bluuebunny/crossref_metadata_2025 huggingface dataset:
Strain effects, electronic parameters, and electronic structures in modulation-doped InxGa1−xAs/InyAl1−yAs coupled step-rectangular quantum wells
Authors: Choo D. C. , Kim T. W. , Yoo K. H. , Meining C. J. , McCombe B. D.
Published: December 2003

The electronic parameters of a two-dimensional electron gas (2DEG) in unique modulation-doped InxGa1−xAs/InyAl1−yAs coupled step-rectangular quantum wells were investigated by using the Shubnikov–de Haas (SdH)–Van der Pauw Hall effect and cyclotron resonance measurements. The SdH measurements and the fast Fourier transformation results for the SdH data at 1.5 K indicated electron occupation of two subbands in the quantum well. The electron effective masses of the 2DEG were determined from the cyclotron resonance measurements, and their values qualitatively demonstrated the nonparabolicity effects of the conduction band on the 2DEGs in the quantum wells. The electronic subband energies, the energy wave functions, and the Fermi energies were calculated by using a self-consistent method taking into account exchange-correlation effects, together with strain and nonparabolicity effects. These results can help in understanding potential applications of unique InxGa1−xAs/InyAl1−yAs coupled step-rectangular quantum wells in high-speed electronic and long-wavelength optoelectronic devices.
Gate-controlled electron g factor in an InAs-inserted-channel In0.53Ga0.47As/In0.52Al0.48As heterostructure
Authors: Nitta Junsaku , Lin Yiping , Akazaki Tatsushi , Koga Takaaki
Published: November 2003

The electron g factor in an InAs-inserted-channel In0.53Ga0.47As/In0.52Al0.48As heterostructure is studied by measuring the angle dependence of magnetotransport properties. The gate voltage dependence of the g factor is obtained from the coincidence method. The g-factor values are surprisingly smaller than the g-factor value of bulk InAs, and close to the bare g-factor value of In0.53Ga0.47As. A large change in the g factor is observed by applying the gate voltage. The gate voltage dependence is not simply explained by the energy dependence of the g factor.
Cathodoluminescence of Cu(In,Ga)Se2 thin films used in high-efficiency solar cells
Authors: Romero Manuel J. , Ramanathan Kannan , Contreras Miguel A. , Al-Jassim Mowafak M. , Noufi Rommel , Sheldon Peter
Published: December 2003

Cathodoluminescence spectroscopy and spectrum imaging are employed to investigate Cu(In,Ga)Se2 (CIGS) thin films used in high-efficiency solar cells. We have found a nonuniform spatial distribution for the photon energy. The shift by decade of the emission spectrum is also found to depend systematically on the location of excitation. In addition, the photon energy at grain boundaries is not affected by the external excitation. A model for radiative recombination to be applied to these chalcopyrite compounds should explain these results, and some suggestions are considered.
Epitaxial growth of quaterphenyl thin films on gold(111)
Authors: Müllegger S. , Salzmann I. , Resel R. , Winkler A.
Published: November 2003

The crystal structure and molecular arrangement of para-quaterphenyl (4P) grown on single crystalline Au(111) was investigated over a wide thickness range. The molecular arrangement in the first monolayer, as investigated with low energy electron diffraction, shows a highly regular structure. This wetting layer is defined by adsorbate–substrate interactions and forms a prestage for the epitaxial growth of 4P single crystalline islands, as observed in x-ray diffraction. Two similar orientations of the 4P bulk phase are observed, with the (211) and (311) planes parallel to the Au(111) surface. The alignment of the molecules was kept unchanged from the first monolayers up to a film thickness of 200 nm.
Magnetic tunnel junctions with a tunnel barrier formed by N2O plasma
Authors: Shim Heejae , Park J. M. , Kim K. P. , Cho B. K. , Kim Jin-Tae , Park Y.
Published: November 2003

We investigated a magnetic tunnel junction (MTJ) with a tunnel barrier formed by N2O plasma. Compared with a MTJ with a tunnel barrier formed by conventional O2 plasma, the MTJ fabricated with N2O plasma shows much lower specific junction resistance and a comparably high tunneling magnetoresistance ratio. In particular, it was found that N2O plasma oxidation is quite important in the junction with a thin tunnel barrier, for which O2 plasma cannot be used. From x-ray photoelectron spectroscopy, we observed that N2O plasma oxidation leads to the slight nitridation of the Al2O3 layer and significantly reduces the oxidation of the bottom electrode, especially for a thin tunnel barrier. Thus, we conclude that the use of N2O plasma in forming the tunnel barrier is effective for achieving a low junction resistance and for minimizing the oxidation of the bottom electrode during plasma oxidation in MTJs.
Focusing light with a single subwavelength aperture flanked by surface corrugations
Authors: Garcı́a-Vidal F. J. , Martı́n-Moreno L. , Lezec H. J. , Ebbesen T. W.
Published: November 2003

In this letter, we show theoretically how a single subwavelength aperture surrounded by a finite array of grooves made on a metallic film can act as a “lens” for electromagnetic radiation within a certain frequency range. The dependence of this resonant focusing ability with the geometrical parameters defining the structure is extensively analyzed. Universal curves for the depth, length and width of the focus as a function of the number of grooves are also given.
Unusually narrowed emission lines from a single crystal of thiophene/phenylene co-oligomer
Authors: Shimizu Kouki , Hoshino Daichi , Hotta Shu
Published: November 2003

