bluuebunny/crossref_metadata_2025 huggingface dataset:
Operative und interventionelle Therapie des Uterus myomatosus
Authors: Schollmeyer  , Meinhold-Heerlein  , Walter  , Venhoff  , Müller-Hülsbeck
Published: June 2007

Myome sind die häufigsten gutartigen, soliden Tumoren des weiblichen Genitaltraktes im reproduktiven Alter. Es handelt sich um östrogenabhängige Tumoren, deren Inzidenz mit zunehmendem Alter steigt. Ein nicht unerheblicher Anteil ist asymptomatisch, während Myome andererseits häufig Blutungsstörungen oder Verdrängungsbeschwerden verursachen. Im reproduktiven Alter stellt sich auch die Frage des Kinderwunsches bei vorliegendem Uterus myomatosus. Des Weiteren besteht bei immer mehr Frauen bei abgeschlossener Familienplanung und myombedingten Beschwerden der Wunsch zum Erhalt der Gebärmutter. Während mit der Verbreitung minimal-invasiver endoskopischer Verfahren der Trend zum Organerhalt aufgegriffen wurde, suchen minimal-invasive radiologische und non-invasive Verfahren noch ihren Platz im mittlerweile breit gefächerten Behandlungsspektrum.
Entzündliche Erkrankungen des weiblichen Genitale
Authors: Hoof
Published: June 2007

Das Spektrum der entzündlichen Erkrankungen im kleinen Becken des weiblichen Genitale umfasst jegliche Kombinationen von entzündlichen Veränderungen des oberen weiblichen Genitaltraktes: Endometritis, Salpingitis, Tuboovarialabzess und Peritonitis im kleinen Becken. Es handelt sich meist um aszendierende Infektionen mit virulenten Keimen, eine Mitbeteiligung von Chlamydien und Gonokokken ist häufig und tendenziell zunehmend. Das klinische Beschwerdebild dieser Erkrankungen ist vielfältig, asymptomatische Verläufe bis hin zu schwersten septischen Krankheitsbildern kommen vor. Die antibiotische Therapie sollte möglichst früh begonnen werden und ein breites Spektrum abdecken. Eine operative Therapie ist bei Therapieversagern sowie bei Beschwerdepersistenz nach der akuten Entzündungsphase notwendig. Als Folgeprobleme können tubare Sterilität, Extrauteringravidität und chronische Unterbauchschmerzen auftreten.
Raumforderung im kleinen Becken – Sicht des Coloproktologen
Authors: Schulte  , Kahlke
Published: June 2007

Das kleine Becken, die Cavitas pelvis, wird kranial durch die Beckeneingangsebene/das Promontorium und kaudal durch den muskulären Beckenboden begrenzt. Zu den Beckenorganen zählen bei der Frau neben den inneren Geschlechtsorganen, die Harnblase und das Rektum sowie in Teilen der Analkanal. Vom Rektum bzw. Analkanal gehen benigne und maligne Raumforderungen aus. Zu den häufigsten tumorösen Raumforderungen zählen neben den gutartigen Adenomen und Hamartome auch bösartige Veränderungen wie das Rektum- sowie das Analkarzinom. Entsprechend der Dignität und der anatomischen Lage unterscheidet sich das diagnostische und therapeutische Vorgehen.
Raumforderungen im kleinen Becken aus Sicht des Urologen
Authors: Stübinger  , van der Horst  , Braun
Published: June 2007

Tumore im kleinen Becken, die ihren Ursprung nicht primär im Urogenitaltrakt haben, können aufgrund der engen räumlichen Beziehung häufig zu einer sekundären Beteiligung des Harntraktes führen. Benigne Tumore (Uterus myomatosus, Ovarialzyste, Kolonadenom) führen ebenso wie maligne Tumore (z.B. Uterus-, Zervix-, Ovarial- und Kolonkarzinome) zu Verdrängungserscheinungen bzw. Infiltrationen der Harnorgane. Häufige urologische Symptome sind Blasenentleerungsstörungen, Harninkontinenz, urogenitale Entzündungen oder Harnabflussstörungen bis hin zum Nierenversagen. Dies sind oft die ersten Krankheitssymptome und erst in der weiteren Diagnostik wird dann der ursächliche Primärtumor entdeckt. Wichtig ist, dass primär urologische Tumore des Beckens – benigner als auch maligner Art – zu einer identischen Symptomatik führen können und somit ebenfalls differentialdiagnostisch miteinbezogen werden müssen. Die therapeutischen Maßnahmen richten sich zunächst nach der klinischen Symptomatik, an welche sich die Behandlung der Ursache anschließt. Kommt es beispielsweise durch einen verdrängenden Tumor im kleinen Becken zu einer akuten Abflussbehinderung des oberen oder unteren Harntraktes, ist eine sofortige interventionelle Entlastung der Harnwege mittels Nieren- oder Blasenfistelung notwendig. Erst im zweiten Schritt sollte dann die Möglichkeit der Tumorsanierung geprüft werden.
Atmospheric bridge, oceanic tunnel, and global climatic teleconnections
Authors: Liu Zhengyu , Alexander Mike
Published: June 2007

