bluuebunny/crossref_metadata_2025 huggingface dataset:
Long‐term trends in catchment export and lake retention of dissolved organic carbon, dissolved organic nitrogen, total iron, and total phosphorus: The Dorset, Ontario, study, 1978–1998
Authors: Dillon Peter J. , Molot Lewis A.
Published: September 2005

Annual catchment export of total phosphorus (TP), dissolved organic carbon (DOC), total iron (Fe), and dissolved organic nitrogen (DON) to seven lakes in central Ontario was measured between 1978 and 1998. Fluctuations in annual water discharge and total DOC load (including precipitation) to the lakes over the 20‐year period were similar in the seven study lakes. DOC export to the lakes responded proportionally to changes in discharge, decreasing during drier and warmer years. There were similar but less accentuated variations in annual DOC lake concentrations. There were no clear regional trends evident during the 20‐year period toward drier or wetter conditions, less DOC load, clearer lakes, etc., that could be interpreted as signaling a shift toward a different equilibrium state. The fraction of the DOC load retained by lakes (transferred to sediments and the atmosphere) increased during an extended dry period. Fe, TP, and DON export decreased more than DOC export during the extended dry period. Runoff appears to affect Fe, TP, and DON export first by controlling export of organic matter and second by affecting water table position and thus redox levels in the surface layer of peatlands. Permanently drier conditions with less runoff would likely lead to clearer lakes that are less productive. Conversely, increased runoff would lead to more colored and productive lakes. Both scenarios have implications for subsistence and sport fishing economies.
Radio tomographic imaging of the northern high‐latitude ionosphere on a wide geographic scale
Authors: Kersley L. , Pryse S. E. , Denton M. H. , Bust G. , Fremouw E. , Secan J. , Jakowski N. , Bailey G. J.
Published: September 2005

Several chains of receivers, measuring total electron content (TEC) during passes of satellites in the U.S. Navy Ionospheric Measuring System (NIMS), are operated at northern high latitudes by members of the International Ionospheric Tomography Community (IITC). Results are presented here of nearly simultaneous latitude‐altitude images of the ionosphere over Scandinavia, Greenland, and Alaska, generated from IITC data obtained on 20 September 2001 and interpreted in the context of an IMF‐dependent convection model. The images are compared with output from a coupled thermosphere‐ionosphere‐plasmasphere model and also with maps of high‐latitude TEC generated from GPS measurements. With Bz and By both weakly negative, the images and map reveal plasma features of a two‐cell convection pattern rotated slightly to earlier local magnetic times. The tomographic images provide details of map features such as a tongue of ionization created by solar EUV radiation on the dayside and entrained by convection into the polar cap from the western Russian sector. Combining latitude versus altitude tomographic images generated in different longitudinal sectors from polar‐orbiting beacon satellites such as those of NIMS with TEC maps from GPS offers an emerging opportunity for polar aeronomic studies, especially if further related to synoptic convection measurements. The results also demonstrate the potential role of wide‐scale radio tomography in the verification of ionospheric models.
Iterative multiregion technique for large‐scale electromagnetic scattering problems: Two‐dimensional case
Authors: Al Sharkawy Mohamed , Demir Veysel , Elsherbeni Atef Z.
Published: September 2005

One of the methods to solve large electromagnetic problems is to divide the computational domain into smaller subregions and solve each subregion separately. Then the subregion solutions are combined to obtain a solution for the complete domain. In this paper, an iterative approach using the finite difference frequency domain method is presented to solve the problems that can be divided into separated subregions.
Paleomagnetic quantification of upper‐plate deformation during Miocene detachment faulting in the Mohave Mountains, Arizona
Authors: Pease V. , Hillhouse J. W. , Wells R. E.
Published: September 2005

Paleomagnetic data from Miocene (∼20 Ma) volcanic rocks and dikes of west central Arizona reveal the tilt history of Proterozoic crystalline rocks in the hanging wall of the Chemehuevi‐Whipple Mountains detachment fault. We obtained magnetization data from dikes and flows in two structural blocks encompassing Crossman Peak and Standard Wash in the Mohave Mountains. In the Crossman block the dike swarm records two components of primary magnetization: (1) CNH, a normal polarity, high‐unblocking‐temperature or high‐coercivity component (inclination, I = 48.5°, declination, D = 6.4°), and (2) CRHm, a reversed polarity, high‐temperature or high‐coercivity component (I = −33.6°, D = 197.5°). Argon age spectra imply that the dikes have not been reheated above 300°C since their emplacement, and a baked‐contact test suggests that the magnetization is likely to be Miocene in age. CRHm deviates from the expected direction of the Miocene axial dipole field and is best explained as a result of progressive tilting about the strike of the overlying andesite flows. These data suggest that the Crossman block was tilted 60° to the southwest prior to intrusion of the vertical dike swarm, and the block continued to tilt during a magnetic field reversal to normal polarity (CNH). Miocene dikes in the Crossman block are roughly coplanar, so the younger dikes with normal polarity magnetization intruded along planes of weakness parallel to the earlier reversed polarity swarm. An alternative explanation involves CNH magnetization being acquired later during hydrothermal alteration associated with the final stages of dike emplacement. In the Standard Wash block, the primary component of magnetization is a dual‐polarity, high‐temperature or high‐coercivity component (SWHl, I = 7.2°, D = 0.7°). To produce agreement between the expected Miocene magnetic direction and the SWH component requires (1) correcting for a 56° tilt about the strike of flow bedding and (2) removing a counterclockwise vertical‐axis rotation of 20°. The two rotations restore the Standard Wash dikes to vertical, make parallel the dike layering in the Crossman and Standard Wash blocks, and align the strikes of bedding in both blocks. Geologic mapping, geochemical evidence, and paleomagnetic data are consistent with the upper plate of the Mohave Mountains having tilted in response to formation of the underlying detachment fault.
High sensitivity to the initial condition for the prediction of stratospheric sudden warming
Authors: Mukougawa Hitoshi , Sakai Hirokazu , Hirooka Toshihiko
Published: September 2005

