bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantification of Free Sialic Acid in Urine by HPLC–Electrospray Tandem Mass Spectrometry: A Tool for the Diagnosis of Sialic Acid Storage Disease
Authors: Valianpour Fredoen , Abeling Nicolaas G G M , Duran Marinus , Huijmans Jan G M , Kulik Willem
Published: February 2004

Background: Sialic acid storage diseases (SSDs) are severe autosomal recessive neurodegenerative disorders caused by a transport defect across the lysosomal membrane, which leads to accumulation of sialic acid in tissues, fibroblasts, and urine. Defective free sialic acid transport can be established by quantification of free sialic acid in urine.

Methods: Urine sample size was adjusted to the equivalent of 100 nmol of creatinine. After addition of 2-keto-3-deoxy-d-glycero-d-galactonononic acid as internal standard, samples were diluted with water to an end volume of 250 μL. We used 10 μL for HPLC–tandem mass spectrometric analysis in the negative electrospray ionization mode, monitoring transitions m/z 308.3→m/z 86.9 (sialic acid) and m/z 267.2→m/z 86.9 (internal standard). The overall method was validated and studied for ion suppression, interfering compounds, and pH effects. Samples from controls (n = 72) and SSD patients (n = 3) were analyzed.

Results: The limit of detection was 3 μmol/L. Intraassay imprecision (CV; n = 10) was 6%, 3%, and 2% at 30, 130, and 1000 mmol/mol creatinine, respectively; corresponding interassay CV (n = 10) were 5%, 5%, and 2%. Recovery was 109% (100–1000 mmol/mol creatinine). The mean (SD) [range] excretion rates (mmol/mol creatinine) were 31.3 (16.6) [0.7–56.9] at 0–1 year (n = 20), 21.2 (9.8) [6.3–38.3] at 1–3 years (n = 15), 14.4 (8.2) [1.7–32.9] at 3–10 years (n = 25), and 4.6 (2.6) [0–9.8] above age 10 years (n = 12). SSD patients 1.2, 3.9, and 12 years of age had concentrations of 111.5, 54.2, and 36.1 mmol/mol creatinine, respectively.

Conclusions: The HPLC-tandem MS method for free sialic acid in urine is more rapid, accurate, sensitive, selective, and robust than earlier methods and may serve as a candidate reference method for free sialic acid in diagnosis of SSD.
Genetic Effects on Baseline Values of C-Reactive Protein and Serum Amyloid A Protein: A Comparison of Monozygotic and Dizygotic Twins
Authors: MacGregor Alex J , Gallimore J Ruth , Spector Tim D , Pepys Mark B
Published: February 2004

Background: C-Reactive protein (CRP) and serum amyloid A protein (SAA) are exquisitely sensitive acute-phase reactants, but their baseline values are surprisingly constant in individuals in the general population. These values, especially of CRP, are associated with future atherothrombotic events, and the determinants of baseline CRP and SAA concentration are therefore of considerable interest.

Methods: CRP and SAA concentrations were measured by well-validated automated microparticle capture enzyme immunoassays, standardized on the respective WHO International Reference Standards, in serum from 146 monozygotic and 164 dizygotic healthy female UK twin pairs from the general population, with mean (range) ages of 58.0 (40–69.6) and 55.7 (40–70.3) years, respectively, who were also very closely matched for height, weight, body mass index, blood pressure, and lifestyle variables. Statistical modeling based on variance components analysis was used to estimate the genetic contribution to the observed values.

Results: As reported previously, CRP values were associated with body mass index, smoking, and hormone replacement therapy. After exclusion of the few samples with CRP concentrations >10 mg/L, which indicate an ongoing acute-phase response rather than baseline values, and inclusion of adjustments for all known confounding variables, there was significantly higher correlation of CRP and SAA results among monozygotic than among dizygotic twins. The estimated hereditability (95% confidence interval) of baseline values was 52% (40–62%) for CRP and 59% (49–67%) for SAA.

Conclusion: There is a substantial genetic contribution to baseline serum concentrations of CRP and SAA.
Extracellular ATP activates c-jun N-terminal kinase signaling and cell cycle progression in hepatocytes
Authors: Thevananther Sundararajah , Sun Hongdan , Li Duo , Arjunan Vijaya , Awad Samir S. , Wyllie Samuel , Zimmerman Tracy L. , Goss John A. , Karpen Saul J.
Published: February 2004

