Stuart Hawkins

Megafaunal meiolaniid horned turtles survived until early human settlement in Vanuatu, Southwest Pacific

Meiolaniid or horned turtles are members of the extinct Pleistocene megafauna of Australia and the southwest Pacific. The timing and causes of their extinction have remained elusive. Here we report the remains of meiolaniid turtles from cemetery and midden layers dating 3,100/3,000 calibrated years before present to approximately 2,900/2,800 calibrated years before present in the Teouma Lapita archaeological site on Efate in Vanuatu. The remains are mainly leg bones; shell fragments are scant and there are no cranial or caudal elements, attesting to off-site butchering of the turtles. The new taxon differs markedly from other named insular terrestrial horned turtles. It is the only member of the family demonstrated to have survived into the Holocene and the first known to have become extinct after encountering humans.

Lapita Diet in Remote Oceania: New Stable Isotope Evidence from the 3000-Year-Old Teouma Site, Efate Island, Vanuatu

Remote Oceania was colonized ca. 3000 BP by populations associated with the Lapita Cultural Complex, marking a major event in the prehistoric settlement of the Pacific Islands. Although over 250 Lapita sites have been found throughout the Western Pacific, human remains associated with Lapita period sites are rare. The site of Teouma, on Efate Island, Vanuatu has yielded the largest burial assemblage (n = 68 inhumations) of Lapita period humans ever discovered, providing a unique opportunity for assessing human adaptation to the environment in a colonizing population. Stable isotope ratios (δ13C, δ15N, δ34S) of human bone collagen from forty-nine Teouma adults were analyzed against a comprehensive dietary baseline to assess the paleodiet of some of Vanuatus earliest inhabitants. The isotopic dietary baseline included both modern plants and animals (n = 98) and prehistoric fauna from the site (n = 71). The human stable isotope data showed that dietary protein at Teouma included a mixture of reef fish and inshore organisms and a variety of higher trophic marine (e.g. marine turtle) and terrestrial animals (e.g. domestic animals and fruit bats). The domestic pigs and chickens at Teouma primarily ate food from a C3 terrestrial environment but their δ15N values indicated that they were eating foods from higher trophic levels than those of plants, such as insects or human fecal matter, suggesting that animal husbandry at the site may have included free range methods. The dietary interpretations for the humans suggest that broad-spectrum foraging and the consumption of domestic animals were the most important methods for procuring dietary protein at the site. Males displayed significantly higher δ15N values compared with females, possibly suggesting dietary differences associated with labor specialization or socio-cultural practices relating to food distribution.

A high-order tangential basis algorithm for electromagnetic scattering by curved surfaces

We describe, analyze, and demonstrate a high-order spectrally accurate surface integral algorithm for simulating time-harmonic electromagnetic waves scattered by a class of deterministic and stochastic perfectly conducting three-dimensional obstacles. A key feature of our method is spectrally accurate approximation of the tangential surface current using a new set of tangential basis functions. The construction of spectrally accurate tangential basis functions allows a one-third reduction in the number of unknowns required compared with algorithms using non-tangential basis functions. The spectral accuracy of the algorithm leads to discretized systems with substantially fewer unknowns than required by many industrial standard algorithms, which use, for example, the method of moments combined with fast solvers based on the fast multipole method. We demonstrate our algorithm by simulating electromagnetic waves scattered by medium-sized obstacles (diameter up to 50 times the incident wavelength) using a direct solver (in a small parallel cluster computing environment). The ability to use a direct solver is a tremendous advantage for monostatic radar cross section computations, where thousands of linear systems, with one electromagnetic scattering matrix but many right hand sides (induced by many transmitters) must be solved.

A spectrally accurate algorithm for electromagnetic scattering in three dimensions

In this work we develop, implement and analyze a high-order spectrally accurate algorithm for computation of the echo area, and monostatic and bistatic radar cross-section (RCS) of a three dimensional perfectly conducting obstacle through simulation of the time-harmonic electromagnetic waves scattered by the conductor. Our scheme is based on a modified boundary integral formulation (of the Maxwell equations) that is tolerant to basis functions that are not tangential on the conductor surface. We test our algorithm with extensive computational experiments using a variety of three dimensional perfect conductors described in spherical coordinates, including benchmark radar targets such as the metallic NASA almond and ogive. The monostatic RCS measurements for non-convex conductors require hundreds of incident waves (boundary conditions). We demonstrate that the monostatic RCS of small (to medium) sized conductors can be computed using over one thousand incident waves within a few minutes (to a few hours) of CPU time. We compare our results with those obtained using method of moments based industrial standard three dimensional electromagnetic codes CARLOS, CICERO, FE-IE, FERM, and FISC. Finally, we prove the spectrally accurate convergence of our algorithm for computing the surface current, far-field, and RCS values of a class of conductors described globally in spherical coordinates.