Predictability and a possible tropospheric precursor of a zonal‐wavenumber (WN) 1 stratospheric sudden warming (SSW) event occurring in December 2001 are examined using all ensemble members of the 1‐month forecasts carried out by the Japan Meteorological Agency (JMA). The SSW is predictable from at least 2 weeks in advance, and high sensitivity to the initial condition for the SSW prediction is observed during the onset period of the SSW. Dipole zonal wind anomaly pattern along 80°N/60°N in the upper troposphere during this period is significantly related to the subsequent warming in polar stratospheric regions through deflecting the WN 1 propagation poleward. The leading EOF of predicted zonal‐mean zonal wind variations among ensemble members for the onset period also shows the similar profile. Thus, this coincidence would be responsible for the high sensitivity to the initial condition observed during the onset period of the SSW.
Electrostatic solitary structures associated with the November 10, 2003, interplanetary shock at 8.7 AU
Authors: Williams J. D. , Chen L.‐J. , Kurth W. S. , Gurnett D. A. , Dougherty M. K. , Rymer A. M.
Published: September 2005

We document the presence of solitary structures in the electric field, measured by the Cassini plasma wave instrument at an interplanetary shock associated with the October/November 2003 solar flares. The occurrence frequency of electrostatic solitary waves increases prior to and during the passage of the initial shock boundary but decreases to almost zero in the post‐shock environment. The electric field amplitudes of the solitary structures are on the order of a few tens of μV/m, while the characteristic scale size is estimated to be ∼500 Debye lengths. The estimated potentials are ∼0.5 V both upstream and downstream of the shock. These measurements present a new plasma regime which support electrostatic solitary structures.
Interannual co‐variability of tropical temperature and humidity: A comparison of model, reanalysis data and satellite observation
Authors: Huang Xianglei , Soden Brian J. , Jackson Darren L.
Published: September 2005

We use a 20‐year record of HIRS radiance measurements to evaluate the fidelity of interannual co‐variability of tropical humidity and temperature in the reanalyses and GFDL AM2 simulations. Large inconsistencies between the NCEP and ECMWF reanalyses are found as are disagreements between the reanalyses and AM2 simulations. The largest discrepancies occur in the middle and upper troposphere where the NCEP and ECMWF tropical‐mean relative humidity anomalies are found to be negatively correlated. When compared to HIRS dataset, NCEP is found to have unrealistically large interannual variablity in both the upper (6.7 μm) and middle (7.3 μm) tropospheric humidity channels. The radiance anomalies simulated from AM2 model output are shown to agree well with those observed by HIRS. These results support the validity of the strong coupling between temperature and humidity variations simulated in the GFDL AM2 and highlight the need to improve the representation of interannual variations of humidity in the reanalyses.
The two‐day wave in EOS MLS temperature and wind measurements during 2004–2005 winter
Authors: Limpasuvan Varavut , Wu Dong L. , Schwartz Michael J. , Waters Joe W. , Wu Qian , Killeen Tim L.
Published: September 2005

Two‐day wave observations during January–March 2005 are reported using the recently launched Microwave Limb Sounder (MLS) aboard NASA's Earth Observing System Aura mission. Wave‐induced disturbances in temperature, water vapor, carbon monoxide, and MLS line‐of‐sight wind appear in early January, peak near the end of January, and persist until late February. Temperature and wind amplitudes as large as 9 K and 50 m/s are observed near 90 km. The wave disturbance is initially confined in the mid to low summer latitudes where the climatological summer easterly jet exhibits strong shear. The wave then develops features akin to the third Rossby‐gravity global normal mode, with a weak temperature disturbance in the winter hemisphere (anti‐symmetric about the equator) and wind disturbance over the equator. Strong wind perturbation episode around 17–23 January 2005 in the mid‐latitude Southern hemisphere coincides with a particularly intense solar proton event.
Warm‐season rainfall variability over the U.S. Great Plains and its correlation with evapotranspiration in a climate simulation
Authors: Wu Wanru , Dickinson Robert E.
Published: September 2005

The warm‐season rainfall variability over the US Great Plains is examined in a climate simulation and compared with observations to explore the role of land‐atmosphere interaction in the model. The results show that compared to observations, the model simulations underestimate summertime rainfall by more than 12% but overestimate its standard deviation by 25–54%, with the larger value referring to interannual variability. Linear regression shows that the rainfall variability is connected with evapotranspiration (ET) anomalies, but mostly to evaporation rather than transpiration. Since the evaporation represents an immediate response of the land surface to atmospheric conditions but the transpiration reflects soil moisture memory with considerably longer time scales, the realism of the correlated variability between separate ET components and precipitation is an important aspect of how climate models realistically address land‐atmosphere interaction.
Evidence of VLP volcanic tremor in the band [0.2–0.5] Hz at Stromboli volcano, Italy
Authors: De Lauro E. , De Martino S. , Falanga M. , Palo M. , Scarpa R.
Published: September 2005

