bluuebunny/crossref_metadata_2025 huggingface dataset:
The 40Ar/39Ar ages of the sill complex of the Karoo large igneous province: Implications for the Pliensbachian‐Toarcian climate change
Authors: Jourdan F. , Féraud G. , Bertrand H. , Watkeys M. K. , Renne P. R.
Published: June 2008

Reliable geochronological results gathered so far (n = 76) have considerably constrained the timing of the emplacement of the Karoo large igneous province (LIP). Yet strikingly missing from this dating effort is the huge southern sill complex cropping out in the >0.6 × 106 km2 Main Karoo sedimentary basin. We present 16 new 40Ar/39Ar analyses carried out on fresh plagioclase and biotite separates from 15 sill samples collected along a N–S trend in the eastern part of the basin. The results show a large range of plateau and miniplateau ages (176.2 ± 1.3 to 183.8 ± 2.4 Ma), with most dates suggesting a ∼3 Ma (181–184 Ma) duration for the main sill events. The available age database allows correlation of the Karoo LIP emplacement with the Pliensbachian‐Toarcian second‐order biotic extinction, the global warming, and the Toarcian anoxic event (provided that adequate calibration between the 40K and 238U decay constant is made). The mass extinction and the isotopic excursions recorded at the base of the Toarcian appear to be synchronous with both the increase of magma emission of the Karoo LIP and the emplacement of the sills. The CO2 and SO2 derived from both volcanic emissions as well as carbon‐rich sedimentary layers intruded by sills might be the main culprits of the Pliensbachian‐Toarcian climate perturbations. We propose that the relatively low eruption rate of the Karoo LIP is one of the main reasons explaining why its impact on the biosphere is relatively low contrary to, e.g., the CAMP (Triassic‐Jurassic) and Siberia (Permo‐Triassic) LIPs.
Organic iron (III) complexing ligands during an iron enrichment experiment in the western subarctic North Pacific
Authors: Kondo Yoshiko , Takeda Shigenobu , Nishioka Jun , Obata Hajime , Furuya Ken , Johnson William Keith , Wong C. S.
Published: June 2008

Complexation of iron (III) with natural organic ligands was investigated during a mesoscale iron enrichment experiment in the western subarctic North Pacific (SEEDS II). After the iron infusions, ligand concentrations increased rapidly with subsequent decreases. While the increases of ligands might have been partly influenced by amorphous iron colloids formation (12–29%), most in‐situ increases were attributable to the <200 kDa fraction. Dilution of the fertilized patch may have contributed to the rapid decreases of the ligands. During the bloom decline, ligand concentration increased again, and the high concentrations persisted for 10 days. The conditional stability constant was not different between inside and outside of the fertilized patch. These results suggest that the chemical speciation of the released iron was strongly affected by formation of the ligands; the production of ligands observed during the bloom decline will strongly impact the iron cycle and bioavailability in the surface water.
Impact of the stratosphere on tropospheric climate change
Authors: Sigmond Michael , Scinocca John F. , Kushner Paul J.
Published: June 2008

The atmospheric circulation response to CO2 doubling in various versions of an atmospheric general circulation model (AGCM) without a well‐resolved stratosphere (“low‐top” model), is compared to the response in a version of the same AGCM with a well‐resolved stratosphere (“high‐top” model). The doubled CO2 response of the “best‐tuned” (i.e. operational) low‐top model version is significantly different from that in the best‐tuned high‐top model version. Additional experiments show that this difference is not caused by the model lid height, but instead can be mainly attributed to differences in the settings of parameterized orographic gravity‐wave drag which control the strength of the zonal wind in the mid‐ to high‐latitude lower stratosphere and the mean sea‐level pressure distribution. These findings suggest a link between the strength of the winds in the mid‐ to high‐latitude lower stratosphere and tropospheric annular mode responses, and have implications for how to proceed with high‐top low‐top model intercomparisons.
First identification of mirror mode waves in Venus' magnetosheath?
Authors: Volwerk M. , Zhang T. L. , Delva M. , Vörös Z. , Baumjohann W. , Glassmeier K.‐H.
Published: June 2008

In this paper first time observations of mirror mode like structures in Venus' magnetosheath are presented. Using magnetometer data from the Venus Express spacecraft it is shown that in two regions in the Venusian magnetosheath strong compressional waves exist, which propagate nearly perpendicular to the ambient magnetic field. They are most likely mirror‐mode waves. The waves have periods between 5 and 15 sec, depending on the location in the magnetosheath. These waves show up just behind the quasi‐perpendicular bow shock, and near the magnetopause during compression of the magnetosheath due to increased solar wind pressure. The characteristics of the waves are similar to mirror mode waves found in the Earth's magnetosheath, however, they are down‐scaled in duration and frequency by a factor of 10, comparable with the difference in size of Venus' and Earth's magnetosheath.
Freeze probability of Florida in a regional climate model and climate indices
Authors: Goto‐Maeda Yoshie , Shin D. W. , O'Brien James J.
Published: June 2008

Severe freezes impacting agriculture in Florida were associated with some major climate patterns, such as El Niño and Southern Oscillation (ENSO) and North Atlantic Oscillation (NAO). In this study, we examined whether seasonal ensemble integrations of a regional model could capture the tendencies of freezes in the Florida peninsula during each ENSO or NAO phase. Mean excess values of minimum temperatures from thresholds on the basis of the Generalized Pareto Distribution (GPD), which represents the extreme data in a dataset, were used to analyze the freezes in the regional model. According to previous studies, El Niño winters are assumed to obtain fewer freezes than the other phases. Although ensembles of only 19 winters were simulated, the ensembles found similar variability patterns in minimum temperatures in each climate phase to the findings in the previous studies based on observed data.
Optimising ice flow law parameters using borehole deformation measurements and numerical modelling
Authors: Chandler David , Hubbard Bryn , Hubbard Alun , Murray Tavi , Rippin David
Published: June 2008