Diet and Human Mobility from the Lapita to the Early Historic Period on Uripiv Island, Northeast Malakula, Vanuatu

Vanuatu was first settled ca. 3000 years ago by populations associated with the Lapita culture. Models of diet, subsistence practices, and human interaction for the Lapita and subsequent occupation periods have been developed mainly using the available archaeological and paleoenvironmental data. We test these models using stable (carbon, nitrogen, and sulfur) and radiogenic (strontium) isotopes to assess the diet and childhood residency of past communities that lived on the small (<1 km2) island of Uripiv, located off the northeast coast of Malakula, Vanuatu. The burials are from the initial Lapita occupation of the island (ca. 2800–2600 BP), the subsequent later Lapita (LL, ca. 2600–2500 BP) and post-Lapita (PL, ca. 2500–2000 BP) occupations, in addition to a late prehistoric/historic (LPH, ca. 300–150 BP) occupation period. The human stable isotope results indicate a progressively more terrestrial diet over time, which supports the archaeological model of an intensification of horticultural and arboricultural systems as local resources were depleted, populations grew, and cultural situations changed. Pig diets were similar and included marine foods during the Lapita and PL periods but were highly terrestrial during the LPH period. This dietary pattern indicates that there was little variation in animal husbandry methods during the first 800 years of prehistory; however, there was a subsequent change as animal diets became more controlled in the LPH period. After comparison with the local bioavailable 87Sr/86Sr baseline, all of the Lapita and LPH individuals appeared to be ‘local’, but three of the PL individuals were identified as “non-local.” We suggest that these “non-locals” moved to the island after infancy or childhood from one of the larger islands, supporting the model of a high level of regional interaction during the post-Lapita period.

A high-order algorithm for multiple electromagnetic scattering in three dimensions

We describe a fully discrete high-order algorithm for simulating multiple scattering of electromagnetic waves in three dimensions by an ensemble of perfectly conducting scattering objects. A key component of our surface integral algorithm is high-order tangential approximation of the surface current on each obstacle in the ensemble. The high-order nature of the algorithm leads to relatively small numbers of unknowns, which allows us to use either a direct method or an iterative boundary decomposition method for simulations of multiple scattering. We demonstrate the algorithm using both of these techniques for near and well separated obstacles. Using a small computing cluster (with 20 processors), we simulate multiple scattering by up to 125 objects for frequencies in the resonance region, and by paired obstacles of diameter 20 to 30 times the incident wavelength. Many physically important problems, such as scattering by atmospheric aerosols or ice crystals, involve multiple scattering by ensembles of particles, each particle having its own distinct shape, but with all particles fitting a stochastic description with a small number of fixed parameters in local spherical coordinates. We demonstrate our algorithm for multiple scattering by ensembles of such unique particles, whose stochastic description corresponds to computer models of ice crystals and dust particles.

A Hybrid High-Order Algorithm for Radar Cross Section Computations

We describe a high-order method for computing the monostatic and bistatic radar cross section (RCS) of a class of three-dimensional targets. Our method is based on an electric field surface integral equation reformulation of the Maxwell equations. The hybrid nature of the scheme is due to approximations based on a combination of tangential and nontangential basis functions on a parametric reference spherical surface. A principal feature of the high-order algorithm is that it requires solutions of linear systems with substantially fewer unknowns than existing methods. We demonstrate that very accurate RCS values for medium (electromagnetic-) sized scatterers can be computed using a few tens of thousands of unknowns. Thus linear systems arising in the high-order method for low to medium frequency scattering can be solved using direct solves. This is extremely advantageous in monostatic RCS computations, for which transmitters and receivers are co-located and hence the discretized electromagnetic linear system must be solved for hundreds of right-hand sides corresponding to receiver locations. We demonstrate the high-order convergence of our method for several three-dimensional targets. We prove the high-order spectral accuracy of our approximations to the RCS for a class of perfect conductors described globally in spherical coordinates.

