bluuebunny/crossref_metadata_2025 huggingface dataset:
Preservation of Arctic landscapes overridden by cold-based ice sheets
Authors: Davis P. Thompson , Briner Jason P. , Coulthard Roy D. , Finkel Robert W. , Miller Gifford H.
Published: November 2005

For nearly 40 years, a massive, well-preserved glaciomarine delta more than 54,000 years old and ancillary landforms have formed the cornerstone of models positing limited ice-sheet extent in Arctic Canada during the late Wisconsinan. We present exposure ages for large boulders on the delta surface, which coupled with preservation of relict landforms demonstrate that the region was covered by minimally erosive, cold-based ice during the late Wisconsinan. Our data suggest that surficial features commonly used to define the pattern of late Wisconsinan ice movement cannot be used on their own to constrain late Wisconsinan ice-sheet margins in Arctic regions.
Pheromone communication in a robot swarm: necrophoric bee behaviour and its replication
Authors: Purnamadjaja Anies Hannawati , Russell R. Andrew
Published: November 2005

This paper describes a project to implement necrophoric bee behaviour in a robot swarm. Pheromone communication is an effective means of coordinating the activities of insect colonies including food gathering, alarm and defense, reproduction and recognition of conspecifics. In a similar manner it is anticipated that pheromones will provide a valuable form of communication between robots. In order to investigate the problems and potential for this form of interaction, it was decided to implement an example of pheromone communication in a physical robotic system. Inspiration for this project came from the necrophoric behaviour of bees. The necrophoric pheromone released by dead bees triggers corpse removal behaviour in passing worker bees. In the context of a robot swarm one of the proposed applications for this behaviour is to locate and rescue disabled robots that release a pheromone as a form of distress signal. This paper provides details of the swarm robots used in the project, their sensors and the simple reactive control algorithm that was developed to mimic the necrophoric behaviour of bees. Results of practical experiments and simulations are also given.
A multi-agent system architecture for mobile robot navigation based on fuzzy and visual behaviour
Authors: Muñoz-Salinas Rafael , Aguirre Eugenio , García-Silvente Miguel , Gómez Moisés
Published: November 2005

A multi-agent system based on behaviour for controlling the navigation task of a mobile robot in office-like environments is presented. The set of agents is structured into a three-layer hybrid architecture. A high level of abstraction plan is created using a topological map of the environment in the Deliberative layer. It is composed by the sequence of rooms and corridors to traverse and doors to cross in order to reach a desired room. The Execution and Monitoring layer translates the plan into a sequence of available skills in order to achieve the desired goal and monitors the execution of the plan. In the Control layer there is a set of agents that implements fuzzy and visual behaviours that run concurrently to guide the robot. Fuzzy behavior manages the vagueness and uncertainty of the range sensor information allowing to navigate safely in the environment. Visual behavior locates a required door to cross and fixate it, indicating the appropriate direction to reach it. Artificial landmarks are placed beside the doors to show its position. The system has been implemented in a Nomad 200 mobile robot and has been validated in numerous experiments in a real office-like environment.
A real-time joint trajectory planner for dynamic walking bipeds in the sagittal plane
Authors: Vermeulen J. , Verrelst B. , Lefeber D. , Kool P. , Vanderborght B.
Published: November 2005

A real-time joint trajectory generator for planar walking bipeds is proposed. This trajectory planner generates dynamically stable motion patterns by using a set of objective locomotion parameters as its input, and by tuning and exploiting the natural upper body dynamics. The latter can be determined and manipulated by using the angular momentum equation. Basically, trajectories for hip and swing foot motion are generated, which guarantee that the objective locomotion parameters attain certain prescribed values. Additionally, the hip trajectories are slightly modified such that the upper body motion is steered naturally, meaning that it requires practically no actuation. This has the advantage that the upper body actuation hardly influences the position of the Zero Moment Point. The effectiveness of the developed strategy is demonstrated by simulation results.
A method for robot navigation toward a moving goal with unknown maneuvers
Authors: Belkhouche F. , Belkhouche B.
Published: November 2005

This paper deals with a method for robot navigation towards a moving goal. The goal maneuvers are not a priori known to the robot. Our method is based on the use of the kinematics equations of the robot and the goal combined with geometrical rules. First a kinematics model for the tracking problem is derived and two strategies are suggested for robot navigation, namely the velocity pursuit guidance law and the deviated pursuit guidance law. It turns out that in both cases, the robot's angular velocity is equal to the line of sight angle rate. Important properties of the navigation strategies are discussed and proven. In the presence of obstacles, two navigation modes are used: the tracking mode, which has a global aspect and the obstacle avoidance mode, which has a local aspect. In the obstacle avoidance mode, a polar diagram combining information about obstacles and directions corresponding to the pursuit is constructed. An extensive simulation study is carried out, where the efficiency of both strategies is illustrated for different scenarios.
Gait synthesis for hexapod robots with a locked joint failure
Authors: Yang Jung-Min
Published: November 2005

