bluuebunny/crossref_metadata_2025 huggingface dataset:
Protective effect of phlorotannin components phloroglucinol and eckol on radiation‐induced intestinal injury in mice
Authors: Moon Changjong , Kim Sung‐Ho , Kim Jong‐Choon , Hyun Jin Won , Lee Nam Ho , Park Jae Woo , Shin Taekyun
Published: September 2007

Components of phlorotannin, which were extracted from Ecklonia species, have been reported to have in vitro radioprotective and antioxidative effects. The radioprotective effects of two of the components of phlorotannin, phloroglucinol and eckol, in intestinal stem cells were examined by evaluating their effects on jejunal crypt survival and apoptosis in gamma‐irradiated mice. Pretreating the mice (i.p. 20 mg/kg of body weight at 12 and 36 h before irradiation) prior to irradiation with either phloroglucinol or eckol significantly improved the survival of the jejunal crypt (p < 0.001 and p < 0.01 vs irradiation controls at 3.5 days after 8 Gy irradiation, respectively). The administration of phloroglucinol and eckol prior to irradiation protected the intestinal crypts from radiation‐induced apoptosis (p < 0.05 vs irradiation controls at 12 h after 1 Gy irradiation). Although the mechanism for this inhibitory effect remains unknown, these results showed that phloroglucinol and eckol might be useful radioprotectors that can defend intestinal stem cells against the oxidative damage caused by gamma‐irradiation. Copyright © 2007 John Wiley & Sons, Ltd.
Inhibition of microglial neurotoxicity by ethanol extract of Artemisia asiatica Nakai
Authors: Lim Beong Ou , Chung Hae Gon , Lee Won‐Ha , Lee Ho Won , Suk Kyoungho
Published: September 2007

Artemisia asiatica Nakai has been used for the treatment of infections and inflammatory disorders in traditional Oriental medicine. Previously, an ethanol extract of A. asiatica has been shown to exert antioxidative and antiinflammatory activities and to exhibit protective effects against experimentally induced damage in the gastrointestinal system, liver and pancreas. This study examined whether the ethanol extract of A. asiatica affects inflammatory activation of microglia in the central nervous system, and whether the antiinflammatory activity of A. asiatica is related to neuroprotective effects. The extract of A. asiatica inhibited inflammatory activation of mouse microglial cells as determined by the production of nitric oxide and the expression of inducible nitric oxide synthase and inflammatory cytokine. The extract also protected nerve growth factor‐differentiated PC12 cells against microglial cytotoxicity, indicating that the ethanol extract of A. asiatica may be neuroprotective by inhibiting microglial neurotoxicity. Copyright © 2007 John Wiley & Sons, Ltd.
Effective error correction method for quantum information processing
Authors: Kawamura Minaru , Morimoto Takuji , Mori Yoshiyuki , Sawae Ryuichi , Takarabe Kenichi , Manmoto Yoshinori , Sakata Toshio
Published: September 2007

In this paper we present an effective error correction method to correct the errors that occur during quantum information processing. (There are various methods of quantum error correction such as error correcting code or decoherence free subspace which protect quantum information from noise, and they are useful for storage and communication; however, it would be difficult to adapt them to quantum information processing practically.) In this method the error detection is carried out through the asymmetry or the irreversibility of quantum computers, which ought to be inherently symmetric and reversible. The irreversibility is usually caused by decoherence and dissipation, and the processing's own adjoint operator can, therefore, be used to condense such errors and enable their detection. The effectiveness of this method is investigated with an NMR quantum computer. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007
Decomposition of deformation density into orbital components
Authors: Pakiari A. H. , Fakhraee S. , Azami S. M.
Published: September 2007

In this research, deformation density matrix has been introduced as matrix representation of the density difference between the complex and fragments. The deformation density matrix is then diagonalized to obtain the magnitude of displaced charges as eigenvalues. Correspondingly, the eigenvectors reveal the spaces responsible for reorganization of the electrons because of the complex formation. The formalism has been applied on some CO2planar clusters, and the results showed that how the deformation density can be successfully separated into in‐plane and out‐of‐plane contributions. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008
Disappearance of interfering alkali‐metal adducted peaks from matrix‐assisted laser desorption/ionization mass spectra of peptides with serine addition to α‐cyano‐4‐hydroxycinnamic acid matrix
Authors: Nishikaze Takashi , Takayama Mitsuo
Published: September 2007

It has been described that ion yield in both positive‐ and negative‐ion matrix‐assisted laser desorption/ionization mass spectrometry (MALDI MS) of peptides is often inhibited by trace amounts of alkali metals and that the MALDI mass spectra are contaminated by the interfering peaks originating from traces of alkali metals, even when sample preparation is carefully performed. Addition of serine to the commonly used MALDI matrix α‐cyano‐4‐hydroxycinnamic acid (CHCA) significantly improved and enhanced the signals of both protonated and deprotonated peptides, [M+H]+ and [M−H]−. The addition of serine to CHCA matrix eliminated the alkali‐metal ion adducts, [M+Na]+ and [M+K]+, and the CHCA cluster ions from the mass spectra. Serine and serinephosphate as additives to CHCA enhanced and improved the formation of molecular‐related ions of phosphopeptides in negative‐ion MALDI mass spectra. Copyright © 2007 John Wiley & Sons, Ltd.
Mendelian randomization: Using genes as instruments for making causal inferences in epidemiology
Authors: Lawlor Debbie A. , Harbord Roger M. , Sterne Jonathan A. C. , Timpson Nic , Davey Smith George
Published: September 2007

