bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical properties of Cd1−xMnxTe∕Cd1−yMnyTe superlattices with high difference of Mn concentration between wells and barriers
Authors: Bellani Vittorio , Stella Angiolino , Chen Chenjia , Wang Xuezhong
Published: April 2005

We studied the optical properties of Cd1−xMnxTe∕Cd1−yMnyTe semiconductor superlattices with medium (x=0.3,y=0.01) and high (x=0.8,y=0) difference of the Mn concentration between wells and barriers, by means of photoluminescence and photoreflectance spectroscopy. Photoluminescence allows us to study the emission due to the fundamental heavy (H) hole 11H interminiband excitonic transition and evidences the emission characteristics. Photoreflectance reveals several heavy and light (L) holes interminiband excitonic transitions, up to the 33H. The experiments are in good agreement with the theory with an envelope-function approximation approach, taking into account strain effects due to lattice mismatch between wells and barriers. The combined use of photoluminescence and photoreflectance gives a complete information on the electronic configuration of these Cd1−xMnxTe∕Cd1−yMnyTe superlattices that can find specific applications in spintronic devices.
Sulfidic photochemical passivation of GaAs surfaces in alcoholic solutions
Authors: Simonsmeier T. , Ivankov A. , Bauhofer W.
Published: April 2005

We report on a remarkable enhancement of the passivation effect of sulfidic solutions through illumination with above band gap light. Luminescence measurements on GaAs surfaces which have been illuminated during chemical passivation reveal in comparison to nonilluminated samples a further reduction of their surface density of states as well as a significantly increased stability of the passivation. Investigations with photoelectron spectroscopy show that illumination leads to a nearly complete removal of oxides on the surface. Measurements on Schottky diodes which have been manufactured with photochemically passivated GaAs indicate a noticeable decrease in band bending and a depinning of the Fermi level.
Mode correlation of product pairs in the reaction OH+CD4→HOD+CD3
Authors: Zhang Bailin , Shiu Weicheng , Lin Jim J. , Liu Kopin
Published: April 2005

The hydrogen abstraction reaction from methane by a hydroxyl radical produces two polyatomic molecules. Each product has several vibrational modes that characterize distinct, concerted motions of the constituent atoms of the molecule. This communication describes the first measurement that maps out the coincident information on how the mode of excitation of one product varies with that of the other co-product. Such information on mode correlation of product pairs is particularly appealing in that it provides intuitively a glimpse of the reaction paths by which the chemical transformation occurs.
Scanning-tunneling-microscopy observation of heterojunctions with a type-II band alignment in ZnSe∕BeTe multiple quantum wells
Authors: Yamakawa I. , Akanuma Y. , Akimoto R. , Nakamura A.
Published: April 2005

Heterojunctions of ZnSe∕BeTe multiple quantum wells (MQW) with a type-II band alignment have been investigated by cross-sectional scanning tunneling microscopy (STM). The brightness of the ZnSe and BeTe layers in the cross-sectional STM image is inverted between filled- and empty-state images, taken by switching the bias polarity of the sample bias voltage in constant current mode. Such inversion of the brightness indicates changes in the band offsets of the conduction and valence bands between the ZnSe and BeTe layers of the type-II MQW. The roughness of interfaces in the filled state images has also been investigated on an atomic scale. It is found that the roughness amplitude Δ, and the correlation length Λ, which characterize the observed interfacial roughness, are comparable to the values observed for III-V heterostructures.
Magnetization manipulation in (Ga,Mn)As by subpicosecond optical excitation
Authors: Astakhov G. V. , Kimel A. V. , Schott G. M. , Tsvetkov A. A. , Kirilyuk A. , Yakovlev D. R. , Karczewski G. , Ossau W. , Schmidt G. , Molenkamp L. W. , Rasing Th.
Published: April 2005

We demonstrate complete reversal of a full magnetic hysteresis loop of the magnetic semiconductor (Ga,Mn)As by ultrashort optical excitation with a single subpicosecond light pulse, with obvious implications for ultrafast magneto-optical recording. Our approach utilizes the fourfold magnetic anisotropy of (Ga,Mn)As, in combination with the magnetic linear dichroism of the material.
Well-ordered large-area arrays of epitaxial ferroelectric (Bi,La)4Ti3O12 nanostructures fabricated by gold nanotube-membrane lithography
Authors: Lee Sung Kyun , Lee Woo , Alexe Marin , Nielsch Kornelius , Hesse Dietrich , Gösele Ulrich
Published: April 2005

Two-dimensionally well-ordered, large-area arrays of epitaxial, ferroelectric, La-substituted Bi4Ti3O12 (BLT) nanostructures are prepared using gold nanotube membranes as a liftoff mask. Epitaxial nanostructures with a height of about 65nm and a lateral size of about 150nm, with either (001) (“c-axis”) orientation, or mixed (118)∕(100) (“non-c-axis”) orientation, are obtained on (001)- and (011)-oriented SrTiO3 substrates, respectively. The ferroelectric properties are probed by piezoresponse scanning force microscopy. Non-c-axis-oriented BLT nanostructures show an effective piezoresponse coefficient (2dzz) of about 38.0pm∕V, whereas c-axis-oriented structures show one of only about 4.9pm∕V.
Fabrication of nanoscale C60 field-effect transistors with carbon nanotubes
Authors: Horiuchi Kazunaga , Kato Tomohiro , Hashii Shinobu , Hashimoto Akira , Sasaki Takahiko , Aoki Nobuyuki , Ochiai Yuichi
Published: April 2005