Partial hepatectomy leads to an orchestrated regenerative response, activating a cascade of cell signaling events necessary for cell cycle progression and proliferation of hepatocytes. However, the identity of the humoral factors that trigger the activation of these pathways in the concerted regenerative response in hepatocytes remains elusive. In recent years, extracellular ATP has emerged as a rapidly acting signaling molecule that influences a variety of liver functions, but its role in hepatocyte growth and regeneration is unknown. In this study, we sought to determine if purinergic signaling can lead to the activation of c-jun N-terminal kinase (JNK), a known central player in hepatocyte proliferation and liver regeneration. Hepatocyte treatment with ATPγS, a nonhydrolyzable ATP analog, recapitulated early signaling events associated with liver regeneration—that is, rapid and transient activation of JNK signaling, induction of immediate early genes c-fos and c-jun, and activator protein-1 (AP-1) DNA-binding activity. The rank order of agonist preference, UTP>ATP>ATPγS, suggests that the effects of extracellular ATP is mediated through the activation of P2Y2 receptors in hepatocytes. ATPγS treatment alone and in combination with epidermal growth factor (EGF) substantially increased cyclin D1 and proliferating cell nuclear antigen (PCNA) protein expression and hepatocyte proliferation in vitro. Extracellular ATP as low as 10 nM was sufficient to potentiate EGF-induced cyclin D1 expression. Infusion of ATP by way of the portal vein directly activated hepatic JNK signaling, while infusion of a P2 purinergic receptor antagonist prior to partial hepatectomy inhibited JNK activation. In conclusion, extracellular ATP is a hepatic mitogen that can activate JNK signaling and hepatocyte proliferation in vitro and initiate JNK signaling in regenerating liver in vivo. These findings have implications for enhancing our understanding of novel factors involved in the initiation of regeneration, liver growth, and development. (Hepatology 2004;39:393-402.)
HBsAg and HBx knocked into the p21 locus causes hepatocellular carcinoma in mice
Authors: Wang Youliang , Cui Fang , Lv Yaxin , Li Cuiling , Xu Xiaoling , Deng Chuxia , Wang Dongping , Sun Yansong , Hu Gengxi , Lang Zhenwei , Huang Cuifen , Yang Xiao
Published: February 2004

Hepatocellular carcinoma (HCC) affects males in a significantly higher proportion than females and is one of the human cancers etiologically related to viral factors. Many studies provide strong evidence of the direct role that hepatitis B virus (HBV) plays in hepatic carcinogenesis, but the functions of HBV surface antigen (HBsAg) and X protein (HBx) in hepatocarcinogenesis through direct or indirect mechanisms are still being debated. We generated two HBV gene knock-in transgenic mouse lines by homologous recombination. HBsAg and HBx genes were integrated into the mouse p21 locus. Both male and female p21-HBx transgenic mice developed HCC after the age of 18 months; however, male p21-HBsAg transgenic mice began to develop HCC 3 months earlier. The expression of a number of genes related to metabolism and genomic instability largely resembled the molecular changes during the development of HCC in humans. ER-β (estrogen receptor-β) was extremely up-regulated only in tumor tissues of male p21-HBsAg mice, providing genetic evidence that HBsAg might be the major risk factor affecting the gender difference in the causes of HCC. In conclusion, these mice might serve as good models for studying the different roles of HBsAg and HBx in early events of HBV-related hepatocarcinogenesis. (Hepatology 2004;39:318-324.)
Chronic liver disease in murine hereditary tyrosinemia type 1 induces resistance to cell death
Authors: Vogel Arndt , van den Berg Inge E.T. , Al-Dhalimy Muhsen , Groopman John , Ou Ching-Nan , Ryabinina Olga , Iordanov Mihail S. , Finegold Milton , Grompe Markus
Published: February 2004

The murine model of hereditary tyrosinemia type 1 (HT1) was used to analyze the relationship between chronic liver disease and programmed cell death in vivo. In healthy fumarylacetoacetate hydrolase deficient mice (Fah
-/-), protected from liver injury by the drug 2-(2- nitro-4-trifluoromethylbenzoyl)-1,3-cyclohexanedione (NTBC), the tyrosine metabolite homogentisic acid (HGA) caused rapid hepatocyte death. In contrast, all mice survived the same otherwise lethal dose of HGA if they had preexisting liver damage induced by NTBC withdrawal. Similarly, Fah
-/- animals with liver injury were also resistant to apoptosis induced by the Fas ligand Jo-2 and to necrosis-like cell death induced by acetaminophen (APAP). Molecular studies revealed a marked up-regulation of the antiapoptotic heat shock proteins (Hsp) 27, 32, and 70 and of c-Jun in hepatocytes of stressed mice. In addition, the p38 and Jun N-terminal kinase (JNK) stress-activated kinase pathways were markedly impaired in the cell-death resistant liver. In conclusion, these results provide evidence that chronic liver disease can paradoxically result in cell death resistance in vivo. Stress-induced failure of cell death programs may lead to an accumulation of damaged cells and therefore enhance the risk for cancer as observed in HT1 and other chronic liver diseases. (Hepatology 2004;39:433-443.)
Can we win them all? Benefits and costs of structured and flexible innovation– implementations
Authors: Drach‐Zahavy Anat , Somech Anit , Granot Michal , Spitzer Ada
Published: February 2004

Bureaucratic job structuring was compared with person–job integration in an attempt to determine which of the two approaches was a better means for innovation implementation in the workplace. The solution was hypothesized to be complex, depending on the criteria chosen for innovation effectiveness. Seventy incumbents of new linking roles in healthcare organizations were recruited. They provided data on the innovation–implementation approach applied in their case. Measures for different stakeholders' perceptions of innovation effectiveness were gathered. Three colleagues of the incumbents provided performance appraisals, reflecting internal customers' criteria for innovation effectiveness, each incumbent completed a questionnaire about burnout as a reversed proxy of innovation effectiveness, and semi‐structured observations of incumbents' activities provided an index of the fit between their role behaviors and role requirements, reflecting external customers' criteria for effectiveness. While performance appraisals were found to gain most from implementation through bureaucratic job structuring, the fit between incumbents' role behaviors and role requirements benefited most from implementation through person–job integration. Decreased burnout required maximizing the two implementation processes. These findings point to possible trade‐offs between the different criteria for innovation effectiveness, and call for combining features from the two implementation processes to produce a superior implementation approach. Copyright © 2004 John Wiley & Sons, Ltd.
A time for everything: how the timing of novel contributions influences project team outcomes
Authors: Ford Cameron , Sullivan Diane M.
Published: February 2004