Observational epidemiological studies suffer from many potential biases, from confounding and from reverse causation, and this limits their ability to robustly identify causal associations. Several high‐profile situations exist in which randomized controlled trials of precisely the same intervention that has been examined in observational studies have produced markedly different findings. In other observational sciences, the use of instrumental variable (IV) approaches has been one approach to strengthening causal inferences in non‐experimental situations. The use of germline genetic variants that proxy for environmentally modifiable exposures as instruments for these exposures is one form of IV analysis that can be implemented within observational epidemiological studies. The method has been referred to as ‘Mendelian randomization’, and can be considered as analogous to randomized controlled trials. This paper outlines Mendelian randomization, draws parallels with IV methods, provides examples of implementation of the approach and discusses limitations of the approach and some methods for dealing with these. Copyright © 2007 John Wiley & Sons, Ltd.
Incorporating intermediate binary responses into interim analyses of clinical trials: A comparison of four methods
Authors: Whitehead Anne , Sooriyarachchi Marina Roshini , Whitehead John , Bolland Kim
Published: September 2007

In clinical trials with a long period of time between randomization and the primary assessment of the patient, the same assessments are often undertaken at intermediate times. When an interim analysis is conducted, in addition to the patients who have completed the primary assessment, there will be those who have till then undergone only intermediate assessments. The efficiency of the interim analysis can be increased by the inclusion of data from these additional patients. This paper compares four methods of increasing information based on model‐free estimates of transition probabilities to incorporate intermediate assessments from patients who have not completed the trial. It is assumed that
the observations are binary and that there is one intermediate assessment. The methods are the score and Wald approaches, each with the log‐odds ratio and probability difference parameterizations. Simulations show that all four approaches have good properties in moderate to large sample sizes. Copyright © 2007 John Wiley & Sons, Ltd.
Stopping rules for surveys with multiple waves of nonrespondent follow‐up
Authors: Rao R. Sowmya , Glickman Mark E. , Glynn Robert J.
Published: September 2007

In surveys with multiple waves of follow‐up, nonrespondents to the first wave are sometimes followed intensively but this does not guarantee an increase in the response rate or an appreciable change in the estimate of interest. Most prior research has focused on stopping rules for Phase I clinical trials. To our knowledge there are no standard methods to stop follow‐up in observational studies. Previous research suggests optimal stopping strategies where decisions are based on achieving a given precision for minimum cost or reducing cost for a given precision. In this paper, we propose three stopping rules that are based on assessing whether successive waves of sampling provide evidence that the parameter of interest is changing. Two of the rules rely on examining patterns of observed responses while the third rule uses missing data methods to multiply impute missing responses. We also present results from a simulation study to evaluate our proposed methods. Our simulations suggest that rules that adjust for nonresponse are preferred for decisions to discontinue follow‐up since they reduce bias in the estimate of interest. The rules are not complicated and may be applied in a straightforward manner. Discontinuing follow‐up would save time and possibly resources, and adjusting for the nonresponse in the analysis would reduce the impact of nonresponse bias. Copyright © 2007 John Wiley & Sons, Ltd.
Risk Factors for Recurrence to the Lymph Node in Papillary Thyroid Carcinoma Patients without Preoperatively Detectable Lateral Node Metastasis: Validity of Prophylactic Modified Radical Neck Dissection
Authors: Ito Yasuhiro , Higashiyama Takuya , Takamura Yuuki , Miya Akihiro , Kobayashi Kaoru , Matsuzuka Fumio , Kuma Kanji , Miyauchi Akira
Published: September 2007

Background

Although papillary carcinoma usually shows mild characteristics, it metastasizes and shows recurrence to the lymph node in high incidences. Of the two representative lymph node compartments to which papillary carcinoma metastasizes, the central compartment can be routinely dissected via the surgical incision made for thyroidectomy. However, the routine application of prophylactic lateral node dissection (modified radical neck dissection [MND]) remains controversial. In this study, we investigated risk factors for lymph node recurrence of papillary carcinoma to determine the appropriate application of prophylactic MND.

Methods

We investigated risk factors for lymph node recurrence in 1,231 patients without preoperatively detectable lateral node metastasis who underwent thyroidectomy, central node dissection, and prophylactic MND for papillary carcinoma between 1987 and 1995.

