bluuebunny/crossref_metadata_2025 huggingface dataset:
Inbred C57BL/6J and DBA/2J Mouse Strains Exhibit Constitutive Differences in Regional Brain Fatty Acid Composition
Authors: McNamara Robert K. , Able Jessica , Jandacek Ronald , Rider Therese , Tso Patrick
Published: October 2008

Major behavioral and neurochemical features observed between inbred C57BL/6 and DBA/2 mouse strains can be reproduced within rodent strains following dietary‐induced reductions in brain docosahexaenoic acid (DHA, 22:6n‐3) composition. It was therefore hypothesized that C57BL/6 and DBA/2 mice exhibit constitutive differences in brain DHA composition that are independent of diet. To test this, adult C57BL/6J and DBA/2J prefrontal cortex, hippocampus, ventral striatum, and midbrain fatty acid composition was determined by gas chromatography. After correction for multiple comparisons, C57BL/6J mice exhibited significantly lower DHA composition in the hippocampus and ventral striatum, but not prefrontal cortex or midbrain, and significantly greater regional arachidonic acid (ARA, 20:4n‐6):DHA ratios, relative to DBA/2J mice. C57BL/6J mice also exhibited significantly lower regional adrenic acid (ADA, 22:4n‐6) composition, and a significantly smaller ADA:ARA ratio, relative to DBA/2J mice. C57BL/6J mice exhibited significantly smaller oleic acid:stearic acid ratio in the hippocampus and ventral striatum relative to DBA/2J mice. Among all mice, DHA composition was positively correlated with the ADA:ARA ratio and inversely correlated with the oleic acid:stearic acid ratio. These data demonstrate that inbred C57BL/6J and DBA/2J mouse strains exhibit constitutive and region‐specific differences in fatty acid composition independent of diet, and suggest that heritable genetic factors are an important determinant of central fatty acid composition.
Quality Changes and Tocopherols and γ‐Orizanol Concentrations in Rice Bran Oil During the Refining Process
Authors: Pestana Vanessa Ribeiro , Zambiazi Rui Carlos , Mendonça Carla R. B. , Bruscatto Mariangela H. , Lerma‐García María Jesús , Ramis‐Ramos Guillermo
Published: October 2008

The quality changes and the concentrations of tocopherols and γ‐oryzanol, during successive steps of rice bran oil refining (RBO), were studied. For this purpose, samples of crude, degummed, neutralized, bleached, dewaxed and deodorized RBO were taken from an industrial plant and analyzed. The moisture, pH, acidity, peroxide value and unsaponifiable matter, were determined. The fatty acid composition was evaluated by GC, and the concentrations of tocopherols and γ‐oryzanol were determined using HPLC with fluorescence and UV–Vis detection, respectively. To identify γ‐oryzanol components, fractions of the HPLC eluant were collected and analyzed using mass spectrometry. Oil refining reduced the peroxide value and acidity to 1 and 3% of the values obtained in crude RBO, respectively. The fatty acid composition were not significantly altered during refining. The concentrations of the tocopherols in RBO followed the order α > (β + γ) > δ. The total concentration of tocopherols was 26 mg/100 g, and remained practically unaltered during refining. Up to nine components were distinguished in γ‐oryzanol. After collecting the elution fractions, up to six components were identified by electrospray mass spectrometry. Refining reduced the total concentration of γ‐oryzanol to 2% of its initial value.
Activity spaces and urban adolescent substance use and emotional health
Authors: Mason Michael J. , Korpela Kalevi
Published: October 2008

This study analyzed routine locations (activity spaces) of urban adolescents enrolled in a substance abuse treatment program to understand the relationship between their spatial lives and health outcomes such as substance use and mental health. Sixty‐eight adolescents were interviewed and produced a list of 199 locations identified as most important, safe, and risky. A TwoStep Cluster analysis resulted in two mutually exclusive groups of adolescents (n= 58). Clusterwise importance analyses showed that sex, distress, anxiety, emotional problems, and drug use significantly distinguish clusters from each other. An important finding was that activity spaces vary according to the frequency of substance use and the amount of emotional problems. School was frequently perceived as a risky place – followed by friend's house and nature – for those who used alcohol and marijuana more frequently and had more emotional distress. The intersection between environment, emotion regulation, and health outcomes is discussed.
Effect of oral N‐acetyl cysteine on recurrent preterm labor following treatment for bacterial vaginosis
Authors: Shahin Ahmed Y. , Hassanin Ibrahim M.A. , Ismail Alaa M. , Kruessel Jan S. , Hirchenhain Jens
Published: October 2008

Objective

To evaluate the effect of N‐acetyl cysteine (NAC) on gestational age at delivery in women with previous preterm labor and bacterial vaginosis.

Methods

A randomized, double‐blind, placebo‐controlled trial with 280 women between 16 and 18 weeks of pregnancy who had 1 previous preterm birth and had just been successfully treated for bacterial vaginosis with metronidazole for 1 week. The women were randomized to receive 0.6 g of NAC per day plus 17‐hydroxyprogesterone caproate (17‐OHPC) or placebo plus 17‐OHPC until 36 completed weeks of pregnancy or active labor. A vaginal swab was taken during labor.

