bluuebunny/crossref_metadata_2025 huggingface dataset:
Finite lifetime effects on the polarizability within time-dependent density-functional theory
Authors: Jensen L. , Autschbach J. , Schatz G. C.
Published: June 2005

We present an implementation for considering finite lifetime of the electronic excited states into linear-response theory within time-dependent density-functional theory. The lifetime of the excited states is introduced by a common phenomenological damping factor. The real and imaginary frequency-dependent polarizabilities can thus be calculated over a broad range of frequencies. This allows for the study of linear-response properties both in the resonance and nonresonance cases. The method is complementary to the standard approach of calculating the excitation energies from the poles of the polarizability. The real and imaginary polarizabilities can then be calculated in any specific energy range of interest, in contrast to the excitation energies which are usually solved only for the lowest electronic states. We have verified the method by investigating the photoabsorption properties of small alkali clusters. For these systems, we have calculated the real and imaginary polarizabilities in the energy range of 1–4eV and compared these with excitation energy calculations. The results showed good agreement with both previous theoretical and experimental results.
Modeling electrical transport in blend heterojunction organic solar cells
Authors: Lacic Sasa , Inganäs Olle
Published: June 2005

In order to understand how to enhance the performance of blend heterojunction organic solar cells, we have developed a theoretical model that enables us to investigate the impact of a number of materials and device parameters on device performance. A full description of the charge transport of photogenerated holes and electrons in a continuum model of the blend is given. The injection of charges at anode and cathode is treated according to previous models. The input of our model is the optical absorption in the active layer of the cell, as calculated within previous optical models, and measured as well as estimated transport parameters. By applying the model to devices with the active layer consisting of an alternating copolymer of fluorene blended with a fullerene derivative, we conclude that the most limiting parameter in these devices is the low hole mobility in the blend. Electron-hole recombination is strongly suppressed compared to Langevin recombination, due to the donor-acceptor separation.
Deep ultraviolet Raman scattering characterization of ion-implanted SiC crystals
Authors: Nakashima S. , Mitani T. , Senzaki J. , Okumura H. , Yamamoto T.
Published: June 2005

Multiple energy phosphorous ions were implanted into 4H-SiC at room temperature and at an elevated temperature (500 °C) followed by annealing at various temperatures. Deep ultraviolet Raman microscopy was used to analyze the effect of the implantation dose and postannealing temperature on the recovery of surface layers damaged by the implantation. The Raman analysis showed that the recovery rate of the crystallinity increased with an increase in the annealing temperature. However, for highly dosed samples, recovery was not complete even with annealing temperatures up to 1700 °C. With room-temperature implantation, part of the implanted layer was converted into a 3C structure with heavy stacking faults. New Raman bands were observed at below 500cm−1 in samples heavily dosed with 4.0×1016cm−2 after annealing, which revealed that excess phosphorus precipitates. A downshift of the phonon Raman bands and a reduction in the LO–TO-phonon frequency splitting were observed in as-implanted samples and ones that are not completely recovered by annealing. This feature is discussed based on several mechanisms.
Nonresonant dielectric hole burning in neat and binary organic glass formers
Authors: Blochowicz T. , Rössler E. A.
Published: June 2005

Binary mixtures of the molecular glass former 2-picoline in oligostyrene, in which the dielectric response of 2-picoline exhibits a particularly broad distribution of correlation times, are investigated by nonresonant dielectric hole-burning (NDHB) spectroscopy and the results are compared with NDHB in neat systems, in particular, glycerol. It turns out that in both substance classes spectral selectivity is achieved, which indicates that dynamics is heterogeneous, i.e., slow and fast responses coexist in the material. However, in binary systems the position of the spectral modifications is completely determined by the spectral density of the pump field, and thus shifts linearly with burn frequency as expected, also at pump frequencies around the α-relaxation maximum. It is shown that in binary systems the lifetime τrec of the spectral modifications is determined by the burn frequency ωp and exceeds its inverse by about one order of magnitude, indicating long-lived dynamic heterogeneity. The data are described in terms of a previously suggested model of dynamically selective heating, which was extended to include intrinsic nonexponential relaxation. It turns out that the spectral broadening in binary mixtures is not only due to pronounced dynamic heterogeneity, but partially also due to intrinsic broadening of the relaxation function.
Test of classical nucleation theory via molecular-dynamics simulation
Authors: Bai Xian-Ming , Li Mo
Published: June 2005

A direct test of classical nucleation theory (CNT) is made using molecular-dynamics simulations. The relation between critical nucleus size and undercooling temperature is extracted and the result yields the solid-liquid interfacial energy. It is shown that the CNT, within the assumptions made for spherical nucleus in supercooled liquid, is valid in the critical regime of nucleation for a large range of undercooling and nucleus size.
Electron photoemission from conducting nitrides (TiNx,TaNx) into SiO2 and HfO2
Authors: Afanas’ev V. V. , Stesmans A. , Pantisano L. , Schram T.
Published: June 2005

