bluuebunny/crossref_metadata_2025 huggingface dataset:
Resonant heating and acceleration of ions in coronal holes driven by cyclotron resonant spectra
Authors: Ofman L. , Gary S. P. , Viñas A.
Published: December 2002

Recent observations and models suggest that the resonant absorption of ion cyclotron waves heats and accelerates the ions in the solar wind. Velocity distributions of minor ions derived from SOHO Ultraviolet Cronagraph Spectrometer (UVCS) observations in coronal holes indicate that the minor ion temperature anisotropy is T⟂/T∣∣ > 10 and that outflow speeds are higher than those of the solar wind protons. Here one‐dimensional hybrid simulations of initially homogeneous, collisionless plasmas are used to study a model of coronal plasmas including kinetic protons, a tenuous component of oxygen ions, and massless fluid electrons. Spectra of ion cyclotron resonant Alfvén waves are imposed on the system to study the resultant heating of both ion species. We investigate the effects of various power spectra of the form f−1 or f−5/3 and vary the input frequency range. We find that the ion heating strongly depends on the power contained in the frequency range of the input spectrum that can resonate with the ions. The minor O5+ ions are easily heated and become anisotropic due to various forms of the spectra. The protons remain nearly isotropic and are weakly heated in most cases in this study. We investigate the self‐consistent fluctuation spectrum generated by the response of the ions and the non‐Maxwellian features in the velocity distribution.
Frequency‐dependent seismic attenuation in the inner core, 1. A viscoelastic interpretation
Authors: Li Xu , Cormier Vernon F.
Published: December 2002

Using reference source time functions, broadband velocity waveforms of PKIKP in the distance range 150–180° are inverted for a viscoelastic model of inner core attenuation. A mean Qα at 1 Hz of 307 ± 90 is determined from 345 available PKIKP ray paths. Both global and regional results find a depth‐dependent attenuation in the deep inner core, with anisotropic attenuation resolved in regional results. Attenuation is much stronger in the upper 300 km of the inner core. The preferred model of viscoelastic attenuation is frequency dependent, with very weak velocity dispersion. Our data do not resolve any hemispherical differences of attenuation in the deep inner core.
Temporal limits of the power law aftershock decay rate
Authors: Narteau C. , Shebalin P. , Holschneider M.
Published: December 2002

We compare the aftershock decay rate in natural data with predictions from a stochastic analytical model based on a Markov process with stationary transition rates. These transition rates vary according to the magnitude of a scalar representing the state of stress and defined as the overload. Thus, the aftershock decay rate in the model is a sum of independent exponential decay functions with different characteristic times. From different shapes of the overload distribution and different expressions of the transition rates, we discuss the magnitude of the exponent of the power law aftershock decay rate and the time interval over which we can expect to observe this regime. Before and after this time interval, we show that the decay is linear and exponential, respectively. From our analytical solutions, we deduce a model of aftershock decay rate in which a power law scaling exponent and two characteristic rates emerge. One rate is a short‐term linear decrease before the onset of the power law decay to account for a finite number of events at zero time, and the other one can be interpreted as an inverse correlation time, after which aftershocks no longer occur. Then, we interpret the empirical modified Omori law (MOL) and its parameters in the framework of our theoretical model. We suggest a technique to systematically estimate and interpret the temporal limits of the power law aftershock decay rate in real sequences. We approximate these temporal limits from data available from several well‐known aftershock sequences and show from an Akaike Information Criteria (AIC) that, in almost all cases examined here, our model fits better the aftershock decay rate than the MOL despite a quantitative penalty for the extra parameter required. From this work, we conclude that the time delay before the onset of the power law decay may be related to the recurrence time of an earthquake. Finally, we suggest that the power law decay rates extend over longer times according to the concentration of the deformation along dominant major faults.
A dynamically consistent analysis of the mesoscale eddy field at the western North Pacific Subarctic Front
Authors: Yaremchuk Maxim I. , Maximenko Nikolai A.
Published: December 2002

In this study, we analyze the energetics of the quasigeostrophic (QG) currents observed in the course of an extensive Soviet field experiment in 1987. The analyzed data span over the period of 1 month and cover the region 37.5°–42.5°N, 151.5°–158°E at an average horizontal resolution of 35 km. The processed data set includes the results of measurements at 668 hydrographic stations, 118 moorings, Geosat sea surface height anomalies, ECMWF winds, and ETOP05 bottom topography. A variational data assimilation method is employed to interpolate observations onto a regular space–time grid. An ensemble average over optimized ocean states is utilized to estimate posterior error bars. Assimilation has shown that the observed mesoscale structures are well described by QG dynamics, which can explain 80–85% of the variability in the velocity and density fields. The model‐data misfits lie within the observational error bars for all the data types used in assimilation. The standard Laplacian‐type parameterization of the small‐scale processes was found to be inconsistent with observations, as the least model‐data misfits were obtained with zero diffusivity coefficients. Analysis of the interpolated patterns revealed a pronounced mesoscale mixing event, characterized by the development of a warm streamer swirling around the upper cold core of an old anticyclonic Kuroshio Extension eddy. The process was accompanied by a fast northwestward displacement of the eddy and induced detachment of a warm elongated vortex from its eastern rim. Within a week, the vortex penetrated northward into the subarctic zone and eventually split into several smaller‐scale eddies. Energy analysis of the optimal solution indicates that baroclinic instability is the likely source of their energy. Computation of energy exchanges between depth‐averaged and shear components of the observed currents reveals the vertical energy cascade (barotropization) of the shear flow at a rate of (29 ± 4) × 10−7 cm2 s−3 and the weaker kinetic energy transfer of opposite sign due to topographic interaction. Mean currents in the region are baroclinically unstable with an estimate of the available potential energy flux from the mean current to the eddies (53 ± 8) × 10−7 cm2 s−3. Potential enstrophy is transferred to mesoscale at a rate of (33 ± 7) × 10−19 s−3. These figures can be considered as experimental evidence of the properties of free geostrophic turbulence, which were predicted by theory and observed in numerical experiments.
MLS observations of atmospheric gravity waves over Antarctica
Authors: Wu Dong L. , Jiang Jonathan H.
Published: December 2002