We review teleconnections within the atmosphere and ocean, their dynamics and their role in coupled climate variability. We concentrate on teleconnections in the latitudinal direction, notably tropical‐extratropical and interhemispheric interactions, and discuss the timescales of several teleconnection processes. The tropical impact on extratropical climate is accomplished mainly through the atmosphere. In particular, tropical Pacific sea surface temperature anomalies impact extratropical climate variability through stationary atmospheric waves and their interactions with midlatitude storm tracks. Changes in the extratropics can also impact the tropical climate through upper ocean subtropical cells at decadal and longer timescales. On the global scale the tropics and subtropics interact through the atmospheric Hadley circulation and the oceanic subtropical cell. The thermohaline circulation can provide an effective oceanic teleconnection for interhemispheric climate interactions.
Coordinated optical and radar observations of ionospheric pumping for a frequency pass through the second electron gyroharmonic at HAARP
Authors: Kosch M. J. , Pedersen T. , Mishin E. , Oyama S. , Hughes J. , Senior A. , Watkins B. , Bristow B.
Published: June 2007

On 4 February 2005, the High‐frequency Active Auroral Research Program (HAARP) facility was operated in O and X mode while pointing into the magnetic zenith to produce artificial optical emissions in the ionospheric F layer. The pump frequency was set to 2.85 MHz to ensure passing through the second electron gyroharmonic of the decaying ionosphere. Optical recordings at 557.7 and 630 nm were performed simultaneously with the side‐viewing high frequency (HF) and colocated ultra high frequency (UHF) ionospheric radars. No X‐mode effects were found. For O‐mode pumping, when passing from below to above the second gyroharmonic frequency, the optical intensity shows a distinct increase when the plasma frequency passes through the second electron gyroharmonic, while the UHF backscatter changes from persistent to overshoot in character. The optical intensity decreases when pump wave reflection ceases, dropping to zero when upper‐hybrid resonance ceases. The HF radar backscatter increases when the upper‐hybrid resonance frequency passes from below to above the second gyroharmonic frequency. These observations are consistent with the coexistence of the parametric decay and thermal parametric instabilities above the second gyroharmonic. The combined optical and radar data provide evidence that up to three electron‐acceleration mechanisms are acting, sometimes simultaneously, depending on the pump frequency relative to the second gyroharmonic. In addition, we provide the first evidence of lower‐hybrid waves in HF radar centerline data and show that the parametric decay instability producing Langmuir waves can be stimulated in the magnetic zenith at high latitudes despite the pump wave not reaching the nominal frequency‐matching height.
On the origin of near‐radial magnetic fields in the heliosphere: Numerical simulations
Authors: Riley Pete , Gosling J. T.
Published: June 2007

Deviations from the direction of the “Parker spiral” can be found in in situ measurements of the interplanetary magnetic field on essentially all scales. One intriguing subset is the intervals of near‐radial magnetic field, lasting for many hours. Some such intervals are obviously associated with coronal mass ejections, while others appear to be embedded within the ambient solar wind. Most occur on declining speed profiles, such that, when mapped back to the Sun, an entire radial field interval appears to have been launched at approximately the same time. It has been proposed that these events are the result of abrupt, semipermanent speed decreases on these field lines close to the Sun, and that such speed changes might be due to interchange reconnection. In this study, we use a three‐dimensional, time‐dependent magnetohydrodynamic model to assess to what extent this can account for near‐radial magnetic fields observed relatively far out in the heliosphere. We find that sudden speed drops on the trailing portions of high‐speed flows can produce strongly underwound (that is near radial) field lines in the heliosphere, although significantly larger speed gradients are required than are typically observed. Moreover, the simulations also reproduce the decreases in density, temperature, and magnetic field strength that are also commonly observed within these events. The question of what produces the abrupt speed drops remains to be answered.
Statistical properties of paleomagnetic directions in Kerguelen lava flows: Implications for the late Oligocene paleomagnetic field
Authors: Camps P. , Henry B. , Nicolaysen K. , Plenier G.
Published: June 2007

We present the results of a paleomagnetic study of seven new volcanic sections (146 flows) from Kerguelen Archipelago. For two of these sections, preliminary (40Ar/39Ar) ages are reported to aid in the calibration of the paleomagnetic results. The primary contribution of this report, however, is a compilation of these new data with those already published in order to describe statistically the characteristics of the paleomagnetic field as recorded by the Kerguelen flood basalts. In total, 258 paleomagnetic directions sampled at 13 stratigraphic sections through the lava pile are available and span an approximately 5 Ma window: from 25 to 30 Ma. The composite section represents at least 11 polarity zones that are correlated to the reference geomagnetic polarity timescale. Our approach is to investigate the average normal and reversed polarity field directions over this 5 Ma window. We calculated a paleomagnetic pole found to be located atλ= 85.5°N, ϕ = 189.3°E (A95= 2.3°, K = 16.5, N = 233). This pole is in close agreement with the coeval paleomagnetic poles obtained from different worldwide places when analyzed in the Indo‐Atlantic hot spot reference frame. In the statistical analysis we tackle the specific question: Is the secular variation isotropic? This question is directly related to the occurrence of a longitudinal confinement of the virtual geomagnetic poles, which is still a matter of debate among paleomagnetists. By means of statistical tests we show that the paleomagnetic data from Kerguelen agree with an isotropic model for paleosecular variation. Finally, we present adjustments to Camps and Prévot's (1996) statistical model, developed for some Northern Hemisphere latitudes, to the Southern Hemisphere paleomagnetic data from Kerguelen.
Continental thermal isostasy: 1. Methods and sensitivity
Authors: Hasterok Derrick , Chapman David S.
Published: June 2007

