bluuebunny/crossref_metadata_2025 huggingface dataset:
Conformational changes at polymer gel interfaces upon saturation with various liquids studied by infrared-visible sum frequency generation vibrational spectroscopy
Authors: Kweskin S. J. , Komvopoulos K. , Somorjai G. A.
Published: March 2006

Molecular restructuring at the free surface of poly(2-hydroxyethyl methacrylate) (PHEMA) films and the buried interface with a sapphire substrate due to submersion into deuterated water (D2O) and acetonitrile (d3ACN) was investigated by infrared-visible sum frequency generation (SFG) vibrational spectroscopy. Film hydration by saturation with D2O and d3ACN resulted in polymer swelling. Because of the amphiphilic nature of PHEMA, direct information about polymer restructuring was obtained due to the existence of hydrophilic and hydrophobic moieties. SFG results provided insight into the restructuring behavior at the PHEMA surface and buried interface upon swelling due to the diffusion of the two different liquids.
X-ray elastic constants for α-Al2O3
Authors: Hovis D. B. , Reddy A. , Heuer A. H.
Published: March 2006

It has recently been discovered that there is a long-standing error in the sign of c14 for α-Al2O3—it is +22 rather than −22GPa. Although c14 is the smallest of the six elastic constants of α-Al2O3 (space group R3¯c), it has a significant effect on the Reuss x-ray elastic constants, particularly for the {022¯4} reflection. Measurements using the Advanced Photon Source have confirmed that the sign of c14 must be positive. Use of the wrong sign of c14 can induce errors in excess of 30% in the measured residual stresses of α-Al2O3 scales.
Afterpulsing in Geiger-mode avalanche photodiodes for 1.06μm wavelength
Authors: Jensen K. E. , Hopman P. I. , Duerr E. K. , Dauler E. A. , Donnelly J. P. , Groves S. H. , Mahoney L. J. , McIntosh K. A. , Molvar K. M. , Napoleone A. , Oakley D. C. , Verghese S. , Vineis C. J. , Younger R. D.
Published: March 2006

We consider the phenomenon of afterpulsing in avalanche photodiodes (APDs) operating in gated and free-running Geiger mode. An operational model of afterpulsing and other noise characteristics of APDs predicts the noise behavior observed in the free-running mode. We also use gated-mode data to investigate possible sources of afterpulsing in these devices. For 30-μm-diam, 1.06-μm-wavelength InGaAsP∕InP APDs operated at 290K and 4V overbias, we obtained a dominant trap lifetime of τd=0.32μs, a trap energy of 0.11eV, and a baseline dark count rate 245kHz.
Photoinduced currents in carbon nanotube/metal heterojunctions
Authors: Sun Jia-Lin , Wei Jinquan , Zhu Jia-Lin , Xu Dong , Liu Xiaomeng , Sun Hongsan , Wu De-Hai , Wu Nian-Le
Published: March 2006

Significant photoinduced currents have been explored in carbon nanotube/metal heterojunctions, i.e., heterodimension junctions containing macrolong carbon nanotubes (CNTs). The experimental measurements clearly show that the net transport direction of the photoexcited electrons is from the lower dimensional CNTs to higher dimensional CNTs or metal electrodes and the photoinduced currents dramatically depend on the laser spot position relative to the junction interface. The currents increase linearly with the increase of the laser intensity as the intensity is not very large. A prototype sensor has been constructed to illustrate applications of the heterodimension junctions in photoelectronics.
Theoretical investigation on photoconductivity of single intrinsic carbon nanotubes
Authors: Guo Jing , Alam Muhammad A. , Yoon Youngki
Published: March 2006

The photoconductivity of carbon nanotube (CNT) Schottky barrier transistors is studied by solving the nonequilibrium Green’s function transport equation. The model provides a detailed and coherent picture of electron-photon coupling and quantum transport effects. The photocurrent shows peaks at photon energies near the subband gaps, which can be engineered by controlling the CNT diameter. Electron-phonon coupling (i) slightly broadens the peaks, (ii) leads to phonon-assisted photocurrent at certain energy ranges, and (iii) changes the energy-resolved photocurrent. We also show that the metal-CNT barrier height has a much smaller effect on the photocurrent than on the dark current.
Fast synthesis method and phase diagram of hydrogen clathrate hydrate
Authors: Lokshin Konstantin A. , Zhao Yusheng
Published: March 2006

We report a very fast method for hydrogen clathrate production. The formation of hydrogen clathrate from H2 gas and ice-Ih at 77–273K occurs at least 100 times faster compared to the reaction with water. This effect is probably the result of a partial penetration of hydrogen into the ice-Ih body, which favors clathrate formation. With the ice method, the ice-Ih∕48H2*136H2O system can quickly trap and release up to 3.77 mass % of hydrogen, which gives it an advantage over other chemical-bonding hydrogen storage technologies. New data on the hydrogen-water phase diagram are presented and discussed.
Deep ultraviolet photoluminescence studies of AlN photonic crystals
Authors: Nepal N. , Shakya J. , Nakarmi M. L. , Lin J. Y. , Jiang H. X.
Published: March 2006

