bluuebunny/crossref_metadata_2025 huggingface dataset:
Neural Control of Motion-to-Force Transitions with the Fingertip
Authors: Venkadesan Madhusudhan , Valero-Cuevas Francisco J.
Published: February 2008

The neural control of tasks such as rapid acquisition of precision pinch remains unknown. Therefore, we investigated the neural control of finger musculature when the index fingertip abruptly transitions from motion to static force production. Nine subjects produced a downward tapping motion followed by vertical fingertip force against a rigid surface. We simultaneously recorded three-dimensional fingertip force, plus the complete muscle coordination pattern using intramuscular electromyograms from all seven index finger muscles. We found that the muscle coordination pattern clearly switched from that for motion to that for isometric force ∼65 ms before contact (p= 0.0004). Mathematical modeling and analysis revealed that the underlying neural control also switched between mutually incompatible strategies in a time-critical manner. Importantly, this abrupt switch in underlying neural control polluted fingertip force vector direction beyond what is explained by muscle activation-contraction dynamics and neuromuscular noise (p≤ 0.003). We further ruled out an impedance control strategy in a separate test showing no systematic change in initial force magnitude for catch trials where the tapping surface was surreptitiously lowered and raised (p= 0.93). We conclude that the nervous system predictively switches between mutually incompatible neural control strategies to bridge the abrupt transition in mechanical constraints between motion and static force. Moreover because the nervous system cannot switch between control strategies instantaneously or exactly, there arise physical limits to the accuracy of force production on contact. The need for such a neurally demanding and time-critical strategy for routine motion-to-force transitions with the fingertip may explain the existence of specialized neural circuits for the human hand.
Mapping White Matter Integrity and Neurobehavioral Correlates in Children with Fetal Alcohol Spectrum Disorders
Authors: Sowell Elizabeth R. , Johnson Arianne , Kan Eric , Lu Lisa H. , Van Horn John Darrell , Toga Arthur W. , O'Connor Mary J. , Bookheimer Susan Y.
Published: February 2008

Brain structural abnormalities and neurocognitive dysfunction have been observed in individuals with fetal alcohol spectrum disorders (FASDs). Little is known about how white matter integrity is related to these functional and morphological deficits. We used a combination of diffusion tensor and T1-weighted magnetic resonance imaging to evaluate white matter integrity in individuals with FASDs and related these findings to neurocognitive deficits. Seventeen children and adolescents with FASDs were compared with 19 typically developing age-and gender-matched controls. Lower fractional anisotropy (FA) was observed in individuals with FASDs relative to controls in the right lateral temporal lobe and bilaterally in the lateral aspects of the splenium of the corpus callosum. White matter density was also lower in some, but not all regions in which FA was lower. FA abnormalities were confirmed to be in areas of white matter inpost hocregion of interest analyses, further supporting that less myelin or disorganized fiber tracts are associated with heavy prenatal alcohol exposure. Significant correlations between performance on a test of visuomotor integration and FA in bilateral splenium, but not temporal regions were observed within the FASD group. Correlations between the visuomotor task and FA within the splenium were not significant within the control group, and were not significant for measures of reading ability. This suggests that this region of white matter is particularly susceptible to damage from prenatal alcohol exposure and that disruption of splenial fibers in this group is associated with poorer visuomotor integration.
Role of Protein Phosphatase 2A in Regulating the Visual Signaling inDrosophila
Authors: Wang Ning , Leung Hung-Tat , Pak William L. , Carl Yonatan T. , Wadzinski Brian E. , Shieh Bih-Hwa
Published: February 2008

Drosophilavisual signaling, a G-protein-coupled phospholipase Cβ (PLCβ)-mediated mechanism, is regulated by eye-protein kinase C (PKC) that promotes light adaptation and fast deactivation, most likely via phosphorylation of inactivation no afterpotential D (INAD) and TRP (transient receptor potential). To reveal the critical phosphatases that dephosphorylate INAD, we used several biochemical analyses and identified protein phosphatase 2A (PP2A) as a candidate. Importantly, the catalytic subunit of PP2A, microtubule star (MTS), is copurified with INAD, and an elevated phosphorylation of INAD by eye-PKC was observed in threemtsheterozygotes. To explore whether PP2A (MTS) regulates dephosphorylation of INAD by counteracting eye-PKC [INAC (inactivation no afterpotential C]in vivo, we performed ERG recordings. We discovered thatinaCP209was semidominant, becauseinaCP209heterozygotes displayed abnormal light adaptation and slow deactivation. Interestingly, the deactivation defect ofinaCP209heterozygotes was rescued by themtsXE2258heterozygous background. In contrast,mtsXE2258failed to modify the severe deactivation ofnorpAP16, indicating that MTS does not modulate NORPA (no receptor potential A) (PLCβ). Together, our results strongly indicate that dephosphorylation of INAD is catalyzed by PP2A, and a reduction of PP2A can compensate for a partial loss of function in eye-PKC, restoring the fast deactivation kineticsin vivo. We thus propose that the fast deactivation of the visual response is modulated in part by the phosphorylation of INAD.
Xenoestrogens modulate vascular endothelial growth factor secretion in breast cancer cells through an estrogen receptor-dependent mechanism
Authors: Buteau-Lozano Hélène , Velasco Guillaume , Cristofari Monique , Balaguer Patrick , Perrot-Applanat Martine
Published: February 2008

