Time-frequency channel modeling and estimation of multi-carrier spread spectrum communication systems

In wireless communications, the channel is typically modeled as a random, linear, time-varying system that spreads the transmitted signal in both time and frequency due to multi-path propagation and Doppler effects. Estimated channel parameters allow system designers to develop coherent receivers that increase the system performance. In this paper, we show how time-frequency analysis can be used to model and estimate the time-varying channel of a multi-carrier spread spectrum (MCSS) system using a complex quadratic sequence as the spreading code. We will show that for this spreading code, the effects of time delays and Doppler frequency shifts, caused by the mobility of environment objects, can be combined and represented effectively as time shifts. The discrete evolutionary transform (DET), as a time-frequency analysis method, enables us to estimate the effective time shifts via a spreading function and to use them to equalize the channel. Using the effective time shifts, the time-varying channel can be represented simply as linear-time invariant system by embedding the Doppler shifts that characterize the time-varying channel into effective time shifts. The channel parameters are used to estimate the data bit sent. To illustrate the performance of the proposed method we perform several simulations with different levels of channel noise, jammer interference, and Doppler frequency shifts.     

Invention in the city: Increasing returns to patenting as a scaling function of metropolitan size

We investigate the relationship between patenting activity and the population size of metropolitan areas in the United States over the last two decades (1980-2001). We find a clear superlinear effect, whereby new patents are granted disproportionately in larger urban centers, thus showing increasing returns in inventing activity with respect to population size. We characterize this relation quantitatively as a power law with an exponent larger than unity. This phenomenon is commensurate with the presence of larger numbers of inventors in larger metropolitan areas, which we find follows a quantitatively similar superlinear relationship to population, while the productivity of individual inventors stays essentially constant across metropolitan areas. We also find that structural measures of the patent co-authorship network although weakly correlated to increasing rates of patenting, are not enough to explain them. Finally, we show that R&D establishments and employment in other creative professions also follow superlinear scaling relations to metropolitan population size, albeit possibly with different exponents.     

Distributed retrieval practice promotes superior recall of anatomy information

Effortful retrieval produces greater long‐term recall of information when compared to studying (i.e., reading), as do learning sessions that are distributed (i.e., spaced apart) when compared to those that are massed together. Although the retrieval and distributed practice effects are well‐established in the cognitive science literature, no studies have examined their additive effect with regard to learning anatomy information. The aim of this study was to determine how the benefits of retrieval practice vary with massed versus distributed learning. Participants used the following strategies to learn sets of skeletal muscle anatomy: (1) studying on three different days over a seven day period (SSSS_7,2,0), (2) studying and retrieving on three different days over a seven day period (SRSR_7,2,0), (3) studying on two different days over a two day period (SSSSSS_2,0), (4) studying and retrieving on two separate days over a two day period (SRSRSR_2,0), and (5) studying and retrieving on one day (SRx6₀). All strategies consisted of 12 learning phases and lasted exactly 24 minutes. Muscle information retention was assessed via free recall and using repeated measures ANOVAs. A week after learning, the recall scores were 24.72 ± 3.12, 33.88 ± 3.48, 15.51 ± 2.48, 20.72 ± 2.94, and 12.86 ± 2.05 for the SSSS_7,2,0, SRSR_7,2,0, SSSSSS_2,0, STSTST_2,0, and SRx6₀ strategies, respectively. In conclusion, the distributed strategies produced significantly better recall than the massed strategies, the retrieval‐based strategies produced significantly better recall than the studying strategies, and the combination of distributed and retrieval practice generated the greatest recall of anatomy information. Anat Sci Educ 10: 339–347. © 2016 American Association of Anatomists.     

Oral presentations in higher education: a comparison of the impact of peer and teacher feedback

In this paper the authors analyse the competency of a sample of economics and business students in orally presenting academic content, as well as the changes that occurred after receiving feedback. The students’ presentations were videotaped, and a total of 96 were analysed at three stages: pre-test, post-test and follow-up. The participants were divided into two groups. In one, each student received feedback from a peer as part of a peer assessment with rubric activity. In the other, they received feedback from the teacher immediately after their presentation. In the post-test, the peer assessment with rubric students improved by 10% in the valuation of their presentation, while the teacher feedback students only improved by 5%. These results support the idea that undergraduates’ evaluations of their peers can be effective in improving oral presentation skills, especially when they are provided with some support instruments (videos and rubrics). However, the improvements in the peer assessment with rubric group were not maintained in the follow-up re-test. This suggests that a single session of peer assessment with rubric is insufficient to generalise any improvements in the said competency. The implications of these results with regard to the implementation of methods of formative peer assessment in higher education are discussed.     

Developing cognitive‐social‐emotional competencies to enhance academic learning

This preliminary study examined intervention effects of a universal prevention program offered by classroom teachers to public elementary school students. The Unique Minds School Program (M.B. Stern, 1999) is a teacher‐led program designed to promote cognitive‐social‐emotional (CSE) skills, including student self‐efficacy, problem solving, social‐emotional competence, and a positive classroom climate, with the dual goal of preventing youth behavioral problems and promoting academic learning. During 2 consecutive school years, 119 students and their teachers were assessed in the fall and spring of Grade 4 and again in the spring of Grade 5. As compared to students in the comparison school, students in the intervention showed gains in student self‐efficacy, problem solving, social‐emotional competencies, and math grades. Incremental gains within CSE domains were found after 1 and 2 years of intervention. © 2005 Wiley Periodicals, Inc. Psychol Schs 42: 405–417, 2005.     

Examining the Perspectives of Latino Families of Children with Autism Spectrum Disorder Towards Advocacy

Rapidly becoming the largest ethnic group of American students, compared to White students with disabilities, Latino students with disabilities receive less services and their parents are more likely to struggle to receive services. Yet, it is unclear how Latino families advocate for their children with disabilities including how cultural values facilitate their advocacy efforts. In this study, four focus groups were conducted with 46 Latino parents of children with autism spectrum disorder. Parents reported advocating by being assertive but not aggressive, being involved in school activities, communicating with the school and documenting the communication, and relying on knowledge and faith. Parents also reported facilitators (i.e., knowledge and resources, increased parent-school communication, and greater peer support) and barriers (i.e., poor school experiences, school related-stress, and stigma and discrimination) to advocacy. Implications for research, policy, and practice are discussed.     

Hybridising Sport Education and Teaching for Personal and Social Responsibility to include students with disabilities

The present study aimed to explore the impact of the combination of two pedagogical models, Sport Education and Teaching for Personal and Social Responsibility, for learners with disabilities experiencing a contactless kickboxing learning unit. Twelve secondary education students agreed to participate. Five had disabilities (intellectual and motor). Additionally, three physical education teachers and the mother of one of the students contributed. Five different research instruments were used to obtain information from all participants: drawings, open-ended questions, discussion groups, diaries and semi-structured interviews. Thematic content analysis and constant comparison guided data analysis resulted in three major categories: part of the team, learning and enjoyment. Several ideas were also identified: inclusion, friendship, cooperation, students’ important role and transference. In conclusion, the hybridisation of Sport Education and Teaching for Personal and Social Responsibility seems to be a powerful tool for including students with disabilities in physical education, helping them and their classmates connect in and out of class.