Topological photonics is a rapidly emerging field of research in which geometrical and topological ideas are exploited to design and control the behavior of light. Drawing inspiration from the discovery of the quantum Hall effects and topological insulators in condensed matter, recent advances have shown how to engineer analogous effects also for photons, leading to remarkable phenomena such as the robust unidirectional propagation of light, which hold great promise for applications. Thanks to the flexibility and diversity of photonics systems, this field is also opening up new opportunities to realize exotic topological models and to probe and exploit topological effects in new ways. This article reviews experimental and theoretical developments in topological photonics across a wide range of experimental platforms, including photonic crystals, waveguides, metamaterials, cavities, optomechanics, silicon photonics, and circuit QED. A discussion of how changing the dimensionality and symmetries of photonics systems has allowed for the realization of different topological phases is offered, and progress in understanding the interplay of topology with non-Hermitian effects, such as dissipation, is reviewed. As an exciting perspective, topological photonics can be combined with optical nonlinearities, leading toward new collective phenomena and novel strongly correlated states of light, such as an analog of the fractional quantum Hall effect.

Topological Photonics

The PANTHER (protein annotation through evolutionary relationship) classification system (http://wwwpantherdborg/) is a comprehensive system that combines gene function, ontology, pathways and statistical analysis tools that enable biologists to analyze large-scale, genome-wide data from sequencing, proteomics or gene expression experiments The system is built with 82 complete genomes organized into gene families and subfamilies, and their evolutionary relationships are captured in phylogenetic trees, multiple sequence alignments and statistical models (hidden Markov models or HMMs) Genes are classified according to their function in several different ways: families and subfamilies are annotated with ontology terms (Gene Ontology (GO) and PANTHER protein class), and sequences are assigned to PANTHER pathways The PANTHER website includes a suite of tools that enable users to browse and query gene functions, and to analyze large-scale experimental data with a number of statistical tests It is widely used by bench scientists, bioinformaticians, computer scientists and systems biologists In the 2013 release of PANTHER (v80), in addition to an update of the data content, we redesigned the website interface to improve both user experience and the system's analytical capability This protocol provides a detailed description of how to analyze genome-wide experimental data with the PANTHER classification system

Large-scale gene function analysis with the PANTHER classification system

A detailed review of the education sector in Australia as in the data provided by the 2006 edition of the OECD's annual publication, 'Education at a Glance' is presented. While the data has shown that in almost all OECD countries educational attainment levels are on the rise, with countries showing impressive gains in university qualifications, it also reveals that a large of share of young people still do not complete secondary school, which remains a baseline for successful entry into the labour market.

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Education at a Glance

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Applied Missing Data Analysis

The data and tools in PANTHER—a comprehensive, curated database of protein families, trees, subfamilies and functions available at http://pantherdb.org—have undergone continual, extensive improvement for over a decade. Here, we describe the current PANTHER process as a whole, as well as the website tools for analysis of user-uploaded data. The main goals of PANTHER remain essentially unchanged: the accurate inference (and practical application) of gene and protein function over large sequence databases, using phylogenetic trees to extrapolate from the relatively sparse experimental information from a few model organisms. Yet the focus of PANTHER has continually shifted toward more accurate and detailed representations of evolutionary events in gene family histories. The trees are now designed to represent gene family evolution, including inference of evolutionary events, such as speciation and gene duplication. Subfamilies are still curated and used to define HMMs, but gene ontology functional annotations can now be made at any node in the tree, and are designed to represent gain and loss of function by ancestral genes during evolution. Finally, PANTHER now includes stable database identifiers for inferred ancestral genes, which are used to associate inferred gene attributes with particular genes in the common ancestral genomes of extant species.

PANTHER in 2013: modeling the evolution of gene function, and other gene attributes, in the context of phylogenetic trees

The present study approaches school violence from the adolescents’ perspective, identifying intervening factors in its emergence. An exploratory qualitative methodology within a grounded theory framework was used, interviewing individually and collectively 28 students of 11 to 14 years old from 3 schools in the Metropolitan Region of Chile. Results show a gap between adult perspectives and students’ socioemotional needs, which would favor their involvement in school violence. Schools and teachers do not have effective strategies to face this phenomenon. Peer dynamics can sustain, reinforce, or inhibit violence, through the establishment of social hierarchies within the peer social ecology. The relational analysis highlights the adolescent demands for structure, contention, and orientation, arguing that the adult system does not satisfy these needs adequately. Adolescents would build through violence a social order aimed to meet their relational needs. Violence might fulfill the function of calling adults’ attention and fill the space of the social and emotional attachment dimension which constitutes a central need during this developmental stage.

