bluuebunny/crossref_metadata_2025 huggingface dataset:
Directional antenna design for wireless power transfer system in electric scooters
Authors: Tsai Jia-Shiun , Hu Jia-Sheng , Chen Sin-Li , Huang Xiaoliang
Published: February 2016

This article presents a cost-effective antenna design for wireless power transfer in electric scooters. The proposed design can be applied to any commercial 48 V/20 Ah electric scooter. In this study, based on the magnetic resonant coupling theory, a circuit that satisfies SAE J2954 specifications is presented. One-directional antenna/receiver pair is designed to meet the requirements of scooter-using scenarios. The transmitting coils are set up under the chassis of the scooter. The receiving coils are embedded in the bottom layer of the chassis, where the air gap between these two coils is larger than 10 cm. Based on SAE J2954 requirements, the operation frequency is tested around 85 kHz. Under proper power supply, the battery can be fully charged wirelessly and the system is user-friendly. The experimental results confirm the desired performance and feasibility.
Research involving pediatric stem cell donors: A way forward
Authors: Wendler David , Shah Nirali N , Pulsipher Michael A , Fry Terry , Grady Christine
Published: February 2016

The most suitable donor for younger patients who undergo hematopoietic stem cell transplantation in the research setting is frequently a minor sibling. These cases raise the question of whether minors who serve as stem cell donors for research subjects should be regarded as research subjects themselves. Regarding pediatric donors as research subjects ensures that an Institutional Review Boards reviews their involvement and determines whether it is appropriate. Yet, Institutional Review Boards must follow the US regulations for pediatric research, which were designed for patients and healthy volunteers, not for healthy donors. As a result, regarding pediatric donors as research subjects also can pose unnecessary obstacles to appropriate and potentially life-saving research. This article considers a new way to address this dilemma. The federal research regulations allow for waiver of some or all of the included requirements when they are unnecessary for a study or a class of studies. We argue that this option offers a way to ensure that the involvement of pediatric donors receives sufficient review and approval without inadvertently undermining valuable and potentially life-saving research.
The Politics of Animation and the Animation of Politics
Authors: Herhuth Eric
Published: February 2016

This article demonstrates how political inquiry can guide the study of animation. It proceeds by investigating animation’s minor status within film and media studies and then the expansion of its definition and conceptual associations. This expansion has philosophical implications, which are explored in this article through the work of Jeff Malpas and Bruno Latour. By examining how these philosophers discuss animation and animated examples – puppets, in particular – this article demonstrates a shift from thinking of animation as expressing mastery and illusion to thinking of animation as expressing transformation, heterogeneous action, and distributed agency. This shift challenges philosophy’s opposition to rhetoric, poetics, and technology, and in turn challenges modern binaries between nature and culture, science and politics, reality and artifice, facts and fetishes, and it presents the world as animated. The author argues that this idea need not obfuscate the many different moving-image technologies that have been designated animation or cinema, and contends that some of these, such as animated cartoons, directly engage the confusion about animation caused by modern binaries. This argument proposes studying animation through multiple modes or lenses in order to prevent dominant realist modes of inquiry from stifling the uncertainty and pluralism that are central to animation’s capacity for political expression.
Establishing a ‘Corstonian’ continuous care pathway for drug using female prisoners: Linking Drug Recovery Wings and Women’s Community Services
Authors: Grace Sharon , Page Geoff , Lloyd Charlie , Templeton Lorna , Kougali Zetta , McKeganey Neil , Liebling Alison , Roberts Paul , Russell Chris
Published: February 2016

This article outlines the findings from a rapid assessment of pilot Drug Recovery Wings (DRWs) in two women’s prisons and compares the DRW approach with work undertaken in Women’s Community Services (WCSs) commended by the Corston Report. The findings indicate that DRW1 was working more successfully in providing a ‘Corstonian’ approach than DRW2 and the reasons behind this are explored. The article argues that, while pockets of good practice such as WCSs and ‘Corstonian’ DRWs are to be commended, unless there is a continuous care pathway, modelled on Corston’s ideas for working with vulnerable female offenders such as recovering drug users, such work will be limited in its effectiveness. Ideas for how such a systematic approach might work will be outlined.
Television aesthetics, media and cultural studies and the contested realm of the social
Authors: Zborowski James
Published: February 2016

This article seeks to intervene in the ‘television aesthetics’ versus ‘media and cultural studies’ debate. It argues that aesthetic evaluation does not necessarily rely upon bad textual others or result in canon construction. It engages with Bourdieu in order to demonstrate that his account of cultural capital and distinction is more nuanced than is suggested by its uptake by scholars who want to use it to argue against evaluative activity. Finally, it argues that television aesthetics cannot be divorced from media and cultural studies to the extent that some of its practitioners appear to want.
Before the history boom
Authors: Sills-Jones Dafydd
Published: February 2016

This article seeks to examine the notion of a ‘history boom’ on UK television (TV) during the second half of the 1990s and 2000s. It does this by sampling the UK TV schedule between 1982 and 2012, presenting material from interviews with leading producers and commissioners, and conducting an analysis of key programmes. What emerges is the contrary notion of a ‘history dip’ between the late 1980s and early1990s, which in turn reveals an earlier high level of history programme output on UK TV. By adding to the previous accounts of history TV production, this article comments on a tendency in media history towards a ‘history of the victor’, with the attendant danger of overlooking important periods of televisual output and industrial transformation.
Eccentric Exercise Versus Eccentric Exercise and Soft Tissue Treatment (Astym) in the Management of Insertional Achilles Tendinopathy
Authors: McCormack Joshua R. , Underwood Frank B. , Slaven Emily J. , Cappaert Thomas A.
Published: February 2016

Background:

Eccentric exercise is commonly used in the management of Achilles tendinopathy (AT) but its effectiveness for insertional AT has been questioned. Soft tissue treatment (Astym) combined with eccentric exercise could result in better outcomes than eccentric exercise alone.