Results

The incidence of lateral node metastasis and the number of metastatic lateral nodes significantly increased with carcinoma size. The lymph node disease‐free survival (LN‐DFS) was also significantly worse in carcinoma with a maximal diameter greater than 3 cm. Massive extrathyroid extension, male gender, and age 55 years or older also reflected a poorer LN‐DFS. The 10‐year LN‐DFS rates of patients with carcinoma having two and three or four of these features were low at 88.5% and 64.7%, respectively, although the rates of those with carcinoma having no or only one characteristic were better than 95%.

Conclusions

Prophylactic MND is recommended for cases of papillary carcinoma demonstrating two or more of the following four characteristics; male gender, age 55 years or older, maximal tumor diameter larger than 3 cm, and massive extrathyroid extension.
From individual interactions to population dynamics: individual resource partitioning simulation exposes the causes of nonlinear intra‐specific competition
Authors: Johst Karin , Berryman Alan , Lima Mauricio
Published: September 2007

Intra‐specific competition defines the relationship between population density and the performance of individual organisms (R‐function). Observation of this relationship in nature shows it to be frequently nonlinear, and it has been argued, on intuitive grounds, that this nonlinearity is due to the type of competition (scramble or contest) being expressed. Here, we use an individual‐based simulation model to investigate the effects of three resource partitioning schemes, representing different types of competition, on the form of the R‐function. Results indicate that all resource partitioning schemes can give rise to concave or convex functions depending on the balance between maximum individual birth rate, maintenance cost, and demand for resources. Given high growth rates and maintenance costs, contest competitors tend to exhibit less concavity than scramblers. Therefore, population stability can be strongly affected by the strategy of resource partitioning. Life histories and environmental conditions that encourage the homogeneous distribution of resources among individuals lead to complex and unstable dynamics. Stable dynamics is fostered by heterogeneous resource distribution, which could result from such things as social hierarchies, individual and environmental variability, and large, indivisible resource packets.
Combined Intrauterine Vascular Insufficiency and Brachial Plexus Palsy: A Case Report
Authors: Sinclair Catherine , Murray Peter M. , Terkonda Sarvam P.
Published: September 2007

A unique case of combined intrauterine vascular insufficiency and complete brachial plexus palsy is described in a newborn delivered by cesarean section. Intrauterine vascular insufficiency resulted in a right below elbow amputation at 3 weeks of age. Amputation length was preserved after a pedicled thoracoabdominal flap. Function of the C5, C6, and C7 nerve roots returned to normal by 3 months of age.
A novel ovary‐specific and ovulation‐associated variant of epoxide hydrolase 2
Authors: Shkolnik Ketty , Ben-Dor Shifra , Galiani Dalia , Hourvitz Ariel , Dekel Nava
Published: September 2007

Ovulation is a complex process initiated by the surge of the pituitary luteinizing hormone (LH) that provokes the expression of specific genes. We report herein the isolation and characterization of an ovulation‐associated, ovary‐specific novel isoform of epoxide hydrolase 2 (Ephx2), Ephx2C. This variant is exclusively expressed in the granulosa cells of preovulatory mouse ovarian follicles. The LH‐induced expression of Ephx2C is mediated by the protein kinase A and partially by the protein kinase C signaling pathways. The involvement of p38 kinase has also been demonstrated.
The MlotiK1 channel transports ions along the canonical conduction pore
Authors: Silverman William R. , Heginbotham Lise
Published: September 2007

Although the cyclic nucleotide‐modulated potassium channel from Mesorhizobium loti, MlotiK1, is easily studied using a 86Rb+ flux assay, its comparatively low activity raises serious concerns about the integrity of the purified protein. We investigated the pathway of uptake using a multi‐pronged approach. First, we probed the conduction pathway using quaternary ammonium compounds known to block conduction in eukaryotic K+ channels. Second, we examined the effect of chemical modification of putative pore‐lining residues. Our results are consistent with ions traversing MlotiK1 along a conduction pathway like that of the eukaryotic channels, but at a much slower rate.
How motivation, opportunity, and ability drive knowledge sharing: The constraining‐factor model
Authors: Siemsen Enno , Roth Aleda V. , Balasubramanian Sridhar
Published: September 2007

We introduce and empirically test a theoretical metamodel that explains knowledge‐sharing behavior among employees. Building on the well‐established motivation–opportunity–ability (MOA) framework, we posit that knowledge sharing among employees is a function of their MOA to do so. Existing literature suggests that the interaction among motivation, opportunity, and ability drives knowledge‐sharing behavior. In contrast, we specify a new model in which the “bottleneck” or constraining factor among the MOA variables determines the degree of knowledge sharing that occurs. This constraining‐factor model (CFM) fits the data better than the traditional multiplicative model and reveals a new, qualitatively different portrait of knowledge sharing that resolves some of the puzzles in the previous literature. The CFM provides macro‐level insights with respect to how operations managers can improve employee knowledge sharing by focusing on the bottleneck MOA variable. As a result, the CFM can help set strategic directions of related policies. The model emphasizes that, counter to conventional wisdom, the MOA variables should not be addressed independently, but rather in a dynamic and coordinated way.
Charcot–Marie–Tooth type 4B demyelinating neuropathy: deciphering the role of MTMR phosphatases
Authors: Previtali Stefano C. , Quattrini Angelo , Bolino Alessandra
Published: September 2007