A nanoscale C60 field-effect transistor has been fabricated with carbon nanotubes (C60CNT-FET). A wire of multiwalled carbon nanotube has been anchored by metal pads on a Si wafer, and cut by bombardment with focused Ga2+ ion beam. The cut ends of the wire have been integrated as source-drain electrodes into the C60CNT-FET, with a vacuum evaporated C60 thin film. The C60CNT-FET has exhibited an excellent performance of a low-voltage drive operation, without any short-channel effect even at as small as 100 nm of channel length.
Unlocking of remanent magnetization of pole heads by medium stray fields
Authors: Richter H. J. , Palmer D. C. , Haftek E.
Published: April 2005

We report investigations of a stochastic phenomenon in which pole heads used for perpendicular recording stay magnetized after the driving current is switched off. This remanent magnetization causes erasure of the information previously written on the disk. The length of the erasure was found to be in the range of several μs up to a few ms. Surprisingly it is found that the remanent magnetization state can be reduced by magnetization patterns that already exist on the disk at the time of writing. Experimental evidence is presented which illustrates that the unlocking of the remanent state can be influenced by the type and location of these magnetization patterns. It is concluded that magnetization patterns creating rotating fields are most efficient in destroying these remanent states.
Self-assembled monolayer cleaning methods: Towards fabrication of clean high-temperature superconductor nanostructures
Authors: Kim Sungwook , Chang In Soon , McDevitt John T.
Published: April 2005

Although extensive amounts of research have been carried out on superconductor-normal metal-superconductor (SNS) electronic devices, the fabrication of superconductor SNS devices still remains difficult. Surface modification of high-temperature superconductors could be a way to control the interface of SNS electronic device fabrication. Here, we developed a cleaning method for thin films of high-temperature superconductor surface based on self-assembled monolayers. High-quality c-axis orientated YBa2Cu3O7−δ (i.e., YBCO) and Y0.6Ca0.4Ba1.6La0.4Cu3O7−δ (i.e., TX-YBCO) thin films were deposited by standard laser ablation methods. YBCO/Au/YBCO and TX-YBCO/Au/TX-YBCO planar type junctions were fabricated by photolithography, focused-ion-beam milling, and ex situ sputter depositions. A 40–50nm nanotrench was ion milled on the thin film by FIB, and a thin gold layer was deposited by an ex situ method on the nanotrench to connect the two separated high-temperature superconductor electrodes. SEM, AFM, and R vs T resistivity measurements were used to compare the corrosion layer formed in the interface of the SNS junctions with the SAM cleaned SNS junction. Evidence here suggests that the SAM cleaning method can be used to remove the degradation layer on the surface of cuprate superconductors. The obtained contact resistivity value, (10−8Ωcm2) for a SNS junction with SAM treatment is comparable with that of SNS junctions fabricated by the in situ methods.
Ferromagnetic percolation in MnxGe1−x dilute magnetic semiconductor
Authors: Li A. P. , Shen J. , Thompson J. R. , Weitering H. H.
Published: April 2005

We have studied the magnetic and magnetotransport properties of Mn-doped Ge grown by molecular-beam epitaxy. This group-IV dilute ferromagnetic semiconductor exhibits two magnetic transitions. An upper critical temperature TC* (∼112K for x∼0.05) is evident from the extrapolated Curie–Weiss susceptibility and from the Arrott plot analysis of anomalous Hall effect data. The existence of a lower critical temperature TC (∼12K for x∼0.05) is established from ac susceptibility and magnetotransport data. The data are fully compatible with the existence of bound magnetic polarons or clusters below TC* which percolate at TC⪡TC*.
Diffusion mechanisms of indium and nitrogen during the annealing of InGaAs quantum wells with GaNAs barriers and GaAs spacer layers
Authors: Oye Michael M. , Govindaraju Sridhar , Sidhu Rubin , Reifsnider Jason M. , Holmes Archie L.
Published: April 2005

In this article, we discuss two indium diffusion mechanisms that are present during the rapid thermal annealing of InxGa1−xAs quantum wells (x=0.18, 0.22, and 0.26) with GaNyAs1−y barriers (y=0.6 or 1.2%). Samples were grown with and without a GaAs spacer layer in between the quantum well and barrier. The dominant mechanism is dependent on the amount of thermal energy applied during the annealing process. At low annealing times and temperatures, we have observed that In-Ga intra-diffusion entirely within the quantum well is dominant. For the higher times and temperatures, In-Ga inter-diffusion between the quantum well and barrier becomes dominant. These observations were confirmed by high-resolution x-ray diffraction and the peak emission wavelengths were measured by room-temperature photoluminescence. We have also observed that nitrogen had diffused from the GaNAs barriers into the InGaAs quantum wells in all of our annealed samples. In addition, the commonly observed indium-content dependent diffusion in GaInNAs-based systems was not observed with InGaAs∕GaNAs-based structures.
Nanofibers from functionalized para-phenylene molecules
Authors: Schiek M. , Lützen A. , Koch R. , Al-Shamery K. , Balzer F. , Frese R. , Rubahn H.-G.
Published: April 2005