Two-dimensional AlN photonic crystals (PCs) with varying periodicity/diameter down to 150∕75nm were fabricated. Deep ultraviolet photoluminescence spectroscopy has been employed to study the optical properties of AlN PCs. With PC formation, a 20-fold enhancement in the band edge emission intensity at 208nm over unpatterned AlN epilayer has been observed. The emission intensity increases with decreasing lattice constant of AlN PCs. However, the spectral peak energy decreases with decreasing lattice constant, indicating a possible release of compressive stresses as a result of PC formation. Successful fabrication of AlN PCs opens up new opportunities for exploring novel physical phenomena in the artificially structured photonic band gap material system and their applications, particularly in the area of deep UV photonics.
Nonlinear magneto-optical rotation with amplitude modulated light
Authors: Gawlik W. , Krzemień L. , Pustelny S. , Sangla D. , Zachorowski J. , Graf M. , Sushkov A. O. , Budker D.
Published: March 2006

The technique of nonlinear magneto-optical rotation with amplitude modulated light is developed. The technique is an alternative to its counterpart with frequency modulated light and can be applied to sensitive measurements of magnetic fields ranging from microgauss to the Earth-field level. The rotation signals exhibit nontrivial features such as narrowed non-Lorentzian line shapes and multicomponent resonances.
Modulated optical transmission of subwavelength hole arrays in metal-VO2 films
Authors: Suh J. Y. , Donev E. U. , Lopez R. , Feldman L. C. , Haglund R. F.
Published: March 2006

We demonstrate the modulation of the transmission of near-infrared light through a periodic array of subwavelength apertures in Ag–VO2 and Au–VO2 double-layer films using the semiconductor-to-metal phase transition in VO2. The transmitted intensity ratio increases by a factor of 8 as the VO2 goes from the semiconductor to the metal phase. We attribute this modulation to the switchable dielectric-permittivity contrast between the air-filled holes in the array and the surrounding VO2 material, a conjecture that is semiquantitatively confirmed by simulation.
Angular dependence of silicon oxide etching yield in fluorocarbon chemistries
Authors: Kwon Ohseung , Jin Weidong , Sawin Herbert H.
Published: March 2006

High density fluorocarbon plasma for silicon oxide etching has various ion and neutral species. Profile evolution modeling can provide understanding of many difficulties caused by the complexity of the plasma in etching. In this research we have measured etching and deposition rates as functions of ion impinging angle, sample temperature, which are necessary for profile evolution modeling of silicon oxide etching in inductively coupled plasma. Angular dependence of etching yield of oxide in fluorocarbon plasma shows very unique behavior unlike typical ion-induced chemical etching or physical sputtering. Ion-induced deposition model is suggested and tested.
Schottky diodes from asymmetric metal-nanotube contacts
Authors: Lu Chenguang , An Lei , Fu Qiang , Liu Jie , Zhang Hong , Murduck James
Published: March 2006

Carbon nanotube Schottky diodes were fabricated using asymmetric metal-nanotube contacts. These devices were prepared from semiconducting single-walled carbon nanotubes contacted by one Al or Ti electrode and one Au electrode. Nanotubes formed a low resistance contact with the Au electrode and a Schottky contact with the Al or Ti electrode. Electronic transport through the Schottky barriers was determined by the competition between tunneling and thermionic emission, which could be tuned by a back gate voltage.
Low-cost fabrication of submicron all polymer field effect transistors
Authors: Wang J. Z. , Gu J. , Zenhausern F. , Sirringhaus H.
Published: March 2006

All polymer field effect transistors have been fabricated combining nanoimprint lithography and inkjet printing. Trenches with hydrophilic bottoms confined by hydrophobic walls with considerable height are patterned by nanoimprint lithography. Conducting polymer solutions were then delivered into these trench liquid containers by inkjet printing. Dried conducting polymer in nearby trenches forms source-drain electrodes with the channel length accurately defined by the gap in between the designed two trenches. Top-gate all polymer field effect transistors with submicron channel lengths were successfully realized by such low-cost process.
Enhanced and oscillatory magnetoresistance of thin Fe(001) films
Authors: Martinez-Boubeta C. , Balcells Ll. , Cebollada A.
Published: March 2006

We have studied the magnetoresistance of single-crystalline (001) Fe films prepared by sputtering techniques and covered by epitaxial MgO or Pt protective layers. The influence of the thickness of the magnetic layer as well as of the nature of the capping layer on the Fe anisotropic magnetoresistance was investigated by four-terminal probe, measurements performed with the current J in the [110] magnetically hard direction. We found an enhancement in the magnetoresistance value with respect to bulk and oscillations in the high field regime in MgO covered Fe∕MgO(001) ultrathin films. A plausible explanation is that the enhanced magnetoresistance is due to electronic confinement effects, not present in similar Pt∕Fe∕MgO(001) samples.
HgCdTe superlattices for solid-state cryogenic refrigeration
Authors: Vashaee Daryoosh , Shakouri Ali
Published: March 2006

A tall barrier superlattice structure based on mercury cadmium telluride material system is proposed that can achieve a large effective thermoelectric figure of merit (ZTmax∼3) at cryogenic temperatures. Calculations based on the Boltzmann transport equation taking into account the quantum mechanical electron transmission show that the Seebeck coefficient can be increased significantly at low temperatures with the use of nonplanar barriers as the thermal spreading of the electron density is tightened around the Fermi level. This provides a better asymmetric differential conductivity around the Fermi level close to the top of the barrier. Consequently, a high thermoelectric power factor is produced resulting in a large ZT.
Heterosis and combining ability in diallel crosses involving maize (Zea mays) S1 lines
Authors: Muraya M. M. , Ndirangu C. M. , Omolo E. O.
Published: March 2006

