De Hoop Research Articles

Proleptus obtusus Dujardin, 1845 (Nematoda: Physalopteridae) from the puffadder shyshark Haploblepharus edwardsii (Scyliorhinidae) from off South Africa.

Specimens of the physalopterid nematode Proleptus obtusus Dujardin, 1845 collected from the intestine of the puffadder shyshark Haploblepharus edwardsii (Voigt) off De Hoop Nature Reserve, Cape Province, South Africa, made possible the redescription this little-known species. The SEM study of the cephalic end revealed the presence of circumoral denticles and some oral structures (lateral transverse mounds on the inner surface of pseudolabia, dorsolateral and ventrolateral band-like formations or lamellae surrounding the buccal cavity) not previously reported for any species of Proleptus. The shape of the tip of the right spicule is considered to be the only reliable feature for differentiating P. obtusus from the closely related P. acutus Dujardin, 1845. The finding of the former in H. edwardsii represents a new host record.

Errata and addendum

June 2002 TLE article “Challenges of complex media” by Levin and De Hoop there was an inadvertent omission of the reference for the captions of Figures 5 and 6.

Applications of Directional Wavefield Decomposition, Phase Space, and Path Integral Methods to Seismic Wave Propagation and Inversion

Recently, de Hoop and coworkers developed an asymptotic, seismic inversion formula for application in complex environments supporting multi-pathed and multi-mode wave propagation (DE HooP et al., 1999; DE HooP and BRANDSBERG-DAHL, 2000; STOLK and DE HooP, 2000). This inversion is based on the Born/Kirchhoff approximation, and employs the global, uniform asymptotic extension of the geometrical method of “tracing rays” to account for caustic phenomena. While this approach has successfully inverted the multicomponent, ocean-bottom data from the Valhall field in Norway, accounting for severe focusing effects (DE HooP and BRANDSBERG-DAHL, 2000), it is not able to account properly for wave phenomena neglected in the “high-frequency” limit (i.e., diffraction effects) and strong scattering effects. To proceed further and incorporate wave effects in a nonlinear inversion scheme, the theory of directional wavefield decomposition and the construction of the generalized Bremmer coupling series are combined with the application of modern phase space and path (functional) integral methods to, ultimately, suggest an inversion algorithm which can be interpreted as a method of “tracing waves.” This paper is intended to provide the seismic community with an introduction to these approaches to direct and inverse wave propagation and scattering, intertwining some of the most recent new results with the basic outline of the theory, and culminating in an outline of the extended, asymptotic, seismic inversion algorithm. Modeling at the level of the fixed-frequency (elliptic), scalar Helmholtz equation, exact and uniform asymptotic constructions of the well-known, and fundamentally important, square-root Helmholtz operator (symbol) provide the most important results.

A new species of rust fungus, Uromyces strumariae (Uredinales: Pucciniaceae), on Strumaria gemmata (Amaryllidaceae) from the Western Cape, South Africa

A new autoecious, macrocyclic, species of rust fungus, Uromyces strumariae, is described from Strumaria gemmata (Amaryllidaceae). The new species is readily distinguished from U. badius, the only other Uromyces species known to attack members of the Amaryllidaceae in South Africa, by its telia which develop separately from the uredinia (the uredinia become telia in U. badius), and the presence of paraphyses in the telia (absent in U. badius). It is currently known only from De Hoop Nature Reserve at the western most edge of its host's distribution, in the winter rainfall region of South Africa. Furthermore, U. badius has also recently been collected on H. pubescens L.f. subsp. pubescens, representing a new host record.

Gnathia pantherina sp. n. (Crustacea: Isopoda: Gnathiidae), a temporary ectoparasite of some elasmobranch species from southern Africa.

Haematophagous larvae of a gnathiid isopod were collected from the gills, nares and buccal cavity of a single leopard catshark Poroderma pantherinum (Smith, 1838) at Jeffreys Bay and five puffadder shysharks Haploblepharus edwardsii (Voight, 1832) and one blackspotted electric ray Torpedo fuscomaculata Peters, 1855, at the De Hoop Nature Reserve on the South African south coast. Larvae were kept in fresh seawater until their moult into adult stages. The morphology of the adult males did not conform to that of any known species and they are therefore described as Gnathia pantherina sp. n. The descriptions of the adult male, female and praniza larva are based on light and scanning electron microscopy observations. Characteristic features of this species include the large size of all the final life-cycle stages, the deeply divided mediofrontal process of the male, the morphology of the pylopods and maxillipedes of the female, and the number of teeth on the mandibles (eight) and maxillules (seven) of the praniza larvae.

