Showing papers by "Iowa State University published in 2011"

Past achievements and future challenges in the development of three-dimensional photonic metamaterials

Abstract: Photonic metamaterials are man-made structures composed of tailored micro- or nanostructured metallodielectric subwavelength building blocks. This deceptively simple yet powerful concept allows the realization of many new and unusual optical properties, such as magnetism at optical frequencies, negative refractive index, large positive refractive index, zero reflection through impedance matching, perfect absorption, giant circular dichroism and enhanced nonlinear optical properties. Possible applications of metamaterials include ultrahigh-resolution imaging systems, compact polarization optics and cloaking devices. This Review describes recent progress in the fabrication of three-dimensional metamaterial structures and discusses some of the remaining challenges.

High plant diversity is needed to maintain ecosystem services

Abstract: Biodiversity is rapidly declining worldwide, and there is consensus that this can decrease ecosystem functioning and services. It remains unclear, though, whether few or many of the species in an ecosystem are needed to sustain the provisioning of ecosystem services. It has been hypothesized that most species would promote ecosystem services if many times, places, functions and environmental changes were considered; however, no previous study has considered all of these factors together. Here we show that 84% of the 147 grassland plant species studied in 17 biodiversity experiments promoted ecosystem functioning at least once. Different species promoted ecosystem functioning during different years, at different places, for different functions and under different environmental change scenarios. Furthermore, the species needed to provide one function during multiple years were not the same as those needed to provide multiple functions within one year. Our results indicate that even more species will be needed to maintain ecosystem functioning and services than previously suggested by studies that have either (1) considered only the number of species needed to promote one function under one set of environmental conditions, or (2) separately considered the importance of biodiversity for providing ecosystem functioning across multiple years, places, functions or environmental change scenarios. Therefore, although species may appear functionally redundant when one function is considered under one set of environmental conditions, many species are needed to maintain multiple functions at multiple times and places in a changing world.

Freshwater Methane Emissions Offset the Continental Carbon Sink

Abstract: Inland waters (lakes, reservoirs, streams, and rivers) are often substantial methane (CH4) sources in the terrestrial landscape. They are, however, not yet well integrated in global greenhouse gas (GHG) budgets. Data from 474 freshwater ecosystems and the most recent global water area estimates indicate that freshwaters emit at least 103 teragrams of CH4 year−1, corresponding to 0.65 petagrams of C as carbon dioxide (CO2) equivalents year−1, offsetting 25% of the estimated land carbon sink. Thus, the continental GHG sink may be considerably overestimated, and freshwaters need to be recognized as important in the global carbon cycle.

The Medicago genome provides insight into the evolution of rhizobial symbioses

Abstract: Legumes (Fabaceae or Leguminosae) are unique among cultivated plants for their ability to carry out endosymbiotic nitrogen fixation with rhizobial bacteria, a process that takes place in a specialized structure known as the nodule. Legumes belong to one of the two main groups of eurosids, the Fabidae, which includes most species capable of endosymbiotic nitrogen fixation. Legumes comprise several evolutionary lineages derived from a common ancestor 60 million years ago (Myr ago). Papilionoids are the largest clade, dating nearly to the origin of legumes and containing most cultivated species. Medicago truncatula is a long-established model for the study of legume biology. Here we describe the draft sequence of the M. truncatula euchromatin based on a recently completed BAC assembly supplemented with Illumina shotgun sequence, together capturing ∼94% of all M. truncatula genes. A whole-genome duplication (WGD) approximately 58 Myr ago had a major role in shaping the M. truncatula genome and thereby contributed to the evolution of endosymbiotic nitrogen fixation. Subsequent to the WGD, the M. truncatula genome experienced higher levels of rearrangement than two other sequenced legumes, Glycine max and Lotus japonicus. M. truncatula is a close relative of alfalfa (Medicago sativa), a widely cultivated crop with limited genomics tools and complex autotetraploid genetics. As such, the M. truncatula genome sequence provides significant opportunities to expand alfalfa's genomic toolbox.