This study was conducted at Egerton University, Njoro, Kenya for 2 growing seasons, 2001 and 2002. A diallel cross, without reciprocal crossings, involving 7 maize S1 lines: KSTP001, KSTP003, KSTP004, KSTP005, KSTP008, E2 and E3 was used to study the heterosis and inheritance of days to 50% flowering, plant height, ear height, leaf angle, number of leaves per plant, leaf area index, cob length, cob diameter, number of lines per cob, number of seeds per line, 100-grain weight and grain yield. A randomised complete block design with 3 replicates was used. Analysis of variance was conducted on the data generated at 0.05 significant level using MSTAT. The results showed that general combining ability (GCA) and specific combining ability (SCA) was significant (P<0.05) for all traits under study, suggesting existence of both additive and non-additive gene effects for the traits. However, GCA : SCA ratio was >1 for all traits except cob diameter and 100 seed weight, indicating preponderance of additive gene effects for inheritance of these traits. The study identified KSTP003 as the best combiner for most of the traits, while KSTP001 and E3 was the best combination for most traits. KSTP004 and E3 was good combiner for grain yield. Hybrid KSTP005 × E3 was the best cross for grain yield. KSTP003 × E2 was the best cross for reduction of leaf angle thus good source for erectophile canopies in a hybridisation program. Heterosis estimates showed that heterosis was more important in grain yield, yield components, plant height, number of leaves per plant and, leaf area index than other traits studied. Most of traits studied had a positive and significant (P≤0.01), while all traits studied except days to 50% flowering had a positive and significant (P≤0.01) genotypic correlations. It is recommended that based on their combining ability the lines be recombined to form synthetic maize varieties which can be released both as a variety or used for further improvement using recurrent selection. The lines which combine well for reduction in leaf angle from vertical should be utilised to develop erective maize varieties.
Towards a better understanding of crop water requirement in orchards: a case study from the Goulburn Valley
Authors: O'Connell M. G. , Goodwin I. , Dunn G. M.
Published: March 2006

Responses of fruit trees to reduced irrigation in micro-irrigated peach and apple orchards in the Goulburn Valley, Victoria were investigated during the 2000–01 season. Field experiments examined the effects of applying 2 irrigation levels on soil water content, crop water relations, vegetative growth, yield, yield components and fruit quality. Irrigation regimes were 50% and 100% of current management practice where inputs are scheduled from pan evaporation and locally derived crop coefficients. Water was applied to only one side of the tree rootzone in the 50% treatment (0.5I) while the current management practice treatment (1.0I), received water on both sides of the tree. Over the season, the irrigation inputs for peach and apple equated to a crop coefficient of 0.93 and 0.87, respectively. Orchard water use (ETpeach and ETapple) was predicted using reference crop evapotranspiration (ET0) and published crop coefficients (Kc) with adjustment for the fraction of shade cast by the trees on the orchard floor at solar noon (effective canopy cover, ECC). Throughout the season, ECC measured as midday tree canopy radiation interception, remained low for both peach and apple (<35%). ETpeach and ETapple were substantially lower than current water scheduling practices (1.0I treatments). For the 0.5I apple regime, irrigation closely matched ETapple suggesting that these trees were adequately irrigated. This was supported by no detrimental effects on crop production, vegetative growth, and fruit quality measures of the 0.5I irrigation regime. However, in the peach orchard the 0.5I regime reduced fruit volume suggesting that these trees may have been water stressed. Based on ECC, we calculated the full crop water requirement Kc for the peach and apple orchards to be 0.42 and 0.37, respectively. In summary, for the apple orchard, our 0.5I treatment was close to predicted full crop water requirement (ETapple). But for the peach orchard, the ETpeach was greater, albeit slightly, than our 0.5I regime. Taken overall, these results demonstrate that better matching of water application to the evaporative surface of the orchard canopies (i.e. ECC) can substantially reduce irrigation water use in Goulburn Valley orchards. It is also apparent that ECC in these orchards where row spacing is typically 4–5 m can be relatively low.
Improved soil and irrigation management for forage production 2. Forage yield and nutritive characteristics
Authors: Greenwood K. L. , Dellow K. E. , Mundy G. N. , Kelly K. B. , Austin S. M.
Published: March 2006

Pastures are the main source of energy and nutrients for dairy cows in the irrigated dairy region of northern Victoria, yet annual production and utilisation of pasture have remained static over the last 20 years. Previous small plot research has shown that pasture yields can be increased through systems of soil modification that improve soil structure and alleviate limitations to root growth. We compared the yield and nutritive characteristics of 4 forage species [tall fescue (Festuca arundinacea), lucerne (Medicago sativa), phalaris (Phalaris aquatica) and perennial ryegrass (Lolium perenne)] on soils which had been modified using commercially-available equipment and using spray irrigation at 2 frequencies.
In year 1 (2000–01), annual yields of the forages were tall fescue: 21.2 t dry matter (DM)/ha; lucerne: 20.5 t DM/ha; phalaris: 19.8 t DM/ha; and perennial ryegrass: 20.8 t DM/ha. In the second year of the experiment, annual yields averaged 28.9 t DM/ha for tall fescue, 26.1 t DM/ha for lucerne, 31.6 t DM/ha for phalaris and 23.2 t DM/ha for perennial ryegrass. There was no consistent response in yield of any species to soil modification. The improvements in soil structure achieved with soil modification were probably not large enough to result in yield responses. Yields were greater when frequently irrigated, with the exception of perennial ryegrass in the second year. Most of the yield benefit due to frequent irrigation was limited to the summer months. No yield data showed significant soil by irrigation frequency interaction.
There were significant differences in forage nutritive characteristics between the 4 species. The lower crude protein content of lucerne would be at least partly due to the frequent application of nitrogen fertiliser to the grasses. Tall fescue usually had similar nutritive characteristics to perennial ryegrass in terms of metabolisable energy, protein and NDF. Phalaris had high fibre contents and low metabolisable energy in summer.
We conclude that it is not feasible, at this time, to improve yields of irrigated forages through soil modification on a commercial scale.
Breeding for Papaya ringspot virus resistance in Carica papaya via hybridisation with Vasconcellea quercifolia
Authors: Drew R. A. , Siar S. V. , O'Brien C. M. , Magdalita P. M. , Sajise A. G. C.
Published: March 2006

