US National Science Research Articles

Geometric Characteristics of Lithium Ion Battery electrodes with Different Packing Densities

The microstructure of electrodes plays a critical role in determining the performance of lithium ion batteries (LIBs), because the microstructure can affect the transport and electrochemical processes within electrodes (1-3). Increasing the volume fraction of active materials in the electrode will increase the energy density. However, the electrodes’ structural properties could also be changed significantly and the critical physical and electrochemical processes in LIBs will be affected. Therefore, the performance of a LIB can be optimized for a specific operating condition by designing electrode microstructures. For instance, Hellweg suggested a spatially varying porous electrode model to improve lithium ion transport in electrolyte phase at high charge/discharge rates (4). He showed that the power density of the graded porosity electrode was higher than a homogeneous porosity electrode without energy loss. In this study, we investigate the realistic geometric characteristics of electrode microstructures under different packing densities and the effect of packing density on the performance of LIBs. Moreover, a spatially varying porous electrode will be studied to increase the electrode energy density without losing rate capability. To investigate geometric characteristics of porous microstructures, cathode electrodes were fabricated from a 94:3:3 (weight %) mixture of LiCoO2 (average particle radius = 5 µm), PVDF, and super-P carbon black. To change the packing density, initial thickness of the electrodes was set in a range of 40 ~ 80 µm. Then all electrodes were pressed down to 40 µm by using a rolling press machine. A synchrotron X-ray nano-computed tomography instrument (nano-CT) at the Advanced Phothon Source of Argonne National Lab was employed to obtain morphological data of the electrodes, with a spatial resolution of 60 nm. The morphology data sets were quantitatively analyzed to characterize their geometric properties. Fig. 1 shows the porosity (ε), specific surface area (As, µm-1), tortuosity (τ), and pore size distribution of 4 different electrode microstructures. The pore size distribution of the un-pressed electrode (ε = 0.56, black color) demonstrates nonuniformly dispersed active material. The highest packing density electrode (ε = 0.36, red color) shows the highest tortuosity. The charge/discharge experiments were also conducted for these 4 different electrodes. The geometric properties and cell testing results will be analyzed and reported. Acknowledgments: This work was supported by US National Science Foundation under Grant No. 1335850.

Geometric Characteristics of Three-Phase Porous Microstructures for All Solid-State Lithium Ion Batteries

Fast lithium ion conducting inorganic solid materials are considered superior candidates for lithium ion batteries (LIBs) to overcome flammable characteristics, leakage, and tight electrochemical window issues of organic liquid electrolytes. Besides high ion conductivities of the inorganic materials, their wide electrochemical window and good chemical stability with electrode materials are great advantages as an electrolyte [1]. However, there are remained challenges to utilize the inorganic solid-state electrolytes for LIBs because of a low specific capacity, rate capability, and cycle life. Our previous study [2] showed a large capacity decay after the first charge and poor cycle life of an all solid-state LIB (Li1+xMn2O2 + Li1.3Ti1.7Al0.3(PO4)3 | Li1.3Ti1.7Al0.3(PO4)3 | Li1-xMn2O2 + Li1.3Ti1.7Al0.3(PO4)3). We concluded that the large capacity decay was caused by dismantled ion and electron pathway due to the structural change after the first charge. The electrochemical impedance spectroscopy results showed that the internal resistance of the solid-state cell has reduced by applying higher pressing pressure. Therefore, it is necessary to investigate the realistic microstructure to understand the capacity decay and poor cycle life of the all solid-state LIB. By using synchrotron nano-computed tomography (nano-CT) at Argonne National Lab, we implemented quantitative study of the microstructures of all solid-state LIBs. The three-phase electrode was fabricated from a 47:47:6 (wt%) mixture of Li(Ni1/3 Mn1/3 Co1/3)O2 as active material (NMC), Li1.3Ti1.7Al0.3(PO4)3as Li-ion conductor (LTAP), and Super P carbon as electron conductor. The electrodes were packed under two different pressures (700 psi and 1300 psi) to control the volume fractions of void phase. To obtain the morphology data of the electrodes, TXM measurements were carried out adjusting energy levels of a synchrotron x-ray source. The x-ray generated images of solid-state electrodes with a 60 nm of spatial resolution at 8 keV are shown in Fig. 1. The gray-scaled intensity values of the images indicate the x-ray absorption rate of the materials. From the Fig. 1 (a) and (b), NMC particles, LTAP particles, and pores can be distinguished due to their different intensity values. Based on the reconstructed microstructure, the geometric characteristics will be presented to understand the lithium ion and electron pathways in all solid-state LIBs. Acknowledgments: This work was supported by US National Science Foundation under Grant No. 1335850.