Internal ice strain rates have been measured along two boreholes drilled through Glacier de Tsanfleuron, Switzerland. Differences between these measurements and the output from a 3D numerical model of glacier motion have been minimized by a scheme that optimizes three rheological parameters in the constitutive equation for ice creep: the stress exponent n, the rate factor A, and a Lower Zone (basal ice) enhancement factor ELZ. Results suggest that a linear rheology dominated by diffusion creep (n = 1) is more appropriate for modelling ice flow in this relatively thin (generally <80 m thick) glacier than the conventional n = 3, and that ELZ is ∼2. For n = 1, the predicted ice crystal size and value of ELZ are both consistent with measurements made on ice cores recovered from the glacier, providing independent support for the optimization technique and the linear creep model.
High‐silica deposits of an aqueous origin in western Hellas Basin, Mars
Authors: Bandfield Joshua L.
Published: June 2008

Data from the Thermal Emission Spectrometer and the Thermal Emission Imaging System have been used to identify isolated high silica surfaces in western Hellas Basin. Deconvolution results indicate that the surfaces are composed of nearly 80% high silica phases (amorphous silica, phyllosilicates, or zeolites). The deposits may be derived from alcoves in the terrain immediately to the north. The high silica deposits are an additional indicator of a variety of past aqueous processes on Mars.
Effects of doubled CO2 on tropical sea surface temperatures (SSTs) for onset of deep convection and maximum SST: Simulations based inferences
Authors: Sud Y. C. , Walker G. K. , Zhou Y. P. , Schmidt Gavin A. , Lau K.‐M. , Cahalan Robert F.
Published: June 2008

A primary concern of CO2‐induced warming is the associated rise of tropical (10S‐10N) sea‐surface temperatures (SSTs). GISS Model‐E was used to produce two sets of simulations‐one with the present‐day and one with doubled CO2 in the atmosphere. The intrinsic usefulness of model guidance in the tropics was confirmed when the model simulated realistic convective coupling between SSTs and atmospheric soundings and that the simulated‐data correlations between SSTs and 300 hPa moist‐static energies were similar to the observed. Model predicted SST limits for (i) the onset of deep convection and (ii) maximum SST, increased in the doubled CO2 environment. Changes in cloud heights, cloud frequencies, and cloud mass‐fractions showed that convective‐cloud changes increased the SSTs, while warmer mixed‐layer of the doubled CO2 contained ∼10% more water vapor; clearly that would be conducive to more intense storms and hurricanes.
Mantle transition zone thickness beneath Ross Island, the Transantarctic Mountains, and East Antarctica
Authors: Reusch Angela Marie , Nyblade Andrew A. , Benoit Margaret H. , Wiens Douglas A. , Anandakrishnan Sridhar , Voigt Donald , Shore Patrick J.
Published: June 2008

The thickness of the mantle transition zone beneath Ross Island, and parts of the Transantarctic Mountains and East Antarctic Craton has been mapped using data from the 2000–2003 Transantarctic Mountain Seismic Experiment to determine if, as indicated by some tomographic images, an upper mantle thermal anomaly centered beneath Ross Island is a deep‐seated feature extending into the mantle transition zone. Some 2700 receiver functions have been stacked using a 3D velocity model, revealing Ps conversions from the mantle transition zone discontinuities at depths of 410 and 660 km. Results yield an average nearly uniform transition zone thickness (266 ± 10 km) that is slightly larger than the global average, implying that the upper mantle thermal anomaly does not likely extend into the transition zone. This finding favors explanations for the upper mantle thermal anomaly invoking a plume head or small‐scale convection.
Estimating the top altitude of optically thick ice clouds from thermal infrared satellite observations using CALIPSO data
Authors: Minnis Patrick , Yost Chris R. , Sun‐Mack Sunny , Chen Yan
Published: June 2008

The difference between cloud‐top altitude Ztop and infrared effective radiating height Zeff for optically thick ice clouds is examined using April 2007 data taken by the Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) and the Moderate‐Resolution Imaging Spectroradiometer (MODIS). For even days, the difference ΔZ between CALIPSO Ztop and MODIS Zeff is 1.58 ± 1.26 km. The linear fit between Ztop and Zeff, applied to odd‐day data, yields a difference of 0.03 ± 1.21 km and can be used to estimate Ztop from any infrared‐based Zeff for thick ice clouds. Random errors appear to be due primarily to variations in cloud ice‐water content (IWC). Radiative transfer calculations show that ΔZ corresponds to an optical depth of ∼1, which based on observed ice‐particle sizes yields an average cloud‐top IWC of ∼0.015 gm−3, a value consistent with in situ measurements. The analysis indicates potential for deriving cloud‐top IWC using dual‐satellite data.
Observational evidence of enhanced middle/upper tropospheric ozone via convective processes over the equatorial tropical Atlantic during the summer of 2006
Authors: Jenkins Gregory S. , Camara Moctar , Ndiaye Seydi A.
Published: June 2008