One of the primary reasons organizations utilize project teams is to encourage members with diverse intellectual resources to produce novel associations that give rise to creative solutions. When creative sparks fly, learning, innovation and superior performance are often the result. However, in this paper we argue that creative sparks often create heat of another sort—frustration resulting from unfocused effort and diminished productivity. Utilizing Gersick's (1988) punctuated equilibrium model of project team development as a theoretical foundation, we argue that the meaning and impact of novel contributions change during a project team's life cycle. Novel contributions are beneficial to a project team early in its development when its primary goals are to learn more about a problem, search for useful information, and articulate tentative solutions. After the midpoint transition, when a team's attention shifts toward executing the proposal and satisfying external stakeholders before a looming deadline, additional attempts to introduce novel ideas are likely to disrupt performance and induce frustration. We develop a model and accompanying research propositions suggesting that the relationship between novel proposals and the value attributed to those proposals is contingent on timing with respect to a project team's midpoint transition. Copyright © 2004 John Wiley & Sons, Ltd.
Potential contribution of maximum subsurface temperature anomalies to the climate variability
Authors: Qian Weihong , Zhu Yafen , Liang Jianyin
Published: February 2004

On the interannual time scale, sea‐surface temperature anomalies (SSTAs) that are concerned with climate variability at global and regional scales have been widely investigated in previous studies. Through the analysis of the monthly 46‐year (1955–2000) expendable bathythermograph data, we show that subsurface temperature anomalies (STAs) can directly affect the SSTAs in the major air–sea interaction regions. Along the equatorial Pacific, four important features for STAs have been characterized. (1) The STAs and SSTAs are well correlated in the eastern equatorial Pacific (EEP) due to the fact that the thermocline anomalies have only to be mixed with the surface over a very short distance. (2) The STAs are always stronger than SSTAs at any location. (3) In the time between El Niño and La Niña, and vice versa, the STAs propagate eastward along the thermocline without mixing with SSTAs in the central Pacific. (4) An El Niño or La Niña can develop only when the maximum positive or the maximum negative STA propagates to the EEP. Inside and outside the tropical basins the STA was more centred on the thermocline than the 20°C isotherm. These features inform us that the maximum STAs (MSTAs) from each vertical STA profile can be used to indicate the anomalous wave‐propagation signal or thermocline variations in the worldwide oceans. This analysis implies that the MSTA is also a potential factor controlling climate variability and is a better indicator than SSTA, because MSTAs memorize the change in air–sea interaction signals and represent a huge deposit of energy in the upper ocean. The correlations between SSTAs and MSTAs with a coefficient of more than 0.60 are predominantly located in the EEP, the northern North Pacific, the southern subtropical Indian Ocean, and the northern North Atlantic Ocean. These correlations are discussed from case and statistical analyses.

The leading pattern of SSTAs and MSTAs in the tropical Pacific, Atlantic and Indian Oceans are decomposed using empirical orthogonal functions (EOFs) and their EOF patterns might be able to explain the difference between MSTAs and SSTAs. Their periods of mode series are performed from a global wavelet spectral analysis. Copyright © 2004 Royal Meteorological Society
Sequential dynamics of inflammatory cytokine, angiogenesis inducing factor and matrix degrading enzymes during spontaneous resorption of the Herniated disc
Authors: Kato Tsuyoshi , Haro Hirotaka , Komori Hiromichi , Shinomiya Kenichi
Published: February 2004

Intervertebral disc herniation (HD) is one of the most common orthopaedic conditions. MRI analysis of HD has revealed a spontaneous resorption mechanism related with neo‐vascularization. It appears that the interaction of activated macrophages with disc tissues leads to the generation of inflammatory cytokines. Moreover, inflammatory cytokines such as tumor necrosis factor‐α (TNF‐α) is required for the induction of angiogenesis inducing factors such as vascular endothelial growth factor (VEGF) or matrix degrading enzymes such as MMP‐3, MMP‐7 and plasmin. We hypothesized that these molecules play a crucial role during spontaneous HD resorption. In this study, we have examined the sequential expression of these molecules using a co‐culture system which is composed of the interaction of activated macrophages and disc tissues as a model of the acute response of inflammation occurred in HD. We have also considered the mechanism of activating latent MMPs during HD resorption process. Current our results indicate that upregulation of both TNF‐α mRNA and protein expressions occur first in the inflammation induced by HD. VEGF upregulation follows the increased level of TNF‐α expression. Both plasmin and MMP‐3 are upregulated at later time points. We also demonstrate that both TNF‐α and VEGF induce upregulated expression of urokinase‐type plasminogen activator (u‐PA). Our previous work has demonstrated that TNF‐α could upregulate the expression of VEGF, MMP‐3 and MMP‐7 in the co‐culture system. It has been reported that plasmin could affect to activate latent MMPs. Based on these findings, we suggest that TNF‐α acts as the initiator of inflammation following contact between macrophages and disc chondrocytes and that plasmin and u‐PA play a crucial role in activation of MMPs. We propose a spontaneous HD resorption cascade. Further understanding of the resorption process may provide future novel therapies for HD. © 2003 Orthopaedic Research Society. Published by Elsevier Ltd. All rights reserved.
Another look at cross-language competition in bilingual speech production: Lexical and phonological factors
Authors: COSTA ALBERT , COLOMÉ ÀNGELS , GÓMEZ OLGA , SEBASTIÁN-GALLÉS NÚRIA
Published: February 2004