Una Aproximación Relacional a la Violencia Escolar Entre Pares en Adolescentes Chilenos: Perspectiva Adolescente de los Factores Intervinientes A Relational Approach to School Violence Among Peers in Chilean Adolescents: Adolescent Perspective About Intervening Factors

Wireless multipath channels can often be characterized as sparse, i.e., the number of significant paths is small even when the channel delay spread is large. This can be taken advantage of when estimating the unknown channel frequency response using pilot assisted modulation. Other work has largely focused on the greedy orthogonal matching pursuit (OMP) algorithm, using a dictionary based on an equivalent finite impulse response filter to model the channel. This is not necessarily realistic, as the physical nature of the channel is continuous in time, while the equivalent filter taps are based on baseband sampling. In this paper, we consider sparse channel estimation using a continuous time path-based channel model. This can be linked to the direction finding problem from the array processing literature and solved using the well-known root-MUSIC and ESPRIT algorithms, which have no formal time resolution. In addition, we show that a dictionary with finer time resolution considerably improves the performance of OMP and the related Basis Pursuit (BP) algorithm.

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Sparse channel estimation for OFDM: Over-complete dictionaries and super-resolution

Underwater acoustic orthogonal frequency division multiplexing (OFDM) enables simple frequency domain equalization, but its performance is often limited by intercarrier interference (ICI) that is induced by channel variation, in addition to the ambient noise. As the signal itself, the variance of the ICI is frequency dependent as (i) the transmitter often has a nonideal transmit voltage response (TVR) and (ii) underwater acoustic propagation introduces frequency dependent attenuation. In this paper, a simple method to account for the frequency dependent spectrum of the ICI plus noise is proposed. Specifically, the power spectrum of the ICI plus noise is approximated using a low-order polynomial in the log domain, by fitting the measurements on the null subcarriers embedded in each OFDM symbol. Prewhitening is then applied to each OFDM symbol before channel estimation and data demodulation. The proposed method is tested using experimental data collected from the SPACE08 and RACE08 experiments, where signals with and without transmitter precompensation are compared side by side in the former. Impressive performance gains are found whenever the signal is significantly colored. This is the case when either the TVR is not compensated or the transmission distance and bandwidth are large.

http://www.engr.uconn.edu/~jhuang/Jasa_04_2010.pdf

A simple and effective noise whitening method for underwater acoustic orthogonal frequency division multiplexing.

We consider a multi-static radar scenario with spatially dislocated receivers that can individually extract delay information only. Furthermore, we assume that the receivers are not phase-synchronized, so the measurements across receivers can only be combined noncoherently. We cast this scenario as a compressive sensing reconstruction problem, where the vector of unknowns consists of complex baseband coefficients of tentative targets at discrete positions within a region of interest. The difference to previous work is that each receiver has to have a separate set of variables to account for the noncoherent measurement model. This leads to multiple reconstruction problems that are individually ill-defined, but can be regularized by a shared sparsity pattern, as studied in jointly- or block-sparse reconstruction problems. We evaluate this approach in a simple scenario with three receivers and three closely spaced targets. Using the popular basis pursuit and orthogonal matching pursuit algorithms, we find that targets can be fully resolved and that the position estimation error is close to the Cramer-Rao lower bound based on an estimator that knows the number of targets.

Noncoherent compressive sensing with application to distributed radar

Precise positioning is one attractive application of ultra wideband (UWB) systems Its enormous bandwidth has generated high expectation on the spatial resolution that it could achieve However, synchronization in the presence of dense multipath is challenging, since the first arrival is not necessarily the strongest one due to channel fading It is unclear how high a spatial resolution can be realized in practical implementation, and how reliable it will be We in this paper address practical synchronization algorithms for multiband OFDM UWB transmission, and analyze the performance of a maximum likelihood (ML) joint timing/channel estimation algorithm We show that the probability of mis-timing in single band OFDM has only diversity order one Most timing errors lie closely around the right timing, as we show that the probability of timing error equal to or greater than Delta having diversity order of min(Delta, L), where L the number of channel taps We reveal the benefit of frequency hopping across multiple subbands that enables an NB-fold diversity increase in timing performance, where NB is the number of subbands used

Christian Berger

Papers

Una Aproximación Relacional a la Violencia Escolar Entre Pares en Adolescentes Chilenos: Perspectiva Adolescente de los Factores Intervinientes A Relational Approach to School Violence Among Peers in Chilean Adolescents: Adolescent Perspective About Intervening Factors

Sparse channel estimation for OFDM: Over-complete dictionaries and super-resolution

A simple and effective noise whitening method for underwater acoustic orthogonal frequency division multiplexing.

Noncoherent compressive sensing with application to distributed radar

Precise Timing for Multiband OFDM in a UWB System