Hypothesis:

Soft tissue treatment (Astym) plus eccentric exercise will be more effective than eccentric exercise alone for subjects with insertional AT.

Study Design:

Prospective randomized controlled trial.

Level of Evidence:

Level 2.

Methods:

Sixteen subjects were randomly assigned to either a soft tissue treatment (Astym) and eccentric exercise group or an eccentric exercise–only group. Intervention was completed over a 12-week period, with outcomes assessed at baseline, 4, 8, 12, 26, and 52 weeks. Outcomes included the Victorian Institute of Sport Assessment Achilles-Specific Questionnaire (VISA-A), the numeric pain rating scale (NPRS), and the global rating of change (GROC).

Results:

Significantly greater improvements on the VISA-A were noted in the soft tissue treatment (Astym) group over the 12-week intervention period, and these differences were maintained at the 26- and 52-week follow-ups. Both groups experienced a similar statistically significant improvement in pain over the short and long term. A significantly greater number of subjects in the soft tissue treatment (Astym) group achieved a successful outcome at 12 weeks.

Conclusion:

Soft tissue treatment (Astym) plus eccentric exercise was more effective than eccentric exercise only at improving function during both short- and long-term follow-up periods.

Clinical Relevance:

Soft tissue treatment (Astym) plus eccentric exercise appears to be a beneficial treatment program that clinicians should consider incorporating into the management of their patients with insertional AT.
Zum Risikocharakter variabler Beteiligungsformen – Überlegungen aus arbeitsökonomischer Sicht
Authors: Hardes Heinz-Dieter , Wickert Heiko
Published: February 2016

Im vorliegenden Beitrag werden vertragstheoretische Überlegungen zur Konzeption von anreizorientierten Entgeltverträgen dargestellt, mit Komponenten variabler Beteiligungsentgelte – neben fixierten Basisentgelten. Das begriffliche Verständnis monetärer Beteiligungsentgelte schließt dabei sowohl Formen periodischer Erfolgsbeteiligungen wie auch langfristige Kapitalbeteiligungen von Mitarbeitern und Führungskräften ein. Der Beitrag konzentriert sich auf einen in der Literatur bisher vernachlässigten Aspekt, insbesondere auf Risikoüberlegungen im Bezug zu variablen Bonussystemen, Mitarbeiter-Aktien-Programmen und Aktienoptionsplänen für Führungskräfte. Auf der Basis der vertragstheoretischen Grundlagen werden mehrere anwendungsbezogene Folgerungen zur Gestaltung betrieblicher Beteiligungsentgelte abgeleitet.
Der Einsatz und die Bewertung von Rückzahlungsklauseln für Weiterbildungsmaßnahmen durch Unternehmen – Ergebnisse einer empirischen Untersuchung
Authors: Alewell Dorothea , Koller Petra
Published: February 2016

Unternehmen können Rückzahlungsklauseln einsetzen, um das Investitionsrisiko bei arbeitgeberseitig finanzierten Weiterbildungsmaßnahmen zu steuern. Allerdings sollte, so theoretische Überlegungen, der Einsatz dieses Instrumentes von der Ausprägung einiger objektiver und subjektiver Faktoren des personalpolitischen und arbeitsjuristischen Kontextes abhängen. Im Beitrag werden zunächst theoretische Hypothesen zum Einsatz von Rückzahlungsklauseln im personalpolitischen und arbeitsjuristischen Kontext vorgestellt, bevor diese dann auf der Basis eines eigenen Datensatzes anhand von Modellen der logistischen Regression überprüft werden. Der starke Einfluss der Humankapitaltransferierbarkeit auf den Einsatz von Rückzahlungsklauseln bestätigt sich dabei. Zudem wird deutlich, dass das Investitionsrisiko in der Sichtweise der Arbeitgeber offenbar stärker von der absoluten Höhe der vom Arbeitgeber getragenen Kosten abhängt als von der Fluktuationsrate. Subjektive Wahrnehmungen der Befragten haben zudem einen stärkeren Erklärungswert für den Einsatz von Rückzahlungsklauseln als „objektive” Gegebenheiten.
Beschäftigungssicherheit auf betrieblicher Ebene – Personalpolitische Implikationen einer Neuinterpretation des Günstigkeitsprinzips
Authors: Bürkle Thomas , Knörzer Michael
Published: February 2016