Results

Reaching 36 weeks of pregnancy was more frequent (P < 0.05) and gestational age at delivery was significantly higher in the NAC than in the placebo group (37.4 weeks ± 0.4 weeks vs 34.1 weeks ± 1.2 weeks, P < 0.05). The discontinuation rate was 11.4% in the NAC group.

Conclusions

Oral NAC was found to reduce the recurrence of preterm birth in patients with bacterial vaginosis.
Profitability of technical stock trading: Has it moved from daily to intraday data?
Authors: Schulmeister Stephan
Published: October 2008

This paper investigates how technical trading systems exploit the momentum and reversal effects in the S&P 500 spot and futures market. When based on daily data, the profitability of 2580 technical models has steadily declined since 1960, and has been unprofitable since the early 1990s. However, when based on 30‐minutes‐data the same models produce an average gross return of 7.2% per year between 1983 and 2007. These results do not change substantially when trading is tested over eight subperiods. In particular, there is no clear trend of a declining profitability of technical stock trading based on 30‐minutes‐data. Those 25 models which performed best over the most recent subperiod produce a significantly higher gross return over the subsequent subperiod than all models. Between 2001 and 2007 the 2580 models perform worse than over the 1980s and 1990s. This result could be due to stock markets becoming recently more efficient or to stock price trends shifting from 30‐minutes‐prices to prices of higher frequencies.
Aperiodic substitution systems and their Bratteli diagrams
Authors: BEZUGLYI S. , KWIATKOWSKI J. , MEDYNETS K.
Published: October 2008

We study aperiodic substitution dynamical systems arising from non-primitive substitutions. We prove that the Vershik homeomorphism φ of a stationary ordered Bratteli diagram is topologically conjugate to an aperiodic substitution system if and only if no restriction of φ to a minimal component is conjugate to an odometer. We also show that every aperiodic substitution system generated by a substitution with nesting property is conjugate to the Vershik map of a stationary ordered Bratteli diagram. It is proved that every aperiodic substitution system is recognizable. The classes of m-primitive substitutions and derivative substitutions associated with them are studied. We discuss also the notion of expansiveness for Cantor dynamical systems of finite rank.
On Anosov diffeomorphisms with asymptotically conformal periodic data
Authors: KALININ BORIS , SADOVSKAYA VICTORIA
Published: October 2008

We consider transitive Anosov diffeomorphisms for which every periodic orbit has only one positive and one negative Lyapunov exponent. We prove various properties of such systems, including strong pinching, C1+β smoothness of the Anosov splitting, and C1 smoothness of measurable invariant conformal structures and distributions. We apply these results to volume-preserving diffeomorphisms with two-dimensional stable and unstable distributions and diagonalizable derivatives of the return maps at periodic points. We show that a finite cover of such a diffeomorphism is smoothly conjugate to an Anosov automorphism of 𝕋4; as a corollary, we obtain local rigidity for such diffeomorphisms. We also establish a local rigidity result for Anosov diffeomorphisms in dimension three.
Resonance between Cantor sets
Authors: PERES YUVAL , SHMERKIN PABLO
Published: October 2008

Let Ca be the central Cantor set obtained by removing a central interval of length 1−2a from the unit interval, and then continuing this process inductively on each of the remaining two intervals. We prove that if log b/log a is irrational, then where dim is Hausdorff dimension. More generally, given two self-similar sets K,K′ in ℝ and a scaling parameter s>0, if the dimension of the arithmetic sum K+sK′ is strictly smaller than dim (K)+dim (K′)≤1 (‘geometric resonance’), then there exists r<1 such that all contraction ratios of the similitudes defining K and K′ are powers of r (‘algebraic resonance’). Our method also yields a new result on the projections of planar self-similar sets generated by an iterated function system that includes a scaled irrational rotation.
Parameter rays in the space of exponential maps
Authors: FÖRSTER MARKUS , SCHLEICHER DIERK
Published: October 2008

We investigate the setIof parametersκ∈ℂ for which the singular orbit (0,eκ,…) ofEκ(z):=exp (z+κ) converges to$\infty $. These parameters are organized in curves in parameter space calledparameter rays, together with endpoints of certain rays. Parameter rays are an important tool to understand the detailed structure of exponential parameter space. In this paper, we construct and investigate these parameter rays. Based on these results, a complete classification of the setIis given in the following paper [M. Förster, L. Rempe and D. Schleicher. Classification of escaping exponential maps.Proc. Amer. Math. Soc.136(2008), 651–663].
Scaling of columnar joints in basalt
Authors: Goehring Lucas , Morris Stephen W.
Published: October 2008

We describe field work, analysis, and modeling of columnar joints from the Columbia River Basalt Group. This work is focused on the regions around the Grand Coulee, Snake River, and Columbia Gorge, which form parts of this unusually homogeneous and very large sample of columnar basalt. We examine in detail the scaling relationship between the column width and the size of the striae and relate these quantitatively to thermal and fracture models. We found that the column radius and stria size are proportional to each other and inversely proportional to the cooling rate of the lava. Near a flow margin, our results put observational constraints on diffusive thermal models of joint formation. Deeper than a few meters into a colonnade, our measurements are consistent with a simple advection‐diffusion model of two‐phase convective cooling within the joints, regardless of the direction of cooling. This model allows an accurate comparison of igneous columnar jointing and joints due to desiccation in laboratory analog systems. We also identify a new length scale in which wavy columns can appear in some colonnades. The mechanisms leading to the wavy columns are likely related to those underlying similar wavy cracks in 2‐D analog systems.
Observations and interpretation of fundamental mode Rayleigh wavefields recorded by the Transportable Array (USArray)
Authors: Pollitz Fred F.
Published: October 2008