Charcot–Marie–Tooth type 4B (CMT4B) is a severe autosomal recessive neuropathy with demyelination and myelin outfoldings of the nerve. This disorder is genetically heterogeneous, but thus far, mutations in myotubularin-related 2 (MTMR2) andMTMR13genes have been shown to underlie CMT4B1 and CMT4B2, respectively. MTMR2 and MTMR13 belong to a family of ubiquitously expressed proteins sharing homology with protein tyrosine phosphatases (PTPs). The MTMR family, which has 14 members in humans, comprises catalytically active proteins, such as MTMR2, and catalytically inactive proteins, such as MTMR13. Despite their homology with PTPs, catalytically active MTMR phosphatases dephosphorylate both PtdIns3Pand PtdIns(3,5)P2phosphoinositides. Thus, MTMR2 and MTMR13 may regulate vesicular trafficking in Schwann cells. Loss of these proteins could lead to uncontrolled folding of myelin and, ultimately, to CMT4B. In this review, we discuss recent findings on this interesting protein family with the main focus on MTMR2 and MTMR13 and their involvement in the biology of Schwann cell and CMT4B neuropathies.
Seeing Gender over the Short and Long Haul
Authors: McConnaughy Corrine M.
Published: September 2007

One might break research questions about gender and politics over time into two basic categories. On the one hand, there are questions that speak to processes unfolding, perhaps rather slowly, over time. In this long-haul category, we might find studies of such things as generational shifts in patterns of attitudes about gendered political roles (Jennings 2006) or of the development of gendered national identities with evolving constitutional interpretations (Ritter 2006). On the other hand, there are inquiries about the dynamics, or instability, of shorter-run patterns. These intellectual pursuits might include seeking to explain short-haul phenomena like changes in partisan gaps between men and women, perhaps even within the duration of a single campaign season (Sapiro and Conover 1997). Both categories, of course, are incredibly important realms of inquiry. My argument is for improvements in our studies of shorter-term dynamics and, ultimately, for the integration of studies of both short- and long-run processes, with improved measurement and modeling strategies as the crucial tools we need to get there.
Gender and Politics over Time
Authors: Ritter Gretchen
Published: September 2007

What can be learned from the broad sweep of history about gender and politics? Are there ways to study gender politics from a more historical perspective that differ from the methods and approaches typically taken by scholars focused on the contemporary political record? Finally, does attentiveness to gender politics over time challenge any of our basic understandings or presumptions about gender politics today, and does it lead us to new questions and research agendas? I begin by exploring the contribution that scholarship within the field of American political development (APD) can make to the study of gender politics over time. The essay then turns to conceptualizing gender, a concept that is defined in a wide variety of ways across the humanities and social sciences. The third section applies some of the conceptual approaches described in the first two parts of this essay to an analysis of three cases in American political history. Finally, I conclude with a call for the inclusion of gender more broadly in the study of politics.
Historical Perspectives in Comparative Politics and Gender Studies
Authors: Tripp Aili Mari
Published: September 2007

Historical perspectives form the backdrop and the context for much work on gender in comparative politics scholarship, yet history itself has rarely been incorporated as the lens through which the theorizing of gender occurs. The current growth of interest in gender studies in American political development is strangely not reflected in contemporary trends of historical institutionalism within comparative politics (see Gretchen Ritter's essay in this issue). Although scholars of comparative politics working on gender or women almost always incorporate historical perspectives in their analyses, history is generally drawn on as background or to provide context. History itself is generally not the primary focus of their analysis and historical processes are not used to generate theory. It has been only recently that scholars, especially in the field of historical institutionalism (HI), have begun to think about new ways in which history could be used to develop theory and create new empirical knowledge in the field of comparative politics and gender.
Theorizing Women's Representation in the United States
Authors: Dovi Suzanne
Published: September 2007

From the perspective of women's experiences, it is easy to see that democratic representative institutions can be tools of oppression. After all, formal democratic institutions have been either a form of governance that has only ruled over women (e.g., women were formally prohibited from holding elected offices) or a form of governance in which women have ruled and been ruled unequally (e.g., the number of female representatives have been significantly lower than the number of male representatives). Moreover, informal representative institutions, for example, interest groups, do not seem to work for women as well as they do for powerful men (Strolovitch 2007). These facts suggest that democratic representative institutions need to be viewed suspiciously. We should not assume that representative institutions in democracies necessarily benefit all women. We need to recognize how they can divide women, pitting some women's interests and preferences against other women's interests and preferences. Democratic representative institutions can function to preserve the status quo, distributing benefits unjustly among different men and women.
Republican Lambs and the Democratic Pipeline: Partisan Differences in the Nomination of Female Gubernatorial Candidates
Authors: Stambough Stephen J. , O'Regan Valerie R.
Published: September 2007

