bluuebunny/crossref_metadata_2025 huggingface dataset:
Variation in Fatty Acid Composition in Muscle and Heart Tissues among Species and Populations of Tropical Fish in Lakes Victoria and Kyoga
Authors: Kwetegyeka Justus , Mpango George , Grahl‐Nielsen Otto
Published: August 2008

The composition of the fatty acids in muscle and heart tissue of seven fish species, Nile perch (Lates niloticus), Nile tilapia (Oreochromis niloticus), marbled lungfish (Protopterus aethiopicus), African catfish (Clarias gariepinus), Lake Victoria squeaker (Synodontis victoriae),Bagrus docmas, andTilapia zilli,from two locations in Lake Kyoga and one location in Lake Victoria was chemometrically determined. The muscle tissue was very lean, with an average of 3.4 mg total fatty acids per g tissue. The lipid level in the heart tissue was approximately five times higher than in the muscle tissue, with an average of 15.5 mg total fatty acids per g tissue. The n‐3/n‐6 level in the muscles was 1.7 ± 0.7 and in the heart tissue 1.0 ± 0.4. The muscle tissue contained an average of 46 mg cholesterol per 100 g, and the heart tissue contained about five times as much. Plasmalogens were detected in 7–8% of the amounts of total fatty acids in both muscle and heart tissue. The seven species had large differences (P < 0.05) in the fatty acid composition for both muscle and heart tissue. Within the species there were differences between fish from the populations in the three locations, although the population differences were smaller than the species differences. These differences appear to be controlled more closely by genetics/transcriptomics than by the diet.
100 Jahre Hardy-Weinberg-Gleichgewicht
Authors: Aichinger E. , Grimm T.
Published: August 2008

Vor 100 Jahren veröffentlichten Godfrey H. Hardy und Wilhelm Weinberg in unabhängigen Publikationen die Formel, die heute das grundlegende Gesetz für die Berechnungen der Populationsgenetik darstellt. Im vorliegenden Artikel sollen die Epoche, die diesem Gesetz vorausging, geschildert und die Umstände, die seine Entstehung begleiteten, beleuchtet werden. Weiterhin sollen die Forscher genannt werden, die durch ihre Arbeit ebenfalls dieser speziellen Formel auf der Spur waren und als Wegbereiter des Hardy-Weinberg-Gleichgewichts gelten dürfen.
Short-term experience with Ponseti casting and the Achilles tenotomy method for clubfeet treatment in arthrogryposis multiplex congenita
Authors: Kowalczyk Bartholomew , Lejman Tadeusz
Published: August 2008

Purpose

This study presents our experience with the Ponseti method of manipulation and casting followed by Achilles tenotomy (AT) in children with arthrogryposis multiplex congenita (AMC).

Methods

Five children (ten feet) were followed for at least 24 months after the AT and are the cohort for this study. Their mean age at follow-up was 38.4 months (26 to 48 months), and the average follow-up period was 35.8 months (24–44 months). Treatment was begun within the first months of life. The AT to correct rigid equinus was performed at a mean of 14.4 weeks of life, after 7–10 cast changes (mean 8.4). Clinical criteria by Niki et al. and standard standing AP and lateral radiographs were analyzed for final evaluation. Efficacy of Ponseti casting and AT tenotomy was assessed according to the amount and continuance of the achieved correction.

Results

Seven feet had clinically satisfactory results. Among the three unsatisfactory feet, there were two (one child) with rocker-bottom pseudocorrections after repeated bilateral AT and one recurrent clubfoot (one child). Six feet required soft tissue releases at 3, 12 and 21 months after the AT due to recurrence of moderate equinus and adductus. Three feet (two children) underwent repeat AT at 10 and 15 months after the primary procedure. The mean interval between initial AT and redo surgical procedures was 11.8 months (range 3–21 months). Two feet (20%) remained without significant deformity after AT.

Conclusion

Clubfoot in AMC responds initially to the Ponseti method of casting, and deformity may be corrected or diminished. In some children, more extensive surgical treatment can be avoided and in others, delayed. Despite the need for additional surgical intervention, the Ponseti method of casting and AT does seem to be an alternative for initial treatment in children with AMC.
What T. R. Took: The Economic Impact of the Panama Canal, 1903–1937
Authors: MAURER NOEL , YU CARLOS
Published: August 2008

The Panama Canal was one of the largest public investments of its time. In the first decade of its operation, the canal produced significant social returns for the United States. Most of these returns were due to the transportation of petroleum from California to the East Coast. The United States also succeeded in leveraging the threat of military force to obtain a much better deal from the Panamanian government than it could have negotiated otherwise.