Environmental chemicals may affect human health by disrupting endocrine function. Their possible role in the mammary gland and breast tumors is still unknown. Previous studies have demonstrated that vascular endothelial growth factor (VEGF), a key factor in angiogenesis and tumor progression, is an estrogen-regulated gene. We analyzed whether VEGF expression is regulated by different xenoestrogens in several breast cancer cells, MELN (derived from MCF-7) and MELP (derived from MDA-MB-231) and stably expressing estrogen receptor α (ERα); these cell lines stably express estrogen response element (β-globin)-luciferase. Genistein, bisphenol A (BPA), 4-(tert-octyl)phenol (OP), dieldrin, and several phthalates, including benzyl butyl phthalate (BBP) and di-ethyl-2-hexyle phthalate (DEHP), were first shown to be estrogenic. These compounds induced a dose-dependent increase of VEGF secretion in MELN and MCF-7 cells; maximal effect was observed at 1–10 μM non-cytotoxic concentrations and was inhibited by the antiestrogen ICI 182 780. VEGF increase was not observed in ERα-negative MDA-MB-231 cells. Most substances increased VEGF transcript levels in MELN cells. In contrast, γ-hexachlorocyclohexane, vinclozolin, and the phthalates (mono-n-butyl ester phthalic acid, di-isononyle phthalate, and di-isodecyle phthalate) were ineffective on both VEGF secretion and estrogenic luciferase induction in these cell lines. Specific kinase inhibitors PD98059, SB203580, or LY294002 suppressed the xenoestrogen-induced VEGF response, suggesting activation of MEK, p38 kinase, and phosphatidylinositol-3-kinase pathways. Our in vitro results show for the first time that genistein and xenoestrogens (BPA, OP, dieldrin, BBP, and DEHP at high concentrations) up-regulate VEGF expression in MELN cells by an ER-dependent mechanism. Since VEGF increases capillary permeability and breast tumor angiogenesis in vivo, the physiological relevance of these findings is discussed.
HLA DR-DQ Haplotypes and Genotypes and Type 1 Diabetes Risk
Authors: Erlich Henry , Valdes Ana Maria , Noble Janelle , Carlson Joyce A. , Varney Mike , Concannon Pat , Mychaleckyj Josyf C. , Todd John A. , Bonella Persia , Fear Anna Lisa , Lavant Eva , Louey Anthony , Moonsamy Priscilla ,   for the Type 1 Diabetes Genetics Consortium
Published: February 2008

OBJECTIVE—The Type 1 Diabetes Genetics Consortium has collected type 1 diabetic families worldwide for genetic analysis. The major genetic determinants of type 1 diabetes are alleles at the HLA-DRB1 and DQB1 loci, with both susceptible and protective DR-DQ haplotypes present in all human populations. The aim of this study is to estimate the risk conferred by specific DR-DQ haplotypes and genotypes.

RESEARCH DESIGN AND METHODS:—Six hundred and seven Caucasian families and 38 Asian families were typed at high resolution for the DRB1, DQA1, and DQB1 loci. The association analysis was performed by comparing the frequency of DR-DQ haplotypes among the chromosomes transmitted to an affected child with the frequency of chromosomes not transmitted to any affected child.

RESULTS—A number of susceptible, neutral, and protective DR-DQ haplotypes have been identified, and a statistically significant hierarchy of type 1 diabetes risk has been established. The most susceptible haplotypes are the DRB1*0301-DQA1*0501-DQB1*0201 (odds ratio [OR] 3.64) and the DRB1*0405-DQA1*0301-DQB1*0302, DRB1*0401-DQA1*0301-DQB*0302, and DRB1*0402-DQA1*0301-DQB1*0302 haplotypes (ORs 11.37, 8.39, and 3.63), followed by the DRB1*0404-DQA1*0301-DQB1*0302 (OR 1.59) and the DRB1*0801-DQB1*0401-DQB1*0402 (OR 1.25) haplotypes. The most protective haplotypes are DRB1*1501-DQA1*0102-DQB1*0602 (OR 0.03), DRB1*1401-DQA1*0101-DQB1*0503 (OR 0.02), and DRB1*0701-DQA1*0201-DQB1*0303 (OR 0.02).

CONCLUSIONS—Specific combinations of alleles at the DRB1, DQA1, and DQB1 loci determine the extent of haplotypic risk. The comparison of closely related DR-DQ haplotype pairs with different type 1 diabetes risks allowed identification of specific amino acid positions critical in determining disease susceptibility. These data also indicate that the risk associated with specific HLA haplotypes can be influenced by the genotype context and that the trans-complementing heterodimer encoded by DQA1*0501 and DQB1*0302 confers very high risk.
Effects of climate change on the distribution of Iberian tree species
Authors: Benito Garzón Marta , Sánchez de Dios Rut , Sainz Ollero Helios
Published: February 2008

Question: Will the predicted climate changes affect species distribution in the Iberian Peninsula?

Location: Iberian Peninsula (Spain and Portugal).

Methods: We modelled current and future tree distributions as a function of climate, using a computational framework that made use of one machine learning technique, the random forest (RF) algorithm. This algorithm provided good predictions of the current distribution of each species, as shown by the area under the corresponding receiver operating characteristics (ROC) curves. Species turnover, richness and the change in distributions over time to 2080 under four Intergovernmental panel on climate change (IPCC) scenarios were calculated using the species map outputs.