Stratospheric gravity waves over Antarctica are studied with the radiance variances observed by Upper Atmosphere Research Satellite Microwave Limb Sounder (UARS MLS). Strong wave activities are found during August and September in 1992–1994 over the Drake Passage region (290°–315° longitude and 50°S–70°S latitude), where the enhancement seems associated with the topography of both South America and Antarctic Peninsula tips. During the same period, significant gravity wave activities are also evident along the Antarctic coastal region. The vertical growth of the wave variance shows a scale height of ∼14 km at low altitudes for both Drake Passage and the coastal regions but reduces substantially at high altitudes. The growth rate transition occurs at a lower altitude in the Drake Passage region where the variance is larger. The gravity wave activities observed near the Antarctic may contribute significantly to the formation of polar stratospheric clouds (PSC) because of the overlapping with the vortex edge and with the PSC activities as observed by CLAES (Cryogenic Limb Array Etalon Spectrometer).
Mesomorphic Properties of 4-Benzoylaminobenzonitrile Derivatives Having an Electron-withdrawing Group with Hydrogen Bonding Ability
Authors: Hashimoto Masashi , Ujiie Seiji , Mori Akira
Published: December 2002

4-Benzoylaminobenzonitrile derivatives having an electron-withdrawing group with hydrogen bonding ability such as a formyl or a nitro group at the C-3 position of the benzonitrile moiety were synthesized. They had the higher transition temperatures than the parent compound. It is explained by the intramolecular hydrogen bonding between the lateral group at C-3 and the amide proton to prohibit the free rotation around the N-benzonitrile bond, which made molecules flat to increase transition temperatures.
On the relationships between catchment scale and streamwater mean residence time
Authors: McGlynn Brian , McDonnell Jeff , Stewart Mike , Seibert Jan
Published: December 2002

The relationship between streamwater mean residence time (MRT) and landscape characteristics is poorly understood. We used tritium (3H) to define our MRT. We tested the hypothesis that baseflow water MRT increases with increasing absolute catchment size at the Maimai catchments. These catchments are simple hydrologic systems relative to many catchments around the world, with uniformly wet climatic conditions, little seasonality, uniform and nearly impermeable bedrock, steep short hillslopes, shallow soils, and well‐characterized hillslope and catchment hydrology. As a result, this is a relatively simple system and an ideal location for new MRT‐related hypothesis testing. Whilst hydrologists have used 3H to estimate water age since the 1960s nuclear testing spike, atmospheric 3H levels have now approached near background levels and are often complicated by contamination from the nuclear industry. We present results for 3H sampled from our set of nested catchments in nuclear‐industry‐free New Zealand. Because of high precision analysis, near‐natural atmospheric 3H levels, and well‐characterized rainfall 3H inputs, we were able to estimate the age of young (i.e. less than 3 years old) waters. Our results showed no correlation between MRT and catchment size. However, MRT was correlated to the median sub‐catchment size of the sampled watersheds, as shown by landscape analysis of catchment area accumulation patterns. These preliminary findings suggest that landscape organization, rather than total area, is a first‐order control on MRT and points the way forward for more detailed analysis of how landscape organization affects catchment runoff characteristics. Copyright © 2003 John Wiley & Sons, Ltd.
Singlet oxygen production in herbicide‐treated photosystem II
Authors: Fufezan Christian , Rutherford A.William , Krieger-Liszkay Anja
Published: December 2002

Photo‐generated reactive oxygen species in herbicide‐treated photosystem II were investigated by spin‐trapping. While the production of OH and O2
−
was herbicide‐independent, 1O2 with a phenolic was twice that with a urea herbicide. This correlates with the reported influence of these herbicides on the redox properties of the semiquinone QA
−
and fits with the hypothesis that 1O2 is produced by charge recombination reactions that are stimulated by herbicide binding and modulated by the nature of the herbicide. When phenolic herbicides are bound, charge recombination at the level of P+
Pheo−
is thermodynamically favoured forming a chlorophyll triplet and hence 1O2. With urea herbicides this pathway is less favourable.
Nitric oxide induces neutral ceramidase degradation by the ubiquitin/proteasome complex in renal mesangial cell cultures
Authors: Franzen Rochus , Pfeilschifter Josef , Huwiler Andrea
Published: December 2002