Biomass burning in Central Africa or lightning in West Africa may serve as mechanisms to enhance tropospheric ozone (O3) during Northern Hemisphere summer (JJA) in Equatorial latitudes. During the summer of 2006, ozonesondes launched from the Ronald H. Brown research cruise in equatorial latitudes (5°N–5°S) along 23°W showed elevated concentrations of O3 in the middle and upper troposphere. The total column ozone (TCO) increased by a factor of 1.2 between Legs 1 (June 11–15) and Legs 2 (June 26–29) from 36.5 to 43.5 DU. Nearly 80% of the TCO ozone was found above 700 hPa and only 10% of the TCO was found between the surface and 850 hPa. Consequently this implies that two mechanisms are responsible for elevated O3: (1) lightning associated with organized convective systems in West Africa which produced O3 via NOX, (2) a northward transport of biomass burning constituents from central Africa over land into regions of deep convection followed by the vertical transport of O3 and O3 precursors to the middle/upper troposphere. While O3 and O3 precursors are transported directly from Central Africa to the tropical Eastern Atlantic near the surface, the stability of the atmosphere inhibits vertical transport to the free troposphere.
Oceanic mesoscale eddies as revealed by Lagrangian coherent structures
Authors: Beron‐Vera F. J. , Olascoaga M. J. , Goni G. J.
Published: June 2008

We demonstrate the feasibility of using dynamical systems tools to unambiguously identify mesoscale oceanic eddies from surface ocean currents derived using climatological hydrography and altimetry. Specifically, our analysis is based on extracting Lagrangian coherent structures (LCSs) from finite‐time Lyapunov exponent (FTLE) fields. The FTLE fields reveal with unprecedented detail an intricate tangle of LCSs, which are hidden in ocean surface topography maps but sometimes are apparent in ocean color images. These LCSs delineate fluid domains with very different advective properties, and thus their detection provides an objective (i.e., frame‐independent) means of identifying eddy boundaries. The importance of considering LCSs in quantifying transport by eddies is highlighted. Such a quantification does not rely on the common assumption—which is shown to be generally not valid—that transport is largely effected by the trapping and subsequent translation of water slugs inside eddies defined as the regions enclosed by sea height (streamfunction) contours within which rotation dominates over strain. LCSs are calculated for the whole globe and compared with satellite‐tracked drogue drifter trajectories within a selected region of the South Atlantic.
Saharan dust, lightning and tropical cyclones in the eastern tropical Atlantic during NAMMA‐06
Authors: Jenkins Gregory S. , Pratt Aaron
Published: June 2008

During the summer of 2006, the downstream component of African Monsoon Multidisciplinary Analyses Campaign (NASA‐AMMA (NAMMA)) examined African Easterly Waves (AEWs) emerging from the coast of Africa. Six of these disturbances went on to become named systems in the Tropical Atlantic. Two of the six systems (Tropical storm Debby and Hurricane Helene) developed in the extreme eastern Atlantic and were associated with dust outbreaks, elevated ice contents and frequent lightning. Here we show that in the early tropical cyclo‐genesis stages of these systems there were thousands of cloud‐to‐ground (CG) lightning flashes as measured by a ground‐lightning network. TRMM overpasses show high precipitation ice content above the freezing level and high latent heat release. Super‐cooled water can be inferred in the lower parts of cloud systems in concert with observed high ice concentrations at high altitudes creating charge separation based on the large numbers of CG flashes.
Meridional SST gradient in the western North Pacific warm pool associated with typhoon generation
Authors: Sato N. , Shirooka R. , Yoshizaki M. , Takayabu Y. N.
Published: June 2008

We examined the sea surface temperature (SST) distribution in the western North Pacific warm pool when a typhoon is generated in northern summer. Analyzing satellite observation data revealed higher (lower) SST north (south) of the typhoon. As a result, the meridional SST gradient became especially steep, and the SST was not homogeneously high, when a typhoon is generated. In‐situ observation data in the oceanic surface layer suggested that the low SST was caused by vertical mixing related to the strong southwesterly monsoon. In contrast, the hot spots north of the typhoon were associated with weak sea surface wind and vertical mixing. According to satellite observation, the maxima of surface heat flux and water vapor shifted northward corresponding to the high SST. They may produce an asymmetry of the thermodynamic structure of a typhoon.
Teleseismic traveltimes, topography and the lithospheric structure across central Mongolia
Authors: Petit Carole , Tiberi Christel , Deschamps Anne , Déverchère Jacques
Published: June 2008

Teleseismic travel times recorded along a 1000 km‐long, ∼N‐S transect across central Mongolia are used together with topography and gravity data to constrain the deep lithospheric structure of this region. Time residuals appear positively correlated with the topography, suggesting that P‐wave velocity changes correspond to density variations which in turn cause an isostatic uplift of the topography. Using a simple local isostasy model and a Monte‐Carlo inversion for the crust and asthenosphere velocities and density/velocity conversion factors, we determine best‐fitting Moho and lithosphere‐asthenosphere boundary (LAB) geometries which satisfyingly reproduce the observed topography and gravity data. The model is validated using previously published 1D S‐wave velocity models obtained from receiver function analyses. Our results indicate that most of the long‐wavelength topography is supported by the asthenosphere buoyancy. The Hangai dome, in the southern half of the transect, appears mainly supported by a rather shallow (60–70 km) asthenospheric uplift, whereas the Siberian platform at the extreme north of the profile is underlain by a very thick (∼200 km) lithosphere. Misfits to the observed Bouguer gravity anomaly occur near major faults, probably because of lithospheric flexure.
Regime shift of snow days in Switzerland
Authors: Marty Christoph
Published: June 2008