Results and Conclusions: The results show a notable reduction in the potential distribution of the studied species under all the IPCC scenarios, particularly so for mountain conifer species such as Pinus sylvestris, P. uncinata and Abies alba. Temperate species, especially Fagus sylvatica and Quercus petraea, were also predicted to suffer a reduction in their range; also sub‐mediterranean species, especially Q. pyrenaica, were predicted to undergo notable decline. In contrast, typically Mediterranean species appeared to be generally more capable of migration, and are therefore likely to be less affected.
Sustained attention and serotonin: a pharmaco‐fMRI study
Authors: Wingen Marleen , Kuypers Kim P.C. , van de Ven Vincent , Formisano Elia , Ramaekers Johannes G.
Published: February 2008

Objective

Evidence suggests that stimulation of serotonergic function in healthy humans causes an impairment of sustained attention. The present study assessed the influence of increased serotonin levels on brain areas involved in sustained attention.

Methods

Ten healthy volunteers (5♀, 5♂) received the selective serotonin reuptake inhibitor (SSRI) escitalopram (20 mg) and placebo in a balanced, double blind, two‐way crossover design. Participants performed the Mackworth Clock Test to measure sustained attention during functional MRI measurements at 3 Tesla. Subjective measurements after pharmacological manipulation were conducted with the Bond and Lader Questionnaire.

Results

Independent of treatment, brain areas associated with task performance on a sustained attention task were activated, including right prefrontal and parietal areas. After escitalopram administration, less activation was shown in the caudate nucleus, thalamus, and frontal areas. No effect of escitalopram was shown on behavioral data although subjective measurements showed decreased alertness after escitalopram.

Conclusions

The results of the current pharmaco‐functional magnetic resonance imaging (fMRI) study give a first indication of involvement of serotonin in sustained attention through modulating activation of selective brain areas including the thalamus and caudate nucleus. Possibly, these areas are involved in a subcortical network for sustained attention, but further research is necessary. Copyright © 2008 John Wiley & Sons, Ltd.
The role of calcium gluconate in electrochemical activation of titanium for biomimetic coating of calcium phosphate
Authors: Shibli S. M. A. , Mathai Suja
Published: February 2008

Supersaturation of calcium and phosphate in the bath solution and activation of the metal substrate is essential for effective biomimetic growth of apatite on orthopedic implants. In this work, bioactivation of titanium surface was achieved by electrodeposition of a thin layer of calcium phosphate followed by an alkaline treatment to obtain pure hydroxyapatite crystals. The influence of calcium gluconate in the electrolyte solution was evaluated and optimized. Adhesive strength, thickness, structural, and surface characteristics were evaluated. A highly adhesive and uniform layer of hydroxyapatite was formed on titanium surface when the electrodeposition was carried out with an electrolyte solution‐containing calcium gluconate. The electrodeposited hydroxyapatite coatings were subjected for biomimetic growth in Kokubo's simulated body fluid (SBF) and Kokubo's modified SBF containing 1.5 times higher concentration of Ca. Biomimetic growth was also improved by the addition of calcium gluconate in the SBF solution. © 2008 Wiley Periodicals, Inc. J Biomed Mater Res 2008
Chondrocytes culture in three‐dimensional porous alginate scaffolds enhanced cell proliferation, matrix synthesis and gene expression
Authors: Lin Yu‐Ju , Yen Chi‐Nan , Hu Yu‐Chen , Wu Yung‐Chih , Liao Chun‐Jen , Chu I‐Ming
Published: February 2008

For the limited availability of autologous chondrocytes, a cultured system for expansion in vitro until sufficient cells are obtained must be developed. These cells must maintain their chondrocyte phenotype in vitro as well as in vivo, following implantation to ensure that differentiated chondrocytes synthesize a normal hyaline cartilage matrix and not a fibro‐cartilage matrix. This study uses porous three‐dimensional (3‐D) alginate scaffolds within a perfusion system to culture low‐density (5 × 105 cells) primary porcine chondrocytes for 1–4 weeks to study their proliferation and differentiation. The results of RT–PCR reveal that most cells could maintain their differentiation state for up to 4 weeks of culturing. Chondrocytes proliferated to 3 × 107 cells after 4 weeks in culture. Alginate scaffolds induced the formation of chondrocyte clusters and stimulated the synthesis of matrix, which effects were evaluated using histology and electron microscopy. These findings demonstrate that culturing chondrocytes in alginate scaffolds may effectively prevent the dedifferentiation and improve autologous chondrocyte transplantation. © 2008 Wiley Periodicals, Inc. J Biomed Mater Res, 2009
Marketing and development out of poverty: introduction to the special issue
Authors: Carr Stuart C. , Rugimbana Robert O.
Published: February 2008

Reducing poverty by meeting the United Nations' Millennium Development Goals (MDGs) is an interdisciplinary undertaking, in which Marketing Science logically plays a role. The papers in this special issue cover a range of methods, from traditional consumer research experiments (on images of poverty, donation behaviour) and sample surveys on the credibility of celebrity marketing, to observational studies of community values and customs (on micro‐finance or agricultural enterprise). Consumers of aid appeals, celebrity lobbying and financial services—these methods reveal—are behaviourally complex. They are infused with contradictory, competing and complementary tendencies. Underlying those different tendencies however is a common but often overlooked thread. For poverty to be significantly reduced by 2015, attention needs to be paid not only to goals, that is to task but also towards understanding the human relationships in the poverty reduction market. Marketing practise and research can contribute to poverty reduction by helping build (1) perspective‐sharing, (2) accommodation to local needs and (3) appreciation of socio‐economic and socio‐cultural behavioural systems.