The energy barrier between the metal Fermi level and the insulator conduction band is directly determined using internal electron photoemission at the interfaces of metallic nitrides (TiNx,TaNx) with SiO2 and HfO2. TiNx yields high barriers both on SiO2(4.15±0.05eV) and HfO2(3.0±0.05eV) stable upon annealing at temperatures up to 1000 °C. Incorporation of a monolayer HfO2 at the TiNx∕SiO2 interface causes ≈0.2eV barrier enhancement upon annealing. The TaNx∕SiO2 interface barrier (3.55±0.05eV) is found to be stable under annealing up to 1000 °C, but Hf contamination leads to a barrier increase similar to that observed for TiNx∕SiO2. The as-deposited TaNx on HfO2 yields a low barrier (2.1±0.05eV), but it significantly increases upon annealing, suggesting a chemical interaction to occur between TaNx and HfO2.
Time-dependent density-functional theory for molecular photoionization with noniterative algorithm and multicenter B-spline basis set: CS2 and C6H6 case studies
Authors: Stener M. , Fronzoni G. , Decleva P.
Published: June 2005

In this work a new direct (noniterative) algorithm to solve the time-dependent density-functional theory equations for molecular photoionization has been proposed and implemented, using a multicentric basis set expansion of B-spline functions and complete exploiting of the molecular point-group symmetry. The method has been applied to study the photoionization dynamics of CS2 and C6H6: the results confirmed the expectation of large screening effects in CS2. For C6H6 the screening effects have been found to play a minor role than in CS2, however, also in this case the quality of the final results is definitely improved. The method has proven suitable to study with confidence molecules of medium size, and there is still room for further improvement working on more elaborate treatment of the exchange-correlation functional.
Spontaneous polarizations of ultrashort-period epitaxial KNbO3∕(KTaO3)m superlattices: An ab initio investigation
Authors: Hao Shaogang , Zhou Gang , Wang Xiaosu , Wu Jian , Duan Wenhui , Gu Bing-Lin
Published: June 2005

Ab initio calculations reveal that ultrashort-period epitaxial KNbO3∕(KTaO3)m superlattice exhibits typical ferroelectricity when m=1 or 2; while it becomes paraelectric when m⩾3. We observe considerable and tantamount dipole moment in each cell, which can be attributed to the continuity of dipole moment at the interface and the short period of the heterostructure. The polarization behavior of KNbO3∕KTaO3 superlattices sensitively depends upon the ratio of two constituents. Our results directly support the experimental finding of the antiferroelectric behavior in the 1×1 KNbO3∕KTaO3 superlattice.
Synthesis and magnetic properties of Fe3Pt nanowire arrays fabricated by electrodeposition
Authors: Gao Jian-Hua , Zhan Qing-Feng , He Wei , Sun Da-Li , Cheng Zhao-Hua
Published: June 2005

Fe 3 Pt nanowire arrays were fabricated by electrodeposition of Fe2+ and Pt2+ into anodic aluminum oxide (AAO) templates. X-ray diffraction (XRD) pattern indicates that the crystallites of Fe3Pt nanowires are fcc structure with existence of strong [110] orientation along the nanowire axes. Transmission electron microscopy reveals that the diameter and length of nanowires are about 10 and 400 nm, respectively. Relatively high coercivities parallel to nanowire arrays of about 2.72 kOe at 5 K and 1.17 kOe at room temperature were achieved. The magnetic hysteresis loops demonstrate that the arrays of nanowires exhibit uniaxial magnetic anisotropy with the easy magnetization direction along the nanowire axes owing to the large shape anisotropy. The magnetization reversal process of the nanowire arrays at 5 K is discussed by symmetric fanning mechanism of sphere chains model. The temperature dependence of the coercivity parallel to nanowire arrays is interpreted by thermally activated magnetization reversal process.
Metal catalyst-free low-temperature carbon nanotube growth on SiGe islands
Authors: Uchino T. , Bourdakos K. N. , de Groot C. H. , Ashburn P. , Kiziroglou M. E. , Dilliway G. D. , Smith D. C.
Published: June 2005

A metal-catalyst-free growth method of carbon nanotubes (CNTs) has been developed using chemical vapor deposition of CNTs on carbon-implanted SiGe islands on Si substrates. From scanning electron microscopy and Raman measurements, the fabricated CNTs are identified as single-walled CNTs with a diameter ranging from 1.2 to 1.6 nm. Essential parts of the substrate preparation after CVD SiGe growth and carbon implant are a chemical oxidization by hydrogen peroxide solution and a heat treatment at 1000 °C prior to CNT growth. We believe that these processes enhance surface decomposition and assist the formation of carbon clusters, which play a role in seeding CNT growth. The growth technique is a practical method of growing metal-free CNTs for a variety of applications, while at the same time opening up the prospect of merging CNT devices into silicon very-large-scale-integration technology.
Self-organization of nonmagnetic spheres by magnetic field
Authors: Takayama Tomohiro , Ikezoe Yasuhiro , Uetake Hiromichi , Hirota Noriyuki , Kitazawa Koichi
Published: June 2005

Two-dimensional crystallization of nonmagnetic gold spheres was achieved by the application of a high magnetic field. This phenomenon is based on the two different forces caused by a magnetic field; interactions between magnetic dipoles induced in the nonmagnetic spheres and magnetic force derived from field gradient. The former force is generally so weak and, hence, negligible. However, under an appropriate condition, we can achieve the subtle balance between the two forces. This phenomenon is a new class of self-assembling phenomena, and we believe that our achievement will be a milestone in the utilization of magnetic fields.
Background-limited terahertz quantum-well photodetector
Authors: Luo H. , Liu H. C. , Song C. Y. , Wasilewski Z. R.
Published: June 2005