We analyze time series of Strombolian volcanic tremor recorded with a network of broadband seismic stations. We evidence the occurrence of a significant component of volcanic tremor in the range [0.2–0.5] Hz by using linear and nonlinear methods. The polarization and ZLCC analysis show that the wave field is characterized by high apparent velocity (∼2 km/s). It comes mainly from the crater area with a clear amplitude decay towards the sea level. The previous properties are loosed when the tremor level is higher suggesting that in this case the wave field is more affected by oceanic noise. The waveform extracted by Independent Component Analysis (ICA) shows a behaviour like nonlinear “beats” as in the case of high frequency waveforms. We conclude that this component displays a behaviour like the wave field at higher frequencies in spite of its low frequency, and it is produced by the vibrations of the volcanic conduit.
Seasonal cycle of the Mindanao Dome in the CCSR/NIES/FRCGC atmosphere‐ocean coupled model
Authors: Suzuki Tatsuo , Sakamoto Takashi T. , Nishimura Teruyuki , Okada Naosuke , Emori Seita , Oka Akira , Hasumi Hiroyasu
Published: September 2005

Using atmosphere‐ocean coupled general circulation models (CGCMs) with different resolution, we investigate the dependency on horizontal resolution to reproduce the seasonal variation of the Mindanao Dome (MD). The seasonal cycle of the MD is successfully simulated in the high resolution CGCM. It is generated by local Ekman upwelling and destroyed by westward warm anomaly propagation during late spring. The warm anomaly is caused by Ekman downwelling induced by westward wind stress and negative wind stress curl anomaly associated with southward shift of the inter‐tropical convergence zone in the central tropical Pacific. However, in the lower resolution model, the seasonal cycle is not represented owing to the insufficient wind forcing. The higher resolution atmospheric model improves the wind forcing in the CGCM, but it doesn't go far enough. The reproduction of the wind forcing depends not only horizontal resolution of an atmospheric model but also on that of an ocean model.
Limits on the burial depth of glacial ice deposits on the flanks of Hecates Tholus, Mars
Authors: Helbert J. , Reiss D. , Hauber E. , Benkhoff J.
Published: September 2005

An analysis of data obtained by the HRSC camera on Mars Express revealed morphological evidence for the existence of glacial deposits on the flank of Hecates Tholus (E. Hauber et al., 2004). Crater counts indicate a very young age in the range of several million years only. In this study we have assessed limits for the burial depth of a still existing ice deposit protected by an overlying dust layer. Our first results indicate a high likelihood to find ice within only a few meters below the surface in this region.
The contribution of sulfuric acid and non‐volatile compounds on the growth of freshly formed atmospheric aerosols
Authors: Wehner B. , Petäjä T. , Boy M. , Engler C. , Birmili W. , Tuch T. , Wiedensohler A. , Kulmala M.
Published: September 2005

The formation of atmospheric aerosol particles (homogeneous nucleation, forming of stable clusters ∼1 nm in size), their subsequent growth to detectable sizes (>3 nm), and to the size of cloud condensation nuclei, remains one of the least understood atmospheric processes upon which global climate change critically depends. However, a quantitative model explanation for the growth of freshly formed aerosols has been missing. In this study, we present observations explaining the nucleation mode (3–25 nm) growth. Aerosol particles typically grow from 3 nm to 60–70 nm during a day, while their non‐volatile cores grow by 10–20 nm as well. The total particle growth rate is 2–8 nm/h while the non‐volatile core material can explain 20–40%. According to our results, sulfuric acid can explain the remainder of the growth, until the particle diameter is around 10–20 nm. After that secondary organic compounds significantly take part in growth process.
Changing snow and shrub conditions affect albedo with global implications
Authors: Sturm Matthew , Douglas Tom , Racine Charles , Liston Glen E.
Published: September 2005

Observations suggest that shrub abundance in the Arctic is increasing owing to climate warming. We investigated the ramifications of a tundra‐to‐shrubland transition on winter energy exchange. At five sites in Alaska we suspended a 50‐m‐long cable above the vegetation and from this measured how the vegetation interacted with the snow and affected albedo. The sites defined a gradient from nearly shrub‐free tundra to a woodland with a continuous shrub canopy. Where the shrubs were small, thin‐stemmed, and supple, they were bent and buried by snow. Where they were tall, thick‐stemmed, and stiff, the shrub canopy remained exposed all winter. Where shrubs were buried, mid‐winter albedo values were high (0.85), but where they were exposed, the values were 30% lower (0.60). At these latter sites, melting began several weeks earlier but proceeded more slowly. Consequently, all sites were free of snow about the same time. Using the measurements and a solar model, we estimate that a land surface transition from shrub‐free tundra to shrubland could produce a 69 to 75% increase in absorbed solar radiation during the snow‐cover period, depending on latitude. This is two thirds the increase associated with a tundra‐to‐forest transition. When combined with measurements showing that a tundra‐to‐shrub transition would also produce a net increase in summer heating, our results suggest a positive feedback mechanism associated with a warming‐induced increase in shrubs. To our knowledge, ours is the first study to document that shrubs could alter the winter energy balance of tundra in such a substantial way.
Forest biomass carbon stocks in China over the past 2 decades: Estimation based on integrated inventory and satellite data
Authors: Piao Shilong , Fang Jingyun , Zhu Biao , Tan Kun
Published: September 2005

