pinecone/core-2020-05-10-deduplication huggingface dataset:
Transport layer protocols and architectures for satellite networks

Designing efficient transmission mechanisms for advanced satellite networks is a demanding task, requiring the definition and the implementation of protocols and architectures well suited to this challenging environment. In particular, transport protocols performance over satellite networks is impaired by the characteristics of the satellite radio link, specifically by the long propagation delay and the possible presence of segment losses due to physical channel errors. The level of impact on performance depends upon the link design (type of constellation, link margin, coding and modulation) and operational conditions (link obstructions, terminal mobility, weather conditions, etc.). To address these critical aspects a number of possible solutions have been presented in the literature, ranging from limited modifications of standard protocols (e.g. TCP, transmission control protocol) to completely alternative protocol and network architectures. However, despite the great number of different proposals (or perhaps also because of it), the general framework appears quite fragmented and there is a compelling need of an integration of the research competences and efforts. This is actually the intent of the transport protocols research line within the European SatNEx (Satellite Network of Excellence) project. Stemming from the authors' work on this project, this paper aims to provide the reader with an updated overview of all the possible approaches that can be pursued to overcome the limitations of current transport protocols and architectures, when applied to satellite communications. In the paper the possible solutions are classified in the following categories: optimization of TCP interactions with lower layers, TCP enhancements, performance enhancement proxies (PEP) and delay tolerant networks (DTN). Advantages and disadvantages of the different approaches, as well as their interactions, are investigated and discussed, taking into account performance improvement, complexity, and compliance to the standard semantics. From this analysis, it emerges that DTN architectures could integrate some of the most efficient solutions from the other categories, by inserting them in a new rigorous framework. These innovative architectures therefore may represent a promising solution for solving some of the important problems posed at the transport layer by satellite networks, at least in a medium-to-long-term perspective. Copyright (c) 2006 John Wiley & Sons, Ltd
Cross-layer enhancement of error control techniques for adaptation layers of DVB satellites

This paper assesses the way error control is managed jointly by Forward Error Codes (FEC) and Cyclic Redundancy Checks (CRC) in the lower layers of today’s Digital Video Broadcasting (DVB) satellites. Mathematical and simulation results clearly show that the outer block codes of the coding schemes used in DVB-S and DVB-S2 (Reed-Solomon and Bose-Chaudhuri-Hocquenghem, respectively) can provide very accurate error-detection information to the receiver in addition to their basic correction task at virtually no cost, making an uncorrected error after decoding an extremely improbable event. For this reason, the workload of CRCs can be ensured safely by the FEC subsystem if a dedicated function allowing the physical layer to share its decoding information with the adaptation layer is set. This particular crosslayer mechanism would allow freeing up the bandwidth currently used by CRCs -which adds up to 10 % for more than 35 % of the total number of IP packets- and pave the way for an enhanced transport of IP over DVB-S2
Development and validation of time-series synthesizers of rain attenuation for Ka-band and Q/V-band satellite communication systems

The aim of this paper is to present recent developments in terms of propagation time-series synthesizers, carried out in the framework of the ESA study 16865/03/NL/EC Development of propagation models for telecommunication satellite systems (ONERA Final Report RF 4/07757/DEMR, 2004). The paper is composed of three parts: a review of the initial requirements related to propagation time series for system performance simulation, a description of a collection of rain attenuation time-series synthesizers and of their related input parameters, and a comparative analysis of the output characteristics of these time-series synthesizers as compared with experimental data collected during the OLYMPUS and ITALSAT propagation experiments
Performance evaluation of TCP-based applications over DVB-RCS DAMA schemes

Transmission Control Protocol (TCP) performance over Digital Video Broadcasting-Return Channel via Satellite (DVB-RCS) standard is greatly affected by the total delay, which is mainly clue to two components, propagation delay and access delay. Both are significant because they are dependent oil the long propagation path of the satellite link. I-lie former is intrinsic and due to radio wave propagation over the satellite channel for both TCP packets and acknowledgements. It is regulated by the control loop that governs TCP. The latter is due to the control loop that governs the demand assignment Multiple access (DAMA) signalling exchange between satellite terminals and the network control center. necessary to manage return link resources. DAMA is adopted in DVB-RCS standard to achieve flexible and efficient use of the shared resources. Therefore, performance of TCP over DVB-RCS may degrade due to the exploitation of two nested control loops also depending oil both file selected DAMA algorithm and the traffic profile. This paper analyses the impact of basic DAMA implementation oil TCP-based applications over a DVB-RCS link for a large Set Of study Cases. To provide a detailed overview of TCP performance in DVB-RCS environment, the analysis includes both theoretical approach and simulation campaign. Copyright (C) 2009 John Wiley & Sons, Ltd
Overview of DVB-RCS+M and its development

