There are two different reconstructions of the tail: (1) strongly asymmetric, with a considerably longer ventral lobe, and a rather concave posterior margin (e.g. White 1935); and (2) almost symmetrical with an only slightly longer ventral lobe and a small notch in the posterior margin (e.g.Blieck 1984). A new reconstruction of theErrivaspiscaudal fin, based on a detailed study of White's specimens is presented here. The ventral lobe is longer than the dorsal one but not so much as in White's reconstruction, and the notch in the posterior margin of the fin is less deep. The comparatively massive ventral lobe and ‘en echelon’ arrangement of three digitations, supporting the fin web and branching off from this lobe, indicate the hypocercal condition of the asymmetrical tail. The same internal structure is present in other heterostracans with nearly symmetrical caudal fins (e.g.Doryaspis,Nahanniaspis,DinaspidellaandAthenaegis) where all, or most, of the intermediate digitations branch off from the ventral lobe.

Binary Phase Diagram of Triphenylene Derivatives: The Role of Hydrogen Bonds

ABSTRACT In this study, the binary phase diagram of two triphenylene derivatives is investigated by using differential scanning calorimetry (DSC), optical polarizing microscopy (OPM), and wide-angle x-ray scattering (WAXS). The triphenylene derivatives studied are based on hexa-alklyoxy-triphenylene. One compound in the binary mixture HAT6 has six symmetrical hexyloxy tails each containing six carbon atoms. The other compound, HAT6-C10UC6, has one asymmetrical tail bearing a urea functionality at a specific distance from the aromatic core. The introduction of this asymmetrical H-bonding unit into the structure results in a complete disruption of liquid crystallinity while a “pseudo re-entrant” phenomenon is observed in the binary mixture phase diagram.

Analysis of the Switching Characteristics of PZT Films by First Order Reversal Curve Diagrams

A new type of characterization of ferroelectric switching using First Order Reversal Curve (FORC) diagrams based on recording of minor hysteresis loops has been recently proposed. We apply this method to polycrystalline and epitaxial PZT thin films measured under various conditions and compare them to PZT ceramics. In each case we have been able to separate the reversible and irreversible contributions to switching and discuss the most dominant of them in relation to hysteresis loop shapes and ferroelectric switching mechanisms. The FORC diagrams of fatigued PZT exhibit features in agreement with its hysteresis probed at nanoscale and confirm a degradation mechanism based on local imprint. The asymmetrical tail present on measured FORC diagrams has been explained in terms of a nucleation-growth switching process triggered by latent nuclei. All these findings attest the usefulness of the FORC diagrams for both characterizing various types of samples as well as the elucidation of ferroelectrics’ physics.

Mechanisms of helical swimming: asymmetries in the morphology, movement and mechanics of larvae of the ascidianDistaplia occidentalis

A great diversity of unicellular and invertebrate organisms swim along a helical path, but it is not well understood how asymmetries in the body shape or the movement of propulsive structures affect a swimmer's ability to perform the body rotation necessary to move helically. The present study found no significant asymmetries in the body shape of ascidian larvae (Distaplia occidentalis) that could operate to rotate the body during swimming. By recording the three-dimensional movement of free-swimming larvae, it was found that the tail possessed two bends, each with constant curvature along their length. As these bends traveled posteriorly, the amplitude of curvature changes was significantly greater in the concave-left direction than in the concave-right direction. In addition to this asymmetry, the tail oscillated at an oblique angle to the midline of the trunk. These asymmetries generated a yawing moment that rotated the body in the counterclockwise direction from a dorsal view, according to calculations from hydrodynamic theory. The tails of resting larvae were bent in the concave-left direction with a curvature statistically indistinguishable from the median value for tail curvature during swimming. The flexural stiffness of the tails of larvae, measured in three-point bending, may be great enough to allow the resting curvature of the tail to have an effect on the symmetry of kinematics. This work suggests that asymmetrical tail motion is an important mechanism for generating a yawing moment during swimming in ascidian larvae and that these asymmetries may be caused by the tail's bent shape. Since helical motion requires that moments also be generated in the pitching or rolling directions, other mechanisms are required to explain fully how ascidian larvae generate and control helical swimming.