How does lexical selection function in highly-proficient bilingual speakers? What is the role of the non-response language during the course of lexicalization? Evidence of cross-language interference was obtained by Hermans, Bongaerts, De Bot and Schreuder (1998) using the picture-word interference paradigm: participants took longer to name the picture when it appeared with a word phonologically related to the target's translation than when it was accompanied by a control (phono-translation interference). Here we report two picture-word interference experiments that explored whether the same pattern of interference is present for highly-proficient bilinguals producing speech in L2. The results of the two experiments partially replicate those of Hermans et al. (1998), revealing the reliability of the phono-translation effect. We discuss some possible loci of this effect during the lexicalization process, and its implications for models of bilinguals speech production.
On the autonomy of the grammatical gender systems of the two languages of a bilingual
Authors: COSTA ALBERT , KOVACIC DAMIR , FRANCK JULIE , CARAMAZZA ALFONSO
Published: February 2004

In five experiments highly-proficient bilinguals were asked to name two sets of pictures in their L2: a) pictures whose names in the L2 and their corresponding L1 translations have the same grammatical gender value, and b) pictures whose names in the L2 and their corresponding L1 translations have different gender values. In Experiments 1, 2, and 3 Croatian-Italian speakers were asked to name the pictures in Italian by means of NPs in various experimental contexts. In Experiment 4A, Spanish-Catalan and Catalan-Spanish bilinguals were asked to name the pictures in Spanish, and in Experiment 4B, Italian-French bilinguals did so in French. The results of these experiments revealed no differences between same- and different-gender pictures. Furthermore, the performance of Italian, Spanish, and French monolingual speakers parallels that of bilingual speakers. However, a robust frequency effect was observed across experiments. This pattern of results supports the notion that the gender value of the words in the non-response language does not affect processing in the response language, and suggests that the two gender systems of a bilingual are functionally autonomous.
Basic skills in a complex task: A graphical model relating memory and lexical retrieval to simultaneous interpreting
Authors: CHRISTOFFELS INGRID K. , DE GROOT ANNETTE M. B. , WALDORP LOURENS J.
Published: February 2004

Simultaneous interpreting (SI) is a complex skill, where language comprehension and production take place at the same time in two different languages. In this study we identified some of the basic cognitive skills involved in SI, focusing on the roles of memory and lexical retrieval. We administered a reading span task in two languages and a verbal digit span task in the native language to assess memory capacity, and a picture naming and a word translation task to tap the retrieval time of lexical items in two languages, and we related performance on these four tasks to interpreting skill in untrained bilinguals. The results showed that word translation and picture naming latencies correlate with interpreting performance. Also digit span and reading span were associated with SI performance, only less strongly so. A graphical models analysis indicated that specifically word translation efficiency and working memory form independent subskills of SI performance in untrained bilinguals.
How word frequency affects morphological processing in monolinguals and bilinguals
Authors: LEHTONEN MINNA , LAINE MATTI
Published: February 2004

The present study investigated processing of morphologically complex words in three different frequency ranges in monolingual Finnish speakers and Finnish-Swedish bilinguals. By employing a visual lexical decision task, we found a differential pattern of results in monolinguals vs. bilinguals. Monolingual Finns seemed to process low frequency and medium frequency inflected Finnish nouns mostly by morpheme-based recognition but high frequency inflected nouns through full-form representations. In contrast, bilinguals demonstrated a processing delay for all inflections throughout the whole frequency range, suggesting decomposition for all inflected targets. This may reflect different amounts of exposure to the word forms in the two groups. Inflected word forms that are encountered very frequently will acquire full-form representations, which saves processing time. However, with the lower rates of exposure, which characterize bilingual individuals, full-form representations do not start to develop.
Character introduction in two languages: Its development in the stories of a Spanish-English bilingual child age 6;11–10;11
Authors: ÁLVAREZ ESTHER
Published: February 2004

It is a matter of debate whether the two differentiated grammatical systems in a bilingual child develop autonomously, or whether there is interdependence and in what areas (Genesee, 2001; Meisel, 2001). Extensive research is being carried out in the emergence of the two grammars, but not much attention has been given to the development of discourse in simultaneous bilinguals. This study examines longitudinal narrative data from a Spanish-English school-age simultaneous bilingual child, and, in particular, the development of character introductions in the story. The child's stories in both languages show similar degrees of appropriate use of grammatical means for discourse purposes during the period under study and inadequacies are related not to the specific language used by the child, but to semantic and syntactic factors that promote or hinder appropriateness and affect both languages equally. The child follows the characteristic style identified for each of the two languages in studies of monolingual Spanish- and English-speaking children and adults. This indicates an autonomous development. However, there is also evidence that the two styles are not as differentiated as might be expected in comparison with monolinguals. These results support the view that, although the two languages of a bilingual child develop autonomously to a great extent, there are certain aspects which develop interdependently (Genesee, 2001).
Non‐Gaussian distribution function of AE‐index fluctuations: Evidence for time intermittency
Authors: Consolini Giuseppe , De Michelis Paola
Published: February 2004