We have observed unusually narrowed emission lines from a single crystal of thiophene/phenylene co-oligomer. Very narrow lines (0.07 nm of linewidth) arise around 493 and 466 nm by photopumping a long slender region of the crystal. The relevant emissions are due to the lasing caused by high gain media. The photopumping configuration of the crystal in the present studies is useful in examining how the relevant lines are gain narrowed under each specific measurement.
Three-dimensional simple cubic woodpile photonic crystals made from chalcogenide glasses
Authors: Feigel A. , Veinger M. , Sfez B. , Arsh A. , Klebanov M. , Lyubin V.
Published: November 2003

Construction of three-dimensional photonic crystals for optical wavelengths presents many technological and material science challenges. The submicron-feature-size sculpturing must be performed in high-refractive-index materials. We present the fabrication and optical characterization of ∼750 nm feature-size simple cubic woodpile photonic crystals from As2S3 (n≈2.2). The process is based on interference lithography and the layer-by-layer construction.
Influence of various donors on nonlinear I–V characteristics of tin dioxide ceramics
Authors: Dhage S. R. , Ravi V.
Published: November 2003

The influence of different donors such as Nb, Ta, Sb, and V on nonlinear current (I)-voltage (V) relations of tin dioxide ceramics is investigated. The room-temperature resistivity (ρ), nonlinear coefficient (α), breakdown electric field (EB) and barrier height (ΦB) are calculated as a function of donor content. The present system contains fewer additives as compared to ZnO varistor wherein small quantities of variety of metal oxides are added. Optimum doping of antimony-doped samples shows promising behavior for low-voltage varistor application.
Ion-irradiation-induced direct ordering of L1 FePt phase
Authors: Lai Chih-Huang , Yang Cheng-Han , Chiang C. C.
Published: November 2003

A highly ordered L10 FePt phase was directly achieved by using 2 MeV He-ion irradiation without conventional postannealing. The coercivity greater than 5700 Oe can be obtained after disordered FePt was irradiated at the beam current of several μA/cm2 with the ion doses of 2.4×1016 ions/cm2. The high beam-current-density results in direct beam heating on samples. In addition, the irradiation-induced heating process provides efficient microscopic energy transfer and creates excess point defects, which significantly enhances the diffusion and promotes the formation of the ordered phase. Consequently, the direct ordering of FePt took place by using ion-irradiation heating at temperature as low as 230 °C. Due to the feasibilities of the fast temperature rise and the focused beam size, this ion-irradiation heating treatment can be potentially used as an alternative technique for the rapid thermal annealing and for the magnetic patterning.
Split ring resonator-based left-handed coplanar waveguide
Authors: Martı́n F. , Bonache J. , Falcone F. , Sorolla M. , Marqués R.
Published: November 2003

In this letter, a planar left-handed propagating medium consisting of a coplanar waveguide (CPW) inductively coupled to split ring resonators (SRR) and periodically loaded with narrow metallic wires is proposed. The wires make the structure behave as a microwave plasma with a negative effective permittivity which covers a broad frequency range. The negative permeability required to achieve left-handed wave propagation is provided by the rings in the vicinity of their resonant frequency. The result is a structure which allows negative wave propagation in a narrow frequency band. The transmission coefficient measured in a fabricated prototype device exhibits very low insertion losses in the pass band and high-frequency selectivity. Since rings are much smaller than signal wavelength at resonance and can be easily tuned, SRR-CPW-based structures are of interest for the design of very compact microwave circuits based on left handedness.
Formation of atomic-scale germanium quantum dots by selective oxidation of SiGe/Si-on-insulator
Authors: Li P. W. , Liao W. M. , Lin S. W. , Chen P. S. , Lu S. C. , Tsai M.-J.
Published: November 2003

A complementary metal-oxide-semiconductor-compatible method is proposed to form atomic-scale germanium (Ge) quantum dots (<10 nm) for application in single-electron devices or optical devices. The formation of Ge quantum dots is realized by the Ge atoms’ segregation and agglomeration during thermal oxidation of Si1−xGex alloys. The size and distribution of the Ge dots are determined by conditions of thermal oxidation process and Ge content in the alloys. An average Ge-dot size of 5.1 nm with standard deviation of 1.79 nm and a comparatively uniform spatial distribution (dot density of 7.9×1011 cm−2) could be obtained by selective oxidation of Si0.85Ge0.15/Si-on-insulator structure.
Photoluminescence properties of in situ Tm-doped AlxGa1−xN
Authors: Hömmerich U. , Nyein Ei Ei , Lee D. S. , Steckl A. J. , Zavada J. M.
Published: November 2003

We report on the photoluminescence (PL) properties of in situ Tm-doped AlxGa1−xN films (0⩽x⩽1) grown by solid-source molecular-beam epitaxy. It was found that the blue PL properties of AlxGa1−xN:Tm greatly change as a function of Al content. Under above-gap pumping, GaN:Tm exhibited a weak blue emission at ∼478 nm from the 1G4→3H6 transition of Tm3+. Upon increasing Al content, an enhancement of the blue PL at 478 nm was observed. In addition, an intense blue PL line appeared at ∼465 nm, which is assigned to the 1D2→3F4 transition of Tm3+. The overall blue PL intensity reached a maximum for x=0.62, with the 465 nm line dominating the visible PL spectrum. Under below-gap pumping, AlN:Tm also exhibited intense blue PL at 465 and 478 nm, as well as several other PL lines ranging from the ultraviolet to near-infrared. The Tm3+ PL from AlN:Tm was most likely excited through defect-related complexes in the AlN host.
Femtosecond timing measurement and control using ultrafast organic thin films
Authors: Naruse Makoto , Mitsu Hiroyuki , Furuki Makoto , Iwasa Izumi , Sato Yasuhiro , Tatsuura Satoshi , Tian Minquan
Published: December 2003