Continental elevations result from a combination of compositional and thermal buoyancy and geodynamic forces. Thermal effects are often masked by compositional variations to crustal density and thickness that produce equal or greater relief. We have developed a method by which compositional variations in the crust may be removed, thereby isolating the thermal contribution to elevation. This isostatic correction normalizes the composition of a region to a standard crustal column 39 km thick having an average density of 2850 kg m−3. The crustal thickness and density are computed using one‐dimensional seismic VP models and an empirical velocity to density conversion. Continental regions adjusted for compositional effects show that thermal isostasy can produce nearly 3 km of relief between cold shield platforms and hot rift zones, comparable to observed relief between young (hot) and old (cold) regions of oceanic lithosphere. A Monte Carlo analysis is used to estimate the uncertainties in the isostatic correction. Uncertainties in the seismic parameters, surface heat flow, and regression coefficients of the velocity‐density relationship are all incorporated into the analysis. The Wyoming Craton is used as a case study to demonstrate the effectiveness of the elevation adjustment. Analyses of seismic VP models yield a crustal thickness of 49.5 ± 4.9 km and density of 2945 ± 13 kg m−3. The computed compositional correction to elevation for the Wyoming Craton is −131 ± 180 m, shifting the raw elevation of 1069 m to an adjusted elevation of 938 m.
Improving the quality of satellite altimetry data over continental shelves
Authors: Volkov Denis L. , Larnicol Gilles , Dorandeu Joël
Published: June 2007

Satellite altimetry has proven to be a useful tool to study oceanic processes in the deep ocean. Over continental shelves, however, the aliasing of unresolved high‐frequency signals of tidal and wind‐induced origin is the source of long‐wavelength errors that corrupt altimetry measurements and limit their use in shallow waters. In 2005, SSALTO/DUACS performed a complete reanalysis of altimeter data to accommodate the latest tidal model (GOT2000) and a correction for the aliased high‐frequency signals using a hydrodynamic model MOG2D‐G. This paper examines the quality and the performance of the newly released altimetry data over the northwest European shelf. This region is known for complex tides and for frequent storm surges. The newly corrected maps of sea level anomalies were compared with a previous altimetry product. Residual tidal aliasing was analyzed, and the impact of MOG2D‐G and GOT2000 models was assessed. Altimeter records were compared with tide gauge measurements. This research showed a significant reduction in the contamination of data by high‐frequency aliasing achieved through the use of the aforementioned models. However, aliased shallow‐water tidal constituents pose a serious problem, and it is obvious that future tidal corrections should feature local tides. Nonaliased, physical sea level variability was also studied focusing on interannual, seasonal, and intra‐annual (periods from 20 days to 1 year) modes. The magnitudes and the contributions of each mode to the total variance were estimated. It was demonstrated that the newly corrected data can successfully be used to study the variability of sea level over continental shelves.
On the use of nonmethane hydrocarbons for the determination of age spectra in the lower stratosphere
Authors: Ehhalt D. H. , Rohrer F. , Blake D. R. , Kinnison D. E. , Konopka P.
Published: June 2007

On 9 April 2001, while approaching the West Coast of the North American continent, flight 20 of the NASA TRACE P campaign penetrated deeply into a stratospheric intrusion. From measurements aboard that flight we derive vertical profiles of nonmethane hydrocarbons (NMHCs) and other short‐lived trace gases in the lower stratosphere using Dichlorofluoromethane, CF2Cl2, as the altitude scale. All profiles show an exponential decrease, which permits the description of their vertical distribution by a single parameter, the scale height. These scale heights are shown to be related to the respective lifetimes in a unique fashion. Using the approximation of a 1‐D diffusive model with a constant eddy diffusion coefficient, K, and assuming constant lifetimes, we establish an analytical solution for this relation. By fitting this theoretical expression to the experimental data we can estimate K and thus obtain an approximate age spectrum of the form given by Hall and Plumb (1994). A much better fit to the experimental scale heights is obtained, when we allow the lifetimes to be height‐dependent and calculate the theoretical scale heights numerically from a 1‐D model. An optimization also suggests a constant K, but with a value of 0.46 m2/s, larger than those obtained from the fit of the analytical solution. The obtained age spectra should be valid for transit times not longer than 300 days.
The 11‐year solar cycle in stratospheric ozone: Comparison between Umkehr and SBUVv8 and effects on surface erythemal irradiance
Authors: Tourpali K. , Zerefos C. S. , Balis D. S. , Bais A. F.
Published: June 2007

Ozone profiles derived from ground‐based Umkehr measurements at five stations and from the merged data set of Solar Backscattered Ultra Violet (SBUVv8) satellite observations are used to estimate the seasonal influence of the 11‐year solar signal in the vertical distribution of stratospheric ozone. Both data sets show a strong response (2–3% of the annual mean) in the upper stratosphere, a very small response in the middle tropical stratosphere and a secondary maximum (∼2%) in the tropical lower stratosphere, in accordance to earlier reports. Thus a sequence of high‐low‐high response is seen in the vertical pattern of the solar cycle effect on ozone in the tropics, with its position sensitive to season, as it appears to move across the equator in direction opposite to the location of the maximum solar insolation. Results from Umkehr and satellite observations are in good agreement at levels up to 35 km, while discrepancies (of up to 2%) found at higher levels (around 40 km) are largest in summer. Finally, the estimated erythemal irradiance response to the 11‐year solar cycle, calculated for the observed ozone change during a solar cycle (minimum to maximum), showed an overall decrease in the irradiance at the surface which is maximum (−2% of annual mean) over the tropics.
Simultaneous observation of noctilucent clouds, mesospheric summer echoes, and temperature at a midlatitude station (54°N)
Authors: Gerding M. , Höffner J. , Rauthe M. , Singer W. , Zecha M. , Lübken F.‐J.
Published: June 2007