This paper presents a strategy for generating fault-tolerant gaits of hexapod walking robots. A multi-legged robot is considered to be fault-tolerant with respect to a given failure if it is capable of continuing its walking after the occurrence of a failure, maintaining its static stability. The failure concerned in this paper is a locked joint failure for which a joint in a leg cannot move and is locked in place. The kinematic condition for the existence of fault-tolerant gaits is derived for straight-line walking of a hexapod robot on even terrain. An algorithm for generating fault-tolerant gaits is described and, especially, periodic gaits are presented for forward walking of a hexapod robot with a locked joint failure. The leg sequence and the stride length formula are analytically driven based on gait study and robot kinematics. A case study on post-failure walking of a hexapod robot with the wave gait is shown to demonstrate the applicability of the proposed method.
Comparative experiments with a multiple model based adaptive controller for a SCARA type direct drive manipulator
Authors: Ciliz M. Kemal , Tuncay M. Ömer
Published: November 2005

In this paper, different adaptive control algorithms will be experimentally tested on a two axis SCARA type direct drive robot arm, and the performance of these algorithms will be compared. Being a direct drive system, the nonlinear effects, arising from the dynamics of the manipulator under high velocities, are directly reflected in the control of the manipulator. This makes the manipulator a more efficient test bed for testing the efficiency of the proposed adaptive schemes. In the experiments, we used fast trajectories rather than slow ones to observe how the proposed controllers compensate the dynamic nonlinear effects of manipulator dynamics. We will test some known adaptive control algorithms given in the literature along with our proposed adaptive control scheme which makes use of multiple models.
Geometric algebra of points, lines, planes and spheres for computer vision and robotics
Authors: Bayro-Corrochano Eduardo , Falcón Luis Eduardo
Published: November 2005

This paper introduces conformal geometric algebra (CGA) for applications in computer vision and robotics. The authors show that CGA deals with our intuition and insight of the geometry and it helps us to reduce considerably the computational burden of the problems. The CGA can be applied not only to describe the geometry of the space, but to handle the algebra of incidence, as well as conformal transformations, to deal with kinematics or projective geometry problems. The authors show with real and simulated applications that this system can be of great advantage in robotics and computer vision.
A three-DOF translational manipulator with decoupled geometry
Authors: Li Weimin , Gao Feng , Zhang Jianjun
Published: November 2005

A new 3-DOF translational parallel manipulator is presented in this paper. This manipulator has decoupled motion in for x, y, and z axes, and employs only revolute joints. The structure and kinematics of the manipulator are studied. The mechanism singularity is examined and the calibration methods are presented.
Robust position-force control of robot manipulator in contact with linear dynamic environment
Authors: Karan Branko
Published: November 2005

The paper presents a control scheme for simultaneous control of position and force of robot manipulator in contact with an elastodynamic environment. The control makes the assumption that interaction force between the robot and environment is adequately modeled by a second-order linear model with constant coefficients, and its implementation requires the knowledge of only boundary values of the environment parameters. It is shown that, provided that robot dynamics is exactly modeled, the scheme ensures asymptotic convergence of errors along nominal trajectories characterized by constant prescribed interaction forces and constant prescribed velocities along the contact surface.
On using delay predictors in controlling force-reflecting teleoperation over the internet
Authors: Mirfakhrai Tissaphern , Payandeh Shahram
Published: November 2005

Using the notation of the wave variables, this paper introduces an autoregressive predictor, which forecasts the future values of the delay based on its previous values. Using this new knowledge, the teleoperation control system can be tuned to achieve a better and more practical performance. The validity of this modeling is first verified by actual experiments and then the results are used in simulated teleoperations.
Multi-Input Fuzzy control of an inverted pendulum using an armature controlled DC motor
Authors: Marzi Hosein
Published: November 2005

This paper presents a design methodology to stabilize a class of multi-variant nonlinear system after a high disturbance occurs. It investigates application of Takagi-Sugeno type fuzzy controller (T-S-FC) to an inverted pendulum mechanism, actuated by an armature-controlled DC electrical motor.

Fuzzy controllers use heuristic information in developing design methodologies for control of non-linear dynamic systems. This approach eliminates the need for comprehensive knowledge and mathematical modeling of the system, and in cases of more complex systems, approximation and simplifications in order to achieve feasible mathematical model is not required.