We show a femtosecond timing measurement and control technique using a squarylium dye J-aggregate film, which is an organic thin film that acts as an ultrafast two-dimensional optical switch. Optical pulse timing is directly mapped to space-domain position on the film, and the large area and ultrafast response offer a femtosecond-resolved, large dynamic range, real-time, multichannel timing measurement capability. A timing fluctuation (jitter, wander, and skew) reduction architecture is presented and experimentally demonstrated.
Magnetization reversal study of CoCrPt alloy thin films on a nanogranular-length scale using magnetic transmission soft x-ray microscopy
Authors: Im Mi-Young , Fischer Peter , Eimüller Thomas , Denbeaux Greg , Shin Sung-Chul
Published: November 2003

We have investigated element-specific magnetization reversal behavior of (Co83Cr17)87Pt13 alloy thin films with a lateral resolution of 35-nm using magnetic transmission soft x-ray microscopy. We report that the magnetization switching is carried out by a random nucleation process that can be attributed to individual grains. We found evidence of a large distribution of the switching fields at the nanogranular-length scale, which has to be considered seriously for applications of CoCrPt systems as high-density magnetic storage materials.
Enhanced magnetoelectric effects in laminate composites of Terfenol-D/Pb(Zr,Ti)O3 under resonant drive
Authors: Dong Shuxiang , Cheng Jinrong , Li J. F. , Viehland D.
Published: December 2003

We have found that laminate composites consisting of longitudinally magnetized magnetostrictive Terfenol-D and longitudinally poled piezoelectric Pb(Zr,Ti)O3 layers have dramatically enhanced magnetoelectric effects when driven near resonance. The maximum induced magnetoelectric voltage at resonance was ∼10 Vp/Oe, which is ∼102 times higher than previous reports at subresonant frequencies.
Optical properties of ZnO/GaN heterostructure and its near-ultraviolet light-emitting diode
Authors: Yu Qing-Xuan , Xu Bo , Wu Qi-Hong , Liao Yuan , Wang Guan-Zhong , Fang Rong-Chuan , Lee Hsin-Ying , Lee Ching-Ting
Published: December 2003

We report on photoluminescence in a ZnO/GaN heterostructure, which showed a donor–acceptor pair emission band at 3.270 eV and the longitudinal optical phonon replicas at 12 K. In comparison with p-type GaN, the positions of the peaks are redshifted. This may be associated with the variation of the residual strain in the GaN layer of the heterostructure. Using this heterostructure, near-ultraviolet light-emitting diodes were fabricated and their electroluminescence properties were characterized.
Origin of etch delay time in Cl2 dry etching of AlGaN/GaN structures
Authors: Buttari D. , Chini A. , Palacios T. , Coffie R. , Shen L. , Xing H. , Heikman S. , McCarthy L. , Chakraborty A. , Keller S. , Mishra U. K.
Published: December 2003

The etch delay time commonly found during dry etching of AlGaN and GaN has been experimentally proven to be due to the presence of hard–to–etch surface oxides. A BCl3 deoxidizing plasma, followed by a Cl2 etching plasma, was found to give dead-time-free aluminum-mole-fraction-independent etch rates. No selectivity between GaN and AlGaN has been observed up to an aluminum mole fraction of 35%. The aluminum-mole-fraction-dependent etch rates commonly reported in literature have been related to the different dead-times associated with dissimilar surface oxides, disproving the more common explanations in terms of the higher binding energy of AlN compared to GaN and/or the lower volatility of AlClx compared to GaClx.
Reduction of grown-in defects by vacancy-assisted oxygen precipitation in high density dynamic random access memory
Authors: Kim Il-Gweon , Kwon Jae-Sun
Published: December 2003

The silicon ingot growing scheme has been investigated to reduce the grown-in defect. It is found that a fast cooling rate suppresses the further growth of crystal-originated particles (COPs) after supersaturating vacancies by increased pulling speed. This reaction makes the COP-rich region with the high density and smaller size extend to wafer edge. Initially higher COPs decrease by subsequent annealing in oxygen ambient through the vacancy-interstitial annihilation mechanism. Since vacancies assist oxygen precipitation, bulk microdefect is easily formed and the intrinsic gettering during the denudation process becomes more efficient. Based on this principle, the ingot growing scheme with a 1.8 mm/min-pulling speed and 9.8 °C/min cooling rate in the range of 1000 to ∼1200 °C is suggested, and its superiority is verified through the improvement of the tail component of retention time by 40% in high density dynamic random access memory.
Plan-view image contrast of dislocations in GaN
Authors: Follstaedt D. M. , Missert N. A. , Koleske D. D. , Mitchell C. C. , Cross K. C.
Published: December 2003

We demonstrate that when vertical threading dislocations in (0001) GaN are imaged in plan-view by transmission electron microscopy, a surface-relaxation contrast operates in addition to that due to the strain fields of dislocations passing through the specimen. We show that all three dislocation types (edge, screw, and mixed) can be detected in the same image using g=(112̄0) and 18° specimen tilt from [0001], allowing total densities to be assessed properly. The type of an individual dislocation can also be readily identified.
Thermal stability of epitaxial Pt films on Y2O3 in a metal-oxide–Si structure
Authors: Cho M.-H. , Moon D. W. , Min K. H. , Sinclair R. , Park S. A. , Kim Y. K. , Jeong K. , Kang S. K. , Ko D.-H.
Published: December 2003