Probable non-vector-borne transmission of Zika virus, Colorado, USA.

Abstract: Clinical and serologic evidence indicate that 2 American scientists contracted Zika virus infections while working in Senegal in 2008. One of the scientists transmitted this arbovirus to his wife after his return home. Direct contact is implicated as the transmission route, most likely as a sexually transmitted infection.

Design concepts for the Cherenkov Telescope Array CTA: An advanced facility for ground-based high-energy gamma-ray astronomy

Abstract: Ground-based gamma-ray astronomy has had a major breakthrough with the impressive results obtained using systems of imaging atmospheric Cherenkov telescopes. Ground-based gamma-ray astronomy has a huge potential in astrophysics, particle physics and cosmology. CTA is an international initiative to build the next generation instrument, with a factor of 5-10 improvement in sensitivity in the 100 GeV-10 TeV range and the extension to energies well below 100 GeV and above 100 TeV. CTA will consist of two arrays (one in the north, one in the south) for full sky coverage and will be operated as open observatory. The design of CTA is based on currently available technology. This document reports on the status and presents the major design concepts of CTA.

Extension of the bayesian alphabet for genomic selection

Abstract: Two Bayesian methods, BayesCπ and BayesDπ, were developed for genomic prediction to address the drawback of BayesA and BayesB regarding the impact of prior hyperparameters and treat the prior probability π that a SNP has zero effect as unknown. The methods were compared in terms of inference of the number of QTL and accuracy of genomic estimated breeding values (GEBVs), using simulated scenarios and real data from North American Holstein bulls. Estimates of π from BayesCπ, in contrast to BayesDπ, were sensitive to the number of simulated QTL and training data size, and provide information about genetic architecture. Milk yield and fat yield have QTL with larger effects than protein yield and somatic cell score. The drawback of BayesA and BayesB did not impair the accuracy of GEBVs. Accuracies of alternative Bayesian methods were similar. BayesA was a good choice for GEBV with the real data. Computing time was shorter for BayesCπ than for BayesDπ, and longest for our implementation of BayesA. Collectively, accounting for computing effort, uncertainty as to the number of QTL (which affects the GEBV accuracy of alternative methods), and fundamental interest in the number of QTL underlying quantitative traits, we believe that BayesCπ has merit for routine applications.

Pathological Video Game Use Among Youths: A Two-Year Longitudinal Study

Abstract: OBJECTIVES: We aimed to measure the prevalence and length of the problem of pathological video gaming or Internet use, to identify risk and protective factors, to determine whether pathological gaming is a primary or secondary problem, and to identify outcomes for individuals who become or stop being pathological gamers. METHODS: A 2-year, longitudinal, panel study was performed with a general elementary and secondary school population in Singapore, including 3034 children in grades 3 ( N = 743), 4 ( N = 711), 7 ( N = 916), and 8 ( N = 664). Several hypothesized risk and protective factors for developing or overcoming pathological gaming were measured, including weekly amount of game play, impulsivity, social competence, depression, social phobia, anxiety, and school performance. RESULTS: The prevalence of pathological gaming was similar to that in other countries (∼9%). Greater amounts of gaming, lower social competence, and greater impulsivity seemed to act as risk factors for becoming pathological gamers, whereas depression, anxiety, social phobias, and lower school performance seemed to act as outcomes of pathological gaming. CONCLUSION: This study adds important information to the discussion about whether video game “addiction” is similar to other addictive behaviors, demonstrating that it can last for years and is not solely a symptom of comorbid disorders.

TAL effectors: Customizable proteins for DNA targeting

Abstract: Generating and applying new knowledge from the wealth of available genomic information is hindered, in part, by the difficulty of altering nucleotide sequences and expression of genes in living cells in a targeted fashion. Progress has been made in engineering DNA binding domains to direct proteins to particular sequences for mutagenesis or manipulation of transcription; however, achieving the requisite specificities has been challenging. Transcription activator-like (TAL) effectors of plant pathogenic bacteria contain a modular DNA binding domain that appears to overcome this challenge. Comprising tandem, polymorphic amino acid repeats that individually specify contiguous nucleotides in DNA, this domain is being deployed in DNA targeting for applications ranging from understanding gene function in model organisms to improving traits in crop plants to treating genetic disorders in people.