Copyright © 2008 John Wiley & Sons, Ltd.
Numerische Beulsicherheitsnachweise bei Schalenbeulfällen mit überkritischen Tragreserven
Authors: Schneider Werner
Published: February 2008

Für viele beulgefährdete Schalenkonstruktionen liegen keine ausreichenden experimentellen Daten vor, um deren Tragfähigkeit abschätzen zu können. Der Eurocode EN 1993‐1‐6 bietet deshalb die Möglichkeit numerisch gestützter Beulsicherheitsnachweise. Als maßgebend für die Tragfähigkeit wird dabei die erste Instabilitätslast angesehen. Das Problem lokaler Instabilitäten und sogenannter überkritischer Tragreserven ist nur am Rand erwähnt, aber nicht anwendungsbereit geregelt. Im Beitrag werden die aus dieser Verengung des Versagensbegriffes resultierenden Probleme diskutiert und Vorschläge zu ihrer Überwindung unterbreitet.
A study on rotational effects and different stall delay models using a prescribed wake vortex scheme and NREL phase VI experiment data
Authors: Breton Simon‐Philippe , Coton Frank N. , Moe Geir
Published: February 2008

Understanding of the stall delay phenomenon on wind turbines remains, to this day, incomplete. A correct modelling of this phenomenon, which results from three‐dimensional rotational effects, is essential in order to make reliable wind turbine simulations on the basis of two‐dimensional airfoil data, such as with the widely used blade element momentum method. The present study addresses this issue by testing six existing models intended to correct for stall delay effects, namely those developed by Snel et al., Chaviaropoulos and Hansen, Raj, Bak et al., Corrigan and Schillings and Lindenburg. For this purpose, the models are implemented into a lifting‐line‐prescribed wake vortex scheme. Forces along the blades as well as power and root flap bending moment in a head‐on flow configuration are predicted based on these models, and are compared to wind tunnel data from NREL's phase VI experiment. While load over‐prediction in the presence of stall is in general observed from the use of the different models, significant differences between the models are still seen. Local over‐prediction is generally seen in the tip region, while discrepancies are obtained, even at low wind speed, for the root flap bending moment. The results obtained are discussed in terms of deficiencies and strengths of the current correction schemes, and from there a basis is provided for the development of improved correction models. Copyright © 2008 John Wiley & Sons, Ltd.
The effects of prey species on food conversion efficiency and growth of an insectivorous lizard
Authors: Rich C. Nelson , Talent Larry G.
Published: February 2008

Little is known about the effects of different prey species on lizard growth. We conducted a 6‐week study to determine the relative effects of prey species on growth parameters of hatchling western fence lizards, Sceloporus occidentalis. Lizards were fed house cricket nymphs, Acheta domesticus, or mealworm larvae, Tenebrio molitor. The effects of prey species on growth were determined by measuring prey consumption, gross conversion efficiency of food [gain in mass (g)/food consumed (g)], gain in mass, and gain in snout–vent length. Lizards grew well on both the prey species. However, lizards that fed on crickets consumed a significantly higher percentage of their body mass per day than those fed mealworms. Nevertheless, lizards that consumed mealworms ingested significantly more metabolizable energy, had significantly higher food conversion efficiencies, significantly higher daily gains in mass, and significantly greater total growth in mass than lizards that fed on crickets. Zoo Biol 27:181–187, 2008. © 2008 Wiley‐Liss, Inc.
An ultrastructural study of the early cercarial development in Prosorhynchoides borealis (Digenea: Bucephalidae) with special reference to formation of the primitive epithelium
Authors: Podvyaznaya I.M. , Galaktionov K.V.
Published: February 2008

Primitive epithelium and outer tegumental layer formation during early cercarial development was studied in Prosorhynchoides borealis using electron microscopy. It demonstrated that germinal cells freely floating in the sporocyst body cavity divide to give rise to naked cell aggregates. These early embryos are highly irregular in outline and are composed of blastomeres differing in size and structure. In embryos consisting of about 12–14 cells a few (possibly only two) superficial macromeres become concave and produce thin extensions which envelop the embryonic mass before fusing to form a syncytial primitive epithelium. This primitive epithelium forms syncytial connections with underlying embryonic cells. Primordial tegumental cells become apparent in late germinal balls below the primitive epithelium. These cells expand and fuse to give rise to an embryonic nucleated tegument. The embryonic tegument is connected to peripheral embryonic cells by thin cytoplasmic bridges until the basement lamina is formed. Subsequently, the primitive epithelium is shed by the embryos and the nuclei in the embryonic tegument undergo pyknotic degeneration. These results are analysed and compared with data from studies on other trematode species and it is concluded that the primitive epithelium is derived from the embryo in at least the majority of digeneans.
The use of basic parameters for monitoring the haemodynamic effects of midazolam and ketamine as opposed to propofol during cardiac catheterization
Authors: Baysal Ayse , Polat Tugcin Bora , Yalcin Yalim , Celebi Ahmet
Published: February 2008

Objective

Our aim is to compare the haemodynamic and adverse effects of propofol versus the mixture of midazolam and ketamine as used in sedation for cardiac catheterization in children.