Development of Ceramic-Polymer Composite Electrolyte for All-Solid Lithium Ion Batteries

In recent years, research on all-solid lithium ion batteries (LIBs) has increased considerably due to raised concerns relating to safety hazards such as the solvent leakage and flammability of liquid electrolytes used in commercial LIBs. All-solid LIBs use fast Li ion conducting solid electrolytes that do not carry the safety burdens of liquid electrolytes and are more effective. In addition, all-solid LIBs can increase the energy density of the entire battery pack by reducing the need for auxiliary systems such as safety monitoring systems. However, even with the highly ionic conductive solid electrolytes, it has been a struggle for a solid electrolyte LIBs to obtain similar specific capacity, rate capability, and cycle life to those of a liquid electrolyte LIBs. Studies conclude that these issues arise from the solid electrolyte’s inability to interface with the solid electrodes mainly due to the volume change of electrode materials during charge and discharge processes (1). In addition, it is difficult to manufacture on large scale the ceramic solid electrolyte LIBs, because the ceramic type solid electrolyte materials are hard and brittle. To overcome this problem, a composite electrolyte was designed and fabricated using the combination of ceramic solid electrolyte and Li ion conducting organic polymer. The flexible polymer electrolyte can improve the interface stability and processibility for large cells. In this study, NASICON-type Li1.3Al0.3Ti1.7 (PO4)3 (LATP) was used as the solid electrolyte, which offers chemical stability and high conductivity at room temperature (2). Poly(ethylene oxide) (PEO) was used as the Li ion conducting polymer. The composite electrolyte was prepared by mixing LATP powders and the PEO binder with lithium salt (lithium bis(trifluoromethanesulfonyl)imide) (LITFSI). The conductivity of the composite electrolyte was studied by varying the composition at different temperatures. As shown in Fig.1, a stable composite film with good conductivity and flexibility was achieved with an optimum ratio of 75:25 of the LATP and the PEO binder. By using the composite electrolyte, all-solid LIBs were fabricated and studied. An initial discharge capacity of 92 mAh/g was achieved with 0.1 C rate at 60 °C. The detailed fabrication processes and charge-discharge characteristics of the all-solid LIBs will be reported. Acknowledgments: This work was supported by US National Science Foundation under Grant No. 1335850.

Statistical power and validity of Ebola vaccine trials in Sierra Leone: a simulation study of trial design and analysis

Safe and effective vaccines could help to end the ongoing Ebola virus disease epidemic in parts of west Africa, and mitigate future outbreaks of the virus. We assess the statistical validity and power of randomised controlled trial (RCT) and stepped-wedge cluster trial (SWCT) designs in Sierra Leone, where the incidence of Ebola virus disease is spatiotemporally heterogeneous, and is decreasing rapidly. We projected district-level Ebola virus disease incidence for the next 6 months, using a stochastic model fitted to data from Sierra Leone. We then simulated RCT and SWCT designs in trial populations comprising geographically distinct clusters at high risk, taking into account realistic logistical constraints, and both individual-level and cluster-level variations in risk. We assessed false-positive rates and power for parametric and non-parametric analyses of simulated trial data, across a range of vaccine efficacies and trial start dates. For an SWCT, regional variation in Ebola virus disease incidence trends produced increased false-positive rates (up to 0·15 at α=0·05) under standard statistical models, but not when analysed by a permutation test, whereas analyses of RCTs remained statistically valid under all models. With the assumption of a 6-month trial starting on Feb 18, 2015, we estimate the power to detect a 90% effective vaccine to be between 49% and 89% for an RCT, and between 6% and 26% for an SWCT, depending on the Ebola virus disease incidence within the trial population. We estimate that a 1-month delay in trial initiation will reduce the power of the RCT by 20% and that of the SWCT by 49%. Spatiotemporal variation in infection risk undermines the statistical power of the SWCT. This variation also undercuts the SWCT's expected ethical advantages over the RCT, because an RCT, but not an SWCT, can prioritise vaccination of high-risk clusters. US National Institutes of Health, US National Science Foundation, and Canadian Institutes of Health Research.