The paper presents the stages of development of the Fuzzy Controller for an inverted pendulum by developing a two-input, Mamdani type system. It evaluates the performance of the system. Then a four-input T-S-FC type is developed. The research compares performances of each controller and presents the result of tests. A model for a DC motor is developed in this study, in order to measure the effect of time delays and response time caused by inherent properties of the physical system. The final part will demonstrate the complete operational system with the DC electrical motor included in the test system.
Specification of operations for a manipulator on a mobile robot using grafcet
Authors: Martínez M. A. , Martínez J. L.
Published: November 2005

This technical note deals with the way of organizing the work of a manipulator on a mobile robot. Every robotic mission is composed of several navigation and manipulation operations. In this research, the robot arm actions have been sequenced, once the mobile robot has stopped, with the help of the graphical specification tool Grafcet. The proposed method has been successfully implemented in the mobile manipulator RAM-2 for transporting videotapes.
The Palimpsest of Vietnamese Contemporary Spoken Drama
Authors: DIAMOND CATHERINE
Published: November 2005

Unlike most Southeast Asian theatres, Vietnam has created a sizeable corpus of scripted spoken dramas that continue to be popular in performance with urban audiences. Initially influenced by French classicism and Ibsenist realism, the Vietnamese spoken drama, kich noi, very quickly adapted to local social realities and survives by readily incorporating topical subjects. While keeping abreast of current social issues, the theatre nonetheless makes use of its multi-cultural heritage, and in any given modern performance one can see the layers of influence – traditional Sino-Vietnamese hat boi/tuong; Vietnamese cheo theatre, Cham dance, French realism, Soviet constructivism and socialist realism, and most recently, western performance art. The Vietnamese playwrights, set designers, directors, and actors have combined aspects of the realistic theatre with the conventions of their suppositional traditional theatre to come up with a hybrid that is uniquely Vietnamese. It is argued that these manifold layers should be regarded as a kind of palimpsest rather than just as pastiche.
Introduction: Festival Culture in Global Perspective
Authors: SAUTER WILLMAR
Published: November 2005

According to the Australia Council, the 152 arts festivals held in that country during the season of 1993–4 had a combined operating expenditure of Australian $58.3 million and were attended by 2.2 million visitors. At the same time, these festivals provided 32,000 paid engagements for Australian artists. Considering this massive expansion of festivals in terms of artistic arena, national marketplace and international industry, the scholarly interest in this phenomenon has taken new directions. To study the productions seemed not to be enough, nor was it satisfactory to survey audience attendance or to investigate economic turnouts. Obviously festivals did something more than promote theatrical performances.
The OUT OF THE BOX Festival of Early Childhood: Fashioning the Boutique Festival for Children
Authors: SEFFRIN GEORGIA
Published: November 2005

In recent years the construct of the festival form has shifted considerably, engaging with contemporary debates regarding issues of community and identity. One manifestation of this engagement is the model of the boutique festival, which focuses on a particular audience, and which positions that audience to substantially produce its own festival experience, in a manner far more rigorous than more conventional festival models.

The OUT OF THE BOX Festival of Early Childhood, produced by the Queensland Performing Arts Centre in Australia, is a potent example of a boutique festival, in which key elements pertaining to the manner in which this model of festival production, including audience positioning, notions of excellence, consultation, philosophy, programming, and the use of space, are evinced.
Iranian Theatre Festivalized
Authors: YEGANEH FARAH
Published: November 2005

This article explores contemporary Iranian theatre festivals and their relation to the whole structure of theatrical playing in the country. It examines in particular the role of the most important decision-making centre for theatre and theatre festivals: the Dramatic Arts Centre (DAC), the theatrical branch of the Ministry of Culture. The main framework of the article is based on Willmar Sauter's model of the theatrical event. Two of his four elements have been selected to develop the concept of festivals as theatrical events. The section titled ‘Organization and cultural context’ will discuss the organizational structure of festivals; and the section ‘Contextual theatricality’ will analyse the framework of the festival culture. Some fifty festivals and mini-festivals are held annually throughout the whole country. They are categorized in the article according to their genre: international, national, regional and community.
A decision-theoretic framework for the evaluation of language models used in speech recognizers
Authors: DELLER J. R. , DESAI K. H. , YANG Y. P.
Published: November 2005

An analytical method for design and performance analysis of language models (LM) is described, and an example interactive software tool based on the technique is demonstrated. The LM performance analysis does not require on-line simulation or experimentation with the recognition system in which the LM is to employed. By exploiting parallels with signal detection theory, a profile of the LM as a function of the design parameters is given in a set of curves analogous to a receiver-operating-characteristic display.
Paraphrasing spoken Chinese using a paraphrase corpus
Authors: ZHANG YUJIE , YAMAMOTO KAZUHIDE
Published: November 2005

One of the key issues in spoken-language translation is how to deal with unrestricted expressions in spontaneous utterances. We have developed a paraphraser for use as part of a translation system, and in this paper we describe the implementation of a Chinese paraphraser for a Chinese-Japanese spoken-language translation system. When an input sentence cannot be translated by the transfer engine, the paraphraser automatically transforms the sentence into alternative expressions until one of these alternatives can be translated by the transfer engine. Two primary issues must be dealt with in paraphrasing: how to determine new expressions, and how to retain the meaning of the input sentence. We use a pattern-based approach in which the meaning is retained to the greatest possible extent without deep parsing. The paraphrase patterns are acquired from a paraphrase corpus and human experience. The paraphrase instances are automatically extracted and then generalized into paraphrase patterns. A total of 1719 paraphrase patterns obtained using this method and an implemented paraphraser were used in a paraphrasing experiment. The results showed that the implemented paraphraser generated 1.7 paraphrases on average for each test sentence and achieved an accuracy of 88%.
Magnetic field variations in the Jovian magnetotail induced by solar wind dynamic pressure enhancements
Authors: Tao Chihiro , Kataoka Ryuho , Fukunishi Hiroshi , Takahashi Yukihiro , Yokoyama Takaaki
Published: November 2005