Tens to hundreds of micrometers long organic nanofibers have been generated from methoxy functionalized quaterphenylene molecules. The mutual alignment of the fibers is similar to that of previously reported nanofibers from para-hexaphenylene, and they emit intense, blue light centered at 400 nm with well resolved higher order vibronic peaks. The morphology is slightly different from that of para-hexaphenylene nanofibers, reflecting the different molecular structure. This study demonstrates that it is possible to generate organic nanofibers from artificially functionalized molecules and thus opens up the route to dedicated applications in new microdevices.
Shallow BF2 implants in Xe-bombardment-preamorphized Si: The interaction between Xe and F
Authors: Werner M. , van den Berg J. A. , Armour D. G. , Carter G. , Feudel T. , Herden M. , Bersani M. , Giubertoni D. , Ottaviano L. , Bongiorno C. , Mannino G. , Bailey P. , Noakes T. C. Q.
Published: April 2005

Si(100) samples, preamorphized to a depth of ∼30nm using 20 keV Xe ions to a nominal fluence of 2×1014cm−2 were implanted with 1 and 3 keV BF2 ions to fluences of 7×1014cm−2. Following annealing over a range of temperatures (from 600 to 1130 °C) and times the implant redistribution was investigated using medium-energy ion scattering (MEIS), secondary ion mass spectrometry (SIMS), and energy filtered transmission electron microscopy (EFTEM). MEIS studies showed that for all annealing conditions leading to solid phase epitaxial regrowth, approximately half of the Xe had accumulated at depths of 7 nm for the 1 keV and at 13 nm for the 3 keV BF2 implant. These depths correspond to the end of range of the B and F within the amorphous Si. SIMS showed that in the preamorphized samples, approximately 10% of the F migrates into the bulk and is trapped at the same depths in a ∼1:1 ratio to Xe. These observations indicate an interaction between the Xe and F implants and a damage structure that becomes a trapping site. A small fraction of the implanted B is also trapped at this depth. EXTEM micrographs suggest the development of Xe agglomerates at the depths determined by MEIS. The effect is interpreted in terms of the formation of a volume defect structure within the amorphized Si, leading to F stabilized Xe agglomerates or XeF precipitates.
Nucleation and growth of platelets in hydrogen-ion-implanted silicon
Authors: Nastasi Michael , Höchbauer Tobias , Lee Jung-Kun , Misra Amit , Hirth John P. , Ridgway Mark , Lafford Tamzin
Published: April 2005

H ion implantation into crystalline Si is known to result in the precipitation of planar defects in the form of platelets. Hydrogen-platelet formation is critical to the process that allows controlled cleavage of Si along the plane of the platelets and subsequent transfer and integration of thinly sliced Si with other substrates. Here we show that H-platelet formation is controlled by the depth of the radiation-induced damage and then develop a model that considers the influence of stress to correctly predict platelet orientation and the depth at which platelet nucleation density is a maximum.
Lateral-field-excited thin-film Lamb wave resonator
Authors: Bjurström Johan , Katardjiev Ilia , Yantchev Ventsislav
Published: April 2005

The basic principles and technology for the development of lateral-field-excited Lamb acoustic wave resonators on sputter-deposited c-oriented thin aluminum nitride films are presented. The experimental results demonstrate that Lamb waves can be successfully used as an alternative to high-velocity surface acoustic waves.
Direct observation of negative electron affinity in hydrogen-terminated diamond surfaces
Authors: Takeuchi D. , Kato H. , Ri G. S. , Yamada T. , Vinod P. R. , Hwang D. , Nebel C. E. , Okushi H. , Yamasaki S.
Published: April 2005

Total photoyield experiments are applied to characterize p-, intrinsic, and n-type diamond with hydrogen-terminated surfaces. On all hydrogen-terminated samples a photoelectron threshold energy of 4.4 eV is detected which is discussed in detail in this letter. We attribute this threshold to the energy gap between the valence-band maximum and the vacuum level, which is 1.1 eV below the conduction-band minimum, and generally referred to as ”negative electron affinity” (NEA). Hydrogen terminated p-type and intrinsic diamond show a rise of secondary photoyield in the excitation regime hν>5.47eV. However, this is not detected on n-type diamond. We ascribe this to the formation of an upward surface band bending in the vicinity of the n-type diamond surface which acts as an energy barrier for electrons.
Pronounced photorefractive effect at wavelength over 1000 nm in monolithic organic materials
Authors: You Wei , Hou Zhanjia , Yu Luping
Published: April 2005

Two monolithic organic materials exhibiting high photorefractive (PR) performances at a wavelength of 1064 nm were prepared and characterized. It was found that thiophene-based molecule T6 demonstrated better PR properties than benzene based molecule B6. A net optical gain of 139.1cm−1 at a low applied field of 43.7V∕μm and a diffraction efficiency of 45.6% at 35.3V∕μm were observed for materials made from T6. Net optical gain at 1300 nm was also observed for T6. The differences in PR behavior between two materials with similar structures were explained based on dipole moment and photoconductivity differences.
Nanoengineered Curie temperature in laterally patterned ferromagnetic semiconductor heterostructures
Authors: Eid K. F. , Sheu B. L. , Maksimov O. , Stone M. B. , Schiffer P. , Samarth N.
Published: April 2005

We demonstrate the manipulation of the Curie temperature of buried layers of the ferromagnetic semiconductor (Ga,Mn)As using nanolithography to enhance the effect of annealing. Patterning the GaAs-capped ferromagnetic layers into nanowires exposes free surfaces at the sidewalls of the patterned (Ga,Mn)As layers and thus allows the removal of Mn interstitials using annealing. This leads to an enhanced Curie temperature and reduced resistivity compared to unpatterned samples. For a fixed annealing time, the enhancement of the Curie temperature is larger for narrower nanowires.
A monopole-dipole model to compute the polarization of metallic carbon nanotubes
Authors: Mayer A.
Published: April 2005