High-quality epitaxial Pt films were grown by a sputtering deposition method using epitaxial Y2O3 as a dielectric buffer layer. A high degree of crystallinity was achieved with an ion-beam minimum channeling yield (χmin) of ∼11%, and a high degree of coherence between the film surface and interface was obtained for the Pt(111)/Y2O3(111)/Si, with a large lattice mismatch. High-resolution transmission electron microscopy results showed that the atomic arrangement at the interface between the Pt and the oxide was well ordered, and no perceptible interdiffusion was observed, even at an annealing temperature of up to 700 °C under an oxygen atmosphere. The atomic arrangement at the Pt/Y2O3 interface was drastically degraded after a high-temperature annealing at 900 °C due to the deformation of Y2O3.
Dephasing mechanisms of Bloch oscillations in GaAs/Al0.3Ga0.7As superlattices investigated by time-resolved terahertz spectroscopy
Authors: Sekine N. , Shimada Y. , Hirakawa K.
Published: December 2003

We systematically investigated the relaxation time of Bloch oscillations (BOs) in GaAs/Al0.3Ga0.7As superlattices as functions of the bias electric field, temperature, and structural parameters using the time-resolved terahertz spectroscopy. It was found that the relaxation time dramatically increases by ∼80% and a clear Wannier–Stark ladder shows up when the bias field exceeds ∼9 kV/cm. The dominant dephasing mechanism of BOs was identified to be interface roughness scattering (alloy disorder scattering) below (above) the critical bias electric field. From the temperature dependence, it was also found that phonon scattering plays a rather minor role in the dephasing process.
High performance field-effect transistors made of a multiwall CNx/C nanotube intramolecular junction
Authors: Xiao Kai , Liu Yunqi , Hu Ping’an , Yu Gui , Fu Lei , Zhu Daoben
Published: December 2003

Field-effect transistors (FETs) based on an individual CNx/C nanotube (NT) were fabricated by focus ion-beam technology. The nanotube transistors exhibited n-type semiconductor characteristics, and the conductance of nanotube FETs can be modulated more than four orders of magnitude at room temperature. The electron mobility of a CNx/C NT FET estimated from its transconductance was as high as 3.84×103 cm2/V s. The n-type gate modulation could be explained as due the effect of bending of the valence band in the Schottky-barrier junction.
Electrostatic discharge effects in AlGaN/GaN high-electron-mobility transistors
Authors: Kuzmı́k J. , Pogany D. , Gornik E. , Javorka P. , Kordoš P.
Published: November 2003

We investigate 50 μm gate width/0.45 μm length AlGaN/GaN high-electron-mobility transistors (HEMTs) subjected to 100 ns long current pulses that simulate an electrostatic discharge. After source–drain breakdown at around 90 V, the pulsed I–V source–drain characteristic is S shaped with an abrupt snap back to about 20 V at stress current of Istress=0.2 A. Backside interferometric thermal mapping of the HEMT shows that current filamentation accompanies the transition to the low-voltage/high-current region. The shift in transistor threshold voltage is explained by electron trapping in the buffer. It is assumed that breakdown in the regime of electrostatic discharge can be explained as an avalanche-injection event that forms a current filament through the device buffer layer.
High-temperature performance of GaAs-based bound-to-continuum quantum-cascade lasers
Authors: Pflügl C. , Schrenk W. , Anders S. , Strasser G. , Becker C. , Sirtori C. , Bonetti Y. , Muller A.
Published: December 2003

GaAs-based quantum-cascade lasers based on a bound-to-continuum transition have been realized and characterized. This band structure design combines the advantages of the well known three-well and superlattice active regions. We observed lasing of Fabry–Pérot lasers in pulsed mode up to a temperature of 100 °C. Multimode emission with a pulsed peak power of 340 mW is observed at room temperature and 42 mW at 80 °C. Further, from aging tests we expect a lifetime of over 60 years for these devices.
Land-use change is the key to protecting biodiversity in salinising landscapes
Authors: Cocks P. S.
Published: December 2003

This paper argues that the loss of biodiversity in salinising landscapes will be reversed only by addressing the source of the problem: farming systems that leak into the water table. Existing farming systems based on annual crops and pastures will need to be replaced by farming systems that have a significant element of perenniality. The literature suggests that 50–80% of the agricultural landscape needs to include perennial plants.The options are perennial pasture plants or trees, the latter for bioenergy, wood products and fuel. Because of the complexities of introducing new industries, the greatest short-term impact will be achieved by using perennial pastures for existing livestock industries. However, the need to introduce trees and shrubs is such that governments and entrepreneurs should be encouraged to see that new industries are an imperative in rural Australia. To achieve this we need substantial private and public investment, both on and off farms.Techniques are available to value biodiversity and these should be used to fortify the moral and philosophical arguments commonly used to protect biodiversity. It is suggested that a financial value placed on biodiversity, however inadequate, may, in time, be persuasive to governments. Contingent valuing and other non-market methods should be developed and, most importantly, used to bolster the moral and philosophical arguments if governments and the community are to respond to the perceived crisis in biodiversity management.The paper warns of possible tradeoffs between water quality and runoff. We have become dependent on high levels of runoff, and reductions are likely to cause problems both in terms of environmental flows and for the irrigation industries. Yet many of our solutions to dryland salinity will reduce runoff. Location will be all important in the development of perennial-based farming systems, avoiding, where possible, the areas of greatest runoff. Therefore, there are no blanket solutions. Policy will need to distinguish areas with high payoffs or low costs of abatement.Finally, the paper outlines some of the initiatives that are open to government and industry to reverse the trend towards dryland salinity. Emphasis is given to the provision of incentives and the removal of disincentives.
Phylogeny of Halgerda (Mollusca : Gastropoda) based on combined analysis of mitochondrial CO1 and morphology
Authors: Fahey Shireen J.
Published: November 2003