The neutral ceramidase is a key enzyme in the regulation of cellular ceramide levels. Previously we have reported that stimulation of rat renal mesangial cells with nitric oxide (NO) donors leads to an inhibition of neutral ceramidase activity which is due to increased degradation of the enzyme. This and the concomitant activation of the sphingomyelinase results in an amplification of ceramide levels. Here, we show that the NO‐triggered degradation of neutral ceramidase involves activation of the ubiquitin/proteasome complex. The specific proteasome inhibitor lactacystin completely reverses the NO‐induced degradation of ceramidase protein and neutral ceramidase activity. As a consequence, the cellular amount of ceramide, which drastically increases by NO stimulation, is reduced in the presence of lactacystin. Furthermore, ubiquitinated neutral ceramidase accumulates after NO stimulation. In summary, our data clearly show that the ubiquitin/proteasome complex is an important determinant of neutral ceramidase activity and thereby regulates the availability of ceramide.
Stimulation of adhesion molecule expression by Helicobacter pylori and increased neutrophil adhesion to human umbilical vein endothelial cells
Authors: Byrne M.F , Corcoran P.A , Atherton J.C , Sheehan K.M , Murray F.E , Fitzgerald D.J , Murphy J.F
Published: December 2002

Helicobacter pylori upregulates endothelial adhesion molecules but the pattern is unclear. Human umbilical vein endothelial cells (HUVEC) were exposed to control medium or H. pylori 60190. Binding of monoclonal antibodies against P‐selectin, E‐selectin, vascular adhesion molecule‐1 (VCAM‐1) and intercellular adhesion molecule‐1 (ICAM‐1) was determined using enzyme‐linked immunosorbent assay. Binding of polymorphonuclear leukocytes to HUVEC was determined on cells exposed as above. After 6 h exposure to H. pylori, there were 30%, 124%, 167% and 100% increases in P‐selectin, E‐selectin, VCAM‐1 and ICAM‐1 levels and a 400% increase in polymorphonuclear leukocyte adhesion in HUVEC exposed to H. pylori. Effects of incubation for other intervals between 0 and 18 h are also described. H. pylori exerts some of its effects on gastric mucosa via gastric vasculature. This study gives insight into the pattern of H. pylori‐associated endothelial adhesion molecule upregulation.
The PLP‐dependent biotin synthase from Escherichia coli: mechanistic studies
Authors: Ollagnier-de-Choudens Sandrine , Mulliez Etienne , Fontecave Marc
Published: December 2002

Biotin synthase (BioB), an iron–sulfur enzyme, catalyzes the last step of the biotin biosynthesis pathway. The reaction consists in the introduction of a sulfur atom into two non‐activated C–H bonds of dethiobiotin. Substrate radical activation is initiated by the reductive cleavage of S‐adenosylmethionine (AdoMet) into a 5′‐deoxyadenosyl radical. The recently described pyridoxal 5′‐phosphate‐bound enzyme was used to show that only one molecule of AdoMet, and not two, is required for the formation of one molecule of biotin. Furthermore 5′‐deoxyadenosine, a product of the reaction, strongly inhibited biotin formation, an observation that may explain why BioB is not able to make more than one turnover. However this enzyme inactivation is not irreversible.
Mouse Apg10 as an Apg12‐conjugating enzyme: analysis by the conjugation‐mediated yeast two‐hybrid method
Authors: Mizushima Noboru , Yoshimori Tamotsu , Ohsumi Yoshinori
Published: December 2002

Autophagosome formation is a central event in macroautophagy. The Apg12–Apg5 conjugate, which is essential in this process, is generated by a ubiquitin‐like protein conjugation system. In yeast, Apg12, following activation by the E1‐like Apg7, forms a thioester with Apg10 (E2‐like). Apg12 is finally conjugated to Apg5 via an isopeptide bond. The possible requirement of an E3‐like protein for the conjugation, however, has not yet been confirmed. The Apg12 system is conserved among eukaryotes, although a mammalian counterpart of Apg10 has not yet been identified. Here, we report the identification and characterization of the mouse Apg10 ortholog. A yeast two‐hybrid screen using the mouse Apg5 (mApg5) as bait identified a novel protein with 19% identity to yeast Apg10. We designated this protein mouse Apg10 (mApg10). We demonstrated by a modified yeast two‐hybrid assay that mApg10 mediates the conjugation of mApg12 and mApg5. The in vivo interaction of mApg12 with mApg10 in HeLa cells suggests that mApg10 is an Apg12‐conjugating enzyme, likely serving as an Apg5‐recognition molecule in the Apg12 system. This novel two‐hybrid method, which we have named ‘conjugation‐mediated yeast two‐hybrid’, proves to be a simple and useful technique with which to analyze protein–protein conjugation.
Evaluating psychological debriefing: Are we measuring the right outcomes?
Authors: Deahl Martin P. , Srinivasan Michael , Jones Norman , Neblett Carl , Jolly Allan
Published: December 2002

The efficacy of critical incident stress debriefing (CISD) and psychological debriefing (PD) following potentially traumatising events has recently been challenged after a number of recent randomised controlled trials (RCTs) failed to demonstrate that CISD or PD prevents or reduces the incidence of posttraumatic stress disorder (PTSD). These studies have used measures of PTSD as the principal outcome and have generally not measured comorbid psychopathology, behavioral or social dysfunction. In a recent RCT of group debriefing amongst British soldiers returning from peacekeeping operations in Bosnia, PD had a significant effect in reducing a worrying level of alcohol misuse in the sample. The findings of this study suggest that that it is premature to conclude that debriefing is ineffective and that a broader range of outcome measures should be employed in future trials of debriefing.
Western conceptualizations and eastern experience: A cross‐cultural study of traumatic stress reactions among Tibetan refugees in India
Authors: Terheggen Maaike A. , Stroebe Margaret S. , Kleber Rolf J.
Published: December 2002