Population profile of brain asymmetry in rats after intra-amniotic administration of vasopressin

The effects of intra-amniotic administration of 1-desamino-8-D-arginine-vasopressin (DDAVP) at 14 days of embryogenesis on movement asymmetry in neonatal and mature mongrel white rats were studied. Controls consisted of intact and sham-operated animals, as well as rats given intra-amniotic saline. The population profile of asymmetry was assessed in terms of the tail position of rats aged two days, and also in terms of the direction of excursions in a T-maze in three-months males. The proportion of animals showing asymmetrical tail poses was no more than 36% in controls; the ratio of left-asymmetrical and right-asymmetrical intact rats was 2:1. DDAVP increased the number of rats with asymmetrical tail poses by a factor of 1.5-2.6, and right-asymmetrical individuals became predominant. This effect was demonstrated graphically as a bell-shaped dose-response curve with a peak response at doses of 3 x 10(-8) and 3 x 10(-6) mg. The selection probability for the right-hand side of the maze in experimental animals was 0.71 +/- 0.06, which was significantly higher than in animals of the three control groups, which showed no preference for the direction of excursions. These results indicate lateralization of the action of DDAVP in the developing central nervous system, leading to a predominance of right-sided motor responses in neonatal and mature rats.

Computational Simulation of Photoluminescence and Reflectivity Spectra of a Strained Layer Superlattice

ABSTRACTPowerful mathematical tools have made it possible to simulate the optical spectra of strained layer superlattices. The results of these calculations are compared to experimental ones obtained on ZnS-ZnSe SLSs. The photoluminescence spectra is dominated by a single major peak with a long asymmetrical tail end or a secondary peak at lower energies. This secondary peak or tail end is attributed to the disorder within the superlattice. The PL spectra is simulated using a novel model based on the following parameters; the free exciton energy, the strain/stress state between the lattice constants, the probability of an occurrence of a dislocation, the probability that the dislocation generates and propagates and the critical thickness. The reflectivity simulation is also novel and is based on an impedance in a spatial dispersion model. It is essential to consider the strain that is induced in the SL, when the dielectric constant is dependent on the variation of the frequency near the fundamental transition energies. As a result only normal incidence is considered.

On the locomotion of ascidian tadpole larvae

This paper describes the locomotor movements of the tadpole larvae of the ascidians Ciona and Dcndrodoa and the associated electrical activity of the caudal muscle cells. Although very different in size and trunk shape, both larvae show essentially the same two movement patterns; symmetrical swimming and asymmetrical tail flicks. Swimming movements at tailbeat frequencies up to 40 Hz and forward speeds up to 10 L s (in the Reynold's number range 5·25) involve large lateral movements of the tail, and large yaw of the trunk. Tail oscillations are produced by muscle cells arranged in three segmented rows along the tail, coupled by gap junctions. Swimming is driven by axons innervating anterior ventral muscle cells. The second type of movement, single or multiple tail flicks, is driven by axons innervating dorsal muscle cells, all of which are innervated along the length of the tail. The middle row of muscle cells is not innervated. This small scale oscillatory swimming system is compared with those of chordates and larvacean tunicates, and it is concluded that both of these are very different from that of the ascidian tadpole.