Broadband recordings of the dense Transportable Array (TA) in the western United States provide unparalleled detailed images of long‐period seismic surface wavefields. With 400 stations spanning most of the western United States, wavefronts of fundamental mode Rayleigh waves may be visualized coherently across the array at periods ≳40 s. In order to constrain the Rayleigh wave phase velocity structure in the western United States, I assemble a data set of vertical component seismograms from 53 teleseismic events recorded by the TA from April 2006 to October 2007. Complex amplitude spectra from these recordings at periods 27–100 s are interpreted using the multiplane wave tomographic method of Friederich and Wielandt (1995) and Pollitz (1999). This analysis yields detailed surface wave phase velocity and three‐dimensional shear wave velocity patterns across the North American plate boundary zone, elucidating the active processes in the highly heterogeneous western U.S. upper mantle.
Ozone and upper troposphere/lower stratosphere variability and change at southern midlatitudes 1980–2000: Decadal variations
Authors: Canziani P. O. , Malanca F. E. , Agosta E. A.
Published: October 2008

Total ozone relationships with selected upper troposphere/lower stratosphere variables (400‐ and 70‐hPa temperatures, tropopause height and temperature, 70‐hPa geopotential height, and 340‐K potential vorticity), as well as between the variables, are analyzed on decadal scales over Southern Hemisphere midlatitudes for the period 1980–2000. Total Ozone Mapping Spectrometer version 8 total ozone and European Centre for Medium Range Weather Forecast ERA‐40 data products for June and October (early winter and spring) are used. Multiple spatial correlation techniques and shared variance estimates are applied to infer relationships between mean fields as well as among decadal difference fields. Wave activity Z and local Eliassen‐Palm fluxes were calculated to further analyze the dynamics of the samples and their variability. The statistical studies show that observed total ozone latitudinal and longitudinal decadal variations can be driven by upper tropospheric and stratospheric variability, depending on latitude and season. The sampled regions, divided into subtropical and subpolar, yield differentiated relationships. October ozone decadal variations during the 1980s, particularly at higher latitudes, are attributed primarily to chemical ozone depletion, while there appear to be links between tropospheric decadal change and some of the stratospheric variables and tropopause behavior. In the 1990s, tropospheric contributions decrease, and stratospheric quasi stationary wave 1 plays a major role. In June, tropospheric change/variability appears to be more important than stratospheric driving, which nevertheless also contributes to change. Ozone change in the 1990s responded more to stratospheric dynamic change at higher latitudes, but despite reduced contributions, the troposphere remains a driver of variation at the lower latitudes of the sample.
Impacts of long‐range transport of global pollutants and precursor gases on U.S. air quality under future climatic conditions
Authors: Huang Ho‐Chun , Lin Jintai , Tao Zhining , Choi Hyun , Patten Kenneth , Kunkel Kenneth , Xu Min , Zhu Jinhong , Liang Xin‐Zhong , Williams Allen , Caughey Michael , Wuebbles Donald J. , Wang Julian
Published: October 2008

The U.S. air quality is impacted by emissions both within and outside the United States. The latter impact is manifested as long‐range transport (LRT) of pollutants across the U.S. borders, which can be simulated by lateral boundary conditions (LBC) into a regional modeling system. This system consists of a regional air quality model (RAQM) that integrates local‐regional source emissions and chemical processes with remote forcing from the LBC predicted by a nesting global chemical transport model (model for ozone and related chemical tracers (MOZART)). The present‐day simulations revealed important LRT effects, varying among the five major regions with ozone problems, i.e., northeast United States, midwest United States, Texas, California, and southeast United States. To determine the responses of the LRT impacts to projected global climate and emissions changes, the MOZART and RAQM simulations were repeated for future periods (2048–2052 and 2095–2099) under two emissions scenarios (IPCC A1Fi and B1). The future U.S. air quality projected by the MOZART is less sensitive to the emissions scenarios than that simulated by the RAQM with or without incorporating the LRT effects via the LBC from the MOZART. The result of RAQM with the LRT effects showed that the southeast United States has the largest sensitivity of surface ozone mixing ratio to the emissions changes in the 2095–2099 climate (−24% to +25%) followed by the northeast and midwest United States. The net increase due to the LRT effects in 2095–2099 ranges from +4% to +13% in daily mean surface ozone mixing ratio and +4% to +11% in mean daily maximum 8‐h average ozone mixing ratios. Correspondingly, the LRT effects in 2095–2099 cause total column O3 mixing ratio increases, ranging from +7% to +16%, and also 2 to 3 more days with the surface ozone exceeding the national standard. The results indicate that future U.S. air quality changes will be substantially affected by global emissions.
Long‐term variations in oxygen green line emission over Kiso, Japan, from ground photometric observations using continuous wavelet transform
Authors: Das Uma , Sinha H. S. S.
Published: October 2008