This study investigated the nature and impact of traumatic experiences among Tibetan refugees in India. It explored the applicability of western conceptualizations of reactions to traumatic events among this cultural group. A randomly selected sample of refugee camp students was assessed on measures of psychological and physical complaints, and on impact as well as severity of traumatic experiences. Respondents had experienced multiple traumatic events. The majority reported ongoing health problems. More than half demonstrated symptoms of intrusion‐avoidance. Those with more traumatic experiences reported more symptoms of anxiety and depression (psychologically and, particularly, somatically manifested). Cultural differences in types of experienced traumatic events and manifestations of distress are discussed, as are implications for cross‐cultural trauma research using western conceptualizations and instruments.
Variability in the emission of carbon‐based trace gases from wildfire in the Alaskan boreal forest
Authors: French Nancy H. F. , Kasischke Eric S. , Williams David G.
Published: December 2002

A study was carried out to assess the variability in trace gas emission from several factors and to estimate the immediate impact of fire on carbon exchange. Using geospatial data, a model of emission was developed for three carbon‐based gases, CO2, CO, and CH4, released during fires from 1950 through 1999 in the boreal region of Alaska. The effect of two factors in the model were investigated: the fractions of carbon consumed and the ratio of flaming to smoldering combustion. We chose 4 years with which to investigate the range of outcomes. An average of 4.5 teragrams of carbon (TgC) has been released annually over the past 50 years. Severe fire years can produce emissions as high as 38 TgC. Wide variations in emissions of total carbon and carbon‐based gas were seen between years. Variations in the estimates of the fractions of biomass consumed during the burn influenced the amount of total carbon emitted; however, the annual area burned strongly determines total carbon released each year, regardless of fraction consumed. Assumptions regarding flaming versus smoldering fire influenced levels of emissions of CO and CH4. These estimates show that wildfire in Alaska's boreal region has contributed a substantial amount of carbon‐based gas to the atmosphere over the five decades of fire records.
An extension of the force‐restore method to estimating soil temperature at depth and evaluation for frozen soils under snow
Authors: Hirota Tomoyoshi , Pomeroy John W. , Granger Raoul J. , Maule Charles P.
Published: December 2002

The force‐restore method (FRM) was originally developed for estimating diurnal fluctuations in the ground surface temperature. Because of its relatively simple parameterization, it is commonly applied in meteorological and other models for this purpose. Its application to the calculation of deeper soil temperatures, to frozen soils, and to soils under snow covers has heretofore not been possible. This study demonstrates an extension of the FRM that permits accurate estimates of seasonal variation in mean daily deep soil temperature. The extended FRM is shown to provide a lower boundary condition for the heat conduction method, permitting a combination of the two approaches that avoids some limitations of each. The combined approach provides representations of the mean daily soil temperature, soil temperature at depth in frozen soils, and ground surface temperature under a snow cover. Diurnal variations can also be calculated. The extended method and combined approaches are tested using field site measurements collected in cold weather periods in Saskatchewan, Canada, and are found to provide a reasonable representation of measurements.
Interaction between electrostatic whistlers and electron holes in the auroral region
Authors: Berthomier M. , Muschietti L. , Bonnell J. W. , Roth I. , Carlson C. W.
Published: December 2002

Electron holes have been discovered in several key regions of the magnetosphere in the past few years. These small‐scale structures seem to play an important role in the global dynamics of the magnetosphere, being most often associated with parallel electron beams and strong ion heating, as shown by the Fast Auroral Snapshot (FAST) spacecraft in the auroral region. Electrostatic whistler waves (EWW) in the VLF frequency range are often associated with these electron holes, suggesting that the generation of whistler waves is related to the holes. We present a model of the interaction between EWW and electron holes. Our analysis is based on the mechanical description of the energy exchange between particles and waves; by the use of the Hamiltonian formalism, action‐angle variables, and canonical perturbation theory, we show that trapped electrons, owing to their periodic motion in the potential structure of the electron hole, enter into a resonance with the wave and can destabilize it at large parallel phase velocity relative to the electron thermal velocity. We derive the growth rate of EWW and compare our model with previous ones. Application to FAST observations shows that this linear instability is able to generate EWW with a normalized growth rate γ/ω varying from a few percents at low frequency (above the lower‐hybrid frequency) up to ∼10% at higher frequency (below the electron plasma frequency).
Jovian auroral signature of Io's corotational wake
Authors: Hill T. W. , Vasyliūnas V. M.
Published: December 2002

Auroral images of Jupiter reveal a distinctive signature of the downstream corotational wake of Io, as well as of Io itself. The wake signature can be understood as a product of the plasma current that accelerates Io's mass‐loaded flux tube up to (almost) corotation with Jupiter. The radially directed acceleration current in the magnetosphere is linked by Birkeland (magnetic field aligned) currents to Jupiter's ionosphere where closure is provided by a meridional Pedersen current. The Pedersen current is proportional to the velocity of the plasma relative to the corotating frame, while the acceleration current is proportional to (minus) the time rate of change of that velocity. Thus the requirement of current closure implies a simple exponential decay of the relative velocity, with a time constant that is proportional to the ratio of flux‐tube mass content to ionospheric Pedersen conductance. For expected values of these parameters, the time constant is ∼ 0.5 hours, implying a length scale ∼ 1 RJ (= Jupiter's radius) for the variation of velocity with downstream distance in the wake, or ∼12° of longitude. This length scale is remarkably close to that of the observed brightness of the wake auroral signature.
Surface M2 tidal currents along the North Carolina shelf observed with a high‐frequency radar
Authors: Cook Thomas M. , Shay Lynn K.
Published: December 2002