Das im Tarifvertragsgesetz verankerte Günstigkeitsprinzip verhindert nach geltender Rechtsauffassung einen Trade-Off von Beschäftigungssicherheit gegen Lohn, sobald Tariflöhne unterschritten werden. Diesbezüglich stellt sich die Frage, welche beschäftigungspolitischen Implikationen sich aus der gegenwärtig geforderten Neudeutung des Günstigkeitsprinzips hinsichtlich einer Unterschreitung des Tariflohnes im Austausch für Beschäftigungssicherheit ergeben. Vor diesem Hintergrund wird in dem vorliegenden Artikel ein Modell zur optimalen Größe interner Arbeitsmärkte, die durch ein hohes Maß an Beschäftigungssicherheit gekennzeichnet sind, formuliert. Die aufgrund der Vereinnahmung von Risikoprämien (Tausch von Beschäftigungssicherheit gegen Lohn) für das Unternehmen vorteilhafte Etablierung interner Arbeitsmärkte wird sich dabei häufig im Rahmen betrieblicher Mitbestimmung vollziehen, so dass Betriebsräte für die Belegschaft Anspruch auf zumindest einen Teil der so erzielbaren Rente erheben und über Mitbestimmungsrechte Einfluss auf die Größe des internen Arbeitsmarktes nehmen werden.
Der Beitrag des Personalmanagements zum Unternehmenserfolg. Eine Metaanalyse nach 20 Jahren Erfolgsfaktorenforschung
Authors: Gmür Markus , Schwerdt Boris
Published: February 2016

Die Metaanalyse beruht auf 61 Primärstudien, die zwischen 1985 und 2003 in internationalen Zeitschriften veröffentlicht wurden und den statistischen Zusammenhang zwischen Personalmanagementmaßnahmen und dem Unternehmenserfolg untersucht haben. Die Analyse ergibt einen positiven Gesamteffekt, der aber nur für Teilgruppen signifikant ist. Aufgeschlüsselt nach Personalfunktionen sind vor allem die Effekte für den Weiterbildungsaufwand, für den Anteil variabler Vergütung und den Rekrutierungsaufwand signifikant — die beiden ersteren allerdings mit abnehmender Signifikanz im Zeitverlauf. Darüber hinaus zeichnen sich auch für die Förderung der Work Life Balance und eine Personalpolitik, die auf die Förderung des individuellen Commitment abzielt, signifikante Effekte ab. Das Ergebnis lässt sich durch ein Zusammenspiel von ‘First Mover’- und Institutionalisierungseffekten erklären. Die Analyse zeigt auch, dass die Ergebnisse von Erfolgsfaktorenstudien stark durch die Wahl der Erfolgsvariable, jedoch weniger durch Moderatorvariablen, wie die Unternehmensgröße oder das Untersuchungsland beeinflusst werden. Für die weitere Personalerfolgsfaktorenforschung ergibt sich die Notwendigkeit einer weitergehenden Standardisierung in der Operationalisierung der Untersuchungsvariablen.
Reaktionen auf Ablehnungsschreiben an Bewerber: Das Beispiel „Eisschreiben”
Authors: Müller Elke , Moser Klaus
Published: February 2016

In den letzten Jahren ist der Bewerberseite in der Forschung zur Personalauswahl vermehrt Aufmerksamkeit zuteil geworden. Zu den Reaktionen von abgelehnten Bewerbern liegen aber nach wie vor kaum Untersuchungen vor. Erste Hinweise existieren, dass Ablehnungsschreiben auch für die einen Bewerber ablehnende Organisation negative Konsequenzen haben können (z.B. geringe Weiterempfehlungsbereitschaft oder negative Einstellung gegenüber den Produkten des Unternehmens). Der vorliegende Beitrag stellt einige Befunde zur Gestaltung von Ablehnungsschreiben vor und berichtet über ein Experiment, in dem die Auswirkungen der Ankündigung untersucht werden, die Bewerbung werde in einen Bewerberpool (auch „Talentpool” genannt) aufgenommen, um den Bewerber zu einem späteren Zeitpunkt abermals ansprechen zu können (= Übersendung eines so genannten „Eisschreibens”). Es zeigt sich, dass Bewerber diese Art von Ablehnungsschreiben positiver einschätzen und die Einstellung zum Unternehmen günstiger ist als bei Standardabsagen. Unternehmen, die Bewerberpools einrichten, können nach den Ergebnissen dieser Studie positive Reaktionen auf der Bewerberseite erwarten.
Reziprozitätsformen in psychologischen Verträgen. Eine empirische Untersuchung am Beispiel von Auslandsentsandten
Authors: Andresen Maike , Göbel Markus
Published: February 2016

Die einschlägige Forschung betrachtet psychologische Verträge primär aus einer individualistisch-rationalen Perspektive. Wie alle Verträge so sind auch psychologische Verträge jedoch in einen soziokulturellen Kontext eingebettet, welcher maßgeblichen Einfluss auf die Handlungsmotive und Tauschprozesse der Akteure hat. Wir verfolgen daher mit unserer Forschung zwei Ziele. Zum einen möchten wir die soziokulturellen Bedingungen erforschen, die das (Tausch-)Verhalten in psychologischen Verträgen beeinflussen, und zum anderen die Motive, die diesen Tauschprozessen zugrunde liegen. Im Rahmen einer qualitativen Studie erhoben wir mittels Interviews Daten von 54 deutschen Expatriates und analysierten diese auf Basis der Grounded Theory. Wir konnten herausarbeiten, dass psychologische Verträge in einen komplexen soziokulturellen Kontext eingebettet sind. Mit Blick auf diesen soziokulturellen Kontext wird deutlich, dass neben den individualistischen Handlungskalkülen auch moralische und prosoziale Handlungsmotive in psychologischen Verträgen relevant sind. Auf der Basis dieser Ergebnisse generierten wir zwei dominante Reziprozitätstypen, die utilitaristische Tauschreziprozität und die solidarische Gabenreziprozität, die den psychologischen Verträgen der Expatriates zugrunde liegen.
Strategische Bindung der Ressourcen von Fach- und Führungskräften. Beurteilung und Umsetzung in Unternehmen
Authors: Grieger Jürgen , Ortlieb Renate , Pantelmann Heike , Sieben Barbara
Published: February 2016