An analysis of 16 years long ground based photometric data of the oxygen green line (557.7 nm) over a mid latitude station Kiso (35.79°N, 137.63°E) was made using the continuous wavelet transform. This analysis shows the presence of semiannual, annual, and quasi‐biennial variations in the airglow emission, which show interannual as well as nocturnal variations. The semiannual component is present during certain epochs and absent at other times. Also, it is statistically significant at 2000 hours JST (UT+09:00 hrs) and weakens as the night progresses. This variation is similar to the variation seen in wind imaging interferometer (WINDII) satellite data and thermosphere‐ionosphere‐mesosphere‐electrodynamics – global circulation model (TIME‐GCM) model as well. The annual component is present during the entire epoch, but its amplitude shows a minimum during the midnight. In addition, a strong quasi‐biennial component is also seen at 2000 and 0200 hours JST, the amplitude of which exceeds the semiannual component during certain epochs. This component was not detected in earlier studies using the same data. These variations in the oxygen airglow show the effect of tidal dynamics in the mesosphere and lower thermosphere.
Atmospheric CO2 stabilization and ocean acidification
Authors: Cao Long , Caldeira Ken
Published: October 2008

We use a coupled climate/carbon‐cycle model to examine the consequences of stabilizing atmospheric CO2 at different levels for ocean chemistry. Our simulations show the potential for major damage to at least some ocean ecosystems at atmospheric CO2 stabilization levels as low as 450 ppm. Before the industrial revolution, more than 98% of corals reefs were surrounded by waters that were >3.5 times saturated with respect to their skeleton materials (aragonite). If atmospheric CO2 is stabilized at 450 ppm only 8% of existing coral reefs will be surrounded by water with this saturation level. Also at this CO2 level 7% of the ocean South of 60°S will become undersaturated with respect to aragonite, and parts of the high latitude ocean will experience a decrease in pH by more than 0.2 units. Results presented here provide an independent and additional basis for choosing targets of atmospheric CO2 stabilization levels.
Spatial structure of hydraulic properties from canopy to interspace in the Mojave Desert
Authors: Caldwell Todd G. , Young Michael H. , Zhu Jianting , McDonald Eric V.
Published: October 2008

Desert piedmonts are a mosaic of interspersed vegetation and bare soil, previously considered to be a binary system of canopy and interspace microsites. The spatial structure of soils and hydraulic properties in these microsites affects our ability to upscale or downscale observed processes. We determined variability and spatial correlation of hydraulic properties using high‐resolution measurements of unsaturated hydraulic conductivity [K(ψ)] along linear transects radiating from canopies of perennial shrubs common to the Mojave Desert into bare soil interspaces. Hydraulic conductivity from −6 < ψ < 0 cm soil water pressures was lower under canopy. Spatial correlations to organic matter, particle‐size, and K(ψ) were observed to approximately 1.4 times canopy diameter, beyond which random processes dominated. Results illustrate that a predictable spatial structure in K(ψ) exists between canopy and interspace microsites and suggest that scaling from the plant to field plot could exploit this relationship.
Electrostatic instabilities triggered by finite amplitude Alfvén/ion‐cyclotron waves and relative drifts among the ion components in the magnetosphere
Authors: Gomberoff L.
Published: October 2008

Alfvén/ion‐cyclotron waves have been observed in several regions of the magnetosphere. Parametric decays of finite amplitude Alfvén/ion‐cyclotron waves in the presence of He+ ions and a mixed population of thermal and hot protons have been shown to lead to several parametric instabilities. These studies assumed that heavy ions are not drifting relative to each other. However, a relative drift velocity among the ions can affect known parametric decays and can also lead to new ones. Moreover, finite amplitude waves in a plasma system with drifting ion species are shown to destabilize nonlinear ion‐acoustic‐like waves supported by each species. Finally, linear ion‐acoustic waves supported by different ion species can also be destabilized because of the relative drift between ion components.
Nonlinear effects in the ionospheric Alfvén resonator
Authors: Sydorenko D. , Rankin R. , Kabin K.
Published: October 2008

A two‐dimensional nonlinear multi‐fluid MHD model of the ionosperic Alfvén resonator is presented. The resonator is excited by a packet of shear Alfvén waves propagating downward toward the ionosphere from high altitudes. It is shown that the nonlinear (ponderomotive) force of standing oscillations in the ionospheric Alfvén resonator creates plasma flows along the geomagnetic field that modify the plasma density profile. Depending on the amplitude of the wave packet exciting the resonator, this effect can be very strong. For the selected plasma density profile in the near‐Earth magnetosphere, an Alfvén wave packet with a smooth symmetric envelope and the maximum transverse electric field amplitude of 0.5 V/m, carrying 10 wave periods with the frequency of the first resonator harmonic, can decrease the plasma density by a factor of two at altitudes between 1000 and 1700 km in less than one minute. The amplitude of the wave packet is nonuniform in the direction across the geomagnetic field, which results in nonuniform density modification and phase mixing of oscillations on neighboring geomagnetic field lines. This increases both the transverse wavenumber of the excited resonator harmonics and the wave electric field along the geomagnetic field.
Low‐latitude mesospheric mean winds observed by Gadanki mesosphere‐stratosphere‐troposphere (MST) radar and comparison with rocket, High Resolution Doppler Imager (HRDI), and MF radar measurements and HWM93
Authors: Kishore Kumar G. , Venkat Ratnam M. , Patra A. K. , Jagannadha Rao V. V. M. , Vijaya Bhaskar Rao S. , Kishore Kumar K. , Gurubaran S. , Ramkumar Geetha , Narayana Rao D.
Published: October 2008