“I took the Isthmus.” President Theodore Roosevelt, 1904

“Why, it's ours, we stole it fair and square.” Senator Samuel Hayakawa, 1977
The Crisis of 1873: Perspectives from Multiple Asset Classes
Authors: MIXON SCOTT
Published: August 2008

This article analyzes asset pricing behavior during the period leading up to the Crisis of 1873. Evidence is presented that equities, options, and bonds priced risks consistently, suggesting that investors were actively monitoring the risk of investing and were not caught up in an irrational, speculative mania. Implied probability density functions for stock returns suggest that option markets exhibited growing concern about substantial price declines prior to the crash. Concerns were concentrated on riskier, more leveraged firms. Deteriorating balance sheet fundamentals for the riskiest U.S. railroads set the stage for a market disruption in 1873 as information asymmetries worsened.
Mexican Exceptionalism: Globalization and De-Industrialization, 1750–1877
Authors: GONZÁLEZ RAFAEL DOBADO , GALVARRIATO AURORA GÓMEZ , WILLIAMSON JEFFREY G.
Published: August 2008

Like the rest of the poor periphery, Mexico fought with de-industrialization in the century before the 1870s. Yet, Mexican manufacturing defended itself better than did the rest of the poor periphery. Why Mexicanexceptionalism? This article decomposes the sources of de-industrialization into productivity events abroad, globalization forces connecting Mexico to those markets, and domestic forces. It uses a neo-Ricardian model to implement the decomposition, advocates a price dual approach, and develops a new price and wage data base. Mexicanexceptionalismwas due to weaker Dutch disease effects, better wage competitiveness, and the policy autonomy to foster industry.
Apprenticeship and Training in Premodern England
Authors: WALLIS PATRICK
Published: August 2008

This article reexamines the economics of premodern apprenticeship in England. I present new data showing that a high proportion of apprenticeships in seventeenth-century London ended before the term of service was finished. I then propose a new account of how training costs and repayments were distributed over the apprenticeship contract such that neither master nor apprentice risked significant loss from early termination. This new account fits both the characteristics of premodern apprenticeship and what is known about the acquisition of skills in modern and premodern societies.
Health, Information, and Migration: Geographic Mobility of Union Army Veterans, 1860–1880
Authors: LEE CHULHEE
Published: August 2008

This article explores how injuries, sickness, and the geographic mobility of Union Army veterans while in service affected their postservice migrations. Wartime wounds and illnesses significantly diminished the geographic mobility of veterans after the war. Geographic moves while carrying out military missions had strong positive effects on their postservice geographic mobility. Geographic moves while in service also influenced the choice of destination among the migrants. I discuss some implications of the results for the elements of self-selection in migration, the roles of different types of information in migration decisions, and the overall impact of the Civil War on geographic mobility.
Resolving the Anglo-German Industrial Productivity Puzzle, 1895–1935: A Response to Professor Ritschl
Authors: BROADBERRY STEPHEN , BURHOP CARSTEN
Published: August 2008

This response offers a critical appraisal of the claim of Albrecht Ritschl to have found a possible resolution to what he calls the Anglo-German industrial productivity puzzle, which arose as the result of a new industrial production index produced in an earlier paper by the same author. Projection back from a widely accepted 1935/36 benchmark using the Ritschl index showed German industrial labor productivity in 1907 substantially higher than in Britain. This presented a puzzle for at least two reasons. First, other comparative information from the pre—World War I period, such as wages, seems difficult to square with much higher German labor productivity at this time. Second, a direct benchmark estimate produced by Stephen Broadberry and Carsten Burhop, using production census information for Britain and industrial survey material of similar quality for Germany, suggested broadly equal labor productivity in 1907. Broadberry and Burhop also showed that if Walther Hoffmann's industrial output index was used instead of the Ritschl index for Germany, the puzzle largely disappeared.
The cult of Awo: the political life of a dead leader
Authors: Adebanwi Wale
Published: August 2008

This essay examines the ‘posthumous career’ of Chief Obafemi Awolowo, the late leader of the Yoruba of Nigeria. It focuses on why he has been unusually effective as a symbol in the politics of Yorubaland and Nigeria. Regarding Awolowo as arecentancestor, the essay elaborates why death, burial and statue are useful in the analysis of the social history of, and elite politics in, Africa. The Awolowo case is used to contest secularist and modernist assumptions about ‘modernity’ and ‘rationality’ in a contemporary African society.
Lifting the blinkers: a new view of power, diversity and poverty in Mozambican rural labour markets
Authors: Cramer Christopher , Oya Carlos , Sender John
Published: August 2008

This paper presents some results from the largest rural labour market survey yet conducted in Mozambique. Evidence from three provinces shows that labour markets have a significant impact on the lives of a large number of poor people, and that employers exercise considerable discretion in setting wages and conditions of casual, seasonal and permanent wage employment. The evidence presented comes from a combination of a quantitative survey based on purposive sampling with other techniques, including interviews with large farmers. The findings contrast with ideas that rural labour markets are of limited relevance to poverty reduction policy formulation in Africa, and the paper concludes with methodological, analytical and policy recommendations.
Imagining the Great Lakes Region: discourses and practices of civil society regional approaches for peacebuilding in Rwanda, Burundi and DR Congo
Authors: van Leeuwen Mathijs
Published: August 2008

