bluuebunny/crossref_metadata_2025 huggingface dataset:
Self‐bonding in an amorphous polymer below the glass transition: A T‐peel test investigation
Authors: Boiko Yuri M. , Bach Anders , Lyngaae‐Jørgensen Jørgen
Published: April 2004

Films of amorphous polystyrene (PS) with a weight‐average molecular weight (Mw) of 225 × 103 g/mol were bonded in a T‐peel test geometry, and the fracture energy (G) of a PS/PS interface was measured at the ambient temperature as a function of the healing time (th) and healing temperature (Th). G was found to develop with (th)1/2 at Th = Tg‐bulk − 33 °C (where Tg‐bulk is the glass‐transition temperature of the bulk sample), and log G was found to develop with 1/Th at Tg‐bulk − 43 °C ≤ Th ≤ Tg‐bulk − 23 °C. The smallest measured value of G = 1.4 J/m2 was at least one order of magnitude larger than the work of adhesion required to reversibly separate the PS surfaces. These three observations indicated that the development of G at the PS/PS interface in the temperature range investigated (<Tg‐bulk) was controlled by the diffusion of chain segments feasible above the glass‐transition temperature of the interfacial layer, in agreement with our previous findings for fracture stress development at several polymer/polymer interfaces well below Tg‐bulk. Close values of G = 8–9 J/m2 were measured for the symmetric interfaces of polydisperse PS [Mw = 225 × 103, weight‐average molecular weight/number‐average molecular weight (Mw/Mn) = 3] and monodisperse PS (Mw = 200 × 103, Mw/Mn = 1.04) after healing at Th = Tg‐bulk − 33 °C for 24 h. This implies that the self‐bonding of high‐molecular‐weight PS at such relatively low temperatures is not governed by polydispersity. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1861–1867, 2004
Analysis of electronic delocalization in buckminsterfullerene (C60)
Authors: Poater J. , Duran M. , Solà M.
Published: April 2004

Buckminsterfullerene (C60) presents an extensive conjugation that, in principle, should lead to a high delocalization of its electrons, together with a notorious aromaticity. However, previous studies have shown that C60behaves chemically and physically as an electron‐deficient alkene rather than an electron‐rich aromatic system. In the current work, we try to better elucidate the extension of electron delocalization in C60by computing the delocalization index for a given carbon atom of C60. We show that, in C60, local electron delocalization per carbon atom is lower than that in benzene and naphthalene. However, C60presents a global electron delocalization per carbon atom that is almost the same as that of clearly aromatic systems such as benzene or naphthalene. This is attributed to the fact that the electron charge of each atom in C60can be shared with a larger number of atoms. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004
Geometry optimization and transition state search in enzymes: Different options in the microiterative method
Authors: Prat‐Resina Xavier , Bofill Josep Maria , González‐Lafont Àngels , Lluch José M.
Published: April 2004

In the current article we present a systematic analysis of the different options in the so‐called “microiterative method” used to locate minima and transition‐state (TS) structures of big systems on quantum mechanics/molecular mechanics potential energy surfaces. The method splits the system in two parts: a core zone in which accurate second‐order search is carried out, and an environment that is kept minimized with a cheap first‐order algorithm. The different options studied here are: the alternating frequency between the environment minimization and the TS search in the core, the number of atoms included in each zone, and two alternative ways to reduce the computational cost in the calculation of core–environment interactions. The tests have been done at two different steps of the enzymatic mechanism of mandelate racemase: a proton transfer and a carbon configuration inversion step. The two selected TS structures differ in the number of atoms involved in their associated transition vectors; the proton transfer TS is an example of a local motion, whereas the carbon configuration inversion TS corresponds to a more global movement of several groups and residues, including an important number of atoms. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004
The first solvation shell of aluminum (III) and magnesium (II) cations in a protein model environment
Authors: Mercero Jose M. , Matxain Jon M. , Rezabal Elixabete , Lopez Xabier , Ugalde Jesus M.
Published: April 2004

Aluminum (III) cation interactions with relevant bioligands have been studied in a protein‐model environment (in the gas and aqueous phases) using density functional theory methods. The protein model consists of the metal cation bound to a chosen bioligand and water molecules interacting with the cation to complete its first coordination shell. The ligands are the functional groups of the amino acid side chains. Binding energies and formation energies are calculated in both phases. Analogous magnesium (II) complexes are also calculated, and the possibility of magnesium/ aluminum exchange is estimated. The effect of the dielectric media is also discussed. This aims to model different regions inside a protein (solvent accessible and buried regions). It is found that the effect of the dielectric is very important, for example, for the negatively charged ligand complexes, magnesium/aluminum exchange is possible only in low dielectric environments such as partially buried protein regions. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004
VisionMark: A media linking method creating synergy of information transmission media and the Internet
Authors: Miyaoku Kento , Shigeyoshi Hiroki , Akutsu Akihito , Tonomura Yoshinobu
Published: April 2004