Resolving Difficult Phylogenetic Questions: Why More Sequences Are Not Enough

Abstract: In the quest to reconstruct the Tree of Life, researchers have increasingly turned to phylogenomics, the inference of phylogenetic relationships using genome-scale data (Box 1). Mesmerized by the sustained increase in sequencing throughput, many phylogeneticists entertained the hope that the incongruence frequently observed in studies using single or a few genes [1] would come to an end with the generation of large multigene datasets. Yet, as so often happens, reality has turned out to be far more complex, as three recent large-scale analyses, one published in PLoS Biology [2]–[4], make clear. The studies, which deal with the early diversification of animals, produced highly incongruent (Box 2) findings despite the use of considerable sequence data (see Figure 1). Clearly, merely adding more sequences is not enough to resolve the inconsistencies.

The pleasure and displeasure people feel when they exercise at different intensities: decennial update and progress towards a tripartite rationale for exercise intensity prescription.

Abstract: The public health problem of physical inactivity has proven resistant to research efforts aimed at elucidating its causes and interventions designed to alter its course. Thus, in most industrialized countries, the majority of the population is physically inactive or inadequately active. Most theoretical models of exercise behaviour assume that the decision to engage in exercise is based on cognitive factors (e.g. weighing pros and cons, appraising personal capabilities, evaluating sources of support). Another, still-under-appreciated, possibility is that these decisions are influenced by affective variables, such as whether previous exercise experiences were associated with pleasure or displeasure. This review examines 33 articles published from 1999 to 2009 on the relationship between exercise intensity and affective responses. Unlike 31 studies that were published until 1998 and were examined in a 1999 review, these more recent studies have provided evidence of a relation between the intensity of exercise and affective responses. Pleasure is reduced mainly above the ventilatory or lactate threshold or the onset of blood lactate accumulation. There are pleasant changes at sub-threshold intensities for most individuals, large inter-individual variability close to the ventilatory or lactate threshold and homogeneously negative changes at supra-threshold intensities. When the intensity is self-selected, rather than imposed, it appears to foster greater tolerance to higher intensity levels. The evidence of a doseresponse relation between exercise intensity and affect sets the stage for a reconsideration of the rationale behind current guidelines for exercise intensity prescription. Besides effectiveness and safety, it is becoming increasingly clear that the guidelines should take into account whether a certain level of exercise intensity would be likely to cause increases or decreases in pleasure.

Nutrient co-limitation of primary producer communities

Abstract: Ecology Letters (2011) 14: 852–862 Abstract Synergistic interactions between multiple limiting resources are common, highlighting the importance of co-limitation as a constraint on primary production. Our concept of resource limitation has shifted over the past two decades from an earlier paradigm of single-resource limitation towards concepts of co-limitation by multiple resources, which are predicted by various theories. Herein, we summarise multiple-resource limitation responses in plant communities using a dataset of 641 studies that applied factorial addition of nitrogen (N) and phosphorus (P) in freshwater, marine and terrestrial systems. We found that more than half of the studies displayed some type of synergistic response to N and P addition. We found support for strict definitions of co-limitation in 28% of the studies: i.e. community biomass responded to only combined N and P addition, or to both N and P when added separately. Our results highlight the importance of interactions between N and P in regulating primary producer community biomass and point to the need for future studies that address the multiple mechanisms that could lead to different types of co-limitation.