We report terahertz quantum-well photodetectors with background-limited infrared performance (BLIP). The device dark current characteristics were improved by employing thick barriers to reduce interwell tunneling. BLIP operations were observed for all samples (three in total) designed for different wavelengths. BLIP temperatures of 17, 13, and 12K were achieved for peak detection frequencies at 9.7THz (31μm), 5.4THz (56μm), and 3.2THz (93μm), respectively.
Electrical properties of Nb–MoSi2–Nb Josephson junctions
Authors: Chong Yonuk , Dresselhaus P. D. , Benz S. P.
Published: June 2005

We present a detailed study of the electrical properties of planar Nb–MoSi2–Nb Josephson junctions. The Nb–MoSi2–Nb junction is an excellent system to study proximity coupling in junctions with rigid superconductor/normal metal boundaries by precisely and independently controlling the barrier thickness and the temperature. With regard to applications, the Josephson properties are very reproducible, and the characteristic voltage can be tuned easily over more than two orders of magnitude while still maintaining a practical critical current density. The characteristic voltage can be controlled within ±5% at 4K, with an exponential dependence on the barrier thickness. The proximity-coupled junction theory fits the temperature dependence of the critical current density, allowing us to quantitatively extract material parameters.
Efficient soft x-ray emission source at 13.5 nm by use of a femtosecond-laser-produced Li-based microplasma
Authors: Higashiguchi Takeshi , Rajyaguru Chirag , Kubodera Shoichi , Sasaki Wataru , Yugami Noboru , Kikuchi Takashi , Kawata Shigeo , Andreev Alex
Published: June 2005

A proof-of-principle experiment was demonstrated to optimize a Li-based microjet target coupled to dual subpicosecond laser pulses as a 13.5 nm soft x-ray emission source. An optimum pulse duration of 450 fs to achieve a maximum emission at 13.5 nm was well explained by the resonant absorption process. Utilization of dual femtosecond pulses revealed that the optimum pulse separation around 500 ps was necessary to achieve a maximum soft x-ray conversion efficiency of 0.2%, where plasma hydrodynamics could not be neglected. A one-fluid two-temperature hydrodynamic simulation reproduced this optimum pulse separation behavior.
In situ resistance measurements of epitaxial cobalt silicide nanowires on Si(110)
Authors: Okino Hiroyuki , Matsuda Iwao , Hobara Rei , Hosomura Yoshikazu , Hasegawa Shuji , Bennett P. A.
Published: June 2005

We have performed in situ resistance measurements for individual epitaxial CoSi2 nanowires (NWs) (approximately 60 nm wide and 5μm long) formed on a Si(110) surface. Two- and four-point probe measurements were done with a multitip scanning tunneling microscope at room temperature. The NWs were well isolated from the substrate by a Schottky barrier with zero-bias resistance of 107Ω. The resistivity of the NWs was 30μΩcm, which is similar to that for high-quality epitaxial films. The NW resistance was essentially unchanged after exposure to air.
Enhanced functionality of cantilever based mass sensors using higher modes
Authors: Dohn Søren , Sandberg Rasmus , Svendsen Winnie , Boisen Anja
Published: June 2005

By positioning a single gold particle at different locations along the length axis on a cantilever based mass sensor, we have investigated the effect of mass position on the mass responsivity and compared the results to simulations. A significant improvement in quality factor and responsivity was achieved by operating the cantilever in the fourth bending mode thereby increasing the intrinsic sensitivity. It is shown that the use of higher bending modes grants a spatial resolution and thereby enhances the functionality of the cantilever based mass sensor.
Air-stable ambipolar organic thin-film transistors based on an organic homostructure
Authors: Ye Rongbin , Baba Mamoru , Oishi Yoshiyuki , Mori Kunio , Suzuki Kazunori
Published: June 2005

Ambipolar organic thin-film transistors (TFTs) based on a fluorinated copper phthalocyanine (F16CuPc)∕copper phthalocyanine (CuPc) homostructure layer were fabricated and characterized. The homostructure TFTs showed typical air-stable ambipolar characteristics, with hole and electron mobilities of 1.44×10−3 and 9.97×10−4cm2∕Vs, respectively, which are comparable to unipolar mobilities in these single-layer devices. X-ray diffraction analysis suggests highly ordered F16CuPc and CuPc polycrystalline thin films could be continuously grown via an intermediate-phase layer in the homostructure.
Polarization-sensitive terahertz detection by multicontact photoconductive receivers
Authors: Castro-Camus E. , Lloyd-Hughes J. , Johnston M. B. , Fraser M. D. , Tan H. H. , Jagadish C.
Published: June 2005

We have developed a terahertz radiation detector that measures both the amplitude and polarization of the electric field as a function of time. The device is a three-contact photoconductive receiver designed so that two orthogonal electric-field components of an arbitrary polarized electromagnetic wave may be detected simultaneously. The detector was fabricated on Fe+ ion-implanted InP. Polarization-sensitive detection is demonstrated with an extinction ratio better than 100:1. This type of device will have immediate application in studies of birefringent and optically active materials in the far-infrared region of the spectrum.
Surface-plasmon-assisted nanoscale photolithography by polarized light
Authors: Shao D. B. , Chen S. C.
Published: June 2005