A methodology to derive precise landslide displacement time series from continuous GPS observations in tectonically active and cold regions: a case study in Alaska

Over the past 15 years, Global Positioning System (GPS) technology has been frequently used as a tool to detect potential earth mass movements and to track creeping landslides. In this study, we investigated 4 years of continuous GPS data (September 2006–July 2010) recorded at a landslide site in Alaska. This GPS station (AC55) was installed on an un-identified creeping site by the Plate Boundary Observatory (PBO) project, which was funded by the US National Science Foundation. The landslide moves with a steady horizontal velocity of 5.5 cm/year toward NEE 15° and experiences a steady subsidence of 2.6 cm/year. There is a considerable correlation between annual snow loading and melting cycles and seasonal variations in the landslide displacements. The seasonal movements vary year to year with an average peak-to-trough amplitude of 1.5 and 1.0 cm in vertical and horizontal directions, respectively. This study addresses three challenging issues in applying GPS for landslide monitoring in tectonically active and cold regions. The three challenges include (1) detecting GPS-derived positions that could be contaminated by the snow and ice accumulated on GPS antennas during cold seasons, (2) establishing a stable local reference frame and assessing its accuracy, and (3) excluding local seasonal ground motions from GPS-derived landslide displacement time series. The methods introduced in this study will be useful for GPS landslide monitoring in other tectonically active and/or cold regions.

Improvements in Data Quality, Integration and Reliability: New Developments at the IRIS DMC

Abstract. With the support of the US National Science Foundation (NSF) and on behalf of the international seismological community, IRIS developed a Data Management Center (DMC; Ahern, 2003) that has for decades acted as a primary resource for seismic networks wishing to make their data broadly available, as well as a significant point of access for researchers and monitoring agencies worldwide that wish to access high quality data for a variety of purposes. Recently IRIS has taken significant new steps to improve the quality of and access to the services of the IRIS DMC. This paper highlights some of the current new efforts being undertaken by IRIS. The primary topics include (1) steps to improve reliability and consistency of access to IRIS data resources, (2) a comprehensive new approach to assessing the quality of seismological and other data, (3) working with international partners to federate seismological data access services, and finally (4) extensions of the federated concept to extend data access to data from other geoscience domains.

Measuring Teachers’ Fidelity of Implementation of the Dynamic Geometry Approach

In a research project funded by the US National Science Foundation, 64 teaches were randomly assigned to an experimental group and a control group to implement the Dynamic Geometry (DG) approach and a Business-as-Usual instructional approach respectively. As a measure of fidelity of implementation of the DG approach, the DG Implementation Questionnaire was developed and administered to the experimental group teachers six times across a school year. Psychometric analyses were conducted, and established validity and reliability of the questionnaire. A quantitative analysis showed that most of the experimental group teachers were faithful in implementing the DG approach in their classrooms.

Qualitative differences in tree species distributions along soil chemical gradients give clues to the mechanisms of specialization: why boron may be the most important soil nutrient at Barro Colorado Island

Qualitative differences in tree species distributions along soil chemical gradients give clues to the mechanisms of specialization: why boron may be the most important soil nutrient at Barro Colorado Island