Surface tidal circulation over the continental shelf of Duck, North Carolina, was explored using surface current observations measured by a high‐frequency (HF) radar. The Ocean Surface Current Radar (OSCR) was deployed at the U.S. Army Corps of Engineers (USACE) Field Research Facility (FRF) in Duck, North Carolina, during 1–30 October 1994 and measured surface current at 20‐min intervals at 700 cells with a 1.2‐km resolution in a 25 × 44 km domain. Harmonic analysis of the surface current indicates fine‐scale (O(1 km)) variability in tidal amplitudes and phases within the study domain. The M2 tidal current amplitudes ranged from 2 to 10 cm s−1, with phases ranging from 100° to 120°, which compared well to previous results. Strong tidal current amplitudes and fine‐scale variability occurred near bathymetric features. Decreasing M2 surface tidal current amplitudes in the far field (∼40 km) of the radar domain are consistent with decreasing spectral quality of the HF radar returns. A 1‐D barotropic tidal model is utilized to examine the physics of the M2 tidal currents over the shelf. Observed M2 tidal currents compare well with those predicted by the model over the inner shelf to the midshelf. However, differences between the observed and the barotropic tidal currents of 5–8 cm s−1 are related to the decrease in spectral quality of the HF radar data in the far field.
Satellite‐based detection of global urban heat‐island temperature influence
Authors: Gallo Kevin P. , Adegoke Jimmy O. , Owen Timothy W. , Elvidge Christopher D.
Published: December 2002

This study utilizes a satellite‐based methodology to assess the urban heat‐island influence during warm season months for over 4400 stations included in the Global Historical Climatology Network of climate stations. The methodology includes local and regional satellite retrievals of an indicator of the presence green photosynthetically active vegetation at and around the stations. The difference in local and regional samples of the normalized difference vegetation index (NDVI) is used to estimate differences in mean air temperature. Stations classified as urban averaged 0.90°C (N. Hemisphere) and 0.92°C (S. Hemisphere) warmer than the surrounding environment on the basis of the NDVI‐derived temperature estimates. Additionally, stations classified as rural averaged 0.19°C (N. Hemisphere) and 0.16°C (S. Hemisphere) warmer than the surrounding environment. The NDVI‐derived temperature estimates were found to be in reasonable agreement with temperature differences observed between climate stations. The results suggest that satellite‐derived data sets can be used to estimate the urban heat‐island temperature influence on a global basis and that a more detailed analysis of rural stations and their surrounding environment may be necessary to assure that temperature trends derived from assumed rural environments are not influenced by changes in land use/land cover.
Mutational analysis of the structural organization of polyglutamine aggregates
Authors: Thakur Ashwani K. , Wetzel Ronald
Published: December 2002

The formation of amyloid-like aggregates by expanded polyglutamine (polyGln) sequences is suspected to play a critical role in the neuropathology of Huntington's disease and other expanded CAG-repeat diseases. To probe the folding of the polyGln sequence in the aggregate, we replaced Gln–Gln pairs at different sequence intervals with Pro–Gly pairs, elements that are compatible with β-turn formation and incompatible with β-extended chain. We find that PGQ
9
and PGQ
10
, peptides consisting of four Q
9
or Q
10
elements interspersed with PG elements, undergo spontaneous aggregation as efficiently as a Q
45
sequence, whereas the corresponding PGQ
7
and PGQ
8
peptides aggregate much less readily. Furthermore, a P
D
GQ
9
sequence containing
d
-prolines aggregates more efficiently than the peptide with
l
-prolines, consistent with β-turn formation in aggregate structure. Introduction of one additional Pro residue in the center of a Q
9
element within PGQ
9
completely blocks the peptide's ability to aggregate. This strongly suggests that the Q
9
elements are required to be in extended chain for efficient aggregation to occur. We determined the critical nucleus for aggregation nucleation of the PGQ
9
peptide to be one, a result identical to that for unbroken polyGln sequences. The PGQ
N
peptide aggregates are structurally quite similar to Q
45
aggregates, as judged by heterologous seeding aggregation kinetics, recognition by an anti-polyGln aggregate antibody, and electron microscopy. The results suggest that polyGln aggregate structure consists of alternating elements of extended chain and turn. In the future it should be possible to conduct detailed and interpretable mutational studies in the PGQ
9
background.
Grafted neural stem cells develop into functional pyramidal neurons and integrate into host cortical circuitry
Authors: Englund Ulrica , Björklund Anders , Wictorin Klas , Lindvall Olle , Kokaia Merab
Published: December 2002