Methods

In a prospective randomized trial, we divided patients needing sedation into 72 receiving a mixture of midazolam and ketamine and 42 receiving propofol. Their ages ranged from 6 months to 12 years, and 1 year to 16 years, respectively. We collected data relative to heart rate, mean arterial pressure, respiratory rate, peripheral saturations of oxygen, and adverse effects. We assessed cyanotic patients to establish any relationship between the haemodynamic data and peripheral arterial saturations of oxygen.

Results

Demographic data, including age, gender, and weight, was not statistically different between the groups. In those receiving midazolam and ketamine, mean systemic arterial pressures before, and 30 minutes after, sedation were 64.3, with standard deviation of 9.8, and 62.5, with standard deviation of 10.2, millimetre of mercury (p equals to 0.237). Heart rates were 131.3, with standard deviation of 13.5, and 109.2, with standard deviation of 17.3 beats per minute, (p less than 0.001) whereas in those given propofol the comparable values were 71.2, with standard deviation of 14.4, and 53.6 with standard deviation of 9.7 millimetres of mercury (p less than 0.001), and 115.2, with standard deviation of 13.6, and 100.5 with standard deviation of 20.1 beats per minute (p less than 0.01), respectively. Mean systemic arterial pressures in the subgroups of cyanotic patients before and 30 minutes after sedation were 74.8, with standard deviation of 14.6, and 72.7, with standard deviation of 12.4 millimetres of mercury for those receiving midazolam and ketamine (p equals to 0.544), and heart rates were 119.3, with standard deviation of 12.2, and 104.6 with standard deviation of 16.1 beats per minute (p equals to 0.001). In those given propofol, the comparable values were 71.1 with deviation of 15.5 and 53.9 with deviation of 9.2 millimetres of mercury (p equals to 0.001), and 126.7 with deviation of 20.8 and 107.2 with deviation of 13.5 beats per minute (p equals to 0.001), respectively.

Conclusions

In cyanotic children, propofol used as a sedative agent during cardiac catheterization causes a decrease in mean arterial pressure and arterial desaturation. Ketamine produces more stable haemodynamic data in children with congenitally malformed hearts.
Eddy forcing of the mean flow in the Southern Ocean
Authors: Hughes Chris W. , Ash Ellis R.
Published: February 2008

We examine the force (or acceleration) exerted by eddies on the mean flow of the Southern Ocean using mapped sea surface height anomalies derived from satellite altimeter measurements. We compare this with the position of jets in the mean flow indicated by regions of increased gradient in the mean sea surface temperature. The eddy force itself is not of primary importance; rather, the curl of that force affects the mean flow, so the irrotational force due to the gradient of eddy kinetic energy can be ignored, leaving a remainder that can be interpreted in terms of the eddy vorticity flux. Unlike previous modeling and altimetric studies, we find that the eddies act to decelerate some of the strongest jets and act as vorticity sources for others. The strongest jets are clearly not accelerated by eddies. A problem of interpretation does remain, however, since it is not clear how sea surface temperatures are related to the mean flow. This ambiguity can only be completely resolved by measurement of the mean flow, requiring a geoid that is accurate at length scales of order 100 km.
Time reverse modeling of low‐frequency microtremors: Application to hydrocarbon reservoir localization
Authors: Steiner Brian , Saenger Erik H. , Schmalholz Stefan M.
Published: February 2008

Time reverse modeling is applied to synthetic and real low‐frequency microtremors measured at the Earth surface with synchronized seismometers. In contrast to previous time‐reverse applications, no single event or first arrival time identification is applied for microtremor localization. Synthetic low‐frequency microtremors are numerically generated within a small underground area and modeled with a finite‐difference algorithm simulating two‐dimensional elastic wave propagation. Time reverse modeling using synthetic microtremors shows that small underground source areas can be accurately located. Different source characteristics which emit mainly P‐waves or S‐waves vertically influence the localization accuracy. Time reverse modeling is applied to two real microtremor data sets acquired 16 months apart above known oil reservoirs nearby Voitsdorf, Austria, to investigate whether spectral anomalies observed above the reservoirs originate from the reservoirs. Time reverse modeling indicates that low‐frequency microtremor signals originate from the reservoir locations and provides a possible method for reservoir localization.
Southern hemisphere tropospheric aerosol microphysics
Authors: Gras John L.
Published: February 2008

Aerosol particle size distribution data have been obtained in the southern hemisphere from approximately 4°S to 44°S and between ground level and 6 km, in the vicinity of eastern Australia. The relative shape of the free‐tropospheric size distribution for particles with radii larger than approximately 0.04 μm was found to be remarkably stable with time, altitude, and location for the autumn‐winter periods considered. This was despite some large concentration changes which were found to be typical of the southeastern Australian coastal region. The majority of free‐troposphere large particles were found to have sulfuric acid or lightly ammoniated sulfate morphology. Large particles in the boundary layer almost exclusively had a sea‐salt morphology.
The quasi‐adiabatic ion distribution in the central plasma sheet and its boundary layer
Authors: Ashour‐Abdalla Maha , Büchner Jorg , Zelenyi Lev M.
Published: February 2008