Between 2003 and 2005, 12.9 h (8 events) of noctilucent clouds (NLC) and 250 h of mesospheric summer echoes (MSE) were observed above Kühlungsborn (54°N, 12°E) by lidar and radar, respectively. The ice‐layer seasons typically last for 50 (NLC) and 70 days (MSE). The observations are compared with simultaneous lidar temperature soundings. Altogether, 79 soundings were performed in the periods 10 May to 8 August of each year. These profiles revealed a minimum mesopause temperature of 145 K at 87 km shortly after summer solstice. The mean temperatures are below the frost point temperature for a period of ∼15 days after summer solstice and in the altitude range ∼85–89 km. Simultaneous observations of temperature, MSE/NLC, and winds by radar and lidar show that ice particles occur primarily during southward winds and during the cold phases of gravity waves and tides, providing temperatures up to ∼20 K lower than the mean. Water vapor saturation profiles are calculated from the temperatures and modeled water vapor concentrations, showing that the ice layers occur at the bottom of the supersaturated region. Only about one fifth of all supersaturation events below 85 km in fact yield NLC above our site. Even saturation ratios of 10–100 lasting for at least 4 h do not necessarily lead to the formation of NLC. We conclude that NLC at midlatitudes are strongly coupled to the advection of preexisting ice particles from northern latitudes. If the ice particles have sublimated prior to the observation, they do not form again even in the cold phases of waves.
Formal and informal decision making on water management at the village level: A case study from the Office du Niger irrigation scheme (Mali)
Authors: Vandersypen Klaartje , Keita Abdoulaye C. T. , Coulibaly Y. , Raes D. , Jamin J.‐Y.
Published: June 2007

Water Users Associations (WUAs) are all too often considered a panacea for improving water management in irrigation schemes. Where grassroots movements are absent, they are usually imposed on farmers by national governments, NGOs, and international donors, without fully considering existing forms of organization. This also happened in the Office du Niger irrigation scheme in Mali, where after a partial irrigation management transfer, WUAs were created to fill the resulting power vacuum. This paper demonstrates that, despite active efforts to organize farmers in WUAs, informal patterns of decision making remain dominant. Given the shortcomings of these informal patterns, WUAs could provide a much‐needed platform for institutionalizing collective action, on the condition that farmers accept them. Therefore WUAs should adopt some crucial characteristics of informal patterns of decision making while avoiding their weaknesses. First, making use of the existing authority of village leadership and the central management can improve the credibility of WUAs. Second, allowing flexibility in procedures and rules can make them more appropriate for dealing with collective action problems that are typically temporary and specific. Last, formalizing the current pattern of conflict management and sanctioning might enhance its sphere of action and tackle the current absence of firm engagement with respect to some informal management decisions. In addition, WUAs should represent and be accountable to all farmers, including those residing outside the village community.
Enhancing volcano‐monitoring capabilities in Ecuador
Authors: Kumagai Hiroyuki , Yepes Hugo , Vaca Mayra , Caceres Vinicio , Naga Takuro , Yokoe Kenichi , Imai Takeharu , Miyakawa Koji , Yamashina Tadashi , Arrais Santiago , Vasconez Freddy , Pinajota Eddy , Cisneros Christian , Ramos Cristina , Paredes Myriam , Gomezjurado Lorena , Garcia‐Aristizabal Alexander , Molina Indira , Ramon Patricio , Segovia Monica , Palacios Pablo , Troncoso Liliana , Alvarado Alexandra , Aguilar Jorge , Pozo Javier , Enriquez Wilson , Mothes Patricia , Hall Minard , Inoue Ikutoshi , Nakano Masaru , Inoue Hiroshi
Published: June 2007

Ecuador has 55 active volcanoes in the northern half of the Ecuadorian Andes. There, consequences of active volcanism include ashfalls, pyroclastic flows (fast moving fluidized material of hot gas, ash, and rock), and lahars (mudflows), which result in serious damage locally and regionally and thus are of major concern to Ecuadorians.