We demonstrate that photolithography can be extended to a subwavelength resolution for patterning of virtually any substrate by exciting surface plasmons on both a metallic mask and a substrate. Without any additional equipment or added complexity to mask design, one-to-one pattern transfer has been achieved. In this letter, a polarized laser beam of 355 nm wavelength was used as light source to photoinitiate an 80 nm thick photoresist on a silicon substrate coated with titanium of 80 nm thick. Array of line apertures of 100 nm in width were made on gold film or titanium film deposited on a quartz substrate, serving as the mask. Simulation results by finite-difference time-domain method have shown that surface plasmons excited on both the metallic mask and the Ti shield help to spatially confine the light behind the apertures. Experimental results show a strong dependence of pattern transfer on the polarization of light as well as the energy dosage of the light. The feature size using such method could be further scaled down, limited theoretically by the validity of the dielectric function of the material, and practically by the fabrication of the mask.
Structural and luminescence properties of Eu-doped ZnO nanorods fabricated by a microemulsion method
Authors: Ishizumi Atsushi , Kanemitsu Yoshihiko
Published: June 2005

We have studied photoluminescence (PL) properties of Eu-doped ZnO (ZnO:Eu) nanorods fabricated by a microemulsion method. The ZnO:Eu nanorods have a hexagonal crystal structure and exhibit a sharp luminescence due to the intra-4f transitions of Eu3+ ions. The excitation energy and temperature dependence of the PL intensity show that the Eu3+-related PL efficiency is determined by the energy relaxation process of excited Eu3+ ions, rather than by the energy transfer process from ZnO nanorods to Eu3+ ions. The energy transfer and luminescence processes in ZnO:Eu nanorods are discussed.
In situ detection of single micron-sized magnetic beads using magnetic tunnel junction sensors
Authors: Shen Weifeng , Liu Xiaoyong , Mazumdar Dipanjan , Xiao Gang
Published: June 2005

We have demonstrated the use of highly sensitive magnetic tunnel junction (MTJ) sensors for the detection of individual micron-sized magnetic labels. By integrating the MTJ sensor into a microfluidic channel, we were able to detect the presence of moving superparamagnetic beads (Dynabeads® M-280) in real time by direct measurement of the magnetic dipole fields associated with single beads. The dipolar fields of a single bead were sufficient to obtain a signal of 80μV with signal to noise ratio of 24dB in an applied field of 15Oe. Our data show conclusively that MTJ sensors are very promising candidates for future applications involving the accurate detection and identification of biomolecules with magnetic labels.
Optical waveguide fabrication with double pulse femtosecond lasers
Authors: Nagata Tetsuya , Kamata Masanao , Obara Minoru
Published: June 2005

We demonstrate the optical waveguide fabrication inside fused silica glasses using double pulse femtosecond lasers to decrease the optical loss which may be caused by nonuniformity of the refractive index change in the modified volume. The pulse separation time of the double pulses is varied from 500fsto200ps. An optical loss of less than 0.8dB∕cm is obtained under the conditions that the first pulse energy and the second pulse energy in the double pulse mode are 30 and 160nJ, respectively, and pulse time interval is 3ps. The weak first pulse would act as a pre-conditioner of the fused silica and then the second subsequent pulse effectively induces the uniform refractive index change. This optical loss is less than 1.3dB∕cm for the waveguides fabricated using a single 160nJ pulse femtosecond laser.
Biomembrane-Active Molecular Switches as Tools for Intracellular Drug Delivery
Authors: Bulmus Volga
Published: June 2005

Many therapeutic strategies, such as gene therapy and vaccine development require the delivery of polar macromolecules (e.g. DNA, RNA, and proteins) to intracellular sites at a therapeutic concentration. For such macromolecular therapeutics, cellular membranes constitute a major transport barrier that must be overcome before these drugs can exert their biological activity inside cells. A number of biological organisms, e.g. viruses and toxins, efficiently destabilize the cellular membranes upon a trigger, such as low pH, and facilitate the delivery of their biological cargo to the cytoplasm of host cell. pH-responsive synthetic peptides and polymers have been designed to mimic the function of membrane-destabilizing natural organisms and evaluated as a part of drug delivery systems. In this Review, pH-dependent membrane activity of natural and synthetic systems is reviewed, focussing on fundamental and practical aspects of pH-responsive, membrane-disruptive synthetic polymers in intracellular drug delivery.
CO2 Foaming of Polymer Nanocomposite Blends
Authors: Han Xiangmin , Lee L. James , Tomasko David L.
Published: June 2005