Papaya ringspot virus type P (PRSV-P) is a major threat to the papaya industry worldwide. F1 hybrids have been produced when Carica papaya L. female flowers have been pollinated with pollen of the PRSV-P resistant species Vasconcellea quercifolia. F1 plant production required embryo rescue 90 days post-pollination, and plantlet regeneration in vitro. Three hundred F1 hybrids were grown to maturity in the field and had morphological characteristics that were identical to 1 or both parents, were intermediate between those of the parents, or were greater than either parent. They had a sex ratio of 2 (male) : 49 (hermaphrodite) : 49(female). Eighteen plants (7 male and 11 hermaphrodite) produced some viable pollen. Pollen viability of these plants as measured by germination on agar medium varied between 1.1 and 6.1% (mean of 3.37 ± 0.18) compared with >90% for C. papaya. Cytogenetic studies showed limited homology between C. papaya and V. quercifolia genomes. The intergeneric hybrids varied in their reaction to strains of PRSV-P in Australia and the Philippines. Of the hybrids, 75% were resistant to PRSV-P while 25% produced virus symptoms.
Progress in backcrossing between Carica papaya × Vasconcellea quercifolia intergeneric hybrids and C. papaya
Authors: Drew R. A. , Siar S. V. , O'Brien C. M. , Sajise A. G. C.
Published: March 2006

Papaya is a major tropical fruit crop worldwide, however, all genotypes are susceptible to Papaya ringspot virus type P (PRSV-P). Protocols have been developed to produce large numbers of intergeneric hybrids between Carica papaya L. and Vasconcellea quercifolia, which is PRSV-P resistant. Although pollen fertility of these hybrids was low, backcross populations were produced in both Australia and the Philippines when papaya flowers were pollinated with pollen from 11 hybrid plants that had been identified as having some pollen fertility and were PRSV-P resistant. Plantlets were produced after embryo rescue and culture in vitro. Second backcross generations (BC2) were easier to produce than first backcross (BC1) generations as pollen fertility was >80% in male BC1 plants. Variation in time to PRSV-P symptom expression and severity of virus symptoms in the backcross generations was observed in both countries. Commercially acceptable fruit were produced in the BC2 generation. The results demonstrate that efforts in wide hybridisation to transfer PRSV-P resistance to C. papaya, are better directed towards crosses between C. papaya and V. quercifolia than with other Vasconcellea species.
Root depth of native and sown perennial grass-based pastures, North-West Slopes, New South Wales. 2. Estimates from changes in soil water content
Authors: Murphy S. R. , Lodge G. M.
Published: March 2006

Root depth of pasture is an important hydrological parameter that has substantial implications for the use of rainfall by plants and in estimating deep drainage using biophysical modelling. Studies were undertaken for native and sown perennial grass-based pastures on the North-West Slopes of New South Wales to investigate 4 approaches that may identify the depth of plant roots based on objective assessments of change in soil water content (SWC). The 4 approaches were to examine traces of SWC measured with a neutron moisture meter (NMM) at about 4-week intervals (0–210 cm profile at 20-cm increments) for defined periods with root depth interpreted as, (i) the maximum depth at which there was a distinct decrease in SWC, (ii) the maximum depth at which there was a >0.01 m3/m3 decrease in SWC, (iii) the uppermost depth at which the change in SWC was significant using t0.05, and (iv) the uppermost depth at which the daily rate of change in SWC was significant using t0.05. For each of these approaches, 4 preliminary criteria were applied as filters to the SWC data before they were used in these analyses, (i) the depth of NMM tubes and maximum depth of measurement of SWC was greater than the anticipated pasture root depth, (ii) the depth of initial profile wetting was greater than the anticipated pasture root depth, (iii) there was a drying period of >3 months duration in the major pasture growth phase to allow pastures to extract soil water to the maximum extent, and (iv) the SWC was measured at a sufficient frequency to determine extraction of soil water by roots. SWC data were available from spring 1997 to spring 2001 for Barraba (45 access tubes, native pasture), Manilla (45 tubes, native pasture) and Nundle (36 tubes, sown pasture). Analyses of monthly rainfall compared with mean values identified 3 times where substantial rainfall was followed by an extended drying period. These periods occurred in 1998, 1999 and 2000. SWC data for the 1998 drying period best met all the preliminary filters, particularly criteria (ii) and (iii). Root depth values estimated from these data using the 4 approaches were not significantly different for Barraba (188 ± 4 to 190 ± 3 cm, n = 45), Nundle (142 ± 5 to 143 ± 7 cm, n = 13) and Manilla Red Chromosol (164 ± 7 to 176 ± 7 cm, n = 14), but were significantly different for Manilla Brown Vertosol (98 ± 7 to 121 ± 7 cm, n = 23). It was concluded that reliable estimates of root depth may be readily obtained for a range of soils and environments by firstly applying the 4 simple criteria used in these studies to the SWC data and by determining the depth of significant drying using t0.05. The depth of significant drying approach was the most objective, providing consistent results among sites and accounting for variance among NMM counts and tubes in these studies.
Sustaining productivity of a Vertosol at Warra, Queensland, with fertilisers, no-tillage or legumes. 9. Production and nitrogen benefits from mixed grass and legume pastures in rotation with wheat
Authors: Strong W. M. , Dalal R. C. , Weston E. J. , Lehane K. J. , Cooper J. E. , King A. J. , Holmes C. J.
Published: March 2006