“VisionMark” is a media linking method for accessing Web content related to information transmission media such as broadcasts or publications. It displays objects called “VisionMarks” that indicate Web content linked to the information transmission medium being viewed by the user. Users can use VisionMarks to refer to the linked Web content, and can store or send VisionMarks to other users. This allows users to easily make the best use of Web‐content‐linked information transmission media. We show how to implement an Internet application linking information transmission media with Web content by using VisionMarks. © 2004 Wiley Periodicals, Inc. Syst Comp Jpn, 35(6): 20–30, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.10606
Smoothing a discrete hazard function for the number of patients colonized with Methicillin‐resistantStaphylococcus Aureusin an intensive care unit
Authors: Ismail Noor Azina , Pettitt A. N.
Published: April 2004

A new method for estimating the time to colonization of Methicillin‐resistantStaphylococcus Aureus(MRSA) patients is developed in this paper. The time to colonization of MRSA is modelled using a Bayesian smoothing approach for the hazard function. There are two prior models discussed in this paper: the first difference prior and the second difference prior. The second difference prior model gives smoother estimates of the hazard functions and, when applied to data from an intensive care unit (ICU), clearly shows increasing hazard up to day 13, then a decreasing hazard. The results clearly demonstrate that the hazard is not constant and provide a useful quantification of the effect of length of stay on the risk of MRSA colonization which provides useful insight. Copyright © 2004 John Wiley & Sons, Ltd.
Analysis of clinical data with breached blindness
Authors: Chow Shein‐Chung , Shao Jun
Published: April 2004

In clinical trials, blinding is usually employed to prevent bias that may be introduced due to the knowledge of the identity of the treatment codes. This bias could alter the conclusion of statistical inference on the treatment effect. The purpose of this article is to propose a method for analysing clinical data with breached blindness. The example regarding the study of the effectiveness of an appetite suppressant in weight loss in obese woman as described in Brownell and Stunkard (Am. J. Psychiatry 1982; 139:1487–1489) is used to illustrate the application of the proposed methods. Copyright © 2004 John Wiley & Sons, Ltd.
Allowing for imprecision of the intracluster correlation coefficient in the design of cluster randomized trials
Authors: Turner Rebecca M. , Toby Prevost A. , Thompson Simon G.
Published: April 2004

The sample size required for a cluster randomized trial depends on the magnitude of the intracluster correlation coefficient (ICC). The usual sample size calculation makes no allowance for the fact that the ICC is not known precisely in advance. We develop methods which allow for the uncertainty in a previously observed ICC, using a variety of distributional assumptions. Distributions for the power are derived, reflecting this uncertainty. Further, the observed ICC in a future study will not equal its true value, and we consider the impact of this on power. We implement calculations within a Bayesian simulation approach, and provide one simplification that can be performed using simple simulation within spreadsheet software. In our examples, recognizing the uncertainty in a previous ICC estimate decreases expected power, especially when the power calculated naively from the ICC estimate is high. To protect against the possibility of low power, sample sizes may need to be very substantially increased. Recognizing the variability in the future observed ICC has little effect if prior uncertainty has already been taken into account. We show how our method can be extended to the case in which multiple prior ICC estimates are available. The methods presented in this paper can be used by applied researchers to protect against loss of power, or to choose a design which reduces the impact of uncertainty in the ICC. Copyright © 2004 John Wiley & Sons, Ltd.
Bayesian inference for randomized clinical trials with treatment failures
Authors: Shaffer Michele L. , Chinchilli Vernon M.
Published: April 2004

During the course of a clinical trial, subjects may experience treatment failure. For ethical reasons, it is necessary to administer emergency or rescue medications for such subjects. However, the rescue medications may bias the set of response measurements. This bias is of particular concern if a subject has been randomized to the control group, and the rescue medications improve the subject's condition. The standard approach to analysing data from a clinical trial is to perform an intent‐to‐treat (ITT) analysis, wherein the data are analysed according to treatment randomization. Supplementary analyses may be performed in addition to the ITT analysis to account for the effect of treatment failures and rescue medications. A Bayesian, counterfactual approach, which uses the data augmentation (DA) algorithm, is proposed for supplemental analysis. A simulation study is conducted to compare the operating characteristics of this procedure with a likelihood‐based, counterfactual approach based on the EM algorithm. An example from the Asthma Clinical Research Network (ACRN) is used to illustrate the Bayesian procedure. Copyright © 2004 John Wiley & Sons, Ltd.
Bayesian estimation of cost‐effectiveness from censored data
Authors: Heitjan Daniel F. , Kim Clara Yuri , Li Huiling
Published: April 2004

We describe a Bayesian methodology for estimating the cost‐effectiveness of a new treatment compared to a standard in a clinical trial, when censoring of survival, the effectiveness variable, induces censoring of total cost. The statistical model assumes that survival follows a Weibull distribution and that total health care cost follows a gamma distribution whose mean has a linear regression on survival time. We summarize the posterior distributions of key parameters by importance sampling. We illustrate the method with an analysis of data from a randomized clinical trial of a treatment for cardiovascular disease. Copyright © 2004 John Wiley & Sons, Ltd.
Parametric modelling of cost data in medical studies
Authors: Nixon R. M. , Thompson S. G.
Published: April 2004

The cost of medical resources used is often recorded for each patient in clinical studies in order to inform decision‐making. Although cost data are generally skewed to the right, interest is in making inferences about the population mean cost. Common methods for non‐normal data, such as data transformation, assuming asymptotic normality of the sample mean or non‐parametric bootstrapping, are not ideal. This paper describes possible parametric models for analysing cost data.