Caudal Fin Locomotion in Ray-finned Fishes: Historical and Functional Analyses

SYNOPSIS. Over the last 20 years, considerable progress has been made in quantifying the movement of the body during locomotion by aquatic vertebrates, and in defining the role of axial musculature in producing these kinematic patterns. Relatively little is known, however, about how specific internal structural features of the axial system in fishes affect body kinematics, and how such structural and functional features have changed during evolution. The major theme of this paper is that historical, phylogenetic patterns in the axial musculoskeletal system need to be integrated with experimental and functional data in order to understand the design of the locomotor apparatus in vertebrates. To illustrate this proposition, the evolution of the tail in ray-finned fishes is presented as a case study in phylogenetic and functional analysis of the vertebrate axial musculoskeletal system. Traditionally, the evolution of the tail in ray-finned fishes has been viewed as a transformation from a primitively heterocercal (functionally asymmetrical) tail to a homocercal tail in which the axis of rotation during locomotion was vertical, generating a symmetrical thrust. Both phylogenetic and functional approaches are used to examine this hypothesis. Major osteological and myological features of the tail in ray-finned fishes are mapped onto a phylogeny of ray-finned fishes to discern historical sequences of morphological change in the axial musculoskeletal system. A key event in locomotor evolution was the origin of the hypochordal longitudinalis muscle, the only intrinsic caudal muscle with a line of action at an appreciable angle to the body axis. This muscle originated prior to the origin of a caudal skeleton bearing both hypaxial and epaxial fin ray supports. The hypochordal muscle is proposed to be a key component of the axial musculoskeletal system that allows most fishes to modulate caudal function and decouples external morphological symmetry from functional symmetry. Experimental data (strain gauge recordings from tail bones, and electromyographic recordings from intrinsic and extrinsic caudal muscles) corroborate this interpretation and suggest that functional symmetry in the tail of ray-finned fishes is not predictable from skeletal morphology alone, but depends on the activity of the hypochordal longitudinalis muscle and on locomotor mode. The homocercal teleost tail may thus function asymmetrically.

Spermatozoa and phylogeny of Curculionoidea (Coleoptera)

In the examined families of Curculionoidea (Coleoptera), the sperm, although characteristic of typical pterygote insects, shows a few peculiarities that suggest Curculionoidea to be a homogeneous group. The curculionid sperm, in fact, always follows a similar structural design, without any variation. For example, it has 2 mitochondrial derivatives of different sizes, the larger of which is almost completely filled with a crystalline protein, the other being more moderately crystallized and almost completely occupied by cristae, and 2 accessory bodies of different sizes that are made up of a crystalline portion, crescent-shaped in section, and a “puff”-like expansion that is of different consistency, shape, and symmetry in various cases. The different extensions of the accessory bodies seem, therefore, to compensate for the high degree of asymmetry due to the largely different sizes of the 2 mitochondrial derivatives. The examined families and subfamilies can be arranged in 2 groups: Rhynchitidae appear drastically isolated, because they have a peculiar “9 + 9 + 0” axoneme, and show, moreover, a limited degree of asymmetry in the tail organelles. The remaining families and subfamilies are more closely related to one another by the presence of a “9 + 9 + 2” classical axoneme and by the same degree of asymmetry in the tail, typical of curculionid sperm. Among them, Apionidae are distinguished for the space containing the extraacrosomal layer, which may be hollow or absent, a twice-stepped nucleus-tail connection, and a thick glycocalyx at the end of the tail. The Curculionidae conserve primitive characters, such as the 3-layered acrosomal complex and “9 + 9 + 2” axoneme, but also present a high degree of differentiation in the shape of the asymmetrical tail organelles. There appear to be 3 clusters: the first cluster includes Brachyderinae, Leptopiinae, Gymnetrinae, Cryptorhynchinae, Rhynchophorinae. The second cluster includes Scolytidae, Cleoninae, Hylobiinae. The third cluster is more numerous and heterogeneous and shows 3 subgroups. The first of these includes only Otiorhynchinae. The sum of their characters shows that they have most of the common features of primitive curculionids; however the differences between a genus and another are so large that they could be assigned to different subfamilies. The second subgroup includes Hyperinae, Pissodinae, Magdalinae, Ceutorhynchinae and Cossoninae, and the third group includes Cioninae, Anthonominae, and Barimae. It is difficult to arrange these subfamilies (frequently recognizable for a different combination of the same recurrent characters) in a phylogenetic tree. However, we observed signs of primitiveness in Brachyderinae (small crescents) and their cluster; advanced ones in the third and fourth clusters all evolved with different patterns of the puff-like expansion of one of the accessory bodies, the latter being the most peculiar character of the superfamily. A tentative reconstruction is given. The functional significance of the variations seems to be that Rhynchitidae seem to be evolving towards immotility (their spermatozoon, in fact, is able to produce only a series of vibrations, not the progressive series of waves as in all other species studied), while all the other families and subfamilies show no signs of alterations in axonemal pattern and motility. The main evolutionary pathways observed in them are towards compensating for an exaggerated lengthening and a greater degree of asymmetry in the tail organelles: one of them, the major mitochondrial derivative, acts as a rigid axis, while the axoneme produces undulations in the opposite portion of the axonemal section.