The use of DVB-S and DVB-RCS for conducting two-way communications from small satellite terminals has become well established in Europe and elsewhere. During the development of DVB-RCS the possibility of limited use for satellite terminals that were moving was considered in January 2004 and incorporated into the Guideline document associated with the Standard in April 2005. It was noted, however, that this matter could be addressed further as a future development. This paper addresses the steps that have been taken since then to realize this objective. During the last few years, it has been shown that the DVB-S2/DVB-RCS specifications are good candidate baselines for the efficient implementation of broadband services to mobile users. Results of these studies were gathered in a study mission report from the TM-RCS ad hoc group. It was demonstrated that both forward and return channel waveforms are impacted by the mobile usage, and should be addressed in the scope of an update of the DVB-RCS standard. Technical analysis identified that DVB-RCS, as it had been originally designed for fixed satellite services, provided most of the features required by mobile applications above 5GHz, and could be turned into a competitive solution with a few carefully crafted modifications. Subsequent activities within the TM-RCS Group have led to an efficient and robust standard that incorporates mobility more definitely into version 1.5.1 of the DVB-RCS specifications, along with appropriate detailed 'Guidelines' documentation giving expanded description of the standard and its use and application. Copyright © 2009 John Wiley & Sons, Ltd
Combining meteorological radar and network of rain gauges\ud
data for space–time model development

Technological developments and the trend to go higher and higher in frequency give rise to the need for\ud
true space–time rain field models for testing the dynamics of fade countermeasures. There are many models\ud
that capture the spatial correlation of rain fields. Worth mentioning are those models based on cell\ud
ensembles. However, the rain rate fields created in this way need the introduction of the time variable to\ud
reproduce their dynamics. In this paper, we have concentrated on addressing the time domain effects while\ud
we have relied on existing spatial rain field models for creating initial fields, which are propagated\ud
(advected) according to proposed models and assumptions, some of which have been drawn from a\ud
combined use of a concurrent weather radar and a network of rain gauges. The dynamic modeling\ud
presented simulates the advection of a synthetically generated rain field according to dynamic, spatially\ud
correlated advection fields extracted from the analysis of weather radar images. Experimental data and\ud
model fits have been presented as well. Further ideas on how to improve the realism of the generated\ud
dynamic fields have also been presented. Furthermore, the limitations of radar data, especially those\ud
related to their limited time resolution, for the required space–time models have been pointed out. These\ud
can be overcome by using data from a network of rain gauges. However, it is important to be aware of the\ud
similarities and differences between these two sources. A comparative study of these two data sets has also\ud
been presented
Modeling the point-spread function in helium-ion lithography

We present here a hybrid approach to modeling helium-ion lithography that combines the power and ease-of-use of the Stopping and Range of Ions in Matter (SRIM) software with the results of recent work simulating secondary electron (SE) yield in helium-ion microscopy. This approach traces along SRIM-produced helium-ion trajectories, generating and simulating trajectories for SEs using a Monte Carlo method. We found, both through simulation and experiment, that the spatial distribution of energy deposition in a resist as a function of radial distance from beam incidence, i.e. the point spread function, is not simply a sum of Gauss functions.Semiconductor Research Corporation. Nanoscale Research InitiativeNational Science Foundation. Graduate Research Fellowship Progra
Reflection on the Measurement and Use of the Topography of the Indentation Imprint

The goal of this paper is to study the main uses of the residual imprint of the indentation test. It also discusses the different technologies and methods employed in this context. The difficulties encountered when trying to exploit the full potentials of the imprint are thoroughly examined. A survey of the literature on the quantification of the pile-up clearly shows that there is a lack of consensus on the measurement of the residual imprint as well as on treatment methods. Therefore, in order to widen the application fields of the indentation residual imprint, relevant and standardized indicators should be established
Effect of surface roughness in the determination of the mechanical properties of material using nanoindentation test