The number of days with a snow depth above a certain threshold is the key factor for winter tourism in an Alpine country like Switzerland. An investigation of 34 long‐term stations between 200 and 1800 m asl (above sea level) going back for at least the last 60 years (1948–2007) shows an unprecedented series of low snow winters in the last 20 years. The signal is uniform despite high regional differences. A shift detection analysis revealed a significant step‐like decrease in snow days at the end of the 1980's with no clear trend since then. This abrupt change resulted in a loss of 20% to 60% of the total snow days. The stepwise increase of the mean winter temperature at the end of the 1980's and its close correlation with the snow day anomalies corroborate the sensitivity of the mid‐latitude winter to the climate change induced temperature increase.
High‐stress strike‐slip faults in the Apennines: An example from the 2002 San Giuliano earthquakes (southern Italy)
Authors: Malagnini Luca , Mayeda Kevin
Published: June 2008

Under the hypotheses that the high‐frequency part of the seismic spectrum is controlled by source duration and by peak slip velocity, we applied a recent coda envelope methodology to obtain stable relative source estimates between selected mainshocks and their aftershocks. We computed stable mainshock/aftershock S‐wave spectral ratios and used a simple source model in order to quantify the scaling of the seismic sources of the San Giuliano sequence (Southern Italy). From the analysis of the ratios obtained between the main shock of 10/31/2002, and 11 aftershocks, and of those computed between the other main event of the sequence, of 11/01/2002, and 10 aftershocks, we observe that the scaling relationships: M0 ∝ fc−(3+ɛ) holds, with ɛ = 0.89 ± 0.05. Despite the strong discrepancy between the moment magnitude and the high‐frequency ground motion excited by the main shocks (ML was much lower than Mw), that would indicate low‐stress drop sources, we compute anomalously high stress parameters for both events.By comparison, the same analysis was carried out on seismic data of the Hector Mine seismic sequence (the main event of October 16, 1999, MW = 7.0, and six of its aftershocks). We found: M0 ∝ fc−(3+ɛ), with ɛ ≈ 0.8 ± 0.4.
Geometric modulation: A more effective method of steerable ELF/VLF wave generation with continuous HF heating of the lower ionosphere
Authors: Cohen M. B. , Inan U. S. , Golkowski M. A.
Published: June 2008

ELF/VLF radio waves (300 Hz–30 kHz) are difficult to generate with practical antennae, because of their extraordinarily long (10–1000 km) wavelengths, and the lossy nature of the Earth's surface at these frequencies. ELF/VLF waves have been successfully generated via amplitude modulated (AM) HF (2–10 MHz) heating of the lower ionosphere. Through the temperature‐dependent conductivity of the lower ionospheric plasma, a patch of the ionospheric current becomes a large radiating ‘antenna’. We implement a new method of ELF/VLF wave generation, herein named ‘geometric modulation’, involving scanning the HF heating beam in a geometric pattern without modulating its power. Utilizing results from the upgraded 3.6 MW radiated HAARP HF antenna array, we show that geometric modulation can enhance ELF/VLF wave generation by up to ∼11 dB over the conventional AM method. Geometric modulation also allows directional launching of the signal into the Earth‐ionosphere waveguide, forming an unprecedented steerable large‐element ELF/VLF ionospheric phased array.
Rainfall characteristics define the value of streamflow observations for distributed watershed model identification
Authors: van Werkhoven Kathryn , Wagener Thorsten , Reed Patrick , Tang Yong
Published: June 2008

We present evidence that the characteristics of rainfall events strongly control the value of streamflow observations for the identification of distributed watershed models. A series of synthetic rainfall events with different spatio‐temporal extents and dynamics are used to investigate spatially‐distributed global parameter sensitivities for a typical watershed model. The model's parametric sensitivities vary greatly with rainfall distribution characteristics, location of the model cell in relation to the watershed's gauged outlet, and, to a lesser degree, the initial model states. This study demonstrates that the information content of streamflow is a dynamic property and that distributed model identification methodologies should consider the impact of spatio‐temporal rainfall dynamics.
Mechanism of water level changes during earthquakes: Near field versus intermediate field
Authors: Wang Chi‐yuen , Chia Yeeping
Published: June 2008

Using a new empirical relation among earthquake magnitude, seismic energy density and hypocentral distance, we show that the documented water level changes during earthquakes occur across seven orders of magnitude of seismic energy density. Combining this relation with a global data set for water level changes, new data from Taiwan, and laboratory data for saturated sediments under cyclic loading, we show that at least two mechanisms may be important for inducing water level changes. Undrained volumetric change may be the dominant mechanism to cause the abrupt decrease or increase of water level documented in the near field, while an earthquake‐enhanced permeability may account for the more gradual and sustained water level changes documented in the intermediate field.
Aerosol and cloud effects on solar brightening and the recent rapid warming
Authors: Ruckstuhl Christian , Philipona Rolf , Behrens Klaus , Collaud Coen Martine , Dürr Bruno , Heimo Alain , Mätzler Christian , Nyeki Stephan , Ohmura Atsumu , Vuilleumier Laurent , Weller Michael , Wehrli Christoph , Zelenka Antoine
Published: June 2008