Forests are major contributor of terrestrial ecosystem carbon (C) pools, and are thus crucial components for assessing the global C budget. On the basis of forest inventory data for three inventory periods of 1984–1988, 1989–1993, and 1994–1998, and synchronous NDVI (Normalized Difference Vegetation Index) data, we developed a satellite‐based approach for estimating China's forest total biomass C stocks. Using this approach, we analyzed the changes in forest C stocks over the last 2 decades to identify the size and distribution of C sinks/sources in the forests. The total forest biomass of China averaged 5.79 Pg C (1 Pg = 1015 g) during the study period, with an average biomass density of 45.31 Mg C/ha (1 Mg = 106 g). The forest biomass C density showed a large spatial heterogeneity: high in southwestern and northeastern areas, and low in the eastern coastal regions. Over the past 2 decades, the total forest biomass C stock increased from 5.62 Pg C in the early 1980s (average for 1981–1983) to 5.99 Pg C by the end of the 1990s (average for 1997–1999), giving a total increase of 0.37 Pg C and an annual sequestration rate of 0.019 Pg C/yr. The C sink appeared mainly in regions with lower C density. Both environmental changes and human activities are likely major drivers of such spatiotemporal patterns.
Incorporating hydrologic variability into nutrient spiraling
Authors: Doyle Martin W.
Published: September 2005

Nutrient spiraling describes the path of a nutrient molecule within a stream ecosystem, combining the biochemical cycling processes with the downstream driving force of stream discharge. To date, nutrient spiraling approaches have been hampered by their inability to deal with fluctuating flows, as most studies have characterized nutrient retention within only a small range of discharges near base flow. Here hydrologic variability is incorporated into nutrient spiraling theory by drawing on the fluvial geomorphic concept of effective discharge. The effective discharge for nutrient retention is proposed to be that discharge which, over long periods of time, is responsible for the greatest portion of nutrient retention. A developed analytical model predicts that the effective discharge for nutrient retention will equal the modal discharge for small streams or those with little discharge variability. As modal discharge increases or discharge variability increases, the effective discharge becomes increasingly less than the modal discharge. In addition to the effective discharge, a new metric is proposed, the functionally equivalent discharge, which is the single discharge that will reproduce the magnitude of nutrient retention generated by the full hydrologic frequency distribution when all discharge takes place at that rate. The functionally equivalent discharge was found to be the same as the modal discharge at low hydrologic variability, but increasingly different from the modal discharge at large hydrologic variability. The functionally equivalent discharge provides a simple quantitative means of incorporating hydrologic variability into long‐term nutrient budgets.
Recombination of polycyclic aromatic hydrocarbon photoions with electrons in a flowing afterglow plasma
Authors: Novotný O. , Sivaraman B. , Rebrion-Rowe C. , Travers D. , Biennier L. , Mitchell J. B. A. , Rowe B. R.
Published: September 2005

A new technique, flowing afterglow with photoions (FIAPI), has been developed to measure the rate coefficient for the recombination of complex ions, and, in particular, polycyclic aromatic hydrocarbon (PAH) cations with electrons. The method is based on the flowing afterglow Langmuir probe - mass spectrometer apparatus at the University of Rennes I. A helium plasma is generated by a microwave discharge in a He buffer gas and downstream, a small amount of argon gas is injected to destroy any helium metastables. A very small amount of neutral PAH molecules is added to the afterglow plasma by evaporation from a plate coated with the PAH to be studied. PAH ions are then produced by photoionization of the parent molecule using a pulsed UV laser (157 nm). The laser beam is oriented along the flow tube and so a constant spatial concentration of photoions is obtained. The electron concentration along the flow tube is measured by means of a movable Langmuir probe. Ion concentration decay in time is measured at a fixed position using a quadrupole mass spectrometer which is triggered by the laser pulse. The recombination of anthracene and pyrene cations has been studied using this technique and we have found a recombination rate of (2.4±0.8)×10−6cm3s−1 for anthracene and (4.1±1.2)×10−6cm3s−1 for pyrene.
The effect of substituents on electronic states’ ordering in meta-xylylene diradicals: Qualitative insights from quantitative studies
Authors: Wang Tao , Krylov Anna I.
Published: September 2005

Equation-of-motion spin-flip coupled-cluster method with single and double substitutions (EOM-SF-CCSD) is employed to study how substituents affect the electronic states’ ordering in meta-xylylene diradicals. The electronegativity of substituents and the incorporation of a heteroatom are found to have a negligible effect. The effect of charges on energy gaps is much more pronounced, in agreement with the proposal of Dougherty and co-workers [J. Am. Chem. Soc. 118, 1452 (1996)]. Resonance structure theory and molecular orbital analysis are employed to explain this phenomenon. The changes in the exocyclic C–C bond length in substituted meta-xylylenes, derived from equilibrium structures calculated by using analytic gradients for the EOM-SF-CCSD method, support the original resonance theory explanation by West et al. However, a similar resonance-theory-based reasoning fails to explain the quantitative difference between positively and negatively charged systems as well as the observed strong stabilization of an open-shell singlet state in the N-oxidized pyridinium analog of meta-xylylene.
Growth kinetics of TiO2 films deposited by aerosol-assisted chemical-vapor deposition from two different precursors (Ti-n-butoxide and Ti diisopropoxide)
Authors: Conde-Gallardo A. , Castillo N. , Guerrero M.
Published: September 2005