A quantitative model is proposed for the estimation of macro-hardness using nanoindentation tests. It decreases the effect of errors related to the non-reproducibility of the nanoindentation test on calculations of macro-hardness by taking into account the indentation size effect and the surface roughness. The most innovative feature of this model is the simultaneous statistical treatment of all the nanoindentation loading curves. The curve treatment mainly corrects errors in the zero depth determination by correlating their positions through the use of a relative reference. First, the experimental loading curves are described using the Bernhardt law. The fitted curves are then shifted, in order to simultaneously reduce the gaps between them that result from the scatter in the experimental curves. A set of shift depths, Δhc, is therefore identified. The proposed approach is applied to a large set of TiAl6V4 titanium-based samples with different roughness levels, polished by eleven silicon carbide sandpapers from grit paper 80 to 4,000. The result reveals that the scatter degree of the indentation curves is higher when the surface is rougher. The standard deviation of the shift Δhc is linearly connected to the standard deviation of the surface roughness, if the roughness is high-pass filtered in the scale of the indenter (15 µm). Using the proposed method, the estimated macro-hardness for eleven studied TiAl6V4 samples is in the range of 3.5–4.1 GPa, with the smallest deviation around 0.01 GPa, which is more accurate than the one given by the Nanoindentation MTS™ system, which uses an average value (around 4.3 ± 0.5 GPa). Moreover, the calculated Young's modulus of the material is around 136 ± 20 GPa, which is similar to the modulus in literature
Scanning electron microscope image signal-to-noise ratio monitoring for micro-nanomanipulation.

International audienceAs an imaging system, scanning electron microscope (SEM) performs an important role in autonomous micro-nanomanipulation applications. When it comes to the sub micrometer range and at high scanning speeds, the images produced by the SEM are noisy and need to be evaluated or corrected beforehand. In this article, the quality of images produced by a tungsten gun SEM has been evaluated by quantifying the level of image signal-to-noise ratio (SNR). In order to determine the SNR, an efficient and online monitoring method is developed based on the nonlinear filtering using a single image. Using this method, the quality of images produced by a tungsten gun SEM is monitored at different experimental conditions. The derived results demonstrate the developed method's efficiency in SNR quantification and illustrate the imaging quality evolution in SEM
Development of an instrument : mentoring for effective primary science teaching (MEPST)

Perceptions of mentors' practices related to primary science teaching from nine Australian universities (n=331 final year preservice teachers) were gathered through a literature-based instrument.  Five factors that characterise effective mentoring practices in primary science teaching were supported by confirmatory factory analysis.  These factors, namely, personal attributes, system requirements, pedagogical knowledge, modelling, and feedback had Cronbach alpha coefficients of internal consistency reliability of .93, .76, .94, .95, and .92 respectively.  Final model fit indices were x2=1335, df=513, CMIDF=2.60, IFI=.922, CFI=.921, RMR=.066, RMSEA=.070 (p<.001).  Specific mentoring interventions for improving primary science teaching practices may be implemented by measuring preservice teachers’ perceptions of their mentoring with a valid and reliable instrument
Highlighting hybridity : a critical discourse analysis of teacher talk in science classrooms

There is evidence that alienation from science is linked to the dominant discourse practices of science classrooms (cf. Lemke, 1990). Yet, in secondary science education it is particularly hard to find evidence of curriculum reform that includes explicit changes in pedagogic discourses to accommodate the needs of students from a wide range of backgrounds. However, such evidence does exist and needs to be highlighted wherever it is found to help address social justice concerns in science education. In this article I show how critical discourse analysis can be used to explore a way of challenging the dominant discourse in teacher-student interactions in science classrooms. My findings suggest a new way of moving towards more socially just science curricula in middle years and secondary classrooms by using hybrid discourses that can serve emancipatory p
Time and temporality as mediators of science learning

Few studies have focused on understanding how teaching and learning in classrooms are mediated by other dimensions of the organizational systems of which education is an integral part. Our seven-year ethnographic study of an urban high school shows how time and temporality constitute key practical and theoretical resources to the actors in the cultural organization of schools, a product of transactions involving individuals and artifacts that traverse multiple cultural fields, each with its own distinctive structure
The link between policy and practice in science education : the role of research

Policy has been a much neglected area for research in science education. In their neglect of policy studies, researchers have maintained an ongoing naivete about the politics of science education. In doing so, they often overestimate the implications of their research findings about practice and ignore the interplay between the stakeholders beyond and in-school who determine the nature of the curriculum for science education and its enacted character. Policies for education (and science education in particular) always involve authority and values, both of which raise sets of fascinating questions for research. The location of authority for science education differs across educational systems in ways that affect the role teachers are expected to play. Policies very often value some groups in society over others, as the long history of attempts to provide science for all students testifies. As research on teaching/learning science identifies pedagogies that have widespread effectiveness, the policy issue of mandating these becomes important. Illustrations of successful policy to practice suggest that establishing conditions that will facilitate the intended implementation is critically important. The responsibility of researchers for critiquing and establishing policy for improving the practice of science education is discussed, together with the role research associations could play if they are to claim their place as key stakeholders in science education
Reproducing successful rituals in bad times : exploring interactions of a new science teacher