We present a monopole-dipole model to compute the polarization of metallic carbon nanotubes. The parameters of this model are adjusted on experimental data. In particular, we aimed at reproducing the mean polarizability of C60 and C70, the transverse polarizability of some carbon nanotubes, as well as the internal over external value ratio of transverse electric fields. As an application, we compute the axial polarizability of finite (5,5) carbon nanotubes. The comparison of these results with those obtained using other techniques shows that the consideration of net charges gives a better account of the metallicity of this kind of nanotubes.
Origin of the stress-induced leakage currents in Al–Ta2O5∕SiO2–Si structures
Authors: Novkovski N. , Atanassova E.
Published: April 2005

The leakage currents in the Al–Ta2O5∕SiO2–Si structures increase as a result of the current stress. The case of the constant current stress was studied and it was found that the I–V characteristics of both unstressed and stressed samples can be described by the previously developed model involving Poole–Frenkel effect in the Ta2O5 and both hopping conductivity and tunneling in the SiO2. After extracting the parameters for both layers from the fitting of the theoretical curves to the experimental results, it was found that the main reason for the increased leakage is the partial destruction of the SiO2 layer.
Life-class stages in coast daisy-bush (Olearia axillaris: Asteraceae) as a possible means of monitoring coastal dunes
Authors: Hinchliffe Julie , Conran John G.
Published: April 2005

Olearia axillaris (DC.) F.Muell. ex Benth.: Asteraceae) shrubs in the remnant coastal foredunes at Tennyson in suburban Adelaide, South Australia, were measured for height, width, largest trunk diameter, percentage stem reflexing, percentage procumbent stems and percentage dead stems. Cluster analysis grouped the plants into three distinct life classes: Juvenile, with erect trunks <1 m tall and main trunk <5 cm in diameter; Mature, at ~1.5 m tall and with numerous reflexed stems 8–12 cm in diameter; and Senescent, at ~2 m tall, trunk 8–12 cm in diameter, with numerous procumbent stems and dead branches. A survey of the site also found that although abundant, indicating continuing recruitment, juveniles were most common on the foredunes. Application of this life-classing technique to several burnt and unburnt sites in the Coorong, South Australia, confirmed its utility for assessing population structure, with recently burnt sites showing significantly fewer specimens from later life classes. The ability to life class O. axillaris permits rapid assessment of population structure in this dominant coastal foredune shrub, allowing dune health and recruitment to be monitored easily and managed more efficiently.
Floral biology of Hemigenia and Microcorys (Lamiaceae)
Authors: Guerin Greg
Published: April 2005

The floral morphology and pollination of Hemigenia R.Br. and Microcorys R.Br. (Lamiaceae) were examined in the field and laboratory. The protandrous flowers have tubular, two-lipped corollas. Nine floral morphotypes are described. The stamens may be completely sterile (staminodal) or have one theca reduced or absent. The anthers typically have elongated connective tissue and are mobile on the filament. When the lower end of the anther is pushed, the upper end is levered towards the mouth of the corolla tube, hence dusting the pollinator precisely where receptive stigmas will later touch. Bearding on the anthers of the adaxial stamens catches adjacent anthers so that they lever in unison. Staminodes guide insect pollinators into the throat to allow precise pollen dusting. Detailed field observations show that bees and flies are the principle pollinators of most species. Floral morphologies are related to pollinator castes, and reproductive isolation and efficiency is enhanced by precise pollen deposition. Bird pollination is likely to have arisen independently in several taxa. The floral arrangement of these taxa is superficially similar but the syndrome is achieved through different anatomy.
Vegetative and reproductive phenologies of four mangrove species from northern Australia
Authors: Coupland Grey T. , Paling Eric I. , McGuinness Keith A.
Published: April 2005

Mangrove communities in the tropical north of Australia are some of the most species rich in the world, yet surprisingly little is known of their reproductive and vegetative phenology. This study investigated the phenology of four mangrove species: Avicennia marina (Forsk.) Vierh., Ceriops australis (C.T.White) Ballment, T.J.Sm & Stoddart, Rhizophora stylosa Griff. and Sonneratia alba J.Smith, in Darwin Harbour over 24 months. Investigations included documenting the flowering and fruiting phenology, periods of leaf flush and leaf longevity. Flowering in these mangroves generally occurred during the dry season (June–October), with the exception of R. stylosa in which flowering occurred in the middle of the wet (December–February). Fruits and propagules were released in the dry and ‘build up’ periods (August–November), with the exception of A. marina, which released propagules in the middle of the wet season. Fruit and/or propagule maturation took less than 2 months in A. marina and S. alba, whereas in C. australis and R. stylosa maturation took 12 and 11 months, respectively. Timing of new leaf production generally coincided with the wet season, after the flowering and fruiting periods of each of the four species. Periods of leaf flush and leaf fall were often closely linked, and species with longer-lived leaves produced fewer leaves at each period of leaf flush. Maximum leaf longevity varied considerably among mangroves, ranging from 8 months in the lower canopy of S. alba to more than 24 months in C. australis. There was also large variability in leaf longevity among different regions of the canopy, with shade leaves generally living longer than sun leaves, and leaves in the upper canopy (3–7 m) longer than those in the lower regions (0–3 m).
Genetic variation in the endemic plant Cycas debaoensis on the basis of ISSR analysis
Authors: Jianguang Xie , Shuguang Jian , Nian Liu
Published: April 2005