The idea has gained ground in recent years that, as conflicts in the countries of the Great Lakes Region are strongly interlinked, regional approaches are necessary to resolve them. This interest in regional dimensions of conflict and peacebuilding also gains currency in other parts of the world. Attention to regional approaches is reflected in the efforts of international organisations and donors to promote civil society peacebuilding. They assume that regional cooperation and exchange between civil society organisations contribute to peace, and provide an alternative to single-country interventions or regional diplomatic initiatives. This paper explores how such assumptions work out in practice. Experiences in the Great Lakes Region show that local and international organisations have difficulty in analysing the regional character of conflict and arriving at collaborative regional strategies. Moreover, local civil society organisations are deeply embedded in the politics of regional conflict. Consequently, the shift to regional peacebuilding approaches remains more theoretical than practical. This paper suggests that international supporting organisations need to adjust their ambitions in regional peacebuilding, but nonetheless have roles in fostering regional identification among civil society organisations.
The Supreme Court and federalism in Nigeria
Authors: Suberu Rotimi T.
Published: August 2008

Since Nigeria's transition from military to civilian rule in 1999, the country's Supreme Court has risen from a position of relative political obscurity and institutional vulnerability into a prominent and independent adjudicator of inter-governmental disputes in this chronically conflicted federation. Examined here is the Court's arbitration, during President Olusegun Obasanjo's two civilian constitutional terms (1999–2007), of fifteen different federal-state litigations over offshore oil resources, revenue allocation, local governance and public order. The Court's federalism decisions were remarkably independent and reasonably balanced, upholding the constitutional supremacy of the Federal Government in several findings, tilting towards the states in some declarations, and simultaneously underwriting federal authority and state autonomy in other rulings. Despite the Court's important and independent role, however, the Nigerian federation was vexed by violent conflicts, underscoring the structural, political and constitutional constraints on judicial federalism in this notoriously complex and divided country.
The West Side Boys: military navigation in the Sierra Leone civil war
Authors: Utas Mats , Jörgel Magnus
Published: August 2008

The West Side Boys were one of several military actors in the Sierra Leonean civil war (1991–2002). A splinter group of the army, the WSB emerged as a key player in 1999–2000. In most Western media accounts, the WSB appeared as nothing more than renegade, anarchistic bandits, devoid of any trace of long-term goals. By contrast, this article aims to explain how the WSB used well-devised military techniques in the field; how their history and military training within the Sierra Leone army shaped their notion of themselves and their view of what they were trying to accomplish; and, finally, how military commanders and politicians employed the WSB as a tactical instrument in a larger map of military and political strategies. It is in the politics of a military economy that this article is grounded.
Stochastic layer scaling in the two-wire model for divertor tokamaks
Authors: ALI HALIMA , PUNJABI ALKESH , BOOZER ALLEN
Published: August 2008

The question of magnetic field structure in the vicinity of the separatrix in divertor tokamaks is studied. The authors have investigated this problem earlier in a series of papers, using various mathematical techniques. In the present paper, the two-wire model (TWM) [Reiman, A. 1996 Phys. Plasmas3, 906] is considered. It is noted that, in the TWM, it is useful to consider an extra equation expressing magnetic flux conservation. This equation does not add any more information to the TWM, since the equation is derived from the TWM. This equation is useful for controlling the step size in the numerical integration of the TWM equations. The TWM with the extra equation is called the flux-preserving TWM. Nevertheless, the technique is apparently still plagued by numerical inaccuracies when the perturbation level is low, resulting in an incorrect scaling of the stochastic layer width. The stochastic broadening of the separatrix in the flux-preserving TWM is compared with that in the low mn (poloidal mode number m and toroidal mode number n) map (LMN) [Ali, H., Punjabi, A., Boozer, A. and Evans, T. 2004 Phys. Plasmas11, 1908]. The flux-preserving TWM and LMN both give Boozer–Rechester 0.5 power scaling of the stochastic layer width with the amplitude of magnetic perturbation when the perturbation is sufficiently large [Boozer, A. and Rechester, A. 1978, Phys. Fluids21, 682]. The flux-preserving TWM gives a larger stochastic layer width when the perturbation is low, while the LMN gives correct scaling in the low perturbation region. Area-preserving maps such as the LMN respect the Hamiltonian structure of field line trajectories, and have the added advantage of computational efficiency. Also, for a $1\frac12$ degree of freedom Hamiltonian system such as field lines, maps do not give Arnold diffusion.
Seasonal dormancy cycles in the biennial Torilis japonica (Apiaceae), a species with morphophysiological dormancy
Authors: Vandelook Filip , Bolle Nele , Van Assche Jozef A.
Published: August 2008