The rapid temperature increase of 1°C over mainland Europe since 1980 is considerably larger than the temperature rise expected from anthropogenic greenhouse gas increases. Here we present aerosol optical depth measurements from six specific locations and surface irradiance measurements from a large number of radiation sites in Northern Germany and Switzerland. The measurements show a decline in aerosol concentration of up to 60%, which have led to a statistically significant increase of solar irradiance under cloud‐free skies since the 1980s. The measurements confirm solar brightening and show that the direct aerosol effect had an approximately five times larger impact on climate forcing than the indirect aerosol and other cloud effects. The overall aerosol and cloud induced surface climate forcing is ∼+1 W m−2 dec−1 and has most probably strongly contributed to the recent rapid warming in Europe.
Wind‐driven particle mobility on Mars: Insights from Mars Exploration Rover observations at “El Dorado” and surroundings at Gusev Crater
Authors: Sullivan R. , Arvidson R. , Bell J. F. , Gellert R. , Golombek M. , Greeley R. , Herkenhoff K. , Johnson J. , Thompson S. , Whelley P. , Wray J.
Published: June 2008

The ripple field known as “El Dorado” was a unique stop on Spirit's traverse where dust‐raising, active mafic sand ripples and larger inactive coarse‐grained ripples interact, illuminating several long‐standing issues of Martian dust mobility, sand mobility, and the origin of transverse aeolian ridges. Strong regional wind events endured by Spirit caused perceptible migration of ripple crests in deposits SSE of El Dorado, erasure of tracks in sandy areas, and changes to dust mantling the site. Localized thermal vortices swept across El Dorado, leaving paths of reduced dust but without perceptibly damaging nearly cohesionless sandy ripple crests. From orbit, winds responsible for frequently raising clay‐sized dust into the atmosphere do not seem to significantly affect dunes composed of (more easily entrained) sand‐sized particles, a long‐standing paradox. This disparity between dust mobilization and sand mobilization on Mars is due largely to two factors: (1) dust occurs on the surface as fragile, low‐density, sand‐sized aggregates that are easily entrained and disrupted, compared with clay‐sized air fall particles; and (2) induration of regolith is pervasive. Light‐toned bed forms investigated at Gusev are coarse‐grained ripples, an interpretation we propose for many of the smallest linear, light‐toned bed forms of uncertain origin seen in high‐resolution orbital images across Mars. On Earth, wind can organize bimodal or poorly sorted loose sediment into coarse‐grained ripples. Coarse‐grained ripples could be relatively common on Mars because development of durable, well‐sorted sediments analogous to terrestrial aeolian quartz sand deposits is restricted by the lack of free quartz and limited hydraulic sediment processing.
Millennial‐scale propagation of Atlantic deep waters to the glacial Southern Ocean
Authors: Kissel Catherine , Laj Carlo , Piotrowski Alexander M. , Goldstein Steven L. , Hemming Sidney R.
Published: June 2008

The compilation of changes in the magnetic properties at various sites distributed along the path of the deepwater mass in North Atlantic shows large‐amplitude short‐term fluctuations reflecting changes in the strength of the North Atlantic Deep Water (NADW). These changes, which suggest a two‐mode deep glacial circulation dynamic, are perfectly concurrent with air temperature changes over Greenland. They also share a similar pattern with those reported in the Nd isotope ratios from the deep Cape Basin during the same time period. Greenland interstadials were accompanied by increased flow speed of NADW and relatively more NADW reaching the Southern Ocean, while during Greenland stadials and Heinrich events, both the North Atlantic flow speed of NADW and its presence in the South Atlantic were reduced. It is demonstrated that both proxies are tracing the same water mass, and their reliability for monitoring changes in the deepwater circulation is therefore clearly established. After using the climatically independent geomagnetic assisted stratigraphy to put the Northern and Southern Hemisphere records on the same age scale, the South Atlantic record appears to lag changes in North Atlantic flow speeds by approximately 860 ± 220 years during the most prominent and best defined cycles (interstadials 12 and 8). Although future work is needed, this significant offset provides a first observation and tentative quantification of the time needed for glacial northern component water to mix downward and to flow from the North to the South Atlantic.
Epigenetic biomarkers in psychiatric disorders
Authors: Peedicayil J
Published: June 2008

The discovery of biomarkers in psychiatric disorders may help in the diagnosis, prevention and treatment of patients with these disorders. Here, I discuss the potential role of epigenetic biomarkers, that is, epigenetically altered genes and/or expression patterns of proteins or metabolites, in psychiatric disorders. Before epigenetic biomarkers can be clinically applied in these disorders, several issues need to be addressed. These include establishing a connection between biomarkers and the disease process; determining the predictive quality of the biomarkers; determining the effects of disease heterogeneity on the biomarkers; and identifying sample sources for the biomarkers that are easily accessible for testing.

British Journal of Pharmacology (2008) 155, 795–796; doi:10.1038/bjp.2008.254; published online 23 June 2008
Raloxifene protects endothelial cell function against oxidative stress
Authors: Wong C M , Yung L M , Leung F P , Tsang S‐Y , Au C L , Chen Z‐Y , Yao X , Cheng C H K , Lau C‐W , Gollasch M , Huang Y
Published: June 2008

Background and purpose:

Maintaining a delicate balance between the generation of nitric oxide (NO) and removal of reactive oxygen species (ROS) within the vascular wall is crucial to the physiological regulation of vascular tone. Increased production of ROS reduces the effect and/or bioavailability of NO, leading to an impaired endothelial function. This study tested the hypothesis that raloxifene, a selective oestrogen receptor modulator, can prevent endothelial dysfunction under oxidative stress.

Experimental approach:

Changes in isometric tension were measured in rat aortic rings. The content of cyclic GMP in aortic tissue was determined by radioimmunoassay. Phosphorylation of endothelial NOS (eNOS) and Akt was assayed by Western blot analysis.