In 2005, a record nine women served as their state's governor. Of these, eight were elected. A crucial and often difficult step for women to be successful in gubernatorial elections is for them to win the nomination for governor by their political party. From 1976 to 2004, only 79 women have won their party's nomination for governor. The record number of women nominees in a single year is 10, set in 1998 and 2002. Even with these recent successes, women as governors are both fairly rare and an understudied area of political science. In this study, we explore two different explanations for the nomination of women to elected office: the pipeline and sacrificial lamb models. Although some research argues that the sacrificial lamb model is outdated and has been replaced by the pipeline model, we find that both of these models are relevant for the study of female gubernatorial nominations, but in the same way for each political party. By examining gubernatorial election data from 1976 to 2004, we present evidence suggesting that the pipeline model helps to explain the nomination of Democratic women, while the sacrificial lamb model helps to explain the nomination of Republican women. Though preliminary, these findings have important implications for the growing, pro-Democratic, partisan imbalance of women officeholders.
Explicit analytical solutions for one‐dimensional steady state flow in layered, heterogeneous unsaturated soils under random boundary conditions
Authors: Lu Zhiming , Zhang Dongxiao , Robinson Bruce A.
Published: September 2007

In this study, we directly derive first‐order analytical solutions to the pressure head moments (mean and variance) for one‐dimensional steady state unsaturated flow in randomly heterogeneous layered soil columns under various random boundary conditions. We assume that the constitutive relation between the unsaturated hydraulic conductivity and the pressure head follows an exponential model, and treat the saturated hydraulic conductivity Ks as a random function and the pore size distribution parameter α as a random constant. Unlike the solution given in Lu and Zhang (2004) in which Kirchhoff transformation was used and the solution to pressure head variance was presented as a function of (cross‐)covariances related to the intermediate, Kirchhoff‐transformed variable, the solution to the pressure head variance presented in this paper is an explicit function of the input variabilities. In addition, we also give analytical solutions to the statistics of the unsaturated hydraulic conductivity and the effective water content. These first‐order analytical solutions are compared with those from Monte Carlo simulations. We also investigated the effect of uncertain boundary conditions, the relative contribution of input variabilities to the head variance, and the possible errors introduced by treating the correlated α field as a random constant in the analytical solutions. The results indicate that the uncertain constant head at the bottom of a deep soil column may not have a significant effect on predicting flow statistics in the upper portion of the column. Furthermore, it is found that treating α as a random constant is justified when the correlation length of α is relatively large as compared to the layer thickness.
Oxygen‐isotope and trace element constraints on the origins of silica‐rich melts in the subarc mantle
Authors: Eiler J. M. , Schiano P. , Valley J. W. , Kita N. T. , Stolper E. M.
Published: September 2007

Peridotitic xenoliths in basaltic andesites from Batan island in the Luzon arc contain silica‐rich (broadly dacitic) hydrous melt inclusions that were likely trapped when these rocks were within the upper mantle wedge underlying the arc. These melt inclusions have been previously interpreted to be slab‐derived melts. We tested this hypothesis by analyzing the oxygen isotope compositions of these inclusions with an ion microprobe. The melt inclusions from Batan xenoliths have δ18OVSMOW values of 6.45 ± 0.51‰. These values are consistent with the melts having been in oxygen isotope exchange equilibrium with average mantle peridotite at temperatures of ≥875°C. We suggest the δ18O values of Batan inclusions, as well as their major and trace element compositions, can be explained if they are low‐degree melts (or differentiation products of such melts) of peridotites in the mantle wedge that had previously undergone extensive melt extraction followed by metasomatism by small amounts (several percent or less) of slab‐derived components. A model based on the trace element contents of Batan inclusions suggests that this metasomatic agent was an aqueous fluid extracted from subducted basalts and had many characteristics similar to slab‐derived components of the sources of arc‐related basalts at Batan and elsewhere. Batan inclusions bear similarities to “adakites,” a class of arc‐related lava widely considered to be slab‐derived melts. Our results suggest the alternative interpretation that at least some adakite‐like liquids might be generated from low‐degree melting of metasomatized peridotites.
Boundary mixing in the thermocline of a large lake
Authors: Lorke Andreas
Published: September 2007

High‐resolution measurements of near‐bottom temperature stratification and current velocity were performed on the sloping boundary of a large lake at the depth of the seasonal thermocline. The measurements cover nearly the entire stratified period and reveal the periodic occurrence of strong temperature and current velocity fluctuations, which can be attributed to shoaling high‐frequency internal waves with periods between 5 and 20 min. Two different techniques are applied to obtain a long‐term record of dissipation rates of turbulent kinetic energy from the current velocity measurements. Shoaling of high‐frequency internal waves is associated with a strong and rapid increase of turbulent dissipation rates of up to four orders of magnitude. Since the occurrence of high‐frequency internal waves on the slope is correlated with the passage of the dominant basin‐scale internal Kelvin wave with a period of four days, energy dissipation rates on the slope vary with the same period. Diapycnal diffusivities, estimated by combining the dissipation estimates with simultaneously measured density stratification, follow a similar dynamics and a comparison with a basin‐scale diffusivity estimate based on tracer measurements reveal the importance of boundary mixing, which, at this particular site, is mainly driven by the interaction of high‐frequency internal waves with the sloping boundary.
Cold‐climate modification of Martian landscapes: A case study of a spatulate debris landform in the Hellas Montes Region, Mars
Authors: van Gasselt S. , Hauber E. , Neukum G.
Published: September 2007