When titanium dioxide films are deposited by delivering a liquid aerosol of titanium-n-butoxide or titanium diisopropoxide, the crystalline and morphological features indicate that the deposition takes place through an aerosol-assisted chemical-vapor deposition (AA-CVD) process. However, the crystalline state depends on the precursor. The evidence of AA-CVD is strongly supported by the quantitative study of the growth rate rg as a function of deposition temperature. The fitting of the experimental rg curves to the equation ∼T3∕2exp(−EA∕RT) indicates that film formation is limited by the gas diffusion + surface reaction of the precursors. The characteristic activation energy EA of such surface reaction depends on the Ti precursor; EA≅112.0kJ∕mol for Ti-n-butoxide and EA≅21.4kJ∕mol for Ti-diisopropoxide.
Surface morphological evolution of epitaxial CrN(001) layers
Authors: Frederick J. R. , Gall D.
Published: September 2005

CrN layers, 57 and 230 nm thick, were grown on MgO(001) at Ts=600–800°C by ultrahigh-vacuum magnetron sputter deposition in pure N2 discharges from an oblique deposition angle α=80°. Layers grown at 600 °C nucleate as single crystals with a cube-on-cube epitaxial relationship with the substrate. However, rough surfaces with cauliflower-type morphologies cause the nucleation of misoriented CrN grains that develop into cone-shaped grains that protrude out of the epitaxial matrix to form triangular faceted surface mounds. The surface morphology of epitaxial CrN(001) grown at 700 °C is characterized by dendritic ridge patterns extending along the orthogonal ⟨110⟩ directions superposed by square-shaped super mounds with ⟨100⟩ edges. The ridge patterns are attributed to a Bales-Zangwill instability while the supermounds form due to atomic shadowing which leads to the formation of epitaxial inverted pyramids that are separated from the surrounding layer by tilted nanovoids. Growth at 800 °C yields complete single crystals with smooth surfaces. The root-mean-square surface roughness for 230-nm-thick layers decreases from 18.8 to 9.3 to 1.1 nm as Ts is raised from 600 to 700 to 800 °C. This steep decrease is due to a transition in the roughening mechanism from atomic shadowing to kinetic roughening. Atomic shadowing is dominant at 600 and 700 °C, where misoriented grains and supermounds, respectively, capture a larger fraction of the oblique deposition flux in comparison to the surrounding epitaxial matrix, resulting in a high roughening rate that is described by a power law with an exponent β>0.5. In contrast, kinetic roughening controls the surface morphology for Ts=800°C, as well as the epitaxial fraction of the layers grown at 600 and 700 °C, yielding relatively smooth surfaces and β⩽0.27.
Charge transport in hydrogenated boron-doped nanocrystalline silicon-silicon carbide alloys
Authors: Myong Seung Yeop , Shevaleevskiy Oleg , Lim Koeng Su , Miyajima Shinsuke , Konagai Makoto
Published: September 2005

We have investigated the carrier transport mechanism of mixed-phased hydrogenated boron-doped nanocrystalline silicon–silicon carbide alloy (p-nc-Si-SiC:H) films. From temperature-dependent dark conductivity measurements, we found that the p-nc-Si-SiC:H alloys have two different carrier transport mechanisms: one is the thermally activated hopping between neighboring crystallites near the room-temperature region and the other is the band tail hopping below 150 K.
Hydration properties and potentials of mean force of nonpolar amino acid residues in water: A pertubation theoretic approach
Authors: Renzi Danilo G. , Stoico César O. , Vericat Fernando
Published: September 2005

We use a perturbation approach to calculate the solute-solvent and solute-solute pair correlations for infinitely dilute solutions of nonpolar amino acid side chains in water. In particular, from the solute-solute correlations we derive potentials of mean force for all the distances between different residues of amino acids. Comparison with molecular dynamics simulations performed using GROMOS package shows that the goodness of the approximation varies with the amino acid considered. We discuss in terms of hydrophobicity the different effect that the inclusion of the attractions causes on the solute-water and solute-solute correlations.
An asymmetry of conduction mechanisms and charge trapping in thin high-k HfxTiySizO films
Authors: Paskaleva A. , Bauer A. J. , Lemberger M.
Published: September 2005

The electrical behavior of high-permittivity (high-k) hafnium titanium silicate (HfxTiySizO) layers with different Hf:Ti ratios in the films is investigated. The films were deposited by metal-organic chemical-vapor deposition using a mixture of two single-source precursors for the deposition of Hf silicate and Ti silicate. The attention is focused on the gate bias asymmetry of leakage currents, conduction mechanisms, and trapping behavior dependent on film composition. The pure Hf silicate, the Ti silicate, and the sample with the lowest Hf content reveal a gate bias symmetry of the conduction process, implying the formation of a single-layer structure, whereas samples containing both Hf and Ti in significant amounts exhibit an asymmetrical behavior to the gate polarity. A continuous change from Poole-Frenkel conduction in pure Hf silicates to phonon-assisted tunneling in pure Ti silicates is established. It is found that a strong negative charge trapping occurs in the samples containing significant amounts of both Hf and Ti. With an increase of Ti content in the films, the density of the trapped charge increases and its centroid moves farther away from the dielectric/Si interface. Two possible processes are considered to explain the observed asymmetry of the conduction process—negative charge trapping and formation of a double-layer structure. It is suggested that both phenomena occur and are consequences of one and the same structural process, phase separation, i.e. the formation of TiO2, HfO2, and SiO2 islands in the film. The degree of phase separation depends strongly on the film composition and defines the process, which has the dominating role in the gate bias asymmetry of the conduction mechanism.
Selectively excited photoluminescence from Eu-implanted GaN
Authors: Wang K. , Martin R. W. , O’Donnell K. P. , Katchkanov V. , Nogales E. , Lorenz K. , Alves E. , Ruffenach S. , Briot O.
Published: September 2005