This paper derives for the first time, the consequences of quasi‐adiabatic ion motion in the magnetospheric tail, which is in fact a chaotic scattering of the ions due to their essentially nonadiabatic behavior. This is caused by the nonlinearity of their equations of motion in the strongly curved tail magnetic field and results from separatrix traversals in the phase space. In this paper it is shown how the continuous violation of adiabaticity of the ion motion in the Earth's magnetotail leads to a redistribution of ions between the central plasma sheet (CPS) and the plasma sheet boundary layer (PSBL). It is also shown that, due to the mechanism described in this paper, ions are accelerated to the PSBL even without any assumption of the existence of an electric field caused by reconnection with an χ line. For the CPS ion distribution this acceleration also results in the depletion of some domains in velocity space that can lead to substantial non‐Maxwellian features.
On the influence of the magnetization of a model solar wind on a laboratory magnetosphere
Authors: Rahman H. U. , Yur G. , White R. S. , Birn J. , Wessel F. J.
Published: February 2008

The interaction of a magnetized plasma beam with a stationary dipole field, analogous to the interaction of the solar wind with the Earth's magnetosphere, is explored in a laboratory experiment. Experimental parameters are chosen to scale qualitatively similar to the parameters in the Earth's magnetosphere. We find that the magnetization of the laboratory “solar wind,” generated by injecting a plasma across a preexisting magnetic field, requires a certain minimum magnetic field strength. Differences between the resulting magnetospheres for northward and southward “solar wind” or “interplanetary” magnetic fields (IMF) are demonstrated by global pictures and by magnetic field measurements above the north polar region. These measurements show patterns of the variation of the transverse field component which are similar to those found by satellite measurements above the Earth. This indicates the presence of similar field‐aligned current systems. We demonstrate particularly the presence (for northward IMF) and absence (for southward IMF) of the pattern attributed to the “NBZ” (northward Bz) current system.
High‐resolution backscatter power observations of 440‐MHz E region coherent echoes at Millstone Hill
Authors: Foster J. C. , Tetenbaum D.
Published: February 2008

A 40‐µs pulse length has been used to provide 10‐s temporal and 6‐km range resolution observations of E region coherent backscatter from the premidnight eastward electrojet region to the north of Millstone Hill. The sensitivity of the Millstone UHF system is such that coherent returns can be observed over a 80‐dB dynamic range and at levels down to the incoherent scatter background. Our observations can be divided into two categories: strong events in which the backscattered amplitude nears saturation and weak events in which spatial structure and large‐amplitude variations are common. Calibrated observations find a typical volume scattering coefficient of ∼10−11m−1 at 440 MHz during strong events with a maximum level of 9×10−10m−1 observed for brief intervals. During less intense events the radar backscatter is modulated by ∼30 dB in amplitude at Pc 5 frequencies (150–500 s) by waves with spatial wavelength 50–100 km. Our observations support the premise that the weak irregularities grow linearly with electric field strength and reach a saturation amplitude beyond which the oscillating electric field of the Pc pulsation has little effect. The observed variation of backscattered power with range is interpreted using a geometrical model which accounts for the detailed antenna beam pattern, a magnetic aspect angle sensitivity of −10 dB per degree, and a thin layer of irregularities centered at 110 km altitude. For strongly driven conditions a comparison of the range variation of backscattered power with our thin layer model suggests that the signal power becomes increasingly dominated by strong scatterers confined to a narrower altitude range. The apparent altitude extent of the strongest irregularities decreases by a factor of 2 as the amplitude of the backscattered signal increases by a factor of 10.
A global model of gyroviscous field line merging at the magnetopause
Authors: Stasiewicz K.
Published: February 2008

A gyroviscous model of the magnetopause current layer is applied to the entire magnetopause with the inner boundary condition provided by a quantitative model of the magnetospheric field (BM) and the outer boundary condition given by the interplanetary magnetic field (IMF) draped against the magnetopause surface. It is found that the magnetopause surface is divided into at least four different regions by a tangential singularity line (Bn = 0) that separates regions with different signs of the normal component and rotation singularity lines (BM ∥ BIMF) that separate regions with different magnetic polarizations (rotations). The tangential singularity line (TSL) has topological properties similar to the classical reconnection line and the rotation singularity lines (RSL) are similar to lines of “antiparallel merging.” The field topology in the regular regions is determined by field line tracing using the model solutions. It is argued that the whole magnetopause surface, except the singular separation regions, possesses a stable rotational structure that can be described locally by a planar model. It is proposed that the singular regions on the magnetopause surface (TSL and RSL) play the role of gates for solar wind plasma entry into the magnetosphere and that rotational singularities are observed as flux transfer events. Observations of velocity jumps at the magnetopause that were previously classified as “high‐speed reconnection flows,” “tangential discontinuity” crossings as well as “diffusive entry” crossings can all be explained as special cases of the gyroviscous merging theory. The paper offers a unified view of such disparate concepts as steady state reconnection, antiparallel merging, viscous interactions, patchy reconnection, flux transfer events, and impulsive penetration.
Anisotropy and minimum variance directions of solar wind fluctuations in the outer heliosphere
Authors: Klein Larry W. , Roberts D. Aaron , Goldstein Melvyn L.
Published: February 2008