Key results:

In rings with endothelium, ACh‐induced relaxations were attenuated by a ROS‐generating reaction (hypoxanthine plus xanthine oxidase, HXXO). The impaired relaxations were ameliorated by acute treatment with raloxifene. HXXO suppressed the ACh‐stimulated increase in cyclic GMP levels; this effect was antagonized by raloxifene. The improved endothelial function by raloxifene was abolished by ICI 182,780, and by wortmannin or LY294002. Raloxifene also protected endothelial cell function against H2O2. Raloxifene increased the phosphorylation of eNOS at Ser‐1177 and Akt at Ser‐473; this effect was blocked by ICI 182,780. Finally, raloxifene was not directly involved in scavenging ROS, and neither inhibited the activity of xanthine oxidase nor stimulated that of superoxide dismutase.

Conclusion and implications:

Raloxifene is effective against oxidative stress‐induced endothelial dysfunctionin vitrothrough an ICI 182,780‐sensitive mechanism that involves the increased phosphorylation and activity of Akt and eNOS in rat aortae.

British Journal of Pharmacology(2008)155, 326–334; doi:10.1038/bjp.2008.262; published online 23 June 2008
The effect of changes in core body temperature on the QT interval in beagle dogs: a previously ignored phenomenon, with a method for correction
Authors: Van Der Linde H J , Van Deuren B , Teisman A , Towart R , Gallacher D J
Published: June 2008

Background and purpose:

Body core temperature (Tc) changes affect the QT interval, but correction for this has not been systematically investigated. It may be important to correct QT intervals for drug‐induced changes in Tc.

Experimental approach:

Anaesthetized beagle dogs were artificially cooled (34.2 °C) or warmed (42.1 °C). The relationship between corrected QT intervals (QTcV; QT interval corrected according to the Van de Water formula) and Tc was analysed. This relationship was also examined in conscious dogs where Tc was increased by exercise.

Key results:

When QTcV intervals were plotted against changes in Tc, linear correlations were observed in all individual dogs. The slopes did not significantly differ between cooling (−14.85±2.08) or heating (−13.12±3.46) protocols. We propose a correction formula to compensate for the influence of Tc changes and standardize the QTcV duration to 37.5 °C: QTcVcT (QTcV corrected for changes in core temperature)=QTcV–14 (37.5 – Tc). Furthermore, cooled dogs were re‐warmed (from 34.2 to 40.0 °C) and marked QTcV shortening (−29%) was induced. After Tc correction, using the above formula, this decrease was abolished. In these re‐warmed dogs, we observed significant increases in T‐wave amplitude and in serum [K+] levels. No arrhythmias or increase in pro‐arrhythmic biomarkers were observed. In exercising dogs, the above formula completely compensated QTcV for the temperature increase.

Conclusions and implications:

This study shows the importance of correcting QTcV intervals for changes in Tc, to avoid misleading interpretations of apparent QTcV interval changes. We recommend that all ICH S7A, conscious animal safety studies should routinely measure core body temperature and correct QTcV appropriately, if body temperature and heart rate changes are observed.

British Journal of Pharmacology (2008) 154, 1474–1481; doi:10.1038/bjp.2008.265; published online 23 June 2008
Paramagnetic nanoparticle‐based detection of hepatitis B virus using cathodic stripping voltammetry
Authors: Fatemi Kamal , Ghourchian Hedayatollah , Ziaee Abed‐Ali , Samiei Shahram , Hanaee Hana
Published: June 2008

A nanoparticle‐based electrochemical method for detection of hepatitis B virus DNA sequences has been developed. This method relies on the adsorption of amplified hepatitis B virus DNA strands on to probe‐coated paramagnetic particles and electrochemical detection of hybridized strands using a hanging mercury drop electrode. For hepatitis B virus detection, a combination of dynamic DNA hybridization on transportable reactive surfaces and label‐free detection of DNA based on the electrochemical determination of adenines was used. Separation of the hybridization area from the detection electrode eliminates non‐specific adsorption of long DNAs, and combining this method with dynamic synthesis of probe may result in new flexible approaches for detection of other infectious agents by lab‐on‐a‐chip technology.
A novel protein phosphatase indirectly regulates phytochrome-interacting factor 3 via phytochrome
Authors: Phee Bong-Kwan , Kim Jeong-Il , Shin Dong Ho , Yoo Jihye , Park Kyoung-Jin , Han Yun-Jeong , Kwon Yong-Kook , Cho Man-Ho , Jeon Jong-Seong , Bhoo Seong Hee , Hahn Tae-Ryong
Published: June 2008

Light signal transduction in plants involves an intricate series of pathways which is finely regulated by interactions between specific signalling proteins, as well as by protein modifications such as phosphorylation and ubiquitination. The identification of novel phytochrome-interacting proteins and the precise signalling mechanisms that they mediate is still ongoing. In our present study, we show that the newly identified putative phytochrome-associated protein, PAPP2C (phytochrome-associated protein phosphatase type 2C), interacts in the nucleus with phyA (phytochrome A) and phyB, both in vitro and in vivo. Moreover, the phosphatase activity of PAPP2C and its association with phytochromes were found to be enhanced by red light, indicating that it plays a role in mediating phytochrome signalling. In particular, PAPP2C specifically binds to the N-terminal PHY domain of the phytochromes. We thus speculate that this interaction reflects a unique regulatory function of this phosphatase toward established phytochrome-associated proteins. We also show that PAPP2C effectively dephosphorylates phytochromes in vitro. Interestingly, PAPP2C indirectly mediates the dephosphorylation of PIF3 (phytochrome-interacting factor 3) in vitro. Taken together, we suggest that PAPP2C functions as a regulator of PIF3 by dephosphorylating phytochromes in the nucleus.
Identification of the human Nα-acetyltransferase complex B (hNatB): a complex important for cell-cycle progression
Authors: Starheim Kristian K. , Arnesen Thomas , Gromyko Darina , Ryningen Anita , Varhaug Jan Erik , Lillehaug Johan R.
Published: June 2008