In diesem Beitrag wird analysiert, welche Strategien zur Bindung der Ressourcen von Fach- und Führungskräften, d. h. ihrer für den Unternehmenserfolg bedeutsamen Kompetenzen, in Unternehmen als geeignet beurteilt und welche tatsächlich umgesetzt werden. Auf der Basis der Ressourcenabhängigkeitstheorie von Pfeffer und Salancik und von Etzionis Ansatz der Compliance-Beziehungen entwickeln wir eine Typologie bestehend aus fünf Bindungsstrategien, mit denen der Zufluss und der Erhalt kritischer Ressourcen gesichert werden können. Die Ergebnisse einer Clusteranalyse auf der Basis der Befragung von 159 Personalmanagern der höchsten Leitungsebene in deutschen Unternehmen unterstützen unsere theoretischen Überlegungen zu dieser Typologie. Zugleich zeigt sich eine Diskrepanz zwischen der Beurteilung von Bindungsstrategien und deren Umsetzung, die wir nicht vollständig erklären können. Wir diskutieren Implikationen für die Personalpraxis und -forschung. Der Beitrag zur Forschung liegt insbesondere im Fokus auf die organisationale Ebene sowie in der Anwendung der Ressourcenabhängigkeitstheorie, mit der wir den Blick für die Verknüpfung von Personalbindung, Personalgewinnung und Wissensmanagement als komplementäre Praktiken der Ressourcenbindung öffnen.
Handling Paradoxical Tensions through Conventions: The Case of Performance Appraisal
Authors: Kozica Arjan , Brandl Julia
Published: February 2016

In this paper, we investigate how conventions enable organisational actors to cope with paradoxical tensions in performance appraisal systems. Building on a case study of a performance appraisal system reform in a public sector organisation, we analyse how this organisation enabled superiors to take into account both accountability and professional logic. When new appraisal rules required superiors to rank their employees according to their qualifications but also to show collegiate solidarity, superiors negotiated an organisation-wide understanding of the rules that enabled them to address both logics simultaneously. The study underlines the importance of collective understandings for individual responses to paradoxical tensions and reveals how performance appraisal systems can be operated according to different logics.
Management by Commitment — Möglichkeiten und Grenzen einer ‚selbstverpflichtenden’ Führung von Mitarbeitern
Authors: Steinle Claus , Ahlers Friedel , Riechmann Carmen
Published: February 2016

Mitarbeiter einer Unternehmung werden heute als ein Schlüsselfaktor für den Unternehmenserfolg betrachtet. Im Mittelpunkt dieses Beitrags steht nun die Kernfrage, unter welchen Rahmenbedingungen und durch welche Maßnahmen Unternehmungen ihre Mitarbeiter motivieren können, ihre Energie und ihre Fähigkeiten im Sinne der Unternehmung einzusetzen. Zunächst wird untersucht, wie ein Management by Commitment diesen Prozess unterstützen kann und welcher Stellenwert dem Konzept bisher in der Forschungsliteratur zugedacht wurde. Dann erfolgt eine nähere Betrachtung des Commitment-Begriffs sowie eine Analyse seines Charakters und der Aufgaben des Managements und der Mitarbeiter bei der Generierung von Mitarbeiter-Commitment. Daran anschließend sollen Commitment-Potentiale im Managementprozess aufgedeckt und Möglichkeiten für ein Management by Commitment durch Anreizstrukturierung beleuchtet werden. Im Anschluss daran erfolgt eine Herausarbeitung von Problemfeldern und Grenzen eines Management by Commitment, wobei exemplarisch das Instrumentalisierungs-, das Steuerungs-, das Gestaltungs- sowie das Motivations- und Qualifikationsproblem betrachtet werden. Vor diesem Hintergrund werden sodann Konturen eines differentiell-evolutionären Management by Commitment herausgearbeitet. Der Beitrag schließt mit einer Einschätzung des Stellenwerts eines Management by Commitment vor dem Hintergrund zukünftiger Herausforderungen an die Personal- und Unternehmensführung.
Drug repurposing to target Ebola virus replication and virulence using structural systems pharmacology
Authors: Zhao Zheng , Martin Che , Fan Raymond , Bourne Philip E. , Xie Lei
Published: February 2016

Background

The recent outbreak of Ebola has been cited as the largest in history. Despite this global health crisis, few drugs are available to efficiently treat Ebola infections. Drug repurposing provides a potentially efficient solution to accelerating the development of therapeutic approaches in response to Ebola outbreak. To identify such candidates, we use an integrated structural systems pharmacology pipeline which combines proteome-scale ligand binding site comparison, protein-ligand docking, and Molecular Dynamics (MD) simulation.

Results

One thousand seven hundred and sixty-six FDA-approved drugs and 259 experimental drugs were screened to identify those with the potential to inhibit the replication and virulence of Ebola, and to determine the binding modes with their respective targets. Initial screening has identified a number of promising hits. Notably, Indinavir; an HIV protease inhibitor, may be effective in reducing the virulence of Ebola. Additionally, an antifungal (Sinefungin) and several anti-viral drugs (e.g. Maraviroc, Abacavir, Telbivudine, and Cidofovir) may inhibit Ebola RNA-directed RNA polymerase through targeting the MTase domain.