Torilis japonica (Apiaceae) has a widespread distribution, extending from western Europe to eastern Asia. In Europe, it usually behaves as a spring-germinating biennial species. Ripe seeds of T. japonica have an underdeveloped embryo and can persist in the soil for several years. The aim of this research was to reveal the mechanisms regulating the seasonal emergence pattern of seedlings. Experiments in a natural environment were performed to study phenology of seedling emergence and embryo growth. Seasonal changes in the dormancy status of T. japonica seeds were examined by regularly exhuming buried seeds and incubating them in controlled conditions. The action of temperature and light in regulating dormancy, embryo growth and germination was studied in the laboratory. Results showed that seeds of T. japonica have non-deep, simple morphophysiological dormancy (MPD), whereby physiological dormancy is broken by moist chilling (5°C). Once MPD was broken, embryo growth and subsequent germination started in spring, when appropriate temperature and light conditions were present. Seeds buried at a depth where light could not reach them showed cyclic changes in their dormancy status; embryo growth in these seeds could not be initiated because of the lack of a light stimulus. As far as we know, this is the first extensive study of seasonal dormancy cycles in a spring-germinating species of the Apiaceae. T. japonica occurs in a temperate climate with cool winters and warm, moist summers. In this climate, spring is often the most favourable season for seedling establishment.
Trends in the evolution of BMI in Belgian army men
Authors: Mullie Patrick , Vansant Greet , Guelinckx Isabelle , Hulens Mieke , Clarys Peter , Degrave Etienne
Published: August 2008

Objectives

The first aim was to evaluate BMI cross-sectionally over a period of 14 years (1992 to 2005) in 43 343 army men and the second was to compare BMI using the paired data of 1497 army men. The data were analysed as a function of the military ranking system, used as an indicator for socio-economic position.

Design

Multiple cross-sectional and longitudinal design.

Results

A significant increase of BMI between age categories was detected over the 14-year period; BMI remained stable in each age category. In the paired cohort, median BMI increased during the same period from 23·9 (interquartile range 3·3) kg/m2 to 24·7 (interquartile range 3·5) kg/m2 (P < 0·0001). This age-dependent evolution was present in all military rankings. From age 40 years or more, BMI indicated a significant increase in the prevalence of overweight and obesity.

Conclusion

For the total cohort, BMI remained stable in each age category. For the paired cohort, BMI increased over time. The military leadership should emphasize prevention in order to reduce the health-care costs and disease burden in this cohort. This emphasis on prevention should target those aged less than 40 years.
Work histories and the access to contributory pensions: the case of Uruguay
Authors: BUCHELI MARISA , FORTEZA ALVARO , ROSSI IANINA
Published: August 2008

Incomplete and highly fragmented work histories threaten to leave many contributors of the pension schemes in Latin America without the minimum pension guarantee or even without access to the ordinary pension. We propose a methodology to assess this risk, identify vulnerable groups and study potential determinants of the history of contributions using information from the work history records of the social security institutions. We apply this methodology to the largest social security institution of Uruguay, the Banco de Previsión Social (BPS), and show that the majority of contributors to this institution might not comply with the minimum number of years of contribution that is currently required to access an ordinary pension when they reach the retirement age.
Performance and governance of Swiss pension funds
Authors: AMMANN MANUEL , ZINGG ANDREAS
Published: August 2008

We investigate the relationship between pension fund governance and investment performance. For this purpose, we develop the Swiss Pension Fund Governance Index (SPGI) which is a standard metric for the governance quality of Swiss pension funds. The empirical analysis is based on a sample of 96 pension funds with total assets of more than CHF 190 billion. We find evidence for governance issues in the area organization and target setting. Our results support the widespread hypothesis of a positive relationship between pension fund governance and investment performance.
The Transformation of the Republican and Democratic Party Coalitions in the U.S.
Authors: Miller Gary , Schofield Norman
Published: August 2008

Because the space of policies is two-dimensional, parties in the United States are coalitions of opposed interests. The Republican Party contains both socially conservative and socially liberal groups, though both tend to be pro-business. The increasing dominance of the social conservatives has angered some prominent Republicans, even causing a number of them to change party allegiance. Over time, the decreasing significance of the economic axis may cause the Republican Party to adopt policies that are analogous to those proposed by William Jennings Bryan in 1896: populist and anti-business. In parallel, the Democratic Party will increasingly appeal to pro-business, social liberals, so the party takes on the mantel of Lincoln.
Without Heirs? Assessing the Decline of Establishment Internationalism in U.S. Foreign Policy
Authors: Busby Joshua W. , Monten Jonathan
Published: August 2008

Is establishment internationalism in decline? Conventional wisdom is becoming that structural shifts in the international environment along with generational, demographic, and cultural changes within the United States are inexorably leading to the decline of the broad, post-war internationalist consensus that dominated American foreign policy after 1945. Despite the frequent assertion that this change has taken place, very few studies have analyzed the extent to which establishment internationalism is in fact in decline. To answer this question, we first track trends in congressional foreign policy votes from the American Conservative Union (1970–2004) and Americans for Democratic Action (1948–2004). Our second set of indicators tracks the state of birth, educational profile, and formative international experience of a cross section of the U.S. foreign policy elite. Our third and fourth sets of indicators track elite attitudes as represented by presidential State of the Union addresses and major party platforms. We find support for increasing partisan polarization in Congress on foreign policy as well as increasing regional concentration of the parties. However, there is only mixed evidence to suggest that internationalism has experienced a secular decline overall. Support for international engagement and multilateral institutions remain important parts of elite foreign policy rhetoric. Moreover, we find that social backgrounds of U.S. foreign policy elites—save for military service—have not substantially changed from the height of the internationalist era.
The Political Theology of Prerogative: The Jurisprudential Miracle in Liberal Constitutional Thought
Authors: Fatovic Clement
Published: August 2008