Nanoparticles are suitable to nucleate small foam cells and simultaneously reinforce the thin foam cell walls. In this paper, it is found that the foam morphology and the physical properties are greatly influenced by the dispersion of nanoclay, the clay surface modification, and the nanocomposite blend morphology. The addition of nanoclay to polystyrene (PS) strongly affects the nucleation of foam bubbles, especially after exfoliation and proper surface modification. CO2 appears to nucleate on the solid clay surface with a CO2-affinitive surface modifier. PS/(PMMA/MHABS) nanocomposite blends composed of polystyrene and poly(methyl methacrylate)/nanoclay exfoliated nanocomposite show an unexpected trend that bubble nucleation inversely correlates with domain size, where the bigger PMMA/MHABS domains are significant in nucleating more bubbles. The total influence volume, formed by the CO2 diffusion from the PMMA/MHABS phase to the PS phase where CO2 concentration decreases from a high value in the former to a low value in the latter, is related to the domain size and determines the nucleation efficiency in the PS phase. The physical properties of PS nanocomposites exhibit unique behaviour in the presence of CO2.
Metabolic engineering of Arabidopsis to produce nutritionally important DHA in seed oil
Authors: Robert Stan S. , Singh Surinder P. , Zhou Xue-Rong , Petrie James R. , Blackburn Susan I. , Mansour Peter M. , Nichols Peter D. , Liu Qing , Green Allan G.
Published: June 2005

Docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) are nutritionally important long-chain (≥ C20) omega-3 polyunsaturated fatty acids (ω3 LC-PUFA) currently obtained mainly from marine sources. A set of genes encoding the fatty acid chain elongation and desaturation enzymes required for the synthesis of LC-PUFA from their C18 PUFA precursors was expressed seed-specifically in Arabidopsis thaliana. This resulted in the synthesis of DHA, the most nutritionally important ω3 LC-PUFA, for the first time in seed oils, along with its precursor EPA and the ω6 LC-PUFA arachidonic acid (ARA). The assembled pathway utilised Δ5 and Δ6 desaturases that operate on acyl-CoA substrates and led to higher levels of synthesis of LC-PUFA than previously reported with acyl-PC desaturases. This demonstrates the potential for development of land plants as alternative sources of DHA and other LC-PUFA to meet the growing demand for these nutrients.
Food of the Black-backed Magpie, Gymnorhina t. tibicen, at Canberra
Authors: Vestjens WJM , Carrick R
Published: June 2005

During 1954–65 at Canberra, stomach contents of 1319 black-backed magpies of known age, sex and social status were examined.
A wide range of ground invertebrates is eaten, mainly insects supplemented by spiders and earthworms. Seasonal fluctuations in diet correspond with the observed abundance of some species, and the effects of weather on others. There are differences between territorial birds in savannah woodland and flock birds in open pasture; the latter showed a higher intake than the sedentary territorial individuals.
Observations have been made on the rate of digestion of some food items.
Food of the Crested and Common Bronzewing Pigeons in Inland New South Wales.
Authors: Frith HJ , Brown BK , Barker RD
Published: June 2005

Crop contents of pigeons were studied near Griffith, NSW. For 740 crested pigeons (Ocyphaps lophotes) in pastoral country, food was 85.5% seeds, 13.5% green leaf and 0.7% insects and other animals, by volume. The most important were seeds of introduced weeds and pasture plants. In drought the pigeons survived mainly on seeds of the introduced weed Paterson's Curse (Echium lycopsis) and during high rainfall they fed mainly on the abundant herbage. On roadsides, during a 6-month period, spilled wheat was 46.9% of food and the rest was introduced weed seed.Common bronzewings (Phaps chalcoptera) ate mainly seeds, 98.8% of food; 79% of food was from cultivated plants and introduced weeds. The most important single source was waste wheat seed, but in late winter and spring, native seeds were important. Both species are secure for the present; further development of agriculture might favour the crested pigeon and affect adversely the bronzewing.
Effect of Severe Drought on Rabbit Numbers and Distribution in a Refuge Area in Semiarid North-western New South Wales
Authors: Myers K , Parker BS
Published: June 2005

During severe drought in north-western New South Wales populations of rabbits in sandy habitats are restricted to certain warrens, which are located in light sandy and gravelly soils in protected and elevated positions close to food supplies in major drainage channels and swamps.
Warrens in less favourable localities become completely covered by drifting sand.

After rain the unfavourable areas become more favourable and are recolonized by rabbits which open the old, buried warrens.

Foxes are less able to excavate the permanently occupied warrens in the more favourable habitats, apparently because of their depth. The more evanescent warrens in less favourable areas show evidence of far more predation by foxes on nestling rabbits.

The importance of these findings for rabbit control in the arid zone is discussed.
Breeding Biology of the Agile Wallaby, Macropus agilis (Gould) (Marsupialia : Macropodidae), in Captivity
Authors: Merchant JC
Published: June 2005

Female agile wallabies in captivity reached sexual maturity at about 12 months old and males produced mature spermatozoa by 14 months.

Breeding was continuous throughout the year and birth and oestrus were recorded in every month. The mean length of the oestrous cycle was 32.4 days, and the mean gestation period 29.4 days. Females exhibited post-partum oestrus, usually mating within 1 day of birth. Sixty-four young born in captivity comprised 24 males, 30 females and 10 of unknown sex.

If a pouch young were removed or lost, the quiescent blastocyst resumed its development, to birth about 26.5 days later. Failure or absence of the blastocyst was followed by an oestrus at about the time of the corresponding post-partum oestrus. Both the oestrous cycle and the interval between removal of a pouch young and oestrus were significantly longer than when a pregnancy
intervened.

The oestrous cycle was characterized by changes in the proportions of the main cell types in the vaginal smear, and by changes in the appearance of the urogenital opening and the pouch and teats. The approach of oestrus could not be predicted from vaginal smears but the post-oestrous condition was always recognizable even without mating.