Conclusions

Identification of safe drug candidates is a crucial first step toward the determination of timely and effective therapeutic approaches to address and mitigate the impact of the Ebola global crisis and future outbreaks of pathogenic diseases. Further in vitro and in vivo testing to evaluate the anti-Ebola activity of these drugs is warranted.
Endothelial progenitor cells and burn injury – exploring the relationship
Authors: Banyard Derek A. , Adnani Blake O. , Melkumyan Satenik , Araniego Cheryl Ann , Widgerow Alan D.
Published: February 2016

Burn wounds result in varying degrees of soft tissue damage that are typically graded clinically. Recently a key participant in neovascularization, the endothelial progenitor cell, has been the subject of intense cardiovascular research to explore whether it can serve as a biomarker for vascular injury. In this review, we examine the identity of the endothelial progenitor cell as well as the evidence that support its role as a key responder after burn insult. While there is conflicting evidence with regards to the delta of endothelial progenitor cell mobilization and burn severity, it is clear that they play an important role in wound healing. Systematic and controlled studies are needed to clarify this relationship, and whether this population can serve as a biomarker for burn severity.
Double-sparsity dictionary for seismic noise attenuation
Authors: Chen Yangkang , Ma Jianwei , Fomel Sergey
Published: February 2016

A key step in sparsifying signals is the choice of a sparsity-promoting dictionary. There are two basic approaches to design such a dictionary: the analytic approach and the learning-based approach. Although the analytic approach enjoys the advantage of high efficiency, it lacks adaptivity to various data patterns. On the other hand, the learning-based approach can adaptively sparsify different data sets but has a heavier computational complexity and involves no prior-constraint pattern information for particular data. We have developed a double-sparsity dictionary (DSD) for seismic data to combine the benefits of both approaches. We have evaluated two models to learn the DSD: the synthesis model and the analysis model. The synthesis model learns DSD in the data domain, and the analysis model learns DSD in the model domain. We tested the analysis model and proposed to use the seislet transform and data-driven tight frame (DDTF) as the base transform and adaptive dictionary, respectively, in the DSD framework. The DDTF obtains an extra structure regularization by learning dictionaries, whereas the seislet transform obtains a compensation for the transformation error caused by slope dependency. The DSD aims to provide a sparser representation than the individual transform and dictionary and, therefore, can help to achieve better performance in denoising applications. Although for the purpose of compression, the DSD is less sparse than the seislet transform, it outperforms the seislet and DDTF in distinguishing the signal and noise. Two simulated synthetic examples and three field data examples confirm a better denoising performance of the proposed approach.
Interpretation of shallow electromagnetic instruments resistivity and magnetic susceptibility measurements using rapid 1D/3D inversion
Authors: Benech Christophe , Dabas Michel , Simon François-Xavier , Tabbagh Alain , Thiesson Julien
Published: February 2016

We have developed an inversion process of electromagnetic induction (EMI) data based on a two-step approach with 1D inversion of the entire studied surface and a fast 3D inversion applied over limited areas. This process is similar to that formerly used in resistivity prospection. For the study of soil (environmental, engineering, or archaeological explorations), low-frequency electromagnetic instruments (referred to as Slingram EMI) have highly useful specificities. They are light, are easy to move in the field, and can simultaneously measure the ground’s electric conductivity and magnetic susceptibility; they have thus been used to map these properties over large surface areas, within relatively short periods of time, and at reasonable expense. The possibility of combining several coil geometries has opened up the potential for multidepth techniques and systematic 1D inversion, which are found to be sufficiently revealing to allow larger portions of surveyed areas to be analyzed. In the “targeted areas” selected for 3D inversion, the geometries of the 3D features and the resistivity and/or susceptibility contrasts are determined. This step is based on the method of moments, where only 3D heterogeneities are meshed, and only a small number of major characteristics, such as contrast, thickness, width, etc., are sought. We first applied this process to synthetic data, then to data acquired at an experimental test site, and finally to field cases. The rapid 3D inversion complements the 1D inversion by solving a series of issues: correction for the apparent anisotropy generated by the instrument configuration, multiarched anomalies, precise location of lateral changes, and determination of the properties contrasts. Our inversion results highlighted the importance of the instrument geometry. We also have determined that apparent magnetic susceptibility data can be more appropriate for the determination of the volume of man-made features and can be highly complementary to conductivity data.
Stochastic structure-constrained image-guided inversion of geophysical data
Authors: Zhou Jieyi , Revil André , Jardani Abderrahim
Published: February 2016

Inverse modeling of geophysical data involves the recovery of a subsurface structural model and the distribution of petrophysical properties. Independent information regarding the subsurface structure is usually available, with some uncertainty, from the expertise of a geologist and possibly accounting for sedimentary and tectonic processes. We have used the available structural information to construct a model covariance matrix and to perform a structure-constrained inversion of the geophysical data to obtain a geophysical tomogram [Formula: see text]. We have considered that the geologic models [Formula: see text] were built from random variables and were described with a priori probability density function in the Bayesian framework. We have explored for the a posteriori probability density of the geologic models (i.e., the structure of the guiding image) with the Markov-chain Monte Carlo method, and we inverted at the same time, in a deterministic framework, the geophysical data. The sampling of the geologic models was performed in a stochastic framework, and each geologic model [Formula: see text] was used to invert the geophysical model [Formula: see text] using image-guided inversion. The adaptive metropolis algorithm was used to find the proposal distributions of [Formula: see text] reproducing the geophysical data and the geophysical information. In other words, we have tried to find a compromise between the a priori geologic information and the geophysical data to get, as end products, an updated geologic model and a geophysical tomogram. To demonstrate our approach, we used here electrical resistivity tomography as a technique to identify a correct geologic model and its a posteriori probability density. The approach was tested using one synthetic example (with three horizontal layers displaced by a normal fault) and one field case corresponding to a sinkhole in a three-layer structure. In both cases, we were able to select the most plausible geologic models that agreed with a priori information and the geophysical data.
Determining the distance to magnetic sources
Authors: Cooper Gordon R. J. , Whitehead Rob C.
Published: February 2016