A phylogeny of the nudibranch Halgerda Bergh, 1880 is presented based on mitochondrial CO1 and compared with a previously published morphology-based phylogeny. Incongruence length difference (ILD) tests indicated possibly conflicting phylogenetic signals. Both separate and combined analyses resulted in trees that were very similar in topology, both to each other and to the morphology-based tree (albeit with lower consistency and retention indices). Some differences are noted in the topology based on the optimality criteria used: parsimony and maximum likelihood. Results of this study indicate that the CO1 gene contains sufficient phylogenetic signal for inferring species-level phylogeny in the Nudibranchia and also supports many of the clades in the morphological phylogeny. Specifically, the more basal clades of the morphology-based phylogeny are supported with differences noted at the most terminal taxa.
Revision of the endemic Australian genus Spinasteron (Araneae : Zodariidae): taxonomy, phylogeny and biogeography
Authors: Baehr B. C. , Churchill T. B.
Published: November 2003

This revision of the endemic Australian zodariid genus Spinasteron Baehr, 2003 revealed 19 species. Sixteen species could be placed in two species-groups: the S. nigriceps-group: S. barlee, sp. nov., S. cavasteroides, sp. nov., S. arenarium, sp. nov., S. knowlesi, sp. nov., S. lemleyi, sp. nov., S. longbottomi, sp. nov., S. mjobergi, sp. nov., S. nigriceps Baehr, 2003, S. waldockae, sp. nov., S. weiri, sp. nov. and S. woodstock, sp. nov.; and the S.�ramboldi-group: S. casuarium, sp. nov., S. kronestedti, sp. nov., S. ramboldi, sp. nov., S. spatulanum, sp. nov. and S. westi, sp. nov. Three species (S. ludwigi, sp. nov., S. sanford Baehr, 2003 and S. peron, sp. nov.) could not be placed in any species-group. Females from only four of the new species (S. arenarium, sp. nov., S. barlee, sp. nov., S. weiri, sp. nov. and S. westi, sp. nov.) were available for this study. The possible relationships of the species-groups and species are analysed with Hennig86, NONA and also reconstructed using the original Hennigian method. All three methods indicate that only two species-groups (S. nigriceps-group and S. ramboldi-group) represent independent lineages, whereas S. sanford and S. ludwigi, sp. nov. can be seen as the basal sister-species of both. The placement of S. peron, sp. nov. is uncertain.
Systematic revision of the western Atlantic file clams, Lima and Ctenoides (Bivalvia : Limoida : Limidae)
Authors: Mikkelsen Paula M. , Bieler Rüdiger
Published: November 2003

Marine file clams of family Limidae d'Orbigny, 1846 (+ Radulidae Adams & Adams), characterised by their often colourful mantle and pallial tentacles and by swimming behaviour, are commonly collected and illustrated bivalves. Based on new material from an extensive Florida Keys biodiversity survey plus museum and literature data, western Atlantic species of Lima Bruguière, 1797 (+ Mantellum R�ding; Radula M�rch; Limaria Rafinesque; Austrolima Iredale; Meotolima Oyama) and Ctenoides M�rch, 1853 (+ Divaricolima Rovereto) are revised. Lima includes L. marioni Fischer, 1882 (+ L. lata Smith; lectotype selected), and L. caribaea d'Orbigny, 1842 (lectotype selected), distinguished from eastern Atlantic L. lima (Linné) and other species by shell rib number. Ctenoides includes C. scaber (Born, 1778) (+ Ostrea glacialis Gmelin; L. asperula Lamarck; Limaria asperula Link), C. mitis (Lamarck, 1807) (+ L. tenera Sowerby; L. floridana Olsson & Harbison), C. planulatus (Dall, 1886) (lectotype selected), C. sanctipauli Stuardo, 1982, and C. miamiensis, C. obliquus, and C. vokesi, spp. nov. Species distinctions rely mainly on shell characters, although body colour and ornamentation are confirming in some cases. Diagnostic shell characters at the genus-level are supported by new anatomical characters of the gut and tentacles. Known anatomical data for worldwide Lima and Ctenoides species are summarised within a phylogenetic context.
Effects of biomass burning and lightning on atmospheric chemistry over Australia and South-east Asia
Authors: Kondo Yutaka , Takegawa Nobuyuki , Miyazaki Yuzo , Ko Malcolm , Koike Makoto , Kita Kazuyuki , Kawakami Shuji , Shirai Tomoko , Ogawa Toshihiro , Blake Donald R. , Liley Ben , Russell-Smith Jeremy
Published: November 2003