Protein Nα-terminal acetylation is a conserved and widespread protein modification in eukaryotes. Several studies have linked it to normal cell function and cancer development, but nevertheless, little is known about its biological function. In yeast, protein Nα-terminal acetylation is performed by the N-acetyltransferase complexes NatA, NatB and NatC. In humans, only the NatA complex has been identified and characterized. In the present study we present the components of hNatB (human NatB complex). It consists of the Nat3p homologue hNAT3 (human N-acetyltransferase 3) and the Mdm20p homologue hMDM20 (human mitochondrial distribution and morphology 20). They form a stable complex and in vitro display sequence-specific Nα-acetyltransferase activity on a peptide with the N-terminus Met-Asp-. hNAT3 and hMDM20 co-sediment with ribosomal pellets, thus supporting a model where hNatB acts co-translationally on nascent polypeptides. Specific knockdown of hNAT3 and hMDM20 disrupts normal cell-cycle progression, and induces growth inhibition in HeLa cells and the thyroid cancer cell line CAL-62. hNAT3 knockdown results in an increase in G0/G1-phase cells, whereas hMDM20 knockdown decreased the fraction of cells in G0/G1-phase and increased the fraction of cells in the sub-G0/G1-phase. In summary, we show for the first time a vertebrate NatB protein Nα-acetyltransferase complex essential for normal cell proliferation.
Ischaemia and insulin, but not ischaemia and contraction, act synergistically in stimulating muscle glucose uptake in vivo in humans
Authors: Bosselaar Marlies , Smits Paul , Tack Cees J.
Published: June 2008

Ischaemia, like muscle contraction, has been reported to induce skeletal muscle glucose uptake in in vitro models. This stimulating effect appears independent of insulin and is probably mediated by activation of AMPK (AMP-activated protein kinase). In the present study, we hypothesized that in vivo in humans ischaemia- and insulin-induced glucose uptake are additive, and that the combined impact of ischaemia and contraction on glucose uptake is of a similar magnitude when each is applied separately. We assessed the effects of ischaemia with and without euglycaemic–hyperinsulinaemia (clamp; protocol 1) and with and without muscle contraction (protocol 2) on muscle FGU (forearm glucose uptake) in healthy subjects. Furthermore, we assessed the impact of ischaemia on FBF (forearm blood flow; plethysmography). In protocol 1, ischaemia increased FGU from 0.6±0.1 at baseline to 5.5±1.9 μmol·min−1·dl−1, and insulin increased FGU to 1.6±0.3 μmol·min−1·dl−1 (P<0.05 for both). The combination of ischaemia+insulin increased FGU to 15.5±2.2 μmol·min−1·dl−1 (P<0.05 compared with each stimulus alone). Maximal FBF obtained after ischaemia was similar with and without hyperinsulinaemia. In protocol 2, isometric contraction increased FGU from 0.3±0.1 to 2.7±0.8 μmol·min−1·dl−1 (P<0.05), but FGU was not significantly different from ischaemia compared with ischaemia+contraction. However, combined ischaemia+contraction resulted in a greater increase in FBF. In summary, ischaemia and insulin independently stimulate skeletal muscle glucose uptake in vivo in humans, whereas ischaemia and contraction do not. The observed differential effects of these stimuli on glucose uptake appear to be unrelated to changes in muscle blood flow.
Photoinduced proton transfer coupled with energy transfer: Mechanism of sensitized luminescence of terbium ion by salicylic acid doped in polymer
Authors: Misra Vinita , Mishra Hirdyesh
Published: June 2008

In the present work, excited state intramolecular proton transfer (ESIPT) in salicylic acid (SA) monoanion and subsequent sensitization of Tb3+ ion in polyvinyl alcohol (PVA) have been studied. The study has been carried out both by steady state and time domain fluorescence measurement techniques at room temperature. It is found that the SA completely ionizes and exists as monoanion in PVA. It exhibits a large Stokes shifted blue emission (10000cm−1) due to ESIPT and shows a decay time of 6.85ns. On the other hand, Tb3+ ion shows a very weak green emission and a decay time of ∼641μs in PVA film. Upon incorporating Tb3+ ion in SA doped PVA film, both intensity and decay time of SA decrease and sensitized emission from Tb+3 ion along with 3.8μs rise time is observed. Energy transfer is found to take place both from excited singlet as well as triplet states. A brief description of the properties of the present system from the viewpoint of luminescent solar collector material is addressed.
Formation of interstellar 2,4-pentadiynylidyne, HCCCCC(XΠ2), via the neutral-neutral reaction of ground state carbon atom, C(P3), with diacetylene, HCCCCH(XΣg+1)
Authors: Sun B. J. , Huang C. Y. , Kuo H. H. , Chen K. T. , Sun H. L. , Huang C. H. , Tsai M. F. , Kao C. H. , Wang Y. S. , Gao L. G. , Kaiser R. I. , Chang A. H. H.
Published: June 2008