The distance to sources of magnetic field anomalies of a known structural index can be determined by using ratios of the analytic signal amplitudes ([Formula: see text]) of different orders, and this can be performed in several different ways. Local minima of the distance correspond to the source depth. If an incorrect structural index has been used, then the different methods will yield different depths. Hence, a comparison of the results obtained from the different methods can help us to differentiate between valid and invalid source depths. These methods are computationally straightforward, and in some of the methods, the orders of the [Formula: see text] that are used can be chosen based on the noise level of the data. Some approaches that do not require the a priori specification of the structural index of the source are introduced, including methods that use data from two different altitudes (obtained by vertical continuation). We have applied the methods to aeromagnetic data sets from the Giyani and Kuruman regions of South Africa with plausible results.
Exact elastic impedance matrices for transversely isotropic medium
Authors: Zhang Feng , Li Xiang-Yang
Published: February 2016

Conventional elastic impedances are derived as scalars by means of the integration of reflectivity. In this sense, they are attributes of the seismic reflection but not the intrinsic physical property of the subsurface media. The derivation of these expressions shares the same assumptions as the reflectivity approximations, such as weak impedance contrast, small angle of incidence, or weak anisotropic media, and thus it limits the accuracy and interpretation capability. The exact P/SV impedance matrices relating the stress and strain represent the mechanical property of the subsurface media and yield reflection coefficients at an arbitrary angle of incidence. We have extended the impedance matrices to a transversely isotropic medium. The resulting elastic impedances (stress/velocity ratios) can be used to characterize those unconventional reservoir formations with strong seismic anisotropy, such as shale-gas and coal-bed methane. Our numerical analyses determined their variations with the phase angle and anisotropy parameters. The exact expressions of the P- and S-wave elastic impedances are used to model the seismic reflection coefficients, and thus they can be inverted simultaneously if all of the types of reflection waves are available. We then derive approximations of quasi-P-wave elastic impedances for seismic inversion of anisotropy parameters and further interpretation. Our applications on real logs and seismic data for a turbidite fan reservoir and a shale-gas reservoir determined the robust interpretation capability of derived elastic impedances in lithology characterizations.
Representative elementary volumes for evaluating effective seismic properties of heterogeneous poroelastic media
Authors: Milani Marco , Rubino J. Germán , Müller Tobias M. , Quintal Beatriz , Caspari Eva , Holliger Klaus
Published: February 2016

Understanding and quantifying seismic energy dissipation in fluid-saturated porous rocks is of considerable interest because it offers the perspective of extracting information with regard to the elastic and hydraulic rock properties. An important, if not dominant, attenuation mechanism prevailing in the seismic frequency band is wave-induced fluid pressure diffusion in response to the contrasts in elastic stiffness in the mesoscopic-scale range. An effective way to estimate seismic velocity dispersion and attenuation related to this phenomenon is through the application of numerical upscaling procedures to synthetic rock samples of interest. However, the estimated seismic properties are meaningful only if the underlying sample volume is at least of the size of a representative elementary volume (REV). In the given context, the definition of an REV and the corresponding implications for the estimation of the effective seismic properties remain largely unexplored. To alleviate this problem, we have studied the characteristics of REVs for a set of idealized rock samples sharing high levels of velocity dispersion and attenuation. For periodically heterogeneous poroelastic media, the REV size was driven by boundary condition effects. Our results determined that boundary condition effects were absent for layered media and negligible in the presence of patchy saturation. Conversely, strong boundary condition effects arose in the presence of a periodic distribution of finite-length fractures, thus leading to large REV sizes. The results thus point to the importance of carefully determining the REV sizes of heterogeneous porous rocks for computing effective seismic properties, especially in the presence of strong dry frame stiffness contrasts.
Three effective inverse Laplace transform algorithms for computing time-domain electromagnetic responses
Authors: Li Jianhui , Farquharson Colin G. , Hu Xiangyun
Published: February 2016

The inverse Laplace transform is one of the methods used to obtain time-domain electromagnetic (EM) responses in geophysics. The Gaver-Stehfest algorithm has so far been the most popular technique to compute the Laplace transform in the context of transient electromagnetics. However, the accuracy of the Gaver-Stehfest algorithm, even when using double-precision arithmetic, is relatively low at late times due to round-off errors. To overcome this issue, we have applied variable-precision arithmetic in the MATLAB computing environment to an implementation of the Gaver-Stehfest algorithm. This approach has proved to be effective in terms of improving accuracy, but it is computationally expensive. In addition, the Gaver-Stehfest algorithm is significantly problem dependent. Therefore, we have turned our attention to two other algorithms for computing inverse Laplace transforms, namely, the Euler and Talbot algorithms. Using as examples the responses for central-loop, fixed-loop, and horizontal electric dipole sources for homogeneous and layered mediums, these two algorithms, implemented using normal double-precision arithmetic, have been shown to provide more accurate results and to be less problem dependent than the standard Gaver-Stehfest algorithm. Furthermore, they have the capacity for yielding more accurate time-domain responses than the cosine and sine transforms for which the frequency-domain responses are obtained by interpolation between a limited number of explicitly computed frequency-domain responses. In addition, the Euler and Talbot algorithms have the potential of requiring fewer Laplace- or frequency-domain function evaluations than do the other transform methods commonly used to compute time-domain EM responses, and thus of providing a more efficient option.
Reverse time migration for microseismic sources using the geometric mean as an imaging condition
Authors: Nakata Nori , Beroza Gregory C.
Published: February 2016