The probability distribution functions (Pdfs) of the AE‐index fluctuations at different time scales have been investigated using a time series covering a period from January 01, 1978 to December 31, 1985. The Pdfs are always non Gaussian for time scales in the range 1–120 min both in quiet and disturbed periods. The scale dependence of the Pdfs indicates that AE‐index is not characterized by a global time self‐similarity, indicating that an intermittency phenomenon characterizes both phases. The results on Pdfs are compared with functional form, proposed by Castaing et al. [1990], to characterize intermittency phenomena in ordinary turbulent fluid flows. Moreover the relevance of these observations to the understanding of the magnetospheric dynamical configuration is pointed out.
The suprathermal seed population for corotating interaction region ions at 1 AU deduced from composition and spectra of H+, He++, and He+ observed on Wind
Authors: Chotoo K. , Schwadron N. A. , Mason G. M. , Zurbuchen T. H. , Gloeckler G. , Posner A. , Fisk L. A. , Galvin A. B. , Hamilton D. C. , Collier M. R.
Published: February 2004

We have measured H+, He++, and He+ distribution functions over the solar wind through the suprathermal energy range during two corotating interaction region (CIR) events observed by the STICS, MASS, and STEP instruments on board the Wind spacecraft at 1 AU during April and May 1995. The major properties we find are as follows: In the suprathermal energy range (∼10–500 keV/nucleon), the particle intensities peak inside the CIR itself, in the compressed and decelerated fast solar wind, in contrast to the situation at MeV energies, where the peak intensities are observed outside the CIR in the fast solar wind. The distribution functions of solar wind H+ and He++ change smoothly from the core at solar wind speeds to a power law or exponential form at higher energies, with no turnover observed at intermediate energies. CIR He+ is observed with an abundance ratio He+/He++ ∼ 16–17%, orders of magnitude higher than that in the bulk solar wind but nevertheless lower than that observed in CIRs at 4.5 AU. The H+, He++, and He+ spectra have similar slopes above speeds of ∼2.5–3 times the solar wind speed (Vsw) in the spacecraft frame. The ion speed at which the CIR He++/H+ ratio changes from typical solar wind values of 4–5% to the higher (>10%) value typical of CIRs is ∼1.5–1.7 Vsw, measured in the space‐craft reference frame. Analyzing these observations in the context of previous global observations and simple models of CIR acceleration and transport [Fisk and Lee, 1980], we conclude the following: (1) Suprathermal CIR ions at 1 AU originated close (within ∼0.5 AU) to the point of observation, not in the outer heliosphere; (2) the injection/acceleration mechanism is not especially sensitive to charge‐to‐mass ratio over the range 0.25–1.0; (3) since the particles are locally accelerated, the low‐energy ion populations we observe contain the seed population; (4) the bulk solar wind itself is not the source of the energetic ions; rather, the source is in the suprathermal tail, with an injection threshold in the spacecraft frame of ∼1.8–2.5 times the solar wind speed; and (5) in at least one of these CIRs, suprathermal particle acceleration is not shock associated and must therefore be associated with a statistical mechanism or compression in the solar wind.
Vertical development of the 2‐day wave in the midlatitude ionospheric F region
Authors: Altadill D. , Apostolov E. M.
Published: February 2004

The altitude development of the 2‐day wave in the ionospheric F region (from 170 to 230 km) has been investigated from the true height electron density profiles obtained at Observatori de l'Ebre station (40.8°N, 0.5°E). We found five time intervals of enhanced activity of the 2‐day wave, bursts type, during 1995. The altitude variations of the 2‐day wave period, amplitude, and phase are presented. The phase and group velocities of the wave are evaluated for each case. The observed changes in the electron density indicate three types of dominant vertical propagation of the 2‐day wave in the F region: (1) upward propagation of the wave, (2) simultaneous 2‐day oscillation of the electron density at all altitude range under study, and (3) downward propagation of the wave. The potential mechanisms proposed for explaining the vertical propagation of the 2‐day wave in the ionospheric F region are discussed in order to evaluate the most likely mechanism.
Three‐dimensional MHD simulations of interplanetary rotational discontinuities impacting the Earth's bow shock and magnetosheath
Authors: Cable S. , Lin Y.
Published: February 2004