Four example data sets are considered, which have different sample sizes and degrees of skewness. Normal, gamma, log‐normal, and log‐logistic distributions are fitted, together with three‐parameter versions of the latter three distributions. Maximum likelihood estimates of the population mean are found; confidence intervals are derived by a parametric BCabootstrap and checked by MCMC methods. Differences between model fits and inferences are explored.

Skewed parametric distributions fit cost data better than the normal distribution, and should in principle be preferred for estimating the population mean cost. However for some data sets, we find that models that fit badly can give similar inferences to those that fit well. Conversely, particularly when sample sizes are not large, different parametric models that fit the data equally well can lead to substantially different inferences. We conclude that inferences are sensitive to choice of statistical model, which itself can remain uncertain unless there is enough data to model the tail of the distribution accurately. Investigating the sensitivity of conclusions to choice of model should thus be an essential component of analysing cost data in practice. Copyright © 2004 John Wiley & Sons, Ltd.
Post‐awakening changes in salivary cortisol in veterans with and without PTSD
Authors: Lauc Gordan , Zvonar Kristina , Vuks̆ić‐Mihaljević Z̆eljka , Flögel Mirna
Published: April 2004

Cortisol shows a well‐documented circadian rhythm with peak levels observed shortly after awakening and steadily decreasing values thereafter. This is a relatively robust diurnal pattern that is displayed by most non‐ill individuals, but recently it has been shown that in the general population some 10–15 per cent of individuals have ‘flat’ circadian cycles of cortisol. We have analyzed post‐awakening variations in levels of salivary cortisol in veterans without post‐traumatic stress disorder (PTSD), veterans with diagnosed PTSD that were not hospitalized, and hospitalized veterans with PTSD. ‘Flat’ circadian cycles of salivary cortisol were observed in 6 per cent of veterans without PTSD, 29 per cent of non‐hospitalized veterans with PTSD, and 42 per cent of veterans hospitalized for PTSD. Copyright © 2004 John Wiley & Sons, Ltd.
Covalent and noncovalent chemical modifications of arginine residues decrease dopamine transporter activity
Authors: Volz Trent J. , Kim M. , Schenk James O.
Published: April 2004

Rotating disk electrode voltammetry was used to measure dopamine (DA) transport in rat striatum and in human embryonic kidney cells expressing the rat dopamine transporter (DAT). The goals of this study were to determine 1) if arginine (Arg) selective agents could alter DA transport, and 2) if DA analogs and DAT inhibitors could attenuate the effects of these agents on the DAT. Phenylglyoxal (PG), Hill coefficient 2.5, and other Arg selective agents decreased DA transport velocities. DA, Hill coefficient 1.0, and its analogs 3‐hydroxyphenethylamine and 4‐hydroxyphenethylamine attenuated the effects of PG on the DAT while phenethylamine did not. The tropane‐based DAT inhibitors cocaine, WIN 35065‐2, and WIN 35428 also attenuated the effects of PG. Benztropine, GBR 12935, and GBR 12909 did not. Thus, Arg residues are important for DAT activity and the results suggest that DA and cocaine both interact with Arg residues. Structure–activity studies suggest that DA interacts with Arg through its catechol hydroxyl groups and cocaine through the ester linkage attached to carbon 2 of the tropane ring. The results that 1) DA and cocaine may interact with the same functionally important Arg residue at the DAT, and 2) some members of the tropane and 1,4‐dialkylpiperazine classes of DAT inhibitors may interact differently with DAT‐derived Arg residue(s) furthers the notion that DAT activity sparing antagonists of cocaine can be designed. Synapse 52:272–282, 2004. © 2004 Wiley‐Liss, Inc.
Novel peripheral benzodiazepine receptor ligand [11C]DAA1106 for PET: An imaging tool for glial cells in the brain
Authors: Maeda Jun , Suhara Tetsuya , Zhang Ming‐Rong , Okauchi Takashi , Yasuno Fumihiko , Ikoma Yoko , Inaji Motoki , Nagai Yuji , Takano Akihiro , Obayashi Shigeru , Suzuki Kazutoshi
Published: April 2004

Peripheral benzodiazepine receptor (PBR) is expressed in most organs and its expression is reported to be increased in activated microglia in the brain. [11C]PK11195 has been widely used for the in vivo imaging of PBRs, but its signal in the brain was not high enough for stable quantitative analysis. We synthesized a novel positron emission tomography (PET) ligand, [11C]DAA1106, for PBR and investigated its in vivo properties in rat and monkey brain. High uptake of [11C]DAA1106 was observed in the olfactory bulb and choroid plexus area, followed by the pons/medulla and cerebellum by in vivo autoradiography of rat brain, correlating with the binding in vitro. [11C]DAA1106 binding was increased in the dorsal hippocampus with neural destruction, suggesting glial reaction. [11C]DAA1106 binding was both inhibited and displaced by 1.0 mg/kg of DAA1106 and 5 mg/kg of PK11195 by 80% and 70%, respectively. Specific binding was estimated as 80% of total binding. [11C]DAA1106 binding was four times higher compared to the binding of [11C]PK11195 in the monkey occipital cortex. These results indicated that [11C]DAA1106 might be a good ligand for in vivo imaging of PBR. Synapse 52:283–291, 2004. © 2004 Wiley‐Liss, Inc.
Influence of tropical Pacific El Niño on the SST of the Southern Ocean Through Atmospheric Bridge
Authors: Li Z. X.
Published: April 2004