Episodic radiations in the fly tree of life

Abstract: Flies are one of four superradiations of insects (along with beetles, wasps, and moths) that account for the majority of animal life on Earth. Diptera includes species known for their ubiquity (Musca domestica house fly), their role as pests (Anopheles gambiae malaria mosquito), and their value as model organisms across the biological sciences (Drosophila melanogaster). A resolved phylogeny for flies provides a framework for genomic, developmental, and evolutionary studies by facilitating comparisons across model organisms, yet recent research has suggested that fly relationships have been obscured by multiple episodes of rapid diversification. We provide a phylogenomic estimate of fly relationships based on molecules and morphology from 149 of 157 families, including 30 kb from 14 nuclear loci and complete mitochondrial genomes combined with 371 morphological characters. Multiple analyses show support for traditional groups (Brachycera, Cyclorrhapha, and Schizophora) and corroborate contentious findings, such as the anomalous Deuterophlebiidae as the sister group to all remaining Diptera. Our findings reveal that the closest relatives of the Drosophilidae are highly modified parasites (including the wingless Braulidae) of bees and other insects. Furthermore, we use micro-RNAs to resolve a node with implications for the evolution of embryonic development in Diptera. We demonstrate that flies experienced three episodes of rapid radiation—lower Diptera (220 Ma), lower Brachycera (180 Ma), and Schizophora (65 Ma)—and a number of life history transitions to hematophagy, phytophagy, and parasitism in the history of fly evolution over 260 million y.

Targeted gene disruption in somatic zebrafish cells using engineered TALENs.