We systematically examine Voyager 2 magnetic field and plasma data over time intervals of 1 to 12 hours in the heliospheric range of 1 to 10 AU to study the evolution of the anisotropy of solar wind fluctuations. Consistent with previous results, we find that, on average, the directions of minimum variance vectors of magnetic fluctuations are close to the mean magnetic field direction with an increasing component of the variance along the field at larger scales. In both compression regions and rarefactions at large radial distances there is more spread in the minimum variance directions about the mean field than at smaller radial distances. The power in smaller‐scale fluctuations in the magnetic field components perpendicular to the local mean field B0 is in the ratio of about 5∶1 near 1 AU (compared to the power in fluctuations parallel to the field) at the scale of 1 hour but decreases to about 3∶1 farther out. We find no evidence for selective enhancement of out‐of‐the‐ecliptic components of fluctuations as predicted by a possible geometrical coupling between refracting Alfvén waves and compressive modes. In contrast to results for field fluctuations, our analysis of fluctuations in the velocity shows that the minimum variance direction systematically remains more radially oriented and becomes increasingly less oriented along B0 with increasing heliocentric distance. The velocity fluctuations are also generally more isotropic than the magnetic fluctuations at all distances examined. Our observations cannot be explained by a superposed wave picture, and thus are consistent with the view that nonlinear turbulent evolution is responsible for the anisotropy in the fluctuations.
Saturation effects in Na lidar temperature measurements
Authors: von der Gathen Peter
Published: February 2008

Na atoms residing in the 80–110 km altitude region can be used to probe the Doppler‐broadened hyperfine structure (hfs) of their D2 resonance transition by ground‐based lidar and hence to deduce atmospheric temperatures. In principle, two different methods may be employed: (1) wavelength scanning of the hfs with a narrow‐band laser and signal detection with a broad‐band receiver, and (2) use of a broad‐band laser and wavelength scanning of the hfs with a narrow‐band receiver. These two methods are affected in different ways by laser‐induced saturation in the Na layer, the effect on the measurements of sodium densities and of atmospheric temperatures being quite different. Density measurements are affected by the absolute level of saturation. Temperature measurements, however, are affected by the difference in saturation at the scanned wavelengths. If, additionally, observed signal levels are taken into account, method 1 is more efficient than method 2 for both types of measurements at nighttime, whereas a modified method 2 surpasses method 1 for temperature measurements at daytime.
Electron signatures of satellite sweeping in the magnetosphere of Uranus
Authors: Cooper J. F. , Stone E. C.
Published: February 2008

The Voyager 2 Cosmic Ray System found large‐scale macrosignatures of satellite sweeping for MeV electrons near the orbits of the satellites Miranda, Ariel, and Umbriel in the magnetosphere of Uranus. Due to the large magnetic inclinations of satellite orbits at Uranus, sweeping rates vary along the orbits with the McIlwain L parameter. However, no evidence was found, where expected, for fresh sweeping signatures at such positions. Although the maximal electron intensity occurs near Voyager 2's minimum L (4.67) as predicted by the Q3 field model, the intensity minima in the macrosignatures show large outward displacements (≤0.5 RU) from minimum‐L positions of the associated satellites. These radial displacements increased with measured electron energy and at higher magnetic latitudes. Pitch angle distributions are generally more anisotropic outside the macrosignatures and more isotropic within, as determined from comparison of inbound and outbound intensity profiles at different latitudes. These anisotropy measurements provide the basis for latitudinal flux extrapolation, which when coupled with power law scaling of spectral distributions allow the calculation of phase space density profiles. The latter show local minima in the macrosignatures and are indicative of distributed electron sources in the inner magnetosphere and/or nonadiabatic transport processes such as pitch angle scattering and magnetospheric recirculation. Preliminary diffusion coefficients with values DLL ∼ 10−7–10−6 RS² and radial dependence DLL ∼ L3–L4 have been estimated for the macrosignatures. The low‐order L dependence of DLL is consistent with diffusion driven by ionospheric dynamo. However, quantitative modeling of radial and pitch angle diffusion is required to assess the formative processes for the macrosignatures before more physically meaningful transport parameters can be determined.
On The initiation of subduction
Authors: Mueller Steve , Phillips Roger J.
Published: February 2008

Estimates of shear resistance associated with lithospheric thrusting and convergence represent lower bounds on the force necessary to promote trench formation. Three environments proposed as preferential sites of incipient subduction are investigated: passive continental margins, transform faults/fracture zones, and extinct ridges. None of these are predicted to convert into subduction zones simply by the accumulation of local gravitational stresses. Subduction cannot initiate through the foundering of dense oceanic lithosphere immediately adjacent to passive continental margins. The attempted subduction of buoyant material at a mature trench can result in large compressional forces in both subducting and overriding plates. This is the only tectonic force sufficient to trigger the nucleation of a new subduction zone. The ubiquitous distribution of transform faults and fracture zones, combined with the common proximity of these features to mature subduction complexes, suggests that they may represent the most likely sites of trench formation if they are even marginally weaker than normal oceanic lithosphere.
Plate reconstruction uncertainties using empirical probability density functions
Authors: Richardson Randall M. , Cole Gregory L.
Published: February 2008