In order to understand the response of the Jovian magnetosphere to solar wind dynamic pressure enhancements, we investigate magnetic field variations observed by the Galileo spacecraft. The lack of solar wind monitoring just upstream of the Jovian magnetosphere is overcome by simulating a one‐dimensional magnetohydrodynamic (MHD) propagation of the solar wind from the Earth. We identify the events with an increase of the solar wind dynamic pressure >0.25 nPa at the Jovian orbit. Characteristic magnetic field variations are found in the Jovian magnetosphere for all of the nine events. The rectangular waveform due to the Jovian rotation disappears for eight of the nine events. Magnetic field disturbances in the frequency range from 0.3 to 10 mHz are enhanced simultaneously. The maximum amplitude of the disturbances is in proportional to the maximum amplitude of the solar wind dynamic pressure. We suggest that the current sheet is greatly deformed and reconnection bursts are induced under the compressed magnetosphere.
GPS crustal strain, postglacial rebound, and seismic hazard in eastern North America: The Saint Lawrence valley example
Authors: Mazzotti Stéphane , James Thomas S. , Henton Joe , Adams John
Published: November 2005

We present Global Positioning System (GPS) measurements that constrain the amplitude, pattern, and origin of crustal deformation in the Saint Lawrence valley, Québec, one of the most seismically active regions of eastern North America. The GPS network shows coherent southeastward motion of 0.6 ± 0.2 mm yr−1, relative to North America, and uplift of 2.6 ± 0.4 mm yr−1. Network average horizontal strain rates are mostly ESE‐WNW shortening at (1.7 ± 1.0) × 10−9yr−1. The shortening rate across the Charlevoix seismic zone is about twice as big as the regional average. These measurements are consistent with both postglacial rebound (PGR) models and the deformation style indicated by earthquake focal mechanisms. Although the GPS data do not discriminate between various models of crustal deformation, they provide important constraints on large earthquake recurrence. Assuming that the GPS strain estimates are representative of seismic moment release, they constrain the maximum magnitude of truncated Gutenberg‐Richter recurrence statistics in the Charlevoix seismic zone toMX= 7.8 ± 0.6 (oneM≥ 7 earthquake per 400–1300 years). The remarkable agreement between the GPS strain rates, seismic catalogue statistics, and PGR predictions suggests that in Charlevoix, most of the PGR‐driven crustal strain may be released by large (M≥ 7) earthquakes. In the rest of the Saint Lawrence valley, PGR strain rates are significantly larger than seismic strain rates, suggesting either that PGR deformation remains mostly elastic or that large events are more frequent than indicated by small earthquake statistics (i.e., characteristic earthquakes).
Variations in climate and ephemeral channel recharge in southeastern Arizona, United States
Authors: Pool D. R.
Published: November 2005

Significant variations in interannual and decadal recharge rates are likely in alluvial basins of the semiarid southwestern United States on the basis of decadal variations in climate and precipitation and correlation of El Niño with high rates of winter precipitation and streamflow. A better understanding of the magnitude of recharge variations in semiarid and arid regions would reduce water budget uncertainty. Variability of ephemeral channel recharge with climate in southeastern Arizona was investigated through analysis of hydrologic monitoring near three ephemeral streams in southeastern Arizona during the middle to late 1990s and by relating the results to long‐term hydrologic and climatic trends. The analysis used precipitation, streamflow, water levels in wells, estimates of groundwater storage change from repeat gravity surveys, and two climatic indicators of El Niño–Southern Oscillation (ENSO), Southern Oscillation index, and Pacific Decadal Oscillation (PDO). Results indicate that variations in winter recharge are related to ENSO. El Niño conditions correspond with a greater probability of high rates of winter precipitation, streamflow, and recharge. La Niña conditions are almost exclusively associated with below‐average recharge. Rates of recharge along Rillito Creek near Tucson during 1977–1998, a period of frequent El Niño conditions and positive PDO values, were 3 times recharge rates during 1941–1957, a period dominated by La Niña conditions and low PDO values. Quantification of recharge variability with decadal climate cycles should improve estimates of rates of aquifer drainage and replenishment in the region. Similar methods are applicable to other regions where thick unsaturated zones can accept significant periodic recharge.
Periodic intensity variations in global ENA images of Saturn
Authors: Paranicas C. , Mitchell D. G. , Roelof E. C. , Brandt P. C. , Williams D. J. , Krimigis S. M. , Mauk B. H.
Published: November 2005