Low‐latitude mesospheric winds are investigated using data collected from 1995 to 2006 (11 years) by Indian MST radar located at Gadanki (13.5°N, 79.2°E). Clear eastward and westward flow in zonal wind is noticed during solstices and equinoxes, respectively. The meridional wind shows equatorward flow below 75 km and poleward flow above 75 km quite consistent with that observed with other techniques. The winds show a clear semiannual oscillation (SAO) with maxima during equinoxes. The strength of the SAO during spring is larger than that of fall equinox, and the first peak occurs at higher altitudes than the second peak. The observed features are compared with other techniques, namely, rocket, High Resolution Doppler Imager (HRDI), and medium frequency (MF) radar and also with horizontal wind model HWM93. In general, good comparison is seen among various techniques, with some discrepancy observed in amplitudes. Interestingly, decrease in eastward wind with time during winter months is noticed. The significance of the present results lies in showing the consistency/inconsistency of various experimental techniques to measure the middle atmospheric winds, which are very important to assess the climate variability.
A sensitivity study of the Kelvin wave and the Madden‐Julian Oscillation in aquaplanet simulations by the Naval Research Laboratory Spectral Element Atmospheric Model
Authors: Kim Young‐Joon , Giraldo Francis X. , Flatau Maria , Liou Chi‐Sann , Peng Melinda S.
Published: October 2008

The dynamical core of the Naval Research Laboratory (NRL) Spectral Element Atmospheric Model (NSEAM) is coupled with full physics and used to investigate the organization and propagation of equatorial atmospheric waves under the aquaplanet conditions. The sensitivity of the model simulation to the amount of horizontal viscosity, distribution of the vertical levels, and selected details of the precipitation physics is examined and discussed mainly utilizing simulated convective precipitation with the aid of time‐longitude plots and the spectral diagrams designed by Wheeler and Kiladis (1999). It is shown that the simulation of the Kelvin wave and Madden‐Julian Oscillation depends strongly on the details of the vertical level distribution and the choice of parameters in the convective parameterization. Efforts are made to calibrate the new model to capture the essential interaction between the dynamics and physics of the atmosphere. The speed and spectrum of the eastward propagating Kelvin waves and the signature of the Madden‐Julian Oscillation simulated by the new model reveal main features similar to those predicted by the simplified theory and found in limited observations. This study attempts to understand the significant variability found among the aquaplanet simulations by various global atmospheric models and highlights the uncertainties concerning convective processes and their coupling to large‐scale wave motion in large‐scale models of the atmosphere.
Modeling aerosol effects on shallow cumulus convection under various meteorological conditions observed over the Indian Ocean and implications for development of mass‐flux parameterizations for climate models
Authors: Wang Hailong , McFarquhar Greg M.
Published: October 2008

To determine conditions over the Indian Ocean, under which cloud fields are most susceptible to modification from aerosols, and to study how turbulent activities and shallow cumuli vary for different meteorological scenarios, a three‐dimensional large‐eddy simulation model was initialized using data collected during the Indian Ocean Experiment (INDOEX). Radiosonde data were used to construct six soundings encompassing the range of temperature and humidity observed. A total of 18 meteorological scenarios were then obtained by adding either an average transition layer (TL), a strong inversion layer (IL), or no stable layer to each sounding. Separate simulations were conducted for each scenario assuming pristine or polluted conditions as observed during INDOEX. For aerosol profiles measured during INDOEX, aerosol semidirect effects always dominated indirect effects, with the positive daytime net indirect forcing (semidirect plus indirect forcings) varying between 0.2 and 4.5 W m−2. Anthropogenic aerosols had a larger net indirect forcing when the environmental relative humidity (RH) was higher and in the absence of the IL and TL. Changes in meteorological factors had larger impacts on the cloud properties than did anthropogenic aerosols, indicating large uncertainties can be introduced when solely using observations to quantify aerosol effects without examining their meteorological context. Because mean lateral detrainment and entrainment rates depended on RH, aerosols, and the presence of stable layers, mass‐flux parameterizations in climate models should not use single values for such rates that may not represent the range of conditions observed where trade cumuli form.
Cloud properties from Atmospheric Infrared Sounder and evaluation with Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observations
Authors: Stubenrauch C. J. , Cros S. , Lamquin N. , Armante R. , Chédin A. , Crevoisier C. , Scott N. A.
Published: October 2008