Young animals first left the pouch for short periods between the ages of 176 and 211 days, and left permanently between 207 and 237 days. Animals of known age were measured and the development of various morphological characters noted at weekly intervals from about birth until 12 months old.
Seasonal Changes in Diet Preferences of Free-Ranging Red Kangaroos, Euros and Sheep in Western New South Wales.
Authors: Ellis BA , Russell EM , Dawson TJ , Harrop CJF
Published: June 2005

Stomach contents of free-ranging animals were analysed botanically for low Atriplex shrubland in western New South Wales, Australia, during 1972-74 in good seasons producing abundant growth and diversity of vegetation. Red kangaroo (Megaleia rufa), euro (Macropus robustus) and sheep (Ovis aries) selected grass and forbs when those were readily available. In poorer pasture sheep selected mainly flat-leaved chenopods (saltbush) and kangaroos selected mainly grass with different amounts of flat- or round-leaved chenopods. Euros were the most selective, eating grass even when there was little grass present. Potential overlaps in diet between kangaroos and sheep were greatest in good pasture and least in the poorest conditions. The other groups of plants considered were non-chenopod shrubs and browse. Extent of overlap was not clear, because animals may have eaten different species within the groups of plants. The study period did not include any severe drought, in which overlap in diet and competition between animal species would have been most significant.
Population monitoring of the vulnerable wallum sedge frog (Litoria olongburensis) in north-eastern New South Wales
Authors: Lewis B. D. , Goldingay R. L.
Published: June 2005

The literature on the population ecology of Australian frogs provides relatively few accounts of population monitoring. This has hampered our ability to understand how frog populations respond to dynamic rainfall patterns and to determine the stability of populations of threatened frog species. We conducted biannual monitoring of the wallum sedge frog (Litoria olongburensis) along transects at 10 sites over a 4-year period (1996–2000). We recorded six environmental parameters to assess their influence on our population indices. Monitoring of transects indicated that populations were rarely stable and fluctuated from year to year. Counts of adults were negatively influenced by rain during the previous day but positively influenced by rain during the previous week. This suggests that timing of recent rainfall has a differing influence on habitat use by adult frogs. Counts of adults were also significantly influenced by site and census period. Numbers of juveniles were influenced by rain during the previous three months, which may suggest that successful recruitment depends on higher water levels in the sedge swamps. Counts of juveniles were also significantly influenced by census period. Our analysis reveals that, after controlling for the influence of rainfall, the number of adult frogs per census varied between 10 and 20 per transect. The number of juveniles varied between 5 and 15 per transect per census. We conclude that the wallum sedge frog across the geographic range of our sites was not in decline during our monitoring period. In light of our findings we provide a review on population monitoring of Australian frogs.
Male and female song structure and singing behaviour in the duetting eastern whipbird, Psophodes olivaceus
Authors: Rogers Amy C.
Published: June 2005

In many tropical bird species, partners combine their songs to form precise duets, of which the function is imperfectly understood. Duet structure and sex differences in vocal strategies may be important indicators of different selective pressures that have led to the evolution and maintenance of these complex acoustic displays. This study examines the singing behaviour of a population of the eastern whipbird, a bird that forms antiphonal duets initiated exclusively by the male. In all, 7% of duets recorded were between a paired female and a male other than her social partner. Males sang more often than females, their songs were longer and moved through a wider frequency range, and they had a larger song repertoire. Females sang two types of song: response songs, used primarily in a duet context, and structurally distinct solo songs, typically used during interactions with other females. Eastern whipbirds lacked unique song types among the repertoires of individual males and females. Males and females combined songs non-randomly to produce specific duets that were shared across the population. Results suggested that song and duet type matching might play an important role in intrasex interactions, such as defence of a territory, or a partner, from same-sex intruders.
Collection and distribution of the early life stages of the Murray cod (Maccullochella peelii peelii) in a regulated river
Authors: Koehn John D. , Harrington D. J.
Published: June 2005

The Murray cod (Maccullochella peelii peelii) is a large fish species keenly sought by anglers. However, this species has declined in distribution and abundance and is now listed nationally as vulnerable. This study was undertaken in the Ovens and Murray rivers, to collect larvae and age-0 Murray cod and determine the distribution of larval Murray cod around the mid-Murray River irrigation storage of Lake Mulwala. Murray cod larvae were collected from 17 of 18 sites: main channels and flowing anabranch channels of regulated and unregulated rivers, sites upstream and downstream of the lake, in the upper and lower reaches of the lake, and in the outflowing Yarrawonga irrigation channel. Larval Murray cod were collected only by methods that sampled drift in flowing waters. Age-0 Murray cod were collected by electrofishing in the main river, but not in off-channel waters, suggesting that cod are likely to settle into habitats in the main channel at a post-larval stage. The widespread occurrence of drifting larvae suggests that this species may be subject to previously unrecognised threats as they pass through hydro-electric power stations or become stranded in anabranch and irrigation channels. Results of this study are likely to be applicable to other species with drifting larval stages, and are relevant to other locations in the Murray–Darling Basin.
Life history and demographics of an island possum
Authors: Isaac Joanne L.
Published: June 2005