El Niño is a major interannual climate signal resulting from complex ocean‐atmosphere interactions in the Tropical Pacific. Its impact on the SST (Sea Surface Temperature) of the Southern Ocean through an atmospheric bridge are investigated with an atmospheric general circulation model coupled to a slab mixed‐layer ocean. Simulated results suggest that SST changes in the mid‐ and high‐latitude oceans and the Tropical Indian Ocean can be explained by modifications of heat‐flux exchange at the air‐sea interface. For the Tropical Atlantic, however, the discrepancy is large, indicating that the oceans dynamics are not negligible.
The simultaneous effect of NAO and SO on the monsoon activity over India
Authors: Kakade S. B. , Dugam S. S.
Published: April 2004

North Atlantic Oscillation (NAO) and Southern Oscillation (SO) are two large‐scale atmospheric oscillations in northern and southern hemisphere respectively. These two oscillations are known to affect Indian summer monsoon (June–September) rainfall (ISMR). It is logical to expect the combined effect of these two oscillations on monsoon rainfall over Indian subcontinent. In the present paper this combined effect of NAO and SO on Indian summer monsoon rainfall is studied. North Atlantic Oscillation (NAO) index in the month of April is showing an inverse and statistically significant relationship with Indian summer monsoon rainfall (ISMR). Southern oscillation (SO) indices from April through December show direct association with ISMR. The present study deals with the simultaneous effect of NAO and SO on monsoon rainfall over India. The effective strength index is newly defined to quantify the simultaneous effect of NAO and SO and its relationship with ISMR is investigated. For this purpose 40 years data (1951–90) has been used.
Constraining ice dynamics at Dome C, Antarctica, using remotely sensed measurements
Authors: Legresy Benoit , Rignot Eric , Tabacco Ignazio E.
Published: April 2004

A first time description is given of the ice flow at Dome C, Antarctica, around the EPICA drilling site. We used satellite radar altimetry to obtain the precise ice surface topography, airborne radio echo sounding to obtain the ice thickness and satellite SAR interferometry to derive one component of the surface velocity field. The balance flux around the Dome C area is then accurately mapped and comparisons made between driving stress, surface and balance velocity to help us describe the ice flow in the region. As a by‐product of the study, we also recover anomalies in the ice flow conditions in sub‐glacial lake locations. These effects result from localy invalid shallow‐ice approximation. The results of this study form the basis for future investigations of the ice flow conditions at Dome C in relation to ice core interpretation.
Diurnal Kelvin wave in the atmosphere of Mars: Towards an understanding of ’stationary’ density structures observed by the MGS accelerometer
Authors: Forbes Jeffrey M. , Hagan Maura E.
Published: April 2004

Mars Global Surveyor (MGS) accelerometer measurements near 125 km [Keating et al., 1998] reveal longitudinal density structures comprised of zonal wavenumbers s=1 and s=2 which are interpreted as stationary waves. An alternative interpretation is that these structures may be nonmigrating tides which appear as quasi‐stationary features due to restricted sampling in local time, and which owe their existence to Mars' topography. One of these oscillations, the diurnal Kelvin wave, is investigated here. It gives rise to density perturbations similar to the measurements. Other nonmigrating tides may also make important contributions.
High‐pressure phase transformation in CaMgSi2O6 and implications for origin of ultra‐deep diamond inclusions
Authors: Irifune T. , Miyashita M. , Inoue T. , Ando J. , Funakoshi K. , Utsumi W.
Published: April 2004

The decomposition of diopside to CaSiO3 cubic and MgSiO3 orthorhombic perovskites was demonstrated by in situ X‐ray diffraction measurements under simultaneous high pressure and high temperature conditions, using a combination of synchrotron radiation and a multianvil apparatus at SPring‐8. Quench experiments also confirmed the decomposition of diopside in a wide temperature range of 1000–1900°C and at pressures 23–27GPa. These results strongly support the idea that some mineral inclusions with pyroxene stoichiometry discovered in natural diamonds may have been originated from the lower mantle. Moreover, observed temperature dependence of MgSiO3 content dissolved in CaSiO3 perovskite suggests that some of the inclusions were formed at relatively low temperatures (<1200°C) in the deep mantle, presumably related to slab subductions.
Trichloroethylene and tetrachloroethylene in Atlantic waters
Authors: Moore Robert M.
Published: April 2004