The Atmospheric Infrared Sounder (AIRS) onboard the NASA Aqua satellite was primarily designed to provide atmospheric temperature and water vapor profiles, and the high spectral resolution of this instrument also allows the retrieval of cloud properties (especially cirrus). We present a retrieval of cloud pressure and effective emissivity, based on a weighted χ2 method using channels around the 15‐micron CO2 absorption band. The cloud property retrieval is applied to all data, and tests based on the retrieved parameters determine cloud amount in a second step. Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO), launched as part of the A‐Train in 2006, made it possible to evaluate the AIRS retrieved cloud height by comparing it to the height of maximum backscatter and of the “apparent middle” of the highest cloud layer determined by CALIPSO. The retrieved cloud height of about 66% (80%) of AIRS high (low) clouds lies within 1.5 km of the apparent middle of the CALIPSO cloud layers. Comparing cloud pressures shows an agreement in cloud height of 72% (59%) for high (low) clouds within 75 hPa. Keeping in mind that (1) low clouds are geometrically thinner (less than 1 km) than high clouds (in general between 1.5 and 3 km), (2) high clouds are also much more heterogeneous, and (3) CALIPSO only samples a small fraction of the AIRS footprint, the comparison is very encouraging. Zonal averages of high‐, midlevel‐, and low‐cloud amount are compared to those of other data sets for January and July. Compared to our cloud retrieval, distributions of cloud pressure provided by AIRS L2 data reveal a strong bias toward lower pressures for low clouds.
Introduction to special section on the Phoenix Mission: Landing Site Characterization Experiments, Mission Overviews, and Expected Science
Authors: Smith P. H. , Tamppari L. , Arvidson R. E. , Bass D. , Blaney D. , Boynton W. , Carswell A. , Catling D. , Clark B. , Duck T. , DeJong E. , Fisher D. , Goetz W. , Gunnlaugsson P. , Hecht M. , Hipkin V. , Hoffman J. , Hviid S. , Keller H. , Kounaves S. , Lange C. F. , Lemmon M. , Madsen M. , Malin M. , Markiewicz W. , Marshall J. , McKay C. , Mellon M. , Michelangeli D. , Ming D. , Morris R. , Renno N. , Pike W. T. , Staufer U. , Stoker C. , Taylor P. , Whiteway J. , Young S. , Zent A.
Published: October 2008

Phoenix, the first Mars Scout mission, capitalizes on the large NASA investments in the Mars Polar Lander and the Mars Surveyor 2001 missions. On 4 August 2007, Phoenix was launched to Mars from Cape Canaveral, Florida, on a Delta 2 launch vehicle. The heritage derived from the canceled 2001 lander with a science payload inherited from MPL and 2001 instruments gives significant advantages. To manage, build, and test the spacecraft and its instruments, a partnership has been forged between the Jet Propulsion Laboratory, the University of Arizona (home institution of principal investigator P. H. Smith), and Lockheed Martin in Denver; instrument and scientific contributions from Canada and Europe have augmented the mission. The science mission focuses on providing the ground truth for the 2002 Odyssey discovery of massive ice deposits hidden under surface soils in the circumpolar regions. The science objectives, the instrument suite, and the measurements needed to meet the objectives are briefly described here with reference made to more complete instrument papers included in this special section. The choice of a landing site in the vicinity of 68°N and 233°E balances scientific value and landing safety. Phoenix will land on 25 May 2008 during a complex entry, descent, and landing sequence using pulsed thrusters as the final braking strategy. After a safe landing, twin fan‐like solar panels are unfurled and provide the energy needed for the mission. Throughout the 90‐sol primary mission, activities are planned on a tactical basis by the science team; their requests are passed to an uplink team of sequencing engineers for translation to spacecraft commands. Commands are transmitted each Martian morning through the Deep Space Network by way of a Mars orbiter to the spacecraft. Data are returned at the end of the Martian day by the same path. Satisfying the mission's goals requires digging and providing samples of interesting layers to three on‐deck instruments. By verifying that massive water ice is found near the surface and determining the history of the icy soil by studying the mineralogical, chemical, and microscopic properties of the soil grains, Phoenix will address questions concerning the effects of climate change in the northern plains. A conclusion that unfrozen water has modified the soil naturally leads to speculation as to the biological potential of the soil, another scientific objective of the mission.
On the accuracy of predicting shear viscosity of molecular liquids using the periodic perturbation method
Authors: Zhao Lifeng , Cheng Tao , Sun Huai
Published: October 2008

Non-equilibrium molecular dynamics simulations are performed to calculate shear viscosities of 16 representative molecular liquids using the periodic perturbation method (PPM). A perturbation index is defined to measure the strength of the perturbation. It is identified that the predictions are systematically underestimated using PPM. The origin of the underestimate is the acoustic wave in the liquid density, which is persistent in the simulation box unless the perturbation is completely removed. However, there is a linear correlation between the perturbation indexes and the apparent viscosities, which can be utilized to accurately predict the shear viscosities. Finally, it is demonstrated that general force fields derived based on equilibrium properties can be used to predict the shear viscosities of small molecular liquids with relative errors less than 10%.
Plasma fluorination of carbon-based materials for imprint and molding lithographic applications
Authors: Schvartzman M. , Mathur A. , Hone J. , Jahnes C. , Wind S. J.
Published: October 2008

Diamondlike carbon nanoimprint templates are modified by exposure to a fluorocarbon-based plasma, yielding an ultrathin layer of a fluorocarbon material on the surface which has a very low surface energy with excellent antiwear properties. We demonstrate the use of these plasma fluorinated templates to pattern features with dimensions ∼20nm and below. Furthermore, we show that this process is extendable to other carbon-based materials. Plasma fluorination can be applied directly to nanoimprint resists as well as to molds used to form elastomer stamps for microcontact printing and other applications requiring easy mold release.
Scattering-based hole burning through volume speckles in a random medium with tunable diffusion constant
Authors: Murai Shunsuke , Fujita Koji , Hirao Takayuki , Nakanishi Kazuki , Hirao Kazuyuki , Tanaka Katsuhisa
Published: October 2008