In particular, Tungurahua (elevation, 5023 meters) and Cotopaxi (elevation, 5876 meters) are high‐risk volcanoes. Since 1999, eruption activity at Tungurahua has continued and has produced ashfalls and lahars that damage towns and villages on the flanks of the volcano. More than 20,000 people live on these flanks.
GeoForschungsZentrum Anomaly Magnetic Map (GAMMA): A candidate model for the World Digital Magnetic Anomaly Map
Authors: Hamoudi M. , Thébault E. , Lesur V. , Mandea M.
Published: June 2007

The World Digital Magnetic Anomaly Map (WDMAM) is an ongoing effort toward the mapping of worldwide available aeromagnetic data. It is led by a task force of the International Association for Geomagnetism and Aeronomy (IAGA) and aims at distributing a global map in printed and digital forms. In this paper, we describe in detail our candidate model which has to be evaluated by the IAGA task force together with five other candidate maps. After discussing the quality of the available data, we show a simple but effective method applied to successfully process, reduce, and merge together individual compilations. The near‐surface data are corrected using global field models and further refined with two‐dimensional polynomial corrections. After the upward continuation to 5 km altitude, data are resampled to a 3 minute grid and merged together. We then calculate a spherical harmonic model up to degree 199 and analyze the magnetic spectrum of the global map. This helps us to confirm that wavelengths larger than 400 km are spurious at a global scale in aeromagnetic compilations. Therefore we substitute them using a satellite‐based lithospheric field model (MF5) to degree 100. Finally, our proposed candidate map for WDMAM is presented.
Geoelectrical evidence of bicontinuum transport in groundwater
Authors: Singha Kamini , Day‐Lewis F. D. , Lane J. W.
Published: June 2007

Bicontinuum models and rate‐limited mass transfer (RLMT) explain complex transport behavior (e.g., long tailing and rebound) in heterogeneous geologic media, but experimental verification is problematic because geochemical samples represent the mobile component of the pore space. Here, we present geophysical evidence of RLMT at the field scale during an aquifer‐storage and recovery experiment in a fractured limestone aquifer in Charleston, South Carolina. We observe a hysteretic relation between measurements of pore‐fluid conductivity and bulk electrical conductivity; this hysteresis contradicts advective‐dispersive transport and the standard petrophysical model relating pore‐fluid and bulk conductivity, but can be explained by considering bicontinuum transport models that include first‐order RLMT. Using a simple numerical model, we demonstrate that geoelectrical measurements are sensitive to bicontinuum transport and RLMT parameters, which are otherwise difficult to infer from direct, hydrologic measurements.
A new meteorological record for Cádiz (Spain) 1806–1852: Implications for climatic reconstructions
Authors: Gallego David , Garcia‐Herrera Ricardo , Calvo Natalia , Ribera Pedro
Published: June 2007

A new documentary source of data for wind, atmospheric pressure and air temperature for the city of Cádiz (southern Spain) has been abstracted, analyzed and compared with present‐day data. Wind records cover the period 1806–1852 with three observations per day. Instrumental pressure and temperature cover the period 1825–1852. While the historical pressure series shows average values very close to that found for the period 1971–2000, temperature shows a large asymmetric seasonal warming, with increments in the order of 2°C for the winter months and almost no change for summer. Wind measurements have been transformed into their numerical equivalents and then compared with present‐day values. The analysis shows that the numerical estimation of ancient wind forces observed at Cádiz, while providing a robust climatic signal, has a strong bias to larger values than their instrumental equivalents. Despite the uncertainties involved in the interpretation of early wind series, this effect could be related to the recording of “average wind gusts” rather than average winds as measured by today's anemometers. In consequence, wind climatologies based on historical data, which recently are becoming available to the scientific community, should be used carefully.
Development of an equation of state for electrolyte solutions by combining the statistical associating fluid theory and the mean spherical approximation for the nonprimitive model
Authors: Zhao Honggang , dos Ramos M. Carolina , McCabe Clare
Published: June 2007

A statistical associating fluid theory to model electrolyte fluids that explicitly accounts for solvent molecules by modeling water as a dipolar square-well associating fluid is presented. Specifically the statistical associating fluid theory for potentials of variable range (SAFT-VR) is combined with integral equation theory and the generalized mean spherical approximation using the nonprimitive model to describe the long-range ion-ion, ion-dipole, and dipole-dipole interactions. Isothermal-isobaric ensemble Monte Carlo simulations have been performed in order to test the new theoretical approach. In particular, simulations are performed for different ion concentrations and different ratios of the cation, anion, and solvent segment diameters. Predictions for the thermodynamic properties from the new equation of state are compared with the computer simulation data. Additionally, results from a combination of the SAFT-VR approach with Debye-Hückel theory and the primitive model are also presented and compared to those obtained with the nonprimitive model to illustrate the advantages of the new statistical associating fluid theory for potentials of variable range plus dipole and electrolytes (SAFT−VR+DE) approach. The results show that the proposed equation of state provides a good description of the PVT properties of electrolyte fluids with different sizes of ions and solvent.
Characteristics of transitional multicomponent gaseous and drop-laden mixing layers from direct numerical simulation: Composition effects
Authors: Selle L. C. , Bellan J.
Published: June 2007