Liberalism ordinarily requires authorities to provide a full public account of their actions so that citizens can critically evaluate those actions for themselves, but in times of life-threatening emergency, liberalism sometimes evinces a willingness to place unquestioning faith in executives who promise to deliver it from such evil. In doing so, liberalism violates its moral and epistemological commitment to “makepublic useof one's reason in all matters.” This article uses the framework provided by Carl Schmitt's concept of political theology to analyze the reluctance of liberals to ask questions of the executive in times of danger and uncertainty. That framework helps explain how both the content and the structure of liberal thought can shift in a theological (and specifically theistic) direction when faced with an emergency. This article demonstrates that the quasi-religious rhetoric sometimes used to justify expansions of executive power in practice has precedents in the theories of John Locke, William Blackstone, and Alexander Hamilton. Analysis of their writings suggests that the use of quasi-theistic language in discussions of emergency powers can have the effect of insulating “godlike” executives from the kind of scrutiny and criticism that liberalism usually promotes.
Concept Formation in Political Science: An Anti-Naturalist Critique of Qualitative Methodology
Authors: Bevir Mark , Kedar Asaf
Published: August 2008

This article offers an anti-naturalist philosophical critique of the naturalist tendencies within qualitative concept formation as developed most prominently by Giovanni Sartori and David Collier. We begin by articulating the philosophical distinction between naturalism and anti-naturalism. Whereas naturalism assumes that the study of human life is not essentially different from the study of natural phenomena, anti-naturalism highlights the meaningful and contingent nature of social life, the situatedness of the scholar, and so the dialogical nature of social science. These two contrasting philosophical approaches inspire, in turn, different strategies of concept formation. Naturalism encourages concept formation that involves reification, essentialism, and an instrumentalist view of language. Anti-naturalism, conversely, challenges reified concepts for eliding the place of meanings, essentialist concepts for eliding the place of contingency, and linguistic instrumentalism for eliding the situatedness of the scholar and the dialogical nature of social science. Based on this philosophical framework, we subject qualitative concept formation to a philosophical critique. We show how the conceptual strategies developed by Sartori and Collier embody a reification, essentialism, and instrumentalist view of language associated with naturalism. Although Collier's work on concept formation is much more flexible and nuanced than Sartori's, it too remains attached to a discredited naturalism.
Congress in the World: Benefits of the Congressional Fellowship Program for the Study of International Relations
Authors: Lavelle Kathryn C.
Published: August 2008

The Congressional Fellowship Program of the American Political Science Association charted new territory in the 1950s when it opened the internal workings of Congress to subsequent generations of political science scholars. Numerous programs incorporating a “Hill” experience into a variety of academic disciplines have imitated it since then. However, scholarship in the subfield of international relations has not benefited from the opportunities the program offers to the same extent as other disciplines and subfields have. I use a sample of legislative and policy matters that I encountered as a fellow in the 2006–2007 year to argue that a wide spectrum of theoretical work in international political economy would profit from insights generated by the type of direct participation the program affords. Specifically, I connect literature across subfields on institutional change, and relate how my experiences with Darfur divestment legislation, Committee on Foreign Investment in the U.S. (CFIUS) legislation, and politics in a financial crisis hold the potential to enrich our understanding of the international political economy. I suggest where more direct experience with other issues by other scholars could prompt additional insights for research on U.S. foreign policy and international relations.
A New Framing? Constitutional Representation at Philadelphia's National Constitution Center
Authors: Zeisberg Mariah
Published: August 2008

The National Constitution Center (NCC) in Philadelphia orients its representation of the Constitution around the role of “We the People” in the conduct of constitutional politics. The self-presentation of the NCC explicitly connects its participatory interpretation of the Constitution to the interactivity of the museum experience itself, and announces its aspiration that visitors “get involved!” In so doing the NCC draws upon an emerging edge in museum theory that emphasizes the capacity of museums to support political citizenship. Although the museum's aspiration to enact participatory citizenship is laudable, its exhibits—because of their technologies, use of space, and content—subvert, rather than sustain, the participatory ideal.
Editor's Introduction
Authors: Isaac Jeffrey C.
Published: August 2008

I am writing this introduction from an internet café in Bucharest. Yesterday, courtesy of CNN, I watched Hillary Clinton officially suspend her Presidential campaign and throw her support behind Barack Obama. In Bucharest they are preparing for a second round of municipal elections, to be followed soon thereafter by parliamentary elections. Here in Bucharest—and also in Budapest, the first leg of my trip—my political science friends watch the U.S. election campaign with fascination and admiration. It seems, to most of them—hardly a representative sample of the population at large—that the U.S. elections are more open, competitive, and less oligopolistic than post-Communism, which some call a “partyocracy.”
The causes of mid‐latitude F layer behavior
Authors: Oliver W. L. , Kawamura S. , Fukao S.
Published: August 2008