Teaching is emotional work. This is especially the case in the first years of teaching when new teachers are particularly vulnerable. By understanding changes in teacher emotions in the early years of teaching we hope to identify strategies that might ultimately reduce teacher attrition. As part of a larger study of the transition of new teachers to the profession, this ethnographic case study explores how a new science teacher produced and reproduced positive emotional interaction rituals with her students in her first year of teaching. We show how dialogical interactions were positive and satisfying experiences for the teacher, and how they were reproduced successfully in different contexts. We also illustrate how both teacher and students used humor to create a structure for dialogical interactions. During these successful interactions the students used shared resources to satisfy their teacher that they were engaging in the relevant science content. The implications of what we have learned for the professional development of new teachers are discussed in relation to an expanded understanding of teacher emotions
Learning to critique and adapt science curriculum materials: Examining the development of preservice elementary teachers' pedagogical content knowledge

Teachers often engage in curricular planning by critiquing and adapting existing curriculum materials to contextualize lessons and compensate for their deficiencies. Designing instruction for students is shaped by teachers' ability to apply a variety of personal resources, including their pedagogical content knowledge (PCK). This study investigated a criterion‐based approach to lesson plan analysis as one way to help preservice elementary teachers develop and use their PCK to plan instruction for students. Results show that the preservice teachers demonstrated a range of strengths and weaknesses in applying their knowledge of science assessment, science curriculum materials, and instructional strategies for teaching science. This range was influenced, in part, by the presence of alternative ideas about science teaching, the extent to which the original curriculum materials aligned with reform‐based standards and practices, and the presence of prompts to use criteria in their analyses. Despite these factors, preservice teachers' PCK improved significantly over time when they had multiple opportunities to practice applying the same criterion in their analyses. Insights into science teacher knowledge and implications for science teacher education are discussed. © 2011 Wiley Periodicals, Inc.  Sci Ed   96: 130–157, 201
The effect of argumentative task goal on the quality of argumentative discourse

In argumentative discourse, there are two kinds of activity-dispute and deliberation-that depend on the argumentative task goal. In dispute the goal is to defend a conclusion by undermining alternatives, whereas in deliberation the goal is to arrive at a conclusion by contrasting alternatives. In this study, we examine the impact of these tasks goals on the quality of argumentative discourse. Sixty-five junior high school students were organized into dyads to discuss sources of energy. Dyads were formed by members who had differing viewpoints and were distributed to one of two conditions: 31 dyads were asked to discuss with the goal to persuade the partner, and 34 were asked to reach consensus. Argumentation was analyzed using a schema based on Toulmin (1958). Eleven different argumentative structures resulted from the combination of Toulmin's basic elements. Students in the consensus group scored significantly higher than students in the persuasion group in 5/6 argumentative structures that included rebuttals. The major implication of the present work is that, similar to Mercer's (2000) claim about types of classroom conversation, not all classroom argumentation tasks promote scientific reasoning equally
Conceptualizing the science curriculum : 40 years of developing assessment frameworks in three large-scale assessments.

The paper analyzes conceptualizations in the science frameworks in three large-scale assessments, Trends in Mathematics and Science Study (TIMSS), Programme for International Student Assessment (PISA), and National Assessment of Educational Progress (NAEP). The assessments have a shared history, but have developed different conceptualizations. The paper asks how and why the frameworks are different and seeks answers by studying their development. The methodology is document analysis by, first, tracing developments within each assessment, next, comparing developments and conceptualization across the assessments, and, last, relating the frameworks to trends of developments in educational theory. The outcome of the analysis provides a complex picture with the assessments following their own lines of development but with influence from trends in assessment and educational theory. Five main conceptualizations are found to have existed over time, with different definition of scientific behavior and explanations to the relationship between knowledge and behavior. The frameworks have moved toward more elaborated explanations of the science domain, providing assessors with better support for operationalizing learning objectives. Currently, the assessments are faced with a challenge of adapting to the “practice turn” in science studies and learning science and thereby accounting for scientific behavior as a community practice. The paper concludes with suggestions for how frameworks may be improved to achieve this aim