Reduced supplies of nitrogen (N) in many soils of southern Queensland that were cropped exhaustively with cereals over many decades have been the focus of much research to avoid declines in profitability and sustainability of farming systems. A 45-month period of mixed grass (purple pigeon grass, Setaria incrassata Stapf; Rhodes grass, Chloris gayana Kunth.) and legume (lucerne, Medicago sativa L.; annual medics, M. scutellata L. Mill. and M. truncatula Gaertn.) pasture was one of several options that were compared at a fertility-depleted Vertosol at Warra, southern Queensland, to improve grain yields or increase grain protein concentration of subsequent wheat crops. Objectives of the study were to measure the productivity of a mixed grass and legume pasture grown over 45 months (cut and removed over 36 months) and its effects on yield and protein concentrations of the following wheat crops.
Pasture production (DM t/ha) and aboveground plant N yield (kg/ha) for grass, legume (including a small amount of weeds) and total components of pasture responded linearly to total rainfall over the duration of each of 3 pastures sown in 1986, 1987 and 1988. Averaged over the 3 pastures, each 100 mm of rainfall resulted in 0.52 t/ha of grass, 0.44 t/ha of legume and 0.97 t/ha of total pasture DM, there being little variation between the 3 pastures. Aboveground plant N yield of the 3 pastures ranged from 17.2 to 20.5 kg/ha per 100 mm rainfall. Aboveground legume N in response to total rainfall was similar (10.6–13.2 kg/ha per 100 mm rainfall) across the 3 pastures in spite of very different populations of legumes and grasses at establishment. Aboveground grass N yield was 5.2–7.0 kg/ha per 100 mm rainfall.
In most wheat crops following pasture, wheat yields were similar to that of unfertilised wheat except in 1990 and 1994, when grain yields were significantly higher but similar to that for continuous wheat fertilised with 75 kg N/ha. In contrast, grain protein concentrations of most wheat crops following pasture responded positively, being substantially higher than unfertilised wheat but similar to that of wheat fertilised with 75 kg N/ha. Grain protein averaged over all years of assay was increased by 25–40% compared with that of unfertilised wheat.
Stored water supplies after pasture were <134 mm (<55% of plant available water capacity); for most assay crops water storages were 67–110 mm, an equivalent wet soil depth of only 0.3–0.45 m. Thus, the crop assays of pasture benefits were limited by low water supply to wheat crops. Moreover, the severity of common root rot in wheat crop was not reduced by pasture–wheat rotation.
Effects of Prima gland clover (Trifolium glanduliferum Boiss cv. Prima) consumption on sheep production and meat quality
Authors: Masters D. G. , Mata G. , Revell C. K. , Davidson R. H. , Norman H. C. , Nutt B. J. , Solah V.
Published: March 2006

Gland clover (Trifolium glanduliferum Boiss) is a recently introduced and released clover species for use in Mediterranean agricultural systems in southern Australia. There is little information on the expected animal production from this pasture plant although it is known to contain coumarins. Coumarins may have a direct effect on the production of grazing ruminants through a reduction in feed intake and may also have the ability to influence the flavour and odour of meat. In this study, Merino hogget ewes were grazed on eight 0.5 ha replicate plots sown to monocultures of either Prima gland clover or Dalkeith subterranean clover (Trifolium subterraneum ssp. subterraneum L.). The Prima gland clover was estimated to contain between 80 and 300 mg coumarin/kg dry matter. Three sheep were allocated to the plots on 7 September and 1 sheep from each plot was slaughtered on 29 September. Two additional sheep were allocated to the plots on 28 September and another 2 on 19 October. At the end of the experiment on 8 November, each plot contained 2 sheep that had grazed for 3, 6 or 9 weeks. All sheep were slaughtered at this time. The 2 sheep that remained on the plots from 7 September to 8 November were used for the comparison of animal production between the 2 clover species. Following slaughter, measurements were made of carcass characteristics and meat eating quality. The liveweight gain and wool growth of the 2 treatments were similar over the 9 weeks, however, the sheep on the Prima gland clover plots grew faster over the first 3 weeks. The faster growth rate is consistent with a higher in vitro digestibility of the Prima gland clover at this time. The similarity in feeding value of the 2 clover species indicates that there was no depression in feed intake associated with the Prima gland clover. There were some small significant differences in meat eating quality between the groups. Meat from sheep grazing the Prima gland clover was drier and had a more pleasant taste. These differences are unlikely to be large enough to have any commercial significance. The results indicate that the Prima gland clover has a feeding value at least equivalent to the Dalkeith subterranean clover and that, under the conditions of this experiment, the coumarin concentrations in the Prima gland clover are not high enough to affect either feed intake or the flavour and odour of meat.
Life stress and diminished expression of genes encoding glucocorticoid receptor and β
2
-adrenergic receptor in children with asthma
Authors: Miller Gregory E. , Chen Edith
Published: March 2006