The first ever fully three‐dimensional magnetohydrodynamic (MHD) simulations of the detailed effects of MHD discontinuities on the magnetosheath have been performed. The simulation results predict that the interaction between a rotational discontinuity (RD) and the bow shock produces an MHD wave pulse that propagates downstream from the bow shock to the magnetopause. The main components of this pulse are two slow shocks sandwiched between two time‐dependent intermediate shocks; in perfectly ideal MHD, these shocks would presumably resolve into slow shocks sandwiched between two RDs. Inside the pulse, the plasma density, thermal pressure, dynamic pressure (ρυ2), and total pressure all increase, while the magnetic field magnitude decreases. The pulse convects with the downstream flow through the magnetosheath at a speed that is markedly slower than that of the original RD. It comes to rest on the magnetopause, where it raises the total pressure by as much as 75% in some locations. The pulse eventually disappears, as it is convected away by the solar wind flow around the magnetopause. The pulse remains in the magnetosheath for a few Alfvén times (i.e., solar wind Alfvén velocity divided by the Earth's radius, perhaps 1–3 min depending on the actual solar wind parameters) after the initial RD has propagated downstream past the magnetopause. Comparisons are made with previous one‐dimensional and two‐dimensional studies of this problem. We conclude that the pulses seen in these simulations are possible causes of magnetic impulse events observed in the ionosphere and slow mode structures observed in the inner subsolar magnetosheath.
Propagation of medium frequency (1–4 MHz) auroral radio waves to the ground via the Z‐mode radio window
Authors: Yoon Peter H. , Weatherwax A. T. , Rosenberg T. J. , LaBelle J. , Shepherd S. G.
Published: February 2004

Recent ground‐based observations of auroral radio waves have identified narrowband emissions near 2 and 3 times the lower ionospheric electron cyclotron frequency (fce) known as auroral roars. In this paper the propagation of these waves in the auroral ionosphere is investigated by means of a ray‐tracing technique. We model one particular scenario in which a large‐scale (tens of kilometers) horizontal density structure, based on density structures observed with the Sondrestrom radar at times of auroral roar emissions, plays a crucial role in both guiding the waves to the ground and enabling mode conversion. The location and the mode characteristics of the initial waves are determined on the basis of local stability properties, which suggests that Z‐mode wave excitation is favored near 2fce. However, since Z‐mode cannot propagate to the ground they must first undergo a mode conversion to one of the free‐space modes (X and O). It is found that for a narrow range of frequencies and initial wave phase angles the trapped Z mode can be converted to O mode via the Ellis radio window. This finding is consistent with the fact that auroral roar emissions are nearly 100% O‐mode polarized. However, it is important to note that the evaluation of the damping of the Z‐mode waves along the ray path is not considered within the context of this preliminary study and will be critical for eventually determining the exact physical scenario of the auroral roar generation mechanism.
Phase gradient approach to stacking interferograms
Authors: Sandwell David T. , Price Evelyn J.
Published: February 2004

The phase gradient approach is used to construct averages and differences of interferograms without phase unwrapping. Our objectives for change detection are to increase fringe clarity and decrease errors due to tropospheric and ionospheric delay by averaging many interferograms. The standard approach requires phase unwrapping, scaling the phase according to the ratio of the perpendicular baseline, and finally forming the average or difference; however, unique phase unwrapping is usually not possible. Since the phase gradient due to topography is proportional to the perpendicular baseline, phase unwrapping is unnecessary prior to averaging or differencing. Phase unwrapping may be needed to interpret the results, but it is delayed until all of the largest topographic signals are removed. We demonstrate the method by averaging and differencing six interferograms having a suite of perpendicular baselines ranging from 18 to 406 m. Cross‐spectral analysis of the difference between two Tandem interferograms provides estimates of spatial resolution, which are used to design prestack filters. A wide range of perpendicular baselines provides the best topographic recovery in terms of accuracy and coverage. Outside of mountainous areas the topography has a relative accuracy of better than 2 m. Residual interferograms (single interferogram minus stack) have tilts across the unwrapped phase that are typically 50 mm in both range and azimuth, reflecting both orbit error and atmospheric delay. Smaller‐scale waves with amplitudes of 15 mm are interpreted as atmospheric lee waves. A few Global Positioning System (GPS) control points within a frame could increase the precision to ∼20 mm for a single interferogram; further improvements may be achieved by stacking residual interferograms.
The convection electric field in auroral substorms
Authors: Gjerloev J. W. , Hoffman R. A.
Published: February 2004

Dynamics Explorer 2 (DE 2) electric field and ion drift data are used in a statistical study of the ionospheric convection electric field in bulge‐type auroral substorms. Thirty‐one individual DE 2 substorm crossings were carefully selected and organized by the use of global auroral images obtained by DE 1. The selected passes, which occurred during substorm expansion phase, maximum, or early recovery phase, cover the entire nighttime substorm. The organization of the data used the method developed by Fujii et al. [1994], which divided the data into six local time sectors covering the nighttime substorm region. Following the procedures employed in the paper by Gjerloev and Hoffman [2000b], the latitudinal width and location of each auroral oval crossing was then adjusted to fit the sector average. In addition to the detailed study of the characteristics of the field within each sector this database enabled us to compile a model of the ionospheric convection electric field. The characteristics of the premidnight convection reversal show a pronounced local time dependency. Far west of the surge it is a fairly well defined point reversal or convection shear. Approaching the surge and within the surge it is a region of weak electric fields increasing in width toward midnight that separates regions of equatorward and poleward electric fields. Therefore we adopt the term Harang region rather than the Harang discontinuity for the premidnight convection reversal. A relatively narrow convection channel is coincident with the highest conductances located just poleward of the Harang region. This channel drives the substorm current wedge component of the westward electrojet in the surge and middle surge sectors. It is present in all premidnight passes and consequently is an integral part of the three‐dimensional substorm current wedge system.
Phase transition‐like behavior of the magnetosphere during substorms
Authors: Sitnov M. I. , Sharma A. S. , Papadopoulos K. , Vassiliadis D. , Valdivia J. A. , Klimas A. J. , Baker D. N.
Published: February 2004