Transitional states are obtained by exercising a model of multicomponent-liquid (MC-liquid) drop evaporation in a three-dimensional mixing layer at larger Reynolds numbers, Re, than in a previous study. The gas phase is followed in an Eulerian frame and the multitude of drops is described in a Lagrangian frame. Complete dynamic and thermodynamic coupling between phases is included. The liquid composition, initially specified as a single-Gamma (SG) probability distribution function (PDF) depending on the molar mass, is allowed to evolve into a linear combination of two SGPDFs, called the double-Gamma PDF (DGPDF). The compositions of liquid and vapor emanating from the drops are calculated through four moments of their PDFs, which are drop-specific and location-specific, respectively. The mixing layer is initially excited to promote the double pairing of its four initial spanwise vortices, resulting into an ultimate vortex in which small scales proliferate. Simulations are performed for four liquids of different compositions, and the effects of the initial mass loading and initial free-stream gas temperature are explored. For reference, simulations are also performed for gaseous multicomponent mixing layers for which the effect of Re is investigated in the direct-numerical-simulation–accessible regime. The results encompass examination of the global layer characteristics, flow visualizations, and homogeneous-plane statistics at transition. Comparisons are performed with previous pretransitional MC-liquid simulations and with transitional single-component (SC) liquid-drop-laden mixing layer studies. Contrasting to pretransitional MC flows, the vorticity and drop organization depend on the initial gas temperature, this being due to drop/turbulence coupling. The vapor-composition mean molar mass and standard deviation distributions strongly correlate with the initial liquid-composition PDF. Unlike in pretransitional situations, regions of large composition standard deviation no longer necessarily coincide with those of large mean molar mass. The rotational and composition characteristics are all liquid-specific and the variation among liquids is amplified with increasing free-stream gas temperature. The classical energy cascade is found to be of similar strength, but the smallest scales contain orders of magnitude less energy than SC flows, which is confirmed by the larger viscous dissipation for MC flows. The kinetic energy and dissipation are liquid-specific and the variation among liquids is amplified with increasing free-stream gas temperature. The gas composition, of which the first four moments are calculated, is shown to be close to, but distinct from, a SGPDF. Eulerian and Lagrangian statistics of gas-phase quantities show that the different observation framework may affect the perception of the flow.
Comment on “Free energy of solvation of simple ions: Molecular dynamics study of solvation of Cl− and Na+ in the ice/water interface” [J. Chem. Phys. 123, 034706 (2005)]
Authors: Feibelman Peter J.
Published: June 2007

Salt uptake by ice requires ions to bind strongly near broken H bonds. Because these favorable binding sites form in oppositely charged pairs, a salt’s heat of solution in ice does not converge at low concentration to the sum of ionic heats of solution taken separately. Individual ion solution heats are diminished by the formation energies of free H-bonding defects, amounting to several tenths of an eV each.
Reply to “Comment on ‘Molecular dynamics study of solvation of Cl− and Na+ in the ice/water interface’ [J. Chem. Phys. 123, 034706 (2005)]”
Authors: Smith E. J. , Bryk T. , Haymet A. D. J.
Published: June 2007

Molecular dynamics simulation of ice/water interfaces is a widely used tool for exploration of their structural and dynamical properties on atomic level. However, little is known about the behavior of solute ions at the ice/water interface and in ice in particular.
Continuous breakdown of Purcell’s scallop theorem with inertia
Authors: Lauga Eric
Published: June 2007

Purcell’s scallop theorem defines the type of motions of a solid body—reciprocal motions—which cannot propel the body in a viscous fluid with zero Reynolds number. For example, the flapping of a wing is reciprocal and, as was recently shown, can lead to directed motion only if its frequency Reynolds number, Ref, is above a critical value of order one. Using elementary examples, we show the existence of oscillatory reciprocal motions which are effective for all arbitrarily small values of the frequency Reynolds number and induce net velocities scaling as Refα (α>0). This demonstrates a continuous breakdown of the scallop theorem with inertia.
Magnetization dependence on carrier doping in epitaxial ZnO thin films co-doped with Mn and P
Authors: Ivill M. , Pearton S. J. , Heo Y. W. , Kelly J. , Hebard A. F. , Norton D. P.
Published: June 2007

The magnetic and transport properties of Mn-doped ZnO thin films co-doped with P are examined. Superconducting quantum interference device magnetometry measurements indicate that the films are ferromagnetic with an inverse correlation between magnetization and electron density as controlled by P doping. In particular, under conditions where the acceptor dopants are activated leading to a decrease in free-electron density, magnetization is enhanced. The result is consistent with hole-mediated ferromagnetism in Mn-doped ZnO, in which bound acceptors mediate the ferromagnetic ordering. Increasing the electron density decreases the acceptor concentration, thus quenching the ferromagnetic exchange. This result is important in understanding ferromagnetism in transition metal doped semiconductors for spintronic devices.
Velocity dependence of friction and Kramers relaxation rates
Authors: Gelin M. F. , Kosov D. S.
Published: June 2007

We study the influence of the velocity dependence of friction on the escape rate of a Brownian particle from the deep potential well (Eb≫kBT, Eb is the barrier height, kB is the Boltzmann constant, and T is the bath temperature). The bath-induced relaxation is treated within the Rayleigh model (a heavy particle of mass M in the bath of light particles of mass m≪M) up to the terms of the order of O(λ4), λ2=m∕M≪1. The term ∼1 is equivalent to the Fokker-Planck dissipative operator, and the term ∼λ2 is responsible for the velocity dependence of friction. As expected, the correction to the Kramers escape rate in the overdamped limit is proportional to λ2 and is small. The corresponding correction in the underdamped limit is proportional to λ2Eb∕(kBT) and is not necessarily small. We thus suggest that the effects due to the velocity-dependent friction may be of considerable importance in determining the rate of escape of an under- and moderately damped Brownian particle from a deep potential well, while they are of minor importance for an overdamped particle.
Chemically sensitive free-volume study of amorphization of Cu60Zr40 induced by cold rolling and folding
Authors: Puff Werner , Rabitsch Herbert , Wilde Gerhard , Dinda Guru P. , Würschum Roland
Published: June 2007