Measurements of trichloroethylene (C2HCl3) and tetrachloroethylene (C2Cl4) in waters of the North Atlantic are reported. They show that at the times of sampling both gases are supersaturated in the surface ocean and that there are therefore fluxes of each into the atmosphere. The water column profiles are unusual in showing increasing concentrations with depth. It is proposed that both gases may be supplied to the ocean from the atmosphere in winter, when their atmospheric mixing ratios are higher due to diminished loss rates resulting from lower concentrations of the hydroxyl radical. This hypothesis is consistent with literature reports of ocean supersaturations of trichloroethylene and tetrachloroethylene but does not require any natural source. In the western Atlantic several profiles of trichloroethylene have, superimposed on the general increase in concentration with depth, maxima lying just beneath the mixed layer which may be indicative of a biological source.
Nonuniform response of the major surface currents in the Nordic Seas to insolation forcing: Implications for the Holocene climate variability
Authors: Andersen C. , Koç N. , Jennings A. , Andrews J. T.
Published: April 2004

High‐resolution sediment cores from the Vøring Plateau, the North Iceland shelf, and the East Greenland shelf have been studied to investigate the stability of major surface currents in the Nordic Seas during the Holocene. Results from diatom assemblages and reconstructed sea‐surface temperatures (SSTs) indicate a division of the Holocene into three periods: the Holocene Climate Optimum (9500–6500 calendar (cal) years BP), the Holocene Transition Period (6500–3000 cal years BP) and the Cool Late Holocene Period (3000–0 cal years BP). The overall climate development is in step with the decreasing insolation on the Northern Hemisphere, but regional differences occur regarding both timing and magnitude of SST changes. Sites under the direct influence of the Norwegian Atlantic Current and the Irminger Current indicate SST cooling of 4–5°C from early Holocene to present, compared to 2°C recorded under the East Greenland Current. Superimposed on the general Holocene cooling trend, there is a high‐frequency SST variability, which is in the order of 1–1.5°C for the Vøring Plateau and the East Greenland shelf and 2.5–3°C on the North Iceland shelf.
Switching perspectives: Do mineral fluxes determine particulate organic carbon fluxes or vice versa?
Authors: Passow Uta
Published: April 2004

It has recently been postulated that mineral material like biogenic silica frustules or carbonate shells as well as lithogenic dust act as ballast material determining particulate organic carbon (POC) fluxes below 2000 m in the ocean. However, correlations do not identify cause and effect, and in this commentary it is proposed that on the contrary, POC fluxes determine fluxes of this mineral material. I suggest that during sedimentation marine snow originating from biological activity in the surface layer collect small, non‐sinking mineral particles of biogenic and lithogenic origin until its carrying capacity is reached.
Sensible heat flux estimated from one‐level air temperature near the land surface
Authors: Fitzmaurice Jean , Wang Jingfeng , Bras Rafael L.
Published: April 2004

A new method for estimating sensible heat flux from one‐level measurements of air temperature in the atmospheric surface layer is presented. An analytical solution of the heat transfer equation with a variable diffusion coefficient has been derived to express the vertical gradient of air temperature in terms of the time series of air temperature at a single height level. The case study indicates that the new method is able to give reasonable estimates of sensible heat flux using near surface air temperature measurements.
Determination of the altitudinal peak of Cosmic Noise Absorption using a vertical parallax technique
Authors: Terkildsen M. B. , Fraser B. J. , Yamagishi H.
Published: April 2004

The riometry technique is limited by its inability to directly determine the altitude of the principal ionospheric absorption layer during periods of enhanced Cosmic Noise Absorption (CNA). We describe here a technique based on the simple vertical parallax principle, enabling direct measurements of this altitude. The technique utilizes the overlapping beams of two closely spaced imaging riometers in Antarctica. Descriptive statistics on peak absorption heights are presented. The altitude determination of a D‐region absorption event and an event that occurred in the F‐region near 200 km altitude are presented in more detail. The identification of an F‐region event using the parallax technique confirms earlier findings that radiowave absorption in the F‐region is a potentially significant contributor to CNA. This technique enables a simple and repeatable ground‐based measurement of the altitude of the CNA layer peak, and can be extended to estimating precipitation spectra based on peak absorption heights.
Real‐time updating of the Simplified Ionospheric Regional Model for operational applications
Authors: Zolesi Bruno , Belehaki Anna , Tsagouri Ioanna , Cander Ljiljana R.
Published: April 2004

A method for mapping of ionospheric conditions over Europe, suitable to be used in real time for operational applications, is described in this paper. The method is based on the Simplified Ionospheric Regional Model (SIRM), a regional model of the standard vertical incidence monthly median ionospheric characteristics that has been updated with real‐time (automatic scaled) ionospheric observations to produce nowcasting maps over Europe. As substantial fluctuations from a monthly median regional ionospheric description occur on day‐to‐day basis, the SIRM results oversimplified a number of the ionospheric phenomena of real significance for radio communications applications. Therefore a rapid conversion of real‐time data from four European digisondes (Digital Portable Sounders) to the driving parameters of the Simplified Ionospheric Regional Model is introduced as the real‐time SIRM updating (SIRMUP). In this approach, values of the ionospheric characteristics from first‐guess model parameters at measurement points are combined with real‐time measurements. To assess the qualitative improvements achieved with the real‐time SIRM update method, observations of foF2 parameter with SIRMUP predictions were compared for various ionospheric conditions. The simulation shows that the SIRMUP prediction results are much improved comparing to SIRM predictions, especially during large‐scale ionospheric disturbances, as well as during quiet conditions, while there was a marginal improvement during localized ionospheric disturbances. In general, the results clearly demonstrate that the proposed procedure of updating SIRM with automatic scaling ionospheric parameters from the four European digisondes has the potential to be used in real time for nowcasting the standard ionospheric characteristics over Europe for operational applications.
Streamline‐based dual‐porosity simulation of reactive transport and flow in fractured reservoirs
Authors: Di Donato Ginevra , Blunt Martin J.
Published: April 2004