Special Section: 2014 Copper Mountain Conference

The Thirteenth Copper Mountain Conference on Iterative Methods was held April 6--11, 2014, in Copper Mountain, Colorado. The meeting featured approximately 130 talks covering a wide range of topics in scientific computing, including multigrid methods, domain decomposition, Krylov and Anderson accelerators, hybrid direct/iterative methods, iterative regularization of inverse problems, nonlinear solvers, algorithms for eigenvalue computations, and iterative methods in optimization. Numerous talks dealt with applications of iterative solvers to fields such as neutronics, image processing, graph mining, quantum chemistry, fluid flow, and wave propagation. Several sessions featured work on the use of iterative methods for solving coupled multiphysics problems arising in magnetohydrodynamics, atmospheric and ocean modeling, continuum mechanics, and so forth. Other presentations offered an overview of recent progress on resilient iterative methods, including work on stochastic solvers and fault-tolerant multigrid variants. As in the past, there were additional talks addressing various discretization methods for partial differential equations and their impact on the performance of iterative solvers. An encouraging sign for the future of the field was the strong student presence, accounting for over a third of the attendees. One of the high points of the Copper Mountain Conference is the traditional Student Paper Award Competition, which this year received an especially high number of very strong submissions. The Student Paper Award Committee charged with the selection of the best student papers had a very difficult job to do but eventually identified four entries deserving of recognition. A plenary session was devoted to the presentations by the four student winners: Jessica Bosch from the Max Planck Institute in Magdeburg, Germany (first place), Sarah Gaaf from the University of Eindhoven in the Netherlands, Scott Ladenheim from Temple University, and Manda Winlaw from Cornell University (the latter three tied for second place). All four speakers gave excellent presentations. It should be stressed that this is the only plenary session at Copper Mountain, all other talks being organized in parallel sessions. This is done in order to give all conference participants the possibility to enjoy the winning student presentations. Michele Benzi (Emory University) and Ray Tuminaro (Sandia National Laboratories) served as conference co-chairs, while Ira Livshits chaired the Student Paper Award Committee. Management services were provided by Annette Anthony of Front Range Scientific Computations, Inc. The Conference gratefully acknowledges financial support from the US Department of Energy, the US National Science Foundation, IBM, Argonne National Laboratory, Lawrence Livermore National Laboratory, Los Alamos National Laboratory, Sandia National Laboratories, and Emory University. The Copper Mountain Conference is organized in cooperation with the Society for Industrial and Applied Mathematics (SIAM) and with the Association for Women in Mathematics (AWM). Submissions to this special section were open to the scientific community, as advertised in advance on web sites of the SIAM Journal on Scientific Computing (SISC) and the Copper Mountain Conference. The 28 papers in this section serve to illustrate the vitality and continuing importance of the ongoing research on iterative methods for a wide variety of areas of applied mathematics and computational science. The guest editorial board worked very hard to ensure a rigorous peer-review process while meeting deadlines. We owe special thanks to Mitch Chernoff (SIAM Publications Manager) and Brittni Holland (SIAM Editorial Associate) for their efforts on this special section. Guest Associate Editors: Xiao-Chuan Cai, Iain Duff, Howard Elman, Kirk Jordan, Tim Kelley, Misha Kilmer, Dana Knoll, Sven Leyffer, Ira Livshits, Tom Manteuffel, Steve McCormick, Luke Olson, John Shadid, David Silvester, Ray Tuminaro, Homer Walker, Carol Woodward, Irad Yavneh

Cooperative Behaviour in Theory and Practice: Leading Undergraduate Research in Behaviour Mathematical Biology

The US National Science Foundation has promoted the early integration of undergraduate students into academic research environments by funding activities such as the Research Experiences for Undergraduates (REU) programs. Here, we discuss the operation of the first year for one REU site held on the campus of the University of North Carolina at Greensboro. Eight students from across the country were brought together for a 10-week summer programme in mathematical biology to work on research topics related to the establishment of cooperative behaviour. The students were paired in four teams, which approached the dynamic tension between cooperation and defection from a variety of mathematical and contextual perspectives. Two projects employed agent-based models on lattice environments: the first consisting of sparse populations of mobile individuals and the second featuring age-structured populations, history-dependent fitness, and the possibility of kinship recognition. A third project looked at the evolutionary dynamics of behavioural frequencies in a model of society comprised of three social strata. The final project focused on the ecological range distribution of non-cooperative, cooperative and kleptoparasitic populations in heterogeneous resource environments. We describe both the general results of the students’ research efforts and our observations on the efficacy of several enrichment activities provided to the students over the course of the REU summer.

Cooperative behaviour in theory and practice: leading undergraduate research in behaviour mathematical biology

The US National Science Foundation has promoted the early integration of undergraduate students into academic research environments by funding activities such as the Research Experiences for Undergraduates (REU) programs. Here, we discuss the operation of the first year for one REU site held on the campus of the University of North Carolina at Greensboro. Eight students from across the country were brought together for a 10-week summer programme in mathematical biology to work on research topics related to the establishment of cooperative behaviour. The students were paired in four teams, which approached the dynamic tension between cooperation and defection from a variety of mathematical and contextual perspectives. Two projects employed agent-based models on lattice environments: the first consisting of sparse populations of mobile individuals and the second featuring age-structured populations, history-dependent fitness, and the possibility of kinship recognition. A third project looked at the evolutio...