A photoreactive random medium with tunable diffusion constant D is fabricated by infiltrating Sm2+-doped macroporous aluminosilicate glass with liquid crystal (LC). Time-resolved transmission experiment reveals that D in the LC-infiltrated sample changes abruptly at around 35°C due to the phase transition of LC between nematic and isotropic. The hole burning effect based on the interference of multiply scattered light is investigated with a particular motivation of controlling hole burning properties externally via temperature. We demonstrate that the holes are separately registered in each LC phase and can be detected selectively depending on the temperature.
Oriented graphite layer formation in Ti/C and TiC/C multilayers deposited by high current pulsed cathodic arc
Authors: Persson P. O. Å. , Ryves L. , Tucker M. D. , McKenzie D. R. , Bilek M. M. M.
Published: October 2008

Ti/C and TiC/C multilayers with periods ranging from 2 to 18 nm were grown by filtered high current pulsed cathodic arc. The growth was monitored in situ by ellipsometry and cantilever stress measurements. The ellipsometry results reveal that the optical properties of the carbon vary as a function of thickness. Correspondingly, the stress in each carbon layer as measured in situ exhibits two well defined values: initially the stress is low and then takes on a higher value for the remainder of the layer. Transmission electron microscopy shows that the initial growth of carbon on Ti or TiC layer is oriented with graphitic basal planes aligned parallel to the interface. After 2–4 nm of growth, the graphitic structure transforms to amorphous carbon. Electron energy loss spectroscopy shows that the carbon layer simultaneously undergoes a transition from sp2 rich to sp3 rich material.
Numerical solution of shock and ramp compression for general material properties
Authors: Swift Damian C.
Published: October 2008

A general formulation was developed to represent material models for applications in dynamic loading. Numerical methods were devised to calculate response to shock and ramp compression and ramp decompression, generalizing previous solutions for scalar equations of state. The numerical methods were found to be flexible and robust, and matched analytic results to a high accuracy. The basic ramp and shock solution methods were coupled to solve for composite deformation paths, such as shock-induced impacts and shock interactions with a planar interface between different materials. These calculations capture much of the physics of typical material dynamics experiments, without requiring spatially resolving simulations. Example calculations were made of loading histories in metals, illustrating the effects of plastic work on the temperatures induced in quasi-isentropic and shock-release experiments and the effect of a phase transition.
Quantum dot resonant tunneling diode single photon detector with aluminum oxide aperture defined tunneling area
Authors: Li H. W. , Kardynał B. E. , Ellis D. J. P. , Shields A. J. , Farrer I. , Ritchie D. A.
Published: October 2008

Quantum dot resonant tunneling diode single photon detector with independently defined absorption and sensing areas is demonstrated. The device, in which the tunneling is constricted to an aperture in an insulating layer in the emitter, shows electrical characteristics typical of high quality resonant tunneling diodes. A single photon detection efficiency of 2.1%±0.1% at 685 nm was measured corresponding to an internal quantum efficiency of 14%. The devices are simple to fabricate, robust, and show promise for large absorption area single photon detectors based on quantum dot structures.
Nanoscale polarization profile across a 180° ferroelectric domain wall extracted by quantitative piezoelectric force microscopy
Authors: Tian Lili , Vasudevarao Aravind , Morozovska Anna N. , Eliseev Eugene A. , Kalinin Sergei V. , Gopalan Venkatraman
Published: October 2008

The structure of a single antiparallel ferroelectric domain wall in LiNbO3 is quantitatively mapped by piezoelectric force microscopy (PFM) with calibrated probe geometry. The PFM measurements are performed for 49 probes with the radius varying from 10 to 300 nm. The magnitude and variation of the experimental piezoelectric coefficient across a domain wall match the profiles calculated from a comprehensive analytical theory, as well as three-dimensional finite element method simulations. Quantitative agreement between experimental and theoretical profile widths is obtained only when a finite disk-type tip radius that is in true contact with the sample surface is considered, which is in agreement with scanning electron microscopy images of the actual tips after imaging. The magnitude of the piezoelectric coefficient is shown to be independent of the tip radius, and the PFM profile width is linearly proportional to the tip radius. Finally we demonstrate a method to extract any intrinsic material broadening of the ferroelectric wall width. Surprisingly wide wall widths of up to 100 nm are observed in the limit of zero tip radius.
High bandwidth control of precision motion instrumentation
Authors: Bristow Douglas A. , Dong Jingyan , Alleyne Andrew G. , Ferreira Placid , Salapaka Srinivas
Published: October 2008