Knowledge of life history and demography is essential for effective management of target species. Here, I describe life history and demographic traits of the common brushtail possum (Trichosurus vulpecula) on Magnetic Island, north Queensland. Data were collected during monthly live-trapping sessions over three years (2001–2004). Density was ~100% higher than reported in most Australian populations, at 5 possums per hectare; losses from the population were more than compensated for by births and immigration. Age-specific survival differed between the sexes: male survival declined earlier and faster than female survival. Males were significantly heavier than females as adults and sexual dimorphism appears to arise through a faster growth rate in males following weaning. Age at maturity in females varied from 1 to 3 years; 61% of females produced their first young at age 2. Males became sexually mature at age 3. Breeding was seasonal, with >50% births occurring in April–May; a smaller birth peak in spring was due to some females producing a second young after they had successfully weaned a first. The Magnetic Island possum population appears to be more similar to New Zealand populations, in terms of their life history and demographics, than to other previously studied mainland Australian populations.
Climatically driven macroevolutionary patterns in the size of marine diatoms over the Cenozoic
Authors: Finkel Zoe V. , Katz Miriam E. , Wright James D. , Schofield Oscar M. E. , Falkowski Paul G.
Published: June 2005

Numerous taxonomic groups exhibit an evolutionary trajectory in cell or body size. The size structure of marine phytoplankton communities strongly affects food web structure and organic carbon export into the ocean interior, yet macroevolutionary patterns in the size structure of phytoplankton communities have not been previously investigated. We constructed a database of the size of the silica frustule of the dominant fossilized marine planktonic diatom species over the Cenozoic. We found that the minimum and maximum sizes of the diatom frustule have expanded in concert with increasing species diversity. In contrast, the mean area of the diatom frustule is highly correlated with oceanic temperature gradients inferred from the δ
18
O of foraminiferal calcite, consistent with the hypothesis that climatically induced changes in oceanic mixing have altered nutrient availability in the euphotic zone and driven macroevolutionary shifts in the size of marine pelagic diatoms through the Cenozoic.
Multiple subsets of side-chain packing in partially folded states of α-lactalbumins
Authors: Mok K. Hun , Nagashima Toshio , Day Iain J. , Hore P. J. , Dobson Christopher M.
Published: June 2005

Photochemically induced dynamic nuclear polarization NMR pulse-labeling techniques have been used to obtain detailed information about side-chain surface accessibilities in the partially folded (molten globule) states of bovine and human α-lactalbumin prepared under a variety of well defined conditions. Pulse labeling involves generating nuclear polarization in the partially folded state, rapidly refolding the protein within the NMR sample tube, then detecting the polarization in the well dispersed native-state spectrum. Differences in the solvent accessibility of specific side chains in the various molten globule states indicate that the hydrophobic clusters involved in stabilizing the α-lactalbumin fold can be formed from interactions between a variety of different hydrophobic residues in both native and nonnative environments. The multiple subsets of hydrophobic clusters are likely to result from the existence of distinct but closely related local minima on the free-energy landscape of the protein and show that the fold and topology of a given protein may be formed from degenerate groups of side chains.
Tunneling rates in electron transport through double-barrier molecular junctions in a scanning tunneling microscope
Authors: Nazin G. V. , Wu S. W. , Ho W.
Published: June 2005

The scanning tunneling microscope enables atomic-scale measurements of electron transport through individual molecules. Copper phthalocyanine and magnesium porphine molecules adsorbed on a thin oxide film grown on the NiAl(110) surface were probed. The single-molecule junctions contained two tunneling barriers, vacuum gap, and oxide film. Differential conductance spectroscopy shows that electron transport occurs via vibronic states of the molecules. The intensity of spectral peaks corresponding to the individual vibronic states depends on the relative electron tunneling rates through the two barriers of the junction, as found by varying the vacuum gap tunneling rate by changing the height of the scanning tunneling microscope tip above the molecule. A simple, sequential tunneling model explains the observed trends.
In vivo
formation and repair of DNA double-strand breaks after computed tomography examinations
Authors: Löbrich Markus , Rief Nicole , Kühne Martin , Heckmann Martina , Fleckenstein Jochen , Rübe Christian , Uder Michael
Published: June 2005

Ionizing radiation can lead to a variety of deleterious effects in humans, most importantly to the induction of cancer. DNA double-strand breaks (DSBs) are among the most significant genetic lesions introduced by ionizing radiation that can initiate carcinogenesis. We have enumerated γ-H2AX foci as a measure for DSBs in lymphocytes from individuals undergoing computed tomography examination of the thorax and/or the abdomen. The number of DSBs induced by computed tomography examination was found to depend linearly on the dose–length product, a radiodiagnostic unit that is proportional to both the local dose delivered and the length of the body exposed. Analysis of lymphocytes sampled up to 1 day postirradiation provided kinetics for the
in vivo
loss of γ-H2AX foci that correlated with DSB repair. Interestingly, in contrast to results obtained
in vitro
, normal individuals repair DSBs to background levels. A patient who had previously shown severe side effects after radiotherapy displayed levels of γ-H2AX foci at various sampling times postirradiation that were several times higher than those of normal individuals. γ-H2AX and pulsed-field gel electrophoresis analysis of fibroblasts obtained from this patient confirmed a substantial DSB repair defect. Additionally, these fibroblasts showed significant
in vitro
radiosensitivity. These data show that the
in vivo
induction and repair of DSBs can be assessed in individuals exposed to low radiation doses, adding a further dimension to DSB repair studies and providing the opportunity to identify repair-compromised individuals after diagnostic irradiation procedures.
Time-varying covariance of neural activities recorded in striatum and frontal cortex as monkeys perform sequential-saccade tasks
Authors: Fujii N. , Graybiel A. M.
Published: June 2005