We present a method of determining plate reconstruction uncertainties using empirical probability density functions (PDFs). We convert estimated positioning errors of fracture zone and magnetic anomaly crossings into data PDFs which describe the uncertainty in the location of each fracture zone or magnetic anomaly crossing. An empirical PDF is formed for the rotation between a single plate pair based on the ability to align the rotated data along a series of ridge and transform segments. Monte Carlo techniques are then used to sample the PDFs for rotations between single plate pairs to form a PDF for a sequence of rotations. This is accomplished with a frequency of occurrence approach for a gridded representation of possible combined rotations. We also develop PDFs for the reconstructed positions of points on the rotated plates from the PDF for the rotation. Confidence regions for any of the PDFs are formed by contouring the cumulative probabilities of grid points within the PDF. We provide comparisons with other previously published studies for the anomaly 13 single plate pair reconstruction between the Pacific and Antarctic plates as well as for the anomaly 6 (19.8 Ma) combined reconstruction between the Pacific and North American plates. Results for the anomaly 13 reconstruction are generally consistent with previous studies, but smaller confidence regions are attributed to the more robust nature of the empirical PDF approach that we have used. The 95% confidence region for the anomaly 6 reconstruction is less than half that of the worst case scenario. The benefit of our Monte Carlo technique is that it adequately samples the PDFs for all of the rotations, thus accurately including the effects of coupling uncertainties between pole location and amount of rotation.
Seismic reflection studies in Long Valley Caldera, California
Authors: Black Ross A. , Deemer Sharon J. , Smithson Scott B.
Published: February 2008

Seismic reflection studies in Long Valley caldera, California, indicate that seismic methods may be successfully employed to image certain types of features in young silicic caldera environments. However, near‐surface geological conditions within these environments severely test the seismic reflection method. Data quality are degraded by static, reverberation, and band‐limiting problems due to these near‐surface conditions. In Long Valley, seismic reflection and refraction methods were used to image both the shallow and deep geothermal aquifers within the area. The deep geothermal aquifer, the welded Bishop Tuff, was imaged as a fairly continuous reflector across the western moat of the caldera. Near‐surface refraction information indicates that there may be a buried paleochannel system or horst and graben system that could control the shallow geothermal flow pattern. High‐amplitude events observed in a wide‐angle survey were originally interpreted as reflections from a contemporary magma body. However, a migration of the events utilizing the new generalized cellular migration algorithm indicates that these events are probably reflections from the faults of the caldera ring fracture system. The reflections may be caused by the high acoustic impedance contrast associated with the juxtaposition of relatively low‐velocity, low‐density, caldera fill against the granite plutons and metasediments of the Sierran basement along this fault system.
The Madden‐Julian oscillation and the angular momentum balance in a barotropic ocean model
Authors: Ponte Rui M. , Gutzler David S.
Published: February 2008

Surface wind stresses associated with the Madden‐Julian oscillation transfer angular momentum between the atmosphere and the underlying ocean. The resulting anomalies in oceanic angular momentum (related to either changes in zonal currents or latitudinal redistribution of mass) and the torques coupling the ocean and the solid Earth are examined for simple zonal stress patterns representing idealized 40‐ to 50‐day fluctuations of Pacific winds. Because the contribution of baroclinic variability to the angular momentum budget is in general small when vertically integrated quantities are considered (Ponte, 1990), only the barotropic response is studied. Numerical solutions of the shallow water equations with linear bottom friction are found for a constant depth basin centered on the equator and extending over 140° in longitude. The angular momentum exchanges between the ocean and solid Earth in the model involve the continental torque (i.e., body forces on eastern and western walls due to coastal sea level anomalies) and the bottom friction torque. Solutions yield a dominant balance between the wind and continental torques, with the bottom friction torque being negligible. The amplitude of the total torque acting on the ocean and the corresponding angular momentum fluctuations are very small compared with the amplitude of the applied wind torque. The ocean delivers to the solid Earth, with no significant time delays, the angular momentum anomalies received from the atmosphere. In general, sea level anomalies are nearly uniform along the eastern boundary, and the respective meridionally integrated torque is much larger than the one exerted on the western wall. Solutions also suggest that coastal (barotropic) sea level fluctuations as small as 0.5–1.5 cm are sufficient to cause variations in the length of day comparable to observed values in the 40‐ to 50‐day band.
Marine biota effects on the compositional structure of the world oceans
Authors: Kheshgi H. S. , Flannery B. P. , Hoffert M. I.
Published: February 2008

The vertical structure of total carbon, alkalinity, nutrients, and dissolved oxygen in the world oceans is examined with a one‐dimensional equatorial ocean/polar ocean box model. Photosynthesis/respiration cycles affect and are affected by fluxes in the ocean and the structure of the profiles. Marine biota produce by‐products that lead to organic and inorganic (calcareous) sediments. In steady state, rates of phosphorous and alkalinity runoff from land are linked to surface nutrient supply, the rates of particulate rain, the degree of anoxia near sediments, the lysocline depth, and thereby control rates of sedimentation. These, in turn, are influenced by internal mixing dynamics and the action of the marine biota. The interdependence of ocean composition and rates of organic and inorganic carbon burial is found to be sensitive to the traits of the marine biosphere.