This article presents a high-bandwidth control design suitable for precision motion instrumentation. Iterative learning control (ILC), a feedforward technique that uses previous iterations of the desired trajectory, is used to leverage the repetition that occurs in many tasks, such as raster scanning in microscopy. Two ILC designs are presented. The first design uses the motion system dynamic model to maximize bandwidth. The second design uses a time-varying bandwidth that is particularly useful for nonsmooth trajectories such as raster scanning. Both designs are applied to a multiaxis piezoelectric-actuated flexure system and evaluated on a nonsmooth trajectory. The ILC designs demonstrate significant bandwidth and precision improvements over the feedback controller, and the ability to achieve precision motion control at frequencies higher than multiple system resonances.
Comment on “First-principles study of high-pressure phonon dispersions of wurtzite, zinc blende, and rocksalt AlN” [J. Appl. Phys. 103, 013506 (2008)]
Authors: Wagner J.-M.
Published: October 2008

The linear pressure coefficients and Grüneisen parameters of AlN calculated by Saib et al. [J. Appl. Phys. 103, 013506 (2008)] are inconsistent in a systematic way, the deviations being largest for modes exhibiting large quadratic pressure coefficients. This indicates that the inconsistency could be eliminated by a careful reexamination of the calculated results. Most likely, the pressure coefficients have to be revised; significantly smaller values for the rocksalt structure should be found.
Lattice Boltzmann study of hydrodynamic effects in lamellar ordering process of two-dimensional quenched block copolymers
Authors: Song Kai-Xu , Jia Yu-Xi , Sun Zhao-Yan , An Li-Jia
Published: October 2008

By incorporating self-consistent field theory with lattice Boltzmann method, a model for polymer melts is proposed. Compared with models based on Ginzburg–Landau free energy, our model does not employ phenomenological free energies to describe systems and can consider the chain topological details of polymers. We use this model to study the effects of hydrodynamic interactions on the dynamics of microphase separation for block copolymers. In the early stage of phase separation, an exponential growth predicted by Cahn–Hilliard treatment is found. Simulation results also show that the effect of hydrodynamic interactions can be neglected in the early stage. For the late stage of phase separation, it is easy to see the effects of hydrodynamic interactions on the ordering process of lamellae phase. From the analysis of structure factor curves, we find that the growth of domains is faster if hydrodynamic interactions are introduced. Furthermore, the scaling of the pattern dynamics is investigated for the late stage at zero thermal noise. By studying the behavior of scaling exponents of the structure factor and the nematic order-parameter correlation function Cnn, we can see that the effects of hydrodynamic interactions lead to bigger growth exponent for both functions.
Multistability and arithmetically period-adding bifurcations in piecewise smooth dynamical systems
Authors: Do Younghae , Lai Ying-Cheng
Published: October 2008

Multistability has been a phenomenon of continuous interest in nonlinear dynamics. Most existing works so far have focused on smooth dynamical systems. Motivated by the fact that nonsmooth dynamical systems can arise commonly in realistic physical and engineering applications such as impact oscillators and switching electronic circuits, we investigate multistability in such systems. In particular, we consider a generic class of piecewise smooth dynamical systems expressed in normal form but representative of nonsmooth systems in realistic situations, and focus on the weakly dissipative regime and the Hamiltonian limit. We find that, as the Hamiltonian limit is approached, periodic attractors can be generated through a series of saddle-node bifurcations. A striking phenomenon is that the periods of the newly created attractors follow an arithmetic sequence. This has no counterpart in smooth dynamical systems. We provide physical analyses, numerical computations, and rigorous mathematical arguments to substantiate the finding.
Vibrational energy transfer between I2(BΠu+3,ν′=21) and He at very low temperatures: Impulsive versus complex formation mechanisms assisted by tunneling through the centrifugal barrier
Authors: Cabanillas-Vidosa Iván , Rinaldi Carlos A. , Pino Gustavo A. , Ferrero Juan C.
Published: October 2008

The temperature dependence of the state-to-state vibrational relaxation rate constant (kν21−Δν) for collisions between I2(B,ν′=21) and He at very low kinetic energies was studied. The fluorescence from I2(B,ν′=21−Δν′) with Δν′=1–5 indicates that in the temperature range of 0.6–8.2K these states are populated by only one collision with He. The behavior of kν21−Δν with temperature can be divided into two groups. The group with quantum changes Δν′=1–3 shows scattering resonances in the low temperature region, with a general monotonical decrease of the rate constant with temperature, suggesting the importance of van der Waals interactions. This behavior is supported by the calculation of the probability of tunneling through the centrifugal barriers. For collisions in which 4–5 quanta are lost in a single event, there are no evidences of scattering resonances and the values of the relaxation rate constants could be determined only at the highest temperatures of this study. This suggests that relaxation occurs via impulsive collisions. The branching ratios for each channel are also temperature dependent and this behavior also suggests that the energy transfer mechanism changes with Δν′.
An exact theory of three-dimensional fixed separation in unsteady flows
Authors: Surana Amit , Jacobs Gustaaf B. , Grunberg Oliver , Haller George
Published: October 2008

We develop a nonlinear theory for separation and attachment on no-slip boundaries of three-dimensional unsteady flows that have a steady mean component. In such flows, separation and attachment surfaces turn out to originate from fixed lines on the boundary, even though the surfaces themselves deform in time. The exact separation geometry is not captured by instantaneous Eulerian fields associated with the velocity field, but can be determined from a weighted average of the wall-shear and wall-density fields. To illustrate our results, we locate separation surfaces and attachment surfaces in an unsteady model flow and in direct numerical simulations of a time-periodic lid-driven cavity.