Drilling to investigate processes in active tectonics and magmatism

Abstract. Coordinated drilling efforts are an important method to investigate active tectonics and magmatic processes related to faults and volcanoes. The US National Science Foundation (NSF) recently sponsored a series of workshops to define the nature of future continental drilling efforts. As part of this series, we convened a workshop to explore how continental scientific drilling can be used to better understand active tectonic and magmatic processes. The workshop, held in Park City, Utah, in May 2013, was attended by 41 investigators from seven countries. Participants were asked to define compelling scientific justifications for examining problems that can be addressed by coordinated programs of continental scientific drilling and related site investigations. They were also asked to evaluate a wide range of proposed drilling projects, based on white papers submitted prior to the workshop. Participants working on faults and fault zone processes highlighted two overarching topics with exciting potential for future scientific drilling research: (1) the seismic cycle and (2) the mechanics and architecture of fault zones. Recommended projects target fundamental mechanical processes and controls on faulting, and range from induced earthquakes and earthquake initiation to investigations of detachment fault mechanics and fluid flow in fault zones. Participants working on active volcanism identified five themes: the volcano eruption cycle; eruption sustainability, near-field stresses, and system recovery; eruption hazards; verification of geophysical models; and interactions with other Earth systems. Recommended projects address problems that are transferrable to other volcanic systems, such as improved methods for identifying eruption history and constraining the rheological structure of shallow caldera regions. Participants working on chemical geodynamics identified four major themes: large igneous provinces (LIPs), ocean islands, continental hotspot tracks and rifts, and convergent plate margins (subduction zones). This workshop brought together a diverse group of scientists with a broad range of scientific experience and interests. A particular strength was the involvement of both early-career scientists, who will initiate and carry out these new research programs, and more senior researchers with many years of experience in scientific drilling and active tectonics research. Each of the themes and questions outlined above has direct benefits to society, including improving hazard assessment, direct monitoring of active systems for early warning, renewable and non-renewable resource and energy exploitation, and predicting the environmental impacts of natural hazards, emphasizing the central role that scientific drilling will play in future scientific and societal developments.

Meeting report: 2nd workshop of the United States culture collection network (May 19–21, 2014, State College, PA, USA)

This report summarizes the activities and outcomes of the second workshop of the US Culture Collection Network, formally an activity of the US National Science Foundation sponsored Research Coordination Network for a Community of ex situ Microbial Germplasm Repositories. The workshop included presentations on topics as diverse as permitting for genetically engineered plant pest organisms to facilitating strain exchange via formal material transfer agreement systems and codes of conduct. Short talks introduced diverse collections held by government, university, and private entities. Participants visited living microbe collections as well as active research and production facilities.

Towards the unification of sequence-based classification and sequence-based identification of host-associated microorganisms.

Towards the unification of sequence-based classification and sequence-based identification of host-associated microorganisms.

Data mining with iPlant: a meeting report from the 2013 GARNet workshop, Data mining with iPlant.

High-throughput sequencing technologies have rapidly moved from large international sequencing centres to individual laboratory benchtops. These changes have driven the 'data deluge' of modern biology. Submissions of nucleotide sequences to GenBank, for example, have doubled in size every year since 1982, and individual data sets now frequently reach terabytes in size. While 'big data' present exciting opportunities for scientific discovery, data analysis skills are not part of the typical wet bench biologist's experience. Knowing what to do with data, how to visualize and analyse them, make predictions, and test hypotheses are important barriers to success. Many researchers also lack adequate capacity to store and share these data, creating further bottlenecks to effective collaboration between groups and institutes. The US National Science Foundation-funded iPlant Collaborative was established in 2008 to form part of the data collection and analysis pipeline and help alleviate the bottlenecks associated with the big data challenge in plant science. Leveraging the power of high-performance computing facilities, iPlant provides free-to-use cyberinfrastructure to enable terabytes of data storage, improve analysis, and facilitate collaborations. To help train UK plant science researchers to use the iPlant platform and understand how it can be exploited to further research, GARNet organized a four-day Data mining with iPlant workshop at Warwick University in September 2013. This report provides an overview of the workshop, and highlights the power of the iPlant environment for lowering barriers to using complex bioinformatics resources, furthering discoveries in plant science research and providing a platform for education and outreach programmes.

Rules of engagement.