Despite evidence that stressful experience can exacerbate the symptoms of asthma, little is known about the biological mechanisms through which this occurs. This study examined whether life stress reduces expression of the genes coding for the glucocorticoid receptor and the β
2
-adrenergic receptor. A total of 77 children were enrolled in the study (59% male; mean age, 13.5 years). Thirty-nine of them were physician-diagnosed with asthma, and 38 were healthy. After an in-depth interview regarding stressful experiences, leukocytes were collected through antecubital venipuncture, and real-time RT-PCR was used to quantify mRNA. Chronic stress was associated with reduced expression of mRNA for the β
2
-adrenergic receptor among children with asthma. In the sample of healthy children, however, the direction of this effect was reversed. The occurrence of a major life event in the 6 months before the study was not sufficient to influence patterns of gene expression. When such events occurred in the context of a chronic stressor, however, their association with patterns of gene expression was accentuated. Children with asthma who simultaneously experienced acute and chronic stress exhibited a 5.5-fold reduction in glucocorticoid receptor mRNA and a 9.5-fold reduction in β
2
-adrenergic receptor mRNA relative to children with asthma without comparable stressor exposure. These findings suggest that stressful experience diminishes expression of the glucocorticoid and β
2
-adrenergic receptor genes in children with asthma. To the extent that it diminishes sensitivity to the antiinflammatory properties of glucocorticoids or the bronchodilatory properties of β-agonists, this process could explain the increased asthma morbidity associated with stress.
Approaches for biological and biomimetic energy conversion
Authors: LaVan David A. , Cha Jennifer N.
Published: March 2006

This article highlights areas of research at the interface of nanotechnology, the physical sciences, and biology that are related to energy conversion: specifically, those related to photovoltaic applications. Although much ongoing work is seeking to understand basic processes of photosynthesis and chemical conversion, such as light harvesting, electron transfer, and ion transport, application of this knowledge to the development of fully synthetic and/or hybrid devices is still in its infancy. To develop systems that produce energy in an efficient manner, it is important both to understand the biological mechanisms of energy flow for optimization of primary structure and to appreciate the roles of architecture and assembly. Whether devices are completely synthetic and mimic biological processes or devices use natural biomolecules, much of the research for future power systems will happen at the intersection of disciplines.
PR130 is a modulator of the Wnt-signaling cascade that counters repression of the antagonist Naked cuticle
Authors: Creyghton Menno P. , Roël Giulietta , Eichhorn Pieter J. A. , Vredeveld Liesbeth C. , Destrée Olivier , Bernards René
Published: March 2006

The Wnt-signaling cascade is required for several crucial steps during early embryogenesis, and its activity is modulated by various agonists and antagonists to provide spatiotemporal-specific signaling. Naked cuticle is a Wnt antagonist that itself is induced by Wnt signaling to keep Wnt signaling in check. Little is known about the regulation of this antagonist. We have recently shown that the protein phosphatase 2A regulatory subunit PR72 is required for the inhibitory effect of Naked cuticle on Wnt signaling. In the present study, we show that PR130, which has an N terminus that differs from that of PR72 but shares the same C terminus, also interacts with Naked cuticle but instead functions as an activator of the Wnt-signaling pathway, both in cell culture and during development. We find that PR130 modulates Wnt signal transduction by restricting the ability of Naked cuticle to function as a Wnt inhibitor. Our data establish PR130 as a modulator of the Wnt-signaling pathway and suggest a mechanism of Wnt signal regulation in which the inhibitory activity of Naked cuticle is determined by the relative level of expression of two transcripts of the same protein phosphatase 2A regulatory subunit.
Solution structure of the N-domain of Wilson disease protein: Distinct nucleotide-binding environment and effects of disease mutations
Authors: Dmitriev Oleg , Tsivkovskii Ruslan , Abildgaard Frits , Morgan Clinton T. , Markley John L. , Lutsenko Svetlana
Published: March 2006

Wilson disease protein (ATP7B) is a copper-transporting P
1B
-type ATPase that regulates copper homeostasis and biosynthesis of copper-containing enzymes in human tissues. Inactivation of ATP7B or related ATP7A leads to severe neurodegenerative disorders, whereas their overexpression contributes to cancer cell resistance to chemotherapeutics. Copper-transporting ATPases differ from other P-type ATPases in their topology and the sequence of their nucleotide-binding domain (N-domain). To gain insight into the structural basis of ATP7B function, we have solved the structure of the ATP7B N-domain in the presence of ATP by using heteronuclear multidimensional NMR spectroscopy. The N-domain consists of a six-stranded β-sheet with two adjacent α-helical hairpins and, unexpectedly, shows higher similarity to the bacterial K
+
-transporting ATPase KdpB than to the mammalian Ca
2+
-ATPase or Na
+
,K
+
-ATPase. The common core structure of P-type ATPases is retained in the 3D fold of the N-domain; however, the nucleotide coordination environment of ATP7B within this fold is different. The residues H1069, G1099, G1101, I1102, G1149, and N1150 conserved in the P
1B
-ATPase subfamily contribute to ATP binding. Analysis of the frequent disease mutation H1069Q demonstrates that this mutation does not significantly affect the structure of the N-domain but prevents tight binding of ATP. The structure of the N-domain accounts for the disruptive effects of >30 known Wilson disease mutations. The unique features of the N-domain provide a structural basis for the development of specific inhibitors and regulators of ATP7B.
Neutral and adaptive variation in gene expression
Authors: Whitehead Andrew , Crawford Douglas L.
Published: March 2006