In vitro
expanded neural stem/progenitor cells can undergo region-specific differentiation after transplantation to the developing or adult brain, and display morphologies and markers characteristic of mature neurons. Here we have used patch-clamp techniques to explore whether grafted stem cells also can develop physiological properties of mature neurons and become functionally integrated within host neural circuitry. The immortalized neural progenitor cell line, RN33B, prelabeled with GFP by using a lentiviral vector, was transplanted into the cortex or hippocampus of neonatal rats. We found that the grafted GFP-positive cells differentiated into cells with morphological features of cortical or hippocampal pyramidal neurons, and that many of them had established appropriate cortico-thalamic and contralateral hippocampal connections, respectively, as revealed by retrograde tracing. Whole-cell patch-clamp recordings from grafted cells with morphological characteristics of pyramidal neurons showed that they were able to generate action potentials, and received functional excitatory and inhibitory synaptic inputs from neighboring cells. These data provide evidence that grafted neural progenitors can differentiate into morphologically mature pyramidal projection neurons, establish appropriate long-distance axonal projections, exhibit normal electrophysiological properties, and become functionally integrated into host cortical circuitry.
Symmetrical dimethylarginine methylation is required for the localization of SMN in Cajal bodies and pre-mRNA splicing
Authors: Boisvert François-Michel , Côté Jocelyn , Boulanger Marie-Chloé , Cléroux Patrick , Bachand François , Autexier Chantal , Richard Stéphane
Published: December 2002

The nuclear structures that contain symmetrical dimethylated arginine (sDMA)–modified proteins and the role of this posttranslational modification is unknown. Here we report that the Cajal body is a major epitope in HeLa cells for an sDMA-specific antibody and that coilin is an sDMA-containing protein as analyzed by using the sDMA-specific antibody and matrix-assisted laser desorption ionization time of flight mass spectrometry. The methylation inhibitor 5′-deoxy-5′-methylthioadenosine reduces the levels of coilin methylation and causes the appearance of SMN-positive gems. In cells devoid of Cajal bodies, such as primary fibroblasts, sDMA-containing proteins concentrated in speckles. Cells from a patient with spinal muscular atrophy, containing low levels of the methyl-binding protein SMN, localized sDMA-containing proteins in the nucleoplasm as a discrete granular pattern. Splicing reactions are efficiently inhibited by using the sDMA-specific antibody or by using hypomethylated nuclear extracts, showing that active spliceosomes contain sDMA polypeptides and suggesting that arginine methylation is important for efficient pre-mRNA splicing. Our findings support a model in which arginine methylation is important for the localization of coilin and SMN in Cajal bodies.
Regulation of Rac1 activation by the low density lipoprotein receptor–related protein
Authors: Ma Zhong , Thomas Keena S. , Webb Donna J. , Moravec Radim , Salicioni Ana Maria , Mars Wendy M. , Gonias Steven L.
Published: December 2002

The low density lipoprotein receptor–related protein (LRP-1) binds and mediates the endocytosis of multiple ligands, transports the urokinase-type plasminogen activator receptor (uPAR) and other membrane proteins into endosomes, and binds intracellular adaptor proteins involved in cell signaling. In this paper, we show that in murine embryonic fibroblasts (MEFs) and L929 cells, LRP-1 functions as a major regulator of Rac1 activation, and that this activity depends on uPAR. LRP-1–deficient MEFs demonstrated increased Rac1 activation compared with LRP-1–expressing MEFs, and this property was reversed by expressing the VLDL receptor, a member of the same gene family as LRP-1, with overlapping ligand-binding specificity. Neutralizing the activity of LRP-1 with receptor-associated protein (RAP) increased Rac1 activation and cell migration in MEFs and L929 cells. The same parameters were unaffected by RAP in uPAR−/− MEFs, prepared from uPAR gene knockout embryos, and in uPAR-deficient LM-TK− cells. Untreated uPAR+/+ MEFs demonstrated substantially increased Rac1 activation compared with uPAR−/− MEFs. In addition to Rac1, LRP-1 suppressed activation of extracellular signal–regulated kinase (ERK) in MEFs; however, it was Rac1 (and not ERK) that was responsible for the effects of LRP-1 on MEF migration. Thus, LRP-1 regulates two signaling proteins in the same cell (Rac1 and ERK), both of which may impact on cell migration. In uPAR-negative cells, LRP-1 neutralization does not affect Rac1 activation, and other mechanisms by which LRP-1 may regulate cell migration are not unmasked.
Influence of Nitrogen Proximity from the Si/SiO2 Interface on Negative Bias Temperature Instability
Authors: Tan Shyue Seng , Chen Tu Pei , Ang Chew Hoe , Tan Yun Ling , Chan Lap
Published: December 2002

The influence of nitrogen proximity from the Si/SiO2 interface on negative-bias temperature instability (NBTI) effect has been studied. It is found that NBTI lifetime increases significantly by removing the nitrogen away from the Si/SiO2 interface. Additionally, thermal activation energy (E
a) which dictating the amount of NBTI degradation, is also found to be strongly dependent on the proximity of nitrogen from the Si/SiO2 interface. The experimental observations in this letter lend support to the mechanisms of nitrogen-enhanced NBTI in which lowering of hole trapping reaction energy induced by interfacial nitrogen.
Impurity Dependence of Vacancy Formation Energy in Silicon Determined by a New Quenching Method
Authors: Fukata Naoki , Suezawa Masashi , Kasuya Atsuo
Published: December 2002

Impurity dependence of the formation energy of vacancies (V) in Si was investigated. Doped impurities were carbon (C), nitrogen (N) and platinum (Pt). Specimens were heated in H2 gas at high temperatures for 1 h followed by quenching in water. The optical absorption spectra were measured at about 5 K. The formation energies of V in Si were found to depend on doped impurities and those in C-, N- and Pt-doped Si were determined to be about 3.2, 3.2 and 2.7 eV, respectively. The result for magnetic field-applied Czochralski (MCZ)-Si showed that the formation energy of V is not significantly different between floating zone (FZ)-Si and CZ-Si.
Fabrication of High-Output-Power AlGaN/GaN-Based UV-Light-Emitting Diode Using a Ga Droplet Layer
Authors: Lee Young-Bae , Wang Tao , Liu Yu-Huai , Ao Jin-Ping , Li Hong-Dong , Sato Hisao , Nishino Katsushi , Naoi Yoshiki , Sakai Shiro
Published: December 2002