Ten years of measurements of the ionospheric F‐layer peak height hmax and peak density nmax and of the horizontal neutral wind at these heights with the Japanese MU Radar are analyzed to detail the causes of the temporal variations of the peak parameters. In the absence of winds hmax rides the height of a constant product of the atomic and molecular densities of the thermosphere. Since the mean wind does not change with solar activity, the hmax change with solar activity is driven almost solely by a thermal expansion of the thermosphere. The seasonal variation of hmax, on the other hand, is driven almost solely by the seasonal change in winds. The diurnal variation of hmax is driven most importantly by winds, secondarily by thermal expansion. nmax is proportional to the ratio of the atomic and molecular densities of the thermosphere at altitude hmax but that ratio is insensitive to thermal expansion. The solar‐activity change in nmax is largely due to the change in solar EUV intensity, secondarily due to changes in neutral composition at the base of the thermosphere. The seasonal change in nmax is semiannual in response to the semiannual change in neutral O density. The wind itself shows features of ion‐drag control in almost every facet of its behavior except that its diurnal amplitude does not change with season, a result consistent with the explanation that one day is insufficient time to set up a nondivergent circulation pattern in the upper atmosphere. Our numerical results are valid only for the location of the MU Radar, but the understandings involved are broadly applicable to the midlatitude ionosphere.
The midlatitude F2 layer during solar eclipses: Observations and modeling
Authors: Le Huijun , Liu Libo , Yue Xinan , Wan Weixing
Published: August 2008

We conducted a statistical analysis on the changes in foF2 during seven eclipse events on the basis of the data derived from 23 ionosonde stations. To model eclipse effects on the ionosphere, we constructed a solar spectrum model for solar eclipses. The background hmF2, local time, solar cycle, and dip angle effects on the ionospheric response to solar eclipses are investigated in the four controlled case studies. Both the measurements and simulations show that the eclipse effect is larger in the midday than in the morning and afternoon and that larger dip angle results in smaller eclipse effect. Furthermore, the simulated results show that the local time effect is actually due to the neutral concentration effect. Compared to at low solar activity, the eclipse effect in the F2 region is larger at high solar activity. This solar cycle effect is caused by the differences not only in the solar radiation but also in the background neutral gas concentration. In addition, an eclipse will produce a smaller change in NmF2 if the hmF2 is higher. In conclusion, the central finding of this paper is that most of the observed differences in the behavior of NmF2 during eclipses can be attributed to the differences in O+loss rate brought about by the background differences in the neutral molecular densities. The solar zenith angle, local time, and dip angle effects should be explained from this starting point.
A new active tectonic model for the construction of the Northern Apennines mountain front near Bologna (Italy)
Authors: Picotti Vincenzo , Pazzaglia Frank J.
Published: August 2008

We integrate existing and new geologic data [REtreating TRench, Extension, and Accretion Tectonics (RETREAT project)], particularly on the origin, growth, and activity of the mountain front at Bologna, Italy, into a new model that explains Apennine orogenesis in the context of a slab rollback ‐ upper plate retreat process. The Bologna mountain front is an actively growing structure driving rock uplift ∼1 mm/year, cored by a midcrustal flat‐ramp structure that accommodates ongoing shortening driven by Adria subduction at a rate of ∼2.5 mm/year. The data we use are assembled from river terraces and associated Pleistocene growth strata, geodesy including releveling surveys, reinterpretation of published reflection lines, and a new high‐resolution reflection line. These data constrain a simple trishear model that inverts for blind thrust ramp depth, dip, and slip. Apennine extension is recognized both in the foreland, as high‐angle normal faults and modest stretching in the carapace of the growing mountain front, and in the hinterland, with larger normal faults that accomplish some crustal thinning as the upper plate retreats. This coevolution of extension and shortening shares some notable characteristics with other basement‐involved collisional orogens including the early Tertiary Laramide orogeny in the American West and the Oligocene to Miocene evolution of the Alps. We propose a possible relationship between underplating and the development of the Po as a sag basin as a Quaternary phenomenon that may also apply to past periods of Apennine deformation (Tortonian). Continued shortening on the structure beneath the Bologna mountain front represents by far the most important and underappreciated seismogenic source in the front of the northern Apennines.
Estimating geocenter variations from a combination of GRACE and ocean model output
Authors: Swenson Sean , Chambers Don , Wahr John
Published: August 2008