Abstract: To the Editor: Miller et al. recently described a TALE nuclease architecture for performing efficient genome editing1. The authors demonstrated that TALE nucleases, composed of an engineered array of TALE repeats fused to the non-specific FokI cleavage domain, could be used to introduce targeted double-stranded breaks (DSBs) in human cells with high efficiency. Repair of these DSBs by normal DNA repair mechanisms such as non-homologous end-joining (NHEJ) or homologous recombination (HR) enables introduction of alterations at or near the site of the break. A single 34 amino acid TALE repeat binds to one bp of DNA and repeats that bind each of the four DNA bases have been described2, 3. These modules can be assembled into arrays capable of binding extended DNA sequences. TALE nucleases may have advantages over engineered zinc finger nucleases (ZFNs) due to the relative ease with which they can be designed and their potential ability to be targeted to a wide range of sequences (with target sites reported to be as frequent as 1 in 35 bps of random DNA sequence4). We sought to determine whether the TALE nuclease framework described by Miller et al. could also be used to efficiently modify endogenous genes in zebrafish. Previous studies have shown that error-prone repair of ZFN-induced DSBs by NHEJ can result in the efficient introduction of small insertions or deletions (indels) at cleavage sites in endogenous zebrafish genes5–7. These indels frequently result in frameshift knockout mutations that can be passed through the germline to create mutant fish5–9. ZFN technology has enabled reverse genetics studies to be performed in zebrafish, a capability that did not previously exist. However, engineering ZFNs can be challenging due to the need to account for context-dependent effects among individual fingers in an array. In addition, although many zebrafish genes can be targeted with ZFNs made by publicly available methods that account for context-dependence7, 10, it can in some instances be difficult to target within some genes in zebrafish due to the currently limited targeting range of publicly available ZFN engineering platforms. Thus, if TALE nucleases could be used to introduce targeted mutations in zebrafish, this platform would provide an important additional capability for this model organism. To test the ability of TALE nucleases to function in zebrafish, we targeted DNA sequences in two endogenous zebrafish genes gria3a and hey2 (Figure 1). To avoid confounding effects that might affect binding and cleavage of DNA sites by TALE nucleases (e.g.--chromatin structure or DNA methylation), we chose to target sequences that we had efficiently altered previously in zebrafish using engineered ZFNs (Supplementary Figures 1 and 2). Using an iterative assembly approach (Supplementary Methods), we constructed four TALE nuclease monomers to partially overlapping sites in the gria3a gene and two TALE nuclease monomers to a site in the hey2 gene (Figure 1 and Supplementary Figure 3). These six TALE nuclease monomers all harbor the wild-type FokI cleavage domain (Supplementary Figures 4 and 5) and can be paired in combinations to make three TALE nuclease dimers to the gria3a gene and one TALE nuclease dimer to the hey2 gene (Figure 1). We injected RNAs encoding the various TALE nuclease pairs into one-cell stage zebrafish embryos and determined the frequency of NHEJ-mediated mutagenesis at the target site by sequence analysis of alleles from pooled injected embryos (Supplementary Methods, Supplementary Figs. 6–10 and Supplementary Table 1). As shown in Figure 1, we found that all four pairs of TALE nucleases induced targeted indels with high mutation frequencies ranging from 11 to 33%. These frequencies are comparable to what we obtained with ZFNs targeted to DNA sequences in the same vicinity of the gene (Supplementary Figure 1); however, we note that TALE nucleases harbor wild-type FokI domains whereas the ZFNs harbor obligate heterodimeric FokI domains11. Although small indels were typically observed with the TALE nucleases, some large deletions (up to 303 basepairs) were also found (Figure 1). Figure 1 Target sequences, frequencies of mutations, and sequences of mutations induced by TALE nucleases in embryonic zebrafish cells To assess the toxicity of our engineered TALE nucleases, we scored the percentages of dead and deformed embryos that resulted from mRNA microinjections (Supplementary Figure 11). Although we cannot directly compare these results with the microinjections of ZFNs due to the differences between the FokI endonuclease domains used (EL/KK heterodimeric FokI11 for ZFNs versus wild-type FokI for the TALE nucleases) and the specific sequences targeted, the toxicity we observed with injection of 600 pg of TALE nuclease mRNAs (ranging between 40–80%) appears similar to that observed with 400–500 pg of mRNAs encoding ZFNs targeted to sequences in the same vicinity and to other genes (Supplementary Figure 12 and Reference 7). An important future experiment will be to demonstrate germline transmission of TALE nuclease-induced mutations. Given that the frequencies of mutation and the extent of toxicities we observe are similar to what we have seen with ZFNs, we expect that TALE nuclease-induced mutations should be efficiently passed through the germline to progeny and we are currently conducting experiments to test this prediction. Successful germline transmission of these mutations will be critical for using TALE nucleases to perform reverse genetics in zebrafish. Progeny fish bearing TALE nuclease-induced mutations, unlike founder F0 fish, will not be mosaic (i.e.--these fish will have uniform mutation of all cells in the organism); such mutant fish will enable determination of whether both mono-allelic and bi-allelic alterations of a gene are possible and will provide a more straightforward background on which to perform analysis of off-target effects. In summary, we show that the TALE nuclease framework described by Miller et al. can be used to efficiently introduce targeted indel mutations in endogenous zebrafish genes at the somatic cell level. Although in this study we chose two genomic loci that have been successfully targeted with ZFNs before, all six TALE nuclease monomers we constructed showed high mutagenesis activities when tested in various pairwise combinations, suggesting that the TALE nuclease framework is also highly robust and effective in zebrafish. As is the case with ZFNs, the complete genome-wide spectrum of off-target mutations introduced by TALE nucleases remains unknown. However, expression of the TALE nucleases we made in zebrafish does not show toxicity substantially different from that observed with expression of ZFNs, suggesting that the magnitude of off-target effects may be comparable with the two types of nucleases. In principle, off-target mutations made by TALE nucleases can be removed by out-crossing the founder assuming that they are not tightly linked to the intended mutation. In addition, mutant phenotypes could also be confirmed by generation of a second mutant allele using nucleases targeted to a different site. For mutagenesis of genes in zebrafish (and other model organisms such as C. elegans12), TALE nucleases may offer potential advantages over ZFNs because they can be easily and quickly assembled in a modular fashion and they can potentially target a greater range of DNA sequences. Thus, we expect that the ability to utilize both ZFNs and TALE nucleases should enable any researcher to rapidly and easily create targeted mutations in their endogenous zebrafish gene of interest.