The intensity of Eu-related luminescence from ion-implanted GaN with a 10nm thick AlN cap, both grown epitaxially by metal organic chemical vapor deposition (MOCVD) is increased markedly by high-temperature annealing at 1300°C. Photoluminescence (PL) and PL excitation (PLE) studies reveal a variety of Eu centers with different excitation mechanisms. High-resolution PL spectra at low temperature clearly show that emission lines ascribed to D05-F27 (∼622nm), D05-F37 (∼664nm), and D05-F17 (∼602nm) transitions each consist of several peaks. PL excitation spectra of the spectrally resolved components of the D05-F27 multiplet contain contributions from above-bandedge absorption by the GaN host, a GaN exciton absorption at 356nm, and a broad subedge absorption band centred at ∼385nm. Marked differences in the shape of the D05-F27 PL multiplet are demonstrated by selective excitation via the continuum/exciton states and the below gap absorption band. The four strongest lines of the multiplet are shown to consist of two pairs due to different Eu3+ centers with different excitation mechanisms.
Characteristics of a Zn0.7Mg0.3O∕ZnO heterostructure field-effect transistor grown on sapphire substrate by molecular-beam epitaxy
Authors: Koike Kazuto , Nakashima Ippei , Hashimoto Kazuyuki , Sasa Shigehiko , Inoue Masataka , Yano Mitsuaki
Published: September 2005

Characterization of a Zn0.7Mg0.3O∕ZnO heterostructure field-effect transistor (HFET) is reported. The HFET was based on a Zn0.7Mg0.3O∕ZnO∕Zn0.7Mg0.3O single quantum well (SQW) grown on an a-plane sapphire substrate by molecular-beam epitaxy, and was fabricated by a conventional photolithography technique combined with dry etching. Room-temperature characteristic of the HFET was a n-channel depletion type with a transconductance of 0.70mS∕mm and a field-effect mobility of 140cm2∕Vs, in good agreement with the electron Hall mobility in SQW of 130cm2∕Vs. The on∕off ratio at VDS=3V was ∼800, which was limited by an insufficiently suppressed leakage current through the bottom Zn0.7Mg0.3O barrier.
Superelasticity of CoNiGa:Fe single crystals
Authors: Dai X. F. , Liu G. D. , Liu Z. H. , Wu G. H. , Chen J. L. , Meng F. B. , Liu H. Y. , Yan L. Q. , Qu J. P. , Li Y. X. , Wang W. G. , Xiao John Q.
Published: September 2005

We have fabricated CoNiFeGa single crystals with excellent superelasticity. The superelastic strains of 4% and 6.7% in compression have been obtained along the [001] and [110] directions, respectively. These single crystals show strong anisotropy in strains, superelastic parameters, and even transformation path related to the different crystalline directions. A large superelastic strain up to 11% has been obtained in tension test. The perfect superelasticities have also displayed in bending and torsion tests.
Forced Kramers escape in single-molecule pulling experiments
Authors: Sheng Yu-Jane , Jiang Shaoyi , Tsao Heng-Kwong
Published: September 2005

The pulling-induced rupture of noncovalent bonds is studied by the overdamped Kramers theory with full account of a time-varying barrier. Mechanic pulling reduces the energy barrier and leads to loading-rate dependence of the rupture force Fu(Ft). Tested against Langevin dynamics, four distinct regimes are identified, including kinetic dominant, weak pulling, strong pulling, and mechanic pulling dominant. Asymptotic analyses show that Fu∼lnFt in weak pulling regime and becomes 1−(Fu∕Fc)∼[ln(Ft)∕Eb]2∕3 in strong pulling regime. Kinetic informations such as activation energy Eb and critical force Fc were extracted from pulling experiments for biotin-streptavidin complex.
Osmosis and pervaporation in polyimide submicron microfluidic channel structures
Authors: Eijkel Jan C. T. , Bomer Johan G. , van den Berg Albert
Published: September 2005

Osmosis and pervaporation of water through the roof of all-polyimide channels of 500nm height is described. The phenomena cause both a liquid flow in the channels and a concentration change of dissolved salt. Both effects are amplified due to the thin channel roof and the small channel height. Osmotic movement of demineralized water was observed towards a salt solution and towards ethanol and isopropanol. Water movement by pervaporation was observed from a salt solution towards the atmosphere. Flow velocities of up to 70μm∕s were generated in the channels. The results are in accordance with predictions from the solution-diffusion model for membrane transport. The observed phenomena can be applied in a nanofluidic osmotic pump or for an osmotic or pervaporative concentrator.
Two-dimensional hydrodynamic focusing in a simple microfluidic device
Authors: Simonnet Claire , Groisman Alex
Published: September 2005