With the aim to contribute to a microscopical understanding of the processes of solid-state amorphization, the chemically sensitive technique of background—reduced Doppler broadening of positron-electron annihilation radiation in combination with positron lifetime spectroscopy and microstructural characterization is applied to a free volume study of the amorphization of Cu60Zr40 induced by consecutive folding and rolling. Starting from the constituent pure metal foils, a nanosale multilayer structure of elemental layers and amorphous interlayers develops in an intermediate state of folding and rolling, where free volumes with a Zr-rich environment occur presumably located in the hetero-interfaces between the various layers or in grain boundaries of the Cu layers. After complete intermixing and amorphization, the local chemical environment of the free volumes reflects the average chemical alloy composition. In contrast to other processes of amorphization, free volumes of the size of few missing atoms occur in the rolling-induced amorphous state. Self-consistent results from three different methods for analyzing the Doppler broadening spectra, i.e., S−W-parameter correlation, multicomponent fit, and the shape of ratio curves, demonstrate the potential of the background-reduced Doppler technique for chemically sensitive characterization of structurally complex materials on an atomic scale.
Electron solvation in water-ammonia mixed clusters: Structure, energetics, and the nature of localization states of the excess electron
Authors: Pratihar Subha , Chandra Amalendu
Published: June 2007

The structure and energetics of water-ammonia mixed clusters with an excess electron, [(H2O)n(NH3)m]− with m=1, n=2–6 and m=2, n=2, and also the corresponding neutral clusters are investigated in detail by means of ab initio quantum chemical calculations. The authors focus on the localization structure of the excess electron with respect to its surface versus interiorlike states, its binding to ammonia versus water molecules, the spatial and orientational arrangement of solvent molecules around the excess electron, the changes of the overall hydrogen-bonded structure of the clusters as compared to those of the neutral ones and associated dipole moment changes, vertical detachment energies of the anionic clusters, and also the vertical attachment energies of the neutral clusters. It is found that the hydrogen-bonded structure of the anionic clusters are very different from those of the neutral clusters unlike the case of water-ammonia dimer anion, and these changes in structural arrangements lead to drastically different dipole moments of the anionic and the neutral clusters. The spatial distribution of the singly occupied molecular orbital holding the excess electron shows only surface states for the smaller clusters. However, for n=5 and 6, both surface and interiorlike binding states are found to exist for the excess electron. For the surface states, the excess electron can be bound to the dangling hydrogens of either an ammonia or a water molecule with different degrees of stability and vertical detachment energies. The interiorlike states, wherever they exist, are found to have a higher vertical detachment energy than any of the surface states of the same cluster. Also, for interiorlike states, the ammonia molecule with its dangling hydrogens is always found to stay on top or on a far side of the charge density of the excess electron without participating in the hydrogen bond network of the cluster; the intermolecular hydrogen bonds are formed by the water molecules only which add to the overall stability of these anionic clusters.
Theoretical investigation of excited and Rydberg states of imidogen radical NH: Potential energy curves, spectroscopic constants, and dipole moment functions
Authors: Owono Owono L. C. , Jaidane N. , Kwato Njock M. G. , Ben Lakhdar Z.
Published: June 2007

A search is conducted for the calculation of potential energy curves (PECs), spectroscopic constants, and dipole moment functions for excited and Rydberg states of imidogen radical NH, with a particular emphasis on the Rydberg states arising from 3s configuration of nitrogen and 2s and 2p configurations of hydrogen. A range of about 11eV above the electronic ground state XΣ−3 atomic separation limit which corresponds to the first eight asymptotes of dissociation is spanned. Computations are carried out at the internally contracted multireference singles plus doubles configuration interaction level of theory, including the Davidson correction to account for quadruple excitations. The Gaussian basis set used has been modified from a standard basis to give a balanced description of valence-Rydberg interactions. States of Σ−1, Π1, Δ1, Σ−3, Π3, Δ3, and Σ−5 symmetries are computed accurately in the range of energy investigated. PECs of the three lowest Π5 states are obtained for the first time. Our spectroscopic constants show good agreement with experimental data in comparison with other theoretical studies reported in the literature. A discussion on the variations of dipole moment functions helps to understand the strong interactions between excited and Rydberg states as well as the avoided crossings. The present study may be of great practical interest for investigations in astrophysical research as well as in laboratory experiments.
Sampling the kinetic pathways of a micelle fusion and fission transition
Authors: Pool René , Bolhuis Peter G.
Published: June 2007

The mechanism and kinetics of micellar breakup and fusion in a dilute solution of a model surfactant are investigated by path sampling techniques. Analysis of the path ensemble gives insight in the mechanism of the transition. For larger, less stable micelles the fission/fusion occurs via a clear neck formation, while for smaller micelles the mechanism is more direct. In addition, path analysis yields an appropriate order parameter to evaluate the fusion and fission rate constants using stochastic transition interface sampling. For the small, stable micelle (50 surfactants) the computed fission rate constant is a factor of 10 lower than the fusion rate constant. The procedure opens the way for accurate calculation of free energy and kinetics for, e.g., membrane fusion, and wormlike micelle endcap formation.
Use of nuclear stiffness in search for a maximum hardness principle and for the softest states along the chemical reaction path: A new formula for the energy third derivative γ
Authors: Ordon Piotr , Tachibana Akitomo
Published: June 2007