TAL nucleases (TALNs): hybrid proteins composed of TAL effectors and FokI DNA-cleavage domain

Abstract: DNA double-strand breaks enhance homologous recombination in cells and have been exploited for targeted genome editing through use of engineered endonucleases Here we report the creation and initial characterization of a group of rare-cutting, site-specific DNA nucleases produced by fusion of the restriction enzyme FokI endonuclease domain (FN) with the high-specificity DNA-binding domains of AvrXa7 and PthXo1 AvrXa7 and PthXo1 are members of the transcription activator-like (TAL) effector family whose central repeat units dictate target DNA recognition and can be modularly constructed to create novel DNA specificity The hybrid FN-AvrXa7, AvrXa7-FN and PthXo1-FN proteins retain both recognition specificity for their target DNA (a 26 bp sequence for AvrXa7 and 24 bp for PthXo1) and the double-stranded DNA cleaving activity of FokI and, thus, are called TAL nucleases (TALNs) With all three TALNs, DNA is cleaved adjacent to the TAL-binding site under optimal conditions in vitro When expressed in yeast, the TALNs promote DNA homologous recombination of a LacZ gene containing paired AvrXa7 or asymmetric AvrXa7/PthXo1 target sequences Our results demonstrate the feasibility of creating a tool box of novel TALNs with potential for targeted genome modification in organisms lacking facile mechanisms for targeted gene knockout and homologous recombination

Field-evolved resistance to Bt maize by western corn rootworm.

Abstract: Background Crops engineered to produce insecticidal toxins derived from the bacterium Bacillus thuringiensis (Bt) are planted on millions of hectares annually, reducing the use of conventional insecticides and suppressing pests. However, the evolution of resistance could cut short these benefits. A primary pest targeted by Bt maize in the United States is the western corn rootworm Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae).

Two-dimensional electron gas with universal subbands at the surface of SrTiO3

Abstract: As silicon is the basis of conventional electronics, so strontium titanate (SrTiO(3)) is the foundation of the emerging field of oxide electronics. SrTiO(3) is the preferred template for the creation of exotic, two-dimensional (2D) phases of electron matter at oxide interfaces that have metal-insulator transitions, superconductivity or large negative magnetoresistance. However, the physical nature of the electronic structure underlying these 2D electron gases (2DEGs), which is crucial to understanding their remarkable properties, remains elusive. Here we show, using angle-resolved photoemission spectroscopy, that there is a highly metallic universal 2DEG at the vacuum-cleaved surface of SrTiO(3) (including the non-doped insulating material) independently of bulk carrier densities over more than seven decades. This 2DEG is confined within a region of about five unit cells and has a sheet carrier density of ∼0.33 electrons per square lattice parameter. The electronic structure consists of multiple subbands of heavy and light electrons. The similarity of this 2DEG to those reported in SrTiO(3)-based heterostructures and field-effect transistors suggests that different forms of electron confinement at the surface of SrTiO(3) lead to essentially the same 2DEG. Our discovery provides a model system for the study of the electronic structure of 2DEGs in SrTiO(3)-based devices and a novel means of generating 2DEGs at the surfaces of transition-metal oxides.

The What, How, Why, and Where of Self-Construal:

Abstract: Since the publication of Markus and Kitayama’s pivotal article on culture and the self, the concepts of independent, relational, and interdependent self-construal have become important constructs in cultural psychology and research on the self. The authors review the history of these constructs, their measurement and manipulation, and their roles in cognition, emotion, motivation, and social behavior. They make suggestions for future research and point to problems still to be sorted out. Researchers interested in these constructs have many opportunities to make important contributions to the literature in a variety of fields, including health psychology, education, counseling, and international relations.

Selection-free zinc-finger-nuclease engineering by context-dependent assembly (CoDA)

Abstract: Context-dependent assembly (CoDA) of zinc finger nucleases is reported. Starting from an archive of zinc finger modules known to function well together, effective multifinger arrays can be constructed using standard techniques. Also in this issue, Doyon et al. report rational design of nucleases with improved cleavage activity.

A brassinosteroid transcriptional network revealed by genome-wide identification of BESI target genes in Arabidopsis thaliana.