A note on current sheet stress balance in the geomagnetic tail for asymmetrical tail lobe plasma conditions

Previous analyses of current sheet equilibrium in the geomagnetic tail based on the one-dimensional field approximation have assumed symmetrical inflow plasma conditions in the two tail lobes. However, recent observations show that large asymmetries in density can exist in the tail lobes due to effects controlled by IMF B y , and simultaneous flow shears are also expected from theory. Here it is shown that the current sheet equilibrium condition can be readily generalized to include lobe plasma asymmetry under the simplifying assumption that all particles incident on the current sheet are transmitted through it. The result is expressed in a form which emphasizes the physical equivalence of stress balance by anisotropic plasma pressure and by net flow through the current sheet. The former case occurs for symmetrical lobe conditions and balance is expressed in terms of the marginal firehose stability condition. The latter case occurs if one lobe dominates, when the field-aligned plasma flow speed in the field line rest frame must equal the tail lobe Alfvén speed. Results are illustrated by a simple example in which the inflow plasmas are approximated as cold ion beams of unequal density and speed. It is shown that equilibrium solutions cease to exist for sufficiently large inflow velocity shears, but that in practice this condition is most unlikely to be encountered in the tail.

XPS‐study of the interaction of air‐oxygen with platinum surfaces

AbstractThe differences in the XPS spectra of the band regions Pt4f, Ols and VB between cleaned and air exposed polycrystalline platinum samples are discussed. After defined exposure it appears PtOads. and a cation configuration of 5d8 6s1 for platinum. This can be shown by line shapes, especially by the double peak structure of oxygen lines and by the asymmetrical tail on the high binding energy region of Pt4f combined with valence band results.

Trapped Electron in the Irradiated Single Crystal of Ice Doped with Some Impurities: Its Formation and Photobleaching at 77°K

It is found that single crystals of ice doped with 10−4–10−2M ammonium fluoride and alkali fluoride color considerably by gamma ray irradiation at 77°K. Their spectra all are the same as the one in the pure crystal (the peak is at 6400 Å), and the largest optical density is about 6 times as high as that in the pure crystal. These enhanced absorptions represent an increase of the concentration of the trapped electrons in the doped samples. D2O crystals doped with NH4F show a similar increase, having the same spectrum as that in pure D2O crystal (the maximum yield is about 10 times of that in the pure H2O crystal). The increased electrons are not due to those produced in the locally amorphous parts. Other samples doped with such impurities as NH4Cl, NH4OH, KCl, NaOH, etc., do not show such coloring. Trapping sites for these electrons are considered. Photobleaching of the pure and the doped crystal shows simple and uniform decays and the original spectrum is almost unchanged by the stimulation at any wavelength. The spectrum represents only one species trapped in one definite form of potential. The trapped electron in the pure and the doped crystal show a low bleaching efficiency for the wavelength corresponding to the peak of the spectrum. Wavelength dependence of the bleaching quantum efficiency shows a steep rise from roughly 5000 Å to the higher energy side. The peak of the optical absorption spectrum is a transition to the bound state. The asymmetrical tail in the high energy side of the spectrum corresponds to the transition to the higher excited levels, bound or in the continuum.