Two-dimensional flow focusing in pressure-driven flow is demonstrated in a microfluidic device made of a single cast of a silicon elastomer. A stream injected into the device is shaped to a variety of rectangular profiles. A flow of particles is focused into a thin layer with homogeneous velocity. A blob of dye injected into a microchannel is transported over a long distance with minimal dispersion. The device can be integrated into lab-on-a-chip systems and used as a low-cost flow cytometry chamber.
Dielectric properties of biological molecules in the Terahertz gap
Authors: Parthasarathy Ramakrishnan , Globus Tatiana , Khromova Tatyana , Swami Nathan , Woolard Dwight
Published: September 2005

In this work, results from parallel measurements of reflection and transmission spectra of biological molecules were utilized to enable detailed and direct calculation of the refractive index and absorption coefficient spectra in the Terahertz gap. The DNA samples from herring and salmon, as well as the protein Ovalbumin sample, have been characterized. The modeling technique is described. The reflection spectra have resonance features similar to those demonstrated earlier for transmission, thereby reaffirming molecular vibrational modes in biological materials. The dispersion of refractive index and absorption coefficient is demonstrated within the Terahertz gap of 10cm−1to25cm−1. The data yielded higher refractive index and absorption coefficient for the single stranded salmon DNA than for the double stranded counterpart, with several different vibrational modes.
Isobar suppression by photodetachment in a gas-filled rf quadrupole ion guide
Authors: Liu Y. , Beene J. R. , Havener C. C. , Liang J. F.
Published: September 2005

A technique based on selective nonresonant laser photodetachment of unwanted negative ion species has been developed for efficient suppression of isobaric contaminants in negative ion beams. A radio-frequency quadrupole ion guide is employed to cool the negative ion beam and dramatically increase the interaction time of the ions with the laser, substantially increasing the efficiency of the photodetachment process. In a proof-of-principle experiment, we achieved 95% suppression of Co−59 ions by photodetachment while under identical conditions 10% of Ni−58 ions were neutralized.
Thrombospondin-1 inhibits endothelial cell responses to nitric oxide in a cGMP-dependent manner
Authors: Isenberg Jeff S. , Ridnour Lisa A. , Perruccio Elizabeth M. , Espey Michael G. , Wink David A. , Roberts David D.
Published: September 2005

Redox signaling plays an important role in the positive regulation of angiogenesis by vascular endothelial growth factor, but its role in signal transduction by angiogenesis inhibitors is less clear. Using muscle explants in 3D culture, we found that explants from mice lacking the angiogenesis inhibitor thrombospondin-1 (TSP1) exhibit exaggerated angiogenic responses to an exogenous NO donor, which could be reversed by providing exogenous TSP1. To define the basis for inhibition by TSP1, we examined the effects of TSP1 on several proangiogenic responses of endothelial cells to NO. NO has a biphasic effect on endothelial cell proliferation. The positive effect at low doses of NO is sensitive to inhibition of cGMP signaling and picomolar concentrations of TSP1. NO stimulates both directed (chemotactic) and random (chemokinetic) motility of endothelial cells in a cGMP-dependent manner. TSP1 potently inhibits chemotaxis stimulated by NO. Low doses of NO also stimulate adhesion of endothelial cells on type I collagen in a cGMP-dependent manner. TSP1 potently inhibits this response both upstream and downstream of cGMP. NO-stimulated endothelial cell responses are inhibited by recombinant type 1 repeats of TSP1 and a CD36 agonist antibody but not by the N-terminal portion of TSP1, suggesting that CD36 or a related receptor mediates these effects. These results demonstrate a potent antagonism between TSP1 and proangiogenic signaling downstream of NO. Further elucidation of this inhibitory signaling pathway may identify new molecular targets to regulate pathological angiogenesis.
Structural role of countertransport revealed in Ca2+pump crystal structure in the absence of Ca2+
Authors: Obara Koji , Miyashita Naoyuki , Xu Cheng , Toyoshima Itaru , Sugita Yuji , Inesi Giuseppe , Toyoshima Chikashi
Published: September 2005

Ca2+-ATPase of sarcoplasmic reticulum is an ATP-powered Ca2+pump but also a H+pump in the opposite direction with no demonstrated functional role. Here, we report a 2.4-Å-resolution crystal structure of the Ca2+-ATPase in the absence of Ca2+stabilized by two inhibitors, dibutyldihydroxybenzene, which bridges two transmembrane helices, and thapsigargin, also bound in the membrane region. Now visualized are water and several phospholipid molecules, one of which occupies a cleft between two transmembrane helices. Atomic models of the Ca2+binding sites with explicit hydrogens derived by continuum electrostatic calculations show how water and protons fill the space and compensate charge imbalance created by Ca2+-release. They suggest that H+countertransport is a consequence of a requirement for maintaining structural integrity of the empty Ca2+-binding sites. For this reason, cation countertransport is probably mandatory for all P-type ATPases and possibly accompanies transport of water as well.
A zebrafish
bmyb
mutation causes genome instability and increased cancer susceptibility
Authors: Shepard Jennifer L. , Amatruda James F. , Stern Howard M. , Subramanian Aravind , Finkelstein David , Ziai James , Finley K. Rose , Pfaff Kathleen L. , Hersey Candace , Zhou Yi , Barut Bruce , Freedman Matthew , Lee Charles , Spitsbergen Jan , Neuberg Donna , Weber Gerhard , Golub Todd R. , Glickman Jonathan N. , Kutok Jeffery L. , Aster Jon C. , Zon Leonard I.
Published: September 2005