In situ aircraft measurements of trace gases and aerosols were made in the boundary layer (BL) and free troposphere (FT) over Indonesia and Australia during the Biomass Burning and Lightning Experiment (BIBLE)-A and B conducted in August–October 1998 and 1999.Concentrations of ozone (O3) and its precursors [CO, reactive nitrogen (NOx), non-methane hydrocarbons (NMHCs)] were measured in these campaigns to identify the sources of NOx and to estimate the effects of biomass burning and lightning on photochemical production of O3. Over Indonesia, in-situ production of NOx by lightning was found to be a major source of reactive nitrogen in the upper troposphere during BIBLE-A. In some circumstances, increases in reactive nitrogen were often associated with enhancements in CO and NMHCs, suggesting that the sources were biomass burning and fossil fuel combustion, followed by upward transport by cumulus convection. Over Australia the levels of O3, CO, reactive nitrogen, and NMHCs were elevated throughout the troposphere compared to those observed in the tropical Pacific. However, the mechanisms responsible for the enhanced concentrations in the BL and FT are distinctly different. The emissions from biomass burning that occurred in northern Australia were restricted to the BL because of strong subsidence in the period. In the FT over Australia, elevated concentrations of O3 and its precursors result from injections of emissions as the air masses travel over Africa, South America, the Indian Ocean, and Indonesia en route to Australia. In all cases, O3 levels in the biomass burning plumes were enhanced due to photochemical production.
Contemporary fire regimes of northern Australia, 1997 - 2001: change since Aboriginal occupancy, challenges for sustainable management
Authors: Russell-Smith Jeremy , Yates Cameron , Edwards Andrew , Allan Grant E. , Cook Garry D. , Cooke Peter , Craig Ron , Heath Belinda , Smith Richard
Published: November 2003

Considerable research has been undertaken over the past two decades to apply remote sensing to the study of fire regimes across the savannas of northern Australia. This work has focused on two spatial scales of imagery resolution: coarse-resolution NOAA-AVHRR imagery for savanna-wide assessments both of the daily distribution of fires ('hot spots'), and cumulative mapping of burnt areas ('fire-scars') over the annual cycle; and fine-resolution Landsat imagery for undertaking detailed assessments of regional fire regimes. Importantly, substantial effort has been given to the validation of fire mapping products at both scales of resolution. At the savanna-wide scale, fire mapping activities have established that: (1) contrary to recent perception, from a national perspective the great majority of burning in any one year typically occurs in the tropical savannas; (2) the distribution of burning across the savannas is very uneven, occurring mostly in sparsely settled, higher rainfall, northern coastal and subcoastal regions (north-west Kimberley, Top End of the Northern Territory, around the Gulf of Carpentaria) across a variety of major land uses (pastoral, conservation, indigenous); whereas (3) limited burning is undertaken in regions with productive soils supporting more intensive pastoral management, particularly in Queensland; and (4) on a seasonal basis, most burning occurs in the latter half of the dry season, typically as uncontrolled wildfire. Decadal fine-resolution fire histories have also been assembled from multi-scene Landsat imagery for a number of fire-prone large properties (e.g. Kakadu and Nitmiluk National Parks) and local regions (e.g. Sturt Plateau and Victoria River District, Northern Territory). These studies have facilitated more refined description of various fire regime parameters (fire extent, seasonality, frequency, interval, patchiness) and, as dealt with elsewhere in this special issue, associated ecological assessments. This paper focuses firstly on the patterning of contemporary fire regimes across the savanna landscapes of northern Australia, and then addresses the implications of these data for our understanding of changes in fire regime since Aboriginal occupancy, and implications of contemporary patterns on biodiversity and emerging greenhouse issues.
Using simulation to map fire regimes: an evaluation of approaches, strategies, and limitations
Authors: Keane Robert E. , Cary Geoffrey J. , Parsons Russell
Published: November 2003

Spatial depictions of fire regimes are indispensable to fire management because they portray important characteristics of wildland fire, such as severity, intensity, and pattern, across a landscape that serves as important reference for future treatment activities. However, spatially explicit fire regime maps are difficult and costly to create requiring extensive expertise in fire history sampling, multivariate statistics, remotely sensed image classification, fire behaviour and effects, fuel dynamics, landscape ecology, simulation modelling, and geographical information systems (GIS). This paper first compares three common strategies for predicting fire regimes (classification, empirical, and simulation) using a 51�000�ha landscape in the Selway-Bitterroot Wilderness Area of Montana, USA. Simulation modelling is identified as the best overall strategy with respect to developing temporally deep spatial fire patterns, but it has limitations. To illustrate these problems, we performed three simulation experiments using the LANDSUM spatial model to determine the relative importance of (1) simulation time span; (2) fire frequency parameters; and (3) fire size parameters on the simulation of landscape fire return interval. The model used to simulate fire regimes is also very important, so we compared two spatially explicit landscape fire succession models (LANDSUM and FIRESCAPE) to demonstrate differences between model predictions and limitations of each on a neutral landscape. FIRESCAPE was developed for simulating fire regimes in eucalypt forests of south-eastern Australia. Finally, challenges for future simulation and fire regime research are presented including field data, scale, fire regime variability, map obsolescence, and classification resolution.
Fire-created patchiness in Australian savannas
Authors: Gill A. Malcolm , Allan Grant , Yates Cameron
Published: November 2003