Cycas debaoensis Y.C.Zhong et C.J.Chen is a rare and endangered cycad species that is endemic to South China. It has divided pinnae. Genetic variation in the species was investigated by using an intersimple sequence repeat (ISSR) marker. The species exhibits a moderate level of genetic diversity (at population level P = 34.7%, H = 0.141, I = 0.204; at species level P = 57.4%, H = 0.215, I = 0.315) and a high level of genetic differentiation among populations (Gst = 0.342). Thus, the indirect estimate of gene flow on the basis of Gst was low (Nm = 0.481). The narrow colonisation area and island pattern of distribution, combined with limited gene flow among populations and genetic drift, may play an important role in shaping the genetic structure of C. debaoensis. On the basis of these findings, strategies are suggested for the conservation and management of the species.
Anatomy of ethylene-induced floral-organ abscission in Chamelaucium uncinatum (Myrtaceae)
Authors: Macnish Andrew J. , Irving Donald E. , Joyce Daryl C. , Vithanage Vasanthe , Wearing Alan H.
Published: April 2005

Postharvest abscission of Geraldton waxflower (Chamelaucium uncinatum Schauer) flower buds and flowers is ethylene-mediated. Exposure of floral organs to exogenous ethylene (1 µL L–1) for 6 h at 20°C induced separation at a morphologically and anatomically distinct abscission zone between the pedicel and floral tube. Flower buds with opening petals and flowers with a nectiferous hypanthium were generally more responsive to exogenous ethylene than were flower buds enclosed in shiny bracteoles and aged (senescing) flowers. The anatomy of abscission-zone cells did not change at sequential stages of floral development from immature buds to aged flowers. The zone comprised a layer of small, laterally elongated-to-rounded, closely packed and highly protoplasmic parenchyma cells. Abscission occurred at a two- to four-cell-wide separation layer within the abscission zone. The process involved degradation of the middle lamella between separation layer cells. Following abscission, cells on both the proximal and distal faces of the separation layer became spherical, loosely packed and contained degenerating protoplasm. Central vascular tissues within the surrounding band of separation layer cells became torn and fractured. For flower buds, bracteoles that enclose the immature floral tube also separated at an abscission zone. However, this secondary abscission zone appeared less sensitive to ethylene than the primary (central) floral-tube abscission zone as bracteoles generally only completely abscised when exposed to 10 µL L–1 ethylene for the longer period of 24 h at 20°C. The smooth surfaces of abscised separation-layer cells suggest that hydrolase enzymes degrade the middle lamella between adjacent cell walls.
Mineral and elemental distribution in soils formed on the River Niger floodplain, eastern Nigeria
Authors: Igwe C. A. , Zarei M. , Stahr K.
Published: April 2005

Studies of mineral distribution in soils provide vital information for understanding the genesis of the soil. We studied the soils formed on the floodplain of the River Niger to determine the occurrence, distribution, and weathering transformations of minerals in a soil chronosequence in eastern Nigeria. Five soil profiles representing 5 depositional stages were studied. The soils have aquic moisture regimes and an isohyperthermic temperature regime by Soil Taxonomy. Gleysation due to poor drainage is very dominant. The soils are low in pH, organic matter, and exchangeable cations. Plinthisation and ferralitisation resulting in high values of Fe2O3 and Al2O3 were observed in the coarse sand, while in the fine sand fractions, quartz and feldspar grains have accumulated with mica being next in abundance. The occurrence of expansible minerals and kaolinite in the clay fractions is as a result of transformation of mica and feldspars giving rise to these minerals. We postulate that the origin and abundance of K2O and MgO in the clay fractions were from the breakdown of the structural units of the expansible minerals, micas and feldspars. Illite undergoes a transformation process to expansible minerals, while kaolinitisation is the major process in the clay fractions. Principal component analysis shows that 23 mineral variables which relate with kaolinite and other silicate clays can be reduced to 5 principal components.
Competitive sorption reactions between phosphorus and organic matter in soil: a review
Authors: Guppy C. N. , Menzies N. W. , Moody P. W. , Blamey F. P. C.
Published: April 2005

The incorporation of organic matter (OM) in soils that are able to rapidly sorb applied phosphorus (P) fertiliser reportedly increases P availability to plants. This effect has commonly been ascribed to competition between the decomposition products of OM and P for soil sorption sites resulting in increased soil solution P concentrations. The evidence for competitive inhibition of P sorption by dissolved organic carbon compounds, derived from the breakdown of OM, includes studies on the competition between P and (i) low molecular weight organic acids (LOAs), (ii) humic and fulvic acids, and (iii) OM leachates in soils with a high P sorption capacity. These studies, however, have often used LOAs at 1–100 mm, concentrations much higher than those in soils (generally <0.05 mm). The transience of LOAs in biologically active soils further suggests that neither their concentration nor their persistence would have a practical benefit in increasing P phytoavailability. Higher molecular weight compounds such as humic and fulvic acids also competitively inhibit P sorption; however, little consideration has been given to the potential of these compounds to increase the amount of P sorbed through metal–chelate linkages. We suggest that the magnitude of the inhibition of P sorption by the decomposition products of OM leachate is negligible at rates equivalent to those of OM applied in the field. Incubation of OM in soil has also commonly been reported as reducing P sorption in soil. However, we consider that the reported decreases in P sorption (as measured by P in the soil solution) are not related to competition from the decomposition products of OM breakdown, but are the result of P release from the OM that was not accounted for when calculating the reduction in P sorption.
Monitoring soil moisture status in a Black Vertosol on the Liverpool Plains, NSW, using a combination of neutron scattering and electrical image methods
Authors: Acworth R. I. , Young R. R. , Bernadi A. L.
Published: April 2005