A major goal of cancer research has been to identify genes that contribute to cancer formation. The similar pathology between zebrafish and human tumors, as well as the past success of large-scale genetic screens in uncovering human disease genes, makes zebrafish an ideal system in which to find such new genes. Here, we show that a zebrafish forward genetic screen uncovered multiple cell proliferation mutants including one mutant,
crash&burn
(
crb
), that represents a loss-of-function mutation in
bmyb
, a transcriptional regulator and member of a putative proto-oncogene family.
crb
mutant embryos have defects in mitotic progression and spindle formation, and exhibit genome instability. Regulation of cyclin B levels by
bmyb
appears to be the mechanism of mitotic accumulation in
crb
. Carcinogenesis studies reveal increased cancer susceptibility in adult
crb
heterozygotes. Gene-expression signatures associated with loss of
bmyb
in zebrafish are also correlated with conserved signatures in human tumor samples, and down-regulation of the B-
myb
signature genes is associated with retention of p53 function. Our findings show that zebrafish screens can uncover cancer pathways, and demonstrate that loss of function of
bmyb
is associated with cancer.
Solid tumor risks after high doses of ionizing radiation
Authors: Sachs Rainer K. , Brenner David J.
Published: September 2005

There is increasing concern regarding radiation-related second-cancer risks in long-term radiotherapy survivors and a corresponding need to be able to predict cancer risks at high radiation doses. Although cancer risks at moderately low radiation doses are reasonably understood from atomic bomb survivor studies, there is much more uncertainty at the high doses used in radiotherapy. It has generally been assumed that cancer induction decreases rapidly at high doses due to cell killing. However, recent studies of radiation-induced second cancers in the lung and breast, covering a very wide range of doses, contradict this assumption. A likely resolution of this disagreement comes from considering cellular repopulation during and after radiation exposure. Such repopulation tends to counteract cell killing and accounts for the large discrepancies between the current standard model for cancer induction at high doses and recent second-cancer data. We describe and apply a biologically based minimally parameterized model of dose-dependent cancer risks, incorporating carcinogenic effects, cell killing, and, additionally, proliferation/repopulation effects. Including stem-cell repopulation leads to risk estimates consistent with high-dose second-cancer data. A simplified version of the model provides a practical and parameter-free approach to predicting high-dose cancer risks, based only on data for atomic bomb survivors (who were exposed to lower total doses) and the demographic variables of the population of interest. Incorporating repopulation effects provides both a mechanistic understanding of cancer risks at high doses and a practical methodology for predicting cancer risks in organs exposed to high radiation doses, such as during radiotherapy.
Induced helicity in biopolymer networks under stress
Authors: Courty S. , Gornall J. L. , Terentjev E. M.
Published: September 2005

By combining dynamic mechanical and optical measurements in probing the internal structure of a biopolymer network (gelatin gel), we studied the quasi-equilibrium evolution of helical content as a function of the applied stress. Assuming that the net optical activity is proportional to the concentration of secondary helices of collagen chains, and assuming that affine mechanical deformation, we find a nonmonotonic relationship between the helical domains and an imposed deformation. The results are in qualitative agreement with theoretical predictions of α-helices induced by chain end-to-end stretching, and give a consistent picture of mechanically stimulated helix-coil transition in networks of denatured polypeptides.
Moving to Opportunity: The Demonstration's Design and its Effects on Mobility
Authors: Feins Judith D. , Shroder Mark D.
Published: September 2005

Poverty concentration in urban neighbourhoods may have detrimental long-term effects on residents. The Moving to Opportunity (MTO) experiment in the US randomly assigned high-poverty public housing residents to a programme that subsidised occupancy in non-poor areas, permitting controlled analysis of neighbourhood impacts. In this paper, MTO data are used to answer the following questions. How much impact can a one-time intervention have on the subsequent residential experience of poor families from high-poverty neighbourhoods? It is found that the impacts on subsequent residential experience are statistically and practically significant. Are poor families who move to non-poor neighbourhoods significantly different from poor families who do not, in (usually) unmeasured characteristics? It is found that yes, they are. What difference does moving to a better neighbourhood make? There are large gains in safety, other improvements in neighbourhood quality and no loss in social ties.
Planning Policy and Retail Property Markets: Measuring the Dimensions of Planning Intervention
Authors: Jackson Catherine , Watkins Craig
Published: September 2005

There is considerable case-study-based evidence that changes in the public policy environment have profoundly altered the structure and operation of retail property markets in England. Despite this, however, few studies of property market performance consider the influence of retail planning policies. This paper seeks to fill the gap. The empirical part of the paper uses data derived from a survey of local planning authorities to construct a range of measures of planning policy stance. The indicators demonstrate that the role of policy is complex and multidimensional. The paper then explores the relationship between planning policies and measures of property market performance. The results show that, while proactive policies do not guarantee a vibrant market, they can play an important part in stimulating occupier and investor demand, even where there are poor economic fundamentals.
Time-series Analysis of Clusters in City Size Distributions
Authors: Garmestani Ahjond S. , Allen Craig R. , Bessey K. Michael
Published: September 2005

Complex systems, such as urban systems, emerge unpredictably without the influence of central control as a result of adaptive behaviour by their component, interacting agents. This paper analyses city size distributions, by decade, from the south-western region of the United States for the years 1890-1990. It determines if the distributions were clustered and documents changes in the pattern of clusters over time. Clusters were determined utilising a kernel density estimator and cluster analysis. The data were clustered as determined by both methods. The analyses identified 4-7 clusters of cities in each of the decades analysed. Cities cluster into size classes, suggesting variability in growth rates at different scales.