Temperature fields generated by impulsive interfacial heat sources

Theoretical study of temperature fields generated by an instantaneous line heat source located at the interface between two different media is presented. Green’s functions for the temperature fields in both media are derived using the Cagniard–de Hoop method. It is shown that in a more conductive medium the temperature field has the character of a wave originating at the point source, while in the less conductive medium the temperature field can be decomposed into the “spherical” wave emanating from the two-dimensional point source and the “head” wave arising due to the heat exchange through the interface. The derived analytical expressions are accompanied by the diagrams of the wave surfaces of temperature fields and numerical examples.

Modeling of interfacial temperature effects due to an impulsive line heat source

Temperature fields generated by an instantaneous line heat source in the medium consisting of two half spaces of different thermal properties are modeled. The analytical calculations employ the Green functions for an impulsive line source derived previously using the Cagniard–de Hoop technique. The analytical model predicts the change of sign of the reflected temperature field along the interface for a certain range of parameters. It has also been found that for the heat source located in the less conductive medium the temperature peak arrival can occur before the peak from the source temperature field. The analytical results are found to be in excellent agreement with numerical modeling using the finite difference method.

An encapsulated haemogregarine from the evileye pufferfish in South Africa

Developmental stages of a haemogregarine were found within polychromatocytes and erythrocytes in Giemsa-stained blood smears from six evileye pufferfish (Amblyrhynchotes honckenii) caught at Koppie Alleen in the De Hoop Nature Reserve, South Africa. This unusual haemogregarine, Haemogregarina (sensu lato) koppiensis sp. nov., was characterized by encapsulated gamonts with recurved tails, features more common in haemogregarines infecting amphibian and reptilian erythrocytes than in those from fish. Haemogregarina koppiensis is only the third species of fish haemogregarine to have been described from South Africa.

An analysis of the indirect boundary element method for seismic modelling

An indirect boundary element method has been used to compute seismic wavefields in layered media. The advantages of this technique over numerical grid methods are that it satisfies radiation conditions, incorporates free surface effects, solves viscoelastic problems and can handle arbitrary source types. The technique is more appropriate for models with high aspect ratios and a limited number of layers. The computational cost increases with the number of layers and frequency content. Examples are presented in this study to illustrate some of the features of the technique. Seismograms are computed for SH and P–SV line sources in 2-D earth models. Finite-difference and the Cagniard–de Hoop methods are used to test the accuracy of the technique. Even though the computation time for the method is several times greater than finite differences, the technique becomes cost effective as the number of computed shot-gathers increases. The technique also allows computation of constant offset gathers at a small additional cost which is very expensive to do by using finite differences.

Reflection and refraction of a transient temperature field at a plane interface using Cagniard-de Hoop approach.

An instantaneous line heat source located in the medium consisting of two half-spaces with different thermal properties is considered. Green's functions for the temperature field are derived using the Laplace and Fourier transforms in time and space and their inverting by the Cagniard-de Hoop technique known in elastodynamics. The characteristic feature of the proposed approach consists in the application of the Cagniard-de Hoop method to the transient heat conduction problem. The idea is suggested by the fact that the Laplace transform in time reduces the heat conduction equation to a Helmholtz equation, as for the wave propagation. Derived solutions exhibit some wave properties. First, the temperature field is decomposed into the source field and the reflected field in one half-space and the transmitted field in the other. Second, the laws of reflection and refraction can be deduced for the rays of the temperature field. In this connection the ray concept is briefly discussed. It is shown that the rays, introduced in such a way that they are consistent with Snell's law do not represent the directions of heat flux in the medium. Numerical computations of the temperature field as well as diagrams of rays and streamlines of the temperature field are presented.