During select time periods in orbit about Saturn, Cassini's Ion and Neutral Camera (INCA) has detected a periodic global ENA signal. Images taken during such periods reveal the presence of a rotating source component in addition to a steady‐state component; both components have peak brightness in the midnight sector, when viewed from near dawn. We present a model that synthesizes some of the basic features of the data and gives good agreement with the integrated signal. Both components, as well as the Compton‐Getting effect whose importance was previously unrecognized in ENA imaging, are needed to explain some aspects of the data.
Joint imaging by teleseismic converted and multiple waves and its application in the INDEPTH‐III passive seismic array
Authors: Tian Xiaobo , Wu Qingju , Zhang Zhongjie , Teng Jiwen , Zeng Rongsheng
Published: November 2005

A joint imaging by teleseismic converted and multiple phases is put forward to image the crustal structure beneath the INDEPTH‐III passive seismic profile in the central Tibet. A depth dependent Vp/Vs ratio is adopted to map common conversion point (CCP) via a Vp/Vs scanning and stacking approach. Our new crustal image shows that the crust is divided into two sections with different Moho depth distributions and amplitudes, with the boundary nearby the Bangong‐Nujiang suture (BNS). A negative P‐to‐S amplitude band is located in the upper‐to‐middle crust, indicating a low velocity zone possibly caused by partial melting beneath the negative amplitude band. The average crustal Vp/Vs ratio estimated by our joint imaging method is higher than previous study, but is consistent with a partial melting middle‐to‐lower crust implied by many other results.
Magnetic field orientation control of GPS occultation observations of equatorial scintillation
Authors: Anderson P. C. , Straus P. R.
Published: November 2005

We use GPS occultation measurements from three satellites in 2002 to quantify the occurrence probability of equatorial scintillation. The occultations with the highest S4 values are almost exclusively seen near the equator and in the post‐sunset sector in agreement with the known MLAT and MLT distribution of equatorial scintillation. Occultations with high S4 values are much more likely to occur when the ray paths are more nearly aligned with the magnetic field. This is attributed to the geometry of the ionospheric bubbles associated with equatorial scintillation. As bubbles are distended in the magnetic field direction, a ray path that is parallel to the magnetic field incorporates a greater path length in depleted regions containing plasma density irregularities. Since scintillation strength increases with irregularity slab thickness, the scintillation occurrence increases for field‐aligned conditions.
A multi‐data comparison of shortwave climate forcing changes
Authors: Pallé E. , Montañés‐Rodriguez P. , Goode P. R. , Koonin S. E. , Wild M. , Casadio S.
Published: November 2005

Traditionally the Earth's reflectance has been assumed to be roughly constant, but large decadal variability, not reproduced by current climate models, has been reported lately from a variety of sources. We compare here the available data sets related to Earth's reflectance, in order to assess the observational constraints on the models. We find a consistent picture among all data sets of an albedo decreased during 1985–2000 between 2–3 and 6–7 W/m2, which is highly climatically significant. The largest discrepancy among the data sets occurs during 2000–2004, when some present an increasing reflectance trend, while CERES observations show a steady decrease of about 2 W/m2.
Amplitude ratio tomography for regional phase Q
Authors: Phillips W. S. , Hartse H. E. , Rutledge J. T.
Published: November 2005

We image regional seismic phase attenuation (Q) by extending amplitude ratio techniques, which are widely used to determine average Q within a sampled region, to obtain laterally varying Q structure using tomographic techniques. The method assumes that source radiation is isotropic and that the amplitude ratios can be modeled by a two‐dimensional Q map and relative site terms. Application to 2286, 1‐Hz Lg amplitudes from 816 events recorded at 35 central and east Asia stations yields a misfit of 0.09 log10 units, a variance reduction of 73%, relative to the uniform Q model that best fits the data, and laterally varying Q from 100 to 1000, with patterns closely following regional geology. The image is resolved, on average, to 2.5°, with resolution peaking at 1.5° in the best covered areas, which is remarkable given the sparse station geometry employed. The high resolution results from the dense distribution of earthquake sources, and is aided by the increased confidence in source locations provided by merging catalogs from many different agencies.
Anthropogenic and natural forcing impacts on ENSO‐like decadal variability during the second half of the 20th century
Authors: Shiogama Hideo , Watanabe Masahiro , Kimoto Masahide , Nozawa Toru
Published: November 2005

Several climate simulations, performed with an atmosphere‐ocean coupled general circulation model, are made to evaluate the influences of anthropogenic and natural external forcing on the observed fluctuation of the Decadal El Niño‐Southern Oscillation (DENSO) during the second half of the 20th century. A comparison of DENSO in the model simulations and the observations suggests that the observed variability includes an unusually large trend relative to that expected from purely natural variations. Moreover, we show that there is a large probability that this trend is mainly attributable to anthropogenic factors.
Radiocarbon in corals from the Cocos (Keeling) Islands and implications for Indian Ocean circulation
Authors: Hua Quan , Woodroffe Colin D. , Smithers Scott G. , Barbetti Mike , Fink David
Published: November 2005