Time reversal is a powerful tool used to image directly the location and mechanism of passive seismic sources. This technique assumes seismic velocities in the medium and propagates time-reversed observations of ground motion at each receiver location. Assuming an accurate velocity model and adequate array aperture, the waves will focus at the source location. Because we do not know the location and the origin time a priori, we need to scan the entire 4D image (3D in space and 1D in time) to localize the source, which makes time-reversal imaging computationally demanding. We have developed a new approach of time-reversal imaging that reduces the computational cost and the scanning dimensions from 4D to 3D (no time) and increases the spatial resolution of the source image. We first individually extrapolate wavefields at each receiver, and then we crosscorrelate these wavefields (the product in the frequency domain: geometric mean). This crosscorrelation creates another imaging condition, and focusing of the seismic wavefields occurs at the zero time lag of the correlation provided the velocity model is sufficiently accurate. Due to the analogy to the active-shot reverse time migration (RTM), we refer to this technique as the geometric-mean RTM or GmRTM. In addition to reducing the dimension from 4D to 3D compared with conventional time-reversal imaging, the crosscorrelation effectively suppresses the side lobes and yields a spatially high-resolution image of seismic sources. The GmRTM is robust for random and coherent noise because crosscorrelation enhances signal and suppresses noise. An added benefit is that, in contrast to conventional time-reversal imaging, GmRTM has the potential to be used to retrieve velocity information by analyzing time and/or space lags of crosscorrelation, which is similar to what is done in active-source imaging.
High-frequency Rayleigh-wave tomography using traffic noise from Long Beach, California
Authors: Chang Jason P. , de Ridder Sjoerd A. L. , Biondi Biondo L.
Published: February 2016

Using a dense seismic array in Long Beach, California, we have investigated the effectiveness of using traffic noise for passive subsurface imaging. Spectral analysis revealed that traffic-induced vibrations dominate the ambient seismic noise field at frequencies between 3 and 15 Hz. Using the ambient-noise crosscorrelation technique at these frequencies, we have extracted fundamental- and first-order-mode Rayleigh waves generated by Interstate 405 and local roads. We picked group traveltimes associated with the fundamental mode and used them in a straight-ray tomography procedure to produce group velocity maps at 3.0 and 3.5 Hz. The velocity trends in our results corresponded to shallow depths and coincided well with lithologies outlined in a geologic map of the survey area. The most prominent features resolved in our velocity maps were the low velocities to the north corresponding to less-consolidated materials, high velocities to the south corresponding to more-consolidated materials, a low-velocity zone corresponding to artificial fill in Alamitos Bay, and a low-velocity linear feature in the Newport-Inglewood Fault Zone. Our resulting near-surface velocities can be useful for identifying regions that are susceptible to serious damage during earthquake-related shaking.
Salinity dependence of the complex surface conductivity of the Portland sandstone
Authors: Niu Qifei , Revil André , Saidian Milad
Published: February 2016

Induced polarization can be used to estimate surface conductivity by assuming a universal linear relationship between the surface and quadrature conductivities of porous media. However, this assumption has not yet been justified for conditions covering a broad range of fluid conductivities. We have performed complex conductivity measurements on Portland sandstone, an illite- and kaolinite-rich sandstone, at 13 different water salinities (NaCl) over the frequency range of 0.1 Hz to 45 kHz. The conductivity of the pore water [Formula: see text] affected the complex surface conductivity mainly by changing the tortuosity of the conduction paths in the pore network from high to low salinities. As the fluid conductivity decreases, the magnitude of the surface conductivity and quadrature conductivity was observed to decrease. At relatively high salinities ([Formula: see text]), the ratio between the surface conductivity and quadrature conductivity was roughly constant. At low salinities ([Formula: see text]), the ratio decreased slightly with the decrease of the salinity. A Stern layer polarization model was combined with the differential effective medium (DEM) theory to describe this behavior. The tortuosity entering the complex surface conductivity was salinity dependent following the prediction of the DEM theory. At high salinity, it reached the value of the bulk tortuosity of the pore space given by the product of the intrinsic formation factor and the connected porosity. The relaxation time distributions were also obtained at different salinities by inverting the measured spectra using a Warburg decomposition. The mode of the relaxation time probability distribution found a small but clear dependence on the salinity. This salinity dependence can be explained by considering the ions exchange between Stern and diffuse layers during polarization of the former. The pore-size distribution obtained from the distribution of the relaxation time agreed with the pore-size distribution from nuclear magnetic resonance measurements.
Demerara Rise, offshore Suriname: Magma-rich segment of the Central Atlantic Ocean, and conjugate to the Bahamas hot spot
Authors: Reuber Kyle R. , Pindell Jim , Horn Brian W.
Published: February 2016