Nuclear stiffness, expressed as a hardness derivative, appears to be a good measure of the slope of global hardness. The authors analyze molecular states for which hardness has a maximum value. Maximum hardness principle (MHP) has been discussed. At the ground state hardness function does not obtain a maximum value versus spatial coordinates within a constant number of electrons (N), but is so within constant chemical potential (μ) constraint. The authors apply this feature to evaluate an energy third derivative (γ). MHP has been analyzed via symmetry considerations of nuclear stiffness and nuclear reactivity. Nuclear stiffness has been also applied to study the hardness profile for a chemical reaction. In this case, the authors seek molecular states for which hardness is at a minimum. They have examined systems for which they have recently obtained regional chemical potentials [P. Ordon and A. Tachibana, J. Mol. Model. 11, 312 (2005); J. Chem. Sci. 117, 583 (2005)]. The transition state is found not to be the softest along the chemical reaction path. Nuclear stiffness reflects well the softest conformation of a molecule, which has been found independently along the intrinsic reaction coordinate profile. Electronic energy-density [A. Tachibana, J. Mol. Mod. 11, 301 (2005)] has been used to visualize the reactivity difference between the softest state and the transition state.
Atomic and electronic structures of neutral and charged Pbn clusters (n=2–15): Theoretical investigation based on density functional theory
Authors: Rajesh Chinagandham , Majumder Chiranjib
Published: June 2007

The geometric and electronic structures of the Pbn+ clusters (n=2–15) have been investigated and compared with neutral clusters. The search for several low-lying isomers was carried out under the framework of the density functional theory formalism using the generalized gradient approximation for the exchange correlation energy. The wave functions were expanded using a plane wave basis set and the electron-ion interactions have been described by the projector augmented wave method. The ground state geometries of the singly positively charged Pbn+ clusters showed compact growth pattern as those observed for neutrals with small local distortions. Based on the total energy of the lowest energy isomers, a systematic analysis was carried out to obtain the physicochemical properties, viz., binding energy, second order difference in energy, and fragmentation behavior. It is found that n=4, 7, 10, and 13 clusters are more stable than their neighbors, reflecting good agreement with experimental observation. The chemical stability of these clusters was analyzed by evaluating their energy gap between the highest occupied and lowest unoccupied molecular orbitals and adiabatic ionization potentials. The results revealed that, although Pb13 showed higher stability from the total energy analysis, its energy gap and ionization potential do not follow the trend. Albeit of higher stability in terms of binding energy, the lower ionization potential of Pb13 is interesting which has been explained based on its electronic structure through the density of states and electron shell filling model of spherical clusters.
Lifting of Ir{100} reconstruction by CO adsorption: An ab initio study
Authors: Ghosh Prasenjit , Narasimhan Shobhana , Jenkins Stephen J. , King David A.
Published: June 2007

The adsorption of CO on unreconstructed and reconstructed Ir{100} has been studied, using a combination of density functional theory and thermodynamics, to determine the relative stability of the two phases as a function of CO coverage, temperature, and pressure. We obtain good agreement with experimental data. At zero temperature, the (5×1) reconstruction becomes less stable than the unreconstructed (1×1) surface when the CO coverage exceeds a critical value of 0.09 ML. The interaction between CO molecules is found to be weakly repulsive on the reconstructed surface but attractive on the unreconstructed, explaining the experimental observation of high CO coverage on growing (1×1) islands. At all temperatures and pressures, we find only two possible stable states: 0.05 ML CO c(2×2) overlayer on the (1×1) substrate and the clean (5×1) reconstructed surface.
Microdevice for measuring friction and adhesion properties of sidewall contact interfaces of microelectromechanical systems
Authors: Timpe S. J. , Komvopoulos K.
Published: June 2007

A microdevice was specifically designed to characterize the static and dynamic friction and adhesion characteristics of sidewall contact interfaces of microelectromechanical systems (MEMS). The microdevice was fabricated by surface micromachining and tested under conditions that accurately mimic those of typical MEMS contacts. The developed experimental scheme enables the direct measurement of the critical normal force at the instant of surface separation and the friction force at the onset of sliding. Additional capabilities include evaluation of the dynamic friction behavior, measurement of the electrical characteristics across the contact interface, and characterization of the tribological response under impact contact loading. The microdevice can operate over a wide range of normal forces and different environmental conditions. Because the design is independent of process environment, the microdevice can be used to study the effects of different surface treatments and variations in fabrication process steps on the tribological properties of MEMS contact interfaces. Characteristic results of static and dynamic friction behaviors, electrical contact resistance, and response to dynamic impact loading illustrate the experimental capabilities and versatility of the designed microdevice.
Noncatalytic dissociation of MgO by laser pulses towards sustainable energy cycle
Authors: Yabe T. , Mohamed M. S. , Uchida S. , Baasandash C. , Sato Y. , Tsuji M. , Mori Y.
Published: June 2007

We succeeded in dissociating MgO using laser pulses without a reducing agent. The energy efficiency from laser to magnesium reaction energy exceeded 42.5%. Although 1kW CO2 cw laser and Nd-YAG pulse laser are used in this experiment, the laser can be pumped by natural resources such as solar light or wind power. Thus natural resources are stored in the form of magnesium, which can be used through the reaction with water whenever we need the energy, and thus a renewable energy system will be established. This paper reports the preliminary experiments of MgO reduction toward a sustainable energy cycle.