We use spaceborne image and topographic data of Mars for a geomorphological study of the origin, development, and postemplacement modification of a 30‐km‐long spatulate landform in the Hellas Montes area, east of Hellas Planitia. The area is characterized by an abundance of lobate debris aprons, all of which have been interpreted as a result of creep and viscous deformation of rock and ice mixtures that make the eastern Hellas Planitia assemblages a type location for possible Martian rock glaciers. The spatulate landform has been discussed controversially in the past. Explanations range from a rock glacier to a wet debris avalanche or debris flow origin. This work scrutinizes arguments provided in earlier works and presents evidence that a landslide origin of the spatulate landform, connected with a sector collapse of a volcanic construct, is conceivable. We also find extensive observational evidence that the landslide has recently undergone or is still undergoing significant postemplacement modifications, which are characteristic of rock glaciers in periglacial environments. Creep deformation as well as disintegration of the original surface by thermokarstic degradation is considered to have obliterated impact craters and, in consequence, create a seemingly younger age. Similar processes are considered to be common on Mars under current climatic conditions. Our results imply that the strong and possible long‐term modification of landforms on Mars by cold‐climate processes often hinders the identification of their original nature and complicates the assessment of true ages.
Predicting downstream hydraulic geometry: A test of rational regime theory
Authors: Eaton Brett C. , Church Michael
Published: September 2007

The classical equations of hydraulic geometry are purely empirical, but the widespread similarity of the scaling (downstream) form of them suggests that they express some important underlying regularities in the morphology of stream channels through the drainage network. A successful physical theory of river regime must be able to reproduce and explain this regularity. In this paper we test the regime theory of Eaton et al. (2004) using selected data of hydraulic geometry. We first use data from environments in which bank strength presumably does not vary greatly, such as in anabranched channel systems and deltas. Regime models parameterized by assuming uniform relative bank strength plausibly describe the observed bankfull channel geometries in these systems. We then test a modified bank strength formulation for vegetated gravel bed rivers against downstream hydraulic geometry data sets in which relative bank strength is supposed to vary with channel scale. Assuming a uniform effective cohesion due to riparian vegetation, the regime model is again able to reproduce details of the channel geometry. Both analyses show that the classical hydraulic geometry represents only an approximation of the variation of channel form. If we have confidence in the theory, we may infer information about bank strength and bed material transport. The pattern of variation in these quantities, as well as discharge, through the drainage system lends approximate regularity to stream channel scaling that is summarized in the empirical relations.
Pleistocene hydrology of North America: The role of ice sheets in reorganizing groundwater flow systems
Authors: Person Mark , McIntosh Jennifer , Bense Victor , Remenda V. H.
Published: September 2007

While the geomorphic consequences of Pleistocene megafloods have been known for some time, it has been only in the past 2 decades that hydrogeologists and glaciologists alike have begun to appreciate the important impact that ice sheet–aquifer interactions have had in controlling subsurface flow patterns, recharge rates, and the distribution of fresh water in confined aquifer systems across North America. In this paper, we document the numerous lines of geochemical, isotopic, and geomechanical evidence of ice sheet hydrogeology across North America. We also review the mechanical, thermal, and hydrologic processes that control subsurface fluid migration beneath ice sheets. Finite element models of subsurface fluid flow, permafrost formation, and ice sheet loading are presented to investigate the coupled nature of transport processes during glaciation/deglaciation. These indicate that recharge rates as high as 10 times modern values occurred as the Laurentide Ice Sheet overran the margins of sedimentary basins. The effects of ice sheet loading and permafrost formation result in complex transient flow patterns within aquifers and confining units alike. Using geochemical and environmental isotopic data, we estimate that the volume of glacial meltwater emplaced at the margins of sedimentary basins overrun by the Laurentide Ice Sheet totals about 3.7 × 104 km3, which is about 0.2% of the volume of the Laurentide Ice Sheet. Subglacial infiltration estimates based on continental‐scale hydrologic models are even higher (5–10% of meltwater generated). These studies in sum call into question the widely held notion that groundwater flow patterns within confined aquifer systems are controlled primarily by the water table configuration during the Pleistocene. Rather, groundwater flow patterns were likely much more complex and transient in nature than has previously been thought. Because Pleistocene recharge rates are believed to be highly variable, these studies have profound implications for water resource managers charged with determining sustainable pumping rates from confined aquifers that host ice sheet meltwater.
Space weather and deep space communications
Authors: Woo Richard
Published: September 2007