The behavior of substorms as sudden transitions of the magnetosphere is studied using the Bargatze et al. [1985] data set of the solar wind induced electric field vBs and the auroral electrojet index AL. The data set is divided into three subsets representing different levels of activity, and they are studied using the singular spectrum analysis. The points representing the evolution of the magnetosphere in the subspace of the eigenvectors corresponding to the three largest eigenvalues can be approximated by two‐dimensional manifolds with a relative deviation of 10–20%. For the first two subsets corresponding to small and medium activity levels the manifolds have a pleated structure typical of the cusp catastrophe. The dynamics of the magnetosphere near these pleated structures resembles the hysteresis phenomenon typical of first‐order phase transitions. The reconstructed manifold is similar to the “temperature‐pressure‐density” diagrams of equilibrium phase transitions. The singular spectra of vBs, AL, and combined data have the power law dependence typical of second‐order phase transitions and self‐organized criticality. The magnetosphere thus exhibits the signatures of both self‐organization and self‐organized criticality. It is concluded that the magnetospheric substorm is neither a pure catastrophe of the low‐dimensional system nor a random set of avalanches of different scales described by the simple sandpile models. The substorms behave like nonequilibrium phase transitions, with features of both first‐ and second‐order phase transitions.
Ionosphere‐magnetosphere simulation of small‐scale structure and dynamics
Authors: Zhu H. , Otto A. , Lummerzheim D. , Rees M. H. , Lanchester B. S.
Published: February 2004

This work presents first results and the numerical methods of a highly improved two‐dimensional three‐fluid simulation model of the ionosphere‐magnetosphere system. The model considers ionization and recombination, ion‐neutral friction, the Hall term in Ohm's law, and various heat sources in the energy equations. The electrodynamic response and the evolution of the collision frequencies are treated self‐consistently in the height‐resolved ionosphere. This model is the first and to our knowledge the only simulation model that can resolve the dynamic and nonlinear electromagnetic interaction between the ionosphere and the magnetosphere. The simulation is aimed at modeling fast temporal and small spatial scale ionospheric structures associated, for instance, with filamentary aurora and ionospheric heating experiments. The results presented in this paper focus on ion and electron heating by different sources, i.e., ion heating due to plasma‐neutral friction, electron heating resulting from energetic particle precipitation and by ohmic dissipation in strong field‐aligned currents. This work is motivated by a specific auroral event that was observed simultaneously with optical and radar instruments. A consistent explanation of this event is possible in the presence of ohmic heating of electrons in a strong field‐aligned electric current layer.
Ohmic heating as evidence for strong field‐aligned currents in filamentary aurora
Authors: Lanchester B. S. , Rees M. H. , Lummerzheim D. , Otto A. , Sedgemore‐Schulthess K. J. F. , Zhu H. , McCrea I. W.
Published: February 2004

A large increase in electron temperature measured in filamentary aurora with the European incoherent scatter radar has been modeled with a one‐dimensional electron transport and ion chemistry code. To account for the observed changes in electron temperature, while also reproducing the measured E region electron density profiles, a source of electron heating is required in addition to local heating from energy degradation of the precipitating electrons. We show that ohmic heating in a strong field‐aligned current can account for the required heat source.
Mesoscale structure of the midlatitude ionosphere during high geomagnetic activity: Airglow and GPS observations
Authors: Garcia F. J. , Kelley M. C. , Makela J. J. , Sultan P. J. , Pi X. , Musman S.
Published: February 2004

On the night of November 22, 1997, the Cornell All‐Sky Imager recorded a spectacular display of structure in the 630.0 nm emission over Arecibo, Puerto Rico. This event is an example of a phenomenon we have termed “intense midlatitude spread F.” In this paper we describe the stormtime geophysical conditions for the period and detail the evolution of the event. The daytime midlatitude ionosphere was disturbed for four consecutive days. The initial daytime doubling of the total electron content (TEC) was associated with equatorward propagation of a high‐TEC patch that seemed to have associated composition changes. The following days had distinct diurnal double maxima (DDM). The TEC in the Caribbean was very high during the first night of the storm and was extremely structured. Airglow depletions and enhancements surged poleward, bifurcating numerous times in the process. The airglow depletions were collocated with TEC minima along similar lines of sight to Global Positioning System satellites. Eventually, four parallel and very similar airglow wave packets were visible and oriented at an angle similar to the less violent structures reported in the companion paper [Garcia et al., this issue] and moving slowly toward the southwest. We explore a number of possible explanations for these features. We are most confident that secondary instabilities of the generalized ExB process can explain the evolution of the structures once they are formed. The initial process itself remains controversial.
A semiempirical equatorial mapping of AMIE convection electric potentials (MACEP) for the January 10, 1997, magnetic storm
Authors: Boonsiriseth A. , Thorne R. M. , Lu G. , Jordanova V. K. , Thomsen M. F. , Ober D. M. , Ridley A. J.
Published: February 2004