The interstellar reaction of ground-state carbon atom with the simplest polyyne, diacetylene (HCCCCH), is investigated theoretically to explore probable routes to form hydrogen-deficient carbon clusters at ultralow temperature in cold molecular clouds. The isomerization and dissociation channels for each of the three collision complexes are characterized by utilizing the unrestricted B3LYP/6-311G(d,p) level of theory and the CCSD(T)/cc-pVTZ calculations. With facilitation of RRKM and variational RRKM rate constants at collision energies of 0–10kcal∕mol, the most probable paths, thus reaction mechanism, are determined. Subsequently, the corresponding rate equations are solved that the evolutions of concentrations of collision complexes, intermediates, and products versus time are obtained. As a result, the final products and yields are identified. This study predicts that three collision complexes, c1, c2, and c3, would produce a single final product, 2,4-pentadiynylidyne, HCCCCC(XΠ2), C5H (p1)+H, via the most stable intermediate, carbon chain HC5H (i4). Our investigation indicates the title reaction is efficient to form astronomically observed 2,4-pentadiynylidyne in cold molecular clouds, where a typical translational temperature is 10K, via a single bimolecular gas phase reaction.
Negative differential resistance behaviors in porphyrin molecular junctions modulated with side groups
Authors: Long Meng-Qiu , Chen Ke-Qiu , Wang Lingling , Qing Wan , Zou B. S. , Shuai Z.
Published: June 2008

By applying nonequilibrium Green’s functions in combination with the density-functional theory, we investigate the electronic transport properties of molecular junctions constructed by the porphyrin molecule with donor or acceptor side groups. The results show that the side groups play important role on the electron transport properties. Negative differential resistance (NDR) is observed in such devices. Especially for the molecule with electron-donating group (−NH2), two NDR appear at different bias voltage regions, and the origins for both NDR behavior are different. A mechanism is proposed for the NDR behavior.
Ion-acoustic solitons in plasmas with two-temperature ions
Authors: Hellberg Manfred A. , Verheest Frank
Published: June 2008

This paper discusses the existence of ion-acoustic solitons in a plasma consisting of hot and cool ions, and hot electrons, where the words “hot” and “cool” reflect the ratio of thermal effects to inertial effects. For the hot species general polytropic pressure relations are considered, as well as the isothermal limit, γ=1 (Boltzmann distribution). It is shown that negative potential solitons are not supported. Existence domains in parameter space (effective soliton Mach number and fractional cool ion density) for positive potential solitons are found, the limits being imposed by physical effects such as vanishing densities. Numerical results are given for a typical value of γ>1 and for γ=1, for three representative values of the hot ion to electron temperature ratio.
Two-dimensional buoyancy driven thermal mixing in a horizontally partitioned adiabatic enclosure
Authors: Mishra Aashwin A. , Hasan Nadeem , Sanghi Sanjeev , Kumar Ranganathan
Published: June 2008

The dynamics of the transient, two-dimensional buoyancy driven thermal mixing of two fluid masses at different temperatures, initially at rest and confined to separate portions of a horizontally partitioned adiabatic enclosure, is investigated numerically within the framework of the Boussinesq approximation. The fluids are allowed to mix through a centrally located opening or vent in the partition. Apart from the geometric parameters, the dynamics is governed by the Rayleigh (Ra) and Prandtl (Pr) numbers. Spanning the range 500⩽Ra⩽104 at Pr=0.71 and unity aspect ratios of the vent and the enclosures, the dominant spatial and temporal flow structures, in the asymptotic approach of the system towards a state of thermomechanical equilibrium, have been identified. These dominant modes have been utilized to classify the flow dynamics observed at different Ra into three distinct flow regimes. An approach utilizing new scalar norms to quantify the instantaneous state of mixing and to track the mixing process in time has been utilized to identify the flow modes favoring or opposing the mixing process. It is shown that the flow mode comprising of counterflowing streams in the vent yields the highest mixing rate. It is also shown that this flow mode results in a large build-up of enstrophy in the system. For Ra⩽5000, an increase in Ra brings about an increase in the overall mixing rate. However, for Ra>5000, there exists a vortex trapped in the vent for a significant length of time, preventing the two fluid masses to mix directly, thereby slowing down the overall mixing rate in comparison to the flows for Ra⩽5000.
Spectral asymmetry due to magnetic coordinates
Authors: Park Jong-kyu , Boozer Allen H. , Menard Jonathan E.
Published: June 2008

The use of magnetic coordinates is ubiquitous in toroidal plasma physics but the distortion in Fourier spectra produced by these coordinates is not well known. A spatial symmetry of the field is not always represented by a symmetry in the Fourier spectrum when magnetic coordinates are used because of the distortion of the toroidal angle. The practical importance of spectral distortion is illustrated with a tokamak example.
Transient currents in electrolyte displacement by asymmetric electro-osmosis and determination of surface zeta potentials of composite microchannels
Authors: Kuo Ang-Tsung , Chang Chien-Hsiang , Wei Hsien-Hung
Published: June 2008

In this article, we demonstrate the determination of surface zeta potentials of composite microchannels using the electric-field-driven solution displacement method. Nonuniform surface charge creates linear electro-osmotic flow, which leads to asymmetric displacement. Simplified circuit models are derived to determine the surface zeta potentials through examining the behavior of transient currents during the displacement. The effects of dispersion on the measured zeta potentials are discussed in line with the flow characteristics under different surface charge conditions.