Abstract: Brassinosteroids (BRs) are important regulators for plant growth and development. BRs signal to control the activities of the BES1 and BZR1 family transcription factors. The transcriptional network through which BES1 and BZR regulate large number of target genes is mostly unknown. By combining chromatin immunoprecipitation coupled with Arabidopsis tiling arrays (ChIP-chip) and gene expression studies, we have identified 1609 putative BES1 target genes, 404 of which are regulated by BRs and/or in gain-of-function bes1-D mutant. BES1 targets contribute to BR responses and interactions with other hormonal or light signaling pathways. Computational modeling of gene expression data using Algorithm for the Reconstruction of Accurate Cellular Networks (ARACNe) reveals that BES1-targeted transcriptional factors form a gene regulatory network (GRN). Mutants of many genes in the network displayed defects in BR responses. Moreover, we found that BES1 functions to inhibit chloroplast development by repressing the expression of GLK1 and GLK2 transcription factors, confirming a hypothesis generated from the GRN. Our results thus provide a global view of BR regulated gene expression and a GRN that guides future studies in understanding BR-regulated plant growth.

Productivity Is a Poor Predictor of Plant Species Richness

Abstract: For more than 30 years, the relationship between net primary productivity and species richness has generated intense debate in ecology about the processes regulating local diversity. The original view, which is still widely accepted, holds that the relationship is hump-shaped, with richness first rising and then declining with increasing productivity. Although recent meta-analyses questioned the generality of hump-shaped patterns, these syntheses have been criticized for failing to account for methodological differences among studies. We addressed such concerns by conducting standardized sampling in 48 herbaceous-dominated plant communities on five continents. We found no clear relationship between productivity and fine-scale (meters−2) richness within sites, within regions, or across the globe. Ecologists should focus on fresh, mechanistic approaches to understanding the multivariate links between productivity and richness.

Do Financing Constraints Matter for R&D?

Abstract: Information problems and lack of collateral value should make R&D more susceptible to financing frictions than other investments, yet existing evidence on whether financing constraints limit R&D is decidedly mixed, particularly in studies of non-U.S. firms. We study a large sample of European firms and also find little evidence of binding finance constraints when we estimate standard investment-cash flow regressions. However, we find strong evidence that the availability of finance matters for R&D once we directly control for: i) firm efforts to smooth R&D with cash reserves, and ii) firm use of external equity finance. Our study provides a framework for evaluating financing constraints when firms rely extensively on external finance and endogenously manage buffer stocks of liquidity to keep investment smooth, and our findings show that controlling for this smoothing behavior is critical for uncovering the full effect of financing constraints. Our findings also indicate a major role for external equity in financing R&D, highlighting a causal channel through which stock market development and liberalization can promote economic growth by increasing firm-level innovative activity.

An Empirically Derived Framework of Global Supply Resiliency

Abstract: In today’s global business environment, supply chains have increased in both length and complexity. This increase in length and complexity coupled with a focus on improving efficiency, such as lean manufacturing practices, may lead to higher levels of supply chain risk where the likelihood of a disruption severely impacting supply chain performance increases. Resilient supply chains have been touted as a means to reduce the likelihood and severity of supply chain disruptions. However, there is little empirical evidence relative to the factors that contribute to or detract from supply resiliency. Using systems theory and the resource-based view of the firm as the theoretical underpinnings, this study provides an in-depth systematic investigation of supply resiliency. Adopting a theory-building approach based on a multi-industry empirical investigation, this study derives empirical generalizations linking 19 supply chain characteristics to supply resiliency. The study culminates in a framework that could be used to assess the level of resiliency in a supply base. Building on this framework, the study also provides a supply resiliency matrix that can be utilized to classify supply chains, or supply chains segments according to the level of resiliency realized. This article concludes by proposing several future research directions and issues that may be investigated in more detail.