Electrical image data were used to estimate soil moisture content beneath smectite-dominated black Vertosol in the Liverpool Plains catchment in northern New South Wales. Measurements carried out over a range of soil moisture conditions included: water use by lucerne sown into a full profile, recharge of profiles after lucerne and long fallow after a cereal crop. Measurements were repeated approximately every 2 months between September 2000 and August 2001. Estimates of bulk electrical conductivity (EC), determined from inversion of apparent conductivity electrical images, were compared to soil moisture measurements made using neutron access tubes. A correlation of 0.77 (n = 228, P < 0.0001) between the 2 datasets indicates that electrical imaging can be used to satisfactorily predict bulk moisture content in soils of this type. Interpretation of the bulk EC images indicates drying of the soil profile to 6 m depth beneath lucerne.
Soil compaction around Eucalyptus grandis roots: a micromorphological study
Authors: Clemente E. P. , Schaefer C. E. G. R. , Novais R. F. , Viana J. H. , Barros N. F.
Published: April 2005

This study aimed to evaluate the effects of Eucalyptus grandis root growth on localised soil compaction and fracturing. Undisturbed soil (Kandiustox) samples subjected to root growth pressure were used, employing 2 methods to study the phenomenon: (i) micromorphological analysis of thin sections of soil samples compacted by roots of 0.3, 0.9, 1.3, 2.8, 3.5, 6.4, 8.0, 9.0, and 10.2 cm diameter, carried out in the zone under direct root influence, up to 1 cm from the root–soil surface, compared with a reference area at a distance of 3 cm from the contact surface; (ii) a localised infiltration test to assess the time taken to infiltrate one drop of water into the surface of root-compacted soils, compared with the time taken in a reference sample without root compaction. The soil compaction was greater around root diameters >3.5 cm, and this effect was accompanied by reduced water infiltration in the soil surface at the root contact. Presence of chiseling fractures at an approximate 45° angle to the soil surface suggested helicoidal growth of the E. grandis root, causing both soil compression and shearing. At microscopic level the soil-root contact showed clay-oriented features, microfractures, fungi coatings, and micro-slickensides. The lower infiltration rate in the compacted soil–root surface is associated with both physical (compaction) and chemical (possibly hydrophobicity) mechanisms. The use of micromorphological techniques and image analysis allowed the observation and quantification of soil porosity in the vicinity of roots.
Quantitative soil - landscape models for the Haldon and Hurunui soil sets, New Zealand
Authors: Schmidt Jochen , Tonkin Phil , Hewitt Allan
Published: April 2005

Limited resources and large areas of steeplands with limited field access forced soil and land resource surveyors in New Zealand often to develop generalised models of soil–landscape relationships and to use these to produce soil maps by manual interpretation of aerial photographs and field survey. This method is subjective and non-reproducible. Recent studies showed the utility of digital information and analysis to complement manual soil survey.
The study presents quantitative soil–landscape models for the Hurunui and Haldon soil sets (New Zealand), developed from conceptual soil–landscape models. Spatial modelling techniques, including terrain analysis and fuzzy classification, are applied to compute membership maps of landform components for the study areas. The membership maps can be used to derive a ‘hard’ classification of land components and uncertainty maps. A soil taxonomic model is developed based on field data (soil profiles), which attaches dominant soil profiles and soil properties, including their uncertainties, to the defined land components. The method presented in this study is proposed as a potential technique for modelling land components of steepland areas in New Zealand, in which the spatial soil variation is dominantly controlled by landform properties. A soil map was developed that includes the uncertainty in the fundamental definitions of landscape units and the variability of soil properties within landscape units.
The influence of potassium and defoliation of ryegrass on the formation of acidic subsurface layers in stock urine patches
Authors: Condon J. R. , Black A. S. , Conyers M. K.
Published: April 2005

This study examined the influence of simulated urine solutions containing various KCl and urea-N rates on the formation of acidic subsurface layers in soil columns. A factorial design was implemented with application rates equivalent to 0, 21, 42, 63, and 84 g urea-N/m2 and 0, 12.5, 25, and 37.5 g KCl-K/m2. The addition of N caused the formation of acidic subsurface layers at depths between 0.02 and 0.10 m. The magnitude of the resultant net acidification and the depth of the most acidic layer increased with N rate. More acidification occurred at depth at the higher N rates due to the downward movement of NH4+-N. The inclusion of K in the simulated urine produced less acidity in the surface layers and more acidity at depth as the K application rate increased owing to competition between K+ and NH4+-N for exchange sites, allowing more NH4+-N to move to depth. The residual acidity in the soil at the completion of the experiment was found to be greater than the alkalinity of plant material. Therefore, acidic subsurface layers are likely to persist after plant death and decomposition. We also examined the impact of defoliation on the resultant pH profiles formed following simulated urine addition. Defoliation accentuated the magnitude of acidic subsurface layers, possibly due to changes in the rate of N uptake. The influence of defoliation was minor compared with the main effects of N addition.
Enumeration of wax-degrading microorganisms in water repellent soils using a miniaturised Most-Probable-Number method
Authors: Roper Margaret M. , Gupta V. V. S. R.
Published: April 2005