We present a streamline‐based formulation to model two processes: transport of a tracer undergoing rate‐limited sorption and two‐phase (water/oil or air/water) transport in fractured systems, using a dual‐porosity approach. We show that these two processes can be simulated using mathematically equivalent formulations. In both cases the system conceptually has two components: a flowing fraction connected to stagnant regions with transfer between the two domains. Streamlines capture movement through the flowing fraction. Fluid transfer between flowing and stagnant regions enters as a source/sink term in the one‐dimensional transport equations along a streamline. To model flow and transport in fractured systems, we develop a new formulation for the transfer function that matches experimental imbibition data. Then we illustrate the streamline approach with synthetic reservoir problems. We use a finely gridded (over one million grid blocks) three‐dimensional domain with a highly heterogeneous permeability field to study both fracture flow and tracer transport. We find breakthrough curves that are consistent with anomalous transport described by an exponent that characterizes the longtime tail of the transit time distribution. For fracture flow we demonstrate that the speed of fluid advance in the fractures is controlled by the imbibition rate. The run times for the simulations scale approximately linearly with system size, making the method appropriate for the simulation of large numerical models.
Shear‐wave splitting observations in the lower Great Lakes region: Evidence for regional anisotropic domains and keel‐modified asthenospheric flow
Authors: Eaton David , Frederiksen Andrew , Miong Soo‐Kyung
Published: April 2004

Fast‐axis directions obtained from shear‐wave splitting analysis of core‐refracted shear waves reveal several distinct anisotropic domains in the lower Great Lakes region. We used data from 27 broadband seismograph stations extending across a low‐velocity anomaly in the lithospheric mantle. Observed splitting times vary from 0.4 to 1.4 s, with a mean of 0.7 s. A subset of the splitting vectors across a failed rift are oriented parallel to one arm of the rift zone; most others show a coherent pattern of fast directions close to the direction of plate motion, but oblique to surface tectonic belts. Within the area of the low‐velocity anomaly, our observations are most simply explained by single‐layer anisotropy induced by asthenospheric flow. Spatial variability in the direction and magnitude of splitting are consistent with a flow regime influenced by basal topology of the lithospheric keel.
Nonlinear temperature response of lake ice breakup
Authors: Weyhenmeyer Gesa A. , Meili Markus , Livingstone David M.
Published: April 2004

A uniquely comprehensive set of four decades of ice breakup data from 196 Swedish lakes covering 13° of latitude (55.7°N to 68.4°N) shows the relationship between the timing of lake ice breakup and air temperature to be an arc cosine function. The nonlinearity inherent in this relationship results in marked differences in the response of the timing of lake ice breakup to changes in air temperature between colder and warmer geographical regions, and between colder and warmer time periods. The spatial and temporal patterns are mutually consistent, suggesting that climate change impacts on the timing of lake ice breakup will vary along a temperature gradient. This has potentially important ramifications for the employment of lake ice phenologies as climate indicators and for the future behavior of lacustrine ecosystems.
Rocket measurements of high‐altitude spread F irregularities at the magnetic dip equator
Authors: Jahn Jörg‐Micha , LaBelle James
Published: April 2004

We present the first rocket measurements of equatorial spread F irregularities at altitudes significantly above 600 km, in what is believed to be the inertially dominated regime of spread F. On October 14, 1994, at 1955 LT (2255 UT) a Black Brant X rocket instrumented to measure plasma density and electric fields was launched from Alcântara, Brazil (2° 18.75'S, 44°22.3'W, dip angle 1.5° at 300 km altitude), into active topside spread F plumes. On upleg the payload remained continuously in these plumes up to an altitude of 822 km. Power spectra of electron density fluctuations show characteristic dual‐power law behavior with spectral indices of −1.7 at frequencies below 60 Hz and −5 at frequencies above 60 Hz. Shocklike coherent structures characterized the density waveforms. The electric field fluctuations had spectral indices ranging from −3 to −4. We observe no evidence of altitude variation in the spectral indices or in the density fluctuation waveforms. Over the entire altitude range of the observations, 350–822 km, the data remain in agreement with previous measurements of collisional spread F below 600 km.
Decreases in the antisunward flux of interstellar pickup He+ associated with radial interplanetary magnetic field
Authors: Möbius E. , Rucinski D. , Lee M. A. , Isenberg P. A.
Published: April 2004