The reflected and transmitted acoustic field excited by a supersonic source in a two media configuration

The acoustic wave field due to a supersonic motion of a rigid object over a half-space is investigated. The analysis presented leads to closed form expressions for the reflected and transmitted conical waves as separate contributions. The linearized acoustic field equations are applied to obtain representations for the fields in a combined Laplace–Fourier transform domain. To these representations, which are mapped into the proper form, we apply the Cagniard–de Hoop technique in order to find closed form time–domain solutions for the reflected and transmitted acoustic fields. Attention is focused on supersonic effects, so the analysis concentrates on application of the Cagniard–de Hoop technique to obtain closed form space–time domain expressions from the contributions of poles, appearing in the transform domain representation for the reflected and transmitted acoustic wave field. It turns out that these pole contributions, next to wave solutions of the conical type also can give rise to headwaves, associated with the reflected conical wave. Numerical results for the reflected as well as the transmitted conical wave field are presented for an air–sea configuration with supersonic source velocities up to MACH 5.

On: “A new insight into the reciprocity principle” (Børge Arntsen and José M. Carcione, GEOPHYSICS, 65, 1604–1612).

Reciprocity is an important property of elastodynamic, electromagnetic, and acoustic wavefields. Combined with optimization techniques, reciprocity theorems can be regarded as providing the basic ingredients to imaging and inversion methods in geophysical exploration and remote sensing (de Hoop, M. V. and de Hoop, A. T., 2000). Furthermore, reciprocity serves as the basis for the elimination procedures of surface‐related multiples in marine seismic data processing (Fokkema and van den Berg, 1993). In view of all this, a thorough and elucidating discussion on the configurations to and the conditions under which reciprocity applies, and what reciprocity leads to, like the recent paper by Arnsten and Carcione (2000), serves a useful purpose. In this paper, also a number of interesting applications are worked out in detail. The aim of this discussion is to indicate briefly how some of the results obtained in that paper are related to the ones that the present author has presented in de Hoop (1995), a reference that does not appear in Arntsen and Carcione (2000).

Reply by the authors to the discussion by A. T. de Hoop

The discussion by A. T. de Hoop is highly appreciated, and we regret to have omitted the reference to de Hoop (1995). Part of the developments in our paper are similar to those of de Hoop and Stam (1988). Mittet and Hokstad (1995) have also presented similar results for the purely elastic case. These are both properly referenced in the Introduction.

Syntactic definiteness in the grammar of Modern Hebrew

Definiteness has often been assumed to play a role in syntax, most notably in relation to various definiteness effects and case alternations (Belletti 1988; De Hoop 1992; and many others). The question whether this involves a semantic property that is relevant in syntax, or an independent syntactic representation of definiteness, remains to a large extent unanswered. This paper shows that, on the one hand, Hebrew provides independent evidence for assuming a definiteness feature in syntax, and on the other hand, this formal definiteness does not simply correlate with semantic definiteness, and there is no simple one-to-one mapping between the two kinds of definiteness. The second part of this paper focuses on the Hebrew object marker et, which appears only in front of DPs having the syntactic definiteness feature. I argue that et' fulfills a requirement for structural case that Hebrew verbs cannot assign, and that this requirement is related to the representation of definiteness as a formal feature and not to any semantic property. In this light I consider Belletti's (1988) theory of abstract partitive and show that Hebrew object marking seems to provide evidence against it.

Dutch Scrambling and the Strong-Weak Distinction

It was first argued by Kerstens (1975) that the meaning of indefinite NP objects in Dutch is affected by scrambling. Kerstens claimed that whether an indefinite NP is [+quantificational] or not (in the sense of Milsark 1974) depends on its absolute position in the structure: it is [+quantificational] iff it is outside VP at S-Structure. This hypothesis has more recently been revived and extended to other languages by De Hoop (1992) and Diesing (1992). In this paper, I will attempt to show that there is insufficient empirical support for this generalization. Although the meaning of a structure containing an indefinite object NP undoubtedly varies with the position of the NP relative to other constituents, it is doubtful whether it can be shown that the semantics of the NP itself depends on its absolute position.