Variation among populations in gene expression should be related to the accumulation of random-neutral changes and evolution by natural selection. The following evolutionary analysis has general applicability to biological and medical science because it accounts for genetic relatedness and identifies patterns of expression variation that are affected by natural selection. To identify genes evolving by natural selection, we allocate the maximum among-population variation to genetic distance and then examine the remaining variation relative to a hypothesized important ecological parameter (temperature). These analyses measure the expression of metabolic genes in common-gardened populations of the fishFundulus heteroclituswhose habitat is distributed along a steep thermal gradient. Although much of the variation in gene expression fits a null model of neutral drift, the variation in expression for 22% of the genes that regress with habitat temperature was far greater than could be accounted for by genetic distance alone. The most parsimonious explanation for among-population variation for these genes is evolution by natural selection. In addition, many metabolic genes have patterns of variation incongruent with neutral evolution: They have too much or too little variation. These patterns of biological variation in expression may reflect important physiological or ecological functions.
Gene expression patterns in human placenta
Authors: Sood Ruchira , Zehnder James L. , Druzin Maurice L. , Brown Patrick O.
Published: March 2006

The placenta is the principal metabolic, respiratory, excretory, and endocrine organ for the first 9 months of fetal life. Its role in fetal and maternal physiology is remarkably diverse. Because of the central role that the placenta has in fetal and maternal physiology and development, the possibility that variation in placental gene expression patterns might be linked to important abnormalities in maternal or fetal health, or even variations in later life, warrants investigation. As an initial step, we used DNA microarrays to analyze gene expression patterns in 72 samples of amnion, chorion, umbilical cord, and sections of villus parenchyma from 19 human placentas from successful full-term pregnancies. The umbilical cord, chorion, amnion, and villus parenchyma samples were readily distinguished by differences in their global gene-expression patterns, many of which seemed to be related to physiology and histology. Differentially expressed genes have roles that include placental trophoblast secretion, signal transduction, metabolism, immune regulation, cell adhesion, and structure. We found interindividual differences in expression patterns in villus parenchyma and systematic differences between the maternal, fetal, and intermediate layers. A group of genes that was expressed in both the maternal and fetal villus parenchyma sections of placenta included genes that may be associated with preeclampsia. We identified sets of genes whose expression in placenta was significantly correlated with the sex of the fetus. This study provides a rich and diverse picture of the molecular variation in the placenta from healthy pregnancies.
Perceptual moments of conscious visual experience inferred from oscillatory brain activity
Authors: Smith Marie L. , Gosselin Frédéric , Schyns Philippe G.
Published: March 2006

Transient periods of synchronized oscillating neuronal discharges in the brain have been proposed to support the discrete perceptual moments underlying conscious visual experience. However, the information content of these perceptual moments remains a critical challenge to the understanding of consciousness. We uncovered this information content in four observers who consciously perceived each interpretation of the ambiguous Dali paintingSlave Market with the Disappearing Bust of Voltaire. For each individual observer, we isolated the stimulus spatial frequency (SF) features underlying their overt judgments of the input as “the nuns” and “Voltaire”. Every 2 ms between stimulus onset and overt response, we derived the sensitivity of the observer's oscillatory brain activity (in the theta, alpha, and beta bandwidths) to these SF features. Then, in each bandwidth, we estimated the moments (between stimulus onset and perceptual judgment) when perception-specific SF features were maximally integrated, corresponding to perceptual moments. We show that the centroparietal beta oscillations support perceptual moments underlying the conscious perception of the nuns, whereas theta oscillations support the perception of Voltaire. For both perceptions, we reveal the specific information content of these perceptual moments.
Simple and accurate estimation of ancestral protein sequences
Authors: Hall Barry G.
Published: March 2006

There are a variety of reasons to reconstruct the sequences of ancient proteins, but whatever the reason, the value of the reconstructed protein depends on the accuracy with which the ancient sequence is inferred. This study uses sequences simulated by a sequence-evolution simulation program that compares parsimony, maximum likelihood, and the Bayesian methods of inferring ancestral sequences and concludes that the Bayesian method, as implemented by
mrbayes 3.11
, is preferred. Estimated ancestral sequences are of necessity the same length as the alignment on which the underlying phylogeny is based. A highly accurate method for correcting the estimated sequences is introduced, and it is shown that the correction permits inferring the sequences of ancient protein sequences with a very high degree of accuracy.
Glucocorticoids reduce phobic fear in humans
Authors: Soravia Leila M. , Heinrichs Markus , Aerni Amanda , Maroni Caroline , Schelling Gustav , Ehlert Ulrike , Roozendaal Benno , de Quervain Dominique J.-F.
Published: March 2006