The ability of a soil to reduce waxes that cause water repellency depends, in part, on the presence of populations of wax-degrading microorganisms. Therefore, estimating the size of populations of wax-degrading bacteria in water repellent soils is likely to be a useful indicator of the potential for bioremediation of water repellency. A Most Probable Number (MPN) method that selects specifically for the function of wax degradation in bacteria was developed and tested using both pure cultures and natural populations of wax-degrading bacteria. Two carbon sources (coconut oil and hexadecane) that contain fatty acids or hydrocarbons implicated as causative agents of water repellency were compared in terms of growth and emulsification by a range of known wax-degrading bacteria. Emulsification resulting from surfactant production, a direct measure of wax degradation, was the criterion for a positive test. All the bacteria tested emulsified coconut oil, which was chosen as the carbon source in subsequent testing of the MPN assay. Population estimates of pure cultures of wax-degrading bacteria (liquid suspensions and inoculated into sterile soils) made using the MPN and a plating technique showed good agreement between the 2 methods, indicating that the MPN method gives an accurate measure of size of the wax-degrading population. Extensive replication of MPN counts of known wax-degrading bacteria inoculated into sterile soils or populations in soils collected from a range of natural habitats showed little variation within samples, indicating that the new method was reproducible. Based on its accuracy and reproducibility the MPN method was deemed suitable for estimating populations in a range of soils. Monitoring wax-degrading populations under different agricultural managements and at different times of the year, i.e. seasonal dynamics, could provide clues for the development of new managements that minimise the risk of water repellency in agricultural soils.
Cholinergic stimulation blocks endothelial cell activation and leukocyte recruitment during inflammation
Authors: Saeed Rubina W. , Varma Santosh , Peng-Nemeroff Tina , Sherry Barbara , Balakhaneh David , Huston Jared , Tracey Kevin J. , Al-Abed Yousef , Metz Christine N.
Published: April 2005

Endothelial cell activation plays a critical role in regulating leukocyte recruitment during inflammation and infection. Based on recent studies showing that acetylcholine and other cholinergic mediators suppress the production of proinflammatory cytokines via the α7 nicotinic acetylcholine receptor (α7 nAChR) expressed by macrophages and our observations that human microvascular endothelial cells express the α7 nAChR, we examined the effect of cholinergic stimulation on endothelial cell activation in vitro and in vivo. Using the Shwartzman reaction, we observed that nicotine (2 mg/kg) and the novel cholinergic agent CAP55 (12 mg/kg) inhibit endothelial cell adhesion molecule expression. Using endothelial cell cultures, we observed the direct inhibitory effects of acetylcholine and cholinergic agents on tumor necrosis factor (TNF)-induced endothelial cell activation. Mecamylamine, an nAChR antagonist, reversed the inhibition of endothelial cell activation by both cholinergic agonists, confirming the antiinflammatory role of the nAChR cholinergic pathway. In vitro mechanistic studies revealed that nicotine blocked TNF-induced nuclear factor–κB nuclear entry in an inhibitor κB (IκB)α- and IκBε-dependent manner. Finally, with the carrageenan air pouch model, both vagus nerve stimulation and cholinergic agonists significantly blocked leukocyte migration in vivo. These findings identify the endothelium, a key regulator of leukocyte trafficking during inflammation, as a target of anti-inflammatory cholinergic mediators.
Interferon-γ acts directly on CD8+ T cells to increase their abundance during virus infection
Authors: Whitmire Jason K. , Tan Joyce T. , Whitton J. Lindsay
Published: April 2005

Interferon-γ (IFNγ) is important in regulating the adaptive immune response, and most current evidence suggests that it exerts a negative (proapoptotic) effect on CD8+ T cell responses. We have developed a novel technique of dual adoptive transfer, which allowed us to precisely compare, in normal mice, the in vivo antiviral responses of two T cell populations that differ only in their expression of the IFNγ receptor. We use this technique to show that, contrary to expectations, IFNγ strongly stimulates the development of CD8+ T cell responses during an acute viral infection. The stimulatory effect is abrogated in T cells lacking the IFNγ receptor, indicating that the cytokine acts directly upon CD8+ T cells to increase their abundance during acute viral infection.
Recruitment of Foxp3+ T regulatory cells mediating allograft tolerance depends on the CCR4 chemokine receptor
Authors: Lee Iris , Wang Liqing , Wells Andrew D. , Dorf Martin E. , Ozkaynak Engin , Hancock Wayne W.
Published: April 2005

Although certain chemokines and their receptors guide homeostatic recirculation of T cells and others promote recruitment of activated T cells to inflammatory sites, little is known of the mechanisms underlying a third function, migration of Foxp3+ regulatory T (T reg) cells to sites where they maintain unresponsiveness. We studied how T reg cells are recruited to cardiac allografts in recipients tolerized with CD154 monoclonal antibody (mAb) plus donor-specific transfusion (DST). Real-time polymerase chain reaction showed that intragraft Foxp3 levels in tolerized recipients were ∼100-fold higher than rejecting allografts or allografts associated with other therapies inducing prolonged survival but not tolerance. Foxp3+ cells were essential for tolerance because pretransplant thymectomy or peritransplant depletion of CD25+ cells prevented long-term survival, as did CD25 mAb therapy in well-functioning allografts after CD154/DST therapy. Analysis of multiple chemokine pathways showed that tolerance was accompanied by intragraft up-regulation of CCR4 and one of its ligands, macrophage-derived chemokine (CCL22), and that tolerance induction could not be achieved in CCR4−/− recipients. We conclude that Foxp3 expression is specifically up-regulated within allografts of mice displaying donor-specific tolerance, that recruitment of Foxp3-expressing T reg cells to an allograft tissue is dependent on the chemokine receptor, CCR4, and that, in the absence of such recruitment, tolerizing strategies such as CD154 mAb therapy are ineffectual.
VEGF-A induces tumor and sentinel lymph node lymphangiogenesis and promotes lymphatic metastasis
Authors: Hirakawa Satoshi , Kodama Shohta , Kunstfeld Rainer , Kajiya Kentaro , Brown Lawrence F. , Detmar Michael
Published: April 2005