In this study, we estimate a time series of geocenter anomalies from a combination of data from the Gravity Recovery and Climate Experiment (GRACE) satellite mission and the output from ocean models. A matrix equation is derived relating total geocenter variations to the GRACE coefficients of degrees two and higher and to the oceanic component of the degree one coefficients. We estimate the oceanic component from two state‐of‐the‐art ocean models. Results are compared to independent estimates of geocenter derived from other satellite data, such as satellite laser ranging and GPS. Finally, we compute degree one coefficients that are consistent with the processing applied to the GRACE Level‐2 gravity field coefficients. The estimated degree one coefficients can be used to improve estimates of mass variability from GRACE, which alone cannot provide them directly.
Stress interaction effect on the occurrence probability of characteristic earthquakes in Central Apennines
Authors: Console R. , Murru M. , Falcone G. , Catalli F.
Published: August 2008

In this study, we compute the effect of stress change due to previous historical earthquakes on the probability of occurrence of future earthquakes on neighboring faults. Following a methodology developed in the last decade, we start from the estimate of the probability of occurrence in the next 50 years for a characteristic earthquake on known seismogenic structures, based on a time‐dependent renewal model. Then a physical model for the Coulomb stress change caused by previous earthquakes on these structures is applied. The influence of this stress change on the occurrence rate of characteristic earthquakes is computed, taking into account both permanent (clock advance) and temporary (rate‐and‐state) perturbations. We apply this method to the computation of earthquake hazard of the main seismogenic structures recognized in the Central and Southern Apennines region, for which both historical and paleoseismological data are available. This study provides the opportunity of reviewing the problems connected with the estimate of the parameters of a renewal model in case of characteristic earthquakes characterized by return times longer than the time spanned by the available catalogues and the applicability of the concept of characteristic earthquake itself. The results show that the estimated effect of earthquake interaction in this region is small compared with the uncertainties affecting the statistical model used for the basic time‐dependent hazard assessment.
Anatomy of the Chesapeake Bay impact structure revealed by seismic imaging, Delmarva Peninsula, Virginia, USA
Authors: Catchings Rufus D. , Powars David S. , Gohn Gregory S. , Horton J. Wright , Goldman Mark R. , Hole John A.
Published: August 2008

A 30‐km‐long, radial seismic reflection and refraction survey completed across the northern part of the late Eocene Chesapeake Bay impact structure (CBIS) on the Delmarva Peninsula, Virginia, USA, confirms that the CBIS is a complex central‐peak crater. We used a tomographic P wave velocity model and low‐fold reflection images, constrained by data from two deep boreholes located on the profile, to interpret the structure and composition of the upper 5 km of crust. The seismic images exhibit well‐defined structural features, including (with increasing radial distance) a collapsed central uplift, a breccia‐filled moat, and a collapsed transient‐crater margin (which collectively constitute a ∼40‐km‐wide collapsed transient crater), and a shallowly deformed annular trough. These seismic images are the first to resolve the deep structure of the crater (>1 km) and the boundaries between the central uplift, moat, and annular trough. Several distinct seismic signatures distinguish breccia units from each other and from more coherent crystalline rocks below the central uplift, moat, and annular trough. Within the moat, breccia extends to a minimum depth of 1.5 km or a maximum of 3.5 km, depending upon the interpretation of the deepest layered materials. The images show ∼350 to 500 m of postimpact sediments above the impactites. The imaged structure of the CBIS indicates a complex sequence of events during the cratering process that will provide new constraints for numerical modeling.
Time dependence in 3‐D mantle convection models featuring evolving plates: Effect of lower mantle viscosity
Authors: Gait A. D. , Lowman J. P. , Gable C. W.
Published: August 2008

Evolving plate configurations and dynamically determined plate velocities are featured in Cartesian geometry mantle convection simulations. The numerical model enables the evolution of plate shape and size by migrating idealized plate triple junctions. The motion of the model triple junctions responds to the time‐dependent velocities of the adjacent plates. Each calculation includes four high‐viscosity plates in a 3 × 3 × 1 solution domain. We analyze the effect of plate evolution on the time dependence of plate velocity and heat flux in three different models characterized by lower mantle to upper mantle viscosity ratios of 30, 90, and 300. We examine the difference in behavior between calculations featuring fixed and mobile plate boundaries for each viscosity model. When plates are permitted to evolve in response to the convective vigor of the system, plate positions and shapes can change considerably while features in the high‐viscosity lower mantle may change very little. In addition, plate velocities and surface heat flux can be highly time dependent. We find that when the contrast between lower mantle and upper mantle viscosity magnitude is a factor of 30, surface velocities may fluctuate by 75% of the mean value and heat flux by 60%. We also find that plate velocity evolution is characterized by periods of reorganization, punctuating more stable periods. When the lower mantle viscosity is increased to 90 times the upper mantle value, plate reorganization events also occur, but only when plate boundary motion is enabled. When the lower mantle to upper mantle viscosity contrast is increased to a factor of 300, we find that the mean surface velocity and heat flux become very steady in cases both with and without plate boundary evolution, despite the substantial migration of convergent plate boundaries in the former case.
Estimates of surface roughness length in heterogeneous under‐ice boundary layers
Authors: Shaw W. J. , Stanton T. P. , McPhee M. G. , Kikuchi T.
Published: August 2008