Phobias are characterized by excessive fear, cued by the presence or anticipation of a fearful situation. Whereas it is well established that glucocorticoids are released in fearful situations, it is not known whether these hormones, in turn, modulate perceived fear. As extensive evidence indicates that elevated glucocorticoid levels impair the retrieval of emotionally arousing information, they might also inhibit retrieval of fear memory associated with phobia and, thereby, reduce phobic fear. Here, we investigated whether acutely administrated glucocorticoids reduced phobic fear in two double-blind, placebo-controlled studies in 40 subjects with social phobia and 20 subjects with spider phobia. In the social phobia study, cortisone (25 mg) administered orally 1 h before a socio-evaluative stressor significantly reduced self-reported fear during the anticipation, exposure, and recovery phase of the stressor. Moreover, the stress-induced release of cortisol in placebo-treated subjects correlated negatively with fear ratings, suggesting that endogenously released cortisol in the context of a phobic situation buffers fear symptoms. In the spider phobia study, repeated oral administration of cortisol (10 mg), but not placebo, 1 h before exposure to a spider photograph induced a progressive reduction of stimulus-induced fear. This effect was maintained when subjects were exposed to the stimulus again 2 days after the last cortisol administration, suggesting that cortisol may also have facilitated the extinction of phobic fear. Cortisol treatment did not reduce general, phobia-unrelated anxiety. In conclusion, the present findings in two distinct types of phobias indicate that glucocorticoid administration reduces phobic fear.
Mitogen-activated protein kinase kinase 3 is a pivotal pathway regulating p38 activation in inflammatory arthritis
Authors: Inoue Tomoyuki , Boyle David L. , Corr Maripat , Hammaker Deepa , Davis Roger J. , Flavell Richard A. , Firestein Gary S.
Published: March 2006

p38 mitogen-activated protein kinase (MAPK) regulates cytokines in arthritis and is, in turn, regulated by MAPK kinase (MKK) 3 and MKK6. To modulate p38 function but potentially minimize toxicity, we evaluated the utility of targeting MKK3 by using MKK3−/−mice. These studies showed that TNF-α increased phosphorylation of p38 in WT cultured synoviocytes but that p38 activation, IL-1β, and IL-6 expression were markedly lower in MKK3−/−synoviocytes. In contrast, IL-1β or LPS-stimulated p38 phosphorylation and IL-6 production by MKK3−/−synoviocytes were normal. Detailed signaling studies showed that NF-κB also contributes to IL-6 production and that TNF-α-induced NF-κB activation is MKK3-dependent. In contrast, LPS-mediated activation of NF-κB does not require MKK3. To determine whether this dichotomy occursin vivo, two inflammation models were studied. In K/BxN passive arthritis, the severity of arthritis was dramatically lower in MKK3−/−mice. Phospho-p38, phospho-MAPK activator protein kinase 2, IL-1β, CXC ligand 1, IL-6, and matrix metalloproteinase (MMP) 3 levels in the joints of MKK3−/−mice were significantly lower than in controls. Exogenous IL-1β administered during the first 4 days of the passive model restored arthritis to the same severity as in WT mice. In the second model, IL-6 production after systemic LPS administration was similar in WT and MKK3−/−mice. Therefore, selective MKK3 deficiency can suppress inflammatory arthritis and cytokine production while Toll-like receptor 4-mediated host defense remains intact.
Physically realistic homology models built with
rosetta
can be more accurate than their templates
Authors: Misura Kira M. S. , Chivian Dylan , Rohl Carol A. , Kim David E. , Baker David
Published: March 2006

We have developed a method that combines the
rosetta
de novo
protein folding and refinement protocol with distance constraints derived from homologous structures to build homology models that are frequently more accurate than their templates. We test this method by building complete-chain models for a benchmark set of 22 proteins, each with 1 or 2 candidate templates, for a total of 39 test cases. We use structure-based and sequence-based alignments for each of the test cases. All atoms, including hydrogens, are represented explicitly. The resulting models contain approximately the same number of atomic overlaps as experimentally determined crystal structures and maintain good stereochemistry. The most accurate models can be identified by their energies, and in 22 of 39 cases a model that is more accurate than the template over aligned regions is one of the 10 lowest-energy models.
Role of the
Yersinia pestis
plasminogen activator in the incidence of distinct septicemic and bubonic forms of flea-borne plague
Authors: Sebbane Florent , Jarrett Clayton O. , Gardner Donald , Long Daniel , Hinnebusch B. Joseph
Published: March 2006

Yersinia pestis
is transmitted by fleas and causes bubonic plague, characterized by severe local lymphadenitis that progresses rapidly to systemic infection and life-threatening septicemia. Here, we show that although flea-borne transmission usually leads to bubonic plague in mice, it can also lead to primary septicemic plague. However, intradermal injection of
Y. pestis
, commonly used to mimic transmission by fleabite, leads only to bubonic plague. A
Y. pestis
strain lacking the plasmid-encoded cell-surface plasminogen activator, which is avirulent by intradermal or s.c. injection, was able to cause fatal primary septicemic plague at low incidence, but not bubonic plague, when transmitted by fleas. The results clarify a long-standing uncertainty about the etiology of primary septicemic plague and support an evolutionary scenario in which plague first emerged as a flea-borne septicemic disease of limited transmissibility. Subsequent acquisition of the plasminogen activator gene by horizontal transfer enabled the bubonic form of disease and increased the potential for epidemic spread.