The Demerara Rise is a prominent bathymetric feature that has been considered as a broad expression of shallow continental basement and used in conjunction with the Guinea Plateau as a pinning point for circum-Atlantic plate reconstructions. Previously, shallow-penetration, poorly imaged seismic data over the Demerara Rise were modeled with the lower sequences interpreted as continental crust at relatively shallow depths. However, new long-offset, deeply penetrating seismic data provide evidence that basement nearly or entirely comprises excessively thick volcanic strata (approximately 21 km). Seismic character and geometry, 2D gravity modeling, and volcanic margin analogs were used to identify unfaulted, convex-upward seaward dipping reflector (SDR) packages. These steeply dipping (approximately 20°) igneous successions are westwardly divergent, and occur as offlapping reflector sets in trains as long as 250 km. This rift-related volcanism now recognized at the Demerara Rise was probably conjugate to syn-rift volcanism in South Florida/Great Bahama Bank, and from this we have predicted a volcanic element for the Guinea Plateau. This volcanism could be linked to a Bahamas hot spot at the initial opening of the Central Atlantic. Six SDR packages have been interpreted below the Late Jurassic-Early Cretaceous carbonate section of the rise, indicating that the early volcanism produced a marine substrate upon which the subsequent carbonate bank section developed. We have inferred that this Early Cretaceous volcanic/carbonate margin continued into the Guinea Plateau of West Africa. The pre-Aptian section was inverted and peneplained with a strong angular unconformity prior to the Early Cretaceous opening of the Equatorial Atlantic seaway. The newly identified Central Atlantic volcanic margin of the Demerara Rise holds implications of a volcanic origin for its conjugate margins. We have confirmed a voluminous magma-rich opening of the southeastern Central Atlantic.
Analysis of coelom development in the sea urchinHolopneustes purpurescensyielding a deuterostome body plan
Authors: Morris Valerie B.
Published: February 2016

An analysis of early coelom development in the echinoid Holopneustes purpurescens yields a deuterostome body plan that explains the disparity between the pentameral plan of echinoderms and the bilateral plans of chordates and hemichordates, the three major phyla of the monophyletic deuterostomes. The analysis shows an early separation into a medial hydrocoele and lateral coelomic mesoderm with an enteric channel between them before the hydrocoele forms the pentameral plan of five primary podia. The deuterostome body plan thus has a single axial or medial coelom and a pair of lateral coeloms, all surrounding an enteric channel, the gut channel. Applied to the phyla, the medial coelom is the hydrocoele in echinoderms, the notochord in chordates and the proboscis coelom in hemichordates: the lateral coeloms are the coelomic mesoderm in echinoderms, the paraxial mesoderm in chordates and the lateral coeloms in hemichordates. The plan fits frog and chick development and the echinoderm fossil record, and predicts genes involved in coelomogenesis as the source of deuterostome macroevolution.
Genetic basis of hindlimb loss in a naturally occurring vertebrate model
Authors: Don Emily K. , de Jong-Curtain Tanya A. , Doggett Karen , Hall Thomas E. , Heng Benjamin , Badrock Andrew P. , Winnick Claire , Nicholson Garth A. , Guillemin Gilles J. , Currie Peter D. , Hesselson Daniel , Heath Joan K. , Cole Nicholas J.
Published: February 2016

Here we genetically characterise pelvic finless, a naturally occurring model of hindlimb loss in zebrafish that lacks pelvic fin structures, which are homologous to tetrapod hindlimbs, but displays no other abnormalities. Using a hybrid positional cloning and next generation sequencing approach, we identified mutations in the nuclear localisation signal (NLS) of T-box transcription factor 4 (Tbx4) that impair nuclear localisation of the protein, resulting in altered gene expression patterns during pelvic fin development and the failure of pelvic fin development. Using a TALEN-induced tbx4 knockout allele we confirm that mutations within the Tbx4 NLS (A78V; G79A) are sufficient to disrupt pelvic fin development. By combining histological, genetic, and cellular approaches we show that the hindlimb initiation gene tbx4 has an evolutionarily conserved, essential role in pelvic fin development. In addition, our novel viable model of hindlimb deficiency is likely to facilitate the elucidation of the detailed molecular mechanisms through which Tbx4 functions during pelvic fin and hindlimb development.
Progressive developmental restriction, acquisition of left-right identity, and cell growth behavior during lobe formation in mouse liver development
Authors: Weiss Mary C. , Le Garrec Jean-Francois , Coqueran Sabrina , Strick-Marchand Helene , Buckingham Margaret
Published: February 2016

To identify cell-based decisions implicated in morphogenesis of the mammalian liver, we performed clonal analysis of hepatocytes/hepatoblasts in mouse liver development, using a knock-in allele of HNF4α/laacZ. This transgene randomly undergoes a low frequency of recombination that generates a functional lacZ gene that produces β-galactosidase in tissues where HNF4α is expressed. Two types of β-galactosidase-positive clones were found. Most have undergone 3-8 cell divisions and result from independent events (Luria-Delbruck fluctuation test); we calculate that they arose between E8.5 and E13.5. A second class was mega-clones derived from early endoderm progenitors, generating many descendants. Some originated from multi-potential founder cells, with labeled cells in the liver, pancreas and/or intestine. A few mega-clones populate only one side of the liver, indicating hepatic cell chirality. The patterns of labeled cells indicate cohesive and often oriented growth, notably in broad radial stripes, potentially implicated in the formation of liver lobes. This retrospective clonal analysis gives novel insights into clonal origins, cell behavior of progenitors and distinct properties of endoderm cells that underlie the formation and morphogenesis of the liver.