Annual bands of a Porites coral from the Cocos (Keeling) Islands, eastern Indian Ocean, were analysed by radiocarbon for 1955–1985 AD. A rapid oceanic response of the site to bomb 14C is found, with a maximum Δ14C value of 132‰ in 1975. This value is considerably higher than those for the northwestern Indian Ocean, suggesting that surface waters reaching Cocos are not derived from the Arabian Sea. Instead, Δ14C values for Cocos and those for Watamu (Kenya) agree well over most of the study interval, suggesting that the South Equatorial Current carries 14C‐elevated water rather than 14C‐depleted water westward across the Indian Ocean. This implies that oceanic upwelling in the northwestern Indian Ocean is spatially confined with little contribution to the upper limb of the global thermohaline circulation.
Radiated energy from the mid Niigata, Japan, earthquake of October 23, 2004, and its aftershocks
Authors: Izutani Y.
Published: November 2005

The Mid Niigata earthquake of October 23, 2004, is a shallow reverse‐faulting event with Mw = 6.6. We analyze transverse component accelerograms of the main shock and four aftershocks (Mw = 4.0 ∼ 5.5) recorded at 29 strong motion observation stations. The epicenters of the four aftershocks are located within 5 km from that of the main shock. The stations are well distributed around the epicenters and their epicentral distances are between 15 and 60 km. We calculate spectral ratio between records of the main shock and each of the aftershocks in order to obtain source spectral ratio by empirically removing the effects of wave propagation path and surface layers at the stations. Thus obtained source spectral ratio is inconsistent with that expected from the self‐similar omega‐square model. Fitting omega‐square source spectral ratio with variable corner frequency to the observed spectral ratio, radiated energy and corner frequency are estimated. Radiated energy from the main shock is 3.2 × 1014 J. Although energy‐to‐moment ratios for the main shock and the aftershocks are all distributed within a narrow range from 8 × 10−6 to 4 × 10−5, they definitely increase with the event size. This scale dependence is quite similar to that obtained previously for strike‐slip events in Japan. The relationship between the seismic moment, M0, and the corner frequency, f0, is M0 ∝ f0−3.3±0.2. These results suggest a break in self‐similarity.
Estimation of the turbulent heat flux in the lower stratosphere from high resolution radar measurements
Authors: Wilson R. , Dalaudier F. , Bertin F.
Published: November 2005

Two estimates of the turbulent diffusivity (i.e., the heat flux per unit gradient) in the lower stratosphere are inferred from high‐resolution radar measurements and compared. First, the local heat flux (within the turbulent patches) is evaluated from the dissipation rate of turbulent kinetic energy εk under the basic assumptions of local homogeneity and stationarity of the fluctuations. We then estimated the effective heat flux per unit gradient as the time‐averaged flux for a given altitude during the measurement period (six hours), taking into account the observed turbulence intermittence. The time‐averaged heat flux per unit gradient is found to be ∼2 × 10−2 m2s−1 typically, in good agreement with some of the weakest estimates of diffusivity already published. The observed ratio between the local and the time averaged fluxes can reach about one order of magnitude. This last result stresses the fact that turbulent diffusivity inferred from MST radars measurements cannot generally be directly interpreted as an effective diffusivity, since radar estimates, in most cases, do not take into account the turbulence intermittence.
Carbon in iron phases under high pressure
Authors: Huang L. , Skorodumova N. V. , Belonoshko A. B. , Johansson B. , Ahuja R.
Published: November 2005

The influence of carbon impurities on the properties of iron phases (bcc, hcp, dhcp, fcc) has been studied using the first‐principles projector augmented‐wave (PAW) method for a wide pressure range. It is shown that the presence of ∼6 at. % of interstitial carbon has a little effect on the calculated structural sequence of the iron phases under high pressure. The bcc → hcp transition both for pure iron and iron containing carbon takes place around 9 GPa. According to the enthalpies comparison, the solubility of carbon into the iron solid is decreased by high pressure. The coexistence of iron carbide (Fe3C) + pure hcp Fe is most stable phase at high pressure compared with other phases. Based on the analysis of the pressure‐density dependences for Fe3C and hcp Fe, we suggest that there might be some fraction of iron carbide present in the core.
Tropical climate described as a distribution of weather states indicated by distinct mesoscale cloud property mixtures
Authors: Rossow William B. , Tselioudis George , Polak Allyson , Jakob Christian
Published: November 2005

An analysis approach that uses the patterns of cloud property joint distributions at mesoscale (cloud type mixtures) from the International Satellite Cloud Climatology Project to identify distinct weather states of the tropical atmosphere is extended to the whole tropics covering the period 1983–2004. These patterns can be used as the basis for multi‐scale, multi‐variate compositing of other observations to understand how tropical cloud systems affect the atmospheric diabatic heating and interact with the large scale circulation. We illustrate how variations of the tropical climate on longer time scales can be described in terms of the changes in the frequency of occurrence of these weather states with their associated multi‐variate relationships.
A numerical simulation of the geomagnetic sudden commencement: 3. A sudden commencement in the magnetosphere‐ionosphere compound system
Authors: Fujita S. , Tanaka T. , Motoba T.
Published: November 2005