We report a new method of increasing the output power of an ultraviolet light-emitting diode (UV-LED) based on an AlGaN/GaN single quantum well (SQW). In this method, a thin Ga droplet layer is intentionally grown before the growth of an AlGaN/GaN SQW active layer. The Ga droplet layer causes a spatial and compositional fluctuation on the SQW active layer, which induces exciton localization in the potential minima. The LEDs fabricated with the Ga droplet layer show an emission peak of 353 nm and a higher optical output power than those of the same structure but without the Ga droplet layer.
Low-Lattice-Strain Long-Wavelength GaAsSb/GaInAs Type-II Quantum Wells Grown on GaAs Substrates
Authors: Kudo Makoto , Ouchi Kiyoshi , Kasai Jun-ichi , Mishima Tomoyoshi
Published: December 2002

To reduce the lattice strain of 1.3 µm-range quantum well lasers on GaAs substrates, symmetric and type-II coupled double quantum wells with a GaAs/GaInAs/GaAsSb/GaInAs/GaAs layer structure were grown by molecular beam epitaxy. By using a `type II' band lineup, net lattice strain in the quantum well layers could be reduced to about 1.6% while maintaining a constant wavelength. Photoluminescence measurements on these quantum well layers revealed a linewidth of 50 meV at a 1.3-µm wavelength at room temperature and small dependence of peak wavelength on excitation power.
Effects of Sapphire (0001) Surface Modification by Gallium Pre-Exposure on the Growth of High-Quality Epitaxial ZnO Film
Authors: Du Xiaolong , Murakami Masashi , Iwaki Hiroyuki , Ishitani Yoshihiro , Yoshikawa Akihiko
Published: December 2002

ZnO films were grown on (0001) sapphire substrates using rf plasma-assisted molecular beam epitaxy. Distinct rotation domain structures were observed in ZnO films grown on Al-terminated or O-terminated sapphire surfaces. Therefore, the Ga pre-exposure process was adopted to modify the sapphire (0001) surface just before the buffer layer growth. It was revealed that the sapphire surface modification by Ga pre-exposure had significant effects on the elimination of the rotation domains in the ZnO epilayer. The full width at half maximum (FWHM) of the X-ray diffraction (XRD) rocking curve of the ZnO (002) reflection plane was as narrow as 67 arcsec. Consequently, a high-quality ZnO film with very good optical and electrical properties was obtained.
A Top-Gate Carbon-Nanotube Field-Effect Transistor with a Titanium-Dioxide Insulator
Authors: Nihey Fumiyuki , Hongo Hiroo , Yudasaka Masako , Iijima Sumio
Published: December 2002

We developed a carbon-nanotube field-effect transistor (CNTFET), in which a gate electrode and a gate insulator are located on top of a semiconducting single-wall carbon nanotube channel on a Si/SiO2 substrate. The gate insulator is made of titanium dioxide and is 2–3 nm thick. The transconductance of this device at a drain voltage of 100 mV is 320 nS, which, due to the high dielectric constant and nanoscale thickness of the gate insulator, is higher than that of any back-gate and top-gate CNTFETs reported so far.
Fabrication of High-Quality YBa2Cu3O7-δ Multilayer Structure Using Chemical Mechanical Planarization for Superconducting Quantum Interference Device Gradiometer
Authors: Takashima Hiroshi , Kasai Naoko , Shoji Akira
Published: December 2002

We have developed a technology to fabricate a YBa2Cu3O7-δ (YBCO) multilayer structure of high quality using chemical mechanical planarization (CMP) for the end of fabricating a high-performance superconducting quantum interference devices (SQUIDs) gradiometer. An annealing process in oxygen gas atmosphere was introduced to achieve epitaxial growth of upper films. A double-cross structure on five layers, YBCO/SrTiO3 (STO)/YBCO/STO/YBCO, was fabricated to show the performance. The insulation resistivity between layers at 77 K, T
c and J
c of each layer at 77 K were more than 1.5×107 Ω·cm, over 88 K and more than 106 A/cm2, respectively. The possibility of fabricating grain boundary Josephson junctions on the top layer with a bicrystal substrate is investigated using STO (100) bicrystal substrates with 24 and 30 degrees misorientation angles on a YBCO trilayer structure. The I
c
R
n products of both junctions were the same as that of a single YBCO layer.
Spectral Properties of Nonaggregative Antimony(V) Phthalocyanine and Its Film as a Novel Near-Infrared Absorber
Authors: Isago Hiroaki , Kagaya Yutaka , Nakajima Shin-ichiro
Published: December 2002

Preparation and spectral properties of antimony complex cation ligating tetra-tert-butylated phthalocyanine and its film having intense optical absorption in the near-infrared region without significant molecular aggregation even in condensed phase are reported.
Hydration of Short-chain Poly(oxyethylene)s in Carbon Tetrachloride Studied by Infrared Spectroscopy
Authors: Matsuura Hiroatsu , Matin Md Ruhul , Okura Koji
Published: December 2002