On the Structure of Indefinite Possessives

I present evidence that indefinite possessives display some peculiar semantic properties distinguishing them from other types of possessive DPs. In particular, indefinite possessives do not license contextual interpretations, which are instead available for the corresponding definite possessives and possessive partitives. This semantic asymmetry argues against existing theories according to which indefinite possessives are structurally equivalent to definite possessives (Kayne (1994)) or to possessive partitives (Barker (1998); Zamparelli (1998)).The unavailability of contextual interpretations for indefinite possessives is accounted for in Storto ([to appear]) in terms of the discourse semantics of these DPs: indefinite possessives cannot be interpreted as discourse-specific DPs. This semantic peculiarity is due to the interaction between their partitive structure and the indefiniteness of the nominal embedded under of The implementation of this idea proposed in Storto ([to appear]), however, is not compatible with the "classic" formulation of the Partitive Constraint. I show that this proposal can be maintained under a reformulation of the Partitive Constraint along the lines of de Hoop (1997), and draw some conclusions on the structural complxity of indefinite possessives in a crosslinguistic perspective.

Some Aspects of Optimality in Natural Language Interpretation

In a series of papers, Petra Hendriks, Helen de Hoop, and Henriette de Swart Lave applied optimality theory (OT) to semantics. These authors argue that there is a fundamental difference between the form of OT as used in syntax on the one hand and its form as used in semantics on the other hand. Whereas in the first case OT takes the point of view of the speaker, in the second case the point of view of the hearer is taken. The aim of this paper is to argue that the proper treatment of OT in natural language interpretation has to take both perspectives at the same time. A conceptual framework is established that realizes the integration of both perspectives. It will be argued that this framework captures the essence of the Gricean maxims and gives a precise explication of Atlas & Levinson's (1981) idea of balancing between informativeness and efficiency in natural language processing. The ideas are then applied to resolve some puzzles in natural language interpretation.

Coastal distribution, movements and site fidelity of right whales Eubalaena australis off South Africa, 1969–1998

Counts and photographs of right whales Eubalaena australis taken on aerial surveys of the southern coast of South Africa between 1969 and 1998 have been used to examine patterns of coastal distribution between successive 20-minute bins of longitude. Some bins had consistently higher densities of whales than others, cither of cows with calves or of unaccompanied adults. Apart from an overall increase in density, the centre of distribution shifted 40–60 minutes of longitude to the west over the 30-year period. Most (>93.4%) female calves born on the South African coast returned there to have their first calf, but only 52.9% were photographed with their first calf in the same or an adjacent bin as that of their natal year. This compares with 60.9% of multigravid females that occurred in the same or an adjacent bin as that of their previous calf, with significantly more west-ward (368) than eastward (255) shifts in distribution between calves. Approximate residence times for cow-calf pairs in the De Hoop region were 12–105 (average = 59.0 ± 3.9) days: dispersal rates were low between July and September but increased thereafter. Incidental records of coastwise movement were mainly to the west, but were probably influenced by the survey direction. Distances moved ranged from 6 to 202 km. at average speeds of 0.08–2.89 km·h−1. Theodolite tracking of undisturbed groups of right whales from Cape Columbine produced a similar range of swimming speeds. Inter-calf movements of cows between the survey area and the coasts to both east and west indicated that the entire South African coast could be considered as one homogeneous winter assemblage area for right whales.

Indefinites between Predication and Reference

No abstract.

New host records for Haemogregarina bigemina from the coast of southern Africa

One hundred and fifty intertidal fishes were captured at Jeffreys Bay in July 1996 and February 1997, and at De Hoop Nature Reserve in April 1997, South Africa. Caffrogobius caffer, Chorisochismus dentex, Clinus superciliosus, and Clinus cottoides were all parasitised by haematophagous larvae of the isopod, Gnathia africana, and between 22 and 81% of fishes were infested with 1 to 76 larvae each. Of those fishes examined for blood parasites, 35/46 (76.1%) had an intraerythrocytic haemogregarine identified as Haemogregarina (sensu lato) bigemina, but only Clinus superciliosus and Clinus cottoides were infected. Gamonts of the haemogregarine, some undergoing syzygy, were also present in 50% of stained batches of the anterior hindgut contents of G. africana larvae which had fed on Clinus superciliosus, but were absent from larvae taken from Clinus cottoides and Chorisochismus dentex. This study provides new host records for H. bigemina and further evidence that gnathiid isopods play a role in the transmission of the haemogregarine.