Global plasma flow convections in the magnetosphere and in the ionosphere, field‐aligned current systems, ionospheric currents, conversion between plasma internal energy and electromagnetic energy, and plasma population regimes are in a self‐consistent state in the steady magnetosphere‐ionosphere region. This system is called the magnetosphere‐ionosphere compound system (Tanaka, 2003). In the context of the compound system, a geomagnetic sudden commencement (SC) is interpreted in terms of transition from the state in the pre‐SC period to that in the post‐SC period. The state transition is featured with the SC transient cell convection and the transient, small‐scale pressure enhancement in the magnetosphere. It is noted that destroy and recovery of the global self‐consistency are associated with formation and extinction of these transient phenomena. The transition phase is also characterized with transiently enhanced field‐aligned current in the ionosphere. These features commonly appear in the state transition phenomena like the theta aurora that is invoked by a sudden change of the By component of the solar wind magnetic field. This paper also discusses that a SC is terminated with recovery of the Region 2 current.
ULF geomagnetic pulsations in the southern polar cap: Simultaneous measurements near the cusp and the geomagnetic pole
Authors: De Lauretis M. , Francia P. , Vellante M. , Piancatelli A. , Villante U. , Di Memmo D.
Published: November 2005

During November 2003, a 1‐week test campaign of ULF geomagnetic field measurements was conducted at the new Italian/French base of Concordia (Dome C, Antarctic plateau), close to the geomagnetic pole, at a corrected geomagnetic latitude of ∼89°S. An analysis of these measurements is presented, together with a comparison with simultaneous measurements conducted at the Italian “Mario Zucchelli” base, at Terra Nova Bay, also located in the polar cap, but at lower latitude (∼80°S). The variable solar wind and interplanetary magnetic field conditions made it possible to monitor the Pc 3–4 ULF pulsation activity under different magnetospheric conditions. For quiet conditions, the pulsation power does not show evidence for a diurnal modulation at Dome C, while at Terra Nova Bay it maximizes around local magnetic noon. This result can be interpreted in terms of the different latitude of the two stations which might be linked to different magnetospheric regions: Dome C deep in the polar cap, and Terra Nova Bay approaching the cusp around noon. Conversely, during a strong geomagnetic storm, the wave activity at the two stations becomes very similar, and major ground manifestations are driven by strong solar wind pressure pulses. The clear dependence of the pulsation frequency with the interplanetary magnetic field strength suggests that upstream waves can be the source of pulsations not only at Terra Nova Bay but also at Dome C, in the deep polar cap. We also find a clear relationship between the pulsation power and the solar wind speed which is more pronounced at Dome C, where cusp‐related phenomena are not present.
Signature of Saturn's auroral cusp: Simultaneous Hubble Space Telescope FUV observations and upstream solar wind monitoring
Authors: Gérard Jean‐Claude , Bunce Emma J. , Grodent Denis , Cowley Stanley W. H. , Clarke John T. , Badman Sarah V.
Published: November 2005

Model simulations by Bunce et al. (2005a) have shown that direct precipitation of electrons in Saturn's dayside cusp regions is not capable of producing significant FUV aurora. Instead, they suggested the possibility that the FUV bright emissions sometimes observed near noon are associated with reconnection occurring at the dayside magnetopause, possibly pulsed, analogous to flux transfer events seen at the Earth. Pulsed reconnection at the low‐latitude dayside magnetopause when the IMF is directed northward (antiparallel to Saturn's magnetic field lines) is expected to give rise to pulsed twin‐vortical flows in the magnetosphere and hence to bipolar field‐aligned currents centered in the vortical flows closing in ionospheric Pedersen current. In the case of southward IMF and high‐latitude lobe reconnection the model predicts that the vortical flows are displaced poleward of the open‐closed field line boundary with reversed field‐aligned currents compared with the former case. During January 2004, a unique campaign took place during which magnetic field and plasma instruments on board the Cassini‐Huygens spacecraft measured the in situ solar wind and embedded interplanetary magnetic field while the Hubble Space Telescope simultaneously observed the far ultraviolet aurora in Saturn's southern hemisphere. The IMF was highly structured during this interval. The electric potential at Cassini is estimated from solar wind magnetic field and velocity measurements for the case of low‐latitude or lobe reconnection. We show that a dayside FUV signature of intense electron precipitation is found poleward of or along the main oval during a period of minor compression period when the dayside reconnection voltage is estimated to be ∼30–100 kV. Overall, we find that the conceptual model of Bunce et al. (2005a) provides a good estimate of the UV brightness and power for the case of northward IMF but somewhat underestimates the power for the southward IMF case, except if the speed of the vortical flow is larger than its value in the nominal model.
An energy balance study of the lower topside ionosphere using the Arecibo incoherent scatter radar and heating facilities
Authors: González Sixto A. , Nicolls Michael J. , Sulzer Michael P. , Aponte Néstor
Published: November 2005