The hydration of short-chain poly(oxyethylene)s in carbon tetrachloride has been studied by infrared spectroscopy. Monodentate and bidentate hydrogen bonds of water are involved in the hydration. The latter hydrogen bond is formed between ether oxygen atoms separated by two or more oxyethylene units.
Observation of the Radical Anion Intermediates in the Photolyses of 4-Cyano- and 4-Nitro-azobenzene in MTHF at 77 K
Authors: Zhao Changli , Horiuchi Hiroaki , Hoshi Toshihiko , Hasegawa Miki , Kobayashi Michio , Hiratsuka Hiroshi
Published: December 2002

Steady-state photolyses of 4-methoxy-4′-cyanoazobenzene and 4-methoxy-4′-nitroazobenzene have been studied in rigid matrices. The radical anions of these azobenzenes have been observed for the first time by the 266 nm and 355 nm light irradiation in 2-methyltetrahydrofuran at 77 K.
Numerical solution of a non‐local boundary value problem with Neumann's boundary conditions
Authors: Dehghan Mehdi
Published: December 2002

Several second‐order finite difference schemes are discussed for solving a non‐local boundary value problem for two‐dimensional diffusion equation with Neumann's boundary conditions. While sharing some common features with the one‐dimensional models, the solution of two‐dimensional equations are substantially more difficult, thus some considerations are taken to be able to extend some ideas of one‐dimensional case. Using a suitable transformation the solution of this problem is equivalent to the solution of two other problems. The former which is a one‐dimensional non‐local boundary value problem gives the value of μthrough using the unconditionally stable standard implicit (3,1) backward time centred space (denoted BTCS) scheme. Using this result the second problem will be changed to a classical two‐dimensional diffusion equation with Neumann's boundary conditions which will be solved numerically by using two unconditionally stable fully implicit finite difference schemes, or using two conditionally stable fully explicit finite difference techniques. For each method investigated the modified equivalent partial differential equation is employed which permits the order of accuracy of the numerical techniques to be determined. The results of a numerical example for all finite difference schemes discussed in this paper are given and computation times are presented. Copyright © 2003 John Wiley & Sons, Ltd.
Improved application of the HLLE Riemann solver for the shallow water equations with source terms
Authors: I. Delis A.
Published: December 2002

The present work addresses the numerical prediction of shallow water flows with the application of the HLLE approximate Riemann solver. This Riemann solver has several desirable properties, such as, ease of implementation, satisfaction of entropy conditions, high shock resolution and positivity preservation. A corrected upwind discretization of the source terms is applied, in conjunction with the HLLE solver, following some resent developments presented in the literature. Numerical results are obtained for a series of one‐dimensional test cases by means of the proposed model and compared with analytical solutions or solutions presented in the literature. Strong numerical evidence shows that the proposed model implementation is accurate, robust, conservative and highly stable in capturing strong gradients and discontinuities in transcritical flows, as well as calculating dry areas (vacuum), and is a reliable model for one‐dimensional (steady and unsteady) practical applications in hydraulics engineering. Copyright © 2003 John Wiley & Sons, Ltd.
Numerical solution of steady free‐surface flows by the adjoint optimal shape design method
Authors: van Brummelen E. H. , Segal A.
Published: December 2002

Numerical solution of flows that are partially bounded by a freely moving boundary is of great importance in practical applications such as ship hydrodynamics. Free‐boundary problems can be reformulated into optimal shape design problems, which can in principle be solved efficiently by the adjoint method. In this work we investigate the suitability of the adjoint shape optimization method for solving steady free‐surface flows. The asymptotic convergence behaviour of the method is determined for free‐surface flows in 2D and 3D. It is shown that the convergence behaviour depends sensitively on the occurrence of critical modes. The convergence behaviour is moreover shown to be mesh‐width independent, provided that proper preconditioning is applied. Numerical results are presented for 2D flow over an obstacle in a channel. The observed convergence behaviour is indeed mesh‐width independent and conform the derived asymptotic estimates. Copyright © 2003 John Wiley & Sons, Ltd.
Anisotropy and depth‐related heterogeneity of hydraulic conductivity in a bog peat. II: modelling the effects on groundwater flow
Authors: Beckwith Clive W. , Baird Andrew J. , Heathwaite A. Louise
Published: December 2002

Anisotropy and heterogeneity of hydraulic conductivity (K) are seldom considered in models of mire hydrology. We investigated the effect of anisotropy and heterogeneity on groundwater flow in bog peat using a steady‐state groundwater model. In five model simulations, four sets of K data were used. The first set comprised measured K values from an anisotropic and heterogeneous bog peat. These data were aggregated to produce the following simplified data sets: an isotropic and heterogeneous distribution of K; an isotropic and homogeneous distribution; and an anisotropic and homogeneous distribution. We demonstrate that, where anisotropy and heterogeneity exist, groundwater flow in bog peat is complex. Fine‐scale variations in K have the potential to influence patterns and rates of groundwater flow. However, for our data at least, it is heterogeneity and not anisotropy that has the greater influence on producing complex patterns of groundwater flow. We also demonstrate that patterns and rates of groundwater flow are simplified and reduced when measured K values are aggregated to create a more uniform distribution of K. For example, when measured K values are aggregated to produce isotropy and homogeneity, the rate of modelled seepage is reduced by 28%. We also show that when measured K values are used, the presence of a drainage ditch can increase seepage through a modelled cross‐section. Our work has implications for the accurate interpretation of hydraulic head data obtained from peat soils, and also the understanding of the effect of drainage ditches on patterns and rates of groundwater flow. Copyright © 2002 John Wiley & Sons, Ltd.