Transforming online teaching practice: critical analysis of the literature on the roles and competencies of online teachers

Abstract: Understanding what is lacking in the online teaching literature is critical to helping researchers and practitioners develop programs and support mechanisms for online teachers in higher education. This review formulates a critique of the standards- and competency-driven vision of online teaching from the perspective of transformative learning theory, in order to offer an alternative exploration of the professional development of online teachers as adult learners. The results indicate that while research about online teacher roles and competencies guides the development of teacher preparation and training programs, it lacks in terms of addressing the issues of empowerment of online teachers, promoting critical reflection, and integrating technology into pedagogical inquiry. An alternative perspective is suggested that considers teachers as adult learners who continuously transform their meaning of structures related to online teaching through a continuous process of critical reflection and action.

Charged-particle multiplicities in pp interactions measured with the ATLAS detector at the LHC

Abstract: Measurements are presented from proton-proton collisions at centre-of-mass energies of root s = 0.9, 2.36 and 7 TeV recorded with the ATLAS detector at the LHC. Events were collected using a single-arm minimum-bias trigger. The charged-particle multiplicity, its dependence on transverse momentum and pseudorapidity and the relationship between the mean transverse momentum and charged-particle multiplicity are measured. Measurements in different regions of phase space are shown, providing diffraction-reduced measurements as well as more inclusive ones. The observed distributions are corrected to well-defined phase-space regions, using model-independent corrections. The results are compared to each other and to various Monte Carlo (MC) models, including a new AMBT1 pythia6 tune. In all the kinematic regions considered, the particle multiplicities are higher than predicted by the MC models. The central charged-particle multiplicity per event and unit of pseudorapidity, for tracks with p(T) > 100 MeV, is measured to be 3.483 +/- 0.009 (stat) +/- 0.106 (syst) at root s = 0.9 TeV and 5.630 +/- 0.003 (stat) +/- 0.169 (syst) at root s = 7 TeV.

Understanding the fast pyrolysis of lignin.

Abstract: In the present study, pyrolysis of corn stover lignin was investigated by using a micro-pyrolyzer coupled with a GC-MS/FID (FID=flame ionization detector). The system has pyrolysis-vapor residence times of 15-20 ms, thus providing a regime of minimal secondary reactions. The primary pyrolysis product distribution obtained from lignin is reported. Over 84 % mass balance and almost complete closure on carbon balance is achieved. In another set of experiments, the pyrolysis vapors emerging from the micro-pyrolyzer are condensed to obtain lignin-derived bio-oil. The chemical composition of the bio-oil is analyzed by using GC-MS and gel permeation chromatography techniques. The comparison between results of two sets of experiments indicates that monomeric compounds are the primary pyrolysis products of lignin, which recombine after primary pyrolysis to produce oligomeric compounds. Further, the effect of minerals (NaCl, KCl, MgCl(2), and CaCl(2)) and temperature on the primary pyrolysis product distribution is investigated. The study provides insights into the fundamental mechanisms of lignin pyrolysis and a basis for developing more descriptive models of biomass pyrolysis.

Genomic Selection in Plant Breeding. Knowledge and Prospects.

Abstract: “Genomic selection,” the ability to select for even complex, quantitative traits based on marker data alone, has arisen from the conjunction of new high-throughput marker technologies and new statistical methods needed to analyze the data. This review surveys what is known about these technologies, with sections on population and quantitative genetic background, DNA marker development, statistical methods, reported accuracies of genomic selection (GS) predictions, prediction of nonadditive genetic effects, prediction in the presence of subpopulation structure, and impacts of GS on long-term gain. GS works by estimating the effects of many loci spread across the genome. Marker and observation numbers therefore need to scale with the genetic map length in Morgans and with the effective population size of the population under GS. For typical crops, the requirements range from at least 200 to at most 10,000 markers and observations. With that baseline, GS can greatly accelerate the breeding cycle while also using marker information to maintain genetic diversity and potentially prolong gain beyond what is possible with phenotypic selection. With the costs of marker technologies continuing to decline and the statistical methods becoming more routine, the results reviewed here suggest that GS will play a large role in the plant breeding of the future. Our summary and interpretation should prove useful to breeders as they assess the value of GS in the context of their populations and resources.