In this paper we describe the results of an experiment to study electron and ion temperature enhancements during an HF modification experiment at the Arecibo Observatory. This experiment is unique in that we pointed the radar away from the interaction region in the F region in order to study heat conduction along the field lines. Although electron temperature enhancements have been frequently observed when high‐power radio waves are injected into the ionosphere, observations generally have occurred in the interaction region and the regions of elevated electron temperatures have been accompanied by small ion temperature increases (50–200 K). Like many such experiments, this one was conducted during winter solar minimum, when f0F2 is low during the night at midlatitudes, but this experiment also had the advantage of the upgraded Arecibo HF facility, first used in 1997. The electron temperature enhancements were accompanied by a significant increase in the ion temperature (nearly 500 K). The observation away from the interaction region allowed the application of the time‐dependent heating equation without having to estimate local heating effects (i.e., by keeping the conduction and loss terms in the energy balance calculation and neglecting the source term). More specifically, the heating rate of conduction was quantified by manipulating the heat equation. Thus the primary purpose was to observe the temperatures as the heat was conducted away from the F region ionosphere. We have observed the gradients in the electron temperature caused by the heater, estimated the conduction along the field lines, and studied the transfer of energy from the hot electrons to the ions and neutrals. At lower altitudes, near the electron‐temperature peak, we show that O+ cooling is dominant, whereas in the lower topside H+ cooling is the most important. Experiments of the type described here could be enhanced with the new dual‐beam system at Arecibo in conjunction with a heating facility.
A statistical investigation of dayside magnetosphere erosion showing saturation of response
Authors: Mühlbachler Stefan , Farrugia Charles J. , Raeder Joachim , Biernat Helfried K. , Torbert Roy B.
Published: November 2005

We present a statistical investigation of dayside magnetospheric erosion based on a survey of 316 cases in 1996–2004. We monitor erosion through the depression in the strength of the terrestrial magnetic field at geostationary heights using magnetic field observations acquired by four GOES spacecraft 2 hours on either side of local magnetic noon. The southward component of the interplanetary magnetic field (IMF) and the solar wind dynamic pressure, quantities which are responsible for opposing effects on the geostationary field, are obtained from the Wind and ACE spacecraft. We extend our previous work to encompass the Bz range [0, −35] nT. We find that dayside erosion saturates when IMF Bz is in the range [−12, −16] nT. This result is consistent with global simulations. With the measured solar wind velocity, this corresponds to an interplanetary electric field (IEF) of 6.2 ± 1.6 mV m−1. We discover that the maximum depression of the geostationary field at saturated erosion is ∼26 nT. In addition, we reveal a direct relation between the saturation of flux erosion of the dayside magnetosphere and that of the cross‐polar cap potential (CPCP), both of which occur at approximately the same electric field. For the latter, we apply the Hill‐Siscoe model for the calculation of CPCP to our data set. We find the CPCP to deviate from a linear increase with IEF at ∼4 and 7 mV/m, which correspond closely to the IEF range at which we find saturation of dayside erosion to start to manifest itself.
Evidence for the interplanetary electric field effect on the OI 630.0 nm airglow over low latitude
Authors: Chakrabarty D. , Sekar R. , Narayanan R. , Devasia C. V. , Pathan B. M.
Published: November 2005

On a geomagnetically disturbed and non‐spread F night (12 February 2004), the OI 630.0 nm airglow intensity variations recorded from Gadanki (13.5°N, 79.2°E, dip 12.5°) reveal quasi‐periodic intensity fluctuations superimposed on the large‐scale temporal variation during 1945–2315 Indian Standard Time (IST, IST = Universal Time (UT) + 5.5 hours). The residual airglow intensity fluctuations (after detrending the large‐scale variation) with periodicities of ∼0.5 hours and ∼1.0 hours, respectively, are found to vary in accordance with the F layer height variations over the dip equator as well as with the Y‐component of the interplanetary electric field (IEFy) variations calculated from the Advanced Composition Explorer (ACE) satellite data on 12 February 2004. Furthermore, these kind of periodic scale sizes in the residual airglow intensity fluctuations are not found on a geomagnetically quiet night (20 February 2004) and those intensity fluctuations do not show any correspondence with the F layer height variations over equator. Similar periodic components are also found in the temporal variations of instantaneous horizontal magnetic field (H) recorded at multiple stations over Indian subcontinent during the same interval on 12 February 2004. It is discussed that the currents responsible for the magnetic fluctuations are probably of magnetospheric origin. These observations using multiple techniques elicit the signature of the penetrating solar wind electric field in the nocturnal airglow intensity variations over low latitude during magnetically disturbed period.