While Pioneer 11 and Galileo are two deep space missions that experienced radio communication disruptions due to space weather, the success of a mission like Solar Probe, whose goal is to fly by the Sun within a few solar radii of its surface, may depend critically on space weather. It is therefore crucial to thoroughly understand how space weather affects radio communications and to identify ways to predict it. In this study, we explain how enhanced small‐scale electron density variations in the solar corona represent adverse space weather to radio communications because they give rise to enhancements in radio propagation phenomena such as spectral broadening and fluctuations in intensity and Doppler of the radio signal known as scintillation. The inability of narrowband radio receivers to track the broadened and rapidly fluctuating radio signal leads to disruption in communication and loss of telemetry. Recent advances have been made in understanding enhanced small‐scale density variations and their relationship to the Sun, and we show how this makes it possible to use daily observations of unprecedented solar missions like the Solar and Heliospheric Observatory (SOHO) or Solar Terrestrial Relations Observatory (STEREO) to diagnose, monitor, and forecast adverse space weather for deep space communications.
Impact of connectivity on the modeling of overland flow within semiarid shrubland environments
Authors: Mueller Eva Nora , Wainwright John , Parsons Anthony J.
Published: September 2007

The objective of this study is the evaluation of the spatial variability and intrinsic connectivity features of model input parameters for the parameterization of process‐based, spatially distributed overland flow models. Parameter scaling tools based on the statistical and geostatistical properties of an extensive field data set were developed. These allowed the reproduction of the spatial heterogeneity of model parameters associated with the soil‐ and vegetation‐related properties of semiarid shrubland environments to a varying degree. The outcome of the study emphasizes that connectivity plays a fundamental role in the modeling of water fluxes within semiarid catchments. The larger the degree to which connected features are represented, the better the model performance. In contrast, the parameterization approaches that did not contain connected patterns of parameter values performed comparatively poorly. A spatially connected overland flow model therefore enabled the generation of realistic overland flow patterns that qualitatively resembles field surveys of overland flow generation not only at the outlet of the model domains but also within the catchments without the need of calibration.
Negative ocean‐atmosphere feedback in the South Atlantic Convergence Zone
Authors: De Almeida R. A. F. , Nobre P. , Haarsma R. J. , Campos E. J. D.
Published: September 2007

The temporal evolution of the coupled variability between the South Atlantic Convergence Zone (SACZ) and the underlying sea surface temperature (SST) during austral summer is investigated using monthly data from the NCEP/NCAR reanalysis. A maximum covariance analysis shows that the SACZ is intensified [weakened] by warm [cold] SST anomalies in the beginning of summer, drifting northward. This migration is accompanied by the cooling [warming] of the original oceanic anomalies. The results confirm earlier analyses using numerical models that suggest the existence of a negative feedback between the SACZ and the underlying South Atlantic SST field. A linear regression of daily anomalies of SST and omega at 500 hPa to the equations of a stochastic oscillator reveals a negative ocean–atmosphere feedback in the western South Atlantic, stronger during January and February directly underneath the oceanic band of the SACZ.
Imaging of colloidal deposits in granular porous media by X‐ray difference micro‐tomography
Authors: Gaillard Jean‐François , Chen Cheng , Stonedahl Susa H. , Lau Boris L. T. , Keane Denis T. , Packman Aaron I.
Published: September 2007

High resolution synchrotron‐based X‐ray computed microtomography (X‐CMT) was used to identify the morphology of colloidal deposits formed in porous media. We show that difference microtomography ‐ whereby a tomographic reconstruction is performed across an absorption edge ‐ provides valuable information on the nature and location of the aggregates formed by the deposition of colloidal particles. Column experiments were performed using an idealized porous medium consisting of glass beads through which colloidal ZrO2 particles were transported. Tomographic reconstructions of the porous medium and of the aggregate structure provide an unique opportunity to observe colloidal particle deposits and of their morphology. These results show that the local pore geometry controls particle deposition and that deposits tend to form in a rather heterogeneous manner in the porous medium.
Acceleration in thinning rate on western Svalbard glaciers
Authors: Kohler J. , James T. D. , Murray T. , Nuth C. , Brandt O. , Barrand N. E. , Aas H. F. , Luckman A.
Published: September 2007

Geodetic measurements indicate that a number of glaciers in western Svalbard ranging in size from 5–1000 km2 are losing mass at an accelerating rate. The average thinning rate for Midtre Lovénbreen, the glacier with the best data coverage, has increased steadily since 1936. Thinning rates for 2003–2005 are more than 4 times the average for the first measurement period 1936–1962 and are significantly greater than presented previously. On Slakbreen, thinning rates for the latest measurement period 1990–2003 are more than 4 times that of the period 1961–1977. Thinning of several glaciers along a previously measured airborne lidar profile in Wedel Jarls Land has also increased, doubling between the period 1990–1996 and 1996–2002. Our results imply an increased sea level contribution from Svalbard. In addition, the mass loss is an important influence on measured rates of rebound on western Svalbard and should be factored into analysis of GRACE results.
Plasma sheet fine structure at high latitude
Authors: Lennartsson O. W. , Kistler L. , Rème H.
Published: September 2007