The mechanisms of tumor metastasis to the sentinel lymph nodes are poorly understood. Vascular endothelial growth factor (VEGF)-A plays a principle role in tumor progression and angiogenesis; however, its role in tumor-associated lymphangiogenesis and lymphatic metastasis has remained unclear. We created transgenic mice that overexpress VEGF-A and green fluorescent protein specifically in the skin, and subjected them to a standard chemically-induced skin carcinogenesis regimen. We found that VEGF-A not only strongly promotes multistep skin carcinogenesis, but also induces active proliferation of VEGF receptor-2–expressing tumor-associated lymphatic vessels as well as tumor metastasis to the sentinel and distant lymph nodes. The lymphangiogenic activity of VEGF-A–expressing tumor cells was maintained within metastasis-containing lymph nodes. The most surprising finding of our study was that even before metastasizing, VEGF-A–overexpressing primary tumors induced sentinel lymph node lymphangiogenesis. This suggests that primary tumors might begin preparing their future metastatic site by producing lymphangiogenic factors that mediate their efficient transport to sentinel lymph nodes. This newly identified mechanism of inducing lymph node lymphangiogenesis likely contributes to tumor metastasis, and therefore, represents a new therapeutic target for advanced cancer and/or for the prevention of metastasis.
TGF-β1 maintains suppressor function and Foxp3 expression in CD4+CD25+ regulatory T cells
Authors: Marie Julien C. , Letterio John J. , Gavin Marc , Rudensky Alexander Y.
Published: April 2005

Transforming growth factor (TGF)-β1 is a major pluripotential cytokine with a pronounced immunosuppressive effect and its deficiency results in lethal autoimmunity in mice. However, mechanisms of its immunosuppressive action are not completely understood. Here, we report that TGF-β1 supports the maintenance of Foxp3 expression, regulatory function, and homeostasis in peripheral CD4+CD25+ regulatory T (T reg) cells, but is not required for their thymic development. We found that in 8–10-d-old TGF-β1–deficient mice, peripheral, but not thymic, T reg cells are significantly reduced in numbers. Moreover, our experiments suggest that a defect in TGF-β–mediated signaling in T reg cells is associated with a decrease in Foxp3 expression and suppressor activity. Thus, our results establish an essential link between TGF-β1 signaling in peripheral T reg cells and T reg cell maintenance in vivo.
Natural killer cell education in mice with single or multiple major histocompatibility complex class I molecules
Authors: Johansson Sofia , Johansson Maria , Rosmaraki Eleftheria , Vahlne Gustaf , Mehr Ramit , Salmon-Divon Mali , Lemonnier François , Kärre Klas , Höglund Petter
Published: April 2005

The ability of murine NK cells to reject cells lacking self MHC class I expression results from an in vivo education process. To study the impact of individual MHC class I alleles on this process, we generated mice expressing single MHC class I alleles (Kb, Db, Dd, or Ld) or combinations of two or more alleles. All single MHC class I mice rejected MHC class I–deficient cells in an NK cell–dependent way. Expression of Kb or Dd conveyed strong rejection of MHC class I–deficient cells, whereas the expression of Db or Ld resulted in weaker responses. The educating impact of weak ligands (Db and Ld) was further attenuated by the introduction of additional MHC class I alleles, whereas strong ligands (Kb and Dd) maintained their educating impact under such conditions. An analysis of activating and inhibitory receptors in single MHC class I mice suggested that the educating impact of a given MHC class I molecule was controlled both by the number of NK cells affected and by the strength of each MHC class I–Ly49 receptor interaction, indicating that NK cell education may be regulated by a combination of qualitative and quantitative events.
What tumors need
Authors: Van Epps Heather L.
Published: April 2005

The field of angiogenesis began in the early 1970s when Judah Folkman proposed that tumor growth would be halted if the tumor were deprived of a blood supply. Thirty years later, Folkman's controversial idea is now widely accepted and angiogenesis inhibitors hold great promise for the treatment of cancer.
Maternal rank and local resource competition do not predict birth sex ratios in wild baboons
Authors: Silk Joan B , Willoughby Elisabeth , Brown Gillian R
Published: April 2005

We test two models of adaptive adjustment of birth sex ratios that are expected to apply to Cercopithecine primate species. It has been predicted that when maternal investment differentially influences the reproductive success of male and female offspring, females in good condition will bias investment in favour of the sex that gains the greatest fitness returns from additional investment. This hypothesis was subsequently amended to take into account the effects of local resource competition on maternal investment strategies of primate females. This body of theory has been applied to primates with contradictory results, prompting some to question the conclusion that primate females facultatively adjust birth sex ratios in an adaptive manner. Here, we present a meta-analysis of the relationship between maternal rank, birth sex ratios and local resource competition in 36 groups of wild savannah baboons,Papio cynocephalus. The results do not support predictions derived from either model of facultative sex ratio adjustment, and we conclude that there is currently no evidence that baboon birth sex ratios are adjusted in an adaptive manner.