Measurements obtained in the under‐ice ocean boundary layer by two autonomous buoys deployed in 2004 and 2005 are used to estimate the roughness length z0 of the underside morphology of Arctic Ocean pack ice. Two techniques are used to estimate z0. The first uses an extension of the law of the wall and directly measured turbulent shear stress and velocity at a single point near the ice‐ocean interface. The second uses a one‐dimensional numerical boundary layer model that is matched to measured velocity profiles in the outer part of the boundary layer with z0 as an adjustable parameter. The stress‐based estimates are sensitive to local morphological features, and the effect of nearby ice ridge keels on the roughness estimates is evident. Averaged over flow direction there is a significant difference in floe roughness between the 2004 and 2005 deployments. Velocity‐profile‐based z0 estimates are more uniform with direction than the stress‐based estimates, and the average value of the profile‐based estimates lies within the range of the stress‐based estimates. Averaged over flow direction, both techniques yield z0 estimates of about 100 mm for the 2005 data set. A central question is how to best estimate a z0 that can be applied to an individual grid cell in large‐scale numerical models. The profile‐based estimates are promising in this regard because they are less affected by local morphology than stress‐based measurements, which must be made fairly close to the interface in order to be interpretable using a framework based on the law of the wall.
Geomagnetic perturbations on stratospheric circulation in late winter and spring
Authors: Lu Hua , Clilverd Mark A. , Seppälä Annika , Hood Lon L.
Published: August 2008

This study investigates if the descent of odd nitrogen, generated in the thermosphere and the upper mesosphere by energetic particle precipitation (EPP‐NOx), has a detectable impact on stratospheric wind and temperature in late winter and spring presumably through the loss of ozone and reduction of absorption of solar UV. In both hemispheres, similar downward propagating geomagnetic signals in the extratropical stratosphere are found in spring for those years when no stratospheric sudden warming occurred in mid‐winter. Anomalous easterly winds and warmer polar regions are found when the 4‐month averaged winter Ap index (Ap) is high, and the signals become clearer when solar F10.7 is low. In May, significant geomagnetic signals are obtained in the Northern Hemisphere when the data are grouped according to the phase of the stratospheric equatorial QBO. The magnitudes of changes in spring stratospheric wind and temperatures associated with Ap signals are in the range of 10–20 m s−1 and 5–10 K, which are comparable with those of the 11‐yr SC signals typically found in late winter. The spring Ap signals show the opposite sign to that expected due to in situ cooling effects caused by catalytic destruction of stratospheric ozone by descending EPP‐NOx. Thus it is unlikely that the in situ chemical effect of descending EPP‐NOx on stratospheric ozone would have a dominant influence on stratospheric circulation. Instead, we suggest that the detected Ap signals in the extratropical spring stratosphere may be an indirect consequence of geomagnetic and solar activity, dynamically induced by changes in wave ducting conditions.
N2O production by high energy auroral electron precipitation
Authors: Semeniuk K. , McConnell J. C. , Jin J. J. , Jarosz J. R. , Boone C. D. , Bernath P. F.
Published: August 2008

The Fourier transform spectrometer on SCISAT‐1 observed enhanced concentrations of N2O above 50 km in February of 2004 and 2006 in the wintertime polar region. These anomalously high concentrations are associated with the transport of high levels of NOx in the polar night region from the upper mesosphere and lower thermosphere in both cases following sudden warming events in the middle of January. The NOx is produced by auroral electron precipitation. Simulations using a middle atmosphere chemistry climate model show significant amounts of N2O are produced in the upper mesosphere from the reaction of NO2 and ground state atomic nitrogen. Thus, N2O acts as a signature of energetic electron precipitation. The model results exhibit polar‐night‐confined descent of NOx in the wake of sudden warmings and other dynamical regimes when the polar vortex intensifies at high latitudes in the mesosphere.
A theoretical analysis of the neutron scattering method of measuring snow and ice density
Authors: Morris E. M.
Published: August 2008

A modified three‐group neutron scattering analysis in cylindrical coordinates is used to predict the neutron flux produced by an annular source of neutrons centralized in an access hole in snow or ice. The diffusion approximation to the constant cross‐section neutron transport equation is used to describe neutron flux in the snow and ice. Neutron flux in the access hole is described either by the diffusion approximation or by a transient approximation depending on the magnitude of the transport mean free path for neutrons in the borehole fluid. For “dry,” air‐filled, access holes the transient solutions are most suitable. A theoretical calibration algorithm, relating snow density to the neutron count rate measured by a cylindrical detector (also centralized in the access hole) and the access hole diameter, is derived. A good fit to experimental data is obtained using values of the physically based parameters of the algorithm within ranges determined a priori from the literature and from manufacturer's specifications. A calibration equation fitted to output from the algorithm for T = −10°C is consistent with field data and shows that the accuracy and precision of density measurements made using the probe can match the accuracy and precision of field gravimetric methods, with the advantage of a continuous and unbiased sampling method.