Human Palaeoecological Interactions and Owl Roosting at Tron Bon Lei, Alor Island, Eastern Indonesia

ABSTRACT We report on tetrapod (Reptilia, Amphibia, Mammalia, Aves) vertebrates recovered during excavations at Tron Bon Lei rockshelter on the south coast of Alor Island, eastern Indonesia. These include both archaeological specimens recovered from a 1 m² test pit dating from ∼21 kya cal BP to the late Holocene, and a modern eastern barn owl deposit recovered nearby. To discern between the depositional processes that accumulated the small numbers of micro- and macrovertebrate remains from the archaeological deposits, the taphonomic signature of the natural assemblage was quantified and compared to the archaeological record. The taphonomic data indicates that the tetrapod archaeofaunal remains are a combination of barn owl predation of microfauna and human predation of larger fauna. This approach provides new information on human-tetrapod interactions on Alor in Wallacea during the late Quaternary, including an apparent increase in cave site use and hunting intensity during the Pleistocene-Holocene transition, sea turtle butchery and probable transport, and extinctions of previously unknown giant to large rat species.

Three dimensional electromagnetic scattering T-matrix computations

The infinite T-matrix method is a powerful tool for electromagnetic scattering simulations, particularly when one is interested in changes in orientation of the scatterer with respect to the incident wave or changes of configuration of multiple scatterers and random particles, because it avoids the need to solve the fully reconfigured systems. The truncated T-matrix (for each scatterer in an ensemble) is often computed using the null-field method. The main disadvantage of the null-field based T-matrix computation is its numerical instability for particles that deviate from a sphere. For large and/or highly non-spherical particles, the null-field method based truncated T-matrix computations can become slowly convergent or even divergent. In this work, we describe an electromagnetic scattering surface integral formulation for T-matrix computations that avoids the numerical instability. The new method is based on a recently developed high-order surface integral equation algorithm for far field computations using basis functions that are tangential on a chosen non-spherical obstacle. The main focus of this work is on the mathematical details required to apply the high-order algorithm to compute a truncated T-matrix that describes the scattering properties of a chosen perfect conductor in a homogeneous medium. We numerically demonstrate the stability and convergence of the T-matrix computations for various perfect conductors using plane wave incident radiation at several low to medium frequencies and simulation of the associated radar cross of the obstacles.

Avifauna from the Teouma Lapita Site, Efate Island, Vanuatu, Including a New Genus and Species of Megapode

Abstract: The avifauna of the Teouma archaeological site on Efate in Vanuatu is described. It derives from the Lapita levels (3,000–2,800 ybp) and immediately overlying middens extending to ∼2,500 ybp. A total of 30 bird species is represented in the 1,714 identified specimens. Twelve species are new records for the island, which, added to previous records, indicates that minimally 39 land birds exclusive of passerines were in the original avifauna. Three-fourths of the 12 newly recorded species appear to have become extinct by the end of Lapita times, 2,800 ybp. The avifauna is dominated by eight species of columbids (47.5% Minimum Number Individuals [MNI]) including a large extinct tooth-billed pigeon, Didunculus placopedetes from Tonga, and a giant Ducula sp. cf. D. goliath from New Caledonia. Seabirds are rare despite the coastal location of the site. Fowl are important contributors to the Teouma avifauna, with the human-introduced Red Junglefowl Gallus gallus accounting for 15% MNI and present in all sampled layers. There are two species of megapodes (∼10% of MNI), with the extant Vanuatu Megapode Megapodius layardi most abundant and represented at all levels in the deposits. A substantially larger extinct megapode, Mwalau walterlinii, n. gen., n. sp., is present only in the Lapita midden area, where it is relatively rare. This extinct species was larger than all extant megapodes but smaller than the extinct Progura gallinacea from Australia, with proportions most similar to those of Alectura, and was a volant bird. The remaining significant faunal component is rails, with four species present, of which Porphyrio melanotus was the most abundant. Rare but notable records include an undescribed large rail; a parrot, Eclectus sp. cf. E. infectus; a hornbill, Rhyticeros sp. cf. R. plicatus; and a coucal, Centropus sp. indet., all conservatively considered likely to be conspecific with known taxa elsewhere in Melanesia.