Models of ecosystem disturbances have been based on either points or patches. In this study, three types of fire-created patch were distinguished: the unburned 'islands' within a fire area; the patches with individual times-since-fire, those of the first year being the individual fire areas; and, patches with individual intervals between fires. Frequency distributions of patch areas were simulated using two randomly filled square grids (with a probability of 0.5, corresponding to 50% burnt each year) with two levels of aggregation—'none' and 'clumped'. Fires were represented by clusters of filled cells on each single grid; years were represented by a set of similar, independent, grids. Results from the simulations were compared to those from Bradshaw Station in the savanna region of the northern part of the Northern Territory using a decade of Landsat MSS and Landsat TM imagery. Maps of times since fire (years) and intervals between fires (years) were constructed. Proportions of the maps with different times since fire and intervals between fires followed negative exponential curves. All frequency distributions of patch area, irrespective of patch type, were found to be log–log linear when data were logged and 'binned' (i.e. placed in categories). In both the simulations and at Bradshaw Station, the numbers of single cell patches first rose then declined as times since fire increased while the largest fire patches rapidly decreased in size. Between-fire interval patches decreased in size with increasing intervals but small-patch number did not increase as it did for times since fire. Errors in accuracy of Landsat imagery could heighten the apparent conformity between interpreted imagery and the simulations.
Fire regimes and vegetation sensitivity analysis: an example from Bradshaw Station, monsoonal northern Australia
Authors: Yates Cameron , Russell-Smith Jeremy
Published: November 2003

The fire-prone savannas of northern Australia comprise a matrix of mostly fire-resilient vegetation types, with embedded fire-sensitive species and communities particularly in rugged sandstone habitats. This paper addresses the assessment of fire-sensitivity at the landscape scale, drawing on detailed fire history and vegetation data assembled for one large property of 9100�km2, Bradshaw Station in the Top End of the Northern Territory, Australia. We describe (1) the contemporary fire regime for Bradshaw Station for a 10 year period; (2) the distribution and status of 'fire sensitive' vegetation; and (3) an assessment of fire-sensitivity at the landscape scale. Fire-sensitive species (FSS) were defined as obligate seeder species with minimum maturation periods of at least 3 years. The recent fire history for Bradshaw Station was derived from the interpretation of fine resolution Landsat MSS and Landsat TM imagery, supplemented with mapping from coarse resolution NOAA-AVHRR imagery where cloud had obstructed the use of Landsat images late in the fire season (typically October–November). Validation assessments of fire mapping accuracy were conducted in 1998 and 1999. On average 40% of Bradshaw burnt annually with about half of this, 22%, occurring after August (Late Dry Season LDS), and 65% of the property burnt 4 or more times, over the 10 year period; 89% of Bradshaw Station had a minimum fire return interval of less than 3 years in the study period. The derived fire seasonality, frequency and return interval data were assessed with respect to landscape units (landsystems). The largest landsystem, Pinkerton (51%, mostly sandstone) was burnt 41% on average, with about 70% burnt four times or more, over the 10 year period. Assessment of the fire-sensitivity of individual species was undertaken with reference to data assembled for 345 vegetation plots, herbarium records, and an aerial survey of the distribution of the long-lived obligate-seeder tree species Callitris intratropica. A unique list of 1310 plant species was attributed with regenerative characteristics (i.e. habit, perenniality, resprouting capability, time to seed maturation). The great majority of FSS species were restricted to rugged sandstone landforms. The approach has wider application for assessing landscape fire-sensitivity and associated landscape health in savanna landscapes in northern Australia, and elsewhere.
Patterns of landscape fire and predicted vegetation response in the North Kimberley region of Western Australia
Authors: Fisher Rohan , Vigilante Tom , Yates Cameron , Russell-Smith Jeremy
Published: November 2003

The paper reports on the development of a decadal fire history, 1990–1999, derived from Landsat imagery, and associated assessment of landscape-scale patterns, in a remote, sparsely human-populated region of the high rainfall zone of monsoonal north-western Australia. The assembled fire history confirms observations, derived from coarser-scale imagery, that substantial areas of the North Kimberley are burnt each year. The annual mean extent of burning was 31% (albeit involving marked inter-annual variability), with most burning occurring in the latter part of the dry season under relatively severe fire weather conditions. Extent of burning was found to be associated with intensity of landuse; most burning occurred on pastoral lands, particularly in association with more fertile basalt soils. Based on previous modelling studies, predicted effects of contemporary fire regimes include increased development of woody regeneration size-classes, especially on non-basalt substrates. In contrast, on sandstone-derived substrata, fire interval data indicate that longer-lived obligate-seeder shrub species are likely to be suppressed and ultimately displaced by contemporary fire regimes. Such observations are supported by recent evidence of regional collapse of the long-lived obligate seeder tree species, Callitris intratropica. Collectively, assembled data point to the need to undertake a thorough appraisal of the status of regional biota in this remote, ostensibly ecologically intact region.
Assessing woody vegetation cover change in north-west Australian savanna using aerial photography
Authors: Fensham R. J. , Fairfax R. J.
Published: November 2003