Observations of interstellar pickup He+ by the Suprathermal Energy Ionic Charge Analyzer (SULEICA) instrument on the AMPTE/IRM spacecraft show significant reductions in the antisunward flux of these particles in the solar wind frame when the interplanetary magnetic field is directed radially. During such times, which can be as short as the 20‐min time resolution of our instrument, the typically sharp cutoff in the pickup ion distribution at spacecraft‐frame energy Ec = 2 MVsw2, where M is the helium mass and Vsw is the solar wind speed, is replaced by a smooth decline to background flux levels over several energy steps. We interpret these reductions as the result of inhibited pitch angle scattering into the observable antisunward region of phase space, implying a strong sunward anisotropy during these times. Thus we unambiguously identify the appearance of such anisotropies with the radial orientation of the magnetic field. We analyze the observations in terms of a steady two‐stream model of the ion distribution and use this model to estimate an effective λ, the scattering mean free path of the ions along the field. We obtain values of λ which range from 0.16 to 0.76 AU and discuss the significance of these results.
Global MHD simulation of the magnetosphere and ionosphere for 1930–2330 UT on November 3, 1993
Authors: Slinker S. P. , Fedder J. A. , Chen J. , Lyon J. G.
Published: April 2004

Using a three‐dimensional, global MHD simulation of the interaction of the Earth's magnetosphere with the solar wind, we examine the configuration of the magnetosphere and ionosphere during the hours from 1930 to 2330 UT on November 3, 1993. Direct measurements of the solar wind are not available. IMP 8 was in the magnetosheath near the dusk flank, and the simulation was run using IMP 8 measurements as an approximation for the solar wind parameters. The simulation prediction of the field and plasma quantities at the IMP 8 position were then compared with the recorded measurements, leading to a correction to the solar wind input to the simulation. Though this process could be iterated, we stopped after making one correction. The polar cap convection patterns compare well with patterns from the assimilated mapping of ionospheric electrodynamics (AMIE) analysis for this period. However, the MHD simulation predicts much higher cross polar cap potentials. We also examine the magnetopause position at the subsolar region and compare to measurements made by the geosynchronous spacecraft.
SAMPEX observations of storm‐associated electron flux variations in the outer radiation belt
Authors: Nakamura R. , Kamei K. , Kamide Y. , Baker D. N. , Blake J. B. , Looper M.
Published: April 2004

Flux variations of the outer radiation belt electrons (> 1‐MeV) during the main phase and early recovery phase of 25 geomagnetic storms are studied using data obtained by the Heavy Ion Large Telescope (HILT) experiment onboard the Solar, Anomalous, and Magnetospheric Particle Explorer (SAMPEX) satellite. Employing a simple model for the ring current field, we examine the degree to which the decrease of electron flux during the early main phase is attributable to adiabatic deceleration processes in response to changes in the magnetic field. Such an adiabatic response is shown to be detected most clearly for 4 < L < 5. In the lower L region (2 < L < 4) the electron flux decrease is less prominent and at times increases during the main phase of intense storms. On the other hand, in the region 5 < L < 7 the level of the electron decrease is larger than that expected from the adiabatic response alone. These observations suggest that the energetic electrons are trapped effectively near the inner edge of the outer radiation belt probably because of sudden inward transport and acceleration of the electrons during the main phase. The reduced flux of electrons returns to the normal level during the early recovery phase, even exceeding the prestorm level after about 1–2 days for intense storms. An outward diffusion process of the electrons at the inner edge, which are trapped during the main phase, could at least account partly for this observation. The low‐altitude observation of precipitating electrons supports the recirculation model for radiation belt electron dynamics during magnetic storms.
The dependence of high‐latitude PcS wave power on solar wind velocity and on the phase of high‐speed solar wind streams
Authors: Engebretson Mark , Glassmeier Karl‐Heinz , Stellmacher Martin , Hughes W. Jeffrey , Lühr Hermann
Published: April 2004

We have calculated the integrated ULF wave power in the Pc5 band at two stations, Kevo (part of the International Monitor for Auroral Geomagnetic Effects (IMAGE) magnetometer array in Scandinavia, at auroral zone latitudes), and Cape Dorset (part of the Magnetometer Array for Cusp and Cleft Studies (MACCS) in Arctic Canada, at cusp latitudes), and compared this power against the solar wind velocity for the last six months of 1993, a period characterized by two persistent high‐speed solar wind streams. We find for both local noon at Cape Dorset, and for local morning at Kevo, the Pc5 band power (0.002 – 0.010 Hz) integrated over a six‐hour period exhibits a clear power‐law dependence on the solar wind velocity. At Cape Dorset we found power α Vsw4, with a correlation coefficient r = 0.73, and at Kevo we found power α Vsw6.5, with r = 0.74. Much of the remaining variation in Pc5 power is due to temporal patterns evident at both stations in response to recurrent high speed streams. Power was strongest at the leading edge of each high speed stream and subsequently decreased more quickly than Vsw. Our observations suggest that it is insufficient to make estimates of Pc5‐range ULF wave power on the basis of Vsw alone: one must consider other physical factors, either intrinsic to the solar wind or related to its interaction with Earth's magnetosphere. The Kelvin‐Helmholtz instability is often considered to play a dominant role in this interaction, and the level of instability depends on both velocity and density. By means of a simple simulation using typical density and velocity values during the passage of a high speed stream, we were able to obtain good agreement with the temporal variations we observed. Finally, this study indicates that ground‐based pulsation observations can provide reliable proxies of the initial passage of high speed solar wind streams past Earth.
Analysis of the ionospheric cross polar cap potential drop using DMSP data during the National Space Weather Program study period
Authors: Hairston Marc R. , Heelis R. A. , Rich Frederick J.
Published: April 2004