Owing to satellite and instrumental limitations, in situ magnetospheric electric field measurements are only available at isolated locations during storm time conditions. A global view of the inner magnetospheric convection electric field can be obtained by mapping ionospheric potentials into the equatorial plane. A mapping procedure for assimilative mapping of ionospheric electrodynamics (AMIE) ionospheric potentials (MACEP) is used to obtain convection patterns for the January 10, 1997, magnetic storm. The results are compared with the widely used empirical Volland‐Stern model and the mapping of Weimer ionospheric potentials. While the gross temporal evolution of the large‐scale potential drop across the magnetosphere is similar in all three models, detailed intercomparison shows that the MACEP procedure is capable of resolving highly variable and relatively small scale features of the electric field that are not treated by the Volland‐Stern model nor seen from the Weimer mapping. The MACEP results are in reasonable agreement with limited electric field measurements from the electric field instrument on the Polar spacecraft and LANL measurements of thermal ion velocities at geosynchronous orbit during prestorm and recovery phase conditions. However, the inner boundary condition employed in the current version of AMIE is unable to reproduce the magnitude of the penetrating electric fields observed in the inner magnetosphere during the main phase of a storm. The addition of a penetration electric field associated with an asymmetric ring current in the dusk sector improved MACEP results at the duskside low‐L region.
Nitric oxide excited under auroral conditions: Excited state densities and band emissions
Authors: Cartwright D. C. , Brunger M. J. , Campbell L. , Mojarrabi B. , Teubner P. J. O.
Published: February 2004

Electron impact excitation of vibrational levels in the ground electronic state and nine excited electronic states in NO has been simulated for an IBC II aurora (i.e., ∼10 kR in 3914 Å radiation) in order to predict NO excited state number densities and band emission intensities. New integral electron impact excitation cross sections for NO were combined with a measured IBC II auroral secondary electron distribution, and the vibrational populations of 10 NO electronic states were determined under conditions of statistical equilibrium. This model predicts an extended vibrational distribution in the NO ground electronic state produced by radiative cascade from the seven higher‐lying doublet excited electronic states populated by electron impact. In addition to significant energy storage in vibrational excitation of the ground electronic state, both the a 4Π and L2 Φ excited electronic states are predicted to have relatively high number densities because they are only weakly connected to lower electronic states by radiative decay. Fundamental mode radiative transitions involving the lowest nine excited vibrational levels in the ground electronic state are predicted to produce infrared (IR) radiation from 5.33 to 6.05 μm with greater intensity than any single NO electronic emission band. Fundamental mode radiative transitions within the a 4Π electronic state, in the 10.08–11.37 μm region, are predicted to have IR intensities comparable to individual electronic emission bands in the Heath and ε band systems. Results from this model quantitatively predict the vibrational quantum number dependence of the NO IR measurements of Espy et al. [1988].
Electron acceleration by Alfvén waves in density cavities
Authors: Génot V. , Louarn P. , Mottez F.
Published: February 2004

A new electromagnetic two‐dimensional guiding center particle in cell (PIC) code is used to investigate the propagation of an Alfvén wave in the perpendicular density gradients that characterize the edges of the auroral density cavities. It is shown that the wave planes are strongly distorted by the inhomogeneities of the plasma and that a significant electric field develops in the direction parallel to the background magnetic field during the propagation. This field efficiently accelerates the electrons in the parallel direction, and the incident wave is thus strongly absorbed. The associated dissipation rate is sufficiently strong to explain a complete wave absorption on the density gradients over a fraction of wavelength. The electron parallel acceleration is also characterized. It corresponds to a global parallel acceleration of the electron population. These PIC simulations suggest that the perpendicular density gradients corresponding to the auroral plasma cavities play an important role in the auroral particle acceleration.
Energetic charged particles near Europa
Authors: Paranicas C. , McEntire R. W. , Cheng A. F. , Lagg A. , Williams D. J.
Published: February 2004

Galileo energetic particles detector (EPD) data are presented from several close encounters of the spacecraft with Jupiter's moon Europa. These data reveal significant decreases in electron and ion count rates very close to the moon and a few Europa radii downstream. The relation between count rate decreases and satellite absorption is analyzed because these particles sputter and chemically modify Europa's surface. Decreases on the plasma wake side of the satellite have radial extents comparable to satellite dimensions. Furthermore, some energetic particle wakes are shifted toward Jupiter from predicted locations. At some wake locations, electron fluxes do not get above instrument background levels. Corresponding electrons are lost preferentially on Europa's trailing hemisphere. Upstream of Europa during the E12 encounter, deep decreases in energetic ion count rates are observed for some instrument look directions. These decreases are associated with satellite absorption because the E12 closest approach altitude is smaller than relevant ion gyroradii. Other E12 decreases, such as a “bite‐out” corresponding to a peak in the measured magnetic field intensity, are associated with “secondary” drifts in the radial direction caused by the field gradient. Pitch angle distributions measured during the E15 encounter (when Galileo was in Europa's wake) show much higher fluxes of locally mirroring particles than would be expected in a simple absorption signature. We suggest that a fraction of the upstream population escapes absorption because of the pileup of magnetic flux on Europa's trailing hemisphere.