The recent discussion about how to handle the results of security‐relevant “dual‐use” research has generated substantial polarization among stakeholders. In essence, there are two major options to prevent the abuse or misuse of research data: to restrict research itself so as to prohibit certain experiments, or to restrict the publication of research that could be abused by the military, terrorists or criminals. The case in question was the gain‐of‐function experiments by a research group in the Netherlands that created a strain of the H5N1 virus with increased transmissibility among mammals. The initial recommendation by the US National Science Advisory Board for Biosecurity (NSABB) was to allow only limited access to crucial data in the publications, which raised the ire of the scientific community who were concerned that their freedom of research could be curtailed in the name of security. When a Dutch district court eventually ruled in favour of the publication of H5N1 gain‐of‐function research—but upheld the requirement to apply for export licences [1]—it was obvious that the final judgment over restricting the publication of security‐sensitive research data will rest on the judicial system and neither on individual or collective self‐governance by the research community, nor advisory boards such as the NSABB. Indeed, a key problem in finding common ground between those who are concerned about security and those who defend the freedom of research is the unresolved issue over who will have to make such decisions and which procedural principles to manage the risks of publication should be applied. This paper addresses this issue by looking into the pros and cons of different risk management concepts that have been suggested to resolve the dilemma, such as risk–benefit assessment, the Precautionary Principle or the Proportionality Principle. Notwithstanding who will eventually have to make decisions about information security—scientists, regulators …

Study of free reed attack transients using high speed video

Earlier methods of studying the motion of free reeds have been augmented with the use of high-speed video, resulting in a more detailed picture of reed oscillation, especially the initial transients. Displacement waveforms of selected points on the reed tongue image can be obtained using appropriate tracking software. The waveforms can be analyzed for the presence of higher modes of vibration and other features of interest in reed oscillation, and they can be used in conjunction with displacement or velocity waveforms obtained by other means, along with finite element simulations, to obtain detailed information about reed oscillation. The high speed video data has a number of advantages. It can provide a two-dimensional image of the motion of any point tracked on the reed tongue, and the freedom to change the points selected for tracking provides flexibility in data acquisition. In addition, the high speed camera is capable of simultaneous triggering of other motion sensors as well as oscilloscopes and spectrum analyzers. Some examples of the use of high speed video are presented and some difficulties in the use of this technique are discussed. [Work partially supported by US National Science Foundation REU Grant PHY-1004860.]

Detailed analysis of free reed initial transients

The motion of the reed tongue in early stages of the attack transient has been studied in some detail for reeds from a reed organ. Oscillation waveforms were obtained using a laser vibrometer system, variable impedance transducer proximity sensors, and high speed video with tracking software. Typically, the motion of the reed tongue begins with an initial displacement of the equilibrium position, often accompanied by a few cycles of irregular oscillation. This is followed by a short transitional period in which the amplitude of oscillation gradually increases and the frequency stabilizes at the steady state oscillation frequency. In the next stage, the amplitude of oscillation continues to increase to the steady state value. The spectra derived from the waveforms in each stage have been analyzed, showing that the second transverse mode and the first torsional mode are both observed in the transient, with the amplitude of the torsional mode apparently especially significant in the earlier stages of oscillation. Comparison of reed tongues of different design have been made to explore the role of the torsional mode the initial excitation. Finite element simulations have been used to aid in the verification and interpretation of some of the results. [Work supported by US National Science Foundation REU Grant PHY-1004860.]

Comparison of traditional and matched grips: Rhythmic sequences played in jazz drumming

Traditional and matched grips have been compared using a series of measurements involving rhythmic sequences played by experienced jazz drummers using each of the two grips. Rhythmic sequences played on the snare drum were analyzed using high speed video as well as other measurement techniques including laser vibrometry and spectral analysis of the sound waveforms. The high speed video images, used with tracking software, allow observation of several aspects of stick-drum head interaction. These include two-dimensional trajectories of the drum stick tip, a detailed picture of the stick-drum head interaction, and velocities of both the stick and the drum head during the contact phase of the stroke. Differences between the two grips in timing during the rhythmic sequences were investigated, and differences in sound spectrum were also analyzed. Some factors that may be player dependent have been explored, such as the effect of tightness of the grip, but an effort has been made to concentrate on factors that are independent of the player. [Work supported by US National Science Foundation REU Grant PHY-1004860.]

Dispatches

Dispatches