Models to calibrate tree and shrub cover assessed from aerial photography with field measurements were developed for a range of vegetation types in north-western Australia. The models verify previous studies indicating that woody cover can be successfully determined from aerial photography. The calibration models were applied to estimates of woody vegetation cover determined for 279 randomly located sample areas in the Ord–Victoria Rivers region using aerial photography from 1948 to 1950 and 1988 to 1997. Overstorey cover increased from a regional average of 11.5% to 13.5% and understorey cover increased from 1.3% to 2.0%. Downs, Limestone Hills and Alluvia land-types showed the most substantial increases in overstorey cover while overstorey cover in the Limestone plains land-type decreased. Relatively open structured vegetation is most susceptible to thickening. Rainfall records reveal an extreme multi-year rainfall deficit in the study area in the 1930s and relatively wet times in the 1970s and 1980s. Interpretation of a limited set of aerial photographs taken between 1964 and 1972 suggests that most of the increases in cover have occurred since this time. The study highlights the possibility that the average trend of vegetation thickening represents recovery during the relatively wet times after the 1970s. There was no relationship between structural change and a grazing intensity surrogate (distance of sample points to stock watering-points). However, the causes of structural change are undoubtedly multi-factored and the relative contributions of climate, fire and grazing vary for different landscapes and tree species.
Fire impacts on surface heat, moisture and carbon fluxes from a tropical savanna in northern Australia
Authors: Beringer J. , Hutley L. B. , Tapper N. J. , Coutts A. , Kerley A. , O'Grady A. P.
Published: November 2003

Savannas form a large fraction of the total tropical vegetation and are extremely fire prone. We measured radiative, energy and carbon exchanges over unburned and burned (both before and after low and moderate intensity fires) open forest savanna at Howard Springs, Darwin, Australia. Fire affected the radiative balance immediately following fire through the consumption of the grass-dominated understorey and blackening of the surface. Albedo was halved following fire of both intensities (from 0.12 to 0.07 and from 0.11 to 0.06 for the moderate and low intensity sites, respectively), but the recovery of albedo was dependent on the initial fire intensity. The low intensity fire caused little canopy damage with little impact on the surface energy balance and only a slight increase in Bowen ratio. However the moderate fire resulted in a comprehensive canopy scorch and almost complete leaf drop in the weeks following fire. The shutdown of most leaves within the canopy reduced transpiration and altered energy partitioning. Leaf death and shedding also resulted in a cessation of ecosystem carbon uptake and the savanna turned from a sink to a source of carbon to the atmosphere because of the continued ecosystem respiration. Post-fire, the Bowen ratio increased greatly due to large increases in sensible heat fluxes. These changes in surface energy exchange following fire, when applied at the landscape scale, may have impacts on climate through local changes in circulation patterns and changes in regional heating, precipitation and monsoon circulation.
Confronting complexity: fire policy choices in South African savanna parks
Authors: Bond William J. , Archibald Sally
Published: November 2003

Changes in ecological concepts and a new focus on biodiversity as a central objective have led to changes in fire policies in South African savanna parks. Prescribed burning using fixed fire intervals is being replaced by systems that promote more variable fire regimes and greater management flexibility. Three policy alternatives have been proposed for Kruger National Park: a lightning fire policy, patch mosaic burning, and burning based on ecological criteria. There is no agreement as yet on which policy to adopt. However there is growing consensus on the use of a management system using 'thresholds of potential concern' to evaluate the outcome of different policies. These thresholds have been established for numerous indicators, help focus monitoring activities, and guide managers on the need for active intervention. We discuss the applicability of the policy alternatives for preventing successional change from savanna to forest and promoting grazing lawns and their associated grazers. We conclude that none of the current policies is universally applicable. A prescriptive program of frequent, high intensity burns will be required in mesic savannas to prevent succession to forests. In arid savannas, fire regimes designed to promote variable fire frequencies and fire sizes would be preferred to maintain greater diversity of grassland swards and grazer communities. The lessons learned from fire policy debates in South African savannas are of wider relevance for managing conservation areas elsewhere.
Fire experiments in northern Australia: contributions to ecological understanding and biodiversity conservation in tropical savannas
Authors: Williams R. J. , Woinarski J. C. Z. , Andersen A. N.
Published: November 2003

The management of fire in savannas has been informed by a strong tradition of fire experiments, especially in Africa. This research tradition is much shorter in the 2 million square kilometres of tropical savannas in northern Australia, but has yielded several natural experiments, and three designed, manipulative, controlled field experiments (hereafter 'manipulative' experiments) of international significance (at Munmarlary, Kapalga and Kidman Springs in the Northern Territory). Here we assess the contributions of experiments, in particular the manipulative experiments, to ecological understanding and biodiversity management in Australia's savannas. Running from 1973 to 1996, the Munmarlary experiment comprised hectare-scale experimental plots with four replicated dry season fire treatments, and was designed to examine interactions between fire, landscape and biodiversity. The Kapalga experiment ran from 1989 to 1995, with a range of fire treatments broadly similar to those at Munmarlary. However, experimental units were 10–20�km2 sub-catchments, making it one of the largest, replicated fire experiments ever conducted. The Kidman Springs experiment focused on grass-layer productivity and composition to meet the needs of the pastoral industry, but also provided an opportunity to examine biodiversity responses to different fire regimes. Methodologically, the experiments have generally focused on phenomena—the responses to different fire treatments of individual taxa—rather than on mechanisms that determine response syndromes. They have highlighted that a range of responses to differences in fire regime is possible, and that no single fire regime can optimise all biodiversity outcomes. For effective conservation of biodiversity in the face of such complexity, conservation goals will need to be made explicit. The existing portfolio of manipulative experiments is incomplete, lacking especially a consideration of some critical savanna taxa and environments, and providing little information on the significance of spatial and temporal variability in fire patterns, especially at small scales. An understanding of fire in Australian savanna landscapes remains inadequate, so there is a continuing need for close partnerships between scientists and conservation managers, with fire management treated as a series of landscape experiments in an adaptive management framework.