High‐resolution ion observations made in recent years, by the TIMAS instrument on the Polar satellite and other instruments, reveal a dynamic and finely structured plasma sheet, at least at high latitude. This study invokes multipoint Cluster observations with the CIS CODIF instruments (ion composition and distribution function) to determine whether transverse density gradients can be of the order of keV proton gyroradii scale size, as suggested by the TIMAS observations. It is shown that the plasma sheet is indeed prominently filamentary and that the proton density with 40 eV ≤ E ≤ 40 keV can vary by Δn = 0.4 cm−3 across less than five average proton gyroradii at R ≈ 5 RE (average E ≈ 7.5 keV at the time). This compares favorably with typical 10‐km‐size (or less) auroral structures when projected earthward.
Asymmetry between trends in spring and autumn temperature and circulation regimes over western North America
Authors: Abatzoglou J. T. , Redmond K. T.
Published: September 2007

Observational evidence shows that spring temperatures over western North America have undergone significant warming over the past half century, while autumn temperatures have shown relatively little change. Low‐frequency modes of atmospheric variability for spring and autumn are demonstrated to account for a great deal of the seasonal asymmetry, with trends in spring circulation patterns exacerbating regional warming, and trends in autumn circulation patterns counteracting warming. After excluding warming associated with the primary modes of atmospheric variability, temperature trends in spring and autumn over western North America are similar to one another and in broad agreement with seasonal trends from a multimodel ensemble.
Ice flow modulated by tides at up to annual periods at Rutford Ice Stream, West Antarctica
Authors: Murray T. , Smith A. M. , King M. A. , Weedon G. P.
Published: September 2007

For over 2‐years we have collected GPS data ∼40 km upstream of the grounding line on Rutford Ice Stream, West Antarctica. Here we examine deviations from mean downstream flow. Although the record is incomplete during winter, there is clear modulation of flow at semi‐diurnal, diurnal, two‐weekly, semi‐annual, and annual ocean tidal frequencies. This is the first observation of ice stream flow variations over such a long time‐period, and such a wide range of frequencies. The ice stream flows fastest at equinoxes when there are two semi‐diurnal tides of equal magnitude, and slowest at solstices when one of the semi‐diurnal tides has lower amplitude. The sensitivity of the downstream flow is greatest to the long‐period forcing, which suggests that ice stream velocity may be affected by future changes in sea level. If so, this effect would provide a feedback whereby rising sea levels could increase ice stream velocity and hence discharge.
Spontaneous and triggered aseismic deformation transients in a subduction fault model
Authors: Liu Yajing , Rice James R.
Published: September 2007

Aseismic deformation transients can emerge as a natural outcome of the rate and state friction processes revealed in laboratory fault‐sliding experiments. When that constitutive formulation is applied to model subduction earthquake sequences, transients can arise spontaneously for certain effective stress () variations with depth. We show that if interstitial fluids are present and pore pressure is near‐lithostatic around and downdip from the frictional stability transition, transients with recurrence intervals of ∼1 year are predicted on the basis of laboratory friction parameters and their temperature (hence depth) variations. The recurrence interval decreases with and reaches 14 months when is ∼2–3 MPa. Dimensional analysis and numerical studies show that the fault response primarily depends on a parameter W/h*. Here the high pore pressure zone extends distance W updip from the stability transition, and h* is the stable patch size for steady sliding. Evidence that such fluid conditions may actually be present is independently provided by the occurrence of nonvolcanic tremors as apparent responses to extremely small stress changes and by petrological constraints on expected regions of dehydration for the shallow dipping subduction zones where transients are observed. Transient sequences can also be triggered by a modest, one‐time, step‐like interseismic stress perturbation on the subduction fault, due to nearby earthquakes, or to pore pressure changes, e.g., during episodes of metamorphic fluid release. Properties of triggered transients and future thrust earthquakes depend on the interseismic time when the perturbation is introduced, its relative location along the subduction fault, and its magnitude.
Gridded data set of the stable isotopic composition of precipitation over the eastern and central Mediterranean
Authors: Lykoudis S. P. , Argiriou A. A.
Published: September 2007

An attempt is made to produce 10′ × 10′ gridded data sets of the isotopic composition of precipitation across the central and eastern Mediterranean. Following previous studies, statistical models are developed using all existing isotopic data from the area, aggregated on seasonal and annual bases. Various combinations of geographical and meteorological parameters are examined. Initial gridded isotopic data sets are obtained by applying these models to gridded geographical and meteorological data. The residuals of the models are interpolated into the desired grid, using ordinary kriging, and the result is added to the model‐derived grids, to provide the final gridded isotopic data sets. Goodness of fit statistics are used to select the best combination of model and residual interpolation method using an independent data set consisting of annual averages. Finally, an estimation of the uncertainty of the gridded isotopic values is attempted. Overall, the produced grids are quite successful in representing the observed patterns as well as the actual values of stable isotopes in precipitation at the studied area.