Cortico-basal ganglia circuits are key parts of the brain's habit system, but little is yet known about how these forebrain pathways function as ingrained habits are performed. We simultaneously recorded spike and local field potential (LFP) activity from regions of the frontal cortex and basal ganglia implicated in visuo-oculomotor control as highly trained macaque monkeys performed sequences of visually guided saccades. The tasks were repetitive, required no new learning, and could be performed nearly automatically. Our findings demonstrate striking differences between the relative timing of striatal and cortical activity during performance of the tasks. At the onset of the visual cues, LFPs in the prefrontal cortex and the oculomotor zone of the striatum showed near-synchronous activation. During the period of sequential-saccade performance, however, peak LFP activity occurred 100–300 msec later in the striatum than in the prefrontal cortex. Peak prefrontal activity tended to be peri-saccadic, whereas peak striatal activity tended to be post-saccadic. This temporal offset was also apparent in pairs of simultaneously recorded prefrontal and striatal neurons. In triple-site recordings, the LFP activity recorded in the supplementary eye field shared temporal characteristics of both the prefrontal and the striatal patterns. The near simultaneity of prefrontal and striatal peak responses at cue onsets, but temporal lag of striatal activity in the movement periods, suggests that the striatum may integrate corollary discharge or confirmatory response signals during sequential task performance. These timing relationships may be signatures of the normal functioning of striatal and frontal cortex during repetitive performance of learned behaviors.
Fire cycles in North American interior grasslands and their relation to prairie drought
Authors: Brown K. J. , Clark J. S. , Grimm E. C. , Donovan J. J. , Mueller P. G. , Hansen B. C. S. , Stefanova I.
Published: June 2005

High-resolution analyses of a late Holocene core from Kettle Lake in North Dakota reveal coeval fluctuations in loss-on-ignition carbonate content, percentage of grass pollen, and charcoal flux. These oscillations are indicative of climate–fuel–fire cycles that have prevailed on the Northern Great Plains (NGP) for most of the late Holocene. High charcoal flux occurred during past moist intervals when grass cover was extensive and fuel loads were high, whereas reduced charcoal flux characterized the intervening droughts when grass cover, and hence fuel loads, decreased, illustrating that fire is not a universal feature of the NGP through time but oscillates with climate. Spectral and wavelet analyses reveal that the cycles have a periodicity of ≈160 yr, although secular trends in the cycles are difficult to identify for the entire Holocene because the periodicity in the early Holocene ranged between 80 and 160 yr. Although the cycles are evident for most of the last 4,500 yr, their occasional muting adds further to the overall climatic complexity of the plains. These findings clearly show that the continental interior of North America has experienced short-term climatic cycles accompanied by a marked landscape response for several millennia, regularly alternating between dual landscape modes. The documentation of cycles of similar duration at other sites in the NGP, western North America, and Greenland suggests some degree of regional coherence to climatic forcing. Accordingly, the effects of global warming from increasing greenhouse gases will be superimposed on this natural variability of drought.
Longitudinal analysis of the group A
Streptococcus
transcriptome in experimental pharyngitis in cynomolgus macaques
Authors: Virtaneva Kimmo , Porcella Stephen F. , Graham Morag R. , Ireland Robin M. , Johnson Claire A. , Ricklefs Stacy M. , Babar Imran , Parkins Larye D. , Romero Romina A. , Corn G. Judson , Gardner Don J. , Bailey John R. , Parnell Michael J. , Musser James M.
Published: June 2005

Identification of the genetic events that contribute to host–pathogen interactions is important for understanding the natural history of infectious diseases and developing therapeutics. Transcriptome studies conducted on pathogens have been central to this goal in recent years. However, most of these investigations have focused on specific end points or disease phases, rather than analysis of the entire time course of infection. To gain a more complete understanding of how bacterial gene expression changes over time in a primate host, the transcriptome of group A
Streptococcus
(GAS) was analyzed during an 86-day infection protocol in 20 cynomolgus macaques with experimental pharyngitis. The study used 260 custom Affymetrix (Santa Clara, CA) chips, and data were confirmed by TaqMan analysis. Colonization, acute, and asymptomatic phases of disease were identified. Successful colonization and severe inflammation were significantly correlated with an early onset of superantigen gene expression. The differential expression of two-component regulators
covR
and
spy0680
(
M1
_
spy0874
) was significantly associated with GAS colony-forming units, inflammation, and phases of disease. Prophage virulence gene expression and prophage induction occurred predominantly during high pathogen cell densities and acute inflammation. We discovered that temporal changes in the GAS transcriptome were integrally linked to the phase of clinical disease and host-defense response. Knowledge of the gene expression patterns characterizing each phase of pathogen–host interaction provides avenues for targeted investigation of proven and putative virulence factors and genes of unknown function and will assist vaccine research.