During the National Space Weather Program (NSWP) event study period of November 2–11, 1993 there were three operational DMSP meteorological satellites (F8, F10, and F11) in orbit, each carrying the Special Sensor for Ions, Electrons, and Scintillation (SSIES) plasma instrument package. Ion flow data from these instruments are used to determine the electrostatic potential drop across both the northern and southern polar caps. The magnitude and distribution of the potential are used to characterize the convection patterns present in the polar ionospheres. The results from all three satellites ate presented to show an overall observational history of the potential drop and the convection pattern during the study period. These observational parameters provide crucial inputs and checks to several ionospheric and magnetospheric models being used in this study. Evidence is presented of an unambiguous difference in the cross polar cap potential drop between the two hemispheres for an extended period of time.
Behavior of the ionosphere and thermosphere at a southern midlatitude station during magnetic storms in early March 1995
Authors: Richards P. G. , Dyson P. L. , Davies T. P. , Parkinson M. L. , Reeves A. J.
Published: April 2004

During the first six days of March 1995, measurements of the ionospheric electron density were made near Melbourne, Australia, with a digisonde and thermospheric winds, temperatures, and 6300‐Å emission rates were measured with a Fabry‐Perot interferometer. The ionograms were inverted to obtain electron density profiles and peak heights of the F2 layer (hmF2). This paper compares modeled and measured electron densities, airglow emission rates, and neutral temperatures. The measured peak electron density shows strong negative effects from magnetic storms and rapid recovery to normal levels afterward. The model daytime peak density is in good agreement with the measurements on the undisturbed days and also shows negative phases at the appropriate times. However, the model negative effects are not as strong as the measured negative effects. A new algorithm is introduced to bring the measured and modeled peak electron density into better agreement by adjusting the exospheric Tn and atomic oxygen density in the MSIS model. The modified Tn at 300 km altitude agrees reasonably well with both the standard MSIS model and the measured Tn before midnight local time. However, the modified Tn, like the measured Tn, has a tendency to increase after about 2200 LT. At night, adjustments to the MSIS model exospheric temperature and atomic oxygen density are generally small. There is reasonably good agreement between the relative variations of the measured and modeled emission rates. However, there is much more variability in the model intensities than in the measured intensities as a result of rapid movements in the height of the F2 layer.
A simple simulation of a plasma void: Applications to Wind observations of the lunar wake
Authors: Farrell W. M. , Kaiser M. L. , Steinberg J. T. , Bale S. D.
Published: April 2004

Previously, the formation of the lunar wake was considered from a magnetohydrodynamic perspective. However, recent Wind particle and field observations suggest the lunar wake may be formed by kinetic processes: those microphysical processes not considered in an MHD formalism. Unfortunately, a full multidimensional and self‐consistent kinetic simulation of the lunar wake is beyond current means. However, some elements of the kinetic structure can be simulated via a simple one‐dimensional electrostatic particle‐in‐cell simulation. We present a self‐consistent simulation of a cross‐sectional element of a plasma void. Essentially, wakeward directed ion beams are formed at the flanks of the simulated void, consistent with the Wind observations of counterstreaming ion beams in the wake region. These wakeward directed beams are generated by ambipolar electric fields formed at the wake edges. Other structures observed by Wind are also seen in the simulation, including an electrostatically turbulent central wake region that causes the wake to fill‐in and a rarefaction wave emanating outward from the wake.
Energetic ion composition and charge state of solar wind plasma during November 3, 1993, magnetic storm
Authors: Lui A. T. Y. , Williams D. J. , McEntire R. W. , Christon S. P. , Galvin A. B. , Knipp D. J.
Published: April 2004

Measurements from the energetic particles and ion composition instrument on Geotail are used to investigate at high time resolution the ion composition and charge state of solar wind plasma (sampled in the magnetosheath) impacting the Earth during the geomagnetic storm which commenced on November 3, 1993. This storm is one in a series of recurrent storms associated with a high‐speed stream from a large coronal hole. Significant changes in the ion composition were found to start at ∼0300 UT on November 4, 1993, near the leading edge of the high‐speed stream, becoming very conspicuous near ∼0500 UT when the solar wind speed reached ∼700 km/s. Changes noted include a large transient enhancement of He++ relative to H+, a transient decrease in the temperatures of both H+ and He++ populations, an apparent enhancement of magnesium‐silicon ions relative to iron ions, and a possible shift of iron ions to higher charge states. These changes may be associated with a coronal mass ejection embedded within the arrival of a new interplanetary sector. The time of these changes coincides well with the start of the second plunge in the Dst index which ultimately leads to the minimum Dst for this geomagnetic storm, suggesting that these changes in composition and possibly charge state of the solar wind ions may be associated with factors which enhance the storm intensity at Earth. These results suggest that this magnetic storm may be exceptional for being a recurrent storm and yet being associated with CME activities for its intensity enhancement.